Two-dimensional correlation analysis of variable-temperature Fourier-transform near-infrared spectra of an amorphous polyamide.
Near-IR spectra of a totally amorphous polyamide measured over the temp. range from 25 DegC-200 DegC were analyzed using generalized two-dimensional (2D) correlation spectroscopy. At least five distinct bands at 5690, 5810, 5900, 5980 and 6010 cm-1 were identified in the region of the n(CH) overtones (5400-6100 cm-1). Among them, two bands at 5810 cm-1 (aliph. CH) and 6010 cm-1 (arom. CH) were found to be very sensitive to the temp.-induced structural changes of the polyamide under examn. In the n(NH) overtone region (6300-6800 cm-1), the asynchronicity of the bands assigned to the vibrations of the free and hydrogen-bonded NH groups indicates a complicated dissocn. mechanism and the existence of different hydrogen-bonded species in the investigated totally amorphous polyamide sample. Owing to the spectral resoln. enhancement in the 2D correlation spectra, a splitting of the first n(NH) overtone of free NH groups into two components at 6780 cm-1 (totally free) and 6740 cm-1 (free-end) can be obsd.
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