A series of castor-oil-modified hyperbranched polyurethanes were synthesized via an A(2) + B-3 approach based on castor oil, macroglycol poly(epsilon-caprolactone)diol or poly(ethylene glycol) (PEG), and diphenyl methane diisocyanate, with or without a chain extender. The yield of the product was 95%, and the polymers were Soluble in common organic polar solvents. The synthesized polymers were characterized with Fourier transform infrared spectroscopy, NMR, wide-angle X-ray diffraction, and gel permeation chromatography measurements. The degree of branching of the polymers was calculated from their respective H-1-NMR spectra with the help of model compounds and found to be varied from 0.7 to 0.8. The hard-segment content, the nature of the macroglycol, and the composition of the polymers had prominent effects on the thermal degradation and crystallization of the hyperbranched polymers. The crystallization of poly(epsilon-caprolactone) and PEG as soft segments occurred well in the hyperbranched polymers. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 736-743, 2009