JPH0227363B2 - ENKABINIRUKEIJUGOTAINOSEIZOHOHO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing vinyl chloride polymers. More specifically, by polymerizing vinyl chloride or an unsaturated monomer mainly composed of vinyl chloride and copolymerizable with vinyl chloride in the presence of an alkali metal salt of thioglycolic acid, a relatively high polymerization degree with excellent thermal stability is obtained. The present invention relates to a method for producing a vinyl chloride polymer having a low average degree of polymerization. The processability of vinyl chloride polymers is highly dependent on the degree of polymerization, and vinyl chloride polymers with a relatively low degree of polymerization are often used in processing methods that require high fluidity. However, vinyl chloride polymers with a low degree of polymerization have the disadvantage that their thermal stability decreases significantly as the average degree of polymerization decreases. In other words, as the degree of polymerization decreases, the thermally unstable molecular chain end group structure of the vinyl chloride polymer increases, and at the same time, the softening temperature decreases, making it easier for thermal fluctuations in the molecular chain to occur. It is known that thermal decomposition is likely to occur even when heated. Conventionally, for the purpose of obtaining a vinyl chloride polymer with a relatively low degree of polymerization, it has been known to raise the temperature of the polymerization system or to add a chain transfer agent to the polymerization system.
Halogenated hydrocarbons and organic mercaptans are often used as chain transfer agents. However, when increasing the temperature of the polymerization system to polymerize a vinyl chloride polymer with a low degree of polymerization, the polymerization temperature approaches the softening temperature of the vinyl chloride polymer, so that the vinyl chloride polymer is There is a drawback that not only decomposition and coloring of the polymer are likely to occur, but also that the thermal stability of the obtained polymer is significantly reduced due to an increase in the ratio of molecular terminal double bonds per molecular chain. In addition, when a chain transfer agent such as a halogenated hydrocarbon or organic mercaptan is added to the polymerization system to polymerize a vinyl chloride polymer with a low degree of polymerization, the chain transfer agent remains in the polymer and stabilizes heat. Not only is sexuality impaired;
The chain transfer agent fragment is bonded to the end of the polymer's molecular chain, making it thermally unstable. In order to solve these drawbacks, the present inventors have conducted research for many years and found that by polymerizing the alkali metal thioglycolic acid salt of the present invention as a chain transfer agent, a relatively high degree of polymerization with excellent thermal stability can be achieved. The present inventors have discovered that a vinyl chloride polymer having a low average degree of polymerization can be obtained, and have completed the present invention. That is, in the present invention, when vinyl chloride or a vinyl monomer mixture mainly composed of vinyl chloride is polymerized in an aqueous medium, 0.01 to 100 parts by weight of the monomer is used.
The present invention provides a method for producing a vinyl chloride polymer, which is characterized in that the polymerization is carried out in the presence of 10 parts by weight of an alkali metal salt of thioglycolic acid. The alkali metal salts of thioglycolate used in the present invention include, for example, lithium thioglycolate, sodium thioglycolate, potassium thioglycolate, rubidium thioglycolate, cesium thioglycolate, etc. used alone or as a mixture. be done. More preferably, thioglycolic acid sodium salt and thioglycolic acid potassium salt are used. In carrying out the present invention, the alkali metal salt of thioglycolic acid is vinyl chloride or a mixture of unsaturated monomers mainly composed of vinyl chloride and copolymerizable with vinyl chloride.
It is generally used in an amount of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight. If the amount used is less than 0.01 part by weight, the chain transfer effect will be slight, making it impossible to obtain a vinyl chloride polymer with a relatively low degree of polymerization and good thermal stability. Furthermore, if the amount used exceeds 10 parts by weight, it is not desirable because a polymer with good thermal stability and a low average degree of polymerization may not be obtained. Further, the alkali metal thioglycolic acid salt of the present invention may be added in its entirety at the beginning of the polymerization, or may be added in portions or continuously during the progress of the polymerization reaction. The method of the present invention may be carried out in the same manner as known methods for polymerizing vinyl chloride in an aqueous medium, such as suspension polymerization and emulsion polymerization, except that the above-mentioned alkali metal thioglycolic acid salt is used. The suspending agent used in this case may be a known suspending agent, such as partially saponified polyvinyl alcohol, vinyl acetate-maleic anhydride copolymer, polyvinylpyrrolidone, gelatin, starch, methyl cellulose, hydroxypropyl cellulose, etc. It will be done. Examples of emulsifiers include potassium laurate, lauryl sulfate, and dodecylbenzenesulfonate. Examples of the polymerization initiator used in the present invention include lauroyl peroxide, tert-butyl peroxypivalate, benzoyl peroxide, isopropyldioxycarbonate, azobisisobutyronitrile, α,α′-azobis-4
-oil-soluble initiators such as methoxy-2,4-dimethylpareronitrile, hydrogen peroxide, potassium persulfate,
Examples include water-soluble initiators such as ammonium persulfate or redox-based initiators containing these with iron salts, sulfites, etc. In the present invention, monomers that can be copolymerized with vinyl chloride monomers include, for example, olefin compounds such as ethylene and propylene; vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid and α-alkyl acrylic acid; Unsaturated monocarboxylic acids and their alkyl esters, amides, namely acrylic acid, methacrylic acid, ethyl acrylate,
Methyl methacrylate, acrylic acid amide, methacrylic acid amide; Unsaturated nitriles such as acrylonitrile; Unsaturated dicarboxylic acids such as maleic acid and fumaric acid, their alkyl esters, and their anhydrides; vinyl methyl ether, vinyl ethyl Examples include vinyl alkyl ethers such as ether; and various other known copolymerizable monomers. In the present invention, the polymerization temperature should be determined in relation to the degree of polymerization of the resulting vinyl chloride polymer and the amount of alkali metal thioglycolate added as a chain transfer agent, and is generally not limited to 45%. A temperature range of ~75°C is preferred. Adding a large amount of thioglycolic acid alkali metal salt at high temperature and polymerizing for a long time is not preferred because the vinyl chloride polymer often becomes colored. The method of the present invention is suitably applied to suspension polymerization of vinyl chloride or a vinyl monomer mixture mainly composed of vinyl chloride. , polymerization time, etc. may be determined according to the conditions conventionally employed when vinyl chloride is polymerized in an aqueous medium, and these are not particularly limited. EXAMPLES In order to explain the present invention more specifically, Examples and Comparative Examples will be given below, but the present invention is not limited to these Examples. Incidentally, the measured values displayed in the examples were based on the following measuring method. (1) Average degree of polymerization Determined according to the method of JIS K-6721. (2) Thermal stability The roll-kneaded sheet was subjected to a thermal deterioration test in a gear oven at 180°C, and the blackening time was measured. (3) Coloring Measure the lightness (L), saturation (a), and hue (b) of the sample using a DN-K5 color difference meter manufactured by Nippon Denshoku Co., Ltd. Next, the standard L ₀ , a ₀ and b ₀ values using the standard sample magnesium oxide plate, that is, L ₀
= 90.8, a ₀ = 0.4, and b ₀ = 4.0, the color difference of the sample (△
E) was calculated in NBS (National Bureau Standards) units. △E (NBS) =√( ₀ −) ² + ( ₀ −) ² + ( ₀ −) ² Example 1 1.6 g of partially saponified polyvinyl alcohol (saponification degree 80%) in a stainless steel autoclave with a stirrer
After charging 1 kg of ion-exchanged water in which 0.8 g of methylcellulose was dissolved, thioglycolic acid alkali metal salt and tert-butyl peroxypivalate in the proportions shown in Table 1, and degassing the autoclave, 350 g of vinyl chloride monomer was added. 4 at 60℃
Polymerized for hours. The obtained vinyl chloride polymer was thoroughly washed with a large amount of water and then dried. The vinyl chloride resin thus obtained, a lead-based stabilizer, and a lubricant were weighed and blended using a Henschel mixer. The mixing ratio is as follows. Vinyl chloride polymer 100 parts by weight Tribasic lead sulfate 2 parts by weight Lead stearate 2 parts by weight Stearic acid 0.2 parts by weight Next, the mixed sample was mixed using a mixing roll.
The mixture was kneaded at ℃ for 2 minutes to form a sheet with a thickness of 1 mm. The coloration of this sheet was measured using a color difference meter. Thermal stability was determined by conducting a heat deterioration test on the sheet at 180°C in a gear oven and measuring the blackening time. These results are shown in Table 1. As a comparative example, Table 1 shows the results of vinyl chloride polymers polymerized using chain transfer agents other than those of the present invention.

