Dispersion stabilizer for suspension polymerization of vinyl compound

In a process comprising polymerizing one or more vinyl compounds in an aqueous dispersion in the presence of a dispersion stabilizer and an oil-soluble initiator, the improvement comprising,

• stabilizing the dispersion with a dispersion stabilizer comprising a modified saponified vinyl ester copolymer (A) having an ethylene content of from 1 to 20 mol %, a degree of saponification of 90 mol % or more and a degree of polymerization of from 100 to 3,000, a saponified vinyl ester polymer (B) having a degree of saponification of from 60 to 90 mol % and a degree of polymerization of 600 to 4,000, and a saponified vinyl ester polymer (C) having a degree of saponification of from 30 to 60 mol % and a degree of polymerization of from 100 to 600,
• wherein the weight ratio of component (A)/{component (B)+component (C)} is from 5/95 to 40/60.

A process comprising

• polymerizing one or more vinyl compounds in the presence of a dispersion stabilizer comprising a modified saponified vinyl ester copolymer (A) having an ethylene content of 1 to 20 mol %, a degree of saponification of 90 mol % or more and a degree of polymerization of 100 to 3,000, a saponified vinyl ester polymer (B) having a degree of saponification of 60 to 90 mol % and a degree of polymerization of 600 to 4,000, and a saponified vinyl ester polymer (C) having a degree of saponification of 30 to 60 mol % and a degree of polymerization of 100 to 600,
• wherein a component (A)/{component (B)+component (C)} weight ratio is from 5/95 to 40/60,
• wherein the polymerization is a suspension polymerization and the vinyl compounds comprise vinyl chloride.