The present invention provides methods of producing high molecular weight polymer. A method of forming polycarbonate includes the step of combining in a reaction mixture a diaryl carbonate, a transesterification catalyst, an aliphatic dihydroxy compound, and a diacid compound in a reactor system. The temperature and pressure of the reactor system are adjusted to a first reactor setpoints and the reaction mixture is monitored to detect initiation of the exothermic oligomerization reaction. The reactor setpoint are adjusted to second reactor setpoints after detection of initiation of the exothermic oligomerization reaction. The reactor system is maintained at the second reactor setpoints to allow the reaction mixture to react to form an oligomer mixture. The oligomer mixture is then introduced 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 to form polycarbonate.