Chemical reaction polymer thermodynamics

Like all other chemical reactions, polymer syntheses may be subdivided into two categories, namely into kinetically controlled (KC) polymerizations and thermodynamically controlled (TC) polymerizations. KC polymerizations are characterized by irreversible reaction steps, equilibration reactions are absent, and the reaction products may be thermodynamically stable or not. TC polymerizations involve rapid equilibration reactions, above all formation of cyclics by back-biting of a reactive chain end (see Formula 5.1), and the reaction products represent the thermodynamic optimum at any stage of the polymerization process. Borderline cases also exist, which means that a rapid KC polymerization is followed by slow equilibration. This combination is typical for many Ring-opening polymerizations (ROPs). 

Tethering may be a reversible or an irreversible process. Irreversible grafting is typically accomplished by chemical bonding. The number of grafted chains is controlled by the number of grafting sites and their functionality, and then ultimately by the extent of the chemical reaction. The reaction kinetics may reflect the potential barrier confronting reactive chains which try to penetrate the tethered layer. Reversible grafting is accomplished via the self-assembly of polymeric surfactants and end-functionalized polymers [59]. In this case, the surface density and all other characteristic dimensions of the structure are controlled by thermodynamic equilibrium, albeit with possible kinetic effects. In this instance, the equilibrium condition involves the penalties due to the deformation of tethered chains. 

The production of fine particles that are either desirable (polymer colloids, ceramic precursors, etc.) or undesirable (soot, condensed matter from stack gases, etc.) involves chemical reactions, transport processes, thermodynamics, and physical processes of concern to the chemical engineer. The optimization and control of such processes and the assurance of the quality of the product requires an understanding of the fundamentals of microparticles. 

The basic theories of physics - classical mechanics and electromagnetism, relativity theory, quantum mechanics, statistical mechanics, quantum electrodynamics - support the theoretical apparatus which is used in molecular sciences. Quantum mechanics plays a particular role in theoretical chemistry, providing the basis for the valence theories which allow to interpret the structure of molecules and for the spectroscopic models employed in the determination of structural information from spectral patterns. Indeed, Quantum Chemistry often appears synonymous with Theoretical Chemistry it will, therefore, constitute a major part of this book series. However, the scope of the series will also include other areas of theoretical chemistry, such as mathematical chemistry (which involves the use of algebra and topology in the analysis of molecular structures and reactions) molecular mechanics, molecular dynamics and chemical thermodynamics, which play an important role in rationalizing the geometric and electronic structures of molecular assemblies and polymers, clusters and crystals surface, interface, solvent and solid-state effects excited-state dynamics, reactive collisions, and chemical reactions. 

As a result of the experimental woik simmarized in this review the value of the gas chromatographic method for studying polymers seems to be well established. Surface and bulk properties of polymers can be measured both from a thermodynamic and kinetic point of view. Because of its simplicity and precision it should become the method of choice for the study of thermoch namic interactions of small molecule probes or solutes in systems where the prfymer is flie m or phase. Further advances in the kinetic theory of the GC process (wld provide even more reliable data about time dependent processes such as diffu on, adsorption, complex fcwmar-tion and possibly even chemical reaction. 

When a polymerization is accompanied by phase transition, the overall thermodynamic parameters are the sum of parameters of the chemical reaction and phase transition (cf. p. 11). Thus, for instance, thermodynamics of polymerization in the crystalline state from a liquid monomer will be given by the thermodynamics of formation of the amorphous (condensed) polymer and polymer crystallization, provided, that polymerization proceeds in the solid state with monomer packing in the crystalline state simultaneously with propagation. 

In the real system, in which the dissolved or liquid (molten) TXN is directly converted into crystalline polymer, the over-all thermodynamic parameters are equal to the sum of AH and AS of the chemical reaction and the phase transition (cf. Chap. 2). It should be remembered, however, that polymerization and crystallization can be separated only formally. 

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