DENSITY-FUNCTIONAL STUDY OF CRYSTALLINE ANALOGS OF POLYCARBONATES

Density functional studies have been performed for two crystalline ana logs of Bisphenol A polycarbonate (BPA-PC) and for the isolated struct ural unit. The calculations are free of adjustable parameters and yiel d equilibrium structures that agree well with available data. Vibratio nal frequencies have been calculated for the molecular unit. For all s tructures we have calculated the energy barriers for rotation of segme nts of the molecule, and we have compared the results with experiment. All phenylene groups rotate freely in the isolated molecular unit, bu t the corresponding pi-flips in the crystalline phases are hindered by the neighboring molecules and reflect the chain packing. The minimum energy barrier for the rotation in the crystal (7.7 kcal/mol) is assoc iated with the rotation of the inner phenylene ring in the molecular u nit. The activation energy for the rotation of the methyl groups is 3. 4 kcal/mol, independent of the chain packing, and the barriers for rot ation of the carbonyl group are 8.7 and 19 kcal/mol in the molecule an d crystal phase, respectively.