JPH0629283B2 - Random styrene-butadiene copolymer rubber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to random styrene in which the molecular weight distribution has a specific bi-modal, and the styrene units in the copolymer chain have a specific styrene chain distribution. -Regarding butadiene copolymer rubber, specifically, slip resistance on wet road surface (hereinafter referred to as wet skid resistance), slip resistance on iced road surface (hereinafter referred to as ice skid resistance), abrasion resistance and impact resilience Random styrene with a relatively low styrene content, which has a good bi-modal in its molecular weight distribution with excellent balance and processability, and a specific styrene chain distribution in the styrene units in its copolymer chain. -Butadiene copolymer rubber.

[Conventional technology]

Conventionally, in cold regions, winter tires having excellent ice skid resistance and general tires having excellent wet skid resistance and wear resistance have been used differently depending on the season. However, it has been inconvenient and economically burdensome for the user to properly use winter tires and general tires. However, due to the development of the highway network in recent years, it has become difficult to properly use the two types of tires, and it has been forced to drive on the highway with winter tires. However, driving on a highway with winter tires is unsuitable in terms of wet skid resistance and poses a danger to the person driving the vehicle. In addition, it is possible to drive on a highway that has been snow-removed with general-purpose tires, but if you move from a highway to a general road that has not been snow-removed, ice skid resistance will be insufficient, and people who drive a car will also be affected. Brought danger. Therefore, the emergence of a tire that can run on any road surface with one tire, that is, an all-season tire is strongly desired. On the other hand, in recent years, due to the social demand for resource saving and energy saving, the economic demand for automobiles has become stronger,
As a result, low fuel consumption has been strongly desired as a characteristic of general-purpose tires. Under such circumstances, wet skid resistance, ice skid resistance, the development of all-season tires excellent in wear resistance and fuel economy is desired, therefore, as a tire rubber, wet skid resistance, ice skid resistance, It is required to have excellent wear resistance and impact resilience. Further, roll processability, extrusion processability, etc., which are important in tire production, are required.

However, wet skid resistance and ice skid resistance, wet skid resistance and abrasion resistance, wet skid resistance and impact resilience are contradictory characteristics, respectively. To balance these conflicting properties, blend compositions of different rubbers have been used in the past. For example, a blend composition of styrene-butadiene copolymer rubber, polybutadiene such as high cis polybutadiene and low cis polybutadiene, and natural rubber has been mainly used. However, these blend compositions have not yet reached a high level of wet skid resistance, ice skid resistance, abrasion resistance and impact resilience, and have not yet achieved the balance between the above characteristics and processability.

First, the present inventors have disclosed in Japanese Patent Application No. 59-69139 that the molecular weight distribution has a specific bi-modal, and the styrene unit in the copolymer chain has a specific styrene chain distribution. It has been found that the styrene-butadiene copolymer rubber has excellent wet skid resistance and processability.
However, this copolymer rubber is a copolymer rubber in which bound styrene is increased to 28% by weight to 55% by weight in order to improve wet skid resistance, and the ice skid resistance and abrasion resistance are not always sufficient. It was insufficient as a rubber for season tires.

[Problems to be solved by the invention]

The present invention has been made in view of the above points, and has excellent processability, and a random styrene-butadiene copolymer having an improved balance of wet skid resistance, ice skid resistance, abrasion resistance and impact resilience. Intended to provide rubber.

[Means for solving problems]

The present invention provides a relatively low styrene content random styrene-butadiene copolymer rubber having a specific structure, which has an excellent balance of wet skid resistance, ice skid resistance, abrasion resistance and impact resilience, and excellent workability. It was made on the basis of finding out that.

