Effect of Polymer Structure on Ion Transport in an Anhydrous Proton Conducting Electrolyte

We have studied the effect of polymer structure of a proton-conducting polymer electrolyte on proton conductivity. Proton conducting electrolytes composed of mixtures of a MePEG7SO3H acid, our MePEGn polymer, and a PEG containing cross-linker have been prepared. We have independently varied two structural parameters in our polymer electrolyte, viscosity and free volume, and studied the effects of these changes on the H+ conductivity. The copolymerization of a PEG13 cross-linker increases the viscosity and the molecular weight distribution (i.e., PDI) of our MePEGn polymers. In addition, the fractional free volume of our MePEGn polymers increases as the length of the PEG side chains in the polymer increases from n = 7 to n = 12. Under certain conditions, high-viscosity, cross-linked MePEGn polymers show almost the same ionic conductivity as less viscous, uncross-linked MePEGn polymers. The effect of this change in viscosity is compensated by a simultaneous change in the free volume of the MePEGn polymer. T...