POLYMER, METHOD FOR PRODUCING POLYMER, AND METHOD FOR PRODUCING MEMBRANE

To provide a polymer wherein a linking group that connects the main chain of the polymer and a cyclic perfluoroaliphatic disulfonimide skeleton, is a fluoroalkylene group which may have an ether oxygen atom. A polymer which has either one or both of units represented by formula u1-1 and units represented by formula u1-2: R, R: a Cperfluoroalkylene group; R: a Cperfluoroalkylene group; m: 0 or 1; and X: a hydrogen atom, an alkali metal atom, a fluorine atom, an alkyl group, ammonium or the like.