Chain Conformations of Polycarbonate from ab Initio Calculations

Abstract

Ab initio calculations with full geometry optimization on diphenyl carbonate (DPC) and diphenylpropane (DPP) are carried out to determine the bond geometries and the conformational energies and then to compute the unperturbed chain dimensions of the polycarbonate of 2,2-bis(4-hydroxyphenyl)propane, or bisphenol A polycarbonate. The bond geometries calculated with the 6-31G* basis sets are in excellent agreement with the experimental values. The conformational energy contours exhibit a rather low energy barrier (ca. 1.9 kcal/mol) in DPP and a nearly flat profile in DPC for the rotations of phenylene groups. Moreover, the trans conformation of the carbonate group is favored by ca. 2.75 kcal/mol over the cis state. Application of these results to the rotational isomeric state model of the polycarbonate chain leads to the prediction of the unperturbed chain dimension of (r2)0/Ai 1.1, which supports the previous calculation of Yoon and Flory. This calculated value is in satisfactory agreement with the experimental results of 1.2-1.3, obtained from small-angle neutron scattering from amorphous polycarbonate by Gawrisch et al. and Ballard et al. © 1988, American Chemical Society. All rights reserved.