Method of preparing vinyl halide polymers and copolymers with polyolefins

In the process for the preparation of a vinyl halide polymer which comprises polymerizing in bulk a vinyl halide monomer, in the liquid phase, either along or in combination with up to about 50% be weight of another ethylenically unsaturated monomer copolymerizable therewith in the initial presence of more than about 1.8% by weight based on said vinyl halide monomer of a polyolefin or mixture of polyolefins having a weight average molecular weight of at least about 50,000, said polyolefin or mixture of polyolefins being present during the polymerization only during the period which commences at 0% to about 20% conversion of the monomer or monomers to polymer and concludes with the end of the polymerization, said polymerization being carried out in a first stage wherein the reaction mixture is subjected to high speed agitation until about 3% to about 20% by weight of said monomer or monomers have been converted to polymer, and further polymerizing the resultant reaction mixture together with additional monomer or monomers in a second stage during which the reaction mixture is subjected to low speed agitation until the polymerization has been completed, the improvement which comprises removing from the polymerization mass during the thick paste state thereof from about 2% to less than about 50% by weight of the vinyl halide charged to the polymerization mass, the effective concentration of said polyolefin or mixture of polyolefins after said vinyl halide removal being above about 3.5 weight percent based on vinyl halide remaining in said polymerization mass after said removal of vinyl halide whereby a more finely divided particulate product of high impact strength is obtained.