JP7123043B2 - Methacrylic copolymer and molding - Google Patents

Description

The present invention relates to methacrylic copolymers and moldings containing such copolymers.

In general, methacrylic resins are excellent in optical properties such as transparency and weather resistance, so they have been used in various applications such as lighting fixtures, display members for signboards, electronic and electrical members, and medical members. ing. In these applications, in addition to optical properties and weather resistance, thermal decomposition resistance and the like are sometimes required.

Methods for improving physical properties of methacrylic resins include copolymerization of monomers having a specific structure. For example, in Patent Document 1, by copolymerizing with a monomer derived from cycloalkyl methacrylate, there is little coloring, high transparency, low haze, high impact strength, low saturated water absorption, low dimensional It is disclosed that the change is small and a molded article having a good appearance can be obtained.

On the other hand, copolymerization of a monomer having a functional group such as a hydroxyl group is also expected to improve the physical properties of the resin. However, Patent Document 2 discloses that when methyl methacrylate and a monomer having a hydroxyl group are copolymerized, gel is generated during the reaction. I had a problem.

WO2013-161267 Japanese Patent No. 3550152

Therefore, an object of the present invention is to provide a copolymer that is resistant to thermal decomposition, has excellent chemical resistance, and suppresses the occurrence of gel lumps during melt molding by using an appropriate amount of a polymerizable monomer containing a hydroxyl group. be.

According to the present invention, the above objects are achieved by the following aspects.
[1]
A methacrylic copolymer containing 5 to 50% by mass of structural units derived from a monomer represented by the following formula (1) and 50 to 95% by mass of structural units derived from methyl methacrylate.

(In formula (1), R ¹ represents a hydrogen atom or a methyl group; R ² and R ³ each independently represent a linear, branched or cyclic monovalent hydrocarbon group having 1 to 15 carbon atoms; or R ² and R ³ may be bonded to each other to form an aliphatic hydrocarbon ring together with the carbon atoms to which they are bonded.)
[2]
The methacrylic copolymer according to [1], wherein the sum of the number of carbon atoms of R ² and R ³ is 2 to 9 in the monomer represented by formula (1).
[3]
The methacrylic copolymer according to [1] or [2], which has a weight average molecular weight of 40,000 to 300,000.
[4]
The methacrylic copolymer according to any one of [1] to [3], which has a weight average molecular weight/number average molecular weight ratio of 1.01 to 3.0.
[5]
Regarding the ratio Mw/Mn of the weight average molecular weight Mw to the number average molecular weight Mn in terms of polystyrene calculated based on the chromatogram obtained by gel permeation chromatography, the value after heat treatment at 260 ° C. for 1 hour is , which is 1.4 times or less the value before treatment, the methacrylic copolymer according to any one of [1] to [4].
[6]
The copolymer according to any one of [1] to [5], wherein Mw/Mn after heat treatment at 260° C. for 1 hour is 1.2 times or less of the value before treatment.
[7]
A molded article containing 80% by mass or more of the copolymer according to any one of [1] to [6].
[8]
The molded article according to [7], which is a molten molded article.
[9]
The molded article according to [7] or [8], which is a sheet having a thickness of 0.5 mm or more.
[10]
The molded article according to [7] or [8], which is a film having a thickness of 1 μm to 500 μm.

The methacrylic copolymer of the present invention has excellent chemical resistance and suppresses the occurrence of gel spots during melt molding.

The methacrylic copolymer of the present invention (hereinafter sometimes simply referred to as "copolymer") contains a structural unit derived from the monomer represented by formula (1).

The monomer represented by formula (1) has a hydroxyl group and can impart chemical resistance when copolymerized. In addition, an improvement in mechanical strength and an improvement in adhesion to dissimilar materials such as metals can be expected. Having the substituents R ² and R ³ can impart high heat resistance to the resulting copolymer. In addition, the carbon atom at the site where the (meth)acryloyloxymethyl group and hydroxymethyl group are bonded is a quaternary carbon atom due to the substituents R ² and R ³ , and Since it is bound by the heat, detachment due to heating does not easily occur, and it is excellent in thermal decomposition resistance. If the carbon atoms are secondary or tertiary carbon atoms, the thermal decomposition resistance of the obtained copolymer will be lowered, and the molding temperature will be restricted.

(In formula (1), R ¹ represents a hydrogen atom or a methyl group; R ² and R ³ each independently represent a linear, branched or cyclic monovalent hydrocarbon group having 1 to 15 carbon atoms; or R ² and R ³ may be bonded to each other to form an aliphatic hydrocarbon ring together with the carbon atoms to which they are bonded.)

The copolymer of the present invention contains 5 to 50% by mass, preferably 8 to 40% by mass, of structural units derived from the monomer represented by formula (1) relative to the mass of the copolymer. , more preferably 10 to 20% by mass. When the content of the structural unit derived from the monomer represented by formula (1) is within this range, the copolymer of the present invention is excellent in thermal decomposition resistance. In a preferred embodiment of the present invention, the sum of the carbon number of R ² and the number of carbon atoms of R ³ in the monomer represented by formula (1) is preferably 2 to 9.

