Method for producing n-alkylmaleimide-based copolymer

Abstract

To provide a method that efficiently produces an N-alkylmaleimide-based copolymer exhibiting superior optical characteristics and thermal resistance.SOLUTION: The present invention provides a method for producing an N-alkylmaleimide-based copolymer, wherein monomers comprising 18 to 95 wt.% of N-alkylmaleimide, 1 to 80 wt.% of a styrene compound, and 1 to 80 wt.% of a (meth)acrylic acid ester are subjected to radical copolymerization to produce the N-alkylmaleimide-based copolymer, wherein the radical copolymerization of the monomers is performed in an ether-based solvent represented by formula (3). (In formula (3), R4 and R5 independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an N-alkylmaleimide copolymer containing structural units derived from an N-alkylmaleimide, a styrene compound, and a (meth)acrylic acid ester. [Background technology]

[0002] Copolymers obtained from N-alkylmaleimides (N-alkylmaleimide copolymers) are known to exhibit higher heat resistance and superior transparency compared to general thermoplastic vinyl polymers, making them promising materials as transparent resins that can be used for a variety of applications in the optical field (see, for example, Non-Patent Document 1).

[0003] Furthermore, it has been reported that an N-alkylmaleimide copolymer containing an N-alkylmaleimide and a styrene compound can realize a polymer material that has a simple composition, low birefringence, and can maintain that low birefringence over a wide range of environmental temperatures (see, for example, Patent Document 1).

[0004] N-Alkylmaleimide copolymers can be produced by radical polymerization. They can be produced by conventional methods such as bulk polymerization, emulsion polymerization, suspension polymerization, and solution polymerization. However, bulk polymerization produces a bulk copolymer, which makes it difficult to remove unreacted monomers, resulting in a loss of transparency. Furthermore, the resulting copolymer has a high molecular weight and contains a low-strength copolymer component with a high N-alkylmaleimide content, which results in flow characteristics during molding. Therefore, adding a chain transfer agent to the resulting copolymer material to reduce its molecular weight results in a decrease in strength. In emulsion polymerization and suspension polymerization, it is difficult to remove the emulsifier and dispersant, respectively. On the other hand, in solution polymerization, where the copolymer dissolves in the polymerization solvent and does not precipitate in particulate form, copolymers with relatively good transparency can be obtained by, for example, precipitating the resulting copolymer solution after polymerization in a poor solvent and purifying it. However, industrial purification of polymers using such reprecipitation methods is difficult and impractical due to the complex manufacturing process.

[0005] In response to this, methods for producing N-alkylmaleimide copolymers by so-called precipitation polymerization have been reported, in which polymerization is carried out using a polymerization solvent in which the monomer dissolves but the resulting copolymer does not, resulting in the copolymer precipitating in particulate form (see, for example, Patent Documents 2 to 4). By using these methods, impurities such as unreacted monomers or modified monomers thereof, which are thought to affect the transparency of the resulting copolymer, are dissolved in the polymerization solvent. Therefore, by separating the resulting copolymer particles from the polymerization solvent, the impurities can be easily removed, and an N-alkylmaleimide copolymer with good transparency can be obtained.

[0006] Furthermore, the methods represented by Patent Documents 2 to 4 are also advantageous in that they do not contain emulsifiers and dispersants that are used in ordinary emulsion polymerization and suspension polymerization, respectively, and therefore can produce copolymers with particularly excellent optical properties.

[0007] Furthermore, in the methods typified by Patent Documents 2 to 4, the resulting copolymer is obtained in the form of particles, which makes it possible to simplify the production process, such as the step of separating it from the solvent and the drying step.

[0008] Patent Document 5 reports a method for producing an N-alkylmaleimide copolymer having structural units derived from N-alkylmaleimide and a styrene compound by radical copolymerizing a monomer containing N-alkylmaleimide and a styrene compound, in which the monomer is radically copolymerized in a polymerization solvent that dissolves the monomer and precipitates the resulting N-alkylmaleimide copolymer in the form of particles. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2020-126229 [Patent Document 2] Japanese Patent Application Publication No. 5-194609 [Patent Document 3] Japanese Patent Application Publication No. 5-209004 [Patent Document 4] Japanese Patent Application Publication No. 5-247145 [Patent Document 5] International Publication No. 2024 / 005126 [Non-patent literature]

[0010] [Non-Patent Document 1] Takayuki Otsu, "Future Materials," Vol. 3, No. 1, pp. 74-79 Summary of the Invention [Problem to be solved by the invention]

[0011] However, even in the methods represented by Patent Documents 2 to 4, precipitation polymerization does not proceed smoothly in the copolymerization of N-alkylmaleimide and a styrene compound, and problems in production occur such as adhesion of the copolymer to the stirring blades and the inner wall of the polymerization vessel, and blocking.

[0012] Furthermore, in the production method described in Patent Document 5, when copolymerization of N-alkylmaleimide, a styrene compound, and a (meth)acrylic acid ester is carried out at a high monomer concentration, similar production problems still remain, and room for improvement is expected.

[0013] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for efficiently producing an N-alkylmaleimide copolymer having excellent optical properties and heat resistance. [Means for solving the problem]

[0014] As a result of extensive research to solve the above problems, the present inventors discovered a method for producing an N-alkylmaleimide copolymer by precipitation polymerization using a specific polymerization solvent, thereby completing the present invention.

