1,2,3-Triazolium-Based Poly(2,6-Dimethyl Phenylene Oxide) Copolymers as Anion Exchange Membranes

Anion exchange membranes (AEMs) based on 1,2,3-triazolium (TAM) were prepared from commercial poly(2,6-dimethyl phenylene oxide) (PPO) via "click chemistry" and subsequent N-alkylation. Flexible and tough membranes with various ion exchange capacities (IECs) were obtained by casting the polymers from NMP solutions. Although the resulting TAM-functionalized PPOs (PPO-TAM) membranes exhibited incomplete ion exchange in 1 M NaOH or NaHCO3 for 24 h even at elevated temperature, the highest hydroxide conductivities of the membranes were above 20 mS/cm at room temperature, which is comparable to many reported AEMs. Alkaline stability tests indicate that the PPO-TAM membranes showed a better alkaline stability than that of membranes containing imidazolium groups in 1 M NaOH at 80 °C, but still require further improvements in long-term stability for alkaline fuel cell application. An investigation of alkaline stability of model compounds demonstrated the instability of TAM cations under alkaline conditions could contribute to the deprotonation of benzylic methylene, C4 and C5 position on the triazolium ring. These results suggests that the alkaline stability of 1,2,3-triazolium cation could be improved by the introduction of substituents at the C4, C5 positions and benzylic methylene, and also provide insight and directions for organic cation designs for AEM application by the facile synthetic strategy of "click chemistry".