Abstract: A nitrile group-containing highly saturated copolymer rubber comprising (a) 0 to 20% by weight of 1,3-butadiene units, (b) 0 to 50% by weight of saturated 1,3-butadiene units, (c) 40 to 50% by weight of &agr;,&bgr;-ethylenically unsaturated nitrile monomer units, and (d) 10 to 35% by weight and at least 8% by mol of other monomer units, wherein the sum of 1,3-butadiene units (a) and saturated 1,3-butadiene units (b) is in the range of 20 to 50% by weight. A rubber composition comprising this copolymer rubber and a crosslinking agent gives a crosslinked product exhibiting good oil resistance, namely, good resistance to rancid gasoline and not hardening even when it is placed in contact with oil containing condensed aromatics.

Abstract: This invention provides a vulcanizable rubber composition for use as hot-water seals comprising 100 parts by weight of a rubber mixture composed of 90 to 50% by weight of a nitrile-containing highly saturated copolymer rubber obtained by hydrogenating the conjugated diene portions of an unsaturated nitrile-conjugated diene copolymer rubber or unsaturated nitrile-conjugated diene-ethylenically unsaturated monomer terpolymer rubber, and 10 to 50% by weight of an ethylene-.alpha.-olefin copolymer rubber; 0.1 to 30 parts by weight of an organic peroxide vulcanizing agent; and optionally 10 to 100 parts by weight of carbon black. Seals formed by vulcanizing this composition show a very low percent change in volume and elongation, and are not liable to the release of carbon black or the production of surface cracks, upon exposure to hot water containing bleaching powder.