The aging of polymers is often monitored by mechanical property measurements such as those of Young's modulus or tensile elongation at break; new methods are required, however, in situations where traditional mechanical methods cannot be employed. A hydroxy-terminated polybutadiene/isophorone diisocyanate elastomer is commonly used as a propellant binder. The thermal degradation of the binder is believed to be an important parameter governing the performance of the propellant. Classical mechanical methods cannot be used to monitor the condition of this material when it has been aged in situ as a highly dispersed binder. In this study, the H-1-NMR spin-spin relaxation times, T-2, of solvent-swelled samples decreased substantially as thermally induced oxidation led to additional crosslinking. A time-temperature superposition analysis of the relaxation times was performed on samples that had been aged at temperatures ranging from 50 to 125degreesC. The acceleration factors derived from the relaxation measurements agreed with those reported earlier for tensile elongation at break and oxygen consumption. The dependence of T-2 on tensile elongation at break was independent of the temperature at which the sample was aged. A shortened version of the experiment, requiring only two spin-echo delay times, is presented.