JPS6248703A - Production of vinyl chloride polymer having low polymerization degree - Google Patents

Abstract

PURPOSE:To obtain a vinyl chloride polymer having sharp particle size distribution and low polymerization degree with small amount of chain transfer agent, by carrying out the suspension polymerization of vinyl chloride and adding a specific chain transfer agent to the polymerization system at a specific stage. CONSTITUTION:Vinyl chloride or a monomer mixture composed mainly of vinyl chloride is subjected to suspension polymerization in an aqueous medium in the presence of a chain transfer agent consisting of an organic compound having mercapto group and hydroxy group or carboxyl group (e.g. mercaptoethanol, thioglycolic acid, thioglycerol, etc.). In the above process, the organic compound is used in an amount of 0.02-0.3wt% based on the monomer charged to the reaction system and is added to the polymerization system within 15min-2hr after heating the system to the polymerization temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a method for producing a vinyl chloride polymer with a low degree of polymerization.

[Conventional technology]

It has been known to add a chain transfer agent to a polymerization system for the purpose of obtaining a vinyl chloride polymer having a relatively low degree of polymerization.

It is known that as such a chain transfer agent, an organic compound having a mercapto group and a hydroxyl group or a carboxy group is effective in a small amount and is therefore preferable from the viewpoint of environmental hygiene (Japanese Patent Publication No. 13515/1983).

However, when such an organic compound is used, there is a drawback that it is difficult to control the particle size of the vinyl chloride polymer because it is added to the polymerization system before polymerization. That is, a vinyl chloride polymer using this material has a wide particle size distribution. Currently, vinyl chloride polymers with a particle size of 42 mesh all-pass are generally used, and in order to produce a 42-mesh all-pass particle, an organic compound having a mercapto group and a hydroxyl group or a carboxyl group is used. Many particles have a particle size of 200 mesh or less. However, fine particles cause problems with environmental pollution, problems due to large amounts of scattering into bag filters because pneumatic transport is usually used when transporting from silos to weighing instruments and intermediate tanks, and problems caused by gelling during extrusion processing. There is a drawback that a normal molded product cannot be obtained due to unevenness of the molded product.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for producing a low degree of polymerization vinyl chloride polymer with a sharp particle size distribution by using a small chain transfer agent.

[Failure to solve the problem]

The gist of the present invention is to add the above-mentioned organic compound within 15 minutes to 2 hours after the temperature of the polymerization system is raised to the polymerization temperature when carrying out suspension polymerization in a mercapto group and a hydroxyl group.

The organic compound having a mercapto group and a hydroxy group or a carboxyl group (hereinafter sometimes referred to as "mercaptoethanol etc.") includes mercaptoethanol,
Flucols such as thiopropylene glycol and thioglycerin, thioglycolic acid, thiohydroacrylic acid,
Examples include thiolactic acid and thiolactic acid.

Among such organic compounds, those having 2 to 7 carbon atoms, preferably 2 to 4 carbon atoms, exhibit excellent effects. Number of carbons is 7
When the compound becomes larger than 100%, its solubility in water decreases and it remains in the resulting vinyl chloride polymer, resulting in deterioration of quality.In addition, this remaining organic compound is gradually released, resulting in environmental sanitation. Not good. That is, it is preferable that the organic compound has relatively high solubility in water.

The amount of this organic compound to be used varies somewhat depending on polymerization conditions such as polymerization temperature, but in general, it is 0.02~
A range of 0.3% by weight is preferred.

If it is less than 0.02% by weight, the chain transfer effect is small;
If it exceeds 1% by weight, the polymerization time will be too long and the thermal stability of the resulting polymer will also deteriorate.
You may use it as a mixture of 2 or more types, without being limited to a type.

The method of the present invention is mainly applied to the polymerization of vinyl chloride monomers, but it is also applicable to copolymerization with vinyl monomers that can be copolymerized with vinyl chloride monomers containing 50% by weight or more of vinyl chloride monomers. can do.

Vinyl monomers that can be copolymerized with vinyl chloride monomers include alkyl vinyl esters such as vinyl acetate, alkyl vinyl ethers such as cetyl vinyl ether, and α-monoolefin monomers such as ethylene or haglobylene. can be mentioned.

In the present invention. - In suspension polymerization, a suspending agent used in suspension polymerization, such as ordinary vinyl chloride monomer, is used.

Suspending agents include polyvinyl alcohol (including partially saponified polyvinyl acetate), cellulose derivatives such as methylcellulose, polyvinylpyrrolidone, synthetic polymeric substances such as maleic anhydride-vinyl acetate copolymer, and starch, gelatin, gum tragacanth, and Arabica. One type or a mixture of two or more types of natural polymeric substances such as rubber can be used.

Initiators include lauroyl peroxide, benzoyl peroxide,
Tert-butyl peroxy pivalate, diisopropyl peroxy dicarbonate, dicyclohexyl peroxy dicarbonate, di2-ethylhexyl peroxy dicarbonate, di-3,5.5-)limethylhexanoyl peroxide, bis (4-tert-butylcyclohexyl) peroxydicarbonate, di3-methoxybutyl peroxydicarbonate, di3-methoxy 3-methylbutyl peroxydicarbonate, di-secondary butyl peroxydicarbonate, acetylcyclohexyl sulfonyl Organic peroxides such as peroxide, and α'-azobisisobutyronitrile, α
, α′-azobis-2,4-dimethylvaleronitrile,
One type or a mixture of two or more types of azo compounds such as a, α'-7zobis-4-methoxy-2,4-dimethylvaleronitrile can be used.

