Two-dimensional correlation analysis of variable-temperature Fourier-transform mid- and near-infrared spectra of polyamide 11.
Two-dimensional (2D) correlation anal. was applied to both the Fourier-transform (FT) mid-IR (MIR) and near-IR (NIR) variable-temp. spectra of polyamide 11 (PA11) to investigate the structural response of the hydrogen bonds and the hydrocarbon chains during heating from 125 to 170 DegC. Homo- and hetero-spectral correlations of the MIR and NIR spectral regions were performed. It is shown that the antisym. stretching vibrations of the methylene groups and the NH-related absorption bands are very sensitive to the temp.-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 dissocn. 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.
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