Proton conducting membranes from sulfonated poly[bis(phenoxy)phosphazenes] with an interpenetrating hydrophilic network

Proton conducting membranes have been prepared using sulfonated poly[bis(phenoxy)phosphazene] (s-BPP) trapped in a cross-linked interpenetrating hydrophilic network of hexa(vinyloxyethoxyethoxy)cyclotriphosphazene (CVEEP). Membranes with good mechanical and thermal stabilities were obtained exhibiting high ion exchange capacities in the range of 1.62–1.79 mmol/g. The proton conductivity was measured as a function of water partial pressure in nitrogen (0 mbar to 25 mbar) in the temperature range 25 °C to 75 °C. At 25 mbar water partial pressure and 75 °C, a conductivity of 2.2 × 10− 4 S/cm was obtained for s-BPP with a network made of 50 wt.% CVEEP. After immersion in water, the conductivity increased up to 0.013 S/cm at 25 °C. The hydrophilic nature of the CVEEP network stabilizes the water content and enhances the proton conductivity at elevated temperatures.