JPH0625358A - Production of acrylic polymer - Google Patents

Abstract

PURPOSE:To obtain an acrylic polymer reduced in coloring, narrow in distribution of molecular weight, excellent in productivity, safety and stability and useful for thermoplastic elastomer, adhesive, etc., by subjecting an acrylic monomer to bulk polymerization under specific conditions. CONSTITUTION:The polymer is obtained by subjecting a monomer component consisting of (A) 51-100wt.% acrylic acid based monomer such as acrylic acid and (B) 49-0wt.% other monomer copolymerizable with the component A, e.g. styrene to bulk polymerization in an inert gas atmosphere such as nitrogen gas in a state containing mercaptan such as ethylmercaptan (in an amount of preferably 0.005-5 pts.wt. based on 100 pts.wt. monomer component) and substantially not containing polymerization initiator.

Description

Detailed Description of the Invention

[0001]

This invention relates to a thermoplastic elastomer, a pressure-sensitive adhesive, an adhesive, a paint, a shrinkage reducing agent, a resin modifier,
The present invention relates to a method for producing an acrylic polymer used as an asphalt additive, a dispersant or the like.

[0002]

Radical polymerization of a polymerizable monomer is generally carried out by emulsion polymerization, suspension polymerization, solution polymerization or bulk polymerization. Emulsion polymerization, suspension polymerization and solution polymerization have the advantage that the reaction liquid easily flows even when the polymerization rate is high because the polymerization temperature is easy to control because the polymerization is performed by dispersing the monomer in the dispersion medium. However, it has the following drawbacks.

In emulsion polymerization and suspension polymerization, a precipitation step (necessary in the case of emulsion polymerization), a filtration step, a washing step and a drying step are required to take out the polymer from the dispersion medium, and the operation is extremely difficult. In addition, it is complicated and poor in productivity, and it is difficult to obtain a pure polymer because an emulsifier or a dispersant is mixed in the polymer. If a polymer in which an emulsifier or the like remains is used for practical purposes, water resistance and strength will be poor. When a polymer having a sufficient high molecular weight is produced, a gel component is generated, which deteriorates the coating workability. In the case of copolymerization, it is necessary to use a plurality of types of monomers having different hydrophilicities depending on the desired polymer composition, but there are cases where emulsion or suspension is not possible, and the polymer composition is limited.

In solution polymerization, since a large amount of organic solvent is used as a dispersion medium, a large amount of low molecular weight substances are produced and the molecular weight distribution of the polymer tends to be large, which causes inconvenience depending on the application. Further, when a large amount of organic solvent is used, it is necessary to volatilize the polymer in order to take it out, and the productivity is low. On the other hand, the bulk polymerization is an industrially advantageous method because it does not use a dispersion medium and does not require an emulsifier or a dispersant and thus does not have the above-mentioned drawbacks. However, it is difficult to control the polymerization when bulk-polymerizing a polymerizable monomer whose polymerization reaction is too radical. For this reason, it is difficult to design the molecular weight and molecular weight distribution of the polymer depending on the type of the monomer, or a gelled substance or a deteriorated product is generated due to a sudden heat generation during the polymerization. Invite them.

Among the polymerizable monomers, styrene and methyl methacrylate are known to be able to control polymerization in bulk polymerization, and bulk polymerization has been studied for a long time and industrialized. Styrenic polymers are industrially produced by bulk polymerization of styrene or a monomer mixture mainly composed of styrene in the presence or absence of a polymerization initiator to a high polymerization rate, and volatilizing a small amount of unreacted styrene that remains. Can be obtained. Further, styrene is a styrene that can be gently polymerized by thermal polymerization in the absence of a polymerization initiator, but mercaptan may be used for controlling the molecular weight. In this case, the chain transfer reaction of mercaptan is active and a polymer having a wide molecular weight distribution is produced.

