Analysis of Hydroperoxides in Solid Polyethylene by MAS ¹³C NMR and EPR

Abstract

13C-enriched polyethylene was subjected to γ-irradiation in the presence of air at 25 and 80 °C for total doses ranging from 71 to 355 kGy. Significant quantities of hydroperoxides were detected in the 25 °C irradiated sample by 13C magic angle spinning NMR spectroscopy. This method of detection was performed on the solid polymer and required no chemical derivatization or addition of solvent. The chemical stability and subsequent products of the hydroperoxide species were studied by annealing the irradiated samples in air at temperatures ranging from 22 to 110 °C. A time−temperature superposition analysis provided an activation energy of 108 kJ/mol for the hydroperoxide decomposition process. The primary products of hydroperoxide decomposition were ketones and secondary alcohols with lesser amounts of acids and esters. EPR measurements suggest that the reactive hydroperoxide species reside in the amorphous phase of polyethylene, consistent with degradation occurring in the amorphous phase.