Nylon-hydrogen bonding

Stuart [39] used FT-Raman spectroscopy to study changes in the spectrum of nylon 6 films due to either heating the material or due to absorption of water. Both increased temperature and increased water content are believed to decrease the number of nylon-nylon hydrogen bonds and both result in similar changes in the mechanical properties. However, Stuart found that they affected the Raman spectra in very different ways. On increasing the temperature, he found that the intensity of the N—H stretch, the amide I and III, the CH2 bending and the C—C stretch all decreased relative to the C—H symmetric stretch (2902 cm ) intensity. Surprisingly, the intensity of all of these bands, relative to the 2902-cm band increased in the presence of water. He attributed the difference... 

Anodier class of representative ferroelectric and piezoelectric polymers is odd-numbered polyamides (nylons). Hydrogen bonding formed by -NH and -C=0 groups provides essential polar elements in the polymer for piezoelectricity. The significant piezoelectiic properties of nylon 11 was studied and reported in the early 1980s (Newman et al. 1980 Mathur et al. 1988). Its ferroelectricity was predicted based on a study on its chemical structures and crystal phases. However, the synopsis of ferroelectiicity in nylons was not confirmed until 1991 when Scheinbeim et al. 

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 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. 

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. 

One of the pol3Tners used for carpet fibers is Nylon 6, in which neighboring polymer strands are held together by hydrogen bonds. 

Draw two strands of Nylon 6, each with four repeat units. Show the two strands connected by hydrogen bonds. 

The molecular structure of nylon 6 is shown in Fig. 23.2 a). Its repeat unit consists of an amide group and a pentamethylene sequence, i.e., -(CH2)5CONH- The polar amide groups from adjacent chains interact with each other to form hydrogen bonds, which link the chains. 

The molecular arrangement within the crystal units cells of nylon is governed by the need to maximize hydrogen bonding between adjacent chains. Hydrogen bonding within crystallites is facilitated by the fact that nylon chains adopt planar zig-zag conformations with dipoles perpendicular to the chain axis to thin the plane of the molecule. Examples of nylon crystallite structures are shown in Figs. 23.8 and 23.9 for nylon 6 and nylon 66, respectively. In the... 

Nylon crystallites consist of sheets of chains that are hydrogen-bonded to their neighbors. On a supermolecular scale, crystallites have a lamellar structure, that is they are many times longer and broader than they are thick. When nylon crystallizes from an isotropic molten state, it generally forms spherulites, which consist of ribbon-like lamellae radiating in all directions... 

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