In this study, a series of aqueous polyurethane (PU) prepolymers were synthesized with 4,4-methylene bis(isocyanatocyclohexane), poly(ethylene glycol) or polycaprolactone diol (PCL), methyl ethyl ketoxime, and dispersing centers produced by isophorone diisocyanate, N-diethanol amine, and poly(ethylene oxide) monomethyl ether (PEO), containing different hydrophobic groups (-CH3 and -C6H4C9H19) at the end. The thermal properties of the prepolymers and the characteristics of poly(ethylene terephthalate) (PET)-treated fabrics were investigated. The glass-transition temperature was the highest in the CC prepolymer containing a benzene ring (-C6HC4H19) and a long PEO side chain, and it was the lowest in the CA prepolymer having a longer PEO side chain. The CB prepolymer containing a shorter PEO side chain did not produce a melting point of PEO, although a heat endothermic peak of the PCL crystal appeared. The melting point and enthalpy from PEO of the CA prepolymer were larger than those of the CC prepolymer. With respect to the hydrophilic finishing effects of aqueous PU prepolymers for PET fabrics, the fabric treated with the CB prepolymer had higher addon and washing durability than the fabrics treated with the CA prepolymer, which was followed by the CC prepolymer with the lowest, but the opposite trend was found for the hydrophilic properties. (c) 2007 Wiley Periodicals, Inc.