JPH02218708A - Method for suspension polymerization of styrene-based monomer - Google Patents

Abstract

PURPOSE:To obtain a styrene-based polymer in a short time without coloring by carrying out suspension polymerization of a styrene-based monomer using a specific compound, such as dimethylbutyl isopropyl peroxycarbonate, as a polymerization initiator. CONSTITUTION:A styrene-based monomer alone or a mixture thereof with a vinylic monomer copolymerizable with the styrene is subjected to suspension polymerization using one or more of the group consisting of 1,1-dimethylbutyl isopropyl peroxycarbonate, 1,1-dimethylpropyl isopropyl peroxycarbonate and 1,1,3,3-tetramethybutyl isopropyl peroxycarbonate as a polymerization initiator.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to the suspension polymerization of a styrenic monomer alone or a mixture of a vinyl monomer copolymerizable with styrene. The present invention relates to a method for suspension polymerization of styrenic monomers in which polymerization can be completed in a relatively short polymerization time by using an agent.

(Prior art) Conventionally, when carrying out suspension polymerization of a styrenic monomer alone or a mixture of a vinyl monomer copolymerizable with styrene,
Methods using various organic peroxides as polymerization initiators are known. Criteria considered when selecting a polymerization catalyst are generally the relationship between the polymerization rate and the molecular weight of the resulting polymer.

The relationship between polymerization rate and molecular weight is usually inversely proportional. When a specific initiator is used, in order to increase the polymerization rate, the amount of initiator used is increased or the polymerization temperature is increased, but as a result, the molecular weight of the resulting polymer decreases. It is also known that the higher the temperature, the higher the molecular weight when using a suitable initiator. However, 12
It is also known that oligomers are produced by thermally initiated polymerization under conditions of high monomer concentration at high temperatures of 0°C or higher. For the reasons described above, a method is known in which two or more types of initiators having different decomposition temperatures are used in combination in order to maintain a high polymerization rate and obtain a polymer with a high molecular weight. That is, Japanese Patent Publications No. 36-5391, Japanese Patent Publication No. 26713-1971, and Japanese Patent Publication No. 7891-1977 describe methods in which two or three types of initiators are used in combination. In these published patents, benzoyl peroxide is used as a low temperature initiator, and a perester type initiator such as t-butyl peroxybenzoate is used as a high temperature initiator. The thermal decomposition temperatures of these initiators in cumene are about 75°C and about 105°C, respectively, at the 10 hour half-life temperature. By using these initiators in combination and carrying out the polymerization while raising the polymerization temperature stepwise, a high molecular weight polymer can be obtained without reducing the polymerization rate.

(Problem to be solved by the invention) By the way, since suspension polymerization is carried out in an aqueous system, the polymerization temperature is set at 100°C or higher in the latter half of the reaction, and -130°C for boat fishing.
The temperature is raised to about C. Therefore, the reaction vessel must be able to withstand high pressure. This is economically disadvantageous, and therefore a polymerization method that completes the polymerization at a relatively low temperature is desired.

Furthermore, when initiators are used in combination, if the difference in thermal decomposition temperature of the initiators used is too large, the polymerization will essentially take place in two stages, resulting in a so-called figure-eight conversion curve, resulting in an extension of the polymerization time.
Alternatively, it becomes difficult to control the polymerization heat. Therefore, it is desirable to use an initiator whose conversion curve is as close to a straight line as possible.

Furthermore, it is known that the decomposition products of the above-mentioned initiator having a benzene ring may cause coloring. It is also known that an initiator with a high decomposition temperature inevitably tends to remain in the polymer, which causes deterioration of the polymer over time. It is also known that the fragments of the initiator become terminal groups of the polymer and the thermal stability of the polymer changes depending on the type of initiator fragment.

Furthermore, the polymerization initiator or its decomposition products must not be harmful to humans or animals.

(Means for Solving the Problems) As a result of long-term research into the problems of the above-mentioned conventional methods, the present inventors found that by using a specific polymerization initiator, polymerization can be achieved in a shorter time than before. The present invention was completed by discovering a method for obtaining a polymer with a high molecular weight.

That is, in the method of the present invention, when a styrenic monomer alone or a mixture of a vinyl monomer copolymerizable with styrene is subjected to suspension polymerization, 1. Dimethylbutylperoxyisopropyl carbonate, 1.1-dimethylpropylperoxyisopropyl carbonate and 1.1.3.3-
This is a method for suspension polymerization of styrenic monomers, characterized in that one or more members of the group consisting of tetramethylbutylperoxyisopropyl carbonate are used as a polymerization initiator.

These initiators each have a thermal decomposition temperature of approximately 87°C.
5 about 95°C and 197°C, which is approximately the intermediate value between benzoyl peroxide and t-butyl peroxybenzoate.

Examples of the styrenic monomer or the vinyl monomer copolymerizable with styrene used in the present invention include styrene,
These include α-methylstyrene, acrylonitrile, acrylic esters, methacrylic esters, maleic esters, fumaric esters, maleimides, butadiene, and the like.

In addition to these monomers, various chain transfer agents, rubber components, or blowing agents such as pentane may be added.

The polymerization initiator used in the present invention consists of 1,1-dimethylbutylperoxyisopropyl carbonate, 1,1-dimethylpropylperoxyisopropyl carbonate, and 1,1.3.3-tetramethylbutylperoxyisopropyl carbonate. One type or two or more types of the group may be used in combination. Moreover, as mentioned above, the effect is further enhanced by using it in combination with other initiators having different thermal decomposition temperatures.

