Polyamide hydrogen bonding

In polymers having polar groups, intermolecular electrostatic attractions exert strong influence on chain conformation in their crystals. In polyamides, hydrogen bonds form between the carbonyls and NH groups of neighboring chains (Fig. 2.11) and influence the crystallization of the polymer in the form of sheets, with the macromolecules themselves packed in planar zigzag conformations [see Fig. 2.11(b)]. 

In polymers having polar groups, intermolecular electrostatic attractions exert strong influence on chain conformation in their crystals. In polyamides, hydrogen bonds form between the carbonyls and NH groups of neighboring chains (Fig. 

Polyamides. The next two compounds are the amide counterparts of the esters listed under item (4). Although the values of AH j are less for the amides than for the esters, the values of T j, are considerably higher. This is a consequence of the very much lower values of AS j for the amides. These, in turn, are attributed to the low entropies of the amide in the liquid state owing to the effects of hydrogen bonding and chain stiffness arising from the contribution of the resonance form... 

The various mechanical properties of polyamides may be traced in many instances to the possibility of intermolecular hydrogen bonding between the polymer molecules and to the relatively stiff chains these substances possess. The latter, in turn, may be understood by considering still another equilibrium, this one among resonance structures along the chain backbone ... 

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. 

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

Fig. 3.2 Pairing rules for polyamide recognition of all four Watson—Crick base pairs of DNA. Putative hydrogen bonds are shown as dashed lines. Circles with dots represent lone pairs of N(3) of purines and 0(2) of pyrimi-...

U-pin is most comparable to a six-ring hairpin polyamide, likely due to a loss of two hydrogen bond donors upon removal of the y-turn element. Thus, the dimeric Py-lm U-turn element may be thought of as a C,G-specific replacement for the y-tum (Fig. 3.4). In combination with removal of the /9-Ala tail (see below), H-pin and U-pin polyamides could potentially bind purely G,C sites, a sequence type that has been difficult to target with other polyamide motifs. 

Fig. 3.15 Model for allosteric inhibition of a protein-DNA complex by a polyamide-inter-calator conjugate. (Top) The GCN4 homodimer (yellow) is displaced by the intercalating moiety (green) of the polyamide conjugate. Blue and red spheres represent pyrrole and imidazole amino acids, respectively. The blue diamond represents / -alanine. (Bottom, left) Hydrogen-bonding model of an eight-ring hairpin polyamide-intercalator conjugate...

We can divide commodity plastics into two classes excellent and moderate insulators. Polymers that have negligible polar character, typically those containing only carbon-carbon and carbon-hydrogen bonds, fall into the first class. This group includes polyethylene, polypropylene, and polystyrene. Polymers made from polar monomers are typically modest insulators, due to the interaction of their dipoles with electrical fields. We can further divide moderate insulators into those that have dipoles that involve backbone atoms, such as polyvinyl chloride and polyamides, and those with polar bonds remote from the backbone, such as poly(methyl methacrylate) and poly(vinyl acetate). Dipoles involving backbone atoms are less susceptible to alignment with an electrical field than those remote from the backbone. 

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