MOLECULAR-WEIGHT POLYDISPERSITY EFFECTS ON THE VISCOELASTICITY OF ENTANGLED LINEAR-POLYMERS

A molecular model is developed to explain the viscoelastic behavior of entangled homopolymer blends of an arbitrary molecular weight distribution in the terminal relaxation regime. This is accomplished by analyzing the entanglement architecture and molecular dynamics of the temporary network formed by the intermeshing species. It is assumed that coupling between any two macromolecular components along a single chain is random and that this occurs proportionally to the fractional participation of these same components in the blend as a whole. The population densities and lifetimes of the various types of entanglements among chains of similar or dissimilar length are thus calculated and related to the composition and corresponding properties of the monodisperse polymeric precursors. These results are then utilized in the derivation of simple blending rules for the time-dependent relaxation modulus, the dynamic moduli, the viscosity, and the recoverable compliance of the dense homopolymer mixtures. The theoretical predictions are compared with experimental evidence for the binary case.