Abstract:
This invention provides a method for preparing polycarbonates, which utilizes polycondensation catalysts which are derivatized pyridyl triazinyl pyridyl macromolecules with the general formula A x   +y [(Triazinyl-Pyridyl)B y   −x ], where A is certain alkali metals, B contains a charge balancing sulfonate, carboxylate, or phosphonate group. We have found that this new class of catalysts provide excellent polymerization rates for the preparation of Bisphenol A polycarbonate from the melt polymerization of diphenyl carbonate and Bisphenol A. Moreover, the catalysts of the invention were found to be very selective in substantially reducing the level of branching side reaction, i.e., formation of Fries product, normally associated with the melt polycarbonate process.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method for preparing polycarbonates by a transesterification reaction between, for example, diaryl carbonate and aromatic bis hydroxy compounds. In particular, this invention relates to the melt polymerization reaction for the preparation of polycarbonates and novel polycarbonate catalysts comprised of certain salts of derivatized triazinyl pyridyl compounds. 
     A large number of catalyst systems have been examined for application to the melt polymerization of polycarbonates. Most of these methods require either a variety of co-catalysts or the subsequent addition of a catalyst quencher to ensure polymer stability. The need for high purity, high quality thermoplastic resins requires the reduction of residual contaminants in the final resin. This need for very low residual impurities is particularly acute in optical quality (OQ) grade polycarbonate resins. One approach towards elimination of residual solvent contamination, particularly methylene chloride, is through the implementation of a solventless (i.e., melt) process. 
     The melt process generally involves a base-catalyzed condensation polymerization of, for example, diphenyl carbonate and a dihydroxy compound such as Bisphenol A. The reaction is conducted at high enough temperatures for the starting monomers and product to remain molten, while the reactor pressure is staged in order to effectively remove phenol, the by-product of the polycondensation reaction. 
     Most current melt technology programs employ a two component catalyst system. The first component is a tetralkylammonium hydroxide (TMAH) co-catalyst which is used to initiate oligomer formation in the melt. The second catalyst is an alkali metal hydroxide (i.e., the “α-catalyst”) which is the second part of the overall catalyst system. Due to its intrinsic thermal stability, the alkali metal salt must be quenched at the end of the polymerization. This quenching process requires the addition of yet another component to the polymer formation. All materials from the quenching process remain in the final resin, further compromising the final properties. 
     Although the alkali metal hydroxides in general are excellent melt polymerization catalysts they tend to generate substantial amounts of an additional undesired by-product which is a branched polycarbonate species typically referred to as Fries product which has the repeat unit as set forth below. The formation of Fries product during melt polycarbonate polymerization leads to changes in ductility and in general Theological properties of the polymer. Polycarbonates produced by the melt process typically have higher Fries content than polycarbonates produced by the interfacial method. As used herein the term “Fries” or “fries” refers to a repeating unit in polycarbonate having the following formula:                           
     wherein the X variable represents 
     wherein variables R c  and R d  each independently represent a hydrogen atom or                           
     a monovalent hydrocarbon group and may form a ring structure. Thus, a need exists for the development of alternative melt polycarbonate polymerization catalysts which produce less Fries product than conventional catalyst systems. 
     SUMMARY OF THE INVENTION 
     This invention provides a method for preparing polycarbonates, which utilizes polycondensation catalysts which are derivatized pyridyl triazinyl macromolecules with the general formula A x   +y [(Triazinyl-Pyridyl)B y   −x ], where A represents certain alkali metals and B is a group which contains a charge balancing sulfonate, carboxylate, or phosphonate group. We have found that this new class of catalysts provide excellent polymerization rates for the preparation of Bisphenol A polycarbonate from the melt polymerization of diphenyl carbonate and Bisphenol A. Moreover, the catalysts of the invention were found to be very selective in substantially reducing the level of branching side reaction, i.e., formation of Fries product, normally associated with the melt polycarbonate process, while at the same time producing such polycarbonates at rates and molecular weights which are comparable to conventional NaOH-catalyzed reactions. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a method for preparing polycarbonates, which comprises the step of contacting a diaryloxy compound with a dihydric phenol compound in the presence of a compound of Formula (I): 
     
       
         A x   +y [(Triazinyl-Pyridyl)B y   −x ],  (I) 
       
     
     wherein A is an alkali metal selected from the group consisting of lithium, sodium, potassium, and cesium; 
     B is a charge balancing sulfonate, carboxylate, or phosphonate group; 
     x is an integer of from 1 to 4; 
     y is an integer of from 1 to 4; and 
     optionally in the presence of a co-catalyst selected from tetraalkyl ammonium and tetraalkyl phosphonium salts; 
     under polycarbonate melt polymerization conditions. 
