GB935996A - Improvements in and relating to the manufacture of graft synthetic rubber products - Google Patents

Abstract

Graft synthetic rubber products are made by mixing (A) an emulsion of a rubbery copolymer of (i) butadiene (60 to 90 parts) (40 to 10 parts) or (ii) butadiene (60 to 90 parts) acrylonitrile (5 to 35 parts) and styrene (5 to 35 parts), and (B) a monomeric material selected from methyl methacrylate, styrene or a mixture of styrene and methyl methacrylate or acry-lonitrile, the proportion of monomer (B) not exceeding 80% of the weight of copolymer (A), the mixture so-obtained is stirred and/or allowed to stand so as to bring about swelling of the rubber by the monomer, and there is then introduced a catalyst which brings about the polymerization of the monomer, the amount of the monomer (B) being such that the butadiene content of the final composition is at least 45% by weight, and the amount and nature of the catalyst and the temperature at which the process is conducted are chosen so as to produce a graft copolymer which is cross-linked so that it has a gel content between 60 and 90% by weight of the product. In a modification of the process there is used a rubbery copolymer (A) which is first cross-linked in latex form before graft polymerization with the monomer (B). As polymerization catalysts there may be used potassium persulphate and a mixture of cumene hydroperoxide and tetraethylene pentamine. The styrene of copolymer (A) and monomer (B) is preferably styrene itself, but may also be a styrene derivative, e.g. vinyl toluene, alpha-methyl styrene, chlorostyrenes and divinyl benzene. The resulting graft copolymers may be used as processing aids for rubbers and in blends with styrene-acrylonitrile copolymers.