Patent ID: 6403754
Filing Date: 2002-06-11
Classification: C08G,Y02P

Abstract:
A method for optimizing polycarbonate formation by a transesterification reaction between the reagents diaryl carbonate and dihydroxyaromatic compound in the presence of a catalyst system comprising at least one alkali metal hydroxide, which comprises:(A) analyzing at least one of said reagents for acidic impurities including at least one of sulfonic acids, mercaptocarboxylic acids, salicylic acid and ferric chloride, to determine whether the following threshold values have been exceeded: sulfonic acidsâ€”0.1 molar ppm based on dihydroxyaromatic compound, mercaptocarboxylic acidsâ€”5 molar ppm based on dihydroxyaromatic compound, salicylic acidâ€”0.15 molar ppm based on dihydroxyaromatic compound, ferric chlorideâ€”200 ppb by weight based on dihydroxyaromatic compound; and either:(B) discarding or recycling any reagent exceeding at least one of said threshold values, or (C) establishing the level of alkali metal hydroxide in the polycarbonate-forming reaction mixture at a value which is at most 1 molar ppm, based on dihydroxyaromatic compound, in excess of that of at least one of sulfonic acid, mercaptocarboxylic acid, salicylic acid and ferric chloride.