[Effect]

Mercap, toethanol, etc. used in the present invention are -8H
and -OHZEN-COOH9#, so it has a high solubility in water, so if it exists in the initial polymerization system, it will affect the suspended dispersion system, producing many fine particles of polymer, resulting in fine particle size. It is thought that the number of polymers increases.

However, when hemerkagtoethanol or the like, which has undergone some degree of polymerization, is added as in the present invention, the polymerization proceeds without any loss of the dispersion system, so it is presumed that the generation of fine particles is prevented.

Regarding the timing of addition of mercaptoethanol, etc., if it is within 15 minutes after the temperature rises, the particle size distribution will still be broad; on the other hand, if it is added after 2 hours, the particle size distribution will become sharp, but the chain transfer effect will occur for 2 hours before addition. As a result, a polymer with a higher degree of polymerization than the intended purpose is produced. Therefore, in order to adjust the degree of polymerization, the amount of mercaptoethanol, etc. must be significantly increased compared to when adding before the temperature rises. This has the disadvantage that physical properties such as thermal stability of the obtained polymer deteriorate. Therefore, the appropriate timing for adding mercaptoethanol, etc. is within 2 hours after the temperature is raised to n degree of polymerization.

〔Example〕

Examples 1 to 2, Comparative Examples 1 to 3 The inside of a polymerization vessel with an internal volume of 2,001 mm and equipped with a stirrer was replaced with nitrogen gas, and then 55% of water was added to 9% and saponification degree of 7% was added as a suspending agent.
0.045 parts by weight of 2% polyvinyl alcohol (based on 100 parts by weight of vinyl chloride. The same applies hereinafter), degree of saponification 6
0.045 parts by weight of 8% polyvinyl alcohol and 0.04 parts by weight of α,α'-azobis-2,4-dimethylvaleronitrile as a polymerization initiator were charged into a polymerization vessel, and while stirring, 100 parts by weight of vinyl chloride (44 kVC) was charged. ,
After raising the temperature to 60°C, mercaptoethanol was supplied to the polymerization reactor in the amount and timing shown in Table 1 (in Comparative Example 1, before vinyl chloride was charged), and the polymerization was proceeded until the pressure inside the polymerization reactor increased from 7 to 9. /dG, the polymerization was stopped, unreacted gas was discharged out of the system, and a polymer was produced.

Table 1 Examples 3 to 4, Comparative Examples 4 to 6 The inside of the same polymerization vessel as in Example 1 was replaced with nitrogen gas, and then 9 parts were added to 55 parts of water, and 0.04 liters of polyvinyl alcohol with a saponification degree of 72% was added as a suspending agent. Parts (based on 100 parts by weight of vinyl chloride. The same applies hereinafter), saponification! 0.04 parts by weight of 68% polyvinyl alcohol and α as a polymerization initiator,
α'-Azobis-2,4-dimethylvaleronitrile 0.
PVC 44# (100,!i parts) was added to the polymerization vessel while stirring, and after raising the temperature to 60°C, mercaptoethanol was added to the polymerization vessel at the time and timing shown in Table 2. In Comparative Example 4, polymerization was proceeded (before charging vinyl chloride), and the pressure inside the polymerization vessel was 7 kg/cdG.
Polymerization was stopped when the temperature was reached, and unreacted gas was discharged to the outside of the system to produce a polymer.

Table 2 Example 5, Comparative Example 7 The inside of the same polymerization vessel as in Example 1 was replaced with nitrogen gas, and then 55 kg of water and polyvinyl alcohol with a saponification degree of 68% were added as a suspending agent in the amounts and polymerization shown in Table 3. As an initiator, 0.02 parts by weight of α,α'-azobis-2,4-dimethylvaleronitrile (based on 100 parts by weight of vinyl chloride).

Same below. ) and 0.05 parts by weight of lauroyl peroxide into a polymerization vessel, and while stirring, 44 kg of vinyl chloride (10
After raising the temperature to 70°C, the chain transfer agent shown in Table 3 was fed to the polymerization vessel in the amount and timing shown in Table 3. In Comparative Examples 7 and 8, vinyl chloride was charged. in front)
The polymerization progresses until the pressure inside the polymerization vessel reaches 9 kg/cti.
When the temperature reached G, the first reaction was stopped and the unreacted gas was discharged to the outside of the system to produce a polymer.

Table 3 [Effects] According to Examples 1 to 5, Comparative Examples 1 to 7, and Tables 1 to 3, the particle size of the vinyl chloride polymer obtained by using mercaptoethanol etc. according to the method of the present invention is 42 mesh all bath. It is clear that most of the particles are larger than 200 mesh, and the particle size distribution is sharp.

that's all Special hit applicant: Chisso Corporation

Claims (1)

[Claims] (1) When carrying out suspension polymerization of vinyl chloride or a monomer mixture mainly consisting of vinyl chloride in an aqueous medium in the presence of an organic compound having a mercapto group and a hydroxyl group or a carboxyl group, the organic compound is added to the polymerization system. A method for producing a low degree of polymerization vinyl chloride polymer, characterized in that the addition is carried out within 15 minutes to 2 hours after the temperature is raised to the polymerization temperature.