JP7706160B2 - Styrenic copolymer, feed liquid, and method for producing styrenic copolymer - Google Patents

Description

The present invention relates to a styrene-based copolymer having excellent weather resistance, a feed liquid for producing the styrene-based copolymer, and a method for producing the styrene-based copolymer using the feed liquid.

Styrene-based resins are not only excellent in terms of material performance such as transparency, rigidity, and dimensional stability, but can also be processed in a variety of ways, such as injection molding, stretched sheets, films, foam sheets, foam boards, and blow molding. Furthermore, many styrene-based resins can be mass-produced inexpensively by bulk polymerization using the radical polymerization method, solution polymerization using a high monomer concentration, suspension polymerization, or emulsion polymerization, and are therefore used in a wide variety of applications.

Generally, styrene-based resins are produced by living anionic polymerization, which is a polymerization method that is easily affected by impurities contained in the raw materials (Patent Document 1). In particular, active anions are known to react easily with polar substances such as water, aldehydes, ketones, and alcohols. If even a trace amount of polar substances is present in the reaction system of anionic polymerization, the active anions react with the polar substances to form stable bonds, causing the polymerization to stop. Therefore, when performing living anionic polymerization, it is necessary to reduce the amount of polar substances in the raw materials and prevent the introduction of polar substances into the reaction system as much as possible.

As a method for purifying α-methylstyrene that solves the above problems, a method has been proposed in which polar substances contained in α-methylstyrene are reacted in the presence of a basic substance, and low-boiling by-products produced by the reaction are separated from the reactants of the polar substances to purify α-methylstyrene (for example, Patent Document 2).

Patent No. 4306682 Patent No. 4327239

In recent years, the effective use of resins has become important, and various recycling laws have been enacted. The ability to recycle, rework, and reuse resins will become an essential need in the resin market going forward.

Resin materials developed in the future must be able to be effectively reused, with almost no reduction in molecular weight due to breakage of polymer chains or generation of monomers even after multiple melt processing cycles, and with little deterioration in physical properties due to weathering over long-term use.

Therefore, there was a need to develop a resin material that has higher melt stability and better weather resistance than existing styrene-based copolymers.

The present invention aims to provide a styrene-based copolymer having excellent weather resistance by controlling the content of a specific compound in the feed liquid to be used for polymerization, a feed liquid for producing the styrene-based copolymer, and a method for producing the styrene-based copolymer using the feed liquid.

Means for Solving the Problems The present inventors have conducted intensive research to solve the above problems, and as a result have found that a styrene-based copolymer having excellent weather resistance can be obtained by controlling the content of a specific compound contained in a trace amount in a feed liquid to be subjected to polymerization within a specific range, thereby completing the present invention.
That is, the present invention has the following aspects.

（式中、Ｒ^１は、水素原子、炭素数２以上のアルキル基またはフェニル基を表し、Ｒ^２は、水素原子、ハロゲン原子、ヒドロキシル基、Ｃ１－Ｃ６アルキル基、Ｃ１－Ｃ６アルコキシ基、カルボキシル基、またはハロＣ１－Ｃ６アルキル基を表す。） (1) A styrene-based copolymer obtained by a living anionic polymerization method, which contains α-methylstyrene units and vinyl aromatic monomer units represented by the following general formula (1), and which shows a change in total light transmittance of 5% or less and a change in yellowness index of 5 or less after 1000 hours of exposure in a weather resistance test using a sunshine weather meter.

(In the formula, R ¹ represents a hydrogen atom, an alkyl group having 2 or more carbon atoms, or a phenyl group, and R ² represents a hydrogen atom, a halogen atom, a hydroxyl group, a C1-C6 alkyl group, a C1-C6 alkoxy group, a carboxyl group, or a haloC1-C6 alkyl group.)

(2) The styrene copolymer according to (1) above, in which the content of α-methylstyrene units in the copolymer is 10 to 65% by mass, the weight average molecular weight (Mw) is in the range of Mw = 50,000 to 300,000, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is in the range of 1.6 to 2.5, and the total mass of the remaining monomers and polymerization solvent is 500 ppm or less.

(3) A feed liquid for producing a styrene-based copolymer, comprising a monomer and a polymerization solvent, the feed liquid having an acetonylacetone content of 2 ppm or less, a benzaldehyde content of 10 ppm or less, and a phenylacetylene content of 15 ppm or less.

(4) A method for producing a styrene-based copolymer using a feed liquid consisting of a monomer and a polymerization solvent, the feed liquid having an acetonylacetone content of 2 ppm or less, a benzaldehyde content of 10 ppm or less, and a phenylacetylene content of 15 ppm or less.

The styrene copolymer of the present invention has excellent weather resistance by controlling the content of a specific compound in the feed liquid used for polymerization within a specific range. In addition, molded products containing the styrene copolymer of the present invention can be used extremely suitably as food containers for heating, housing parts, automobile interior parts, and optical parts.

