The Influence of Crystallization Conditions on Radiation Effects in Polyethylene - I. Crystallization from Dilute Solution and from the Melt

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Abstract
Samples of Marlex 50 crystallized from dilute solution (yielding single crystals) and in the bulk form were irradiated by high-energy electrons and the solubilities compared. The single-crystal specimens remained fully soluble after a dose of 20 megarads, which rendered the bulk two-thirds to three-quarters insoluble. Since the initial free-radical concentration was identical and the chemical changes induced were not widely different in the two kinds of specimens, it is suggested that intramolecular crosslinks, occurring in a larger number in the single crystals, are responsible for this behavior. At high doses the same solubility limit is approached by both specimens, which is ascribed to the possibility of chain cutting becoming increasingly ineffective in the single crystal. In the light of these findings, the limitations of the conventional treatment of radiation effects are discussed and the possible significance of the present results for morphological problems is pointed out. A number of further effects are reported in connection with melting behavior and spin resonance spectra that are at variance with results in the literature.