JPH0132848B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a copolymer of styrene and methyl methacrylate, in particular a method for producing a copolymer of styrene and methyl methacrylate, in particular a method for producing a copolymer of styrene and methyl methacrylate, in particular a method for producing a copolymer of styrene and methyl methacrylate. The present invention relates to a method for producing a copolymer of styrene and methyl methacrylate, which uses a specific amount of styrene and methyl methacrylate, has a low content of poorly water-soluble inorganic salts, and has excellent transparency. Conventionally, various suspension stabilizers have been proposed when styrene and methyl methacrylate are subjected to suspension polymerization in an aqueous medium. For example, there are partially saponified polyvinyl alcohol, sodium polyacrylate, etc., but these partially form emulsified micelles, which become fine powder particles, so post-treatment after polymerization is complicated. In addition, unless a large amount of these is used, a stable suspension state cannot be obtained, and since these suspension stabilizers are contained in the copolymer, the transparency becomes poor and the commercial value is low. In order to improve these problems, the present inventors have discovered that it is known that when styrene is suspended polymerized in an aqueous medium, a poorly water-soluble inorganic salt is used as a suspension stabilizer, and a surfactant is used as an auxiliary agent. This was applied to the production of a copolymer of styrene and methyl methacrylate, but as the polymerization progressed, the dispersion became unstable and eventually formed into agglomerates, making it impossible to obtain a particulate copolymer. Furthermore, when a poorly water-soluble inorganic salt was used as a suspension stabilizer and a persulfate salt was used as an auxiliary agent, the dispersion was stable and particles were obtained. It contained a large amount and it was not possible to obtain a product with excellent transparency. The purpose of the present invention is to solve these drawbacks by using a poorly water-soluble inorganic salt as a suspension stabilizer and an anionic salt as an auxiliary agent for suspension polymerization of styrene and methyl methacrylate in an aqueous medium. By using specific amounts of ionic surfactants and persulfates, styrene and methacrylic acid have high dispersion stability, do not produce fine powder copolymers, and have a content of poorly water-soluble inorganic salts of 10 ppM or less. The purpose is to provide a method for producing a copolymer with methyl. That is, the present invention involves suspension polymerization of styrene and methyl methacrylate in an aqueous medium by suspending a poorly water-soluble inorganic salt as a suspension stabilizer in the aqueous medium in an amount of 0.1 to 2% by weight based on the total suspension. It is characterized in that 1×10 ^-5 to 1×10 ⁻⁴ weight % of an anionic surfactant and 5×10 ⁻⁷ to 1×10 ⁻⁵ weight % of persulfate are used as stabilizing aids. The present invention will be further explained in detail below. The present invention involves the copolymerization of styrene and methyl methacrylate by suspension polymerization using a monomer in the presence of a poorly water-soluble inorganic salt as a suspension stabilizer and an anionic surfactant and a persulfate as its auxiliaries. This is a method for producing a copolymer using a polymerization initiator that is soluble in the polymer. First, suspension stabilizers and their auxiliaries will be explained. The poorly water-soluble inorganic salt used as a suspension stabilizer must have a positively charged surface and must also have the property of keeping the entire suspension neutral or alkaline. is necessary. If the persulfate is not positively charged, it will not be adsorbed to the surface of the poorly water-soluble inorganic salt as an auxiliary agent for the suspending agent, making it impossible to obtain good dispersibility.Also, if the suspension becomes acidic, the persulfate The salt becomes unstable and does not function as a surfactant, making it impossible to obtain good dispersibility. Examples of sparingly water-soluble inorganic salts that meet the above conditions include tribasic calcium