Assessment of two methods for application in the prediction of the infrared spectra of polymers

Two simple simulation methods, which will be useful for the prediction of the infrared (IR) spectral features of polymers, are reported. This paper focusses on simple aromatic models of the main aromatic backbones of structural polymeric resins. These methods were normal coordinate analysis (NCA) using the PM3 Hamiltonian implemented under MOPAC6 and a dipole autocorrelation function (DACF) calculated using coordinates and velocities from a series of molecular dynamics runs performed using the universal force-field (UFF) as implemented in the Cerius² modelling package. The semi-empirical NCA approach yielded useful information about the fundamental modes of vibration of the molecules but, as expected, could not be used to predict combination modes for anything but the simplest of molecules. The DACF approach showed potential for the prediction of combination bands but thorough evaluation of the method was found to be extremely difficult, owing to problems with band assignment for all but the simplest of molecules. An estimate of the accuracy of prediction for the different types of vibrational mode is included for each method.