Four new models of Uni-HEUR associative thickener were designed and synthesized using various molecular weights of poly(ethylene glycol) (PEG) as hydrophilic segments. The PEG chain ends were capped with octadecyl isocyanate as hydrophobic segments. The structure of the prepared Uni-HEUR thickness was confirmed by infrared spectroscopy. The steady shear viscosity measurements of aqueous solution of HEUR models showed that the size of hydrophilic segments to hydrophobic segments is very important. Oscillatory measurements confirmed the steady shear viscosity results. It is found, there is an optimum relative size of hydrophilic segments to hydrophobic segments to achieve the thickener with a good performance. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1751-1754, 2009