Stress Relaxation Study of Fine Structure of γ-Loss Band of Branched Polyethylene

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Abstract
The shear relaxation modulus of polyethylene samples with various degrees of branching is measured at many temperatures in the so-called γ-loss band, between –190°C and –100°C, using a torsional stress relaxation apparatus. Three relaxations, named γ1, γ2 and γ3 in order of descending temperature, are observed separately. Their master curves and relaxation spectra are determined by the method of reduced variables. The activation energies obtained from the shift factors for the γ1-, γ2- and γ3-relaxations are ca. 20, 11 and 6 kcal/mol respectively. For each of these relaxations the activation energy and the shape of the spectrum are found to be independent of the crystallinity and degree of branching. Using these results, the molecular mechanisms responsible for these three relaxations are discussed.

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