NMR analysis of oxidatively aged HTPB/IPDI polyurethane rubber: Degradation products, dynamics, and heterogeneity

NMR spectroscopy experiments on thermally aged cross-linked hydroxyl-termin ated 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 het erogeneities. The samples were aged in sealed ampules containing either oxy gen 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 domina nt oxygen-containing degradation products (similar to 60%). Ester and acid functional groups were also detected, but there was no significant amount o f ketones. Gel permeation chromatography (GPC) showed evidence of both chai n scission and cross-linking during degradation. The dynamics in the rubber system was probed with wide-line H-1 spectra, H-1 spin diffusion measureme nts, and 2D wide-line-separation (WISE) experiments. Dynamic and chemical h eterogeneities were detected in highly aged materials. The smallest dimensi on of the chemically pristine mobile regions is similar to 20 nm.