Density functional study of polycarbonate. 2. Crystalline analogs, cyclic oligomers, and their fragments

Density functional studies have been performed for the crystalline forms of the cyclic dimer and tetramer of bisphenol A polycarbonate (BPA-PC), as we ll as for the isolated structural units and their fragments (including carb onic acid, benzene, phenol, monophenyl carbonate, and BPA). There are no ad justable parameters in the calculation, and the optimized structures agree well with the results of X-ray diffraction analyses where available. Calcul ated vibration frequencies are compared with experimental data and with ear lier calculations. Ring-opening of the cyclic oligomers is an important pol ymerization technique, and the cyclic tetramer provides an interesting mode l for future calculations of reactions between polymer segments and additio nal molecules.