A Simulation System for Viscoelastic Properties of Polydisperse Polymer Melts

Abstract

A simulation system is developed for evaluating viscoelastic properties of polymer melts with arbitrary polydispersity in molecular weight, starting from the known chemical structure of the polymers. The critical molecular weight for entanglement and molecular weight dependence of zero shear viscosity are evaluated based on theories of van Krevelen and Berry-Fox by optimizing parameters associated with chain flexibility, chain length and effective molar weight per repeating unit. In the evaluation of viscoelastic properties of polymer melts, simple and reasonable shape of relaxation spectrum is assumed for polydisperse systems. Using molecular parameters evaluated above, frequency dependence of viscoleastic functions is calculated from the relaxation spectrum. This method is shown to be superior to the usual way of calculation of viscoelasticity based on blending rules: The time needed for the calculation is very short and does not depend on the polydispersity in molecular weight. Combination of the present method with an appropriate constitutive equation gives a system for evaluating nonlinear viscoelastic properties of polydisperse polymers.