High polymer

Practically all of the book so far has dealt with the properties of aggregations of simple molecules, that is, of molecules that consist of, at most, a few atoms or ions. From the point of view of their interactions, these simple molecules can be treated more or less as Newtonian particles. There are, however, many molecules that consist of a large number of component atoms or ions and consequently show some rather different properties from the simple solids and liquids. Some properties of two types of molecule, high polymers and liquid crystals, will be examined briefly in this chapter. 

High polymers are long-chain molecules with relative molecular masses of from thousands to many millions. The polymer molecule may consist of a single chain (known as a linear polymer), it may have secondary chains branching from the main molecular chain (a branched polymer) or the polymer chains may be bonded together at various points by covalent bonds (a cross-linked polymer). 

A polymer molecule is composed of a large number of repeating units (each of which is known as a mer) supplied by a molecule known as a monomer in a process called polymerisation. The bonds between adjacent mers are strong covalent bonds but, in the absence of cross-linking, the chains themselves only interact through weak van der Waals forces. 

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However, for more complex fluids such as high-polymer solutions and concentrated ionic solutions, where the range of intemiolecular forces is much longer than that for simple fluids and Nq is much smaller, mean-field behaviour is observed much closer to the critical point. Thus the crossover is sharper, and it can also be nonmonotonic. 

The way in which these factors operate to produce Type III isotherms is best appreciated by reference to actual examples. Perhaps the most straightforward case is given by organic high polymers (e.g. polytetra-fluoroethylene, polyethylene, polymethylmethacrylate or polyacrylonitrile) which give rise to well defined Type III isotherms with water or with alkanes, in consequence of the weak dispersion interactions (Fig. S.2). In some cases the isotherms have been measured at several temperatures so that (f could be calculated in Fig. 5.2(c) the value is initially somewhat below the molar enthalpy of condensation and rises to qi as adsorption proceeds. In Fig. 5.2(d) the higher initial values of q" are ascribed to surface heterogeneity. 

Structures [VIII] and [IX] are not equivalent they would not superimpose if the extended chains were overlaid. The difference has to do with the stereochemical configuration at the asymmetric carbon atom. Note that the asymmetry is more accurately described as pseudoasymmetry, since two sections of chain are bonded to these centers. Except near chain ends, which we ignore for high polymers, these chains provide local symmetry in the neighborhood of the carbon under consideration. The designations D and L or R and S are used to distinguish these structures, even though true asymmetry is absent. 

Alfrey, T., Jr., Mechanical Behavior of High Polymers, Interscience, New York, 1948. 

In the nondraining limit of Eq. (9.47), the coils are unperturbed in both senses of the word nondraining and 0 conditions. To emphasize the latter we attach the subscript 0 to [r ] when these conditions are met. Thus for high polymers under 0 conditions... 

Solution polyacrylamides can also be prepared at high polymer soHds by radiation processes (80,81). Polyacrylamides with molecular weights up to 20 million can be prepared by inradiation of acrylamide and comonomers in a polyethylene bag with cobalt-60 gamma radiation at dose rates of 120-200 J/kg-h. The total dose of radiation is controlled to avoid cross-linking. 

K. Stueben, ia E. C. Leonard, ed.. Vinyl and Diene Monomers, Part I, High Polymers Series Vol. XXIV, Wiley-Interscience, New York, 1970, Chapt. l,p. 181. 

L. Segal, in N. M. Bikales and L. Segal, eds.. Cellulose and Cellulose Derivatives, High Polymers Series, Vol. V, Wiley-Interscience, New York, 1971,... 

The direction of nucleophilic ring opening of unsymmetrical perfluoroepoxides has been shown to be a function of the nature of the nucleophile and the solvent (23,28). Although many oligomeric products have been prepared by this procedure and variations of it, no truly high polymers have been obtained... 

AppHcations of soHd-state nmr include measuring degrees of crystallinity, estimates of domain sizes and compatibiHty in mixed systems from relaxation time studies in the rotating frame, preferred orientation in Hquid crystalline domains, as weU as the opportunity to characterize samples for which suitable solvents are not available. This method is a primary tool in the study of high polymers, zeoHtes (see Molecular sieves), and other insoluble materials. 

The first attempt to formulate a systematic nomenclature for polymers was based on the smallest repeating stmctural unit it was pubHshed in 1952 by a Subcommission on Nomenclature of the lUPAC Commission on Macromolecules (95). The report covered not only the naming of polymers, but also symbology and definitions of terms. However, these nomenclature recommendations did not receive widespread acceptance. Further progress was slow, with a report on steric regularity in high polymers pubHshed in 1962 and updated in 1966 (96). 

H. Mark and G. S. Whiby, eds.. Collected Papers of Wallace Hume Carothers on High Polymeric Substances, High Polymers, Vol. I, Interscience Pubhshers, New York, 1940. 

D. B. Jacobs and J. Zimmerman, in C. E. Schildknecht and I. Skeist, eds.. Polymerisation Processes, High Polymers, Vol. XXIX. Wiley-Interscience, New York, 1977, pp. 424, 467. A very detailed review of nylon-6,6 polymerization. 

The single-monomer route (eq. 5) is preferred as it proves to give more linear and para-linked repeat unit stmctures than the two-monomer route. Other sulfone-based polymers can be similarly produced from sulfonyl haUdes with aromatic hydrocarbons. The key step in these polymerisations is the formation of the carbon—sulfur bond. High polymers are achievable via this synthesis route although the resulting polymers are not always completely linear. 

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