Vinyl mercaptoacetate S-sulfate sodium salt (VMAS) was prepared with a yield of 74% from a reaction of vinyl chloroacetate and sodium thiosulfate. Polymerization of VMAS with 2-hydroxyethyl acrylate (HEA) in the presence of ammonium persulfate and N,N,N',N'-tetramethylethylenediamine afforded a colorless copolymer bearing the S-SO3- Na+ group in 3.2-4.3 mol-% and having a MW of 2.4-13 x 10(4). The polymer water-soluble but, upon treatment with an oxidizing lit, was transformed quickly into a water-tolerant material. It again became water-soluble on the addition of a reducing agent. The unique solubility, alternation was explained by the formation and fission of S-S bond crosslinking in the polymer.