Condensation or Step-Reaction Polymerization

Another approach is to start with two difunctional molecules. 

The reaction continues until one of the reagents is almost completely used up equilibrium is established that can be shifted at will at high temperatures by controlling the amounts of reactants and products. In step-growth polymerization, the monomer molecules are consumed rapidly, and chains of any length x and y combine to form longer chains. 

An example of a condensation polymerization is the synthesis of nylon-66 by condensation of adipic acid and hexamethylene diamine as shown earlier in the equation. 

This polymerization is accompanied by the liberation of two molecules of water for each repeating unit. 

This simple equation demonstrates one fundamental aspect of step-reaction polymerizations—that very high conversions are necessary to achieve practical molecular weight. At 98 percent conversion, for example, DP is only 50. For DP= 100, the monomer conversion must be 99 percent. 

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Later, in 1953, P.J. Flory divided the polymers by their reaction mechanism into chain-reaction and step-reaction, rather than by comparing the polymer s constitutional unit and the monomer. The addition polymers are generally produced by a chain reaction mechanism, and the condensation polymers produced by a step-reaction mechanism. Currently it is customary, though not scientifically correct, to refer to addition or chain-reaction polymerization and to condensation or step-reaction polymerization. Some have suggested that the classification of polymers... 

Chemists usually synthesize polymers by condensation (or step-reaction polymerization) or addition (also known as chain-reaction polymerization). A good example of chain polymerization is the free-radical mechanism in which free radicals are created (initiation), fecilitating the addition of monomers (propagation), and ending when two free radicals react with each other (termination). A general example of step-reaction polymerization is the reaction of two or more polyfunctional molecules to produce... 

Instead of the addition pol)nnerization described above, some polymers are formed by a chemical reaction between two monomers that produces the repeating units together with a byproduct. This process is called condensation or step reaction polymerization. An example would be the reaction between dimethyl terephthalate and ethylene glycol to produce polyethylene terephthalate (PET) and methyl alcohol as a byproduct. The nylons and polycarbonates are linear chain pol)nners that also pol)nnerize by the condensation process. 

Condensation (or step reaction) polymerization is the formation of polymers by stepwise intermolecular chemical reactions that may involve more than one monomer species. There is usually a low-molecular-weight by-product such as water that is eliminated (or condensed). No reactant species has the chemical formula of the repeat unit, and the intermolecular reaction occurs every time a repeat unit is formed. For example, consider the formation of the polyester poly(ethylene terephthalate) (PET) from the reaction between dimethyl terephthalate and ethylene glycol to form a linear... 

Monomers can be joined by means of two principal methods to form polymers, and these methods are used as the broad basis for classification of synthetic polymers. The first of these, condensation, or step-growth polymerization, involves the use of functional group reactions such as esterification or amide formation to form polymers. When each of the molecules involved has only one functional group then the reaction between a carboxylic acid and an alcohol gives an ester (Eq. 20.3). In this equilibrium reaction water removal will help drive the reaction to the right. 

We will first discuss addition or chain-reaction polymerization and then discuss condensation or step-reaction polymers in Section 3.8. Addition polymers used in packaging include, among others, polyethylene, polypropylene, polyvinyl chloride, and polystyrene. Polyesters, nylons, and polycarbonate are condensation polymers. 

The term condensation polymerization was originally used because this form of polymerization involves condensation reactions. Such transformations normally involve combining two functionalized molecules through an addition-elimination process, termed nucleophilic acyl substitution (Sec. 20.1), that results in the loss of a small molecule, H-L, such as water (Eq. 22.4). The aldol condensation (Sec. 18.3) and esterification (Sec. 20.2) are examples of such reactions. In the case of condensation or step-growth polymerization, difunctionalized substrates are required as monomers, as illustrated in Equation 22.5. 

In the next group of chapters we shall discuss condensation or step-growth polymers and polymerizations in Chap. 5, addition or chain-growth polymers and polymerizations in Chap. 6, and copolymers and stereoregular polymers in Chap. 7. It should not be inferred from this that these are the only classes of polymers and polymerization reactions. Topics such as ring-opening polymeri-... 

Polymerizations are classified as either step (condensation) or chain (addition) polymerizations. The two differ in the time-scale of various reaction events, specifically in the length of time required for the growth of large-sized molecules. The synthesis of polysulfides (Eq. 1) and polyurethanes (Eq. 2) are... 

Coordination polymers can be prepared by a number of routes, among which the three most common being (1) preformed coordination metal complexes polymerized through functional groups where the actual polymer-forming step may be a condensation or addition reaction ... 

