Ring-Opening and Branching in Polycarbonates: A Density Functional-Monte Carlo Study

Abstract

Density functional calculations of the structures, potential energy surfaces, and reactivities for systems closely related to bisphenol A-polycarbonate (BPA-PC) provide the basis for a model describing the ring opening polymerization of its cyclic oligomers by nucleophilic molecules. The model comprises a fixed number of difunctional particles and harmonic bonds, and includes a low concentration (0.01% < C a < 0.36%) of monofunctional active particles able to modify pattern of the bonds without changing the total number. Monte Carlo simulations using this model show that in 2D and 3D there is a transition from unpolymerized cyclic oligomers at low density to a system of linear chains at high density. Entropy in the distribution of inter-particle bonds drives chain formation. The effects of branching defects are investigated by adding trifunctional units (of concentration c 3 ). At sufficiently high density and c 3 values, the linking of polymer chains by trifunctional units gives rise to an aggregate (gel) incorporating most of the system mass.