Process to prepare stable trifluorostyrene containing compounds grafted to base polymers using a solvent/water mixture
A fluorinated ion exchange polymer is prepared by grafting at least one grafting monomer derived from trifluorostyrene on to at least one base polymer in a organic solvent/water mixture. These ion exchange polymers are useful in preparing catalyst coated membranes and membrane electrode assemblies used in fuel cells.
1. A grafting process for making a fluorinated ion exchange polymer membrane comprising:
(a) forming an monomer composition comprising at least one grafting monomer, in a mixture of water and one or more organic solvent;
wherein the grafting monomer comprises one or more of 1a or 1b:
wherein
Z is chosen from O, S, SO 2 , or POR wherein R comprises a linear or branched perfluoroalkyl group of 1 to 14 carbon atoms optionally containing oxygen or chlorine, an alkyl group of 1 to 8 carbon atoms, an aryl group of 6 to 12 carbon atoms or a substituted aryl group of 6 to 12 carbon atoms;
R F is chosen from a linear or branched perfluoroalkylene group of 1 to 20 carbon atoms, optionally containing oxygen, sulfur or chlorine;
Q is chosen from F, —OM, —NH 2 , —N(M)SO 2 R 2 F , and —C(M)(SO 2 R 2 F ) 2 , wherein M is chosen from H, an alkali cation, or ammonium;
R 2 F groups are chosen from alkyl of 1 to 14 carbon atoms which may optionally include ether oxygens or aryl of 6 to 12 carbon atoms where the alkyl or aryl groups may be perfluorinated or partially fluorinated;
and k is 0 or 1, n is 1 or 2 for 1a, and n is 1, 2, or 3 for 1b;
(b) irradiating at least one base polymer with ionizing radiation, and
(c) contacting at least one base polymer with the monomer composition from step (a), at a temperature of about 0° C. to about 120° C. for about 0.1 hours to about 500 hours.
2. The process of claim 1 wherein the organic solvent is miscible or at least partially soluble with water, and wherein the monomer is partially soluble in the organic solvent.
3. The process of claim 2 wherein the organic solvent is acetonitrile, dimethylformamide, dimethylacetamide, dimethylsulfoxide, or glycol ethers of the formula R(OCH 2 CH 2 ) p OR, wherein R is an alkyl group and p is 1 to 12.
4. The process of claim 1 wherein the weight % of water to the sum of water and organic solvent in the mixture is in the range of 10% to 99.99%.
5. The process of claim 4 wherein the weight % of water to the sum of water and organic solvent in the mixture is in the range of 40% to 90%.
6. The process of claim 1 wherein the organic solvent and water mixture optionally includes an enhancing additive.
7. The process of claim 6 wherein the enhancing additive is α,α,α-trifluorotoluene, dichlorobenzotrifluoride, chlorobenzotrifluoride, chlorobenzene, dichlorobenzene, trichlorobenzene, fluorobenzene, difluorobenzene, trifluorobenzene, perfluorobenzene, toluene, p-xylene, m-xylene, o-xylene, or C5-C10 aliphatic hydrocarbon, fluorohydrocarbon, fluorocarbon, or fluoroether.
8. The process of claim 4 wherein the enhancing additive is present at an amount of 0.5 to 300 weight % of the monomer.
9. The process of claim 1 wherein the at least one base polymer is in film form.
10. The process of claim 1 wherein steps (b) and (c) are performed simultaneously.
11. The process of claim 1 wherein steps (b) and (c) are performed sequentially.
12. The process of claim 1 wherein Q comprises F.
13. The process of claim 1 wherein R F is chosen from (CF 2 ) q wherein q=1 to 16, (CH 2 ) q OCF 2 CF 2 wherein q=1 to 12, and (CF 2 CF(CF 3 )O) q CF 2 CF 2 where q is 1 to 6, and R 2 F is chosen from methyl, ethyl, propyl, butyl, and phenyl, each of which may be partially fluorinated or perfluorinated.
14. The process of claim 13 wherein R F is chosen from
(CF 2 ) q wherein q=1 to 4, (CF 2 ) q OCF 2 CF 2 wherein q=1 to 4, and (CF 2 CF(CF 3 )O) q CF 2 CF 2 where q is 1 to 2, and R 2 F is chosen from perfluoromethyl, perfluoroethyl, and perfluorophenyl.
15. The process of claim 1 wherein the base polymer comprises a homopolymer or copolymer prepared from non-fluorinated, fluorinated, or perfluorinated monomers.
16. The process of claim 15 wherein the base polymer is chosen from poly(ethylene-tetrafluoroethylene), poly(ethylene-chlorotrifluoroethylene), poly(tetrafluoroethylene-hexafluoropropylene), poly(tetrafluoroethylene-perfluoroalkyl vinyl ether), poly(tetrafluoroethylene-perfluoromethyl vinyl ether), poly(tetrafluoroethylene-perfluoropropyl vinyl ether), polytetrafluoroethylene, modified polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene), polyethylene, and polypropylene.
17. The process of claim 15 wherein the base polymer comprises a partially or completely fluorinated polymer.
18. The process of claim 17 wherein the base polymer is chosen from poly(ethylene-tetrafluoroethylene), poly(ethylene-tetrafluoroethylene-termonomer), poly(tetrafluoroethylene-hexafluoropropylene), poly(tetrafluoroethylene-perfluorovinylether), polytetrafluoroethylene, poly(ethylene-chlorotrifluoroethylene); poly(vinylidene fluoride), and poly(vinylidenefluoride-hexafluoropropylene).
19. A polymer membrane made by the process of claim 1 .