The present invention is described in detail below.

（式中、Ｒ^１は、水素原子、炭素数２以上のアルキル基またはフェニル基を表し、Ｒ^２は、水素原子、ハロゲン原子、ヒドロキシル基、Ｃ１－Ｃ６アルキル基、Ｃ１－Ｃ６アルコキシ基、カルボキシル基、またはハロＣ１－Ｃ６アルキル基を表す。） <Styrene-based copolymer>
The styrene copolymer of the present invention will be described. The styrene copolymer of the present invention is a copolymer obtained by controlling the content of a specific compound in a feed liquid to be subjected to polymerization, which contains α-methylstyrene units and vinyl aromatic monomer units represented by the following formula (1) as constituent units, and is a styrene copolymer in which the change in total light transmittance after 1000 hours of irradiation in a weather resistance test using a sunshine weather meter is 5% or less and the change in yellowness index is 5 or less. This provides excellent weather resistance. The copolymer also has excellent properties in heat resistance, melt stability, moldability, strength, and rigidity.

(In the formula, R ¹ represents a hydrogen atom, an alkyl group having 2 or more carbon atoms, or a phenyl group, and R ² represents a hydrogen atom, a halogen atom, a hydroxyl group, a C1-C6 alkyl group, a C1-C6 alkoxy group, a carboxyl group, or a haloC1-C6 alkyl group.)

The term "C1-C6 alkyl group" as used herein means a straight-chain or branched alkyl group having 1 to 6 carbon atoms, specifically including methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1-ethyl-2-methylpropyl, and 1,1,2-trimethylpropyl. Examples include 1-ethylbutyl group, 1-methylbutyl group, 2-methylbutyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,3-dimethylbutyl group, 2-ethylbutyl group, 2-methylpentyl group, and 3-methylpentyl group, and preferably include methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, and n-hexyl group.

The term "C1-C6 alkoxy group" as used herein means an oxy group to which the above-defined "C1-C6 alkyl group" is bonded, and specifically includes a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group, an iso-butoxy group, a sec-butoxy group, a tert-butoxy group, an n-pentyloxy group, an iso-pentyloxy group, a sec-pentyloxy group, an n-hexyloxy group, an iso-hexyloxy group, a 1,1-dimethylpropoxy group, a 1,2-dimethylpropoxy group, a 2,2-dimethyl Examples include a propoxy group, a 2-methylbutoxy group, a 1-ethyl-2-methylpropoxy group, a 1,1,2-trimethylpropoxy group, a 1,1-dimethylbutoxy group, a 1,2-dimethylbutoxy group, a 2,2-dimethylbutoxy group, a 2,3-dimethylbutoxy group, a 1,3-dimethylbutoxy group, a 2-ethylbutoxy group, a 2-methylpentyloxy group, and a 3-methylpentyloxy group. Preferred are a methoxy group, an ethoxy group, an n-propoxy group, and an iso-propoxy group, and more preferably a methoxy group and an ethoxy group.

As used herein, the term "alkyl group having 2 or more carbon atoms" refers to a linear or branched alkyl group having 2 or more carbon atoms (preferably 2 to 6), specifically including an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 1,1-dimethylpropyl group, a 1,2-dimethylpropyl group, a 2,2-dimethylpropyl group, a 1-ethylpropyl group, an n-hexyl group, a 1-ethyl-2-methylpropyl group, a 1,1, Examples include 2-trimethylpropyl group, 1-ethylbutyl group, 1-methylbutyl group, 2-methylbutyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,3-dimethylbutyl group, 2-ethylbutyl group, 2-methylpentyl group, and 3-methylpentyl group, and preferably include ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, and n-pentyl group.

As used herein, the term "halogen atom" refers to a fluorine atom, chlorine atom, bromine atom, iodine atom, etc.

As used herein, the term "halo C1-C6 alkyl group" refers to a group in which a "halogen atom" as defined above is bonded to a "C1-C6 alkyl group" as defined above.

Examples of vinyl aromatic monomers used in the present invention include alkyl-substituted styrenes such as styrene, p-methylstyrene, m-methylstyrene, o-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, p-ethylstyrene, m-ethylstyrene, and o-ethylstyrene, and other styrene derivatives such as p-hydroxystyrene, p-methoxystyrene, p-chlorostyrene, and 1,1-diphenylethylene. A preferred vinyl aromatic monomer is styrene. These vinyl aromatic monomers may be used individually or in combination of two or more. In the present invention, the most preferred combination is α-methylstyrene and styrene.

