PURPOSE: To obtain a vinylidene fluoride polymer useful for high gloss paint of a metal sheet by adding a specific chain regulator at an initial stage of polymerization when vinylidene fluoride is polymerized in an aq. medium in the absence of an emulsifier.
CONSTITUTION: Vinylidene fluoride is subjected to discontinuous polymerization in an aq. medium in the absence of an emulsifier by using an alkali metal peroxydisulfate or ammonium peroxydisulfate as a polymerization initiator and using 1-3C alkyl acetate, for example, ethyl acetate as a chain regulator to obtain a vinylidene fluoride polymer with a particle size of 0.1-3 μm. The polymerization initiator is used in an amt. of 0.005-0.5 g per 1 l of an aq. phase and the chain regulator is added in an amt. of 0.5-3%, pref., 1-2% by wt. of the monomer. The initiator may be wholly added to a prepared soln. at an initial stage but is pref. added gradually with the advance of polymerization. Polymerization temp. is 80-95°C advantageously and polymerization pressure is pref. 30-45 bar.