Fluorinated sulfo-pendants poly(arylenethioethersulfone) copolymer, which contained 50 mol% sulfonate content per repeat unit (6F-SPTES-50). were synthesized by a nucleophilic polycondensation from 4,4-(hexafluoroisopropylidene)-diphenylthiol, 3,3'-disulfonate-4,4'-difluorodiphenylsulfone and 4,4'-difluorodiphenylsulfone. The 6F-SPTES-50 copolymer possessed high molecular weight, exhibited good film formability and thermal stability, and maintained adequate mechanical strength after immersion in water for 24 h. The proton conductivities of the 6F-SPTES-50 copolymer membrane increased with temperatures, reaching values above 120 mS/cm at 85 degrees C and 85% relative humidity. Preliminary MEA test shows acceptable performance, which indicated that these materials are promising proton exchange membranes (PEMs) for fuel cells operated at medium temperatures. (C) 2009 Elsevier Ltd. All rights reserved.