High resolution x3C n.m.r, spectra were obtained from two ethylene-propylene copolymers containing 23% (EP23) and 36% (EP36) propylene swollen with CDC13 after v-irradiation, although the line widths increased and the intensities of the original resonances decreased with increasing radiation dose. A resonance at 42 ppm after low doses (0.02-0.14 MGy) was attributed to methine carbons in H-crosslinks. New resonances at 11.3, 14.1, 14.5, 22.7 and 23.1 ppm were assigned to methyl and methylene groups on various chain-end structures arising from main chain scission, and yields (G values) were derived for doses up to 2 MGy. G(scission) values of 0.16 and 0.37 for EP23 and EP36, respectively, were in good agreement with values derived previously from soluble fraction measurements and from solid-state n.m.r, spectra after much higher radiation doses. The proportions of different chain-end structures suggested that scission was favoured by a factor of 1.6 at C-C bonds adjacent to the methyl substituents compared with other main-chain C-C bonds.
Посилання на статтю:
Observation by 13C n.m.r, of H-crosslinks and methyl end groups due to main-chain scission in ethylene-propylene copolymers after -irradiation / James H. O'Donnell and Andrew K. Whittaker* // Polymer. – 1992. – Vol 33. – P. 62-67.
