(Meth)acrylic resin

Abstract

Provided is a (meth)acrylic resin that exhibits a higher thermal decomposition temperature. [Solution] (Meth)acrylic monomers are polymerized while continuously adding a chain transfer agent and a polymerization initiator to the (meth)acrylic monomers. The chain transfer agent / polymerization initiator ratio (by mass) is maximized (addition ratio A) while the conversion rate of the (meth)acrylic monomer is 10% by mass or more but less than 60% by mass. The resulting (meth)acrylic resin has a sulfur terminal ratio of 30 mol% or more, calculated by the following formula, and a thermal decomposition temperature of 335°C or more. Sulfur terminal fraction (mol%) = (Sx / 32) × Mn

Description

[Technical Field]

[0001] The present invention relates to a (meth)acrylic resin and a method for producing the same. [Background technology]

[0002] (Meth)acrylic resins are well-balanced in various properties, including optical properties, mechanical strength, moldability, and surface hardness, making them suitable for use in optical components. However, (meth)acrylic resins are generally susceptible to thermal decomposition. For example, methyl methacrylate (MMA) is prone to disproportionation termination during the polymerization process. When disproportionation termination occurs, polymethyl methacrylate (PMMA) has double bonds at the molecular end, which makes depolymerization likely to proceed from the molecular end at relatively low temperatures. Depolymerization can cause foaming during melt molding of (meth)acrylic resins, and resin decomposition products can contaminate the molding machine, resulting in poor appearance of the molded product. Therefore, the use of a chain transfer agent such as an organic thiol compound during polymerization has been proposed (e.g., Patent Documents 1 and 2). For example, Patent Document 1 proposes adding a chain transfer agent when the polymerization conversion rate is 60% by weight or more and 92% by weight or less. When an organic thiol compound is used, radicals generated during polymerization react with the organic thiol compound, suppressing the formation of double bonds at the molecular end. Furthermore, S is introduced into the molecular end, producing a polymer with ends that are more resistant to thermal decomposition. For example, Patent Document 1 shows that the thermal decomposition temperature can be increased to a maximum of 334°C and the residual MMA content can be reduced to a minimum of 1,500 ppm.

[0003] Patent Document 2 describes a method in which the value of "amount of chain transfer agent added / amount of polymerization initiator added" for the polymerization initiator and chain transfer agent added from the start of polymerization until one-fourth of the polymerization time has elapsed is set to 2 to 6 times the value of "amount of chain transfer agent added / amount of polymerization initiator added" for the polymerization initiator and chain transfer agent added from the start of polymerization until the end of polymerization, and describes that by adding substantially most of the chain transfer agent at the start of the reaction and polymerizing it, a methacrylic polymer with excellent thermal stability can be obtained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-172328 [Patent Document 2] Japanese Patent Application Publication No. 2018-35225 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even the methods of increasing thermal stability by introducing a chain transfer agent into the molecular terminals, such as those described in Patent Documents 1 and 2, have not been able to sufficiently increase the thermal decomposition temperature. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a (meth)acrylic resin that exhibits a higher thermal decomposition temperature. [Means for solving the problem]

[0006] As a result of extensive research to solve the above problems, the present inventors have found that the thermal decomposition temperature can be further increased by continuously adding both a chain transfer agent and a polymerization initiator to a (meth)acrylic monomer and maximizing the ratio of the chain transfer agent / polymerization initiator addition amounts at an appropriate stage during the progress of the reaction, and have thus completed the present invention. That is, the present invention is defined by the following constituent features. [1] A (meth)acrylic resin having a sulfur terminal ratio calculated by the following formula of 30 mol% or more and a thermal decomposition temperature of 335°C or more. Sulfur terminal fraction (mol%) = (Sx / 32) × Mn (In the formula, Sx represents the sulfur content (mass%) in the (meth)acrylic resin, and Mn represents the number average molecular weight of the (meth)acrylic resin.) [2] The (meth)acrylic resin according to [1], wherein the proportion of terminal double bonds is 6 mol % or less. [3] The (meth)acrylic resin according to [1] or [2], which has a weight average molecular weight Mw of 100,000 or more. [4] The (meth)acrylic resin according to [1], wherein the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) is 2.1 or more. [5] The (meth)acrylic resin according to any one of [1] to [4], wherein the proportion of terminal sulfur groups is 70 mol % or less. [6] The (meth)acrylic resin according to any one of [1] to [5], which has a glass transition temperature of 110° C. or higher. [7] The (meth)acrylic resin according to any one of [1] to [6], which contains 65% by mass or more of units derived from methacrylic acid esters and generates 8000 ppm or less of methacrylic acid esters after heating at a temperature of 290°C for 10 minutes. [8] The (meth)acrylic resin according to any one of [1] to [7], which has a ring structure in the main chain. [9] A method for polymerizing a (meth)acrylic monomer while continuously adding a chain transfer agent and a polymerization initiator to the (meth)acrylic monomer, A method for producing a (meth)acrylic resin having an addition ratio (addition ratio A) of chain transfer agent / polymerization initiator at a maximum (by mass) while the conversion rate of the (meth)acrylic monomer is 10% by mass or more but less than 60% by mass.

[10] The method for producing a (meth)acrylic resin according to [9], wherein the addition amount ratio A is 1.1 to 2.0 times the addition amount ratio B (by mass) of the chain transfer agent / polymerization initiator after all of the chain transfer agent and polymerization initiator have been added.

[11] A molded article comprising the (meth)acrylic resin according to any one of [1] to [8].

[12] An optical member comprising the (meth)acrylic resin according to any one of [1] to [8].

[13] The molded article according to

[11] , which is in the form of a film or a lens. [Effects of the Invention]

[0007] According to the present invention, the thermal decomposition temperature of the (meth)acrylic resin can be further improved. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a graph showing the relationship between the ratio of the amount of chain transfer agent / polymerization initiator added and the polymerization time in Examples 1 and 2 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] In this specification, the term "resin" refers to a broader concept than polymer. A resin may contain one or more polymers, and may further contain materials other than polymers, such as additives such as ultraviolet absorbers, antioxidants, fillers, compatibilizers, and stabilizers, as necessary. 1. (Meth)acrylic resin 1.1 Building Blocks The (meth)acrylic resin refers to a resin composition composed of a (meth)acrylic polymer having (meth)acrylic acid, a (meth)acrylic acid ester, or a derivative thereof (hereinafter, these may be collectively referred to as a (meth)acrylic monomer) as a monomer unit. Examples of the (meth)acrylic acid ester include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate (preferably methacrylic acid C). 1-10 alkyl); (meth)acrylate aralkyl such as benzyl (meth)acrylate (preferably methacrylic acid C 2-20 aralkyl); esters of (meth)acrylic acid with hydroxy cyclic saturated hydrocarbons (preferably hydroxy cyclic saturated hydrocarbons having 5 to 20 carbon atoms), such as cyclohexyl (meth)acrylate and dicyclopentanyl (meth)acrylate.

