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.

Increased 29Si NMR sensitivity in glasses with a Carr–Purcell–Meiboom–Gill echotrain

“…In nuclear magnetic resonance, SER is commonly observed for spin-lattice relaxation in disordered materials, e.g., [22][23][24][25], and the case of b = 0.5 has been justified theoretically for a random distribution of paramagnetic centers in the absence of spin diffusion [26,27]. To the best of our knowledge, stretched exponential spin-spin relaxation has not been experimentally or theoretically studied in detail for glasses.…”

A structural investigation relating to the pozzolanic activity of rice husk ashes

“…Considering the fact that a distribution in particle size and porosity/morphology occurs in the samples a strong distribution of spin-lattice relaxation is to be expected in the samples as is confirmed experimentally. For the RHA samples burnt at 500°C an average spin-lattice relaxation time [24] bT 1 N = 147 s has been determined showing that with a recycle delay of 600 s a quantitative analysis of the spectra is possible with good accuracy as the intensities of the sites with the longest T 1 's are underestimated by a maximum of 5%. For the samples processed at 700°C the average bT 1 N more than doubled to 337 s. By extrapolating the KWW stretched exponential function it was estimated that for these samples a prohibitively long relaxation delay of ∼ 2000 s would be needed to get fully quantifiable results.…”

Synthesis of GAP and PAMMO Homopolymers from Mesylate Polymeric Precursors

“…Among the proposed binders, polyethers containing azidic functionalities are very promising and glycidyl azide polymer (GAP) is the most studied one. Several publications may be found concerning the synthesis as well as the thermal behavior and explosive properties of GAP [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The GAP synthesis was first described in a patent filed in 1972 by Vandenburg [23] who did azidation of polyepichlorohydrin (PECH) by using sodium azide in dimethylformamide.…”