In bulk polymerization of methyl methacrylate, methyl methacrylate or a monomer mixture mainly containing methyl methacrylate is polymerized in the presence of a polymerization initiator, but at a high polymerization rate, a polymer having a narrow molecular weight distribution is obtained. Since it is difficult to do so, the polymerization is stopped at a low polymerization rate of about 60% to volatilize a large amount of unreacted monomer. This is because the polymerization rate of methyl methacrylate is faster than that of styrene, and the polymerization rate is accelerated by the gel effect (a phenomenon in which the polymerization rate increases as the viscosity of the reaction mixture increases and the viscosity of the reaction mixture increases) when the polymerization rate increases. This is because a temperature distribution occurs in the liquid, and a portion where the polymerization does not proceed so much and a portion where the polymerization proceeds rapidly coexist.

As described above, even in the case of methyl methacrylate, which has a much slower polymerization reaction than acrylic acid-based monomers such as acrylic acid and acrylic acid ester, the bulk polymerization is stopped at a low polymerization rate. Therefore, bulk polymerization of an acrylic acid-based monomer, which has a more radical polymerization reaction than that of methyl methacrylate, is difficult to control in temperature and is not generally used at all.

As far as the patent is concerned, Japanese Patent Publication No. 62-415
No. 23 and Japanese Patent Publication No. 2-55448 propose bulk polymerization of acrylic acid type monomers using a screw extruder. Bulk polymerization of acrylic acid-based monomers proposed in these publications introduces a polymerization initiator and an acrylic acid-based monomer into a screw extruder having a specific structure, and utilizes a rapid reaction to reduce the viscosity in a short time. It is to raise and raise it so that liquid can be sent with a screw. Japanese Patent Publication No. 55-401 proposes bulk polymerization using an organic mercaptan in the presence of oxygen.

[0009]

According to the methods described in Japanese Patent Publication No. 62-41523 and Japanese Patent Publication No. 2-55448, the temperature of the reaction solution rises stepwise rather than abruptly as the polymerization rate increases. Therefore, bulk polymerization of the acrylic acid-based monomer can be performed without causing a runaway reaction. However, the obtained acrylic polymer has a molecular weight distribution Mw / Mn of 8
Since it is very large at about -13, for example, when it is used in a coating polymer, a low molecular weight component lowers the coating strength and stain resistance, and an unnecessarily high molecular weight component increases the solution viscosity. Workability may be poor. Moreover, the bulk polymerization described in the above two publications can be carried out on a small scale such as a laboratory level because it utilizes the rapid reaction of acrylic acid type monomers, but it is safe on an industrial scale. It is difficult to implement considering the sex.

On the other hand, according to the method described in Japanese Patent Publication No. 55-401, the heat generation can be controlled relatively easily, but since the presence of oxygen causes the gas phase portion to enter the explosive range, Risk of explosion due to the presence of ignition sources. Even if the danger is avoided, the polymer is markedly colored, which is not a preferable method for producing an acrylic polymer characterized by transparency.

According to the present invention, no emulsifier or dispersant is mixed,
It is an object of the present invention to provide a method for producing an acrylic polymer having a desired composition, little coloring, and a small molecular weight distribution with high productivity and safety.

[0012]

In order to solve the above problems, the present invention produces an acrylic polymer by bulk polymerizing a monomer component containing an acrylic acid monomer as a main component. In the method, the polymerization system in which the bulk polymerization of the monomer component is performed contains an mercaptan under an inert gas atmosphere, and is substantially free of a polymerization initiator. A method for producing a polymer is provided.

As a result of various studies on the bulk polymerization of acrylic acid type monomers, which are said to be substantially impossible for bulk polymerization, the inventors have found that "rapid heat generation due to a very large polymerization rate". We have investigated a technique that can be controlled, and have found a method for obtaining a homogenous polymer having a small molecular weight distribution, by which the copolymer composition can be arbitrarily designed. According to the present invention, a rapid heat generation during bulk polymerization can be suppressed and a moderate polymerization rate can be controlled, and a uniform acrylic polymer having a small molecular weight distribution is produced.

When bulk-polymerizing a monomer component containing an acrylic acid-based monomer as a main component, the polymerization system is not limited to mercaptan as in styrene polymerization, and a polymerization initiator is substantially used. However, even if the polymerization system does not substantially contain the polymerization initiator, it is often the case that the polymerization cannot be controlled due to the rapid heat generation, and sometimes a gel is formed.

