DYNAMIC MECHANICAL PROPERTIES OF POLYMER MELTS - DEPENDENCE OF VISCOELASTIC PROPERTIES ON MOLECULAR WEIGHT DISTRIBUTION

An investigation of the dynamic mechanical properties of several molten polymers was performed using the Maxwell Orthogonal Rheometer. Relaxation spectra derived from experimental data for the terminal region of viscoelastic response indicate that as molecular weight distribution broadens, terminal relaxation phenomena associated with molecular disentanglement and translation extend over a corresponding wider frequency range. The same data indicate that a true maximum relaxation time beyond which no elastic response is observed exists for the materials studied. Moreover, the maximum relaxation time corresponds to the reciprocal of the frequency where the dynamic viscosity deviates from its zero‐shear value. Thus an estimate of the time necessary for complete elastic recovery in polymer melts is readily obtained experimentally. Copyright © 1969 Society of Plastics Engineers, Inc.