Chain entanglement and free-volume effects in branched poly(arylene piperidinium) anion-exchange membranes: Random-branched versus end-branched

• Published in: Journal of membrane science 2025-02, Vol.717, p.123519, Article 123519
• Main Authors: Xue, Jiandang, Douglin, John C., Huang, Tong, Jiang, Haifei, Zhang, Junfeng, Yin, Yan, Dekel, Dario R., Guiver, Michael D.
• Format: Article
• Language: English
• Subjects: Anion-exchange membrane; Branched architecture; Chain entanglement; Free volume; Poly(arylene piperidinium)
• ISSN: 0376-7388
• DOI: 10.1016/j.memsci.2024.123519

Poly(arylene piperidinium) (PAP) anion-exchange membranes (AEMs) are attractive platform materials currently used for anion-exchange membrane fuel cells (AEMFCs) and chain branching modifications on PAP polymer structures have recently drawn much attention for effectively regulating the membrane properties. To better understand the influence and interplay of the polymer chain entanglement and free-volume effect from various branched architectures, herein, lightly end-branched EB-PTP/TPB AEMs, using poly(p-terphenyl dimethylpiperidinium) (PTP) as the polymer backbone and bulky rigid 1,3,5-triphenylbenzene (TPB) as the branching agent, are designed and compared to previously reported random-branched RB-PTP/TPB and linear-chain PTP membranes. Intrinsic viscosity, bulk density and positron annihilation lifetime spectroscopy suggest a lesser extent of chain entanglement, but more evident free-volume elements for end-branched EB-PTP/TPB, particularly for higher branched EB-PTP/TPB-1% containing 1 mol% of TPB branching agent, compared with the random-branched RB-PTP/TPB that exhibits a more predominant chain entanglement effect. EB-PTP/TPB AEMs with increased free volume exhibit faster water sorption kinetics and slightly higher ion conductivity, but the concurrent high water sorption levels are disadvantageous to high-temperature ion transport, alkaline stability and water balance management. Even so, EB-PTP/TPB AEMs still show sufficient mechanical robustness, restricted swelling and higher alkaline stability than linear-chain PTP membranes, aided by the considerable extent of chain entanglement. This work reveals branched architecture–AEM property relationships and provides valuable insights towards branched architecture design. [Display omitted] •Anion-exchange membrane (AEM) structure‒property relationship investigated.•Lightly random-branched versus end-branched polymer architecture.•Differences observed in polymer chain entanglement and free volume effects.•End-branched AEM has improved properties and AEMFC performance than unbranched AEM.