[0010] Examples of the (meth)acrylic acid ester derivatives include derivatives having a hydroxy group introduced therein, such as hydroxyalkyl (meth)acrylates (preferably hydroxy (meth)acrylic acid C) such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, and 2,3,4,5-tetrahydroxypentyl (meth)acrylate. 1-20 alkyl; α-(1-hydroxyalkyl) alkyl acrylate (preferably α-(1-hydroxy C 1-20 Alkyl)acrylic acid C 1-20 alkyl), etc. 1-20 Alkyl)acrylic acid C 1-20 Alkyl includes α-(hydroxymethyl)acrylic acid C such as methyl α-(hydroxymethyl)acrylate, ethyl α-(hydroxymethyl)acrylate, isopropyl α-(hydroxymethyl)acrylate, n-butyl α-(hydroxymethyl)acrylate, and t-butyl α-(hydroxymethyl)acrylate. 1-20 Alkyl; α-(1-hydroxy C) such as methyl α-(1-hydroxyethyl)acrylate 2-20 Alkyl)acrylic acid C 1-20 Alkyl and the like are included.

[0011] In addition, (meth)acrylic acid ester derivatives include β-C methyl crotonate. 1-10 Alkyl acrylic acid C 1-10 Alkyl; halogen-introduced derivatives such as chloromethyl (meth)acrylate and 2-chloroethyl (meth)acrylate; and ether-bond-introduced derivatives such as dicyclopentanyloxyethyl (meth)acrylate.

[0012] Examples of the (meth)acrylic acid derivatives include compounds obtained by hydrolyzing the ester bond of the methacrylic acid ester derivatives, such as crotonic acid, α-(hydroxymethyl)acrylic acid, 2-(1-hydroxyethyl)acrylic acid, and other α-hydroxyalkylacrylic acids. The (meth)acrylic monomer may be a single monomer or a combination of two or more monomers. Among the (meth)acrylic monomers, it is preferable to contain (meth)acrylic acid or a (meth)acrylic acid ester as an essential unit, and it is preferable to contain a (meth)acrylic acid alkyl ester (particularly a methacrylic acid ester such as methyl methacrylate) as an essential unit. The proportion of the essential units in the (meth)acrylic polymer is, for example, 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and most preferably 70% by mass or more, and for example, 100% by mass or less, preferably 90% by mass or less, more preferably 85% by mass or less, and particularly preferably 80% by mass or less. The proportion of the (meth)acrylic monomer units does not include units derived from the (meth)acrylic monomer that have become different units after polymerization through a cyclization reaction, as described below, or the like.

[0013] The (meth)acrylic polymer may have a structural unit introduced by copolymerizing the (meth)acrylic monomer with another monomer. Examples of such other monomers include styrene-based monomers such as styrene, vinyltoluene, α-methylstyrene, α-hydroxymethylstyrene, and α-hydroxyethylstyrene; nitrogen-containing heterocyclic vinyl compounds such as N-vinylpyrrolidone and N-vinylcarbazole; vinyl nitriles such as acrylonitrile and methacrylonitrile; vinyl alcohols such as methallyl alcohol and allyl alcohol; olefins such as ethylene, propylene, and 4-methyl-1-pentene; vinyl acetate, 2-hydroxymethyl-1-butene, and methyl vinyl ketone. Styrenic monomers and nitrogen-containing heterocyclic vinyl compounds are preferred, and styrene-based monomers are more preferred. These other monomers (structural units) may be present alone or in combination. The content of other monomers (structural units) in the (meth)acrylic polymer is, for example, 0% by mass or more, preferably 1% by mass or more, and for example, 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0014] The total proportion of structural units derived from (meth)acrylic monomers (i.e., structural units derived from (meth)acrylic acid ester units, (meth)acrylic acid units, and derivatives thereof) in all structural units of the (meth)acrylic polymer is, from the viewpoint of transparency of the molded article, preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. There is no particular upper limit, and it is most preferably 100% by mass.

[0015] The (meth)acrylic polymer also preferably has a ring structure in the main chain. By having a ring structure in the main chain, the thermal decomposition temperature of the (meth)acrylic resin can be further increased. Examples of the main chain ring structure include a lactone ring structure, a glutaric anhydride structure, a glutarimide structure, a structure derived from maleic anhydride, and a structure derived from N-substituted maleimide. Furthermore, when the resin is used as an optical component, optical components with excellent optical properties can be obtained; therefore, a lactone ring structure, a glutaric anhydride structure, or a glutarimide structure is preferred, and a lactone ring structure is more preferred. Furthermore, from the viewpoint of moist heat resistance, a lactone ring structure, a glutarimide structure, or a structure derived from N-substituted maleimide is preferred, and a lactone ring structure is more preferred.

[0016] The lactone ring structure is, for example, a 4- to 8-membered ring, preferably a 5- or 6-membered ring, and more preferably a 6-membered ring, due to its excellent stability. Examples of 6-membered lactone ring structures include the structure represented by the following general formula (1):

[0017] [ka]

[0018] In the above general formula (1), R 1 , R 2 and R 3 are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms, and the organic residue may contain an oxygen atom. Examples of the organic residue in general formula (1) include saturated aliphatic hydrocarbon groups (e.g., alkyl groups) having 1 to 20 carbon atoms, such as a methyl group, an ethyl group, or a propyl group; unsaturated aliphatic hydrocarbon groups (e.g., alkenyl groups) having 2 to 20 carbon atoms, such as an ethenyl group or a propenyl group; aromatic hydrocarbon groups (e.g., aryl groups) having 6 to 20 carbon atoms, such as a phenyl group or a naphthyl group; and groups in which one or more hydrogen atoms in these saturated aliphatic hydrocarbon groups, unsaturated aliphatic hydrocarbon groups, or aromatic hydrocarbon groups have been substituted with at least one group selected from a hydroxy group, a carboxyl group, an ether group, and an ester group, with alkyl groups being preferred.

[0019] The lactone ring structure can be formed, for example, by homopolymerizing a hydroxy group-containing (meth)acrylic monomer A such as an α-(1-hydroxyalkyl) alkyl acrylate, or by copolymerizing the hydroxy group-containing (meth)acrylic monomer A with a (meth)acrylic monomer B such as (meth)acrylic acid or a (meth)acrylic acid ester, thereby introducing a hydroxy group and an ester group or a carboxyl group into the molecular chain, and then causing dealcoholization or dehydration cyclocondensation between the hydroxy group and the ester group or the carboxyl group.

[0020] When the (meth)acrylic polymer has a lactone ring structure in the main chain, the content of the lactone ring structure in the polymer is, for example, 1 to 70 mass%, preferably 5 to 50 mass%, and more preferably 10 to 30 mass%. According to the present invention, even when the content of the lactone ring structure in the polymer is 25 mass% or less, or even 20 mass% or less, the thermal decomposition temperature of the (meth)acrylic resin can be further improved.

