JP3434225B2 - Method for producing methacrylic polymer - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an improved process for producing methacrylic polymers. More specifically, when continuously polymerizing a methyl methacrylate or a monomer mixture containing methyl methacrylate as a main component using a complete mixing type reactor, it relates to a production method that employs specific reaction conditions and is extremely excellent in operational stability. .

[0002]

2. Description of the Related Art Conventional polymethylmethacrylate (PM
The main industrial production method of MA) was a batch polymerization method using a suspension polymerization method. This method is a manufacturing method suitable for high-mix low-volume production, but since auxiliary agents such as dispersants are used, these remain in the molding material and deteriorate the quality,
The post-treatment required washing with a large amount of water and subsequent drying. Further, since the polymerization operation is batch type, the operation operation is inefficient and complicated, and at the same time, the required costs such as equipment cost and operation cost are high. Further, as the pollution control is becoming more strict, it is not preferable to release a large amount of water or washing water used for polymerization including an auxiliary agent such as a dispersant and an unreacted monomer. If a new processing device is installed, the required cost is further increased, and the manufacturing method is inevitably industrially disadvantageous. In order to solve the problems of the suspension polymerization method, a method of continuously producing MMA by bulk polymerization has been proposed.

For example, in Japanese Examined Patent Publication No. 52-32665, the half-life and the addition amount of a radical polymerization initiator at the polymerization temperature are specified, and the conversion rate of the polymer is 50% by weight to 78% by weight at a polymerization reaction temperature of 130 ° C to 160 ° C. % Is disclosed. According to this method, it was possible to produce a methacrylic polymer molding material having excellent heat resistance and thermal decomposability at the time of molding and having a wide molding temperature range. However, in this method, since the conversion rate of the polymer greatly varies depending on the variation of the polymerization temperature, it is necessary to strictly control the polymerization conditions, and it is difficult to manage the operation. Therefore, improvement is required.

Further, Japanese Patent Laid-Open No. 3-111408 discloses that a monomer mixture containing methyl methacrylate as a main component is used as a radical initiator to produce a monomer mixture having a half-life of 0.5 to 0.5 at a polymerization temperature. Using 120 seconds, while stirring with a stirrer having a stirring power of 0.5 to 20 kW per 1 m ^{3 of} the reaction solution, the average residence time is 1/200 to 1/10000 as a ratio to the half-life of the radical initiator. And a method for producing a methacrylic polymer in which the polymerization rate is set to 130 ° C. to 160 ° C. and the conversion of the polymer is 45 to 70% by weight.

This method is advantageous in that the runaway reaction can be suppressed by finding a phenomenon that the polymer conversion rate becomes lower as the polymerization temperature becomes higher, which is different from the conventional common sense of reaction kinetics. In addition, if the reaction temperature rises for some reason, the polymer conversion rate decreases, so the amount of heat generated decreases, and the polymerization temperature automatically lowers and is restored to the original temperature, which is advantageous for stable operation. It is said that there is. However, since the polymerization temperature in the completely mixed reactor is controlled so as to maintain a constant temperature by actually adjusting the monomer feed temperature and the reactor jacket temperature, the fluctuation of the polymerization temperature is amplified on the contrary. There is a risk that the polymer conversion rate is not stable due to the fluctuation of the polymerization temperature.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is excellent in operation stability in control of polymerization temperature and polymer conversion. The purpose is to provide a method.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the object can be achieved by adopting a specific reaction condition. Has been completed.

That is, according to the present invention, a raw material containing methylmethacrylate or a monomer mixture containing methylmethacrylate as a main component and a raw material containing a polymerization initiator or a raw material containing a solvent is continuously supplied to a complete mixing type reactor to perform bulk polymerization or In the solution polymerization method, the average residence time of the reaction solution in the reactor is kept constant, and the peak temperature at which the polymer conversion rate is highest in the relationship between the polymerization temperature and the polymer conversion rate is between 110 and 160 ° C. A method for producing a methacrylic polymer, characterized in that the polymerization initiator and the mixing time of the reactor are selected so as to exist, and the polymerization is carried out at a constant temperature within a range of ± 10 ° C. around the peak temperature.

