STABLE EMULSIONS OF WATER RESISTANT POLYVINYL ALCOHOL-STABILIZED VINYL CHLORIDE-ETHYLENE COPOLYMERS

A method for preparing a stable vinyl chloride based resin emulsion which comprises a copolymer colloidally dispersed in an aqueous medium, the copolymer having a Tg from 0 to 50 DEG C, about 65 to 90 wt% vinyl chloride, about 5 to 35 wt% ethylene, 0 to 10 wt% olefinically unsaturated copolymerizable monomer and prepared by emulsion polymerization of vinyl chloride, ethylene and, optionally, an olefinically unsaturated comonomer in the presence of about 3 to 15 wt% polyvinyl alcohol as the dispersing agent, the polymerization method comprising (a) forming an aqueous emulsion reaction mixture containing substantially all the polyvinyl alcohol and a portion, preferably at least 5%, of teh total vinyl chloride monomer, (b) pressurizing the reaction mixture with an ethylene pressure sufficient to provide the copolymer with a 5 to 35 wt% ethylene content. (c) initiating the reaction mixture by the addition of a free radical generating source and continuing polymerization until the rate of polymerization begins to decrease to provide a prepolymer emulsion, and (d) adding the remaining vinyl chloride at a substantially uniform rate and continuing polymerization until the polymerization reaction is no longer self-sustaining, ethylene being neither withdrawn nor added during the polymerization in one embodiment.