Photo-Cross-Linked Anion Exchange Membranes with Improved Water Management and Conductivity

Robust, cross-linked anion exchange membranes (AEMs) were prepared from solvent-processable polyisoprene-ran-poly(vinylbenzyltrimethylammonium chloride) (PI-ran-P[VBTMA][Cl]) ionomers via photoinitiated thiol-ene chemistry. Two series of membranes were prepared choosing two dithiol cross-linkers, 1,10-decanedithiol and 2,2'-(ethylenedioxy)diethanethiol, selected for their different hydrophobicities. A strong correlation was found between the choice of dithiol cross-linker, water uptake, morphology, and the ion conductivity of the membranes. Results were compared with previous findings of thermally cross-linked AEMs from analogous random copolymers. Comparably high chloride ion conductivities were obtained at low to moderate ion exchange capacities (IECs) with significantly low water uptake values. It was shown that by choosing a hydrophilic cross-linker ion cluster formation may be suppressed and ion conduction improved. This study highlights that it is possible to promote ion conductivities for low IEC membranes (<1 mmol/g) by forming well-connected, ion conducting network morphology. This observation paves the way for mechanically robust ion conducting membranes with enhanced conductivities and better water management.