That is, the present invention copolymerizes styrene and butadiene with an organolithium compound as a polymerization initiator in a hydrocarbon solvent containing at least one Lewis base, and then a polyfunctional cup having at least three reactive sites. A Mooney viscosity (ML _{1 + 4} , 100 ° C.) having a branched structure of three or more branches, added with a ring agent, of 40 to 150, bound styrene of 5% by weight or more and less than 28% by weight, vinyl of butadiene portion A styrene-butadiene copolymer rubber having a bond content of 16% by weight or more and less than 40% by weight and a molecular weight distribution of bi-modal, and a weight average molecular weight of the copolymer rubber having a molecular weight distribution of bi-modal. (Mw-bi) has substantially the same structural factor except that it is copolymerized using an organolithium compound under the same conditions as the copolymer rubber, and is branched by coupling, and has the same Mooney. The molecular weight distribution of the viscosity
Weight average molecular weight of mono-modal copolymer rubber (Mw-mo
No) and Mw-bi / Mw-mono ≧ 1.3, and the styrene single chain with one styrene monomer is 75% by weight or more of the total bound styrene, and the styrene monomer is continuous with 8 or more. Styrene long chain is 5.0% by weight of total bound styrene
The present invention relates to a random styrene-butadiene copolymer rubber characterized by the following.

The random styrene-butadiene copolymer rubber of the present invention exhibits excellent processability and physical properties and is used for various rubber applications, and is particularly useful as a rubber for all season tire treats.

The present invention will be described in detail below.

The random styrene-butadiene copolymer rubber of the present invention is a copolymer rubber copolymerized with an organolithium compound, the molecular weight distribution of which is bi-modal, the weight average molecular weight (Mw-bi) is Copolymer rubber that has substantially the same structural factor except that it is copolymerized under the same conditions as the copolymer rubber and is branched by coupling, and that the molecular weight distribution of the same Mooney viscosity is mono-modal. Weight average molecular weight (M
(w-mono), the relationship of Mw-bi / Mw-mono ≧ 1.3 is satisfied. The weight average molecular weight here is a polystyrene-equivalent molecular weight measured using a gel permeation chromatogram (GPC), but in the present invention, specifically
GPC is manufactured by Water (trade name: 204 compact type)
The column is manufactured by Showa Denko (trade name: SHYO DEX
A80M, 1 piece) was used. A more detailed measuring method of GPC will be described later. The molecular weight distribution here is mono-m.
The copolymer rubber that is odal will be described in detail later,
Using an organolithium compound as an initiator, the polymerization method and conditions other than the bi-modalization technique are those in which the polymerization is performed in conformity with the copolymer rubber whose molecular weight distribution is bi-modal as much as possible. Factors such as the microstructure of the butadiene part, bound styrene, styrene chain distribution, and the Mooney viscosity are substantially the same as those of the copolymer rubber having a bi-modal molecular weight distribution.

When the ratio of Mw-bi / Mw-mono is less than 1.3, the impact resilience and the degree of decrease in the Mooney viscosity of the compound are insufficient.

On the other hand, when the ratio of Mw-bi / Mw-mono is 1.3 or more, the larger the ratio is, the more excellent the physical properties and processability are.
If the above ratio becomes extremely large, a slightly different phenomenon will be observed. That is, according to the results of studies conducted by the present inventors, a copolymer rubber having a molecular weight distribution of bi-modal up to the above ratio of about 4 was obtained, but in view of processability,
The larger the ratio is, the better the rubber is. However, from the viewpoint of physical properties, when the ratio is 2.5 or more, the breaking strength and the wear resistance are gradually decreased. In this sense,
The ratio of Mw-bi / Mw-mono is preferably 3.0 or less, particularly preferably 2.5, considering the balance between processability and overall physical properties.
The following is good.

Furthermore, the copolymer rubber of the present invention has a tri-molar molecular weight distribution.
Even dal was found to be as effective as bi-modal.

Mooney viscosity (ML _{1 + 4} , 100 ° C) of the copolymer rubber of the present invention
Is 40 to 150, preferably 50 to 100, particularly preferably 60 to 75. If the Mooney viscosity is less than 40, the physical properties are M _W -bi / M _W -mono ≧ 1.3,
Not only the workability improving effect, but the effect is not sufficient. However, as the Mooney viscosity increases, the compound Mooney viscosity increases relatively, so the Mooney viscosity of the rubber used is limited to 150. When the Mooney viscosity exceeds 150, problems remain in the processability such as calendering processability and extrusion processability of the compound.

