Alkaline stability of pendant C2-protected poly(imidazolium)s

Abstract

Non-fluorinated anion exchange polymers with sufficient ion exchange capacity, mechanical integrity and hydroxide-ion stability are required for the progression of alkaline electrochemical energy conversion devices. In this work, we present a new class of polycations, that possess C2-sterically protected imidazolium pendant groups which are incorporated via an olefinic backbone, and a synthetic route that requires no post-functionalization. The versatile 5-step synthetic route is a platform for future modifications of this family of C2-protected imidazolium-functionalised ion conducting polymers. Hydroxide-promoted degradation studies, along with DFT calculations, predict the robustness of polymers, with the benzyl-modified, C2-sterically protected imidazolium group showcasing a 8000 h half-life in 3 M NaOD/CD₃OD/D₂O at 80 °C. A humidity cycling degradation protocol, exposing the polymers to as low as 10 % relative humidity at 80 °C was implemented to reveal the relative chemical (in)stabilities of the polymers in extreme caustic conditions under accelerated timeframes.