The perfluoroalkylsulfonate monomer, N,N-diisopropylethylammonium 2,2-bis(p-hydroxyphenyl)pentafluoropropanesulfonate (H PPS), was synthesized in three steps. Using triethyl phosphite, hexafluoroacetone was first converted to ethyl pentafluoroisopropenyl ether. Reaction of the ether with sulfur trioxide produced 2-ketopentafluoropropanesulfonic acid. The acid was condensed with 2 equiv of phenol, and the product was isolated as the N,N-diisopropylethylammonium salt. The structure of the final product was confirmed by X-ray crystallography. Poly(arylene ether sulfone)s (PAES) were prepared by homopolymerization of HPPS with bis(4-fluorophenyl) sulfone (FPS) and copolymerization of varying molar ratios of HPPS/biphenol (BP) with FPS. Copolymer number-average molecular weights were in the range 27 000-34 000 g/mol (GPC). Copolymer compositions ranged from 20 to 61 mol % HPPS (HPPS/BP molar ratio 0.25-1.56) as determined by F-19 NMR spectroscopy. Ion exchange capacity of the copolymers (by titration) ranged from 0.36 to 1.25 mequiv/g. Equilibrium water uptake of the copolymers at 80 degrees C and 90% relative humidity increased from 7.2 to 14.3 mol H2O/mol H+, and proton conductivity increased from 1.6 to 23 mS/cm, as the HPPS/PB ratio increased from 0.25 to 1.56.