Reactions classification of polymerization

The most basic requirement for polymerization is that each molecule of monomer must be capable of being linked to two (or more) other molecules of monomer by chemical reaction, i.e. monomers must have a functionality of two (or higher). Given this relatively simple requirement, there are a multitude of chemical reactions and associated monomer types that can be used to effect polymerization. To discuss each of these individually would be a major task which fortunately is not necessary since it is possible to place most polymerization reactions in one of two classes, each having distinctive characteristics. 

The classification used in the formative years of polymer science was due to Carothers and is based upon comparison of the molecular formula of a polymer with that of the monomer(s) from which it was formed. Condensation polymerizations are those which yield polymers with repeat units having fewer atoms than present in the monomers from which they are formed. This usually arises from chemical reactions which involve the elimination of a small molecule (e.g. H2O, HCl). Addition polymerizations are those which yield polymers with repeat units having identical molecular formulae to those of the monomers from which they are formed. Table 1.1 (Section 1.2.2) contains examples of each class the latter three examples are condensation polymerizations involving elimination of H2O, whereas the others are addition polymerizations. 

Definition of symbols used o, molecule of monomer -, chemical link I, initiator species 

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The proceeding classification of polymerization reactions concentrates essentially on the organic chemical character of the involved monomers... 

The three tables embody a certain classification of polymerization reactions similar to that of the much simpler division of ordinary gas reactions into mono-, bi- and tri-molecular. However, through the inevitable overlapping of the three component reactions described, the conditions prove more complex and the systematization of polymerization reactions is less simple. 

The present Report makes no pretence at covering the field in all its many facets. Only work related to copolymerization chemistry will be reported and that is taken from the scientific literature, ignoring multitudinous patents which have appeared. The Report is largely confined to addition polymerization processes, although the sharp demarcation between the traditional classifications of polymerization reactions is to some extent becoming blurred, particularly when attempts have been made to incorporate both non-polar and polar structural units within a polymer chain, as will be seen later. 

The foregoing proposals by Carothers are also commonly used as the basis of a scheme of classification of polymerization reactions. In this scheme, the processes by which polymers are formed are divided into condensation polymerizations and addition polymerizations. Thus a condensation polymerization leads to a polymer in which the structural unit contains fewer atoms than the monomer whilst an addition polymerization results in a polymer having a... 

In the last section we examined some of the categories into which polymers can be classified. Various aspects of molecular structure were used as the basis for classification in that section. Next we shall consider the chemical reactions that produce the molecules as a basis for classification. The objective of this discussion is simply to provide some orientation and to introduce some typical polymers. For this purpose a number of polymers may be classified as either addition or condensation polymers. Each of these classes of polymers are discussed in detail in Part II of this book, specifically Chaps. 5 and 6 for condensation and addition, respectively. Even though these categories are based on the reactions which produce the polymers, it should not be inferred that only two types of polymerization reactions exist. We have to start somewhere, and these two important categories are the usual place to begin. 

The study of the molecular weight of the intermediate course is an effective method for the classification of polymerization as chain or stepwise reaction. In Figure 3, the molecular weight of the obtained polymer is plotted against the yield, for the oxidative polymerization of dimethylphenol with the copper catalyst and for the electro-oxidative polymerization. The molecular weight rises sharply in the last stage of the reaction for the copper-catalyzed polymerization. This behavior is explained by a stepwise growth mechanism. 

Basic classification and definitions of polymerization reactions (lUPAC Recommendations 1994), Pure Appl. Chem. 66, 2483-2486 (1994). Reprinted as Chapter 4, this edition. 

Basic Classifications and Definitions of Polymerization Reactions, Pure Appl. Chem. 66,... 

Fig. 7. Classification of the reactions of pendant double bonds during free radical crosslinking polymerizations...

