UNSATURATED NITRILE-CONJUGATED DIENE COPOLYMER, PROCESS FOR PRODUCING THE SAME, AND VULCANIZABLE RUBBER COMPOSITION

摘要

An saturated nitrile-conjugated diene copolymer obtained by copolymerizing acrylonitrile with butadiene in the presence of a free radical initiator and an alkylthiol compound as a molecular weight modifier. A part of the molecular weight modifier is incorporated in a monomer charge before polymerization, and the remainder thereof is incorporated in a polymerization mixture during polymerization. The alkylthiol compound has 12 to 16 carbon atoms, which include at least three tertiary carbon atoms, and further has a sulfur atom directly bound to at least one of the tertiary carbon atoms. The copolymer has a Mooney viscosity of 15 to 150 and contains 3 to 20 weight % of a fraction having a number average molecular weight of not larger than 35,000. The copolymer is used in combination with a sulfur-containing vulcanizer.