Star-shaped MePEGn polymers as H+ conducting electrolytes.

Proton conducting electrolytes composed of a mixture of MePEG(7)SO(3)H acid and a four-armed, PEG-based, star molecule were prepared. Four MePEG(n) (n = 3, 7, 12) arms were attached to a pentaerythritol or tetrakis(dimethylsilyl) orthosilicate core to form the star molecules. We have examined the structure of these star electrolytes to observe how the structure of an electrolyte affects the observed ionic conductivity. In terms of structural parameters, these star electrolytes showed large volume fractions of PEG, high fluidities, and large fractional free volumes, all of which predict larger ionic conductivities. Through a comparison of the conductivity and structural parameters in a variety of different star electrolytes, we have shown that each of these three structural parameters are important and can strongly affect the observed ionic conductivity. Walden plots indicated a large extent of ion-pairing in our star electrolytes and that MePEG(7)SO(3)H acid was a weak acid in our star electrolytes.