The amount of initiator added varies depending on the type of monomers used for polymerization or their combination, but in general, the amount of monomers added is 100
The amount is from o, oos to 5 parts by weight, preferably from 0.05 to 0.5 parts by weight, in terms of pure product. If the amount is less than 0.01 parts by weight, the polymerization rate tends to be slow. Moreover, if the amount exceeds 1 part of 51i, it is uneconomical and undesirable.

The polymerization method used in the present invention is a normal suspension polymerization method, and the polymerization temperature is generally 60 to 150°C, preferably 80 to 130°C. It is preferable that the polymerization temperature is usually carried out at a relatively low temperature at the initial stage of the polymerization, and then gradually raised to a lower temperature as the polymerization progresses. Specifically, an optimal time program of polymerization temperature is set based on the relationship between the polymerization conversion rate, the remaining amount of initiator, and the initiation rate at that temperature. If this setting is not appropriate, the purpose of the present invention cannot be achieved.

The polymers obtained in the present invention include GP type polystyrene, high-impact polystyrene, expanded polystyrene, styrene/acrylonitrile copolymer, styrene/acrylonitrile/phenylmaleimide copolymer, etc. used in general molding materials.

(Effects of the Invention) The present invention, which uses a specific polymerization initiator, has the following characteristics.

That is, according to the present invention, the conversion rate curve for polymerization is closer to a straight line than in the past, and the polymerization can be completed at a relatively low temperature and in a short time.

The polymerization initiator used in the present invention has a high polymerization initiator content, and the initiator itself or its decomposition products do not cause coloring and are not harmful compounds to humans or animals.

(Example) Hereinafter, the present invention will be specifically explained with reference to Examples.

The abbreviations for vinyl monomers used in the examples mean the following compounds.

ST; styrene Static; acrylonitrile α-MS: α-methylstyrene P old; phenylmaleimide In addition, the abbreviation for peroxide means the following compounds.

Am-1; 1,1-dimethylpropylperoxyisopropyl carbonate) tex-I; Ll-dimethylbutylperoxyisopropyl carbonate 0ct-1; LL3+3-tetramethylbutylperoxyisopropyl carbonate BPO; benzoyl peroxide Bu-Z; t -Butyl peroxybenzoate All molecular weights of products obtained by polymerization were measured in terms of polystyrene using gel permeation chromatography (GPC).

Examples 1 to 3 and Comparative Examples 1 to 2 In a stainless steel autoclave with a capacity of 500 d, 200 d of ion-exchanged water and 0.1 g of polyvinyl alcohol were charged and dissolved. Then 200g of styrene and Table 1.2
0.005 of the initiator peroxide shown in
mol/1 was added.

After the space in the autoclave was sufficiently replaced with nitrogen gas, it was sealed tightly. It was polymerized in a constant temperature oil bath at 100°C for 10 hours. For stirring, place the autoclave in an oil tank for 32 hours.
This was done by rotating at r, p, and m. After polymerization, it was cooled, and the polymerized product was poured into methanol for reprecipitation. The polymerization conversion rate was calculated from the weight of the obtained white powder. In addition, the number average molecular weight (Mn) and weight average molecular weight it (Mw) were measured by CPC. The results were as shown in Tables 1 and 2.

Examples 4 to 6 and Comparative Example 3 Using the same equipment as in Example 1, 200 mfl of ion-exchanged water
and 0.1 g of polyvinyl alcohol were added and dissolved.

Thereafter, 200 g of styrene and the initiator peroxide shown in Tables 1 and 2 were added.

After the space in the autoclave was sufficiently replaced with nitrogen gas, it was sealed tightly. It is heated from 80″C to 120″ in a constant temperature oil bath.
Polymerization was carried out in 10 hours until the temperature reached C, while the temperature was raised continuously at a constant rate. Thereafter, the same operation as in Example 1 was performed.

The results were as shown in Table 1.2 and Figure 1.

Examples 7 to 9 The same operations as in Example 4 were performed except that the vinyl monomer shown in Table 3 was used instead of styrene. The results are shown in Table 3.

Example Comparative example I can see that it is happening.

As is clear from the Examples and Comparative Examples above, the method of the present invention can obtain a high polymerization conversion rate under relatively mild conditions in suspension polymerization.

For example, when using an initiator alone, Examples 1 to 3 and Comparative Examples 1 to
As shown in No. 2, the polymerization conversion rate is high, and also in a system in which an initiator is used in combination, it is shown that by using the initiator of the present invention in combination, a high polymerization conversion rate can be obtained without reducing the molecular weight.

[Brief explanation of the drawing]

FIG. 1 shows polymerization conversion rate curves of Example 4 and Comparative Example 3. Figure 1 shows that the method of the present invention has a relatively linear polymerization conversion rate that is higher than that of the conventional method.

Claims (1)

[Claims] 1. When carrying out suspension polymerization of a styrene monomer alone or a mixture of a vinyl monomer copolymerizable with styrene, 1.
, 1-dimethylbutylperoxyisopropyl carbonate, 1,1-dimethylpropylperoxyisopropyl carbonate and 1,1,3,3-tetramethylbutylperoxyisopropyl carbonate.
A method for suspension polymerization of styrenic monomers, characterized in that one or more species of styrenic monomers are used as polymerization initiators.