JP7595446B2 - Method for producing branched conjugated diene polymer, method for producing rubber composition, method for producing tire, branched conjugated diene polymer, and branched conjugated diene polymer composition - Google Patents

Description

The present invention relates to a method for producing a branched conjugated diene polymer, a method for producing a rubber composition, a method for producing a tire, a branched conjugated diene polymer, and a branched conjugated diene polymer composition.

From the viewpoint of environmental load, there has been an increasing demand for automobiles to have lower fuel consumption. In particular, there is a demand for improved fuel consumption in the materials used for the tread portion of automobile tires, which is in direct contact with the ground.
In recent years, there has been a demand for the development of materials having low rolling resistance, i.e., low hysteresis loss.
At the same time, there is a trend to reduce the weight of tires, which requires a reduction in the thickness of the tire tread, and at the same time, materials with high abrasion resistance are required for the tire tread.
On the other hand, from the viewpoint of safety, materials used in the tire tread portion are required to have excellent wet skid resistance and sufficient fracture properties for practical use.

Materials that meet the various requirements as described above include rubber materials that contain a rubber-like polymer and a reinforcing filler such as carbon black or silica.
The use of a rubber material containing silica can improve the balance between low hysteresis loss (an index of fuel economy) and wet skid resistance. In addition, by introducing a functional group having affinity or reactivity with silica to the molecular end of a rubber-like polymer with high mobility, the dispersibility of silica in the rubber material can be improved, and further, the mobility of the molecular end of the rubber-like polymer can be reduced by bonding with silica particles, thereby reducing the hysteresis loss.
On the other hand, one method for improving the abrasion resistance is to increase the molecular weight of the rubber-like polymer, but increasing the molecular weight of the rubber-like polymer tends to deteriorate the processability when the rubber-like polymer is kneaded with a reinforcing filler.
In view of these circumstances, attempts have been made to introduce a branched structure into rubber-like polymers in order to increase the molecular weight without impairing processability.

For example, a resin composition has been proposed in the past that contains silica and a modified conjugated diene polymer obtained by reacting an alkoxysilane containing an amino group with an active terminal of a conjugated diene polymer.
In addition, modified conjugated diene polymers have been proposed that have a branched structure obtained by subjecting an active terminal of a polymer to a coupling reaction with a polyfunctional silane compound (see, for example, Patent Documents 1 and 2).

International Publication No. 2007/114203 International Publication No. 2016/133154

However, in the method of introducing a branched structure into a conjugated diene polymer by subjecting an active terminal of the polymer to a coupling reaction with a polyfunctional silane compound, the degree of branching of the modified conjugated diene polymer obtained thereby depends greatly on the number of groups capable of reacting with the active terminal of the polymer possessed by the polyfunctional silane compound, and does not exceed the number of reactive groups. From the viewpoint of synthetic feasibility, there is a limit to the number of reactive groups that can be imparted to one polyfunctional silane, and therefore there is a problem in that there is also a limit to the degree of branching of the modified conjugated diene polymer obtained.

In this invention, therefore, by introducing a branch point into the main chain, it is possible to produce a conjugated diene polymer with a higher degree of branching than when a branched structure is introduced into a conjugated diene polymer using only a modifier or coupling agent, and it is also possible to adjust the length of the main chain and side chains, thereby providing a method for producing a branched conjugated diene polymer with a high degree of freedom in polymer design. The object of the invention is to provide a method for producing a branched conjugated diene polymer with excellent fuel economy, abrasion resistance, wet skid resistance, and breaking strength.

Means for Solving the Problems of the Prior Art As a result of intensive research and investigation, the present inventors have found a method for producing a branched conjugated diene polymer, which can introduce a branch point into the main chain by reacting a conjugated diene polymer having an active terminal with a specific styrene derivative as a branching agent, and have thus completed the present invention.
That is, the present invention is as follows.

[1]
a polymerization step of polymerizing or copolymerizing a conjugated diene compound, or a conjugated diene compound and an aromatic vinyl compound, using an alkali metal compound or an alkaline earth metal compound as a polymerization initiator to obtain a conjugated diene polymer having an active terminal;
a branching step of reacting an active terminal of the conjugated diene polymer with a styrene derivative as a branching agent to introduce a branched structure;
The present invention relates to a method for producing a branched conjugated diene polymer comprising the steps of:
[2]
The method for producing a branched conjugated diene polymer according to the above item [1], further comprising a step of adding a conjugated diene compound and/or an aromatic vinyl compound to the reaction system during and/or after the branching step.
[3]
The method for producing a branched conjugated diene polymer according to the above [1] or [2], further comprising a reaction step of reacting an active terminal of the conjugated diene polymer obtained in the branching step with a coupling agent or a polymerization terminator.
[4]
In the reaction step,
The method for producing a branched conjugated diene polymer according to the above item [3], wherein the coupling agent is a silane sulfide compound represented by the following formula (3):

(In formula (3), Si represents a silicon atom, O represents an oxygen atom, and S represents a sulfur atom.
x is an integer of 1 to 3, y is 0 or an integer of 1 to 2, and x+y is 3.
R ¹ , R ² , and R ⁴ may be the same or different and each represents an alkyl group having 1 to 16 carbon atoms, and R ³ represents an aryl group having 6 to 16 carbon atoms, an alkylene group having 1 to 16 carbon atoms, or an alkyl chain having 1 to 16 carbon atoms.

[5]
The styrene derivative is
The method for producing the branched conjugated diene-based polymer according to any one of [1] to [4] above, which is a compound represented by the following formula (1) and/or the following formula (2):

In formulas (1) and (2), R ¹ represents any one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, and an aryl group having 6 to 20 carbon atoms, and may have a branched structure in part.
X ¹ , X ² and X ³ each represent a single bond or an organic group containing any one selected from the group consisting of carbon, hydrogen, nitrogen, sulfur and oxygen.
^Y1 , ^Y2 , and ^Y3 each represent any one selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and a halogen atom. They may be independent and the same or different.

[6]
A step of obtaining a branched conjugated diene polymer by the production method according to any one of [1] to [5] above;
obtaining a rubber component containing 10% by mass or more of the branched conjugated diene polymer;
and adding a filler in an amount of 5.0 parts by mass or more and 150 parts by mass or less to 100 parts by mass of the rubber component to obtain a rubber composition.
[7]
Obtaining a rubber composition by the method for producing a rubber composition according to [6] above;
molding the rubber composition to obtain a tire;
A tire manufacturing method comprising the steps of:
[8]
having one or more side chains in the polymer chain,
A branched conjugated diene polymer having a branching degree (Bn) of 1 or more as measured by a viscosity detector-equipped GPC-light scattering method,
the branched conjugated diene-based polymer contains sulfur atoms and silicon atoms, and the molar ratio of the silicon atoms to the sulfur atoms is 1.05 or more and less than 10;
The Mooney viscosity measured at 100°C is 40 or more and 170 or less.
Branched conjugated diene polymers.
[9]
The branched conjugated diene polymer according to [8] above, which has a branching degree (Bn) of 2 or more and 25 or less, as measured by a GPC-light scattering method with a viscosity detector.
[10]
The polymer chain has a portion derived from a vinyl monomer containing an alkoxysilyl group or a halosilyl group,
The moiety derived from the vinyl monomer containing an alkoxysilyl group or a halosilyl group has a side chain.
The branched conjugated diene polymer according to [8] or [9] above.
[11]
The portion derived from the vinyl monomer containing an alkoxysilyl group or a halosilyl group is
A monomer unit based on a compound represented by the following formula (4) or (5):
The branched conjugated diene polymer according to [10] above, having a polymer chain branching point due to a monomer unit based on a compound represented by the following formula (4) or (5):

In formula (4), R ¹ represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, which may have a branched structure in part.
R ² and R ³ each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, which may partially have a branched structure.
When a plurality of R ¹ to R ³ are present, they are each independent.
^X1 independently represents a halogen atom.
m represents an integer of 0 to 2, n represents an integer of 0 to 3, and l represents an integer of 0 to 3. (m+n+l) represents 3.
In formula (5), R ² to R ⁵ each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and may partially have a branched structure. When a plurality of R ² to R ⁵ are present, each is independent of each other.
X ² and X ³ each independently represent a halogen atom.
m represents an integer of 0 to 2, n represents an integer of 0 to 3, and l represents an integer of 0 to 3. (m+n+l) represents 3.
a represents an integer from 0 to 2, b represents an integer from 0 to 3, and c represents an integer from 0 to 3. (a+b+c) represents 3.)

[12]
The branched conjugated diene polymer according to any one of [8] to [11] above, wherein at least one end of the branched conjugated diene polymer is modified with a silane sulfide compound represented by the following formula (3):

(In formula (3), Si represents a silicon atom, O represents an oxygen atom, and S represents a sulfur atom.
x is an integer of 1 to 3, y is 0 or an integer of 1 to 2, and x+y is 3.
R ¹ , R ² , and R ⁴ may be the same or different and each represents an alkyl group having 1 to 16 carbon atoms, and R ³ represents an aryl group having 6 to 16 carbon atoms, an alkylene group having 1 to 16 carbon atoms, or an alkyl chain having 1 to 16 carbon atoms.

[13]
The branched conjugated diene polymer composition contains 10% by mass or more and less than 100% by mass of a branched conjugated diene polymer having one or more side chains in a polymer chain and having a branching degree (Bn) of 1 or more as measured by a viscosity detector-equipped GPC-light scattering method, the conjugated diene polymer containing sulfur atoms and silicon atoms, the molar ratio of the silicon atoms to the sulfur atoms being 1.05 or more and less than 10, and the Mooney viscosity measured at 100°C being 40 or more and 170 or less.
[14]
The branched conjugated diene polymer comprises
The branched conjugated diene polymer composition according to [13] above, which contains a branched conjugated diene polymer coupled with at least one compound selected from the group consisting of tin halides, tin alkoxides, silicon halides, and alkoxysilanes.

According to the present invention, by introducing a branch point into the main chain, it is possible to produce a branched conjugated diene polymer with a higher degree of branching than when only a coupling agent is used, and it is also possible to provide a method for producing a branched conjugated diene polymer with a high degree of freedom in polymer design, by allowing the length of the main chain and side chains to be adjusted, thereby providing a method for producing a branched conjugated diene polymer with excellent fuel efficiency, abrasion resistance, wet skid resistance, and breaking strength.

Hereinafter, an embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described in detail.
It should be noted that the following embodiment is merely an example for explaining the present invention, and the present invention is not limited to the following embodiment. The present invention can be practiced with appropriate modifications within the scope of the gist of the present invention.

[Method for producing branched conjugated diene polymer]
The method for producing a branched conjugated diene polymer of the present embodiment includes the steps of:
The method includes a polymerization step of polymerizing or copolymerizing a conjugated diene compound, or a conjugated diene compound and an aromatic vinyl compound, using an alkali metal compound or an alkaline earth metal compound as a polymerization initiator to obtain a conjugated diene polymer having an active end, and a branching step of reacting a styrene derivative as a branching agent with the active end of the conjugated diene polymer to introduce a branched structure.
The conjugated diene polymer constituting the branched conjugated diene polymer may be any of a homopolymer of a single conjugated diene compound, a polymer or copolymer of different types of conjugated diene compounds, and a copolymer of a conjugated diene compound and an aromatic vinyl compound.
According to the method for producing a branched conjugated diene polymer of the present embodiment, by introducing a branch point into the main chain, it is possible to produce a conjugated diene polymer having a higher degree of branching than when a branched structure is introduced into a conjugated diene polymer using only a coupling agent, and it is also possible to adjust the lengths of the main chain and side chains.

(Polymerization process)
In the polymerization step in the method for producing a branched conjugated diene polymer of the present embodiment, an alkali metal compound or an alkaline earth metal compound is used as a polymerization initiator to polymerize or copolymerize a conjugated diene compound, or a conjugated diene compound and an aromatic vinyl compound, to obtain a conjugated diene polymer having an active end.
In the polymerization step, it is preferable to carry out polymerization by a propagation reaction through a living anionic polymerization reaction, whereby a conjugated diene polymer having an active terminal can be obtained.

<Polymerization initiator>
As the polymerization initiator, an alkali metal compound or an alkaline earth metal compound is used.
As the polymerization initiator, an organolithium compound is preferably used, and an organomonolithium compound is more preferably used.
The organomonolithium compound is not limited to the following, but examples thereof include organomonolithium compounds of low molecular weight compounds and solubilized oligomeric organomonolithium compounds.
In addition, the organic monolithium compound can be any of compounds having a carbon-lithium bond, a nitrogen-lithium bond, and a tin-lithium bond in terms of the bonding mode between the organic group and the lithium.

The amount of the polymerization initiator used is preferably determined depending on the targeted molecular weight of the conjugated diene polymer.
The amount of a monomer such as a conjugated diene compound used relative to the amount of a polymerization initiator used relates to the degree of polymerization of a target conjugated diene polymer, i.e., tends to relate to the number average molecular weight and/or weight average molecular weight.
Therefore, in order to increase the molecular weight of the conjugated diene polymer, the amount of the polymerization initiator should be adjusted to decrease, and in order to decrease the molecular weight, the amount of the polymerization initiator should be adjusted to increase.

From the viewpoint that the organomonolithium compound is used as one method for introducing nitrogen atoms into the conjugated diene polymer, it is preferably an alkyllithium compound having a substituted amino group or a dialkylaminolithium.
In this case, a conjugated diene polymer having a nitrogen atom consisting of an amino group at the polymerization initiation terminal is obtained.

The substituted amino group is an amino group that does not have an active hydrogen or has a structure in which the active hydrogen is protected.
Examples of alkyllithium compounds having an amino group that does not have an active hydrogen include, but are not limited to, 3-dimethylaminopropyllithium, 3-diethylaminopropyllithium, 4-(methylpropylamino)butyllithium, and 4-hexamethyleneiminobutyllithium.
Examples of alkyllithium compounds having an amino group with an active hydrogen protected structure include, but are not limited to, 3-bistrimethylsilylaminopropyllithium and 4-trimethylsilylmethylaminobutyllithium.

Examples of dialkylaminolithium include, but are not limited to, lithium dimethylamide, lithium diethylamide, lithium dipropylamide, lithium dibutylamide, lithium di-n-hexylamide, lithium diheptylamide, lithium diisopropylamide, lithium dioctylamide, lithium di-2-ethylhexylamide, lithium didecylamide, lithium ethylpropylamide, lithium ethylbutylamide, lithium ethylbenzylamide, lithium methylphenethylamide, lithium hexamethyleneimide, lithium pyrrolidide, lithium piperidide, lithium heptamethyleneimide, lithium morpholide, 1-lithioazacyclooctane, 6-lithio-1,3,3-trimethyl-6-azabicyclo[3.2.1]octane, and 1-lithio-1,2,3,6-tetrahydropyridine.

These organomonolithium compounds having substituted amino groups can also be used as oligomeric organomonolithium compounds solubilized in normal hexane or cyclohexane by reacting them with small amounts of polymerizable monomers such as 1,3-butadiene, isoprene, and styrene.

The organomonolithium compound is preferably an alkyllithium compound from the viewpoints of industrial availability and ease of control of the polymerization reaction, in which case a conjugated diene-based polymer having an alkyl group at the polymerization initiation terminal can be obtained.
Examples of the alkyl lithium compound include, but are not limited to, n-butyl lithium, sec-butyl lithium, tert-butyl lithium, n-hexyl lithium, benzyl lithium, phenyl lithium, and stilbene lithium.
As the alkyllithium compound, n-butyllithium and sec-butyllithium are preferred from the viewpoints of industrial availability and ease of control of the polymerization reaction.

These organomonolithium compounds may be used alone or in combination of two or more kinds, and may also be used in combination with other organometallic compounds.
Examples of the other organometallic compounds include alkaline earth metal compounds, other alkali metal compounds, and other organometallic compounds.
Alkaline earth metal compounds include, but are not limited to, organomagnesium compounds, organocalcium compounds, and organostrontium compounds, as well as alkaline earth metal alkoxides, sulfonates, carbonates, and amides.
Organomagnesium compounds include, for example, dibutylmagnesium and ethylbutylmagnesium.
Other examples of organometallic compounds include organoaluminum compounds.

In the polymerization step, the polymerization reaction mode is not limited to the following modes, but examples thereof include batch and continuous polymerization reaction modes.
In the continuous system, one or more connected reactors can be used. The continuous reactor may be, for example, a tank type or a tube type equipped with an agitator. In the continuous system, preferably, the monomer, the inert solvent, and the polymerization initiator are continuously fed into the reactor, a polymer solution containing a polymer is obtained in the reactor, and the polymer solution is continuously discharged.
The batch reactor may be, for example, a tank-type reactor equipped with a stirrer. In the batch reactor, preferably, a monomer, an inert solvent, and a polymerization initiator are fed, and if necessary, a monomer is added continuously or intermittently during polymerization to obtain a polymer solution in the reactor, and the polymer solution is discharged after the polymerization is completed.
In the method for producing a branched conjugated diene polymer of this embodiment, in order to obtain a conjugated diene polymer having a high proportion of active ends in the polymerization step, a continuous system is preferred, which allows the polymer to be continuously discharged and subjected to the next reaction in a short time. In the continuous system, the number of reactors is not particularly limited, and one or two or more connected reactors can be used. The reactor is preferably one that can sufficiently contact the monomer and the polymerization initiator in a solution, and a tank type or a tube type with a stirrer is used. The number of reactors can be appropriately selected, but one is preferred from the viewpoint of space saving of the production equipment, and two or more are preferred from the viewpoint of improving productivity. When two or more reactors are used, it is more preferable to add the branching agent described later to the second or subsequent reactors.

In the polymerization step of the conjugated diene polymer, the polymerization is preferably carried out in an inert solvent.
Examples of the inert solvent include hydrocarbon solvents such as saturated hydrocarbons and aromatic hydrocarbons. Examples of the hydrocarbon solvent include, but are not limited to, aliphatic hydrocarbons such as butane, pentane, hexane, and heptane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane, and methylcyclohexane; aromatic hydrocarbons such as benzene, toluene, and xylene, and hydrocarbons consisting of mixtures thereof.
By treating the impurities, that is, allenes and acetylenes, with an organometallic compound before subjecting the polymer to the polymerization reaction, a conjugated diene-based polymer having a high concentration of active ends tends to be obtained, which is preferable since a modified conjugated diene-based polymer having a high modification rate tends to be obtained.

In the polymerization process, a polar compound (polar substance) may be added. This allows the aromatic vinyl compound to be randomly copolymerized with the conjugated diene compound. Polar compounds also tend to be usable as vinylating agents for controlling the microstructure of the conjugated diene portion. Furthermore, they tend to be effective in promoting the polymerization reaction.

Examples of polar compounds that can be used include, but are not limited to, ethers such as tetrahydrofuran, diethyl ether, dioxane, ethylene glycol dimethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, dimethoxybenzene, and 2,2-bis(2-oxolanyl)propane; tertiary amine compounds such as tetramethylethylenediamine, dipiperidinoethane, trimethylamine, triethylamine, pyridine, and quinuclidine; alkali metal alkoxide compounds such as potassium tert-amylate, potassium tert-butylate, sodium tert-butylate, and sodium amylate; and phosphine compounds such as triphenylphosphine.
These polar compounds may be used alone or in combination of two or more.

The amount of the polar compound used is not particularly limited and can be selected depending on the purpose, but is preferably 0.01 moles or more and 100 moles or less per mole of the polymerization initiator.
Such a polar compound (vinylating agent) can be used as an adjuster for the microstructure of the conjugated diene portion of the conjugated diene polymer in an appropriate amount according to the desired vinyl bond amount.
Many polar compounds simultaneously have an effective randomizing effect in the copolymerization of a conjugated diene compound and an aromatic vinyl compound, and tend to be usable as an adjuster for the distribution of the aromatic vinyl compound and as an adjuster for the amount of styrene blocks.
As a method for randomizing the conjugated diene compound and the aromatic vinyl compound, for example, as described in JP-A-59-140211, a copolymerization reaction may be initiated with the total amount of styrene and a portion of 1,3-butadiene, and the remaining 1,3-butadiene may be intermittently added during the copolymerization reaction.

The polymerization temperature in the polymerization step is preferably a temperature at which living anionic polymerization proceeds, and from the viewpoint of productivity, is more preferably 0° C. or higher and 120° C. or lower.
By setting the temperature within this range, it is possible to ensure a sufficient amount of the branching agent and the coupling agent to react with the active terminals after the polymerization is completed.

(Branching process)
In the method for producing a branched conjugated diene polymer of the present embodiment, a branching step is carried out in which a styrene derivative is reacted as a branching agent with the active terminal of the conjugated diene polymer obtained in the polymerization step.
While the branching agent maintains its polymerization activity and polymerizes with the monomer, the functional group of the branching agent reacts with the active end of another polymer chain, forming a branched structure in the polymer. It is also possible to form a further branched structure by polymerizing and reacting the branched conjugated diene polymer into which the branched structure has been introduced with a monomer and a branching agent, or to react the branched conjugated diene polymer with a functional group to form a modified conjugated diene polymer, or to further extend the polymer chain by a coupling reaction. In this way, a branched conjugated diene polymer can be obtained by continuing the polymerization reaction as an aromatic vinyl compound and using a styrene derivative whose functional group reacts with the active end of the polymer as a branching agent.

<Branching Agent>
From the viewpoints of polymerization continuity and gelation prevention, the styrene derivative used as a branching agent in the branching step must have a main skeleton that leaves only one active end at the branch site after the branching reaction, and further, the styrene derivative portion formed after the branching reaction must have sufficient reactivity to react with other polymer active ends.
More specifically, the styrene derivative as the branching agent is preferably a compound having a vinyl group on the benzene ring and a functional group that quantitatively reacts with the polymer active end of living anionic polymerization. The functional group of the styrene derivative reacts one-to-one with the polymer active end, and the functional group is eliminated to form a single bond, while the vinyl group is polymerized with other monomers in the reactor, forming a branched structure in the polymer. The functional group other than the vinyl group of the styrene derivative is a group that is eliminated by nucleophilic substitution reaction with the polymer active end of living anionic polymerization, and examples of such functional groups include alkoxy groups, halogens, ester groups, formyl groups, ketone groups, amide groups, acid chloride groups, acid anhydride groups, and epoxy groups.
By having the above-mentioned structure, the styrene derivative is incorporated into the main chain while maintaining its polymerization activity as styrene, and another monomer is polymerized to the terminal that maintains its activity, thereby further extending the polymer chain. In addition, the functional group of the incorporated styrene derivative reacts with the active terminal of another polymer chain to form a bond, resulting in a branched structure. By repeating this reaction, the number of branches in the polymer chain increases, the polymer structure becomes more complex, and the molecular weight becomes larger.
From the viewpoint of the continuity of polymerization and the controllability of the polymer structure, it is also necessary that the functional group which is eliminated after the styrene derivative portion reacts with the active end of another polymer chain has little inhibitory effect on polymerization.
Here, "low inhibition of polymerization" means that, for example, side reactions of anionic polymerization such as chain transfer reactions, deactivation during polymerization, and decrease in activity due to an increase in the degree of association of the polymer are low.
The functional group of the styrene derivative as the branching agent must not excessively improve the polymerization activity, and must not deactivate the polymerization activity. When polymerizing a polymer by living anionic polymerization, it is important that the functional group does not have a hydrogen atom as a functional group that does not deactivate the active terminal, and is a hard base as defined based on Pearson's HASB rule, and more specifically, an alkoxy group or a halogen group can be mentioned. Among these, the structure of the styrene derivative as the branching agent used in the production method of this embodiment can be selected from the viewpoint of reactivity with the active terminal and that the eliminated functional group does not inhibit polymerization.
More specifically, it is preferable to use a branching agent represented by the following formula (1) having a styrene skeleton as the main skeleton, or a branching agent represented by the following formula (2) having a diphenylethylene skeleton as the main skeleton, from the viewpoints of suppressing chain transfer reactions, suppressing deactivation of active terminals, and preventing gelation.

In formulas (1) and (2), R ¹ represents any one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, and an aryl group having 6 to 20 carbon atoms, and may have a branched structure in part.
X ¹ , X ² and X ³ each represent a single bond or an organic group containing any one selected from the group consisting of carbon, hydrogen, nitrogen, sulfur and oxygen.
^Y1 , ^Y2 , and ^Y3 each represent any one selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and a halogen atom. They may be independent and the same or different.

From the viewpoint of improving the degree of branching in polymerization, the styrene derivative used as a branching agent in the branching step is preferably such that, in the formula (1), R ¹ is a hydrogen atom and Y ¹ is any one selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and a halogen atom.

In the present embodiment, from the viewpoint of improving the degree of branching, the styrene derivative used as the branching agent in the branching step is preferably such that ^Y2 in the formula (2) is any one selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and a halogen atom.

In the present embodiment, from the viewpoint of continuity of polymerization and improvement of the degree of branching, it is more preferable that in the styrene derivative used as the branching agent in the branching step, R ¹ in the formula (1) is a hydrogen atom and Y ¹ is an alkoxy group having 1 to 20 carbon atoms or a halogen atom.

In the present embodiment, from the viewpoint of continuity of polymerization and improvement of the degree of branching, it is more preferable that, in the styrene derivative used as a branching agent in the branching step, ^Y2 in the formula (2) is an alkoxy group or a halogen atom, and ^Y3 is an alkoxy group having 1 to 20 carbon atoms or a halogen atom.

In the present embodiment, from the viewpoints of improving the continuity of polymerization, the degree of branching, and the modification rate, it is more preferable that R ¹ in the styrene derivative used as the branching agent in the branching step is a hydrogen atom and Y ¹ in the formula (1) is an alkoxy group having 1 to 20 carbon atoms.

In the present embodiment, from the viewpoints of continuity of polymerization, improvement of the branching degree, and further improvement of the modification rate, it is even more preferable that, in the styrene derivative used as the branching agent in the branching step, R ¹ is a hydrogen atom, X ¹ is a single bond, and Y ¹ is an alkoxy group having 1 to 20 carbon atoms in the formula (1).

In the present embodiment, from the viewpoints of continuity of polymerization, improvement of the branching degree, and further improvement of the modification rate, it is even more preferable that, in the formula (2), ^X2 is a single bond, ^Y2 is an alkoxy group having 1 to 20 carbon atoms or a halogen atom, and ^X3 is a single bond, and ^Y3 is an alkoxy group having 1 to 20 carbon atoms or a halogen atom, in the styrene derivative used as a branching agent in the branching step.

Examples of the branching agent represented by the formula (1) include, but are not limited to, trimethoxy(4-vinylphenyl)silane, triethoxy(4-vinylphenyl)silane, tripropoxy(4-vinylphenyl)silane, tributoxy(4-vinylphenyl)silane, triisopropoxy(4-vinylphenyl)silane, trimethoxy(3-vinylphenyl)silane, triethoxy(3-vinylphenyl)silane, tripropoxy(3-vinylphenyl)silane, tributoxy(3-vinylphenyl)silane, triisopropoxy(3-vinylphenyl)silane, trimethoxy(2-vinylphenyl)silane, triethoxy(2-vinylphenyl)silane, tripropoxy(2-vinylphenyl)silane, tributoxy(2-vinylphenyl)silane, triisopropoxy(3-vinylphenyl)silane, trimethoxy(2-vinylphenyl)silane, triethoxy(2-vinylphenyl)silane, tripropoxy(2-vinylphenyl)silane, tributoxy(2-vinylphenyl)silane, triisopropoxy(2-vinylphenyl)silane, trimethoxy(2-vinylphenyl)silane, triethoxy(2-vinylphenyl)silane, tripropoxy(2-vinylphenyl)silane, triisoprop ... isopropoxy(2-vinylphenyl)silane, dimethoxymethyl(4-vinylphenyl)silane, diethoxymethyl(4-vinylphenyl)silane, dipropoxymethyl(4-vinylphenyl)silane, dibutoxymethyl(4-vinylphenyl)silane, diisopropoxymethyl(4-vinylphenyl)silane, dimethoxymethyl(3-vinylphenyl)silane, diethoxymethyl(3-vinylphenyl)silane, dipropoxymethyl(3-vinylphenyl)silane, dibutoxymethyl(3-vinylphenyl)silane, diisopropoxymethyl(3-vinylphenyl)silane, dimethoxymethyl(2-vinylphenyl)silane, diethoxymethyl(2-vinylphenyl)silane, dipropoxymethyl(2-vinylphenyl)silane, dibutoxymethyl(2-vinylphenyl)silane dimethylphenyl)silane, diisopropoxymethyl(2-vinylphenyl)silane, dimethylmethoxy(4-vinylphenyl)silane, dimethylethoxy(4-vinylphenyl)silane, dimethylpropoxy(4-vinylphenyl)silane, dimethylbutoxy(4-vinylphenyl)silane, dimethylisopropoxy(4-vinylphenyl)silane, dimethylmethoxy(3-vinylphenyl)silane, dimethylethoxy(3-vinylphenyl)silane, dimethylpropoxy(3-vinylphenyl)silane, dimethylbutoxy(3-vinylphenyl)silane, dimethylisopropoxy(3-vinylphenyl)silane, dimethylmethoxy(2-vinylphenyl)silane, dimethylethoxy(2-vinylphenyl)silane, dimethylpropoxy(2-vinylphenyl)silane, dimethyl Tributoxy(2-vinylphenyl)silane, dimethylisopropoxy(2-vinylphenyl)silane, trimethoxy(4-isopropenylphenyl)silane, triethoxy(4-isopropenylphenyl)silane, tripropoxy(4-isopropenylphenyl)silane, tributoxy(4-isopropenylphenyl)silane, triisopropoxy(4-isopropenylphenyl)silane, trimethoxy(3-isopropenylphenyl)silane, triethoxy(3-isopropenylphenyl)silane, tripropoxy(3-isopropenylphenyl)silane, tributoxy(3-isopropenylphenyl)silane, triisopropoxy(3-isopropenylphenyl)silane, trimethoxy(2-isopropenylphenyl)silane, triethoxy(2-isopropenylphenyl)silane (phenyl)silane, tripropoxy (2-isopropenylphenyl)silane, tributoxy (2-isopropenylphenyl)silane, triisopropoxy (2-isopropenylphenyl)silane, dimethoxymethyl (4-isopropenylphenyl)silane, diethoxymethyl (4-isopropenylphenyl)silane, dipropoxymethyl (4-isopropenylphenyl)silane, dibutoxymethyl (4-isopropenylphenyl)silane, diisopropoxymethyl (4-isopropenylphenyl)silane, dimethoxymethyl (3-isopropenylphenyl)silane, diethoxymethyl (3-isopropenylphenyl)silane, dipropoxymethyl (3-isopropenylphenyl)silane, dibutoxymethyl (3-isopropenylphenyl)silane, diisopropoxy Dimethyl(3-isopropenylphenyl)silane, dimethoxymethyl(2-isopropenylphenyl)silane, diethoxymethyl(2-isopropenylphenyl)silane, dipropoxymethyl(2-isopropenylphenyl)silane, dibutoxymethyl(2-isopropenylphenyl)silane, diisopropoxymethyl(2-isopropenylphenyl)silane, dimethylmethoxy(4-isopropenylphenyl)silane, dimethylethoxy(4-isopropenylphenyl)silane, dimethylpropoxy(4-isopropenylphenyl)silane, dimethylbutoxy(4-isopropenylphenyl)silane, dimethylisopropoxy(4-isopropenylphenyl)silane, dimethylmethoxy(3-isopropenylphenyl)silane, dimethylethoxy(3-isopropenylphenyl)silane (vinylphenyl)silane, dimethylpropoxy(3-isopropenylphenyl)silane, dimethylbutoxy(3-isopropenylphenyl)silane, dimethylisopropoxy(3-isopropenylphenyl)silane, dimethylmethoxy(2-isopropenylphenyl)silane, dimethylethoxy(2-isopropenylphenyl)silane, dimethylpropoxy(2-isopropenylphenyl)silane, dimethylbutoxy(2-isopropenylphenyl)silane, dimethylisopropoxy(2-isopropenylphenyl)silane, trichloro(4-vinylphenyl)silane, trichloro(3-vinylphenyl)silane, trichloro(2-vinylphenyl)silane, tribromo(4-vinylphenyl)silane, tribromo(3-vinylphenyl)silane, tribromo(2-vinylphenyl)silane, methylphenyl)silane, dichloromethyl(4-vinylphenyl)silane, dichloromethyl(3-vinylphenyl)silane, dichloromethyl(2-vinylphenyl)silane, dibromomethyl(4-vinylphenyl)silane, dibromomethyl(3-vinylphenyl)silane, dibromomethyl(2-vinylphenyl)silane, dimethylchloro(4-vinylphenyl)silane, dimethylchloro(3-vinylphenyl)silane, dimethylchloro(2-vinylphenyl)silane, dimethylbromo(4-vinylphenyl)silane, dimethylbromo(3-vinylphenyl)silane, dimethylbromo(2-vinylphenyl)silane, trimethoxy(4-vinylbenzyl)silane, triethoxy(4-vinylbenzyl)silane, tripropoxy(4-vinylbenzyl)silane.
Among these, trimethoxy(4-vinylphenyl)silane, triethoxy(4-vinylphenyl)silane, tripropoxy(4-vinylphenyl)silane, tributoxy(4-vinylphenyl)silane, triisopropoxy(4-vinylphenyl)silane, trimethoxy(3-vinylphenyl)silane, triethoxy(3-vinylphenyl)silane, tripropoxy(3-vinylphenyl)silane, tributoxy(3-vinylphenyl)silane, triisopropoxy(3 ... tributoxy(3-vinylphenyl)silane, triisopropoxy(3-vinylphenyl)silane, trimethoxy(3-vinylphenyl)silane, triethoxy(3-vinylphenyl)silane, tripropoxy(3-vinylphenyl)silane, tributoxy(3-vinylphenyl)silane, triisopropoxy(3-vinylphenyl)silane, trimethoxy(3-vinylphenyl)silane, triethoxy(3-vinylphenyl)silane, tripropoxy(3-vinylphenyl)silane, triisopropoxy(3-vinylphenyl)silane, trimethoxy(3-vinylphenyl)silane, triethoxy(3-vinylphenyl)silane, tripropoxy(3-vinylphenyl)silane, tripeptoxy(3-vinylphenyl)silane, tripeptoxy(3-vinylphenyl)sil Preferred is trimethoxy(4-vinylphenyl)silane, triethoxy(4-vinylphenyl)silane, tripropoxy(4-vinylphenyl)silane, tributoxy(4-vinylphenyl)silane, triisopropoxy(4-vinylphenyl)silane, trimethoxy(4-vinylbenzyl)silane, and triethoxy(4-vinylbenzyl)silane, and further preferred are trimethoxy(4-vinylphenyl)silane and triethoxy(4-vinylphenyl)silane.

