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.