Preparation of polycarbonates in a homogeneous solution
AssigneeThe Dow Chemical Company
InventorsKevin F. Dick, George E. Ham, James R. Gross
Life of this patent
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Abstract
Polycarbonates are prepared in homogeneous solutions from dihydric phenols and phosgene wherein the stoichiometric end point for the addition of phosgene is accurately controlled by using 4-(p-nitrobenzyl) pyridine as a colorometric indicator for the end point in a series of samples of the reaction solution.
Claims10
A method for the preparation of a polycarbonate resin using substantially equimolar proportions of phosgene and one or more dihydric phenols dissolved in an organic solvent mixture containing pyridine and a halogenated solvent which comprises
- (a) adding phosgene incrementally to said one or more dihydric phenols in said solvent mixture to form a polycarbonate solution,
- (b) periodically mixing a sample of said polycarbonate solution in an organic solution of 4-(p-nitrobenzyl) pyridine to visually detect a color change at the stoichiometric end point whereby the addition of phosgene is stopped when said sample solution changes from colorless to slightly yellow, and
- (c) recovering said polycarbonate resin.
A method for the preparation of a polycarbonate resin using substantially equimolar proportions of phosgene and one or more dihydric phenols which comprises
- (a) adding phosgene incrementally to one or more dihydric phenols having the formula ##STR3## herein A is a divalent hydrocarbon radical containing 1-15 carbon atoms, ##STR4## X is independently hydrogen, chlorine, bromine, fluorine, or a monovalent hydrocarbon radical such as an alkyl group of 1-4 carbons, an aryl group of 6-8 carbons such as phenyl, tolyl, xylyl, an oxyalkyl group of 1-4 carbons or an oxyaryl group of 6-8 carbons and n is 0 or 1, wherein said one or more dihydric phenols are dissolved in an organic solvent mixture containing pyridine and a halogenated solvent,
- (b) periodically mixing a sample of said polycarbonate solution in an organic solution of 4-(p-nitrobenzyl) pyridine to visually detect a color change at the stoichiometric end point whereby the addition of phosgene is stopped when said sample solution changes from colorless to slightly yellow, and
- (c) recovering said polycarbonate resin.
Dependencies are inferred from the claim text.