The branching agent represented by the formula (2) is not limited to the following, but may be, for example,
1-bis(4-trimethoxysilylphenyl)ethylene, 1,1-bis(4-triethoxysilylphenyl)ethylene, 1,1-bis(4-tripropoxysilylphenyl)ethylene, 1,1-bis(4-tripentoxysilylphenyl)ethylene, 1,1-bis(4-triisopropoxysilylphenyl)ethylene, 1,1-bis(3-trimethoxysilylphenyl)ethylene, 1,1-bis(3-triethoxysilylphenyl)ethylene, 1,1-bis(3-tripentoxysilylphenyl)ethylene, 1,1-bis(3-triisopropoxysilylphenyl)ethylene, 1,1-bis(2-trimethoxysilylphenyl)ethylene, 1,1-bis(2-triethoxysilylphenyl)ethylene, 1,1-bis(3-tripentoxysilylphenyl)ethylene, Examples thereof include 1,1-bis(2-tripentoxysilylphenyl)ethylene, 1,1-bis(2-triisopropoxysilylphenyl)ethylene, 1,1-bis(4-(dimethylmethoxysilyl)phenyl)ethylene, 1,1-bis(4-(diethylmethoxysilyl)phenyl)ethylene, 1,1-bis(4-(dipropylmethoxysilyl)phenyl)ethylene, 1,1-bis(4-(dimethylethoxysilyl)phenyl)ethylene, 1,1-bis(4-(diethylethoxysilyl)phenyl)ethylene, 1,1-bis(4-(dipropylethoxysilyl)phenyl)ethylene, 1,1-bis(4-trimethoxysilylbenzyl)ethylene, 1,1-bis(4-triethoxysilylbenzyl)ethylene, 1,1-bis(4-trippropoxysilylbenzyl)ethylene, and 1,1-bis(4-tripentoxysilylbenzyl)ethylene.
Among these, 1,1-bis(4-trimethoxysilylphenyl)ethylene, 1,1-bis(4-triethoxysilylphenyl)ethylene, 1,1-bis(4-tripropoxysilylphenyl)ethylene, 1,1-bis(4-tripentoxysilylphenyl)ethylene and 1,1-bis(4-triisopropoxysilylphenyl)ethylene are preferred, with 1,1-bis(4-trimethoxysilylphenyl)ethylene being more preferred.
By using the branching agents represented by the formulas (1) and (2), the number of branches is increased, and the effects of improving the wear resistance and processability can be obtained.

The timing of adding the branching agent is not particularly limited and can be selected depending on the purpose, etc., but from the viewpoint of improving the absolute molecular weight of the branched conjugated diene-based polymer and improving the coupling rate, the timing is preferably when the raw material conversion rate after addition of the polymerization initiator is 20% or more, more preferably 40% or more, even more preferably 50% or more, even more preferably 65% or more, and even more preferably 75% or more.
During and/or after the branching step, a monomer as a desired raw material may be further added to the reaction system, and the polymerization step may be continued after the branching step, or the above-described contents may be repeated.
Incidentally, "after the branching step" refers to after the branching agent is added.
The monomer to be added is not particularly limited, but is preferably a conjugated diene compound and/or an aromatic vinyl compound. In particular, when a monomer is added during the branching step, from the viewpoint of improving the modification rate by alleviating steric hindrance at the branching point of the conjugated diene polymer, the monomer is preferably 5% or more of the total amount of conjugated diene monomers used in the polymerization step, for example, the total amount of butadiene, more preferably 10% or more, even more preferably 15% or more, even more preferably 20% or more, and even more preferably 25% or more. In such a case, it is particularly preferable to add a monomer using a continuous polymerization process at the branching step, in an amount of 5% or more of the total amount of conjugated diene monomers used in the polymerization step, for example, the total amount of butadiene, from the viewpoint of improving the modification rate.
The length of the main chain and side chains can be adjusted by changing the timing of adding the branching agent and the amount of monomer added, allowing for a high degree of freedom in polymer design.

The branched structure of the branched conjugated diene polymer obtained in the branching step in the production method for a branched conjugated diene polymer of the present embodiment preferably has 3 or more and 24 or less branches, more preferably has 4 or more and 20 or less branches, and further preferably has 5 or more and 18 or less branches.
By restricting the number of branches to 24 or less, it tends to be easier to react with a modifier having a functional group to form a modified conjugated diene polymer or to further extend the polymer chain by a coupling reaction, and by restricting the number of branches to 3 or more, the obtained branched conjugated diene polymer tends to be excellent in processability and abrasion resistance.

The amount of branching agent added is not particularly limited, and can be selected depending on the purpose, etc., but from the viewpoint of improving the terminal termination reaction rate of the conjugated diene polymer, improving the coupling rate, and continuity of polymerization after branching, the molar ratio of the branching agent to the amount of active polymerization initiator is preferably 1/2 or less and 1/100 or more, more preferably 1/3 or less and 1/50 or more, even more preferably 1/4 or less and 1/30 or more, even more preferably 1/6 or less and 1/25 or more, and even more preferably 1/8 or less and 1/12 or more.

As mentioned above, further monomer may be added during and/or after the branching step and the polymerization step may be continued after branching, or further branching agent may be charged after the further addition of monomer and further monomer addition may be repeated.
By adding monomers, the steric hindrance around the branching points is alleviated, and the continuity of the polymerization is improved, and the coupling rate and modification rate are improved, so that the molecular weight of the polymer can be increased while a branched structure can be formed at a desired position.
The monomer to be added may be an aromatic vinyl compound such as styrene, a conjugated diene compound such as butadiene, or a mixture thereof, and may be the same as or different from the type and ratio of the monomer to be polymerized initially, but from the viewpoint of continuity of polymerization, a conjugated diene compound is preferred. From the viewpoint of improving the heat resistance of the polymer, it is preferable to add an aromatic vinyl compound.

The branched conjugated diene polymer obtained in the branching step in the production method of the present embodiment has a Mooney viscosity measured at 110° C. of preferably 10 or more and 150 or less, more preferably 15 or more and 140 or less, even more preferably 20 or more and 130 or less, and still more preferably 30 or more and 100 or less.
When the Mooney viscosity is within the above range, the branched conjugated diene polymer obtained by the production method of the present embodiment tends to have excellent processability and abrasion resistance.

The weight average molecular weight of the branched conjugated diene polymer obtained in the branching step in the production method of this embodiment is preferably 10,000 or more and 1,500,000 or less, more preferably 100,000 or more and 1,000,000 or less, and even more preferably 200,000 or more and 900,000 or less.
When the weight average molecular weight is within the above range, the branched conjugated diene polymer obtained by the production method of the present embodiment tends to be excellent in processability, abrasion resistance, and a balance of these properties.
In producing an unmodified branched conjugated diene polymer, in order to reach a weight average molecular weight range of 100,000 or more and 1,000,000 or less, it is necessary to control the amount of branching agent added to be within a range of 1/3 or less and 1/5 or more in molar ratio to the polymerization initiator, thereby preventing the polymerization initiator from being completely consumed before the coupling step while forming branches, and to make the number of functional groups of the coupling agent 2 or more. In order to reach a weight average molecular weight range of 200,000 or more and 900,000 or less, it is necessary to control the amount of branching agent added to be within a range of 1/3 or less and 1/50 or more in molar ratio to the polymerization initiator, while making the number of functional groups of the coupling agent 3 or more.
In producing a modified branched conjugated diene polymer, in order to reach a weight average molecular weight in the range of 100,000 or more and 1,000,000 or less, it is necessary to control the amount of branching agent added within a range of 1/3 or less and 1/50 or more in molar ratio to the polymerization initiator, thereby preventing the polymerization initiator from being completely consumed before the coupling step while forming branches, and to make the number of functional groups of the coupling agent two or more. In order to reach a weight average molecular weight in the range of 200,000 or more and 900,000 or less, it is necessary to control the amount of branching agent added within a range of 1/3 or less and 1/50 or more in molar ratio to the polymerization initiator, and to make the number of functional groups of the coupling agent three or more.

The branched conjugated diene-based polymer obtained by the production method of the present embodiment may be a polymer of a conjugated diene monomer and a branching agent, or may be a copolymer of a conjugated diene monomer, a branching agent, and a monomer other than these.
For example, when the conjugated diene monomer is butadiene or isoprene and is polymerized with a branching agent containing an aromatic vinyl moiety, the polymer chain is a so-called polybutadiene or polyisoprene, and the branching portion is a polymer containing a structure derived from aromatic vinyl. By having such a structure, it is possible to improve the linearity per polymer chain and improve the crosslinking density after vulcanization, and the effect of improving the abrasion resistance of the polymer is achieved. Therefore, it is suitable for applications such as tires, resin modification, automobile interior and exterior parts, vibration-proof rubber, and footwear.
When the conjugated diene polymer is used for tire tread applications, a copolymer of a conjugated diene monomer, an aromatic vinyl monomer, and a branching agent is suitable, and in the copolymer for this application, the amount of bound conjugated diene is preferably 40% by mass or more and 100% by mass or less, and more preferably 55% by mass or more and 80% by mass or less.
Furthermore, the amount of bound aromatic vinyl in the branched conjugated diene polymer obtained by the production method of the present embodiment is not particularly limited, but is preferably 0% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 45% by mass or less.
When the bound conjugated diene amount and bound aromatic vinyl amount are within the above ranges, the balance between low hysteresis loss and wet skid resistance, abrasion resistance, and fracture properties tend to be excellent when made into a vulcanizate.
The amount of bound aromatic vinyl can be measured by ultraviolet absorption of the phenyl group, and the amount of bound conjugated diene can also be calculated from the amount. Specifically, the amount can be measured according to the method described in the examples below.

In the branched conjugated diene polymer obtained by the production method of the present embodiment, the amount of vinyl bonds in the conjugated diene bond units is not particularly limited, but is preferably 10 mol % or more and 75 mol % or less, and more preferably 20 mol % or more and 65 mol % or less.
If the amount of vinyl bonds is within the above range, the balance between low hysteresis loss and wet skid resistance, abrasion resistance, and breaking strength tend to be excellent when made into a vulcanizate.
Here, when the branched conjugated diene polymer is a copolymer of butadiene and styrene, the vinyl bond amount (1,2-bond amount) in the butadiene bond unit can be determined by the Hampton method (R.R. Hampton, Analytical Chemistry, 21, 923 (1949)). Specifically, it can be measured by the method described in the examples below.

Regarding the microstructure of the branched conjugated diene polymer, when the bond amounts in the branched conjugated diene polymer obtained by the production method of the present embodiment are within the above-mentioned numerical ranges, and further, when the glass transition temperature of the branched conjugated diene polymer is within the range of −80° C. or more and −15° C. or less, a vulcanizate having an even better balance between low hysteresis loss and wet skid resistance tends to be obtained.
The glass transition temperature is measured in accordance with ISO 22768:2006 by recording a DSC curve while increasing the temperature within a predetermined temperature range, and the peak top (inflection point) of the DSC differential curve is determined as the glass transition temperature.

When the branched conjugated diene polymer obtained by the manufacturing method of this embodiment is a conjugated diene-aromatic vinyl copolymer, the branched conjugated diene polymer preferably has a small number of blocks in which 30 or more aromatic vinyl units are linked, or has no blocks. More specifically, when the branched conjugated diene polymer obtained by the manufacturing method of this embodiment is a butadiene-styrene copolymer, the polymer is decomposed by the Kolthoff method (the method described in I.M. KOLTHOFF, et al., J. Polym. Sci. 1, 429 (1946)) and the amount of polystyrene insoluble in methanol is analyzed. In this method, the amount of blocks in which 30 or more aromatic vinyl units are linked is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, based on the total amount of the branched conjugated diene polymer.

When the branched conjugated diene polymer obtained by the production method of the present embodiment is a conjugated diene-aromatic vinyl copolymer, it is preferable that the proportion of aromatic vinyl units present alone is high from the viewpoint of improving fuel saving performance.
Specifically, when the branched conjugated diene polymer obtained by the production method of the present embodiment is a butadiene-styrene copolymer, when the branched conjugated diene polymer is decomposed by an ozonolysis method known as the Tanaka et al. method (Polymer, 22, 1721 (1981)) and the styrene chain distribution is analyzed by GPC, it is preferable that the amount of isolated styrene is 40% by mass or more and the amount of chain styrene structures having 8 or more styrene chains is 5.0% by mass or less relative to the total bound styrene amount.
In this case, the resulting vulcanized rubber tends to have excellent performance, particularly low hysteresis loss.

(Reaction step)
In the method for producing a branched conjugated diene polymer of the present embodiment, it is preferable to carry out a step of performing a coupling reaction on the active terminal of the conjugated diene polymer obtained through the above-mentioned polymerization step and branching step using a coupling agent, for example, a reactive compound having three or more functionalities, for example, a step of performing a coupling reaction using a coupling agent consisting of a silane sulfide compound represented by the following formula (3), or a step of performing a polymerization termination reaction on the active terminal of the conjugated diene polymer using a polymerization terminator, for example, a reactive compound having two or less functionalities.
Hereinafter, the step of reacting a coupling agent (coupling step) and the step of reacting a polymerization terminator (polymerization terminator step) will be collectively referred to as a reaction step.
In the reaction step, one of the active terminals of the conjugated diene polymer is reacted with a coupling agent or a polymerization terminator.

<Coupling step>
In the method for producing a branched conjugated diene polymer of the present embodiment, it is preferable that the reaction step involves subjecting the conjugated diene polymer obtained through the above-mentioned polymerization step and branching step to a coupling reaction using a coupling agent.
The coupling reaction can efficiently lengthen the molecular chain, and by using a coupling agent having three or more functionalities, it is also possible to introduce branches into the polymer. Although the function of forming branches is common to the process using a branching agent, it is preferable to carry out the coupling process in terms of being able to form branches while introducing desired elements such as nitrogen, sulfur, and silicon using a known coupling agent.
In the coupling step, for example, a tri- or higher functional reactive compound, a coupling agent having a nitrogen atom-containing group, or a coupling agent consisting of a silane sulfide compound represented by the following formula (3) (hereinafter, these may be collectively referred to as "coupling agent") is preferably used for the active terminal of the conjugated diene polymer.

In the reaction step, for example, a branched conjugated diene polymer can be obtained by coupling reaction with a reactive compound having three or more functionalities, a coupling agent having a nitrogen atom-containing group, or a silane sulfide compound represented by the following formula (3), which is a modifier containing silicon and sulfur atoms, at one active end of the conjugated diene polymer.

[Reactive compounds with three or more functional groups]
In the method for producing a branched conjugated diene-based polymer of this embodiment, the tri- or higher functional reactive compound used in the coupling step is preferably a tri- or higher functional reactive compound having a silicon atom.

Examples of reactive compounds having silicon atoms and a functionality of three or more include, but are not limited to, halogenated silane compounds, epoxy silane compounds, vinyl silane compounds, alkoxy silane compounds, etc.

Examples of halogenated silane compounds that serve as coupling agents include, but are not limited to, methyltrichlorosilane, tetrachlorosilane, tris(trimethylsiloxy)chlorosilane, tris(dimethylamino)chlorosilane, hexachlorodisilane, bis(trichlorosilyl)methane, 1,2-bis(trichlorosilyl)ethane, 1,2-bis(methyldichlorosilyl)ethane, 1,4-bis(trichlorosilyl)butane, and 1,4-bis(methyldichlorosilyl)butane.

Epoxy silane compounds that are coupling agents include, but are not limited to, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, epoxy-modified silicone, etc.

Examples of alkoxysilane compounds that serve as coupling agents include, but are not limited to, tetramethoxysilane, tetraethoxysilane, triphenoxymethylsilane, 1,2-bis(triethoxysilyl)ethane, and methoxy-substituted polyorganosiloxane.

[Coupling agents having nitrogen atom-containing groups]
Examples of coupling agents having a nitrogen atom-containing group include, but are not limited to, isocyanate compounds, isothiocyanate compounds, isocyanuric acid derivatives, carbonyl compounds having a nitrogen atom-containing group, vinyl compounds having a nitrogen atom-containing group, epoxy compounds having a nitrogen atom-containing group, alkoxysilane compounds having a nitrogen atom-containing group, and protected amine compounds having a nitrogen atom-containing group and capable of forming a primary or secondary amine.

In coupling agents having a nitrogen atom-containing group, the nitrogen atom-containing functional group is preferably a functional group derived from an amine-based compound that does not have active hydrogen, and examples of such amine-based compounds include tertiary amine compounds and protected amine compounds in which the above-mentioned active hydrogen is replaced with a protecting group. Other compounds that can form a nitrogen atom-containing functional group include imine compounds represented by the general formula -N=C and alkoxysilane compounds bonded to the nitrogen atom-containing group.

Examples of isocyanate compounds that are coupling agents having a nitrogen atom-containing group include, but are not limited to, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, polymeric diphenylmethane diisocyanate (C-MDI), phenyl isocyanate, isophorone diisocyanate, hexamethylene diisocyanate, butyl isocyanate, and 1,3,5-benzene triisocyanate.

Examples of isocyanuric acid derivatives, which are coupling agents having a nitrogen atom-containing group, include, but are not limited to, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate, 1,3,5-tris(3-triethoxysilylpropyl)isocyanurate, 1,3,5-tris(oxiran-2-yl)-1,3,5-triazinane-2,4,6-trione, 1,3,5-tris(isocyanatomethyl)-1,3,5-triazinane-2,4,6-trione, and 1,3,5-trivinyl-1,3,5-triazinane-2,4,6-trione.

Examples of carbonyl compounds that are coupling agents having a nitrogen atom-containing group include, but are not limited to, 1,3-dimethyl-2-imidazolidinone, 1-methyl-3-ethyl-2-imidazolidinone, 1-methyl-3-(2-methoxyethyl)-2-imidazolidinone, N-methyl-2-pyrrolidone, N-methyl-2-piperidone, N-methyl-2-quinolone, 4,4'-bis(diethylamino)benzophenone, and 4,4'-bis(dimethylamino)benzophenone. , methyl-2-pyridyl ketone, methyl-4-pyridyl ketone, propyl-2-pyridyl ketone, di-4-pyridyl ketone, 2-benzoylpyridine, N,N,N',N'-tetramethylurea, N,N-dimethyl-N',N'-diphenylurea, N,N-methyl diethylcarbamate, N,N-diethylacetamide, N,N-dimethyl-N',N'-dimethylaminoacetamide, N,N-dimethylpicolinic acid amide, N,N-dimethylisonicotinic acid amide, etc.

Examples of vinyl compounds that are coupling agents having a nitrogen atom-containing group include, but are not limited to, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N-methylmaleimide, N-methylphthalimide, N,N-bistrimethylsilylacrylamide, morpholinoacrylamide, 3-(2-dimethylaminoethyl)styrene, (dimethylamino)dimethyl-4-vinylphenylsilane, 4,4'-vinylidenebis(N,N-dimethylaniline), 4,4'-vinylidenebis(N,N-diethylaniline), 1,1-bis(4-morpholinophenyl)ethylene, 1-phenyl-1-(4-N,N-dimethylaminophenyl)ethylene, etc.

Epoxy compounds, which are coupling agents having a nitrogen atom-containing group, include, but are not limited to, for example, epoxy group-containing hydrocarbon compounds bonded to amino groups, and further include epoxy group-containing hydrocarbon compounds bonded to ether groups. Examples of such epoxy compounds include, but are not limited to, the epoxy compounds represented by the general formula (i).

In the formula (i), R is a divalent or higher organic group having at least one polar group selected from the group consisting of a divalent or higher hydrocarbon group, or an oxygen-containing polar group such as an ether, epoxy, or ketone, a sulfur-containing polar group such as a thioether or thioketone, or a nitrogen-containing polar group such as a tertiary amino group or an imino group.

The divalent or higher hydrocarbon group may be a saturated or unsaturated straight-chain, branched or cyclic hydrocarbon group, and includes an alkylene group, an alkenylene group, a phenylene group, etc. Preferably, it is a hydrocarbon group having 1 to 20 carbon atoms. Examples include methylene, ethylene, butylene, cyclohexylene, 1,3-bis(methylene)-cyclohexane, 1,3-bis(ethylene)-cyclohexane, o-, m-, p-phenylene, m-, p-xylene, bis(phenylene)-methane, etc.

In the formula (i), R ¹ and R ⁴ are hydrocarbon groups having 1 to 10 carbon atoms, and R ¹ and R ⁴ may be the same or different.
In the above formula (i), R ² and R ⁵ are hydrogen or a hydrocarbon group having 1 to 10 carbon atoms, and R ² and R ⁵ may be the same or different.
In the above formula (i), R ³ is a hydrocarbon group having 1 to 10 carbon atoms or a structure represented by the following formula (ii):
R ¹ , R ² and R ³ may be bonded to each other to form a cyclic structure.
In addition, when ^R3 is a hydrocarbon group, it may be a cyclic structure bonded to R. In the case of the cyclic structure, the N bonded to ^R3 and R may be directly bonded to each other.
In the above formula (i), n is an integer of 1 or more, and m is 0 or a natural number of 1 or more.

In the formula (ii), R ¹ and R ² are defined in the same manner as R ¹ and R ² in the formula (i), and R ¹ and R ² may be the same or different.

As the epoxy compound, which is a coupling agent having a nitrogen atom-containing group, it is preferable that the compound has an epoxy group-containing hydrocarbon group, and more preferably has a glycidyl group-containing hydrocarbon group.

The epoxy group-containing hydrocarbon group bonded to the amino group or ether group is not particularly limited, but examples thereof include a glycidylamino group, a diglycidylamino group, and a glycidoxy group. More preferred molecular structures are epoxy group-containing compounds each having a glycidylamino group or a diglycidylamino group, and a glycidoxy group, and examples of such compounds include those represented by the following general formula (iii).

In the formula (iii), R is defined as R in the formula (i), and R ⁶ is a hydrocarbon group having 1 to 10 carbon atoms or a structure represented by the following formula (iv).
When R ⁶ is a hydrocarbon group, it may be bonded to R to form a cyclic structure, and in this case, the N bonded to R ⁶ and R may be directly bonded to each other.
In formula (iii), n is an integer of 1 or more, and m is 0 or an integer of 1 or more.

The epoxy compound, which is a coupling agent having a nitrogen atom-containing group, is particularly preferably a compound having one or more diglycidylamino groups and one or more glycidoxy groups in the molecule.

Epoxy compounds used as coupling agents having a nitrogen atom-containing group include, but are not limited to, the following: N,N-diglycidyl-4-glycidoxyaniline, 1-N,N-diglycidylaminomethyl-4-glycidoxy-cyclohexane, 4-(4-glycidoxyphenyl)-(N,N-diglycidyl)aniline, 4-(4-glycidoxyphenoxy)-(N,N-diglycidyl)aniline, 4-(4-glycidoxybenzyl)-(N,N-diglycidyl)aniline, 4-(N,N'-diglycidyl-2-piperazinyl)-glycidoxybenzene, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl Examples of the glycidylamino methyl ester include m-xylylenediamine, 4,4-methylene-bis(N,N-diglycidylaniline), 1,4-bis(N,N-diglycidylamino)cyclohexane, N,N,N',N'-tetraglycidyl-p-phenylenediamine, 4,4'-bis(diglycidylamino)benzophenone, 4-(4-glycidylpiperazinyl)-(N,N-diglycidyl)aniline, 2-[2-(N,N-diglycidylamino)ethyl]-1-glycidylpyrrolidine, N,N-diglycidylaniline, 4,4'-diglycidyl-dibenzylmethylamine, N,N-diglycidylaniline, N,N-diglycidylorthotoluidine, and N,N-diglycidylaminomethylcyclohexane. Among these, particularly preferred are N,N-diglycidyl-4-glycidoxyaniline and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

Examples of alkoxysilane compounds that are coupling agents having a nitrogen atom-containing group include, but are not limited to, 3-dimethylaminopropyltrimethoxysilane, 3-dimethylaminopropylmethyldimethoxysilane, 3-diethylaminopropyltriethoxysilane, 3-morpholinopropyltrimethoxysilane, 3-piperidinopropyltriethoxysilane, 3-hexamethyleneiminopropylmethyldiethoxysilane, 3-(4-methyl-1-piperazino)propyltriethoxysilane, 1-[3-(triethoxysilyl)propyl]-3-methylhexyl tetrahydropyrimidine, 3-(4-trimethylsilyl-1-piperazino)propyltriethoxysilane, 3-(3-triethylsilyl-1-imidazolidinyl)propylmethyldiethoxysilane, 3-(3-trimethylsilyl-1-hexahydropyrimidinyl)propyltrimethoxysilane, 3-dimethylamino-2-(dimethylaminomethyl)propyltrimethoxysilane, bis(3-dimethoxymethylsilylpropyl)-N-methylamine, bis(3-trimethoxysilylpropyl)-N-methylamine, bis(3-triethoxysilylpropyl)methylamine, tris( N,N,N',N'-tetra(3-trimethoxysilylpropyl)ethylenediamine, 3-isocyanatopropyltrimethoxysilane, 3-cyanopropyltrimethoxysilane, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane, 2,2-diethoxy-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-(4-trimethoxysilylbutyl)-1-aza-2-silacyclohexane , 2,2-dimethoxy-1-(3-dimethoxymethylsilylpropyl)-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-phenyl-1-aza-2-silacyclopentane, 2,2-diethoxy-1-butyl-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-methyl-1-aza-2-silacyclopentane, 2,2-dimethoxy-8-(4-methylpiperazinyl)methyl-1,6-dioxa-2-silacyclooctane, 2,2-dimethoxy-8-(N,N-diethylamino)methyl-1,6-dioxa-2-silacyclooctane, etc.

As a coupling agent having a nitrogen atom-containing group and a protected amine compound capable of forming a primary or secondary amine, examples of compounds having an unsaturated bond and a protected amine in the molecule include, but are not limited to, 4,4'-vinylidenebis[N,N-bis(trimethylsilyl)aniline], 4,4'-vinylidenebis[N,N-bis(triethylsilyl)aniline], 4,4'-vinylidenebis[N,N-bis(t-butyldimethylsilyl)aniline], 4,4'-vinylidenebis[N-methyl-N-(trimethylsilyl)aniline], 4,4'-vinylidenebis[N-ethyl-N-(trimethylsilyl)aniline], 4,4 '-vinylidenebis[N-methyl-N-(triethylsilyl)aniline], 4,4'-vinylidenebis[N-ethyl-N-(triethylsilyl)aniline], 4,4'-vinylidenebis[N-methyl-N-(t-butyldimethylsilyl)aniline], 4,4'-vinylidenebis[N-ethyl-N-(t-butyldimethylsilyl)aniline], 1-[4-N,N-bis(trimethylsilyl)aminophenyl]-1-[4-N-methyl-N-(trimethylsilyl)aminophenyl]ethylene, 1-[4-N,N-bis(trimethylsilyl)aminophenyl]-1-[4-N,N-dimethylaminophenyl]ethylene, etc.

A coupling agent having a nitrogen atom-containing group, which is a protected amine compound capable of forming a primary or secondary amine, and which has an alkoxysilane and a protected amine in the molecule, includes, but is not limited to, the following: N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, N,N-bis(trimethylsilyl)aminopropyltriethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminoethyltrimethoxysilane, N ,N-bis(trimethylsilyl)aminoethylmethyldiethoxysilane, N,N-bis(triethylsilyl)aminopropylmethyldiethoxysilane, 3-(4-trimethylsilyl-1-piperazino)propyltriethoxysilane, 3-(3-triethylsilyl-1-imidazolidinyl)propylmethyldiethoxysilane, 3-(3-trimethylsilyl-1-hexahydropyrimidinyl)propyltrimethoxysilane, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane, 2,2-diethoxy-1-(3-triethoxysilylpropyl)-1-aza- 2-Silacyclopentane, 2,2-dimethoxy-1-(4-trimethoxysilylbutyl)-1-aza-2-silacyclohexane, 2,2-dimethoxy-1-(3-dimethoxymethylsilylpropyl)-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-phenyl-1-aza-2-silacyclopentane, 2,2-diethoxy-1-butyl-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-methyl-1-aza-2-silacyclopentane, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, N-(1-methylethylidene)-3-(triethyl N-(1-methylpropylidene)-3-(triethoxysilyl)-1-propanamine, N-(4-N,N-dimethylaminobenzylidene)-3-(triethoxysilyl)-1-propanamine, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, 3-(benzylideneamino)propyltrimethoxysilane, 3-(benzylideneamino)propyltriethoxysilane, 3-(benzylideneamino)propyltripropylsilane, etc.

Particularly preferred alkoxysilane compounds that are coupling agents having a nitrogen atom-containing group include, but are not limited to, the following: tris(3-trimethoxysilylpropyl)amine, tris(3-triethoxysilylpropyl)amine, tris(3-tripropoxysilylpropyl)amine, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethyl-1-sila-2-azacyclopentane)propyl]- 1,3-propanediamine, bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tetrakis(3-trimethoxysilylpropyl)-1,6-hexamethylenediamine, pentakis(3-trimethoxysilylpropyl)-diethylenetriamine, tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine, tetrakis[3-(2, 2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)silane, tris[3-(2,2-dimethoxy-1-aza-2-silacic 1-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-3,4,5-tris(3-trimethoxysilylpropane), 1-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-3,4,5-tris(3-trimethoxysilylpropane), silylpropyl)-cyclohexane, 1-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-3,4,5-tris(3-trimethoxysilylpropyl)-cyclohexane, 3,4,5-tris(3-trimethoxysilylpropyl)-cyclohexyl-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]ether, (3-trimethoxysilylpropyl)phosphate, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]phosphate, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)phosphate, and tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]phosphate.

A preferred coupling agent used in the reaction step is a silane sulfide compound represented by the following formula (3):

(In formula (3), Si represents a silicon atom, O represents an oxygen atom, and S represents a sulfur atom.
x is an integer of 1 to 3, y is 0 or an integer of 1 to 2, and x+y is 3.
R ¹ , R ² , and R ⁴ may be the same or different and each represents an alkyl group having 1 to 16 carbon atoms, and R ³ represents an aryl group having 6 to 16 carbon atoms, an alkylene group having 1 to 16 carbon atoms, or an alkyl chain having 1 to 16 carbon atoms.