Several reviews of early work on topotactic polymerizations and isomeriza-tions are available, and the reader is referred to the summaries of Morawetz [88] and Gougoutas [8] for a more complete account. The earliest study of a topotactic reaction appears to have been the observation, in 1932, of the polymerization of trioxane to poly-oxy-methylene [89]. Similar polymerizations of tetraoxane [90] and of trithiane [91 ] have also been reported to show retention of crystallographic axes from the monomer lattice. Other examples are discussed below. The topo-tacticity of a reaction can be determined solely by x-ray crystallographic analysis at the reactant and product endpoints. Thus a simple classification of a reaction as topotactic tells very little about how the structure of the crystal lattice changed in the course of reaction. 

Some possible subdivisions of the field are listed in Table I. We can characterize the type of polymerization process—i.e., mass, suspension, emulsion, etc.—and the type of reactor and how it is operated. The chemical classification of the reaction affects the mathematics as well as the product. The last distinction is between the rate of product formation and the distribution of the products obtained. 

Polymer degradation reactions are frequently categorized based on the site in the macromolecule structure where the reaction occurs. This leads to the following classification of scission reactions a) polymeric chain scission, b) side group reactions, c) combined reactions [5, 3]. These reactions follow one of the mechanisms described previously, but this different classification allows a better correlation of the nature of the reaction products with the structure of the polymer and provides more understanding regarding the expected pyrolysis products. 

There are two fundamental polymerization mechanisms. Classically, they have been differentiated as addition polymerization and condensation polymerization. In the addition process, no by-product is evolved, as in the polymerization of vinyl chloride (see below) whereas in the condensation process, just as in various condensation reactions (e.g., esterification, etherification, amidation, etc.) of organic chemistry, a low-molecular-weight by-product (e.g., H2O, HCl, etc.) is evolved. Polymers formed by addition polymerization do so by the successive addition of unsaturated monomer units in a chain reaction promoted by the active center. Therefore, addition polymerization is called chain polymerization. Similarly, condensation polymerization is referred to as step polymerization since the polymers in this case are formed by stepwise, intermolecular condensation of reactive groups. (The terms condensation and step are commonly used synonymously, as we shall do in this book, and so are the terms addition and chain. However, as it will be shown later in this section, these terms cannot always be used synonymously. In fact, the condensation-addition classification is primarily applicable to the composition or structure of polymers, whereas the step-chain classification applies to the mechanism of polymerization reactions.)... 

Definitions, chemical and physical properties, and general features of the most relevant catalyst types used in coordination polymerizations are described in Section 5.3, after the classification by type of monomers most frequently used and studied in this kind of polymerization reactions. 

As disciissed in Chapter 1, under a scheme proposed by Carothers, polymers are classified as addition or condensation polymers depending on the type of polymerization reaction involved in their synthesis. This classification scheme, however, does not permit a complete difierentiation between the two classes of polymers. A more complete but still oversimplified scheme that is still based on the dilTerent polymerization processes places polymers into three classes condensation, addition, and ring-opening polymers. This scheme reflects the stractures of the starting monomers. Probably the most general classification scheme is based on the polymerization mechanism involved in polymer synthesis. Under this scheme, polymerization processes are classified as step-reaction (condensation) or chain-reaction (addition) polymerization. In this chapter, we will discuss the different types of polymers based on the different polymerization mechanisms. 

The foregoing discussion has shown that termination reactions in cationic polymerization may be of many different kinds, that they may differ for apparently closely related systems, and that they may even be entirely absent. However, the polymers produced in many of these reactions are of low molecular weight and this means that transfer reactions are dominant. They may take on an even greater variety of forms than the termination reactions and their classification and discussion are still in an early stage of development. 

The classification of a condensation polymer Is historically based on the observation that during polymerization a small molecule, such as water, is condensed or removed as part of the reaction. There are a large number of polymers produced from condensation reactions and only a representative sample is presented in... 

The U.S. rubber processing industry encompasses a wide variety of production activities ranging from polymerization reactions closely aligned with the chemical processing industry to the extrusion of automotive window sealing strips. The industry is regulated by seven Standard Industrial Classification (SIC) codes [1] ... 

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