Milner Linear viscoelasticity

It is not clear why this transition should occur at such a higher level of arm entanglement for polystyrene stars than for other star polymers. This observation is in direct conflict with the standard assumption that through a proper scaling of plateau modulus (Go) and monomeric friction coefficient (0 that rheological behavior should be dependent only on molecular topology and be independent of molecular chemical structure. This standard assumption was demonstrated to hold fairly well for the linear viscoelastic response of well-entangled monodisperse linear polyisoprene, polybutadiene, and polystyrene melts by McLeish and Milner [24]. 

Figure 38 Master curves of elastic storage (S, ) and viscous loss (S", o) linear viscoelastic moduli of the 12-arm 12 828 (a) and 64-am 6430 (b) star-PBd polymers in the temperature range from 150 up to -103°C, with reference temperature-83 °C. Solid arrows represent the various transitions and corresponding crossover frequencies (cos. glass to Rouse-like transition cof.. transition to rubber plateau

Comparison of Milner-McLeish Theory to Linear Viscoelastic Data 9.3.3.1 Monodisperse Stars... 

Figure 9 Linear viscoelastic behavior of monodisperse linear PS at 180 °C. The numbers indicate 10 M Data taken from Milner, S. T. McLeish, T. C. B. Phys. Rev. Lett. 1998, 81,725 and Schausberger, A, Schindlauer, G. Janeschitz-Kriegl, H. Rheol. Ada 1985,24,220 ° with permission.

The current version of the tube model combines all the above mechanisms to describe the linear viscoelastic data of linear and star-branched chains. For example, the Milner-McLeish (MM) model, " adopting the DTD molecular picture for the CR mechanism, considerably well describes the data, as shown with the solid curves in Figures 9 and 10. Equally good description can be obtained for some other models combining those mechanisms in a way different from that in the MM modd. - - ... 

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