Densities, Viscosities, and Self-Diffusion Coefficients of Ethylene Glycol Oligomers

Polyethylene glycol (PEG) is gaining interest as an alternative green solvent in chemical synthesis and processing. This report presents density and viscosity data from 293.15 K to 358.15 K as well as self-diffusion coefficient data from 298.15 K to 358.15 K for oligomers of PEG from di- to nonaethylene glycol. The results were obtained by extrapolation from measurement series where water, the most common impurity in PEGs, was intentionally added in several increments. The obtained results are carefully compared to literature data, which are widely available only for density and viscosity, and only for the lower oligomers. Densities are found to be linearly dependent on temperatures for all studied oligomers. The temperature dependence of viscosity and self-diffusion coefficients show only slight deviations from the Arrhenius equation over the investigated temperature range. The activation energies obtained from the viscosity data agree well with the activation energies from the self-diffusion coefficient data and appear to be linearly dependent with respect to the number of ethylene oxide repeat units in the PEG oligomer. This linearity combined with the observation that the pre-exponential factor appears to be the same for all studied oligomers may serve as a tool to estimate viscosities and self-diffusion coefficients for higher oligomers within the investigated temperature range. The densities of the oligomers all fall within a rather narrow range without a clear trend in homologous series.