JP7572377B2 - METHACRYLIC COPOLYMER AND PROCESS FOR PRODUCING SAME - Patent application - Google Patents

Description

The present invention relates to a methacrylic copolymer essentially containing methyl methacrylate units and α-methylstyrene units, and a manufacturing method suitable for producing the same.

Methacrylic copolymers that essentially contain methyl methacrylate units and α-methylstyrene units are known as resin materials with excellent transparency.

For example, Patent Document 1 discloses a resin material for optical prisms or lenses which is composed of a copolymer composed of 10 to 65% by weight of α-methylstyrene units, 10 to 40% by weight of methyl methacrylate units, and 10 to 80% by weight of styrene units, has a weight average molecular weight range of 50,000 to 400,000, a Vicat softening temperature of 105°C or higher, a refractive index of 1.550 to 1.580, a water absorption rate of 0.13% or lower, and has a birefringence value of 300 nm or lower when made into a prism with a thickness of 10 mm.

Patent Document 2 discloses a molding material consisting of a copolymer having a weight-average molecular weight in the range of 50,000 to 200,000, a proportion of α-methylstyrene units in the range of 10 to 30% by weight, a proportion of methyl methacrylate units in the range of 40 to 70% by weight, and a proportion of styrene units in the range of 10 to 30% by weight, the MFR value of the copolymer at 220°C under a load of 10 kg being in the range of 4 to 18 g/10 min, and the Vicat softening temperature of the copolymer being 130°C or higher.

Patent Document 3 discloses a resin molded product in which the surface of a transparent thermoplastic plastic is coated with an α-methylstyrene copolymer having a weight-average molecular weight in the range of 50,000 to 200,000, a proportion of α-methylstyrene units of 10 to 40% by weight, a proportion of methyl methacrylate units of 40 to 90% by weight, and a proportion of monomer units copolymerizable therewith of 0 to 30% by weight.

α-Methylstyrene copolymers having a ring structure in the main chain, such as a copolymer consisting of α-methylstyrene-methyl methacrylate-maleic anhydride, are known as molding materials with excellent transparency, heat resistance, etc. (Patent Document 4, Patent Document 5, etc.). Various methods for producing a copolymer consisting of α-methylstyrene-methyl methacrylate-maleic anhydride have been proposed.

For example, Patent Document 6 discloses a method for producing a methyl methacrylate-α-methylstyrene-maleic anhydride copolymer, which comprises adding 5 to 15% (by weight of the monomer mixture) of maleic anhydride to a monomer mixture consisting of a predominant amount of methyl methacrylate and a minor amount of α-methylstyrene, and copolymerizing the mixture in the presence of a free radical generating catalyst using either bulk or solution polymerization methods, or a combination of these.

Patent Document 7 discloses a method for producing an α-methylstyrene copolymer, which is characterized by using α-methylstyrene, methyl methacrylate, and maleic anhydride as monomers, adding a polyfunctional organic peroxide having a 10-hour half-life temperature of 60 to 110°C as a polymerization initiator in the range of 0.05 to 1.0% by weight based on the total monomer amount, and carrying out bulk polymerization at 100 to 150°C.

Patent Document 8 discloses a method for producing a heat-resistant methacrylic resin plate, which comprises supplying a polymerization raw material consisting of a polymerizable mixture of 40 to 89% by weight of methyl methacrylate monomer, 1 to 20% by weight of α-methylstyrene, 5 to 20% by weight of styrene, and 5 to 20% by weight of maleic anhydride from the upstream end of a molding space formed by the opposing surfaces of two endless belts running opposite each other with a certain gap between them and a gasket that runs following the running of the belts while being sandwiched between the belts, 0.01 to 0.5 parts by weight of an acidic phosphoric acid ester per 100 parts by weight of the mixture, and a polymerization initiator, continuously polymerizing the mixture inside the molding space to a polymerization rate of 98.5% or more, and continuously removing a heat-resistant methacrylic resin plate from the downstream end.

Patent Document 9 discloses a method for producing a methacrylic copolymer, which comprises charging a monomer mixture containing 70-95% by mass of methyl methacrylate, 0-15% by mass of α-methylstyrene, 0-20% by mass of styrene, and 2-15% by mass of maleic anhydride, the total amount of α-methylstyrene and styrene being in a molar ratio of 1.0 to 2.5 relative to maleic anhydride, into a polymerization vessel containing at least one polymer membrane layer having an oxygen permeability of 1.5×10 ^-13 (mol m ^-2 s ^-1 Pa ^-1 ) or less, sealing the vessel, and heating the vessel in the gas phase to polymerize the monomer mixture. Patent Document 9 states that in this production method, it is preferable to add a terpenoid compound to the monomer mixture and polymerize the monomer mixture.

Patent Document 10 discloses a method for producing a heat-resistant methacrylic resin, which comprises supplying a monomer mixture consisting of methyl methacrylate, maleic anhydride, and at least one aromatic vinyl compound to a polymerization reactor and carrying out solution polymerization or bulk polymerization at a temperature of 100 to 180°C to obtain a resin consisting of a copolymer consisting of 35 to 98% by weight of methyl methacrylate units, 1 to 40% by weight of maleic anhydride units, and a total of 1 to 35% by weight of aromatic vinyl compound units, and having an intrinsic viscosity of 0.35 to 3.5 dl/g.

As a method for producing a methyl methacrylate copolymer, which conceptually includes an α-methylstyrene-methyl methacrylate copolymer, for example,
Patent Document 11 discloses a method for continuously producing a methyl methacrylate-based syrup, which comprises continuously supplying a monomer mainly composed of methyl methacrylate to a first reaction zone of a reaction zone having two or more reaction zones arranged in series in which substantially complete mixing is achieved, continuously supplying a radical polymerization initiator to at least two reaction zones including the first reaction zone, maintaining the conditions of each reaction zone such that the residual initiator concentration in at least each reaction zone to which the polymerization initiator is supplied is 1/2 to 1/1000 times the concentration of the supplied initiator, and producing a polymer while the reaction mixture passes through each reaction zone in sequence to obtain a syrup. Patent Document 11 states that other monomers such as α-methylstyrene can be used within the range of 20% by weight or less in the monomer mainly composed of methyl methacrylate.

Patent Document 12 discloses a process for continuously supplying methyl methacrylate (1), a chain transfer agent (3), and a radical polymerization initiator (4) to a tank reactor while controlling the respective amounts thereof, a process for obtaining a reaction product by bulk polymerization in the tank reactor at a polymerization conversion rate of 40 to 70% by mass, a process for recovering a mixture (A) containing methyl methacrylate (1') and the chain transfer agent (3') from the reaction product, and a process for continuously supplying the mixture (A) to the tank reactor, in which the control of the respective amounts of methyl methacrylate (1) and the chain transfer agent (3) supplied to the tank reactor is performed based on information including the amount of mixture (A) supplied to the tank reactor and the respective proportions of methyl methacrylate (1') and the chain transfer agent (3') in the mixture (A), and the complete mixing time (θ _M [hr]) of the tank reactor and the half-life (τ _1/2 [hr]), the stirring power of the tank reactor (PV [kW/m ³ ]), the average residence time of the reactants in the tank reactor (θ [hr]), and the radical polymerization initiator concentration in the reactants (I [ppm]) are θ _M > τ _1/2 and PV × θ × I × τ _1/2 < 4
The present invention discloses a method for producing a (meth)acrylic resin composition that satisfies the above requirements.

Patent Document 13 discloses a method for producing a colorless and transparent methacrylic polymer with excellent moldability, which is characterized in that, when a monomer mixture mainly composed of methyl methacrylate is continuously bulk polymerized in one complete mixing reactor without using a solvent, an inert gas is introduced into the monomer to reduce the dissolved oxygen in the monomer to 1 ppm or less, a radical initiator having a half-life of 0.5 to 120 seconds at the polymerization temperature is used, and while stirring with a stirrer having a stirring consumption power of 0.5 to 20 kW per 1 ^m3 of reaction liquid, the average residence time is set so that the ratio of the half-life of the radical initiator at the polymerization temperature to the average residence time is 1/200 to 1/10,000, and polymerization is performed at 130 to 160°C so that the monomer conversion rate is 45 to 70%.

Patent Document 14 discloses a method for producing a methacrylic polymer in which a monomer mainly composed of methyl methacrylate is bulk polymerized in a complete mixing type reaction tank to give a polymer content of 40 to 70% by weight, characterized in that the reaction tank is filled with liquid with substantially no gas phase and is in an adiabatic state with substantially no heat entering or leaving the reaction tank from the outside, the polymerization temperature is 120 to 180°C, the average residence time is 15 minutes to 2 hours, a radical initiator having a half-life of 1 minute or less at the polymerization temperature is used, and the concentration C (mol/100 g monomer) of the radical initiator is within the range calculated by 4× ^10-5 ·exp(0.019T)<C·θ<3×10-8·exp(0.079T) (wherein θ represents the average residence time ⁽ minutes), and T represents the polymerization temperature (°C)). Patent Document 14 states that in a monomer mainly composed of methyl methacrylate, other vinyl monomers such as α-methylstyrene can be used within the range of 20% by weight or less.

Patent Document 15 discloses a method for producing an α-methylstyrene copolymer consisting of 6 to 34% by weight of α-methylstyrene units, 0 to 50% by weight of styrene units, and 94 to 16% by weight of methyl methacrylate units, characterized in that, when producing the α-methylstyrene copolymer, 0.05 to 1.0 part by weight of a polyfunctional organic peroxide having a 10-hour half-life temperature in the range of 60 to 110°C is added as a polymerization initiator to 100 parts by weight of monomer consisting of 6 to 40% by weight of α-methylstyrene, 0 to 50% by weight of styrene, and 94 to 16% by weight of methyl methacrylate, and bulk polymerization is carried out at 100 to 150°C.

Patent Document 16 discloses a method for producing an α-methylstyrene copolymer containing, as constituent units, 10 to 35% by weight of α-methylstyrene units, 94 to 15% by weight of methyl methacrylate units, and 0 to 50% by weight of a vinyl monomer copolymerizable with these monomers, characterized in that 0.05 to 1.0 part by weight of an organic peroxide is added as a polymerization initiator to 100 parts by weight of monomer, and 0.01 to 0.15 part by weight of divinylbenzene is added to 100 parts by weight of monomer, and polymerization is carried out at 100 to 150°C. Patent Document 16 states that this production method enables continuous production of α-methylstyrene copolymers by bulk polymerization.

WO2005/070978A Japanese Patent Application Publication No. 4-300908 Japanese Patent Application Publication No. 5-59321 JP 61-152758 Publication JP 61-155443 Publication Special Publication No. 49-10156 Japanese Unexamined Patent Publication No. 4-300907 Japanese Patent Application Laid-Open No. 61-271313 JP 2001-270905 A Japanese Unexamined Patent Publication No. 60-147417 Japanese Unexamined Patent Publication No. 54-54189 WO2015/099118A1 Japanese Patent Application Publication No. 3-111408 Japanese Patent Application Publication No. 7-126308 Japanese Patent Application Publication No. 4-218515 Japanese Patent Application Publication No. 4-328111

The object of the present invention is to provide a novel copolymer essentially containing methyl methacrylate units and α-methylstyrene units, and a method for producing the copolymer suitable for producing the copolymer.

The copolymer of the present invention includes the following aspects:

[1] A methacrylic copolymer comprising 70 to 93 mass% of methyl methacrylate units, 7 to 30 mass% of α-methylstyrene units, and 0 to 23 mass% of other monomer units copolymerizable therewith, and satisfying the relationship of formula (1).

(|A-B|)/B < 0.05 (1)

In the above, A is the molecular weight at the peak top in a differential molecular weight distribution curve obtained by gel permeation chromatography measurement using a differential refractive index detector, and B is the molecular weight at the peak top in a differential molecular weight distribution curve obtained by gel permeation chromatography measurement using an absorbance detector with a detection wavelength of 254 nm.