The monovalent hydrocarbon group represented by R ² and R ³ has 1 to 15 carbon atoms, preferably 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, still more preferably 1 to 6 carbon atoms, and particularly preferably 1 to 4 carbon atoms. be. Specifically, the monovalent hydrocarbon groups having 1 to 15 carbon atoms represented by R ² and R ³ each independently include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group and a sec-butyl group. group, tert-butyl group, amyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclopentylmethyl group, cyclopentylethyl group, cyclopentylbutyl group, cyclohexyl group, cyclohexylmethyl group, cyclohexylethyl group, cyclohexylbutyl group, methylcyclohexylmethyl group, ethylcyclohexylmethyl group, ethylcyclohexylethyl group, bicyclo [2.2.1] heptyl group, bicyclo[2.2.1]heptylmethyl group, bicyclo[2.2.1]heptylethyl group, bicyclo[2.2.1]heptylbutyl group, methylbicyclo[2.2.1]heptylmethyl group, ethylbicyclo[2.2.1]heptylmethyl group, ethylbicyclo[2.2.1]heptylethyl group, bicyclo[2.2.2]octyl group, bicyclo[2.2.2]octylmethyl group , bicyclo[2.2.2]octylethyl group, bicyclo[2.2.2]octylbutyl group, methylbicyclo[2.2.2]octylmethyl group, ethylbicyclo[2.2.2]octylmethyl group , ethylbicyclo[2.2.2]octylethyl group, tricyclo[5.2.1.0 ^2,6 ]decyl group, tricyclo[5.2.1.0 ^2,6 ]decylmethyl group, tricyclo[5. 2.1.0 ^2,6 ]decylethyl group, tricyclo[5.2.1.0 ^2,6 ]decylbutyl group, methyltricyclo[5.2.1.0 ^2,6 ]decylmethyl group, ethyltricyclo[ 5.2.1.0 ^2,6 ]decylmethyl group, ethyltricyclo[5.2.1.0 ^2,6 ]decylethyl group, adamantyl group, adamantylmethyl group, adamantylethyl group, adamantylbutyl group, methyladamantylmethyl group, ethyladamantylmethyl group, ethyladamantylethyl group, tetracyclo[4.4.0.1 ^2,5 . 1 ^7,10 ]dodecyl group, tetracyclo[4.4.0.1 ^2,5 . 1 ^7,10 ]dodecylmethyl group, tetracyclo[4.4.0.1 ^2,5 . 1 ^7,10 ]dodecylethyl group, tetracyclo[4.4.0.1 ^2,5 . 1 ^7,10 ]dodecylbutyl group, ethyltetracyclo[4.4.0.1 ^2,5 . 1 ^7,10 ]dodecylmethyl group, ethyltetracyclo[4.4.0.1 ^2,5 . 1 ^7,10 ]dodecylethyl group, phenyl group, tolyl group, naphthyl group and other linear, branched or cyclic monovalent hydrocarbon groups can be exemplified. Among these monovalent hydrocarbon groups, methyl group, ethyl group, n-propyl group, isopropyl group and n-butyl group are preferred. When ^R2 and R3 ^are different, the carbon atom to which ^R2 and R3 ^are attached becomes an asymmetric carbon ^, and ^R2 and R3 can have an asymmetric carbon. When the monomer represented by the formula (1) of the present invention is an optically active compound having one or more asymmetric carbons, the pure enantiomer of R or S for each asymmetric carbon or the R-form All monomers (including racemic mixtures) in which S-isomers are mixed at any ratio are included.

R ² and R ³ may be bonded to each other to form an aliphatic hydrocarbon ring together with the carbon atoms to which they are bonded. [2.2.1]heptane, bicyclo[2.2.2]octane, tricyclo[5.2.1.0 ^2,6 ]decane, adamantane, tetracyclo[4.4.0.1 ^2,5 . 1 ^7,10 ]dodecane and other alicyclic hydrocarbons having 3 to 12 carbon atoms can be exemplified, and condensed rings containing these can be used. It may be substituted with a monovalent hydrocarbon group having 1 to 15 carbon atoms in a cyclic or monovalent form. Among these aliphatic hydrocarbon rings, cyclopentane, cyclohexane, bicyclo[2.2.1]heptane, bicyclo[2.2.2]octane, tricyclo[5.2.1.0 ^2,6 ]decane, Adamantane and the like are preferred, and among these, cyclopentane and cyclohexane are particularly preferred.

More specific examples of the monomer represented by Formula (1) of the present invention include the following, but are not limited to these.

（式中、Ｒ^１は上記と同様である。）

(In the formula, R ¹ is the same as above.)

The copolymer of the present invention contains 50% by mass to 95% by mass of structural units derived from methyl methacrylate in addition to the monomer represented by the above formula (1) with respect to the mass of the copolymer. The content of structural units derived from methyl methacrylate is more preferably 60% by mass to 92% by mass, particularly preferably 80% by mass to 90% by mass.

The copolymer of the present invention is derived from a monomer represented by formula (1) and a radically polymerizable monomer other than methyl methacrylate (hereinafter sometimes referred to as a radically polymerizable monomer (2)). You may have a structural unit that As such a radically polymerizable monomer (2),
Methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, s-butyl acrylate, t-butyl acrylate, amyl acrylate, isoamyl acrylate, acrylic acid Acrylic acid alkyl esters such as n-hexyl, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate; 2-hydroxyethyl acrylate, 2-ethoxyethyl acrylate, glycidyl acrylate, allyl acrylate, acrylic Acrylic acid derivatives such as benzyl acid; vinyl aromatic hydrocarbons such as styrene, α-methylstyrene, p-methylstyrene, m-methylstyrene; vinylcyclohexane, vinylcyclopentane, vinylcyclohexene, vinylcycloheptane, vinylcycloheptene , vinyl alicyclic hydrocarbons such as vinyl norbornene; ethylenically unsaturated carboxylic acids such as maleic anhydride, maleic acid and itaconic acid; olefins such as ethylene, propylene, 1-butene, isobutylene and 1-octene; butadiene, isoprene , myrcene; acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl ketone, vinyl chloride, vinylidene chloride, vinylidene fluoride; 2-vinylfuran, 2-isopropenylfuran, 2-vinylbenzofuran, 2 - isopropenylbenzofuran, 2-vinyldibenzofuran, 2-vinylthiophene, 2-isopropenylthiophene, 2-vinyldibenzothiophene, 2-vinylpyrrole, N-vinylindole, N-vinylcarbazole, 2-vinyloxazole, 2-iso propenyloxazole, 2-vinylbenzoxazole, 3-vinylisoxazole, 3-isopropenylisoxazole, 2-vinylthiazole, 2-vinylimidazole, 4(5)-vinylimidazole, N-vinylimidazole, N-vinylimidazoline, 2-vinylbenzimidazole, 5(6)-vinylbenzimidazole, 5-isopropenylpyrazole, 2-isopropenyl 1,3,4-oxadiazole, vinyltetrazole, 2-vinylpyridine, 4-vinylpyridine, 2- isopropenylpyridine, 3-vinylpyridine, 3-isopropenylpyridine, 2-vinylquinoline, 2-isopropenylquinoline, 4-vinylquinoline, 4-vinylpyrimidine, 2,4-dimethyl-6-vinyl-S-triazine, 3-methylidenedihydrofuran-2(3H)-one, 4-methyl-3-methylidenedihydrofuran-2(3H)-one, 4-decyl- ethylenically unsaturated heterocyclic compounds such as 3-methylidenedihydrofuran-2(3H)-one; and acid esters.

The amount of the structural unit derived from the radically polymerizable monomer (2) contained in the copolymer of the present invention is , preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. The amount of structural units derived from the radically polymerizable monomer (2) contained in the copolymer of the present invention may be 0.5% by mass or more.

The weight average molecular weight of the copolymer of the present invention is preferably 40,000 to 300,000, more preferably 60,000 to 250,000, particularly preferably 80,000 to 200,000. When the weight average molecular weight is within this range, strength and moldability are excellent.

