Synthesis and property of novel anion exchange membrane based on poly(aryl ether sulfone)s bearing piperidinium moieties

A novel bisphenol monomer bearing a cyclic tertiary amine was prepared in good yields by the acid-catalyzed reaction of N-methyl-4-piperidone and phenol. Tertiary amine poly(aryl ether sulfone) (TAPES) with high molecular weights of up to 95.3 kg mmol−1 and good thermal stability was synthesized by nucleophilic substitution of the bisphenol monomer with 4,4′-dichlorodiphenyl sulfone. The spatial separation between the cyclic tertiary amine groups and the hydroxyl ortho-position improves the stability of the intermediate and was the key to the polymerization. The anion exchange membranes (AEMs) QPES or DQPES are obtained by quaternization of TAPES with methyl iodide or (3-bromopropyl)trimethylammonium bromide, respectively. DQPES (ion exchange capacity = 3.12 mmol g−1) shows a higher ion conductivity of 59.8 mS cm−1 and reasonable dimensional stability in water at 80 °C. DQPES membrane revealed that the high conductivity might be due to its phase-separated structure in small-angle X-ray scattering test. The alkaline stability of QPES and the methoxy-capped QPES was compared, end-capping was found to improve the stability of piperidinium cations. This method offers a versatile platform for cost-effective synthesis of piperidinium-based AEMs with poly (aryl ether) backbones, and may provide a strategy to improve alkaline stability.