POLYCARBONATE HAVING EXCELLENT HYDROLYTIC STABILITY

Abstract: This invention is related to polycarbonate produced by the melt process having excellent hydrolytic stability. The invention further relates to a method for preparing polycarbonate having improved hydrolytic stability, and articles made from the polycarbonate having improved hydrolytic stability.

Description: POLYCARBONATE HAVING EXCELLENT HYDROLYTIC STABILITY FIELD OF THE INVENTION This invention is related to polycarbonate produced by the melt process having excellent hydrolytic stability. The invention further relates to a method for preparing polycarbonate having improved hydrolytic stability, and articles made from the polycarbonate having improved hydrolytic stability. BACKGROUND OF THE INVENTION Conventional industrial plants synthesize polycarbonate by mixing together an aqueous solution of dihydric compound (e.g., bisphenol-A) with an organic solvent (e.g., dichloromethane) containing a carbonyl halide (e.g., phosgene) Upon mixing the immiscible organic and aqueous phases, the dihydric compound reacts with the carbonyl halide at the phase interface. Typically, a phase transfer catalyst, such as a tertiary amine, is added to the aqueous phase to enhance this reaction. This synthesis method is commonly known as the "interfacial" synthesis method for preparing polycarbonate. The interfacial method for making polycarbonate has several inherent disadvantages. First it is a disadvantage to operate a process which requires phosgene as a reactant due to obvious safety concerns. Second it is a disadvantage to operate a process which requires using large amounts of an organic solvent because expensive precautions must be taken to guard against any adverse environmental impact. Third, the interfacial method requires a relatively large amount of equipment and capital investment. Fourth, the polycarbonate produced by the interfacial process is prone to having inconsistent color, higher levels of particulates, and higher chlorine content, which can cause corrosion. Some new commercial polycarbonate plants synthesize polycarbonate by a transesterification reaction whereby a diester of carbonic acid (e.g., diphenylcarbonate) is condensed with a dihydric compound (e.g., bisphenol-A). This reaction is performed without a solvent, and is driven to completion by mixing the reactants under reduced pressure and high temperature with simultaneous distillation of the phenol produced by the reaction. This synthesis technique is commonly referred to as the "melt" technique. The melt technique is superior over the interfacial technique because it does not employ phosgene, it does not require a solvent, and it uses less equipment. Moreover, the polycarbonate produced by the melt process does not contain chlorine contamination from the reactants, has lower particulate levels, and has a more consistent color. Therefore it is highly desirable to use the melt technique in a commercial manufacturing process. In the production of polycarbonates by the melt polymerization process, alkali metal hydroxides, in particular sodium hydroxide, are used as polymerization catalysts. While alkali metal hydroxides are useful polymerization catalysts, they also effect side reactions which results in branched side reaction products. This causes changes in the melt behavior of the polycarbonate, which can lead to difficulties in processing. Another disadvantage of the use of alkaline catalysts is that the catalysts remaining in the resulting polycarbonate adversely affect the properties of the polycarbonate. In particular, the hydrolytic stability of the polycarbonate is affected by the remaining catalysts. The hydrolytic stability required for a given application may vary. For certain applications, for instance in sheet resin which may be used for production of twin wall sheet applications, the hydrolytic stability of the polycarbonate becomes even more critical. US 5,606,607 discloses a process for preparing aromatic polycarbonates in which an epoxide is added in the presence of a sulfur containing acid component. There is no mention of the effect of additives to the polycarbonate on the hydrolytic stability. There exists a need for a polycarbonate produced by the melt process that has improved hydrolytic stability. In particular, there exists a need for a polycarbonate having improved hydrolytic stability that is useful in the production of sheet resin that may be used in twin wall applications. SUMMARY OF THE INVENTION In one aspect, the invention relates to a hydro lyrically stable polycarbonate composition, the hydrolytically stable polycarbonate composition having less than about 98 mol % terminal aryl carbonate groups, and 2 mol % or greater terminal hydroxyl groups, based on the molar total of all terminal