Measurement by gel permeation chromatography can be performed as follows. Tetrahydrofuran is used as an eluent, and two columns of TSKgel Super Multipore HZM-M manufactured by Tosoh Corporation and Super HZ4000 connected in series are used as columns. As an analyzer, HLC-8320 (product number) manufactured by Tosoh Corporation equipped with a differential refractive index detector (RI detector) is used. A resin material to be tested, that is, 4 mg of a methacrylic copolymer is dissolved in 5 ml of tetrahydrofuran and filtered through a 0.1 μm filter to prepare a solution to be tested. Set the column oven temperature to 40° C., inject 20 μl of the solution to be tested at an eluent flow rate of 0.35 ml/min, and measure the chromatogram. A chromatogram is a chart in which an electrical signal value (intensity Y) derived from a refractive index difference between a test solution and a reference solution is plotted against retention time X.

A standard polystyrene having a molecular weight ranging from 400 to 5,000,000 was measured by gel permeation chromatography to prepare a calibration curve showing the relationship between retention time and molecular weight. A line connecting the point where the slope of the high molecular weight side of the chromatogram changes from zero to positive and the point where the slope of the low molecular weight peak changes from negative to zero is taken as the baseline. If the chromatogram shows multiple peaks, draw a line connecting the point where the slope of the highest molecular weight peak changes from zero to positive and the point where the slope of the lowest molecular weight peak changes from negative to zero. be the baseline.

In the copolymer of the present invention, the ratio of weight average molecular weight/number average molecular weight (hereinafter, this ratio is referred to as "molecular weight distribution") is preferably 1.01 to 3.0, more preferably 1.05 to 2.7, still more preferably 1.10 to 2.5. When the molecular weight distribution is in such a range, a copolymer having good moldability can be obtained. The weight average molecular weight and number average molecular weight are values converted to standard polystyrene measured by GPC (gel permeation chromatography).

Such weight average molecular weight and molecular weight distribution can be controlled by adjusting the types and amounts of the polymerization initiator and chain transfer agent during the polymerization reaction.

In the copolymer of the present invention, the Mw/Mn value after heat treatment at 260° C. for 1 hour is preferably 1.0 to 1.4 times the value before treatment, and 1.0 to 1.2 times is more preferable, 1.0 to 1.15 times is more preferable, and 1.0 to 1.1 times is particularly preferable. The smaller this value, the more likely it is that gel spots will be suppressed during melt molding.

Heat treatment at 260° C. for 1 hour is used to evaluate the gelation of methacrylic copolymers. Part of the product may gel during the flight, causing gel butts.

The methacrylic copolymer of the present invention includes molding materials in various shapes such as powder and pellets. For example, a pellet-shaped molding material can be obtained, for example, by extruding the methacrylic copolymer of the present invention in a molten state in an extruder from a die plate into strands, cooling and cutting the resin. As a method for cutting the strand into pellets, methods such as underwater cutting, hot cutting, and strand cutting can be employed.

A methacrylic copolymer undergoes a heat history when it is molded into a shape such as pellets. However, it may be in the form of a powder that has been purified by reprecipitation or the like and dried and has little heat history, or it may be formed into various shapes such as pellets and subjected to a heat history.

The copolymer of the present invention preferably has a glass transition temperature of 100 to 350°C, more preferably 110 to 250°C. If the glass transition temperature is too low, the heat resistance of the copolymer will be insufficient, and the applications that can be used will be limited. If the glass transition temperature is too high, the copolymer becomes brittle and easily cracked. The glass transition temperature is a value measured according to JIS K7121. That is, the copolymer of the present invention is heated once to 270 ° C., then cooled to room temperature, and then heated from room temperature to 270 ° C. at a rate of 10 ° C./min. can be measured, and the midpoint glass transition temperature obtained from the DSC curve measured during the second heating can be used as the glass transition temperature of the present invention.

The thermal decomposition temperature of the copolymer of the present invention is preferably 270° C. or higher, more preferably 290° C. or higher, still more preferably 295° C. or higher, and particularly preferably 300° C. or higher. The thermal decomposition temperature may be 320° C. or lower. The thermal decomposition temperature can be measured by the method described in Examples.

There are no particular restrictions on the method for producing the copolymer of the present invention. Usually, from the viewpoint of productivity, a copolymer is produced by adopting a radical polymerization method and adjusting the polymerization temperature, polymerization time, type and amount of chain transfer agent, type and amount of polymerization initiator, etc. A method is preferred. In addition, since the monomer represented by formula (1) can also be anionically polymerized, an anionic polymerization method should be adopted when obtaining block copolymers or copolymers with high stereoregularity. is also possible.

The radical polymerization method for producing the copolymer of the present invention is preferably carried out without solvent or in a solvent, and preferably without solvent from the viewpoint of obtaining a copolymer with a low impurity concentration. From the viewpoint of suppressing the generation of silver or coloration in the molded article, the polymerization reaction is preferably carried out with a low dissolved oxygen content in the polymerization reaction raw material. Moreover, the polymerization reaction is preferably carried out in an inert gas atmosphere such as nitrogen gas.

The polymerization initiator used in the radical polymerization method for producing the copolymer of the present invention is not particularly limited as long as it generates reactive radicals. For example, t-hexylperoxyisopropyl monocarbonate, t-hexylperoxy 2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, t-butylperoxypivalate , t-hexyl peroxypivalate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, 1 , 1-bis(t-hexylperoxy)cyclohexane, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, 2,2′-azobisisobutyronitrile, 2,2′- azobis(2-methylbutyronitrile), dimethyl 2,2'-azobis(2-methylpropionate) and the like. Among these, t-hexylperoxy 2-ethylhexanoate, 1,1-bis(t-hexylperoxy)cyclohexane, and dimethyl 2,2'-azobis(2-methylpropionate) are preferred.

The one-hour half-life temperature of such a polymerization initiator is preferably 60 to 140°C, more preferably 80 to 120°C. In addition, the polymerization initiator used for producing the copolymer preferably has a hydrogen abstraction ability of 20% or less, more preferably 10% or less, and even more preferably 5% or less. Such polymerization initiators can be used singly or in combination of two or more. The amount of the polymerization initiator used is preferably 0.0001 to 0.02 parts by mass, more preferably 0.001 to 0.01 parts by mass, and still more preferably 100 parts by mass of the monomers subjected to the polymerization reaction. is 0.005 to 0.007 parts by mass.

The hydrogen abstraction ability can be known from the technical data of the polymerization initiator manufacturer (for example, technical data of NOF Co., Ltd. "Hydrogen abstraction ability and initiator efficiency of organic peroxide" (created in April 2003)). . It can also be measured by a radical trapping method using α-methylstyrene dimer, that is, an α-methylstyrene dimer trapping method. The measurement is generally performed as follows. First, the polymerization initiator is cleaved in the coexistence of α-methylstyrene dimer as a radical trapping agent to generate radical fragments. Of the generated radical fragments, radical fragments with low hydrogen abstraction ability are added to the double bond of the α-methylstyrene dimer and captured. On the other hand, a radical fragment with a high hydrogen abstraction ability abstracts hydrogen from cyclohexane to generate a cyclohexyl radical, which is captured by addition to the double bond of α-methylstyrene dimer to generate a cyclohexane capture product. Therefore, the ratio (molar fraction) of radical fragments with high hydrogen abstraction ability to the theoretical amount of radical fragments generated, which is obtained by quantifying cyclohexane or cyclohexane-scavenging products, is defined as hydrogen abstraction ability.

