Preparation and Properties of Crosslinked Multiblock Sulfonated Poly(arylene ether sulfone) Membranes for Fuel Cell Applications

Novel multiblock poly(arylene ether sulfone)s were prepared by a two-pot method from a phenoxide-end-capped fully disulfonated poly(arylene ether sulfone) oligomer and a fluoride-end-capped nonsulfonated poly(arylene ether sulfone) oligomer with block length of 10 as the hydrophilic and hydrophobic moieties, respectively, and were subsequently used as starting materials to be treated with phosphorous pentoxide (P2O5) to get crosslinked membranes. The crosslinking reaction occurred between the sulfonic acid groups and activated ortho-hydrogen atoms to the ether linkage of the hydrophobic units in the presence of P2O5 during solution casting. The crosslinking ratio was simply controlled by the amount of P2O5, and the fundamental properties of the resulting crosslinked multiblock membranes were investigated in detail. The water uptake and solution uptake in methanol solutions decreased with increasing crosslinking ratio, but a comparable high proton conductivity was maintained in the uncrosslinked membranes. They exhibited isotropic swelling behavior and largely enhanced dimensional stability in water and methanol solutions, whereas the uncrosslinked one showed anisotropic swelling behavior. The oxidative stability of the crosslinked membranes was significantly enhanced by the formation of sulfonyl linkages. The high proton conductivities at 120 degrees C and 50% relative humidity suggested promising applications in elevated temperatures. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 1707-1716, 2011