[0021] The content of the lactone ring structure in the (meth)acrylic polymer can be calculated from the copolymerization amount of the monomers involved in lactone cyclization (hydroxy group-containing (meth)acrylic monomer A and (meth)acrylic monomer B) and the lactone cyclization rate using the following formula: Lactone ring structure content (mass%) = Z1 × Z2 × M R / M m (wherein Z1 is the mass content of structural units derived from raw material monomers involved in lactone cyclization (hydroxy group-containing (meth)acrylic monomer A and (meth)acrylic monomer B) in the polymer before lactone cyclization, and M R is the formula weight of the resulting lactone ring structural unit (meaning the total formula weight of the lactone ring-forming elements and groups other than the main chain bonded to the lactone ring), and M m is the molecular weight (total) of the raw material monomers involved in lactone cyclization (hydroxy group-containing (meth)acrylic monomer A and (meth)acrylic monomer B), and Z2 is the lactone cyclization rate.

[0022] The content of the lactone ring structure in the (meth)acrylic polymer can be determined by a known method, for example, nuclear magnetic resonance ( 1 This can be evaluated by H-NMR and / or infrared spectroscopy (IR).

[0023] The glutaric anhydride structure or the glutarimide structure may be, for example, a structure represented by the following general formula (2) (in the following general formula (2), X 1 When X is an oxygen atom, it becomes a glutaric anhydride structure, and 1 is a nitrogen atom, it becomes a glutarimide structure).

[0024] [ka]

[0025] R in the above general formula (2) 4 , R 5 are each independently a hydrogen atom or a methyl group, and X 1 is an oxygen atom or a nitrogen atom. X 1 is an oxygen atom, R 6 does not exist, and X 1 When is a nitrogen atom, R 6 is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms (methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group), a cyclopentyl group, a cyclohexyl group, or a phenyl group.

[0026] X in the above general formula (2) 1 A glutaric anhydride structure in which is an oxygen atom can be formed, for example, by intramolecular dealcoholization cyclocondensation of a copolymer of a (meth)acrylic acid ester and (meth)acrylic acid. X in the above general formula (2) 1 A glutarimide structure in which is a nitrogen atom can be formed, for example, by imidizing a (meth)acrylic acid ester polymer with an imidizing agent such as methylamine.

[0027] When the (meth)acrylic polymer has a glutaric anhydride structure or a glutarimide structure in the main chain, the content of the glutaric anhydride structure or the glutarimide structure in the polymer is, for example, 1 to 70 mass%, preferably 5 to 50 mass%, more preferably 10 to 30 mass%. The content of the glutaric anhydride structure and the glutarimide structure in the (meth)acrylic polymer can be determined, for example, by the method described in JP-A-2006-131689.

[0028] Examples of the structure derived from maleic anhydride or the structure derived from N-substituted maleimide include a structure represented by the following general formula (3) (in the following general formula (3), X 2 When X is an oxygen atom, the structure is derived from maleic anhydride, 2 is a nitrogen atom, the structure is derived from an N-substituted maleimide).

[0029] [ka]

[0030] R in the above general formula (3) 7 , R 8 are each independently a hydrogen atom or a methyl group, and X 2 is an oxygen atom or a nitrogen atom. X 2 is an oxygen atom, R 9 does not exist, and X2 When is a nitrogen atom, R 9 is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms (methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group), cyclopentyl group, cyclohexyl group, benzyl group, or phenyl group.

[0031] X in the above general formula (3) 2 The structure derived from maleic anhydride in which is an oxygen atom can be introduced, for example, by copolymerizing maleic anhydride with a (meth)acrylic monomer. X in the above general formula (3) 2 A structure derived from an N-substituted maleimide in which is a nitrogen atom can be introduced, for example, by copolymerizing an N-substituted maleimide such as phenylmaleimide with a (meth)acrylic monomer.

[0032] When the (meth)acrylic polymer has a structure derived from maleic anhydride or a structure derived from N-substituted maleimide in the main chain, the content of the structure derived from maleic anhydride or the structure derived from N-substituted maleimide in the polymer is, for example, 1 to 70 mass%, preferably 5 to 50 mass%, and more preferably 10 to 30 mass%.

[0033] The (meth)acrylic resin in the present invention may contain a polymer other than a (meth)acrylic polymer. Examples of such a polymer include olefin polymers such as polyethylene, polypropylene, ethylene-propylene polymer, and poly(4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl resin; styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, and acrylonitrile-butadiene-styrene copolymer; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyamides such as nylon 6, nylon 66, and nylon 610; polyacetal; polycarbonate; polyphenylene oxide; polyphenylene sulfide; polyether ether ketone; polysulfone; polyethersulfone; polyoxybenzylene; polyamide imide; cycloolefin polymers; cellulose derivatives; and rubbery polymers such as polybutadiene rubber and ABS resin or ASA resin blended with (meth)acrylic rubber. The amount of the (meth)acrylic polymer is, for example, 50 parts by mass or more, preferably 70 parts by mass or more, more preferably 90 parts by mass or more, and even more preferably 95 parts by mass or more, relative to 100 parts by mass of the total of the (meth)acrylic polymer and the polymer other than the (meth)acrylic polymer, and may be 100 parts by mass.

[0034] The (meth)acrylic resin of the present invention may contain various additives as long as they do not impair the effects of the present invention. Examples of additives include ultraviolet absorbers; antioxidants such as phenolic, phosphorus, and sulfur-based; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fiber and carbon fiber; near-infrared absorbers; flame retardants such as tris(dibromopropyl)phosphate, triallyl phosphate, and antimony oxide; retardation adjusters such as retardation increasers, retardation decreasers, and retardation stabilizers; antistatic agents including anionic, cationic, and nonionic surfactants; compatibilizers; stabilizers; colorants such as inorganic pigments, organic pigments, and dyes; organic and inorganic fillers; resin modifiers; and organic and inorganic fillers. The content of each additive in 100% by mass of the solids content of the resin composition is preferably 0 to 5% by mass, more preferably 0 to 2% by mass.

[0035] Examples of UV absorbers include benzophenone compounds, salicylate compounds, benzoate compounds, triazole compounds, and triazine compounds, and known UV absorbers can be used. Examples of benzophenone compounds include 2,4-dihydroxybenzophenone, 4-n-octyloxy-2-hydroxybenzophenone, and 2,2'-dihydroxy-4,4'-dimethoxybenzophenone. Examples of salicylate compounds include pt-butylphenyl salicylate. Examples of benzoate compounds include 2,4-di-t-butylphenyl-3',5'-di-t-butyl-4'-hydroxybenzoate. Examples of triazole compounds include 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(2H-benzotriazol-2-yl)-p-cresol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2-benzotriazol-2-yl-4,6-di-tert-butylphenol, 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-t-butylphenol, 2-(2H-benzotriazol-2-yl)-4,6-di-t-butylphenol, and 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol. Examples of triazine compounds include 2-[4,6-bis(biphenyl-4-yl)-1,3,6-triad-2-yl]-5-[(2-ethylhexyl)oxy]phenol, 2-mono(hydroxyphenyl)-1,3,5-triazine compounds, 2,4-bis(hydroxyphenyl)-1,3,5-triazine compounds, and 2,4,6-tris(hydroxyphenyl)-1,3,5-triazine compounds.Examples of commercially available ultraviolet absorbers include triazine-based ultraviolet absorbers such as Tinuvin (registered trademark) 1577, Tinuvin (registered trademark) 460, and Tinuvin (registered trademark) 477 (manufactured by BASF Japan Ltd.), and Adekastab (registered trademark) LA-F70 (manufactured by ADEKA Corporation), and triazole-based ultraviolet absorber such as Adekastab (registered trademark) LA-31 (manufactured by ADEKA Corporation). Only one type of ultraviolet absorber may be used, or two or more types may be used in combination.

