Reaction Kinetics of the Solid-State Polymerization of Poly(bisphenol A carbonate) Facilitated by Supercritical Carbon Dioxide

Abstract

The kinetics of solid-state polymerization (SSP) of poly(bisphenol A carbonate) was investigated with supercritical CO2 (scCO2) as the sweep fluid. The CO2 flow rate and polymer particle size were chosen to ensure that the kinetics was controlled by the rate of the forward transesterification reaction, i.e., so that both external and internal phenol diffusion limitations were negligible. The forward reaction rate constants were determined between 90 and 135 °C, at CO2 pressures of 138, 207, and 345 bar. At a given temperature, the reaction rate was higher with scCO2 as the sweep fluid than with N2, especially at lower temperatures. The rate constant for the forward transesterification reaction increased with increasing CO2 pressure up to about 207 bar, at which point the rate constant was no longer sensitive to CO2 pressure. The activation energy decreased from 23.9 kcal/mol in N2 to 15.5, 11.6, and 11.4 kcal/mol at CO2 pressures of 138, 207, and 345 bar, respectively. The effect of scCO2 on the rate of polymerization can be understood in terms of the solubility of CO2 in the polymer.