Many polymerization techniques have been combined with CRP through site transformation of the active species. These include non-living techniques like condensation (or step) and conventional free radical processes or living methods like anionic, cationic, and ring-opening polymerizations, as well as others. Early examples were undertaken perhaps just to show that two different techniques could be combined, while later examples show how elegant the combinations have become and provide a foundation for controlled synthesis of materials from any type of monomers. These types of reactions are detailed below. 

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. 

Condensation (step reaction) polymerization Polymerization in which two or more chemicals are reacted to form a polymer by condensing out small molecules such as water and alcohol. 

Although these definitions were perfectly adequate at the time, it soon became obvious that notable exceptions existed and that a fundamentally sounder classification should be based on a description of the chain-growth mechanism. It is preferable to replace the term condensation with step-growth or step-reaction. Reclassification as step-growth polymerization now logically includes polymers such as polyurethanes, which grow by a step-reaction mechanism without elimination of a small molecule. 

The many ways to make polymers can be broken into two types of reactions based on the mechanisms of the polymerization, step and chain reactions (5). This reaction classification was termed condensation or addition reactions in the past but this archaic nomenclature is slowly dying away. The labels step and chain were developed for the two types of polymerizations by Flory and Mark (5, 6). All step reactions conduct the same stepwise reaction between all reactive entities in the reaction mixture. The... 

Silicones are widely used in industry, for example, as adhesives, sealants and release agents see Silicone properties and Silicone adhesion. Silicone adhesives may cure by condensation or addition reactions. The former is considered here and the latter in Silicone adhesives addition cure (see also Step polymerization). 

Condensation polymerization or step-growth polymerization is a process by which two molecules join together, resulting in loss of small molecules, which are often water. The type of end product resulting from a condensation polymerization is dependent on the type of reactive functional groups at the monomeric end, such as -OH, -COOH, -COOR, -COCl, -NH2, -CHO, and -NCO. The reaction is usually a non-catalyzed chemical condensation reaction and continues until the entire... 

Carothers, in 1929, classified synthetic polymers into two classes, according to the method of their preparation, i.e., condensation polymers and addition polymers. In polycondensation, or step-growth polymerization, polymers are obtained by reaction between two polyfunctional molecules and elimination of a small molecule, for example water. Typical condensation polymers are shown in Figure 2. Addition (or chain reaction) polymers are formed from unsaturated monomers in a chain reaction. Examples of addition polymers are shown in Figure 2. 

Polymerization, bulk Also called mass polymerization or step-growth polymerization. It is from undiluted low molecular weight starting materials. It is the simplest and oldest method for the synthesis of macromolecules. This method has a reaction, which is relatively simple, and rapid, plastics of high purity are formed, and the plastics obtained are immediately processable. Basically, the polymerization process involves only monomer and polymerization initiator or catalyst. It is carried out in the absence of a solvent or other dispersion media. This technique is applicable to both addition and condensation polymerization. Fundamentally differences exist. 

Step-growth polymerization involves the condensation or addition reactions of molecular entities carrying X and Y antagonist functional groups. In other words, molecules would be formed by condensation of monovalent A-X and Y- species, and polycondensates would result from the reaction between monomers of valence equal to or greater than 2 (u > 2). Two situations are encountered in the latter case ... 

In step-reaction polymerization, also called condensation polymerization, the monomers typically have two or more functional groups that react to join... 

Polymers are a very important dass of substances in modern life. One method of polymerization, the joining of monomers to form polymers, is called step-reaction polymerization, or condensation polymerization. It produces polymers of moderate molecular mass. Another type of polymerization mechanism is chain-reaction polymerization, a three-step process involving initiation (reaction 27.16), propagation (reaction 27.17), and termination (reaction 27.18), producing polymers of high molecular mass. 

It is the third of these criteria that offers the most powerful insight into the nature of the polymerization process for this important class of materials. We shall frequently use the terms step-growth and condensation polymers as synonyms, although by the end of the chapter it will be apparent that step-growth polymerization encompasses a wider range of reactions and products than either criteria (1) or (2) above would indicate. 

This situation seems highly probable for step-growth polymerization because of the high activation energy of many condensation reactions. The constants for the diffusion-dependent steps, which might be functions of molecular size or the extent of the reaction, cancel out. 

Synthesis and Properties. Polyquinolines are formed by the step-growth polymerization of o-aminophenyl (aryl) ketone monomers and ketone monomers with alpha hydrogens (mosdy acetophenone derivatives). Both AA—BB and AB-type polyquinolines are known as well as a number of copolymers. Polyquinolines have often been prepared by the Friedlander reaction (88), which involves either an acid- or a base-catalyzed condensation of an (9-amino aromatic aldehyde or ketone with a ketomethylene compound, producing quinoline. Surveys of monomers and their syntheses and properties have beenpubhshed (89—91). 

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