Elastic Behavior, Birefringence, and Swelling of Amorphous Polyethylene Networks

Abstract

Abstract Polyethylene networks were prepared by γ-irradiation of linear polyethylene, both molten and crystalline. Elastic and. photoelastic properties of the networks were studied at high temperatures, i.e., in the molten state. Equilibrium swelling was also measured in several solvents. Values of the crosslinking efficiency G of γ-radiation, the molecular weight Me between entanglements, the optical anisotropy α of the equivalent random link, and the polymer-solvent interaction parameter μ are deduced. Samples prepared by irradiation in the amorphous state showed markedly nongaussian elastic behavior. The presence of a large nongaussian term in the optical anisotropy is also deduced. The value of α obtained for swollen samples, which showed substantially gaussian elastic behavior, was 3.9×10−24, about one half of that obtained for dry samples. It corresponds to an equivalent random link of only about 5 CH2 units, on the basis of Denbigh's values for bond polarizabilities. The samples prepared by irradiation in the crystalline state also showed lower values for α, depending on the degree of crosslinking. This is attributed to the nonrandom chain configurations prevailing at the time of crosslinking. The same samples were found to show more nearly gaussian elastic behavior, which is attributed to the same cause.