Polycarbonate production

Abstract: This invention relates to polycarbonate prepolymers which are produced by adding phosgene, one or more dihydric phenols, a halogenated organic solvent, and an aqueous caustic solution together with mixing in motionless mixers to form fine dispersions of partially phosgenated phenols, allowing for interfacial reactions to occur in residence sections and repeating the steps after the addition of caustic to form high molecular weight prepolymers. These prepolymers are then polymerized with amines to form high molecular weight polycarbonates.

Description: This invention relates to an interfacial process for the production of high molecular weight polycarbonates wherein high molecular weight prepolymers are first formed using motionless mixers and then coupled to form the polycarbonates. It is known from US Patent 3,674,740 that polycarbonates can be made from the usual monomers using a series of mixing tubes and residence tubes. However, this known process is designed to produce emulsions which are then difficult to process for the recovery of the polycarbonate resins. Other related processes for the production of polycarbonates are known from US Patents 3,974,126 and 3,530,094 but none of these patents teaches the making of high molecular weight prepolymers and the polymerization thereof. The present invention is directed to a process wherein high molecular weight polycarbonates are prepared by first forming a polycarbonate prepolymer having a molecular weight range of from 4000 to 12000 and mixing an amine catalyst with the prepolymer to form a high molecular weight polycarbonate resin. The process for making the prepolymer comprises the following steps : (a) preparing a mixture of one or more dihydric phenols, an aqueous caustic solution, a halogenated organic solvent and phosgene, (b) mixing by means of at least one motionless mixer said mixture to form a fine dispersion of the partially phosgenated derivatives of said phenols in said aqueous solution, (c) reacting said dispersion in a residence section with a residence time in the range of from 5 to 75 seconds into a coarse dispersion containing said partially phosgenated derivatives of said phenols, (d) repeating one or more times the mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, until said phenols are completely phosgenated, (e) mixing additional aqueous caustic solution with said dispersion, (f) cooling said dispersion to a temperature in the range of from 25 to 45°C, and (g) further mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, whereby a dispersion of a polycarbonate prepolymer having a weight average molecular weight range of 4000 to 12000 is obtained. The process for the production of high weight average molecular weight polycarbonate resins comprises the steps of (a) mixing a tertiary amine catalyst with the dispersion obtained by the above described process to form said polycarbonate resin, and (b) recovering said polycarbonate resin. A further process for the production of high weight average molecular weight polycarbonate resins comprises the steps of (a) preparing a mixture of one or more dihydric phenols, an aqueous caustic solution, a halogenated organic solvent and phosgene, (b) mixing by means of at least one motionless mixer said mixture to form a fine dispersion of the partially phosgenated derivatives of said phenols in said aqueous solution, (c) reacting said dispersion in a residence section with a residence time in the range from 5 to 75 seconds into a coarse dispersion containing said partially phosgenated derivatives of said phenols, (d) repeating one or more times the mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, until said phenols are completely phosgenated, (e) mixing additional aqueous caustic solution with said dispersion, (f) further mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, whereby a dispersion of a polycarbonate prepolymer having a weight average molecular weight range of from 4000 to 12000 is obtained, and (g) simultaneously cooling said dispersion to a temperature in the range of from 25 to 45°C and mixing a tertiary amine catalyst with said disperion to form said polycarbonate resin, and (h) recovering said polycarbonate resin. In one embodiment the dihydric phenol is Bisphenol-A and the halogenated organic solvent is methylene chloride. In a further embodiment a trialkylamine is mixed with the dispersion obtained by the process using bisphenol A and methylene chloride to form said polycarbonate resin. A preferred interfacial process for the production of a polycarbonate prepolymer having a weight average molecular weight range of 4000 to 12000 consists essentially of the steps of (a) preparing a mixture of one or more dihydric phenols, an aqueous caustic solution, a halogenated organic solvent and phosgene, (b) mixing by means of a motionless mixer said mixture to form a fine dispersion of the partially phosgenated derivatives of said phenols in said aqueous solution, (c) reacting said dispersion in a residence section with a residence time in the range from 5 to 75 seconds into a coarse dispersion containing said partially phosgenated derivatives of said phenols; (d) mixing said coarse dispersion containing said partially phosgenated derivatives of said phenols in a second motionless mixer to form a second fine