[2] A methacrylic copolymer comprising 70 to 93% by mass of methyl methacrylate units, 7 to 30% by mass of α-methylstyrene units, and 0 to 10% by mass of other monomer units copolymerizable therewith, and satisfying the relationship of formula (1).

(|A-B|)/B < 0.05 (1)

In the above, A is the molecular weight at the peak top in a differential molecular weight distribution curve obtained by gel permeation chromatography measurement using a differential refractive index detector, and B is the molecular weight at the peak top in a differential molecular weight distribution curve obtained by gel permeation chromatography measurement using an absorbance detector with a detection wavelength of 254 nm.

[3] The methacrylic copolymer according to [1] or [2], wherein the other copolymerizable monomer unit is a monomer unit having a ring structure.
[4] The methacrylic copolymer according to any one of [1] to [3], having a glass transition temperature of 125° C. or higher.
[5] The methacrylic copolymer according to any one of [1] to [4], having a photoelastic coefficient of −4.3×10 ⁻¹² /Pa to +4.3× ^{10 −12} /Pa.
[6] The methacrylic copolymer according to any one of [1] to [5], wherein a sheet of the methacrylic copolymer having a size of 20 mm × 40 mm × thickness of 1.0 mm is stretched 100% in one direction at a speed of 3 mm/min at a temperature 10°C higher than the glass transition temperature to obtain a stretched film having a birefringence (sometimes referred to as orientation birefringence Δn) of -10 × 10 ^-4 to +10 × 10 ^-4 .

Uses of the copolymer of the present invention include the following aspects.
[7] A resin composition comprising the methacrylic copolymer according to any one of [1] to [6].
[8] A resin composition comprising an antioxidant and the methacrylic copolymer according to any one of [1] to [6].

[9] A molded article comprising the methacrylic copolymer according to any one of [1] to [6] or the resin composition according to [7] or [8].
[10] A film comprising the methacrylic copolymer according to any one of [1] to [6] or the resin composition according to [7] or [8].
[11] An optical film comprising the methacrylic copolymer according to any one of [1] to [6] or the resin composition according to [7] or [8].
[12] A laminate having a layer containing the methacrylic copolymer according to any one of [1] to [6] and a layer containing another thermoplastic resin.

The method for producing the methacrylic copolymer of the present invention includes the following aspects.

[13] A method of continuously supplying a reaction raw material containing a monomer mixture containing 70 to 93 mass % of methyl methacrylate, 7 to 30 mass % of α-methylstyrene, and 0 to 23 mass % of other monomers copolymerizable therewith, and a radical polymerization initiator, to a tank-type reactor;
The monomer mixture is bulk polymerized in a tank reactor at a polymerization conversion rate of 30 to 60 mass% to obtain a reaction product;
continuously withdrawing the reaction product from the tank reactor; and removing from the reaction product the monomer mixture remaining in the withdrawn reaction product.
A method for producing the methacrylic copolymer according to any one of [1] to [6].

The manufacturing method suitable for producing the methacrylic copolymer of the present invention includes the following aspects.

[14] A method of continuously supplying a reaction raw material containing a monomer mixture containing 70 to 93 mass % of methyl methacrylate, 7 to 30 mass % of α-methylstyrene, and 0 to 10 mass % of other monomers copolymerizable therewith, and a radical polymerization initiator, to a tank-type reactor;
The monomer mixture is bulk polymerized in a tank reactor at a polymerization conversion rate of 30 to 60% by mass to obtain a reaction product;
continuously withdrawing the reaction product from the tank reactor; and removing the monomer mixture remaining in the withdrawn reaction product from the reaction product;
When the average concentration of the radical polymerization initiator present in the liquid in the tank reactor is I mol/L and the average residence time of the reaction raw materials in the tank reactor is θ hr, their product I×θ exceeds 1× ^10-4 mol·hr/L and is less than 1× ^10-3 mol·hr/L.
Method for producing copolymers.

[15] A method of continuously supplying reaction raw materials including 100 parts by mass of a monomer mixture consisting of 40 to 92% by mass of methyl methacrylate, 7 to 25% by mass of α-methylstyrene, 1 to 25% by mass of a monomer capable of introducing a ring structure into the main chain by a polymerization reaction, and 0 to 10% by mass of other monomers copolymerizable therewith, 0 to 30 parts by mass of an organic solvent, and a radical polymerization initiator, into a tank-type reactor;
subjecting the monomer mixture to a polymerization reaction in a tank-type reactor to obtain a reaction product;
continuously withdrawing the reaction product from the tank reactor; and removing the monomer mixture remaining in the withdrawn reaction product from the reaction product;
When the average concentration of the radical polymerization initiator present in the liquid in the tank reactor is I mol/L and the average residence time of the reaction raw materials in the tank reactor is θ hr, the product I×θ exceeds 1.0×10 ⁻⁵ mol·hr/L and is less than 1.5×10 ⁻⁴ mol·hr/L, the polymerization conversion is 30 to 65% by mass.
Method for producing copolymers.

[16] The production method according to any one of [13] to [15], wherein the temperature inside the tank reactor is 110° C. or higher and 140° C. or lower, and the average residence time θ of the reaction raw materials in the tank reactor is 1.5 to 5 hours.
[17] The production method according to any one of [13] to [16], wherein the step of removing the monomer mixture remaining in the withdrawn reaction product from the reaction product is carried out by an adiabatic flash evaporation method.
[18] The method according to any one of [13] to [17], further comprising a step of adding an antioxidant to the withdrawn reaction product.
[19] The production method according to any one of [13] to [18], wherein the reaction raw materials further contain a chain transfer agent.

The methacrylic copolymer of the present invention has high heat resistance, low saturated water absorption, and low absolute values of orientation birefringence and photoelastic coefficient. The molded article of the present invention is suitable as an optical component such as a polarizing plate protective film.

According to the production method of the present invention, continuous bulk polymerization of methyl methacrylate, α-methylstyrene, and, if necessary, other monomers copolymerizable therewith, can be carried out with a short average residence time and a high polymerization conversion rate, so that the above-mentioned copolymers and the like can be produced with high productivity, high flexibility, or high responsiveness. The production method of the α-methylstyrene copolymer of the present invention is suitable for producing the methacrylic copolymer of the present invention.

The methacrylic copolymer of the present invention is composed of structural units derived from methyl methacrylate (sometimes referred to in the present application as "methyl methacrylate units"), structural units derived from α-methylstyrene (sometimes referred to in the present application as "α-methylstyrene units"), and structural units derived from other copolymerizable monomers (sometimes referred to in the present application as "other copolymerizable monomer units").

The total content of structural units derived from methyl methacrylate is usually from 70 to 93% by mass, preferably from 73 to 93% by mass, and more preferably from 75 to 92% by mass.
The total content of structural units derived from α-methylstyrene is usually from 7 to 30% by mass, preferably from 7 to 27% by mass, and more preferably from 8 to 25% by mass.
The total content of structural units derived from other copolymerizable monomers is usually 0 to 23 mass%, preferably 0 to 20 mass%, more preferably 0 to 17 mass%, even more preferably 0 to 10 mass%, and still more preferably 0 to 5 mass%.
The total of the methyl methacrylate units, the α-methylstyrene units, and other monomer units copolymerizable therewith is 100% by mass.

Other copolymerizable monomers include, for example, alkyl methacrylate esters having an alkyl group with two or more carbon atoms, such as ethyl methacrylate and butyl methacrylate; aryl methacrylate esters such as phenyl methacrylate; cycloalkyl methacrylate esters such as cyclohexyl methacrylate and norbornenyl methacrylate; alkyl acrylate esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; aryl acrylate esters such as phenyl acrylate; cycloalkyl acrylate esters such as cyclohexyl acrylate and norbornenyl acrylate; vinyl monomers having only one polymerizable carbon-carbon double bond in one molecule, such as styrene, p-methylstyrene, m-methylstyrene; acrylamide; methacrylamide; acrylonitrile; methacrylonitrile; methacrylic acid; and acrylic acid.

In the methacrylic copolymer of the present invention, the other copolymerizable monomer unit may be a structural unit derived from a monomer capable of introducing a ring structure into the main chain by a radical polymerization reaction (sometimes referred to as a "monomer unit having a ring structure" in the present application).
Examples of monomers capable of introducing a ring structure into the main chain by radical polymerization reaction include N-alkylmaleimide monomers such as N-methylmaleimide, N-ethylmaleimide, N-butylmaleimide, and N-cyclohexylmaleimide; N-arylmaleimide monomers such as N-phenylmaleimide, N-methylphenylmaleimide, and N-chlorophenylmaleimide; maleic anhydride, itaconic anhydride; and cycloolefins such as norbornene, ethylidenenorbornene, dicyclopentadiene, and tetracyclododecene. The monomers capable of introducing a ring structure into the main chain by radical polymerization reaction can be used alone or in combination of two or more. Of these, maleic anhydride is preferred.
The total content of monomer units having a ring structure is preferably from 1 to 23% by mass, more preferably from 2 to 20% by mass.

The methacrylic copolymer of the present invention has a value of |A-B|/B, which is calculated by the formula: usually less than 0.05, preferably less than 0.04, and more preferably less than 0.03. This suggests that the methacrylic copolymer of the present invention contains structural units that absorb light at a wavelength of 254 nm in equal proportions regardless of the molecular weight, and that the degree of growth of the molecular chain has almost no effect on the copolymerization composition ratio. A is the molecular weight at the peak top in the differential molecular weight distribution curve obtained by gel permeation chromatography measurement using a differential refractive index detector, and B is the molecular weight at the peak top in the differential molecular weight distribution curve obtained by gel permeation chromatography measurement using an absorbance detector with a detection wavelength of 254 nm. |A-B| is the absolute value of the difference between A and B. The molecular weight of the methacrylic copolymer is calculated from the elution time of the methacrylic copolymer using a calibration curve showing the relationship between the molecular weight of standard polystyrene and the elution time (retention time). The peak top molecular weight in the differential molecular weight distribution curve is the molecular weight at the inflection point or maximum slope point in the integrated molecular weight distribution curve.

The methacrylic copolymer of the present invention has a weight average molecular weight Mw of preferably 30,000 to 200,000, more preferably 40,000 to 180,000, and even more preferably 50,000 to 160,000. Mw is calculated using formula (2) from the molecular weight distribution obtained by gel permeation chromatography measurement using a differential refractive index detector.
Mw=Σ(M _i ² ×N _i )/Σ(M _i ×N _i )=Σ(C _i ×M _i )/Σ(C _i ) (2)
N is the number of polymer molecules, M is the molecular weight, and C is the concentration, with the relationship C=M×N.
The smaller the Mw, the more brittle the molded product tends to be. The larger the Mw of a methacrylic copolymer, the lower the productivity tends to be.
The number average molecular weight Mn is calculated from the molecular weight distribution obtained by gel permeation chromatography measurement using a differential refractive index detector using formula (3).
Mn=Σ(M _i ×N _i )/Σ(N _i )=Σ(C _i )/Σ(N _i ) (3)
N is the number of polymer molecules, M is the molecular weight, and C is the concentration, with the relationship C=M×N.

Gel permeation chromatography measurements can be performed as follows. Tetrahydrofuran is used as the eluent, and two TSKgel SuperMultipore HZMM columns manufactured by Tosoh Corporation and a SuperHZ4000 column connected in series are used as the column. The analytical device used is a Tosoh Corporation HLC-8320 (product number) equipped with a differential refractive index detector (RI detector) and an absorbance detector (detection wavelength 254 nm). 4 mg of the resin material is dissolved in 5 ml of tetrahydrofuran, and the solution is filtered through a 0.1 μm filter to prepare a test solution. The temperature of the column oven is set to 40°C, and 20 μl of the test solution is injected at an eluent flow rate of 0.35 ml/min to obtain a chromatogram. There are two types of chromatograms: a chart in which the electric signal value (intensity Y) derived from the refractive index difference between the test solution and the reference solution is plotted against the retention time X, and a chart in which the electric signal value (intensity Y) derived from the absorbance at a wavelength of 254 nm is plotted against the retention time X. Standard polystyrenes with molecular weights in the range of 400 to 5,000,000 are measured by gel permeation chromatography, and a calibration curve showing the relationship between retention time and molecular weight is created. The line connecting the point where the slope of the high molecular weight side of the peak changes from zero to positive and the point where the slope of the low molecular weight side of the peak changes from negative to zero is taken as the baseline.

