Monitoring the Aging Dynamics of Glycidyl Azide Polyurethane by NMR Relaxation Times

Abstract

We have used solid-state NMR to monitor the aging dynamics of a polyurethane based on glycidyl azide polymer (GAP) used as a binder in solid rocket propellants. We have shown by deuterium NMR longitudinal relaxation time ( T 1 ) measurements that it is possible to monitor the degradation of the binder as a function of time for samples with different NCO/OH ratios. The longitudinal relaxation was found to be nonexponential. Thus, we have used a stretched exponential equation of the type Kohlrausch−Williams−Watts to determine the value of T 1ww. With the help of the gamma function, the average value of T 1 (〈 T 1 〉) was determined without knowing the shape of its distribution function. Since the solid-state NMR method has the advantage of being nondestructive, we were able to monitor the aging of the polyurethane samples that were kept in ambient conditions rather than in the extreme thermal conditions usually applied in aging studies of polymers.