| 摘要 |
PURPOSE:To obtain a high-bulk density vinyl chloride resin from which the residual monomer is easily stripped and which is excellent in processability, productivity, and physical properties, by polymerizing a vinyl chloride monomer in two stages under a specified condition in the presence of a dispersant, an oil- soluble polymerization initiator and an aqueous medium. CONSTITUTION:In the first stage, vinyl chloride or a monomer mixture of vinyl chloride and a monomer copolymerizable therewith is polymerized at 30-55 deg.C to a conversion of 20-50wt% in the presence of 0.01-1wt% dispersant (e.g., partially saponified polyvinyl acetate with a degree of saponification of 65- 75%), 0.01-1wt% oil-soluble polymerization initiator (e.g., isobutylroyl peroxide) and an aqueous medium. In the second stage, the polymerization is conducted at a temperature at least 5 deg.C higher than that in the first-stage polymerization. Before the pressure in the polymerizer is lowered, vinyl chloride monomer is added and the polymerization is continued so that the polymer weight W1 in the first-stage polymerization and the final polymer weight W2 will satisfy the relationship of (W2-W1)/W1>=1.0.
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