Interplay Between Hydroxyl Density and Relaxations in Poly(vinylbenzyltrimethylammonium)-b-poly(methylbutylene) Membranes for Electrochemical Applications

Anion-exchange membranes (AEMs) consisting of poly(vinyl benzyl trimethylammonium)-b-poly(methylbutylene) of three different ion exchange capacities (IECs), 1.14, 1.64, and 2.03 mequiv g\u20131, are studied by High-Resolution Thermogravimetry, Modulated Differential Scanning Calorimetry, Dynamic Mechanical Analysis, and Broadband Electrical Spectroscopy in their OH\u2013 form. The thermal stability and transitions are elucidated, showing a low temperature Tg and a higher temperature transition assigned to a disorder\u2013order transition, T\u3b4, which depends on the IEC of the material. The electric response is analyzed in detail, allowing the identification of three polarizations (only two of which contribute significantly to the overall conductivity, \u3c3EP and \u3c3IP,1) and two dielectric relaxation events (\u3b21 and \u3b22), one associated with the tolyl side groups (\u3b21) and one with the cationic side chains (\u3b22). The obtained results are integrated in a coherent picture and a conductivity mechanism is proposed, involving two distinct conduction pathways, \u3c3EP and \u3c3IP,1. Importantly, we observed a reordering of the ion pair dipoles which is responsible for the T\u3b4 at temperatures higher than 20 \ub0C, which results in a dramatic decrease of the ionic conductivity. Clustering is highly implicated in the higher IEC membrane in the hydroxyl form, which reduces the efficiency of the anionic transport