| abstract |
To provide a sulfonic acid group-containing polymer which is capable of forming a low hydrogen permeable membrane, which shows a high ion exchange capacity, and which shows a proper softening temperature. The sulfonic acid group-containing polymer has units u1 represented by the following formula u1, units u2 represented by the following formula u2, and units u3 based on tetrafluoroethylene,n nin the formula u1, R F1 and R F2 are each independently a C 1-3 perfluoroalkylene group, and Z + is a hydrogen ion, a metal ion, or an ammonium ion, n n -[CF 2 -CF(CF 2 O-R f1 )]- Formula u2 n nin the formula u2, R f1 is a perfluoroalkyl group which may contain a SO 3 - Z + group. |