In this method, it is preferable to polymerize at a temperature lower than the above-mentioned peak temperature.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The production method of the present invention is applied to the production of a methacrylic polymer, that is, a homopolymer or copolymer of methyl methacrylate. In the case of producing a copolymer, a monomer mixture containing methyl methacrylate as a main component, that is, 80% by weight or more of methyl methacrylate and 20% by weight of copolymerizable methyl methacrylate
It is preferable to use a monomer mixture containing the following other monomers.

Other monomers used for copolymerization include:
Although not particularly limited, (meth) acrylates such as methyl acrylate, ethyl acrylate, n-butyl acrylate, fluoroalkyl methacrylate, and benzyl methacrylate are preferably used. Hereinafter, the methyl methacrylate or the monomer mixture is referred to as "raw material monomer".

In the present invention, first, an inert gas such as nitrogen is introduced into a raw material monomer or a reaction raw material containing a raw material monomer and a solvent, or the pressure is maintained under reduced pressure for a certain period of time to reduce the dissolved oxygen to 2 ppm or less. Is preferred.
This is because if the amount of dissolved oxygen is more than 2 ppm, not only the polymerization reaction is not stable, but also the color is easily colored by being kept at high temperature for a long time in the polymerization step. More preferably, it is 1 ppm or less.

A raw material monomer or reaction raw material from which dissolved oxygen is removed as described above is mixed with a polymerization initiator and, if necessary, a mercaptan compound as a chain transfer agent,
Continuously feed a fully mixed reactor. Then, the polymerization reaction starts in the reactor, and the raw material becomes a reaction liquid.

The mercaptan compound used in the present invention is not particularly limited, but n-butyl, n-octyl, n-dodecyl, tert-butyl mercaptan and the like are preferably used.

Polymers end-terminated by the chain transfer reaction of mercaptan have excellent thermal decomposition resistance, and the higher the ratio of the number of mercaptan-terminated ends to the total number of terminals of the polymer, the better the thermal decomposition resistance of the polymer. can get. However, when the amount is too large, the degree of polymerization of the polymer becomes low and the strength of the polymer decreases. Therefore, an appropriate degree of polymerization that allows molding while maintaining the strength (in the present invention, after the final removal of volatile components) In order to obtain a polymer having a weight average molecular weight of 70,000 to 150,000, and having excellent thermal decomposition resistance, the amount of mercaptan used is 1.0 per mol of the monomer. It is x10 ^{-4 to} 1.0 x 10 ^-2 mol, preferably 5.0 x 10 ^{-4 to} 5.0 x 10 ^-3 mol.

The polymerization initiator has a relationship with the mixing time of the reactor so that the peak temperature at which the polymer conversion is highest in the relationship between the polymerization temperature and the polymer conversion exists between 110 and 160 ° C. Select an appropriate one. That is, when the ratio between the half-life of the polymerization initiator and the mixing time of the reactor is selected so as to satisfy the following formula (1), there is a peak temperature at which the polymer conversion rate becomes the highest. The manufacturing method of the present invention can be implemented. 0.35 ≦ (τ _1/2 / θ _M ) ≦ 2.0 (1) where τ _1/2 : Half time of polymerization initiator at polymerization temperature [sec] θ _M : Mixing time of reactor [sec] That is, the small value of (τ _1/2 / θ _M ) means
This means that most of the initiator decomposes before the polymerization initiator supplied to the reactor spreads uniformly in the reactor. Applying an analytical model of a reactor that is often used in the field of reaction engineering, it is not a completely mixed model as a reaction behavior even though it is a completely mixed reactor, and it shows intermediate behavior with the plug flow model. I mean. vice versa,
A large value of (τ _1/2 / θ _M ) can be considered as a perfect mixing model according to the type of the reactor because the polymerization initiator spreads uniformly in the reactor without being decomposed.

It is known that in the polymerization of methyl methacrylate, the polymerization rate is accelerated by the gel effect when the content of the polymer in the reaction liquid exceeds about 30% by weight. Therefore, in a completely mixed reactor, it is possible to efficiently increase the polymer conversion rate of the monomer with an extremely small amount of polymerization initiator, while in the plug flow reactor, the polymerization initiator decomposes rapidly. Since it disappears, it becomes dead end polymerization, and the polymer conversion rate becomes low under the same temperature and the same amount of the polymerization initiator. Of course, even if the amount of the polymerization initiator is the same, it is theoretically possible to obtain a high polymer conversion rate by sufficiently lowering the polymerization temperature and slowly decomposing the polymerization initiator. Stable operation is difficult because of internal blockage.

