High molecular weight sulfonated poly(arylenethioethersulfone) homopolymer containing hexafluoroisopropylidene moiety (6F-SPTES-100) was synthesized from the monomers 3,3'-disulfionated-4,4'difluorodiphenylsulfone and 4,4'-(hexafluoroisopropylidene)diphenylthiol, using 4-fluorobenzophenone as the end-capping agent in polar aprotic solvents at temperatures up to 180 degrees C to provide the desired polymeric composition for utilization as proton exchange membrane (PEM) in fuel cells applications. Tough, ductile freestanding membranes were fabricated from N,N-dimethylacetamide (DMAc) by solvent-casting. The end-capped 6F-SPTES-100 polymer was fully characterized and the membrane was found to have proton conductivity as high as 180 mS/cmwhich was measured at 85 degrees C and 65% relative humidity. The proton conductivity of 6F-SPTES-100 was approximately two and half times higher than that of Nafion-117 under comparable conditions. The swelling and solubility characteristics of the 6F-SPTES-100 polymer in water are directly related to the high degree of sulfonation of the polymer backbone. (C) 2009 Elsevier Ltd. All rights reserved.