EFFECTS OF POLYDISPERSITY ON LINEAR VISCOELASTICITY IN ENTANGLED POLYMER MELTS

The relationship between molecular weight distribution (MWD) and linear viscoelastic response of polymer melts was investigated with three commercial polymers and two blends (11 and 13 components, respectively) of nearly monodisperse materials. Dynamic modulus master curves in the plateau and terminal zones were compared with predictions based on theoretically motivated combining rules, various descriptions of response for monodisperse melts, and the molecular weight distribution of each of the samples. Agreement with the Tsenoglou combining rule was excellent for the model mixtures, in which MWD was known by construction. Departures at low frequencies were found for the commercial samples, in which MWD was determined by size exclusion chromatography and light scattering. The discrepancy is attributed to uncertainties in the high molecular tail of distributions obtained by the dilute solution methods.