groups of the polycarbonate, the hydrolytically stable polycarbonate further comprising about 3.6 ppm or less of a catalyst quencher; about 1 ,000 ppm or less of a phosphite component and about 200 ppm or less of an epoxide hydrolysis stabilizer. The invention further relates to articles made from the hydrolytically stable polycarbonate. In one embodiment, the article formed is a sheet, in a further embodiment, the article is a twin wall sheet. In a further aspect, the invention relates to a method of preparing a hydrolytically polcarbonate composition having less than about 98 mol % terminal aryl carbonate groups, and 2 mol % or greater terminal hydroxyl groups, based on the molar total of all terminal groups of the polycarbonate, the method comprising the steps of maintaining the level of catalyst quencher at 3.6 ppm or lower; maintaining the level of phosphite component at about 1,000 ppm or lower; and maintaining the level of epoxide hydrolysis stabilizer at about 200 ppm or lower during the preparation and processing of the hydrolytically stable polycarbonate. In a further aspect, the invention relates to a method for preparing a hydrolytically stable polycarbonate, the method comprising the step of a) adding up to about 3.6 ppm, based on the melt prepared polycarbonate, of a catalyst quencher; b) adding up to about 1000 ppm, based on the melt prepared polycarbonate of a phosphite component; and c) adding up to about 200 ppm, based on the melt prepared polycarbonate, of an epoxide hydrolysis stabilizer wherein at least one of components a), b) or c) is present in an amount greater than 0 ppm, and wherein the hydrolytically stable polycarbonate exhibits less than about 30% loss of molecular weight in a steam autoclave at 120° C and 100% relative humidity . DESCRIPTION OF THE INVENTION The present invention addresses these concerns and provided further surprising properties. The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the examples included therein. Before the present compositions of matter and methods are disclosed and described, it is to be understood that this invention is not limited to specific synthetic methods or to particular formulations, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. In the following specification, reference will be made to a number of terms which shall be defined to have the following meanings: The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. As used herein, the term "melt polycarbonate" refers to a polycarbonate made by the transesterification of a carbonate diester with a dihydroxy compound. "BPA" is herein defined as bisphenol A or 2,2-bis(4- hydroxyphenyl)propane. The terms "diphenol" and "dihydric phenol" as used herein are synonymous. An "acid species" as used herein is a component having a pKa value in water at 25 ° C of 4.0 or less. "Hydrolytically stable" as used herein means that the melt prepared polycarbonate exhibits less than about 30% loss of molecular weight in a steam autoclave at 120° C and 100% relative humidity for a period of 120 hours. In the present invention, it was unexpectedly found that the levels of typical additives to polycarbonate prepared by the melt process interact to create problems in the stability of melt polycarbonate, in particular the hydrolytic stability. The criticality of the hydrolytic stability depends on the intended use of the polycarbonate. By maintaining the levels of certain additives to the melt polycarbonate, in particular the levels of catalyst quencher, phosphite component, and epoxide hydrolysis stabilizer in certain critical range, the hydrolytic stability of the polycarbonate is dramatically improved. The polycarbonate having improved hydrolytic stability is suitable for use in sheet resin which may be used in twin wall sheet applications. Specifically, the present invention provides hydrolytically stable polycarbonate that may be used in applications where, previously, melt prepared polycarbonate was unsuitable due to problems with hydrolytic stability. In one embodiment, for instance, the hydrolytically stable polycarbonate prepared by the melt process may be used in sheet applications, for instance as a twin wall sheet in a green house. Interfacially prepared polycarbonate and melt prepared polycarbonate usually require the addition of certain additives after preparation to stabilize the remaining product. The additives required for interfacially produced polycarbonate and melt produced polycarbonate differ, however, in that the melt produced polycarbonate requires the addition of a catalyst quencher to neutralize residual alkaline material, such as residual alkali or alkaline earth metal salts. Typical additives for this purpose include, for instance, sulfur acids ("S" acids) or phosphorous acids ("P" acids) and their corresponding