SITE-SPECIFIC REVERSIBLE SCISSION OF HYDROGEN-BONDS IN POLYMERS - AN INVESTIGATION OF POLYAMIDES AND THEIR LEWIS ACID-BASE COMPLEXES BY INFRARED-SPECTROSCOPY

Lewis acid-base complexation in conjunction with Fourier transform infrared spectroscopy was used to study the scission and re-formation of N-H...O=C hydrogen bonds in seven aliphatic polyamides and one aromatic polyamide. The characteristic shifts of the N - H stretch frequency, the amide I mode, and the amide II mode in the vibrational spectra of several polyamides on GaCl3 complexation were examined at room temperature (25-degrees-C). Complete scission of the intermolecular hydrogen bonds in polyamides was achieved by the 1:1 Lewis acid complexation of the basic oxygen sites of the carbonyl groups in the polymers, thus "liberating" the N-H groups from hydrogen bonding. Facile decomplexation of the polyamide-Lewis acid complexes resulted in the reformation of the hydrogen bonds and, consequently, the characteristic solid-state structure and properties of the polyamides. Thus, the hydrogen bonds in polyamides function like a molecular zipper: Lewis acid-base complexation "unzips" and decomplexation "zips" the macromolecular chains. These results have important implications for the understanding of hydrogen bonding in polymers and its effects on structure and properties. The results also suggest a possible application of our approach of reversible hydrogen bond scission to ultradrawing of polymers with hydrogen bonding to highly oriented materials with high strength and high modulus.