The vinyl bond content of the butadiene portion of the copolymer rubber of the present invention is 16% by weight or more and less than 40% by weight, preferably 16% by weight to 33% by weight. Although skid resistance and abrasion resistance are improved, wet skid resistance is lowered, which is not preferable. On the other hand, if the vinyl bond content exceeds 40% by weight, the ice skid resistance, abrasion resistance, fracture characteristics and impact resilience are reduced, which is not preferable.

Further, the copolymer rubber of the present invention has a distribution of vinyl groups in the copolymer chain, even if it is uniform in the molecular chain,
Moreover, as shown in Japanese Patent Publication No. 45-875, along the molecular chain,
It may be gradually changed, or may be distributed blockwise (USP3301840). In short, it may be determined according to the purpose of use.

The bound styrene of the copolymer rubber of the present invention is 5% by weight or more and less than 28% by weight, preferably 7 to 24% by weight,
It is particularly preferably 10 to 20% by weight. If the bound styrene content is less than 5% by weight, the wet skid resistance is lowered, which is not preferable. On the other hand, bound styrene is 28% by weight
Above, it is not preferable because the ice skid resistance and wear resistance are lowered.

The styrene unit chain having one styrene unit (hereinafter referred to as S ₁ ) of the copolymer rubber of the present invention is 75% by weight or more, preferably 80% by weight or more, and 8% by weight or more of bound styrene.
FOB communicating Natsuta styrene length chain (hereinafter S ₈ ~ hereinafter) is 5.0 wt% of bound styrene, preferably must be 2.5 wt% or less. If S ₁ is less than 75% by weight of the bound styrene or if S ₈ is more than 5% by weight, the ice skid resistance, impact resilience, and abrasion resistance are unfavorably reduced.

The ratio M _W -bi / M _N -bi of the weight average molecular weight (M _W -bi) and the number average molecular weight (M _N -bi) of the copolymer rubber of the present invention is not particularly limited, but has excellent physical properties. M _W -bi / M _N -bi in order to obtain a copolymer rubber having a preferably 1.5 to 3.0. Further, the ratio of the weight average molecular weight (M _W ) to the number average molecular weight (M _W ) of each of the high molecular weight part and the low molecular weight part of the copolymer rubber of the present invention M _W /
M _N is also not particularly limited, but M _W / M _N is 1.
1-2.5 is sufficient.

The random styrene-butadiene copolymer rubber of the present invention is, under a hydrocarbon solvent containing at least one Lewis base, after the total amount of styrene and a part of butadiene are copolymerized with an organolithium compound, and finally. Within the specific range of the polymerization conversion rate of the resulting copolymer, the remaining butadiene is continuously or intermittently added to the polymerization system so that the styrene monomer content in the monomer composition in the polymerization system falls within the specific concentration range. It is obtained by feeding and after the copolymerization is completed, and then adding a polyfunctional coupling agent having at least 3 reactive sites.

In the present invention, the content of styrene monomer in the monomer composition in the polymerization system is always 9 at least until the polymerization conversion rate of the finally obtained copolymer rubber reaches 98% by weight.
It is required to be 2% by weight or less and 1.5X + 7.5% by weight or less at the end of supplying the remaining butadiene.
(However, X is bound styrene of the finally obtained copolymer rubber.) Further, when the remaining butadiene is supplied, the polymerization conversion rate of the finally obtained copolymer rubber is -0.5Y + 10.
It must be done after reaching 2% by weight. (However, Y
Is the vinyl bond content of the finally obtained copolymer rubber.) Even when the styrene monomer content in the monomer composition in this polymerization system exceeds the above concentration, the balance of the butadiene supply end time is less than the above polymerization conversion rate. Even if S ₁
Is decreased, while S ₈ is increased, which is not preferable in terms of physical properties.

