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-transform (FT) mid-infrared (MIR) and near-infrared (NIR) variable-temperature spectra of polyamide 11 (PA11) to investigate the structural response of the hydrogen bonds and the hydrocarbon chains during heating from 125 to 170 degrees C. Homo- and hetero-spectral correlations of the MIR and MR spectral regions were performed. It is shown that the antisymmetric stretching vibrations of the methylene groups and the NH-nlated absorption bands are very sensitive to the temperature-induced structural changes of the investigated PA11 sample. The sequence of the spectral changes of different NH and CH2 fundamental vibrations and overtones during heating the polymer were inferred from the signs of the asynchronous peaks. The advantages of NIR spectroscopy for the study of the dissociation process of the amide hydrogen bonds are demonstrated. Evidence that the conformational changes of the methylene groups precede the loosening of amide hydrogen bonds is provided. (C) 2000 Elsevier Science B.V. All rights reserved.