COPOLYMER, RUBBER COMPOSITIONS, CROSSLIKNED RUBBER, CROSSLINKED FOAM, AND USES OF SAME

The present invention provides a rubber composition having adequate foamability, uses thereof, a copolymer contained in the rubber composition, a rubber composition capable of providing a cross-linked foam, which has a low specific gravity and an excellent shape-retaining property even when the usage of a nonconjugated polyene is reduced, and a cross-linked rubber and a cross-linked foam, which are produced from the rubber composition. A copolymer (A) according to the present invention is a copolymer including structural units derived from ethylene [A], an ±-olefin [B], a nonconjugated polyene [C-1], in which one carbon-carbon double bond (C=C) polymerizable with a metallocene catalyst is present in one molecule, and a nonconjugated polyene [C-2], in which two bonds of C=C polymerizable with the metallocene catalyst are present in one molecule, and being synthesized with the metallocene catalyst, wherein (1) the units derived from the component [B] constitute 10 to 50 percent by mole, (2) the total of the units derived from the component [C-1] and the units derived from the component [C-2] is 1.0 to 6.0 percent by mole, (3) the molar ratio of the units derived from the component [C-1] to the units derived from the component [C-2] is 75/25 to 99.5/0.5, (4) [ML (1 + 4) 100°C] is 10 to 200, and (5) 50 > activation energy of fluidization (kJ/mol) > 35 is satisfied.