An object of the invention is to provide copolymers which have a double bond in a side chain and are substantially free of unsaturated bonds in the main chain, copolymers which have a cyclic structure and are substantially free of unsaturated bonds in the main chain, and processes for economically synthesizing these copolymers.
A copolymer of the invention is obtained by copolymerizing at least ethylene and a conjugated diene. In the copolymer, structural units derived from the conjugated diene represent 1 to 90 mol%. Structural units resulting from 1,2-addition of the conjugated diene and having a side-chain double bond represent 0 to 90 mol%, structural units resulting from 1, 4-addition of the conjugated diene represent 0 to 3 mol%, structural units resulting from 1, 3-addition of the conjugated diene represent 0 to 3 mol%, and the total of structural units resulting from 1,2-addition of the conjugated diene and having a 1,2-cyclopropane skeleton and structural units resulting from 1,2-addition of the conjugated diene and having a 1,2-cyclopentane skeleton represent 4 to 100 mol%.