Abstract: This process uses, as dispersion stabilizers, (A) a partially saponified polyvinyl alcohol having an average polymerization degree of 300 to 2,000, a saponification degree of 70 to 85 mol %, and a mercapto group at least one terminal ends of its molecule chain, and (B) a hydroxypropylmethyl cellulose having a methoxy substitution of 26 to 30% by weight, a hydroxypropoxy substitution of 4 to 15% by weight, and a viscosity of 5 to 4,000 cP at 20.degree. C. in the state of a 2 weight % aqueous solution, in subjecting a vinyl monomer comprised mainly of vinyl chloride to suspension polymerization in an aqueous medium. A polymer which is high in porosity and will provide a molded item having few fish eyes can be produced in high productivity. Furthermore, since deposition of polymer scale on the inner wall of a polymerization vessel is little, removing the scale is easy and the polymerization vessel can be efficiently used.

Abstract: Polyvinyl chloride is prepared by suspension polymerization of a monomeric charge of vinyl chloride dispersed and suspended in an aqueous medium while agitating the suspension. An oil-soluble partially saponified polyvinyl alcohol is added to the monomeric charge as a dispersant at the start of polymerization. A water-soluble partially saponified polyvinyl alcohol and/or a hydroxypropylmethyl cellulose is continuously added as a suspending agent from the start of polymerization. The suspending agent is entirely added while the polymerization rate is in the range of 5-50%. The agitating power applied to the aqueous suspension is 50-110 kg.multidot.m/s.multidot.ton while the suspending agent is being added, and increased above 110 kg.multidot.m/s.multidot.ton after the completion of addition. The resulting polymer has a high bulk density and a sharp particle size distribution and is susceptible to extrusion.

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.multidot.m/s.multidot.ton from the start of polymerization to a conversion of 20 to 50%, and to 130-200 kg.multidot.m/s.multidot.ton from then to the completion of polymerization.