AbstractHigh polymers of ethylene oxide have been shown to have a number of unique properties in water solution. In this study, these properties have been investigated from the view of the behavior of large neutral molecules in media of high dielectric constant. Predictably, these high polymers of ethylene oxide undergo salting‐out effects which are reflected in changes of solution viscosity with salt concentration. Salts vary in effectiveness in a manner similar to that observed in the case of small neutral solute molecules. The salting‐out and viscosity effects are paralleled by the inverse solubility‐temperature relationship in water. Above a minimum molecular weight of about 50,000, the precipitation temperature (the temperature at which polymer separates from solution as a separate phase as the temperature is raised) becomes essentially independent of molecular weight. For these very high polymers the upper temperature limit of solubility in water is independent of polymer concentration over a wide range of concentration. These effects are discussed in terms of the balance of hydrophilic and hydrophobic character in the polymer structure which can be altered by increasing the hydrocarbon content of the polymer through copolymerization of ethylene oxide with other olefin oxides such as propylene oxide. This investigation permits the development of an interpretation of the unusual rheology of high molecular weight poly(ethylene oxide) in water sol