In addition, the random styrene-butadiene copolymer rubber having a bi-modal molecular weight distribution in the present invention has M _W -bi / M _W -mo.
A copolymer rubber whose molecular weight is mono-modal, which is a comparison target for determining the ratio of no (M _W -bi / M _W -mono), is
Using an organolithium compound as an initiator, it has substantially the same structural factor except that it is copolymerized under the same conditions as a copolymer rubber having a bi-modal molecular weight distribution and is branched by coupling. And have the same Mooney viscosity. Polymerization under the same conditions as used herein means that the polymerization method of a copolymer rubber whose molecular weight distribution is mono-modal is bi-m.
It means that the odalization technique, that is, the polymerization method and conditions other than the coupling reaction with the polyfunctional coupling agent, is as consistent as possible with the polymerization method of the copolymer rubber whose molecular weight distribution is bi-modal. For example, the copolymer rubber whose molecular weight distribution is bi-modal is batch polymerized,
Alternatively, if it is obtained by continuous polymerization, a copolymer rubber whose molecular weight distribution is mono-modal must also be obtained by a corresponding polymerization method. Further, the substantially same structural factor as used herein means a bi-modal of a copolymer rubber whose molecular weight distribution is bi-modal when the rubber structure of the copolymer rubber whose molecular weight distribution is mono-modal. It is meant to be substantially matched with a rubber structure other than that. For example, the bound styrene, microstructure, styrene chain distribution, etc. of the copolymer rubber must be substantially matched to the copolymer rubber whose molecular weight distribution is bi-modal.

Examples of the organolithium compound used in the present invention include n-
Monoorganolithium compounds such as propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, dilithiomethane, 1,4
-Dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, 1,2-dilithio-1,2-diphenylethane, 1,
There are polyfunctional organolithium compounds such as 3,5-trilithiobenzene and the like, and these are used alone or in a mixture of two or more kinds.

Further, as the polyfunctional organolithium compound used in the present invention, a compound which can be substantially a polyfunctional organolithium compound by reacting the above monoorganolithium compound with another compound is also used. For example, a reaction product of a monoorganolithium compound and a polyvinylaromatic compound (Japanese Patent Publication No. 55-6652), a monoorganolithium compound and a conjugated diene, and / or a monovinylaromatic compound are reacted, and then a polyvinylaromatic compound Or a reaction product obtained by simultaneously reacting a monoorganolithium compound, a conjugated diene, and / or a monovinylaromatic compound, and a polyvinyl compound (West German Patent 2003384).

Aliphatic, alicyclic, and aromatic hydrocarbons can be used as the hydrocarbon solvent used in the present invention. For example, hydrocarbon solvents include propane, isobutane,
Examples of the solvent include n-hexane, isooctane, cyclopentane, cyclohexane, benzene, and toluene, and particularly preferable solvents are n-hexane, cyclohexane, and benzene. These may be used alone or as a mixture of two or more.

As the Lewis base used in the present invention, diethyl ether, ethylene glycol dimethyl ether,
Ethylene glycol di-n-butyl ether, ethylene glycol n-butyl tert-butyl ether, ethylene glycol di-tert-butyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetrahydrofuran, α-
Methoxytetrahydrofuran, 2-methoxymethyltetrahydrofuran, dioxane, 1,2-dimethoxybenzene, triethylamine, N, N, N ', N'-tetramethylethylenediamine, potassium-tert-amyl oxide and the like can be mentioned. These compounds are used alone or as a mixture of two or more.

Examples of the polyfunctional coupling agent used in the present invention include epoxidized soybean oil, epoxidized linseed oil, epoxidized liquid polybutadiene, dimethyl terephthalate, diethyl terephthalate, dimethyl phthalate, dimethyl isophthalate, diethyl adipate, and terephthalate. Acid dichloride, phthalic acid dichloride, isophthalic acid dichloride, adipic acid chloride, phthalic anhydride, maleic anhydride, silicon tetrachloride, methyltrichlorosilane, hexachlorosilane, tetramethoxysilane, carbon tetrachloride, second chloride chloride, methyl Examples include trichlorotin, stannic bromide, dodecyltrichlorotin, and the like. Of these, particularly preferred are silicon tetrachloride and stannic chloride. When the copolymer rubber that has been coupled with stannic chloride is kneaded with carbon black, process oil, etc., the amount of carbon gel increases, and the vulcanized product thereof exhibits excellent impact resilience. On the other hand, a copolymer rubber that has been coupled with silicon tetrachloride exhibits excellent processability, particularly excellent extrusion characteristics. Therefore, in order to obtain a copolymer rubber having more excellent processability, it is preferable to use silicon tetrachloride as the coupling agent.

