Preparation of polycarbonate having reduced cyclic carbonate oligomer content
AssigneeThe Dow Chemical Company
InventorDuane B. Priddy
Life of this patent
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Abstract
The present invention is directed to a continuous process which removes the 1 to 3% cyclic oligomers formed in the polycarbonate process and after hydrolysis of the oligomers recycles the resulting monomer for use in the reaction forming the polycarbonates. To remove the cyclic oligomers to a level so as to produce an improved polycarbonate product and to recover the oligomers in an economical manner for recycling in a continuous process, the selection of a solvent is unique and essential to achieve the continuous process. The solvent for the cyclic oligomers must be immiscible with water, must not react with an alkali and have a cohesive energy density of less than 90.
Claims21
A process for producing a polycarbonate mixture product that contains less than one (1) percent cyclic carbonate oligomers, comprising the steps of:
- reacting in the presence of an inert organic solvent a carbonyl halide and a comonomer which together with the carbonyl halide is capable of producing a polycarbonate to obtain a polycarbonate mixture that contains the polycarbonate and more than one (1) percent of cyclic carbonate oligomers;
- separating the cyclic carbonate oligomers from the polycarbonate by mixing the polycarbonate mixture with an extraction solvent having a cohesive density of less than 90 and being immiscible with water and inert to a strong base;
- and
- hydrolyzing the separated cyclic carbonate oligomers to form the comonomer that is suitable for reacting with the carbonyl halide to form the polycarbonate.
A process for producing a polycarbonate mixture product that contains less than one (1) percent cyclic carbonate oligomers, comprising the steps of:
- reacting a carbonyl halide and a comonomer which together with the carbonyl halide is capable of producing a polycarbonate to obtain a polycarbonate mixture product that contains the polycarbonate, linear carbonate oligomers and more than one (1) percent of cyclic carbonate oligomers;
- separating the linear and cyclic carbonate oligomers from the polycarbonate by mixing the polycarbonate mixture with an extraction solvent having a cohesive density of less than 90 and being immiscible with water and inert to a strong base;
- and
- hydrolyzing the separated linear and cyclic carbonate oligomers to form the comonomer that is suitable for reacting with the carbonyl halide to form the polycarbonate.
In a process of producing a polycarbonate by reacting a first comonomer with a carbonyl halide comonomer wherein the polycarbonate product contains the polycarbonate and more than one (1) percent carbonate oligomers, an improvement comprising the steps of:
- separating the carbonate oligomers from the polycarbonate by mixing the polycarbonate product with an extraction solvent having a cohesive density of less than 90 and being immiscible with water and inert to a strong base;
- and
- hydrolyzing the carbonate oligomers to form the first comonomer which is suitable for the production of the polycarbonate by reacting with the carbonyl halide comonomer.
Dependencies are inferred from the claim text.