From the above-mentioned polymerization behavior of methyl methacrylate, the phenomenon occurring in the complete mixing type reactor will be explained. Using the same polymerization initiator, the concentration of the supplied polymerization initiator and the reaction solution in the reactor are When the average residence time is made the same and the polymerization temperature is changed by several points, the polymer conversion rate is calculated.
In the low polymerization temperature region where the decomposition rate of the polymerization initiator becomes slow, it is regarded as a perfect mixing model, and thus the higher the temperature, the higher the polymer conversion rate, as in general reaction kinetics. If the temperature is further increased, the polymerization behavior of the plug flow model will coexist, and the conversion rate of the polymer will not gradually increase.On the contrary, if the temperature is further increased, the polymerization behavior of the plug flow model will become dominant and the polymer will become dominant. The conversion rate decreases.

In the method of the present invention, the presence of a peak polymerization temperature at which such a polymer conversion rate becomes the highest is determined, and the polymerization is carried out at a constant temperature within the range of ± 10 ° C. around this peak temperature. It has been found that when the polymerization is carried out within a range of ± 10 ° C. centered on this peak temperature, the change in the polymer conversion rate is extremely small, and only changes by about 3% by weight.

That is, according to the method of the present invention, even if the polymerization temperature rises or falls for some reason, the polymer conversion rate is almost constant, and the polymer conversion rate is not affected by the polymerization temperature. It is possible to automatically perform the operation of maintaining a constant value. Further, since the amount of heat generated by the reaction is always constant, the control of the polymerization temperature only controls the jacket temperature or the monomer supply temperature, and does not affect the fluctuation of the polymer conversion rate.

Since the conversion rate of the polymer is almost constant, not only the control of the polymerization process is facilitated, but also the reaction mixture containing the polymer and unreacted monomer taken out from the reactor or the reaction mixture further containing a solvent is removed. Since the volatile matter removal step following the polymerization step is always supplied at a constant polymer conversion rate, the operation stability of the volatile matter removal step is improved.

Further, when obtaining a copolymer of methyl methacrylate and another monomer, the fact that the polymer conversion rate in the reactor is constant means that the composition ratio of the copolymer is always constant, and the copolymerization composition is constant. It means that the unevenness of the ratio is very small, which is very effective in terms of quality. In particular, since methyl methacrylate has many uses as an optical material and a uniform material without optical distortion is required, it is highly commercialized that the composition of the copolymer is constant. Above all, the use as a plastic optical fiber is the most demanding in terms of optical performance, and is a field in which the effect of the present invention is most exerted as a method for producing a core material and a sheath material.

In the present invention, by utilizing the specific phenomenon that the polymer conversion rate does not fluctuate even when the polymerization temperature changes, not only the process stabilization but also the composition ratio of the copolymer is automatically made constant. It is an industrially important point that it has the significance of producing the effect of improving the quality of converging to a value.

It is generally known that when a double helical ribbon impeller is used as a stirrer for a complete mixing type reactor, the mixing time in the formula (1) can be calculated by the following formula (2). θ _M = 33 / n (2) where θ _M : mixing time [sec], n: agitation rotation speed [1 / sec] Therefore, when agitating with the double helical ribbon blade, equations (1) and (2) The present invention can be carried out by selecting a combination of polymerization initiators having a stirring rotation number and a half-life that satisfy the above condition. However, when the stirring blade is not a double helical ribbon blade, the formula (2) cannot be applied, and therefore, it is necessary to measure the mixing time of the stirring blade to be used and apply it to the formula (1).

Specific examples of the polymerization initiator used in the method of the present invention include tert-butylperoxyneodecanate, tert-hexylperoxypivalate and t.
ert-butyl peroxypivalate, 1,1,3,3
-Tetramethylbutylperoxy-2-ethylhexanate, 1-cyclohexylperoxy-2-ethylhexanate, tert-hexylperoxy-2-ethylhexanate, tert-butylperoxy-2-ethylhexanate, etc. Organic peroxide or 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-
Azobisisobutyronitrile, 2,2'-azobis (2
-Methyl butyronitrile), dimethyl compounds such as dimethyl-2,2'-azobisisobutyrate, and the like, and can be selected in consideration of the polymerization temperature and the formulas (1) and (2).