[0015] In order to solve the above problems, one aspect of the present invention provides a method for producing an N-alkylmaleimide copolymer, which comprises radical copolymerizing monomers containing 18 to 95% by weight of an N-alkylmaleimide represented by the following formula (1), 1 to 80% by weight of a styrene compound, and 1 to 80% by weight of a (meth)acrylic acid ester represented by the following formula (2) to produce an N-alkylmaleimide copolymer having structural units derived from the N-alkylmaleimide, the styrene compound, and the (meth)acrylic acid ester, and radical copolymerizing the monomers in an ether-based solvent represented by the following formula (3): 1 represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms, and in formula (2), R 2 is hydrogen or a methyl group, and R 3represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms, and in formula (3), R 4 and R 5 are each independently a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms. [ka] [ka] [ka] [Effects of the Invention]

[0016] According to the production method of the present invention, an N-alkylmaleimide copolymer having excellent optical properties and heat resistance can be efficiently produced. DETAILED DESCRIPTION OF THE INVENTION

[0017] Each aspect of the present invention will be described in detail below. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0018] A method for producing a copolymer according to one embodiment of the present invention involves radical copolymerization of monomers containing 18 to 95% by weight of an N-alkylmaleimide represented by the following formula (1), 1 to 80% by weight of a styrene compound, and 1 to 80% by weight of a (meth)acrylic acid ester represented by the following formula (2), to produce an N-alkylmaleimide-based copolymer having structural units derived from the N-alkylmaleimide, the styrene compound, and the (meth)acrylic acid ester. [ka] [ka] [ka] [N-Alkylmaleimide] In formula (1), R 1 represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms. Examples of linear alkyl groups having 1 to 12 carbon atoms include methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, and dodecyl groups. Examples of branched alkyl groups having 3 to 12 carbon atoms include isopropyl, isobutyl, sec-butyl, and tert-butyl groups. Examples of cyclic alkyl groups having 3 to 6 carbon atoms include cyclopropyl, cyclobutyl, and cyclohexyl groups. The N-alkylmaleimide represented by formula (1) may be used alone or in combination.

[0019] Among these, from the viewpoint of further improving the heat resistance of the resulting N-alkylmaleimide copolymer, R 1 is preferably a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a hexyl group, a cyclohexyl group, or an octyl group, and more preferably a methyl group, an ethyl group, an isopropyl group, a tert-butyl group, or a cyclohexyl group.

[0020] Furthermore, as an N-alkylmaleimide compound, it has a relatively low impact on the surrounding environment and can simplify the equipment, which allows for efficient and economical production of N-alkylmaleimide copolymers. 1 is particularly preferably an ethyl group, a tert-butyl group or a cyclohexyl group.

[0021] Furthermore, even when copolymerization is carried out at a high monomer concentration, precipitation polymerization proceeds smoothly, and adhesion of the copolymer to the stirring blades and the inner wall of the polymerization vessel, as well as blocking, are unlikely to occur. Therefore, from the viewpoint of efficient and economical production of N-alkylmaleimide copolymers, R 1 is most preferably an ethyl group.

[0022] Specific examples of the N-alkylmaleimide represented by formula (1) include N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-isobutylmaleimide, N-sec-butylmaleimide, N-tert-butylmaleimide, N-pentylmaleimide, N-hexylmaleimide, N-octylmaleimide, N-decylmaleimide, N-dodecylmaleimide, N-cyclopropylmaleimide, N-cyclobutylmaleimide, and N-cyclohexylmaleimide. Among these, from the viewpoint of obtaining an N-alkylmaleimide copolymer having superior heat resistance, the N-alkylmaleimide represented by formula (1) is preferably N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, N-tert-butylmaleimide, or N-cyclohexylmaleimide. Furthermore, from the viewpoints of N-alkylmaleimide compounds having a relatively low impact on the surrounding environment and enabling efficient and economical production of N-alkylmaleimide copolymers using simpler equipment, the N-alkylmaleimide represented by formula (1) is more preferably N-ethylmaleimide, N-tert-butylmaleimide, or N-cyclohexylmaleimide. Furthermore, even when copolymerization is carried out at a high monomer concentration, precipitation polymerization proceeds smoothly, and adhesion of the copolymer to the stirring blades, the inner walls of the polymerization vessel, and the like, as well as blocking, are unlikely to occur. Therefore, from the viewpoint of efficient and economical production of N-alkylmaleimide copolymers, the most preferred N-alkylmaleimide represented by formula (1) is N-ethylmaleimide.

[0023] [Styrene compounds] The styrene compound used in one embodiment of the present invention is a general term for styrene and its derivatives, and is not limited as long as it is a monomer having a styrene skeleton. Examples of styrene compounds include alkylstyrenes, halogenated styrenes, alkoxystyrenes, and styrenes. Alkylstyrenes are styrenes substituted with a linear alkyl group having 1 to 3 carbon atoms. Examples of alkylstyrenes include o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, and α-methylstyrene. Halogenated styrenes are styrenes substituted with halogen atoms, such as fluorine, chlorine, and bromine. Examples of halogenated styrenes include o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, o-bromostyrene, m-bromostyrene, and p-bromostyrene. Alkoxystyrenes are styrenes substituted with an alkoxy group having 1 to 3 carbon atoms. Examples of alkoxystyrenes include o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, o-ethoxystyrene, m-ethoxystyrene, and p-ethoxystyrene. Among these, from the viewpoint of obtaining an N-alkylmaleimide copolymer having more excellent optical properties, the styrene compound is preferably styrene or α-methylstyrene. The styrene compound may be used alone or in combination of two or more types.

[0024] [(Meth)acrylic acid ester] In formula (2), R 2 is hydrogen or a methyl group, and R 3 R represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms. 3 In the formula (1), the linear alkyl group having 1 to 12 carbon atoms, the branched alkyl group having 3 to 12 carbon atoms, or the cyclic alkyl group having 3 to 6 carbon atoms is preferably R 1Among them, from the viewpoint of obtaining an N-alkylmaleimide copolymer having superior optical properties, R 3 is preferably a methyl group, an ethyl group or a butyl group, and particularly preferably a methyl group.

