Condition monitoring of a thermally aged hydroxy-terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) elastomer by nuclear magnetic resonance cross-polarization recovery times

A hydroxy-terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) el astomer is commonly used as propellant binder material. The thermal degrada tion of the binder is believed to be an important parameter governing the p erformance of the propellant. The aging of these binders can be monitored b y mechanical property measurements, such as modulus or tensile elongation. These techniques, however, are not easily adapted to binder agents that are dispersed throughout a propellant. In this paper we investigated solid-sta te nuclear magnetic resonance (NMR) relaxation times as a means to predict the mechanical properties of the binder as a function of aging time. Proton (H-1) spin-lattice and spin-spin relaxation times were insensitive to the degree of thermal degradation of the elastomer. Apparently, these relaxatio n times depend on localized motions that are only weakly correlated with me chanical properties. A strong correlation was found between the C-13 cross- polarization (CP) NMR time constant, T-cp, and the tensile elongation at br eak of the elastomer as a function of aging time. A ramped-amplitude CP exp eriment was less sensitive to imperfections in setting critical instrumenta l parameters for this mobile material. (C) 2001 John Wiley & Sons, Inc.