Novel styrene/N-phenylmaleimide alternating 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 x 10(-2) S cm(-1) at 50 degrees C under 95% relative humidity; its proton conductivity is comparable to that of Nafion 112. A H-2/O-2 fuel cell comprising a si-PPMS gel membrane could be operated at 1 A cm(-2) and an open circuit voltage of 0.93 V.