Novel styrene/N-phenylmaleimidealternating copolymers with pendant sulfonimide acid groups for polymer electrolyte fuel cell applications

Alternating terpolymers, si-PPMSs, are synthesized from styrene, N-phenylmaleimide (PMI), and PMI with a sulfonimide acid group for polymer electrolyte fuel cell applications. The ion-exchange capacity (IEC) of si-PPMSs can be easily controlled by changing the feed ratios of the comonomers, and the resulting si-PPMSs (IEC = 0.89–1.19 meq g−1) exhibit good thermal and chemical stabilities. In order to fabricate mechanically strong membranes with a high IEC, polymer gels consisting of substituted PMI, styrene, and divinylbenzene are prepared using porous polytetrafluoroethylene membranes. A gel-filling membrane with an IEC of 1.70 meq g−1, si-PPMS gel, exhibits a proton conductivity of ca. 1.0 × 10−2 S cm−1 at 50 °C under 95% relative humidity; its proton conductivity is comparable to that of Nafion 112. A H2/O2fuel cell comprising a si-PPMS gel membrane could be operated at 1 A cm−2 and an open circuit voltage of 0.93 V.