Process for producing acrylonitrile polymers

Claim 1

The acrylonitrile homopolymer or copolymer prepared by the process which comprises polymerizing acrylonitrile or a mixture comprising at least 85% by weight of acrylonitrile and at most 15% by weight of other copolymerizable monoethylenically unsaturated compounds in an aqueous medium at 30° C to 70° C at a pH of 1.5 - 5.0, wherein the monomer to water ratio is 1/10 to 1/3, in contact with a redox catalyst comprising nitrous acid or a salt thereof and sulfurous acid or salt thereof, wherein the ratio of said nitrous acid or salt to said sulfurous acid or salt thereof is 1/30 to 1/3 by weight, and the sulfurous acid or salt thereof is present in an amount of 1/10,000 to 1/50 by weight, based on the amount of water in the aqueous medium, and further in contact with 0.005%-5% by weight based on the weight of monomer of a water insoluble mercaptan selected from the group consisting of alkyl mercaptans containing at least 4 carbon atoms and mercaptan carboxylate acid ester.