The methacrylic copolymer of the present invention has a glass transition temperature Tg of preferably 125°C or higher, more preferably 126°C or higher, and even more preferably 128°C or higher. There is no particular upper limit to the glass transition temperature of the methacrylic copolymer of the present invention, but it is preferably 140°C.

The glass transition temperature is the midpoint glass transition temperature obtained from the DSC curve. The DSC curve is obtained by using a differential scanning calorimeter to heat the resin to be measured to 230°C in accordance with JIS K7121, then cooling it to room temperature, and then heating it from room temperature to 230°C at a rate of 10°C/min, and then performing differential scanning calorimetry during the second heating. The higher the glass transition temperature of the methacrylic copolymer, the less likely it is that a molded product made of it will deform or shrink due to heat, i.e., the higher its heat resistance.

The methacrylic copolymer of the present invention has a photoelastic coefficient K of preferably −4.3×10 ⁻¹² /Pa to +4.3×10 ⁻¹² /Pa, more preferably −4.0×10 ⁻¹² /Pa to +4.0×10 ⁻¹² /Pa, and even more preferably −3.0×10 ⁻¹² /Pa to +3.0 ^{×10 −12} /Pa. A methacrylic copolymer having a photoelastic coefficient within the above range is likely to provide a molded article with small stress birefringence.
The photoelastic coefficient is a slope calculated by approximating the relationship between the measured stress and the birefringence to a linear function using the least squares method, when a tension is applied to a press-molded sheet of 15 mm width x 60 mm length x 1.0 mm thickness made of a methacrylic copolymer, with a chuck distance of 45 mm and a temperature of 23°C, increasing the tension from 0 N to 100 N by 10 N increments, and measuring the birefringence of the central part of the sheet at a temperature of 23°C and a D-line wavelength of Na each time the tension is increased. The stress is the value obtained by dividing the tension by the cross-sectional area of the sheet. The cross-sectional area of the sheet was calculated as the product of the sheet width of 15 mm and the thickness at the measurement point of the central part of the sheet. The birefringence is defined as the difference (Δn=n _p -n _o ) between the refractive index n _p of light having a polarization plane parallel to the tensile direction and the refractive index n _o of light having a polarization plane perpendicular to the tensile direction.

The methacrylic copolymer of the present invention has an orientation birefringence Δn of preferably -10×10 ^-4 to +10×10 ^-4 , more preferably -2.5×10 ^-4 to +2.5×10 ^-4 , even more preferably -2.4×10 ^-4 to +2.4×10 ^-4 , still more preferably -2.3×10 ^-4 to +2.3×10 ^-4 , and most preferably -2.2×10 ^-4 to +2.2×10 ^-4 . Here, the orientation birefringence is the birefringence measured at a temperature of 23°C, at a D-line wavelength of Na, at the central part of a stretched film obtained by stretching a press-molded sheet of a methacrylic copolymer having a width of 20 mm, a length of 40 mm, and a thickness of 1.0 mm in one direction at a temperature 10°C higher than the glass transition temperature and at a speed of 3 mm/min, without applying tension.

The methacrylic copolymer of the present invention preferably has a saturated water absorption As of less than 1.9%, more preferably less than 1.8%.
The saturated water absorption is determined as follows. A press-molded sheet of 50 mm x 50 mm x 1.0 mm thick made of a methacrylic copolymer is placed in a dryer at 80 ° C. and dried for 16 hours or more. The dried sheet is returned to room temperature and the initial weight W _O is weighed to an accuracy of 0.1 mg. Then, it is immersed in distilled water at 23 ° C. for 24 hours, drained, wiped off with a dry cloth, etc., and weighed to an accuracy of 0.1 mg within 1 minute after wiping. It is again immersed in distilled water at 23 ° C. for 24 hours, drained, wiped off with a dry cloth, etc., and weighed to an accuracy of 0.1 mg within 1 minute after wiping, and this is repeated. The weight when the weight change is less than 0.02% of the initial weight W _O is taken as the saturated weight W _S , and the saturated water absorption As is calculated by the following formula.
Saturated water absorption rate As = (( _WS - W _O )/W _O )×100

The methacrylic copolymer of the present invention is not particularly limited by its manufacturing method as long as it satisfies the above characteristic values. The methacrylic copolymer of the present invention can be obtained, for example, by the manufacturing method of the methacrylic copolymer of the present invention.

The method for producing a methacrylic copolymer of the present invention comprises continuously supplying reaction raw materials to a tank reactor, polymerizing the monomer mixture in the tank reactor to obtain a reaction product, continuously withdrawing the reaction product from the tank reactor, and removing the monomer mixture remaining in the withdrawn reaction product from the reaction product.

(Production Method I)
One embodiment of the method for producing the methacrylic copolymer of the present invention (production method I) comprises continuously supplying a reaction raw material comprising a monomer mixture containing 70 to 93 mass % of methyl methacrylate, 7 to 30 mass % of α-methylstyrene, and 0 to 23 mass % of other monomers copolymerizable therewith, and a radical polymerization initiator, to a tank reactor, bulk polymerizing the monomer mixture in the tank reactor at a polymerization conversion rate of 30 to 60 mass % to obtain a reaction product, continuously withdrawing the reaction product from the tank reactor, and removing the monomer mixture remaining in the withdrawn reaction product from the reaction product.

The reaction raw materials used in manufacturing method I of the present invention contain a monomer mixture and a radical polymerization initiator, preferably a monomer mixture, a chain transfer agent, and a radical polymerization initiator.

The monomer mixture contains methyl methacrylate and α-methylstyrene, and, optionally, other monomers copolymerizable therewith.

The amount of methyl methacrylate contained in the monomer mixture is usually from 67 to 93% by mass, preferably from 69 to 92% by mass, and more preferably from 70 to 90% by mass.
The amount of α-methylstyrene contained in the monomer mixture is usually 7 to 33 mass%, preferably 7 to 31 mass%, more preferably 7 to 30 mass%, even more preferably 8 to 30 mass%, and still more preferably 10 to 30 mass%.
The amount of other copolymerizable monomers contained in the monomer mixture is usually 0 to 23 mass%, preferably 0 to 20 mass%, more preferably 0 to 17 mass%, even more preferably 0 to 10 mass%, and still more preferably 0 to 5 mass%.
The monomer mixture is 100% by mass in total of methyl methacrylate, α-methylstyrene, and other monomers copolymerizable therewith.
The amount of the monomer capable of introducing a ring structure into the main chain by a radical polymerization reaction as the other copolymerizable monomer contained in the monomer mixture is preferably 1 to 23% by mass, and preferably 2 to 20% by mass. By including such an amount of the monomer in the monomer mixture, the polymerization rate of α-methylstyrene, which has low copolymerization reactivity with methyl methacrylate, is likely to increase, and in a continuous polymerization system, the polymerization conversion rate can be easily increased with a short average residence time and a moderate amount of initiator. The other copolymerizable monomer and the monomer capable of introducing a ring structure into the main chain by a polymerization reaction are as described above.

The monomer mixture preferably has b ^* of -1 to 2, more preferably -0.5 to 1.5. When b ^* is in this range, it is advantageous for obtaining molded products with almost no coloring at high productivity when the resulting α-methylstyrene-methyl methacrylate copolymer is molded. Note that b ^* is a value measured in accordance with the Commission Internationale de l'Eclairage (CIE) standard (1976) or JIS Z-8722.

In the step of removing the monomer mixture remaining in the reaction product discharged from the tank reactor from the reaction product, the monomer mixture removed from the reaction product can be recovered and reused in the present invention. If the b ^* of the recovered monomer mixture becomes high due to heat applied during recovery, it is preferable to purify it by an appropriate method to make the b ^* within the above range.

A chain transfer agent can be included in the reaction raw materials in order to adjust the molecular weight of the copolymer. Examples of chain transfer agents that can be used in the present invention include alkyl mercaptans such as n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, 1,4-butanedithiol, 1,6-hexanedithiol, ethylene glycol bisthiopropionate, butanediol bisthioglycolate, butanediol bisthiopropionate, hexanediol bisthioglycolate, hexanediol bisthiopropionate, trimethylolpropane tris-(β-thiopropionate), and pentaerythritol tetrakisthiopropionate; α-methylstyrene dimer; and terpinolene. Among these, monofunctional alkyl mercaptans such as n-octyl mercaptan and n-dodecyl mercaptan are preferred. These chain transfer agents can be used alone or in combination of two or more. The amount of the chain transfer agent used is preferably 0 to 1 part by mass, with the lower limit being more preferably 0.0001 part by mass, even more preferably 0.01 part by mass, and even more preferably 0.02 part by mass, and the upper limit being more preferably 0.8 part by mass, even more preferably 0.6 part by mass, and still more preferably 0.4 part by mass, relative to 100 parts by mass of the monomer mixture.

The radical polymerization initiator used in the present invention generates reactive radicals. As the radical polymerization initiator, for example, t-hexylperoxy isopropyl monocarbonate, t-hexylperoxy 2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, t-butylperoxypivalate, t-hexylperoxypivalate, t-butylperoxyneodecanoate, t-hexylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1,1-bis(t-hexylperoxy)cyclohexane, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, 2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2-methylbutyronitrile), and dimethyl 2,2'-azobis(2-methylpropionate) are preferable; Examples of the radical polymerization initiator include t-hexylperoxy 2-ethylhexanoate, 1,1-bis(t-hexylperoxy)cyclohexane, and dimethyl 2,2'-azobis(2-methylpropionate). These radical polymerization initiators can be used alone or in combination of two or more. The amount of the radical polymerization initiator used is preferably set so as to satisfy the average concentration of the radical polymerization initiator present in the liquid in the tank-type reactor, which will be described later.

The method of preparing the reaction raw materials is not particularly limited. The reaction raw materials are preferably prepared immediately before being supplied to the tank-type reactor. The reaction raw materials are also preferably prepared in an inert atmosphere such as nitrogen gas. For example, it is preferable to continuously supply each component constituting the reaction raw materials from a tank storing the components to a mixer through a pipe, and mix the components in the mixer to obtain the reaction raw materials. The radical polymerization initiator can be prepared as a solution by dissolving it in methyl methacrylate. The mixer can be equipped with a dynamic stirrer or a static stirrer. The obtained reaction raw materials are then continuously supplied to the tank-type reactor.

The monomer mixture can be prepared before mixing with the chain transfer agent and/or radical polymerization initiator. The radical polymerization initiator is preferably dissolved in methyl methacrylate to form a polymerization initiator solution, which is then mixed with the monomer or with a mixture of the monomer and the chain transfer agent in a predetermined ratio. The polymerization initiator solution may have a dissolved oxygen content of preferably more than 3 ppm, more preferably more than 5 ppm, and even more preferably more than 10 ppm. The monomer mixture or the reaction raw material may be prepared in the presence of oxygen. The monomer mixture or the reaction raw material immediately after preparation may have a dissolved oxygen content of preferably more than 3 ppm, more preferably more than 5 ppm, and even more preferably more than 10 ppm.

The amount of dissolved oxygen in the reaction raw materials immediately before being fed to the tank reactor is preferably 10 ppm or less, more preferably 5 ppm or less, even more preferably 4 ppm or less, and most preferably 3 ppm or less. If the amount of dissolved oxygen is within this range, the polymerization reaction proceeds smoothly, making it easier to obtain molded products without silver streaks or coloring. The amount of dissolved oxygen in the reaction raw materials immediately before being fed can be adjusted by purging the reaction raw materials with nitrogen immediately after preparation to expel the oxygen.