The method of adding these polyfunctional coupling agents is not particularly limited, but usually the polyfunctional coupling agent is added after the copolymerization of styrene and butadiene is completed.
However, if the amount of the polyfunctional coupling agent used is such an amount that does not stop the polymerization, and the styrene monomer content in the monomer composition in the polymerization system is within the above concentration range, then the polymerization, preferably the final The polyfunctional coupling agent may be converted when the polymerization conversion rate of the copolymer rubber obtained in the above is 90% by weight or more. Alternatively, a polyfunctional coupling agent may be added after a small amount of butadiene is added after the completion of the copolymerization. In short, the method of adding the polyfunctional coupling agent should be decided according to the purpose of use.

The polymerization temperature in the present invention is in the range of 20 to 130 ° C. In the batch polymerization method, it is recommended to start the polymerization at 35 to 87 ° C and to perform the polymerization at an elevated temperature so that the maximum temperature reaches 90 to 125 ° C.

The copolymer rubber of the present invention may be used as an oil-extended rubber by mixing it with a process oil in a solution state, removing the solvent after mixing.

The copolymer rubber of the present invention can be used alone or blended with natural rubber or other synthetic rubbers such as polybutadiene, polyisoprene, emulsion-polymerized styrene-butadiene copolymer and the like. When used by blending with natural rubber or other synthetic rubber, it is customary to blend the copolymer rubber of the present invention in an amount of 30% by weight or more, as is generally said. Further, the copolymer rubber of the present invention is blended with a known compounding agent, for example, carbon black, process oil, etc., and after mixing and vulcanization, as a product, for example, tire applications such as tire tread, carcass, sidewalls,
Alternatively, it can be used in applications such as extruded products, automobile window frames, and industrial products, but especially as an all-season tire tread.

Hereinafter, the present invention will be described with reference to examples, but these examples do not limit the present invention. The various properties were measured by the following methods.

The styrene chain distribution of the styrene-butadiene copolymer rubber is analyzed by the method recently developed by Tanaka et al.
Specifically, the styrene chain distribution is analyzed by gel permeation chromatogram (GPC) of a decomposition product obtained by ozone cleavage of all double bonds of butadiene unit (Proceedings of the Polymer Society of Japan, Vol. 29, 9). No. 2055). The Mooney viscosity was measured at 100 ° C. using an L rotor by a usual method. The bound styrene was calculated from the absorption based on the phenyl group at 262 nm by the ultraviolet absorption spectrum method.
For the microstructure of the butadiene part, use an infrared spectrophotometer,
Calculated by the Hampton method. The weight average molecular weight is GPC (trade name: 204 compact type) manufactured by Water Co., and the column is manufactured by Showa Denko (trade name: Syodex A8).
0M, 1 piece), 0.5cc of a rubber solution in which 0.5g of rubber is dissolved in 100cc of tetrahydrofuran is injected, and the injection time is about 0.5.
Expressed as polystyrene-converted weight average molecular weight from the GPC curve measured at seconds, flow rate 1 cc / min, and measurement temperature room temperature. The hardness, tensile strength, 300% module and elongation of the vulcanizate were measured according to JIS K6301. The impact resilience was measured at a test temperature of 70 ° C. using a Dunlop trypsometer. Abrasion resistance was measured using a pico abrasion tester. The wet skid resistance was measured with a device manufactured by the British Road Research Institute. The ice skid resistance was measured in a low temperature laboratory at -8 ° C using the same device as above and an icy road surface having a smooth polished surface. For the styrene monomer content and the polymerization conversion rate in the monomer composition in the polymerization system, use the monomer conversion rate obtained by analyzing the sample extracted from the polymerization vessel using a Shimadzu gas chromatograph (GC-7A). Calculated.

