Rheology application entanglement

Taking into account the relevance of the range of semi-dilute solutions (in which intermolecular interactions and entanglements are of increasing importance) for industrial applications, a more detailed picture of the interrelationships between the solution structure and the rheological properties of these solutions was needed. The nature of entanglements at concentrations above the critical value c leads to the viscoelastic properties observable in shear flow experiments. The viscous part of the flow behaviour of a polymer in solution is usually represented by the zero-shear viscosity, rj0, which depends on the con-... 

As we conjectured in the introduction, the fundamental role of topology in this approach to entangled polymer dynamics would indicate that changes to the topology of the molecules themselves would radically affect the dynamic response of the melts. In fact rheological data on monodisperse star-branched polymers, in which a number of anionically-polymerised arms are coupled by a multifunctional core molecule, pre-dated the first application of tube theory in the presence of branching [22]. Just the addition of one branch point per molecule has a remarkable effect, as may be seen by comparing the dissipative moduli of comparable linear and star polymer melts in Fig. 5. 

The purpose of our study was a rheological evaluation of the effect of composition on the properties of ABS resins in the molten state. Steady-state viscosity was determined over a wide range of temperatures and shear rates. The shear modulus in the molten state was determined by measurement of the diameter of the extrudate. ABS resins in the molten state behaved as an amorphous homophase polymer. The effect of the elastomer phase on the viscoelastic properties which characterize the behavior of the continuous matrix, i.e. monomer friction coefficient and molecular weight between entanglements (Me), was calculated by the application of the molecular theories. The significance of these properties in heterophase systems is discussed. 

While Eq. (2.33) is valid for monodispersedathermal polymers, in reality polymers are polydispersed and do interact with each other. Consequently, application of the model to a real system requires that the influence of individual molecular weight fractions on the rheological functions is taken into account. For example, in the simplest case of the zero-shear viscosity-composition dependence for entangled systems [194, 195] the prediction is ... 

Polystyrene is an important commercial thermoplastic that has been described by Priddy [121]. Its entanglement molecular weight is aroimd 18,000 and for both structure-rheology studies and commercial applications, molecular weights much higher than this are of primary interest. Nearly all commercial polystyrene is atactic and is thus a transparent glass at temperatures below its Tg, which is 100 °C. New catalyst systems are able to produce isotactic and syndiotactic versions, but these have not found practical applications to date due to their brittleness. 

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