Light scattering measurements show that, below molecular weights of about 10(6), PEO chains in aqueous solution follow the expected pattern of behavior for a flexible chain in a thermodynamically good solvent, although the coils are unusually extended because of specific interactions with water. For higher molecular weight chains, the molecular weight scaling exponent for the radius of gyration decreases and the parameter rho = (R-g/R-h) consequently decreases. The observed collapse to a more compact coil conformation is because of microgel formation, probably stabilized by intramolecular hydrogen bonding via solvent molecules. (C) 2000 Elsevier Science Ltd. All rights reserved.