NITRILE-GROUP-CONTAINING COPOLYMER RUBBER, CROSSLINKABLE RUBBER COMPOSITION, AND CROSSLINKED RUBBER

A nitrile group-containing copolymer rubber containing ±,²-ethylenically unsaturated nitrile monomer units in a ratio of 10 to 60 wt% and having a Z-average radius of gyration of 100 nm or more is provided. Preferably, the nitrile group-containing copolymer rubber of the present invention has an iodine value of 120 or less. Further, preferably, the nitrile group-containing copolymer rubber of the present invention has a plasticity number of 14 to 90. According to the present invention, it is possible to provide a nitrile group-containing copolymer rubber able to give a cross-linked rubber excellent in tensile stress, compression set resistance, and low heat buildup property.