Bulk polymerization of a monomer component containing an acrylic acid-based monomer as a main component is allowed to proceed slowly up to a high polymerization rate, the molecular weight is controlled, and a polymer having a small molecular weight distribution is obtained. It is mercaptan that is used for the purpose of solving the problems which occur not only when the system contains a polymerization initiator but also when it does not contain a polymerization initiator. The role of mercaptan in the method of the present invention is important and has a role of controlling the polymerization rate and a role of controlling the molecular weight. In the present invention, it is further necessary to carry out bulk polymerization in an inert gas atmosphere. By doing so, coloring of the polymer is prevented, and more exothermic heat is generated as compared with polymerization in the presence of oxygen. It becomes possible to control easily.

The term "inert gas atmosphere" as used herein means one that does not affect radical polymerization, and examples thereof include nitrogen gas and argon gas. In the production method of the present invention, the amount of mercaptan used is 1 total amount of monomer components.
The amount is preferably 0.001 to 20 parts by weight, more preferably 0.005 to 5 parts by weight, relative to 00 parts by weight. With styrene and methyl methacrylate, bulk polymerization can be carried out stably without a catalyst, but since the acrylic acid monomer has a high polymerization rate, it often causes a runaway reaction without a catalyst, so the amount of mercaptan used is 0. If it is less than 0.001 part by weight, a rapid reaction may occur during the polymerization, which is not preferable. When mercaptan is used in an amount of more than 20 parts by weight, on the contrary, the polymerization rate may be too slow and productivity may be deteriorated, which is not preferable.

The mercaptan used in the present invention is not particularly limited as long as it is an organic compound having an SH group, but alkyl mercaptans such as ethyl mercaptan, butyl mercaptan, hexyl mercaptan, dodecyl mercaptan; phenyl mercaptan and benzyl mercaptan. Thiophenols; carboxyl group-containing mercaptans such as thioglycolic acid, 3-mercaptopropionic acid, and thiosalicylic acid; esterification products of C ₁ -C ₁₈ alcohols and carboxyl group-containing mercaptans;
A hydroxyl group-containing mercaptan such as 2-mercaptoethanol; a diester compound of a diol such as ethylene glycol and 1,4-butanediol and a carboxyl group-containing mercaptan; a compound having three or more hydroxyl groups such as trimethylolpropane and pentaerythritol. Polyester product of carboxyl group-containing mercaptans; Compound having three or more mercapto groups such as trithioglycerin; Compound obtained by adding hydrogen sulfide to polyvalent epoxy compound; Mercaptoethanol ester product of polyvalent carboxylic acid; 2-mercaptobenzo Thiazole; 2-mercaptobenzimidazole and the like can be mentioned, and at least one of them is used.

The monomer component used in the present invention contains an acrylic acid type monomer (A) as a main component, and is usually 51 to 100% by weight of an acrylic acid type monomer (A), and
It comprises the rest of the other monomer (B) copolymerizable with the monomer (A). When the amount of the monomer (A) is less than 51% by weight, the polymer can be obtained safely and stably by bulk polymerization without applying the method of the present invention, but the amount of the monomer (A) is 51% by weight or more. Therefore, bulk polymerization is difficult unless the method of the present invention is applied.

