Patent ID: 7683144

Claim:
A process for chain stopping vinyl chloride polymerization, which process comprises adding to a vinyl chloride polymerization reaction system a) a stable free nitroxyl radical and b) a phenolic antioxidant wherein the reaction system comprises initial unreacted vinyl chloride monomer or unreacted vinyl chloride monomer and partially polymerized vinyl chloride monomer, where the nitroxyl radical is of formula (A), (B) or (O) wherein G 1 , G 2 , G 3 , G 4 are independently alkyl of 1 to 4 carbon atoms or G 1 and G 2 , or G 3 and G 4 , or G 1 and G 2 , and G 3 and G 4 together are pentamethylene; G 5 , G 6 are independently hydrogen or C 1 -C 4 alkyl; R, if m is 1, is hydrogen, C 1 -C 18 alkyl which is uninterrupted or C 2 -C 18 alkyl interrupted by one or more oxygen atoms, cyanoethyl, benzoyl, glycidyl, a monovalent radical of an aliphatic carboxylic acid having 2 to 18 carbon atoms, of a cycloaliphatic carboxylic acid having 7 to 15 carbon atoms, or of an aromatic carboxylic acid having 7 to 15 carbon atoms; or R is a monovalent radical of a carbamic acid or phosphorous containing acid or a monovalent silyl radical; R, if m is 2, is C 2 -C 12 alkylene, C 4 -C 12 alkenylene, xylylene, a divalent radical of an aliphatic dicarboxylic acid having 2 to 36 carbon atoms, or a cycloaliphatic or aromatic dicarboxylic acid having 8-14 carbon atoms or of an aliphatic, cycloaliphatic or aromatic dicarbamic acid having 8-14 carbon atoms; or R is a divalent radical of a phosphorus-containing acid or a divalent silyl radical; R, if m is 3, is a trivalent radical of an aliphatic, cycloaliphatic or aromatic tricarboxylic acid; R, if m is 4, is a tetravalent radical of an aliphatic, cycloaliphatic or aromatic tetracarboxylic acid; p is 1; R 1 is C 1 -C 12 alkyl, C 5 -C 7 cycloalkyl or benzoyl; and R 2 is C 1 -C 12 alkyl, C 5 -C 7 cycloalkyl or a group of the formula —CO-Z wherein Z is hydrogen, methyl or phenyl.