Polymers, synthetic polyamides

We only need to recall the trade name of synthetic polyamides, nylon, to recognize the importance of these polymers and the reactions employed to prepare them. Remember from Sec. 1.5 the nylon system for naming these... 

Nylon—any long-chain synthetic polyamide having recurring amide groups as an integral part of the polymer chain. 3.8-9.2 E F-P G F-P G 1.14 225... 

Polyamide (Section 20.17) A polymer in which individual structural units are joined by amide bonds. Nylon is a synthetic polyamide proteins are naturally occurring polyamides. 

We ve seen on several occasions in previous chapters that a polymer, whether synthetic or biological, is a large molecule built up by repetitive bonding together of many smaller units, or monomers. Polyethylene, for instance, is a synthetic polymer made from ethylene (Section 7.10), nylon is a synthetic polyamide made from a diacid and a diamine (Section 21.9), and proteins are biological polyamides made from amino acids. Note that polymers are often drawn by indicating their repeating unit in parentheses. The repeat unit in polystyrene, for example, comes from the monomer styrene. 

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

The name Nylon was given by the Du Pont company of America to their first synthetic condensation polymer formed by the reaction of difuncfional acids with difuncfional amines, ft had been made as part of the fundamental programme of W. H. Carothers to investigate the whole topic of polymerisation. The term has gradually been extended to other related polymers. These materials are strictly polyamides, but this term includes that otherwise distinct class of natural macromolecules, the proteins. The term nylon is retained for its usefulness in distinguishing synthetic polyamides from the broader class of such polymers. 

Synthetic organic pigments, 19 418-422t history of, 19 423-424 Synthetic organic polymers, manufactured fibers based on, 24 616-618 Synthetic polyamide fibers, dyeing, 9 188-191, 469-470... 

An alternate synthetic approach to organometallic polymers is to perform reactions where the metal atom is not the reaction site. An example is a polyesterification between an organometallic monomer containing two carboxyl groups and a diol (Eq. 2-238). Reaction of the diacid with a diamine would yield an organometallic polymer via polyamidation. A wide range of other reactions covered in this chapter can be used to synthesize organometallic polymers. 

There are relatively few data available for the synthetic polyamides. From the studies of Schaefgen and Flory (224) on 6-Nylon in sulfuric acid and those of Howard (127) on 66-Nylon in formic acid-sodium formate we derive identical values of A and of isomeric polymers is also shown in the work of Batzer and Moschle (32 f), who found that both of these Nylons and their copolymers obeyed the same viscosity-molecular weight relationship. 

Also the diffusivity of water in polymers is highly dependent on the polymer-water interaction. When a polymer contains many hydrogen-bonding groups (cellulose, poly (vinyl alcohol), proteins, etc., and to a lesser extent synthetic polyamides) the diffusivity increases with the water content. This is explained by the strong localisation of the initially sorbed water over a limited number of sites, whereas at higher water contents the polymer... 

These synthetic polyamides are made up of the same repeating unit but will inevitably have a range of molecular weights as the polymer length will vary. This is a different story from that of the natur polyamides—peptides and proteins—that you met in Chapter 49. Those polymers were made of twenty or so different monomers (the amino acids) combined in a precise order with a precise stereochemistry and all molecules of the same protein have the same length. Nonetheless, some of their uses are almost identical both nylon and wool are polyamides, for example. 

There is also an alternative numbering system for synthetic polyamides. Polymers that could be made from amino acids are called nylon-.r, where x is the number of carbon atoms in the repeating unit. Thus, polycaprolactam (1-13) is nylon-6, while the polymer from m-aminoundecanoic acid is nylon-11. Nylons from diamines and dibasic acids are designated by two numbers, in which the first represents the number of carbons in the diamine chain and the second the number of carbons in the dibasic acid. Structure 1-6 is thus nylon-6,6. Nylon-6,6 and nylon-6 differ in repeating unit length and symmetry and their physical properties are not identical. 

One of the characteristic properties of rod-like polymers is that their concentrated solutions form lyotropic liquid crystals. Such examples among synthetic polymers are polyamides -and polyisocyanates " which form cholesteric or nematic liquid crystals in selected solvents. 

Polyamides. Nylon 6,6 was the first synthetic polyamide developed that reached technical importance as a fiber. Later, nylon 6 also became a commercial product and assumed an important position among synthetic fibers. In both nylon polymers one chain end consists of an amino group, which can be presented in the free state or in the acetylated form, as shown in the following structures ... 

Proceeding to more complex compounds, let us consider the synthetic polymers. A fairly large number have been synthesized, and some of the amides are in commercial production in very large quantities. The most important examples of synthetic polyamides have a medium length carbon chain between the amide groups and differ in structure from the polypeptides. As a result, they are model compounds for proteins only in the /3 or stretched form (see Section 10.4.3 on structural models). 

Synthetic PAs are produced by polycondensation of bifunctional monomers or by cationic and anionic ring-opening polymerization of lactams. Polymers obtained with the first technique are linear, whereas chain branching may occur with anionic polymerization. Based on their chemical structure, synthetic polyamides may be classified into two categories [1] ... 

Interfacial reactions to produce thin polymer films date back to the early work of Wallace Carothers starting in 1929. Synthetic polyamides for producing nylon fibers were formed by long, carefully... 

As you saw in Section 15.5, synthetic polyamides (such as nylon-66) are formed from two monomers, one with a carboxyl group at each end and the other with an amine group at each end. Proteins, the polyamides of nature, are unbranched polymers formed from monomers called amino acids, each of which has a carboxyl group and an amine group. 

Nylon is the common name of a synthetic polyamide. Nylon 6 is an example of a step-growth polymer formed by a monomer with two different functional groups. The carboxylic acid group of one monomer reacts with the amino group of another monomer, resulting in the formation of amide groups. Stmcturally, the reaction is similar to the polymerization of a-amino acids to form proteins (Section 23.7). This particular nylon is called nylon 6 because it is formed from the polymerization of 6-aminohexanoic acid, a compound that contains six carbons. 

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