A Hybrid Organic/Inorganic Ionomer from the Copolymerization of Vinylphosphonic Acid and Zirconium Vinylphosphonate

Copolymers of vinylphosphonic acid with zirconium vinylphosphonate have been synthesized via free radical polymerization from immiscible mixtures into amorphous, transparent, water stable, and flexible membranes. Ion exchange capacities range from 6 to 10 mequiv/g, corresponding to equivalent weights well below 200 g/mol. A 20 wt % loading of the vinyl zirconium phosphonate comonomer is XRD amorphous. It is shown that 1.5 of the 2 protons in the beginning acidic groups are dissociated in the 20 wt % VZP loaded ionomer, allowing these materials to have high proton conductivities, up to and exceeding 0.1 S cm(-1) at 80 degrees C and 80% RH. Water uptake measurements show very little swelling of the material below 70% RH land ca. 1 water per proton at low RH. Proton conductivity under dry conditions, roughly 0.05 S cm-1 with a lambda < 1, indicates that he material conducts protons under limiting hydration conditions and strongly implicates transport by a pure Grotthuss mechanism.