NMR Analysis of Oxidatively Aged HTPB/IPDI Polyurethane Rubber: Degradation Products, Dynamics, and Heterogeneity

Abstract

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 17O2 gas at temperatures ranging from ambient temperature to 125 °C. The 17O and 13C NMR spectra showed that alcohols are the dominant oxygen-containing degradation products (∼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 1H spectra, 1H spin diffusion measurements, and 2D wide-line-separation (WISE) experiments. Dynamic and chemical heterogeneities were detected in highly aged materials. The smallest ...