A series of polyurethane (PU) elastomers were prepared by the reaction of poly (epsilon-caprolactone) (PCL) and 4, 4'-diphenylmethane diisocyanate (MD1), extended with a series of chain extenders (CEs) having 2-10 methylene units in their structure. The synthesized samples were irradiated for 50, 100, and 200 h as such the spectral distribution of the light is good match for terrestrial solar radiation. Fourier transform infrared (FTIR) spectroscopy was used to study the chemistry of monomers and final PU samples. The structural changes in the PU samples upon ultraviolet (UV) irradiation were characterized using FTIR spectroscopic technique. In comparison with non irradiated samples, there was a continuous decrease of the bands upon long-term UV irradiation. The results revealed that final PU sample extended with 1,6-hexane diol (1,6-HDO) to 1, 10 decane diol (1,10-DDO) have been fully degraded at 200 h irradiation. Comparing PU sample extended with 1, 6-HDO and 1, 10-DDO, it was found that the degradation rate of later is higher than former. It was concluded that CEs length has considerable effect on thermal degradation of PU and by increasing CEs length thermal degradation upon UV irradiation shifted to lower temperature. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 2843-2850, 2009