Vinyl chloride is first polymerized in mass with high turbulent agitation to from 7 to 15 percent completion forming suspended polymer seeds in the liquid monomer, the suspension is added to a mixture of liquid vinyl chloride and low molecular weight olefin, and polymerization in mass is continued to completion, producing grains having a seed of the homopolymer of vinyl chloride surrounded by the copolymer. The first stage with high turbulence is carried out under warm conditions of usually about 50* to 60* C. and the second stage is carried out at from about -40* to +80* C. with mild agitation. The product is concentrated in a narrow range of particle sizes, e.g. 80 percent between 100 and 250 microns.