Fluorinated elastic copolymer and production process

1. A process for producing a fluorinated elastic copolymer, which comprises copolymerizing tetrafluoroethylene and propylene and optionally a perfluoro(alkyl vinyl ether) in the presence of a radical polymerization initiator and an iodine compound represented by the formula RI 2 wherein R is an alkylene group or perfluoroalkylene group having at least 3 carbon atoms at a polymerization temperature of from 0° C. to 50° C.,

wherein the radical polymerization initiator comprises a redox polymerization initiator.

2. The process for producing a fluorinated elastic copolymer according to claim 1 , wherein the copolymerizing comprises carrying out emulsion polymerization in an aqueous medium in the presence of an emulsifier at a pH of the aqueous medium of from 7 to 14.

3. The process for producing a fluorinated elastic copolymer according to claim 1 , wherein the redox polymerization initiator comprises ammonium persulfate and hydroxymethanesulfinate.

4. The process for producing a fluorinated elastic copolymer according to claim 1 , wherein the iodine compound represented by the formula RI 2 is at least one member selected from the group consisting of 1,3-diiodopropane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane and 1,8-diiodoperfluorooctane.

5. The process for producing a fluorinated elastic copolymer according to claim 2 , wherein the emulsifier is a fluorinated ether carboxylic acid compound represented by the formula (1): R f1 OR f2 COOA, wherein R f1 is a C 1-8 perfluoroalkyl group, R f2 is a linear fluorinated alkylene group, the fluorinated alkylene group may have an etheric oxygen atom, and the fluorinated alkylene group may have a side chain of a C 1-3 perfluoroalkyl group, and A is a hydrogen atom, an alkali metal or NH 4 .

6. The process for producing a fluorinated elastic copolymer according to claim 2 , wherein the emulsifier is a fluorinated ether carboxylic acid compound represented by the formula (2): F(CF 2 ) p O(CF(X)CF 2 O) q CF(X)COOA, wherein X is a fluorine atom or a C 1-3 perfluoroalkyl group, A is a hydrogen atom, an alkali metal or NH 4 , p is an integer of from 1 to 10, and q is an integer of from 0 to 3.

7. The process for producing a fluorinated elastic copolymer according to claim 1 , wherein the redox polymerization initiator is included in an amount of from 0.001 to 1 mass % of a total mass of monomers.

8. The process for producing a fluorinated elastic copolymer according to claim 1 , wherein the redox polymerization initiator is present with disodium ethylenediaminetetraacetate.

9. The process for producing a fluorinated elastic copolymer according to claim 1 , wherein tetrafluoroethylene, propylene and a perfluoro(alkyl vinyl ether) are copolymerized.

10. The process for producing a fluorinated elastic copolymer according to claim 1 , wherein tetrafluoroethylene, propylene and a perfluoro(alkyl vinyl ether) are copolymerized such that a molar ratio of repeating units based on tetrafluoroethylene/repeating units based on propylene/repeating units based on perfluoro(alkyl vinyl ether) in the fluorinated elastic copolymer is 30 to 60/10 to 40/10 to 40.

11. The process for producing a fluorinated elastic copolymer According to claim 1 . wherein the polymderization temperature is 24° C. or lower.

12. The process for producing a fluorinated elastic copolymer according to claim 1 , wherein the emulsifier comprises one selected from the group consisting of F(CF 2 ) 2 OCF 2 CF 2 OCF 2 COONH 4 , F(CF 2 ) 2 O(CF 2 CF 2 O) 2 CF 2 COONH 4 , F(CF 2 ) 3 O(CF(CF 3 )CF 2 O) 2 CF(CF 3 )COONH 4 , F(CF 2 ) 3 OCF 2 CF 2 OCF 2 COONH 4 , F(CF 2 ) 3 O(CF 2 CF 2 O) 2 CF 2 COONH 4 , F(CF 2 ) 4 OCF 2 CF 2 OCF 2 COONH 4 , F(CF 2 ) 4 O(CF 2 CF 2 O)) 2 CF 2 COONH 4 and F(CF 2 ) 2 OCF(CF 3 )CF 2 OCF(CF 3 )COONH 4 .

13. The process for producing a fluorinated elastic copolymer according to claim 2 , wherein the emulsifier is included in an amount of from 0.1 to 3 parts by mass per 100 parts by mass of the aqueous medium.

14. The process for producing a fluorinated elastic copolymer According to claim 2 , wherein the pH of the aqueous medium is in a range from 8 to 10.5.

15. The process for producing a fluorinated elastic copolymer according to claim 2 , wherein the pH of the aqueous medium is in a range of from 8 to 10.5, and the pH is within the range at least 95° A of an entire polymerization period.

16. The process for producing a fluorinated elastic copolymer according to claim 2 , wherein the redox polymerization initiator comprises ammonium persulfate and hydroxymethanesulfinate, ammonium persulfate is included in an amount of from 0.05 to 0.5 mass % per 100 mass % of the aqueous medium, and hydroxymethanesulfinate is included in an amount of from 0.05 to 0.5 mass % per 100 mass % of the aqueous medium.