METHOD OF PREPARING POLYCARBONATE Russian patent published in 1999 - IPC

FIELD: manufacture of sheets, films, optical products and pyrormation carriers. SUBSTANCE: polycarbonate is prepared by phosgenation of bisphenol in the presence of sodium hydroxide in mixture of solvent of methylene chloride and chlorobenzene by polycondensation of catalyst followed by evaporation of methylene chloride in thin layer to attain polycarbonate concentration in chlorobenzene at 15-30%, 5-50% chlorobenzene containing methylene chloride vapors are rectified where fraction with melting temperature of 60- 85 C in amount of 0.5-5% based on amount of methylene chloride to be rectified is withdrawn from process. Chlorobenzene is evaporated in two stages in thin layer in vacuum. Condensed solvents are recycled. Methylene chloride is evaporated at 80-140 C for 20-120 s. Prior to evaporation, thermostabilizer and/or lubricant and/or antipyrene are added to thermostabilizer and/or lubricant. EFFECT: reduced yellowness index, higher light transmission stability. 4 cl, 6 ex, 1 tbl