The content of α-methylstyrene units in the styrene copolymer is preferably 10 to 65% by mass (hereinafter also referred to as wt%), more preferably 12 to 63 wt%, and even more preferably 15 to 60 wt%. If the content of α-methylstyrene units is 10 wt% or more, the effect of improving heat resistance in practical use is greater, and if it is 65 wt% or less, the thermal stability during melt molding processing is higher, gas generation during molding can be further suppressed, and the amount of monomer components associated with decomposition in the resin can also be further suppressed.

In addition to the above-mentioned monomers, other polymerizable monomers can be used together as long as the object of the present invention is not impaired. Examples of copolymerizable monomers include conjugated diene monomers such as butadiene and isoprene; methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate; and acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate. These monomers are useful when improving or adjusting the impact strength, elongation, chemical resistance, etc. of the resin.

The styrene copolymer in the present invention is synthesized by a living anionic polymerization method. Any known method can be used as the living anionic polymerization method. For example, an organic lithium compound is used as the initiator, specifically, n-butyl lithium, sec-butyl lithium, t-butyl lithium, ethyl lithium, benzyl lithium, 1,6-dilithiohexane, styryl lithium, butadienyl lithium, etc. are used. Of these, n-butyl lithium and sec-butyl lithium are preferred.

The polymerization solvent is preferably a hydrocarbon compound that does not contain a heteroatom. Specific examples include aliphatic hydrocarbon compounds such as n-hexane, cyclohexane, and heptane, and aromatic hydrocarbon compounds such as benzene, toluene, ethylbenzene, and xylene. These hydrocarbon compounds may be used alone or in combination of two or more. A particularly preferred compound is cyclohexane.

From the viewpoints of productivity, coloration of the resin after production, and weather resistance, the polymerization temperature is preferably in the range of 40°C to 110°C, more preferably in the range of 50°C to 100°C, and even more preferably in the range of 55°C to 95°C.

The styrene copolymer of the present invention can be produced, for example, by a continuous living polymerization method using a complete mixing type polymerization reactor. Alternatively, a complete mixing type polymerization reactor may be combined with a non-complete mixing type polymerization reactor. In particular, a complete mixing type polymerization reactor is preferred for obtaining a random copolymer. Complete mixing type polymerization refers to a method of polymerization using a continuous complete mixing type reactor in which the concentrations of α-methylstyrene, vinyl aromatic monomer, and living copolymer present in the living polymerization reaction system are always constant.

If you want to increase productivity by increasing the monomer concentration in the raw material solution, it is desirable to attach a condenser to the polymerization reactor to efficiently remove the heat from the polymerization reaction and remove the heat of polymerization using the latent heat of vaporization of the solvent. In particular, if cyclohexane (which may contain n-hexane) is used primarily as the polymerization solvent, the boiling point is 82°C, making it easy to control the polymerization temperature at around 80°C to 90°C.

When using a non-completely mixed tubular polymerization reactor, for example, when the ratio L/D of the length (L) to the inner diameter (D) of the reactor is 1 or more, or when the stirring efficiency is poor, making it difficult to achieve a completely mixed state within the polymerization reactor, the styrene copolymer of the present invention can be produced by adding a solution of the vinyl aromatic monomer midway through the reactor.

The copolymer of the present invention can also be obtained by connecting two or more incompletely mixed type polymerization reactors in series and adding a solution of the vinyl aromatic monomer to the second polymerization reactor after polymerization in the first polymerization reactor. Furthermore, it is also possible to obtain a block copolymer of a homopolymer and copolymer of vinyl aromatic units by polymerizing only the vinyl aromatic monomer in the first polymerization reactor and then copolymerizing α-methylstyrene and the vinyl aromatic monomer in the second polymerization reactor.

The specific compounds that are minor components contained in the monomers used to obtain the styrene-based copolymer of the present invention and that are to be controlled in the present invention are carbonyl group-containing compounds, phenol, catechols including t-butylcatechol, which is a polymerization inhibitor, and phenylacetylene. Specific examples of carbonyl group-containing compounds include acetonylacetone, 3-methyl-2-cyclopentenone, benzaldehyde, and acetophenone.

When producing poly-α-methylstyrene and its copolymers by anionic polymerization, etc., these compounds are substances that cause polymerization inhibition, polymer discoloration, and reduced weather resistance, so it is preferable to remove them as much as possible.

A preferred method for removing specific compounds to be controlled from α-methylstyrene is to add a specific basic substance to α-methylstyrene and separate the high-boiling and low-boiling compounds produced by the reaction from α-methylstyrene by distillation.

The basic substance used in this case may be a basic compound containing an alkali metal or an alkaline earth metal, such as a metal alkoxide such as sodium ethoxide, potassium ethoxide, or sodium methoxide; a metal hydroxide such as sodium hydroxide, potassium hydroxide, or magnesium hydroxide; a metal oxide such as sodium oxide, potassium oxide, or magnesium oxide; a metal amide such as lithium diisopropylamide; or an alkyl metal such as butyl lithium or methyl lithium.