     As used herein, the term “Triazinyl-Pyridyl” refers to an organic moiety having both a triazinyl group and a pyridyl group. 
     In a preferred embodiment, the compounds of Formula (I) have the following structure:                           
     wherein each R 10  is independently selected from 
     hydrogen; 
     pyridyl; 
     pyridyl substituted by 1-4 groups selected from C 1 -C 6  alkyl, C 1 -C 6  alkoxy, phenyl, and naphthyl; 
     phenyl; and 
     phenyl substituted by 1-4 groups selected from C 1 -C 6  alkyl, C 1 -C 6  alkoxy, phenyl, pyridyl, and naphthyl; 
     provided that at no more than one of said R 10  groups is hydrogen, further provided that at least one of said phenyl or pyridyl groups is substituted by at least one group selected from the alkali metal salt of a sulfonate, carboxylate, or phosphonate group, and further provided that at least one of the R 10  groups is a pyridyl group or is a group containing a pyridyl group. 
     Examples of preferred R 10  groups include the following                           
     and                           
     While certain positional isomers for the pyridyl rings and sulfonate groups are depicted, it should be appreciated that other positional isomers are within the scope of Formula (I) above, as well as phosphonate and carboxylate as substitutes for sulfonate, along with other alkali metal salts such as potassium and lithium. 
     Especially preferred compounds of Formula (I) include the following:                           
     and 
     In the method of the present invention, certain diaryloxy compounds which are useful in preparing the polycarbonates 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; and 
     wherein n and n 1  are independently selected from integers having a value of from 0 to 4 inclusive. 
     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 1′  wherein R 1′  is a monovalent hydrocarbon radical of the type described herein. Preferred monovalent hydrocarbonoxy radicals are the alkoxy and aryloxy radicals. 
     Especially preferred diesters are the diesters of carbonic acid. 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. Preferred 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-trichlorophenyl)carbonate; bis(2-cyanophenyl)carbonate; bis(o-nitrophenyl)carbonate; bis(o-methoxycarbonylphenyl) 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 at least one is diphenyl carbonate. 
     Preferred dihydric phenols include those represented by the formula 
     
       
         HO—D—OH 
       
     
     wherein D is a divalent aromatic radical. Preferably, D has the formula:                           
     wherein A 1  represents an aromatic group such as phenylene, biphenylene, naphthalene and the like; E represents an alkylene or alkylidene group such as methylene, ethylene, ethylidine, propylene, propylidene, isopropylidene, butylene, isobutylene, amylene, isoamylidene, and the like. Where E is an alkylene or alkylidene group, it may also consist of two or more alkylene or alkylidene groups connected by a moiety different from alkylene or alkylidene, such as an aromatic linkage; a tertiary amino linkage; an ether linkage; a carbonyl linkage; a silicon-containing linkage; or a sulfur-containing linkage such as sulfide, sulfoxide, sulfone, etc.; or a phosphorus-containing linkage such as phosphinyl, phosphonyl, etc. In addition, E may be a cycloaliphatic group (e.g., cyclopentylidene, cyclohexylidene, 3,3,5-trimethylcyclohexylidene, methylcyclohexylidene, 2-[2.2.1]-bicycloheptylidene, neopentylidene, cyclopentadecylidene, cyclodecylidene, adamantylidene, and the like); a sulfur-containing linkage, such as sulfide, sulfoxide or sulfone; a phosphorus-containing linkage, such as phosphinyl, phosphonyl; an ether linkage; a carbonyl group; a tertiary nitrogen group; or a silicon-containing linkage such as silane or siloxy. R 2  represents hydrogen or a monovalent hydrocarbon group such as alkyl, aryl, aralkyl, alkaryl, or cycloalkyl. Y 1  may be an inorganic atom such as halogen (fluorine, bromine, chlorine, or iodine); an inorganic group such as nitro; an organic group such as R 2  above, or an oxy group such as —OR 2  . It is only necessary that Y 1  be inert to and unaffected by reactants and reaction conditions used to prepare the polycarbonate. The letter m represents any integer from and including zero through the number of positions on A 1  available for substitution; p represents an integer from and including zero through the number of positions on E available for substitution; t represents an integer equal to at least one; s is either zero or one; and u represents zero or any integer. 
     In the dihydric phenol compound in which D is represented by the formula above, when more than one Y substituent is present, they may be the same or different. The same holds true for the R 2  substituent. Where s is zero in the above formula and u is not zero, the aromatic rings are directly joined with no intervening alkylidene or other bridging group or bond. The positions of the hydroxyl groups and Y 1  on the aromatic nuclear residues A 1  can be varied in the ortho, meta or para positions and the groupings can be vicinal, asymmetrical or symmetrical relationship, where two or more ring carbon atoms of the hydrocarbon residue are substituted with Y 1  and hydroxyl groups. 
