A SOLID-STATE C-13-NMR STUDY OF CROSS-LINKING IN POLYBUTADIENE BY GAMMA-RADIATION - EFFECT OF MICROSTRUCTURE AND DOSE

Solid-state C-13 NMR spectroscopy has been used to determine the decrease in C = C bonds, formation of crosslinks and cis to trans isomerization during the gamma-irradiation of (a) > 99% cis, 1,4-polybutadiene, (b) 54% trans, 41% cis, 1,4-polybutadiene, and (c) 86% 1,2-polybutadiene. G(-cis C = C) and G(-trans C = C), were similar and decreased with dose from almost-equal-to 40 for 0-1 MGy to 5 for 5-10 MGy. G(-double bonds) and G(crosslink) were comparable, indicating that crosslinking occurred through the double bonds. G(crosslink) was much higher than values derived from physical properties, confirming that NMR measures the total of inter- and intramolecular crosslinking (cyclization). The 1,2 polybutadiene was much more sensitive to crosslinking, and a value of G(-C = C) = 240 was obtained at low doses. Crosslinking evidently proceeds by a kinetic chain reaction in all three types of polybutadiene.