Polymer chemistry condensation polymerization reaction

This volume contains 18 papers on the kinetics and technology of addition and condensation polymerization processes. These papers were presented at the sixth symposium on this subject held by the Division of Industrial and Engineering Chemistry and the Division of Polymer Chemistry during the A.C.S. Meeting, Boston April 9-14, 1972. They are concerned with known commercial products. New polymers and novel polymerization reactions presented at the same symposium are collected in the companion volume, Advances in Chemistry Series No. 129. 

Referring to the ADMET mechanism discussed previously in this chapter, it is evident that both intramolecular complexation as well as intermolecular re-bond formation can occur with respect to the metal carbene present on the monomer unit. If intramolecular complexation is favored, then a chelated complex, 12, can be formed that serves as a thermodynamic well in this reaction process. If this complex is sufficiently stable, then no further reaction occurs, and ADMET polymer condensation chemistry is obviated. If in fact the chelate complex is present in equilibrium with re complexation leading to a polycondensation route, then the net result is a reduction in the rate of polymerization as will be discussed later in this chapter. Finally, if 12 is not kinetically favored because of the distant nature of the metathesizing olefin bond, then its effect is minimal, and condensation polymerization proceeds efficiently. Keeping this in perspective, it becomes evident that a wide variety of functionalized polyolefins can be synthesized by using controlled monomer design, some of which are illustrated in Fig. 2. 

This section introduces simple polymer reaction chemistry used to produce many commodity polymers. Understanding this simplified approach to the chemistry of polymer production Is Important In troubleshooting many extrusion processes, especially those that are producing unwanted degradation products that contaminate the discharge resin. There are two general types of polymer production processes 1) step or condensation reactions, and 2) addition or vinyl polymerization reactions. An overview of the reaction mechanisms wifi be presented in the next sections. 

Nearly all synthetic polymers are synthesized by the polymerization or copolymerization of different "monomers." The chain growth process may involve the addition chain reactions of unsaturated small molecules, condensation reactions, or ringopening chain-coupling processes. In conventional polymer chemistry, the synthesis of a new polymer requires the use of a new monomer. This approach is often unsatisfactory for Inorganic systems, where relatively few monomers or cyclic oligomers can be Induced to polymerize, at least under conditions that have been studied to date. The main exception to this rule is the condensation-type growth that occurs with inorganic dl-hydroxy acids. 

The fact that silsesquioxane molecules like 2-7 contain covalently bonded reactive functionalities make them promising monomers for polymerization reactions or for grafting these monomers to polymer chains. In recent years this has been the basis for the development of novel hybrid materials, which offer a variety of useful properties. This area of applied silsesquioxane chemistry has been largely developed by Lichtenhan et al With respect to catalysis research, the chemistry of metallasilsesquioxanes also receives considerable current interest. As mentioned above, incompletely condensed silsesquioxanes of the type R7Si70g(0H)3 (2-7, Scheme 4) share astonishing structural similarities with p-tridymite and p-cristobalite and are thus quite realistic models for the silanol sites on silica surfaces. Metal... 

As shown by Carothers in the 1930s, the chemistry of condensation polymerizations is essentially the same as classic condensation reactions, leading to the formation of monomeric esters, amides, etc. The principle difference is that the reactions used for polymer formation are bifunctional instead of monofunctional. 

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.)... 

Stepwise Polymerization. Although condensation polymers account for only about one-fourth of synthetic polymers (bulkwise), most natural polymers are of the condensation type. As shown by Carothers in the 1930s 2, ), the chemistry of condensation polymerizations is essentially the same as classic condensation reactions that result in the synthesis of monomeric amides, urethanes, esters, etc. the principle difference is that the reactants employed for polymer formation are bifunctional (or higher) instead of monofunctional. Although more complicated situations can occur, we will consider only the kinetics of simple polyesterification. The kinetics of most other common condensations follow an analogous pathway. 

Basic polyurethane chemistry was discovered by Otto Bayer in 1937, but polyurethane polymers were first developed as replacements for rubber at the start of World War II. Numerous applications followed including fibres, rigid and flexible foams, mouldings and elastomers (Brydson, 1999). The preparation of polyurethane polymers occurs via a reaction process intermediate between those of addition and condensation (Brydson, 1999). Like addition polymerization, there is no splitting off of small molecules, but the kinetics are otherwise similar to condensation polymerization. 

Acrylic adhesives cure by addition polymerization reactions. These chain reactions are initiated by the formation of free radicals that result in the adhesive curing by way of a very rapid polymer chain growth. This cure chemistry is significantly more rapid than a typical cure curve (i.e., condensation type) found in epoxy and urethane adhesives. A comparison of the cure profile of condensation (epoxy and urethane) versus addition... 

An alternative approach to the synthesis of polyphosphazenes has also been reported [29, 30). In this process, the condensation reactions of N-silylphosphor-animines yield medium molecular weight poly(alkyl- and atyl-phosphazenes). The advantage of this route is that it yields polymers in which all the side groups are alkyl-or aryl- units bonded to phosphorus through carbon-phosphorus bonds - precisely those structures that are the most difficult to prepare by the classical route. Catalysis of these condensation polymerizations by BU4NF has also been described [31]. It has been demonstrated [32] that alkyl side groups can be lithiated, and these sites can form the basis of a lithium-replacement macromolecular substitution chemistry. 

Step addition and step condensation polymerization processes give rise to polymers containing distinctive functional groups at chain ends. The nature of the end groups will depend on the precise chemistry of the polymerization process. For example, linear polyurethanes are produced by reaction between diisocyanates and diols. If a perfect 1 1 stoichiometry of the reactants is used in the synthesis, on average each polymer chain must contain one isocyanate functional group and one alcohol group. If a 2 1 molar ratio of reactants is used, when the isocyanate is in excess, all the chain ends will have isocyanate functionality, and all will have alcohol functionality at the chain ends if a two-fold excess of diol is used. 

Several polymerization routes can be employed for the synthesis of suifone polymers. The synthesis route that is most practical and that is used almost exclusively today for the production of these polymers is the aromatic nucleophilic substitution polymerization route. This synthesis route involves the condensation polymerization of 4,4 -dihalodiphenylsulfone with a dihydroxy compound in the presence of a base to convert the phenolic hydroxyl group to a nucleophilic aromatic phenoxide group. The polymerization takes place in a dipolar aprotic solvent that will solvate aU components of the reaction medium. This suifone polymer chemistry was pioneered by Johnson and Famham in the early 1960s [1, 2]. 

The chemistry of the production of polyamide resin is very similar to the original process by which nylon was produced. In the Nylon 66 process a dicarboxylic acid, such as adipic acid is reacted with a six carbon amine, for example hexamethylene-diamine, to produce a synthetic fiber In the case of polyamide resin, a dicarboxylic add is reacted or condensed with an amine such as diethylenetriamine to form an amino polyamide. The secondary amine groups of this water soluble polymer are then reacted with epichlorohydrin to form the aminopolyamide epichlorohydrin intermediate. This is then crosslinked to build molecular weight whilst maintaining solubility. The polymerization reaction is terminated by dilution and acidification. 

The chemistry of the maleic anhydride molecule seems to be uniquely suited to illuminate many facets of organic chemistry. In addition to its important role in functional-group chemistry, study of maleic anhydride lends itself to analysis of such diverse processes as ionic, radical, and cycloaddition reactions. Similarly, polymer chemistry is exemplified in a variety of ways by reactions of maleic anhydride, including its role in charge-transfer, addition, and condensation polymerizations. 

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