NMR spectroscopy experiments on thermally aged cross-linked hydroxyl-terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) based polyurethane rubber indicated only a slight temperature dependence for the degradation products distribution but revealed the presence of chemical and dynamic heterogeneities. The samples were aged in sealed ampules containing either oxygen or O-17(2) gas at temperatures ranging from ambient temperature to 125 degreesC. The O-17 and C-13 NMR spectra showed that alcohols are the dominant oxygen-containing degradation products (similar to 60%). Ester and acid functional groups were also detected, but there was no significant amount of ketones. Gel permeation chromatography (GPC) showed evidence of both chain scission and cross-linking during degradation. The dynamics in the rubber system was probed with wide-line H-1 spectra, H-1 spin diffusion measurements, and 2D wide-line-separation (WISE) experiments. Dynamic and chemical heterogeneities were detected in highly aged materials. The smallest dimension of the chemically pristine mobile regions is similar to 20 nm.