FT-IR spectroscopic studies of polyurethanes Part I. Bonding between urethane C-O-C groups and the NH Groups

Fourier-transform-infrared-attenuated total internal reflectance (FT-IR-ATR)has been used to study polyurethanes containing different hard segments but the same soft segment. The spectra of a series of blended polyurethanes have been systematically studied. The changes in the urethane C-O-C regions of the olyurethanes with respect to the hard segments make a strong case for the existence of hydrogen-bonding interactions between the urethane C-O-C groups and the NH groups. The decreases in the relative intensities of carbonyl bands and shifts of NH stretching bands (as the urethane C-O-C bonding with NH groups increases)are in support of this proposal. The urethane C-O-C region is shown to be a useful region in interpreting ATR spectra of polyu- rethanes. The implications of these results to the present methods of estimating phase separations in polyurethanes are discussed. Results obtained from ab initio quantum hemical computational methods show this hydrogen bond to be directional and to have an energy of 6.32 kcal mol-' (compared with carbonyl hydrogen bond energy of 8.37 kcal mol-')which is surprisingly high.