The acrylic acid-based monomer (A) has CH ₂ = C
It has an HCO- structure. Specific examples of the monomer (A) include acrylic acid; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, acrylic acid. Acrylic alkyl esters such as nonyl, decyl acrylate, dodecyl acrylate and their substitutions; Aryl aryl esters such as phenyl acrylate and benzyl acrylate; methoxyethyl acrylate, ethoxyethyl acrylate, butoxyethyl acrylate Acrylic acid alkoxyalkyl esters such as ethoxypropyl acrylate; diacrylic acid esters of polyethylene glycol such as ethylene glycol, diethylene glycol and triethylene glycol; propylene glycol Acrylates of alicyclic alcohols such as cyclohexyl acrylate; polyvalent acrylates such as trimethylolpropane triacrylate ester; dipropylene glycol diacrylate esters of polypropylene glycols such as tripropylene glycol;
Aziridine group-containing monomers such as acryloyl aziridine and 2-aziridinylethyl acrylate; epoxy group-containing monomers such as glycidyl acrylate and 2-methylglycidyl acrylate; 2-hydroxyethyl acrylate, acrylic 2-hydroxypropyl acid, a monoester of acrylic acid and polypropylene glycol or polyethylene glycol, a hydroxyl group-containing monomer such as an adduct of lactones and 2-hydroxyethyl acrylate; a compound having a hydroxyl group and a carboxyl group Carboxyl group-containing monomer such as ester of acrylic acid and acrylic acid, acrylic acid, acrylate; acrylic acid 2-
Reactive halogen-containing monomers such as chloroethyl; amide group-containing monomers such as acrylamide, N-methylolacrylamide, N-methoxymethylacrylamide, N-butoxymethylacrylamide; γ-acryloxypropyltrimethoxysilane, 2 At least one selected from organosilicon group-containing monomers such as acryloxyethoxytrimethoxysilane.

The monomer (B) is another monomer copolymerizable with the acrylic acid type monomer (A), and CH ₂ ═C
It has no HCO- structure. Specific examples of the monomer (B) include aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene, vinylnaphthalene and halogenated styrene; acrylonitrile; methacrylonitrile; vinyl acetate; vinyl chloride; Vinylidene; methacrylic acid esters of alicyclic alcohols such as cyclohexyl methacrylate; methacrylic acid esters of aromatic alcohols such as benzyl methacrylate; methacrylic acid esters such as methacrylic acid alkyl esters, methacrylic acid alkoxyalkyl esters; 2- Vinyl
Oxazoline group-containing polymerizable monomers such as 2-oxazoline, 2-vinyl-5-methyl-2-oxazoline and 2-isopropenyl-2-oxazoline; like methacryloyl aziridine and 2-aziridinyl ethyl methacrylate. Aziridine group-containing polymerizable monomer; allyl glycidyl ether, glycidyl methacrylate, methacrylic acid 2
-Epoxy group-containing vinyl monomers such as methylglycidyl; 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, monoesters of methacrylic acid and polypropylene glycol or polyethylene glycol, lactones and 2-hydroxyethyl methacrylate. Hydroxyl group-containing polymerizable monomers such as adducts of unsaturated monocarboxylic acids such as methacrylic acid and itaconic acid (excluding acrylic acid) and salts thereof, such as crotonic acid, maleic acid and fumaric acid. Carboxyl group-containing vinyl monomers such as unsaturated dicarboxylic acids or their half-esterified products; reactive halogen-containing vinyl monomers such as 2-chloroethyl vinyl ether and monochlorovinyl acetate; methacrylamide, N-methylol methacrylamide. , N- Butoxy methyl methacrylamide,
Amide group-containing vinyl monomers such as N-butoxymethylmethacrylamide; vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, allyltriethoxysilane, trimethoxysilylpropylallylamine, 2-methacryloxyethoxytrimethoxysilane. Unsaturated monomers containing organic silicon groups such as ethylidene norbornene, piperylene, isoprene, pentadiene,
Examples thereof include diene-based monomers such as vinylcyclohexene, chloroprene, butadiene, methylbutadiene, cyclopentadiene, and methylpentadiene.
At least one of these is used.

In the present invention, a small amount of an additive other than the polymerizable monomer component, such as a solvent, which does not substantially affect the bulk polymerization, may be added. However, in the bulk polymerization, it is necessary that the polymerization system does not substantially contain a general radical polymerization initiator, so-called azo compound, peroxide and the like. Here, when the polymerization initiator is not substantially contained, the polymerization initiator is not contained at all, or the polymerization initiator is contained in an amount smaller than the amount in which the mercaptan does not play the above-mentioned role and a rapid reaction occurs. Say include. When a general amount of radical polymerization initiator is used, a rapid heat generation occurs during the polymerization and the reaction goes out of control, so that the polymerization cannot be stably performed up to a high polymerization rate of more than 80%. Even if the polymerization can be controlled within a certain temperature range, the polymer produced will have a large molecular weight distribution.

