Nuclear magnetic relaxation study of poly(ethylene oxide) complexed with lithium trifluoromethanesulfonate

Abstract

A 19F and 1H NMR spin–lattice relaxation investigation of two PEO–LiCF3SO3 samples, with molar ratios O:Li of 3.5:1 and 9:1, in the temperature range 190–330 K is reported. The 19F NMR measurements from the main focus of the study and these are shown to reflect the properties of the single crystalline complex which is known to be present in PEO–LiCF3SO3 mixtures. A 19F relaxation model is developed in which the motion of the CF3 groups about their threefold axes gives rise to an intramolecular dipolar mechanism but in addition there is a contribution from heteronuclear dipolar interactions between the CF3 groups of the CF3SO3– anions and the CH2 groups of the polymer chain. The simulation of the observed experimental spin–lattice relaxation behaviour is based upon a detailed discussion of the properties of a 19F, 1H model system and involves the analysis of reduced second moment ratios. It is suggested that this type of approach has general applicability in cases where a detailed motional model is not available. Reasonable agreement is found between the simulated and experimental relaxation behaviour.