Patent ID: 6232432
Filing Date: 2001-05-15
Classification: C08G

Abstract:
A process for the preparation of polycarbonates which comprises:(a) preparing a prepolymer having a viscosity average molecular weight of 4,000-18,000 g/mole through melt polymerization of aromatic dihydroxide and diarylcarbonate, wherein the viscosity average molecular weight is determined from intrinsic viscosity measurements at 25.degree. C. using dilute polycarbonate chloroform solutions;(b) preparing a microporous foam having a specific gravity of 0.4-1.15 by introducing high-pressure inert gas, stirring, and discharging said prepolymer;(c) preparing a solid particle having 10-50% of crystallinity by crushing said prepolymer foam to a mean particle size of 0.1-2 mm and stirring in the solvent; and(d) preparing polycarbonates by a solid-state polymerization of the solid particle at 190-240.degree. C.