IONIC ASSOCIATION AND CONDUCTIVITY IN POLY(ETHYLENE OXIDE) AND POLY(PROPYLENE OXIDE) METAL SALT SYSTEMS

Complexes of poly(propylene oxide) and poly(ethylene oxide) with mixed salts of composition (PPO)(20)-(ZnBr2)(x)(LiBr)(1-x) and (PEO)(20)-(ZnBr2)(x)(LiBr)(1-x) have been studied by Raman spectroscopy and ionic conductivity measurements. The relative concentrations of ZnBr2, ZnBr3- and ZnBr42- (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 ZnBr2 to ZnBr3- to ZnBr42-. The complex with x = 0.5 in all polymer-salt complex systems studied contains only the ZnBr3- species. Complex impedance measurements indicate that the ionic conductivity of ZnBr3- is highest in the PEO (CH3-capped) system. Interesting conclusions are drawn regarding the mobility of these species in the different polymer environments.