While research and development has been focused primarily on proton exchange membrane (PEM) devices in recent decades, devices based on anion exchange membranes (AEM) have garnered increased interest as a potential cost-saving alternative. To be viable for use in electrochemical devices, AEMs must have good long-term alkaline and thermal stability, high hydroxide ion conductivity, lower water uptake, high molecular weight, and low oxygen or fuel permeability.

Polar groups in the polymer backbone are susceptible to nucelophilic attack by the hydroxide ion, which is a major concern for the long-term stability of these materials. In the past, AEMs containing aryl ether bonds degraded under alkaline conditions. Alternatively, materials with a fully hydrocarbon polymer backbone have been shown to provide a route to low-cost and chemically resilient AEMs.

In this study, several new classes of AEMs with fully hydrocarbon backbones were synthesized and characterized. Multiblock copolymers with tethered quaternary ammonium conducting groups were chosen to promote phase segregation and enhance the ionic conductivity. The AEMs were made from vinyl addition and ring-opening metathesis polymerization (ROMP) of norbornenes. These results were compared to a previous study involving AEMs made from partially fluorinated poly(arylene ether)s. The mechanical and thermal stability, ionic conductivity, long-term alkaline stability of all classes of polymers are discussed in detail in the context of performance in an AEM fuel cell or electrolyzer.