Star-shaped polymers dynamics

The paper is organized in the following way In Section 2, the principles of quasi-elastic neutron scattering are introduced, and the method of NSE is shortly outlined. Section 3 deals with the polymer dynamics in dense environments, addressing in particular the influence and origin of entanglements. In Section 4, polymer networks are treated. Section 5 reports on the dynamics of linear homo- and block copolymers, of cyclic and star-shaped polymers in dilute and semi-dilute solutions, respectively. Finally, Section 6 summarizes the conclusions and gives an outlook. 

Fig. 47a, b. Structure and dynamics of star-shaped polymers with different functionalities, a Kratky plot of the static structure factor (S(Q, 0) Q2 vs. Q Rg. b Q(Q)/Q3 vs. Q Rg, as derived from Eqs (94) and (123), assuming Rouse dynamics... 

A star-shaped polymer chain (Fig. 4d) is a structure consisting of three or more linear arms connected to a central core. Star polymers more closely resemble a hard sphere with more compacted stmcture, higher degrees of segmental density and dynamic entanglement, compared to their linear counterparts of the same molecular weight [95]. 

The contour length fluctuation plays an essential role in the dynamics of branched polymers. Consider for example the star-shaped polymer shown in Fig. 6.11. Obviously simple reptation is not possible, but the polymer can change its conformation by utilizing the contour length fluctuation. 

As discussed in Section 6.4.5, reptation is severely suppressed if the polymer has long branches. Indeed it has been observed that the dynamical properties of branched polymers are quite distinct from those of linear polymers. So far studies have been done for branched polymers of the simplest type, the star-shaped polymer in which / chains are connected to a centre. The observed phenomena are ... 

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. 

Microtubules are hollow cylinders about 23 nm in diameter, most commonly comprising 13 protofilaments, which in turn are polymers of a- and /3-tubulin. They have a very dynamic behaviour, binding GTP for polymerisation. They are commonly organised by the centrosome. In nine triplet sets (star-shaped), they form the centrioles, and in nine doublets oriented about two additional microtubules (wheel-shaped) they form cilia and flagella. The latter formation is commonly referred to as a 9-1-2 arrangement, wherein each doublet is connected to another by the protein dynein. Microtubules play key roles in ... 

M. Bishop and J. H. R. Clarke, /. Chem. Phys., 90, 6647 (1989). Brownian Dynamics Study of the Shape of Star and Linear Polymers in Different Regimes. 

Computer studies (both Monte Carlo and molecular dynamic simulations) have become a very powerful tool for studying the conformational and dynamic behavior of polymer chains. They can be used for testing the predictions of theoretical models concerning the equilibrium properties and moreover they provide information on dynamic characteristics, e.g., on instantaneous fluctuations of chain shapes which is important because most experimental techniques (e.g., scattering techniques) yield the ensemble-average characteristics only. Large numbers of studies have been performed on neutral chains— not only on linear ones but also on stars, combs, etc. [78-85]. The most important advances in understanding the behavior of polyelectrolytes have been made mainly thanks to computer studies. As aheady mentioned, quenched PEs have been studied both by Monte Carlo [86-89] and by molecular dynamics simulations [59, 63, 71, 73, 87, 90]. Simulation of annealed... 

Jabbarzadeh, A., Atkinson, ID. and Tanner, R.I. (2003) Effect of molecular shape on rheological properties in molecular dynamics simulation of star, H, comb, and linear polymer melts. Macromolecules. 36(13) pp. 5020-5031. 

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