[0036] 1.2 Characteristics As described below, the (meth)acrylic resin is produced by polymerizing a (meth)acrylic monomer in the presence of a chain transfer agent and a polymerization initiator, and by maximizing the ratio of the chain transfer agent to the polymerization initiator at an appropriate stage during the reaction. The (meth)acrylic resin has a high thermal decomposition temperature. The thermal decomposition temperature is, for example, 335°C or higher, preferably 335.3°C or higher, more preferably 335.5°C or higher, even more preferably 336°C or higher, and most preferably 337°C or higher. While a higher thermal decomposition temperature is preferable, it may be, for example, 350°C or lower, 345°C or lower, or 342°C or lower.

[0037] When the (meth)acrylic resin contains a methacrylic acid ester unit (preferably a methyl methacrylate unit) as an essential unit, the amount of methacrylic acid ester (preferably methyl methacrylate) generated after heating the (meth)acrylic resin in an air atmosphere at 290°C for 10 minutes is, for example, 8000 ppm or less, preferably 3000 ppm or less, more preferably 1500 ppm or less, and particularly preferably 1300 ppm or less. Reducing the amount of methacrylic acid ester generated can reduce foaming during melt molding and contamination of the molding machine, and can prevent poor appearance of molded articles. The lower the amount of methacrylic acid ester generated, the better, but it may be, for example, 100 ppm or more, 500 ppm or more, or 1000 ppm or more.

[0038] The thermal decomposition temperature of the (meth)acrylic resin is improved by introducing sulfur atoms derived from the chain transfer agent into the molecular terminals, reducing the proportion of terminal double bonds and suppressing depolymerization. The sulfur terminal proportion of the (meth)acrylic resin is defined by the following formula, and its value is, for example, 30 mol% or more, preferably 40 mol% or more, and more preferably 45 mol% or more. The sulfur terminal proportion may be 100 mol%, but is preferably 80 mol% or less, more preferably 70 mol% or less, even more preferably 60 mol% or less, and particularly preferably 50 mol% or less. Reducing the sulfur terminal proportion in turn reduces the amount of chain transfer agent used, thereby suppressing odor. Furthermore, it can suppress a decrease in the molecular weight of the (meth)acrylic resin, thereby increasing resin strength, reducing the burden of removing unreacted chain transfer agent, and preventing a decrease in the conversion rate of the polymerization reaction. Sulfur terminal fraction (mol%) = (Sx / 32) × Mn (In the formula, Sx represents the sulfur content (mass%) in the (meth)acrylic resin, and Mn represents the number average molecular weight of the (meth)acrylic resin.)

[0039] The proportion of terminal double bonds in the (meth)acrylic resin is, for example, 6 mol% or less, preferably 5 mol% or less. A lower proportion of terminal double bonds can prevent thermal decomposition of the (meth)acrylic resin. The lower the proportion of terminal double bonds, the better, but it may be, for example, 1 mol% or more, 2 mol% or more, or 3 mol% or more.

[0040] The weight-average molecular weight Mw of the (meth)acrylic resin is, for example, 100,000 or more, preferably 120,000 or more, and more preferably 135,000 or more. The use of a chain transfer agent tends to decrease the weight-average molecular weight Mw, but in the present invention, the chain transfer agent is used according to a specific method, so that decrease in the weight-average molecular weight can be prevented. The higher the weight-average molecular weight, the higher the resin strength. The weight-average molecular weight Mw is, for example, 300,000 or less, preferably 250,000 or less, and more preferably 200,000 or less.

[0041] The molecular weight distribution of the (meth)acrylic resin (Mw / Mn; Mw represents the weight-average molecular weight of the (meth)acrylic resin, and Mn represents the number-average molecular weight of the (meth)acrylic resin) is, for example, 2.1 or more, preferably 2.3 or more, and more preferably 2.5 or more. The larger the molecular weight distribution, the more fluidity can be maintained during molding even if the weight-average molecular weight is high (even if the resin strength is high), and both strength and moldability can be achieved. The molecular weight distribution is, for example, 3.5 or less, preferably 3.2 or less, and more preferably 3.0 or less.

[0042] The glass transition temperature of the (meth)acrylic resin is, for example, 110°C or higher, or may be 115°C or higher, or may be 120°C or higher. The higher the glass transition temperature, the better the stability of the dimensions and optical properties of the molded product under high humidity and heat. Furthermore, the higher the glass transition temperature, the higher the molding temperature. However, in the present invention, since the thermal decomposition temperature is improved, molding can be performed even at high temperatures without risk of decomposition. The glass transition temperature is, for example, 160°C or lower, preferably 150°C or lower, and more preferably 140°C or lower.

[0043] 2. Method for producing (meth)acrylic resin The (meth)acrylic resin is produced by polymerizing a (meth)acrylic monomer in the presence of a chain transfer agent and a polymerization initiator. 2.1 Chain transfer agents Examples of chain transfer agents include butanethiol, octanethiol, 1-dodecanethiol (also called n-dodecyl mercaptan), octadecanethiol, cyclohexyl mercaptan, thiophenol, octyl thioglycolate, octyl 2-mercaptopropionate, octyl 3-mercaptopropionate, 2-ethylhexyl mercaptopropionate, 2-mercaptoethyl octanoate, 1,8-dimercapto-3,6-dioxaoctane, ethylene glycol bisthioglycolate, trimethylolpropane tristhioglycolate, trimethylolpropane tristhiopropionate, and trimethylolpropane tristhiobutanol. Examples of suitable chain transfer agents include organic thiol compounds such as pentaerythritol tetrakis(thioglycolate), pentaerythritol tetrakis(thiopropionate), pentaerythritol tetrakis(4-mercaptobutanate), pentaerythritol tetrakis(6-mercaptohexanate), and dipentaerythritol hexakis(3-mercaptopropionate); halogen compounds such as carbon tetrachloride, carbon tetrabromide, methylene chloride, bromoform, and bromotrichloroethane; and unsaturated hydrocarbon compounds such as α-methylstyrene dimer, α-terpinene, γ-terpinene, dipentene, and terpinolene. These chain transfer agents may be used alone or in combination of two or more. Among these, organic thiol compounds are preferred because they can suppress a decrease in conversion rate, and organic thiol compounds having a hydrocarbon group with 3 or more carbon atoms, preferably 6 to 20, and more preferably 10 to 20, are preferred because they can reduce odor.