Chain transfer agents used when a radical polymerization method is selected for the production of the copolymer of the present invention include n-octylmercaptan, n-dodecylmercaptan, t-dodecylmercaptan, 1,4-butanedithiol, 1 , 6-hexanedithiol, ethylene glycol bisthiopropionate, butanediol bisthioglycolate, butanediol bisthiopropionate, hexanediol bisthioglycolate, hexanediol bisthiopropionate, trimethylolpropane tris-( β-thiopropionate), and alkyl mercaptans such as pentaerythritol tetrakisthiopropionate. Among these, monofunctional alkylmercaptans such as n-octylmercaptan and n-dodecylmercaptan are preferred. These chain transfer agents can be used singly or in combination of two or more.

The amount of the chain transfer agent to be used is preferably 0.1 to 1 part by mass, more preferably 0.15 to 0.8 part by mass, and still more preferably 0 part by mass with respect to 100 parts by mass of the monomers subjected to the polymerization reaction. .2 to 0.6 parts by weight, most preferably 0.2 to 0.5 parts by weight. The amount of the chain transfer agent to be used is preferably 2500 to 10000 parts by mass, more preferably 3000 to 9000 parts by mass, and still more preferably 3500 to 6000 parts by mass with respect to 100 parts by mass of the polymerization initiator. When the amount of the chain transfer agent used is within the above range, the molecular weight of the obtained copolymer can be controlled, so that the obtained copolymer can have good moldability and high mechanical strength.

When the radical polymerization method is selected for the production of the copolymer of the present invention, the solvent used is not limited as long as it can dissolve the monomers and the copolymer. Group hydrocarbons are preferred. These solvents can be used singly or in combination of two or more. The amount of solvent to be used can be appropriately set from the viewpoint of the viscosity of the reaction solution and productivity. The amount of the solvent used is, for example, preferably 100 parts by mass or less, more preferably 90 parts by mass or less with respect to 100 parts by mass of the polymerization reaction raw material.

When the radical polymerization method is selected for the production of the copolymer of the present invention, the temperature during the polymerization reaction is preferably 100-200°C, more preferably 110-180°C. When the polymerization temperature is 100° C. or higher, the productivity tends to improve due to the improvement of the polymerization rate and the low viscosity of the polymerization liquid. Further, when the polymerization temperature is 200° C. or lower, the polymerization rate can be easily controlled, and furthermore, the formation of by-products can be suppressed, so that the copolymer of the present invention can be prevented from being colored. The polymerization reaction time is preferably 0.5 to 4 hours, more preferably 1.5 to 3.5 hours, still more preferably 1.5 to 3 hours. In the case of a continuous flow reactor, the polymerization reaction time is the average residence time in the reactor. When the polymerization reaction temperature and the polymerization reaction time are within the above ranges, a copolymer excellent in transparency can be produced with high efficiency.

Radical polymerization may be carried out using a batch reactor, but is preferably carried out using a continuous flow reactor from the viewpoint of productivity. In the continuous flow reaction, for example, the polymerization reaction raw materials (monomer (monomer represented by formula (1), methyl methacrylate, optionally added radically polymerizable monomer ( (meaning 2)), a mixture containing a polymerization initiator, a chain transfer agent, etc.) is prepared, supplied to the reactor at a constant flow rate, and the liquid in the reactor is withdrawn at a flow rate corresponding to the supplied amount . As the reactor, a tubular reactor that can be brought to close to plug flow and/or a tank reactor that can be brought to close to complete mixing can be used. Further, continuous flow polymerization may be performed in one reactor, or continuous flow polymerization may be performed by connecting two or more reactors.

In the present invention, it is preferable to employ at least one continuous flow tank reactor. The amount of liquid in the tank reactor during the polymerization reaction is preferably 1/4 to 3/4, more preferably 1/3 to 2/3, of the volume of the tank reactor. The reactor is usually equipped with a stirring device. Stirring devices include static stirring devices and dynamic stirring devices. Examples of the dynamic stirring device include a Maxblend stirring device, a stirring device having grid-shaped blades rotating around a central vertical rotating shaft, a propeller stirring device, a screw stirring device, and the like. Among these, a Maxblend stirring device is preferably used from the viewpoint of uniform mixing.

When a radical polymerization method is selected for the production of the copolymer of the present invention, the polymerization conversion rate is preferably 50 to 100% by mass, more preferably 70 when suspension polymerization is performed using a batch reactor. ~99% by mass.

Further, when a continuous flow tank reactor is used, the polymerization conversion rate is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, still more preferably 35 to 65% by mass. When the polymerization conversion rate is 20% by mass or more, the remaining unreacted monomers can be easily removed, and the appearance of the molded article made of the copolymer tends to be good. When the polymerization conversion rate is 80% by mass or less, the viscosity of the polymerization liquid tends to be low and the productivity tends to be improved.

In the methacrylic copolymer of the present invention, the ratio (% by mass) of the structural unit derived from the monomer represented by formula (1) and the structural unit derived from methyl methacrylate is determined by the amount of the raw material monomer approximately equal to the ratio. The ratio of each structural unit can be determined by ¹ H-NMR.

After completion of the polymerization, volatile matter such as unreacted monomers is removed, if necessary. The removal method is not particularly limited, but heating devolatilization is preferred. The devolatilization method includes an equilibrium flash method and an adiabatic flash method. The devolatilization temperature by the adiabatic flash method may be lower than the thermal decomposition temperature of the methacrylic copolymer, preferably 200 to 280°C, more preferably 220 to 260°C. The time for heating the resin by the adiabatic flash method is preferably 0.3 to 5 minutes, more preferably 0.4 to 3 minutes, still more preferably 0.5 to 2 minutes. Volatilizing in such a temperature range and heating time makes it easy to obtain a copolymer with little coloration. The removed unreacted monomers can be recovered and reused in the polymerization reaction. Since the yellow index of the recovered monomer may be high due to the heat applied during the recovery operation, etc., the recovered monomer should be purified by an appropriate method to reduce the yellow index. is preferred.

