Crosslinked poly(arylene ether sulfone) block copolymers containing quinoxaline crosslinkage and pendant butanesulfonic acid groups as proton exchange membranes

Abstract

Crosslinkable poly (arylene ether sulfone) block copolymers (bSPAES (x/y)) containing pendant butanesulfonic acid and ethanedione groups were prepared from a new side-chain difluoro aromatic monomer 1-(2,6-difluorophenyl)-2-(3,5-dimethoxyphenyl)-1,2-ethanedione via block copolycondensation, demethylation, and further nucleophilic substitution of 1,4-butane sultone. Meanwhile, quinoxaline-based crosslinked block copolymers (C-bSPAES (x/y)) were obtained via cyclocondensation. The corresponding block copolymer membranes have high mechanical properties and anisotropic membrane swelling for either crosslinked or uncrosslinked ones. bSPAES (5/10) with ion exchange capacity (IEC) of 2.05 mequiv. g−1 has low water uptake (WU) of 59.1% at 80 °C but relatively high conductivity of 225 mS cm−1, which is ascribed to its good microphase separation. Meanwhile, the crosslinked C-bSPAES (5/10) with IEC of 1.76 mequiv. g−1 exhibits a decreased WU by half, an improved oxidative stability by 200% and a reduced membrane swelling by 40% than the uncrosslinked bSPAES (5/10). The results suggest that quinoxaline-based crosslinking can obviously improve properties of bSPAES (x/y). In addition, even though maximum power density of C-bSPAES (5/10) is lower than that of Nafion 212, C-bSPAES (5/10) still has an acceptable good single-cell performance, indicating a possible fuel cell application.