[0044] The amount of the chain transfer agent used is, relative to the total amount of the monomer components, for example, 500 ppm (by mass) or more, preferably 1000 ppm (by mass) or more, more preferably 1200 ppm (by mass) or more, and for example, 3000 ppm (by mass) or less, preferably 2500 ppm (by mass) or less, more preferably 2000 ppm (by mass) or less.

[0045] 2.2 Polymerization initiator Examples of polymerization initiators that can be used include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, dimethyl-2,2'-azobis(2-methylpropionate), and 4,4'-azobis(4-cyanopentanoic acid); persulfates such as potassium persulfate; and organic peroxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexanoate, t-amylperoxyoctoate, t-amylperoxyisononanoate, t-amylperoxyisopropyl carbonate, and t-amylperoxy-2-ethylhexyl carbonate. These may be used alone or in combination of two or more. Among these, it is preferable to use organic peroxides which have a strong hydrogen abstracting power. The amount of the polymerization initiator used is, for example, 500 ppm (by mass) or more, preferably 1000 ppm (by mass) or more, more preferably 1500 ppm (by mass) or more, and for example, 1% by mass or less, preferably 0.6% by mass or less, more preferably 0.4% by mass or less, relative to the total amount of the monomer components.

[0046] 2.3 Addition method The (meth)acrylic resin is preferably produced by a batch polymerization method in which the chain transfer agent and polymerization initiator are added to the (meth)acrylic monomer. Compared to continuous polymerization, batch polymerization can reduce the amount of unreacted chain transfer agent remaining and suppress the odor of the resin. Furthermore, both the chain transfer agent and polymerization initiator are continuously added to the (meth)acrylic monomer. The addition may be continuous or intermittent, such as by divided addition, but is preferably continuous or intermittent at intervals of 10 minutes or less, and more preferably continuous.

[0047] The ratio of the amounts added after the addition of both the chain transfer agent and the polymerization initiator has been completed (chain transfer agent / polymerization initiator; mass ratio) (hereinafter referred to as addition amount ratio B) is, for example, 0.3 or more, preferably 0.5 or more, more preferably 0.55 or more, and for example, 2.0 or less, preferably 1.5 or less, more preferably 1.3 or less, and even more preferably 1.1 or less.

[0048] When the chain transfer agent and polymerization initiator are continuously added, the addition ratio (based on mass) of the chain transfer agent to the polymerization initiator is maximized (hereinafter referred to as addition ratio A) while the conversion rate of the (meth)acrylic monomer is 10% by mass or more but less than 60% by mass. By maximizing the addition ratio of the chain transfer agent to the polymerization initiator while the conversion rate is 10% by mass or more but less than 60% by mass, the thermal decomposition temperature of the (meth)acrylic resin can be further improved. This method also suppresses a decrease in the molecular weight of the (meth)acrylic resin. This method is also advantageous in that it is less likely to cause a decrease in the conversion rate. The addition ratio is the ratio of the mass of all chain transfer agents to the mass of all polymerization initiators added up to that point.

[0049] The chain transfer agent / polymerization initiator addition ratio reaches its maximum when the (meth)acrylic monomer conversion rate is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is preferably 58% by mass or less, more preferably 56% by mass or less. The more appropriate the timing at which the chain transfer agent / polymerization initiator addition ratio reaches its maximum, the more the thermal decomposition temperature of the (meth)acrylic resin increases.

[0050] The addition amount ratio (addition amount ratio A) when the addition amount ratio (mass basis) of the chain transfer agent / polymerization initiator is at its maximum is, for example, 1.1 times or more, preferably 1.2 times or more, and more preferably 1.3 times or more, and for example, 2.5 times or less, preferably 2.0 times or less, and more preferably 1.8 times or less, relative to the addition amount ratio B after the addition is completed.

[0051] The timing for starting the addition of the chain transfer agent and the polymerization initiator is not particularly limited as long as the addition ratio A is achieved at the predetermined timing, and the polymerization initiator may be added later after the addition of the chain transfer agent has started, or the addition of the chain transfer agent may be started later after the addition of the polymerization initiator has started, or the addition of the chain transfer agent and the polymerization initiator may be started at the same timing, or it is preferable that the addition of the chain transfer agent and the polymerization initiator be started at the same timing. The timing for ending the addition of the chain transfer agent and the polymerization initiator is also not particularly limited as long as the addition ratio A is achieved at the predetermined timing, and the addition of the chain transfer agent may be ended first, or the addition of the polymerization initiator may be ended first, or the addition of the chain transfer agent and the polymerization initiator may be ended at the same timing, but it is preferable that the addition of the chain transfer agent be ended first. When the addition of the chain transfer agent and the polymerization initiator is started at the same time and the addition of the chain transfer agent is finished first, the duration of the addition of the chain transfer agent relative to the duration of the addition of the polymerization initiator is, for example, 0.2 or more, preferably 0.3 or more, more preferably 0.4 or more, and for example, 0.65 or less, preferably 0.60 or less, more preferably 0.55 or less.

[0052] The entire amount of the chain transfer agent and / or polymerization initiator may be introduced into the reaction system by addition, or a certain amount may be initially mixed with the (meth)acrylic monomer, and then the chain transfer agent and polymerization initiator may be added to this mixture. Mixing the chain transfer agent and / or polymerization initiator with the (meth)acrylic monomer before the start of polymerization is also referred to as initial charging. The initial amount of chain transfer agent is preferably 30 to 0 parts by mass, preferably 20 to 0 parts by mass, more preferably 10 to 0 parts by mass, and even more preferably 5 to 0 parts by mass, per 100 parts by mass of the total amount of chain transfer agent added. The initial amount of polymerization initiator is 60 to 0 parts by mass, preferably 50 to 10 parts by mass, more preferably 50 to 20 parts by mass, and even more preferably 50 to 30 parts by mass, per 100 parts by mass of the total amount of polymerization initiator added.

[0053] In the polymerization of (meth)acrylic monomers, the total amount of all monomers may be charged from the beginning, or some of the monomers may be added later. When some of the monomers are added later, it is preferable to charge the (meth)acrylic monomers from the beginning and add other monomers that copolymerize with the (meth)acrylic monomers later. It is preferable to start and finish the addition of the monomers added later at the same time as the chain transfer agent.

[0054] After all the monomers, chain transfer agent, and polymerization initiator have been added, aging may be carried out as necessary. Aging further improves the monomer conversion rate. In the aging step, it is preferable to continue stirring at an appropriate temperature, for example, about ±30°C of the polymerization temperature (preferably at the polymerization temperature or above). The aging time is, for example, 0 to 10 hours, preferably about 1 to 5 hours.

[0055] The conversion rate of the monomer at the end of the reaction is, for example, 80% by mass or more, preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 92% by mass or more.

