| 摘要 |
A subject of the invention is to provide a polycarbonate having excellent mechanical strength, heat resistance, a low refractive index, a large Abbe number, reduced birefringence, and excellent transparency. The invention relates to a process for producing a polycarbonate by subjecting one or more dihydroxy compounds comprising a dihydroxy compound having at least one linking group -CH 2 -O- in the molecule thereof to melt polycondensation with a carbonic acid diester with heating with a heating medium, characterized by comprising a first-stage polycondensation step in which a mixture of the dihydroxy compounds and the carbonic acid diester is fed in a molten state to a vertical reactor equipped with a vertical rotating shaft and a stirring blade attached to the vertical rotating shaft, and a polycondensation reaction is conducted at a temperature of 150°C to 270°C to obtain a polycarbonate having a reduced viscosity of 0.03-0.40 dL/g and a second-stage polycondensation step in which the polycarbonate obtained in the first-stage polycondensation step is fed to a horizontal stirring reactor which has a horizontal rotating shaft and mutually discontinuous stirring blades attached approximately perpendicularly to the horizontal rotating shaft and in which when the length of the horizontal rotating shaft and the rotation diameter of the stirring blades are respectively expressed by L and D, then L/D is 1-15, and a polycondensation reaction is conducted at a temperature of 210°C to 270°C to obtain a polycarbonate having a reduced viscosity of 0.20-1.70 dL/g. |