Examples 1 to 3 and Comparative Example 1 In a nitrogen atmosphere, a stainless steel-made stirrer having an internal volume of 1.0 was provided with a predetermined amount of cyclohexane, tetrahydrofuran, styrene, and a part of 1,3-butadiene as shown in Table 1. (Hereinafter referred to as "first butadiene"), the mixture in the polymerization vessel was vigorously stirred, the temperature of the mixture was adjusted to 85 ° C, and then a predetermined amount of n-butyllithium was added to start copolymerization. . When the temperature in the polymerization vessel increased and the polymerization addition rate of the finally obtained copolymer reached about 20% by weight, a predetermined amount of the remaining 1,3-butadiene (hereinafter referred to as the second
The supply of butadiene) to the polymerization system was continuously started at a constant rate by a metering pump. After the supply of the second butadiene was completed, the polymerization temperature reached the maximum temperature and the copolymerization was completed, a predetermined amount of stannic chloride was added and the reaction was carried out for about 10 minutes to obtain the copolymer thus obtained. 2,6-di-tert-butyl-4-methylphenol 5 was added to the solution as a stabilizer.
g was added and the solvent was removed by heating to obtain a random styrene-butadiene copolymer rubber having a bi-modal molecular weight distribution. The styrene monomer content in the monomer composition in the polymerization system was always 92% by weight or less when the polymerization conversion rate of the copolymer rubber was 0 to 98% by weight. The polymerization conversion rate at the end of the supply of the second butadiene was about 95% by weight, and the styrene monomer content in the monomer composition in the polymerization system at that time was about 20% by weight. The basic properties of the obtained copolymer rubber are shown in Table 1. Further, these copolymer rubbers were kneaded and mixed in a small pressure kneader according to the compounding recipe in Table 2, and the workability and physical properties were measured. The processability was judged by the magnitude of the Mooney viscosity of the compound. The physical properties were evaluated after vulcanizing the unvulcanized rubber composition at 145 ° C.
The measurement results are shown in Table-3.

Comparative Example 2 The same polymerization method as in Example 1 was used to obtain the M _W -bi / M _W -mono ratio, except that the amount of n-butyllithium used and the polyfunctional coupling agent were changed to methyl alcohol. The copolymerization was carried out and the Mooney viscosity was the same as in Example 1 and the other polymer structures were the same as in Example 1
A random styrene-butadiene copolymer rubber that is mono-modal was obtained. The content of styrene monomer in the monomer composition in the polymerization system is such that the polymerization conversion rate of the copolymer rubber is 0.
In the range of up to 98% by weight, it was always 92% by weight or less. The polymerization conversion rate at the end of the supply of the second butadiene was about 95% by weight, and the styrene monomer content in the monomer composition in the polymerization system at that time was about 20% by weight. The basic properties of the obtained copolymer rubber are shown in Table 1. The characteristics of the obtained copolymer rubber compounded and vulcanized in the same manner as in Example 1 are shown in Table 3.

Comparative Examples 3 to 5 In the same manner as in Example 1, except that the remaining 1,3-butadiene was not continuously added to the polymerization system, but the entire amount of 1,3-butadiene was added to the polymerization vessel before the addition of n-butyllithium. Was added and copolymerization was carried out under the polymerization conditions shown in Table-1, and the molecular weight distribution was
A copolymer rubber that is bi-modal was obtained. In Comparative Example 5, 0.042 g of potassium tert-butyl oxide (KTB) was newly added to the polymerization system.

Further, in order to obtain the ratio of M _W -bi / M _W -mono of the above copolymer rubber, the same polymerization method as described above is used, except that the amount of n-butyllithium used and the polyfunctional coupling agent are methyl. Copolymerization was performed by changing to alcohol to obtain a copolymer rubber having the same Mooney viscosity and other polymer structures as those of the above-mentioned copolymer rubbers and a mono-modal molecular weight distribution.

The basic properties of various copolymer rubbers having a bi-modal molecular weight distribution obtained in the above manner are shown in Table 1. Table-3
Shows the properties that were compounded and vulcanized in the same manner as in Example 1.

As can be seen from Table-3, Examples 1-3 have low Mooney viscosity formulations, suggesting excellent processability. In terms of physical properties, wet skid resistance, ice skid resistance, wear resistance, and impact resilience are excellent. Comparative Examples 3 and 5 have low Mooney viscosities, but are poor in wet-to-skid resistance, ice-skid resistance and impact resilience.

