Polyphosphazenes Bearing Branched and Linear Oligoethyleneoxy Side Groups as Solid Solvents for Ionic Conduction

Abstract

A new series of solid polymer electrolyte materials based on the poly(organophosphazene) system has been designed and synthesized. The new polymers contain linear or branched oligoethyleneoxy side chains. The polymers were characterized by 31P, 13C, and 1H-NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and elemental analysis. The ambient temperature (25 °C) ionic conductivities of the polymers complexed with lithium triflate were measured by complex impedance analysis. The polymers that bear linear oligoethyleneoxy side chains [NP{O(CH2CH2O)nCH3}2], have low glass transition temperatures that range from −84 to −75 °C. These polymers have properties that are similar to those of the classical counterpart poly[bis(2-(2-methoxyethoxy)ethoxy)phosphazene. They have low dimensional stabilities and undergo viscous flow even at room temperature. The polymers with branched oligoethyleneoxy side chains (podands) have similar glass transition temperatures, in the range of −82 to −79 °C. However, the bulk dimensional stabilities of the branched polymers are significantly higher than those of the corresponding linear side chain series. The branched side chain polymers resist viscous flow and readily form thin, free-standing films. The podand polymers also dissolve lithium triflate to form ionically conducting materials with conductivity levels similar to those of the polymers bearing linear side chains.