[0025] Specific examples of the (meth)acrylic acid ester represented by formula (2) include methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate, and among these, methyl (meth)acrylate is preferred. [Monomer content] The monomer used in one embodiment of the present invention includes an N-alkylmaleimide represented by formula (1), a styrene compound, and a (meth)acrylic acid ester represented by formula (2). The content of the N-alkylmaleimide in the monomer is 18 to 95 wt %, the content of the styrene compound is 1 to 80 wt %, and the content of the (meth)acrylic acid ester is 1 to 80 wt %. Among these, since an N-alkylmaleimide-based copolymer having particularly excellent heat resistance and optical properties can be obtained, the content of the N-alkylmaleimide in the monomer is preferably 25 to 90 wt %, and more preferably 30 to 85 wt %. For the same reason, the content of the styrene compound in the monomer is preferably 1 to 65 wt %, and more preferably 1 to 50 wt %. For the same reason, the content of the (meth)acrylic acid ester in the monomer is preferably 5 to 75 wt %, and more preferably 5 to 70 wt %. Furthermore, from the viewpoint of obtaining an N-alkylmaleimide copolymer with a better photoelastic coefficient and intrinsic birefringence, it is preferable that the content of N-alkylmaleimide in the above-mentioned monomers is 30 to 70 wt%, the content of styrene compound is 2 to 35 wt%, and the content of (meth)acrylic acid ester is 5 to 65 wt%. Furthermore, even when copolymerization is carried out at a high monomer concentration, precipitation polymerization proceeds smoothly and adhesion of the copolymer to the stirring blades and the inner wall of the polymerization vessel, as well as blocking, are unlikely to occur. Therefore, from the viewpoint of efficiently and economically producing an N-alkylmaleimide copolymer, it is most preferable that the content of N-alkylmaleimide in the above-mentioned monomers is 45 to 70 wt%, the content of styrene compound is 5 to 35 wt%, and the content of (meth)acrylic acid ester is 10 to 40 wt%.

[0026] [Other monomers] In one embodiment of the present invention, other copolymerizable monomers can also be copolymerized, if necessary. The other copolymerizable monomers are not limited as long as they are copolymerizable with N-alkylmaleimide. Examples of other copolymerizable monomers include olefins and vinyl carboxylic acid esters. Examples of olefins include ethylene, propylene, 1-butene, isobutene, 2-methyl-1-butene, 2-methyl-1-pentene, 2,3-dimethyl-1-butene, 2,4-dimethyl-1-pentene, 2,4,4-trimethyl-1-pentene, and indene. Examples of vinyl carboxylic acid esters include vinyl acetate, vinyl propionate, and vinyl pivalate.

[0027] [Polymerization method] In one embodiment of the present invention, an N-alkylmaleimide copolymer is produced by precipitation polymerization using the above-mentioned monomers as raw materials, i.e., in one embodiment of the present invention, the monomers are radically copolymerized in a specific ether solvent that dissolves the monomers and precipitates the resulting N-alkylmaleimide copolymer in particulate form.

[0028] [Polymerization Solvent] In one embodiment of the production method of the present invention, polymerization is carried out in an ether-based solvent represented by formula (3). By carrying out polymerization in such an ether-based solvent, precipitation polymerization proceeds smoothly even when copolymerization is carried out at a high monomer concentration, and adhesion of the copolymer to the stirring blades, the inner wall of the polymerization vessel, etc., and blocking are unlikely to occur, thereby providing the excellent effect of enabling efficient and economical production of N-alkylmaleimide copolymers.

[0029] In formula (3), R 4 and R 5 R each independently represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms. 4 and R 5 may be the same as or different from each other. 4 and R 5In the formula (1), the linear alkyl group having 1 to 12 carbon atoms, the branched alkyl group having 3 to 12 carbon atoms, or the cyclic alkyl group having 3 to 6 carbon atoms is preferably R 1 Among them, R 4 and R 5 are preferably, independently, a propyl group, an isopropyl group, a butyl group, an isobutyl group, or a tert-butyl group, and particularly preferably, are, independently, an isopropyl group or a butyl group.

[0030] Specific examples of the ether solvent represented by formula (3) include dimethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, di-tert-butyl ether, and cyclopentyl methyl ether, among which dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, and di-tert-butyl ether are preferred, and diisopropyl ether and dibutyl ether are particularly preferred. The ether solvent may be used alone or in combination of two or more.

[0031] In one embodiment of the present invention, other solvents can be dissolved in the ether solvent represented by formula (3). The other solvents are not particularly limited, as long as the mixed solvent obtained by dissolving the other solvent in the ether solvent is a solvent that can dissolve the above-mentioned monomers and can precipitate the resulting N-alkylmaleimide copolymer in particulate form. Examples of other solvents include aliphatic hydrocarbons, aromatic hydrocarbons, water-soluble organic solvents, ketone-based organic solvents, ester-based organic solvents, glycol ether-based organic solvents, and water. Among these, aliphatic hydrocarbons are preferred from the viewpoint of promoting smooth precipitation polymerization even when copolymerization is performed at a high monomer concentration, and reducing adhesion of the copolymer to the stirring blades and the inner wall of the polymerization vessel, as well as blocking. This further enhances the effect of efficiently and economically producing an N-alkylmaleimide copolymer. Aliphatic hydrocarbons include, for example, propane, butane, isobutane, hexane, heptane, octane, isooctane, 2,2,4-trimethylpentane, nonane, decane, undecane, dodecane, tetradecane, hexadecane, octadecane, cyclohexane, methylcyclohexane, and ethylcyclohexane. Aromatic hydrocarbons include benzene, toluene, and xylene. Glycol ether organic solvents include, for example, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, and diethylene glycol monobutyl ether acetate. Water-soluble organic solvents include, for example, methanol, ethanol, propanol, isopropanol, acetone, and acetonitrile. Ketone organic solvents include ketone organic solvents other than acetone, such as methyl ethyl ketone and methyl isobutyl ketone. Examples of the ester-based organic solvent include ethyl acetate, butyl acetate, dimethyl carbonate, diethyl carbonate, and propylene carbonate.Only one type of other solvent may be dissolved in the ether-based solvent, or multiple types may be dissolved and used. The amount of other solvent used when dissolving other solvents is not particularly limited, as long as the mixed solvent obtained by dissolving the other solvent in the ether-based solvent is a solvent that can dissolve the monomer and can precipitate the resulting N-alkylmaleimide copolymer in particulate form.

