Patent ID: 7674872

Claim:
A method of forming polycarbonate comprising the steps of: (a) introducing to a reactor system a reaction mixture comprising a diaryl carbonate, a transesterification catalyst, an aliphatic dihydroxy compound, and a diacid compound, (b) adjusting the temperature of the reactor system to a first reactor temperature setpoint and adjusting the pressure of the reactor system to a first reactor pressure setpoint between 0.7 bar and 1.2 bar, wherein the first reactor temperature setpoint is selected such that: (i) it is sufficiently high to provide a molten reaction mixture, (ii) it is sufficiently high to initiate an exothermic oligomerization reaction in the reaction mixture to form a polycarbonate oligomer and a phenolic byproduct, and (iii) it is below the boiling point of the phenolic byproduct at the first reactor pressure, wherein during step (b) the reaction mixture is monitored to detect initiation of the exothermic oligomerization reaction, (c) adjusting the temperature of the reactor system to a second reactor temperature setpoint and adjusting the pressure of the reactor system to a second reactor pressure setpoint that is greater than or equal to the first reactor pressure setpoint, after detection of initiation of the exothermic oligomerization reaction, wherein the second reactor temperature setpoint and second reactor pressure setpoint are selected in combination to: (i) ensure that the reaction mixture is molten, (ii) ensure that the temperature of the reaction mixture is below the boiling point of the phenolic byproduct at the second reactor pressure setpoint, and (iii) maintain the oligomerization reaction in the reaction mixture, (d) maintaining the reactor system at the second reactor temperature setpoint and the second reactor pressure setpoint for a sufficient period of time to allow the reaction mixture to react to form an oligomer mixture, (e) introducing the oligomer mixture to a polymerization reactor system operating under melt polymerization conditions sufficient to polymerize the oligomer mixture to a Mw of at least 9,000 g/mol (PC) and to remove the phenolic byproduct from the oligomer mixture, thereby forming polycarbonate.