Poly(ethylene oxide) does not aggregate in dilute water solutions. The slow-mode behavior frequently observed by dynamic light scattering from poly(ethylene oxide) solutions in water already below and around the coil overlap concentration, often interpreted as the onset of semidilute behavior and/or clustering, is shown to be a result of the presence of an impurity. The impurity may be conveniently described as microdroplets or compact microparticles, sterically stabilized by the presence of poly(ethylene oxide) macromolecules, formed from a hydrophobic organic substance sparingly soluble or insoluble in water and increasingly soluble in methanol and collected within samples at the ppm level during their whole history. A solid phase extraction mechanism governs the successful removal of the impurity from polyethylene oxide)-water solutions when hydrophobic filters are used.
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