Linear macromolecules, comparison

The somewhat spherical shape of dendimers gives them some different properties in comparison to more linear macromolecules. On a macroscopic level, dendimers act as ball bearings rather than strings. In solution, viscosity increases as molecular weight increases for linear polymers. With dendrimers, viscosity also increases with molecular weight up to a point after which viscosity decreases as molecular weight continues to increase. 

In 1996, Hawker and Frechet83 discussed a comparison between linear hyperbranched and dendritic macromolecules (Fig. 5.17) obtained with the same monomeric structure, 3,5-dihydroxybenzoic. The thermal properties (glass transition and thermal decomposition) were not affected by the architecture. 

The concept of the similarity of molecules has important ramifications for physical, chemical, and biological systems. Grunwald (7) has recently pointed out the constraints of molecular similarity on linear free energy relations and observed that Their accuracy depends upon the quality of the molecular similarity. The use of quantitative structure-activity relationships (2-6) is based on the assumption that similar molecules have similar properties. Herein we present a general and rigorous definition of molecular structural similarity. Previous research in this field has usually been concerned with sequence comparisons of macromolecules, primarily proteins and nucleic acids (7-9). In addition, there have appeared a number of ad hoc definitions of molecular similarity (10-15), many of which are subsumed in the present work. Difficulties associated with attempting to obtain precise numerical indices for qualitative molecular structural concepts have already been extensively discussed in the literature and will not be reviewed here. 

FIGURE 16.3 Dependences of the polymer retention volume on the logarithm of its molar mass M or hydrodynamic volume log M [T ] (Section 16.2.2). (a) Idealized dependence with a long linear part in absence of enthalpic interactions. Vq is the interstitial volume in the column packed with porous particles, is the total volume of liquid in the column and is the excluded molar mass, (b) log M vs. dependences for the polymer HPLC systems, in which the enthalpic interaction between macromolecules and column packing exceed entropic (exclusion) effects (1-3). Fully retained polymer molar masses are marked with an empty circle. For comparison, the ideal SEC dependence (Figure 16.3a) is shown (4). (c) log M vs. dependences for the polymer HPLC systems, in which the enthalpic interactions are present but the exclusion effects dominate (1), or in which the full (2) or partial (3,4) compensation of enthalpy and entropy appears. For comparison, the ideal SEC dependence (Figure 16.3a) is shown (5). (d) log M vs. dependences for the polymer HPLC systems, in which the enthalpic interactions affect the exclusion based courses. This leads to the enthalpy assisted SEC behavior especially in the vicinity of For comparison, the ideal SEC dependence (Eigure 16.3a) is shown (4). 

Pluen, A., Netti, P. A., Jain, R.K. and Berk, D.A.(1999) Diffusion of macromolecules in agarose gels comparison of linear and globular configurations. Biophys. J., 77, 542-552. 

One can see that the investigated equations of dynamics even in linear approximation describe anomalous diffusion of the mass centre of macromolecule moving amongst the other macromolecules. The displacement of every particle of the chain is also anomalous in comparison with case of a macromolecule in a viscous liquid. Now we shall consider, following work by Kokorin and Pokrovskii (1990, 1993), the displacement of each internal particle of the chain... 

Comparison with experimental data demonstrates that the bead-spring model allows one to describe correctly linear viscoelastic behaviour of dilute polymer solutions in wide range of frequencies (see Section 6.2.2), if the effects of excluded volume, hydrodynamic interaction, and internal viscosity are taken into account. The validity of the theory for non-linear region is restricted by the terms of the second power with respect to velocity gradient for non-steady-state flow and by the terms of the third order for steady-state flow due to approximations taken in Chapter 2, when relaxation modes of macromolecule were being determined. 

I used the opportunity of this edition to correct some minor mistakes and clarify, wherever it possible, exposition of the theory in comparison with the previous edition of this book (Kluwer, Dordrecht et cet, 2000). It provokes enlargement of the book, though I tried to present the modern theory of thermic motion of long macromolecules in compact form. I have tried to accumulate the common heritage and to take into account different approaches in the theory of dynamics of linear polymers, at least, to understand and make clear the importance of various ideas for explanation of relaxation phenomena in linear polymers, to present recent development in the field. 

Figure 13.22 Damping functions hf y) and hs y) for the fast and slow relaxation processes of a 15 wt% solution of a micelle-forming polystyrene-polyisoprene diblock copolymer (molecular weights, respectively, of 14,000 and 29,000) in a low-molecular-weight (A/ = 4,000) polyisoprene. Damping functions for linear and star polymers and for silica dispersion are shown for comparison. (From Watanabe et al. 1997, with permission from Macromolecules 30 5905. Copyright 1997, American Chemical Society.)...

Figure 5-8. Molecular weight trends in the glass transition temperature trends in cyclic and linear oligomers of poly(dimethyl siloxane), and the comparison of these data with the prediction of the Gibbs-DiMarzio theory. [Reprinted with permission from E. A. DiMarizio and C. M. Guttman, Macromolecules, 20, 1403 (1987). Copyright 1987, American Chemical Society]...

Spherical micelles with a polybutadiene core were formed for a certain range of compositions of the mixed solvent. The equilibrium between micelles and nonas-sociated macromolecules was found to be consistent with a closed association mechanism. In comparison with a linear triblock copolymer, the star-block sample showed a lower aggregation number. 

A MINDO/3 method has been used to calculate the electronic structure of polyethylene,127 and comparison has been made with the photoelectron spectrum. Extended Huckel calculations on six fluorinated compounds derived from linear polyethylene have been carried out with the same objective.128 The circular dichroism of unordered polymers has been treated on the basis of time-dependent Hartree theory,129 130 131 and high-resolution inelastic tunnelling spectroscopy of macromolecules has been reported.180... 

A method which allows testing NMR data such as dipolar couplings, anisotropic chemical shieldings and quadrupolar interactions has been proposed by Zidek et aV The authors have used the fact that only a limited number of frequencies corresponding to these parameters can be measured indepedently in a rigid fragment of the macromolecule. Additional values can be predicted as linear combinations of a set of independent frequencies. Comparison of the experimental data with the predicted values of the parameters studied provides a test of the reliability of the former. 

Graessley, W. W., and Struglinski, M. 1986. Effects of polydispersity on the linear viscoelastic properties of entangled polymers. 2. Comparison of viscosity and recoverable compliance with tube model predictions. Macromolecules, 19(6) 1754-1760. 

Rlur, K., Winkler, R. G., and Yoon, D. Y, 2006. Comparison of ring and linear polyethylene from molecular dynamics simulations. Macromolecules, 39 3975-3977. 

Kawaguchi, D., Masuoka, K., Takano, A., Tanaka, K., Nagamura, T., Torikai, N., et al. Comparison of interdiffusion behavior between cyclic and linear polystyrenes with high molecular weights. Macromolecules 39, 5180-5182 (2006)... 

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