IR spectroscopic study of conformational properties of a short-chain poly(oxyethylene) (C1E3C1) in binary mixtures with liquids of different hydrogen-bonding abilities

Abstract

The conformational properties of a short-chain poly(oxyethylene), CH₃(OCH₂CH₂)₃OCH₃ (C₁E₃C₁), in binary mixtures with water, methanol, chloroform, N,N-dimethylformamide and carbon tetrachloride have been studied by IR spectroscopy. The changes in the conformation populations of the C–C and C–O bonds of C₁E₃C₁ with varying composition were examined by observing relative intensities of the conformation key bands. The results of the spectral analysis show that the conformational changes around the C–C bond depending on the properties of the added liquid are much larger than those around the C–O bond. Hydrogen bonding between the ether oxygens of the POE chain and the second component liquid dominates over electrostatic interactions in stabilizing the gauche conformation around the C–C bond. The magnitudes of the gauche preference of the C–C bond in the hydrogen-bonding liquids are well correlated with their hydrogen bond acidities. It is suggested that the stability of the gauche conformation around the major C–C bond in hydrogen-bonding liquids is reinforced by the trans conformation around the minor C–O bond. Most of the unusual properties of POE are closely related to the conformational flexibility of the polymer chain, or more specifically the conformational flexibility of the C–C bond.