The bulk polymerization reaction can be carried out using a conventionally known polymerization apparatus. For example, a tank reactor equipped with stirring blades of various shapes, a complete mixing reactor such as a kneader, a piston flow reactor having a driving unit such as an extruder, a drive such as a static mixer that stirs the liquid by an obstacle Examples thereof include a piston flow type reactor having no part. By using these devices individually or in combination of two or more, batch polymerization or continuous bulk polymerization can be carried out. In particular, the production method of the present invention is characterized by the fact that the reaction is sufficiently mild and bulk polymerization can be carried out using a large-capacity tank reactor having a small cooling surface area per volume. The stirring conditions of the reaction mixture during the bulk polymerization according to the present invention can be set in the same manner as in the case of the normal bulk polymerization.

The polymerization temperature is preferably 60 to 200 ° C., 1
More preferably, it is from 00 to 150 ° C. If the temperature is lower than 60 ° C, the polymerization is slow and is not industrially practical. If the temperature is higher than 200 ° C, the polymerization rate becomes too fast and control becomes difficult. According to the present invention, a monomer component composed of at least the monomer (A) of the acrylic acid-based monomer (A) and the other monomer (B) is bulk polymerized to obtain a high polymerization rate or polymerization. It is possible to obtain an acrylic polymer by polymerizing up to a rate of 100%. From the viewpoint of productivity, it is preferable to raise the polymerization rate to 60% or more, more preferably 80% or more even when the volatile components are removed from the reaction solution under reduced pressure after the bulk polymerization.

The resulting acrylic polymer has a polymerization rate of 10
When it is polymerized to 0%, it can be obtained by removing the reaction solution from the reactor as it is, and when the polymerization is stopped on the way, it can be obtained by removing volatile components from the reaction solution under reduced pressure. The polymer thus obtained has a polystyrene-equivalent molecular weight distribution (M
w / Mn) is 1.5 to 3.0 and the number average molecular weight is 1.00
0-4,000,000, glass transition temperature (Tg)-
80 ° C to 40 ° C, the type or amount of mercaptan,
By changing the polymerization temperature, an acrylic polymer having an arbitrary molecular weight can be obtained safely and stably.

The resulting acrylic polymer is used in all applications in which conventional acrylic polymers are used, for example, thermoplastic elastomers, damping agents, pressure-sensitive adhesives, adhesives, paints, shrinkage reducing agents, asphalt. Additives, dispersants, fiber treatment agents,
It is effectively used as a resin modifier.

[0026]

In the present invention, the polymerization system for performing bulk polymerization of the monomer component containing the acrylic acid-based monomer as the main component is in an inert gas atmosphere, contains mercaptan, and contains substantially no polymerization initiator. By not including in, the rapid heat generation is suppressed and the polymerization rate becomes moderate. Therefore, bulk polymerization is performed safely and stably up to a high polymerization rate, and an acrylic polymer having a small molecular weight distribution and little coloring is produced.

[0027]

EXAMPLES Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to the following examples.
In the following, "part by weight" means "part" and "% by weight" means "%"
I wrote. (Example 1) After replacing the inside of a flask equipped with a stirrer, a nitrogen introduction tube, a thermometer and a reflux condenser with nitrogen, 1200 parts of ethyl acrylate, 225 parts of methyl methacrylate, 75 parts of hydroxyethyl methacrylate were added to the flask. 30 parts of octyl thioglycolate were charged and stirred. The mixture was heated to 100 ° C. with stirring while slowly blowing nitrogen gas into the mixture. When the polymerization was continued for 2 hours at the same temperature, the polymerization intermediate was continuously taken out from the bottom of the flask at a rate of 750 parts / hour, introduced into a static mixer type polymerization apparatus, and further polymerized at 100 ° C. for 1 hour. Similarly, a monomer mixture having the same composition as described above was supplied to the flask at 750 parts / hour to continuously polymerize the mixture. The resulting acrylic polymer had a polymerization rate of 85%, and the polymer-containing reaction mixture was subjected to the APHA method (American Publ.
The color value (hereinafter referred to as “APHA value”) according to the ic Health Association's method) is 5 or less, and the polystyrene equivalent analysis value by gel permeation chromatography (GPC) (hereinafter, similarly measured) is the number average molecular weight. (Mn) = 5,000, weight average molecular weight (Mw)
= 90,000, and the molecular weight distribution (Mw / Mn) was 1.8. This polymer-containing liquid is heated to 150 ° C., 20 mmH
It was continuously supplied to a flash tank depressurized to g to remove volatile components and taken out as a 100% polymer.