esters. Polycarbonate prepared by the interfacial method typically contains greater than about 98 mol % terminal aryl carbonate based on the molar total of all terminal groups of the polycarbonate. Polycarbonate prepared by the melt process contains less than about 98 mol % terminal aryl carbonate groups, and 2 mol % or greater terminal hydroxyl groups, based on the molar total of all terminal groups of the polycarbonate. This leads to performance problems in some applications, in part due to the hydrolysis of the terminal hydroxyl groups present in the polycarbonate. In addition, it is common in the melt process to include the addition of phosphorous acid to provide protection against occasional iron contamination caused by breakthroughs in the plant to inhibit color formation. In one aspect, the present invention relates to a hydrolytically stable polycarbonate produced in a melt polymerization system in which a dihydric phenol and a diester of carbonic acid are reacted. Dihydric phenols which are useful in preparing the polycarbonate of the invention may be represented by the general formula wherein: R is independently selected from halogen, monovalent hydrocarbon, and monovalent hydrocarbonoxy radicals; R 1 is independently selected from halogen, monovalent hydrocarbon, and monovalent hydrocarbonoxy radicals: W is selected from divalent hydrocarbon radicals, 0 0 0 II I' ι> - S - , - S - S - , -0 - , - S - , - S - , a n d - C - ; 0 n and n 1 are independently selected from integers having a value of from 0 to 4 inclusive; and b is either zero or one. The monovalent hydrocarbon radicals represented by R and R 1 include the alkyl, cycloalkyl, aryl, aralkyl and alkaryl radicals. The preferred alkyl radicals are those containing from 1 to about 12 carbon atoms. The preferred cycloalkyl radicals are those containing from 4 to about 8 ring carbon atoms. The preferred aryl radicals are those containing from 6 to 12 ring carbon atoms, i.e., phenyl, naphthyl, and biphenyl. The preferred alkaryl and aralkyl radicals are those containing from 7 to about 14 carbon atoms. The preferred halogen radicals represented by R and R 1 are chlorine and bromine. The divalent, hydrocarbon radicals represented by include the alkylene, alkylidene, cycloalkylene and cycloalkylidene radicals. The preferred alkylene radicals are those containing from 2 to about 30 carbon atoms. The preferred alkylidene radicals are those containing from 1 to about 30 carbon atoms. The preferred cycloalkylene and cycloalkylidene radicals are those containing from 6 to about 16 ring carbon atoms. The monovalent hydrocarbonoxy radicals represented by R and R 1 may be represented by the formula — OR 2 wherein R 2 is a monovalent hydrocarbon radical of the type described hereinafore. Preferred monovalent hydrocarbonoxy radicals are the alkoxy and aryloxy radicals. Suitable dihydric phenols include, but are not limited to, BPA; 2,2- bis(3,5-dibromo-4-hydroxyphenyl)propane; 2,2-bis(3,5-dimethyl-4- * hydroxyphenyl)propane; l,l-bis(4-hydroxyphenyl)cyclohexane; l,l-bis(3,5-dimethyl- 4-hydroxyphenyl)cyclohexane; 1 , 1 -bis(4-hydroxyphenyl)decane; 1 , 1 -bis(4- hydroxyphenyl)propane; 1 , 1 -bis(4-hydroxyphenyl)cyclodecane; 1 , 1 -bis(3,5-dimethyl- 4-hydroxyphenyl)cyclododecane; 4,4-dihydroxyphenyl ether; 4,4-thiodiphenol; 4-4- dihydroxy-3,3-dichlorodiphenyl ether; 4,4-thiodiphenol; 4,4-dihydroxy-3,3- dichlorodiphenyl ether; 4,4-dihydroxy-2,5-dihydroxydiphenyl ether; BPI; l,l-bis(4- hydroxyphenyl)- 1 -phenylethane; 1 , 1 -bis(3-methyl-4-hydroxyphenyl)- 1 -phenylethane, and mixtures thereof. In one embodiment, the residues of dihydric phenol in the polycarbonate comprise 100 mol% of residues derived from BPA. Optionally, polyfunctional compounds may be utilized. Suitable polyfunctional compounds used in the polymerization of branched polycarbonate include, but are not limited to, ' l,l,l-tris(4-hydroxyphenyl)ethane, 4-[4-[ 1 , 1 -bis(4-hydroxyphenyl)-ethyl]-dimethylbennzyl], trimellitic anhydride, trimellitic acid , or their acid chloride derivatives. As the diester of carbonic acid, various compounds may be used, including, but not limited to diaryl carbonate compounds, dialkyl carbonate compounds and alkylaryl carbonate compounds. Suitable diesters of carbonic acid include, but are not limited to, diphenyl carbonate; bis(4-t-butylphenyl)carbonate; bis(2,4-dichlorophenyl)carbonate; bis(2,4,6-trichlorphenyl)carbonate; bis(2- cyanophenyl)carbonate; bis(o-nitrophenyl)carbonate; ditolyl carbonate; m-cresol carbonate; dinaphthyl carbonate; bis(diphenyl)carbonate; diethylcarbonate; dimethyl carbonate; dibutyl carbonate; dicyclohexyl carbonate; and mixtures thereof. Of these, diphenyl carbonate is preferred. If two or more of these compound are utilized, it is preferable that one is diphenyl carbonate. In