FTIR analysis of hydrogen bonding in amorphous linear aromatic polyurethanes. I. Influence of temperature

Abstract Fourier‐transform infrared spectral studies of an amorphous linear aromatic polyurethane at various temperatures were performed. Hydrogen bonding was studied in the NH stretching (3347 cm −1 ) and the bending (1535 cm −1 ) regions, using the band decomposition technique. The variations with temperature are used to calculate the ratio of the absorptivity coefficients for the H‐bonded to the “free” NH vibrations. This ratio is found to be independent of temperature. The enthalpy and the entropy of hydrogen bond dissociation are also obtained as 9.6 kJ mol −1 and 44.8 J mol −1 K −1 , respectively. Two CC in‐plane vibrational bands of the aromatic rings at 1614 and 1598 cm −1 were studied at different temperatures. The integrated absorbance for both bands decreases clearly and regularly with increasing temperature, and both bands shift to lower wavenumbers. This strongly suggests a specific interaction for the aromatic rings, probably NH … π hydrogen bonds, which will be discussed in detail in the second part of this series. © 1994 John Wiley & Sons, Inc.