The tank reactor used in the present invention is capable of simultaneously supplying the reaction raw materials, polymerizing the monomer mixture, and withdrawing the reaction product in parallel. The tank reactor is usually equipped with a stirring means for stirring the liquid in the tank reactor, a supply port for supplying the reaction raw materials to the tank reactor, and a withdrawal port for withdrawing the reaction product from the tank reactor. The amount of the reaction raw materials supplied to the tank reactor and the amount of the reaction product withdrawn from the tank reactor are balanced so that the amount of liquid in the tank reactor is almost constant. The amount of liquid in the tank reactor (volume V) is preferably 1/4 or more, more preferably 1/4 to 3/4, and even more preferably 1/3 to 2/3 of the volume of the tank reactor.

The tank reactor used in the present invention preferably has a plurality of supply ports for supplying the reaction raw materials. The reaction raw materials are continuously supplied from at least two supply ports simultaneously or alternately, preferably simultaneously. The supply ports may be installed on the top surface of the tank reactor, on the side surface of the tank reactor, on the bottom surface of the tank reactor, or on at least two of the top surface, side surface, and bottom surface. It is also preferable that the supply ports are arranged in symmetrical positions. The height of the supply port may be higher than the liquid level in the tank reactor, or lower than the liquid level in the tank reactor. The shape of the supply port may be the shape of the cut end of the circular tube itself, or may be a shape that allows the reaction raw materials to be widely spread over the liquid surface in the tank reactor. By providing at least two supply ports, the efficiency of the radical generation reaction is increased, and the amount of radical polymerization initiator required to achieve the desired polymerization conversion rate can be reduced.

Examples of mixing means include a Max Blend type mixer, a lattice blade type mixer, a propeller type mixer, a screw type mixer, a helical ribbon type mixer, a paddle type mixer, etc. Of these, a Max Blend type mixer is preferred from the viewpoint of uniform mixing.

The temperature inside the tank reactor, i.e., the temperature of the liquid inside the tank reactor, is preferably 110 to 140° C., more preferably 114 to 135° C. The temperature of the liquid can be controlled by an external heat exchanger control method such as a jacket or a heat transfer tube, or a self-heat exchanger control method in which a tube through which the reaction raw materials or reaction products flow is arranged inside the reaction tank.

The average residence time of the reaction raw materials in the tank reactor is preferably 1.5 to 5 hours, more preferably 2 to 4.5 hours, and further preferably 2.5 to 4 hours. The average concentration of the radical polymerization initiator present in the liquid in the tank reactor is preferably 5.1×10 ^-5 mol/L or more and 2.4×10 ^-4 mol/L or less.

In principle, no solvent is used in bulk polymerization, but if it is necessary to adjust the viscosity of the liquid in the tank reactor, a solvent can be included in the reaction raw materials. As the solvent, aromatic hydrocarbons such as benzene, toluene, and ethylbenzene are preferable. These solvents can be used alone or in combination of two or more. The amount of such a solvent to be used is preferably 30 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 0 parts by mass, per 100 parts by mass of the monomer mixture.

In the manufacturing method I of the present invention, the amount of water contained in the liquid in the tank reactor is preferably 1000 ppm or less, more preferably 700 ppm or less, and even more preferably 280 ppm or less. By reducing the water content, it is possible to suppress the generation of resin foreign matter of several μm to several tens of μm during the polymerization reaction, and it is possible to significantly reduce the occurrence of defects with an outer diameter of several tens of μm caused by the foreign matter when the composition containing the obtained copolymer is formed into a film or sheet by melt molding.

Methods for reducing the amount of water contained in the liquid in a tank reactor include, for example, a method involving pretreating the reaction raw materials in an adsorption/dehydration tower or the like, and a method involving introducing an inert gas into the gas phase of the tank reactor, entraining some of the water vapor with the inert gas, condensing it in a brine-cooled condenser, and withdrawing it from the system.

In a tank reactor, bulk polymerization is carried out until the polymerization conversion rate is 30 to 65% by mass, preferably 35 to 60% by mass, more preferably 35 to 45% by mass, and even more preferably 35 to 40% by mass. The polymerization conversion rate can be calculated from the content of the copolymer or monomer mixture present in the reaction product extracted from the tank reactor relative to the content in the reaction raw materials. Bulk polymerization in a tank reactor is preferably carried out in an atmosphere of an inert gas such as nitrogen gas.

An additional reactor may be connected to the rear of the tank reactor. The additional reactor that can be connected to the rear may be tank type or tubular type. In the additional reactor, bulk polymerization continues. Bulk polymerization in the additional reactor may be performed until the polymerization conversion rate is 30 to 65 mass%, preferably 35 to 60 mass%, more preferably 35 to 45 mass%, and even more preferably 35 to 40 mass%. The polymerization conversion rate can be calculated as a value relative to the content in the reaction raw materials from the content of the copolymer or monomer mixture present in the reaction product extracted from the additional reactor. Bulk polymerization in the additional reactor is preferably performed in an atmosphere of an inert gas such as nitrogen gas.

According to Production Method I of the present invention, the ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture can be preferably 0.7 to 1.0, more preferably 0.79 to 0.99. Specifically, the mass fraction of α-methylstyrene in the monomer mixture is 7 to 30 mass%, preferably 10 to 25 mass%, but according to Production Method I of the present invention, the mass fraction of α-methylstyrene units in the copolymer can be 5 to 27 mass%, preferably 8 to 24 mass%.

The manufacturing method I of the present invention has a step of removing the monomer mixture from the reaction product. In this step, the solvent is also removed at the same time, if necessary. The copolymer is isolated by this step. The removal method is not particularly limited, but a thermal devolatilization method is preferred. Examples of the thermal devolatilization method include an equilibrium flash evaporation method and an adiabatic flash evaporation method, but the adiabatic flash evaporation method is preferred. The temperature at which the adiabatic flash evaporation method is performed is preferably 200 to 300°C, more preferably 200 to 280°C, more preferably 210 to 280°C, and even more preferably 220 to 270°C. If the temperature at which the adiabatic flash evaporation method is performed is too low, devolatilization takes time, devolatilization becomes insufficient, and the molded product may have a poor appearance such as silver. On the other hand, if the temperature at which the adiabatic flash evaporation method is performed is too high, the copolymer tends to be colored due to oxidation, burning, decomposition, etc., or the copolymer tends to undergo a depolymerization reaction. The adiabatic flash evaporation method may be performed in multiple stages. In this case, the reaction product flowing through the heat transfer tube is heated with the vapor of the flash evaporated monomer mixture, and the heated reaction product is supplied to a low-pressure flash tank for flash evaporation. The reaction product can be pressurized by a pump or the like.

The copolymer obtained by removing the monomer mixture from the reaction product can be made into pellets or powder according to a known method to facilitate easy handling as a molding material. The amount of the monomer mixture contained in the copolymer after removing the monomer mixture is preferably 1 mass % or less, more preferably 0.5 mass % or less. It is preferable to use a vented extruder to remove the monomer mixture and to convert the isolated copolymer into a molding material and/or to mix the additives described below.

(Production Method II)
One embodiment of a production method (production method II) suitable for producing the methacrylic copolymer of the present invention comprises continuously supplying reaction raw materials comprising a monomer mixture containing 70 to 93 mass % methyl methacrylate, 7 to 30 mass % α-methylstyrene, and 0 to 10 mass % of other monomers copolymerizable therewith, and a radical polymerization initiator to a tank reactor, bulk polymerizing the monomer mixture in the tank reactor at a polymerization conversion rate of 30 to 60 mass % to obtain a reaction product, continuously withdrawing the reaction product from the tank reactor, and removing the monomer mixture remaining in the withdrawn reaction product from the reaction product, wherein when the average concentration of the radical polymerization initiator present in the liquid in the tank reactor is I mol/L and the average residence time of the reaction raw materials in the tank reactor is θ hr, their product I×θ exceeds 1×10 ^-4 mol hr/L and is less than 1×10 ^-3 mol hr/L. By the production method II, not only the methacrylic copolymer of the present invention but also other copolymers can be obtained.

The amount of methyl methacrylate contained in the monomer mixture is usually from 70 to 93% by mass, preferably from 75 to 90% by mass.
The amount of α-methylstyrene contained in the monomer mixture is usually from 7 to 30% by mass, preferably from 10 to 25% by mass.
The content of other copolymerizable monomers contained in the monomer mixture is usually 0 to 10% by mass, preferably 0 to 5% by mass.
The monomer mixture was 100% by mass in total of methyl methacrylate, α-methylstyrene, and other monomers copolymerizable therewith.

In production method II, the amount of reactant material supplied to the tank reactor, Q ^m3 /hr, and the concentration of the radical polymerization initiator in the reactant material supplied to the tank reactor, _I0 mol/L, are set so that the product I×θ of the average concentration I mol/L of the radical polymerization initiator present in the liquid in the tank reactor and the average residence time θ hr of the reactant material in the tank reactor exceeds 1× ^10-4 mol·hr/L and is less than 1× ^10-3 mol·hr/L. The average residence time θ hr is the ratio V/Q of the volume V ^m3 of the liquid in the tank reactor to the amount Q ^m3 /hr of the reactant material supplied to the tank reactor.
The average concentration I of the radical polymerization initiator present in the liquid in the tank reactor is a value calculated by the following formula from the concentration I ₀ mol/L of the radical polymerization initiator in the reaction raw material supplied to the tank reactor, the half-life τ _1/2 hr of the radical polymerization initiator at the temperature of the liquid in the tank reactor, and the average residence time θ hr of the reaction raw material in the tank reactor.
I=I ₀ /(1+k _d ×θ×3600)
k _d = ln(2)/τ _1/2 or k _d = A×exp(-ΔE/RT)
In addition, A is the frequency factor, ΔE is the activation energy, R is the gas constant (8.314 J/mol/K), T is the absolute temperature (K), τ _1/2 is the half-life of the radical polymerization initiator at absolute temperature T (K), and k _d is the decomposition rate constant (1/sec) of the radical polymerization initiator at absolute temperature T (K).

In manufacturing method II, the average residence time θ of the reaction raw materials in the tank reactor is not particularly limited as long as the above relationship is satisfied, but is preferably 1.5 to 5 hours, more preferably 2 to 4.5 hours, and even more preferably 2.5 to 4 hours.

In Production Method II, the average concentration I of the radical polymerization initiator present in the liquid in the tank reactor is not particularly limited as long as the above relationship is satisfied, but is preferably 5.1×10 ⁻⁵ mol/L or more and 2.4×10 ⁻⁴ mol/L or less.

Other conditions in manufacturing method II are the same as in manufacturing method I.

According to the manufacturing method II, the ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture can be preferably 0.7 to 1.0, more preferably 0.79 to 0.99. Specifically, the mass fraction of α-methylstyrene in the monomer mixture of 7 to 30% by mass, preferably 10 to 25% by mass, can be changed by the manufacturing method of the present invention to a mass fraction of α-methylstyrene units in the copolymer of 5 to 27% by mass, preferably 8 to 24% by mass.

By using the manufacturing method II, copolymers having various molecular weight distributions can be obtained. For example, the copolymers obtained by the manufacturing method II preferably have a weight average molecular weight of 35,000 to 200,000, more preferably 40,000 to 150,000, and even more preferably 45,000 to 130,000, from the viewpoints of flowability, moldability, impact resistance, toughness, and the like. In addition, the ratio of the weight average molecular weight to the number average molecular weight is preferably 1.5 to 3.0, more preferably 1.6 to 2.6, and particularly preferably 1.7 to 2.3. The weight average molecular weight and the number average molecular weight are calculated by converting the molecular weight of standard polystyrene based on a chromatogram measured by gel permeation chromatography.

