Tuning poly(arylene piperidinium) anion-exchange membranes by copolymerization, partial quaternization and crosslinking

Abstract Ion exchange membranes with high ionic contents typically suffer from excessive water uptake and dilution effects which compromise both mechanical properties and ion conductivity. In the present work we develop and compare partial quaternization, copolymerization and crosslinking as three different synthetic strategies to balance the ion exchange capacity (IEC), water uptake and hydroxide conductivity of poly(arylene piperidinium)s, which belong to a new class of alkali-stable anion-exchange membrane materials. Poly(biphenyl N-methylpiperidine) (PBPip) was first produced in a polyhydroxyalkylation reaction of biphenyl and N-methyl-4-piperidone, and then partly quaternized with controlled stoichiometric shortages of alkyl halide to regulate the IEC. In the second approach, a series of copolymers with controlled IEC were prepared by introducing precise amounts of ketone co-monomers in the polyhydroxyalkylations. In the final approach, crosslinked AEMs were fabricated in a reactive casting procedure, followed by partial quaternization. The overall results of the study reveals that the copolymerization approach gives AEMs with the most attractive set of properties. Hence, at a given IEC and moderate water uptake, the copolymer AEMs reach the highest hydroxide conductivity, up to 120 mS cm−1 at 80 °C, and retain the high alkaline stability of the original poly(arylene piperidinium) AEM. The study demonstrates the versatility and efficiency of these synthetic strategies to tailor and significantly improve the properties of functional high-performance AEMs for different electrochemical applications.