Patent ID: 7501481

Claim:
A method of producing a copolycarbonate with improved color wherein the method comprises the steps of, i. preparing a molten reaction mixture in a monomer mix tank wherein the reaction mixture comprises a first dihydroxy aromatic compound comprising monomer residue (a), a second dihydroxy aromatic compound comprising monomer residue (b), and a carbonate source, wherein monomer residue (a) is a quinone structure, or a structure capable of forming a quinone structure upon oxidation, wherein monomer residue (b) is a quinone structure, or a structure capable of forming a quinone structure upon oxidation different from monomer residue (a) or is, where B is —O—, —CO—, —S—, —SO 2 —, a C 6 -C 20 aromatic radical, or a C 6 -C 20 cycloaliphatic radical; the groups R 1 and R 2 are independently a hydrogen atom, C 1 -C 20 alkyl radical, C 4 -C 20 cycloalkyl radical, or C 4 -C 20 aryl radical; or R 1 and R 2 together form a C 4 -C 20 cycloaliphatic ring which is optionally substituted by one or more C 1 -C 20 alkyl, C 6 -C 20 aryl, C 5 -C 21 aralkyl, C 5 -C 20 cycloalkyl groups or a combination thereof, R 3 is a divalent hydrocarbylene group, and R 4 and R 5 are independently a hydrogen atom, halogen atom, nitro group, cyano group, C 1 -C 20 alkyl radical C 4 -C 20 cycloalkyl radical, or C 6 -C 20 aryl radical and p and q are both integers from 0 to 4, ii. introducing a polymerization catalyst to the reaction mixture or monomer residues prior to melting in said monomer mix tank with the proviso that the residence time of the process from the start of melting until substantial polymerization has occurred is less than 4 hours, wherein the polymerization catalyst is an inorganic catalyst, an organic catalyst, or both an inorganic catalyst and an organic catalyst which may be introduced separately or together, iii. introducing the reaction mixture to a series of process units, wherein said series of process units comprises a plurality of polymerization process units in which polymerization occurs and copolymer molecular weight increases, and iv. allowing the reaction mixture to polymerize in the series of process units thereby forming copolycarbonate, wherein the copolycarbonate has improved color as compared to a copolycarbonate formed in a melt process wherein said residence time is not less than 4 hours.