(Production Method III)
One embodiment of the production method (production method III) suitable for producing the methacrylic copolymer of the present invention comprises continuously supplying reaction raw materials comprising 100 parts by mass of a monomer mixture consisting of 40 to 92 mass% methyl methacrylate, 7 to 25 mass% α-methylstyrene, 1 to 25 mass% of a monomer capable of introducing a ring structure into the main chain by polymerization reaction, and 0 to 10 mass% of other monomers copolymerizable therewith, 0 to 30 parts by mass of an organic solvent, and a radical polymerization initiator to a tank reactor, polymerizing the monomer mixture in the tank reactor to obtain a reaction product, continuously withdrawing the reaction product from the tank reactor, and removing the monomer mixture remaining in the withdrawn reaction product from the reaction product, wherein when the average concentration of the radical polymerization initiator present in the liquid in the tank reactor is I mol/L and the average residence time of the reaction raw materials in the tank reactor is θ hr, the product I× ^θ exceeds 1.0× ¹⁰ When the conversion rate is less than mol·hr/L, the polymerization conversion rate is 30 to 65% by mass. By the production method III, not only the methacrylic copolymer of the present invention but also other copolymers can be obtained.

In Production Method III, the amount of methyl methacrylate contained in the monomer mixture is usually from 40 to 92% by mass, preferably from 53 to 86% by mass.
In Production Method III, the amount of α-methylstyrene contained in the monomer mixture is usually from 7 to 25% by mass, preferably from 10 to 20% by mass.
In Production Method III, the amount of the monomer capable of introducing a ring structure into the main chain by polymerization reaction contained in the monomer mixture is usually 1 to 25% by mass, and preferably 2 to 20% by mass. By including such an amount of the monomer capable of introducing a ring structure into the main chain by polymerization reaction in the monomer mixture, the polymerization rate of α-methylstyrene, which has low copolymerization reactivity with methyl methacrylate, tends to increase, and in a continuous polymerization system, the polymerization conversion rate can be easily increased with a short average residence time and an appropriate amount of initiator.
In the production method III, the amount of the other monomer contained in the monomer mixture is usually from 0 to 10% by mass, preferably from 2 to 7% by mass.
In addition, the monomer mixture in Production Method III is 100 mass % in total of methyl methacrylate, α-methylstyrene, a monomer capable of introducing a ring structure into the main chain by a polymerization reaction, and other monomers copolymerizable therewith.

Examples of other monomers in the manufacturing method III include aromatic vinyl monomers other than α-methylstyrene, such as styrene, p-methylstyrene, and m-methylstyrene; cyanide vinyl monomers such as acrylonitrile and methacrylonitrile; alkyl methacrylate esters having an alkyl group with 2 or more carbon atoms, such as ethyl methacrylate and butyl methacrylate; aryl methacrylate esters, such as phenyl methacrylate; cycloalkyl methacrylate esters, such as cyclohexyl methacrylate and norbornenyl methacrylate; alkyl acrylate esters, such as methyl acrylate, ethyl acrylate, and butyl acrylate; aryl acrylate esters, such as phenyl acrylate; cycloalkyl acrylate esters, such as cyclohexyl acrylate and norbornenyl acrylate; vinyl carboxylic acid monomers, such as acrylic acid and methacrylic acid. The other monomers can be used alone or in combination of two or more.

In production method III, the amount of reaction raw materials supplied to the tank reactor, Q ^m3 /hr, and the concentration of the radical polymerization initiator in the reaction raw materials supplied to the tank reactor, _I0 mol/L, are set so that the product I×θ of the average concentration I mol/L of the radical polymerization initiator present in the liquid in the tank reactor and the average residence time θ hr of the reaction raw materials in the tank reactor exceeds 1× ^10-5 mol·hr/L and is less than 1.5× ^10-4 mol·hr/L. The average residence time θ hr is the ratio V/Q of the volume V ^m3 of the liquid in the tank reactor to the amount Q ^m3 /hr of the reaction raw materials supplied to the tank reactor.
The average concentration I of the radical polymerization initiator present in the liquid in the tank reactor is a value calculated by the following formula from the concentration I ₀ mol/L of the radical polymerization initiator in the reaction raw material supplied to the tank reactor, the half-life τ _1/2 hr of the radical polymerization initiator at the temperature of the liquid in the tank reactor, and the average residence time θ hr of the reaction raw material in the tank reactor.
I=I ₀ /(1+k _d ×θ×3600)
k _d = ln(2)/τ _1/2 = A×exp(-ΔE/RT)
In addition, A is the frequency factor, ΔE is the activation energy, R is the gas constant (8.314 J/mol/K), T is the absolute temperature (K), τ _1/2 is the half-life of the radical polymerization initiator at absolute temperature T (K), and k _d is the decomposition rate constant (1/sec) of the radical polymerization initiator at absolute temperature T (K).

In manufacturing method III, the average residence time θ of the reaction raw materials in the tank reactor is not particularly limited as long as the above relationship is satisfied, but is preferably 1 to 6 hours, more preferably 1.5 to 5 hours, even more preferably 2 to 4.5 hours, and even more preferably 2.5 to 4 hours.

In production method III, the average concentration I of the radical polymerization initiator present in the liquid in the tank reactor is not particularly limited as long as the above relationship is satisfied, but is, for example, 5.1×10 ⁻⁵ mol/L or more and 2.4×10 ⁻⁴ mol/L or less, preferably 1.0×10 ⁻⁶ mol/L or more and 2.4×10 ⁻⁴ mol/L or less, more preferably 5.0×10 ⁻⁶ mol/L or more and 8.0×10 ⁻⁵ mol/L or less, and even more preferably 6.0×10 ⁻⁶ mol/L or more and 5.5×10 ⁻⁵ mol/L or less.

In the manufacturing method III, an organic solvent can be included in the reaction raw materials. Examples of the organic solvent include aromatic hydrocarbons such as benzene, toluene, xylene, chlorobenzene, and ethylbenzene; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and acetophenone; and ethers such as tetrahydrofuran and 1,4-dioxane. From the viewpoint of the solubility of the monomer and copolymer and the ease of solvent recovery, methyl ethyl ketone, methyl isobutyl ketone, and toluene are preferred. The organic solvent can be used alone or in combination of two or more. The upper limit of the amount of the organic solvent used is preferably 30 parts by mass, more preferably 25 parts by mass, and even more preferably 20 parts by mass, relative to 100 parts by mass of the monomer mixture. The lower limit of the amount of the organic solvent used is usually 0 parts by mass, and preferably 1 part by mass.

Other conditions in manufacturing method III are the same as those in manufacturing method I.

According to the manufacturing method III, the ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene can be preferably 0.8 or more, more preferably 0.9 or more. For example, the mass fraction of α-methylstyrene in the monomer mixture is 7 to 25% by mass, preferably 10 to 20% by mass, but the mass fraction of α-methylstyrene units in the copolymer can be 6 to 30.0% by mass, preferably 7 to 24.9% by mass, more preferably 8 to 19.9% by mass, according to the manufacturing method of the present invention.

By using the production method III, copolymers having various molecular weight distributions can be obtained. For example, the copolymers obtained by the production method III preferably have a weight average molecular weight of 35,000 to 200,000, more preferably 40,000 to 150,000, and even more preferably 45,000 to 130,000, from the viewpoints of flowability, moldability, impact resistance, toughness, and the like. In addition, the ratio of the weight average molecular weight to the number average molecular weight is preferably 1.5 to 3.0, more preferably 1.6 to 2.6, and particularly preferably 1.7 to 2.3. The weight average molecular weight and the number average molecular weight are calculated by converting the molecular weight of standard polystyrene based on a chromatogram measured by gel permeation chromatography.

The methacrylic copolymer of the present invention or the copolymer obtained by Production Method I, II, or III of the present invention can be subjected to a polymer reaction by a known method. Examples of the polymer reaction include the imidization reaction described in JP-A-2010-254742 and JP-A-2010-261025, and the grafting reaction described in JP-A-2012-201831.

Various additives can be blended with the methacrylic copolymer of the present invention as necessary to form a resin composition. The amount of the additive is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, based on the resin composition. If the amount of the additive is too large, it may cause appearance defects such as silver streaks in the molded product.

In addition, the manufacturing method I, II or III of the present invention may further include a step of adding various additives to obtain a resin composition, if necessary. The amount of additives contained in the resin composition is preferably 0.5 mass% or less, more preferably 0.2 mass% or less, based on the copolymer. If the amount of additives contained in the resin composition is too large, it may cause a molded product to have a poor appearance such as silver. The additives may be added to the reaction raw materials, the reaction product, or the copolymer.

Additives include antioxidants, heat degradation inhibitors, UV absorbers, light stabilizers, lubricants, release agents, polymer processing aids, antistatic agents, flame retardants, dyes and pigments, light diffusing agents, organic dyes, matting agents, impact resistance modifiers, and phosphors.

The antioxidant alone exhibits an effect of preventing the oxidative deterioration of the resin in the presence of oxygen. Examples of the antioxidant include phosphorus-based antioxidants, hindered phenol-based antioxidants, and thioether-based antioxidants. These antioxidants can be used alone or in combination of two or more. Among these, from the viewpoint of the effect of preventing the deterioration of optical properties due to coloring, phosphorus-based antioxidants or hindered phenol-based antioxidants are preferred, and a combination of a phosphorus-based antioxidant and a hindered phenol-based antioxidant is more preferred.
When the phosphorus-based antioxidant and the hindered phenol-based antioxidant are used in combination, their ratio is not particularly limited, but the mass ratio of the phosphorus-based antioxidant/the hindered phenol-based antioxidant is preferably 1/5 to 2/1, and more preferably 1/2 to 1/1.

Preferred phosphorus-based antioxidants include 2,2-methylenebis(4,6-di-t-butylphenyl)octyl phosphite (manufactured by Asahi Denka Co., Ltd.; product name: Adeka STAB HP-10) and tris(2,4-di-t-butylphenyl)phosphite (manufactured by Ciba Specialty Chemicals; product name: IRUGAFOS168).

Preferred examples of hindered phenol-based antioxidants include pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (manufactured by Ciba Specialty Chemicals; product name IRGANOX 1010) and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (manufactured by Ciba Specialty Chemicals; product name IRGANOX 1076).

The heat deterioration inhibitor is capable of preventing the thermal deterioration of a resin by capturing polymer radicals that are generated when the resin is exposed to high heat in a substantially oxygen-free state.
As the heat deterioration inhibitor, 2-t-butyl-6-(3'-t-butyl-5'-methyl-hydroxybenzyl)-4-methylphenyl acrylate (manufactured by Sumitomo Chemical Co., Ltd.; product name: Sumilizer GM), 2,4-di-t-amyl-6-(3',5'-di-t-amyl-2'-hydroxy-α-methylbenzyl)phenyl acrylate (manufactured by Sumitomo Chemical Co., Ltd.; product name: Sumilizer GS), etc. are preferred.

An ultraviolet absorber is a compound that has the ability to absorb ultraviolet rays. An ultraviolet absorber is a compound that is said to have the function of converting light energy into heat energy.
Examples of the ultraviolet absorbent include benzophenones, benzotriazoles, triazines, benzoates, salicylates, cyanoacrylates, oxalic acid anilides, malonic acid esters, formamidines, etc. These may be used alone or in combination of two or more.
Among these, benzotriazoles or ultraviolet absorbents having a maximum molar absorption coefficient ε _max of 1200 dm ³ ·mol ⁻¹ cm ⁻¹ or less at wavelengths of 380 to 450 nm are preferred.

Benzotriazoles are highly effective in suppressing the deterioration of optical properties, such as coloration, caused by exposure to ultraviolet light, and are therefore preferred as ultraviolet absorbents when the resin composition of the present invention is applied to applications requiring the above-mentioned properties.

Preferred benzotriazoles include 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (manufactured by Ciba Specialty Chemicals; product name TINUVIN 329) and 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (manufactured by Ciba Specialty Chemicals; product name TINUVIN 234).

Furthermore, an ultraviolet absorber having a maximum molar absorption coefficient ε _max of 1200 dm ³ ·mol ⁻¹ cm ⁻¹ or less at wavelengths of 380 to 450 nm can suppress yellowing of the resulting molded product.