In the production of the molded article of the present invention, the copolymer of the present invention may be mixed with other polymers to the extent that the effect of the present invention is not impaired. Such other polymers include polyolefin resins such as polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1, and polynorbornene; ethylene-based ionomers; polystyrene, styrene-maleic anhydride copolymers, high-impact polystyrene , AS resin, ABS resin, AES resin, AAS resin, ACS resin, MBS resin and other styrene resins; methyl methacrylate polymers, methyl methacrylate-styrene copolymers; polyethylene terephthalate, polybutylene terephthalate and other polyester resins; nylon 6, polyamides such as nylon 66, polyamide elastomer; polycarbonate, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyacetal, polyvinylidene fluoride, polyurethane, modified polyphenylene ether, polyphenylene sulfide, silicone modified resin acrylic rubber, acrylic thermoplastic elastomer, silicone rubber; styrene thermoplastic elastomer such as SEPS, SEBS and SIS; olefin rubber such as IR, EPR and EPDM.

The molded article of the present invention preferably contains the copolymer of the present invention in an amount of 80% by mass or more, more preferably 90% by mass or more. The method for producing the molded article of the present invention is not particularly limited. The copolymer of the present invention or a molding material containing the copolymer of the present invention, for example, T-die method (laminate method, coextrusion method, etc.), inflation method (coextrusion method, etc.), compression molding method, blow molding method, calendar molding method, vacuum molding method, injection molding method (insert method, two-color method, press method, core-back method, sandwich method, etc.) and other melt molding methods and solution casting methods. Among these, the T-die method, the inflation method, and the injection molding method are preferable from the viewpoints of high productivity and cost. The molded article of the present invention is preferably a melt molded article obtained by a melt molding method.

The copolymers of the present invention can be in the form of pellets and the like for convenience in storage, transportation, or molding. Moreover, in obtaining the molded article of the present invention, the molding may be performed multiple times. For example, after molding the copolymer of the present invention to obtain a pellet-shaped molded article, the pellet-shaped molded article can be further molded to obtain a molded article having a desired shape. The compact of the present invention includes pellets.

Antioxidants, heat deterioration inhibitors, ultraviolet absorbers, light stabilizers, lubricants, release agents, polymer processing aids, antistatic agents, flame retardants, dyes, may be added to the copolymer of the present invention, if necessary. Various additives such as pigments, light diffusing agents, organic dyes, matting agents, and phosphors may be added. The blending amount of such various additives is preferably 7% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less, relative to the copolymer of the present invention.

Various additives may be added to the polymerization reaction solution when producing the copolymer, may be added to the copolymer produced by the polymerization reaction, or may be added during production of the molded product. Also good.

Antioxidants are effective by themselves to prevent oxidation deterioration of resins in the presence of oxygen. Examples include phosphorus antioxidants, hindered phenol antioxidants, thioether antioxidants, and the like. These antioxidants may be used alone or in combination of two or more. Among them, from the viewpoint of the effect of preventing deterioration of optical properties due to coloring, phosphorus antioxidants and hindered phenol antioxidants are preferable, and combined use of phosphorus antioxidants and hindered phenol antioxidants is more preferable.

When a phosphorus-based antioxidant and a hindered phenol-based antioxidant are used in combination, the amount of phosphorus-based antioxidant used: the amount of hindered phenol-based antioxidant used is in a mass ratio of 1:5 to 2: 1 is preferred, and 1:2 to 1:1 is more preferred.

Phosphorus-based antioxidants include 2,2-methylenebis(4,6-di-t-butylphenyl)octylphosphite (manufactured by ADEKA; trade name: ADEKA STAB HP-10), tris(2,4-di-t -Butylphenyl)phosphite (manufactured by BASF; trade name: IRGAFOS168), 3,9-bis(2,6-di-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3, 9-diphosphaspiro[5.5]undecane (manufactured by ADEKA; trade name: ADEKA STAB PEP-36) and the like are preferred.

Hindered phenolic antioxidants include pentaerythrityl-tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (manufactured by BASF; trade name IRGANOX1010), octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl)propionate (manufactured by BASF; trade name IRGANOX1076) and the like are preferred.

Thermal degradation inhibitors can prevent thermal degradation of resins by scavenging polymer radicals generated when exposed to high heat under substantially oxygen-free conditions.

Examples of the heat deterioration inhibitor include 2-t-butyl-6-(3′-t-butyl-5′-methyl-hydroxybenzyl)-4-methylphenyl acrylate (manufactured by Sumitomo Chemical; trade name Sumilizer GM), 2,4-di-t-amyl-6-(3′,5′-di-t-amyl-2′-hydroxy-α-methylbenzyl)phenyl acrylate (manufactured by Sumitomo Chemical; trade name Sumilizer GS), etc. preferable.

An ultraviolet absorber is a compound having the ability to absorb ultraviolet rays, and is said to have a function of mainly converting light energy into heat energy.

Examples of ultraviolet absorbers include benzophenones, benzotriazoles, triazines, benzoates, salicylates, cyanoacrylates, oxalic acid anilides, malonic acid esters, formamidines and the like. These may be used individually by 1 type, or may use 2 or more types together.

Benzotriazoles are highly effective in suppressing deterioration of optical properties such as coloration due to exposure to ultraviolet light, and are therefore preferable as ultraviolet absorbers for use when the film of the present invention is applied to optical applications. Benzotriazoles include 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (manufactured by BASF; trade name TINUVIN329), 2-(2H- benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (manufactured by BASF; trade name TINUVIN234), 2,2′-methylenebis[6-(2H-benzotriazole-2 -yl)-4-t-octylphenol] (ADEKA; LA-31), 2-(5-octylthio-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol, etc. are preferred. .

Further, as a triazine UV absorber, 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine (ADEKA; LA-F70) and its analogues, hydroxyphenyltriazine-based UV absorbers (manufactured by BASF; TINUVIN477 and TINUVIN460), 2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5- Triazines and the like can be mentioned.

Furthermore, if you want to absorb light with a wavelength of 380 to 400 nm particularly effectively, WO 2011/089794, WO 2012/124395, JP 2012-012476, JP 2013-023461, JP-A-2013-112790, JP-A-2013-194037, JP-A-2014-62228, JP-A-2014-88542, JP-A-2014-88543 and the like disclosed heterocyclic structure arrangement It is preferable to use a metal complex having ligands as the ultraviolet absorber.

A photostabilizer is a compound that is said to have a function of scavenging radicals generated mainly by oxidation by light. Suitable light stabilizers include hindered amines such as compounds having a 2,2,6,6-tetraalkylpiperidine backbone.

Lubricants include, for example, stearic acid, behenic acid, stearamic acid, methylenebisstearamide, hydroxystearic acid triglyceride, paraffin wax, ketone wax, octyl alcohol, hardened oil and the like.

