PROCESS FOR PREPARING LINEAR POLYCARBONATE WITH IMPROVED IMPACT PROPERTIES
The present invention relates to an improved process for preparing linear polycarbonates having an improved technique for adding a coupling catalyst compound, specifically the addition of the coupling catalyst at two or more separate, different points in the process. Linear polycarbonate resins prepared by said process demonstrate a lower level of polycarbonate oligomers and an improved balance of properties, in particular improved impact strength and lower ductile brittle transition temperature.
1 . A method for producing a linear polycarbonate by split addition of a coupling catalyst, wherein the coupling catalyst is added in two or more portions at two or more separate, different points in the polycarbonate manufacturing process.
2 . An interfacial process for producing a linear polycarbonate composition from dihydric phenol, carbonate precursor, and monophenolic chain terminator using a coupling catalyst which process comprises the sequential steps of:
a) combining a dihydric phenol, base and water to form the reaction mixture,
b) then adding at least part of the carbonate precursor and the water immissible organic solvent and reacting the polymerization mixture, partially oligomerizing the dihydric phenol,
c) then adding a monophenolic chain terminator and base to the reaction mixture,
d) at the same time as or after c) add a first portion of the coupling catalyst,
e) adding the balance of the carbonate precursor (if any) and continuing the reaction of the polymerization mixture,
f) adding a second portion of the coupling catalyst,
g) completing the polymerization reaction.
3 . The process according to claim 2 for producing a linear polycarbonate wherein the coupling catalyst added in step d) is added to the oligomerizing reaction mixture at the point where the Mw is between about 1,200 and about 4,500 g/mole.
4 . The process according to claim 3 for producing a linear polycarbonate wherein the coupling catalyst is added to the oligomerizing reaction mixture at the point where the Mw is between about 2,000 and about 3,500 g/mole.
5 . The process according to claim 4 for producing a linear polycarbonate wherein the second the coupling catalyst component is added to the reaction mixture at the point where the Mw has increased to at least about 4,000 to 10,000 g/mole.
6 . The process according to claim 4 for producing a linear polycarbonate wherein the second the coupling catalyst component is added to the reaction mixture at the point where the Mw has increased to at least about 10,000.
7 . A process according to claim 2 for producing a linear polycarbonate wherein the first addition of the coupling catalyst is in an amount of from 0.1 to 20 mole percent of the total coupling catalyst amount that is added.