[0032] In one embodiment of the present invention, the ratio (by weight) of the monomer to the ether solvent is monomer:ether solvent=5:95 to 50:50. In particular, from the viewpoint that precipitation polymerization proceeds smoothly even when copolymerization is carried out at a high monomer concentration, adhesion of the copolymer to the stirring blades and the inner wall of the polymerization vessel, blocking, etc., is unlikely to occur, and thus an N-alkylmaleimide copolymer can be produced efficiently and economically, the ratio (by weight) of the monomer to the ether solvent is more preferably monomer:ether solvent=15:85 to 50:50, even more preferably 20:85 to 50:50, and most preferably 25:80 to 50:50.

[0033] [Polymerization initiator] In one embodiment of the present invention, a radical polymerization initiator may be used. As the radical polymerization initiator, an oil-soluble radical polymerization initiator is preferably used. Examples of the oil-soluble radical polymerization initiator include organic peroxides and azo-based initiators. Examples of organic peroxides include benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tert-butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-butyl peroxypivalate, tert-hexyl peroxypivalate, tert-butyl peroxyneodecanoate, and tert-hexyl peroxyneodecanoate. Azo initiators include 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-butyronitrile), 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, and 1,1'-azobis(cyclohexane-1-carbonitrile).

[0034] The amount of radical polymerization initiator used can be set appropriately. For example, the amount of radical polymerization initiator used may be 0.0001 to 2 parts by weight per 100 parts by weight of the total amount of monomers. In particular, from the viewpoint of obtaining an N-alkylmaleimide copolymer having more excellent optical properties and mechanical strength, the amount of radical polymerization initiator used is preferably 0.001 to 1 part by weight, and more preferably 0.01 to 0.5 parts by weight.

[0035] [Polymerization temperature] The polymerization temperature in one embodiment of the present invention can be appropriately set depending on the decomposition temperature of the radical polymerization initiator. In particular, from the viewpoint of efficiently producing an N-alkylmaleimide copolymer having excellent optical properties and mechanical strength, the polymerization temperature is preferably in the range of 10 to 80°C, more preferably in the range of 20 to 70°C, and particularly preferably in the range of 30 to 60°C.

[0036] [Cleaning] In one aspect of the present invention, from the viewpoint of efficiently and economically producing particulate N-alkylmaleimide copolymers having excellent optical properties and mechanical strength, it is preferable to filter the N-alkylmaleimide copolymer particles obtained by precipitation polymerization and then wash the particles with a washing solvent.

[0037] The cleaning solvent is not limited as long as it dissolves the unreacted monomer without dissolving the N-alkylmaleimide copolymer. Examples of cleaning solvents include water, methanol, ethanol, a methanol / toluene mixed solvent, an ethanol / toluene mixed solvent, a methanol / water mixed solvent, and an ethanol / water mixed solvent. For example, the unreacted N-alkylmaleimide monomer is soluble in water. Meanwhile, the unreacted N-alkylmaleimide, the unreacted styrene compound, and the unreacted (meth)acrylic acid ester are all soluble in methanol, ethanol, a methanol / toluene mixed solvent, an ethanol / toluene mixed solvent, a methanol / water mixed solvent, and an ethanol / water mixed solvent.

[0038] [Other additives] In one embodiment of the present invention, a chain transfer agent such as an alkyl mercaptan or a hindered phenol-based or phosphorus-based antioxidant may be used at the initial stage of polymerization, during polymerization, or after polymerization, if necessary.

[0039] In one embodiment of the present invention, an N-alkylmaleimide copolymer is produced by a polymerization reaction, and particles of the copolymer are obtained. In one embodiment of the present invention, neither an emulsifier nor a dispersant is required to enhance the dispersion stability of the particles. Therefore, in one embodiment of the present invention, neither an emulsifier nor a dispersant is added to the raw material composition (monomer mixture) for the polymerization reaction.

[0040] [Properties of N-Alkylmaleimide Copolymers] The N-alkylmaleimide copolymer obtained by the production method according to one embodiment of the present invention is particulate. Effective removal of the polymerization solvent, unreacted monomer, or both results in an N-alkylmaleimide copolymer with excellent optical properties and mechanical strength. From the perspective of obtaining an N-alkylmaleimide copolymer with excellent optical properties and mechanical strength through effective removal of the polymerization solvent or unreacted monomer, the average particle size of the N-alkylmaleimide polymer particles produced in the polymerization solvent is preferably 20 to 2,000 μm, more preferably 30 to 1,000 μm, and even more preferably 50 to 900 μm. Note that the average particle size herein refers to the particle size at which the cumulative particle amount on a volume basis is 50%, as determined by laser diffraction / scattering. The average particle size can be adjusted by classifying the particles and blending the classified products. It can also be adjusted by adjusting the stirring speed, polymerization solvent, and monomer content during precipitation polymerization. For example, the average particle size can be increased by decreasing the stirring speed, decreasing the polymerization solvent content, or increasing the monomer content.