The coupling agent represented by the formula (3) is not limited to the following, but may be, for example, S-trimethylsilylmercaptopropyltrimethoxysilane, S-trimethylsilylmercaptopropyltriethoxysilane, S-trimethylsilylmercaptopropyltripropoxysilane, S-trimethylsilylmercaptopropyltributoxysilane, S-trimethylsilylmercaptoethyltrimethoxysilane, S-trimethylsilylmercaptoethyltriethoxysilane, S-trimethylsilylmercaptoethyltripropoxysilane, S-trimethylsilylmercaptoethyltributoxysilane, S-trimethylsilylmercaptomethyltrimethoxysilane, S-trimethylsilylmercaptomethyltriethoxysilane, S-trimethylsilylmercapto Examples include methyl tripropoxysilane, S-trimethylsilyl mercapto methyl tributoxysilane, S-trimethylsilyl mercapto-2,2-dimethylpropyl trimethoxysilane, S-trimethylsilyl mercapto-2,2-dimethylpropyl triethoxysilane, S-trimethylsilyl mercapto-2,2-dimethylpropyl tripropoxysilane, S-trimethylsilyl mercapto-2,2-dimethylpropyl tributoxysilane, S-trimethylsilyl mercapto-2-methylpropyl trimethoxysilane, S-trimethylsilyl mercapto-2-methylpropyl triethoxysilane, S-trimethylsilyl mercapto-2-methylpropyl tripropoxysilane, and S-trimethylsilyl mercapto-2-methylpropyl tributoxysilane.

Also, S-trimethylsilylmercaptopropylmethyldimethoxysilane, S-trimethylsilylmercaptopropylmethyldiethoxysilane, S-trimethylsilylmercaptopropylmethyldipropoxysilane, S-trimethylsilylmercaptopropylmethyldibutoxysilane, S-trimethylsilylmercaptoethylmethyldimethoxysilane, S-trimethylsilylmercaptoethylmethyldiethoxysilane, S-trimethylsilylmercaptoethylmethyldipropoxysilane, S-trimethylsilylmercaptoethylmethyldibutoxysilane, S-trimethylsilylmercaptomethylmethyldimethoxysilane, S-trimethylsilylmercaptomethylmethyldiethoxysilane, S-trimethylsilylmercaptomethylmethyldibutoxysilane trimethyldipropoxysilane, S-trimethylsilylmercaptomethylmethyldibutoxysilane, S-trimethylsilylmercapto-2,2-dimethylpropylmethyldimethoxysilane, S-trimethylsilylmercapto-2,2-dimethylpropylmethyldiethoxysilane, S-trimethylsilylmercapto-2,2-dimethylpropylmethyldipropoxysilane, S-trimethylsilylmercapto-2,2-dimethylpropylmethyldibutoxysilane, S-trimethylsilylmercapto-2-methylpropylmethyldimethoxysilane, S-trimethylsilylmercapto-2-methylpropylmethyldiethoxysilane, S-trimethylsilylmercapto-2-methylpropylmethyldipropoxysilane.

Also, S-trimethylsilylmercapto-2-methylpropylmethyldibutoxysilane, S-trimethylsilylmercaptopropyldimethylmethoxysilane, S-trimethylsilylmercaptopropyldimethylethoxysilane, S-trimethylsilylmercaptopropyldimethylpropoxysilane, S-trimethylsilylmercaptopropyldimethylbutoxysilane, S-trimethylsilylmercaptoethyldimethylmethoxysilane, S-trimethylsilylmercaptoethyldimethylethoxysilane, S-trimethylsilylmercaptoethyldimethylpropoxysilane, S-trimethylsilylmercaptoethyldimethylbutoxysilane, S-trimethylsilylmercaptomethyldimethylmethoxysilane, Examples of such silylmercaptomethyldimethylethoxysilane include S-trimethylsilylmercaptomethyldimethylpropoxysilane, S-trimethylsilylmercaptomethyldimethylbutoxysilane, S-trimethylsilylmercapto-2,2-dimethylpropyldimethylmethoxysilane, S-trimethylsilylmercapto-2,2-dimethylpropyldimethylethoxysilane, S-trimethylsilylmercapto-2,2-dimethylpropyldimethylpropoxysilane, S-trimethylsilylmercapto-2,2-dimethylpropyldimethylbutoxysilane, S-trimethylsilylmercapto-2-methylpropyldimethylmethoxysilane, and S-trimethylsilylmercapto-2-methylpropyldimethylethoxysilane.

Also, S-trimethylsilylmercapto-2-methylpropyldimethylpropoxysilane, S-trimethylsilylmercapto-2-methylpropyldimethylbutoxysilane, S-triethylsilylmercaptopropyltrimethoxysilane, S-triethylsilylmercaptopropyltriethoxysilane, S-triethylsilylmercaptopropyltripropoxysilane, S-triethylsilylmercaptopropyltributoxysilane, S-triethylsilylmercaptoethyltrimethoxysilane, S-triethylsilylmercaptoethyltriethoxysilane, S-triethylsilylmercaptoethyltripropoxysilane, S-triethylsilylmercaptoethyltributoxysilane, S-triethylsilylmercaptomethyltrimethoxysilane, S-triethyl Examples include silylmercaptomethyltriethoxysilane, S-triethylsilylmercaptomethyltripropoxysilane, S-triethylsilylmercaptomethyltributoxysilane, S-triethylsilylmercapto-2,2-dimethylpropyltrimethoxysilane, S-triethylsilylmercapto-2,2-dimethylpropyltriethoxysilane, S-triethylsilylmercapto-2,2-dimethylpropyltripropoxysilane, S-triethylsilylmercapto-2,2-dimethylpropyltributoxysilane, S-triethylsilylmercapto-2-methylpropyltrimethoxysilane, S-triethylsilylmercapto-2-methylpropyltriethoxysilane, and S-triethylsilylmercapto-2-methylpropyltripropoxysilane.

Also, S-triethylsilylmercapto-2-methylpropyltributoxysilane, S-triethylsilylmercaptopropylmethyldimethoxysilane, S-triethylsilylmercaptopropylmethyldiethoxysilane, S-triethylsilylmercaptopropylmethyldipropoxysilane, S-triethylsilylmercaptopropylmethyldibutoxysilane, S-triethylsilylmercaptoethylmethyldimethoxysilane, S-triethylsilylmercaptoethylmethyldiethoxysilane, S-triethylsilylmercaptoethylmethyldipropoxysilane, S-triethylsilylmercaptoethylmethyldibutoxysilane, S-triethylsilylmercaptomethylmethyl Examples include dimethoxysilane, S-triethylsilylmercaptomethylmethyldiethoxysilane, S-triethylsilylmercaptomethylmethyldipropoxysilane, S-triethylsilylmercaptomethylmethyldibutoxysilane, S-triethylsilylmercapto-2,2-dimethylpropylmethyldimethoxysilane, S-triethylsilylmercapto-2,2-dimethylpropylmethyldiethoxysilane, S-triethylsilylmercapto-2,2-dimethylpropylmethyldipropoxysilane, S-triethylsilylmercapto-2,2-dimethylpropylmethyldibutoxysilane, and S-triethylsilylmercapto-2-methylpropylmethyldimethoxysilane.

Also, S-triethylsilylmercapto-2-methylpropylmethyldiethoxysilane, S-triethylsilylmercapto 2-methylpropylmethyldipropoxysilane, S-triethylsilylmercapto 2-methylpropylmethyldibutoxysilane, S-triethylsilylmercaptopropyldimethylmethoxysilane, S-triethylsilylmercaptopropyldimethylethoxysilane, S-triethylsilylmercaptopropyldimethylpropoxysilane, S-triethylsilylmercaptopropyldimethylbutoxysilane, S-triethylsilylmercaptoethyldimethylmethoxysilane, S-triethylsilylmercaptoethyldimethylethoxysilane, S-triethylsilylmercaptoethyldimethylpropoxy Examples include silane, S-triethylsilylmercaptoethyldimethylbutoxysilane, S-triethylsilylmercaptomethyldimethylmethoxysilane, S-triethylsilylmercaptomethyldimethylethoxysilane, S-triethylsilylmercaptomethyldimethylpropoxysilane, S-triethylsilylmercaptomethyldimethylbutoxysilane, S-triethylsilylmercapto-2,2-dimethylpropyldimethylmethoxysilane, S-triethylsilylmercapto-2,2-dimethylpropyldimethylethoxysilane, S-triethylsilylmercapto-2,2-dimethylpropyldimethylpropoxysilane, and S-triethylsilylmercapto-2,2-dimethylpropyldimethylbutoxysilane.

In addition, S-dimethyl tert-butylsilyl mercaptopropyl trimethoxysilane, S-dimethyl tert-butylsilyl mercaptopropyl triethoxysilane, S-dimethyl tert-butylsilyl mercaptopropyl tripropoxysilane, S-dimethyl tert-butylsilyl mercaptopropyl tributoxysilane, S-dimethyl tert-butylsilyl mercaptoethyl trimethoxysilane, S-dimethyl tert-butylsilyl mercaptoethyl triethoxysilane, S-dimethyl tert-butylsilyl mercaptoethyl Examples include ethyl tripropoxysilane, S-dimethyl tert butyl silyl mercapto ethyl tributoxysilane, S-dimethyl tert butyl silyl mercapto methyl trimethoxysilane, S-dimethyl tert butyl silyl mercapto methyl triethoxysilane, S-dimethyl tert butyl silyl mercapto methyl tripropoxysilane, S-dimethyl tert butyl silyl mercapto methyl tributoxysilane, and S-dimethyl tert butyl silyl mercapto-2,2-dimethylpropyl trimethoxysilane.

In addition, S-dimethyl tertbutylsilylmercapto-2,2-dimethylpropyltriethoxysilane, S-dimethyl tertbutylsilylmercapto-2,2-dimethylpropyltrippropoxysilane, S-dimethyl tertbutylsilylmercapto-2,2-dimethylpropyltributoxysilane, S-dimethyl tertbutylsilylmercapto-2-methylpropyltrimethoxysilane, S-dimethyl tertbutylsilylmercapto-2-methylpropyltriethoxysilane, S-dimethyl tertbutylsilylmercapto-2-methylpropyltrippropoxysilane, S-dimethyl tertbutylsilylmercapto-2 -methylpropyltributoxysilane, S-dimethyltertbutylsilylmercaptopropylmethyldimethoxysilane, S-dimethyltertbutylsilylmercaptopropylmethyldiethoxysilane, S-dimethyltertbutylsilylmercaptopropylmethyldipropoxysilane, S-dimethyltertbutylsilylmercaptopropylmethyldibutoxysilane, S-dimethyltertbutylsilylmercaptoethylmethyldimethoxysilane, S-dimethyltertbutylsilylmercaptoethylmethyldiethoxysilane, S-dimethyltertbutylsilylmercaptoethylmethyldipropoxysilane.

In addition, S-dimethyl tert-butylsilyl mercaptoethyl methyl dibutoxysilane, S-dimethyl tert-butylsilyl mercaptomethyl methyl dimethoxysilane, S-dimethyl tert-butylsilyl mercaptomethyl methyl diethoxysilane, S-dimethyl tert-butylsilyl mercaptomethyl methyl dipropoxysilane, S-dimethyl tert-butylsilyl mercaptomethyl methyl dibutoxysilane, S-dimethyl tert-butylsilyl mercapto-2,2-dimethylpropyl methyl dimethoxysilane, S-dimethyl tert-butylsilyl mercapto-2,2-dimethylpropyl methyl diethoxysilane, S-dimethyl tert-butylsilyl mercapto Examples of the silylmercapto include S-dimethyl tert-butylsilylmercapto-2,2-dimethylpropylmethyldipropoxysilane, S-dimethyl tert-butylsilylmercapto-2,2-dimethylpropylmethyldibutoxysilane, S-dimethyl tert-butylsilylmercapto-2-methylpropylmethyldimethoxysilane, S-dimethyl tert-butylsilylmercapto-2-methylpropylmethyldiethoxysilane, S-dimethyl tert-butylsilylmercapto-2-methylpropylmethyldipropoxysilane, S-dimethyl tert-butylsilylmercapto-2-methylpropylmethyldibutoxysilane, and S-dimethyl tert-butylsilylmercaptopropyldimethylmethoxysilane.

Further examples include S-dimethyl tert-butylsilyl mercaptopropyl dimethylethoxysilane, S-dimethyl tert-butylsilyl mercaptopropyl dimethylpropoxysilane, S-dimethyl tert-butylsilyl mercaptopropyl dimethylbutoxysilane, S-dimethyl tert-butylsilyl mercaptoethyl dimethylmethoxysilane, S-dimethyl tert-butylsilyl mercaptoethyl dimethylethoxysilane, S-dimethyl tert-butylsilyl mercaptoethyl dimethylpropoxysilane, S-dimethyl tert-butylsilyl mercaptoethyl dimethylbutoxysilane, S-dimethyl tert-butylsilyl mercaptomethyl dimethylmethoxysilane, S-dimethyl tert-butylsilyl mercaptomethyl dimethylethoxysilane, S-dimethyl tert-butylsilyl mercaptomethyl dimethylpropoxysilane, and S-dimethyl tert-butylsilyl mercaptomethyl dimethylbutoxysilane.

Further examples include S-dimethyl tert-butylsilyl mercapto-2,2-dimethylpropyl dimethyl methoxy silane, S-dimethyl tert-butyl silyl mercapto-2,2-dimethylpropyl dimethyl ethoxy silane, S-dimethyl tert-butyl silyl mercapto-2,2-dimethylpropyl dimethyl propoxy silane, S-dimethyl tert-butyl silyl mercapto-2,2-dimethylpropyl dimethyl butoxy silane, S-dimethyl tert-butyl silyl mercapto-2-methylpropyl dimethyl methoxy silane, S-dimethyl tert-butyl silyl mercapto-2-methylpropyl dimethyl ethoxy silane, S-dimethyl tert-butyl silyl mercapto-2-methylpropyl dimethyl propoxy silane, and S-dimethyl tert-butyl silyl mercapto-2-methylpropyl dimethyl butoxy silane.

<Branched conjugated diene polymer obtained through polymerization step, branching step, and reaction step>
In the method for producing a branched conjugated diene polymer of the present embodiment, the branched conjugated diene polymer obtained through the above-mentioned reaction step, particularly the step of reacting a coupling agent, preferably contains a structure derived from a compound having a nitrogen atom-containing group represented by the following general formula (i) or any of general formulas (A) to (C).

In the formula (i), R is a divalent or higher organic group having at least one polar group selected from a divalent or higher hydrocarbon group, a polar group having oxygen such as ether, epoxy, or ketone, a polar group having sulfur such as thioether or thioketone, or a polar group having nitrogen such as a tertiary amino group or an imino group.

The divalent or higher hydrocarbon group may be a saturated or unsaturated straight-chain, branched or cyclic hydrocarbon group, and includes an alkylene group, an alkenylene group, a phenylene group, etc. Preferably, it is a hydrocarbon group having 1 to 20 carbon atoms. Examples include methylene, ethylene, butylene, cyclohexylene, 1,3-bis(methylene)-cyclohexane, 1,3-bis(ethylene)-cyclohexane, o-, m-, p-phenylene, m-, p-xylene, bis(phenylene)-methane, etc.

In the formula (i), R ¹ and R ⁴ are hydrocarbon groups having 1 to 10 carbon atoms, and R ¹ and R ⁴ may be the same or different.
In the above formula (i), R ² and R ⁵ are hydrogen or a hydrocarbon group having 1 to 10 carbon atoms, and R ² and R ⁵ may be the same or different.
In the above formula (i), R ³ is a hydrocarbon group having 1 to 10 carbon atoms or a structure represented by the following formula (ii):
R ¹ , R ² and R ³ may be bonded to each other to form a cyclic structure.
In addition, when ^R3 is a hydrocarbon group, it may be a cyclic structure bonded to R. In the case of the cyclic structure, the N bonded to ^R3 and R may be directly bonded to each other.
In the above formula (i), n is an integer of 1 or more, and m is 0 or an integer of 1 or more.

In the formula (ii), R ¹ and R ² are defined in the same manner as R ¹ and R ² in the formula (i), and R ¹ and R ² may be the same or different.

(In formula (A), R ¹ to R ⁴ each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, R ⁵ represents an alkylene group having 1 to 10 carbon atoms, and R ⁶ represents an alkylene group having 1 to 20 carbon atoms.
m represents an integer of 1 or 2, n represents an integer of 2 or 3, and (m+n) represents an integer of 4 or more. When a plurality of R ¹ to R ⁴ are present, each of them is independent.

(In formula (B), R ¹ to R ⁶ each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and R ⁷ to R ⁹ each independently represent an alkylene group having 1 to 20 carbon atoms.
m, n, and l each independently represent an integer of 1 to 3, and (m+n+l) represents an integer of 4 or greater. When a plurality of R ¹ to R ⁶ are present, each of them is independent.

(In formula (C), R ¹² to R ¹⁴ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms, R ¹⁵ to R ¹⁸ and R ²⁰ each independently represent an alkyl group having 1 to 20 carbon atoms, R ¹⁹ and R ²² each independently represent an alkylene group having 1 to 20 carbon atoms, and R ²¹ represents an alkyl group having 1 to 20 carbon atoms or a trialkylsilyl group.
m represents an integer of 1 to 3; p represents 1 or 2.
When each of R ¹² to R ²² , m, and p is present in plurality, they are independent and may be the same or different.
i is an integer of 0 to 6, j is an integer of 0 to 6, k is an integer of 0 to 6, and (i+j+k) is an integer of 4 to 10.
A represents a hydrocarbon group having 1 to 20 carbon atoms, or an organic group having at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfur atom, and a phosphorus atom, and having no active hydrogen.

Coupling agents having a nitrogen atom-containing group represented by the formula (A) are not limited to the following, but include, for example, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane, 2,2-diethoxy-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-(4-trimethoxysilylbutyl)-1-aza-2-silacyclohexane, 2,2-dimethoxy-1-(5-trimethoxysilylpentyl)-1-aza-2-silacycloheptane, 2,2-dimethoxy-1-(3-dimethoxymethylsilylpropyl)-1-aza -2-silacyclopentane, 2,2-diethoxy-1-(3-diethoxyethylsilylpropyl)-1-aza-2-silacyclopentane, 2-methoxy-2-methyl-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane, 2-ethoxy,2-ethyl-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane, 2-methoxy-2-methyl-1-(3-dimethoxymethylsilylpropyl)-1-aza-2-silacyclopentane, and 2-ethoxy-2-ethyl-1-(3-diethoxyethylsilylpropyl)-1-aza-2-silacyclopentane.

Among these, from the viewpoint of reactivity and interaction between the functional group of the coupling agent having a nitrogen atom-containing group and inorganic fillers such as silica, as well as from the viewpoint of processability, those in which m is 2 and n is 3 are preferred. Specifically, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane and 2,2-diethoxy-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane are preferred.

The reaction temperature, reaction time, etc., when reacting the coupling agent having the nitrogen atom-containing group represented by formula (A) with the polymerization active terminal are not particularly limited, but it is preferable to react at 0°C or higher and 120°C or lower for 30 seconds or more.

The total number of moles of alkoxy groups bonded to silyl groups in the coupling agent compound having a nitrogen atom-containing group represented by formula (A) is preferably in the range of 0.6 to 3.0 times the number of moles of the alkali metal compound and/or alkaline earth metal compound added as the polymerization initiator, more preferably in the range of 0.8 to 2.5 times, and even more preferably in the range of 0.8 to 2.0 times. From the viewpoint of obtaining a sufficient modification rate, molecular weight, and branched structure of the obtained branched conjugated diene polymer, it is preferable to set it to 0.6 times or more, and it is preferable to obtain a branched conjugated diene polymer component by coupling the polymer ends together to improve processability, and from the viewpoint of the cost of the coupling agent, it is preferable to set it to 3.0 times or less.

The number of moles of the polymerization initiator is preferably 3.0 times or more, more preferably 4.0 times or more, relative to the number of moles of the coupling agent having a nitrogen atom-containing group represented by formula (A).

Coupling agents having a nitrogen atom-containing group represented by formula (B) include, but are not limited to, tris(3-trimethoxysilylpropyl)amine, tris(3-methyldimethoxysilylpropyl)amine, tris(3-triethoxysilylpropyl)amine, tris(3-methyldiethoxysilylpropyl)amine, tris(trimethoxysilylmethyl)amine, tris(2-trimethoxysilylethyl)amine, and tris(4-trimethoxysilylbutyl)amine.

Among these, from the viewpoint of reactivity and interaction between the functional group of the coupling agent and inorganic fillers such as silica, and from the viewpoint of processability, it is preferable that n, m, and l in the formula (B) all represent 3. Preferred examples include tris(3-trimethoxysilylpropyl)amine and tris(3-triethoxysilylpropyl)amine.

When the coupling agent having the nitrogen atom-containing group represented by formula (B) is reacted with the active terminal of the conjugated diene polymer obtained in the branching step, the reaction temperature, reaction time, etc. are not particularly limited, but it is preferable to react at 0°C or higher and 120°C or lower for 30 seconds or longer.

The total number of moles of alkoxy groups bonded to silyl groups in the coupling agent compound represented by formula (B) is preferably in the range of 0.6 to 3.0 times the number of moles of lithium constituting the above-mentioned polymerization initiator, more preferably in the range of 0.8 to 2.5 times, and even more preferably in the range of 0.8 to 2.0 times. In order to obtain a sufficient modification rate, molecular weight, and branched structure in the branched conjugated diene polymer obtained by the production method of this embodiment, it is preferable to set it to 0.6 times or more, and it is preferable to couple the polymer ends together to obtain a branched conjugated diene polymer component to improve processability, and in terms of the cost of the coupling agent, it is preferable to set it to 3.0 times or less.

The number of moles of the polymerization initiator is preferably 4.0 times or more, more preferably 5.0 times or more, relative to the number of moles of the coupling agent having a nitrogen atom-containing group represented by formula (B).

In the formula (C), A is preferably represented by any one of the following general formulas (II) to (V).

(In formula (II), ^B1 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. When there are a plurality of B1, each B1 is independent.)

(In formula (III), ^B2 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, ^B3 represents an alkyl group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. When there are multiple ^B2 and ^{multiple B3} , each of them is independent.)

(In formula (IV), ^B4 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. When there are multiple B4s, each ^B4 is independent.)

(In formula (V), ^B5 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. When there are multiple B5s, each ^B5 is independent.)

In the formula (C), when A is represented by formula (II), examples of coupling agents having a nitrogen atom-containing group include, but are not limited to, tris(3-trimethoxysilylpropyl)amine, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)amine, tris[3 -(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, tris(3-ethoxysilylpropyl)amine, bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]amine, bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)amine, tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl dimethylaminoethyl]amine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine cyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine pentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-triethoxysilylpropyl)-1,3-propanediamine, tris(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, bis(3-triethoxysilylpropyl)-bis[3-(2,2-diethoxy-1-aza- 2-silacyclopentane)propyl]-1,3-propanediamine, tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-1,3-propanediamine, tetrakis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tris(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane propyl]-1,3-propanediamine, bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila -2-azacyclopentane)propyl]-1,3-propanediamine, tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silyl)propyl]-1,3-propanediamine bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, -silacyclopentane)propyl]-1,3-propanediamine, tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl] -1,3-bisaminomethylcyclohexane, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclo pentane)propyl]-1,3-bisaminomethylcyclohexane, tetrakis(3-triethoxysilylpropyl)-1,3-propanediamine, tris(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, bis(3-triethoxysilylpropyl)-bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethyl Cyclohexane, tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-1,3-propanediamine, tetrakis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tris(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane San, bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tetrakis(3-trimethoxysilylpropyl)-1,6-hexamethylenediamine, and pentakis(3-trimethoxysilylpropyl)-diethylenetriamine.

In the formula (C), when A is represented by formula (III), examples of the coupling agent having a nitrogen atom-containing group include, but are not limited to, tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine, bis(2-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-methyl-1,3-propanediamine, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine, tris(3-triethoxysilylpropyl)-methyl-1,3-propanediamine, bis(2-triethoxysilylpropyl)-[3-(2,2-di ethoxy-1-aza-2-silacyclopentane)propyl]-methyl-1,3-propanediamine, bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-methyl-1,3-propanediamine, N1,N1'-(propane-1,3-diyl)bis(N1-methyl-N3,N3-bis(3-(trimethoxysilyl)propyl)-1,3-propanediamine), and N1-(3-(bis(3-(trimethoxysilyl)propyl)amino)propyl)-N1-methyl-N3-(3-(methyl(3-(trimethoxysilyl)propyl)amino)propyl)-N3-(3-(trimethoxysilyl)propyl)-1,3-propanediamine.

In the formula (C), when A is represented by formula (IV), examples of the coupling agent having a nitrogen atom-containing group include, but are not limited to, tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)silane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)silane, silane, bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, (3-trimethoxysilyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane silane, bis[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, bis(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-silane bis[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-bis(3-trimethoxysilylpropyl)silane, and bis(3-trimethoxysilylpropyl)-bis[3-(1-methoxy-2-methyl-1-sila-2-azacyclopentane)propyl]silane.

In the formula (C), when A is represented by formula (V), examples of the coupling agent having a nitrogen atom-containing group include, but are not limited to, 3-tris[2-(2,2-dimethoxy-1-aza-2-silacyclopentane)ethoxy]silyl-1-(2,2-dimethoxy-1-aza-2-silacyclopentane)propane and 3-tris[2-(2,2-dimethoxy-1-aza-2-silacyclopentane)ethoxy]silyl-1-trimethoxysilylpropane.

In the formula (C), A is preferably represented by formula (II) or formula (III), and k is 0.

Coupling agents having such a nitrogen atom-containing group tend to be easily available, and when the branched conjugated diene polymer obtained by the manufacturing method of this embodiment is vulcanized, it tends to have better abrasion resistance and low hysteresis loss performance. Coupling agents having such a nitrogen atom-containing group include, but are not limited to, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, tris(3-trimethoxysilylpropyl)amine, tris(3-triethoxysilylpropyl)amine, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis ... bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine, and bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trismethoxysilylpropyl)-methyl-1,3-propanediamine.

In the formula (C), it is more preferable that A is represented by formula (II) or formula (III), k is 0, and in formula (II) or formula (III), a is an integer of 2 to 10.
This tends to result in better abrasion resistance and low hysteresis loss performance when vulcanized.
Examples of coupling agents having such a nitrogen atom-containing group include, but are not limited to, tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, and _N1- (3-(bis(3-(trimethoxysilyl)propyl)amino)propyl) _-N1 -methyl-N3-(3-(methyl( _3- (trimethoxysilyl)propyl)amino)propyl) _-N3- (3-(trimethoxysilyl)propyl)-1,3-propanediamine.

The amount of the compound represented by formula (C) added as a coupling agent having a nitrogen atom-containing group can be adjusted so that the moles of the conjugated diene polymer to the moles of the coupling agent react in the desired stoichiometric ratio, which tends to achieve the desired highly branched star structure.

The number of moles of the polymerization initiator is preferably 5.0 times or more, more preferably 6.0 times or more, relative to the number of moles of the coupling agent having a nitrogen atom-containing group represented by formula (C).

In this case, in formula (C), the number of functional groups of the coupling agent ((m-1) x i + p x j + k) is preferably an integer from 5 to 10, and more preferably an integer from 6 to 10.

In the branched conjugated diene polymer obtained by the production method of the present embodiment, the proportion of the polymer having a nitrogen atom-containing group in the polymer is represented by a modification rate.
The modification rate is preferably 60% by mass or more, more preferably 65% by mass or more, even more preferably 70% by mass or more, still more preferably 75% by mass or more, still more preferably 80% by mass or more, and particularly preferably 82% by mass or more.
By setting the modification rate to 60% by mass or more, the processability when vulcanized is excellent, and the vulcanized product tends to have better abrasion resistance and low hysteresis loss performance.

<Polymerization Termination Step>
In the method for producing a branched conjugated diene polymer of the present embodiment, a reaction step can be carried out in which the above-mentioned coupling agent or polymerization terminator is reacted with the active terminal of the conjugated diene polymer obtained through the above-mentioned polymerization step and branching step.
As the polymerization termination step, for example, a polymerization termination step performed using a bifunctional reactive compound on the active terminal of the conjugated diene polymer, or a polymerization termination step performed using a polymerization terminator having a nitrogen atom-containing group (hereinafter, these may be collectively referred to as "polymerization terminator") is preferable.

In the polymerization termination step, for example, the active terminal of the polymer obtained in the branching step described above is subjected to a polymerization termination reaction with a bifunctional reactive compound or a polymerization terminator having a nitrogen atom-containing group, thereby obtaining the desired branched conjugated diene polymer.

[Bifunctional reactive compounds]
In the method for producing a branched conjugated diene-based polymer of the present embodiment, the bifunctional reactive compound used in the polymerization termination step may have any structure, but is preferably a bifunctional reactive compound having a silicon atom.

[Polymerization terminator having nitrogen atom-containing group]
In the method for producing a branched conjugated diene polymer of the present embodiment, the polymerization terminator having a nitrogen atom-containing group used in the polymerization termination step may have any structure, but preferably has a functional group that reacts with the conjugated diene polymer.

As the polymerization terminator having a nitrogen atom-containing group, from the viewpoint of improving fuel economy performance, an alkoxy compound having a nitrogen atom-containing group is preferred.
Examples of the polymerization terminator having a nitrogen atom-containing group include 3-(N,N-dimethylaminopropyl)dimethoxymethylsilane, 3-(N,N-diethylaminopropyl)dimethoxymethylsilane, 3-(N,N-dipropylaminopropyl)dimethoxymethylsilane, 3-(N,N-dimethylaminopropyl)diethoxymethylsilane, 3-(N,N-diethylaminopropyl)diethoxymethylsilane, 3-(N,N-dipropylaminopropyl)diethoxymethylsilane, 3-(N,N-dimethylaminopropyl)dimethoxyethylsilane, 3-(N,N-diethylaminopropyl)dimethoxyethylsilane, 3-(N,N-dipropylaminopropyl)dimethoxyethylsilane, 3-(N,N-dimethylaminopropyl)diethoxyethylsilane, 3-(N,N-diethylaminopropyl)diethoxyethylsilane, 3-(N,N-dipropylaminopropyl)diethoxyethylsilane, and the like.

The branched conjugated diene polymer obtained by the production method of this embodiment through the above-mentioned polymerization step, branching step, and reaction step has a branched structure of preferably 8 to 36 branches, more preferably 10 to 24 branches, and even more preferably 12 to 20 branches.
The total number of branching points in the branched conjugated diene polymer obtained by the production method of this embodiment is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, and even more preferably 5 or more.
When the branched structure and the total number of branching points are within the above ranges, the processability, fuel economy, and abrasion resistance tend to be excellent.
In order to construct a branched conjugated diene polymer having a branched structure of 8 to 36 branches and, in the case of a modified polymer, having a total number of branching points of 2 to 15, it is necessary to use a branching agent in a molar ratio of 1/2 or less and 1/100 or more of that of the polymerization initiator and a coupling agent having three or more functional groups. In the case of a polymer that does not require modification, the branching point may be one or more.
In order to construct a branched structure having 8 to 36 branches and a total number of branching points of 3 to 12, it is preferable to use a branching agent having a molar ratio of 1/3 or less and 1/50 or more of the polymerization initiator and a coupling agent having 4 or more functional groups.
In order to construct a branched structure having 10 to 24 branches and a total number of branching points of 4 to 10, it is preferable to use a branching agent having a molar ratio of 1/6 or less and 1/25 or more of the polymerization initiator and a coupling agent having 5 or more functional groups.
In order to construct a branched structure having 12 to 20 branches and a total number of branching points of 5 to 9, it is preferable to use a branching agent having a molar ratio of 1/8 or less and 1/12 or more of that of the polymerization initiator and a coupling agent having 6 or more functional groups.

(Condensation reaction process)
In the method for producing a branched conjugated diene polymer of the present embodiment, a condensation reaction step of carrying out a condensation reaction in the presence of a condensation promoter may be carried out after the above-mentioned coupling step or before the coupling step.

