Synthesis of high molecular weight polycarbonate by solid-state polymerization

Abstract

The solid-state polymerization (SSP) of small particles (20 pm) 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 CO2 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 Tg of polycarbonate at normal conditions. This should suppress the side reactions that lead to color body formation, thereby resulting in a product with good optical clarity and color.