Star polymers static properties

Much experimental work has appeared in the literature concerning the microphase separation of miktoarm star polymers. The issue of interest is the influence of the branched architectures on the microdomain morphology and on the static and dynamic characteristics of the order-disorder transition, the ultimate goal being the understanding of the structure-properties relation for these complex materials in order to design polymers for special applications. 

The applications described in this chapter have been selected to illustrate the power of the solvent-effects approach to biochemical and physicochemical problems. The techniques are being now used in other fields. Thus, molecular dynamics simulations are being used to study solvent effects on static and dynamic properties of linear and star polymer [97, 98]. A generalized Langevin equation has been used to represent solvent around a polymer with stochastic forces the solution of this equation agrees well with corresponding MD simulations [99]. 

Poly(N,N-dimethylacrylamide) (PDMA) star polymers with 2, 3, and 4 arms and with dodecyl chains as hydrophobic end-caps were obtained in high yield with narrow polydis-persities by means of the RAFT technique. At sufficiently high concentration they form interconnected hydrophobic domains, i.e., a transient network. SANS experiments show that these hydrophobic domains contain about 20 dodecyl chains and they interact repulsively due to the PDMA chains that separate them. While the static structure is only very little affected by the number of arms this applies not at all to the dynamic properties as observed by DLS and rheology. Here one observes in DLS a complex, trimodal relaxation process, where the slower modes become more pronounced with increasing munber of arms. The fast mode corresponds to the diffusion of the hydrophobic domains while the second mode shows no q-dependence and corresponds in its values to the time deduced from the cross-over of G and G" in the oscillatory rheological experiments. Finally the slowest motion shows a rather pronounced q-dependence and is pre-stunably linked to a more complex relaxation mechanism of... 

Simulations, both MC and MD, have been used to test these scaling predictions and to determine other properties of a star polymer, including the static structure factor in the dilute limit. At present, it is not possible to simulate a melt or even a semi-dilute solution of many-arm star polymers due to the long relaxation times. For few-arm stars f 12) MC methods are clearly most efficient, while for large number of arms, MD methods work very well. For small /, the density of monomers of the star is low almost everywhere and static MC methods in which one generates the chains by constructing walks can be Using this method,... 

Concurrent to the development of theoretical models to describe planar and curved polymer bmsh systems a wide range of experimental techniques (such as neutron scattering, evanescent static and dynamic light scattering or fluorescence, and rheological techniques) were applied to elucidate the effect of bmsh architecture on the stmcture and dynamic properties of polymer bmsh systems. Similar to the development of theoretical models, early experimental studies were focused on planar polymer bmsh architectures as well as on star polymer and block copolymer micellar systems. Only recently, experimental studies were extended to particle bmsh systems. 

This review deals with the static and dynamic properties of regular star polymers at zero concentration and with the dependence of these properties on the polymer concentration in dilute solution. We stress the experimental results and make comparisons with theoretical models and computer simulations. 

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. 

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