These polymerization initiators may be used alone or as a mixture of two or more kinds, but when two or more kinds are used, the polymerization mechanism becomes complicated.
Preference is given to the use of one type alone.

In the present invention, the half-life values of the polymerization initiators are as follows: organic peroxides are catalogs published by NOF CORPORATION, and azo compounds are technical bulletins published by Wako Pure Chemical Industries, Ltd. The value described in can be adopted.

In the production method of the present invention, it is preferable to stir and mix substantially uniformly in a complete mixing type reactor at a constant polymerization temperature of a reaction solution selected from the range of 110 to 160 ° C. If the polymerization temperature is too low, the acceleration phenomenon of the polymerization rate due to the gel effect becomes large when the temperature is too low. in this case,
In order to avoid the influence of the acceleration phenomenon, it becomes difficult to operate stably only under the condition that the polymer conversion rate is low, and the productivity is lowered, which is economically disadvantageous. The preferred polymerization temperature is 120 ° C or higher.

On the other hand, if this temperature is too high, the polymerization reaction becomes stable and the conversion rate of the polymer can be increased, but the formation of dimers becomes so large that the polymer becomes transparent after removal of the volatile matter. Properties and mechanical strength are reduced. The polymerization temperature is more preferably 140 ° C or lower.

Further, the polymerization temperature in the present invention is the most polymer conversion in the relation between the temperature and the polymer conversion rate under the condition that the average residence time of the reaction solution in the reactor and the supply concentration of the polymerization initiator are constant. Peak temperature is 110
It is important to set the polymerization temperature to a constant temperature in the range of ± 10 ° C., which exists between −160 ° C. and the peak temperature.

Under the condition that the average residence time and the supply concentration of the polymerization initiator are constant, in the range of ± 10 ° C. around the peak temperature at which the polymer conversion rate becomes the highest in the relationship between the temperature and the polymer conversion rate. Even if the polymerization temperature fluctuates due to some factor, the polymer conversion rate hardly changes. Therefore, the operation stability is remarkably improved. More preferably, the polymerization temperature is set within a range of ± 5 ° C. centering on the temperature at which the polymer conversion rate is highest. When the polymerization temperature exceeds the range of ± 10 ° C. around the peak temperature, the fluctuation of the polymer conversion rate with respect to the temperature fluctuation is large, and therefore it becomes necessary to strictly control the polymerization conditions.

Further, in the method of the present invention, it is preferable to carry out the polymerization at a temperature lower than the peak temperature at which the polymer conversion is highest. As described above, the phenomenon that there is a peak temperature at which the polymer conversion becomes the highest occurs because the polymerization behavior changes from the perfect mixing model to the plug flow model, and thus the formation of low molecular weight products such as oligomers is generated. Is likely to occur. Therefore, as the temperature rises above this peak temperature, the production of low molecular weight compounds is promoted. As a result, the heat distortion temperature and the thermal decomposition resistance of the polymer after the removal of volatile matter are lowered. Therefore,
The polymerization temperature is preferably lower than the peak temperature.

The amount of the polymerization initiator used depends on the polymerization temperature, the average residence time of the reaction solution in the reactor, and the target conversion rate of the polymer. In order to obtain an excellent polymer, the upper limit of the amount used is 1.0 × 10 ⁻⁴ mol per 1 mol of the monomer, and the lower limit is 5.0 × 10 ^{−6 in} consideration of industrial productivity.
It is preferable to supply in the molar range.

The average residence time of the reaction liquid in the completely mixed reactor is preferably 1 to 6 hours. Within this range, polymerization control can be stabilized, and a polymer having excellent moldability can be produced. If the residence time is too short, it is necessary to increase the amount of polymerization initiator used, which makes it difficult to control the polymerization reaction due to the increase in polymerization initiator, and the amount of terminal double bonds in the polymer increases, resulting in thermal decomposition resistance. No excellent polymer is obtained. It is more preferably 2 hours or more. On the other hand, if the average residence time is too long, the productivity is lowered and the amount of dimers is increased, which is not preferable. It is more preferably 5 hours or less. The average residence time of the reaction solution must be kept constant during the polymerization reaction. When the average residence time changes, the peak temperature at which the polymer conversion rate becomes the highest also changes in the relationship between the temperature and the polymer conversion rate, so that the method of the present invention cannot be carried out.

