Raman Studies of Hydrogen Bonding in Polyamides

We report Raman and pre-resonant Raman spectra of the polyamides N,N- tetramethylene bisbutamide, N,N-hexamethylene bishexamide, and 7,14-diazacyclotetradecane-1,6-dione, as well as of a low molecular weight prepolymer of nylon 6,6 aimed at characterizing the nature of hydrogen bonding in these compounds. The relative intensities of the C=O stretch and C-N stretch bands, the frequency width of the C=O band, the frequency of the N-H stretch band, and the frequency width of the N-H band indicate that these compounds do not show the Raman signatures of hydrogen bonding that we have established in our previous studies of many model amides. In this regard, these polyamides behave like the lactams 2-azacyclononanone and 2-azacyclotridecanone, for which all the Raman spectral indicators of hydrogen bonding are similarly negative. These results indicate that whatever the nature of the intermolecular interactions in these polyamides, they do not result in the changes in vibrational and electronic structure that we believe are associated with hydrogen bonding.