Quasi-Static Modeling of Chain Dynamics in the Amorphous Glassy Polycarbonate of 4,4′-Isopropylidenediphenol

A detailed static atomistic model of the dense, glassy polycarbonate of 4,4′-isopropylidenediphenol (Bisphenol A polycarbonate (PC)) is used for a quasi-static simulation of localized motions. These motions include the phenylene ring “flip”, conformational changes of the carbonate group, and cooperative main-chain motion. The frequency distribution for the simulated ring flip motion covers several orders of magnitude. The average energy barrier to phenylene ring flip is calculated as 10.4 (±6.7) kcal/mol, and the average barrier for the conformational change of the carbonate group is 10.1 (±6.5) kcal/mol. No significant reorientation of the ring axis was observed in the simulations, with 90% of the axes changing less than 15°. A slight main-chain motion was found superimposed upon the ring flip and the carbonate group conformational changes. The intermolecular effects of the analyzed processes were found dominant and farreaching, widely influencing the cooperative motions of molecular groups. Cooperativity between neighboring rings along the chain and between rings and carbonate groups along the chain was observed, but no cooperative process involving two carbonate groups along the chain was found.