Two-dimensional correlation analysis of variable-temperature Fourier-transform mid- and near-infrared spectra of polyamide 11

Two-dimensional (2D) correlation analysis was applied to both the Fourier-t ransform (FT) mid-infrared (MIR) and near-infrared (NIR) variable-temperatu re spectra of polyamide 11 (PA11) to investigate the structural response of the hydrogen bonds and the hydrocarbon chains during heating from 125 to 1 70 degrees C. Homo- and hetero-spectral correlations of the MIR and MR spec tral regions were performed. It is shown that the antisymmetric stretching vibrations of the methylene groups and the NH-nlated absorption bands are v ery sensitive to the temperature-induced structural changes of the investig ated PA11 sample. The sequence of the spectral changes of different NH and CH2 fundamental vibrations and overtones during heating the polymer were in ferred from the signs of the asynchronous peaks. The advantages of NIR spec troscopy for the study of the dissociation process of the amide hydrogen bo nds are demonstrated. Evidence that the conformational changes of the methy lene groups precede the loosening of amide hydrogen bonds is provided. (C) 2000 Elsevier Science B.V. All rights reserved.