Abstract
Polyethylenes, irradiated to doses just short of the gel dose, have been examined for structural changes using 13C NMR in a study of the effects of ionizing radiation on polyethylene. Radiation gelled polyethylenes do not produce high resolution NMR resonances possibly because NMR dipolar interactions in the gel phase are not effectively averaged by the available molecular motions. One of the major structural units formed during irradiation of polyethylene is the Y type of long chain branch. Other structural entities monitored and followed versus radiation conditions were trans and cis double bonds, terminal vinyl end groups, saturated end groups, hydroperoxide groups and carbonyl groups. In addition to NMR measurements, molecular weight changes were monitored through intrinsic viscosity, gel permeation chromatography and low angle laser light scattering measurements. It was possible through the appropriate experimental conditions both before and during irradiation, to convert a linear, high density polyethylene to a medium density, exclusively long chain branched polymer, which was free of gel. Attempts to detect the H-link in polyethylenes irradiated to doses short of the gel dose met with little success.
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