Step-growth polymers polyesters

Polyesters and polyamides are two of the most studied step-growth polymers, as well as being substances of great commercial importance. We shall consider polyesters in the next section, and polyamides in Sec. 5.6. 

As with polyesters, the amidation reaction of acid chlorides may be carried out in solution because of the enhanced reactivity of acid chlorides compared with carboxylic acids. A technique known as interfacial polymerization has been employed for the formation of polyamides and other step-growth polymers, including polyesters, polyurethanes, and polycarbonates. In this method the polymerization is carried out at the interface between two immiscible solutions, one of which contains one of the dissolved reactants, while the second monomer is dissolved in the other. Figure 5.7 shows a polyamide film forming at the interface between an aqueous solution of a diamine layered on a solution of a diacid chloride in an organic solvent. In this form interfacial polymerization is part of the standard repertoire of chemical demonstrations. It is sometimes called the nylon rope trick because of the filament of nylon produced by withdrawing the collapsed film. 

The alkene and diene polymers discussed in Sections 7.10 and 14.6 are called chain-growth polymers because they are produced by chain reactions. An initiator adds to a C=C bond to give a reactive intermediate, which adds to a second alkene molecule to produce a new1 intermediate, which adds to a third molecule, and so on. By contrast, polyamides and polyesters are called step-growth polymers because each bond in the polymer is formed independently of the others. A large number of different step-growth polymers have been made some of the more important ones are shown in Table 21.2. 

Step-growth polymers, such as polyamides and polyesters, are prepared by reactions between difunctional molecules. Polyamides (nylons) are formed by reaction between a diacid and a diamine polyesters are formed from a diacid and a diol. 

Step-growth polymers are produced by reactions in which each bond in the polymer is formed stepwise, independently of the others. Like the polyamides (nylons) and polyesters that we saw in Section 21.9, most step-growth polymers... 

Step-growth polymer (Sections 21.9, 31.4) A polymer in which each bond is formed independently of the others. Polyesters and polyamides (nylons) are examples. 

Polyamides and Polyesters Step-Growth Polymers 818 21.10 Spectroscopy of Carboxylic Acid Derivatives 822... 

Aldiough they were the first step-growth polymers fully characterized, it is interesting to note that die first commercial applications of aliphatic polyesters appeared only in the late 1950s and the 1960s, widi die development of polyurediane foams and elastomers (see Chapter 5). 

Thermoplastic resins, self-reinforced, 26 Thermoplastics, preparation of, 257-258 Thermoplastic step-growth polymers, 3 Thermosetting polyester resins, 29-31 Thermosetting resins, 3-4, 19 Thermotropic compounds, 49 THF. See Tetrahydrofuran (THF) Thiobisphenol S (TBPS), 364 Thionyl chloride, 80 activation of, 111 3,3 -linked polymers, 480 Tin-amine coordination complex, 234 Tin compounds, 86, 232-233... 

The functional groups that typically participate in this type of polymerization are carboxyl, amine, and alcohol groups. Examples of step growth polymers include polyesters and nylons, which are often spun into fibers used to manufacture carpeting and fabrics, and polycarbonates, which are converted into compact discs, jewel cases, and the large bottles used in water coolers. 

Step growth polymers, such as polyesters, are often manufactured via bulk polymerization. The reactive species are mixed together in a stirred reactor designed to promote intimate contact between the reactants. Variables such as temperature and pressure are used to control the molecular properties of the final polymer. 

Although we will not be discussing the mechanism of each type of step growth polymer because these reactions are very similar to the corresponding monomer chemistry, we should be aware of this analogy. For instance, an acid reacts with an alcohol under acid-catalyzed conditions by a certain well-studied and proven mechanism. This same mechanism is followed each time an ester linkage of a polyester is formed. One such transformation is outlined in Fig. 14.8. The equilibrium is shifted in the direction of the product by distillation of the water from the reaction mixture (and condensing it in a separate container—hence the name condensation polymers for this type). 

Step-growth, or condensation, polymers are usually formed in a reaction between two monomers, each of which is at least difunctional. Polyesters, polyamides, polyurethanes, and epoxy resins are typical examples of step-growth polymers. These polymers grow by steps or leaps rather than one monomer unit at a time. 

Many of our common polymers are made by this type of reaction, including polyesters, nylons, polycarbonates, polyurethanes, and polyaramids (e.g., Kevlar). Many natural polymers, including cellulose, starch, proteins, and polynucleotides are also step-growth polymers. 

Interfaciarpolymerization can be used to make many types of step-growth polymers such as polyamides, polyesters, polycarbonates, and polyurethanes. Although most step-growth polymers are prepared by a melt process, somd specialty polymers are prepared by the interfacial technique, allowing rapid reaction at low temperatures. 

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. 

The synthesis of step-growth polymers—polytimides such as nylon and Kevlar, polyesters such as Dacron, polyurethanes such as spandex, and polycarbonates such as Lexan (Section 30.6)... 

Step-growth polymers, also called condensation polymers, are formed when mono- -mers containing two functional groups come tc ether and lose a small molecule such as H2O or HCl. In this method, any two reactive molecules can combine, so the monomer is not necessarily added to the end of a growing chain. Step-growth polymerization is used to prepare polyamides and polyesters, as discussed in Section 22.16. 

Polyester (Sections 22.16B, 30.6B) A step-growth polymer consisting of many ester bonds between diols and dicarboxylic acids. 

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