Star polymers hydrodynamic properties

Homopolymerization of macromonomer provides regular star- or comb-shaped polymers with a very high branch density as shown in Fig. 1 a,c,e. Such polymacromonomers, therefore, are considered to be one of the best models for understanding of branched architecture-property relationships. Their properties are expected to be very different from the corresponding linear polymers of the same MW both in solution and the bulk state. Indeed, during the past decade, remarkable progress has been accomplished in the field of static, dynamic, and hydrodynamic properties of the polymacromonomers in dilute and concentrated solutions, as well as by direct observation of the polymers in bulk. 

The exploration of new polymer architectures has been the focus of significant recent research, motivated by the fundamental hypothesis that a polymer s properties are intimately related to its structure. This concept has led to the development and optimization of synthetic techniques for the preparation of graft, star, dendritic, ladder, and hyperbranched polymers as well as a variety of hybrid and more complex architectures. Cyclic polymers are of particular interest because their circular shape and lack of end groups has a profound effect on their physical properties such as intrinsic viscosity and hydrodynamic volumes (/). 

We have dealt with the long-time hydrodynamic properties of star polymers in dilute solution in Sections III. A and III.B. The intrinsic viscosity is the sum of products of moduli and relaxation times. In term of frequency (time" )... 

It has been clearly shown that the hydrodynamic properties of star polymers cannot be compared with those of linear polymers within the Kirkwood-Riseman model with preaveraged hydrodynamic interactions. In order to match calculated with experimental results, non-preaveraging of hydrodynamic interactions becomes increasingly more important as /increases. It is interesting to note that non-preaveraging increases but decreases from the calculated preaveraged values. 

The viscoelastic properties of solutions of linear and 4-armed star polybutadienes were studied by Osaki and co-workers (117), who compared the storage and loss shear moduli extrapolated to zero concentration with theoretical values. The results for the branched polymer could be accounted for well in terms of the Zimm and Kilb theory (34) a lower value of the hydrodynamic interaction parameter was indicated for the branched polymer than for the linear one, which may be associated with the higher density of polymer segments in the former. 

For the restricted case of low molecular weights and no coupling entanglements, the viscoelastic properties of star-branched undiluted polymers can be described by a special case of the Zimm-Kilb theory o in which there is no hydrodynamic interaction. Calculations were made by Ham i by use of a method which is somewhat different from that of Rouse but yields the same results for unbranched molecules. Stars with arms of unequal length were included. For such a branched molecule, the terminal relaxation time ti, the viscosity r/o, and the steady-state compliance are always smaller than for an unbranched molecule of the same molecular weight the more branches and the more nearly equal their lengths, the... 

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