Synthesis and characterization of poly(aryl ether ketone) copolymers containing (hexafluoroisopropylidene)-diphenol moiety as proton exchange membrane materials

Sulfonated poly(aryl ether ketone)s (SPAEK) copolymers were synthesized by aromatic nucleophilic polycondensation from 4,4′-(hexafluoroisopropylidene)-diphenol, 1,3-bis(4-fluorobenzoyl)benzene and di-sulfonated difluorobenzophenone. The copolymers exhibited good thermal and oxidative stability. The SPAEK membranes with sulfonic acid content (SC) ranging from 0.6 to 1.16 maintained adequate mechanical strength after immersion in water at 80 °C for 24 h. The proton conductivities of the SPAEK films increased with SC and temperature, reaching values above 3.3×10−2 S/cm at 80 °C for SC≥0.76. Tensile strength measurement indicated that SPAEK membranes with SC 0.76, 0.98 and 1.16 are tough and strong at ambient conditions. Consequently, these materials are promising as proton exchange membranes (PEM) for fuel cells operated at medium temperatures.