Condensation polymer step-growth

Step-growth condensation polymers, such as polyesters and polyamides, are formed by reversible reactions. In the case of PET, the commercial synthesis is essentially carried out by two reactions. The first is the formation of bishydroxyethyl terephthalate by esterification of a diacid with a glycol or by transesterification of a diester with a glycol. The second is the formation of the polymer by a polycondensation reaction. 

In a step-growth polymerization, any two monomers having the correct functionality can react with each other, or two polymer chains can combine. Most step-growth polymers are condensation polymers, bonded by some kind of condensation (bond formation with loss of a small molecule) between the monomers or the polymer segments. The most common condensations involve the formation of amides and esters. Dacron polyester is an example of a step-growth condensation polymer. 

Step-growth polymer (See also Condendsadon polymer. Section 17.12 and Specif Topic C in WileyPLUS)-. A polymer produced when bifunctional monomers (or potentially bifunctional monomers) react with each other through the intermolecular elimination of water or an alcohol. Polyesters, polyamides, and polyurethanes are all step-growth (condensation) polymers... 

A step-growth (condensation) polymer is formed by reaction of two different funotionai groups with ioss of a smaii moiecuie. 

PET is a step-growth (condensation) polymer derived from terephthalic acid (TPA) or dimethyl terephthalate (DMT) and ethylene glycol (EG) according to the... 

Step-growth condensation reactions, for water- soluble polymers, 20 441 Step-growth copolymerization, 7 611, 632-635... 

An interesting thing is that the polyether with low polydispersity from chain-growth condensation polymerization possessed higher crystallinity than the one with broad molecular weight distribution from conventional step-growth condensation polymerization. The XRD pattern of the former polymer showed a stronger intensity, and the DSC profile showed the... 

ADMET differs from ROMP in one major respect. Whereas ROMP is a chain-growth polymerization, ADMET is a step-growth, condensation process.58 Manifestation of this difference lies in both the molecular weights and the molecular weight distributions of polymer chains that result from the two path-... 

Synthetic polymers are used in a number of areas of life and range from the nylon used in various articles of clothing to the polyvinyl chloride (PVC) used in plumbing and other applications. Synthetic polymerization of organic monomers can take place by addition polymerization or by step-growth (condensation) polymerization. Polystyrene is a common product of addition polymerization, and nylon is a common product of step-growth polymerization. 

Another advantage of the DPE functionalization methodology is that it can be used to prepare condensation macromonomers, 34, which are polymers with two polymerizable ftmctional groups at one chain end. This type of macromonomer can participate in step-growth (condensation) polymerization with other diftmctional monomers to form model comb-type, branched condensation copolymers. 

Table 1.3 summarizes the different types of polymerizations [8]. Chain-growth polymerization involves chain growth by reaction of an active polymer chain with single monomer molecules. In step-growth polymerization, polymer growth involves reactions between macromolecules. In addition, non-polymeric byproducts may be formed in both types of polymerization. However, condensative chain polymerization is very rare. Table 1.4 summarizes the differences between chain-growth polymerization and step-growth polymerization. 

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. 

Step-growth condensation reactions may be carried out in organic solvents, interfacially, in bulk, microheterogeneously, or on a solid support. Active esters are often employed in solution methods at relatively low temperatures to yield water-soluble polyesters or polyamides. Synthetic polypeptides, polynucleotides, and polysaccharides are commonly made by sequential addition of protected monomer imits onto polymer supports. 

In efforts to control polymer synthesis and thus polymer composition, kinetics plays a key role. Building off our development of the essentials of kinetics in Chapter 7, here we develop the basics of polymerization kinetics. A key issue is the difference between step-growth/ condensation polymerization and the chain mechanism. We will see that after a few basic assumptions, the kinetics of polymerization are not too different from those of conventional reactions. 

Synthetic polymers used to form fibers are often classified on the basis of their mechanism of polymerization--step growth (condensation) or chain growth (addition) polymerization. Step growth polymerization involves multifunctional monomers which undergo successive condensation with a second monomer or with itself to form a dimer, which in turn condenses with another dimer to form a tetramer, etc., usually with loss of a small molecule such as water. Chain growth involves the instantaneous growth of a long molecular chain from unsaturated monomer units, followed by initiation of a second chain, etc. The two methods are outl ined below schematically ... 

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-... 

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. 

To see why the assumption of equal reactivity is so important to step-growth polymers, recall from Table 1.2 the kind of chemical reactions which produce typical condensation polymers ... 

Discussion of ladder polymers also enables us to introduce a step-growth polymerization that deviates from the simple condensation reactions which we have described almost exclusively in this chapter. The Diels-Alder reaction is widely used in the synthesis of both ladder and semiladder polymers. In general, the Diels-Alder reaction occurs between a diene [XVI] and a dienophile [XVll] and yields an adduct with a ring structure [XVlll] ... 

I ovolac Synthesis and Properties. Novolac resins used in DNQ-based photoresists are the most complex, the best-studied, the most highly engineered, and the most widely used polymers in microlithography. Novolacs are condensation products of phenoHc monomers (typically cresols or other alkylated phenols) and formaldehyde, formed under acid catalysis. Figure 13 shows the polymerization chemistry and polymer stmcture formed in the step growth polymerization (31) of novolac resins. 

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