Relation Between Flow Properties, Molecular Mass and Branching of Polymer

Text taken from:

Vinogradov, Georgii Vladimirovich; Malkin, Aleksandr Yakovievich. Rheology of Polymers: Viscoelasticity and Flow of Polymers. Mir Publishers. Moscow; 1980. p. 153-154

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Relation Between Flow Properties, Molecular Mass and Branching of Polymer

Introduction

While considering the temperature dependence of the viscosity of linear polymers, we introduced the concept of the macromolecular segment as a molecular-kinetic unit performing elementary acts of translation in space from one equilibrium state to another. if the size of the segment is much smaller than that of the macromolecule, these transfers --the elementary acts of flow --are independent of molecular mass. However, for the macromolecule to be transferred irreversibly, it is necessary that the centre of gravity of the entire molecule be shifted as a result of the displacement of its constituent segments. But the higher the molecular mass of the polymer, i. e., the greater the number of segments in the macromolecule, the larger is the number of cooperative segment motions that must be effected for its centre of gravity to be shifted and the higher must be the viscosity.

Study of the effect of molecular mass on the flow properties of polymers is supposed to provide answers to a number of questions. How doe molecular mass affect the initial viscosity and non-Newtonian flow behavior (anomalous viscosity) of polymer? How can one compare the flow properties of polymers with the different structures of the macromolecular chain, considering that at one and the same molecular mass the chain length and flexibility may strongly differ for polymers of different nature? How does the molecular mass distribution affect the dependence of the Newtonian (initial) viscosity on molecular mass and how does the non-Newtonian flow behavior change? In evaluating the effect of molecular-mass distribution (MMD) on the flow properties of polymers there also arises the most important question: What characteristics of MMD and what values of molecular mass of polydisperse polymers about be used to compare the flow properties of various polymer?

…to be continued