(Hydrogenation step)
In the method for producing a branched conjugated diene polymer of the present embodiment, a hydrogenation step of hydrogenating the conjugated diene portion may be carried out.
The method for hydrogenating the conjugated diene portion of the conjugated diene polymer is not particularly limited, and any known method can be used.
A suitable hydrogenation method is to blow gaseous hydrogen into a polymer solution in the presence of a catalyst.The catalyst is not particularly limited, but may be, for example, a heterogeneous catalyst such as a catalyst in which a precious metal is supported on a porous inorganic material; a catalyst in which a salt of nickel, cobalt, or the like is solubilized and reacted with an organoaluminum, or a homogeneous catalyst such as a catalyst using a metallocene such as titanocene.Among these, a titanocene catalyst is preferred from the viewpoint of being able to select mild hydrogenation conditions.Also, the hydrogenation of aromatic groups can be carried out by using a catalyst supported on a precious metal.

Examples of hydrogenation catalysts include, but are not limited to, (1) supported heterogeneous hydrogenation catalysts in which metals such as Ni, Pt, Pd, and Ru are supported on carbon, silica, alumina, diatomaceous earth, and the like; (2) so-called Ziegler-type hydrogenation catalysts that use transition metal salts such as organic acid salts or acetylacetone salts of Ni, Co, Fe, Cr, and the like and reducing agents such as organoaluminum; and (3) so-called organometallic complexes such as organometallic compounds of Ti, Ru, Rh, Zr, and the like. Furthermore, examples of hydrogenation catalysts include, but are not limited to, known hydrogenation catalysts described in JP-B-42-8704, JP-B-43-6636, JP-B-63-4841, JP-B-1-37970, JP-B-1-53851, JP-B-2-9041, and JP-A-8-109219. A preferred hydrogenation catalyst is a reaction mixture of a titanocene compound and a reducing organometallic compound.

(Step of adding deactivator and neutralizer)
In the method for producing a branched conjugated diene polymer of this embodiment, after the above-mentioned coupling step, a deactivator, a neutralizer, and the like may be added to the polymer solution, if necessary.
Examples of the quenching agent include, but are not limited to, water; and alcohols such as methanol, ethanol, and isopropanol.
Examples of the neutralizing agent include, but are not limited to, carboxylic acids such as stearic acid, oleic acid, and versatic acid (a highly branched carboxylic acid mixture having 9 to 11 carbon atoms, with the majority having 10 carbon atoms); aqueous solutions of inorganic acids; and carbon dioxide gas.

(Rubber stabilizer addition process)
In the method for producing a branched conjugated diene-based polymer of the present embodiment, it is preferable to add a rubber stabilizer from the viewpoint of preventing gel formation after polymerization and improving stability during processing.
The rubber stabilizer is not limited to the following ones, and known ones can be used. For example, antioxidants such as 2,6-di-tert-butyl-4-hydroxytoluene (hereinafter also referred to as "BHT"), n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenol)propionate, and 2-methyl-4,6-bis[(octylthio)methyl]phenol are preferred.

(Rubber softener addition process)
In the method for producing a branched conjugated diene polymer of the present embodiment, from the viewpoint of further improving the productivity of the branched conjugated diene polymer and the processability when a filler or the like is blended to form a resin composition, a rubber softener can be added as necessary.
The rubber softener is not particularly limited, but examples thereof include extender oil, liquid rubber, and resin.
The method of adding a rubber softener to a branched conjugated diene polymer is not limited to the following, but a preferred method is to add a rubber softener to a branched conjugated diene polymer solution, mix, and remove the solvent from the resulting polymer solution containing the rubber softener.

Examples of preferred extender oils include aromatic oils, naphthenic oils, and paraffin oils. Among these, aromatic substitute oils having a polycyclic aromatic (PCA) content of 3% by mass or less according to the IP346 method are preferred from the viewpoint of environmental safety, oil bleeding prevention, and wet grip properties. Examples of aromatic substitute oils include TDAE (Treated Distillate Aromatic Extracts), MES (Mild Extraction Solvate), and RAE (Residual Aromatic Extracts) shown in Kautschuk Gummi Kunststoffe 52(12)799(1999).
Preferred liquid rubbers include, but are not limited to, liquid polybutadiene, liquid styrene-butadiene rubber, and the like.
The effects of adding liquid rubber include the ability to improve the processability of a resin composition containing a branched conjugated diene polymer and a filler, etc., and the ability to shift the glass transition temperature of the resin composition to a lower temperature, which tends to improve the abrasion resistance, low hysteresis loss, and low-temperature properties of a vulcanized product.
Resins as rubber softeners include, but are not limited to, aromatic petroleum resins, coumarone-indene resins, terpene resins, rosin derivatives (including paulownia oil resins), tall oil, tall oil derivatives, rosin ester resins, natural and synthetic terpene resins, aliphatic hydrocarbon resins, aromatic hydrocarbon resins, mixed aliphatic/aromatic hydrocarbon resins, coumarin-indene resins, phenolic resins, p-tert-butylphenol-acetylene resins, phenol-formaldehyde resins, xylene-formaldehyde resins, monoolefin oligomers, diolefin oligomers, hydrogenated aromatic hydrocarbon resins, cyclic aliphatic hydrocarbon resins, hydrogenated hydrocarbon resins, hydrocarbon resins, hydrogenated paulownia oil resins, hydrogenated oil resins, esters of hydrogenated oil resins and monofunctional or polyfunctional alcohols, etc. These resins may be used alone or in combination of two or more. When hydrogenating, all of the unsaturated groups may be hydrogenated, or some may be left.
Effects of adding a resin as a rubber softener include improving the processability of a resin composition obtained by blending a branched conjugated diene polymer with a filler or the like, tending to improve the breaking strength of a vulcanized product, and tending to improve wet skid resistance by shifting the glass transition temperature of the resin composition to a higher temperature.

The amount of the rubber softener, such as an extender oil, liquid rubber, or resin, added is not particularly limited, but is preferably 1 part by mass or more and 60 parts by mass or less, more preferably 5 parts by mass or more and 50 parts by mass or less, and even more preferably 10 parts by mass or more and 37.5 parts by mass or less, relative to 100 parts by mass of the branched conjugated diene-based polymer obtained by the production method of the present embodiment.
When the rubber softener is added within the above range, the processability of a resin composition obtained by blending the branched conjugated diene-based polymer obtained by the production method of the present embodiment with a filler or the like becomes good, and the breaking strength and abrasion resistance of a vulcanizate tend to be good.

(Solvent removal process)
In the method for producing a branched conjugated diene polymer of the present embodiment, a known method can be used to obtain the obtained branched conjugated diene polymer from the polymer solution. The method is not particularly limited, but examples thereof include a method of separating the solvent by steam stripping or the like, filtering the polymer, and then dehydrating and drying it to obtain the polymer, a method of concentrating the polymer in a flashing tank and further devolatilizing the polymer with a vent extruder or the like, and a method of directly devolatilizing the polymer with a drum dryer or the like.

[Branched conjugated diene polymer]
Hereinafter, a preferred embodiment of the branched conjugated diene polymer obtained by the method for producing a branched conjugated diene polymer of the present embodiment will be described.
In a preferred embodiment of the branched conjugated diene polymer of the present embodiment, the branched conjugated diene polymer has one or more side chains in the polymer chain and has a branching degree (Bn) of 1 or more as measured by a GPC-light scattering method with a viscosity detector, the branched conjugated diene polymer contains sulfur atoms and silicon atoms, the molar ratio of the silicon atoms to the sulfur atoms is 1.05 or more and less than 10, and the Mooney viscosity measured at 100° C. is 40 or more and 170 or less.
The branched conjugated diene-based polymer of the present embodiment, particularly due to having the above-mentioned structure, has excellent processability when vulcanized, and when vulcanized, exhibits particularly excellent abrasion resistance and breaking strength.

A branching degree (Bn) of 1 or more as measured by GPC-light scattering method with a viscosity detector means that the polymer chain has one or more side chains.
After specifying the structure of the polymer chain, the Mooney viscosity and the number of moles of silicon atoms relative to sulfur atoms are specified within specific ranges, and further the amount of vinyl bonds in the conjugated diene bond units and the amount of aromatic vinyl compound are adjusted arbitrarily, whereby the glass transition temperature (hereinafter also referred to as "Tg") can be adjusted arbitrarily while maintaining processability when made into a vulcanizate.
For example, by setting the amount of vinyl bonds in the conjugated diene bond units and the amount of aromatic vinyl compounds low, the Tg of the branched conjugated diene polymer decreases, and the abrasion resistance and rupture strength of the vulcanized product improve, and a rubber composition having excellent low hysteresis loss tends to be obtained.
In addition, by setting the vinyl bond amount in the conjugated diene bond unit and the aromatic vinyl compound amount high, the Tg of the branched conjugated diene polymer increases, the processability when vulcanized improves, and a rubber composition having excellent wet skid resistance tends to be obtained.

(Mooney Viscosity)
The branched conjugated diene-based polymer of the present embodiment described above has one or more side chains in the polymer, has a branching degree (Bn) of 1 or more as measured by a GPC-light scattering method with a viscosity detector, and may have a branched structure in the side chain as described later.
Generally, a polymer having a branched structure tends to have a smaller molecular size than a linear polymer having the same molecular weight. Therefore, the molecular weight of a polymer having a branched structure tends to be underestimated by the polystyrene-equivalent molecular weight obtained by screening the polymer according to its molecular size and measuring it by gel permeation chromatography (hereinafter also referred to as "GPC"), which is a relative comparison method with a standard polystyrene sample.
In addition, the absolute molecular weight measured by the GPC-light scattering method with a viscosity detector tends to be able to accurately measure the molecular weight because the molecular size is directly observed by the light scattering method and the molecular weight (absolute molecular weight) is measured, without being influenced by the polymer structure or interactions with the column packing material, and without being influenced by the polymer structure such as the branched structure of the conjugated diene-based polymer, compared with the polystyrene-equivalent molecular weight determined by gel permeation chromatography (GPC). However, it is easily influenced by the detection method of the light scattering detector, and although it is effective for relative comparison under specific measurement conditions, it is difficult to identify the true structure of the conjugated diene-based polymer.

On the other hand, Mooney viscosity is an index showing the overall characteristics of a branched conjugated diene polymer, including information on the molecular weight, molecular weight distribution, branching degree, and softener content of the branched conjugated diene polymer. The method for measuring Mooney viscosity is specified in ISO289, and the measurement error due to the difference in the instrument is small, so that Mooney viscosity is extremely effective in controlling the performance of the branched conjugated diene polymer.
Generally, viscosity can be regarded as an index that can replace molecular weight. However, since it is difficult to accurately grasp the molecular weight of a polymer having a branched structure, the present inventors set Mooney viscosity as one of the requirements for the branched conjugated diene-based polymer of the present embodiment.
The branched conjugated diene polymer of this embodiment preferably has a Mooney viscosity (hereinafter also referred to as "ML") measured at 100°C of 40 or more and 170 or less.
Usually, when the ML is adjusted to a low value by decreasing the molecular weight or by adding a softener (oil, etc.), the abrasion resistance and breaking strength of the vulcanized product tend to be impaired.
That is, in order to obtain a branched conjugated diene-based polymer exhibiting desired performance, it is insufficient to only control the molecular weight or the Mooney viscosity. Therefore, in this embodiment, from the viewpoint of increasing the elastic modulus of the rubber composition, the structure of the side chain of the polymer, the degree of branching, and the molar ratio of silicon atoms to sulfur atoms in the polymer are specified in addition to the Mooney viscosity, and the abrasion resistance and breaking strength of the vulcanizate are improved without impairing the processability of the rubber composition.

The branched conjugated diene polymer of the present embodiment has a Mooney viscosity measured at 100° C. of preferably 40 or more and 170 or less, more preferably 50 or more and 150 or less, and even more preferably 55 or more and 130 or less, from the viewpoints of productivity of the branched conjugated diene polymer, processability when the polymer is made into a rubber composition containing a filler or the like, and abrasion resistance and breaking strength when the rubber composition is made into a vulcanizate.
When the Mooney viscosity measured at 100°C is 40 or more, the abrasion resistance and breaking strength of the vulcanized product tend to be improved. When the Mooney viscosity measured at 100°C is 170 or less, problems in the production of the branched conjugated diene polymer are prevented, and the processability of the rubber composition containing a filler or the like tends to be good.

In the branched conjugated diene polymer of this embodiment, the Mooney viscosity can be controlled by adjusting the molecular weight as described above or by adding a predetermined amount of a rubber softener.
Specifically, the above numerical range can be controlled by adding 1 part by mass or more and 60 parts by mass or less of a rubber softener described later to 100 parts by mass of the branched conjugated diene polymer. When the branched conjugated diene polymer of the present embodiment is produced by continuous polymerization, it is common to extend the branched conjugated diene polymer with oil or the like within a range that does not impair the performance of the branched conjugated diene polymer from the viewpoint of productivity in the solvent removal step. The present inventors have focused on the fact that the processability of the polymer can be appropriately controlled by specifying the physical properties in the extended and finished state rather than in the state of the polymer alone, and have considered that when a softener is added to finish the polymer, the Mooney viscosity should be specified in the state containing the softener, and have defined it as above.
In measuring the Mooney viscosity, a sample of a branched conjugated diene polymer formed into a plate shape by a pressure press is set in the apparatus, the sample is preheated at 100° C. for 1 minute, the rotor is rotated at 2 rpm, and the torque is measured after 4 minutes, and the measured value is regarded as the Mooney viscosity (ML ₍₁₊₄₎ ). More specifically, it can be measured by the method described in the examples described later.

(Side Chain)
The branched conjugated diene-based polymer of the present embodiment in the above-mentioned preferred embodiment has a branching degree (Bn) of 1 or more as measured by a GPC-light scattering method with a viscosity detector. This means that the polymer has a structure having one or more side chains in the polymer chain.
The side chain in the branched conjugated diene polymer of the present embodiment means that there is one or more polymer chains branched from the longest polymer chain.
Specifically, the side chains can be formed by a method of introducing a polymer chain into the longest polymer chain via a branching agent, which will be described later.
The number of side chains in the polymer chain can be controlled to a desired value by selecting the structure and amount of the branching agent to be added, as well as the structure of the modifying agent to be described later.

The branched conjugated diene polymer of the present embodiment has one or more side chains, preferably two or more, more preferably four or more, and further preferably five or more.
A branched conjugated diene polymer having the number of side chains within the above range tends to have excellent processability when vulcanized, and tends to have excellent abrasion resistance and fracture properties when vulcanized.
The upper limit of the number of side chains in the branched conjugated diene polymer of the present embodiment is not particularly limited, but in terms of industrial production, it is practically 25 or less, more preferably 23 or less, and even more preferably 20 or less.
For example, when the number of side chains in the polymer chain of the branched conjugated diene-based polymer of the present embodiment is 25 or less, a compound having an excellent balance of processability when vulcanized, abrasion resistance when vulcanized, and fracture properties, which are mutually contradictory properties, tends to be obtained.
In addition, when the number of side chains in the polymer chain is one or more, the processability when vulcanized becomes good, and a compound having an excellent balance between fuel efficiency and wet skid resistance, which are mutually contradictory properties, when vulcanized tends to be obtained.

A structure having one or more side chains in a polymer chain has generally been formed by carrying out a coupling reaction at the end of the polymer chain to introduce a branched structure, and forming a structure in which uniform polymer chains are bonded in a star shape, starting from a coupling agent. However, when a side chain is formed using a branching agent, the polymer chain length bonded to the side chain, the number of polymer chains, and the polymer chain length of the main chain can be freely adjusted by adjusting the timing of adding the branching agent, the structure of the branching agent, and the amount added, which allows for a high degree of freedom in designing the polymer structure and tends to make it easier to obtain a polymer with a desired balance of physical properties, which is preferable.
The number of side chains of the branched conjugated diene polymer is the sum of the branches due to the coupling reaction at the terminals and the branches due to the branching agent, and can be appropriately set depending on the structure of the branched conjugated diene polymer to be produced, such as the Mooney viscosity, the ratio of silicon atoms to sulfur atoms, the molecular weight, the vinyl content, the aromatic vinyl content, and the like, and the production process, such as the setting of the polymerization initiator and the presence or absence of a branching process or a modification process.
In the present embodiment, the number of side chains theoretically determined from the type and amount of the coupling agent and the type and amount of the branching agent can be determined as the degree of branching (Bn) measured by a GPC-light scattering method with a viscosity detector, which will be described later.

(Conjugated diene polymer containing silicon and sulfur atoms)
The branched conjugated diene-based polymer of the present embodiment in the above-mentioned preferred embodiment contains a silicon atom and a sulfur atom.
The branched conjugated diene polymer of the present embodiment has a branching degree of 1 or more and contains silicon atoms and sulfur atoms, and therefore has excellent processability when vulcanized, and the vulcanized product has excellent abrasion resistance and fracture properties.
From the viewpoint of the effect of making the processability excellent when vulcanized, the molar ratio of silicon atoms to sulfur atoms tends to contribute greatly.Specifically, when the molar ratio of silicon atoms to sulfur atoms (silicon atoms/sulfur atoms) is large, the amount of branching agent added is large, and the number of side chains in the polymer chain tends to be large.In this case, the processability when vulcanized tends to be excellent.

In the branched conjugated diene polymer of the above-mentioned preferred embodiment, the positions at which the silicon atoms and sulfur atoms are introduced have little effect on the properties, so that the silicon atoms and sulfur atoms may be introduced in any position.
Silicon atoms can be introduced into the branched conjugated diene polymer as a branching agent residue while increasing the number of branches in the polymer by main chain branching, for example, by reacting the conjugated diene polymer with a branching agent having a silicon atom. Also, silicon atoms can be introduced into the branched conjugated diene polymer as a modifier residue by reacting the branched conjugated diene polymer with a modifier having a silicon atom.
The sulfur atom can be introduced into the conjugated diene polymer as a modifier residue, for example, by reacting the conjugated diene polymer with a modifier having a sulfur atom.
When a modifier having a sulfur atom is reacted with the active end of a conjugated diene polymer, a sulfur atom can be placed at the end of the polymer chain, and vulcanization can be performed at the end of the polymer chain. This reduces the number of free polymer ends from the crosslinking points, improves crosslinking efficiency, and strengthens the interface between the surface of the silica as a filler and the polymer, tending to provide a rubber composition with excellent fuel saving performance.

(molar ratio of silicon atoms to sulfur atoms)
The branched conjugated diene-based polymer of the present embodiment in the above-mentioned preferred embodiment has a degree of branching of 1 or more and a structure containing silicon atoms and sulfur atoms, and the molar ratio of silicon atoms to sulfur atoms (silicon atoms/sulfur atoms) is 1.05 or more and less than 10, preferably 1.07 or more and less than 8, more preferably 1.1 or more and less than 7, and even more preferably 1.12 or more and less than 6.
A branched conjugated diene polymer having a molar ratio of silicon atoms to sulfur atoms within this range tends to exhibit excellent abrasion resistance and fracture properties when vulcanized.
In the case where the branching agent forming the main chain branch contains a silicon atom and the terminal modifier contains a sulfur atom, the silicon atom is derived from the total amount of the branching agent residue and the modifier residue, and the sulfur atom is derived from the modifier residue. When the molar number of silicon atoms relative to the sulfur atom is large, it indicates that the amount of the branching agent added is large, and the processability when the vulcanizate is made tends to be excellent. When the molar number of silicon atoms relative to the sulfur atom is small, it indicates that the amount of the branching agent added is small, and the wear resistance and fracture properties when the vulcanizate is made tend to be excellent.
The molar ratio of silicon atoms to sulfur atoms can be controlled within the above numerical range by adjusting the types and amounts of the branching agent and the modifying agent added.

(Degree of branching (Bn))
The number of side chains in the branched conjugated diene polymer of the present embodiment can be expressed as a branching degree (Bn) measured by a GPC-light scattering method with a viscosity detector (hereinafter, also simply referred to as the branching degree (Bn)).
In a preferred embodiment of the branched conjugated diene polymer of the present invention, that is, a branched conjugated diene polymer having the above-mentioned configuration, i.e., having one or more side chains in the polymer chain and having a branching degree (Bn) of 1 or more as measured by a GPC-light scattering method with a viscosity detector, the branched conjugated diene polymer contains sulfur atoms and silicon atoms, the molar ratio of the silicon atoms to the sulfur atoms is 1.05 or more and less than 10, and the Mooney viscosity measured at 100° C. is 40 or more and 170 or less, the branching degree (Bn) as measured by a GPC-light scattering method with a viscosity detector is 1 or more, preferably 2 or more and 25 or less, and more preferably 3 or more and 20 or less, from the viewpoints of processability, abrasion resistance, and breaking strength.

For example, the degree of branching (Bn) being 4 or more means that the branched conjugated diene-based polymer of the present embodiment has substantially 4 or more side polymer chains relative to the longest polymer main chain.
The branching degree (Bn) of the branched conjugated diene polymer is defined as g'=6Bn/[(Bn+1)(Bn+2)], using the shrinkage factor (g') measured by GPC-light scattering method with a viscosity detector.
In general, a polymer having branches tends to have a smaller molecular size when compared to a linear polymer having the same absolute molecular weight.
The shrinkage factor (g') is a measure of the ratio of the molecular size to that of a linear polymer of the same supposed absolute molecular weight, i.e., the greater the degree of branching of a polymer, the smaller the shrinkage factor (g') tends to be.
In this embodiment, the intrinsic viscosity is used as an index of molecular size for this shrinkage factor, and the linear polymer is assumed to follow the relational expression: intrinsic viscosity [η] = -3.883 M ^0.771 , where M is the absolute molecular weight.
However, the shrinkage factor represents the rate of reduction in molecular size and does not accurately represent the branched structure of a polymer.
Therefore, the branching degree (Bn) of the branched conjugated diene polymer is calculated using the value of the shrinkage factor (g') at each absolute molecular weight of the branched conjugated diene polymer. The calculated "branching degree (Bn)" accurately represents the number of polymers directly or indirectly bonded to each other with respect to the longest main chain structure.
The calculated branching degree (Bn) is an index expressing the branching structure of a branched conjugated diene polymer. For example, in the case of a typical four-branched star polymer (four polymer chains connected to the center), two arms of the polymer chain are bonded to the longest highly branched main chain structure, and the branching degree (Bn) is evaluated as 2.

The branched conjugated diene-based polymer of the present embodiment in the above-mentioned preferred embodiment has a branching degree (Bn) of 1 or more, preferably 2 or more and 25 or less. In such a case, it means that the modified conjugated diene-based polymer has a star polymer structure having 3 to 27 branches similar to the star polymer structure.
Here, "branch" refers to a structure formed by direct or indirect bonding of one polymer to another polymer, and "degree of branching (Bn)" refers to the number of polymers that are directly or indirectly bonded to each other in the longest main chain structure.
Since the branching degree (Bn) is 1 or more, preferably 2 or more and 25 or less, the branched conjugated diene-based polymer of the present embodiment has extremely excellent processability when vulcanized, and when vulcanized, has excellent abrasion resistance and breaking strength.

In general, an increase in absolute molecular weight tends to deteriorate processability. When the absolute molecular weight is increased in a linear polymer structure, the viscosity of the vulcanizate increases significantly, and processability deteriorates significantly.
Therefore, even if a large number of functional groups are introduced into the polymer to improve the affinity and/or reactivity with silica blended as a filler, the silica cannot be sufficiently dispersed in the polymer during the kneading process, which causes a problem that the function of the introduced functional groups is not exhibited, and the effects of low hysteresis loss and improved wet skid resistance that should be expected due to the introduction of functional groups tend not to be exhibited.
On the other hand, since the branched conjugated diene polymer of the present embodiment is specified to have a branching degree (Bn) of 1 or more, preferably from 2 to 25, an increase in viscosity when vulcanized due to an increase in absolute molecular weight is significantly suppressed, so that the polymer is thoroughly mixed with silica or the like in the kneading step, and it becomes possible to disperse silica around the branched conjugated diene polymer. As a result, it becomes possible to improve abrasion resistance and fracture strength by setting the molecular weight of the branched conjugated diene polymer to be large, and it becomes possible to disperse silica around the polymer by thorough kneading, and it becomes possible for the functional group to act and/or react, so that the polymer has low hysteresis loss and wet skid resistance sufficient for practical use.
The absolute molecular weight of the branched conjugated diene polymer can be measured by the method described in the examples below.
The degree of branching (Bn) of the branched conjugated diene polymer of the present embodiment can be controlled to a desired value by adjusting the type and amount of the branching agent described below.

(Side Chain Structure)
The branched conjugated diene polymer of the present embodiment preferably has a portion derived from a vinyl monomer containing an alkoxysilyl group or a halosilyl group in a part of the polymer chain, and the portion derived from the vinyl monomer containing an alkoxysilyl group or a halosilyl group preferably has a side chain.
The side chain has one or more branching points, preferably three or more branching points, and more preferably four or more branching points, at a branching point derived from a vinyl monomer containing an alkoxysilyl group or a halosilyl group.
In addition, the branch point forming the side chain preferably has at least one polymer chain, more preferably has two or more polymer chains that are not the main chain, and further preferably has four or more polymer chains that are not the main chain.
In particular, in the case of a main chain branched structure consisting of a vinyl monomer containing an alkoxysilyl group or a halosilyl group, when signal detection is performed by 29Si-NMR, a peak derived from the main chain branched structure is detected in the range of −45 ppm to −65 ppm, more specifically in the range of −50 ppm to −60 ppm.

A preferred embodiment of the branched conjugated diene polymer of the present embodiment is a structure in which a terminal of a polymer chain is modified with a modifying agent containing a sulfur atom, a part of the polymer chain has a portion derived from a vinyl monomer containing an alkoxysilyl group or a halosilyl group, and the portion derived from the vinyl monomer containing an alkoxysilyl group or a halosilyl group has a further main chain branched structure.
A method for obtaining a branched conjugated diene polymer having the above-mentioned structure includes, for example, a method in which an organolithium compound is used as a polymerization initiator to carry out polymerization, a branching agent that provides a specific branching point is added during or after polymerization, and the polymerization is continued, followed by modification with a sulfur atom-containing modifier that provides a specific branching rate. In this case, the modifying group can be controlled by adjusting the number of functional groups and the amount added of the sulfur-containing modifier, and the main chain branched structure can be controlled by adjusting the number of functional groups, the amount added, and the timing of addition of the branching agent.
Such means for controlling the polymerization conditions will be described in the production process in the examples given below.

(Details of side chain structure)
In the branched conjugated diene polymer of the present embodiment, the portion derived from the vinyl monomer containing an alkoxysilyl group or a halosilyl group is preferably a monomer unit based on a compound represented by the following formula (4) or (5), and the polymer chain preferably has a branching point due to the monomer unit based on a compound represented by the following formula (4) or (5).
Moreover, the branched conjugated diene polymer of the present embodiment is more preferably a branched conjugated diene polymer obtained by using a coupling agent, and further preferably a modified conjugated diene polymer in which at least one end of the conjugated diene polymer is modified with a sulfur atom-containing group.

In formula (4), R ¹ represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, which may have a branched structure in part.
R ² and R ³ each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, which may partially have a branched structure.
When a plurality of R ¹ to R ³ are present, they are each independent.
^X1 independently represents a halogen atom.
m represents an integer of 0 to 2, n represents an integer of 0 to 3, and l represents an integer of 0 to 3. (m+n+l) represents 3.
In formula (5), R ² to R ⁵ each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and may partially have a branched structure. When a plurality of R ² to R ⁵ are present, each is independent of each other.
X ² and X ³ each independently represent a halogen atom.
m represents an integer of 0 to 2, n represents an integer of 0 to 3, and l represents an integer of 0 to 3. (m+n+l) represents 3.
a represents an integer from 0 to 2, b represents an integer from 0 to 3, and c represents an integer from 0 to 3. (a+b+c) represents 3.)

The branched conjugated diene polymer of the present embodiment is preferably a branched conjugated diene polymer having monomer units based on a compound represented by the above formula (4), in which ^R1 is a hydrogen atom and m = 0. This increases the number of branches, and provides the effect of improving abrasion resistance and processability.

The branched conjugated diene polymer of this embodiment is preferably a branched conjugated diene polymer having monomer units based on the compound represented by formula (5), where m = 0 and b = 0. This provides an improved effect in terms of abrasion resistance and processability.

The branched conjugated diene polymer of this embodiment is preferably a branched conjugated diene polymer having monomer units based on a compound represented by formula (5), where m = 0, l = 0, n = 3, a = 0, b = 0, and c = 3. This provides the effect of improving abrasion resistance and processability.

Further, the branched conjugated diene polymer of the present embodiment is more preferably a branched conjugated diene polymer having monomer units based on a compound represented by formula (4) in which ^R1 is a hydrogen atom, m = 0, l = 0, and n = 3. This improves the modification rate and branching degree, and provides the effects of improving fuel saving performance, abrasion resistance, and processability.

(Branching Agent)
In the branched conjugated diene polymer of the present embodiment, when constructing a main chain branched structure, it is preferable to use a branching agent represented by the following formula (4) or formula (5) as a branching agent.
The portion derived from the vinyl monomer containing an alkoxysilyl group or a halosilyl group is a monomer unit based on a compound represented by the following formula (4) or (5), and the branched conjugated diene polymer of the present embodiment preferably has a structure having a polymer chain branching point due to a monomer unit based on a compound represented by the following formula (4) or (5).

In formula (4), R ¹ represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, which may have a branched structure in part.
R ² and R ³ each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, which may partially have a branched structure.
When a plurality of R ¹ to R ³ are present, they are each independent.
^X1 independently represents a halogen atom.
m represents an integer of 0 to 2, n represents an integer of 0 to 3, and l represents an integer of 0 to 3. (m+n+l) represents 3.
In formula (5), R ² to R ⁵ each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and may partially have a branched structure. When a plurality of R ² to R ⁵ are present, each is independent of each other.
X ² and X ³ each independently represent a halogen atom.
m represents an integer of 0 to 2, n represents an integer of 0 to 3, and l represents an integer of 0 to 3. (m+n+l) represents 3.
a represents an integer from 0 to 2, b represents an integer from 0 to 3, and c represents an integer from 0 to 3. (a+b+c) represents 3.)

From the viewpoints of continuity of polymerization and improvement of the degree of branching, the branching agent used in constructing the main chain branched structure of the branched conjugated diene polymer of the present embodiment is preferably a compound in which R ¹ in formula (4) is a hydrogen atom and m=0.

In addition, in this embodiment, the branching agent used to construct the main chain branched structure of the branched conjugated diene polymer is preferably a compound in which m = 0 and b = 0 in formula (5) from the viewpoint of improving the degree of branching.

In the present embodiment, the branching agent used in constructing the main chain branched structure of the branched conjugated diene polymer is more preferably a compound in which R ¹ in formula (4) is a hydrogen atom, m=0, 1=0, and n=3, from the viewpoints of continuity of polymerization and improvement of the modification rate and degree of branching.

In addition, in this embodiment, the branching agent used to construct the main chain branched structure of the branched conjugated diene polymer is preferably a compound in which m = 0, l = 0, n = 3, a = 0, b = 0, and c = 3 in the above formula (5), from the viewpoint of improving the modification rate and the degree of branching.

