Block Copolymers Containing Quaternary Benzyl Ammonium Cations for Alkaline Anion Exchange Membrane Fuel Cells (AAEMFC)

Block copolymers of polystyrene-b-poly (vinylbenzyltrimethylammonium tetrafluoroborate) (PS-b-[PVBTMA][BF4]) were synthesized by sequential monomer addition using atom transfer radical polymerization (ATRP). Block copolymers of polystyrene-b-poly (vinylbenzyltrimethylammonium hydroxide) (PS-b-[PVBTMA][OH]) was prepared as polymeric alkaline anion exchange membranes (AAEMC) materials by ion exchange from PS-b-[PVBTMA][BF4] with hydroxide in order to investigate the morphology relationship to ion conductivity. Membranes of the block copolymers were made by drop casting from dimethylformamide. Initial evaluation of the microphase separation in these PS-b-[PVBTMA][BF4] materials via SAXS revealed the formation of spherical, cylindrical and lamellar morphologies. Studies of humidity (RH)-dependent conductivity at 80°C showed that a strong effect of microstructures on conductivity. Moreover, the investigation of the temperature-dependent conductivity at RH = 50%, 70% and 90% showed a significant effect of grain boundaries in the membranes against the formation of continuous conductive channels which is an important requirement for achieving high ion conductivity.