the process of the present invention, an endcapping agent may optionally be used. Suitable endcapping agents include monovalent aromatic hydroxy compounds, haloformate derivatives of monovalent aromatic hydroxy compounds, monovalent carboxylic acids, halide derivatives of monovalent carboxylic acids, and mixtures thereof. Suitable endcapping agents include, but are not limited to phenol, p- tert-butylphenol; p-cumylphenol; p-cumylphenolcarbonate; undecanoic acid, lauric acid, stearic acid; phenyl chloroformate, t-butyl phenyl chloroformate, p-cumyl chloroformate, chroman chloroformate, octyl phenyl; nonyl phenyl chloroformate or a mixture thereof. ' If present, the endcapping agent is preferably present in amounts of about 0.01 to about 0.20 moles, preferably about 0.02 to about 0.15 moles, even more preferably about 0.02 to about 0.10 moles per 1 mole of the dihydric phenol. In the process of the present invention, the catalyst system comprises at least one alkali and/or alkali earth metal compounds. These compounds are preferably used in the forms of derivatives of alkali metals and alkali earth metals, such as organic acid salts; inorganic acid salts; oxides; hydroxides; hydrides; alcoholates; or a mixture thereof. Suitable alkali metal compounds which may be used as catalysts include, but are not limited to, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium hydrogen carbonate, sodium carbonate, potassium carbonate, lithium carbonate, sodium acetate, potassium acetate, lithium acetate, sodium stearate, potassium stearate, lithium stearate and mixtures thereof. Suitable alkaline-earth metal compounds which may be used as catalyst include, but are not limited to, calcium hydroxide, barium hydroxide, magnesium hydroxide, strontium hydroxide, calcium hydrogen carbonate, barium hydrogen carbonate, magnesium hydrogen carbonate, strontium hydrogen carbonate, calcium carbonate, barium carbonate, magnesium carbonate, strontium carbonate, calcium acetate, barium acetate, magnesium acetate, strontium acetate, calcium stearate, barium stearate, magnesium stearate, strontium stearate and mixtures thereof. The catalyst or catalysts is preferably used in an amount of from 10 '8 to 10 "3 moles of catalyst per 1 mole of dihydric phenol compound, more preferably 10 "7 to 10 '5 moles of catalyst per 1 mole of dihydric phenol compound. When the amount is less than 10 '8 mol, there is the possibility that catalyst activity is not exhibited. When the amount is greater than 10 "3 moles per 1 mole of dihydric phenol, the properties of the final polycarbonate product may be adversely affected. In addition to the catalysts described above, the catalyst system may optionally comprise a quaternary ammonium salt and/or a phosphonium catalyst. Examples of suitable quaternary ammonium salts include, but are not limited to ammonium hydroxides having alkyl groups, aryl groups and alkaryl groups, such as tetraamethylammonium hydroxide (TMAH) and tetrabutylammonium hydroxide (TBAH). Suitable phosphonium salts include, but are not limited to tetraethylphosphonium hydroxide and tetrabutylphosphonium hydroxide. If present, the quaternary ammonium salt and/or phosphonium catalyst are preferably present in amounts of from 10 "2 to about 10 "6 , preferably 10 '2 to 10 "5 moles per 1 mole of dihydric phenol compound, in addition to the alkali and or alkali earth metal salt of the chelating agent and ,optionally, the alkali metal hydroxide. The reaction conditions of the melt polymerization are not particularly limited and may be conducted in a wide range of operating conditions. The reaction temperature is typically in the range of about 100 to about 350° C, more preferably about 180 to about 310° C. The pressure may be at atmospheric, or at an added pressure of from atmospheric to about 15 torr in the initial stages of the reaction, and at a reduced pressure at later stages, for example in the range of about .2 to about 15 torr. The reaction time is generally about .1 hours to about 10 hours. The hydrolytically stable polycarbonate of the present invention exhibits dramatically improved hydrolytic stability based on accelerated aging tests. As mentioned, the criticaiity of the hydrolytic stability depends on the intended use of the polycarbonate. In certain applications, the hydrolytic stability becomes even more critical. For instance, in sheet applications, such as a twin wall sheet in a green house, the exposure of the polycarbonate to water and sunlight requires higher hydrolytic stability than the hydrolytic stability required for polycarbonate prepared for indoor uses. The hydrolytically stable polycarbonate of the present invention exhibits less than about 30% loss of molecular weight in a steam autoclave at 120° C and 100% relative humidity for a period of 120 