DETERMINATION OF CROSS-LINK DENSITY IN THERMOSET POLYMERS BY USE OF SOLID-STATE H-1-NMR TECHNIQUES

Solid-state **1H NMR techniques were used to determine the cross-link density of highly cross-linked polymers common in the aerospace industry. As the temperature was increased, the spin-spin relaxation times of cross-linked epoxy polymers were observed to reach a plateau value which increased linearly with increasing molecular weight between cross-links, as predicted by theory. The results show that, for the epoxy system studied, approximately 10 rotatable backbone bonds are needed to form a statistical segment, the portion of the polymer backbone that moves independently of the other backbone motions.