**AUTHORS:**Grigory Pyshnograi, Darina Merzlikina, Petr Filip, Radek Pivokonsky

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**ABSTRACT:**
The Vinogradov and Pokrovskii rheological model was extended for a description of rheological behaviour
of branched polymer melts. Since stationary elongational viscosity is a nonmonotonic function of the
elongational rate, it required a generalization of the law of internal friction for beads of macromolecule. To achieve
high prediction accuracy was proposed multi-mode approximation. The contribution of each independent mode
to a stress tensor corresponds to the individual polymer fractions differing in relaxation time and viscosity. The
theoretical predictions of the generalized model provide a good agreement with the measured steady and transient
rheological characteristics of two samples branched low density polyethylenes.

**KEYWORDS:**
Constitutive equations, Mesoscopic approach, Polymer dynamics, Polymer melts, Viscometric flows,
Viscoelasticity

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[33] Pivokonsky R., Filip P., Predictive/fitting capabilities of differential constitutive models for polymer melts-reduction of nonlinear parameters in the eXtended Pom-Pom model// Colloid and Polymer Science 292 (2014) 2753-2763

[34] Pivokonsky R., Filip P., Zelenkova J., The role of the GordonSchowalter derivative term in the constitutive modelsimproved flexibility of the modified XPP model// Colloid Polymer Science 293 (2015) 1227-1236