To remove the specific compounds to be controlled from styrene and the polymerization solvent, conventional purification methods can be applied, such as bubbling with nitrogen and then passing the mixture through a purification column filled with activated alumina.

By using the above method and others, it is possible to control the content of specific compounds in the feed liquid to be used for polymerization, which is composed of monomers and polymerization solvent. When the content of these specific compounds is controlled within a certain range, it is effective in controlling the polymerization and preventing the yellowing of the polymer, and is particularly effective in improving the weather resistance of the polymer.

The lower the content of the specific compounds to be controlled in the feed liquid, the better, but acetonylacetone 2 ppm or less, benzaldehyde 10 ppm or less, and phenylacetylene 15 ppm or less are preferred. Phenylacetylene is more preferably 10 ppm or less. In this specification, ppm is a unit of mass. If these values are exceeded, the weather resistance of the obtained polymer will decrease significantly, and in some cases, living polymerization will be inhibited.

The yellow index of the styrene copolymer of the present invention is preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less. As mentioned above, reducing the content of specific compounds in the feed liquid is effective for reducing the yellow index. In particular, during the production of biaxially oriented sheets (OPS) and foamed sheets (PSP) used in the food packaging field, the yellowing of the resin is very noticeable and can cause quality problems because the sheets are wound and collected. Therefore, users of such applications are particularly sensitive to the yellowing of the resin, and it is one of the important required performances.

The styrene copolymer of the present invention exhibits a change in total light transmittance of 5% or less and a change in yellowness index of 5 or less after 1000 hours of irradiation in a weather resistance test using a sunshine weather meter.
In this specification, the change in total light transmittance and the change in yellowness index after 1000 hours of irradiation in a weather resistance test using a sunshine weather meter are values measured by the method described in the Examples section below.

The weight average molecular weight (Mw) of the styrene copolymer of the present invention is preferably in the range of Mw = 50,000 to 300,000, more preferably Mw = 60,000 to 290,000, and even more preferably Mw = 70,000 to 280,000. From the viewpoint of mechanical strength, Mw is preferably 50,000 or more, and from the viewpoint of the fluidity of the resin during molding, Mw is preferably 300,000 or less. As a result, not only does it become easier to mold precision parts, but the molecular orientation of the polymer chains is further suppressed, and various problems such as the appearance of anisotropy in optical properties, a decrease in the surface impact strength of sheet-shaped extrusion molded products and sheet-shaped injection molded products, and the difficulty of molding large molded products can be further suppressed.

Furthermore, it is preferable that the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is in the range of 1.6 to 2.5. More preferably, Mw/Mn is in the range of 1.8 to 2.4. When Mw/Mn is 1.6 to 2.5, the balance between the fluidity and mechanical properties of the resin is good, and sufficient performance can be obtained as a resin molded product, and the occurrence of the above problems tends to be suppressed at the same time.

The glass transition temperature in this invention can be determined by DSC, and the temperature determined by the method specified in JIS-K7121 is regarded as the glass transition temperature.

The bonding mode of the α-methylstyrene units and the vinyl aromatic monomer units in the styrene copolymer of the present invention is not particularly limited, but the most preferred bonding mode is a copolymer consisting of random bonds. In general, the presence of many chains of α-methylstyrene units tends to make the copolymer more susceptible to thermal decomposition. Therefore, depending on the application, it is preferable to control the chains of α-methylstyrene units to 2 to 4 chains or less.

The vinyl aromatic monomer units may have a long chain structure, since there is no risk of impairing thermal stability even if they are in a chain. The present inventors have found that AB-type or ABA-type block copolymers (A is a homopolymer component mainly composed of vinyl aromatic monomer unit components; B is a random copolymer component containing α-methylstyrene units and vinyl aromatic monomer units) in which the long chain of vinyl aromatic monomer units is present at the end of the molecular chain of the copolymer have the same properties as random copolymers, including heat resistance, thermal stability, mechanical properties, and fluidity, and are extremely compatible with homopolymers having the same structure as the vinyl aromatic monomer units, which are one component of the block. Taking advantage of this property, when it is desired to reuse the styrene-based copolymer of the present invention as a recyclable material, for example by melt-kneading it with polystyrene, a copolymer in which a polystyrene chain is blocked at the end of the polymer chain of the copolymer can be used.

There are no particular limitations on the block chain length of the vinyl aromatic monomer unit, and it is preferable that the number average molecular weight of the block chain portion is in the range of 1,000 to 250,000. In addition, it is preferable that the Mw/Mn of the block component consisting of the vinyl aromatic monomer unit is in the range of 1.0 to 2.5.

