Nylon hydrogen bonds

Nylon fibers are semicrystalline, that is, they consist of crystallites separated by amorphous regions. Hydrogen bonding is an important secondary valence interaction in nylon-6 and nylon-6,6. Individual chains in the microcrystalline regions of nylons are held together by hydrogen bonds. Nylons are resistant to aqueous alkali but deteriorate more readily on exposure to mineral acids. 

Thus because of the presence of the amide stiffening group and hydrogen bonding, nylon 66 has a Tg of about 60 °C. In contrast, the F, of hexamethylene adipate is about — 70 °C. 

Figure 5.8. The intermolecular forces involved in adjacent polymer chains. Shown are (a) covalent crosslinMng (vulcanized rubber), (b) hydrogen bonding (nylon 6,6), (c) dipole-dipole (PVC), and (d) van der Waal interactions (polyethylene).

Due to this hydrogen bonding, nylon 11 melts at 184—187 C and is soluble only in very strong solvents. Linear polyethylene, on the other hand, melts at 130-134 C and is soluble in hot aromatic solvents. 

It has, however, been possible to find solvents for some polar crystalline polymers such as the nylons, poly(vinyl chloride) and the polycarbonates. This is because of specific interactions between polymer and solvent that may often occur, for instance by hydrogen bonding. 

Polyamides such as nylon 6, nylon 66, nylon 610, nylon 11 and nylon 12 exhibit properties which are largely due to their high molecular order and the high degree of interchain attraction which is a result of their ability to undergo hydrogen bonding. 

Examine the structure of the short strand of Nylon 6 in which all amide bonds are Z. What is the monomer unit How many monomers are in the strand Note Each end of the polymer strand has been capped by one or more atoms. Do not count these caps as monomers. Compare the strand to that of a simple polypeptide, for example, polyglycine (see also Chapter 16, Problem 9), and point out any obvious similarities. Pay particular attention to hydrogen bonds. 

Examine the structure of a strand of Nylon 6 in which all amide bonds are E. Describe how this differs from the strand in which the amide linkages are Z. In particular, are the same hydrogen-bond patterns found ... 

The elasticity of nylon fibers is due in part to hydrogen bonds between adjacent polymer chains. These hydrogen bonds join carbonyl oxygen atoms on one chain to NH groups on adjacent chains (Figure 23.4). 

Nylon-6,6, 2, 136, 530. See also PA-6,6 acid-catalyzed hydrolysis of, 568 acidolysis of, 568 alkaline hydrolysis of, 568-569 ammonolysis of, 555, 570 chemistry and catalysis of, 546 creation of, 1 hydrogen bonding in, 539 hydrolysis of, 531, 544, 552-555 phase-transfer-catalyzed alkaline hydrolysis of, 569-570... 

One example of a familiar amide is the pain-relieving drug sold as Tylenol (14) we shall see another important example when we consider the polymer known as nylon in Section 19.10. Many amides have N—H bonds that can rake part in hydrogen bonding, and so the intermolecular forces between their molecules are relatively strong. 

FIGURE 19.13 The strength of nylon fibers is an indication of the strength of the hydrogen bonds between neighboring polyamide chains. 

Koberstein J.T., Gancarz I., and Clarke T.C., The effect of morphological transition on hydrogen bonding in PU Preliminary results of simultaneous DSC-FTIR experiments, J. Polym. Sci. B, 24, 2487, 1986. Skrovanek D.J., Painter P.C., and Coleman M.M., Hydrogen bonding in polymers 2. Infra red temperature studies on nylon 11, Macromolecules, 19, 699, 1986. 

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