| abstract |
Vinyl chloride polymer is prepared by suspension polymerization of monomeric vinyl chloride or a mixture of vinyl chloride and another monomer in an aqueous medium while agitating the suspension. A first partially saponified polyvinyl alcohol having a degree of saponification of 60 - 80 mol% and an average degree of polymerization of 500-1,000 is added as a suspension stabilizer at the start of polymerization, and a second partially saponified polyvinyl alcohol having a degree of saponification of 75 - 85 mol% and an average degree of polymerization of 1,500-2,700 is added while the conversion is 30% to 60%. The agitating power is controlled to 80 - 120 kg·m/s·ton from the start of polymerization to a conversion of 20 to 50%, and to 130-200 kg·m/s·ton from then to the completion of polymerization. The resulting vinyl chloride polymer is of quality as demonstrated by a high bulk density and improved free flow, monomer removal, gelation, and plasticizer absorption as well as minimal fish eye. Scale build-up on the reactor wall is minimized. |