N‑Methylquinuclidinium versus N,N‑Dimethylpiperidinium Cations on Flexible Side Chains in Anion Exchange Membranes

The conductivity and stability of anion exchange membranes (AEMs) may be significantly enhanced by attaching the cations to the polymer backbones via flexible side chains. Here, we have tethered polydimethylfluorene with the bicyclic "cage-like" N-methylquinuclidinium (PdF-Qui) and the monocyclic N,N-dimethylpiperidinium (PdF-Pip) cations, respectively, via flexible side chains, and studied key AEM properties. Morphological investigations revealed efficient ion clustering in both AEMs, with OH^- conductivities exceeding 120 mS cm^-1 at 80 °C. Alkaline stability studies showed no ionic loss or structural changes in PdF-Qui after storage in a 5 M aqueous NaOH solution at 90 °C for 360 h. In contrast, the benchmark PdF-Pip suffered a 7% loss under the same conditions, primarily via Hofmann elimination. This work presents an efficient synthetic strategy to tether N-methylquinuclidinium cations to polymers for AEMs combining outstanding alkaline stability, efficient ionic clustering, and high OH^- conductivity.