ON THE STRUCTURES AND YIELDS OF THE 1ST PEROXYL RADICALS IN GAMMA-IRRADIATED POLYOLEFINS

Peroxyl radicals generated as a result of γ -irradiation of isotactic and atactic polypropylene and high-density polyethylene have been identified and quantified by a combination of electron spin resonance (ESR) and derivitization infrared spectroscopies. When samples are maintained at ≤-60 °C, peroxyl radicals are indefinitely stable in polyolefins yet react smoothly with nitric oxide to give nitrates. From infrared spectroscopy it is possible to identify the structure of some of these nitrates (primary, secondary, or tertiary) and hence the structure of the peroxyl radicals that are the origin of all oxidative chains in the polymers. Good agreement was found between total peroxyl species measured by ESR and the total level of nitrate products from infrared. From polyethylene, the dominant peroxyl species is proposed to be ~CH2CH(O2)-CH2~, whereas in the polypropylenes the secondary peroxyl dominated over the tertiary species. This dominance is very different from that expected from peroxyl radical selectivity for attack on polymer CH groups in the subsequent propagation reactions. © 1990, American Chemical Society. All rights reserved.