[0056] 2.4 Solvent The polymerization of (meth)acrylic resins can be any of bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization as long as it is batch polymerization, but solution polymerization is preferred. Solvents that can be used in solution polymerization include aromatic hydrocarbon solvents such as toluene, xylene, and ethylbenzene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ether solvents such as tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and anisole; ester solvents such as ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, and 3-methoxybutyl acetate; cellosolve solvents such as methyl cellosolve, ethyl cellosolve, and butyl cellosolve; alcohol solvents such as methanol, ethanol, isopropanol, and n-butanol; nitrile solvents such as acetonitrile, propionitrile, butyronitrile, and benzonitrile; halogenated solvents such as chloroform and dichloromethane; and dimethyl sulfoxide. The polymerization solvent is preferably an aromatic hydrocarbon solvent or a ketone solvent, more preferably an aromatic hydrocarbon solvent, and particularly preferably toluene. These polymerization solvents may be used alone or in combination of two or more.

[0057] The total concentration of the monomers in the polymerization reaction liquid is, for example, 5% by mass or more, preferably 10% by mass or more, more preferably 30% by mass or more, and for example, 90% by mass or less, preferably 80% by mass or less, more preferably 70% by mass or less.

[0058] The polymerization temperature is, for example, at least the 10-hour half-life temperature of the polymerization initiator used, for example, 40°C or higher, preferably 60°C or higher, and more preferably 80°C or higher. The 10-hour half-life temperature refers to the temperature at which the half-life of the polymerization initiator is 10 hours. The polymerization temperature is, for example, at most the reflux temperature of the solvent used, for example, 180°C or lower, preferably 150°C or lower, and more preferably 120°C or lower.

[0059] 2.5 Cyclization process If the polymerized product of the (meth)acrylic monomer after the completion of the reaction contains a hydroxy group-containing (meth)acrylic monomer A unit, it may be cyclized to form a lactone ring structure, if necessary. Furthermore, if the polymerized product of the (meth)acrylic monomer contains a (meth)acrylic acid unit, it may be cyclized to form a glutaric anhydride structure or a glutarimide structure, if necessary. In these ring structure forming steps, the cyclization condensation reaction is preferably carried out in the presence of a catalyst (cyclization catalyst). The cyclization catalyst may be at least one selected from the group consisting of acids, bases, and salts thereof. The acids, bases, and salts thereof may be organic or inorganic, and are not particularly limited. In particular, an organic phosphorus compound is preferably used as the catalyst for the cyclization reaction. Using an organic phosphorus compound as the cyclization catalyst allows the cyclization condensation reaction to be carried out efficiently, and reduces the coloration of the resulting (meth)acrylic resin.

[0060] Examples of organic phosphorus compounds that can be used as cyclization catalysts include alkyl (aryl) phosphonous acids and their monoesters or diesters; dialkyl (aryl) phosphinic acids and their esters; alkyl (aryl) phosphonic acids and their monoesters or diesters; alkyl (aryl) phosphinic acids and their esters; phosphorous monoesters, diesters, or triesters; methyl phosphate, ethyl phosphate, 2-ethylhexyl phosphate, octyl phosphate, isodecyl phosphate, lauryl phosphate, stearyl phosphate, isostearyl phosphate, phenyl phosphate, dimethyl phosphate, phosphorous Examples of suitable phosphate monoesters, diesters, or triesters include diethyl phosphate, di-2-ethylhexyl phosphate, diisodecyl phosphate, dilauryl phosphate, distearyl phosphate, diisostearyl phosphate, diphenyl phosphate, trimethyl phosphate, triethyl phosphate, triisodecyl phosphate, trilauryl phosphate, tristearyl phosphate, triisostearyl phosphate, and triphenyl phosphate; mono-, di-, or tri-alkyl(aryl)phosphines; alkyl(aryl)halogen phosphine; mono-, di-, or tri-alkyl(aryl)phosphine oxide; and tetraalkyl(aryl)phosphonium halides. These may be used alone or in combination. Among these, phosphoric acid monoesters or diesters are particularly preferred due to their high catalytic activity and low colorability. The amount of the cyclization catalyst used is preferably 0.001 to 1 part by mass per 100 parts by mass of the polymer obtained in the polymerization step.

[0061] The reaction temperature in the cyclization step is, for example, 50°C to 300°C, and the reaction time is, for example, about 5 minutes to 6 hours. The cyclization step is preferably carried out in a reaction vessel in which a polymerization reaction is carried out, and furthermore, the cyclization step is preferably carried out in an autoclave, a shell-and-tube heat exchanger, or the like. After the cyclization step, the solvent is preferably removed by reducing the pressure at a temperature of about 200 to 350°C and a reduced pressure of 13.3 hPa or more (for example, about 13.3 to 800 hPa) using a vacuum dryer, a twin-screw extruder, or the like.

[0062] When a twin-screw extruder is used for devolatilization, the extruder preferably has a cylinder and a screw provided within the cylinder, and is equipped with a heating means. The cylinder is preferably provided with one or more vents, and the vents are more preferably provided at least downstream of the raw material input section with respect to the transport direction within the extruder, and may also be provided upstream of the raw material input section. A die is preferably provided downstream of the extruder, and the polymer can be extruded from the die to be molded into a predetermined shape (film or rod). In addition, a polymer filter is preferably provided in the die section of the extruder.

[0063] 3. Molded body The (meth)acrylic resin can be molded into various forms and used as various products or parts. The shape of the molded product can be appropriately set depending on the application, and examples include plate-like, granular, powder-like, block-like, particle aggregate-like, spherical, ellipsoidal, lenticular, cubic, columnar, rod-like, conical, cylindrical, needle-like, fibrous, hollow fiber-like, and porous shapes. These (meth)acrylic resin molded products can be produced, for example, by a process of thermally fusing (meth)acrylic resin particles, such as injection molding, extrusion molding, or blow molding, or by further subjecting the primary molded product to secondary molding (vacuum molding, compression molding, etc.). The shape of the (meth)acrylic resin particles is preferably, for example, powder having a particle diameter of 1 μm to 1000 μm, cylindrical or spherical pellets having a major axis of about 1 mm to 10 mm, or a mixture thereof. The (meth)acrylic resin particles may be further formed into a film. The film can be used for any purpose, including optical components. Examples of optical components include polarizer protective films, retardation films, viewing angle compensation films, light diffusion films, reflective films, antireflection films, antiglare films, brightness enhancement films, and conductive films for touch panels. [Example]

[0064] The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to the following experimental examples, and it is of course possible to carry out the present invention with appropriate modifications within the scope of the above and below-mentioned aims, and all such modifications are included within the technical scope of the present invention. In the following experimental examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

[0065] First, the measurement methods employed in the following experimental examples will be described. (1) Conversion rate The conversion rate (polymerization rate) (mass%) during the polymerization reaction was calculated from the formula (1) by measuring the concentration (mass%) of unreacted monomer in the obtained polymerization solution using gas chromatography (manufactured by Shimadzu Corporation, apparatus name: GC17A). Conversion rate (polymerization rate) = 100 × (1 - M1 / M0) ... (1) In the formula, M1 represents the concentration (mass%) of unreacted monomer in the polymerization solution, and M0 represents the concentration (mass%) of monomer in the charged raw material solution.

