Butan-l-of modified toluene diisocyanate trimer (TDI-trimer) was synthesized and characterized with Fourier transform infrared spectroscopy, gel permeation chromatography, and thermal gravimetry analysis techniques. The modified TDI-trimer showed good dissolvable ability with hydroxy resin and can be used to produce paints with acrylic polyol resin. The thermal stability of the modified TDI-trimer was improved by simply increasing both the amount of catalyst and the ratio of -NCO/-OH, less depended on the kind of catalyst. (c) 2006 Wiley Periodicals, Inc.