JP2859915B2 - Method for producing styrenic copolymer - Google Patents

Description

The present invention relates to a method for producing a styrenic copolymer. More specifically, the present invention relates to a method for producing a styrene monomer-methacrylic acid copolymer having excellent heat resistance, transparency and strength by suspension polymerization.

(B) Conventional technology Various methods have been proposed for obtaining a copolymer of styrene and methacrylic acid, and a relatively transparent styrene-methacrylic acid copolymer can be produced by a suspension polymerization method. What is important is JP-A-60-54983 and JP-A-6-54983.
It is publicly known as disclosed in Japanese Patent Application Publication No. 1-266418.

(C) Problems to be Solved by the Invention However, under the conventional suspension polymerization conditions, the methacrylic acid monomer is dissolved in both water and the styrene-based monomer, and is absorbed into the suspended particles from water at the latter stage of the polymerization. Therefore, there is a problem that the composition tends to be non-uniform, and it is not possible to obtain a copolymer having sufficient properties such as heat resistance, transparency and strength.

(D) Means and action for solving the problem Therefore, the present inventor conducted various studies to solve the problem, and as a result, obtained a finding to solve the non-uniformity of the composition in suspension polymerization, and obtained heat resistance, A method for producing a styrene-based monomer-methacrylic acid-based copolymer having excellent transparency and strength has been completed.

That is, the present invention provides a method of suspension polymerization of a styrene monomer and a methacrylic acid monomer, wherein the ratio of the total amount of the styrene monomer to the methacrylic acid monomer is styrene monomer: methacrylic acid. 75 to 95% by weight as acid monomer: 5 to
25% by weight (total of 100% by weight), 75-99% by weight of styrene monomer at the start of polymerization and 20-80% by weight of methacrylic acid monomer at the start of polymerization % Of the remaining monomer during the polymerization, ie, 1% of the total amount used.
A method for producing a styrenic copolymer, characterized in that a styrene-based monomer of from 25 to 25% by weight and a methacrylic acid monomer of from 20 to 80% by weight of the total amount are added and copolymerized in a polymerization system. About.

 Hereinafter, the present invention will be described in more detail.

The styrene monomer used in the present invention is styrene, α-metallystyrene, vinyltoluene, tert-butyltoluene, etc. alone or a mixture thereof.

The ratio of the styrene monomer to the methacrylic acid monomer used in the present invention is 75 to 95% by weight as a styrene monomer: methacrylic acid monomer: 5 to 25% by weight, but is 85 to 93% by weight. % By weight: 7 to 15% by weight (the total of both is 100% by weight). 5 methacrylic acid monomers
If the amount is less than 10% by weight, the obtained copolymer is inferior in heat resistance,
If it exceeds 25% by weight, the suspension stability during polymerization deteriorates, leading to a decrease in yield and the like.

In the present invention, copolymerizable monomers such as acrylonitrile and methyl methacrylate can be copolymerized in addition to the styrene monomer and the methacrylic acid monomer. The amount of these monomers is preferably 10 parts by weight or less based on 100 parts by weight of the total of the styrene monomer and the methacrylic acid monomer. These monomers can be added to the polymerization system together with, for example, a styrene-based monomer.

The production method of the present invention is characterized in that each monomer is divided and added to a polymerization system. That is, at the start of the polymerization, the styrene-based monomer and the methacrylic acid monomer are each present in an amount of 75 to 99% by weight and 20 to 80% by weight, respectively, and the polymerization is started. Each is added to the polymerization system to continue the polymerization. The timing for adding the monomer during the polymerization is as follows.
It is preferred to add up to 80%. Each monomer added during the polymerization may be separately added to the polymerization system.However, if a mixture of a part or all of them is added, the freezing of the monomer in winter can be prevented. Is preferred.

The method for adding the monomer during the polymerization is not particularly limited, and it is sufficient to add the monomer at least once, may be added several times intermittently, or may be added continuously.

If the amount of the styrene-based monomer added during the polymerization is less than 1% by weight of the total amount of the styrene-based monomer, the ratio of methacrylic acid in the copolymer absorbed and formed in the suspended particles is increased in the later stage of the polymerization. If it exceeds 25% by weight, the proportion of methacrylic acid in the copolymer absorbed and formed in the suspended particles becomes lower in the latter stage of the polymerization, resulting in a copolymer having a non-uniform composition distribution. The heat resistance, transparency and strength of the resulting copolymer are impaired. When the amount of the methacrylic acid monomer added during the polymerization is less than 20% by weight of the total amount of the methacrylic acid monomer, the methacrylic acid content in the copolymer formed in the early stage of the polymerization increases, %, The methacrylic acid content in the copolymer formed in the early stage of the polymerization decreases,
Since the copolymer has a non-uniform composition distribution, the heat resistance, transparency and strength of the obtained copolymer are impaired.