Examples of branching agents represented by the formula (4) include, but are not limited to, trimethoxy(4-vinylphenyl)silane, triethoxy(4-vinylphenyl)silane, tripropoxy(4-vinylphenyl)silane, tributoxy(4-vinylphenyl)silane, triisopropoxy(4-vinylphenyl)silane, trimethoxy(3-vinylphenyl)silane, triethoxy(3-vinylphenyl)silane, tripropoxy(3-vinylphenyl)silane, tributoxy(3-vinylphenyl)silane, triisopropoxy(3-vinylphenyl)silane, trimethoxy(2-vinylphenyl)silane, triethoxy(2-vinylphenyl)silane, tripropoxy(2-vinylphenyl)silane, tributoxy(2-vinylphenyl)silane, ) silane, triisopropoxy(2-vinylphenyl)silane, dimethoxymethyl(4-vinylphenyl)silane, diethoxymethyl(4-vinylphenyl)silane, dipropoxymethyl(4-vinylphenyl)silane, dibutoxymethyl(4-vinylphenyl)silane, diisopropoxymethyl(4-vinylphenyl)silane, dimethoxymethyl(3-vinylphenyl)silane, diethoxymethyl(3-vinylphenyl)silane, dipropoxymethyl(3-vinylphenyl)silane, dibutoxymethyl(3-vinylphenyl)silane, diisopropoxymethyl(3-vinylphenyl)silane, dimethoxymethyl(2-vinylphenyl)silane, diethoxymethyl(2-vinylphenyl)silane, dipropoxymethyl(2-vinylphenyl)silane , dibutoxymethyl(2-vinylphenyl)silane, diisopropoxymethyl(2-vinylphenyl)silane, dimethylmethoxy(4-vinylphenyl)silane, dimethylethoxy(4-vinylphenyl)silane, dimethylpropoxy(4-vinylphenyl)silane, dimethylbutoxy(4-vinylphenyl)silane, dimethylisopropoxy(4-vinylphenyl)silane, dimethylmethoxy(3-vinylphenyl)silane, dimethylethoxy(3-vinylphenyl)silane, dimethylpropoxy(3-vinylphenyl)silane, dimethylbutoxy(3-vinylphenyl)silane, dimethylisopropoxy(3-vinylphenyl)silane, dimethylmethoxy(2-vinylphenyl)silane, dimethylethoxy(2-vinylphenyl)silane, dimethyl dimethylpropoxy(2-vinylphenyl)silane, dimethylbutoxy(2-vinylphenyl)silane, dimethylisopropoxy(2-vinylphenyl)silane, trimethoxy(4-isopropenylphenyl)silane, triethoxy(4-isopropenylphenyl)silane, tripropoxy(4-isopropenylphenyl)silane, tributoxy(4-isopropenylphenyl)silane, triisopropoxy(4-isopropenylphenyl)silane, trimethoxy(3-isopropenylphenyl)silane, triethoxy(3-isopropenylphenyl)silane, tripropoxy(3-isopropenylphenyl)silane, tributoxy(3-isopropenylphenyl)silane, triisopropoxy(3-isopropenylphenyl)silane, trimethoxy(2 -isopropenylphenyl)silane, triethoxy(2-isopropenylphenyl)silane, tripropoxy(2-isopropenylphenyl)silane, tributoxy(2-isopropenylphenyl)silane, triisopropoxy(2-isopropenylphenyl)silane, dimethoxymethyl(4-isopropenylphenyl)silane, diethoxymethyl(4-isopropenylphenyl)silane, dipropoxymethyl(4-isopropenylphenyl)silane, dibutoxymethyl(4-isopropenylphenyl)silane, diisopropoxymethyl(4-isopropenylphenyl)silane, dimethoxymethyl(3-isopropenylphenyl)silane, diethoxymethyl(3-isopropenylphenyl)silane, dipropoxymethyl(3-isopropenylphenyl)silane silane, dibutoxymethyl(3-isopropenylphenyl)silane, diisopropoxymethyl(3-isopropenylphenyl)silane, dimethoxymethyl(2-isopropenylphenyl)silane, diethoxymethyl(2-isopropenylphenyl)silane, dipropoxymethyl(2-isopropenylphenyl)silane, dibutoxymethyl(2-isopropenylphenyl)silane, diisopropoxymethyl(2-isopropenylphenyl)silane, dimethylmethoxy(4-isopropenylphenyl)silane, dimethylethoxy(4-isopropenylphenyl)silane, dimethylpropoxy(4-isopropenylphenyl)silane, dimethylbutoxy(4-isopropenylphenyl)silane, dimethylisopropoxy(4-isopropenylphenyl)silane Silane, dimethylmethoxy(3-isopropenylphenyl)silane, dimethylethoxy(3-isopropenylphenyl)silane, dimethylpropoxy(3-isopropenylphenyl)silane, dimethylbutoxy(3-isopropenylphenyl)silane, dimethylisopropoxy(3-isopropenylphenyl)silane, dimethylmethoxy(2-isopropenylphenyl)silane, dimethylethoxy(2-isopropenylphenyl)silane, dimethylpropoxy(2-isopropenylphenyl)silane, dimethylbutoxy(2-isopropenylphenyl)silane, dimethylisopropoxy(2-isopropenylphenyl)silane, trichloro(4-vinylphenyl)silane, trichloro(3-vinylphenyl)silane, trichloro(2-vinylphenyl)silane (4-vinylphenyl)silane, tribromo(3-vinylphenyl)silane, tribromo(2-vinylphenyl)silane, dichloromethyl(4-vinylphenyl)silane, dichloromethyl(3-vinylphenyl)silane, dichloromethyl(2-vinylphenyl)silane, dibromomethyl(4-vinylphenyl)silane, dibromomethyl(3-vinylphenyl)silane, dibromomethyl(2-vinylphenyl)silane, dimethylchloro(4-vinylphenyl)silane, dimethylchloro(3-vinylphenyl)silane, dimethylchloro(2-vinylphenyl)silane, dimethylbromo(4-vinylphenyl)silane, dimethylbromo(3-vinylphenyl)silane, and dimethylbromo(2-vinylphenyl)silane.

Among these, trimethoxy(4-vinylphenyl)silane, triethoxy(4-vinylphenyl)silane, tripropoxy(4-vinylphenyl)silane, tributoxy(4-vinylphenyl)silane, triisopropoxy(4-vinylphenyl)silane, trimethoxy(3-vinylphenyl)silane, triethoxy(3-vinylphenyl)silane, tripropoxy(3-vinylphenyl)silane, tributoxy(3-vinylphenyl)silane, triisopropoxy(3-vinylphenyl)silane, and trichloro(4-vinylphenyl)silane are preferred, and trimethoxy(4-vinylphenyl)silane, triethoxy(4-vinylphenyl)silane, tripropoxy(4-vinylphenyl)silane, tributoxy(4-vinylphenyl)silane, and triisopropoxy(4-vinylphenyl)silane are more preferred.

Examples of branching agents represented by the formula (5) include, but are not limited to, 1,1-bis(4-trimethoxysilylphenyl)ethylene, 1,1-bis(4-triethoxysilylphenyl)ethylene, 1,1-bis(4-tripropoxysilylphenyl)ethylene, 1,1-bis(4-tripentoxysilylphenyl)ethylene, 1,1-bis(4-triisopropoxysilylphenyl)ethylene, 1,1-bis(3-trimethoxysilylphenyl)ethylene, 1,1-bis(3-triethoxysilylphenyl)ethylene, 1,1-bis(3-tripropoxysilylphenyl)ethylene, 1,1-bis(3-tripentoxysilylphenyl)ethylene, 1,1-bis(3-triisopropoxysilylphenyl)ethylene, 1,1-bis(2 -trimethoxysilylphenyl)ethylene, 1,1-bis(2-triethoxysilylphenyl)ethylene, 1,1-bis(3-tripropoxysilylphenyl)ethylene, 1,1-bis(2-tripentoxysilylphenyl)ethylene, 1,1-bis(2-triisopropoxysilylphenyl)ethylene, 1,1-bis(4-(dimethylmethoxysilyl)phenyl)ethylene, 1,1-bis(4-(diethylmethoxysilyl)phenyl)ethylene, 1,1-bis(4-(dipropylmethoxysilyl)phenyl)ethylene, 1,1-bis(4-(dimethylethoxysilyl)phenyl)ethylene, 1,1-bis(4-(diethylethoxysilyl)phenyl)ethylene, 1,1-bis(4-(dipropylethoxysilyl)phenyl)ethylene.

Of these, 1,1-bis(4-trimethoxysilylphenyl)ethylene, 1,1-bis(4-triethoxysilylphenyl)ethylene, 1,1-bis(4-tripropoxysilylphenyl)ethylene, 1,1-bis(4-tripentoxysilylphenyl)ethylene, and 1,1-bis(4-triisopropoxysilylphenyl)ethylene are preferred, with 1,1-bis(4-trimethoxysilylphenyl)ethylene being more preferred.

(Modifier)
In the branched conjugated diene polymer of the present embodiment, as a preferred embodiment, the branched conjugated diene polymer contains a sulfur atom and a silicon atom.
The branched conjugated diene-based polymer of the present embodiment is preferably modified with a predetermined modifying agent, and the modifying agent used in the modification step is preferably a compound having a sulfur atom, more preferably a compound having a silicon atom and a sulfur atom.
The branched conjugated diene polymer containing silicon atoms and sulfur atoms of the present embodiment can be obtained, for example, by reacting a branched conjugated diene polymer with a modifier containing silicon atoms and sulfur atoms described below.
The branched conjugated diene polymer of the present embodiment is more preferably a branched conjugated diene polymer obtained by subjecting an active terminal of a branched conjugated diene polymer obtained through a polymerization and branching step to a modification reaction using a reactive compound containing a silicon atom and a sulfur atom.

A branched conjugated diene polymer modified with a modifier containing silicon atoms and sulfur atoms is made into a rubber composition blended with a filler such as silica, and when the rubber composition is vulcanized, the number of free polymer ends from the crosslinking points decreases, crosslinking efficiency improves, and the interface between the silica surface as a filler and the polymer becomes strong, which tends to result in excellent fuel economy performance.
That is, the branched conjugated diene-based polymer modified with the above-mentioned modifier has good dispersibility of silica, and the rubber composition containing a filler or the like has good processability, and when the rubber composition is vulcanized, the abrasion resistance and breaking strength tend to be good.

The modifying agent containing silicon atoms and sulfur atoms is not limited, but is preferably, for example, a sulfide group-containing alkoxysilane compound, and more preferably, a compound having a silane sulfide structure in which the sulfide group is substituted with an alkylsilane compound.
In the silane sulfide structure in which the sulfide group is replaced by an alkylsilane compound, the alkoxysilane is eliminated to form a thiol group in the solvent removal step described below. When a rubber composition is made by compounding a filler such as silica, the generated thiol group has an increased interaction with the silica, which improves the dispersion of the silica in the polymer, improving the fuel saving performance and improving the processability.
In addition, when the rubber composition is vulcanized, the ends of the polymer chains are crosslinked by the sulfur atoms introduced at the ends of the polymer chains, which reduces the number of free polymer ends from the crosslinking points and improves crosslinking efficiency, which tends to result in excellent abrasion resistance and fracture properties when the rubber composition is vulcanized.

As a modifier containing silicon atoms and sulfur atoms, a silane sulfide compound represented by the following formula (3) is preferred, and the branched conjugated diene polymer of this embodiment is preferably modified with a silane sulfide compound represented by the following formula (3).

(In formula (3), Si represents a silicon atom, O represents an oxygen atom, and S represents a sulfur atom.
x is an integer of 1 to 3, y is 0 or an integer of 1 to 2, and x+y is 3.
R ¹ , R ² , and R ⁴ may be the same or different and each represents an alkyl group having 1 to 16 carbon atoms, and R ³ represents an aryl group having 6 to 16 carbon atoms, an alkylene group having 1 to 16 carbon atoms, or an alkyl chain having 1 to 16 carbon atoms.

Specific examples of the silane sulfide compound represented by formula (3) are as described above.

(Coupling Agent)
In the above-described preferred embodiment, the branched conjugated diene-based polymer of the present embodiment is preferably coupled with a coupling agent comprising at least one compound selected from the group consisting of tin halides, tin alkoxides, silicon halides, and alkoxysilanes.
The branched conjugated diene-based polymer of the present embodiment may be in the form of a branched conjugated diene-based polymer composition partially containing the above-mentioned coupled polymer, or may be entirely coupled.

The coupling agent may have only a coupling function, or may also have a modifying function of introducing sulfur and/or silicon into the polymer.
When the coupling agent does not contain silicon and/or sulfur, from the viewpoint of controlling the physical properties of a rubber composition containing a filler such as silica, it is preferable to modify a part of the polymer with the above-mentioned modifier and further add a coupling agent to adjust the molecular weight and/or branching degree of the remaining unmodified conjugated diene polymer.
A branched conjugated diene polymer to which a coupling agent has been added has a high ratio of high molecular weight components, and tends to have excellent abrasion resistance and fracture properties when vulcanized.

The coupling agent is selected from the group consisting of tin halides, tin alkoxides, silicon halides, and alkoxysilanes. These coupling agents may be used alone or in combination of two or more.
In the present embodiment, the preferred amount of the coupling agent to be added is, in terms of the number of moles of the functional group of the coupling agent relative to the number of moles of the polymerization initiator involved in the polymerization (hereinafter referred to as the number of equivalents), 0 or more and 0.6 or less equivalents, more preferably 0.1 or more and 0.5 or less equivalents, and even more preferably 0.2 or more and 0.4 or less equivalents.
In the case of a coupling agent that is a tin halide compound or a silicon halide compound, the number of functional groups is the number of moles of halogen.
In the case of tin alkoxide compounds and alkoxysilane compounds, generally, all alkoxy groups bonded to tin atoms and silicon atoms tend not to react, and one alkoxy group remains per tin atom or silicon atom.Therefore, the number of functional groups of tin alkoxide compounds and alkoxysilane compounds is the number of alkoxy groups bonded to the same tin atom or silicon atom minus 1.More specifically, the number of functional groups of coupling agents is calculated by assuming that tetraalkoxytin (silyl) compounds are trifunctional, trialkoxytin (silyl) compounds are bifunctional, dialkoxytin (silyl) compounds are monofunctional, and monoalkoxysilyl groups are 0 functional.

Examples of the tin halide compound that is a coupling agent include, but are not limited to, tin tetrachloride, tin tetrabromide, tin tetrafluoride, methyltrichlorostannane, tris(trimethylsiloxy)chlorostannane, tris(dimethylamino)chlorostannane, hexachlorodistannane, bis(trichlorostannane)methane, 1,2-bis(trichlorostannane)ethane, 1,2-bis(methyldichlorostannane)ethane, 1,4-bis(trichlorostannane)butane, and 1,4 bis(methyldichlorostannane)butane.
Examples of halogenated silicon compounds that are coupling agents include, but are not limited to, methyltrichlorosilane, tetrachlorosilane, tris(trimethylsiloxy)chlorosilane, tris(dimethylamino)chlorosilane, hexachlorodisilane, bis(trichlorosilyl)methane, 1,2-bis(trichlorosilyl)ethane, 1,2-bis(methyldichlorosilyl)ethane, 1,4-bis(trichlorosilyl)butane, and 1,4 bis(methyldichlorosilyl)butane.
Examples of the tin alkoxide compound that is a coupling agent include, but are not limited to, tetramethoxystannane, tetraethoxystannane, triphenoxymethylstannane, and 1,2-bis(triethoxystannane)ethane.
The alkoxysilane compound serving as the coupling agent is not limited to the following, but examples thereof include tetramethoxysilane, tetraethoxysilane, triphenoxymethylsilane, 1,2-bis(triethoxysilyl)ethane, and methoxy-substituted polyorganosiloxane.

[Branched conjugated diene polymer composition]
The branched conjugated diene polymer composition of the present embodiment contains a branched conjugated diene polymer produced by the method for producing a branched conjugated diene polymer of the present embodiment described above, or a branched conjugated diene polymer having the preferred embodiment described above.
That is, the branched conjugated diene polymer composition preferably contains 10% by mass or more and less than 100% by mass of a branched conjugated diene polymer which has one or more side chains in the polymer chain and has a branching degree (Bn) of 1 or more as measured by a GPC-light scattering method equipped with a viscosity detector, the branched conjugated diene polymer contains sulfur atoms and silicon atoms, the molar ratio of the silicon atoms to the sulfur atoms is 1.05 or more and less than 10, and the Mooney viscosity as measured at 100° C. is 40 or more and 170 or less.
By the content of the branched conjugated diene polymer of the present embodiment in the branched conjugated diene polymer composition of the present embodiment being 10% by mass or more, the effect of excellent abrasion resistance and fracture properties can be obtained when the composition is vulcanized. From this viewpoint, the content of the branched conjugated diene polymer is preferably 20% by mass or more, and more preferably 30% by mass or more.

The branched conjugated diene polymer composition of the present embodiment may contain, in the branched conjugated diene polymer, a coupled conjugated diene polymer obtained by the above-mentioned coupling step.
Preferably, the polymer may contain a branched conjugated diene polymer coupled with at least one compound selected from the group consisting of tin halides, tin alkoxides, silicon halides, and alkoxysilanes.

The branched conjugated diene polymer composition of the present embodiment may be in an embodiment containing the branched conjugated diene polymer of the present embodiment described above and a rubber softener.
In such a configuration, the amount of the rubber softener is preferably 1 to 60 parts by mass, more preferably 5 to 55 parts by mass, and even more preferably 10 to 50 parts by mass, per 100 parts by mass of the branched conjugated diene polymer, from the viewpoint of productivity in producing the branched conjugated diene polymer.

[Rubber composition and method for producing rubber composition]
The rubber composition of the present embodiment contains a rubber component containing 10% by mass or more of the branched conjugated diene-based polymer produced by the production method of the present embodiment described above, and 5.0 parts by mass or more and 150 parts by mass or less of a filler per 100 parts by mass of the rubber component.
The method for producing the rubber composition of the present embodiment includes the steps of obtaining a branched conjugated diene-based polymer by the above-described production method, obtaining a rubber component containing 10% by mass or more of the branched conjugated diene-based polymer, and incorporating 5.0 parts by mass or more and 150 parts by mass or less of a filler per 100 parts by mass of the rubber component.
Furthermore, by containing 10% by mass or more of the branched conjugated diene polymer obtained by the production method of this embodiment in the rubber component, it is possible to improve fuel economy performance, processability, and abrasion resistance.

The filler preferably includes a silica-based inorganic filler.
By dispersing a silica-based inorganic filler as a filler, the rubber composition tends to have excellent processability when vulcanized, and the vulcanized product tends to have an excellent balance between abrasion resistance, breaking strength, and low hysteresis loss and wet skid resistance.
The rubber composition preferably contains a silica-based inorganic filler even when it is used for vulcanized rubber applications such as automobile parts such as tires and anti-vibration rubbers, and shoes.

The rubber composition of the present embodiment is obtained by mixing a rubber component containing 10% by mass or more of the branched conjugated diene-based polymer obtained by the above-mentioned production method with the filler.
The rubber component may contain a rubbery polymer (hereinafter simply referred to as "rubbery polymer") other than the above-mentioned branched conjugated diene-based polymer.
Examples of such rubber-like polymers include, but are not limited to, conjugated diene polymers or hydrogenated products thereof, random copolymers of conjugated diene compounds and vinyl aromatic compounds or hydrogenated products thereof, block copolymers of conjugated diene compounds and vinyl aromatic compounds or hydrogenated products thereof, and others include non-diene polymers and natural rubber.

Examples of rubber-like polymers include styrene-based elastomers such as butadiene rubber or its hydrogenated product, isoprene rubber or its hydrogenated product, styrene-butadiene rubber or its hydrogenated product, styrene-butadiene block copolymer or its hydrogenated product, and styrene-isoprene block copolymer or its hydrogenated product, and acrylonitrile-butadiene rubber or its hydrogenated product.

Non-diene polymers include, but are not limited to, olefin elastomers such as ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-butene-diene rubber, ethylene-butene rubber, ethylene-hexene rubber, and ethylene-octene rubber, butyl rubber, brominated butyl rubber, acrylic rubber, fluororubber, silicone rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, α,β-unsaturated nitrile-acrylate-conjugated diene copolymer rubber, urethane rubber, and polysulfide rubber.

Natural rubber is not limited to the following, but examples include smoked sheets RSS3-5, SMR, and epoxidized natural rubber.

The various rubber-like polymers mentioned above may be modified rubbers to which polar functional groups such as hydroxyl groups and amino groups have been added. When used for tires, butadiene rubber, isoprene rubber, styrene-butadiene rubber, natural rubber, and butyl rubber are preferably used.

From the viewpoint of the balance between various performances and processing characteristics of the rubber composition, the weight average molecular weight of the rubber polymer is preferably from 2000 to 2,000,000, and more preferably from 5000 to 1,500,000. Also, a low molecular weight rubber polymer, so-called liquid rubber, can be used.
These rubber-like polymers may be used alone or in combination of two or more.

In the case where the rubber composition using the branched conjugated diene polymer obtained by the production method of this embodiment is used as a rubber composition containing the above-mentioned rubbery polymer, the content ratio (mass ratio) of the above-mentioned branched conjugated diene polymer to the rubbery polymer (above-mentioned branched conjugated diene polymer/rubbery polymer) is preferably 10/90 or more and 100/0 or less, more preferably 20/80 or more and 90/10 or less, and even more preferably 50/50 or more and 80/20 or less.
Therefore, the rubber component contains the above-mentioned branched conjugated diene-based polymer in an amount of preferably 10% by mass or more and 100% by mass or less, more preferably 20% by mass or more and 90% by mass or less, and even more preferably 50% by mass or more and 80% by mass or less, based on the total amount (100% by mass) of the rubber component.

By having the content ratio of (branched conjugated diene polymer/rubber-like polymer) within the above range, the vulcanizate tends to have excellent abrasion resistance and fracture strength, and also tends to have a good balance between low hysteresis loss and wet skid resistance.

The filler contained in the rubber composition is not limited to the following, but examples thereof include, in addition to the silica-based inorganic filler, carbon black, metal oxides, and metal hydroxides. Among these, silica-based inorganic fillers are preferred.
The fillers may be used alone or in combination of two or more.
The content of the filler in the rubber composition is 5.0 parts by mass or more and 150 parts by mass or less, preferably 20 parts by mass or more and 100 parts by mass or less, and more preferably 30 parts by mass or more and 90 parts by mass or less, based on 100 parts by mass of the rubber component containing the branched conjugated diene-based polymer.
In the rubber composition, the content of the filler is 5.0 parts by mass or more per 100 parts by mass of the rubber component from the viewpoint of expressing the effect of adding the filler, and is 150 parts by mass or less per 100 parts by mass of the rubber component from the viewpoint of sufficiently dispersing the filler and making the processability and mechanical strength of the rubber composition practically sufficient.

The silica-based inorganic filler is not particularly limited and any known filler can be used, but solid particles containing _SiO2 or _Si3Al as a constituent unit are preferred, and solid particles containing _SiO2 or _Si3Al as a main component of the constituent unit are more preferred. Here, the main component refers to a component contained in the silica-based inorganic filler in an amount of 50 mass% or more, preferably 70 mass% or more, and more preferably 80 mass% or more.

Examples of silica-based inorganic fillers include, but are not limited to, inorganic fibrous substances such as silica, clay, talc, mica, diatomaceous earth, wollastonite, montmorillonite, zeolite, glass fiber, etc. Other examples include silica-based inorganic fillers whose surfaces have been hydrophobized, and mixtures of silica-based inorganic fillers and inorganic fillers other than silica-based fillers.
Among these, silica and glass fiber are preferred from the viewpoints of strength, abrasion resistance, and the like, and silica is more preferred.
Examples of silica include dry silica, wet silica, and synthetic silicate silica. Among these silicas, wet silica is preferred from the viewpoint of excellent balance between the effect of improving fracture strength and wet skid resistance.

From the viewpoint of obtaining practically good abrasion resistance and breaking strength in the rubber composition, the nitrogen adsorption specific surface area of the silica-based inorganic filler determined by the BET adsorption method is preferably 100 ^m2 /g or more and 300 ^m2 /g or less, and more preferably 170 ^m2 /g or more and 250 ^m2 /g or less.
If necessary, a silica-based inorganic filler having a relatively small specific surface area (e.g., a specific surface area of less than 200 ^m2 /g) can be used in combination with a silica-based inorganic filler having a relatively large specific surface area (e.g., 200 ^m2 /g or more).
In particular, when using a silica-based inorganic filler with a relatively large specific surface area (e.g., 200 ^m2 /g or more), a rubber composition containing the above-mentioned branched conjugated diene polymer improves the dispersibility of silica, is particularly effective in improving abrasion resistance, and tends to achieve a high level of balance between good fracture strength and low hysteresis loss.

The content of the silica-based inorganic filler in the rubber composition is preferably 5.0 parts by mass or more and 150 parts by mass or less, and more preferably 20 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the rubber component containing the branched conjugated diene polymer obtained by the manufacturing method of this embodiment. In the rubber composition, the content of the silica-based inorganic filler is preferably 5.0 parts by mass or more per 100 parts by mass of the rubber component from the viewpoint of expressing the effect of adding the silica-based inorganic filler, and is preferably 150 parts by mass or less per 100 parts by mass of the rubber component from the viewpoint of sufficiently dispersing the silica-based inorganic filler and making the processability and mechanical strength of the rubber composition practically sufficient.

Examples of carbon black include, but are not limited to, carbon black of various classes such as SRF, FEF, HAF, ISAF, SAF, etc. Among these, carbon black having a nitrogen adsorption specific surface area of 50 ^m2 /g or more and a dibutyl phthalate (DBP) oil absorption of 80 mL/100 g or less is preferred.

The content of carbon black in the rubber composition is preferably 0.5 parts by mass or more and 100 parts by mass or less, more preferably 3.0 parts by mass or more and 100 parts by mass or less, and even more preferably 5.0 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the rubber component containing the branched conjugated diene polymer obtained by the manufacturing method of this embodiment. In the rubber composition, the content of carbon black is preferably 0.5 parts by mass or more per 100 parts by mass of the rubber component from the viewpoint of expressing the performance required for applications such as tires, such as dry grip performance and electrical conductivity, and is preferably 100 parts by mass or less per 100 parts by mass of the rubber component from the viewpoint of dispersibility.

Metal oxide refers to solid particles whose main component is a structural unit of the chemical formula MxOy (M represents a metal atom, and x and y each independently represent an integer from 1 to 6).

Metal oxides include, but are not limited to, alumina, titanium oxide, magnesium oxide, and zinc oxide.

Metal hydroxides include, but are not limited to, aluminum hydroxide, magnesium hydroxide, and zirconium hydroxide.

In the method for producing the rubber composition of the present embodiment, a step of incorporating a silane coupling agent may be carried out.
The silane coupling agent has a function of strengthening the interaction between the rubber component and the inorganic filler. Specifically, it has a group having affinity or binding properties for both the rubber component and the silica-based inorganic filler, and is preferably a compound having a sulfur bond portion and an alkoxysilyl group or silanol group portion in one molecule.
Examples of such compounds include, but are not limited to, bis-[3-(triethoxysilyl)-propyl]-tetrasulfide, bis-[3-(triethoxysilyl)-propyl]-disulfide, and bis-[2-(triethoxysilyl)-ethyl]-tetrasulfide.

In the rubber composition, the content of the silane coupling agent is preferably 0.1 parts by mass or more and 30 parts by mass or less, more preferably 0.5 parts by mass or more and 20 parts by mass or less, and even more preferably 1.0 parts by mass or more and 15 parts by mass or less, relative to 100 parts by mass of the inorganic filler described above. When the content of the silane coupling agent is within the above range, the above-mentioned effect of the addition of the silane coupling agent tends to be more pronounced.

The rubber composition may contain a rubber softener from the viewpoint of improving the processability thereof.
The amount of rubber softener added is expressed as the total amount including the amount of rubber softener previously contained in the above-mentioned branched conjugated diene polymer or other rubber-like polymers, and the amount of rubber softener added when producing the rubber composition, per 100 parts by mass of the rubber component containing the branched conjugated diene polymer obtained by the production method of the present embodiment.
As the rubber softener, mineral oil or a liquid or low molecular weight synthetic softener is preferable.
Mineral oil-based rubber softeners, called process oils or extender oils, which are used to soften rubber, increase its volume, and improve its processability, are mixtures of aromatic rings, naphthene rings, and paraffin chains, and those in which the carbon number of the paraffin chain is 50% or more of the total carbon are called paraffin-based, those in which the carbon number of the naphthene ring is 30% to 45% of the total carbon are called naphthene-based, and those in which the aromatic carbon number is more than 30% of the total carbon are called aromatic. When the branched conjugated diene polymer of this embodiment is a copolymer of a conjugated diene compound and a vinyl aromatic compound, it is preferable to use a rubber softener having an appropriate aromatic content, since it tends to be compatible with the branched conjugated diene polymer.
In the rubber composition, the content of the rubber softener is preferably 0 parts by mass or more and 100 parts by mass or less, more preferably 10 parts by mass or more and 90 parts by mass or less, and even more preferably 30 parts by mass or more and 90 parts by mass or less, per 100 parts by mass of the rubber component. By making the content of the rubber softener 100 parts by mass or less per 100 parts by mass of the rubber component, bleeding out is suppressed, and stickiness of the surface of the rubber composition tends to be suppressed.

The method for mixing the branched conjugated diene polymer obtained by the production method of the present embodiment with additives such as other rubber-like polymers, silica-based inorganic fillers, carbon black and other fillers, silane coupling agents, and rubber softeners is not limited to the following, but examples thereof include a melt-kneading method using a general mixer such as an open roll, a Banbury mixer, a kneader, a single-screw extruder, a twin-screw extruder, or a multi-screw extruder, and a method in which the components are dissolved and mixed and then the solvent is removed by heating.
Among these, the melt kneading method using a roll, a Banbury mixer, a kneader, or an extruder is preferred from the viewpoints of productivity and good kneading properties. In addition, either a method of kneading the rubber component, other fillers, a silane coupling agent, and additives all at once or a method of mixing them in several batches can be applied.

The rubber composition may be a vulcanized composition that has been vulcanized with a vulcanizing agent. Examples of the vulcanizing agent include, but are not limited to, radical generators such as organic peroxides and azo compounds, oxime compounds, nitroso compounds, polyamine compounds, sulfur, and sulfur compounds. Examples of the sulfur compounds include sulfur monochloride, sulfur dichloride, disulfide compounds, and polymeric polysulfur compounds.
In the rubber composition, the content of the vulcanizing agent is preferably 0.01 parts by mass to 20 parts by mass, and more preferably 0.1 parts by mass to 15 parts by mass, per 100 parts by mass of the rubber component. As the vulcanization method, a conventionally known method can be applied, and the vulcanization temperature is preferably 120° C. to 200° C., and more preferably 140° C. to 180° C.

In vulcanization, a vulcanization accelerator and a vulcanization aid may be used, if necessary.
As the vulcanization accelerator, a conventionally known material can be used, and examples thereof include, but are not limited to, sulfenamide-based, guanidine-based, thiuram-based, aldehyde-amine-based, aldehyde-ammonia-based, thiazole-based, thiourea-based, and dithiocarbamate-based vulcanization accelerators.
Furthermore, the vulcanization aid may include, but is not limited to, zinc oxide and stearic acid.
The amount of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 0.01 parts by mass or more and 20 parts by mass or less, and more preferably 0.1 parts by mass or more and 15 parts by mass or less.

The rubber composition may contain various additives such as other softeners, other fillers, heat stabilizers, antistatic agents, weather stabilizers, antioxidants, colorants, and lubricants, in addition to those described above, within the scope of the present embodiment.
As the other softening agents, known softening agents can be used.
Other fillers include, but are not limited to, calcium carbonate, magnesium carbonate, aluminum sulfate, and barium sulfate.
As the heat resistance stabilizer, antistatic agent, weather resistance stabilizer, antioxidant, colorant, and lubricant, known materials can be used.

[Tire and tire manufacturing method]
The tire of the present embodiment contains the rubber composition of the present embodiment described above.
The method for producing a tire according to the present embodiment includes a step of obtaining a branched conjugated diene polymer by the production method according to the present embodiment, a step of obtaining a rubber composition containing the branched conjugated diene polymer, and a step of molding the rubber composition.
The rubber composition containing the branched conjugated diene polymer obtained by the production method of the present embodiment described above is suitably used as a rubber composition for tires.

The rubber composition for tires can be used in various tire parts such as treads, carcasses, sidewalls, and beads of various tires such as fuel-efficient tires, all-season tires, high-performance tires, and studless tires, although the tire parts are not limited thereto.
The rubber composition for tires containing the branched conjugated diene-based polymer of the present embodiment has an excellent balance between abrasion resistance, breaking strength, low hysteresis loss and wet skid resistance when vulcanized, and is therefore suitably used for the treads of fuel-saving tires and high-performance tires.

Hereinafter, the present embodiment will be described in more detail with reference to specific examples and comparative examples, but the present embodiment is not limited in any way to the following examples and comparative examples.
[First embodiment]
As a first example, the present embodiment will be described in detail by giving a specific example and a comparative example.
Hereinafter, a conjugated diene polymer coupled with a nitrogen atom-containing modifier will be referred to as a "coupled conjugated diene polymer".
Moreover, the conjugated diene polymer in an unmodified state is referred to as an "unmodified conjugated diene polymer." In the tables, it is simply referred to as a "conjugated diene polymer."
Furthermore, a conjugated diene polymer having a branched structure is referred to as a "branched conjugated diene polymer."
Various physical properties in the examples and comparative examples were measured by the methods shown below.

