Aliphatic Side-Chain Engineering in Poly(2,6-dimethyl-1,4-phenylene Oxide) for Enhanced Physicochemical and...

The development of chemically stable and high-performance anion exchange membranes (AEMs) is crucial for advancing alkaline electrochemical energy technologies. In this study, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based AEMs containing different cationic head groups were synthesized to investigate the influence of headgroup structure on membrane properties. Brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BrPPO) was quaternized with trimethylamine (TMA) and trioctylamine (TOA) via the Menshutkin reaction to obtain PPO-TMA and PPO-TOA membranes, respectively. The PPO-TOA membrane exhibited significantly lower water uptake and swelling ratio compared to PPO-TMA due to the bulky and hydrophobic nature of the trioctylammonium group, which restricts water penetration and polymer chain mobility. The ion exchange capacity values were determined to be 0.96 and 1.28 mequiv g-1 for PPO-TOA and PPO-TMA, respectively. Atomic force microscopy revealed more pronounced microphase separation in PPO-TOA, indicating improved hydrophobic-hydrophilic domain segregation. Thermogravimetric analysis confirmed thermal stability up to 200 °C, while contact angle measurements demonstrated increased surface hydrophobicity for PPO-TOA. These results suggest that incorporating long aliphatic chains into PPO-based AEMs provides controlled hydrophilicity and improved structural stability, highlighting PPO-TOA as a promising candidate for durable alkaline electrochemical applications.