Method for producing -SO3H group-containing fluoropolymer and -SO3H group-containing fluoropolymer

The present invention provides a production process by which unstable terminal groups can be sufficiently stabilized under mild conditions. The present invention is related to a method for producing an -O 3 H group-containing fluoropolymer comprising terminal stabilization treatment of a fluoropolymer containing an -SO 2 X group-containing monomer unit and an unstable terminal group, comprising the steps of (P) obtaining an -SO 3 H group-containing fluoropolymer in which at least 90% of the unstable terminal groups are -CFTCO 2 Z, wherein T is F, or C 1-10 -perfluoroalkyl or C 2-15 -perfluoroalkoxy each optionally containing an ether oxygen [-O-] and/or -SO 2 X, wherein X is F or Cl, and Z is H, NR 1 R 2 R 3 R 4 or an alkali metal element, and R 1 -R 4 each independently are H or C 1-4 -alkyl; and (Q) converting, by reacting with a fluorinating agent, -CFTCO 2 Z to -CF 2 T.