(Physical Property 1) Polymer Mooney Viscosity An unmodified conjugated diene polymer or a conjugated diene polymer coupled with a nitrogen atom-containing modifier (hereinafter also referred to as a "coupled conjugated diene polymer") was used as a sample, and the Mooney viscosity was measured using a Mooney viscometer (manufactured by Ueshima Seisakusho Co., Ltd., product name "VR1132") in accordance with ISO 289 using an L-type rotor.
The measurement temperature was 110° C. when an unmodified conjugated diene polymer (simply referred to as conjugated diene polymer in the table) was used as the sample, and 100° C. when a coupled conjugated diene polymer was used as the sample.
First, the sample was preheated at the test temperature for 1 minute, and then the rotor was rotated at 2 rpm. The torque after 4 minutes was measured and taken as the Mooney viscosity (ML ₍₁₊₄₎ ).

(Physical Property 2) Mooney Relaxation Rate A coupled conjugated diene polymer was used as a sample, and the Mooney viscosity was measured using a Mooney viscometer (manufactured by Ueshima Seisakusho Co., Ltd. under the trade name "VR1132") with an L-shaped rotor in accordance with ISO 289. Then, the rotation of the rotor was immediately stopped, and the torque was recorded in Mooney units every 0.1 seconds for 1.6 seconds to 5 seconds after the rotation was stopped. The slope of the straight line obtained by plotting the torque versus time (seconds) on a double logarithmic scale was determined, and the absolute value of the slope was taken as the Mooney relaxation rate (MSR).

(Physical Property 3) Degree of Branching (Bn)
The branching degree (Bn) of the coupling conjugated diene polymer was measured by a GPC-light scattering method equipped with a viscosity detector as follows.
A coupling conjugated diene polymer was used as a sample, and a gel permeation chromatography (GPC) measuring device (trade name "GPCmax VE-2001" manufactured by Malvern) having three columns packed with polystyrene gel connected together was used to measure the molecular weight using three detectors connected in this order: a light scattering detector, an RI detector, and a viscosity detector (trade name "TDA305" manufactured by Malvern). Based on standard polystyrene, the absolute molecular weight was determined from the measurement results of the light scattering detector and the RI detector, and the intrinsic viscosity was determined from the measurement results of the RI detector and the viscosity detector.
The linear polymer was used as having an intrinsic viscosity [η] = -3.883 M ^0.771 , and the shrinkage factor (g') was calculated as the ratio of the intrinsic viscosity corresponding to each molecular weight, where M represents the absolute molecular weight.
The obtained shrinkage factor (g') was then used to calculate the branching degree (Bn), defined as g'=6Bn/[(Bn+1)(Bn+2)].
The eluent used was tetrahydrofuran (hereinafter also referred to as "THF") containing 5 mmol/L triethylamine.
The columns used were "TSKgel G4000HXL", "TSKgel G5000HXL", and "TSKgel G6000HXL" manufactured by Tosoh Corporation.
20 mg of a measurement sample was dissolved in 10 mL of THF to prepare a measurement solution, and 100 μL of the measurement solution was injected into a GPC measurement device and measured under conditions of an oven temperature of 40° C. and a THF flow rate of 1 mL/min.

(Physical property 4) Molecular weight <Measurement conditions 1>:
Using an unmodified conjugated diene polymer or a coupled conjugated diene polymer as a sample, a GPC measuring device (trade name "HLC-8320GPC" manufactured by Tosoh Corporation) having three columns packed with polystyrene gel was used. The chromatogram was measured using an RI detector (trade name "HLC8020" manufactured by Tosoh Corporation) and the weight average molecular weight (Mw) and number average molecular weight (Nm) were calculated based on a calibration curve obtained using standard polystyrene. The average molecular weight (Mn) and the molecular weight distribution (Mw/Mn) were determined.
The eluent used was 5 mmol/L triethylamine-containing THF (tetrahydrofuran). Three columns, both of which were manufactured by Tosoh Corporation under the trade name "TSKgel SuperMultiporeHZ-H", were connected, and a guard column, both of which were manufactured by Tosoh Corporation under the trade name "TSKgel SuperMultiporeHZ-H", was connected in front of the columns. "TSKguardcolumn SuperMP(HZ)-H" was connected and used.
10 mg of a measurement sample was dissolved in 10 mL of THF to prepare a measurement solution, and 10 μL of the measurement solution was injected into a GPC measurement device and measured under conditions of an oven temperature of 40° C. and a THF flow rate of 0.35 mL/min.
Among the various samples measured under the above measurement condition 1, samples whose molecular weight distribution (Mw/Mn) was less than 1.6 were measured again under the following measurement condition 2. For samples whose molecular weight distribution was 1.6 or more, the measured value under measurement condition 1 was adopted.
<Measurement condition 2>:
Using an unmodified conjugated diene polymer or a coupled conjugated diene polymer as a sample, a chromatogram was measured using a GPC measuring device in which three columns packed with polystyrene gel were connected, and a standard polystyrene was used. The weight average molecular weight (Mw) and number average molecular weight (Mn) were determined based on a calibration curve using the above.
The eluent used was THF containing 5 mmol/L triethylamine. The columns were: guard column: Tosoh Corporation's product name "TSKguardcolumn SuperH-H"; column: Tosoh Corporation's product names "TSKgel SuperH5000" and "TSKgel SuperH6000". "TSKgel Super H7000" was used.
An RI detector (HLC8020, product name, manufactured by Tosoh Corporation) was used under the conditions of an oven temperature of 40° C. and a THF flow rate of 0.6 mL/min. 10 mg of a sample to be measured was dissolved in 20 mL of THF to prepare a measurement solution. Then, 20 μL of the measurement solution was injected into a GPC measurement device and measurement was performed.
For samples that were measured under measurement condition 1 and had a molecular weight distribution value of less than 1.6, measurement was performed under measurement condition 2, and the measured value was adopted.

(Physical Property 5) Modification Ratio The modification ratio of the coupling conjugated diene polymer was measured by a column adsorption GPC method as follows.
The coupling conjugated diene polymer was used as a sample, and the measurement was carried out by utilizing the characteristic of the modified basic polymer component being adsorbed to a GPC column filled with silica gel.
The amount of the sample adsorbed to the silica-based column was measured by subtracting the chromatogram of the sample solution containing the sample and the low molecular weight internal standard polystyrene measured using the polystyrene-based column from the chromatogram measured using the silica-based column, and the modification rate was calculated.
Specifically, it is as follows:
For samples that were measured under the above-mentioned (Physical Property 4) Measurement Condition 1 and had a molecular weight distribution value of 1.6 or more, the samples were measured under the following Measurement Condition 3, and the measured value was adopted. For samples that were measured under the above-mentioned (Physical Property 4) Measurement Condition 1 and had a molecular weight distribution value of less than 1.6, the samples were measured under the following Measurement Condition 4, and the measured value was adopted.

<Preparation of sample solution>:
10 mg of a sample and 5 mg of standard polystyrene were dissolved in 20 mL of THF to prepare a sample solution.
<Measurement condition 3>:
GPC measurement conditions using a polystyrene column:
A Tosoh Corporation product name "HLC-8320GPC" was used, and 10 μL of the sample solution was injected into the device using THF containing 5 mmol/L triethylamine as an eluent. A chromatogram was obtained using an RI detector under the conditions of a column oven temperature of 40° C. and a THF flow rate of 0.35 mL/min.
The columns used were three Tosoh Corporation products under the trade name "TSKgel SuperMultiporeHZ-H" connected together, and a Tosoh Corporation product under the trade name "TSKguardcolumn SuperMP(HZ)-H" was connected in front of them as a guard column.

<Measurement condition 4>:
THF containing 5 mmol/L triethylamine was used as the eluent, and 20 μL of the sample solution was injected into the device for measurement.
The columns used were a guard column manufactured by Tosoh Corporation under the trade name "TSKguardcolumn SuperH-H" and columns manufactured by Tosoh Corporation under the trade names "TSKgel SuperH5000", "TSKgel SuperH6000", and "TSKgel SuperH7000". Measurement was performed using an RI detector (manufactured by Tosoh Corporation, HLC8020) under conditions of a column oven temperature of 40°C and a THF flow rate of 0.6 mL/min to obtain a chromatogram.

GPC measurement conditions using a silica-based column: A Tosoh Corporation product name "HLC-8320GPC" was used, THF was used as the eluent, 50 μL of the sample solution was injected into the device, and a chromatogram was obtained using an RI detector under the following conditions: column oven temperature 40°C, THF flow rate 0.5 ml/min. The columns used were Zorbax PSM-1000S, PSM-300S, and PSM-60S, with a DIOL 4.6 x 12.5 mm 5 micron product name connected to the front of the columns as a guard column.

How to calculate the denaturation rate:
The total peak area of the chromatogram using the polystyrene-based column was set to 100, the peak area of the sample was set to P1, the peak area of the standard polystyrene was set to P2, the total peak area of the chromatogram using the silica-based column was set to 100, the peak area of the sample was set to P3, and the peak area of the standard polystyrene was set to P4, and the modification rate (%) was calculated according to the following formula.
Denaturation rate (%) = [1 - (P2 x P3) / (P1 x P4)] x 100
(where P1 + P2 = P3 + P4 = 100)

(Physical Property 6) Bound Styrene Amount A coupling conjugated diene polymer not containing a rubber softener was used as a sample, and 100 mg of the sample was dissolved in chloroform up to 100 mL to prepare a measurement sample.
The amount of bound styrene (mass %) relative to 100 mass % of the sample coupled conjugated diene polymer was measured based on the amount of absorption of ultraviolet light at a wavelength (around 254 nm) by the phenyl group of styrene (measuring device: Shimadzu Corporation spectrophotometer "UV-2450").

(Physical Property 7) Microstructure of Butadiene Moiety (1,2-Vinyl Bond Amount)
A coupling conjugated diene polymer not containing a rubber softener was used as a sample, and 50 mg of the sample was dissolved in 10 mL of carbon disulfide to prepare a measurement sample.
Using a solution cell, an infrared spectrum was measured in the range of 600 to 1000 cm ^-1 , and the microstructure of the butadiene portion, i.e., the amount of 1,2-vinyl bonds (mol%) was determined from the absorbance at a predetermined wave number according to the calculation formula of the Hampton method (the method described in R. R. Hampton, Analytical Chemistry 21, 923 (1949)) (measuring device: Fourier transform infrared spectrophotometer "FT-IR230" manufactured by JASCO Corporation).

(Physical Property 8) Molecular weight (absolute molecular weight) measured by GPC-light scattering method
A chromatogram was measured using a GPC-light scattering measuring device in which three columns packed with polystyrene gel were connected, and the weight average molecular weight (Mw-i) was determined based on the solution viscosity and the light scattering method (also referred to as "absolute molecular weight").
The eluent used was a mixed solution of tetrahydrofuran and triethylamine (THF in TEA: prepared by mixing 5 mL of triethylamine in 1 L of tetrahydrofuran).
The columns used were a guard column (manufactured by Tosoh Corporation under the trade name "TSKguardcolumn HHR-H") and columns (manufactured by Tosoh Corporation under the trade names "TSKgel G6000HHR", "TSKgel G5000HHR", and "TSKgel G4000HHR").
A GPC-light scattering measuring device (trade name "Viscotek TDAmax" manufactured by Malvern Instruments) was used under conditions of an oven temperature of 40° C. and a THF flow rate of 1.0 mL/min.
10 mg of a sample to be measured was dissolved in 20 mL of THF to prepare a measurement solution, and 200 μL of the measurement solution was injected into a GPC measurement device and measured.

[Branched conjugated diene polymer]
( Reference Example 1-1) Coupling conjugated diene polymer (sample 1-1)
The internal volume is 10 L, and the ratio (L/D) of the internal height (L) to the diameter (D) is 4.0.
Two tank-type pressure vessels each having an inlet at the bottom and an outlet at the top, and each having an agitator as a tank-type reactor and a jacket for temperature control, were connected together as polymerization reactors.
The mixture was mixed at 18.6 g/min of 1,3-butadiene, 10.0 g/min of styrene, and 175.2 g/min of n-hexane, from which moisture had been removed in advance.
0.103 mmol/min of 2,2-butyllithium was added and mixed, and then continuously fed to the bottom of the reactor.
At a rate of 81 mmol/min, 0.143 mmol of n-butyl lithium was used as a polymerization initiator.
The mixture was fed to the bottom of the first reactor, which was vigorously mixed with an agitator, at a rate of 1/min, and the temperature inside the reactor was kept at 67°C.
The temperature was kept at .degree.
The polymer solution was continuously withdrawn from the top of the first reactor and continuously fed to the bottom of the second reactor to continue the reaction at 70°C, and further fed to the static mixer from the top of the second reactor. When the polymerization was sufficiently stabilized, 1,3-butadiene and styrene were copolymerized while
From the bottom of the second reactive group, trimethoxy(4-vinylphenyl)silane (
In the table, this is abbreviated as "BS-1.") was added at a rate of 0.0190 mmol/min to carry out a polymerization reaction and a branching reaction to obtain a conjugated diene polymer having a main chain branched structure.
Furthermore, when the polymerization reaction and the branching reaction became stable, a small amount of the conjugated diene polymer solution before the addition of the coupling agent was withdrawn, and an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of the polymer, after which the solvent was removed and the Mooney viscosity at 110° C. and various molecular weights were measured. The physical properties are shown in Table 1.
Next, tetraethoxysilane (abbreviated as "A" in the table) was continuously added as a coupling agent to the polymer solution flowing out from the outlet of the reactor at a rate of 0.0480 mmol/min, and mixed using a static mixer to carry out a coupling reaction. At this time, the time until the coupling agent was added to the polymer solution flowing out from the outlet of the reactor was 4.8 minutes, the temperature was 68°C, and the difference between the temperature in the polymerization step and the temperature before the coupling agent was added was 2°C. A small amount of the conjugated diene polymer solution after the coupling reaction was withdrawn, and an antioxidant (BHT) was added so that the amount was 0.2 g per 100 g of polymer, and then the solvent was removed, and the bound styrene amount (physical property 6) and the microstructure of the butadiene portion (1,2-vinyl bond amount: physical property 7) were measured. The measurement results are shown in Table 1.
Next, an antioxidant (BHT) was continuously added to the polymer solution after the coupling reaction at 0.055 g/min (n-hexane solution) so that the amount was 0.2 g per 100 g of polymer, and the coupling reaction was terminated. Simultaneously with the antioxidant, SRAE oil (JOMO Process NC140 manufactured by JX Nippon Oil & Energy Corporation) was continuously added as a rubber softener so that the amount was 25.0 g per 100 g of polymer, and mixed with a static mixer. The solvent was removed by steam stripping, and a coupling conjugated diene polymer (Sample 1) having a 4-branched structure derived from a branching agent (hereinafter also referred to as "branching agent structure (1)"), which is a compound represented by the following formula (1), in a part of the main chain and a 3-branched star polymer structure derived from the coupling agent was obtained.
-1) was obtained.
The physical properties of Sample 1-1 are shown in Table 1.
The structure of the coupled conjugated diene polymer was identified by comparing the molecular weight measured by GPC with the branching degree measured by GPC equipped with a viscometer for the polymer before the addition of the branching agent, the polymer after the addition of the branching agent, and the polymer in each step after the addition of the coupling agent.
The structure of each sample was identified in the same manner.

In formula (1), R ¹ represents any one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, and an aryl group having 6 to 20 carbon atoms, and may have a branched structure in part.
X ¹ is a single bond or an organic group containing any one selected from the group consisting of carbon, hydrogen, nitrogen, sulfur, and oxygen.
Y ¹ represents any one selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and a halogen atom. Each may be independent and the same or different.

( Reference Example 1-2) Coupling conjugated diene polymer (sample 1-2)
A coupling conjugated diene polymer ( sample 1-2) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and a 4-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the coupling agent was changed from tetraethoxysilane to 1,2-bis(triethoxysilyl)ethane (abbreviated as "B" in the table) and the amount of the coupling agent was changed to 0.0360 mmol/min. The physical properties of Sample 1-2 are shown in Table 1.

( Reference Example 1-3) Coupling conjugated diene polymer (sample 1-3)
The coupling agent was changed from tetraethoxysilane to 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (abbreviated as "C" in the table), and the amount added was 0.0360
A coupling conjugated diene polymer (sample 1-3) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and a 4-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to mmol/min. The physical properties of sample 1-3 are shown in Table 1.

( Reference Example 1-4) Coupling conjugated diene polymer (sample 1-4)
A coupling conjugated diene polymer (sample 1-4) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and a 4-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the coupling agent was changed from tetraethoxysilane to 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (abbreviated as "D" in the table) and the amount of the coupling agent was changed to 0.0360 mmol/min. The physical properties of sample 1-4 are shown in Table 1.

( Reference Example 1-5) Coupling conjugated diene polymer (sample 1-5)
A coupling conjugated diene polymer (sample 1-5) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and a 6-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the coupling agent was changed from tetraethoxysilane to tris(3-trimethoxysilylpropyl)amine (abbreviated as "E" in the table) and the amount of the coupling agent was changed to 0.0250 mmol/min. The physical properties of sample 1-5 are shown in Table 1.

( Reference Example 1-6) Coupling conjugated diene polymer (sample 1-6)
The coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table), and the amount added was increased from 0.
A coupling conjugated diene polymer ( sample 1-6) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 0.190 mmol/min. The physical properties of sample 1-6 are shown in Table 1.

( Reference Example 1-7) Coupling conjugated diene polymer (sample 1-7)
The coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table), and the amount added was increased from 0.
A coupling conjugated diene polymer ( sample 1-7) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 0160 mmol/min. The physical properties of sample 1-7 are shown in Table 1.

( Reference Example 1-8) Coupling conjugated diene polymer (sample 1-8)
The addition rate of 1,3-butadiene was changed from 18.6 g/min to 24.3 g/min, the addition rate of styrene was changed from 10.0 g/min to 4.3 g/min, and further, 2,2-bis(
The addition rate of 2-oxolanylpropane was changed from 0.081 mmol/min to 0.044 mmol/min.
A coupled conjugated diene polymer (sample 1-8) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 1/min, the coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table), and the amount added was changed to 0.0160 mmol/min. The physical properties of Sample 1-8 are shown in Table 1.

( Reference Example 1-9) Coupling conjugated diene polymer (sample 1-9)
The addition rate of 1,3-butadiene was changed from 18.6 g/min to 17.1 g/min, the addition rate of styrene was changed from 10.0 g/min to 11.5 g/min, and the addition rate of 2,2-bis(2-oxolanyl)propane as a polar substance was changed from 0.081 mmol/min to 0.089 mmol/min.
ol/min, and the coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table).
A coupling conjugated diene polymer (sample 1-9) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the amount of the branching agent was changed to 0.0160 mmol/min. The physical properties of sample 1-9 are shown in Table 2.

( Reference Example 1-10) Coupling conjugated diene polymer (sample 1-10)
The addition rate of the polar substance 2,2-bis(2-oxolanyl)propane was 0.081 mmo
The flow rate was changed from 1/min to 0.200 mmol/min, and the coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (
A coupling conjugated diene polymer (sample 1-10) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the amount of the branching agent was changed to 0.0160 mmol/min. The physical properties of Sample 1-10 are shown in Table 2.

( Reference Example 1-11) Coupling conjugated diene polymer (sample 1-11)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to dimethylmethoxy(4-vinylphenyl)silane (abbreviated as "BS-2" in the table), and the amount added was 0.0350 m
mol/min, the coupling agent was changed from tetraethoxysilane to 1,2-bis(triethoxysilyl)ethane (abbreviated as "B" in the table), and the amount added was 0.0360 mmol/min.
A coupling conjugated diene polymer (sample 1-11) having a two-branched structure derived from the branching agent structure (1) in a part of the main chain and a four-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 1/min. The physical properties of Sample 1-11 are shown in Table 2.

( Reference Example 1-12) Coupling conjugated diene polymer (sample 1-12)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to dimethylmethoxy(4-vinylphenyl)silane (abbreviated as "BS-2" in the table), and the amount added was 0.0350 m
mol/min, and the coupling agent was changed from tetraethoxysilane to 2,2-dimethoxy-1
-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (in the table, "
A coupling conjugated diene polymer (sample 1-12) having a two-branched structure derived from the branching agent structure (1) in a part of the main chain and a four-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the amount of the branching agent was changed to 0.0360 mmol/min. The physical properties of Sample 1-12 are shown in Table 2.

( Reference Example 1-13) Coupling conjugated diene polymer (sample 1-13)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to dimethylmethoxy(4-vinylphenyl)silane (abbreviated as "BS-2" in the table), and the amount added was 0.0350 m
mol/min, and the coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table).
A coupling conjugated diene polymer (sample 1-13) having a bi-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the amount of the branching agent was changed to 0.0160 mmol/min. The physical properties of sample 1-13 are shown in Table 2.

( Reference Example 1-14) Coupling conjugated diene polymer (sample 1-14)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-(dimethylmethoxysilyl)phenyl)ethylene (abbreviated as "BS-3" in the table), the amount of addition was changed to 0.0120 mmol/min, and the coupling agent was changed from tetraethoxysilane to 1,
A branching agent represented by the following formula (2) (hereinafter also referred to as "branching agent structure (2)") was added to a part of the main chain in the same manner as in Reference Example 1-1, except that 2-bis(triethoxysilyl)ethane (abbreviated as "B" in the table) was used and the amount of the branching agent added was changed to 0.0360 mmol/min.
A coupled conjugated diene polymer (Sample 1-14) having a three-branched structure derived from the coupling agent and a four-branched star polymer structure derived from the coupling agent was obtained. The physical properties of Sample 1-14 are shown in Table 2.

In formula (2), X ² and X ³ are single bonds or organic groups containing any one selected from the group consisting of carbon, hydrogen, nitrogen, sulfur, and oxygen.
^Y2 and ^Y3 each represent one selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and a halogen atom. They may be independent and the same or different.

( Reference Example 1-15) Coupling conjugated diene polymer (sample 1-15)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-(dimethylmethoxysilyl)phenyl)ethylene (abbreviated as "BS-3" in the table), the amount of addition was changed to 0.0120 mmol/min, and the coupling agent was changed from tetraethoxysilane to 2,
A coupled conjugated diene polymer ( Sample 1-15) having a three-branched structure derived from the branching agent structure (2) in a part of the main chain and a four-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that 2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (abbreviated as "D" in the table) was used and the amount of the added agent was changed to 0.0360 mmol/min. The physical properties of Sample 1-15 are shown in Table 2.

( Reference Example 1-16) Coupling conjugated diene polymer (sample 1-16)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-(dimethylmethoxysilyl)phenyl)ethylene (abbreviated as "BS-3" in the table), and the addition amount was changed to 0.0120 mmol/min. The coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table).
) and its addition amount was changed to 0.0160 mmol/min, in the same manner as in Reference Example 1-1, a coupling conjugated diene polymer (sample 1-16) having a three-branched structure derived from the branching agent structure (2) in a part of the main chain and an eight-branched star polymer structure derived from the coupling agent was obtained. The physical properties of sample 1-16 are shown in Table 2.

( Reference Example 1-17) Coupling conjugated diene polymer (sample 1-17)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-trimethoxysilylphenyl)ethylene (abbreviated as "BS-4" in the table), and the amount added was 0.
The flow rate was changed to 0.03 to 0.210 mmol/min, the coupling agent was changed from tetraethoxysilane to 1,2-bis(triethoxysilyl)ethane (abbreviated as "B" in the table), and the amount of the added agent was changed to 0.03
A coupling conjugated diene polymer (sample 1-17) having a 7-branched structure derived from the branching agent structure (2) in a part of the main chain and a 4-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 60 mmol/min. The physical properties of Sample 1-17 are shown in Table 3.

( Reference Example 1-18) Coupling conjugated diene polymer (sample 1-18)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-trimethoxysilylphenyl)ethylene (abbreviated as "BS-4" in the table), and the amount added was 0.
A coupled conjugated diene polymer (sample 1-18) having a 7-branched structure derived from the branching agent structure (2) in a part of the main chain and a 4-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 0.0210 mmol/min, the coupling agent was changed from tetraethoxysilane to 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (abbreviated as "D" in the table), and the amount of addition was changed to 0.0360 mmol/min. The physical properties of Sample 1-18 are shown in Table 3.

( Reference Example 1-19) Coupling conjugated diene polymer (sample 1-19)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-trimethoxysilylphenyl)ethylene (abbreviated as "BS-4" in the table), and the amount added was 0.
The coupling agent was changed from tetraethoxysilane to tetrakis(
3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table.
) and its addition amount was changed to 0.0160 mmol/min, in the same manner as in Reference Example 1-1, to obtain a coupled conjugated diene polymer (Sample 1-19) having a hepta-branched structure derived from the branching agent structure (2) in a part of the main chain and an eight-branched star polymer structure derived from the coupling agent. The physical properties of Sample 1-19 are shown in Table 3.

( Reference Example 1-20) Coupling conjugated diene polymer (sample 1-20)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to trichloro(4-vinylphenyl)silane (abbreviated as "BS-5" in the table), and the amount added was 0.0190 mmol.
A coupled conjugated diene polymer (sample 1-20) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 0.0360 mmol/min, the coupling agent was changed from tetraethoxysilane to 1,2-bis(triethoxysilyl)ethane (abbreviated as "B" in the table), and the amount of addition was changed to 0.0360 mmol/min. The physical properties of Sample 1-20 are shown in Table 3.

( Reference Example 1-21) Coupling conjugated diene polymer (sample 1-21)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to trichloro(4-vinylphenyl)silane (abbreviated as "BS-5" in the table), and the amount added was 0.0190 mmol.
/min, and the coupling agent was changed from tetraethoxysilane to 2,2-dimethoxy-1-(3
A coupled conjugated diene polymer ( Sample 1-21) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the 4-trimethoxysilylpropyl-1-aza-2-silacyclopentane (abbreviated as "D" in the table) was used and the amount of the 4-trimethoxysilylpropyl-1-aza-2-silacyclopentane added was changed to 0.0360 mmol/min. The physical properties of Sample 1-21 are shown in Table 3.

( Reference Example 1-22) Coupling conjugated diene polymer (sample 1-22)
The branching agent was changed from trimethoxy(4-vinylphenyl)silane to trichloro(4-vinylphenyl)silane (abbreviated as "BS-5" in the table), and the amount added was 0.0190 mmol.
A coupled conjugated diene polymer (sample 1-22) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 0.0160 mmol/min, the coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table), and the amount of addition was changed to 0.0160 mmol/min. The physical properties of Sample 1-22 are shown in Table 3.

( Reference Example 1-23) Coupling conjugated diene polymer (sample 1-23)
The amount of the branching agent trimethoxy(4-vinylphenyl)silane (abbreviated as "BS-1" in the table) added was changed from 0.0190 mmol/min to 0.0100 mmol/min, and the coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3
-propanediamine (abbreviated as "F" in the table), and the amount added was 0.0190 mmo
A coupling conjugated diene polymer (sample 1-23) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 1/min. The physical properties of Sample 1-23 are shown in Table 3.

( Reference Example 1-24) Coupling conjugated diene polymer (sample 1-24)
The amount of the branching agent trimethoxy(4-vinylphenyl)silane (abbreviated as "BS-1" in the table) added was changed from 0.0190 mmol/min to 0.0250 mmol/min, and the coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3
-propanediamine (abbreviated as "F" in the table), and the amount added was 0.0190 mmo
A coupling conjugated diene polymer (sample 1-24) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 1/min. The physical properties of Sample 1-24 are shown in Table 4.

( Reference Example 1-25) Coupling conjugated diene polymer (sample 1-25)
The amount of the branching agent trimethoxy(4-vinylphenyl)silane (abbreviated as "BS-1" in the table) added was changed from 0.0190 mmol/min to 0.0350 mmol/min, and the coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3
-propanediamine (abbreviated as "F" in the table), and the amount added was 0.0190 mmo
A coupling conjugated diene polymer (sample 1-25) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 1/min. The physical properties of Sample 1-25 are shown in Table 4.

( Reference Example 1-26) Coupling conjugated diene polymer (sample 1-26)
The coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table), and the amount added was increased from 0.
A coupling conjugated diene polymer ( sample 1-26) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 0.190 mmol/min, and the SRAE oil added as a rubber softener was replaced with liquid rubber (liquid polybutadiene LBR-302 manufactured by Kuraray Co., Ltd.). The physical properties of Sample 1-26 are shown in Table 4.

( Reference Example 1-27) Coupling conjugated diene polymer (sample 1-27)
The coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table), and the amount added was increased from 0.
A coupling conjugated diene polymer ( sample 1-27) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 0.190 mmol/min, the SRAE oil added as a rubber softener was changed to resin (Yasuhara Chemical Co., Ltd., terpene resin YS Resin PX1250). The physical properties of Sample 1-27 are shown in Table 4.

( Reference Example 1-28) Coupling conjugated diene polymer (sample 1-28)
The coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table), and the amount added was increased from 0.
The flow rate was changed to 0.190 mmol/min, and naphthenic oil (Nytex 810 naphthenic oil manufactured by Nynas) was added in place of the SRAE oil added as a rubber softener.
In the same manner as in Reference Example 1-1, a coupling conjugated diene polymer (sample 1-28) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained. The physical properties of sample 1-28 are shown in Table 4.

( Reference Example 1-29) Coupling conjugated diene polymer (sample 1-29)
The coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table), and the amount added was increased from 0.
A coupling conjugated diene polymer (sample 1-29) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 0.190 mmol/min and no rubber softener was added. The physical properties of Sample 1-29 are shown in Table 4.

( Reference Example 1-30) Coupling conjugated diene polymer (sample 1-30)
The coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table), and the amount added was increased from 0.
A coupling conjugated diene polymer (sample 1-30) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed to 0.190 mmol/min and the amount of SRAE oil added as a rubber softener was changed from 25.0 g to 37.5 g per 100 g of polymer. The physical properties of Sample 1-30 are shown in Table 4.

( Reference Example 1-31) Conjugated diene polymer (sample 1-31)
When the polymerization was sufficiently stabilized, 0.0190 mmo of trimethoxy(4-vinylphenyl)silane (abbreviated as "BS-1" in the table) was added as a branching agent to the bottom of the second reactive group.
In the same manner as in Reference Example 1-1, except that the coupling agent was not added, the main chain had a 4-branched structure derived from the branching agent structure (1) in a part of the main chain, and did not show a star-shaped coupling structure derived from the coupling agent, and a conjugated diene polymer (sample 1-31) was obtained. The physical properties of sample 1-31 are shown in Table 5.

( Reference Example 1-32) Coupling conjugated diene polymer (sample 1-32)
When the polymerization was sufficiently stabilized, 0.0190 mmo of trimethoxy(4-vinylphenyl)silane (abbreviated as "BS-1" in the table) was added as a branching agent to the bottom of the second reactive group.
The procedure of Reference Example 1-1 was repeated except that the amount of tetraethoxysilane (referred to as "A" in the table) added as a coupling agent was changed from 0.0480 mmol/min to 0.0120 mmol/min, and a coupling conjugated diene polymer (sample 1-32) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and a 3-branched star polymer structure derived from the coupling agent was obtained. The physical properties of Sample 1-32 are shown in Table 5.

( Reference Example 1-33) Coupling conjugated diene polymer (sample 1-33)
When the polymerization was sufficiently stabilized, 0.0190 mmo of trimethoxy(4-vinylphenyl)silane (abbreviated as "BS-1" in the table) was added as a branching agent to the bottom of the second reactive group.
The coupling agent was tetraethoxysilane to tetrakis(
3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table.
) and its addition amount was changed to 0.0038 mmol/min, in the same manner as in Reference Example 1-1, to obtain a coupled conjugated diene polymer (Sample 1-33) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and an 8-branched star polymer structure derived from the coupling agent. The physical properties of Sample 1-33 are shown in Table 5.

( Reference Example 1-34) Coupling conjugated diene polymer (sample 1-34)
When the polymerization was sufficiently stabilized, dimethylmethoxy(4-vinylphenyl)silane (abbreviated as "BS-2" in the table) was added as a branching agent at 0.0350 to the bottom of the second reactive group.
The amount of the coupling agent, tetraethoxysilane, added was 0.0 mmol/min.
A coupling conjugated diene polymer (sample 1-34) having a two-branched structure derived from the branching agent structure (1) in a part of the main chain and a three-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the flow rate was changed from 480 mmol/min to 0.0120 mmol/min. The physical properties of Sample 1-34 are shown in Table 5.

( Reference Example 1-35) Coupling conjugated diene polymer (sample 1-35)
When the polymerization is sufficiently stable, the 1,1-
A coupled conjugated diene polymer (Sample 1-35) having a three-branched structure derived from the branching agent structure (2) in a part of the main chain and a three-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that bis(4-(dimethylmethoxysilyl)phenyl)ethylene (abbreviated as "BS-3" in the table) was added at a rate of 0.0120 mmol/min and the amount of tetraethoxysilane added as a coupling agent was changed from 0.0480 mmol/min to 0.0120 mmol/min. The physical properties of Sample 1-35 are shown in Table 5.