For the suspension polymerization in the present invention, a known dispersant such as tribasic calcium phosphate or polyvinyl alcohol can be used. Its use amount is suitably from 0.01 to 0.5% by weight based on water.

As the polymerization initiator, for example, known organic peroxides such as benzoyl peroxide and tert-butyl peroxybenzoate, and azo compounds such as azobisisobutyronitrile can be used. The amount of the polymerization initiator used is suitably from 0.01 to 0.5% by weight based on the total amount of the monomers.

The polymerization is preferably carried out at a temperature between the 10-hour half-life temperature and the 30-minute half-life temperature of the polymerization initiator.

Further, if necessary, similarly to the case of polystyrene, a known additive such as a plasticizer, a lubricant, a release agent, a heat stabilizer and an antioxidant may be added to the monomer for polymerization.

(E) Examples Examples will be given below, but the present invention is not limited to these examples.

Example 1 6 kg of pure water and 6 g of polyvinyl alcohol were added to an autoclave having a capacity of 15 L, and the mixture was stirred at 300 rpm.
g, 300 g of methacrylic acid and 6 g of tertiary butyl peroxybenzoate were added, and the inside of the autoclave was replaced with nitrogen gas and then sealed. Then, the temperature was raised and polymerization was carried out at 110 ° C. for 5 hours. At this time, a mixture of 300 g of styrene and 300 g of methacrylic acid was added over 5 hours from when the temperature reached 110 ° C. The polymerization rate at the end of the addition was 78.2%. Further, the temperature was kept at 140 ° C. for 3 hours to complete the polymerization.
Next, the polymerized copolymer was neutralized, dehydrated and dried according to a conventional method, and formed into a pellet by an extruder. Table 1 shows physical properties
Shown in

Example 2 The amount of styrene added to the autoclave before the polymerization was started
The procedure was performed in the same manner as in Example 1 except that the weight was changed to 5.3 kg and 100 g during the polymerization. The polymerization rate at the end of the addition was 79.5%. Table 1 shows the physical properties.

Example 3 The amount of styrene added to the autoclave was changed before the polymerization was started.
The procedure was performed in the same manner as in Example 1 except that the weight was changed to 4.4 kg and 1000 g during the polymerization. The polymerization rate at the end of the addition was 76.8%. Table 1 shows the physical properties.

Example 4 The same procedure as in Example 1 was carried out except that the amount of methacrylic acid added to the autoclave was 150 g before the start of the polymerization and 450 g during the polymerization. The polymerization rate at the end of the addition was 77.7%. Table 1 shows the physical properties.

Example 5 The same procedure as in Example 1 was carried out except that the amount of methacrylic acid added to the autoclave was 450 g before the start of the polymerization and 150 g during the polymerization. The polymerization rate at the end of the addition was 79.0%. Table 1 shows the physical properties.

Comparative Example 1 The amount of styrene added to the autoclave was changed before the polymerization was started.
The same procedure as in Example 1 was carried out except that the weight was 5.4 kg, and that no component was added during the polymerization. Table 1 shows the physical properties.

Comparative Example 2 The amount of styrene added to the autoclave was changed before the polymerization was started.
The procedure was the same as in Example 1 except that the weight was 4.0 kg and the weight was 1.4 kg during the polymerization. The polymerization rate at the end of the addition was 69.8%. Table 1 shows the physical properties.

Comparative Example 3 The same procedure as in Example 1 was carried out except that the amount of methacrylic acid added to the autoclave was changed to zero (no addition) before the start of the polymerization and to 600 g during the polymerization. The polymerization rate at the end of the addition was 75.6%. Table 1 shows the physical properties.

Comparative Example 4 The same procedure as in Example 1 was carried out except that the amount of methacrylic acid added to the autoclave was 600 g before the start of the polymerization and was not added during the polymerization. The polymerization rate at the end of the addition was 80.3%. Table 1 shows the physical properties.

(F) Effects of the Invention According to the production method of the present invention, a styrene-based monomer-methacrylic acid-based copolymer having excellent heat resistance, transparency, and strength can be efficiently obtained, and is industrially extremely useful. is there.

Claims (1)

(57) [Claims] 1. A method of suspension polymerization of a styrene monomer and a methacrylic acid monomer, wherein the ratio of the total amount of the styrene monomer to the methacrylic acid monomer is such that the styrene monomer: methacrylic monomer is used. 75 to 95% by weight as an acid monomer: 5 to 25% by weight (the total of both is 100% by weight). At the start of polymerization, a styrene monomer is used in an amount of 75 to 99% by weight of the total amount thereof and methacrylic acid. The monomer is present in an amount of 20 to 80% by weight based on the total amount thereof, and the remaining monomer during the polymerization, namely, 1 to 25%
A method for producing a styrene-based copolymer, characterized in that a styrene-based monomer in an amount of 20% by weight and a methacrylic acid monomer in an amount of 20 to 80% by weight of the total amount are added to a polymerization system and copolymerized.