Surface tension, density, and viscosity in chain-folded polymer melts

Abstract

Abstract Molecular weight dependence of polymer packing density in the amorphous state as predicted by the intermolecular bundle (IMB) model of Kargin, Kitaigorodskii, and Slonimskii, by the entangled statistical coils (ESC) model of Flory and Bueche, and by the statistical chain folding (SCF) model of Robertson is compared with experimental data for density and surface tension of molten polyethers. An experimentally observed sudden drop of ρ and γ at some characteristic molecular weight Mcr and the subsequent gradual increase of these parameters with MW is best accounted for by the SCF model. On the basis of some phenomenological considerations in conjunction with an extension of the SCF model to allow for the segregation of macromolecular coils at MW = Mcr, an empirical equation predicting the dependence of the zero-shear rate viscosity of high-molecular weight polymers on the 3.5 power of MW is obtained. The relationship between Mcr and the “critical” viscosity molecular weight Mc is briefly discussed.