Perfluoroelastomer, perfluoroelastomer composition, crosslinked rubber product, and method for manufacturing perfluoroelastomer

1. A perfluoroelastomer comprising structural units (a) derived from tetrafluoroethylene, a structural unit (b) derived from a perfluoroalkyl vinyl ether represented by a formula (1) wherein the structural unit (b) consists of one type of structural unit, and structural units (c) derived from a perfluorooxaalkyl vinyl ether represented by a formula (2):

CF 2 ═CFOR f1   (1)

wherein R f1 is a C 1-10 linear or branched perfluoroalkyl group;

CF 2 ═CF(OCF 2 CF 2 ) n —(OCF 2 ) m —OR f2   (2)

wherein R f2 is a C 1-4 linear or branched perfluoroalkyl group, n is an integer of from 0 to 3, m is an integer of from 0 to 4, and (n+m) is an integer of from 1 to 7,

wherein a content of the structural units (a) is from 40 to 70 mol %, a content of the structural unit (b) is from 16 to 40 mol %, and a content of the structural units (c) is from 3 to 57 mol % based on a total number of moles of the structural units (a), (b) and (c) and the total mol % of structural units (a)+(b)+(c) is at least 98 mol % based on the total number of moles of all the structural units in the perfluoroelastomer.

2. The perfluoroelastomer according to claim 1 , wherein in the formula (2), R f2 is a C 1-3 linear or branched perfluoroalkyl group, and m=3 or 4 when n=0, m=2 to 4 when n=1, and m=0 when n=2 or 3.

3. The perfluoroelastomer according to claim 1 , wherein the perfluorooxaalkyl vinyl ether represented by the formula (2) is at least one member selected from the group consisting of

CF 2 ═CFOF 2 CF 2 OCF 2 OCF 2 OCF 2 OCF 2 OCF 3 ,

CF 2 ═CFOCF 2 CF 2 OCF 2 OCF 2 OCF 3 and

CF 2 =CFOCF 2 CF 2 OCF 2 CF 2 OCF 2 CF 3 .

4. A perfluoroelastomer composition comprising the perfluoroelastomer of claim 1 and a crosslinking agent.

5. A crosslinked rubber product obtained by crosslinking the perfluoroelastomer of claim 1 .

6. A method for producing a perfluoroelastomer, which comprises radical copolymerizing tetrafluoroethylene, a perfluoroalkyl vinyl ether represented by a formula (1) and a perfluorooxaalkyl vinyl ether represented by a formula (2) as materials in the presence of a radical polymerization initiator to form a perfluoroelastomer comprising structural units (a), (b) and (c):

CF 2 ═CFOR f1   (1)

wherein R f1 is a C 1-10 linear or branched perfluoroalkyl group,

CF 2 ═CF(OCF 2 CF 2 ) n —(OCF 2 ) m —OR f2   (2)

wherein R f2 is a C 1-4 linear or branched perfluoroalkyl group, n is an integer of from 0 to 3, m is an integer of from 0 to 4, and (n+m) is an integer of from 1 to 7,

wherein the perfluoroelastomer a content of the structural units (a) is from 40 to 70 mol %, a content of the structural unit (b) is from 16 to 40 mol % and the structural unit (b) consists of one structural unit, and a content of the structural units (c) is from 3 to 57 mol % based on a total number of moles of the structural units (a), (b) and (c) and the total mol % of structural units (a)+(b)+(c) is at least 98 mol % based on the total number of moles of all the structural units in the perfluoroelastomer.

7. The method according to claim 6 , wherein the radical copolymerization is carried out in the presence of a chain transfer agent represented by R f2 wherein R f4 is a C 1-6 linear or branched polyfluoroalkylene group.

8. The method according to claim 6 , wherein the radical copolymerization is an emulsion polymerization carried out in the presence of an aqueous medium and an emulsifier.

9. The method according to claim 7 , wherein the chain transfer agent is 1,4-diiodoperfluorobutane.

10. The perfluoroelastomer according to claim 1 , wherein a content of the structural unit (b) is from 18 to 40 mol %.

11. The perfluoroelastomer according to claim 1 , wherein a content of the structural unit (b) is from 19 to 40 mol %.

12. The perfluoroelastomer of claim 1 , wherein the terminals of the perfluoroelastomer comprise iodine.

13. The perfluoroelastomer of claim 1 , wherein the perfluoroelastomer has a main chain consisting of the structural units (a), the structural unit (b), and the structural units (c), and chain transfer reagent residue terminals comprising iodine.

14. The perfluoroelastomer of claim 13 , wherein the perfluoroelastomer comprises iodine in an amount of from 0.01 to 1.5 mass % based on the mass of the perfluoroelastomer.

15. The method according to claim 6 , wherein the perfluorooxaalkyl vinyl ether represented by the formula (2) is at least one member selected from the group consisting of

CF 2 ═CFOCF 2 CF 2 OCF 2 OCF 2 OCF 2 OCF 3 ,

CF 2 ═CFOCF 2 CF 2 OCF 2 OCF 2 OCF 3 and

CF 2 ═CFOCF 2 CF 2 OCF 2 CF 2 OCF 2 CF 3 .

16. The method according to claim 6 , wherein the radical copolymerization is carried out in the presence of diiodoperfluorobutane.

17. The method according to claim 6 , wherein a content of the structural unit (b) in the perfluoroelastomer is from 18 to 40 mol %.

18. The method according to claim 6 , wherein a content of the structural unit (b) in the perfluoroelastomer is from 19 to 40 mol %.

19. The method according to claim 6 , wherein the terminals of the perfluoroelastomer comprise iodine.

20. The method according to claim 6 , wherein the perfluoroelastomer has a main chain consisting of the structural units (a), the structural unit (b), the structural units (c), and chain transfer reagent residue terminals comprising iodine.

21. The method according to claim 20 , wherein the perfluoroelastomer comprises iodine in an amount of from 0.01 to 1.5 mass % based on the mass of the perfluoroelastomer.

22. The perfluoroelastomer of claim 1 , wherein the structural unit (b) is perfluoro(methyl vinyl ether).

23. The method according to claim 6 , wherein the structural unit (b) is perfluoro(methyl vinyl ether).