Journal of Molecular Structure, 263 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE (1991) 45-57 Elsevier Science Publishers B.V., Amsterdam 45 FT-IR spectroscopic studies of polyurethanes Part I. Bonding between urethane C-O-C groups and the NH Groups zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Jagdeesh Bandekar and Suzanne Klima The BOC Group Technical Center, 100 Mountain Avenue, Murray Hill, NJ 07974 (USA) (Received 9 May 1991) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC Abstract 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 polyurethanes 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 chemical 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. INTRODUCTION Polyurethane polymers are an important class of biomaterials and a better understanding of their structure is essential to understand their performance. Studies of hydrogen-bonding (H-bonding) in polyurethanes have been shown to be an effective means of studying structure-property relationships [ 1, 21. FT-IR spectroscopy, employing the ATR technique, has proved to be an ex- cellent tool for studying surface properties of polyurethanes. These surface properties are important in understanding the blood-compatibility aspects of polyurethanes. Based on infrared spectroscopic studies of model polyurethane compounds, Boyarchuk et al. [3] proposed three types of H-bonding in polyurethanes in which the NH groups are H-bonded to any of the three likely proton-accepting groups; namely, (a) carbonyl groups, (b) polyether C-O-C groups, and (c) 0022-2860/91/$03.50 0 1991 Elsevier Science Publishers B.V. All rights reserved.