Application of high resolution NMR spectroscopy on the solid state to the degradation of polyethylene by high dosages of γ-radiation

High resolution (HR) NMR spectroscopy of solid polymer by the cross-polarization (CP) and magic angle spinning (MAS) method was applied to the study of the degradation of polyethylene (PE) by γ-irradiation. No change in the HR NMR spectra was observed in high density polyethylene irradiated up to 300 M rad. Above 300 M rad, deviation of chemical shifts of the main peak corresponding to methylene carbons occurred to higher field. Fractions of the methylene in the gauche form were quantitatively estimated from the observed deviations of the main peaks. Several new peaks, including methyl and carbonyl peaks, were detected after irradiation. The relative concentrations of the methyl and carbonyl groups produced by irradiation were estimated from the observed intensities of the corresponding peaks. Chemical reactions resulting in the formation of the methyl and carbonyl groups are discussed on the basis of the observed changes in the relative concentrations of these groups.