High vinyl ether modified sinterable polytetrafluoroethylene
View Patent ↗Modified polytetrafluoroethylene powder of a sinterable copolymer of tetrafluoroethylene containing about 0.5 to about 10 weight % of fluorinated vinyl ether, the copolymer having a melt creep viscosity of greater than about 1×10 6 Pa·S. In preferred embodiments, the sinterable copolymer has a melt creep viscosity of greater than about 1×10 7 Pa·S and fluorinated vinyl ether content of from about 1 to about 7 weight %. The polymer has a combination of a high level of fluorinated vinyl ether and a melt creep viscosity which is high enough to enable the fabrication of articles by sintering.
1. Modified polytetrafluoroethylene powder comprising a sinterable copolymer of tetrafluoroethylene containing about 0.5 to about 10 weight % of fluorinated vinyl ether, said copolymer having a melt creep viscosity of greater than about 1×10 6 Pa·S.
2. The modified polytetrafluoroethylene powder of claim 1 wherein said sinterable copolymer contains from about 1 to about 7 weight % of said fluorinated vinyl ether.
3. The modified polytetrafluoroethylene powder of claim 1 wherein said sinterable copolymer contains from about 1.5 to about 7 weight % of said fluorinated vinyl ether.
4. The modified polytetrafluoroethylene powder of claim 1 wherein said sinterable copolymer has a melt creep viscosity of greater than about 1×10 7 Pa·S.
5. The modified polytetrafluoroethylene powder of claim 1 wherein said fluorinated vinyl ether is perfluoro(alkyl vinyl ether) and the alkyl group contains 1 to 5 carbon atoms.
6. The modified polytetrafluoroethylene powder of claim 5 wherein said perfluoro(alkyl vinyl ether) is perfluoro(propyl vinyl ether).
7. The modified polytetrafluoroethylene powder of claim 5 wherein said perfluoro(alkyl vinyl ether) is perfluoro(ethyl vinyl ether).
8. The modified polytetrafluoroethylene powder of claim 5 wherein said perfluoro(alkyl vinyl ether) is perfluoro(methyl vinyl ether).
9. The modified polytetrafluoroethylene powder of claim 1 having a stress crack resistance as measured by MIT flex life of greater than 50,000 cycles.
10. A process for polymerizing tetrafluoroethylene and fluorinated vinyl ether in a suspension polymerization process by feeding pressurized tetrafluoroethylene into a polymerization vessel containing an agitated liquid medium containing a dissolved free radical initiator, said polymerization vessel containing an initial amount of fluorinated vinyl ether, conducting the polymerization in the absence of any significant amount of telogenic agent, and after the initiation of the polymerization, adding fluorinated vinyl ether on a predetermined basis in an amount to produce a sinterable copolymer of tetrafluoroethylene with from about 0.5 to about 10 weight % of said fluorinated vinyl ether, said copolymer having a melt creep viscosity of greater than about 1×10 6 Pa·S.
11. The process of claim 10 wherein said liquid medium is water.
12. The process of claim 10 wherein a sufficient amount of fluorinated vinyl ether is added to produce sinterable copolymer containing from about 1 to about 7 weight % of said fluorinated vinyl ether.
13. The process of claim 10 wherein said sinterable copolymer has a melt creep viscosity of greater than about 1×10 7 Pa·S.
14. The process of claim 10 wherein said fluorinated vinyl ether is perfluoro(alkyl vinyl ether) and the alkyl group contains 1 to 5 carbon atoms.
15. The process of claim 14 wherein said perfluoro(alkyl vinyl ether) is perfluoro(propyl vinyl ether).
16. The process of claim 14 wherein said perfluoro(alkyl vinyl ether) is perfluoro(ethyl vinyl ether).
17. The process of claim 14 wherein said perfluoro(alkyl vinyl ether) is perfluoro(methyl vinyl ether).
18. The process of claim 10 wherein said sinterable copolymer has a stress crack resistance as measured by MIT flex life of greater than 50,000 cycles.
19. The process of claim 10 wherein the polymerization is conducted in the presence of non-telogenic fluorinated surfactant.
20. The process of claim 19 wherein the fluorinated surfactant is perfluoro(polyether) carboxylic acid or perfluoro(polyether) dicarboxylic acid.