Process to prepare crosslinkable trifluorostyrene polymers and membranes
View Patent ↗Described herein is a process to prepare crosslinkable polymers based on trifluorostyrene, and their use as polymer electrolyte membranes.
1. A process to prepare a crosslinked membrane, comprising the steps:
a. providing a copolymer comprising repeat units of Formulae (V) and (VI)
wherein Rf and Rf′ are independently a linear or branched perfluoroalkylene group, optionally containing oxygen or chlorine; X is Br or Cl; and Q is F, Br, or Cl;
b. forming a membrane from the copolymer;
c. hydrolyzing the —SO 2 Q moiety to form a —SO 3 H moiety or salt thereof; and
d. exposing the copolymer to radiation to form a crosslinked polymer, either before or after formation into a membrane;
wherein the monomer of Formula VI can enable copolymerization, crosslinking and oxidation to a stable polymer electrolyte membrane that is conductive at low relative humidity, having through-plane conductivity, at 25% relative humidity and 80° C., of at least 13 mS/cm, and transverse direction swelling of not more than 78%.
2. The process of claim 1 wherein Rf and Rf′ are independently selected from the group consisting of (CF 2 ) r wherein r=1 to 20, (CF 2 CF 2 ) r OCF 2 CF 2 wherein r=1 to 6, and (CF 2 CF(CF 3 )O) r CF 2 CF 2 wherein r=1 to 8.
3. The process of claim 1 wherein the copolymer additionally comprises repeat units of Formula (VII)
4. The process of claim 1 wherein Formula (V) is Formula (Va) and Formula (VI) is Formula (VIa)
wherein Q is F and X is Br.
5. The process of claim 1 , further comprising converting the —S moieties of both Formulae (V) and (VI) into —SO 2 — moieties to form an oxidized copolymer by contacting said —S— moieties with an oxidizing agent, either before or after formation into a membrane.
6. The process of claim 4 , wherein the membrane has through-plane conductivity, at 25% relative humidity and 80° C., of at least 24 mS/cm, and transverse direction swelling of not more than 57%.