Abstract: A highly saturated nitrile group-containing copolymer rubber having a Mooney viscosity lowered by 15 points or more by applying a high shearing force thereto in the presence of an aging inhibitor, which has a Mooney viscosity of 5-35 and a weight average molecular weight/number average molecular weight ratio of 3-5, and exhibits an increase in Mooney viscosity of 10 points or fewer while the rubber is allowed to stand in the air at room temperature for 30 days. The viscosity of the copolymer rubber changes only to a minor extent with the lapse of time, and the copolymer rubber has excellent processability and storage stability. The copolymer rubber can be used as a heat-resistant rubber composition comprising the copolymer rubber and other heat-resistant rubber. The copolymer rubber can be used as a composite thereof with a fiber, which has good mechanical strength.

Abstract: The invention relates to a carboxylated nitrile group-containing copolymer rubber having the following physical properties: (a) the acid equivalent being at least 1×10−4 ephr, (b) the ratio of [peak height of a carboxylic acid anhydride group]/([peak height of the carboxylic acid anhydride group]+[peak height of a carboxyl group]) in its infrared absorption analysis being at least 0.5, (c) the Mooney viscosity being 15 to 200, and (d) the iodine value being at most 80 grams per 100 grams, and a production process thereof.

Abstract: Disclosed is a curable rubber composition comprising (a) 100 parts by weight of an ethylenically unsaturated nitrile/conjugated diene type highly saturated rubber in which the content of conjugated diene units in the polymer chain is not higher than 30% by weight, (b) 10 to 100 parts by weight of zinc salt of methacrylic acid, (c) 5 to 50 parts by weight of silicic anhydride and (d) 0.2 to 10 parts by weight of an organic peroxide. The curable rubber composition provides a cured product having an excellent strength, abrasion resistance, and compression set.

Abstract: Disclosed is a curable rubber composition comprising (a) 100 parts by weight of a rubber comprising 90 to 60% by weight of any ethylenically unsaturated nitrile/conjugated diene type highly saturated rubber and 10 to 40% by weight of an ethylene/propylene copolymer rubber, (b) 10 to 100 parts by weight of a zinc salt of methacrylic acid, and (c) 0.2 to 10 parts by weight of an organic peroxide. The curable rubber composition provides a cured product having an excellent strength, and ozone resistance.