USE OF PULSED NMR TECHNIQUES IN THE MEASUREMENT OF RADIATION EFFECTS IN POLYMER

Changes in polymer structure (crosslinking, degradation) induced by radiation can be readily seen in the T2 NMR relaxation spectrum. For low molecular weight linear polymer T2 is a direct measure of Mn. For high molecular weight polymer, T2 comprises at least two time dependant components, of relative initial amplitude f and 1-f, corresponding respectively to the non-network and network fractions. The network fraction is formed not only by permanent crosslinks induced by radiation, but also by chain entanglements whose lifetime (on the scale of NMR measurements) may be adequate to act as temporary crosslinks. The density of these entanglements, derived from NMR data, agrees with that from earlier hydrodynamic experiments. The model proposed can account for the viscoelastic behaviour of flexible polymers, as studied here. The NMR technique provides a simple, rapid and non-destructive method of measuring radiation - induced changes in polymers, and has advantages over the solubility method often used for quality control. The use of this technique for more fundamental research (e.g G values, effect of temperatures and additives, solutions, fillers and eventually biopolymers) is outlined. © 1979.