[0041] As described above, in the production method of N-alkylmaleimide copolymers by precipitation polymerization, adhesion of the copolymer to the stirring blades, the inner wall of the polymerization vessel, etc. can occur. The amount of adhesion can be expressed as the adhesion yield. The adhesion yield is expressed as a weight percent (wt%) obtained by recovering the copolymer adhering to the stirring blades, the inner wall of the polymerization vessel, etc. after polymerization, washing, and drying the copolymer, and dividing the weight of the adhesion by the total weight of the charged monomers. The adhesion yield can be controlled by the polymerization solvent, polymerization solvent composition, charged monomer composition, charged monomer concentration, polymerization temperature, etc. For example, decreasing the charged monomer concentration decreases the adhesion yield. Furthermore, decreasing the polymerization temperature decreases the adhesion yield. The adhesion yield is preferably 10 wt% or less, more preferably 4 wt% or less, particularly preferably 2 wt% or less, and most preferably 1 wt% or less. In the production method according to one embodiment of the present invention, the deposit yield is smaller than that of a production method represented by formula (3) that does not use an ether-based solvent under the conditions of the same charged monomer composition, the same charged monomer concentration, and the same polymerization temperature.

[0042] [N-Alkylmaleimide copolymer] The weight average molecular weight (M w ) is not particularly limited. From the viewpoint of obtaining an N-alkylmaleimide copolymer having excellent optical properties and mechanical strength, the weight average molecular weight of the N-alkylmaleimide copolymer is preferably 100,000 to 2,000,000, more preferably 100,000 to 1,800,000, and particularly preferably 150,000 to 1,500,000.

[0043] The glass transition temperature (Tg) of the N-alkylmaleimide copolymer obtained by the production method according to one embodiment of the present invention is an index of heat resistance. The glass transition temperature (Tg) of the N-alkylmaleimide copolymer obtained by one embodiment of the production method according to the present invention is not particularly limited. Since an N-alkylmaleimide copolymer having excellent heat resistance can be obtained, the glass transition temperature is preferably 120°C or higher, more preferably 135°C or higher, particularly preferably 150°C or higher, and most preferably 160°C or higher.

[0044] The tensile stress of the N-alkylmaleimide copolymer obtained by the production method according to one embodiment of the present invention is an index of mechanical strength. The tensile stress of the N-alkylmaleimide copolymer obtained by one embodiment of the production method according to the present invention is not particularly limited. Since an N-alkylmaleimide copolymer having excellent mechanical strength can be obtained, the tensile stress is preferably 30 MPa or more, more preferably 35 MPa or more, and particularly preferably 40 MPa or more. The tensile stress of the N-alkylmaleimide copolymer can be measured by the M w It can be controlled by.

[0045] The tensile elongation, which is an index of the mechanical strength of the N-alkylmaleimide copolymer obtained by the production method according to one embodiment of the present invention, is not particularly limited. Since an N-alkylmaleimide copolymer having excellent mechanical strength can be obtained, the tensile elongation is preferably 2% or more, more preferably 2.5% or more, and particularly preferably 3% or more.

[0046] The haze of the N-alkylmaleimide copolymer obtained by the production method according to one embodiment of the present invention is one index of optical properties. The haze of the N-alkylmaleimide copolymer obtained by one embodiment of the production method according to the present invention is not particularly limited. Since an N-alkylmaleimide copolymer with excellent transparency is obtained, the haze is preferably less than 3%, more preferably less than 2.5%, and particularly preferably less than 2%. The haze of the N-alkylmaleimide copolymer can be controlled by the amount of remaining monomer.

[0047] The photoelastic constant (C) and intrinsic birefringence (Δn 0 ) is one of the indexes of optical properties. The photoelastic constant (C) and intrinsic birefringence (Δn 0 ) are not particularly limited to their absolute values. Since an N-alkylmaleimide copolymer with low birefringence can be obtained, the photoelastic constant of the N-alkylmaleimide copolymer is preferably 50×10 in absolute value. -12 Pa -1 Preferably, it is less than 10 × 10 -12 Pa -1 More preferably, it is 2×10 or less. -12 Pa -1 For the same reason, the intrinsic birefringence of the N-alkylmaleimide copolymer is more preferably 20×10 in absolute value or less. -3 Preferably, it is 5 x 10 or less. -3 More preferably, it is 1×10 or less. -3 It is more preferable that the C and Δn of the N-alkylmaleimide copolymer are as follows: 0 can be controlled by the type of monomer and the ratio of the monomer units in the N-alkylmaleimide copolymer.

[0048] The temperature constant of intrinsic birefringence (dΔn 0 The temperature constant of intrinsic birefringence (dΔn / dT) of the N-alkylmaleimide copolymer obtained by one embodiment of the production method of the present invention is 0 / dT) is not particularly limited in its absolute value. Since an N-alkylmaleimide copolymer capable of maintaining low birefringence over a wide range of environmental temperatures can be obtained, the temperature constant is preferably 2×10 -5 °C -1 or less, and more preferably 1×10 -5 °C -1 The dΔn of the N-alkylmaleimide copolymer is as follows: 0 / dT can be controlled by the type of monomer and the ratio of the monomer units in the N-alkylmaleimide copolymer.

