Poly(phenylene oxide) copolymer anion exchange membranes

Poly(phenylene oxide) block and random copolymers are synthesized by oxidative polymerization of 2,6‐dimethylphenol and 2,6‐diphenylphenol for potential alkaline exchange membrane application. The copolymers are functionalized on the methyl substituted repeat units through a two‐step process to produce pendent quaternary ammonium cationic groups. The amount of quaternary ammonium cations and the ion exchange capacity are quantified through titration measurements. Ionic conductivity of the copolymer membranes is measured by electrochemical impedance spectroscopy. Block copolymers show increased bromide conductivity at higher ion exchange capacities compared with the random copolymer analogs. The bromide conductivity for a block copolymer film with an ion exchange capacity of 1.27 mequiv/g reaches 26 mS/cm at 90 °C and 95% relative humidity. The hydroxide conductivity for the same film was measured to be 84 mS/cm at 80 °C and 95% relative humidity.