GB1110736A - Transesterification process for the production of high molecular weight thermoplasticpolycarbonates - Google Patents

Abstract

Polycarbonates are made by (a) reacting substantially equimolecular quantities of a diaryl carbonate and an organic dihydroxy compound at 150 DEG to 250 DEG C. in a closed system to produce a mixture of a monohydric phenol and a monomeric mixed carbonate containing the residues of one mole of the organic dihydroxy compound and one mole of the monohydric phenol component of the diaryl carbonate, (b) distilling off the monohydric phenol under reduced pressure and (c) polycondensing the monomeric mixed carbonate at 150 DEG to 350 DEG C., preferably under reduced pressure. Step (a) may be effected under reflux of the liberated monohydric phenol, or in an autoclave under pressure or continuously in a pressure tube. Transesterification catalysts may be used. Step (c) may be effected by a batch process, or first in a thin film evaporator and then in a screw evaporator, or in a cascade of three stirred reaction vessels in which the temperatures are respectively 210 DEG , 230 DEG and 260 DEG C., and the pressures are respectively 30, 10 and less than 2 mm. of Hg. Specified organic dihydroxy compounds are various alkanediols, 1:4 - dihydroxycyclohexane and various dihydric phenols. Examples describe reacting diphenyl carbonate and bisphenol A.