STABILIZED FLUOROPOLYMER AND METHOD FOR PRODUCING SAME

1 . A method for producing a stabilized fluoropolymer which comprises producing said stabilized fluoropolymer by subjecting a treatment target substance containing a sulfonic-acid-derived-group-containing fluoropolymer to a fluorination treatment,

wherein said sulfonic-acid-derived-group-containing fluoropolymer is a fluoropolymer containing —SO 3 M (in which M represents H, NR 1 R 2 R 3 R 4 or M 1 1/L ; R 1 , R 2 , R 3 and R 4 are the same or different and each represents H or an alkyl group containing 1 to 4 carbon atoms; and M 1 represents an L-valent metal), and

said treatment target substance has a moisture content of not higher than 500 ppm by mass.

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

wherein the sulfonic-acid-derived-group-containing fluoropolymer further contains —SO 2 X and/or —COZ (wherein X represents F, Cl, Br, I or —NR 5 R 6 and Z represents —NR 7 R 8 or —OR 9 ; R 5 , R 6 , R 7 and R 8 are the same or different and each represents H, an alkali metal element, an alkyl group or a sulfonyl-containing group and R 9 represents an alkyl group containing 1 to 4 carbon atoms).

3 . The method for producing a stabilized fluoropolymer according to claim 1 ,

wherein the sulfonic-acid-derived-group-containing fluoropolymer further contains —COOH at the polymer chain terminus or termini.

4 . The method for producing a stabilized fluoropolymer according to claim 1 ,

wherein the fluorination treatment is carried out using a gaseous fluorinating agent comprising a fluorine source,

said fluorine source is at least one species selected from the group consisting of F 2 , SF 4 , IF 5 , NF 3 , PF 5 , ClF and ClF 3 and

said fluorine source amounts to not less than 1% by volume of said gaseous fluorinating agent.

5 . The method for producing a stabilized fluoropolymer according to claim 4 ,

wherein the fluorine source is F 2 .

6 . The method for producing a stabilized fluoropolymer according to claim 1 ,

wherein the sulfonic-acid-derived-group-containing fluoropolymer is a copolymer which is at least binary comprising

an acid-derived group-containing perhalovinyl ether represented by the general formula (I):

CF 2 ═CF—O—(CF 2 CFY 1 —O) n —(CFY 2 ) m -A  (I)

(wherein Y 1 represents F, Cl, Br, I or a perfluoroalkyl group, n represents an integer of 0 to 3; n atoms/groups of Y 1 are the same or different; Y 2 represents F, Cl, Br or I; m represents an integer of 1 to 5; when m is an integer of 2 to 5, m atoms of Y 2 are the same or different; A represents

—SO 2 X or —COZ; X represents F, Cl, Br, I or —NR 5 R 6 and Z represents —NR 7 R 8 or —OR 9 ; R 5 , R 6 , R 7 and R 8 are the same or different and each represents H, an alkali metal element, an alkyl group or a sulfonyl-containing group and R 9 represents an alkyl group containing 1 to 4 carbon atoms) and

a copolymerizable monomer with said acid-derived group-containing perhalovinyl ether,

said copolymerizable monomer is an “other vinyl ether” other than said acid-derived group-containing perhalovinyl ether and an ethylenic monomer,

said copolymer comprises 5 to 40 mole percent of an acid-derived group-containing perhalovinyl ether unit derived from said acid-derived group-containing perhalovinyl ether, 60 to 95 mole percent of an ethylenic monomer unit derived from said ethylenic monomer and 0 to 5 mole percent of an “other vinyl ether unit” derived from said “other vinyl ether”.

7 . The method for producing a stabilized fluoropolymer according to claim 6 ,

wherein n is 0 (zero).

8 . The method for producing a stabilized fluoropolymer according to claim 6 ,

wherein Y 2 is F and m is 2.

9 . (canceled)

10 . (canceled)

11 . (canceled)

12 . (canceled)

13 . (canceled)

14 . A stabilized fluoropolymer,

which is obtained by the method for producing a stabilized fluoropolymer according to claim 1 .

15 . The stabilized fluoropolymer according to claim 14 ,

which has a melt index of 0.1 to 20 g/10 minutes as measured under the conditions of 270° C. and a load of 2.16 kg according to JIS K 7210.

16 . A polymer electrolyte membrane,

which contains a hydrolyzate of the stabilized fluoropolymer according to claim 14 .

17 . The polymer electrolyte membrane according to claim 16 ,

wherein the amount of fluoride ion eluted by Fenton treatment comprising immersing b grams of said polymer electrolyte membrane in a liters of an aqueous hydrogen peroxide solution having an initial iron(II) cation concentration of 2 ppm and an initial hydrogen peroxide concentration of 1% by mass at a membrane/bath ratio [b/a] of 3.2 and maintaining the whole at 80° C. for 2 hours is not greater than 11×10 −4 parts by mass per 100 parts by mass of said polymer electrolyte membrane.

18 . An active substance-immobilized material which comprises a hydrolyzate of the stabilized fluoropolymer according to claim 14 and an active substance.

19 . The active substance-immobilized material according to claim 18 ,

wherein the active substance is a catalyst.

20 . The active substance-immobilized material according to claim 19 ,

wherein the catalyst is a platinum-containing metal.

21 . A membrane/electrode assembly comprising a polymer electrolyte membrane and an electrode,

wherein said membrane/electrode assembly satisfies at least one condition selected from the group consisting of the conditions (1) and (2) given below:

(1) said polymer electrolyte membrane is the polymer electrolyte membrane according to claim 16 , and

(2) said electrode is the active substance-immobilized material according to claim 18 .

22 . A solid polymer electrolyte fuel cell which comprises the membrane/electrode assembly according to claim 21 .