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Synthesis and Structure-Conductivity Relationship of Polystyrene-block-Poly(vinyl benzyl trimethylammonium) for Alkaline Anion Exchange Membrane Fuel Cells
ARGONNE NATIONAL LAB IL
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Block copolymers of polystyrene-b-polyvinyl benzyl trimethylammonium tetrafluoroborate PS-b-PVBTMABF4 were synthesized by sequential monomer addition using atom transfer radical polymerization. Membranes of the block copolymers were prepared by drop casting from dimethylformamide. Initial evaluation of the microphase separation in these PS-b-PVBTMABF4 materials via SAXS revealed the formation of spherical, cylindrical, and lamellar morphologies. Block copolymers of polystyrene-b-polyvinyl benzyl trimethylammonium hydroxide PS-b-PVBTMAOH were prepared as polymeric alkaline anion exchange membranes materials by ion exchange from PS-b-PVBTMABFsub 4 with hydroxide in order to investigate the relationship between morphology and ionic conductivity. Studies of humidity relative humidity RH- dependent conductivity at 80 deg C showed that the conductivity increases with increasing humidity. 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.
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