Aromatic Polymers Incorporating Bis-N-spirocyclic Quaternary Ammonium Moieties for Anion-Exchange Membranes

We have prepared and studied a new class of anion-conducting membrane materials functionalized with N-spirocyclic quaternary ammonium (QA) cations formed via cycloquaternization reactions involving pyrrolidine, piperidine, and azepane, respectively. These cations were introduced in pairs, adjoined through fused phenyl rings along poly(arylene ether sulfone) backbones. Despite their bulkiness, the bis-N-spirocyclic QA moieties efficiently formed ionic clusters in anion-exchange membranes (AEMs) and showed thermal stability up to 309 °C, as well as a reasonable alkaline stability. The hydroxide ion conductivity of the AEMs increased with decreasing ring size, and a fully hydrated pyrrolidine-based AEM reached a conductivity of 110 mS cm^-1 at 80 °C. The results of this study indicate new synthetic pathways to high-performance AEMs based on N-spirocyclic QA groups.