[0049] The production method according to this embodiment can efficiently produce an N-alkylmaleimide copolymer with excellent optical properties and heat resistance by precipitation polymerization using a specific polymerization solvent. Specifically, films formed using the copolymer obtained by this production method have superior transparency compared to films formed using copolymers obtained by conventional suspension polymerization or emulsion polymerization. Furthermore, while the production method according to this embodiment is simpler to operate than bulk polymerization, films formed using the copolymer obtained by this production method have excellent optical properties (transparency, low birefringence) and heat resistance, similar to films formed using copolymers obtained by bulk polymerization. Therefore, N-alkylmaleimide copolymers with excellent optical properties and heat resistance can be produced more efficiently than by bulk polymerization. The N-alkylmaleimide copolymers obtained by the production method according to one embodiment of the present invention have excellent optical properties and heat resistance, and can therefore be used for various optical components, optical lenses, optical sheets, optical films, and the like.

[0050] According to one aspect of the present invention, an N-alkylmaleimide copolymer having excellent optical properties and heat resistance can be efficiently produced. Therefore, the present invention is expected to contribute to the achievement of the Sustainable Development Goals (SDGs) regarding ensuring a stable consumption and production pattern and developing industrial infrastructure.

[0051] 〔summary〕 A method for producing an N-alkylmaleimide copolymer according to a first aspect of the present invention involves radical copolymerizing monomers containing 18 to 95% by weight of an N-alkylmaleimide represented by the above formula (1), 1 to 80% by weight of a styrene compound, and 1 to 80% by weight of a (meth)acrylic acid ester represented by the above formula (2) to produce an N-alkylmaleimide copolymer having structural units derived from the N-alkylmaleimide, the styrene compound, and the (meth)acrylic acid ester, by radical copolymerizing the monomers in an ether-based solvent represented by the above formula (3).

[0052] A method for producing an N-alkylmaleimide copolymer according to a second aspect of the present invention comprises the steps of: 1 may be a methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, hexyl, cyclohexyl or octyl group.

[0053] In the method for producing an N-alkylmaleimide copolymer according to Aspect 3 of the present invention, in Aspect 1 or 2, the styrene compound may be styrene or α-methylstyrene.

[0054] In the method for producing an N-alkylmaleimide copolymer according to Aspect 4 of the present invention, in any one of Aspects 1 to 3, the (meth)acrylic acid ester may be methyl (meth)acrylate.

[0055] In the method for producing an N-alkylmaleimide copolymer according to Aspect 5 of the present invention, in any one of Aspects 1 to 4, the average particle size of the N-alkylmaleimide polymer particles produced in the ether solvent may be 20 to 2,000 μm.

[0056] A sixth aspect of the present invention relates to a method for producing an N-alkylmaleimide copolymer, and in any one of the first to fifth aspects, the ether solvent may be dipropyl ether, diisopropyl ether, or dibutyl ether.

[0057] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Example]

[0058] The present invention will be described below based on examples, but the present invention is not limited to these examples. Unless otherwise specified, commercially available products were used as reagents. Perhexyl ND from NOF Corporation was used as tert-hexylperoxyneodecanoate. The tert-hexylperoxyneodecanoate content in Perhexyl ND was 71%.

[0059] The evaluation and measurement methods for the N-alkylmaleimide copolymers obtained in the examples are described below, followed by specific examples of the production of N-alkylmaleimide copolymers.

[0060] [Copolymer composition] After polymerization for a predetermined time, a portion (100 mg) of the polymerization reaction solution (slurry) before filtration was extracted and dissolved in 1.5 g of deuterated chloroform. The obtained polymerization reaction solution was analyzed using a 400 MHz NMR (JNM-ECZ400S / L1) manufactured by JEOL Ltd. 1 H-NMR measurements were performed. The amount of each monomer consumed was calculated from the change in the peak intensity of the double bond of each monomer before and after the polymerization reaction relative to the peak intensity of the solvent used in the polymerization reaction. Assuming that all of the consumed monomers were incorporated as components in the copolymer, the copolymer composition was calculated from the amount of each monomer consumed.

[0061] [Polymer weight average molecular weight Mw and molecular weight distribution Mw / Mn] The molecular weight distribution of N-alkylmaleimide copolymers was measured using a Tosoh GPC (HLC-8320GPC). Two Tosoh TSKgel Super HM-H columns were used, the column temperature was set to 40°C, and tetrahydrofuran was used as the eluent. A molecular weight calibration curve was prepared using Tosoh standard polystyrenes with known molecular weights.

[0062] Example 1 A 500 mL four-neck flask equipped with a stirrer, nitrogen inlet tube, and thermometer was charged with 307.1 g of diisopropyl ether as a solvent, 15.4 g of styrene, 17.5 g of methyl methacrylate, and 43.8 g of N-ethylmaleimide as monomers (monomer concentration = 20 wt%), and 131 mg of tert-hexylperoxyneodecanoate as a polymerization initiator, and nitrogen bubbling was performed for 1 hour. The contents of the four-neck flask were then heated to 40°C with stirring to initiate precipitation polymerization. Precipitation of particulate copolymer was observed over the course of the polymerization period.

[0063] After 24 hours, the contents were filtered to recover the resulting N-alkylmaleimide copolymer particles. 0.50 g (0.65 wt. % yield) of amorphous copolymer was confirmed to be attached to the inner wall of the flask and the stirring blade / stirring shaft. The recovered copolymer particles were washed three times with 396 g of methanol. The washed copolymer particles were placed in a dryer set at 95°C and dried under vacuum. Drying was stopped when there was no further weight loss due to drying, yielding 66.6 g of N-ethylmaleimide / styrene / methyl methacrylate copolymer.

[0064] Example 2 Precipitation polymerization was carried out in the same manner as in Example 1, except that the solvent was changed to 320.5 g of butyl ether, the monomers were changed to 16.1 g of styrene, 18.3 g of methyl methacrylate, and 45.8 g of N-ethylmaleimide (monomer concentration = 20 wt%), and the polymerization initiator was changed to 137 mg of tert-hexylperoxyneodecanoate. 0.42 g (deposit yield = 0.52 wt%) of amorphous copolymer was confirmed to adhere to the inner wall of the flask and the stirring blade / stirring shaft. Meanwhile, 71.0 g of particulate N-ethylmaleimide / styrene / methyl methacrylate copolymer was obtained.

