Patent ID: 8034880

Claim:
A method for producing an —SO 3 H group-containing fluoropolymer comprising terminal stabilization treatment of a fluoropolymer to be treated containing an —SO 2 X group-containing monomer unit and an unstable terminal group, wherein the terminal stabilization treatment comprises the steps P and Q defined below: P: Step of obtaining an —SO 3 H group-containing fluoropolymer in which at least 90% of the unstable terminal groups are —CFTCO 2 Z groups; Q: Step of converting the —CFTCO 2 Z groups to —CF 2 T groups by reacting with a fluorinating agent, and wherein X represents F or Cl, T represents F, a perfluoroalkyl group containing 1 to 10 carbon atoms or a perfluoroalkoxy group containing 2 to 15 carbon atoms and Z represents H or NR 1 R 2 R 3 R 4 or an alkali metal element, R 1 , R 2 , R 3 and R 4 , each of which is the same or different, represents H or an alkyl group containing 1 to 4 carbon atoms; said perfluoroalkyl group and perfluoroalkoxy group each optionally contains an ether oxygen [—O—] and/or an —SO 2 X group.