1,053,597. Butadiene - acrylonitrile - unsaturated acid terpolymer. UNITED STATES RUBBER CO. July 26, 1965 [Aug. 28, 1964], No. 31687/65. Heading C3P. A butadiene, an ethylenically unsaturated acid and an acrylonitrile are terpolymerized using an azo initiator in aqueous emulsion in the presence of a cationic emulsifier and a mercaptan modifier and short-stopping the terpolymerization at 40 to 80% conversion so as to form an emulsion of a liquid rubber, the terpolymerization being effected in the presence of from 0À001 to 0À1 parts per 100 monomers of a ferric salt dissolved in the emulsion. Specified monomers are butadiene, isoprene, 2-3-dimethyl butadiene and chlorobutadiene, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid maleic acid, fumaric acid and ataconic acid. Preferred proportions are 60 to 95 parts butadiene, 1 to 39 parts acrylonitrile and 1-39 parts acid. The preferred emulsion is cetyldimethyl benzyl ammonium chloride, while n-dodecyl and tertiary dodecyl mercaptan are the preferred modifiers and azo-bis(isobutyronitrile) is the preferred initiator. Specified ferric salts are the nitrate, chloride, bromide, phosphite and (preferred) sulphate. Benzoquinone, carbamates and (preferred) hydroxyl ammonium sulphate are the short-stoppers.