Crosslinked sulfonated poly(arylene ether sulfone) membranes for fuel cell application

A series of sulfonated poly(arylene ether sulfone) with photocrosslinkable moieties is successfully synthesized by direct copolymerization of 3,3′-disulfonated 4,4′-difluorodiphenyl sulfone (SDFDPS) and 4,4′-difluorodiphenyl sulfone (DFDPS) with 4,4′-biphenol (BP) and 1,3-bis-(4-hydroxyphenyl) propenone (BHPP). The content of crosslinkable moieties in the polymer repeat unit is controlled from 0 to 10 mol% by changing the monomer feed ratio of BHPP to BP. The polymer membranes can be crosslinked by irradiating UV with a wavelength of 365 nm. From FT-IR analysis, it can be identified that UV crosslinking mainly occurs due to the combination reaction of radicals that occurs in conjunction with the breaking of the carbon–carbon double bonds (–CH = CH-) of the chalcone moieties in the backbone. Consequently, a new bond is created to form cyclobutane. The crosslinked membranes show less water uptake, a lower level of methanol permeability, and good thermal and mechanical properties compared to pristine (non-crosslinked) membranes while maintaining a reasonable level of proton conductivity. Finally, the fuel cell performance of the crosslinked membranes is comparable to that of the Nafion 115 membrane, demonstrating that these membranes are promising candidates for use as polymer electrolyte membranes in DMFCs.