phosphate, calcium pyrophosphate, calcium carbonate, and magnesium carbonate, among which it is most preferable to use tribasic calcium phosphate. The amount of tricalcium phosphate added is preferably 0.1 to 2% by weight based on the aqueous medium; if it is less than 0.1% by weight, stable dispersibility cannot be obtained, and if it exceeds 2.0% by weight, the suspended particles will become fine and the overall particle size will decrease. The surface area becomes large, and a large amount of tribasic calcium phosphate is contained in the copolymer particles. Next, surfactants will be explained, and it is necessary to use an anionic surfactant as a suspension aid. Specific examples are sodium lauryl sulfate, sodium alkylbenzene sulfonate,
Examples include, but are not limited to, sodium alkylnaphthalene sulfonate. The amount of these anionic surfactants added is preferably 1 x 10 ^-5 to 1 x 10 ^-4 weight % based on the total suspension. If it is less than 1×10 ^-5 % by weight, stable dispersibility cannot be obtained, and if it exceeds 1×10 ^-4 % by weight, the suspended particles will become finer and the overall particle surface area will increase, resulting in a decrease in tricalcium phosphate. are contained in large amounts in the copolymer particles. In addition, persulfates include potassium persulfate, ammonium persulfate, sodium persulfate, etc., and the amount added is preferably 5 x 10 ^-7 to 1 x 10 ^-5 % by weight based on the total suspension, and 5 x 10 If the amount is less than ^-7 % by weight, suspended particles will fuse together in the latter stage of polymerization, leading to agglomeration phenomenon. Moreover, if it exceeds 1×10 ⁻⁵ % by weight, a large amount of tribasic calcium phosphate will be contained in the copolymer particles, which is not preferable. These persulfates decompose in water into cations such as alkali metal ions or ammonium ions and persulfate anions (S ₂ O ^2- ₈ ), and further form persulfate anions (S ₂ O ^{2- 8} ). ₈ ) by pyrolysis,
It decomposes into two anion radicals (SO ^- _4. ), and these anion radicals (SO ^- _4. ) undergo radical polymerization with the monomer (M), forming a kind of anionic surfactant (~M _o OSO ^- ₃ ) form. This anionic surfactant acts as a suspension stabilizing agent and has a significant effect on the stability of suspension copolymerization of styrene and methyl methacrylate. This anionic surfactant is stable against hydrolysis even at a temperature of 150° C. under neutral or alkaline conditions, but is unstable under acidic conditions. The polymerization catalyst used in the present invention may be any catalyst commonly used for suspension copolymerization of styrene or methyl methacrylate, such as organic polymers such as benzoyl peroxide, lauroyl peroxide, tertiary butyl peroxyisobutyrate, etc. Examples include peroxide, azo compounds such as azobisisobutyronitrile, azobiscyclohexanecarbonitrile, etc.
It is also possible to use more than one species. In addition, examples of chain transfer agents include n-octylmercaptan, n-dodecylmercaptan, t-
Dodecyl mercaptan, α-methylstyrene dimer, etc. can be used, but are not limited to these, and known chain transfer agents can be used, and it is also possible to use one or more of these in combination. . The present invention will be explained below with reference to Examples, but it should be understood that the present invention is not limited by these and that there are various embodiments within the scope of the claims. Note that all percentages stated in the specification are expressed on a weight basis. Example 1 4 kg of pure water, 40 g of tribasic calcium phosphate, 0.16 g of sodium lauryl sulfate, and 0.02 g of potassium persulfate were placed in a polymerization container with an internal volume of 10, and thoroughly stirred. Next, 2 kg of styrene, 2 kg of methyl methacrylate, and 15.2 g of benzoyl peroxide were added, and after expelling the air in the container with nitrogen gas, the container was sealed and the temperature was raised to 90° C. to initiate polymerization. 90 as is
Polymerize for 7 hours at a temperature of ℃, then raise the temperature to 130℃,
Polymerization was carried out for 2 hours. After cooling the polymerization liquid, the contents were taken out, neutralized, washed with water, dehydrated, and dried to obtain a granular polymer.