dispersion, (e) reacting said dispersion in a second residence section into a coarse dispersion containing said phosgenated derivatives of said phenols, (f) mixing additional aqueous caustic solution with said dispersion, (g) cooling said dispersion to a temperature in the range of from 25 to 45°C, and (h) further mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, mixing again said coarse dispersion in a second motionless mixer to form a second fine dispersion and reacting said fine dispersion in a second residence section into a coarse dispersion, wherein a dispersion of a polycarbonate prepolymer having a weight average molecular weight range of from 4000 to 12000 is obtained. The high weight average molecular weight polycarbonate being prepared by cooling said dispersion to a temperature in the range of from 25 to 45°C and mixing a tertiary amine catalyst with said dispersion to form said polycarbonate resin, and recovering said polycarbonate resin. Examples of halogenated solvents useful in this invention are chlorobenzene, chloroform, carbon tetrachloride, 1,2-dichloroethane, methylene chloride, 1,1,2-trichloroethane, tetrachloroethane, and mixtures thereof. Normally, from 1.2 to 2.0 moles of phosgene will he used per mole of dihydric phenol in this process. A slight excess of phosgene is used in order to achieve complete reaction. The pH of the final reaction mixture after the amine addition is maintained in the range of from 11 to 13 depending on the bisphenol used and preferably in the range of from 11 to 11.5. Any suitable aromatic dihydroxy compound can be used in the present invention. There are vast numbers of suitable dihydroxy compounds cited in the patent literature as is illustrated by U.S. 3,530,094. For the purposes of this invention, the interfacial process used herein produces a dispersion of the prepolymers suspended in the aqueous phase and the droplets in the dispersion have a size in the range of from 100 to 1000 microns. This excludes the known emulsions which have a drop size of about one micron. The motionless mixers used herein are well known in the art as shown by the article by Chen et al in Chemical Engineering March 19, 1973 pages 105-111. The invention is further illustrated by the following examples. Example 1 Using a flow rate of 100 ml per minute, a mixture of p-tertiarybutyl phenol, water, methylene chloride, phosgene, sodium hydroxide and bisphenol A. was pumped through a series of two in-line motionless mixers having a diameter of 0.187 inches (4.75 mm) and connected by a pipe having a diameter of 0.375 inches (9.53 mm) with a total residence time of one minute for the series. The weight ratio of the ingredients compared to bisphenol A were 0.023; 5.20; 7.14; 0.61: and 0.74 respectively. After the monomers were mixed. 10.5 g per minute of a 50 percent aqueous solution of sodium hydroxide was added to the reactants and further mixing was done in a third motionless mixer followed by a continuously stirred reactor having a residence time of 3 minutes. A sample of the prepolymer mixture was analyzed and found to have a weight average molecular weight of 4380, a polydispersity of 2.75, 384 parts per million of phenolic end groups, and a chloroformate to hydroxyl mole ratio of 30. By using published correlations, the droplet size was calculated to be 1000 µm. Alter the addition of 1.5 g of triethylamine to the prepolymers and three minutes of mixing, a sample of the mixture was processed and the bisphenol A polycarbonate was isolated. It was found to have a weight average molecular weight of 28.390, a polydispersity of 236, and 80 parts per million of phenolic end groups. Control A The procedure of Example 1 was repeated except that the 50 percent NaOH was not added. The results are shown in Table I. Control 3 The procedure of Example 1 was repeated except that the motionless mixer in the NaOH section was not used but a continuously stirred tank reactor was used instead. The results are shown in Table I. Prepolymer Properties Run Mol. Wt. Polydispersity Phenolic End Groups (ppm) Chloroformate OH Mole Ratio Example I 4380 2.75 384 30 Control A 800 2.0 800 40 Control B 2300 2.2 2372 n.a. Example 2 This Example is a process similar to Example 1, except that the continuous addition of triethylamine was used. A monomer mixture consisting of 213 pounds per hour (pph) (97 kg/hr) of bisphenol A, 157 pph (71 kg/hr) of 50 percent sodium hydroxide solution, 1112 pph (504 kg/hr) of water, and 3.3 pph (1.5 kg/hr) of p-tertiarybutyl phenol was continuously mixed together in a mixing tank. In a similar tank, 122 pph (55 kg/hr) of phosgene, and 778 pph (353 kg/hr) of methylene chloride were mixed together to form a solvent mixture. These two mixtures were combined and pumped through a series of two motionless mixers having a diameter of 1.0 inch (25.4 mm) connected together by piping to give 30 seconds of residence time in the pipes between the mixers. After the last mixer and residence time lag, 92 pph (42 kg/hr) of 50 percent sodium hydroxide solution was added to the reactants. The heat of the reaction was removed with a tube and shell heat exchanger so as to keep the reaction mixture at a temperature in the range of from 25° to 50°C. A sample of the reaction mixture at this point indicated that the prepolymer had a molecular weight of 6,187, a polydispersity