Low Tg Siloxane Phosphonium Ionomers with Superior Ionic Conductivity

Polysiloxane phosphonium single-ion conductors grafted with oligomeric PEO and with ion contents ranging from 5 to 22 mol % were synthesized via hydrosilylation reaction. Low glass transition temperatures (below −70 °C) with only a weak dependence on both ion content and counteranion type were observed. The low Tg is attributed to (1) the inherent flexibility of the polysiloxane backbone, (2) the presence of ion-solvating PEO side chains that facilitate ion conduction, (3) lack of ionic aggregation, and (4) the electronic structure of the phosphonium cation. The highest conductivity at 30 °C is 20 μS/cm for dry neat ionomer, with the TFSI− anion, consistent with its relatively delocalized negative charge and large size that weaken interactions between TFSI− and the phosphonium cation. This suggests a new direction for materials synthesis of low-Tg single-ion conductors for superior ambient ionic conductivity.


S. Liang, M. V. O'Reilly, U. H. Choi, H.-S. Shiau, J. Bartels, Q. Chen, J. Runt, K. I. Winey*, R. H. Colby*, Macromolecules, 47 (13), 4428-4437, 2014.
"High Ion Content Siloxane Phosphonium Ionomers with Very Low Tg"