Macromolecules stiff

The wide variety of ketomethylene and amino ketone monomers that could be synthesized, and the abiUty of the quinoline-forming reaction to generate high molar mass polymers under relatively mild conditions, allow the synthesis of a series of polyquinolines with a wide stmctural variety. Thus polyquinolines with a range of chain stiffness from a semirigid chain to rod-like macromolecules have been synthesized. Polyquinolines are most often prepared by solution polymerization of bis(i9-amino aryl ketone) and bis (ketomethylene) monomers, where R = H or C H, in y -cresol with di-y -cresyl phosphate at 135—140°C for a period of 24—48 h (92). 

The main chain of dendronized polymers, due to die large size of the mon-odendrons, is usually forced to take a stretched shape thus the whole molecule exists as a rigid rod architecture both in solution and in the solid state.32d Depending on the backbone stiffness, the degree of monodendron coverage, and the size of die monodendron, the architecture of these macromolecules is no longer a sphere but a cylinder this dictates die properties of the dendronized polymers. 

Pectins are longchain macromolecules. In aqueous solutions they form more or less stiff rods or coils, depending on their degree of branching and linking as well as their molecular weight. In addition interparticular or intermolecular physical-chemical interactions like Van-der-Waals forces, ionic interactions or hydrogen bonds influence the active volume of the molecule, the stiffness and the viscosity. 

Fig.1. Regular star macromolecules with/=3,4, and 8 arms of identical length. The arms or rays can consist of rather stiff chains, but are in most cases flexible chains. The global structure is determined by the overall shape of the whole macromolecule the internal structure is indicated by a domain that is much smaller than the overall dimension but still larger than a few Kuhn segments...

This conjecture was found to hold for flexible chains, stiff worm-like chains, star macromolecules, and hard spheres [156]. A few results are shown in Fig. 32. 

Macromolecules with polar and stiff main chains (e.g., cellulose, polyara-mides) are often only soluble via complexation. 

The stiffness of the main chain of a polymer is of great importance for the solution viscosity the stiffer the chain is, the higher is the viscosity for polymers with the same molecular weight (see Sect. 2.3.3.3.1 for the dependency of K and a in the viscosity equation on the shape of macromolecules in solution). 

The chemical nature of the rubber determines which bonds are the weakest and are therefore more likely to be ruptured during mastication by the statistical concentration of mechanical energy about such bonds. An increase in the degree of asymmetry, an increase in the stiffness and the packing density of macromolecules facilitate mechanical scission resonance stability will influence the... 

A theoretical approach is applied to elucidate the molecular conformations, associated flexibility, and dynamics of polylp-hydroxybenzoic acid) esters, pHB. Properties such as the radius of gyration and persistence length which are characteristic for the stiffness of a macromolecule are calculated on the basis of two different theoretical methods (a) Molecular dynamics and (b) the RIS model augmented by the more recent scheme for the matrix computations. The analysis of the results obtained by the latter method reflects a strong dependence on the choice of the structural parameters of the system. 

The concept of a unique hydrodynamic volume for all rodlike polymers was derived from examination of the Mark-Houwink constants, K and a, of the equation [rj ] = KMa. Macromolecules with values of a greater than unity are commonly accepted to be stiff or rigid rods. However, it was also found that such molecules (even for values of a less than unity) obey a relation illustrated by close concordance with the curve in Fig. lb (13) flexible, branched or otherwise irregular polymers, on the other hand, show dispersion around the upper part of the curve. The straight line curve in Fig. lb implies that the constants K and a are not independent parameters for the regular macromolecules to which they apply. Poly (a- and polyQJ-phenylethyl isocyanide) fall on this line the former has a value of a > 1 while the latter has a value a < 1 (14) both polymers give linear concentration dependence of reduced specific viscosity for fractionated samples... 

It is important for the molecular design of a superior barrier materials to take into account the balance and distribution of hydrophilic and hydrophobic microdomains as well as the stiffness and flexibility of a macromolecule, in order to place the subject on the fundamental understanding of the interactions among solvents, solutes, and macromolecules. 

The molecular characterization of polyelectrolytes in general, and of DADMAC polymers in particular is complicated for several reasons. First, in aqueous solution the individual properties of the macromolecules are dominated by Coulom-bic interactions. Therefore, the resulting polyelectrolyte effects have to be suppressed through the addition of low molecular electrolyte, such as NaCl. The increase of the ionic strength results in a decrease of the chain stiffness of the polyelectrolyte molecules (see Sect. 5). The chains then revert to the coil dimensions of neutral macromolecules in dilute solutions. However, problems may still arise, particularly since the mode of action of these effects is quite different in various characterization methods [27]. 

Ha, B. Y., and Thirumalai, D. (2003). Bending rigidity of stiff polyelectrolyte chains A single chain and a bundle of multichains. Macromolecules 36, 9658—9666. 

D. W. Mead and R. G. Larson, Rheooptical study of isotropic solutions of stiff polymers, Macromolecules, 23,2524 (1990). 

For a solution of stiff-chain macromolecules (for example, PBLG), with p 3 x 103 Debye [153], the corresponding estimation shifts to Eq > 4 kV/cm but still remains within the experimentally feasible range. 

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