| 摘要 |
PROBLEM TO BE SOLVED: To produce a polymer highly productively which has a high bulk density and a sharp distribution of particle diameter and is suitable for high speed extrusion by using polyvinyl alcohol or the like as a dispersing agent for polymerization having a specific degree of saponification and a degree of polymerization. SOLUTION: A dispersion-stabilizing agent used for suspension polymerization of a vinyl chloride-based monomer in water in the presence of an oil-soluble polymerization initiator includes partially saponified PVA (A) having a degree of saponification of 85-00 mol% and an average degree of polymerization of 1,500-3,500, partially saponified PVA (B) having a degree of saponification of 70-84 mol% and an average degree of polymerization of 700-2,500 and hydroxypropoxymethyl cellulose and/or hydroxypropyl cellulose (C). The total amount of the added dispersion-stabilizing agent is 500-1,500 ppm based on the monomer and the amount of the added component A is 20-60 wt.% of the total amount of the added dispersion-stabilizing agent. The polymerization system includes 2.0×10-5-1.0×10-2 mol% of oxygen based on the monomer. Further the initial diameter of a liquid drop represented by weight average diameter of a suspension liquid drop of the monomer is designed to be 40-80μm.
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