Structure-property relationship of poly(2,6-dimethyl-1,4-phenylene oxide) anion exchange membranes with pendant sterically crowded quaternary ammoniums

Abstract Steric hindrance engineering is of great significance to the preparation of new stable organic cations and durable polymeric anion exchange membrane materials. In this work, we presented a study of the structure-property relationship in quaternized poly (2,6-dimethyl-1,4-phenylene oxide) containing bulky n-propyl, isopropyl, or cyclohexyl-functionalized quaternary ammonium moieties. To our surprise, PPO-iP membranes possessing isopropyl-based QA cations showed higher water uptake than n-propyl- and cyclohexyl-containing analogues (PPO-nP and PPO-CH), in which obvious microphase-separated morphology was found. Thus, PPO-iP membranes displayed the highest hydroxide conductivity at 20 °C in water (37.3 mS/cm, IEC = 1.90 mmol/g). A standard protocol (1 M or 2 M NaOH at 60 °C) was used to determine the chemical stability of model cations and membranes both having sterically crowded QAs. Minor loss (