     Further illustrative examples of dihydric phenols include the dihydroxy-substituted aromatic hydrocarbons disclosed in U.S. Pat. No. 4,217,438, incorporated herein by reference. 
     Further preferred dihydric phenols include the following: 
     Resorcinol; 
     4-bromoresorcinol; 
     hydroquinone; 
     4,4′-dihydroxybiphenyl ether; 
     4,4-thiodiphenol; 
     1,6-dihydroxynaphthalene; 
     2,6-dihydroxynaphthalene; 
     bis(4-hydroxyphenyl)methane; 
     bis(4-hydroxyphenyl)diphenylmethane; 
     bis(4-hydroxyphenyl)-1-naphthylmethane; 
     1,1-bis(4-hydroxyphenyl)ethane; 
     1,1-bis(4-hydroxyphenyl)propane; 
     1,2-bis(4-hydroxyphenyl)ethane; 
     1,1-bis(4-hydroxyphenyl)-1-phenylethane; 
     1,1-bis(3-methyl-4-hydroxyphenyl)-1-phenylethane; 2,2-bis(4-hydroxyphenyl)propane (“Bisphenol A”); 
     2-(4-hydroxyphenyl)-2-)3-hydroxyphenyl)propane; 
     2,2-bis(4-hydroxyphenyl)butane; 
     1,1-bis(4-hydroxyphenyl)isobutene; 
     1,1-bis(4-hydroxyphenyl)decane; 
     1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane; 
     1,1-bis(3,5-dibromo-4-hydroxyphenyl)cyclohexane; 
     1,1-bis(4-hydroxyphenyl)cyclohexane; 
     1,1-bis(4-hydroxyphenyl)cyclododecane; 
     1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclododecane; 
     trans-2,3-bis(4-hydroxyphenyl)-2-butene; 
     4,4-dihydroxy-3,3-dichlorodiphenyl ether; 
     4,4-dihydroxy-2,5-dihydroxy diphenyl ether; 
     2,2-bis(4-hydroxyphenyl)adamantine; 
     α,α′-bis(4-hydroxyphenyl)toluene; 
     bis(4-hydroxyphenyl)acetonitrile; 
     2,2-bis(3-methyl-4-hydroxyphenyl)propane; 
     2,2-bis(3-ethyl-4-hydroxyphenyl)propane; 
     2,2-bis(3-n-propyl-4-hydroxyphenyl)propane; 
     2,2-bis(3-isopropyl-4-hydroxyphenyl)propane; 
     2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane; 
     2,2-bis(3-t-butyl-4-hydroxyphenyl)propane; 
     2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane; 
     2,2-bis(3-allyl-4-hydroxyphenyl)propane; 
     2,2-bis(3-methoxy-4-hydroxyphenyl)propane; 
     2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane; 
     2,2-bis(2,3,5,6-tetramethyl-4-hydroxyphenyl)propane; 
     2,2-bis(3-5-dichloro-4-hydroxyphenyl)propane; 
     2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane; 
     2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane; 
     α,α-bis(4-hydroxyphenyl)toluene; 
     α,α,α′,α′-Tetramethyl-α,α′-bis(4-hydroxyphenyl)-p-xylene; 
     2,2-bis(4-hydroxyphenyl)hexafluoropropane; 
     1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene; 
     1,1-dibromo-2,2-bis(4-hydroxyphenyl)ethylene; 
     1,1-dichloro-2,2-bis(5-phenoxy-4-hydroxyphenyl)ethylene; 
     4,4′-dihydroxybenzophenone; 
     3,3-bis(4-hydroxyphenyl)-2-butanone; 
     1,6-bis(4-hydroxyphenyl)-1,6-hexanedione; 
     ethylene glycol bis(4-hydroxyphenyl)ether; 
     bis(4-hydroxyphenyl)ether; 
     bis(4-hydroxyphenyl)sulfide; 
     bis(4-hydroxyphenyl)sulfoxide; 
     bis(4-hydroxyphenyl)sulfone; 
     bis(3,5-dimethyl-4-hydroxyphenyl)sulfone 
     9,9-bis(4-hydroxyphenyl)fluorine; 
     2,7-dihydroxypyrene; 
     6,6′-dihydroxy-3,3,3′,3′-tetramethylspiro(bis)indane(“spirobiindane Bisphenol”); 3,3-bis(4-hydroxyphenyl)phthalide; 
     2,6-dihydroxydibenzo-p-dioxin; 
     2,6-dihydroxythianthrene; 
     2,7-dihydroxyphenoxathiin; 
     2,7-dihydroxy-9,10-dimethylphenazine; 
     3,6-dihydroxydibenzofuran; 
     3,6-dihydroxydibenzothiophene; and 
     2,7-dihydroxycarbazole. 