A method for producing a copolymer having vinyl aromatic monomer units as block components is, for example, to produce a homopolymer consisting of vinyl aromatic monomer units in a batch reactor, a continuous tube reactor, a continuous static mixer reactor, a continuous tank reactor with stirring blades, a continuous coil reactor, or the like, and then feed a homopolymer consisting of α-methylstyrene, vinyl aromatic monomer, and living vinyl aromatic monomer units into a continuous complete mixing reactor for copolymerization to obtain an AB type block copolymer. When obtaining an ABA type block copolymer, it can be produced by producing an AB type block copolymer and then carrying out living polymerization of the vinyl aromatic monomer units in a separate reactor. Alternatively, an ABA type block copolymer can be obtained by producing an AB type living copolymer and then adding a bifunctional compound that reacts with living propagating species in a separate reactor.

As a result of further intensive research, the present inventors have discovered that a styrene-based copolymer containing α-methylstyrene units and vinyl aromatic monomer units obtained by a continuous living polymerization method, which is obtained by continuously or intermittently changing the composition ratio of α-methylstyrene in the raw material and the vinyl aromatic monomer represented by the formula (1) and feeding the resulting copolymer into a polymerization reactor, has at least two or more different composition ratios, and has the same properties as a random copolymer, including heat resistance, thermal stability, mechanical properties, and flowability, and is also extremely compatible with polymers mainly composed of vinyl aromatic monomer units.

This suggests that when moldings of the copolymer are recycled, they can be blended with polymers whose main component is vinyl aromatic monomer units, such as polystyrene, as a recyclable material and reused. A different copolymer refers to a copolymer whose glass transition temperature differs by at least 3°C.

Continuously or intermittently changing the composition ratio of α-methylstyrene and vinyl aromatic monomer in the monomers and feeding them into the polymerization reactor means that the concentration of each monomer introduced into the polymerization reaction system changes continuously or intermittently, and as a result, the composition ratio of each aromatic unit in the resulting copolymer changes continuously, and at least two or more copolymers with different composition ratios are sequentially obtained.

Two or more copolymers having different composition ratios may be mixed in solution in a batch tank and then flushed into a heated tank under vacuum to remove the solvent, or an extruder or kneader may be used to remove the solvent and recover the copolymer in pellet form. Alternatively, the copolymers may be recovered in pellet form without being stored in a batch tank, and the pellets may be mixed and homogenized in a batch or continuous mixing vessel. Alternatively, the pellets may be homogenized in the mixing vessel and then melt-mixed using an extruder.

To give a specific example of production, a raw material with a component composition ratio of α-methylstyrene (M1) and vinyl aromatic monomer (M2) of M1/M2 = 50/50 (wt%) is fed into a reactor and polymerized, and then a raw material with a different composition ratio, for example M1/M2 = 40/60 (wt%), is switched to and introduced into the reactor for polymerization. In this case, the raw material composition is said to be changed intermittently. By polymerizing in this way, copolymers with compositions that change continuously from the copolymer obtained by polymerization with M1/M2 = 50/50 (wt%) to the copolymer obtained with M1/M2 = 40/60 (wt%) are obtained one after another. The obtained copolymers are mixed in solution or in pellet form in a batch-type tank, stirred and mixed, and then melt-kneaded to obtain a copolymer with a certain composition.

The copolymer obtained by this method can be considered to be a copolymer composition with different composition ratios of α-methylstyrene unit components and vinyl aromatic monomer unit components. The copolymer obtained in this way has excellent compatibility with homopolymers of vinyl aromatic monomers, and is highly useful as a recycled material because it does not cause a decrease in mechanical properties and can maintain transparency.

In the living anionic polymerization method, which is the method for producing the copolymer of the present invention, the polymerization reaction is preferably completed when the reaction rate of the vinyl aromatic monomer reaches 99% or more, and α-methylstyrene may remain in the reaction system. The polymerization reaction can be terminated by adding a compound having an oxygen-hydrogen bond such as water, alcohol, phenol, or carboxylic acid as a terminator, and epoxy compounds, ester compounds, ketone compounds, carboxylic acid anhydrides, or compounds having a carbon-halogen bond can also be expected to have a similar effect. The amount of these additives used is preferably about 10 times the equivalent of the growing species. If too much is used, not only is it disadvantageous in terms of cost, but the inclusion of remaining additives often becomes a hindrance.

By using the living growth species to carry out a coupling reaction with a polyfunctional compound, the polymer molecular weight can be increased and the polymer chain can be branched. The polyfunctional compound used in such a coupling reaction can be selected from known compounds. Examples of polyfunctional compounds include polyhalogen compounds, polyepoxy compounds, mono- or polycarboxylic acid esters, polyketone compounds, mono- or polycarboxylic acid anhydrides, etc. Specific examples include silicon tetrachloride, di(trichlorosilyl)ethane, 1,3,5-tribromobenzene, epoxidized soybean oil, tetraglycidyl 1,3-bisaminomethylcyclohexane, dimethyl oxalate, tri-2-ethylhexyl trimellitate, pyromellitic dianhydride, diethyl carbonate, etc.

