Enhanced performance of proton-conducting poly(arylene ether sulfone)s via multiple alkylsulfonated side-chains and block copolymer structures

A novel difluoro aromatic monomer DFTMTE is prepared, which contains five pendant ionizable methoxy and crosslinkable ethanedione groups. Block copolymers are developed via block copolycondensation of the monomers DFTMTE, 4,4′-difluorodiphenyl sulfone and 4,4′-diphenol. Sulfonated block ionomers are obtained via the following demethylation and nucleophilic substitution of the copolymers. The ionomer membranes with ion exchange capacity (IEC) of 1.80–2.16 mequiv. g−1 display high conductivity of 234–319 mS cm−1 at 80 °C and large maximum power density of 1730–2140 mW cm−2, which is obviously larger than Nafion 212 (117 mS cm−1 and 1350 mW cm−2) in the same condition. Their enhanced performances are attributed to excellent microphase separations caused by block copolymer structures and multiple sulfonated side-chains integrating both rigid aromatic and flexible aliphatic units. Meanwhile, crosslinking further improves the balance among the properties of the membranes. For example, CB1SP having IEC of 1.80 mequiv. g−1 displays high comprehensive performance because of DFTMTE units and crosslinking structures, wherein low membrane swelling below 15% at 80 °C, large conductivity of 234 mS cm−1, high maximum power density of 1730 mW cm−2 and good stability of the membrane electrolyte assembly indicate a high potential in the application of fuel cell.