( Reference Example 1-36) Coupling conjugated diene polymer (sample 1-36)
The coupling agent was changed from tetraethoxysilane to 3-(benzylideneamino)propyltriethoxysilane (abbreviated as "G" in the table), and the amount added was 0.0620 mmol/L.
A coupling conjugated diene polymer (sample 1-36) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and a 2-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the branching agent structure (1) was changed to the coupling agent structure (2). The physical properties of Sample 1-36 are shown in Table 5.

( Reference Example 1-37) Coupling conjugated diene polymer (sample 1-37)
The 1,3-butadiene added to the first reactor was changed from 18.6 g/min to 13.95 g/min, and 1,3-butadiene was added at 4.65 g/min from the bottom of the second reactor together with the branching agent.
A coupling conjugated diene polymer (sample 1-37) having a 4-branched structure derived from the branching agent structure (1) in a part of the main chain and a 4-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1-1, except that the addition rate of the branching agent was 100 g/min. The physical properties of sample 1-37 are shown in Table 5.

( Reference Example A-1) Coupling conjugated diene polymer (sample A-1)
The internal volume is 10 L, and the ratio (L/D) of the internal height (L) to the diameter (D) is 4.0.
Two tank-type pressure vessels each having an inlet at the bottom and an outlet at the top, and each having an agitator as a tank-type reactor and a jacket for temperature control, were connected together as polymerization reactors.
1,3-butadiene, from which moisture had been removed in advance, at 14 g/min, and styrene at 10.0 g/min,
n-Hexane was mixed at 175.2 g/min.
In a static mixer provided in the middle of the pipe supplying this mixed solution to the inlet of the reactor, n-butyllithium for inactivating remaining impurities was added at 0.103 mmol/min.
After mixing, the mixture was continuously fed to the bottom of the reactor.
C. In the first reactor, n-oxolanylpropane was fed at a rate of 0.081 mmol/min and n-butyllithium as a polymerization initiator was fed at a rate of 0.143 mmol/min to the bottom of the first reactor, which was being vigorously mixed with a stirrer, and the internal temperature of the reactor was maintained at 67.degree.
The polymer solution was continuously withdrawn from the top of the first reactor and continuously fed to the bottom of the second reactor to continue the reaction at 70°C, and further fed to the static mixer from the top of the second reactor. When the polymerization was sufficiently stabilized, 1,3-butadiene and styrene were copolymerized while
From the bottom of the second reactive group, a branching agent, trimethoxy(4-vinylphenyl)silane (
In the table, this is abbreviated as "BS-1.") was injected at a rate of 0.0190 mmol/min, and in parallel, 1,
3-Butadiene was added at a rate of 4.6 g/min to carry out a polymerization reaction and a branching reaction to obtain a conjugated diene polymer having a main chain branched structure.
When the polymerization reaction and the branching reaction became stable, a small amount of the conjugated diene polymer solution before the addition of the coupling agent was withdrawn, and an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of the polymer, after which the solvent was removed and the Mooney viscosity at 110° C. and various molecular weights were measured. The physical properties are shown in Table 7.
Next, a coupling agent, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (abbreviated as "D" in the table), was continuously added at a rate of 0.0360 mmol/min to the polymer solution flowing out from the outlet of the reactor, and the mixture was mixed using a static mixer to carry out a coupling reaction.
At this time, the time until the coupling agent was added to the polymer solution flowing out from the outlet of the reactor was 4.8 minutes, the temperature was 68°C, and the difference between the temperature in the polymerization process and the temperature until the coupling agent was added was 2°C.
A small amount of the conjugated diene polymer solution after the coupling reaction was withdrawn, and an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of the polymer, and the solvent was then removed. The amount of bound styrene (physical property 6) and the microstructure of the butadiene portion (amount of 1,2-vinyl bonds: physical property 7) were measured. The measurement results are shown in Table 7.
Next, an antioxidant (BHT) was continuously added to the polymer solution after the coupling reaction at a rate of 0.055 g/min (n-hexane solution) so that the amount was 0.2 g per 100 g of the polymer, and the coupling reaction was terminated.
At the same time as the antioxidant, SRAE oil (J
25.0 g of X (JOMO Process NC140, manufactured by Nippon Oil & Energy Corporation) was continuously added and mixed with a static mixer.
The solvent was removed by steam stripping to obtain a coupled conjugated diene polymer (sample A-1) having, in a part of its main chain, a four-branched structure derived from the branching agent (hereinafter also referred to as "branching agent structure (1)"), which is a compound represented by the above formula (1), and having a four-branched star polymer structure derived from the coupling agent.
The physical properties of sample A-1 are shown in Table 7.
The structure of the coupled conjugated diene polymer was identified by comparing the molecular weight measured by GPC with the branching degree measured by GPC equipped with a viscometer for the polymer before the addition of the branching agent, the polymer after the addition of the branching agent, and the polymer in each step after the addition of the coupling agent.

( Reference Example A-2) Coupling conjugated diene polymer (sample A-2)
The internal volume is 10 L, and the ratio (L/D) of the internal height (L) to the diameter (D) is 4.0.
Two tank-type pressure vessels each having an inlet at the bottom and an outlet at the top, and each having an agitator as a tank-type reactor and a jacket for temperature control, were connected together as polymerization reactors.
The water was removed in advance, and the 1,3-butadiene was fed at 14 g/min, styrene at 8.0 g/min, and n
- Hexane was mixed at 175.2 g/min.
In a static mixer provided in the middle of the pipe supplying this mixed solution to the inlet of the reactor, n-butyl lithium for inactivating remaining impurities was added at a rate of 0.103 mmol/min.
After mixing, the mixture was continuously fed to the bottom of the reactor.
C. In the first reactor, n-oxolanylpropane was fed at a rate of 0.081 mmol/min and n-butyllithium as a polymerization initiator was fed at a rate of 0.143 mmol/min to the bottom of the first reactor, which was being vigorously mixed with a stirrer, and the internal temperature of the reactor was maintained at 67.degree.
The polymer solution was continuously withdrawn from the top of the first reactor and continuously fed to the bottom of the second reactor to continue the reaction at 70°C, and further fed to the static mixer from the top of the second reactor. When the polymerization was sufficiently stabilized, 1,3-butadiene and styrene were copolymerized while
From the bottom of the second reactive group, a branching agent, trimethoxy(4-vinylphenyl)silane (
In the table, this is abbreviated as "BS-1.") was injected at a rate of 0.0190 mmol/min, and in parallel, 1,
3-Butadiene was added at 4.6 g/min and styrene at 2.0 g/min to carry out a polymerization reaction and a branching reaction to obtain a conjugated diene polymer having a main chain branched structure.
When the polymerization reaction and the branching reaction became stable, a small amount of the conjugated diene polymer solution before the addition of the coupling agent was withdrawn, and an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of the polymer, after which the solvent was removed and the Mooney viscosity at 110° C. and various molecular weights were measured. The physical properties are shown in Table 7.
Next, a coupling agent, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (abbreviated as "D" in the table), was continuously added to the polymer solution discharged from the outlet of the reactor at a rate of 0.0360 mmol/min.
The mixture was mixed using a static mixer and subjected to a coupling reaction.
At this time, the time until the coupling agent was added to the polymer solution flowing out from the outlet of the reactor was 4.8 minutes, the temperature was 68° C., and the difference between the temperature in the polymerization step and the temperature before the coupling agent was added was 2° C. A small amount of the conjugated diene polymer solution after the coupling reaction was withdrawn, and an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of polymer, and the solvent was then removed. The amount of bound styrene (physical property 6) and the microstructure of the butadiene portion (1
The results are shown in Table 7.
Next, an antioxidant (BHT) was continuously added to the polymer solution after the coupling reaction at a rate of 0.055 g/min (n-hexane solution) so that the amount was 0.2 g per 100 g of polymer, and the coupling reaction was terminated.
At the same time as the antioxidant, SRAE oil (J
25.0 g of X (JOMO Process NC140, manufactured by Nippon Oil & Energy Corporation) was continuously added and mixed with a static mixer.
The solvent was removed by steam stripping to obtain a coupled conjugated diene polymer (sample A-2) having a four-branched structure derived from the branching agent (hereinafter also referred to as "branching agent structure (1)"), which is a compound represented by the above formula (1), in a part of the main chain and a four-branched star polymer structure derived from the coupling agent. The physical properties of sample A-2 are shown in Table 7.
The structure of the coupled conjugated diene polymer was identified by comparing the molecular weight measured by GPC with the branching degree measured by GPC equipped with a viscometer for the polymer before the addition of the branching agent, the polymer after the addition of the branching agent, and the polymer in each step after the addition of the coupling agent.

[Coupling Conjugated Diene Polymer]
(Comparative Example 1-1) Coupling conjugated diene polymer (sample 1-38)
Two tank-type pressure vessels each having an internal volume of 10 L, an internal height (L) to diameter (D) ratio (L/D) of 4.0, an inlet at the bottom and an outlet at the top, and equipped with an agitator as a tank-type reactor and a jacket for temperature control were connected together as polymerization reactors.
1,3-butadiene, which had been previously dehydrated, was mixed under the conditions of 18.6 g/min, styrene at 10.0 g/min, and n-hexane at 175.2 g/min. In a static mixer provided in the middle of the pipe supplying this mixed solution to the inlet of the reactor, n-butyllithium for inactivating remaining impurities was added at 0.103 mmol/min, mixed, and then continuously supplied to the bottom of the reactor. Furthermore, 2,2-bis(2-oxolanyl)propane as a polar substance was supplied at a rate of 0.081 mmol/min, and n-butyllithium as a polymerization initiator was supplied at a rate of 0.143 mmol/min to the bottom of the first reactor, which was vigorously mixed with a stirrer, and the temperature inside the reactor was maintained at 67°C.
The polymer solution was continuously withdrawn from the top of the first reactor and continuously fed to the bottom of the second reactor to continue the reaction at 70°C, and further fed to a static mixer from the top of the second reactor. When the polymerization was sufficiently stabilized, a small amount of the polymer solution before the addition of the coupling agent was withdrawn, and an antioxidant (BHT) was added so that the amount was 0.2 g per 100 g of polymer, after which the solvent was removed, and the Mooney viscosity at 110°C and various molecular weights were measured. The physical properties are shown in Table 6.
Next, tetraethoxysilane (abbreviated as "A" in the table) was continuously added as a coupling agent to the polymer solution flowing out from the outlet of the reactor at a rate of 0.0480 mmol/min, and mixed using a static mixer to carry out a coupling reaction. At this time, the time until the coupling agent was added to the polymer solution flowing out from the outlet of the reactor was 4.8 minutes, the temperature was 68°C, and the difference between the temperature in the polymerization step and the temperature before the coupling agent was added was 2°C. A small amount of the conjugated diene polymer solution after the coupling reaction was withdrawn, and an antioxidant (BHT) was added so that the amount was 0.2 g per 100 g of polymer, and then the solvent was removed, and the bound styrene amount (physical property 6) and the microstructure of the butadiene portion (1,2-vinyl bond amount: physical property 7) were measured. The measurement results are shown in Table 6.
Next, an antioxidant (BHT) was continuously added to the polymer solution after the coupling reaction at 0.055 g/min (n-hexane solution) so that the amount was 0.2 g per 100 g of polymer, and the coupling reaction was terminated. Simultaneously with the antioxidant, SRAE oil (JOMO Process NC140 manufactured by JX Nippon Oil & Energy Corporation) was continuously added as a rubber softener so that the amount was 25.0 g per 100 g of polymer, and mixed with a static mixer. The solvent was removed by steam stripping to obtain a coupling conjugated diene polymer (sample 1-38) having no main chain branching derived from the branching agent and having a three-branched star polymer structure derived from the coupling agent. The physical properties of sample 1-38 are shown in Table 6.

(Comparative Example 1-2) Coupling conjugated diene polymer (sample 1-39)
A coupling conjugated diene polymer (Sample 1-39) having no main chain branching derived from the branching agent and having a four-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Comparative Example 1-1, except that the coupling agent was changed from tetraethoxysilane to 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (abbreviated as "D" in the table) and the amount of the coupling agent added was changed to 0.0360 mmol/min. The physical properties of Sample 1-39 are shown in Table 6.

(Comparative Example 1-3) Coupling conjugated diene polymer (sample 1-40)
A coupling conjugated diene polymer (Sample 1-40) having no main chain branching derived from the branching agent and having an 8-branched star polymer structure derived from the coupling agent was obtained in the same manner as in Comparative Example 1-1, except that the coupling agent was changed from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table) and the amount of the coupling agent added was changed to 0.0190 mmol/min. The physical properties of Sample 1-40 are shown in Table 6.

(Comparative Example B-1) Coupling conjugated diene polymer (sample B-1)
Two tank-type pressure vessels each having an internal volume of 10 L, an internal height (L) to diameter (D) ratio (L/D) of 4.0, an inlet at the bottom and an outlet at the top, and equipped with an agitator as a tank-type reactor and a jacket for temperature control were connected together as polymerization reactors.
1,3-butadiene, from which moisture had been removed in advance, was mixed under the conditions of 18.6 g/min, styrene at 10.0 g/min, and n-hexane at 175.2 g/min.
In a static mixer provided in the middle of the piping supplying this mixed solution to the inlet of the reactor, n-butyllithium for inactivating remaining impurities was added and mixed at 0.103 mmol/min, and then continuously supplied to the bottom of the reactor. Furthermore, 2,2-bis(2-oxolanyl)propane as a polar substance at a rate of 0.081 mmol/min and n-butyllithium as a polymerization initiator at a rate of 0.143 mmol/min were supplied to the bottom of the first reactor, which was being vigorously mixed with a stirrer, and the temperature inside the reactor was maintained at 67°C.
The polymer solution was continuously withdrawn from the top of the first reactor and continuously fed to the bottom of the second reactor to continue the reaction at 70°C, and further fed to the static mixer from the top of the second reactor. When the polymerization was sufficiently stabilized, a small amount of the polymer solution before the addition of the coupling agent was withdrawn, and an antioxidant (BHT) was added so that the amount was 0.2 g per 100 g of polymer, after which the solvent was removed, and the Mooney viscosity at 110°C and various molecular weights were measured. The physical properties are shown in Table 7.
Next, trimethoxy(4-vinylphenyl)silane (abbreviated as "BS-1" in the table) was added to the polymer solution flowing out from the outlet of the reactor at a rate of 0.0190 mmol/min, and simultaneously tetraethoxysilane (abbreviated as "A" in the table) was continuously added at a rate of 0.0480 mmol/min, and mixed using a static mixer to carry out a coupling reaction.
At this time, the time until the coupling agent was added to the polymer solution flowing out from the outlet of the reactor was 4.8 minutes, the temperature was 68°C, and the difference between the temperature in the polymerization step and the temperature before the coupling agent was added was 2°C. A small amount of the conjugated diene polymer solution after the coupling reaction was withdrawn, and an antioxidant (BHT) was added so that the amount was 0.2 g per 100 g of polymer, and then the solvent was removed, and the bound styrene amount (physical property 6) and the microstructure of the butadiene portion (1,2-vinyl bond amount: physical property 7) were measured. The measurement results are shown in Table 7.
Next, an antioxidant (BHT) was continuously added to the polymer solution after the coupling reaction at 0.055 g/min (n-hexane solution) so that the amount was 0.2 g per 100 g of polymer, and the coupling reaction was terminated. Simultaneously with the antioxidant, SRAE oil (JOMO Process NC140 manufactured by JX Nippon Oil & Energy Corporation) was continuously added as a rubber softener so that the amount was 25.0 g per 100 g of polymer, and mixed with a static mixer. The solvent was removed by steam stripping to obtain a coupled conjugated diene polymer (sample B-1). The physical properties of sample B-1 are shown in Table 7.
In Comparative Example B-1 of Table 7 below, "BS-1" is listed in the column for branching agent. However, in the addition method in which "BS-1" and "A" were added simultaneously as in this example, a main chain branch point could not be formed, and thus the branching agent did not function.
The structure of the coupled conjugated diene polymer was identified by comparing the molecular weight measured by GPC and the branching degree measured by GPC equipped with a viscometer for the polymer before the addition of "BS-1", the polymer after the addition of "BS-1", and the polymer in each step after the addition of "A".

(Comparative Example B-2) Coupling conjugated diene polymer (sample B-2)
No branching agent was used.
The coupling agent used was the coupling agent shown in (Z-1) below (abbreviated as "Z-1" in the table), and the amount added was 0.0360 mmol/min. Otherwise, the procedure was the same as in Comparative Example B-1 to obtain a coupled conjugated diene polymer (Sample B-2) having no main chain branching derived from the branching agent and having a 10-branched star polymer structure derived from the coupling agent. The physical properties of Sample B-2 are shown in Table 7.

( Reference Examples 1-38 to 1-74, Reference Examples a-1 and a-2, and Comparative Examples 1-4 to 1-6, and Comparative Examples b-1 and b-2)
Samples 1-1 to 1-40 shown in Tables 1 to 6 and samples (A-1 to 2, B-1 to
2) was used as raw rubber, and rubber compositions containing each raw rubber were obtained according to the formulations shown below.

(Rubber component)
Branched conjugated diene polymers and coupled conjugated diene polymers (Samples 1-1 to 1-40, A-1 to 2, B-1 to 2)
: 80 parts by mass (parts by mass excluding rubber softener)
- High cis polybutadiene (product name "UBEPOL BR150" manufactured by Ube Industries, Ltd.)
: 20 parts by mass

(Mixing conditions)
The amount of each compounding ingredient added is shown in parts by mass per 100 parts by mass of the rubber component not including the rubber softener.
Silica 1 (product name "Ultrasil 7000GR" manufactured by Evonik Degussa)
Nitrogen adsorption specific surface area 170 m2/g): 50.0 parts by mass Silica 2 (manufactured by Rhodia under the trade name "Zeosil Premium 200MP"
Nitrogen adsorption specific surface area 220 m2/g): 25.0 parts by mass Carbon black (product name "Seat KH (N339)" manufactured by Tokai Carbon Co., Ltd.)
Silane coupling agent (product name "Si75" manufactured by Evonik Degussa, bis(triethoxysilylpropyl) disulfide): 6.0 parts by mass SRAE oil (product name "Process NC140" manufactured by JX Nippon Oil & Energy Corporation)
42.0 parts by mass (including the amount previously added as a rubber softener contained in Samples 1-1 to 1-40, A-1 to 2, and B-1 to 2)
Zinc oxide: 2.5 parts by mass Stearic acid: 1.0 part by mass Antioxidant (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine): 2.0 parts by mass Sulfur: 2.2 parts by mass Vulcanization accelerator 1 (N-cyclohexyl-2-benzothiazylsulfinamide)
: 1.7 parts by mass Vulcanization accelerator 2 (diphenyl guanidine): 2.0 parts by mass Total: 239.4 parts by mass

(Kneading method)
The above materials were kneaded by the following method to obtain rubber compositions. Using an internal kneader (capacity 0.3 L) equipped with a temperature control device, the raw rubber (samples 1-1 to 1-40, samples A-1 to 2, samples B-1 to 2), fillers (silica 1, silica 2, carbon black), silane coupling agent, SRAE oil, zinc oxide, and stearic acid were kneaded in the first stage under conditions of a filling rate of 65% and a rotor rotation speed of 30 to 50 rpm. At this time, the temperature of the internal kneader was controlled, and each rubber composition (compound) was obtained at a discharge temperature of 155 to 160°C.
Next, in the second stage of kneading, the mixture obtained above was cooled to room temperature, and then the antioxidant was added and kneaded again to improve the dispersion of the silica. In this case, the discharge temperature of the mixture was adjusted to 155 to 160°C by controlling the temperature of the kneader.
After cooling, in the third stage of kneading, sulfur and vulcanization accelerators 1 and 2 were added and kneaded using an open roll set at 70°C.
Thereafter, the product was molded and vulcanized in a vulcanization press at 160° C. for 20 minutes.
The rubber compositions before and after vulcanization were evaluated. Specifically, the evaluation was performed by the following methods. The results are shown in Tables 8 to 14.

[Evaluation of characteristics]
(Evaluation 1) Blend Mooney Viscosity The blend obtained above after the second stage kneading and before the third stage kneading was used as a sample, and the viscosity was measured using a Mooney viscometer in accordance with ISO 289 after preheating at 130°C for 1 minute and rotating the rotor at 2 revolutions per minute for 4 minutes. The results of Comparative Examples 1-4 were indexed to 100. The smaller the index, the better the processability.

(Evaluation 2) Tensile strength and tensile elongation Tensile strength and tensile elongation were measured according to the tensile test method of JIS K6251, and indexed with the results of Comparative Examples 1-4 set at 100. A larger index indicates better tensile strength and tensile elongation (breaking strength).

(Evaluation 3) Abrasion resistance Using an Acron abrasion tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.), the amount of abrasion was measured at a load of 44.4 N and 1000 revolutions in accordance with JIS K6264-2, and indexed with the result of Comparative Example 1-4 set at 100. A larger index indicates better abrasion resistance.

(Evaluation 4) Viscoelasticity parameters Viscoelasticity parameters were measured in a torsion mode using a viscoelasticity tester "ARES" manufactured by Rheometrics Scientific Co. Each measured value was indexed, with the result for the rubber composition of Comparative Example 1-4 being set at 100.
Tan δ measured at 0° C., a frequency of 10 Hz, and a strain of 1% was used as an index of wet skid resistance. A larger index indicates better wet skid resistance.
In addition, tan δ measured at 50° C., a frequency of 10 Hz, and a strain of 3% was used as an index of fuel economy. A smaller index value indicates better fuel economy.
Furthermore, the elastic modulus (G') measured at 50° C., a frequency of 10 Hz and a strain of 3% was used as an index of steering stability. A larger index indicates better steering stability.

As shown in Tables 8 to 13, it was confirmed that, compared with Comparative Examples 1-4 to 1-6, Examples 1-38 to 1-74 had low Mooney viscosity of the compound when vulcanized, exhibited good processability, and were excellent in abrasion resistance, handling stability, and fracture strength when vulcanized, and were excellent in balance between low hysteresis loss and wet skid resistance.
As shown in Table 14, it was confirmed that, compared with Comparative Examples b-1 and b-2, Examples a-1 and a-2 had low Mooney viscosity of the compound when vulcanized, exhibited good processability, and, when vulcanized, were excellent in abrasion resistance, handling stability, and fracture strength, and also had an excellent balance between low hysteresis loss and wet skid resistance.

Second Example
Hereinafter, as a second example, the present embodiment will be described in more detail by giving specific examples and comparative examples, but the present embodiment is not limited in any way by the following examples and comparative examples.
Hereinafter, a conjugated diene polymer modified with a modifying agent will be referred to as a "modified conjugated diene polymer", and a conjugated diene polymer coupled with a coupling agent will be referred to as a "coupled conjugated diene polymer".
Moreover, the conjugated diene polymer in an unmodified state is referred to as an "unmodified conjugated diene polymer." In the tables, it is simply referred to as a "conjugated diene polymer."
Furthermore, a conjugated diene polymer having a branched structure is referred to as a "branched conjugated diene polymer."
Various physical properties in the examples and comparative examples were measured by the methods shown below.

(Physical Property 1) Polymer Mooney Viscosity The conjugated diene polymer before modification reaction, the conjugated diene polymer modified with a silicon atom- and sulfur atom-containing modifier (modified conjugated diene polymer), and the conjugated diene polymer modified with a silicon atom- and sulfur atom-containing modifier and further coupled with a coupling agent (coupled conjugated diene polymer) were used as samples, and the Mooney viscosity was measured using a Mooney viscometer (manufactured by Ueshima Seisakusho Co., Ltd., product name "VR1132") with an L-type rotor in accordance with ISO 289.
The measurement temperature was 110° C. when the sample was a conjugated diene polymer before the modification reaction, and 100° C. when the sample was a conjugated diene polymer modified with a silicon atom- and sulfur atom-containing modifier, or a polymer modified with a silicon atom- and sulfur atom-containing modifier and further coupled with a coupling agent.
First, the sample was preheated at the test temperature for 1 minute, and then the rotor was rotated at 2 rpm. The torque after 4 minutes was measured and taken as the Mooney viscosity (ML ₍₁₊₄₎ ).

(Physical Property 2) Branching Degree (Bn)
The branching degree (Bn) of the conjugated diene polymer was measured by a GPC-light scattering method equipped with a viscosity detector as follows.
The modified conjugated diene polymer and the coupled conjugated diene polymer were used as samples, and measurements were performed using a gel permeation chromatography (GPC) measuring device (manufactured by Malvern under the trade name "GPCmax VE-2001") in which three columns packed with polystyrene gel were connected together, and three detectors were connected in this order: a light scattering detector, an RI detector, and a viscosity detector (manufactured by Malvern under the trade name "TDA305"). Based on standard polystyrene, the absolute molecular weight was determined from the results of the light scattering detector and the RI detector, and the intrinsic viscosity was determined from the results of the RI detector and the viscosity detector.
The linear polymer was used as having an intrinsic viscosity [η] = -3.883 M ^0.771 , and the shrinkage factor (g') was calculated as the ratio of the intrinsic viscosity corresponding to each molecular weight, where M represents the absolute molecular weight.
The obtained shrinkage factor (g') was then used to calculate the branching degree (Bn), defined as g'=6Bn/[(Bn+1)(Bn+2)].
The eluent used was tetrahydrofuran (hereinafter also referred to as "THF") containing 5 mmol/L triethylamine.
The columns used were "TSKgel G4000HXL", "TSKgel G5000HXL", and "TSKgel G6000HXL" manufactured by Tosoh Corporation.
20 mg of a measurement sample was dissolved in 10 mL of THF to prepare a measurement solution, and 100 μL of the measurement solution was injected into a GPC measurement device and measured under conditions of an oven temperature of 40° C. and a THF flow rate of 1 mL/min.

(Physical Property 3) Silicon Atom Content Sample Purification:
The modified conjugated diene polymer and the coupled conjugated diene polymer were used as samples, and the samples were dissolved in toluene. A poor solvent, which was a mixture of ethanol and acetone in a volume ratio of 7:3, was then added to the toluene solution of the samples to precipitate the polymers, and the rubber softener and stabilizer contained in the samples were removed.
The recovered polymer was dissolved again in toluene, and the poor solvent was added to precipitate the polymer.
After repeating this operation five times, the sample was dried for five hours in a vacuum dryer adjusted to 40° C. to obtain a purified sample from which the rubber softener and stabilizer contained in the sample had been completely removed (hereinafter referred to as the purified sample).
Sample digestion:
After weighing the purified sample, 5 mL of 96% sulfuric acid (for atomic absorption spectrometry) and 3 mL of 60% nitric acid (for atomic absorption spectrometry) were added, and the purified sample was subjected to acid decomposition using a microwave decomposition device (ETHOS-1 manufactured by Milestone General Co., Ltd.). After acid decomposition, the sample was diluted to 50 mL with pure water to prepare a sample for ICP analysis.
Determination of silicon atomic weight:
The amount of silicon in the purified sample prepared by the above method was measured using an inductively coupled plasma emission spectrometer (iCAP 7400 Duo, manufactured by Thermo Fisher Scientific).
A calibration curve was prepared using a silicon standard solution for ICP (manufactured by Agilent) to quantify the amount of silicon in the purified sample.

(Physical Property 4) Sulfur Atom Content Sample Purification:
The modified conjugated diene polymer and the coupled conjugated diene polymer were used as samples. The samples were dissolved in toluene, and then a poor solvent obtained by mixing ethanol and acetone in a volume ratio of 7:3 was added to the toluene solution of the samples to precipitate the polymers, and the rubber softener and stabilizer contained in the samples were removed.
The recovered polymer was dissolved again in toluene, and the poor solvent was added to precipitate the polymer.
After repeating this operation five times, the sample was dried for five hours in a vacuum dryer adjusted to 40° C. to obtain a purified sample from which the rubber softener and stabilizer contained in the sample had been completely removed (hereinafter referred to as the purified sample).
Determination of sulfur atomic weight:
The amount of sulfur in the refined sample was measured by oxidative decomposition-ultraviolet fluorescence method using a trace sulfur analyzer (TS-2100H manufactured by Mitsubishi Chemical Analytech Co., Ltd.).
A calibration curve was prepared using a toluene solution of dibutyl disulfide to quantify the amount of sulfur in the purified sample.

(Physical property 5) Molecular weight Measurement conditions 1:
The conjugated diene polymer before modification, the modified conjugated diene polymer, and the coupled conjugated diene polymer were used as samples, and the samples were analyzed using a GPC measuring device (manufactured by Tosoh Corporation) with three columns connected together, each column containing a polystyrene gel as a packing material. A chromatogram was measured using a RI detector (trade name "HLC-8320GPC" manufactured by Tosoh Corporation, trade name "HLC8020"), and based on a calibration curve obtained using standard polystyrene, The weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) were determined.
The eluent used was 5 mmol/L triethylamine-containing THF (tetrahydrofuran). Three columns, both of which were manufactured by Tosoh Corporation under the trade name "TSKgel SuperMultiporeHZ-H", were connected, and a guard column, both of which were manufactured by Tosoh Corporation under the trade name "TSKgel SuperMultiporeHZ-H", was connected in front of the columns. "TSKguardcolumn SuperMP(HZ)-H" was connected and used.
10 mg of a measurement sample was dissolved in 10 mL of THF to prepare a measurement solution, and 10 μL of the measurement solution was injected into a GPC measurement device and measured under conditions of an oven temperature of 40° C. and a THF flow rate of 0.35 mL/min.
Among the various samples measured under the above measurement condition 1, samples whose molecular weight distribution (Mw/Mn) was less than 1.6 were measured again under the following measurement condition 2.
For samples that were measured under measurement condition 1 and had a molecular weight distribution value of 1.6 or more, measurement was performed under measurement condition 1.
Measurement condition 2:
The conjugated diene polymer before modification, the modified conjugated diene polymer, and the coupled conjugated diene polymer were used as samples, and a GPC measuring device having three columns packed with polystyrene gel was used. The chromatogram was measured, and the weight average molecular weight (Mw) and number average molecular weight (Mn) were determined based on a calibration curve using standard polystyrene.
The eluent used was THF containing 5 mmol/L triethylamine. The columns were: guard column: Tosoh Corporation's product name "TSKguardcolumn SuperH-H"; column: Tosoh Corporation's product names "TSKgel SuperH5000" and "TSKgel SuperH6000". "TSKgel Super H7000" was used.
An RI detector (HLC8020, product name, manufactured by Tosoh Corporation) was used under the conditions of an oven temperature of 40° C. and a THF flow rate of 0.6 mL/min. 10 mg of a sample to be measured was dissolved in 20 mL of THF to prepare a measurement solution. Then, 20 μL of the measurement solution was injected into a GPC measurement device and measurement was performed.
For samples that were measured under measurement condition 1 and had a molecular weight distribution value of less than 1.6, measurement was performed under measurement condition 2.

(Physical Property 6) Bound Styrene Amount A modified conjugated diene polymer not containing a rubber softener and a coupled conjugated diene polymer were used as samples. 100 mg of the sample was dissolved in chloroform to make up 100 mL to prepare a measurement sample.
The amount of bound styrene (mass%) relative to 100 mass% of the sample modified conjugated diene polymer or coupled conjugated diene polymer was measured based on the amount of absorption of ultraviolet light by the phenyl group of styrene (near 254 nm) (measuring device: Shimadzu Corporation spectrophotometer "UV-2450").

(Physical Property 7) Microstructure of Butadiene Moiety (1,2-Vinyl Bond Amount)
The modified conjugated diene polymer not containing a rubber softener and the coupled conjugated diene polymer were used as samples, and 50 mg of each sample was dissolved in 10 mL of carbon disulfide to prepare a measurement sample.
Using a solution cell, an infrared spectrum was measured in the range of 600 to 1000 cm ^-1 , and the microstructure of the butadiene portion, i.e., the amount of 1,2-vinyl bonds (mol%) was determined from the absorbance at a predetermined wave number according to the calculation formula of the Hampton method (the method described in R. R. Hampton, Analytical Chemistry 21, 923 (1949)) (measuring device: Fourier transform infrared spectrophotometer "FT-IR230" manufactured by JASCO Corporation).

