Phase separated methylated polybenzimidazole (O-PBI) based anion exchange membranes

Methylated polybenzimidazole (O-PBI) based anion exchange membranes with a degree of methylation of ca. 78% were prepared in the iodide, chloride, carbonate, bicarbonate, and hydroxide form. Swelling in water showed a high anisotropy for chloride and carbonate exchanged membranes and a strong plasticizing effect of water was confirmed by DMA. Carbonate and bicarbonate exchanged membranes revealed an ionomer peak around 0.25 Å^-¹ in SAXS measurements suggesting a phase separated morphology. Theoretical DFT calculations were used to characterize geometries and electronic structure of polymer models and interactions with different anions, and to rationalize the water uptake/swelling behavior. Anion exchange membranes are prepared from methylated polybenzimidazole and are exchanged with various anions. Thermal and mechanical properties are evaluated. Unlike other anions, carbonate and bicarbonate exchanged membranes reveal an ionomer peak in SAXS measurements suggesting a phase separated morphology. Water uptake and swelling behavior are rationalized by theoretical DFT calculations.