IR spectra and hydration of short-chain polyethyleneglycols

IR spectra of pure polyethyleneglycol PEG-200, PEG-400, monomethylether of PEG-350, dimethyl ether of PEG-250, several related compounds and water solutions in PEG-200 were recorded in the range of the skeletal band at 1100 cm^-1. The observed structured band in pure liquid PEGs and solutions was deconvoluted into five components shown to be due to non-interacting vibrations. The component near 1068 cm^-1 is mainly due to the (C-OH) group and the 1104 and 1127 cm^-1 components to the (C-O-C) groups. Of these the former is free or in the trans conformation and the latter is involved in an intramolecular H-bond or gauche conformation relative to the C-C bond. The changes band component parameters in PEG-200, on addition of small amounts of water, are ascribed to the attachment of the first water molecules to the terminal OH-group hydrogen bond system of the PEG molecule.