Stabilized fluoropolymer and method for producing same

Abstract

The present invention provides a method for producing a stabilized fluoropolymer which comprises producing the stabilized fluoropolymer by subjecting a treatment target substance containing a sulfonic-acid-derived-group-containing fluoropolymer to a fluorination treatment, wherein the 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 the treatment target substance has a moisture content of not higher than 500 ppm by mass.

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 4carbon 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 , CIF and CIF 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 2to 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 . A stabilized fluoropolymer obtained via polymerization of an acid-derived group-containing perhalovinyl ether represented by the general formula (II):  
       CF 2 ═CF—O—(CFY 2 ) m —A  (II)  
     (wherein 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; and 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 tetrafluoroethylene, wherein said stabilized fluoropolymer shows an intensity ratio [x/y] between carboxyl group-due peak [x] and —CF 2 — due peak [y] of not higher than 0.05 in IR measurement.  
   
   
       10 . A stabilized fluoropolymer obtained via polymerization of an acid-derived group-containing perhalovinyl ether represented by the general formula (II):  
       CF 2 ═CF—O—(CFY  2 ) m —A  (II)  
     (wherein 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; and 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 tetrafluoroethylene, wherein, in a hydrolyzate of said stabilized fluoropolymer, the number [X] of main chain terminal —CF 3  groups per 1×10 5  main chain carbon atoms of said hydrolyzate is not smaller than 10 as calculated using an integrated intensity due to main chain terminal —CF 3  groups and an integrated intensity due to —CF 2 — adjacent to an ether bond in side chains branched from the main chain in said hydrolyzate, each determined by solid state  19 F nuclear magnetic resonance spectrometry of said hydrolyzate in a state swollen in an oxygen-containing hydrocarbon compound having a dielectric constant of not lower than 5.0 and further using an ion exchange equivalent weight Ew value determined by titrimetric method.  
   
   
       11 . The stabilized fluoropolymer according to  claim 10 , 
 wherein said fluoropolymer further shows an intensity ratio [x/y] between carboxyl group-due peak [x] and —CF 2 — due peak [y] of not higher than 0.05 in IR measurement.    
   
   
       12 . The stabilized fluoropolymer according to  claim 9 , 
 wherein the polymerization of the acid-derived group-containing perhalovinyl ether and tetrafluoroethylene is carried out in the manner of emulsion polymerization.    
   
   
       13 . The stabilized fluoropolymer according to  claim 9 , 
 which is obtained by the method for producing a stabilized fluoropolymer according to  claim 7 .    
   
   
       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 9 , 
 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 9 .    
   
   
       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 9 , 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.