Monitoring the aging dynamics of glycidyl azide polyurethane by NMR relaxation times

We have used solid-state NMR to monitor the aging dynamics of a polyurethan e based on glycidyl azide polymer (GAP) used as a binder in solid rocket pr opellants. me 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 longit udinal relaxation was found to be nonexponential. Thus, we have used a stre tched exponential equation of the type Kohlrausch-Williams-Watts to determi ne the value of T-1ww. With the help of the gamma function, the average val ue of T-1 ([T-1]) was determined without knowing the shape of its distribut ion function. Since the solid-state NMR method has the advantage of being n ondestructive, we were able to monitor the aging of the polyurethane sample s that; were kept in ambient conditions rather than in the extreme thermal conditions usually applied in aging studies of polymers.