[0065] Comparative Example 1 Precipitation polymerization was carried out in the same manner as in Example 1, except that the solvent was changed to 291.9 g of methylcyclohexane and 32.4 g of butyl acetate, the monomers were changed to 16.3 g of styrene, 18.6 g of methyl methacrylate, and 46.4 g of N-ethylmaleimide (monomer concentration = 20 wt%), and the polymerization initiator was changed to 138 mg of tert-hexylperoxyneodecanoate. 2.24 g (2.76 wt%) of amorphous copolymer was confirmed to be attached to the inner wall of the flask and the stirring blade / stirring shaft. 72.5 g of particulate N-ethylmaleimide / styrene / methyl methacrylate copolymer was obtained.

[0066] Comparative Example 2 Precipitation polymerization was carried out in the same manner as in Example 1, except that the solvent was changed to 272.5 g of methanol and 68.1 g of distilled water, the monomers were changed to 14.4 g of styrene, 17.0 g of methyl methacrylate, and 53.5 g of N-ethylmaleimide (monomer concentration=20 wt%), and the polymerization initiator was changed to 285 mg of tert-hexylperoxyneodecanoate. During the polymerization, a large amount of material adhered to the inner wall of the flask and the stirring blade / stirring shaft, and stirring became impossible after 3 hours of polymerization, so the polymerization was terminated.

[0067] [Reference example 1] Precipitation polymerization was carried out in the same manner as in Example 1, except that the solvent was changed to 304.1 g of methylcyclohexane and 33.8 g of butyl acetate, the monomers were changed to 13.0 g of styrene, 14.7 g of methyl methacrylate, and 36.8 g of N-ethylmaleimide (monomer concentration = 16 wt%), and the polymerization initiator was changed to 110 mg of tert-hexylperoxyneodecanoate. 0.59 g (0.91 wt%) of amorphous copolymer was confirmed to be attached to the inner wall of the flask and the stirring blade / stirring shaft. 58.7 g of particulate N-ethylmaleimide / styrene / methyl methacrylate copolymer was obtained.

[0068] [Reference example 2] Precipitation polymerization was carried out in the same manner as in Example 1, except that the solvent was changed to 284.3 g of methanol and 71.1 g of distilled water, the monomers were changed to 8.3 g of styrene, 12.0 g of methyl methacrylate, and 47.6 g of N-ethylmaleimide (monomer concentration = 16 wt%), the polymerization initiator was changed to 225 mg of tert-hexylperoxyneodecanoate, and the polymerization time was changed to 10 hours. 0.68 g (1.00 wt%) of amorphous copolymer was observed adhering to the inner wall of the flask and the stirring blade / stirring shaft. Meanwhile, 33.3 g of particulate N-ethylmaleimide / styrene / methyl methacrylate copolymer was obtained.

[0069] Example 3 Precipitation polymerization was carried out in the same manner as in Example 1, except that the solvent was changed to 304.9 g of butyl ether, the monomers were changed to 20.4 g of styrene, 23.2 g of methyl methacrylate, and 58.0 g of N-ethylmaleimide (monomer concentration = 25 wt%), and the polymerization initiator was changed to 173 mg of tert-hexylperoxyneodecanoate. 3.64 g (deposit yield = 3.58 wt%) of amorphous copolymer was confirmed to be attached to the inner wall of the flask and the stirring blade / stirring shaft. Meanwhile, 88.7 g of particulate N-ethylmaleimide / styrene / methyl methacrylate copolymer was obtained.

[0070] Example 4 Precipitation polymerization was carried out in the same manner as in Example 1, except that the solvent was changed to 271.8 g of butyl ether and 30.2 g of heptane, the monomers were changed to 20.2 g of styrene, 23.0 g of methyl methacrylate, and 57.4 g of N-ethylmaleimide (monomer concentration = 25 wt%), and the polymerization initiator was changed to 171 mg of tert-hexylperoxyneodecanoate. Adhesion of 1.92 g (adhesion yield = 1.91 wt%) of amorphous copolymer was confirmed on the inner wall of the flask and the stirring blade / stirring shaft. Meanwhile, 88.9 g of particulate N-ethylmaleimide / styrene / methyl methacrylate copolymer was obtained.

[0071] Comparative Example 3 Precipitation polymerization was carried out in the same manner as in Example 1, except that the solvent was changed to 276.6 g of methylcyclohexane and 30.7 g of butyl acetate, the monomers were changed to 20.6 g of styrene, 23.4 g of methyl methacrylate, and 58.4 g of N-ethylmaleimide (monomer concentration = 25 wt%), and the polymerization initiator was changed to 175 mg of tert-hexylperoxyneodecanoate. 75.6 g (yield = 73.9 wt%) of amorphous copolymer was confirmed to adhere to the inner wall of the flask and the stirring blade / stirring shaft. Meanwhile, 16.6 g of particulate N-ethylmaleimide / styrene / methyl methacrylate copolymer was obtained.

[0072] Comparative Example 4 3.15 g of N-ethylmaleimide, 0.85 g of styrene, and 1.0 g of methyl methacrylate were mixed in a test tube. The test tube was sealed and shaken thoroughly to mix the contents. The test tube was placed in a 70°C water bath for 24 hours to allow bulk polymerization. The resulting N-alkylmaleimide copolymer was a cylindrical mass adhered to the inside of the test tube. To remove unreacted monomer, the cylindrical mass was removed from the test tube, crushed into approximately 1 cm cubes, and then placed in methylene chloride to produce a transparent N-alkylmaleimide copolymer solution. The resulting N-alkylmaleimide copolymer solution was then added dropwise to methanol to precipitate the N-alkylmaleimide copolymer. The mixture was filtered through filter paper, and the filtrate containing the dissolved unreacted monomer was removed. The N-alkylmaleimide copolymer remaining on the filter paper was then collected and dried under reduced pressure in a desiccator for 3 hours. Thereafter, the mixture was further dried under reduced pressure in a vacuum dryer at 105° C. for 24 hours to obtain 4.0 g of an N-alkylmaleimide copolymer.