After polymerization is complete, unreacted monomers and solvents are volatilized away from the polymer for recovery and reuse. Known methods can be used for volatilization. For example, a method of flushing into a vacuum tank and/or a method of heating and evaporating under vacuum using an extruder or kneader are preferably used as a volatilization device. Although it depends on the volatility of the solvent, volatile components such as the solvent and residual monomers are generally volatilized away at a temperature of 180 to 300°C and a vacuum of 100 Pa to 50 KPa.

It is also effective to connect volatile removal devices in series and arrange them in two or more stages. In addition, a method can be used in which water is added between the first and second stages to increase the volatilization ability of the monomer in the second stage. After the volatile components are removed in the flashing tank, a vented extruder can be used to remove the remaining volatile components. The styrene-based copolymer from which the solvent has been removed can be made into pellets by a known method.

In the present invention, the total mass of monomers and polymerization solvent remaining in the pelletized styrene copolymer is preferably 500 ppm or less. More preferably, it is 400 ppm or less.

If necessary, known compounds used in styrene-based resins can be added to the styrene-based copolymer of the present invention for the purpose of improving thermal and mechanical stability, fluidity, and colorability. Examples of the primary antioxidant include 2,6-di-t-butyl-4-methylphenol, triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], pentaerythritol tetrakis[-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, n-octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2[1-(2- hydroxy 3,5-di-t-pentylphenyl)]-4,6-di-t-pentylphenyl acrylate, tetrakis [methylene 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, 3,9 bis [2- {3- (t-butyl-4-hydroxy-5-methylphenyl) propynyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxa [5,5] undecane, 1,3,5-tris (3',5'-di-t-butyl-4'-hydroxybenzyl)-s-triazine-2,4,6 (1H,2H,3H)-trione, 1,1,4-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4'-butylidene bis (3-methyl-6-t-butylphenol), and other 2,4,6-3 substituted phenols.

It is also possible to add phosphorus-based antioxidants and sulfur-based antioxidants as secondary antioxidants, hindered amine stabilizers as weather resistance agents, and UV absorbers. In addition, it is also possible to add plasticizers such as mineral oil, lubricants such as long-chain aliphatic carboxylic acids and/or their metal salts, and organic dyes and organic pigments to improve colorability.

Anthraquinone-based organic dyes for improving colorability are particularly preferred because they do not impair the thermal stability of the copolymer.

Silicone-based and fluorine-based release agents, antistatic agents, etc. can be made using the same known technology used for styrene-based resins.

These stabilizers can be added and mixed into the polymer solution after polymerization is complete, or melt mixed using an extruder after the polymer is recovered.

The styrene copolymer of the present invention is preferably processed by melt processing, which allows for inexpensive mass production, and injection molding, extrusion molding, foam extrusion molding, blow molding, etc. can be suitably used.

In addition, the styrene copolymer of the present invention is a material excellent in transparency, heat resistance, weather resistance, dimensional stability, and rigidity, and is therefore suitable for use as optical parts, such as light guide plates, diffusion plates, reflecting plates, reflective films, anti-reflective films, polarizing plates, polarizing films, retardation films, lenses, and Fresnel lenses.
As liquid crystal displays and projectors become larger, these optical parts are required to have greater dimensional stability and higher processability than ever before, and since they are used in close proximity to light sources, light resistance and heat resistance are also becoming increasingly important. The styrene copolymer of the present invention is an excellent material that can solve all of the conventional problems at once and satisfy future performance needs, and is expected to have many applications other than those for food heating containers, housing parts, automobile interior parts, and optical parts.

The following provides a detailed explanation of the present invention using examples and comparative examples. However, these are merely examples and do not limit the scope of the present invention in any way.

The analysis and evaluation methods used in the examples and comparative examples are described below.

<Analysis and evaluation method>
(1) Content of specific compounds in feed liquid Acetonylacetone, benzaldehyde, and phenylacetylene in the feed liquid were quantified by gas chromatography (apparatus: GC-14A manufactured by Shimadzu Corporation, column: DB-WAX 30 m).

(2) Residual volatile matter in the pellets (total mass of monomer and polymerization solvent)
The measurements were carried out using a GC-MS manufactured by Shimadzu Corporation under the following conditions.
Equipment: GC-2010, MS-QP2010, with headspace sampler Column: Rtx-1, 0.25 mm, 1.00 μm, 60 m (Shimadzu GLC)
Temperature conditions: After holding at 60° C. for 2 minutes, the temperature was increased to 145° C. at 10° C./min, and then increased to 160° C. at 3° C./min.
Preparation of measurement sample: 0.4 g of polymer was placed in a dedicated vial, 10 ml of DMF and 1 ml of chloroform containing the internal standard (n-nonane) were added, the vial was sealed, and the sample was dissolved, after which trace amounts of monomer and cyclohexane (ppm by weight) in the resin were measured.
A calibration curve was prepared using styrene, α-methylstyrene, and cyclohexane.

