Coordination and conformation in PEO, PEGM and PEG systems containing lithium or lanthanum triflate

Abstract

The effect of chain length, cation type and polymer end group on the coordination and conformation in polymer electrolytes has been studied using high molecular weight poly(ethylene oxide) (PEO), poly(ethylene glycol) (PEG(400)) and poly(ethylene glycol)dimethyl ether (PEGM(400)) as polymers, with LiCF 3SO 3 and La(CF 3SO 3) 3 as salts. The experimental technique used has been Fourier transform infra-red spectroscopy. A coordination of nine to ten ether oxygens to the lanthanum ions has been found for the PEGM system by increasing the concentration of lanthanum triflate in the polymers and following the disappearance of the COC stretching vibration of non-coordinated ether oxygens. The same coordination seems to be present also for the PEG and PEO systems. Conformational changes have been observed on addition of salt to the polymer, by following the disappearance of an absorption band at about 990 cm −1, indicative of a trans conformation around the CH 2CH 2 bond. For all three polymer types the gauche conformation is dominant at high salt concentrations. The OH end groups present in the PEG samples are important for the coordination in this system and both the cations and the triflate anions are coordinated by the OH groups to some extent.