Molecular design and synthesis of hydroxide ion exchange membranes carrying alicyclic quaternary ammonium cations

Significantresearch efforts are currently directed towards the synthesis and studies of durable anion exchange membranes (AEMs) with the aim to develop alkaline fuel cells and electrolyzers able to operate efficiently without platinum-groupmetal catalysts [1]. The grand challenge is to identify and synthesize polymeric AEM materials possessingthe necessary chemical and thermal stability. Studies of different small cationic model compounds have revealed that aliphatic mono-and bicyclicquaternary ammonium (QA) cations have a very high alkaline stability, most probably because the constrained ring conformations increase the transition state energy of the degradation reactions [2].We have previously reported on the functionalization of poly(phenylene oxide) with different cyclo-aliphatic QA cations attached via flexible alkyl spacers [3]. In a different approach, we have designed, synthesized and studied polyelectrolytes containing N-spirocyclic cations, including N-spirocyclic quaternary ammonium ionenes ("spiro-ionenes") [4]. In addition, our group recently reported on the preparation and properties of ether-free poly(arylene piperidinium)s as a new class of high-performance AEMsdirectly accessible from commercially available and quiteinexpensive starting materials[5,6]. Very recently we have also prepared studied poly(arylene alkylene)swith different configurations and locationsof the cations(Scheme 1). In the current presentation we will discuss molecular design principles, syntheticprocedures and important structure-property relationships of these new polymer electrolyte material