Viscoelasticity and molecular parameters of commercial polymers

Abstract

The influence of the accuracy of determining the molecular weight distribution (MWD) of polymers on the accuracy of calculating the mean molecular weight is discussed. It is shown that for industrial polymers only two mean values can be determined with sufficient accuracy, which is satisfactory only for the description of similar MWD's. An analysis of a large number of experimental data on polyethene shows that similar MWD's are obtained in the case of material manufactured on one and the same reaction unit. Such MWD's can be described by an equation containing a small number of parameters. Using the viscosity summation rule in melts, a model has been developed for the dependence of the viscoelastic characteristics that determine the relaxation spectra on molecular parameters of the polymer. The model takes it possible to predict the effect of molecular composition (molecular weight, polydispersity index and degree of long-chain branching) on viscoelastic functions of the melt. A simplified method of reverse calculation is suggested for obtaining the molecular composition from viscoelastic characteristics and an estimate of the accuracy of such a calculation is given.