[Table] Example 2 1.6 g of partially saponified polyvinyl alcohol (saponification degree 80%) in a stainless steel autoclave with a stirrer
After charging 1 kg of ion-exchanged water in which 0.8 g of methyl cellulose was dissolved, sodium thioglycolate and tert-butyl peroxypivalate in the proportions shown in Table 2, the autoclave was degassed, and 350 g of vinyl chloride monomer was charged. , polymerization was carried out at the temperatures shown in Table 2. The obtained vinyl chloride polymer was thoroughly washed with a large amount of water and then dried. The vinyl chloride polymer thus obtained was prepared in Example 1.
After blending the stabilizer and lubricant in the same manner as
A sheet was prepared and the coloring and thermal stability of the rolled sheet were investigated. The results are shown in Table 2. As a comparative example, Table 2 shows the results of vinyl chloride polymers polymerized using chain transfer agents other than those of the present invention.

[Table] Example 3 1.2 g of partially saponified polyvinyl alcohol (saponification degree 80%) in a stainless steel autoclave with a stirrer
After charging 1 kg of ion-exchanged water in which 0.6 g of methyl cellulose was dissolved, a chain transfer agent, a copolymerization monomer, and tert-butyl peroxypivalate in the proportions shown in Table 3, the autoclave was degassed.
250 g of vinyl chloride monomer was charged and polymerized at 55°C for 3 hours. The obtained vinyl chloride copolymer was thoroughly washed with a large amount of methanol and then dried under reduced pressure. After blending the vinyl chloride copolymer thus obtained with a stabilizer and a lubricant in the same manner as in Example 1, a sheet was prepared, and the coloring and thermal stability of the rolled sheet were examined. The results are shown in Table 3.

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Claims (1)

[Claims] 1. Production of a vinyl chloride polymer characterized by polymerizing vinyl chloride or a vinyl monomer mixture mainly composed of vinyl chloride in an aqueous medium in the presence of an alkali metal thioglycolic acid salt. Method.