Investigating the effect of 9-methyl-9<i>H</i>-carbazole functionalization on the properties of a poly(2,6-dimethyl-1,4-phenylene oxide)-based anion exchange membrane.

Abstract

The nature of the cationic head group tethered to the polymer has a major impact on the performance of anion exchange membranes (AEMs). In this work, a membrane is designed based on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) by incorporating 9-methyl-9<i>H</i>-carbazole (NMC) through Menshutkin reaction, introducing a planar aromatic cationic headgroup. The confirmation of the targeted product was carried out using various spectroscopic techniques. The properties, such as water uptake and swelling ratio, were in the controlled limit, implying adequate hydrophilicity and efficient water retention, supporting the favourable ion transport characteristics. The ion exchange capacity (IEC) of PPO-NMC was found to be 1.34 mmol g^-1. FESEM and AFM analyses revealed a uniform, phase-separated morphology indicative of well-developed ionic channels. Thermogravimetric analysis showed a thermal degradation onset above 250 °C, indicating the thermal stability of the membrane under typical operating conditions of an alkaline fuel cell. Contact angle measurements further demonstrated the hydrophilic nature of the membrane, consistent with the polar aromatic character of the carbazole moiety. Overall, the study highlights that incorporating an aromatic quaternary head group notably enhances the ionic, structural, and thermal characteristics of PPO-based AEMs.