The maximum molar absorption coefficient _εmax of the ultraviolet absorber is measured as follows. 10.00 mg of ultraviolet absorber is added to 1 L of cyclohexane, and dissolved until no undissolved matter is found by visual observation. This solution is poured into a quartz glass cell measuring 1 cm x 1 cm x 3 cm, and the absorbance at wavelengths of 380 to 450 nm is measured using a Hitachi U-3410 spectrophotometer. The maximum molar absorption coefficient εmax is calculated from the molecular weight (Mw) of the ultraviolet absorber and the maximum absorbance ( _Amax ) measured according to the following formula.
ε _max = [A _max /(10×10 ^-3 )]×Mw

Examples of ultraviolet absorbents having a maximum molar absorption coefficient ε _max of 1200 dm ³ ·mol ⁻¹ cm ⁻¹ or less in the wavelength range of 380 to 450 nm include 2-ethyl-2'-ethoxy-oxalanilide (manufactured by Clariant Japan KK; trade name: Sanduvoir VSU).
Among these ultraviolet absorbents, benzotriazoles are preferably used from the viewpoint of suppressing resin deterioration due to exposure to ultraviolet light.

Light stabilizers are compounds that are said to have the function of capturing radicals generated mainly by oxidation due to light. Suitable light stabilizers include hindered amines such as compounds with a 2,2,6,6-tetraalkylpiperidine skeleton.

A release agent is a compound that has the function of facilitating the release of a molded product from a mold. Examples of release agents include higher alcohols such as cetyl alcohol and stearyl alcohol; and higher fatty acid esters of glycerin such as monoglyceride stearate and diglyceride stearate. In the present invention, it is preferable to use a combination of higher alcohols and a glycerin fatty acid monoester as the release agent. When a combination of higher alcohols and a glycerin fatty acid monoester is used, the ratio is not particularly limited, but the mass ratio of higher alcohols/glycerin fatty acid monoester is preferably 2.5/1 to 3.5/1, more preferably 2.8/1 to 3.2/1.

The polymer processing aid is a compound that is effective in achieving thickness accuracy and thinning when molding the resin composition of the present invention. The polymer processing aid is usually a polymer particle having a particle size of 0.05 to 0.5 μm that can be produced by emulsion polymerization.
The polymer particles may be single-layer particles made of a polymer with a single composition ratio and a single intrinsic viscosity, or may be multi-layer particles made of two or more polymers with different composition ratios or intrinsic viscosities. Among these, preferred are particles with a two-layer structure having an inner polymer layer with a low intrinsic viscosity and an outer polymer layer with a high intrinsic viscosity of 5 dl/g or more.

It is preferable that the polymer processing aid has an intrinsic viscosity of 3 to 6 dl/g. If the intrinsic viscosity is too low, the effect of improving moldability tends to be low. If the intrinsic viscosity is too high, the melt fluidity of the resin composition tends to decrease.

The resin composition of the present invention may contain an impact resistance modifier. Examples of the impact resistance modifier include a core-shell type modifier containing an acrylic rubber or a diene rubber as a core layer component; a modifier containing multiple rubber particles, and the like.

As the organic dye, a compound having a function of converting ultraviolet rays, which are considered to be harmful to resins, into visible light is preferably used.
Examples of the light diffusing agent and the matting agent include glass particles, crosslinked polysiloxane particles, crosslinked polymer particles, talc, calcium carbonate, and barium sulfate.
Examples of fluorescent materials include fluorescent pigments, fluorescent dyes, fluorescent white dyes, fluorescent brighteners, fluorescent bleaches, and the like.

These additives may be added at the stage of the reaction raw materials, at the stage of the reaction product, or at the stage of the methacrylic copolymer or resin composition obtained after devolatilization.

Various molded articles can be obtained by molding (melt-heat molding) the methacrylic copolymer of the present invention or a resin composition thereof, or the copolymer obtained by the manufacturing method of the present invention or a resin composition thereof, using a conventional molding method such as injection molding, compression molding, extrusion molding, vacuum molding, etc. Examples of the molded articles of the present invention include signboard parts such as advertising towers, stand signs, side signs, transom signs, and rooftop signs; display parts such as showcases, partitions, and store displays; lighting parts such as fluorescent light covers, mood lighting covers, lampshades, light ceilings, light walls, and chandeliers; interior parts such as pendants and mirrors; architectural parts such as doors, domes, safety window glass, partitions, staircase wainscoting, balcony wainscoting, and roofs of leisure buildings; transportation parts such as aircraft windshields, pilot visors, motorcycle and motorboat windshields, bus visors, automobile side visors, rear visors, head wings, and headlight covers; electronic equipment parts such as audiovisual nameplates, stereo covers, television protective masks, and vending machines; and X-ray parts; equipment-related parts such as machine covers, instrument covers, experimental equipment, rulers, dials, and observation windows; optical parts such as liquid crystal protection plates, light guide plates, light guide films, Fresnel lenses, lenticular lenses, front panels of various displays, and diffusion plates; traffic-related parts such as road signs, information boards, convex mirrors, and soundproof walls; film components such as polarizer protective films, polarizing plate protective films, retardation films, surface materials for automobile interiors, surface materials for mobile phones, and marking films; home appliance components such as washing machine canopy materials and control panels, and rice cooker top panels; and others.

The present invention will be described in more detail below with reference to the following examples. Note that the present invention is not limited to the following examples. Furthermore, the present invention encompasses all aspects that are any combination of the items expressing the technical characteristics, such as the characteristic values, shapes, manufacturing methods, and uses, described above.

Measurements of physical properties were carried out using the following methods.

(Polymerization Conversion Rate)
A gas chromatograph GC-14A manufactured by Shimadzu Corporation was connected to an INERTCAP1 column (df=0.4 μm, 0.25 mm ID×60 m manufactured by GL Sciences Inc.) under the following conditions, and the analysis was performed based on the results.
Injection temperature = 250℃
Detector temperature = 250℃
Temperature conditions: hold at 60°C for 5 minutes → heat to 250°C at 10°C/min → hold at 250°C for 10 minutes

(Weight average molecular weight Mw, molecular weight distribution Mw/Mn)
The molecular weight of the copolymer was determined as a value corresponding to the molecular weight of standard polystyrene from a chromatogram measured by GPC (gel permeation chromatography).
Apparatus: Tosoh GPC device HLC-8320
Separation column: TSKguard column Super HZ-H, TSKgel HZM-M, and TSKgel Super HZ4000 manufactured by Tosoh Corporation connected in series Eluent: tetrahydrofuran Eluent flow rate: 0.35 ml/min Column temperature: 40° C.
Detection method: Differential refractive index (RI), absorbance detector (UV)

(Composition of each unit in the copolymer)
For the α-methylstyrene-methyl methacrylate copolymer, the proton ratio between the phenyl group of the α-methylstyrene unit and the methoxy group of the methyl methacrylate unit was determined by ¹ H-NMR, from which the αMS of the α-methylstyrene unit was calculated.
For α-methylstyrene-methyl methacrylate-maleic anhydride copolymer, the carbon ratios of the phenyl group of the α-methylstyrene unit, the carbonyl group of the methyl methacrylate unit, and the carbonyl group of the maleic anhydride unit were determined by ¹³ C-NMR, and the αMS of the α-methylstyrene unit and Mah of the maleic anhydride unit were calculated from this.

(Glass transition temperature Tg)
In accordance with JIS K7121, a DSC curve was measured using a differential scanning calorimeter (Shimadzu Corporation, DSC-50 (product number)) under conditions of heating once to 250° C., then cooling to room temperature, and then heating from room temperature to 200° C. at a rate of 10° C./min. The midpoint glass transition temperature determined from the DSC curve measured during the second heating was taken as the glass transition temperature in the present invention.

(Photoelastic coefficient K)
A 1.0 mm sheet was obtained by press molding the methacrylic copolymer. A test piece of 15 mm x 60 mm was cut out from the center of the obtained press molded sheet. Both ends of the long side direction of the cut out sheet were fixed so that the distance between the chucks was 45 mm, and tension was applied to the sheet in stages from 0 N to 100 N in 10 N increments using an X-axis dovetail stage B05-11BM manufactured by Suruga Seiki. The tension T was monitored by a sensor separate type digital force gauge ZPS-DPU-50N manufactured by Imada Co., Ltd. The phase difference PD in the state in which each tension was applied was measured at the D-line wavelength of Na using KOBRA-WR manufactured by Oji Scientific Instruments. After the phase difference measurement, the sheet was removed from the jig, and the thickness d of the phase difference measurement part was measured. From the measured values, the cross-sectional area S of the sheet = 15 mm × d, stress σ (= T/S), and birefringence Δn (= PD/d) were calculated, and the stress σ was plotted on the horizontal axis and the birefringence Δn on the vertical axis. The slope of the straight line obtained by the least squares method was determined as the photoelastic coefficient.

(Orientation birefringence Δn)
A 1.0 mm sheet was obtained by press molding the methacrylic copolymer. A 20 mm x 40 mm test piece was cut out from the center of the obtained press molded sheet, and the test piece was placed in an autograph with a heating chamber (manufactured by Shimadzu Corporation). The grip distance in the autograph was set to 20 mm, and the sample was held at glass transition temperature +10 ° C for 3 minutes. Thereafter, the sample was stretched 100% in one direction at a speed of 3 mm / min (grip distance became 40 mm). The obtained stretched film was cooled to 23 ° C, removed from the autograph, and the retardation PD of the central part of the stretched film was measured at the D line wavelength of Na using KOBRA-WR manufactured by Oji Scientific Instruments. The thickness d of the retardation measurement part was measured. From the measured value, the birefringence Δn (= PD / d) was calculated, and this was taken as the orientation birefringence.

The effects of the methacrylic copolymer of the present invention are shown in the following examples. The results of Examples Ie-1 to Ie-3 and Ic-1 to Ic-4 are shown in Table 1.

Example Ie-1
The methacrylic copolymer produced and isolated in Example IIe-3 described later was extruded into a strand, and the strand was cut with a pelletizer to obtain resin pellets. The obtained methacrylic copolymer had a weight average molecular weight Mw of 133,000, a number average molecular weight Mn of 66,500, a mass fraction MMA of methyl methacrylate units of 92 mass%, a mass fraction α-methylstyrene units αMS of 8 mass%, a glass transition temperature Tg of 128°C, a saturated water absorption coefficient As of 1.7%, an orientation birefringence Δn of -2.2× ^10-4 , a photoelastic coefficient K of -4.0× ^10-12 Pa ^-1 , and |A-B|/B of 0.011.

Example Ie-2
Resin pellets were obtained in the same manner as in Example Ie-1, except that the copolymer produced in Example IIe-1 described later was used instead. The obtained methacrylic copolymer had a weight average molecular weight Mw of 110,000, a number average molecular weight Mn of 55,000, a mass fraction MMA of methyl methacrylate units of 88 mass%, a mass fraction αMS of α-methylstyrene units of 12 mass%, a glass transition temperature Tg of 131°C, a saturated water absorption coefficient As of 1.6%, an orientation birefringence Δn of -2.0× ^10-4 , a photoelastic coefficient K of -2.5× ^10-12 Pa ^-1 , and |A-B|/B of 0.012.

Example Ie-3
Resin pellets were obtained in the same manner as in Example Ie-1, except that the copolymer produced in Example IIe-6 described later was used instead. The resulting methacrylic copolymer had a weight average molecular weight Mw of 90,000, a number average molecular weight Mn of 42900, a mass fraction MMA of methyl methacrylate units of 82 mass%, a mass fraction αMS of α-methylstyrene units of 18 mass%, a glass transition temperature Tg of 134°C, a saturated water absorption coefficient As of 1.3%, an orientation birefringence Δn of -1.6×10 ^-4 , a photoelastic coefficient K of -1.0×10 ^-12 Pa ^-1 , and |A-B|/B of 0.025.