When carrying out the solution polymerization in the present invention, toluene, xylene, acetone, methyl ethyl ketone, methanol, ethanol, ethylbenzene, methyl isobutyl ketone, n-butyl acetate or the like can be used as a solvent. Among these, methyl ethyl ketone, methanol, ethanol, n-butyl acetate and the like are preferable. The content of the solvent with respect to the raw material containing the solvent is preferably 20% by weight or less, and more preferably 10% by weight or less.

Since heat is generated in the reactor due to the polymerization reaction and stirring and mixing, heat is removed and, if necessary, heated to control the polymerization temperature to a predetermined value. Temperature control can be performed by a known method. For example, methods such as heat transfer heat removal or heat transfer by circulating a heat medium to a jacket, a draft tube or a coil installed in the reactor, cooling supply of raw materials, and reflux cooling of monomer vapor can be adopted.

The content of the polymer in the reaction solution in the reactor of the present invention is preferably in the range of 30 to 70% by weight. If the content of the polymer is too high, the viscosity is high and the polymerization rate is rapidly accelerated by the gel effect, which makes stable operation difficult.

If the content of the polymer is too low, the cost is increased due to the separation of the volatile matter containing the unreacted monomer as the main component, which is industrially disadvantageous. Further, the conditions for more stable and economically advantageous production are preferably a polymerization temperature of 1
It is in the range of 40 to 55% by weight in the range of 20 to 140 ° C.

As the complete mixing type reactor used in the present invention, a tank type reaction device equipped with a feed port for raw materials, an outlet for the reaction mixture and a stirring device can be used, and the stirring device is provided throughout the reactor. It is necessary to have mixing performance. As a preferable stirring device, a double helical ribbon blade or a Max blend blade (Sumitomo Heavy Industries, Ltd.)
Manufactured) and the like.

In the present invention, after such a polymerization step,
Usually, it has a volatiles separation step whose main component is an unreacted monomer or an unreacted monomer containing a solvent, and a reaction mixture having a predetermined polymer conversion rate that is continuously fed is reduced in pressure. Most of the volatile matter is continuously separated and removed by heating at 170 to 290 ° C, and the residual monomer content in the obtained polymer is preferably 1.0% by weight or less, more preferably 0.3% by weight. % Or less.

In the volatile separation step, the dimer is also removed. The dimer content is preferable because it causes coloring of the polymer during heat molding and lowers the heat distortion temperature. The content of the residual dimer in the obtained polymer is preferably 0.1% by weight or less, more preferably 0.05% by weight or less.

When the methacrylic polymer thus produced is used as a molding material, a lubricant such as higher alcohols and higher fatty acid esters can be added. If necessary, an ultraviolet absorber, a heat stabilizer, a colorant, an antistatic agent, etc. can be added.

[0043]

EXAMPLES The present invention will be described in more detail with reference to examples below, but these do not limit the present invention.

The thermal decomposition resistance of the polymers of Examples and Comparative Examples was evaluated by using a differential thermoelectric balance (SSC500) manufactured by Seiko Denshi Kogyo Co. The bending temperature (° C.) when the temperature was raised to 400 ° C. at a temperature rising rate of ° C./min was measured, and this was used as an index of whether thermal decomposition is easy.

Examples 1 to 4 and Comparative Example 1 1.71 × 10 ⁻³ mol (0.25) of n-octyl mercaptan per 1 mol of a monomer mixture consisting of 98% by weight of methyl methacrylate and 2% by weight of methyl acrylate. %) And dimethyl-2,2′-azobisisobutyrate as a polymerization initiator 1.95 × 10 ⁻⁵ mol (45 pp)
The dissolved oxygen content is 2 ppm
The following was continuously fed to the completely mixed reactor. The raw materials fed into the reactor were mixed by stirring with a double helical ribbon blade at 65 rpm. The average residence time of the reaction solution in the polymerization vessel was 4 hours, and the polymerization temperature was 125
Polymerization was carried out by changing to constant temperatures of 130 ° C, 135 ° C, 140 ° C (Examples 1 to 4) and 145 ° C (Comparative Example 1) (all other conditions remained the same).

