Method for producing stabilized fluoropolymer

1. A method for producing a stabilized fluoropolymer comprising subjecting a fluoropolymer to be treated containing no —SO 2 X (X representing F or Cl) group-containing monomer units to the following step A, step B and step C in that order:

A: Step of reacting with a halogenating agent;

B: Step of reacting with a degradation treatment agent;

C: Step of reacting with a fluorinating agent.

2. The method for producing a stabilized fluoropolymer according to claim 1 , wherein:

the step A is a step A1 of converting the unstable terminal groups to readily degradable terminal groups by reacting with a halogenating agent;

the step B is a step B1 of converting the above-mentioned readily degradable terminal groups to —CFTCOOZ groups (in which T represents F, a perfluoroalkyl group or a perfluoroalkoxy group and Z represents H, NR 1 R 2 R 3 R 4 or an alkali metal element; R 1 , R 2 , R 3 and R 4 may be the same or different and each represents H or an alkyl group containing 1 to 4 carbon atoms; the above-mentioned perfluoroalkyl or perfluoroalkoxy group may contain at least one ether oxygen [—O—]) by reacting with a degradation treatment agent; and

the step C is a step C1 of converting the above-mentioned —CFTCOOZ groups to —CF 2 T groups (T and Z being as defined above) by reaction with a fluorinating agent.

3. The method for producing a stabilized fluoropolymer according to claim 2 , wherein the readily degradable terminal group species comprises at least one species selected from the groups consisting of —CFTCOX 1 (T being as defined above and X 1 representing F or Cl) and —CFTCOORx (T being as defined above and Rx representing a haloalkyl group).

4. The method for producing a stabilized fluoropolymer according to claim 1 , wherein the halogenating agent comprises at least one species selected from the group consisting of F 2 , NF 3 , SF 4 , PF 5 , IF 5 , IF 7 , Br 2 , BrF 3 , BrF 5 , AgF 2 , CoF 3 , K 3 NiF 7 , Cl 2 , SCl 2 , SCl 4 , PCl 3 , POCl 3 , PCl 5 , ClF and ClF 3 .

5. The method for producing a stabilized fluoropolymer according to claim 1 , wherein the reaction with the halogenating agent is carried out at 0 to 180° C.

6. The method for producing a stabilized fluoropolymer according to claim 1 , wherein the degradation treatment agent is a liquid degradation treatment agent or gaseous degradation treatment agent comprising water, a fluoroalcohol or a mixture containing these.

7. A method for producing a stabilized fluoropolymer comprising subjecting a fluoropolymer to be treated containing no —SO 2 X (X representing F or Cl) group-containing monomer units to stabilization treatment,

said stabilization treatment comprises the following steps P and Q:

P: Step of obtaining a fluoropolymer in which at least 90% of the unstable terminal groups are —CFTCOOZ groups (in which T represents F, a perfluoroalkyl group or a perfluoroalkoxy group; the perfluoroalkyl group or perfluoroalkoxy group may contain at least one ether oxygen (—O—); Z represents H, NR 1 R 2 R 3 R 4 or an alkali metal element; R 1 , R 2 , R 3 and R 4 may be the same or different and each represents H or an alkyl group containing 1 to 4 carbon atoms);

Q: Step of converting the above-mentioned —CFTCOOZ to —CF 2 T (T and Z being as defined above) by reaction with a fluorinating agent.

8. The method for producing a stabilized fluoropolymer according to claim 1 , wherein the fluorinating agent comprises at least one fluorine source selected from the group consisting of F 2 , NF 3 , SF 4 , PF 5 , IF 5 , IF 7 , BrF 3 , BrF 5 , ClF, ClF 3 , AgF 2 , CoF 3 and K 3 NiF 7 .