(3) Molecular weight measurement (Mn, Mw, Mw/Mn)
Two columns (TSKgel Super HZM-H, 40°C) were connected to a Tosoh Corporation HLC-8220, and measurements were performed using a SEC apparatus equipped with an RI detector. THF was used as the mobile phase. Molecular weight calculations were performed in terms of polystyrene, using a calibration curve prepared using polystyrene standards (Tosoh Corporation).

(4) Glass transition temperature (Tg)
The glass transition temperature was measured in accordance with JIS-K-7121 using a DSC-7 manufactured by PerkinElmer Co., Ltd. Specifically, the temperature was raised from room temperature to 250° C. at 10° C./min under nitrogen, then returned to room temperature at 10° C./min, and again raised to 250° C. at 10° C./min. The glass transition temperature measured during the second temperature rise was taken as Tg.

(5) Composition of α-methylstyrene in styrene copolymer The composition (mass%) of α-methylstyrene in the styrene copolymer was determined using a BRUKER NMR (DPX-400). The composition (mass%) of α-methylstyrene in the styrene copolymer was calculated from the peak area ratio of methyl, methylene, and methine by measuring ^{the 1H} -NMR of the styrene copolymer.

(6) Injection Molding Method Molding was performed under the following conditions using PNX60 (manufactured by Nissei Plastic Industrial Co., Ltd.). The cylinder temperatures were set to 215°C, 225°C, 230°C, and 230°C from the hopper side. The mold temperature was set to 50°C, the injection time to 10 seconds, and the cooling time to 10 seconds. The molten resin was filled by applying a pressure 5 MPa higher than the injection pressure at which the resin was filled into the mold. The test piece had a flat plate shape of 80 mm x 80 mm x 3 mm, and was used as a sample for weather resistance testing.

(7) Total light transmittance Tt
Measurement was performed using Hazeguard II (manufactured by Toyo Seiki Seisakusho, Ltd.) under conditions of light source D65 in accordance with ASTM D1003.

(8) Yellowness Yi
Measurements were carried out using SD6000 (manufactured by Nippon Denshoku Industries Co., Ltd.) under conditions of light source: D65 and field of view: 10°.

(9) Weather resistance evaluation (SWOM irradiation test)
Using a Dew Cycle Sunshine Weather Meter S80DHBBR type (manufactured by Suga Test Instruments Co., Ltd.), irradiation was performed under the following conditions: light source: Sunshine carbon arc, black panel temperature: 63°C, rainfall conditions: 18 min/120 min, and the total light transmittance Tt and yellowness index Yi were measured before and after 1000 hours of irradiation.

[Production Example]
(1) Raw Materials Styrene (St) and cyclohexane (CH: manufactured by Idemitsu Kosan Co., Ltd.) were stored in a storage tank and bubbled with nitrogen, and then the solution was purified by passing it through a 5 L purification column filled with activated alumina (KHD-24 manufactured by Sumika Alchem Co., Ltd.). St was manufactured by Sumitomo Chemical Co., Ltd. and Taiwan Chemical Fibers Corporation.

α-Methylstyrene (αMeSt) was refined under the following conditions. The αMeSt used was manufactured by Mitsui Chemicals, Inc. and Shinsho Chemical Industry Co., Ltd.

<MeSt purification method>
The distillation was performed by simple distillation. Specifically, a thermometer for measuring the liquid temperature was attached to a 300 ml reaction kettle flask with a rotor, and a Claisen head with a thermometer for measuring the vapor temperature, a Liebig condenser, a bifurcated adapter, and a receiving flask were connected to it. Furthermore, a vacuum pump was connected to the adapter via a vacuum controller (manufactured by Okano Seisakusho Co., Ltd., VC-30S) so that the degree of reduced pressure could be adjusted. An oil bath was used as the heat source.

200 ml of αMeSt was placed in a reaction flask, and the liquid temperature was raised to 80°C. Then, 0.08% by mass of sodium ethoxide (20% by mass ethanol solution, Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a basic substance to the reaction flask while stirring with a rotor. The degree of vacuum was adjusted to 230 mmHg, and the liquid temperature was slowly raised until it reached 120°C to 125°C.

The low boiling point fraction reached its boiling point during the temperature increase and was cooled and recovered as a first fraction.
When the liquid temperature reached 120°C to 125°C and the vapor temperature also reached 120°C to 125°C, the main fraction was recovered.
The main fraction was divided into 10 fractions and recovered, and in the examples, only the fraction containing acetonylacetone or less than 2 ppm, benzaldehyde or less than 10 ppm, and phenylacetylene or less than 15 ppm was used.