of 1.98, and 209 parts per million of phenolic end groups. The cooled mixture was pumped through another series of four motionless mixers similar to the first series connected together by piping to give 30 seconds of residence time in the pipes between the mixers. The total residence time in this set of mixers was 2 minutes. An estimation of the droplet sizes of the dispersion based on published correlations indicated that it had droplet sizes ranging from 300 to 500 µm which is much less than the dispersion of Example 1. After the last mixer, 3.1 pph (1.4 kg/hr) of triethylamine and 1556 pph (706 kg/hr) of methylene chloride was added to the dispersion and it was pumped through another series of five similar motionless mixers connected together by icing to give 30 seconds of residence time in the pipes between the mixers. The dispersion after these mixers contained no detectable chloroformate end groups. Alter recovering the polycarbonate resin, it was found to have a weight average molecular weight of 39,800, a polydispersity of 2.8, and 51 parts per million of phenolic end groups. Examples 3 and 4 The procedure of Example 2 was repeated with the same and different amounts of the p-tertiarybutyl phenol chain terminator. The results are set forth in Table II. Run Amount of Terminator kg/hr (pph) Prepolymer MW Polymer MW Example 3 2.92 (6.43) 5.900 21.300 Example 4 1.50(3.30) 11.200 44.000 Example 5 The procedure of Example 2 was substantially repeated except that the heat exchanger was removed and the three-minute stirred reactor was replaced with a stirred flash tank equipped with a reflux condenser for cooling. The flash tank had a residence time of 15 minutes. A sample of the prepolymer before the flash tank was found to have a molecular weight of 7500. Triethylamine at the rate of 0.02 g per minute was added to the tank. The resulting polycarbonate resin had a molecular weight of 30,200 and a polydispersity of 2.5.

Claims: An interfacial process for the production of a polycarbonate prepolymer having a weight average molecular weight range of from 4000 to 12000 which comprises the steps of (a) preparing a mixture of one or more dihydric phenols, an aqueous caustic solution, a halogenated organic solvent and phosgene, (b) mixing by means of at least one motionless mixer said mixture to form a fine dispersion of the partially phosgenated derivatives of said phenols in said aqueous solution, (c) reacting said dispersion in a residence section with a residence time in the range of from 5 to 75 seconds into a coarse dispersion containing said partially phosgenated derivatives of said phenols, (d) repeating one or more times the mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse disperion, until said phenols are completely phosphenated, (e) mixing additional aqueous caustic solution with said dispersion, (f) cooling said dispersion to a temperature in the range of from 25 to 45°C, and (g) further mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, whereby a dispersion of a polycarbonate prepolymer having a weight average molecular weight range of 4000 to 12000 is obtained. A process For the production of high weight average molecular weight polycarbonate resins which comprises the steps of (a) mixing a tertiary amine catalyst with the dispersion obtained by the process of Claim 1 to form said polycarbonate resin, and (b) recovering said polycarbonate resin. A process for the production of high weight average molecular weight polycarbonate resins which comprises the steps of (a) preparing a mixture of one or more dihydric phenols, an aqueous caustic solution, a halogenated organic solvent and phosgene, (b) mixing by means of at least one motionless mixer said mixture to form a fine dispersion of the partially phosgenated derivatives of said phenols in said aqueous solution, (c) reacting said dispersion in a residence section with a residence time in the range from 5 to 75 seconds into a coarse dispersion containing said partially phosgenated derivatives of said phenols, (d) repeating one or more times the mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, until said phenols are completely phosgenated, (e) mixing additional aqueous caustic solution with said dispersion, (f) further mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse disperion, whereby a dispersion of a polycarbonate prepolymer having a weight average molecular weight range of from 4000 to 12000 is obtained, and (g) simultaneously cooling said dispersion to a temperature in the range of from 25 to 45°C and mixing a tertiary amine catalyst with said dispersion to form said polycarbonate resin, and (h) recovering said polycarbonate resin. An interfacial process as claimed in Claim 1 wherein the dihydric phenol is Bisphenol-A and the halogenated organic solvent is methylene chloride. A process for the production of high weight average molecular weight polycarbonate resins which comprises the steps of (a) mixing a trialkylamine with the dispersion obtained by the process of Claim 4 to form said polycarbonate resin, and (b) recovering said polycarbonate resin. A process as claimed in Claim 3 wherein the dihydric phenol is Bisphenol-A and the halogenated organic solvent is methylene chloride. An interfacial process for the production of a polycarbonate prepolymer having a weight average molecular weight