Stiff chain macromolecules

Four types of macromolecules of largely different Kuhn length are listed at the top of Fig. 1.50. Below this list, the repeating units which lead to molecules of different stiffness are drawn. The repeating units I and II can be found in most of the flexible molecules. Their inclusion in a polymer backbone introduces the angle in the structure which, together with a rather unhindered rotation about the connecting 

In this last section of Chap. 1, experimental methods are discussed to obtain data for the characterization of macromolecular sizes and shapes. The scattering of light is selected as the major method. It provides three pieces of information, the molecular size, shape, and the interaction parameters of the macromolecule with solvents [17,18]. The scattering of light is thus a versatile technique. Furthermore, its theory describes also the scattering of other electromagnetic radiation, as is summarized in Fig. 1.51, and even the scattering of neutrons and electrons, as described in Fig. 1.72, 

A colligative property depends on the number of molecules, not on their nature. The main examples of colligative properties are the pressure of an ideal gas (pV = nRT), the depression of the freezing point of a solvent in the presence of a solute, the elevation of the boiling point by a solute and also the osmotic pressure. The latter three are used for Mn determination. 

In all cases the properties are truely colligative only at the limit of infinite dilution, so that there is no effect of the substance-specific interaction contributing to the property. 

Taking the gas as an example, one can describe its non-ideal properties by the van der Waals equation  

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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. 

This article deals with some topics of the statistical physics of liquid-crystalline phase in the solutions of stiff chain macromolecules. These topics include the problem of the phase diagram for the liquid-crystalline transition in die solutions of completely stiff macromolecules (rigid rods) conditions of formation of the liquid-crystalline phase in the solutions ofsemiflexible macromolecules possibility of the intramolecular liquid-crystalline ordering in semiflexible macromolecules structure of intramolecular liquid crystals and dependence of die properties of the liquid-crystalline phase on the microstructure of the polymer chain. 

It is well-known that the tendency to form a liquid-crystalline phase is most pronounced for those substances which molecules have an elongated shape. Stiff-chain macromolecules are obviously good examples of this kind. Their asymmetry can be so large that they can form liquid-crystalline phase not only in the bulk but also in the solution. In the latter case, liquid crystals are called polymeric lyotropic liquid crystals. It is the theory of this type of liquid crystals that will be considered in the present paper. 

Some examples of stiff-chain polymers able to form a liquid-crystalline phase in the solution are listed in Table l1. The ratio of the statistical segment length1 of a polymer chain, 1, to its width, d, (last column of Table 1) measures the degree of chain stiffness. For flexible macromolecules fid 1 stiff-chain macromolecules are those for which fid t> 1. 

Olga E. Philippova s main research interests are polyelearolyte and ionomer behavior of polymer gels, linear and cross-linked polyelectrolytes with associating hydrophobic groups, polymer gel/surfactant interactions, interpolymer complexes, and polymer gels with entrapp l linear stiff-chain macromolecules. 

In light of the above, we will utilize only four families of p>olymers (polymethacrylates, polyolefins, polydienes, and stiff chain macromolecules) for trying to illustrate empirical trends. These polymers are chosen because they provide a broad spectrum of structures that have been carefully studied. No attempt is made to provide a comprehensive listing the Polymer Handbook [87] serves this function. 

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...

Expansion of plastics into new and replacement markets promises a high rate of growth. Twenty five years ago suitable applications had to be found for the synthetic polymers manufactured at that time. Today s inventors visualize the need for certain materials. They prepare these materials and develop a feasible manufacturing process since macromolecules can be designed for a specific end use. Synthetic polymers can be made with flexible or stiff chains and tailored in length. 

Bohdanecky, M., New method for estimating the parameters of the wormhke chain model from the intrinsic viscosity of stiff-chain polymers, Macromolecules, 16, 1483-1492 (1983). 

Sato, T., Takada, Y, and Teramoto, A., Dynamics of stiff-chain polymers in isotropic solution, flexibility effect. Macromolecules, 24, 6220-6226 (1991). 

Hofmann, D., Enhialgo-Castano, M., Lebret, A., Heuchel, M., and Yampolsldi, Y., Molecular modeling investigation of free volume distributions in stiff chain polymers with conventional and ultrahigh free volume comparison between molecular modeling and positron lifetime studies. Macromolecules, 36, 8528-8538 (2003). 

G. Brodowski, A. Horvath, M. Ballauff, M. Rehahn, Synthesis and intrinsic viscosity in salt free solution of a stiff chain cationic poly(p-phenylene) polyelectrolyte, Macromolecules 1996, 29, 6962. 

Shibaev PV, Tang K, Genack AZ, Kopp V, Green MM (2002) Lasing from a stiff chain polymeric lyotropic cholesteric liquid crystal. Macromolecules 35 3022-3025... 

Hofmaim, D., et al.. Molecular Modeling Investigation of Free Volume Distributions in Stiff Chain Polymers with Conventional and Ultrahigh Free Volume Comparison Between Molecular Modeling and Positron Lifetime Studies. Macromolecules, 2003, 36(22), 8528-8538. 

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