Quinoxaline-based semi-interpenetrating polymer network of sulfonated poly(arylene ether)s and sulfonated polyimides as proton exchange membranes

Abstract

Semi-interpenetrating polymer network (sIPN) proton exchange membranes are prepared from sulfonated polyimides (SPIs) and cross-linkable sulfonated poly(arylene ether)s (SPAEs) with 3,3′-diaminobenzidine (DAB) as cross-linker. The cyclocondensation between DAB and benzyl moiety in SPAEs results in a covalently cross-linked SPAE networks where SPIs can be immobilized by interlocking; meanwhile, the interlocked structure is also strengthened by acid–base ionic interactions between the sulfonic acid groups of sulfonated polymers (SPAEs and SPIs) and quinoxaline moieties formed in cross-linking. For comparison, the corresponding SPAE/SPI blend membranes are also prepared and evaluated. The proton conductivity, dimensional changes, mechanical properties, oxidative stability, water stability as well as methanol permeability are investigated for the membranes. The results show that the sIPN membranes have obviously higher performance than the pristine SPAE, SPI and SPAE/SPI blend membranes due to the interlocked structures. The sIPN membrane sIPN-SPAEK(2/1)-SPI with ion exchange capacity of 2.00 mequiv g−1 shows good mechanical properties, high stability, reasonably high proton conductivity of 128 mS cm−1 and low methanol permeability of 0.58 × 10–6 cm2 s−1.