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 degrees C to 75 degrees C. At 25 mbar water partial pressure and 75 degrees C, a conductivity of 2.2 x 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 degrees C. The hydrophilic nature of the CVEEP network stabilizes the water content and enhances the proton conductivity at elevated temperatures. (c) 2006 Elsevier B.V. All rights reserved.