[0073] For the above examples and comparative examples, the feed compositions of the monomers and polymerization solvents used in the production of N-alkylmaleimide copolymer particles are shown in Table 1, and the feed compositions of the initiator, production conditions, and results of the production of N-alkylmaleimide copolymer particles are shown in Table 2.

[0074] In the table, "RMI" represents N-alkylmaleimide, "St" represents a styrene compound (styrene), "EMI" represents N-ethylmaleimide, and "MMA" represents methyl methacrylate. [Table 1] [Table 2] [Consideration] In Examples 1 to 4, a sufficient amount of N-alkylmaleimide copolymer was produced as particles, and it is clear that the ether solvents in the examples are sufficiently useful as polymerization solvents for precipitation polymerization in the production of a copolymer of N-alkylmaleimide, a styrene compound, and a (meth)acrylic acid ester.

[0075] Comparing Examples 1 and 2 with Example 3, it is clear that the deposit yield increases as the monomer concentration relative to the polymerization solvent increases (from 20% by weight to 25% by weight).

[0076] On the other hand, a comparison between Example 3 and Example 4 shows that dissolving an aliphatic hydrocarbon in an ether-based solvent reduces the deposit yield.

[0077] Comparative Example 1 is an example of the production of an N-alkylmaleimide copolymer by precipitation polymerization using a mixed solvent of methylcyclohexane and butyl acetate as the polymerization solvent. Compared with Examples 1 and 2 in which polymerization was carried out using an ether solvent at the same monomer concentration, it can be seen that the deposit yield was greater.

[0078] Comparative Example 2 is an example of the production of an N-alkylmaleimide copolymer by precipitation polymerization using a mixed solvent of methanol and distilled water as the polymerization solvent. Compared with Examples 1 and 2 in which polymerization was carried out using an ether solvent at the same monomer concentration, it can be seen that the deposit yield was greater.

[0079] Comparative Example 3 is an example of producing an N-alkylmaleimide copolymer by precipitation polymerization using a mixed solvent of methylcyclohexane and butyl acetate as the polymerization solvent. Compared with Examples 3 and 4, in which polymerization was carried out using an ether solvent at the same monomer concentration, it can be seen that the deposit yield was greater.

[0080] Comparative Example 4 is an example of the production of an N-alkylmaleimide copolymer by bulk polymerization. In Comparative Example 3, the copolymer produced is in the form of a mass, and therefore requires steps of crushing the mass, dissolving it in a solvent, and precipitating the copolymer in a solvent in which the unreacted monomer dissolves.

[0081] Reference Example 1 is an example of the production of an N-alkylmaleimide copolymer by precipitation polymerization using a mixed solvent of methylcyclohexane and butyl acetate. Compared to Comparative Example 1, in which polymerization was carried out using the same solvent, it can be seen that the deposit yield is reduced by lowering the monomer concentration. However, compared to Examples 1 and 2, in which polymerization was carried out using an ether-based solvent, the deposit yield in Reference Example 1 is also high, and it can be seen that in order to achieve the same deposit yield, it is necessary to further lower the monomer concentration, which reduces production efficiency.

[0082] Reference Example 2 is an example of the production of an N-alkylmaleimide copolymer by precipitation polymerization using a mixed solvent of methanol and distilled water. Compared to Comparative Example 2, in which polymerization was carried out using the same solvent, it can be seen that the deposit yield is reduced by lowering the monomer concentration. However, compared to Examples 1 and 2, in which polymerization was carried out using an ether-based solvent, the deposit yield in Reference Example 2 is also high, and it is clear that in order to achieve the same deposit yield, it is necessary to further lower the monomer concentration, which reduces production efficiency. [Industrial Applicability]

[0083] The present invention can be used to produce materials for various optical members (optical lenses, optical sheets, optical films, etc.) that have excellent optical properties and heat resistance.

Claims

1. The following formula (1) 【Chemical 1】 (In formula (1), R １ represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms), 18 to 95% by weight of an N-alkylmaleimide represented by the formula: 1 to 80% by weight of a styrene compound; The following formula (2) 【Chemistry 2】 (In formula (2), R ２ is hydrogen or a methyl group, and R ３ represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms) and 1 to 80% by weight of a (meth)acrylic acid ester represented by the following formula (3): 【Chemistry 3】 (In formula (3), R ４ and R ５ each independently represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms. and (iii) subjecting the monomer to radical copolymerization in an ether solvent represented by the formula (I):

2. The R １ is a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a hexyl group, a cyclohexyl group, or an octyl group.

3. 3. The method for producing an N-alkylmaleimide copolymer according to claim 1, wherein the styrene compound is styrene or α-methylstyrene.

4. 3. The method for producing an N-alkylmaleimide copolymer according to claim 1, wherein the (meth)acrylic acid ester is methyl (meth)acrylate.

5. 3. The method for producing an N-alkylmaleimide copolymer according to claim 1, wherein the particles of the N-alkylmaleimide polymer produced in the ether solvent have an average particle size of 20 to 2,000 μm.

6. 3. The method for producing an N-alkylmaleimide copolymer according to claim 1, wherein the ether solvent is dipropyl ether, diisopropyl ether or dibutyl ether.

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