Example Ic-1
A reaction raw material having a dissolved oxygen content of more than 10 ppm, which contained a monomer mixture consisting of 95 mass % of methyl methacrylate and 5 mass % of α-methylstyrene and 400 ppm of 2,2'-azobis(2-methylpropionitrile), was obtained, and resin pellets were obtained at a polymerization conversion rate of 42% in the same manner as in Example Ie-1, except that the reaction raw material having a dissolved oxygen content of more than 10 ppm obtained in Example Ie-1 was used instead of the reaction raw material having a dissolved oxygen content of more than 10 ppm obtained in Example Ie-1. The obtained methacrylic copolymer had a weight average molecular weight Mw of 141,000, a number average molecular weight Mn of 70,500, a mass fraction of methyl methacrylate units MMA of 96 mass%, a mass fraction of α-methylstyrene units αMS of 4 mass%, a glass transition temperature Tg of 122°C, a saturated water absorption As of 1.9%, an orientation birefringence Δn of -2.5 x 10 ^-4 , a photoelastic coefficient K of -4.3 x 10 ^-12 Pa ^-1 , and |A-B|/B of 0.011.

Example Ic-2
A reaction raw material having a dissolved oxygen content of more than 10 ppm, containing a monomer mixture consisting of 62.5% by mass of methyl methacrylate and 37.5% by mass of α-methylstyrene and 400 ppm of 2,2'-azobis(2-methylpropionitrile), was obtained and used instead of the reaction raw material having a dissolved oxygen content of more than 10 ppm obtained in Example Ie-1. Except for this, bulk polymerization was carried out in the same manner as in Example Ie-1. The polymerization conversion rate was 3%. The withdrawn reaction product was poured into methanol, and the solid content was precipitated and dried to obtain a methacrylic copolymer. The obtained methacrylic copolymer had a weight average molecular weight Mw of 80,000, a number average molecular weight Mn of 38,100, a mass fraction of methyl methacrylate units MMA of 80 mass%, a mass fraction of α-methylstyrene units αMS of 20 mass%, a glass transition temperature Tg of 125°C, a saturated water absorption As of 1.7%, an orientation birefringence Δn of -7.4 × 10 ^-4 , a photoelastic coefficient K of -4.7 × 10 ^-12 Pa ^-1 , and |A-B|/B of 0.052.

Example Ic-3
A reaction raw material having a dissolved oxygen content of more than 10 ppm, which contained a monomer mixture consisting of 85% by mass of methyl methacrylate and 15% by mass of α-methylstyrene and 400 ppm of 2,2'-azobis(2-methylpropionitrile), was obtained, and was used in place of the reaction raw material having a dissolved oxygen content of more than 10 ppm obtained in Example Ie-1. Except for changing the temperature during bulk polymerization to 150°C, resin pellets were obtained at a polymerization conversion rate of 50% in the same manner as in Example Ie-1. The obtained methacrylic copolymer had a weight average molecular weight Mw of 92,000, a number average molecular weight Mn of 46,000, a mass fraction of methyl methacrylate units MMA of 94 mass%, a mass fraction of α-methylstyrene units αMS of 6 mass%, a glass transition temperature Tg of 123°C, a saturated water absorption As of 1.8%, an orientation birefringence Δn of -2.7 x 10 ^-4 , a photoelastic coefficient K of -4.4 x 10 ^-12 Pa ^-1 , and |A-B|/B of 0.055.

Example Ic-4
Into the autoclave, 85 parts by mass of methyl methacrylate, 15 parts by mass of α-methylstyrene, 0.47 parts by mass of pentaerythritol tetrakisthiopropionate, 0.06 parts by mass of azobisisobutyronitrile, 0.01 parts by mass of 1,1-bis(1,1-dimethylperoxy)cyclohexane, 231 parts by mass of water, 1.4 parts by mass of dispersant, and 17.5 parts by mass of pH adjuster were placed. While stirring in the autoclave, the temperature in the autoclave was raised from room temperature to 70°C, held at 70°C for 120 minutes, and then held at 120°C for 60 minutes to perform suspension polymerization. Thereafter, the temperature was lowered to room temperature, and the reaction product was extracted from the autoclave. The solid content was removed from the reaction product by filtration, washed with water, and dried with hot air at 80°C for 24 hours. The obtained solid content was supplied to the hopper of a twin-screw extruder, melt-kneaded at a cylinder temperature of 230°C, and the molten resin was extruded to obtain resin pellets. The resulting copolymer had a weight average molecular weight Mw of 19,000, a number average molecular weight Mn of 9,000, and |A-B|/B of 0.122. Since polymers with different average molecular weights were simultaneously produced, no further evaluation was performed.

As the above results show, the methacrylic copolymer of the present invention has a high glass transition temperature (an index of heat resistance), a low saturated water absorption As, and small absolute values of orientation birefringence Δn and photoelastic coefficient K. The methacrylic copolymer of the present invention is suitable for optical components that require highly precise control of physical properties.

The effects of the manufacturing method II of the present invention are shown in the following examples. The manufacturing conditions of Examples IIe-1 to IIe-6 and IIc-1 to IIc-4 are shown in Table 2.

Example IIe-1
85 parts by mass of purified methyl methacrylate (MMA) and 15 parts by mass of α-methylstyrene (αMS) were mixed in an autoclave equipped with a stirrer and a collection tube. 2,2'-azobis(2-methylpropionitrile) (AIBN) was mixed in to a concentration of 400 ppm. The amount of dissolved oxygen was over 10 ppm. Nitrogen gas was blown into the mixture to remove the amount of dissolved oxygen to 3 ppm, and the reaction raw material was obtained.
The atmosphere in a continuous flow tank reactor equipped with a brine cooling condenser was replaced with nitrogen gas. The reaction raw materials were continuously supplied to the tank reactor at a constant flow rate so that the average residence time θ was 180 minutes, and bulk polymerization was carried out at a temperature of 120°C. At the same time, the reaction product was continuously withdrawn from the tank reactor. The pressure in the tank reactor was regulated by a pressure control valve connected to the brine cooling condenser. The amount of water present in the liquid in the tank reactor was maintained at 280 ppm or less, and the average concentration I of the radical polymerization initiator was 5.2 x ^10-5 mol/L. I x θ was 1.6 x ^10-4 mol·hr/L. The polymerization conversion rate was 40%.
The reaction product was subjected to devolatilization to remove the remaining monomer mixture, thereby obtaining the α-methylstyrene-methyl methacrylate copolymer of Example Ie-2. The ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture was 0.796.

Example IIe-2
An α-methylstyrene-methyl methacrylate copolymer having a weight average molecular weight of 108,000, a number average molecular weight of 54,000, and a mass fraction of α-methylstyrene units of 13 mass% was obtained in the same manner as in Example IIe-1, except that 400 ppm of 2,2'-azobis(2-methylpropionitrile) was changed to 400 ppm of 1,1-bis(t-butylperoxy)cyclohexane. The average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was 2.3×10 ^-4 mol/L. I×θ was 6.8×10 ^-4 mol·hr/L. The polymerization conversion rate was 43%. The ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture was 0.796.

Example IIe-3
90 parts by mass of purified methyl methacrylate, 10 parts by mass of α-methylstyrene, and 0.05 parts by mass of n-octyl mercaptan were mixed in an autoclave equipped with a stirrer and a collection tube. 2,2'-azobis(2-methylpropionitrile) was mixed with this to a concentration of 300 ppm to obtain a reaction raw material. Nitrogen gas was blown into the reaction raw material to remove dissolved oxygen to 3 ppm.
The atmosphere in a continuous flow tank reactor equipped with a brine cooling condenser was replaced with nitrogen gas. The reaction raw materials were continuously supplied to the tank reactor at a constant flow rate so that the average residence time θ was 180 minutes, and bulk polymerization was carried out at a temperature of 120°C. At the same time, the reaction product was continuously withdrawn from the tank reactor. The pressure in the tank reactor was regulated by a pressure control valve connected to the brine cooling condenser. The average concentration I of the radical polymerization initiator present in the liquid in the tank reactor was 3.9 x ^10-5 mol/L. I x θ was 1.2 x ^10-4 mol hr/L. The polymerization conversion rate was 41%.
The withdrawn reaction product was subjected to adiabatic flash evaporation to remove the remaining monomer mixture, thereby obtaining the α-methylstyrene-methyl methacrylate copolymer of Example Ie-1 described above. The ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture was 0.798.

Example IIe-4
An α-methylstyrene-methyl methacrylate copolymer having a weight average molecular weight of 117,000, a number average molecular weight of 59,000, and a mass fraction of α-methylstyrene units of 8 mass% was obtained in the same manner as in Example IIe-3, except that the temperature during bulk polymerization was changed from 120°C to 110°C and the concentration of 2,2'-azobis(2-methylpropionitrile) was changed to 500 ppm. The average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was 1.8×10 ^-4 mol/L. I×θ was 5.4×10 ^-4 mol·hr/L. The polymerization conversion rate was 41%. The ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture was 0.798.

Example IIe-5
An α-methylstyrene-methyl methacrylate copolymer having a weight average molecular weight of 59,000, a number average molecular weight of 30,000, and a mass fraction of α-methylstyrene units of 13 mass% was obtained in the same manner as in Example IIe-2, except that the temperature during bulk polymerization was changed from 120°C to 130°C and the concentration of 1,1-bis(t-butylperoxy)cyclohexane was changed to 300 ppm. The average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was 7.0×10 ^-5 mol/L. I×θ was 2.1×10 ^-4 mol·hr/L. The polymerization conversion rate was 41%. The ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture was 0.796.

Example IIe-6
The α-methylstyrene-methyl methacrylate copolymer of Example Ie-3 was obtained in the same manner as in Example IIe-1, except that the amount of methyl methacrylate was changed to 75 parts by mass and the amount of α-methylstyrene was changed to 25 parts by mass. The average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was 5.2×10 ^-5 mol/L. I×θ was 1.6×10 ^-4 mol·hr/L. The polymerization conversion rate was 35%.
The ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture was 0.712.

Example IIc-1
An α-methylstyrene-methyl methacrylate copolymer having a weight average molecular weight of 102,000 and a number average molecular weight of 51,000 was obtained in the same manner as in Example IIe-1, except that the temperature during bulk polymerization was changed from 120° C. to 90° C. The average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was 9.1×10 ^-4 mol/L. I×θ was 2.7×10 ^-3 mol·hr/L. The polymerization conversion rate was low at 13%.

Example IIc-2
An α-methylstyrene-methyl methacrylate copolymer having a weight average molecular weight of 83,000 and a number average molecular weight of 42,000 was obtained in the same manner as in Example IIe-1, except that 400 ppm of 2,2'-azobis(2-methylpropionitrile) was replaced with 400 ppm of t-hexylperoxyneodecanoate. The average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was 1.9×10 ^-6 mol/L. I×θ was 5.7×10 ^-6 mol·hr/L. The polymerization conversion rate was low at 22%.

Example IIc-3
An α-methylstyrene-methyl methacrylate copolymer having a weight average molecular weight of 295,000 and a number average molecular weight of 147,000 was obtained in the same manner as in Example IIe-1, except that the concentration of 2,2'-azobis(2-methylpropionitrile) was changed to 100 ppm. The average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was 1.3×10 ^-5 mol/L. I×θ was 3.9×10 ^-5 mol·hr/L. The polymerization conversion rate was low at 24%.

Example IIc-4
An α-methylstyrene-methyl methacrylate copolymer having a weight average molecular weight of 398,000 and a number average molecular weight of 199,000 was obtained in the same manner as in Example IIc-3, except that the average residence time θ was changed to 600 minutes. The average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was 3.9×10 ^-6 mol/L. I×θ was 3.9×10 ^-5 mol·hr/L. The polymerization conversion rate was 43%. However, since the average residence time is long, the flexibility or responsiveness of production is low. Specifically, the production process cannot be immediately rearranged in response to sudden small-lot production orders or changes in delivery dates.

As can be seen from the above results, according to the production method II of the present invention, α-methylstyrene-methyl methacrylate copolymer can be produced with a moderately high polymerization conversion rate and a moderately long average residence time suitable for continuous bulk polymerization.

The effects of the manufacturing method III of the present invention are shown in the following examples. The manufacturing conditions of Examples IIIe-1, IIIe-2 and IIIc-1 to IIIc-4 are shown in Table 3.

