Nylon, chain type

Before analyzing in detail the conformational behaviour of y9-peptides, it is instructive to look back into the origins and the context of this discovery. The possi-bihty that a peptide chain consisting exclusively of y9-amino acid residues may adopt a defined secondary structure was raised in a long series of studies which began some 40 years ago, on y9-amino acid homopolymers (nylon-3 type polymers), such as poly(/9-alanine) 3 [14, 15], poly(y9-aminobutanoic acid) 4 [16-18], poly(a-dialkyl-/9-aminopropanoic acid) 5 ]19], poly(y9-L-aspartic acid) 6 ]20, 21], and poly-(a-alkyl-/9-L-aspartate) 7 [22-36] (Fig. 2.1). 

Because the rules for organic nomenclature determine the priority of naming different carbon chains from their relative lengths, the systematic names for type AABB polyamides depend on the relative length of the carbon chains between the amide nitrogens and the two carbonyl functions of the polymer for aUphatic nylon-Ayy, when x < the lUPAC name is poly[imino-R imino(l2y-dioxo-R )]. When x > then the name is... 

In a study of the adsorption of soap and several synthetic surfactants on a variety of textile fibers, it was found that cotton and nylon adsorbed less surfactant than wool under comparable conditions (59). Among the various surfactants, the cationic types were adsorbed to the greatest extent, whereas nonionic types were adsorbed least. The adsorption of nonionic surfactants decreased with increasing length of the polyoxyethylene chain. When soaps were adsorbed, the fatty acid and the aLkaU behaved more or less independently just as they did when adsorbed on carbon. The adsorption of sodium oleate by cotton has been shown independently to result in the deposition of acid soap (a composition intermediate between the free fatty acid and the sodium salt), if no heavy-metal ions are present in the system (60). In hard water, the adsorbate has large proportions of lime soap. 

Nylon, also a linear polymer, is made by a condensation reaction. Two different kinds of molecule react to give a larger molecule, and a by-product (usually HjO) the ends of large molecules are active, and react further, building a polymer chain. Note how molecules of one type condense with those of the other in this reaction of two symmetrical molecules... 

Nylons, long-chain synthetic polymeric amides, are fabricated in many different types. The most commonly used forms are described in Table 3.46. 

Linear condensation polymers are produced when the constituent monomers contain two functional groups each. When a single monomer is polymerized, the product is made of chains whose repeat unit corresponds to the monomer. An example of this type is nylon 6, the structure of which is shown in Fig. 1.10. If two different monomers are polymerized, the result most often is a chain whose repeat unit corresponds to the two different monomers arranged alternately. An example of this type is nylon 66, the structure of which is shown in... 

The polymerization process for nylon 6 consists primarily of the three types of reaction illustrated in Fig. 23.6. Each of the reactions is reversible, tvith the equilibrium of the products being controlled primarily by the concentration of water in the reaction vessel. The reaction is initiated by the hydrolytic ring opening of caprolactam to form 6-aminohexanoic acid, as shown in Fig. 23.6 a). Chain extension of the type shotvn in Fig. 23.6 b) dominates when water is abundant (10 to 20%) in the reaction mixture. At lower water levels (2 to 5%) chains grow primarily by the mechanism shown in Fig. 23.6 c). In order to limit the average molecular... 

The first successful synthetic fibre. The term is applied to any long-chain synthetic polymeric amide and the best known commercial type is nylon 66 produced by the condensation polymerisation of adipic acid with hexamethylene diamine. 

The generic name given to the nylon type of polymer, which consists of short carbon chains connected by amide groups -NHCO-. See Nylon. Polybutadiene... 

Most addition polymers are formed from polymerizations exhibiting chain-growth kinetics. This includes the typical polymerizations, via free radical or some ionic mode, of the vast majority of vinyl monomers such as vinyl chloride, ethylene, styrene, propylene, methyl methacrylate, and vinyl acetate. By comparison, most condensation polymers are formed from systems exhibiting stepwise kinetics. Industrially this includes the formation of polyesters and polyamides (nylons). Thus, there exists a large overlap between the terms stepwise kinetics and condensation polymers, and chainwise kinetics and addition (or vinyl) polymers. A comparison of the two types of systems is given in Table 4.1. 

Polymerization by a ring-opening reaction is confined to cyclic monomers which contain at least one heteroatom. The mechanism is very often a polyaddi-tion-type with a product which has a polycondensation-type character. For example, ethylene oxide and other cyclic esters can be polymerized into linear chains by this type of reaction. An even more complicated example of this type of polymerization reaction is the polymerization of e-caprolactam into Nylon 6 (PA 6). 

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