The unperturbed molecular dimensions of poly(ethylene glycol) (PEG) samples (of different molecular weights) have been evaluated in aqueous solutions from viscosity measurements at 25, 30, 35, and 40 degrees C. The unperturbed dimension, K., has been determined from extrapolation methods, i.e., Kurata-Stockmayer-Fixman (KSF), Inagaki-Suzuki-Kurata (ISK), and Berry equations. The hydrodynamic expansion factor, a, as well as the unperturbed root-mean-square end-to-end distance, < r(2)>(1/2)(0), found for the 0 system indicated that the polymer coils contract as the temperature is raised from 25 to 40 degrees C. The long-range interaction (excluded volume) parameter, B, was also evaluated and a significant decrease was found for the PEG/water system between 25 and 40 degrees C. The theta temperatures, theta, were obtained from the temperature dependence of (1/2 - chi) and the second virial coefficient was detected in the temperature interval of 25-40 degrees C for the system and quite a good agreement with the calculated values evaluated via extrapolation and interpolation methods was observed. The thermodynamic interaction parameter chi was evaluated through the sum of the individual values of enthalpy and entropy dilution parameters, X-H and X-S for PEG samples. All the unperturbed molecular dimensions of PEG/water system were calculated and compared according to M-w and M-n values of PEG samples. Calculated values were interpreted mainly on the basis of hydrogen-bond formation between polymer segments and PEG-water molecules in solution. (c) 2006 Wiley Periodicals, Inc.