OH end-group coordination to cations and triflate ions in PPG systems

Abstract

In poly(propylene glycol) (PPG) the polymer chains are terminated by hydroxy groups. These polar ends are capable of coordinating to both cations and anions when a salt is dissolved in the polymer. This coordination has been monitored using shifts in the OH stretching vibration band at about 3400 cm −1, as measured by Fourier transform infra-red spectroscopy. In the LiCF 3SO 3PPG(3000) system, the Li + ions preferred to coordinate to OH groups rather than to ether oxygens; at the composition LiCF 3SO 3PPG 10, all OH groups were coordinated by both lithium and triflate ions, suggesting that the properties of these electrolytes depend to a large extent on metal ion to OH end-group interactions. Solvent-shared ion pairs, where the ions are separated by an OH group rather than free triflate ions, are present in these samples. The triflate ions in the solvent-shared ion pairs are suggested to have a v(SO 3) s absorption band at 1032 cm −1, i.e. at the same position as has been found for non-coordinated triflate ions.