Ionic association and conductivity in polyethylene oxide) and poly(propylene oxide) metal salt systems

Abstract

Complexes of poly(propylene oxide) and poly(ethylene oxide) with mixed salts of composition (PPO) 20-(ZnBr 2) x (LiBr) 1 − x and (PEO) 20-(ZnBr 2) x (LiBr) 1 − x have been studied by Raman spectroscopy and ionic conductivity measurements. The relative concentrations of ZnBr 2, ZnBr 3 − and ZnBr 4 2 − (as deduced from the relative intensities of the symmetric stretching modes) have been measured as a function of x. The effect of chain length, end-capping and temperature was also examined. The analysis shows that with increasing bromide concentration the dominant species varies from ZnBr 2 to ZnBr 3 − to ZnBr 4 2 −. The complex with x = 0.5 in all polymer-salt complex systems studied contains only the ZnBr 3 − species. Complex impedance measurements indicate that the ionic conductivity of ZnBr 3 − is highest in the PEO (CH 3-capped) system. Interesting conclusions are drawn regarding the mobility of these species in the different polymer environments.