JPH03140304A - Polymerization of vinylic monomer - Google Patents

Abstract

PURPOSE:To obtain a polymer suitable as a molding material and having a low melt viscosity and excellent thermal stability by employing a specific organic peroxide as a polymerization initiator when a vinylic monomer is polymerized. CONSTITUTION:When a vinylic monomer is polymerized to obtain a polymer, an organic peroxide of the formula (R is 2-5C alkyl) (e.g. 1,1- dimethylpropylperoxyacetate, 1,1-dimethylbutylperoxyacetate or 1,1,3,3- tetramethylperoxyacetate) is employed as a polymerization initiator.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention produces a polymer with low melt viscosity and excellent thermal stability, which is particularly suitable as a general molding material, by polymerizing vinyl monomers. Concerning polymerization methods.

<Prior Art> Conventionally, methods have been known in which various organic peroxides are used as polymerization initiators when a vinyl monomer alone or a mixture thereof with a vinyl monomer copolymerizable therewith is polymerized.

Generally, in polymerization, the relationship between polymerization rate and molecular weight is usually inversely proportional. For example, when a polymerization initiator is used, in order to increase the polymerization rate, the amount of initiator used is increased or the polymerization temperature is raised, but as a result, the molecular weight of the resulting polymer decreases.

On the other hand, the mechanical properties of a polymer are generally better as the molecular weight of the polymer increases. Therefore, it is practically desirable to be able to produce a polymer with a high polymerization rate and a high molecular weight.

For this purpose, methods using various organic peroxides as initiators have been developed.

For example, Tokuko Sho 36-5391. Special Public Service No. 40-26713
, Japanese Patent Publication No. 47-7891, and Japanese Patent Publication No. 63-42921 describe a method of using two or three types of initiators in combination. In the methods described in these publications, benzoyl peroxide is used as a low-temperature initiator, and a peroxyester-based 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 10 hour half-life temperatures. 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.

(Problems to be Solved by the Invention) However, organic peroxides conventionally used as polymerization initiators also have the property of causing crosslinking or molecular cleavage (cleavage) of polymers. Therefore, in the latter half of polymerization, while a relatively large amount of vinyl monomer remains (probably 1% or more), crosslinking of the polymer occurs preferentially, and when only a small amount of monomer remains, cleavage takes place preferentially. It's allowed to happen.

Crosslinking of polymers increases melt viscosity and reduces processability. Furthermore, cleavage of the polymer lowers the molecular weight and mechanical strength, and also produces unsaturated bonds at the ends of the polymer. It is known that this results in a decrease in heat resistance stability. That is, the conventional polymers produced by polymerization using organic peroxides as polymerization initiators still have some points to be improved in practical terms.

(Another means to solve the problem) As a result of long-term research into the problems of the above-mentioned conventional methods, the present inventors found that by using the following specific organic peroxide as a polymerization initiator, The present invention was completed by discovering that a polymer with less crosslinking reaction and less cleavage in the later stages of polymerization can be obtained.

That is, in the method of the present invention, when a vinyl monomer alone or a mixture of a vinyl monomer copolymerizable with the vinyl monomer is polymerized, an organic peroxide CH represented by the following formula is used.

(However, R represents a straight chain or branched alkyl group having 2 to 5 carbon atoms.) The present invention relates to a method for polymerizing vinyl monomers, characterized in that one selected from the above is used as a polymerization initiator.

Specifically, the organic peroxide represented by the above formula which is a polymerization initiator used in the present invention includes 1,1-dimethylpropyl peroxyacetate, 1,1-dimethylbutylperoxyacetate, and 1,1, Examples include 3.3-tetramethylbutylperoxyacetate.

Examples of the vinyl monomer used in the present invention include styrene, α-methylstyrene, acrylonitrile, acrylic esters, methacrylic esters, maleic esters, fumaric esters, maleimides, butadiene, and vinyl acetate. etc.

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

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 0.001 to 5 parts by weight, preferably 0.01 to 0.5 parts by weight, in terms of pure product. If the amount is less than 0.001 part by weight, the polymerization rate tends to be slow. Moreover, if it exceeds 5 parts by weight, it is uneconomical and undesirable.

The polymerization method used in the present invention is a conventional bulk polymerization, solution polymerization, or suspension polymerization method, and the polymerization temperature is generally 60 to 60°C.
The temperature is 150°C, preferably 80 to 130°C. The polymerization temperature is a constant temperature or a relatively low temperature in the initial stage of polymerization, and a method is used in which the temperature is raised stepwise as the polymerization progresses.

The polymers obtained in the present invention are GP type polystyrene, impact polystyrene, expanded polystyrene, polymethyl methacrylate, styrene/acrylonitrile copolymer, styrene/acrylonitrile/
Phenylmaleimide copolymer, butyl methacrylate/2
- Copolymers of various acrylic acids or methacrylic esters such as ethylhexyl methacrylate copolymers.

<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 occurrence of polymer bridging or cleavage in the latter half of polymerization is significantly reduced compared to conventional initiators.

The resulting polymer had lower melt viscosity and better thermal stability than polymers obtained by conventional methods.

