The influence of the oxyethylene spacer length between terminal hydrophobes of hydrophobically-modified ethoxylated urethanes (HEURs) is examined through the synthesis of two series of welldefined terminally-modified HEUR thickeners. In the first series, octadecyl isocyanate is reacted with poly (oxyethylene) (POE) of varying molecular weight. In the second synthesis, excess isophorone diisocyanate is reacted with POE to prepare an isocyanate functional precursor, followed by reaction of the terminal isocyanate group with nonylphenol. Viscous aqueous solutions are obtained with only partial terminal modification of POE; with full terminal modification swollen gels are realized. At moderate concentrations the phase separation of HEUR thickeners is dependent on the size of the hydrophobe and the number of oxyethylene units between the hydrophobes. In both series of HEURs, the critical aggregation concentration is lowest when 500 oxyethylene units separate the terminal hydrophobes. In the presence of surfactant, both anionic and nonionic, the fully-modified HEURs also exhibit a maximum in viscosity when the spacer is ~500 oxyethylene units. The viscosities realized in both HEUR series are equal or greater (with smaller HEUR oxyethylene spacings) with the nonionic surfactant relative to the anionic surfactant, sodium dodecyl sulfate.

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