A sulfonimide-containing comonomer derived from 4,4 '-dichlorodiphenylsulfone was synthesized and copolymerized with 4,4 '-dichlorodiphenylsulfone and 4,4 '-biphenol to prepare sulfonimide-containing poly(arylene ether sulfone) random copolymers (BPSIs). These copolymers showed slightly higher water uptake than disulfonated poly(arylene ether sulfone) copolymer (BPSH) controls, but their proton-conductivity values were very comparable to those of the BPSH series with similar ion contents. The proton conductivity increased with the temperature for both systems. For samples with 30 mol % ionic groups, BPSI showed less temperature dependence in proton conductivity and slightly higher methanol permeability in comparison with BPSH. The thermal characterization of the suffortimide copolymers showed that both the acid and salt forms were stable up to 250 degrees C under a nitrogen atmosphere. The results suggested that the presumed enhanced stability of the sulfonimide systems did not translate into higher protonic conductivity in liquid water. (c) 2006 Wiley Periodicals, Inc.