Method for producing polycarbonate copolymer and polycarbonate copolymer

A method for producing a polycarbonate copolymer comprising repeating units represented by the following formulas (I) and (II):

• where:
• R1 and R2 are each independently a halogen atom or an alkyl group having 1 to 6 carbon atoms;
• when there are two or more R1s, each R1 can be different from or the same as the other(s);
• when there are two or more R2s, each R2 can be different from or the same as the other(s);
• a and b are each independently an integer from 0 to 4;
• and
• X represents a single bond, an alkylene group having 1 to 8 carbon atoms, an alkylidene group having 2 to 8 carbon atoms, a cycle alkylidene group having 5 to 15 carbon atoms, —S—, —SO—, —SO2—, —O—, —CO—, or a bond represented by the following formula (III-1) or (III-2):
• where:
• R is an alkyl group having 1 to 3 carbon atoms;
• Y is a straight chain or branched alkylene group having 2 to 15 carbon atoms;
• m is an integer of 0 to 4;
• and
• r is an integer of 2 to 450;
• the method comprising:
• reacting a diester diol-containing monomer, a divalent phenol, and a carbonate precursor by interfacial polymerization, wherein;
• the diester diol-containing monomer is a mixture of a diester diol according to the following formula (3) and a monoester diol represented by the following formula (4)
• the mixture is obtained by reaction of a hydroxybenzoic acid or an esterified product thereof represented by the following formula (1) and a polyalkylene glycol represented to by the following formula (2):
• where R′ is a hydrogen or a lower alkyl group;
• an esterification degree of hydroxyl groups of the polyalkylene glycol is 50 to 90 mol %.