Abstract: The toughness of thermoplastic polyesters can essentially be improved by addition of a new type of graft polymers which contain one grafting site for about 400 to 2000 carbon atoms, the average molecular weight M.sub.w of the graft branches being from 2000 to 40,000.

Abstract: An improved vinyl halide or vinyl halide copolymer containing up to 50 percent of a comonomer can be obtained by polymerizing in contact with an aliphatic hydrocarbon olefin homopolymer, copolymer or terpolymer in a process of bulk polymerization comprising single stage or two-stage bulk polymerization wherein high speed agitation is used during the first stage and low speed agitation is used in the second stage. By polymerizing in the presence of the olefin polymer or copolymer, reduced particle size, reduced lump formation, and lower melt viscosity and improved impact strength can be obtained in the resin product. Small amounts of the olefin polymer or copolymer are effective in providing particle size control, reducing lump formation and eliminating scale build-up. Larger amounts of olefin polymer increase impact strength, reduce melt viscosity and provide excellent mold release properties in the final product.