The reaction mixture was continuously taken out of the reactor, fed with a pump and continuously fed to a vent extruder type extruder to separate and remove volatile matter to obtain a polymer.

From the reaction mixture immediately after being taken out from the reactor, the polymer conversion rate of the monomer in the reactor, the residual monomer content rate of the obtained polymer, the residual dimer content rate and the thermal decomposition temperature were measured. The results shown in Table 1 and FIG. 1 were obtained. From FIG. 1, it was confirmed that the temperature at which the polymer conversion rate was the highest was around 133 ° C. Moreover, although the operation was continuously performed at each temperature for 100 hours (total of 500 hours), the fluctuation of the polymer conversion rate with respect to the fluctuation of the polymerization temperature was small, and therefore the operation was extremely stable in Examples 1 to 4. As a result of observing the inside of the reactor after the operation was completed, neither adhesion of the polymer to the apparatus nor generation of foreign matter was observed. However, the residual dimer content increased as the polymerization temperature increased. The higher the polymerization temperature, the lower the thermal decomposition temperature of the polymer.
The polymer produced at the polymerization temperature was high in thermal decomposition temperature and excellent in thermal decomposition resistance.

[Comparative Examples 2 to 6] The polymerization initiator was replaced with tert-butylperoxy-3,5,5-trimethylhexanoate, and 2.2 x 10 was added to 1 mol of the monomer mixture.
-1 as in the example except that ^-5 mol (50 ppm) was added
25 ° C, 130 ° C, 135 ° C, 140 ° C and 145 ° C
Polymerization was carried out at a constant polymerization temperature, and the polymer conversion rate was measured. The results shown in Table 1 and FIG. 2 were obtained. As is clear from FIG. 2, the polymer conversion rate becomes higher as the polymerization temperature becomes higher, which is in agreement with the common knowledge of the reaction kinetics, and the fluctuation of the polymer conversion rate with respect to the fluctuation of the polymerization temperature is It was large as compared with Examples 1 to 4. Therefore, 100 hours of continuous operation was performed at each temperature (total 500
Time), the operation was unstable as compared with Examples 1 to 4.

[0049]

[Table 1]

[0050]

According to the production method of the present invention, the polymerization reaction is controlled by continuously polymerizing methyl methacrylate or a monomer mixture containing methyl methacrylate as a main component under a specific condition using a complete mixing type reactor. It is possible to produce a methacrylic polymer useful as an optical material having a very small variation in copolymerization composition ratio.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a polymerization temperature and a polymer conversion rate when a method of the present invention is carried out.

FIG. 2 is a diagram showing a relationship between a polymerization temperature and a polymer conversion rate in the method of Comparative Example.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeaki Sasaki 3 Kaigan Dori, Toyama City, Toyama Prefecture Mitsubishi Rayon Co., Ltd. Toyama Works (56) Reference JP-A-7-126308 (JP, A) JP-A-58 -88701 (JP, A) JP-B 52-32665 (JP, B2) JP-A 2001-516774 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08F 2/00-2 / 60,20 / 14

Claims (2)

(57) [Claims] 1. A method for continuously performing bulk polymerization or solution polymerization by continuously supplying a raw material containing methyl methacrylate or a monomer mixture containing methyl methacrylate as a main component and a polymerization initiator or a raw material containing a solvent to a completely mixed reactor. In the above, the average residence time of the reaction liquid in the reactor is kept constant, and the peak temperature at which the polymer conversion rate becomes the highest in the relationship between the polymerization temperature and the polymer conversion rate is 110-110.
The mixing time of the polymerization initiator and the reactor was selected so that it existed between 160 ° C., and the peak temperature was ± 10
A method for producing a methacrylic polymer, which comprises polymerizing at a constant temperature in the range of ° C. 2. The method for producing a methacrylic polymer according to claim 1, wherein the polymerization is carried out at a temperature lower than the peak temperature.