[Branched conjugated diene polymer]
(Example 2-1) Modified conjugated diene polymer (sample 2-1)
Two tank-type pressure vessels each having an internal volume of 10 L, an internal height (L) to diameter (D) ratio (L/D) of 4.0, an inlet at the bottom and an outlet at the top, and equipped with an agitator as a tank-type reactor and a jacket for temperature control were connected together as polymerization reactors.
1,3-butadiene, which had been previously dehydrated, was mixed at 18.6 g/min, styrene at 10.0 g/min, and n-hexane at 175.2 g/min to obtain a mixed solution. In a static mixer provided in the middle of the piping supplying this mixed solution to the inlet of the reaction unit, n-butyllithium for inactivating remaining impurities was added at 0.103 mmol/min, mixed, and then continuously supplied to the bottom of the reaction unit. Furthermore, 2,2-bis(2-oxolanyl)propane as a polar substance was supplied at a rate of 0.081 mmol/min, and n-butyllithium as a polymerization initiator was supplied at a rate of 0.143 mmol/min to the bottom of the first reactor, which was vigorously mixed with a stirrer, and the temperature inside the reactor was maintained at 67°C.
The polymer solution was continuously withdrawn from the top of the first reactor, continuously fed to the bottom of the second reactor, and the reaction was continued at 70°C, and further fed to a static mixer from the top of the second reactor. When the polymerization was sufficiently stabilized, trimethoxy(4-vinylphenyl)silane (abbreviated as "BS-1" in the table) was added as a branching agent from the bottom of the second reactor at a rate of 0.0191 mmol/min, and when the polymerization reaction and branching reaction were further stabilized, a small amount of the conjugated diene polymer solution before the addition of the modifier was withdrawn, an antioxidant (BHT) was added so that the amount was 0.2 g per 100 g of polymer, and then the solvent was removed, and the Mooney viscosity at 110°C and various molecular weights were measured. The physical properties are shown in Table 15.
Next, S-trimethylsilylmercaptopropyltrimethoxysilane (abbreviated as "T-1" in the table) was continuously added as a modifier to the polymer solution flowing out from the outlet of the reactor at a rate of 0.073 mmol/min, and the mixture was mixed using a static mixer to carry out a modification reaction. At this time, the time until the modifier was added to the polymer solution flowing out from the outlet of the reactor was 4.8 minutes, the temperature was 68°C, and the difference between the temperature in the polymerization step and the temperature before the modifier was added was 2°C. An antioxidant (BHT) was continuously added to the modified polymer solution at 0.055 g/min (n-hexane solution) so that the amount was 0.2 g per 100 g of polymer, and the modification reaction was terminated. Simultaneously with the antioxidant, SRAE oil (JOMO Process NC140 manufactured by JX Nippon Oil & Energy Corporation) was continuously added as a rubber softener so that the amount was 25.0 g per 100 g of polymer, and the mixture was mixed using a static mixer. The solvent was removed by steam stripping to obtain a modified conjugated diene polymer (sample 2-1). The physical properties of sample 2-1 are shown in Table 15.

(Example 2-2) Modified conjugated diene polymer (sample 2-2)
A modified conjugated diene polymer (sample 2-2) was obtained in the same manner as in Example 2-1, except that the modifying agent was changed from S-trimethylsilylmercaptopropyltrimethoxysilane to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table) and the amount of the modifying agent was changed to 0.145 mmol/min. The physical properties of sample 2-2 are shown in Table 15.

(Example 2-3) Coupling conjugated diene polymer (sample 2-3)
Before the addition of the modifying agent, tin tetrachloride was continuously added as a coupling agent at a rate of 0.011 mmol/min, and mixed using a static mixer to carry out a coupling reaction.
Thereafter, S-trimethylsilylmercaptopropyltrimethoxysilane (abbreviated as "T-1" in the table) was continuously added as a modifying agent at a rate of 0.045 mmol/min, and mixed using a static mixer in the latter stage to carry out a modification reaction. In the same manner as in Example 2-1, a coupled conjugated diene polymer (sample 2-3) was obtained. The physical properties of sample 2-3 are shown in Table 15.

(Example 2-4) Coupling conjugated diene polymer (sample 2-4)
Before the addition of the modifying agent, tin tetrachloride was continuously added as a coupling agent at a rate of 0.011 mmol/min, and mixed using a static mixer to carry out a coupling reaction.
Thereafter, the modifying agent was changed from S-trimethylsilylmercaptopropyltrimethoxysilane to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table), the amount of the modifying agent was changed to 0.099 mmol/min and added continuously, and the mixture was mixed using a static mixer in the latter stage to carry out the modification reaction. A coupling conjugated diene polymer (sample 2-4) was obtained in the same manner as in Example 2-1. The physical properties of sample 2-4 are shown in Table 15.

(Example 2-5) Modified conjugated diene polymer (sample 2-5)
The addition rate of 1,3-butadiene was changed from 18.6 g/min to 24.3 g/min, the addition rate of styrene was changed from 10.0 g/min to 4.3 g/min, and the amount of the polar substance 2,2-bis(2-oxolanyl)propane added was changed from 0.081 mmol/min to 0.022 mmol/min, and the temperature of the second reactor was set to 80° C. At this time, the difference between the temperature in the polymerization step and the temperature before the addition of the modifier was 3° C., and the temperature at which the modifier was added was 77° C. Except for this, a modified conjugated diene polymer (sample 2-5) was obtained in the same manner as in Example 2-1. The physical properties of sample 2-5 are shown in Table 15.

(Example 2-6) Modified conjugated diene polymer (sample 2-6)
The addition rate of 1,3-butadiene was changed from 18.6 g/min to 17.2 g/min, the addition rate of styrene was changed from 10.0 g/min to 11.4 g/min, and the addition amount of the polar substance 2,2-bis(2-oxolanyl)propane was changed from 0.081 mmol/min to 0.283 mmol/min, and the temperature of the second reactor was set to 65°C. At this time, the difference between the temperature in the polymerization step and the temperature before the addition of the modifier was 2°C, and the temperature at which the modifier was added was 63°C. Otherwise, a modified conjugated diene polymer (sample 2-6) was obtained in the same manner as in Example 2-1. The physical properties of sample 2-6 are shown in Table 15.

(Example 2-7) Modified conjugated diene polymer (sample 2-7)
A modified conjugated diene polymer (sample 2-7) was obtained in the same manner as in Example 2-1, except that the amount of n-butyllithium added as a polymerization initiator was changed from 0.143 mmol/min to 0.101 mmol/min, and the amount of 2,2-bis(2-oxolanyl)propane added as a polar substance was changed from 0.081 mmol/min to 0.059 mmol/min. The physical properties of sample 2-7 are shown in Table 15.

(Example 2-8) Modified conjugated diene polymer (sample 2-8)
A modified conjugated diene polymer (sample 2-8) was obtained in the same manner as in Example 2-1, except that the amount of n-butyllithium added as a polymerization initiator was changed from 0.143 mmol/min to 0.152 mmol/min, and the amount of 2,2-bis(2-oxolanyl)propane added as a polar substance was changed from 0.081 mmol/min to 0.086 mmol/min. The physical properties of sample 2-8 are shown in Table 15.

(Example 2-9) Modified conjugated diene polymer (sample 2-9)
A modified conjugated diene polymer (sample 2-9) was obtained in the same manner as in Example 2-1, except that the branching agent was changed from trimethoxy(4-vinylphenyl)silane to dimethylmethoxy(4-vinylphenyl)silane (abbreviated as "BS-2" in the table) and the amount of the branching agent was changed to 0.0383 mmol/min. The physical properties of sample 2-9 are shown in Table 15.

(Example 2-10) Modified conjugated diene polymer (sample 2-10)
A modified conjugated diene polymer (sample 2-10) was obtained in the same manner as in Example 2-1, except that the branching agent was changed from trimethoxy(4-vinylphenyl)silane to dimethylmethoxy(4-vinylphenyl)silane (abbreviated as "BS-2" in the table), the amount of addition was changed to 0.0383 mmol/min, and the modifying agent was changed from S-trimethylsilylmercaptopropyltrimethoxysilane to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table), the amount of addition was changed to 0.145 mmol/min. The physical properties of sample 2-10 are shown in Table 15.

(Example 2-11) Modified conjugated diene polymer (sample 2-11)
A modified conjugated diene polymer (sample 2-11) was obtained in the same manner as in Example 2-1, except that the branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-(dimethylmethoxysilyl)phenyl)ethylene (abbreviated as "BS-3" in the table) and the amount of the branching agent added was changed to 0.0255 mmol/min. The physical properties of sample 2-11 are shown in Table 16.

(Example 2-12) Modified conjugated diene polymer (sample 2-12)
A modified conjugated diene polymer (sample 2-12) was obtained in the same manner as in Example 2-1, except that the branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-(dimethylmethoxysilyl)phenyl)ethylene (abbreviated as "BS-3" in the table) and the amount added was changed to 0.0255 mmol/min, and the modifying agent was changed from S-trimethylsilylmercaptopropyltrimethoxysilane to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table) and the amount added was changed to 0.145 mmol/min. The physical properties of sample 2-12 are shown in Table 16.

(Example 2-13) Modified conjugated diene polymer (sample 2-13)
A modified conjugated diene polymer (sample 2-13) was obtained in the same manner as in Example 2-1, except that the branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-trimethoxysilylphenyl)ethylene (abbreviated as "BS-4" in the table) and the amount of the branching agent was changed to 0.0109 mmol/min. The physical properties of sample 2-13 are shown in Table 16.

(Example 2-14) Modified conjugated diene polymer (sample 2-14)
A modified conjugated diene polymer (sample 2-14) was obtained in the same manner as in Example 2-1, except that the branching agent was changed from trimethoxy(4-vinylphenyl)silane to 1,1-bis(4-trimethoxysilylphenyl)ethylene (abbreviated as "BS-4" in the table) and the amount added was changed to 0.0109 mmol/min, and the modifying agent was changed from S-trimethylsilylmercaptopropyltrimethoxysilane to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table) and the amount added was changed to 0.145 mmol/min. The physical properties of sample 2-14 are shown in Table 16.

(Example 2-15) Modified conjugated diene polymer (sample 2-15)
A modified conjugated diene polymer (sample 2-15) was obtained in the same manner as in Example 2-1, except that the branching agent was changed from trimethoxy(4-vinylphenyl)silane to trichloro(4-vinylphenyl)silane (abbreviated as "BS-5" in the table). The physical properties of sample 2-15 are shown in Table 16.

(Example 2-16) Modified conjugated diene polymer (sample 2-16)
A modified conjugated diene polymer (sample 2-16) was obtained in the same manner as in Example 2-1, except that the branching agent was changed from trimethoxy(4-vinylphenyl)silane to trichloro(4-vinylphenyl)silane (abbreviated as "BS-5" in the table), the modifying agent was changed from S-trimethylsilylmercaptopropyltrimethoxysilane to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table), and the amount of the modified agent was changed to 0.145 mmol/min. The physical properties of sample 2-16 are shown in Table 16.

(Example 2-17) Modified conjugated diene polymer (sample 2-17)
A modified conjugated diene polymer (sample 2-17) was obtained in the same manner as in Example 2-1, except that SRAE oil, a rubber softener, was not added. The physical properties of sample 2-17 are shown in Table 16.

(Example 2-18) Modified conjugated diene polymer (sample 2-18)
A modified conjugated diene polymer (sample 2-18) was obtained in the same manner as in Example 2-1, except that the amount of SRAE oil added as a rubber softener was changed from 25.0 g to 37.5 g per 100 g of polymer. The physical properties of sample 2-18 are shown in Table 16.

(Example 2-19) Modified conjugated diene polymer (sample 2-19)
A modified conjugated diene polymer (sample 2-19) was obtained in the same manner as in Example 2-1, except that naphthenic oil (Nytex 810 naphthenic oil manufactured by Nynas Corp.) was used instead of the SRAE oil added as a rubber softener. The physical properties of sample 2-19 are shown in Table 16.

(Example 2-20) Modified conjugated diene polymer (sample 2-20)
A modified conjugated diene polymer (sample 2-20) was obtained in the same manner as in Example 2-1, except that the SRAE oil added as a rubber softener was replaced with liquid rubber (liquid polybutadiene LBR-302 manufactured by Kuraray Co., Ltd.). The physical properties of sample 2-20 are shown in Table 16.

(Example 2-21) Modified conjugated diene polymer (sample 2-21)
A modified conjugated diene polymer (sample 2-21) was obtained in the same manner as in Example 2-1, except that the SRAE oil added as a rubber softener was replaced with a resin (Yasuhara Chemical Co., Ltd., terpene resin, YS Resin PX1250). The physical properties of sample 2-21 are shown in Table 16.

(Example 2-22) Coupling conjugated diene polymer (sample 2-22)
A tank-type pressure vessel having an internal volume of 10 L and an internal height (L) to diameter (D) ratio (L/D) of 4.0, which is a tank-type reactor equipped with a stirrer, and a jacket for temperature control was used as the polymerization reactor. 5,000 g of n-hexane and n-butyllithium for neutralizing impurities present in the reactor that may hinder the polymerization reaction were placed in the reactor and stirred at 70° C. for 5 minutes, followed by cooling to room temperature and removing the solution, and then emptying the reactor.
Next, 5022 g of n-hexane, from which impurities had been removed in advance, 286.2 g of styrene, 478.3 g of 1,3-butadiene, 1.83 mmol of 2,2-bis(2-oxolanyl)propane as a polar substance, and 0.546 mmol of trimethoxy(4-vinylphenyl)silane (abbreviated as "BS-1" in the table) as a branching agent were placed in a reactor, and the internal temperature of the reactor was controlled to 40° C. After the internal temperature of the reactor stabilized, 4.402 mmol of n-butyllithium was added as a polymerization initiator to initiate polymerization.
Immediately after the start of polymerization, the temperature inside the reactor began to rise and reached a peak temperature of 76° C. Immediately after the peak temperature was reached, 53.1 g of 1,3-butadiene was added and stirred for 5 minutes, after which a small amount of the polymer solution was sampled, and an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of polymer. The solvent was removed by vacuum drying, and the Mooney viscosity at 110° C. and various molecular weights were measured. The physical properties are shown in Table 18.
Next, 0.314 mmol of tin tetrachloride as a coupling agent was added and stirred for 5 minutes, and then 1.286 mmol of S-trimethylsilylmercaptopropyltrimethoxysilane (abbreviated as "T-1" in the table) as a modifying agent was added and stirred for 5 minutes.
As a polymerization terminator, 0.15 mmol of ethanol was added to terminate the reaction, thereby obtaining a conjugated diene polymer.
To the obtained polymer solution, an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of the polymer, and the solvent was removed by steam stripping to obtain a coupled conjugated diene polymer (sample 2-22). The physical properties of sample 2-22 are shown in Table 18.

(Example 2-23) Coupling conjugated diene polymer (sample 2-23)
A coupling conjugated diene polymer (sample 2-23) was obtained in the same manner as in Example 2-22, except that the modifying agent was changed from S-trimethylsilylmercaptopropyltrimethoxysilane (abbreviated as "T-1" in the table) to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table) and the amount of the modifying agent was changed to 2.572 mmol. The physical properties of sample 2-23 are shown in Table 18.

[Coupling or modified conjugated diene polymer]
(Comparative Example 2-1) Modified conjugated diene polymer (sample 2-24)
Two tank-type pressure vessels each having an internal volume of 10 L, an internal height (L) to diameter (D) ratio (L/D) of 4.0, an inlet at the bottom and an outlet at the top, and equipped with an agitator as a tank-type reactor and a jacket for temperature control were connected together as polymerization reactors.
1,3-butadiene, which had been previously dehydrated, was mixed under the conditions of 18.6 g/min, styrene at 10.0 g/min, and n-hexane at 175.2 g/min. In a static mixer provided in the middle of the pipe supplying this mixed solution to the inlet of the reactor, n-butyllithium for inactivating remaining impurities was added at 0.103 mmol/min, mixed, and then continuously supplied to the bottom of the reactor. Furthermore, 2,2-bis(2-oxolanyl)propane as a polar substance was supplied at a rate of 0.081 mmol/min, and n-butyllithium as a polymerization initiator was supplied at a rate of 0.143 mmol/min to the bottom of the first reactor, which was vigorously mixed with a stirrer, and the temperature inside the reactor was maintained at 67°C.
The polymer solution was continuously withdrawn from the top of the first reactor and continuously fed to the bottom of the second reactor to continue the reaction at 70°C, and further fed to a static mixer from the top of the second reactor. When the polymerization reaction was stabilized, a small amount of the conjugated diene polymer solution before the addition of the modifier was withdrawn, and an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of polymer, followed by removal of the solvent, and the Mooney viscosity at 110°C and various molecular weights were measured. The physical properties are shown in Table 17.
Next, S-trimethylsilylmercaptopropyltrimethoxysilane (abbreviated as "T-1" in the table) was continuously added as a modifier to the polymer solution flowing out from the outlet of the reactor at a rate of 0.073 mmol/min, and the mixture was mixed using a static mixer to carry out a modification reaction. At this time, the time until the modifier was added to the polymer solution flowing out from the outlet of the reactor was 4.8 minutes, the temperature was 68°C, and the difference between the temperature in the polymerization step and the temperature before the modifier was added was 2°C. An antioxidant (BHT) was continuously added to the modified polymer solution at 0.055 g/min (n-hexane solution) so that the amount was 0.2 g per 100 g of polymer, and the modification reaction was terminated. Simultaneously with the antioxidant, SRAE oil (JOMO Process NC140 manufactured by JX Nippon Oil & Energy Corporation) was continuously added as a rubber softener so that the amount was 25.0 g per 100 g of polymer, and the mixture was mixed using a static mixer. The solvent was removed by steam stripping to obtain a modified conjugated diene polymer (Sample 2-24). The physical properties of Sample 2-24 are shown in Table 17.

(Comparative Example 2-2) Modified conjugated diene polymer (sample 2-25)
A modified conjugated diene polymer (sample 2-25) was obtained in the same manner as in Comparative Example 2-1, except that the modifying agent was changed from S-trimethylsilylmercaptopropyltrimethoxysilane to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table) and the amount of the modifying agent was changed to 0.145 mmol/min. The physical properties of sample 2-25 are shown in Table 17.

(Comparative Example 2-3) Coupling conjugated diene polymer (sample 2-26)
Before the addition of the modifier, tin tetrachloride was added continuously as a coupling agent at a rate of 0.011 mmol/min, and mixed using a static mixer to carry out a coupling reaction. Thereafter, S-trimethylsilylmercaptopropyltrimethoxysilane (abbreviated as "T-1" in the table) was added continuously as a modifier at a rate of 0.045 mmol/min, and mixed using a static mixer in the latter stage to carry out a modification reaction. A coupled conjugated diene polymer (sample 2-26) was obtained in the same manner as in Comparative Example 2-1. The physical properties of sample 2-26 are shown in Table 17.

(Comparative Example 2-4) Coupling conjugated diene polymer (sample 2-27)
Before the addition of the modifier, tin tetrachloride was added continuously as a coupling agent at a rate of 0.011 mmol/min, and the mixture was mixed using a static mixer to carry out a coupling reaction. Thereafter, the modifier was changed from S-trimethylsilylmercaptopropyltrimethoxysilane to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table), and the amount of the modifier was changed to 0.099 mmol/min and added continuously, and the mixture was mixed using a static mixer in the latter stage to carry out a modification reaction. A coupled conjugated diene polymer (sample 2-27) was obtained in the same manner as in Comparative Example 2-1. The physical properties of sample 2-27 are shown in Table 17.

(Comparative Example 2-5) Conjugated diene polymer (sample 2-28)
A tank-type pressure vessel having an internal volume of 10 L and an internal height (L) to diameter (D) ratio (L/D) of 4.0, which is a tank-type reactor equipped with a stirrer, and a jacket for temperature control was used as the polymerization reactor. 5,000 g of n-hexane and n-butyllithium for neutralizing impurities present in the reactor that may hinder the polymerization reaction were placed in the reactor and stirred at 70° C. for 5 minutes, followed by cooling to room temperature and removing the solution, and then emptying the reactor.
Next, 5022 g of n-hexane, 286.2 g of styrene, 478.3 g of 1,3-butadiene, and 1.83 mmol of 2,2-bis(2-oxolanyl)propane as a polar substance, from which impurities had been removed in advance, were placed in a reactor, and the internal temperature of the reactor was controlled at 40° C. After the internal temperature of the reactor became stable, 4.402 mmol of n-butyllithium was added as a polymerization initiator to initiate polymerization.
Immediately after the start of polymerization, the temperature inside the reactor began to rise and reached a peak temperature of 76° C. Immediately after the peak temperature was reached, 53.1 g of 1,3-butadiene was added and stirred for 5 minutes, after which a small amount of the polymer solution was sampled, and an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of polymer. The solvent was removed by vacuum drying, and the Mooney viscosity at 110° C. and various molecular weights were measured. The physical properties are shown in Table 18.
Next, 0.314 mmol of tin tetrachloride as a coupling agent was added and stirred for 5 minutes, and then 1.286 mmol of S-trimethylsilylmercaptopropyltrimethoxysilane as a modifying agent was added and stirred for 5 minutes.
As a polymerization terminator, 0.15 mmol of ethanol was added to terminate the reaction, thereby obtaining a conjugated diene polymer.
To the obtained polymer solution, an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of polymer, and the solvent was removed by steam stripping to obtain a conjugated diene polymer (sample 2-28). The physical properties of sample 2-28 are shown in Table 18.

(Comparative Example 2-6) Conjugated diene polymer (sample 2-29)
A conjugated diene polymer (sample 2-29) was obtained in the same manner as in Comparative Example 2-5, except that the modifying agent was changed from S-trimethylsilylmercaptopropyltrimethoxysilane (abbreviated as "T-1" in the table) to S-trimethylsilylmercaptopropylmethyldimethoxysilane (abbreviated as "T-2" in the table) and the amount of the modifying agent was changed to 2.572 mmol. The physical properties of sample 2-29 are shown in Table 18.

(Examples 2-24 to 2-46 and Comparative Examples 2-7 to 2-12)
Using Samples 2-1 to 2-29 shown in Tables 15 to 18 as raw rubbers, rubber compositions containing each raw rubber were obtained according to the formulations shown below.

(Rubber component)
Conjugated diene polymers (samples 2-1 to 2-29)
: 80 parts by mass (excluding rubber softener)
- High cis polybutadiene (product name "UBEPOL BR150" manufactured by Ube Industries, Ltd.)
: 20 parts by mass

(Mixing conditions)
The amount of each compounding ingredient added is shown in parts by mass based on the rubber component not including the softener.
Silica 1 (product name "Ultrasil 7000GR" manufactured by Evonik Degussa)
Nitrogen adsorption specific surface area 170 m2/g): 50.0 parts by mass Silica 2 (manufactured by Rhodia under the trade name "Zeosil Premium 200MP"
Nitrogen adsorption specific surface area 220 m2/g): 25.0 parts by mass Carbon black (product name "Seat KH (N339)" manufactured by Tokai Carbon Co., Ltd.)
Silane coupling agent (product name "Si75" manufactured by Evonik Degussa, bis(triethoxysilylpropyl) disulfide): 6.0 parts by mass SRAE oil (product name "Process NC140" manufactured by JX Nippon Oil & Energy Corporation)
: 30.0 parts by mass (including the amount previously added as a rubber softener contained in samples 2-1 to 2-29)
Zinc oxide: 2.5 parts by mass Stearic acid: 1.0 part by mass Antioxidant (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine): 2.0 parts by mass Sulfur: 2.2 parts by mass Vulcanization accelerator 1 (N-cyclohexyl-2-benzothiazylsulfinamide)
: 1.7 parts by mass Vulcanization accelerator 2 (diphenyl guanidine): 2.0 parts by mass Total: 239.4 parts by mass

(Kneading method)
The above materials were kneaded in the following manner to obtain a rubber composition.
Using an internal mixer (capacity 0.3 L) equipped with a temperature control device, the raw rubber (samples 1 to 29), fillers (silica 1, silica 2, carbon black), silane coupling agent, process oil, zinc oxide, and stearic acid were kneaded in the first stage under conditions of a filling rate of 65% and a rotor rotation speed of 30 to 50 rpm. At this time, the temperature of the internal mixer was controlled, and each rubber composition (compound) was obtained at a discharge temperature of 155 to 160°C.
Next, in the second stage of kneading, the mixture obtained above was cooled to room temperature, and then an antioxidant was added and kneaded again to improve the dispersion of silica. In this case, the discharge temperature of the mixture was adjusted to 155 to 160°C by controlling the temperature of the mixer. After cooling, in the third stage of kneading, sulfur and vulcanization accelerators 1 and 2 were added and kneaded with an open roll set at 70°C. Then, the mixture was molded and vulcanized in a vulcanization press at 160°C for 20 minutes.
The rubber composition before vulcanization and the rubber composition after vulcanization were evaluated.
Specifically, the evaluation was carried out by the following methods.
The results are shown in Tables 19 to 22.

(Evaluation 1) Mooney Viscosity of Blend The blend obtained above after the second stage kneading and before the third stage kneading was used as a sample, and the viscosity was measured using a Mooney viscometer in accordance with ISO 289 after preheating at 130° C. for 1 minute and rotating the rotor at 2 revolutions per minute for 4 minutes.
The results of Comparative Examples 2-7 and 2-11 were indexed to 100. The smaller the index, the better the processability.

(Evaluation 2) Tensile strength and tensile elongation Tensile strength and tensile elongation were measured according to the tensile test method of JIS K6251, and the results of Comparative Examples 2-7 and 2-11 were indexed to 100. A larger index indicates better tensile strength and tensile elongation.

(Evaluation 3) Abrasion resistance Using an Acron abrasion tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.), the amount of abrasion was measured at a load of 44.4 N and 1000 revolutions in accordance with JIS K6264-2, and the results of Comparative Examples 2-7 and 2-11 were indexed as 100. A larger index indicates better abrasion resistance.

(Evaluation 4) Viscoelasticity parameters Viscoelasticity parameters were measured in a torsion mode using a viscoelasticity tester "ARES" manufactured by Rheometrics Scientific Co., Ltd. The measured values were indexed with the results for the rubber compositions of Comparative Examples 2-7 and 2-11 being set at 100.
The elastic modulus (G') measured at 50° C., a frequency of 10 Hz and a strain of 3% was used as an index of steering stability. A larger index indicates better steering stability.

Compared to Comparative Examples 2-7 to 2-12, Examples 2-24 to 2-46 showed low compound Mooney viscosity when vulcanized, good processability, excellent fracture properties and abrasion resistance when vulcanized, and good handling stability.

The branched conjugated diene polymer of the present invention has industrial applicability in fields such as tire treads, interior and exterior parts of automobiles, anti-vibration rubber, belts, footwear, foams, and various industrial product applications.

Claims (11)

a polymerization step of polymerizing or copolymerizing a conjugated diene compound, or a conjugated diene compound and an aromatic vinyl compound, using an alkali metal compound or an alkaline earth metal compound as a polymerization initiator to obtain a conjugated diene polymer having an active terminal;
a branching step of reacting an active terminal of the conjugated diene polymer with a styrene derivative as a branching agent to introduce a branched structure;
having
a reaction step of reacting a coupling agent with the active terminal of the conjugated diene polymer obtained in the branching step,
Furthermore,
In the reaction step,
The coupling agent is a silane sulfide compound represented by the following formula (3):
A method for producing a branched conjugated diene polymer.

(In formula (3), Si represents a silicon atom, O represents an oxygen atom, and S represents a sulfur atom.
x is an integer of 1 to 3, y is 0 or an integer of 1 to 2, and x+y is 3.
R ¹ , R ² , and R ⁴ may be the same or different and each represents an alkyl group having 1 to 16 carbon atoms, and R ³ represents an aryl group having 6 to 16 carbon atoms, an alkylene group having 1 to 16 carbon atoms, or an alkyl chain having 1 to 16 carbon atoms. The method further comprises a step of adding a conjugated diene compound and/or an aromatic vinyl compound to the reaction system during and/or after the branching step.
A method for producing the branched conjugated diene polymer according to claim 1. The styrene derivative is
A compound represented by the following formula (1) and/or the following formula (2):
A method for producing the branched conjugated diene polymer according to claim 1 or 2 .

In the formulas (1) and (2), R ¹ is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a cyclic alkyl group having 6 carbon atoms.
The aryl group may have a branched structure in part.
X ¹ , X ² and X ³ each represent a single bond or an organic group containing any one selected from the group consisting of carbon, hydrogen, nitrogen, sulfur and oxygen.
^Y1 , ^Y2 , and ^Y3 each represent any one selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and a halogen atom. They may be independent and the same or different. A step of obtaining a branched conjugated diene polymer by the production method according to any one of claims 1 to 3 ;
obtaining a rubber component containing 10% by mass or more of the branched conjugated diene polymer;
a step of obtaining a rubber composition by adding 5.0 parts by mass or more and 150 parts by mass or less of a filler to 100 parts by mass of the rubber component;
The method for producing a rubber composition comprising the steps of: Obtaining a rubber composition by the method for producing a rubber composition according to claim 4 ;
molding the rubber composition to obtain a tire;
A tire manufacturing method comprising the steps of: having one or more side chains in the polymer chain,
A branched conjugated diene-based polymer having a branching degree (Bn) of 1 or more as measured by a viscosity detector-equipped GPC-light scattering method,
the branched conjugated diene-based polymer contains sulfur atoms and silicon atoms, and the molar ratio of the silicon atoms to the sulfur atoms is 1.05 or more and less than 10;
The Mooney viscosity measured at 100° C. is 40 or more and 170 or less,
A polymer or copolymer of a conjugated diene compound, or a conjugated diene compound and an aromatic vinyl compound,
The branched conjugated diene polymer has a branched structure based on a styrene derivative at a terminal thereof,
At least one end of the branched conjugated diene polymer is modified with a silane sulfide compound represented by the following formula (3):
Branched conjugated diene polymers.

(In formula (3), Si represents a silicon atom, O represents an oxygen atom, and S represents a sulfur atom.
x is an integer of 1 to 3, y is 0 or an integer of 1 to 2, and x+y is 3.
R ¹ , R ² , and R ⁴ may be the same or different and each represents an alkyl group having 1 to 16 carbon atoms, and R ³ represents an aryl group having 6 to 16 carbon atoms, an alkylene group having 1 to 16 carbon atoms, or an alkyl chain having 1 to 16 carbon atoms. 7. The branched conjugated diene polymer according to claim 6 , which has a branching degree (Bn) of 2 or more and 25 or less, as measured by a GPC-light scattering method with a viscosity detector. The polymer chain has a portion derived from a vinyl monomer containing an alkoxysilyl group or a halosilyl group,
The moiety derived from the vinyl monomer containing an alkoxysilyl group or a halosilyl group has a side chain.
The branched conjugated diene polymer according to claim 6 or 7 . The portion derived from the vinyl monomer containing an alkoxysilyl group or a halosilyl group is
A monomer unit based on a compound represented by the following formula (4) or (5):
The branched conjugated diene-based polymer according to claim 8 , having a polymer chain branching point due to a monomer unit based on a compound represented by the following formula (4) or (5):

In formula (4), R ¹ represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, which may have a branched structure in part.
R ² and R ³ each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, which may partially have a branched structure.
When a plurality of R ¹ to R ³ are present, they are each independent.
^X1 independently represents a halogen atom.
m is an integer of 0 to 2, n is an integer of 0 to 3, and 1 is an integer of 0 to 3.
(m+n+l) represents 3.)
In formula (5), R ² to R ⁵ each independently represent an alkyl group having 1 to 20 carbon atoms or a group having 6 to 8 carbon atoms.
When a plurality of R ² to R ⁵ are present, they are each independent of each other.
X ² and X ³ each independently represent a halogen atom.
m is an integer of 0 to 2, n is an integer of 0 to 3, and 1 is an integer of 0 to 3.
(m+n+l) represents 3.
a represents an integer of 0 to 2, b represents an integer of 0 to 3, and c represents an integer of 0 to 3.
(a+b+c) represents 3. A branched conjugated diene polymer composition comprising the branched conjugated diene polymer according to any one of claims 6 to 9,
The branched conjugated diene polymer is contained in an amount of 10% by mass or more and less than 100% by mass.
A branched conjugated diene-based polymer composition. The branched conjugated diene polymer comprises
The branched conjugated diene-based polymer includes a branched conjugated diene-based polymer coupled with at least one compound selected from the group consisting of tin halides, tin alkoxides, silicon halides, and alkoxysilanes.
The branched conjugated diene-based polymer composition according to claim 10 .