(2) Preparation of Feed Liquid The raw materials purified by the method in (1) above were mixed in a ratio of St/αMeSt/CH=12.5/19.5/68 (wt %) to prepare a feed liquid to be subjected to polymerization.

(3) Initiator n-butyllithium (15 wt % n-hexane solution, manufactured by Wako Pure Chemical Industries, Ltd.) was diluted 1/61 with cyclohexane.

(4) Terminating Agent Methanol (special grade, manufactured by Wako Pure Chemical Industries, Ltd.) was diluted with cyclohexane to a concentration of 3 wt %.

(5) Polymerization method The polymerization reactor used was a jacketed 5L reactor (R1) equipped with an agitator (Max Blend Agitator manufactured by Sumitomo Heavy Industries, Ltd.) and a condenser, and further equipped with a raw material introduction nozzle, an initiator introduction nozzle, and a polymerization solution discharge nozzle. The outlet of the condenser was sealed with nitrogen gas to prevent air from being mixed in from the outside. The volume of the polymerization solution in the polymerization reactor was controlled to be always 3L. A part of the polymerization solution was always boiled, and the internal temperature was controlled between 79°C and 81°C. The rotation speed of the agitator was set to 320 rpm. Gear pumps were attached to the raw material inlet and outlet of the polymerization reactor, respectively, and the adjusted feed liquid was controlled to flow at a constant flow rate of 1.5L/Hr. The initiator solution was introduced into the polymerization reactor at 0.09L/Hr.

The living polymer solution discharged from the polymerization reactor was further guided by a gear pump through a 10 mm diameter pipe to the inlet of the polymerization terminator solution. The length of the pipe from the reactor to the terminator mixing point was about 2 m, and the pipe was kept at 65 to 70 ° C. The terminator solution was introduced into the polymerization reaction liquid at a flow rate of 0.13 L / Hr, and then passed through a 1.2 L capacity static mixer (Sulzer Co., Ltd., SMX type) to completely terminate the polymerization reaction. Furthermore, the polymer solution was heated to 260 ° C in a preheater, and then flushed into a container of about 50 L heated to a set temperature of 260 ° C under a reduced pressure of 60 torr, and the solvent and unreacted monomer were separated and recovered from the polymer. The polymer temperature in the flushing container was about 240 to 250 ° C, and the residence time of the polymer in the tank was about 20 to 30 minutes. The polymer, from which the volatile components had been sufficiently removed, was then discharged in the form of a rope, cooled underwater, and pelletized with a cutter to recover the styrene-based copolymer.

[Examples 1 to 3, Comparative Examples 1 to 3]
Various analyses and evaluations were carried out using pellets obtained by polymerizing feed solutions prepared by changing the raw material lots. The results are shown in Tables 1 and 2. The composition of α-MeSt units in the obtained copolymer was 52% by mass.

As is clear from Tables 1 and 2, the styrene copolymer of the present invention has excellent weather resistance.

The styrene copolymer of the present invention has excellent weather resistance by controlling the content of a specific compound in the feed liquid used for polymerization within a specific range. In addition, molded products containing the styrene copolymer of the present invention can be used extremely suitably as food containers for heating, housing parts, automobile interior parts, and optical parts.

Claims (4)

A styrene-based copolymer obtained by a living anionic polymerization method, which contains α-methylstyrene units and vinyl aromatic monomer units represented by the following general formula (1), and which shows a change in total light transmittance of 5% or less and a change in yellowness index of 5 or less after 1000 hours of irradiation in a weather resistance test using a sunshine weather meter.

(In the formula, R ¹ represents a hydrogen atom, an alkyl group having 2 or more carbon atoms, or a phenyl group, and R ² represents a hydrogen atom, a halogen atom, a hydroxyl group, a C1-C6 alkyl group, a C1-C6 alkoxy group, a carboxyl group, or a haloC1-C6 alkyl group.) The styrene copolymer according to claim 1, in which the content of α-methylstyrene units in the copolymer is 10 to 65% by mass, the weight average molecular weight (Mw) is in the range of Mw = 50,000 to 300,000, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is in the range of 1.6 to 2.5, and the total mass of the remaining monomers and polymerization solvent is 500 ppm or less. A feed liquid for producing a styrene-based copolymer, comprising a monomer and a polymerization solvent, the monomer containing α-methylstyrene and a vinyl aromatic monomer represented by the following general formula (1), the feed liquid having an acetonylacetone content of 2 ppm or less, a benzaldehyde content of 10 ppm or less, and a phenylacetylene content of 15 ppm or less:

The present invention relates to a method for producing a styrene-based copolymer using a feed liquid comprising a monomer and a polymerization solvent, the monomer comprising α-methylstyrene and a vinyl aromatic monomer represented by the following general formula (1), and the feed liquid has an acetonylacetone content of 2 ppm or less, a benzaldehyde content of 10 ppm or less, and a phenylacetylene content of 15 ppm or less: