Step-growth polymers polyamides

Recently a series of papers was published in which the end-group modification of the step-growth polymers polyamide 6 [71-73] and poly(butylene ter-ephthalate) [74] in SCCO2 was described. In some cases, the carbon dioxide, in which the end capping agent was dissolved, also contained a polar additive in order to enhance the sorption of the sc fluid by the relatively polar polymers. These papers illustrate the scope and limitations of the SCCO2 modification technique in a rather complete and subjective way, which wiU be discussed in detail in the rest of this chapter. 

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

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. 

The best known step-growth polymers are the polyamides, or nylons, first prepared by Wallace Carothers at the DuPont Company by heating a diamine with a diacid. Por example, nylon 66 is prepared by reaction of adipic acid (hexanedioic acid) with hexamethylenediamine (.1.,6-hexanediamine) at 280 °C. The designation "66" tells the number of carbon atoms in the diamine (the first 6) and the diacid (the second 6). 

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... 

Nylon (Section 21.9) A synthetic polyamide step-growth polymer. 

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... 

Step growth polymerization. Important polymers manufactured by step growth are polyamides (nylons), polyesters, and polyurethanes. 

Condensation polymers, which are also known as step growth polymers, are historically the oldest class of common synthetic polymers. Although superseded in terms of gross output by addition polymers, condensation polymers are still commonly used in a wide variety of applications examples include polyamides (nylons), polycarbonates, polyurethanes, and epoxy adhesives. Figure 1.9 outlines the basic reaction scheme for condensation polymerization. One or more different monomers can be incorporated into a condensation polymer. 

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. 

Imai Y (1996) A new facile and rapid synthesis of polyamides and polyimides by microwave-assisted polycondensation. In Hedrick JL, Labadie JW (eds) Step-growth polymers for high-performance materials. Am Chem Soc Washington, p421... 

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. 

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. 

Polyamide (Sections 22.16A, 30.6A) A step-growth polymer that contains many amide bonds. Nylon 6,6 and nylon 6 are polyamides. 

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