Process for reducing content of free vinyl chloride by posttreating copolymer with redox catalyst

Claim 1

A process for the production of vinyl chloride copolymer dispersions having a reduced content of free vinyl chloride comprising the steps of polymerizing a monomer mixture containing from 15% to 90% by weight of vinyl chloride and the remainder, mono-olefinically unsaturated monomers copolymerizable with vinyl chloride selected from the group consisting of vinyl alkanoates having from 1 to 18 carbon atoms in the alkanoate, esters of alkanols having from 1 to 8 carbon atoms with acrylic acid and methacrylic acid, diesters of alkanols having from 1 to 8 carbon atoms with maleic acid, fumaric acid and itaconic acid, ethylene, propylene and mixtures thereof, with from 0 to 5% of the monomer mixture, mono-olefinically-unsaturated monomers copolymerizable with vinyl chloride and having functional groups and from 0 to 2% of the monomer mixture, poly-olefinically-unsaturated monomers copolymerizable with vinyl chloride, under aqueous emulsion polymerization conditions at temperatures of 30° C., to 80° C., in the presence of from 0 to 10% by weight of emulsifiers and from 0 to 5% by weight of protective colloids, with a minimum of 0.1% of at least one of said emulsifiers and said protective colloids, as well as from 0.05% to 2% by weight of free-radical-former polymerization catalysts, all based on the polymerization product, post-polymerizing until a decrease in the autogeneous pressure occurs, releasing the pressure, flushing the gas space above the copolymer dispersion free of monomer, cooling the copolymer dispersion by at least 10° C. to 40° C., to a temperature of from 10° C. to 40° C., said cooled copolymer dispersion having a vinyl chloride content of over 50 ppm, adding a redox catalyst to the cooled dispersion consisting of from 0.002% to 0.5% by weight of the dispersion, of an oil-soluble peroxy compound, and a water-soluble sulfur-containing reducing agent in a ratio of reducing agent to peroxy compound of 0.5 to 3 equivalents, allowing the dispersion to stand at a temperature of from 10° C. to 40° C. for a period of two hours to two days and recovering a copolymer dispersion having a vinyl chloride content of less than 50 ppm.