50 parts of 100 parts of the obtained acrylic polymer was used.
Heat to ℃, add 10 parts of isophorone diisocyanate to make a uniform liquid, cast on a tetrafluoroethylene resin (Teflon, trade name manufactured by DuPont) and react at 150 ℃ for 30 minutes to form a 0.2 mm thick film. Got As a result of measuring the strength of this film, the breaking strength was 120 kg / cm ² ,
The elongation was 400%.

From these results, it can be seen that the polymer obtained in Example 1 has large strength and elongation and can be suitably used for coating materials and sealing agents. (Comparative Example 1) 1200 parts of ethyl acrylate, 225 parts of methyl methacrylate, hydroxyethyl methacrylate 75
Parts and 10 parts of azobisisobutyronitrile were dissolved in 1500 parts of xylene to prepare a raw material mixture. A 1/3 volume of this mixed solution was placed in a flask equipped with a stirrer, a nitrogen inlet tube, a dropping funnel, a thermometer and a reflux condenser, and the mixture was stirred at 100 ° C. while slowly blowing nitrogen gas. The mixture was heated up to, the remaining amount of the mixed solution was added dropwise over 3 hours, and the mixture was aged for 1 hour for polymerization. The obtained acrylic polymer had an APHA value of 5 or less and Mn = 0.4.
The molecular weight distribution was very wide, with Mw of 80,000 and Mw / Mn of 10.0.

In the same manner as in Example 1, 5 parts of isophorone diisocyanate was added to 100 parts of the obtained acrylic polymer solution to obtain a uniform solution, and a tetrafluoroethylene resin (Teflon trade name manufactured by DuPont) plate was prepared. Cast it on 1
The reaction was carried out at 50 ° C. for 30 minutes to obtain a film having a thickness of 0.2 mm. As a result of measuring the strength of this film, the breaking strength was 9
The strength was 8 kg / cm ² and the elongation was 300%, and the strength was inferior to that of Example 1.

This result is considered to be because the molecular weight distribution is wide and many low molecular weight polymers having no hydroxyl group as a crosslinkable group are present. (Comparative Example 2) The same procedure as in Example 1 was carried out except that, in Example 1, 1.5 parts of benzoyl peroxide as a polymerization initiator was charged instead of 30 parts of octyl thioglycolate. After 30 minutes, the temperature could not be kept constant, the temperature rose to 160 ° C., and stable polymerization could not be performed. This suggests that on an industrial manufacturing scale there is a risk of explosion due to a rapid reaction.

Comparative Example 3 The same operation as in Example 1 was carried out except that 30 parts of mercaptan octyl thioglycolate was not charged.
After 0 minutes, the temperature rose to 130 ° C and stable polymerization could not be performed. The obtained polymer was gel-like. In this case as well, the risk of explosion due to a rapid reaction is suggested on an industrial scale.

(Comparative Example 4) The same apparatus and polymerizable monomer mixture as in Example 1 were charged with 20 parts of azobiscyclohexanecarbonitrile as a polymerization initiator, and the temperature was raised to 80 ° C while gently blowing nitrogen gas. Polymerization was carried out.
The temperature could not be kept constant after 1 hour, so it was continuously taken out from the bottom of the flask at a rate of 1000 parts / hour and started to be introduced into a KRC kneader (Kurimoto Iron Works self-cleaning continuous kneader). The temperature inside the flask was kept constant by dropping a monomer mixture having the same composition as above into the flask at a rate. K
Polymerization was carried out for 1.5 hours in the RC kneader, but the temperature at the inlet of the kneader was 80 ° C, whereas it was 150 ° C near the outlet, and a temperature rise in the kneader was observed. The resulting acrylic polymer has a polymerization rate of 96.0.
%, APHA value of 5 or less, Mn = 40,000, Mw =
It was 60,000 and Mw / Mn = 15.0. From this polymer-containing liquid, a 100% polymer was taken out in the same manner as in Example 1. 100 parts of the obtained acrylic polymer was added to 1000 parts of tetrahydrofuran and stirred sufficiently to dissolve it, but an insoluble portion was observed and a uniform solution was not obtained.

