Patent ID: 6797802
Filing Date: 2004-09-28
Classification: C08G

Abstract:
A method of preparing polycarbonate, said method comprising (A) oligomerising in the presence of a catalyst, at least one diaryl carbonate and at least one dihydroxyaromatic compound at a temperature in a range between about 220 and about 280Â° C. and a pressure in a range between about 180 mbar and about 20 mbar, said catalyst consisting of a tetraaryl phosphonium compound and optionally an alkali metal hydroxide co-catalyst, to provide an oligomeric polycarbonate having a number average molecular weight in a range between about 1000 and about 7500 daltons and (B) in a second step hearing the oligomeric polycarbonate formed in step (A) at a temperature in a range between about 280 and about 310Â° C. and at pressure in a range between about 15 mbar and about and about 0.1 mbar to provide a polycarbonate having a weight average molecular weight between about 15000 daltons and about 50,000 daltons, said method comprising less than about 1000 parts per million Fries product.