Release agents include higher alcohols such as cetyl alcohol and stearyl alcohol; glycerin higher fatty acid esters such as stearic acid monoglyceride and stearic acid diglyceride; In the present invention, it is preferable to use higher alcohols and glycerin fatty acid monoester in combination as the release agent. When higher alcohols and glycerin fatty acid monoesters are used in combination, the ratio is not particularly limited, but the amount of higher alcohols used: the amount of glycerin fatty acid monoesters used is in a mass ratio of 2.5:1 to 3.5. 5:1 is preferred, and 2.8:1 to 3.2:1 is more preferred.

As the polymer processing aid, polymer particles having a particle size of 0.05 to 0.5 μm, which can be produced by an emulsion polymerization method, are usually used. The polymer particles may be monolayer particles composed of a polymer having a single composition ratio and a single intrinsic viscosity, or may be multilayer particles composed of two or more polymers having different composition ratios or intrinsic viscosities. may Among these, particles having a two-layer structure having an inner layer of a polymer layer having a low intrinsic viscosity and an outer layer of a polymer layer having a high intrinsic viscosity of 5 dl/g or more are preferred. The polymeric processing aid preferably has a limiting viscosity of 3 to 6 dl/g. If the intrinsic viscosity is too low, the moldability-improving effect tends to be low. If the intrinsic viscosity is too high, there is a tendency for the copolymer to deteriorate in moldability.

Antistatic agents include sodium heptylsulfonate, sodium octylsulfonate, sodium nonylsulfonate, sodium decylsulfonate, sodium dodecylsulfonate, sodium cetylsulfonate, sodium octadecylsulfonate, sodium diheptylsulfonate, heptylsulfonic acid Potassium, potassium octylsulfonate, potassium nonylsulfonate, potassium decylsulfonate, potassium dodecylsulfonate, potassium cetylsulfonate, potassium octadecylsulfonate, potassium diheptylsulfonate, lithium heptylsulfonate, lithium octylsulfonate, nonylsulfonate Alkyl sulfonates such as lithium oxide, lithium decylsulfonate, lithium dodecylsulfonate, lithium cetylsulfonate, lithium octadecylsulfonate, and lithium diheptylsulfonate.

Examples of flame retardants include magnesium hydroxide, aluminum hydroxide, hydrated aluminum silicate, hydrated magnesium silicate, metal hydrates having hydroxyl groups or water of crystallization such as hydrotalcite, and phosphoric acids such as amine polyphosphate and phosphate esters. compounds, silicone compounds, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, tricyclohexyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, dimethylethyl Phosphate flame retardants such as phosphate, methyldibutyl phosphate, ethyldipropyl phosphate and hydroxyphenyldiphenyl phosphate are preferred.

As dyes and pigments, there are red organic pigments such as para red, fire red, pyrazolone red, thioindicor red, and perylene red; blue organic pigments such as cyanine blue and indanthrene blue; and green organic pigments such as cyanine green and naphthol green. Pigments may be mentioned, and one or more of these may be used.

A compound having a function of converting ultraviolet light into visible light is preferably used as the organic dye.

Examples of phosphors include fluorescent pigments, fluorescent dyes, fluorescent white dyes, fluorescent whitening agents, and fluorescent whitening agents.

Light diffusing agents and matting agents include fine glass particles, polysiloxane-based crosslinked fine particles, crosslinked polymer fine particles, talc, calcium carbonate, barium sulfate, and the like. The copolymer of the present invention preferably does not contain an acid generator.

The molded article of the present invention contains the copolymer of the present invention. The molded article of the present invention is not particularly limited in its manufacturing method. The molded article of the present invention can be produced by, for example, a T-die method (laminate method, coextrusion method, etc.), an inflation method (coextrusion method, etc.), a compression molding method, a blow molding method, a calendar molding method, a vacuum molding method, or an injection molding method. (Insert method, two-color method, press method, core-back method, sandwich method, etc.) and other melt molding methods and reaction molding methods such as cell-cast polymerization are obtained by molding the copolymer of the present invention. be able to. Among these molding methods, the T-die method, the inflation method, the injection molding method, and the cell cast polymerization method are preferable from the viewpoints of high productivity and cost.

Moreover, in obtaining the molded article of the present invention, the molding may be performed multiple times. For example, after molding the methacrylic resin composition of the present invention to obtain a pellet-shaped molded article, the pellet-shaped molded article can be further molded to obtain a molded article having a desired shape.

A sheet or film, which is one form of the molded article of the present invention, is preferably produced by an extrusion method or a cell-cast polymerization method. The thickness of the obtained sheet is preferably 0.5 mm or more, for example 0.5 to 20 mm. The thickness of the resulting film is preferably 1 μm to 500 μm, more preferably 10 μm to 300 μm, still more preferably 15 to 50 μm.

Applications of the molded product of the present invention include, for example, signboard members such as advertising towers, stand signboards, sleeve signboards, transom signboards, and rooftop signboards; display parts such as showcases, partitions, and store displays; fluorescent lamp covers and mood lighting covers. Lighting parts such as lampshades, light ceilings, light walls, and chandeliers; interior parts such as pendants and mirrors; doors, domes, safety window glass, partitions, stair wainscots, balcony wainscots, roofs of leisure buildings, etc. Parts; Transportation parts such as aircraft windshields, pilot visors, motorcycle and motor boat windshields, bus shading, automotive side visors, rear visors, head wings, headlight covers; Audio-visual nameplates, stereo covers, TV protective masks , electronic device parts such as vending machine display covers; medical device parts such as incubators and X-ray parts; equipment-related parts such as machine covers, instrument covers, laboratory equipment, rulers, dials, observation windows; Optical parts such as light plates, light guide films, Fresnel lenses, lenticular lenses, front panels of various displays, diffusion plates; traffic-related parts such as road signs, information boards, curved mirrors, and soundproof walls; automotive interior surface materials, mobile phones Film materials such as surface materials for telephones and marking films; home appliance materials such as canopies and control panels for washing machines and top panels for rice cookers; greenhouses, large water tanks, box water tanks, clock panels, bathtubs, sanitary , desk mats, game parts, toys, face protection masks during welding, and the like.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples. Measurements of physical properties and the like were carried out by the following methods.

(Chromatogram measurement by GPC and determination of molecular weight distribution etc. based on chromatogram)
4 mg of the resin material to be tested was dissolved in 5 ml of tetrahydrofuran and filtered through a 0.1 μm filter to prepare a solution to be tested. A GPC device (manufactured by Tosoh Corporation, HLC-8320) in which a column in which two TSKgel SuperMultiporeHZM-M manufactured by Tosoh Corporation and SuperHZ4000 are connected in series is attached, and the detection unit is a differential refractive index detector (HLC-8320, manufactured by Tosoh Corporation). 20 μl was injected and the chromatogram was measured. Tetrahydrofuran was run as an eluent at a flow rate of 0.35 ml/min, and the column temperature was set to 40°C.

