Crystallization and solid-state polymerization of poly(bisphenol A carbonate) facilitated by supercritical CO2

Poly(bisphenol A carbonate) was synthesized by solid-state polymerization ( SSP) using supercritical CO2 to induce crystallinity in low molecular weigh t polycarbonate beads. The CO2-induced crystallization was studied as a fun ction of time, temperature, molecular weight, and pressure. There was an op timum temperature for crystallization which depended on the molecular weigh t of the polymer. The molecular weight and percent crystallinity of the pol ymer produced by SSP were determined as a function of time and radial posit ion in the bead. The molecular weight and percent crystallinity were strong functions of the particle radius, probably because of the slow diffusion o f phenol out of the polymer particles. Nitrogen and supercritical CO2 were used as sweep fluids for the SSP process. The polymerization rate was alway s higher in supercritical CO2 at otherwise comparable conditions. We hypoth esize that supercritical CO2 plasticizes the amorphous regions of the polym er, thereby increasing chain mobility and the rate of phenol diffusion out of the polymer. This permits the reaction temperature to be reduced, thereb y suppressing side reactions that lead to color body formation. These advan tages result in higher molecular weight product with good optical clarity w hen supercritical CO2 is the sweep fluid.