In a process of bulk vinyl chloride polymerization involving a two stage stationary reaction zone polymerization wherein high speed agitation is used during the first stage and slow speed agitation is used in the second stage, the polymerization in the first stage is conducted in contact with an organic or inorganic, inert, fine particle size material, solid at least at reaction temperatures and insoluble in the monomer or monomers used, or an anionic, cationic, or nonionic surfactant, or mixtures thereof. By the present polymerization method using economical conventional agitation equipment, small particle size polyvinyl chloride homopolymers or copolymers are produced which are useful as extender resins in plastisols.