A calibration curve was created using data from 10 points of standard polystyrene. A standard polystyrene having a molecular weight ranging from 400 to 5,000,000 was measured by gel permeation chromatography to prepare a calibration curve showing the relationship between retention time and molecular weight. A line connecting the point where the slope of the high molecular weight side of the chromatogram changes from zero to positive and the point where the slope of the low molecular weight peak changes from negative to zero was used as the baseline. If the chromatogram shows multiple peaks, draw a line connecting the point where the slope of the highest molecular weight peak changes from zero to positive and the point where the slope of the lowest molecular weight peak changes from negative to zero. made the baseline.

Further, the weight average molecular weight Mw and the number average molecular weight Mn in terms of polystyrene, and the molecular weight distribution (Mw/Mn) were calculated from the chromatogram by a known calculation method.

( ¹ H-NMR measurement)
¹ H-NMR was used to confirm the structure of the compounds synthesized in Production Examples and to determine the composition of copolymers in the copolymers of Examples and Comparative Examples. The ¹ H-NMR spectrum was measured using a nuclear magnetic resonance apparatus (ULTRA SHIELD 400 PLUS manufactured by Bruker) using 1 mL of deuterated chloroform as a solvent for 10 mg of the sample at room temperature under the conditions of 64 integration times. It was measured.

(thermal decomposition temperature)
Thermal mass spectrometry (TG) of the copolymer was performed in a nitrogen atmosphere at a temperature increase rate of 10° C./min according to JIS K7120. The weight at 250° C. was taken as the origin, and the temperature at which the weight decreased by 2.5% was defined as the thermal decomposition temperature. As a measuring device, TGA-50 (product number) manufactured by Shimadzu Corporation was used.

(Heating retention test)
Using a melt indexer (Tateyama Kagaku Kogyo L-220), the copolymer was heated at 260° C. for 1 hour. GPC measurement was performed on the samples before and after heating to determine Mw/Mn, and the rate of change (rate of change in Mw/Mn in the heating test) was calculated.

(Chemical resistance test (methanol resistance))
The copolymer was hot-press molded to obtain a test piece of 80 mm x 10 mm x 1.0 mm thick. The test piece was allowed to stand under conditions of 23° C. and 50% RH for 16 hours or more to condition the humidity. A microsyringe was used to drop 10 mL of a solvent (methanol) onto the test piece, and the appearance was visually observed.
A: No change B: Traces of droplets remain C: Cloudy D: Swelling/dissolving

The following monomers were prepared for use in Examples and Comparative Examples.

- Methyl methacrylate (hereinafter referred to as "MMA")
・Methyl acrylate (hereinafter referred to as “MA”)
・(3-Hydroxy-2,2-dimethyl)propyl methacrylate (see formula (2), hereinafter referred to as “NPGMA”)
- (3-Hydroxy-2-cyclohexyl)propyl methacrylate (see formula (3), hereinafter referred to as "CHDMA")
・(3-Hydroxy-2,2-diethyl)propyl methacrylate (see formula (4), hereinafter referred to as “PRDMA”)
・(3-Hydroxy-2-butyl-2-ethyl)propyl methacrylate (see formula (5), hereinafter referred to as “BEPMA”)
・Methacrylic acid (2-hydroxyethyl) (hereinafter referred to as “HEMA”)
The above NPGMA was obtained from Production Example 1 described below, the PRDMA was obtained from Production Example 2 described below, the BEPMA was obtained from Production Example 3 described below, and the CHDMA was obtained from Production Example 4 described below.

<Production Example 1>
Synthesis of (3-hydroxy-2,2-dimethyl)propyl methacrylate (NPGMA) In a four-necked flask equipped with a thermometer, a stirrer and a dropping funnel, 644 parts by mass of toluene and 313 parts by mass of 2,2-dimethyl- 1,3-propanediol, 12 parts by mass of sodium methoxide (28% methanol solution), and 0.75 parts by mass of hydroquinone were charged and stirred. The temperature was raised to 60° C., and 180 parts by mass of methyl methacrylate was added dropwise from the dropping funnel over 1 hour. Thereafter, the pressure was reduced to 600 Torr, and the reaction was carried out for 4 hours while distilling off the by-product methanol. After completion of the reaction, it was washed twice with 750 parts by mass of deionized water. After concentration by vacuum distillation, purification by column chromatography gave 113 parts by mass of (3-hydroxy-2,2-dimethyl)propyl methacrylate (NPGMA, see formula (2)).

<Production Example 2>
Synthesis of (3-hydroxy-2-cyclohexyl)propyl methacrylate (CHDMA) Using 2-cyclohexyl-1,3-propanediol instead of 2,2-dimethyl-1,3-propanediol, the reaction was carried out at 70°C. 98 parts by mass of (3-hydroxy-2-cyclohexyl)propyl methacrylate (CHDMA, see formula (3)) was obtained in the same manner as in Production Example 1 except for the above.

<Production Example 3>
Synthesis of (3-hydroxy-2,2-diethyl)propyl methacrylate (PRDMA) except using 2,2-diethyl-1,3-propanediol instead of 2,2-dimethyl-1,3-propanediol was carried out in the same manner as in Production Example 1 to obtain 105 parts by mass of (3-hydroxy-2,2-diethyl)propyl methacrylate (PRDMA, see formula (4)).

<Production Example 4>
Synthesis of (3-hydroxy-2-butyl-2-ethyl)propyl methacrylate (BEPMA) 2-Butyl-2-ethyl-1,3-propanediol instead of 2,2-dimethyl-1,3-propanediol 110 parts by mass of (3-hydroxy-2-butyl-2-ethyl)propyl methacrylate (BEPMA, see formula (5)) was obtained in the same manner as in Production Example 1 except that . It was confirmed by ¹ H-NMR that the methacrylic acid esters of formulas (2) to (5) were obtained.

<Example 1>
The inside of the thoroughly dried pressure vessel with a stirring device was replaced with nitrogen. 7.9 parts by weight of MMA, 2.0 parts by weight of NPGMA, 0.1 parts by weight of MA, and 0.012 parts by weight of n-octylmercaptan were charged into the pressure vessel.

After sufficiently purging the pressure vessel with nitrogen gas, the temperature was raised to 140° C. while stirring. 0.00015 parts by mass of di-t-butyl peroxide (Nippon Oil & Fats Co., Ltd.: Perbutyl D) was added to the pressure vessel to initiate polymerization. After 4 hours from the initiation of polymerization, the polymerization was terminated by cooling to room temperature. After diluting the resulting solution by adding 50 parts by mass of toluene, the solution was poured into 4000 parts by mass of methanol to precipitate a solid. The precipitated solid matter was separated by filtration and sufficiently dried to obtain 7.4 parts by mass of copolymer (A1). When the ¹ H-NMR of the copolymer (A1) was measured, the content of structural units derived from MMA was 81.6% by mass, the content of structural units derived from NPGMA was 17.7% by mass, and the content of structural units derived from MA was 17.7% by mass. The structural unit content was 0.8% by weight. The copolymer (A1) had a weight average molecular weight (Mw) of 209,000 and a molecular weight distribution (Mw/Mn) of 2.09. Other evaluation results are shown in Table 1.