hours; more preferably less than about 20% loss of molecular weight in a steam autoclave at 120° C and 100%) relative humidity for a period of 120 hours; even more preferably less than about 10% loss of molecular weight in a steam autoclave at 120 ° C and 100% relative humidity for a period of 120 hours. In the present invention, the levels of the catalyst quencher, phosphite component and epoxide hydrolysis stabilizer are carefully controlled. It was unexpectedly found that the phosphite component and acid species present in melt produced polycarbonate interact and, as a result, reduce the hydrolytic stability of melt polycarbonate. Acid species may be generated by the hydrolysis of catalyst quenchers typically used as additives in polycarbonate produced by melt transesterification, the catalyst quencher may be an acid species, or the acid species may be added for other purposes. Butyl tosylate, a common catalyst quencher, may be hydrolyzed to form tosic acid in a polycarbonate in which it is used as a catalyst quencher in a polycarbonate. Phosphorous acid or its derivatives may also be used as catalyst quenchers. It was found that by carefully controlling the levels the phosphite component and catalyst quencher in the polycarbonate, polycarbonate having higher hydrolytic stability could be prepared. Further, the concentration of other acid species in the polycarbonate is preferably kept to a minimum. In particular the total amount of the acid species 'in the polycarbonate resin, present as the catalyst quencher or added for other purposes is preferably maintained at about 3.6 ppm or less. It was further found that addition of a suitable epoxide hydrolysis stabilizer further enhanced the hydrolytic stability of the melt prepared polycarbonate. Suitable catalyst quenchers that may be used to prepare hydrolytically stable polycarbonate include , but are not limited to, sulfur and phosphorus acids and their esters; preferably alkyl esters of sulfur and phosphorous acids; more preferably alkyl tosylates such as butyl tosylate and n-butyl tosylate. Suitable phosphites that may be used to prepare hydrolytically stable polycarbonate include, but are not limited to triphenyl phosphite; 2,4 di-t-butyl phosphite; tris (nonylphenyl) phosphite; tris iso- decyl phosphite; and mixtures thereof; preferably triphenyl phosphite. Suitable epoxide hydrolysis stabilizers that may be used to prepare hydrolytically stable polycarbonate include, but are not limited to epoxy-containing fats and oils; glycidyl compounds, such as phenylglycidyl ether; epoxycylohexane compounds; tetraphenylethylene epoxide. The total amount of acid species, phosphite component and epoxide hydrolysis stabilizer that should be employed should be the total amount sufficient to stabilize the polycarbonate against discoloration and improve hydrolytic stability, for the intended application, while maintaining good properties. This amount depends on the article to be formed from the polycarbonate and the conditions in which the polycarbonate will be used. The catalyst quencher component is present in the hydrolytically stable polycarbonate at from about 0 to about 3.6 ppm; preferably from about 0.5 to about 2.0 ppm; even more preferably at from about 0 to about 1.0 ppm, based upon the polycarbonate. The phosphite component is present at from about 0 ppm to about 1,000 ppm; more preferably about 50 to 700 ppm; even more preferably from about 100 to 500 ppm, based upon the weight of the polycarbonate. The epoxide hydrolysis stabilizer is present at from about 0 to about 200 ppm; even more preferably from about 100 to 200 ppm, based upon the weight of the polycarbonate. As described above, the amount of additives depends on the intended use of the polycarbonate In some applications, such as indoor applications, the concentration of the catalyst quencher, phosphite and epoxide hydrolysis stabilizer may be low, for instance in a compact disk. In other applications the concentrations may need to be higher, for instance, in a sheet material that will be exposed to water and sunlight. In one embodiment, the melt prepared polycarbonate is formed into a twin wall sheet for use in a greenhouse. In one embodiment, a hydrolytically stable sheet grade material according to the invention contains from .5 to about 3.6 ppm, more preferably 0.5 to 2.0 of a catalyst quencher; from about about 50 to about 700 ppm, more preferably from 50 to 500 ppm, even more preferably from 50 to 250 ppm of a phosphite component; and from about 100 to 200 ppm of an epoxide hydrolysis stabilizer. It is further preferable that the total amount of the acid species in the hydrolytically stable sheet grade material, present as the catalyst quencher or added for other purposes is preferably maintained at about 3.6 ppm or less. The