Suppressing Water Uptake and Increasing Hydroxide Conductivity in Ring-Opened Polynorbornene Ion-Exchange Materials via Backbone Design

In this study, we aimed to decrease segmental mobility in ring-opened polynorbornene anion-exchange membranes (AEMs) as a strategy to suppress swelling. This was accomplished by copolymerization of a norbornene-anthracene cycloadduct with cationic tetraaminophosphonium norbornene monomers to afford AEMs with glass transition temperatures above 100 °C. The anthracenyl side groups appended to the poly(vinylene-1,3-cyclopentylene) chain resulted in lower water uptake for the phosphonium-functionalized AEM when compared to an analogue without the arene moiety. Though chemical aging of these AEMs was noted over time, the benefits of rigidifying the polymer backbone were clear. Additionally, we have noted that the choice of dialkylamino groups around the phosphorus center plays a key role in alkaline stability of these phosphonium-based AEMs.