Radical polymerization basic principles

Working in emulsion is essentially limited to radical polymerization in water. Similar to suspension polymerization, the basic principle is to disperse a sparingly water-soluble monomer in water and bring about polymerization in this state. There are, however, some essential differences between the two procedures ... 

Much attention has been focused on free-radical polymerization in the presence of transfer agents such processes yield -functional precursors that can in turn be reacted with unsaturated compounds carrying an antagonist function. This is the basic principle of what was referred to as a two-step macromonomer synthesis. 

We have left this subject to the end of the chapter because it uses all of the principles we have established earlier on. It requires an understanding of radical polymerization, co-polymerization, cross-linking, functionalization of polymers after they have been made, and so on. This is a rapidly growing subject and we can only outline the basics. 

We turn our attention now to chain-growth polymerizations. The reader should recall that the Features which distinguish chain-growth and step-growth polymerizations were summarized in Section 5.2. The present chapter is devoted to the basic principles of chain polymerizations in which the active centers are free radicals. Chain-growth reactions with active centers having ionic character are reviewed in Chapter 9. 

In the present chapter, the basic principles of chain polymerizations in which the reactive centers are free radicals will be considered in detail, focusing on the polymerization reactions in which only one monomer is involved. Copolymerizations involving more than one monomer are considered separately in Chapter 7. Chain-growth polymerizations in which the active centers are ionic are reviewed in Chapter 8. 

One of the basic principles of controlling the properties of adhesives considered here is inclusion of surface-active substances (surfactants) capable of chemical interaction with the adhesive components and entering into the adhesives composition. Such reactive surface-active (RS) substances differ radically from chemically indifferent surface-active (IS) substances. In the course of polymerization of oligomers containing IS substances there is a decrease of the critical concentration for micelle formation (CCMF) and formation of substanti d quantities of large micelles of surfactant, which results in weak layers on the boundary between the adhesive and substrate and in decrease of the adhesion strength. 

The hrst section covers the basic principles and characteristics necessary for polymer preparation by polymerization, being either (a) stepwise polymerization of bifunctional monomers by polycondensation, stepwise polyaddition and ringopening processes, or (b) chain polymerization of vinyl monomers by free radical, cationic, anionic, and coordination addition processes. Both of these polymerization techniques are used for polymer preparation from monomer. The goal of the polymerization technique is to obtain polymers with specific structures and properties -this generally requires specialized polymerization conditions. Also described are the factors affecting the rates of homo- and copolymerizations and the reactivity ratios of different comonomers. 

The basic principles underlying all controlled radical-based polymerization processes, using the direct addition or in situ formation of the four reagents, Pn-X, and... 

Radical polymerization processes are of great scientific and economic importance. Knowledge about their kinetic principles is a prerequisite for the elficient synthesis of a wide range of polymeric products. Since the dawn of macromolecular chemistry in the 1920 s, the study of these principles has been a central topic of academic research. Although a radical polymerization process is basically constituted by just four types of reactions, which are initiation, propagation, transfer and termination, the coupled nature of these reactions leads to a complexity that makes it difficult to determine the individual rate constants and to evaluate their effects on the properties of the final polymer, like its molecular weight distribution. Scheme 1.1 shows a set of fundamental reaction equations for a radical polymerization process. 

Ionic-polymerization Kinetics. The kinetics of ionic polymerization share some common principles with that of the free-radical reaction. Both are based on the basic steps of initiation, propagation, termination, and chain transfer, and in both the ultimate average molecular weight depends on the ratio of the reaction rates of propagation and termination. There are, however, important differences. In ionic polymerization the termination step appears to be unimolecular, while it is bimolecular in free-radical type polymerization. The dependence of the kinetic scheme of the reaction on the various parameters is therefore different in the two reactions. Likewise, the fact that a cocatalyst has to be brought into the ionic reaction scheme has to be taken into account. 

New kinetic regularities at polymerization of vinyl monomers in homophase and heterophase conditions in the presence of additives of transition metal salts, azonitriles, peroxides, stable nitroxyl radicals and radical anions (and their complexes), aromatic amines and their derivatives, emulsifiers and solvents of various nature were revealed. The mechanisms of the studied processes have been estabhshed in the whole and as elementary stages, their basic kinetic characteristics have been determined. Equations to describe the behavior of the studied chemical systems in polymerization reactions proceeding in various physicochemical conditions have been derived. Scientific principles of regulating polymer synthesis processes have been elaborated, which allows optimization of some industrial technologies and solving most important problems of environment protection. 

Finally, according to basic equilibrium principles, additional Co favors recombination with propagating radicals. Consequently, in spite of the low propensity of Co(acac)2 to deactivate poly(acrylate) radicals, the successful controlled polymerization of acrylates was demonstrated when using a substantial excess of Co(acac)2 [30]. The drawback of this approach, however, was an ampHfied contamination of the final material by the metal. 

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