catalyst quencher, phosphite and epoxide hydrolysis stabilizer may be added to the polycarbonate in the molten state in the reactor or extruder after the polycondensation reaction, followed by kneading or by any other, technique known to introduce additives to a polycarbonate material. The additives may also be introduced as a powder concentrate in the same or a different polycarbonate. The weight average molecular weight of the polycarbonate is from about 1,000 to about 300,000. Preferred molecular weights depend on the intended use of the polycarbonate. For example, for sheet applications, preferred molecular weights are in the range of about 10,000 to about 80,000, even more preferably about 18,000 to about 50,000. As mentioned in one embodiment of the invention, the polycarbonate comprising the resin quenching composition may be formed into a sheet. In one particular application, the polycarbonate may be formed into a twin wall sheet for use in the construction of green houses. The polycarbonate may be formed into sheets directly from the polymerization melt, or in the alternative may be formed an easily handled shape, such as pellets, from the melt and subsequently formed into a sheet. The sheet of the present invention may be formed by a variety of methods known in the art, including, but not limited to extrusion, solution casting, or injection molding. Additional additives may also be added to the polycarbonate product as long as they do not adversely affect the properties of the product. These additives include a wide range of substances that are conventionally added to the polycarbonates for a variety of purposes. Specific examples include heat stabilizers, epoxy compounds, ultraviolet absorbers, mold release agents, colorants, antistatic agents, slipping agents, anti-blocking agents, lubricants, antifogging agents, natural oils, synthetic oils, waxes, organic fillers, flame retardants, inorganic fillers and any other commonly known class of additives. The reaction can be conducted as a batch or a continuous process. Any desired apparatus can be used for the reaction. The material and the structure of the reactor used in the present invention is not particularly limited as long as the reactor has an ordinary capability of stirring. It is preferable that the reactor is capable of stirring in high viscosity conditions as the viscosity of the reaction system is increased in later stages of the reaction. The hydrolytically stable polycarbonate compositions of present invention may be mixed with conventional additives, such as plasticizers, pigments, lubricants, mold release agents, stabilizers and organic fillers. Mold release agents are a preferred additive. It was further found that mold release agents, such as pentaerythritol tetra stearate, do not negatively affect the hydrolytic stability of the hydrolytically stable polycarbonate of the present invention. In addition to the uses described, the hydrolytically stable polycarbonate of the present invention may be used in outdoor applications, such as automobile parts, for housing of various instruments, and for optical articles, such as lenses and compact disks. As mentioned, in one embodiment the hydrolytically stable polycarbonate is used to prepare a twin wall sheet for a greenhouse. It is also possible to blend the polycarbonate with other polymers, including but not limited to, polyolefms, polystyrenes, polysulfonates, polyamides and polyphenylene ethers. EXAMPLES The following examples are set forth to provide those of ordinary skill in the are with a complete description of how the compositions of matter and methods claimed herein are made and evaluated, and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to insure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are by weight, temperature is in ° C. Molecular weights are reported as number average (Mw) and were determined by GPC analysis of polycarbonate prepared by melt polymerization using a polystyrene standard. In the following examples, polycarbonate prepared by the interfacial and melt process are exhibited. The interfacially prepared polycarbonate used was LEXAN LF 100 grade resin, commercially available from the General Electric Company. The melt prepared polycarbonate used was LEXAN LX 140 grade resin, commercially available for the General Electric Company. The polycarbonate was compounded using 100 grade LEXAN LF as a concentrate feed for the additives blended in a ratio of 95:5 bulk feed to concentrate feed (w:w) The additives were blended with the powder concentrate using a 1 gallon Henschel mixer. Materials were then compounded using a twin screw extruder with the barrel set temperature of 280° C, feed rate 25 lbs/hour and a screw speed between 350 and 400 rotations per minute (rpms). In the autoclaving