Synthesis of Alkaline Anion Exchange Membranes with Chemically Stable Imidazolium Cations: Unexpected Cross-Linked Macrocycles from Ring-Fused ROMP Monomers

In order to prepare base-stable, mechanically strong, and synthetically feasible alkaline anion exchange membranes (AAEMs) for applications in alkaline fuel cells, an imidazolium-fused cyclooctene monomer was prepared and subjected to ring-opening metathesis polymerization (ROMP) conditions. Surprisingly, macrocyclic oligomers were obtained instead of high molecular weight polymers. High-performance AAEMs were synthesized by using a bifunctional monomer to cross-link the macrocycles. The resultant AAEMs showed high ionic conductivities (σ_OH^– = 59 mS/cm at 50 °C), robust mechanical properties, and excellent alkaline stabilities.