PURPOSE: To obtain a polymer large in a gelling and melting rate and a bulk density and good in moldability by polymerizing vinyl chloride monomer, etc., while raising the polymerization temperature with time, and subsequently adding a chain transfer agent, when the polymerization reaches a specific polymerizatior conversion.
CONSTITUTION: Vinyl chloride monomer or a mixture containing the vinyl chloride monomer as a main monomer and further another copolymerilzable monomer (e.g. ethylene) is polymerized in the presence of the partially saponified product of polyvinyl acetate and a polymerization initiator in an aqueous medium, while the polymerization temperature is raised within a raising change width of 2-35°C with time in a period occupying ≥50% of the whole period during when the polymerization reaction proceeds. When the polymerization conversion reaches 40-70% based on the charged vinyl chloride monomer, a chain transfer agent (e.g. 2-mercaptnethanol) is added to the polymerization system to obtain the objective vinyl chloride polymer large in a gelling and melting rate and a bulk density and excellent in moldability.
MORIMOTO TADASHI