Process for the preparation of polycarbonates
View Patent ↗An improvement to the phase interface process of preparing aromatic polycarbonate is disclosed. The process is characterized in that the phosgenation is carried out at 0 to 40° C., and in that the temperature of the reaction mixture at the time of addition of the catalyst at 10 to 40° C., and in that the molar ratio of aromatic dihydroxy compounds to phosgene at 1:1.05 to 1:1.20. The polycarbonate thus produced is characterized in its low content of carbamates, making it particularly suitable for the preparation of optical storage media.
1. In a phase interface process for preparing aromatic polycarbonate comprising from 0.25 to 180 ppm of one or more carbamates of formula (1)
wherein
R 1 and R 2
are, independently of one another, H or C 1 to C 12 alkyl or together are a C 4 to C 12 alkylidene; and
R 3 and R 4
are, independently of one another, H, C 1 to C 12 alkyl, or phenyl or together with the carbon atom to which they are bonded are cyclohexyl or trimethylcyclohexyl;
comprising reacting at least one aromatic dihydroxy compound and phosgene in an alkaline medium, the improvement comprising
(i) phosgenating at 0 to 40° C.,
(ii) maintaining the temperature of the reaction mixture at the time of addition of the catalyst at 10 to 40° C., and
(iii) maintaining the molar ratio of aromatic dihydroxy compounds to phosgene at 1:1.05 to 1:1.20.
2. The process of claim 1 which is performed as a continuous process.
3. The process of claim 1 wherein said molar ratio of aromatic dihydroxy compounds to phosgene is maintained at 1:1.08 to 1:1.17.
4. In a phase interface process for preparing aromatic polycarbonate comprising from 0.25 to 180 ppm of one or more carbamates of formula (1)
wherein
R 1 and R 2
are, independently of one another, H or C 1 to C 12 alkyl or together are a C 4 to C 12 alkylidene; and
R 3 and R 4
are, independently of one another, H, C 1 to C 12 alkyl, or phenyl or together with the carbon atom to which they are bonded are cyclohexyl or trimethylcyclohexyl;
comprising reacting at least one aromatic dihydroxy compound and phosgene in an alkaline medium, the improvement comprising
(i) phosgenating at 0 to 40° C.,
(ii) maintaining the temperature of the reaction mixture at the time of addition of the catalyst at 5 to 36° C., and
(iii) maintaining the molar ratio of aromatic dihydroxy compounds to phosgene at 1:1.05 to 1:1.20.