The amount of calcium element contained in this granular polymer was determined by atomic absorption spectrometry to determine the amount of tribasic calcium phosphate contained. Further, this granular polymer was made into pellets, and the pellets were further injection molded at a temperature of 230°C to obtain a transparent test piece having a thickness of 3 mm. The total light transmittance and haze value of this test piece were measured. These results are shown in the table. Comparative Example 1 The same procedure as in Example 1 was carried out except that 0.27 g of sodium lauryl sulfate was used and potassium persulfate was not added. In this case, since no persulfate was used, poor dispersion occurred during polymerization, resulting in agglomeration. Comparative Example 2 No sodium lauryl sulfate added,
The same procedure as in Example 1 was carried out except that 0.16 g of potassium persulfate was used. In this case, since too much potassium persulfate was used, a large amount of tribasic calcium phosphate was incorporated into the polymer particles, resulting in deterioration of the transparency of the resin. Example 2 Using 0.27 g of sodium lauryl sulfate and replacing 0.02 g of potassium persulfate with sodium persulfate.
The same procedure as in Example 1 was carried out except that 0.012g was added. Comparative Example 3 The same procedure as in Example 2 was carried out except that 1.6 g of sodium lauryl sulfate was used. The results are shown in Comparative Example 3 in the table. In this case, because too much sodium lauryl sulfate was used, the suspended particles became fine and a large amount of tribasic calcium phosphate was incorporated into the resulting polymer particles, resulting in a worsening of the transparency of the resin. Comparative Example 4 The same procedure as in Example 1 was carried out except that 100 g of tribasic calcium phosphate was used. The results are shown in Comparative Example 4 in the table. In this case, because too much tribasic calcium phosphate was used, the suspended particles became fine and a large amount of tribasic calcium phosphate was incorporated into the resulting polymer particles, which deteriorated the transparency of the resin. . Example 3 The same procedure as in Example 1 was carried out except that 0.107 g of sodium dodecylbenzenesulfonate and 0.04 g of potassium persulfate were used in place of 20 g of tribasic calcium phosphate and 0.16 g of sodium lauryl sulfate. Example 4 In a polymerization container with an internal volume of 10, 4 kg of pure water, 40 g of tribasic calcium phosphate, 0.16 g of sodium dodecylbenzenesulfonate, and 0.01 g of potassium persulfate.
and stirred thoroughly. Next, add 1.2 kg of styrene, 2.8 kg of methyl methacrylate, and 8.8 g of tertiary butyl peroxyisobutyrate, and after expelling the air in the container with nitrogen gas, seal the container and lower the temperature to 95.
The temperature was raised to 0.degree. C. to initiate polymerization. Polymerization was continued at a temperature of 95°C for 7 hours, then the temperature was raised to 130°C, and polymerization was continued for 2 hours. The following steps were carried out in the same manner as in Example 1. Comparative Example 5 Example 4 except that 0.0016 g of potassium persulfate was used
I went in the same way. In this case, the amount of potassium persulfate was not sufficient, resulting in poor dispersion during polymerization and formation of lumps. Example 5 The same procedure as in Example 1 was carried out except that 2.8 kg of styrene, 1.2 kg of methyl methacrylate, and 18 g of benzoyl peroxide were used. Comparative Example 6 The same procedure as in Example 1 was carried out except that 0.16 g of octyltrimethylammonium salt was used instead of 0.16 g of sodium lauryl sulfate. The results are shown in Comparative Example 6 in the table. In this case, the use of a cationic surfactant caused poor dispersion during polymerization, resulting in agglomeration. 【table】

Claims (1)

[Claims] 1. In suspension polymerizing styrene and methyl methacrylate in an aqueous medium, 0.1 to 2% by weight of a poorly water-soluble inorganic salt as a suspension stabilizer to the aqueous medium;
1 x 10 ^-5 to 1 x 10 ^-4 weight % of anionic surfactant and 5 x 10 ^-7 to 1 x 10 ^-5 weight % of persulfate are used as suspension stabilizing aids based on the total suspension. A method for producing a copolymer of styrene and methyl methacrylate, which is characterized by excellent transparency. 2. The production method according to claim 1, wherein the poorly water-soluble inorganic salt is a substance whose surface is positively charged in the suspension and has the property of keeping the suspension neutral or alkaline. . 3. The manufacturing method according to claim 1 or 2, wherein the poorly water-soluble inorganic salt is tricalcium phosphate.