Poly(2,6-dimethyl-1,4-phenylene oxide) Blended with Poly(vinylbenzyl chloride)‑b‑polystyrene for the Formation of Anion Exchange Membranes

A block copolymer of poly(vinylbenzyl chloride)-b-polystyrene (PVBC-b-PS) was synthesized through nitroxide-mediated polymerization, then blended with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at different compositions, and solution cast to prepare a series of blend films. Differential scanning calorimetry analysis of the PVBC-b-PS and PVBC-b-PS blended with the PPO showed a single glass transition temperature for each of the compositions examined, suggesting that all components in the blend membranes are compatible. The benzyl chloride groups in the blend films were converted to quaternary ammonium groups by reaction with trimethylamine, and the functionalization reached high conversion as characterized by ion exchange capacity (IEC) measurements. The PPO blend anion exchange membranes (AEMs) show improved mechanical properties compared to the styrenic copolymer, particularly in a hydrated condition. The membranes were subjected to thermal and THF/water annealing procedures to study the effect on membrane properties. Small-angle X-ray scattering (SAXS) experiments indicated the formation of a phase-separated morphology in the membrane after annealing with solvent vapor in the presence of water. The ionic conductivities of the blended membranes show an expected increase with increasing IEC and corresponding water uptake. Ionic conductivity and water uptake were found to increase significantly after either annealing in the presence of water and THF or high-temperature annealing in the presence of water. The highest hydroxide conductivity reached 43 mS/cm measured at 60 °C in water.