E.s.r. study of γ-irradiated isotactic and atactic polypropylene

An e.s.r. study of γ-irradiated isotactic (i-) and atactic (a-) polypropylene (PP) was carried out. Both the 17 line (or 9 line) spectrum for i-PP and the 6 line spectrum for a-PP are attributed to the tertiary carbon radical, CH₂C(CH₃)CH₂. The difference in the hyperfine structure between the spectrum of i-PP and that of a-PP can be explained by different radical conformations owing to the stereoregularity. Hyperfine coupling and the radical conformation for the tertiary carbon radical in i- and a-PP were determined from the cos² ? rule. It is shown that the δ methylene proton as well as the β methylene proton contribute to the slight anisotropy in the stretched sample. The spectral change from 9 lines to 17 lines with elevation of temperature, observed at low temperature in i-PP, could be explained by the hindered oscillation of the β methylene proton.