step, dynatup disks were molded on a Nissei FE 160 injection molder and subjected to autoclaving at 120 ° C at 15 psi of steam for a period of five days. Samples (one to five) were taken daily by first cooling the autoclave to room temperature, followed by removing the disk and cutting a section of the molded disk to measure molecular weight. The remainder of the disk was placed back in the oven. Measurements were taken daily over five days in this manner. The slopes of the curves generated for the molecular weight loss over this time was then used to determine the relative hydrolytic stabilities of the samples. In Table 1, results are shown where these slopes are expresses as the"-(log Mw/(T/1000)" or "K slope". It is preferable that the -K slope of samples according to the invention be below about 1.615. The phosphite used was IRGAPHOS 168, manufactured by Ciba-Geigy, the catalyst quencher used was n-buytl tosylate, the epoxide hydrolysis stabilizer used was ERL-4221 , manufactured by Union Carbide.The mold release agent was pentaerythritol tetra-stearate and the UV stabilizer was CYASORB 5411, manufactured by Ciba -Geigy. The concentrations shown in table 1 are parts per million (ppm). Table 1 This invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims: WHAT IS CLAIMED IS: 1. A hydrolytically stable polycarbonate composition, the hydrolytically stable polycarbonate composition having less than about 98 mol % terminal aryl carbonate groups, and 2 mol % or greater terminal hydroxyl groups, based on the molar total of all terminal groups of the polycarbonate, the hydrolytically stable polycarbonate further comprising about 3.6 ppm or less of a catalyst quencher and about 1,000 ppm or less of a phosphite component. 2. The hydrolytically stable polycarbonate of claim 1, further comprising about 200 ppm or less of an epoxide hydrolysis stabilizer. 3 . A sheet prepared from the hydrolytically stable polycarbonate of claim 1. 4. A twin wall sheet prepared from the hydrolytically stable polycarbonate of claim 1. 5. The hydrolytically stable polycarbonate of claim 1, wherein the catalyst quencher is n-butyl tosylate. 6. The hydrolytically stable polycarbonate of claim 1 , wherein the phosphite component is triphenylphosphite. 7. The hydrolytically stable polycarbonate of claim 1 comprising less than about 4 ppm of acid species. 8. A method of preparing a hydrolytically stable polycarbonate, the method comprising the step of a) adding up to about 3.6 ppm, based on the melt prepared polycarbonate, of a catalyst quencher; b) adding up to about 1000 ppm, based on the melt prepared polycarbonate of a phosphite component; and c) adding up to about 200 ppm, based on the melt prepared polycarbonate, of an epoxide hydrolysis stabilizer wherein at least one of components a), b) or c) is present in an amount greater than 0 ppm, and wherein the hydrolytically stable polycarbonate exhibits less than about 30% loss of molecular weight in a steam autoclave at 120° C and 100%) relative humidity . 9. A method of preparing a hydrolytically stable polycarbonate, the method comprising the step of a) maintaining the level of a catalyst quencher at about 3.6 ppm or less, based on polycarbonate, of a catalyst quencher; b) maintaining the level of a phosphite component at about 1000 ppm or less based on polycarbonate of a phosphite component; and c) maintaining the level of an epoxide hydrolysis stabilizer at about 200 ppm or less, based polycarbonate, of an epoxide hydrolysis stabilizer. 10. A hydrolytically stables sheet comprising polycarbonate having at least 2% terminal hydroxyl groups. 11. A hydrolytically stable twin wall sheet comprising polycarbonate having at least 2%> terminal hydroxyl groups. 12. A hydrolytically stable sheet comprising polycarbonate having at least 5% terminal hydroxyl groups. 13. A resin quenching composition consisting essentially of a catalyst quencher, a phosphite, and an epoxide hydrolysis stabilizer. 14. A hydrolytically stable polycarbonate composition, the hydrolytically stable polycarbonate composition having less than about 98 mol %> terminal aryl carbonate groups, and 2 mol % or greater terminal hydroxyl groups, based on the molar total of all terminal groups of the polycarbonate, the hydrolytically stable polycarbonate further comprising about 3.6 ppm or less of a catalyst quencher, about 1,000 ppm or less of a phosphite component, and about 200 ppm or less of an epoxide hydrolysis stabilizer.

Inventors: BRUNELLE DANIEL JOSEPH, BURNELL TIMOTHY BRYDON, FACTOR ARNOLD NMN, MCCLOSKEY PATRICK JOSEPH, BRUNELLE, DANIEL, JOSEPH, BURNELL, TIMOTHY, BRYDON, FACTOR, ARNOLD (NMN), MCCLOSKEY, PATRICK, JOSEPH
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 2000
Main classification: C08L69
IPC codes: C08G64, C08J5, C08K5, C08L63, C08L69