[0066] (2) Weight average molecular weight, number average molecular weight, molecular weight distribution The weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the (meth)acrylic resin in the polymerization solution and after polymerization were determined in terms of polystyrene using gel permeation chromatography (GPC). The apparatus and conditions used for the measurements are as follows: Measurement system: Tosoh GPC system HLC-8220 Measurement column configuration: Guard column (Tosoh, TSK guardcolumn SuperHZ-L) Separation columns (Tosoh, TSK Gel Super HZM-M), two connected in series Reference column configuration: Reference column (Tosoh, TSK gel SuperH-RC) Developing solvent: chloroform (Wako Pure Chemical Industries, special grade) Developing solvent flow rate: 0.6 mL / min Standard sample: TSK standard polystyrene (Tosoh, PS-oligomer kit)

[0067] (3) Sulfur terminal fraction (mol%) The proportion (mol %) of sulfur terminal groups in the (meth)acrylic resin was calculated by the following method. Sample preparation: Three parts of the resin was dissolved in 30 parts of acetone, and the resulting solution was added dropwise to 300 parts of hexane to obtain a precipitate. Next, the precipitate was filtered and dried to obtain a powdery polymer, which was then dissolved in 2-butanone to obtain a sample solution. Measurements and calculations: The sulfur content (Sx; mass%) of the resin was measured using an ICP atomic emission spectrometer (iCAP6500 Duo, manufactured by Thermo Fisher Scientific) for the obtained sample solution, and calculated using formula (2). The sulfur terminal percentage of the polymer refers to the ratio of the number of sulfur-bonded terminals to the number of polymer molecules; for example, if 100 sulfur atoms are bonded to 100 polymer molecules, the sulfur terminal percentage of the polymer is 100 mol%. Sulfur terminal fraction (mol%) = (Sx / 32) × Mn ... (2) (In the formula, Mn represents the number average molecular weight of the (meth)acrylic resin.)

[0068] (4) Terminal double bond ratio The proportion (mol %) of terminal double bonds in the (meth)acrylic resin was calculated by the following method. Sample preparation: Three parts of the resin were dissolved in 30 parts of acetone, and the resulting solution was added dropwise to 300 parts of hexane to obtain a precipitate. Next, the precipitate was filtered and dried to obtain a powdery polymer, which was then dissolved in deuterated dimethyl sulfoxide to a concentration of 10% by mass to obtain a sample solution. Measurements and calculations: The obtained sample solution was analyzed using Agilent's "VNMRS600". 1H-NMR was measured, and the proportion of terminal double bonds was calculated based on the following formula (3). In the formula, D1 and D2 represent the sum of the integrated intensities of the terminal double bonds (resonance frequencies 5.6 ppm and 6.1 ppm) in the NMR chart obtained by integrating for 3 to 4 hours (D1), and the integrated intensity of the methoxy group (resonance frequency 3.6 ppm) in the polymer main chain (D2), respectively. Mn represents the number-average molecular weight of the (meth)acrylic resin, Nm represents the molar composition ratio (mol%) of the monomer having a methoxy group in the copolymer, Mpx represents the molecular weight (Mp) of the monomer x unit constituting the copolymer, Npx represents the molar composition ratio (Np; mol%) of the monomer x in the copolymer, and ΣMpxNpx represents the sum of the values ​​obtained by multiplying Mp and Np calculated for each monomer by changing monomer x to monomer 1 (x = 1), monomer 2 (x = 2), etc. Terminal double bond ratio (mol%) = 3 / 2 × D1 / D2 × Mn × Nm / (ΣMpxNpx) × 100 … (3) For example, in the case of the polymer of the example, the molecular weight (Mpx) / molar composition ratio (Npx) of each monomer x is 100.12 / 85.1 mol% for methyl methacrylate, 84.07 / 10.5 mol% for units formed by elimination of methanol from 2-(hydroxymethyl)methyl acrylate through lactone cyclization, and 104.15 / 4.4 mol% for styrene (St), and Nm and ΣMpxNpx are as follows. Nm=85.1+10.5=95.6 ΣMpxNpx=100.12×85.1+84.07×10.5 +104.15×4.4=9860.59 The terminal double bond ratio of a polymer refers to the ratio of the number of terminal double bonds to the number of polymer molecules. For example, if 100 of 200 molecular ends of 100 polymer molecules are double bonds, the terminal double bond ratio of the polymer is 100%.

[0069] (5) Thermal decomposition temperature The thermal decomposition temperature (Td) of the (meth)acrylic resin was analyzed by the following method (dynamic TG method). Measurement equipment: Differential thermobalance (Rigaku Corporation, ThermoPlus2 TG-8120, Dynamic TG) Measurement conditions: sample amount 10 mg Heating rate: 10°C / min Atmosphere: Nitrogen flow 200 mL / min method: The temperature was raised using a stepwise isothermal control method (controlling the mass loss rate to 0.005% / sec or less within the range from 150°C to 500°C), and the temperature at which the temperature was first raised using stepwise isothermal control to maintain the mass loss rate (the lowest temperature in the range raised using stepwise isothermal control) was defined as the Td of the (meth)acrylic resin.

[0070] (6) Amount of methyl methacrylate (MMA) generated The MMA monomer content (X0) of the (meth)acrylic resin and the MMA monomer content (X1) of the strand obtained by heating at 290°C for 10 minutes in an air atmosphere using a melt flow rate measuring device were each measured using gas chromatography (Shimadzu Corporation, device name: GC17A) to determine the amount of MMA monomer increased by heating and retention (X1 - X0). The gas chromatography measurement conditions were the same as when determining the conversion rate (polymerization rate).

[0071] (7) Glass transition temperature The glass transition temperature (Tg) of the (meth)acrylic resin was determined by the initial point method in accordance with JIS K7121. Specifically, a differential scanning calorimeter (Rigaku Corporation, Thermo plus EVO DSC-8230) was used to measure the glass transition temperature (Tg) of approximately 10 mg of a sample, heated from room temperature to 200°C (heating rate: 20°C / min) under a nitrogen gas flow (100 ml / min). α-Alumina was used as a reference.

[0072] Example 1 A reactor equipped with a stirrer, temperature sensor, cooling condenser, and nitrogen inlet tube was charged with 83.5 parts of methyl methacrylate (MMA), 12 parts of 2-(hydroxymethyl)methyl acrylate (MHMA; also known as α-(hydroxymethyl)methyl acrylate), and 88.7 parts of toluene. The mixture was heated to 105°C while nitrogen was passed through. When refluxing began, 0.435 parts of a 20 wt% toluene solution of t-amyl peroxyisononanoate (Luperox® 570T20, manufactured by Arkema Yoshitomi Co., Ltd.) was added as a polymerization initiator. Subsequently, 4.5 parts of styrene (St) and 0.15 parts of n-dodecyl mercaptan (nDM) were added dropwise over 2 hours. 0.865 parts of a 20 wt% toluene solution of t-amyl peroxyisononanoate was added dropwise over 4 hours. During the dropwise addition of St, nDM, and t-amyl peroxyisonanoate, the mixture was refluxed at approximately 105-110°C to allow solution polymerization to proceed. After the dropwise addition was completed, the mixture was aged for an additional 2 hours at the same temperature. Portions of the polymerization solution were sampled and evaluated for the conversion rates at the end of the nDM dropwise addition (2 hours after the start of polymerization) and at the end of polymerization (6 hours after the start of polymerization). These were 55.3% by mass and 93.5% by mass, respectively. The change over time in the ratio of the chain transfer agent to the initiator added is shown in Figure 1.