range of 4000 to 12000 which consists essentially of the steps of (a) preparing a mixture of one or more dihydric phenols, an aqueous caustic solution, a halogenated organic solvent and phosgene, (b) mixing by means of a motionless mixer said mixture to form a fine dispersion of the partially phosgenated derivatives of said phenols in said aqueous solution, (c) reacting said dispersion in a residence section with a residence time in the range from 5 to 75 seconds into a coarse dispersion containing said partially phosgenated derivatives of said phenols, (d) mixing said coarse dispersion containing said partially phosgenated derivatives of said phenols in a second motionless mixer to form a second fine dispersion, (e) reacting said dispersion in a second residence section into a coarse dispersion containing said phosgenated derivatives of said phenols, (f) mixing additional aqueous caustic solution with said dispersion, (g) cooling said dispersion to a temperature in the range of from 25 to 45°C, and (h) further mixing and reacting steps in which said dispersion is mixed by means of a motionless, mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, mixing again said coarse dispersion in a second motionless mixer to form a second fine dispersion and reacting said fine dispersion in a second residence section into a coarse dispersion, wherein a dispersion of a polycarbonate prepolymer having a weight average molecular weight range of from 4000 to 12000 is obtained. A process for the production of high weight average molecular weight polycarbonate resins which comprises the steps of (a) mixing a tertiary amine catalyst with the dispersion obtained by the process of Claim 7 to form said polycarbonate resin, and (b) recovering said polycarbonate resin. A process for the production of high weight average molecular weight polycarbonate resins which consists essentially of the steps of (a) preparing a mixture of one or more dihydric phenols, an aqueous caustic solution, a halogenated organic solvent and phosgene, (b) mixing by means of a motionless mixer said mixture to form a fine dispersion of the partially phosgenated derivatives of said phenols in said aqueous solution, (c) reacting said dispersion in a residence section with a residence time in the range of from 5 to 75 seconds into a coarse dispersion containing said partially phosgenated derivatives of said phenols, (d) mixing said coarse dispersion containing said partially phosgenated derivatives of said phenols in a second motionless mixer to form a second fine dispersion, (e) reacting said dispersion in a second residence section into a coarse dispersion containing said phosgenated derivatives of said phenols, (f) mixing additional aqueous caustic solution with said dispersion, (g) cooling said dispersion to a temperature in the range of from 25 to 45°C, and (h) further the mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, mixing again said coarse dispersion in a second motionless mixer to form a second fine dispersion and reacting said fine dispersion in a second residence section into a coarse dispersion, wherein a dispersion of a polycarbonate prepolymer having a weight average molecular weight range of from 4000 to 12000 is obtained. (i) cooling said dispersion to a temperature in the range of from 25 to 45°C and mixing a tertiary amine catalyst with said dispersion to form said polycarbonate resin, and (j) recovering said polycarbonate resin. An interfacial process for the production of a polycarbonate prepolymer having a weight average molecular weight range of from 4000 to 12000 which consists essentially of the steps of (a) preparing a mixture of Bisphenol-A, an aqueous caustic solution, a chlorinated organic solvent and phosgene (b) mixing by means of a motionless mixer said mixture to form a fine dispersion of the partially phosgenated derivatives of said bisphenol in said aqueous solution, (c) reacting said dispersion in a residence section with a residence time in the range of from 5 to 75 seconds into a coarse dispersion containing said partially phosgenated derivatives of said bisphenol, (d) mixing said coarse dispersion containing said partially phosgenated derivatives of said bisphenol in a second motionless mixer to form a second fine dispersion, (e) reacting said dispersion in a second residence section into a coarse dispersion containing said phosgenated derivatives of said bisphenol, (f) mixing additional aqueous caustic solution with said dispersion, (g) cooling said dispersion to a temperature in the range of from 25 to 45° C, and (h) further mixing and reacting steps in which said dispersion is mixed by means of a motionless mixer to form a fine dispersion, and said fine dispersion is reacted in a residence section for 5 to 75 seconds to form a coarse dispersion, mixing again said coarse dispersion in a second motionless mixer to form a second fine dispersion and reacting said fine dispersion in a second residence section into a coarse dispersion, wherein a dispersion of a polycarbonate prepolymer having a weight average molecular weight range of from 4000 to 12000 is obtained.

Inventors: AGUILAR JOSE LOUIS, SMITH II RONALD R, WESTON JOHN W, AGUILAR, JOSE LOUIS, SMITH II, RONALD R., WESTON, JOHN W.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1988
Main classification: C08G64
IPC codes: C08G64