A series of novel sulfonated poly(arylene-co-naphthalimide)s (SPPIs) were synthesized by Ni(0) catalytic coupling of sodium-(2,5-dichlorobenzoyl)benzenesulfonate and a naphthalimide dichloride comprising benzophenone groups at the meta-position of the imido groups. These materials were to be used as proton exchange membranes. Viscosity measurements revealed that the as-synthesized SPPI copolymers possessed high-molecular weights. Flexible and tough membranes of considerable mechanical strength were obtained by solution casting after which the electrolyte properties of the polymers were intensively investigated. In boiling water, a low water swelling ratio of less than 10% was found, as characterized by dimensional stability testing; a result superior to that for Nafion 117 (i.e., 21.5 %). Hydrolytic testing indicated that the SPPIs displayed an excellent hydrolytic stability, and in addition, their corresponding membranes demonstrated higher proton conductivities than those of Nafion 117, especially at elevated temperatures. The SPPI-80 membrane presented the highest conductivity of 0.302 S cm(-1) for an TEC of 2.35 mequiv g(-1) at 100 degrees C, which was much higher than the corresponding value of Nafion 117 (0.178 S cm(-1), at 100 degrees C). A combination of a low methanol crossover with excellent thermo-oxidative properties indicated that the SPPI membranes were good candidate materials for proton exchange membranes in fuel cell applications. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 3187-3196, 2010