[0073] Next, 0.075 parts of stearyl phosphate (Phoslex A-18, manufactured by SC Organic Chemical Co., Ltd.) was added to the resulting polymerization solution (hereinafter also referred to as polymerization solution A) as a catalyst for the cyclization condensation reaction (cyclization catalyst), and the cyclization condensation reaction to form a lactone ring structure was carried out for 2 hours under reflux at approximately 90 to 110°C. The polymerization solution after the cyclization condensation reaction was then placed in an autoclave and heated at 240°C for 1.5 hours to complete the cyclization condensation reaction. The solution was then dried under vacuum at 240°C for 1 hour to remove the solvent, yielding (meth)acrylic resin (A-1). The physical properties of the resulting (meth)acrylic resin (A-1) are shown in Table 1.

[0074] Example 2 Polymerization and aging were carried out in the same manner as in Example 1, except that the polymerization initiator added at the start of polymerization was 0.360 parts of a 20 wt% toluene solution of t-amyl peroxyisononanoate, and the polymerization initiator added dropwise was 0.715 parts of a 20 wt% toluene solution of t-amyl peroxyisononanoate. The conversion rates at the end of the nDM addition (2 hours after the start of polymerization) and at the end of polymerization (6 hours after the start of polymerization) were 53.6% by mass and 92.8% by mass, respectively. The change in the chain transfer agent / initiator ratio over time is shown in Figure 1. Thereafter, a (meth)acrylic resin (A-2) was obtained in the same manner as in Example 1. The physical properties of the obtained (meth)acrylic resin (A-2) are shown in Table 1.

[0075] Comparative Example 1 A reactor equipped with a stirrer, temperature sensor, cooling condenser, and nitrogen inlet tube was charged with 83.5 parts of MMA, 12 parts of MHMA, 90.4 parts of toluene, 0.05 parts of tris(2,4-di-t-butylphenyl)phosphite, and 0.07 parts of nDM. Nitrogen was introduced into the reactor, and the pressure inside the reactor was maintained at a constant range. The temperature was raised to 105°C. When refluxing began, 0.435 parts of the above 20 wt% t-amyl peroxyisononanoate toluene solution (Arkema Yoshitomi Co., Ltd.: Luperox® 570T20) was added as a polymerization initiator. Subsequently, 0.865 parts of the 20 wt% t-amyl peroxyisononanoate toluene solution and 4.5 parts of St were added dropwise over 2 hours, while solution polymerization was allowed to proceed under reflux at approximately 105-110°C. After the dropwise addition, the mixture was aged for an additional 4 hours at the same temperature. The reaction rate (conversion rate) at 2 hours after the start of polymerization and at the end of polymerization (6 hours after the start of polymerization) was 62.1% by mass and 95.4% by mass, respectively. The change in the chain transfer agent / initiator ratio over time is shown in Figure 1. Thereafter, a (meth)acrylic resin (A-3) was obtained in the same manner as in Example 1. The physical properties of the obtained (meth)acrylic resin (A-3) are shown in Table 1.

[0076] [Table 1]

[0077] Example 3 To the polymerization solution A obtained in the same manner as in Example 1, 0.075 parts of stearyl phosphate (Phoslex A-18 manufactured by SC Organic Chemical Co., Ltd.) was added as a catalyst for the cyclization condensation reaction (cyclization catalyst), and the cyclization condensation reaction to form a lactone ring structure was allowed to proceed for 2 hours under reflux at approximately 90 to 110°C. The polymerization solution that had undergone the cyclization condensation reaction was then passed through a multi-tube heat exchanger heated to 240°C to complete the cyclization condensation reaction. Devolatilization was then carried out using a vent-type twin-screw extruder (L / D = 52) with a barrel temperature of 250°C, one rear vent and four fore vents (referred to as the first, second, third, and fourth vents from the upstream side), and a leaf disk-type polymer filter (filtration accuracy 5 μm) at the tip. At that time, the polymerization solution after the completion of the cyclization condensation reaction was introduced at a treatment rate of 100 parts / hour in terms of the amount of resin, and ion-exchanged water was introduced at a rate of 1.5 parts / hour from the upstream of the second and fourth vents, and a toluene solution containing 35% by mass of an ultraviolet absorber (ADEKA CORPORATION: ADK STAB (registered trademark) LA-F70) was introduced at a rate of 1.92 parts / hour from the upstream of the third vent. After devolatilization was complete, the resin remaining in the extruder in a molten state was discharged from the tip of the extruder while being filtered through a polymer filter. The resin then passed through a die attached to the tip of the extruder and cooled in a water tank filled with cooling water maintained at a temperature within the range of 30±10°C, yielding a (meth)acrylic resin strand. The cooling water was filtered through a filter with a pore size of 1 μm (Micropore Filter 1EU, manufactured by Organo Corporation). The cooled strand was then introduced into a cutter (pelletizer) to obtain pellets of (meth)acrylic resin (A-4). The physical properties of the resulting (meth)acrylic resin (A-4) are shown in Table 2. [Table 2] [Industrial Applicability]

[0078] The (meth)acrylic resin of the present invention has excellent resistance to thermal decomposition and can be used for any purpose including optical components.

Claims

1. A (meth)acrylic resin having a ring structure in its main chain and a sulfur atom derived from a chain transfer agent at a molecular end, the proportion of sulfur terminals calculated by the following formula being 30 mol % or more. Sulfur terminal ratio (mol%) = (Sx / 32) × Mn (In the formula, Sx represents the sulfur content (mass%) in the (meth)acrylic resin, and Mn represents the number average molecular weight of the (meth)acrylic resin.)

2. 2. The (meth)acrylic resin according to claim 1, wherein the proportion of terminal double bonds is 6 mol % or less.

3. 3. The (meth)acrylic resin according to claim 1, which has a weight average molecular weight Mw of 100,000 or more.

4. 4. The (meth)acrylic resin according to claim 1, wherein the ratio of weight average molecular weight Mw to number average molecular weight Mn (Mw / Mn) is 2.1 or more.

5. The (meth)acrylic resin according to any one of claims 1 to 4, wherein the proportion of terminal sulfur groups is 70 mol% or less.

6. The (meth)acrylic resin according to any one of claims 1 to 5, which has a glass transition temperature of 110°C or higher.

7. The (meth)acrylic resin according to any one of claims 1 to 6, which contains 65% by mass or more of units derived from a methacrylic acid ester, and which generates 8000 ppm or less of a methacrylic acid ester after heating at a temperature of 290°C for 10 minutes.

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