Polymer Electrolyte Membranes Based on Cross-Linked Highly Sulfonated Multiblock Copoly(ether sulfone)s

Polymer electrolyte membranes based on cross-linked highly sulfonated multiblock copoly(ether sulfone)s (IEC = 2.99−3.40 mequiv/g) were prepared successfully by the reaction between the sulfonic acid groups in the main chains and 1,4-diphenoxybenzene as a cross-linker in the presence of the condensation agent. The HSPx1−3 membranes, which represent the cross-linked HSP1−3 membranes, demonstrated good mechanical strength in the dry state regardless of their high IEC values and the introduction of the cross-linking structure. Additionally, the multiblock polymer and the cross-linking structure suppressed unacceptable water uptake and dimensional change of the HSPx1−3 membranes even in the hydrated state, while maintaining relatively high water uptake under low relative humidity (10.3−17.6 wt % at 30% RH) due to their high IEC values. The HSPx1−3 membranes showed higher proton conductivity than that of Nafion 117 in the range of 30−95% RH (at 80 °C). Especially, the HSPx3 membrane with the highest IEC value (3.40 mequiv/g) showed 2.4−3.6 times higher proton conductivity compared to Nafion 117 in the whole range of 30−95% RH and still maintained excellent proton conductivity of 1.0 × 10−2 S/cm even at 80 °C and 30% RH.