<Example 2>
The same procedure as in Example 1 was performed except that 7.9 parts by mass of MMA, 2.0 parts by mass of CHDMA, 0.1 parts by mass of MA, and 0.012 parts by mass of n-octylmercaptan were charged into the pressure vessel. to obtain 7.2 parts by mass of copolymer (A2). When the ¹ H-NMR of the copolymer (A2) was measured, the content of structural units derived from MMA was 83.3% by mass, the content of structural units derived from CHDMA was 16.1% by mass, and the content of structural units derived from MA was 16.1% by mass. The structural unit content was 0.7% by weight. The copolymer (A2) had a weight average molecular weight (Mw) of 165,000 and a molecular weight distribution (Mw/Mn) of 1.99. Other evaluation results are shown in Table 1.

<Example 3>
The same procedure as in Example 1 was performed except that 5.9 parts by mass of MMA, 4.1 parts by mass of CHDMA, 0.1 parts by mass of MA, and 0.012 parts by mass of n-octylmercaptan were charged into the pressure vessel. to obtain 7.4 parts by mass of copolymer (A3). When the ¹ H-NMR of the copolymer (A3) was measured, the content of structural units derived from MMA was 65.3% by mass, the content of structural units derived from CHDMA was 35.5% by mass, and the content of structural units derived from MA was 35.5% by mass. The structural unit content was 0.8% by weight. The copolymer (A3) had a weight average molecular weight (Mw) of 158,000 and a molecular weight distribution (Mw/Mn) of 2.08. Other evaluation results are shown in Table 1.

<Example 4>
7.9 parts by mass of MMA, 2.0 parts by mass of PRDMA, 0.1 parts by mass of MA, and 0.012 parts by mass of n-octylmercaptan were charged into the pressure vessel and cooled 2 hours after the initiation of polymerization. 7.4 parts by mass of copolymer (A4) was obtained in the same manner as in Example 1 except for the above. When the ¹ H-NMR of the copolymer (A4) was measured, the content of structural units derived from MMA was 83.3% by mass, the content of structural units derived from PRDMA was 16.0% by mass, and the content of structural units derived from MA was 16.0% by mass. The structural unit content was 0.7% by weight. The copolymer (A4) had a weight average molecular weight (Mw) of 186,000 and a molecular weight distribution (Mw/Mn) of 1.68. Other evaluation results are shown in Table 1.

<Example 5>
7.9 parts by mass of MMA, 2.0 parts by mass of BEPMA, 0.1 parts by mass of MA, and 0.012 parts by mass of n-octyl mercaptan were charged into the pressure vessel and cooled after 2 hours from the start of polymerization. 7.2 parts by mass of copolymer (A5) was obtained in the same manner as in Example 1 except for the above. When the ¹ H-NMR of the copolymer (A5) was measured, the content of structural units derived from MMA was 83.7% by mass, the content of structural units derived from BEPMA was 15.5% by mass, and the content of structural units derived from MA was 15.5% by mass. The structural unit content was 0.8% by weight. The copolymer (A5) had a weight average molecular weight (Mw) of 187,000 and a molecular weight distribution (Mw/Mn) of 1.73. Other evaluation results are shown in Table 1.

<Comparative Example 1>
The same procedure as in Example 1 was performed except that 7.9 parts by mass of MMA, 2.0 parts by mass of HEMA, 0.1 parts by mass of MA, and 0.012 parts by mass of n-octylmercaptan were charged into the pressure vessel. to obtain a copolymer (B1). Since most of it was insolubilized (gelled) at the bottom of the container, only the soluble portion was collected and physical properties were evaluated. Table 1 shows the evaluation results.

<Comparative Example 2>
The same procedure as in Example 1 was performed except that the pressure vessel was charged with 5.9 parts by mass of MMA, 4.1 parts by mass of HEMA, 0.1 parts by mass of MA, and 0.012 parts by mass of n-octylmercaptan. to obtain a copolymer (B2). Since most of it was insolubilized (gelled) at the bottom of the container, only the soluble portion was collected and physical properties were evaluated. Table 1 shows the evaluation results.

As can be seen from Table 1, the copolymers (A1) to (A5) containing structural units derived from the monomer represented by formula (1) did not gel during polymerization. Moreover, since the thermal decomposition temperature is high, it turns out that it is excellent in thermal decomposition resistance. Furthermore, since the rate of change in Mw/Mn before and after the heating test is small, it can be seen that gel spots are suppressed during melt molding. Moreover, it turns out that it is excellent in chemical resistance.

Claims (8)

Molding containing 80% by mass or more of a methacrylic copolymer containing 5 to 50% by mass of structural units derived from a monomer represented by the following formula (1) and 50 to 95% by mass of structural units derived from methyl methacrylate wherein the methacrylic copolymer has a weight average molecular weight of 80,000 to 200,000 .

(In formula (1), R ¹ represents a hydrogen atom or a methyl group; R ² and R ³ each independently represent a linear, branched or cyclic monovalent hydrocarbon group having 1 to 15 carbon atoms; or R ² and R ³ may be bonded to each other to form an aliphatic hydrocarbon ring together with the carbon atoms to which they are bonded.) The monomer represented by the formula (1) is R ² carbon number and R ³ The molded article according to claim 1, wherein the sum of the carbon numbers of is 2 to 9. 3. The molded article according to claim 1, wherein the methacrylic copolymer has a weight average molecular weight/number average molecular weight ratio of 1.01 to 3.0. The ratio Mw/Mn of the weight average molecular weight Mw to the number average molecular weight Mn in terms of polystyrene calculated based on the chromatogram obtained by gel permeation chromatography of the methacrylic copolymer is heat-treated at 260°C for 1 hour. The molded article according to any one of claims 1 to 3, wherein the value after performing the treatment is 1.4 times or less the value before treatment. 5. The methacrylic copolymer according to any one of claims 1 to 4, wherein the Mw/Mn after the heat treatment at 260°C for 1 hour is 1.2 times or less the value before the treatment. molded body. The molded article according to any one of claims 1 to 5, which is a melt molded article. The molded article according to any one of claims 1 to 6, which is a sheet having a thickness of 0.5 mm or more. The molded article according to any one of claims 1 to 6, which is a film having a thickness of 1 µm to 500 µm.