Macromol. Symp. 119, 157-164 (1997) 157 INFRARED ABSORPTION SPECTRA OF POLYMERS FROM CLASSICAL MOLECULAR SIMULATION Armand Soldera* and Jean-Pierre Dognon CEA / Le Ripault, B.P. 16, 37260 - MONTS, FRANCE Abstract: A method is proposed to predict the infrared spectra of amorphous polymers. Based on classical molecular simulation and Kramers-Kronig relations, it allows the computations of absorption and transmittance spectra of polymer films in near and middle infrared domains with good agreement with experimental data. INTRODUCTION Molecular simulation has shown a positive rise these recent years. This is in accordance with the increase of computer capacity and the refinement of the force fields used. Consequently, predictions of molecular properties become more and more accurate. In this context, a computation of amorphous polymers infrared spectra from molecular simulation is presented. The suggested calculation method combines molecular and amorphous phase simulations with Kramers-Kronig relations. To compare the computed and measured optical properties, the method is applied to an amorphous polymer, the poly(methyl methacrylate), PMMA. RESULTS AND DISCUSSION COMPUTATIONAL PART Calculation of Infrared Spectra and Optical Properties Some quantum chemical methods are available to simulate vibrational spectra of organic molecules (Refs. 1, 2). When the number of atoms in a molecule increases, they can no longer be used. Empirical force field methods, mainly deriving from experimental data, are best suited to study polymers (Ref. 3, 4).