Example IIIe-1
In an autoclave equipped with a stirrer and a sampling tube, 82.0 parts by mass of methyl methacrylate (MMA), 15.0 parts by mass of α-methylstyrene (αMS), 3.00 parts by mass of maleic anhydride (MAh), and 0.02 parts by mass of n-octyl mercaptan were mixed. 2,2'-azobis(2-methylpropionitrile) was mixed as a radical polymerization initiator to a concentration of 300 ppm. Nitrogen gas was blown into the mixture to obtain a reaction raw material with a dissolved oxygen content of 3 ppm.
The atmosphere in a continuous flow tank reactor equipped with a brine cooling condenser was replaced with nitrogen gas. The reaction raw materials were continuously supplied to the tank reactor at a constant flow rate so that the average residence time θ was 2.50 hours, and a bulk polymerization reaction was carried out at a temperature of 130°C and an average concentration I of the radical polymerization initiator present in the liquid in the tank reactor of 1.75 x ^10-5 mol/L. At the same time, a reaction product with a polymerization conversion rate of 40% was continuously extracted from the tank reactor. The pressure in the tank reactor was adjusted by a pressure regulating valve connected to the brine cooling condenser. I x θ was 4.37 x ^10-5 mol hr/L.

The withdrawn reaction product was subjected to adiabatic flash evaporation to remove the remaining monomer mixture, yielding an α-methylstyrene-methyl methacrylate-maleic anhydride copolymer shown in Example IVe-1 of Table 4 below. The ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture was 0.830.

Example IIIe-2
In an autoclave equipped with a stirrer and a sampling tube, 70.0 parts by mass of methyl methacrylate, 20.0 parts by mass of α-methylstyrene, 10.0 parts by mass of maleic anhydride, and 0.005 parts by mass of n-octyl mercaptan were mixed. 2,2'-azobis(2-methylpropionitrile) was mixed as a radical polymerization initiator to a concentration of 300 ppm. Nitrogen gas was blown into the mixture to obtain a reaction raw material with a dissolved oxygen content of 3 ppm.
The atmosphere in a continuous flow tank reactor equipped with a brine cooling condenser was replaced with nitrogen gas. The reaction raw materials were continuously supplied to the tank reactor at a constant flow rate so that the average residence time θ was 2.50 hours, and a bulk polymerization reaction was carried out at a temperature of 130°C and an average concentration I of the radical polymerization initiator present in the liquid in the tank reactor of 1.79 x ^10-5 mol/L. At the same time, a reaction product with a polymerization conversion rate of 58% was continuously extracted from the tank reactor. The pressure in the tank reactor was adjusted by a pressure regulating valve connected to the brine cooling condenser. I x θ was 4.48 x ^10-5 mol hr/L.

The withdrawn reaction product was subjected to adiabatic flash evaporation to remove the remaining monomer mixture, yielding an α-methylstyrene-methyl methacrylate-maleic anhydride copolymer shown in Example IVe-2 of Table 4 below. The ratio of the molar fraction of α-methylstyrene units in the copolymer to the molar fraction of α-methylstyrene in the monomer mixture was 1.02.

Example IIIc-1
A reaction product with a polymerization conversion rate of 20% was obtained in the same manner as in Example IIIe-1, except that the temperature was changed to 90°C and the average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was changed to 7.70 x ^10-6 mol/L. A copolymer was obtained in the same manner as in Example IIIe-1, except that this reaction product was used. I x θ was 1.91 x ^10-3 mol·hr/L. The copolymer obtained had a weight average molecular weight of 104,000 and a number average molecular weight of 52,000. Since the polymerization conversion rate was low, the yield per reactor volume was low.

Example IIIc-2
A reaction raw material was obtained in the same manner as in Example IIIe-1, except that 2,2'-azobis(2-methylpropionitrile) was replaced with 400 ppm of t-hexylperoxyneodecanoate. Using this reaction raw material, a reaction product with a polymerization conversion rate of 28% was obtained in the same manner as in Example IIIe-1, except that the average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was changed to 9.77 x ^10-7 mol/L. A copolymer was obtained in the same manner as in Example IIIe-1, except that this reaction product was used. I x θ was 2.40 x ^10-6 mol hr/L. The copolymer obtained had a weight average molecular weight of 112,000 and a number average molecular weight of 56,000. Since the polymerization conversion rate was low, the yield per reactor volume was low.

Example IIIc-3
A reaction raw material was obtained in the same manner as in Example IIIe-1, except that the concentration of 2,2'-azobis(2-methylpropionitrile) was changed to 60 ppm. Using this reaction raw material, a reaction product with a polymerization conversion rate of 23% was obtained in the same manner as in Example IIIe-1, except that the average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was changed to 3.49×10 ^-6 mol/L. A copolymer was obtained in the same manner as in Example IIIe-1, except that this reaction product was used. I×θ was 8.74×10 ^-6 mol·hr/L. The obtained copolymer had a weight average molecular weight of 121,000 and a number average molecular weight of 60,500. Since the polymerization conversion rate was low, the yield per reactor volume was low.

Example IIIc-4
The reaction raw materials were obtained in the same manner as in Example IIIc-3, and a reaction product with a polymerization conversion rate of 38% was obtained in the same manner as in Example IIIc-3, except that the average residence time θ was changed to 10.0 ^hours and the average concentration I of the radical polymerization initiator present in the liquid in the tank-type reactor was changed to 8.80×10 −7 . A copolymer was obtained in the same manner as in Example IIIe-1, except that this reaction product was used. I×θ was 8.80×10 ⁻⁶ mol·hr/L. The copolymer obtained had a weight average molecular weight of 130,000 and a number average molecular weight of 65,000. Since a long average residence time is required to reach the desired polymerization conversion rate, the flexibility or responsiveness of production is low. Specifically, the production process cannot be immediately rearranged in response to sudden production orders for small lots or changes in delivery dates.

As can be seen from the above results, according to Production Method III, a copolymer having a ring structure in the main chain can be produced with a moderately high polymerization conversion rate and a moderately long average residence time, which are suitable for continuous polymerization methods.

Example IVe-1
The copolymer obtained in Example IIIe-1 was evaluated.

Example IVe-2
The copolymer obtained in Example IIIe-2 was evaluated.

Example IVc-1
Resin pellets were obtained in the same manner as in Example IIIe-1, except that the polymerization temperature was increased to 150° C. The resulting α-methylstyrene-methyl methacrylate-maleic anhydride copolymer had a weight average molecular weight of 85,000, a number average molecular weight of 42,500, a mass fraction of α-methylstyrene units of 10 mass%, a mass fraction of maleic anhydride units of 2 mass%, a glass transition point of 122° C., an orientation birefringence of −6.6×10 ⁻⁴ , a photoelastic coefficient of −4.5×10 ⁻¹² Pa ⁻¹ , and |A−B|/B of 0.055.

Example IVc-2
Resin pellets were obtained by the same process as in Example IIIe-1, except that the monomer mixture was changed to 97% by mass of methyl methacrylate, 2% by mass of α-methylstyrene, and 1% by mass of maleic anhydride. The resulting α-methylstyrene-methyl methacrylate-maleic anhydride copolymer had a weight average molecular weight of 90,000, a number average molecular weight of 40,900, a mass fraction of α-methylstyrene units of 1% by mass, a mass fraction of maleic anhydride units of 0.5% by mass, a glass transition point of 124°C, an orientation birefringence of -2.6 x ^10-4 , a photoelastic coefficient of -4.6 x ^10-12 Pa ^-1 , and |A-B|/B of 0.003.

Claims (15)

A methacrylic copolymer comprising 70 to 93 mass % of methyl methacrylate units, 7 to 30 mass % of α-methylstyrene units, and 0 to 23 mass % of other monomer units copolymerizable therewith, and satisfying the relationship of formula (1).

|A-B|/B < 0.05 (1)

In the above, A is the molecular weight at the peak top in a differential molecular weight distribution curve obtained by gel permeation chromatography measurement using a differential refractive index detector, and B is the molecular weight at the peak top in a differential molecular weight distribution curve obtained by gel permeation chromatography measurement using an absorbance detector with a detection wavelength of 254 nm. The methacrylic copolymer according to claim 1, wherein the other copolymerizable monomer unit is a monomer unit having a ring structure. The methacrylic copolymer according to claim 1 or 2, having a glass transition temperature of 125°C or higher. 4. The methacrylic copolymer according to claim 1, which has a photoelastic coefficient of -4.3×10 ⁻¹² /Pa to +4.3× ^{10 −12} /Pa. The methacrylic copolymer according to any one of claims 1 to 4, wherein a sheet of the methacrylic copolymer having dimensions of 20 mm x 40 mm x 1.0 mm thickness is stretched 100% in one direction at a speed of 3 mm/min at a temperature 10°C higher than the glass transition temperature to obtain a stretched film having a birefringence of -10 x 10 ^-4 to +10 x 10 ^-4 . A resin composition containing the methacrylic copolymer according to any one of claims 1 to 5. A resin composition containing an antioxidant and the methacrylic copolymer described in any one of claims 1 to 5. A molded article made of the methacrylic copolymer according to any one of claims 1 to 5 or the resin composition according to claim 6 or 7. A film comprising the methacrylic copolymer according to any one of claims 1 to 5 or the resin composition according to claim 6 or 7. An optical film comprising the methacrylic copolymer according to any one of claims 1 to 5 or the resin composition according to claim 6 or 7. A laminate having a layer containing the methacrylic copolymer according to any one of claims 1 to 5 and a layer containing another thermoplastic resin. A reaction raw material including a monomer mixture containing 70 to 93 mass % of methyl methacrylate, 7 to 30 mass % of α-methylstyrene, and 0 to 10 mass % of other monomers copolymerizable therewith, and a radical polymerization initiator is continuously supplied to a tank-type reactor;
The monomer mixture is bulk polymerized in a tank reactor at a polymerization conversion rate of 30 to 60 mass% to obtain a reaction product;
continuously withdrawing the reaction product from the tank reactor; and removing the monomer mixture remaining in the withdrawn reaction product from the reaction product;
The temperature in the tank reactor is 110° C. or higher and 140° C. or lower,
The average residence time θ of the reaction raw materials in the tank reactor is 1.5 to 4.5 hours,
When the average concentration of the radical polymerization initiator present in the liquid in the tank reactor is I mol/L and the average residence time of the reaction raw materials in the tank reactor is θ hr, their product I×θ exceeds 1× ^10-4 mol·hr/L and is less than 1× ^10-3 mol·hr/L.
A method for producing the methacrylic copolymer according to claim 1 . The process of claim 12 , wherein the reactants further comprise a chain transfer agent. A reaction raw material including 100 parts by mass of a monomer mixture consisting of 40 to 92% by mass of methyl methacrylate, 7 to 25% by mass of α-methylstyrene, 1 to 25% by mass of a monomer capable of introducing a ring structure into the main chain by a polymerization reaction, and 0 to 10% by mass of another monomer copolymerizable therewith, 0 to 30 parts by mass of an organic solvent, and a radical polymerization initiator is continuously supplied to a tank-type reactor;
subjecting the monomer mixture to a polymerization reaction in a tank-type reactor to obtain a reaction product;
continuously withdrawing the reaction product from the tank reactor; and removing the monomer mixture remaining in the withdrawn reaction product from the reaction product;
The temperature in the tank reactor is 110° C. or higher and 140° C. or lower,
The average residence time θ of the reaction raw materials in the tank reactor is 1.5 to 4.5 hours,
When the average concentration of the radical polymerization initiator present in the liquid in the tank reactor is I mol/L and the average residence time of the reaction raw materials in the tank reactor is θ hr, the product I×θ exceeds 1.0×10 ⁻⁵ mol·hr/L and is less than 1.5×10 ⁻⁴ mol·hr/L, the polymerization conversion is 30 to 65% by mass.
A method for producing a methacrylic copolymer. The process of claim 14 , wherein the reactants further comprise a chain transfer agent.