That is, as in Comparative Example 4, when 20 parts of azobiscyclohexanecarbonitrile which is a polymerization initiator and 30 parts of octyl thioglycolate which is a mercaptan were charged in a monomer mixture, the temperature in the flask was kept constant. In order to maintain the temperature, a low temperature monomer mixture for dripping has to be added dropwise, the polymerization is progressing on a delicate balance, and it is not preferable as an industrial method from the viewpoint of safety, and the gel content in the reaction solution is high. Will be generated.

COMPARATIVE EXAMPLE 5 The same apparatus and polymerizable monomer mixture as in Example 1 were charged with 36% air instead of nitrogen gas.
The mixture was heated to 100 ° C. with stirring, with gentle bubbling at a rate of ml / min. 1 hour after the start of polymerization 105
Although the temperature was raised to 0 ° C., stable polymerization could be carried out thereafter, and the same operation as in Example 1 was carried out. The acrylic polymer produced had a polymerization rate of 92% and an APHA value of 3
0, Mn = 55,000, Mw = 10,000, Mw / Mn =
It was 2.0. Heating the polymer-containing liquid to 150 ° C.,
It was continuously supplied to a flash tank depressurized to 20 mmHg to remove volatile matter and taken out as a 100% polymer.

A film obtained by using this polymer in the same manner as in Example 1 had a breaking strength of 110 kg / cm ² and an elongation of 3
It was 80%. That is, the polymer obtained as in Comparative Example 5 had satisfactory film strength, but it was not preferable as an acrylic polymer characterized by its coloration and transparency. It was In addition, since a slight temperature rise is observed during the polymerization, there is concern about explosion due to a rapid reaction on an industrial scale.

Examples 2 to 5 The procedure of Example 1 was repeated except that the monomer mixture having the composition shown in Table 1 was used to obtain an acrylic polymer as a 100% polymer. In each of the examples, the polymerization was mild and stable, and an acrylic polymer having a small molecular weight distribution without coloring was obtained.

Table 1 also shows the composition of the monomer mixture of Example 1 and Comparative Example 5, the type and amount of mercaptan, the presence or absence of a polymerization initiator, the polymerization temperature, the type of polymerization atmosphere, and the physical properties of the polymer. It was

[0039]

[Table 1]

[0040]

EFFECTS OF THE INVENTION According to the method for producing an acrylic polymer of the present invention, an acrylic polymer having a desired composition, less coloring, and a small molecular weight distribution, in which an emulsifier and a dispersant are not mixed, is industrially used. Safe and stable on a large scale and with high productivity. When the copolymerization is carried out, the composition of the monomer mixture is not limited, so that an acrylic copolymer having a desired composition can be obtained.

In bulk polymerization of a conventional acrylic polymer,
A special device has been proposed to control the sudden heat generation, but in the present invention, the acrylic acid-based monomer can be easily bulk polymerized even in a general reaction device, which is industrial in terms of safety. It is a very meaningful method. The acrylic polymer obtained by the production method of the present invention has transparency, and since the molecular weight distribution is small, for example, a high molecular weight component expresses the required performance, and a low molecular weight component causes performance degradation. It is very useful in such applications and vice versa.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masuji Izumibayashi 5-8 Nishimitabicho, Suita City, Osaka Pref.

Claims (1)

[Claims] 1. A method for producing an acrylic polymer by bulk-polymerizing a monomer component containing an acrylic acid-based monomer as a main component, wherein the bulk polymerization of the monomer component is performed. A method for producing an acrylic polymer, wherein the known polymerization system is in an inert gas atmosphere, contains mercaptan, and does not contain a polymerization initiator substantially.