This paper reports the performance of direct methanol fuel cells (DMFCs) using novel disulfonated poly(arylene ether benzonitrile) copolymers derived from hexafluoro-isopropylidene diphenol (6F), 2,6-dichlorobenzonitrile, and 3,3'-disulfonated 4,4'-dichloro diphenyl sulfone (SDCDPS). The membrane electrode assembly (MEA) which employed the sulfonated copolymer with 35 mol % of disulfonated comonomer as the proton exchange membrane had approximately 2-fold lower methanol crossover and slightly higher (about 10%) cell resistance than the MEA using the perfluorosulfonic acid Nafion membrane, resulting in an approximately 50% improvement in selectivity, regardless of membrane thickness. Accordingly, this MEA outperformed the Nafion MEA control in a DMFC single-cell test. For example, 200 mA/cm(2) was obtained (compared with 150 mA/cm(2) for the Nafion MEA) at 0.5 V at a temperature of 80 degreesC and ambient air pressure. Similar experiments performed with nonfluorine-containing biphenol-based sulfonated poly(arylene ether sulfone) copolymers (BPSH) indicated that the compatibility of the polymer electrolyte with the electrodes likely has a critical role in initial DMFC performance. (C) 2004 The Electrochemical Society.