Step-growth polymerizations facilitated by supercritical carbon dioxide: The synthesis of poly(bisphenol A carbonate)

Supercritical fluid extraction methods using carbon dioxide were employed to remove the condensate (phenol) for the step-growth polymerization of diphenylcarbonate and bisphenol A to yield aromatic polycarbonates. The mechanism of this polymerization was found to be compatible with the added CO2 which allows the use of such an inert, non-toxic diluent to be employed as a polymerization aid to swell the melt phase, reducing its viscosity.; Poly(bisphenol A carbonate) was synthesized by solid state polymerization (SSP) using supercritical CO2 to induce crystallinity in low molecular weight polycarbonate beads. The CO2 induced crystallization was studied as a function of time, temperature, molecular weight, and pressure. There was an optimum temperature for crystallization which depended on the molecular weight of the polymer. The molecular weight and percent crystallinity of the polymer produced by SSP were determined as a function of time and radial position in the bead. The molecular weight and percent crystallinity were strong functions of the particle radius, probably because of the slow diffusion of phenol out of the polymer particles.; The SSP of small particles (20 mum) of poly(bisphenol A carbonate) resulted in high molecular weight material (Mw of 36,000 g/mol). Molecular weight distribution broadening was not observed in polycarbonate in the form of small granulated powders, but did occur in large polycarbonate beads (3.6 mm diameter). We hypothesize that this broadening is due to slow diffusion of phenol inside the larger polymer particles. A systematic investigation of the role of CO2 pressure and temperature was performed. It was found that the increase in molecular weight was a strong function of CO 2 pressure and temperature. Additionally, the chain extension reactions occurred faster at higher supercritical CO2 flow rates. The SSP of polycarbonate in the presence of supercritical CO2 can be accomplished at temperatures as low as 90°C, which is 60°C lower than the T g of polycarbonate at normal conditions. This should suppress the side reactions that lead to colorbody formation, thereby resulting in a product with good optical clarity and color.; The equilibrium constant was directly determined for the reaction between bisphenol A and diphenyl carbonate over the temperature range of 150 to 230°C. This allowed for the determination of the enthalpy and entropy of this reaction.