Process to make polycarbonate from bismethylsalicylcarbonate (BMSC)

A method for preparing polycarbonate wherein the method comprises the steps of,

• (i) forming a reaction mixture comprising at least one dihydroxy compound, an activated carbonate, and a transesterification catalyst,
• (ii) heating the reaction mixture at a temperature in a range between 100° C. and 300° C. to provide the reaction components comprising a polycarbonate oligomer, an activated carbonate residue, and a transesterification catalyst,
• (iii) removing activated carbonate residue from the reaction components prior to introduction to an extruder,
• (iv) heating the reaction components to a temperature greater than the boiling point of the activated carbonate residue, the boiling point being the boiling point of the activated carbonate residue at a flash pressure, the heating being carried out at a feed pressure, the feed pressure being greater than the flash pressure to provide superheated reaction components,
• (v) flashing the superheated reaction components to the extruder at the flash pressure through at least one pressure control valve feed port, wherein the extruder comprises the feed port, a first back vent port, and a polycarbonate exit port, wherein the feed port is located between the first back vent port and the polycarbonate exit port, and wherein the resistance to flow of the reaction components from the feed port to the first back vent port is less than or equal to the resistance to flow of the reaction components from the feed port to the polycarbonate exit port, and
• (vi) extruding the reaction components at one or more temperatures in a range between 100° C. and 400° C., wherein during the extrusion of the reaction components activated carbonate residue is removed through the first back vent port,
• thereby preparing a polycarbonate.

A method for making a molded article formed from polycarbonate produced by the method comprising the steps of:

• (a) preparing a polycarbonate by,
• (i) introducing to an extruder through a feed port a plurality of reaction components comprising a polycarbonate oligomer, an activated carbonate residue, and a transesterification catalyst, wherein the extruder comprises the feed port, a first back vent port, and a polycarbonate exit port, wherein the feed port is located between the first back vent port and the polycarbonate exit port, and wherein the resistance to flow of the reaction components from the feed port to the first back vent port is less than or equal to the resistance to flow of the reaction components from the feed port to the polycarbonate exit port, and
• (ii) extruding the reaction components at one or more temperatures in a range between 100° C. and 400° C., wherein during the extrusion of the reaction components, activated carbonate residue is removed through the first back vent port, thereby forming a polycarbonate, and
• (b) forming a molded article from the polycarbonate.