Comparative Examples 1, 2, and 4 suggest that the formulations have high Mooney viscosity and poor processability.

Examples 4 to 8 and Comparative Examples 6 to 9 In the same manner as in Example 1, except that stannic chloride was changed to tetrachlorosilane, copolymerization was carried out under the polymerization conditions shown in Table 4, and the molecular weight was changed. A copolymer rubber with a bi-modal distribution was obtained.

Further, in order to obtain the M _W -bi / M _W -mono ratio of the above-mentioned copolymer rubber, the same polymerization method as described above was used, except that the amount of n-butyllithium used and the polyfunctional coupling agent were changed to methyl alcohol. Copolymerization was carried out under different conditions to obtain copolymer rubbers having the same Mooney viscosity and polymer structure as those of the above-mentioned copolymer rubbers and the molecular weight distribution being mono-modal.

The styrene monomer content in the monomer composition ratio in each polymerization system of the above various copolymer rubbers was always 92% by weight or less when the conversion rate of the copolymer rubber was 0 to 98% by weight. . The polymerization conversion rate at the end of the supply of the second butadiene was -0.5Y + 102% by weight or more, and the styrene monomer content in the styrene monomer composition in the polymerization system at that time was 1.5X + 7.5% by weight or less. (However, X is the bound styrene of the finally obtained copolymer rubber, and Y is the vinyl bond content.) The basics of the copolymer rubber having the bi-modal molecular weight distribution obtained by the above procedure. The characteristics are shown in Table-4. In addition, Table 5 shows the properties that were compounded and vulcanized in the same manner as in Example 1.

As can be seen from Table 5, Examples 4 to 8 have an excellent balance of wet skid resistance, ice skid resistance, abrasion resistance and impact resilience. On the other hand, Comparative Examples 6 and 9 are excellent in impact resilience, wear resistance and ice skid resistance, but are inferior in wet skid resistance. In addition, Comparative Example 6 is also inferior in tensile strength. Comparative Examples 7 and 8 are excellent in wet skid resistance, but are inferior in impact resilience, wear resistance, and ice skid resistance.

[Effects of the Invention] As described above, the random styrene-butadiene copolymer rubber of the present invention has a relatively low styrene content and a specific bi-modal molecular weight distribution, and in the copolymer chain thereof. Based on a specific structure in which the styrene unit has a specific chain distribution, it has an excellent balance of wet skid resistance, ice skid resistance, abrasion resistance and impact resilience, and has excellent processability. Therefore, it is particularly suitable for use in all-season tire treds. In addition, it can also be used for tire applications such as carcass and sidewalls, extruded products, automobile window frames, industrial products, etc.
Industrial significance is great.

Claims (1)

[Claims] 1. A multifunctional cup having styrene and butadiene copolymerized with an organolithium compound as a polymerization initiator in a hydrocarbon solvent containing at least one Lewis base, and then having at least three reactive sites. A Mooney viscosity (ML _{1 + 4} , 100 ° C.) having a branched structure of three or more branches, added with a ring agent, of 40 to 150, bound styrene of 5% by weight or more and less than 28% by weight, vinyl of butadiene portion A bond content of 16% by weight or more and less than 40% by weight,
A styrene-butadiene copolymer rubber having a molecular weight distribution of bi-modal, wherein the weight average molecular weight (Mw-bi) of the copolymer rubber having a molecular weight distribution of bi-modal is the above-mentioned copolymer using an organolithium compound. It has substantially the same structure factor except that it is copolymerized under the same conditions as the polymer rubber and is branched by coupling, and the molecular weight distribution of the same Mooney viscosity is mo.
Weight average molecular weight of no-modal copolymer rubber (Mw-mon
o) has a relationship of Mw-bi / Mw-mono ≧ 1.3, and the styrene single chain having one styrene monomer is 75% by weight or more of the total bound styrene, and the styrene monomer has 8 or more continuous chains. A random styrene-butadiene copolymer rubber having a long styrene chain content of 5.0% by weight or less based on the total bound styrene.