Covalent-ionically crosslinked sulfonated poly(arylene ether sulfone)s bearing quinoxaline crosslinkages as proton exchange membranes

Crosslinkable sulfonated poly(arylene ether sulfone)s (SPAESs) were synthesized by copolymerization of 4,4′-biphenol with 2,6-difluorobenzil, 4,4′-difluorodiphenyl sulfone, and 3,3′-disulfonated-4,4′-difluorodiphenyl sulfone disodium salt. The corresponding covalent-ionically crosslinked SPAESs were prepared via the cyclocondensation reaction of benzil moieties in polymer chain with 3,3′-diaminobenzidine. The crosslinking significantly improved the membrane performance, that is, the crosslinked membranes had the lower membrane dimensional swelling, lower methanol permeability, and higher oxidative stability than the corresponding precursor membranes, with keeping the reasonably high proton conductivity. The crosslinked membrane (CS5) with measured ion exchange capacity of 1.47 meq g⁻¹ showed a reasonably high proton conductivity of 112 mS cm⁻¹ with water uptake of 42 wt % at 80°C, and exhibited a low methanol permeability of 2.1 × 10⁻⁷ cm² s⁻¹ for 32 wt % methanol solution at 25°C. The crosslinked SPAES membranes have potential for PEFC and DMFCs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012