Furthermore, the polymerization initiator used in the present invention has a high ability to initiate polymerization, and the initiator itself or its decomposition products do not cause coloration and are not harmful compounds to the human body or animals.

<Examples> The present invention will be specifically explained below using examples. In addition, the abbreviations of initiators used in the table mean the following compounds.

A-A: 1,1-dimethyl 10-bilberoxyacetate A-A: 1,1-dimethylbutylperoxy 1cetate 0-A: 1,1,3.3-tetramethylbutylperoxy 1cetate B-A : 1,
1-dimethylethylperoxyacetate BPO:
Bensoyl peroxide B-Z: t-Butyl peroxybenzoate All molecular weights of products obtained by polymerization were measured in terms of polystyrene using gel permeation chromatography (GCP).

Examples 1-3 and Comparative Examples 1-3 10 g of styrene and the initiator shown in Table 1.2 were added to a glass ampoule with a volume of 20 ml.

The ampoule was vacuum degassed, then melted and sealed.

It was polymerized in a constant temperature oil bath at the temperature shown in Table 1.2 for 10 hours. After that, transfer the ampoule to a constant temperature bath at 250℃.
heated for an hour.

Every 2 hours of polymerization, the final polymer was poured into methanol for reprecipitation. The polymerization conversion rate was calculated from the weight of the obtained white powder. Furthermore, the weight average molecular weight (Mw) was measured by GPC. Furthermore, the MI value was separately determined using a melt flow indexer for a sample with a conversion rate of 100%. The respective results are shown in Table 1.2.

Example 4 Methyl methacrylate 1 using the same ampoule as Example 1
0g and 1,1,3.3-tetramethylbutylperoxyacetate as initiator) 0.003moj! /I! was added and polymerized at 110°C. The same analysis as in Example 1 was performed. The conversion rate was 68.0% after 2 hours of polymerization and 100% after 4 hours. The weight average molecular weight was 508,000 at a conversion rate of 80%, and 752,000 at a conversion rate of 100%. Also, after heating at 250℃ for 1 hour? It was 20,000.

Comparative Example 4 In Example 4, benzoyl peroxide 0.004+++offi71 was used as an initiator, and the polymerization temperature was 90°C.
The same operation as in Example 4 was performed except that . The conversion rate was 48.3% after 2 hours of polymerization and 100% after 4 hours. The weight average molecular weight at a conversion rate of 80% is 49,900
0, 931,000 at 100% conversion, and 1 at 250°C.
After heating for hours, it was 420,000.

Example 5 In a stainless steel autoclave with a capacity of 500 mj, 200 mN of ion-exchanged water and 0.1 g of polyvinyl alcohol were charged and dissolved. Then 30g of α-methylstyrene,
20 g of acrylonitrile, 50 g of styrene, and 0.03 moffi# of 1,1,3.3-tetramethylbutylperoxyacetate as an initiator were added, and after replacing the space with nitrogen, polymerization was carried out at 110°C. The same analysis as in Example 1 was performed. 33.0% at 2 hours of polymerization time, 7 at 4 hours
The conversion rate was 2.5% and 100% in 6 hours. The weight average molecular weight was 343,000 at a conversion rate of 80%, and 386,000 at a conversion rate of 100%. Moreover, it was 362,000 after heating at 250°C for 1 hour.

Comparative Example 5 The same operation as in Example 5 was carried out except that 0.05 moj, # of benzoyl peroxide was used as an initiator and the polymerization temperature was changed to 90°C. 2 in 2 hours of polymerization time
The conversion rate was 8.5%, 71.1% in 4 hours, and 98.4% in 6 hours. The weight average molecular weight was 312,000 at a conversion rate of 80%, 435,000 at a conversion rate of 100%, and 329,000 after heating at 250°C for 1 hour.

As is clear from the Examples and Comparative Examples where the conversion rate is 80%, 100%, and the weight average molecular weight conversion after Ih heating at 250°C is 100% or higher, the method of the present invention does not carry out the crosslinking reaction or A polymer without cleavage can be obtained. As a result, the melt viscosity of the polymer was reduced and processability was improved.

It also improved thermal stability.

For example, when looking at the molecular weight at a polymerization conversion rate of 80% and 100% as shown in Examples 1 to 3 and Comparative Examples 1 to 3 of the initiator, there is a large difference in the molecular weight in the comparative example, indicating that the molecular weight has increased due to the crosslinking reaction. Indicated.

Also, the MI value was relatively large in the comparative example.

Also, when looking at the molecular weights at polymerization conversion rates of 80% and 100% in Example 4 and Comparative Example 4, and Example 5 and Comparative Example 5, the difference is large in the Comparative Example, and the molecular weight becomes thicker due to the crosslinking reaction. It was shown that

Claims (1)

[Claims] When a vinyl monomer alone or a mixture of a vinyl monomer copolymerizable with it is polymerized, an organic peroxide represented by the following formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ( (wherein R represents a straight chain or branched alkyl group having 2 to 5 carbon atoms) A method for polymerizing vinyl monomers, characterized in that at least one of the following is used as a polymerization initiator.