A series of polyurethane (PU) elastomers was prepared by the reaction of poly(epsilon-caprolactone) and 4,4'-diphenylmethane diisocyanate, which was extended with a series of chain extenders (CEs) having 2-10 methylene units in their structure. The completion of the reaction was confirmed by Fourier transform infrared spectroscopy. The chemical structures of the synthesized PU samples were characterized with Fourier transform infrared, H-1-NMR, and C-13-NMR spectroscopy, and the thermal properties were determined by thermogravimetric analysis, DSC, and dynamic mechanical thermal analysis techniques. The mechanical properties were also studied and are discussed. The thermogravimetric analysis and DSC analysis showed that CE length had a considerable effect on the thermal properties of the prepared samples. The dynamic mechanical thermal analysis and damping peaks were also affected by the number of methylene units in the CE length. The elastomer extended with 1,2-ethane diol exhibited optimum thermal properties, whereas the elastomer based on 1,10-decane diol displayed the worst thermal properties. Tensile strength and elongation at break decreased with increasing CE length, whereas hardness showed the opposite trend. The glass-transition temperature moved toward lower temperatures with increasing CE length. The decrease in the glass-transition temperature and tensile properties were interpreted in terms of decreasing hard segments and increasing chain flexibility. (C) 2008 Wiley Periodicals, Inc.