Dipole moments and the structures of polyethylene glycols

The dipole moments of polyethylene glycols (from a monomer to a heptamer) were measured in dioxane solution. Measurements were made also of the infrared absorptions of these compounds in carbon tetrachloride and in dioxane. Unlike the case of polyoxymethylene dimethyl ethers, the moment of the series of polyethylene glycols increases progressively with the degree of polymerization. This fact cannot be explained by assuming a helical structure of the chain molecule. Such a structure could result from the gauche minima of the internal rotation about single bonds in the case of a polyoxymethylene chain. The free rotation model, in the sense that the trans and the gauche minima are equally important, is suitable for the polyoxyethylene chain, presumably because the chain has CC bonds of a vanishing bond moment. A systematic increase of the theoretical moment for the free rotation model over the experimental data was observed for the higher members of this series of compounds. This effect is attributable to the volume effect. Infrared absorption measurements made in carbon tetrachloride and dioxane solutions revealed that in the latter solution all the OH groups are hydrogen‐bonded with the ether‐type oxygen of the solvent. This explains the fact that the theoretical moments of the lower members of polyethylene glycols are slightly lower than the observed ones.