     A further example of suitable dihydric phenols include those containing spirobiindane structural units such as those represented by the formula:                           
     wherein each R 3  is independently selected from monovalent hydrocarbon radicals and halogen radicals; each R 4 , R 5 , R 6 , and R 7  is independently C 1 -C 6  alkyl; each R 8  and R 9  is independently H or C 1 -C 6  alkyl; and each n is independently selected from positive integers having a value of from 0 to 3, inclusive. The monovalent hydrocarbon radicals represented by R 3  are preferably those containing from 1 to about 12 carbon atoms, and include branched alkyl radicals and straight chain alkyl radicals. Some illustrative, non-limiting examples of these alkyl radicals include methyl, ethyl, propyl, isopropyl, butyl, tertiary-butyl, pentyl, neopentyl, and hexyl. Cycloalkyl radicals represented by R 3  are preferably those containing from about 3 to about 12 ring carbon atoms. Some illustrative non-limiting examples of these cycloalkyl radicals include cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, and cycloheptyl. Aryl radicals represented by R 3  are preferably those containing from 6 to 12 ring carbon atoms. Some illustrative non-limiting examples of these aryl radicals include phenyl, biphenyl, and naphthyl. Preferred aralkyl and alkaryl radicals represented by R 3  are those containing from 7 to about 14 carbon atoms. These include, but are not limited to benzyl, ethylphenyl, phenylbutyl, phenylpropyl, propylphenyl, and phenylethyl. The preferred halogen radicals represented by R 3  are fluorine, chlorine and bromine. 
     In the dihydric phenols of the above formula, when more than one R 3  substituent is present, they may be the same or different. The relative positions of the hydroxyl groups and R 3  on the aromatic nuclear residues may be varied in the ortho or meta positions. The position of each hydroxy group is independently at any unsubstituted site on each of the aromatic rings. More preferably, each hydroxy group is independently in positions 5 or 6 and 5′ and 6′ of each aromatic ring. 
     The spirobiindane dihydric phenols of the above formula are compounds that are known in the art and are commercially available or may be readily prepared by known methods. Methods of preparation include those described in U.S. Pat. No. 4,701,566; and by R. F. Curtis and K. O. Lewis in Journal of the Chemical Society (England), 1962, p. 420; and by R. F. Curtis in Journal of the Chemical Society (England), 1962, p. 417. In one illustrative, non-limiting example, these spiro dihydric phenols may be conveniently prepared by (i) reacting two moles of a phenolic compound with one mole of a carbonyl-containing compound such as acetone, and (ii) thereafter coreacting 3 moles of the product of (i) under acidic conditions to form the spiro dihydric phenol and 4 moles of a phenolic compound. The acids which may be utilized in (ii) can include acids as anhydrous methanesulfonic acid, anhydrous hydrochloric acid, and the like. 
     The most preferred spiro dihydric phenol for forming polycarbonates is 6,6′-dihydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobiindane (“SBI”), in which n in the above formula is 0 and the linkages with the rest of the polymer molecule are in a specific position on the aromatic rings. 
     The dihydric phenols set forth above may be used alone or as mixtures of two or more dihydric phenols. For reasons of availability and particular suitability for many end-uses, a preferred dihydric phenol is 2,2-bis(4-hydroxyphenyl)propane, otherwise known as Bisphenol-A or “BPA”. 
     Optionally, polyfunctional compounds may be utilized if the desired product is a branched polycarbonate. Such branched materials may be preferred in certain applications, for example in films for packaging applications. Suitable polyfunctional compounds used in the polymerization of branched polycarbonate include, but are not limited to, 
     1,1,1-tris(4-hydroxyphenyl)ethane; 
     4-[4-[1,1-bis(4-hydroxyphenyl)-ethyl]-dimethylbenzyl]; 
     trimellitic anhydride; 
     trimellitic acid, or its acid chloride derivatives; 
     trimethylolpropane; glycerol; and the like. 
     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. 
     It was found that catalyst systems comprising compounds of the formula 
     A x   +y [(Triazinyl-Pyridyl)B y   −x ] provide polymerization rates comparable to alkali metal hydroxides, such as sodium hydroxide, while providing less branched side products. The branched side products include, but are not limited to Fries products. In addition to the catalysts described above, the catalyst system may optionally comprise a quaternary ammonium salt and/or a phosphonium co-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. 
     In a preferred embodiment, a substantially equal molar mixture of the diester and the dihydric phenol compound, preferably 1.0 to 1.2, most preferably 1.04-1.14 on a molar basis, is heated at atmospheric pressures in a substantially inert atmosphere at temperatures in the range of from 150° C. to 210° C. Agitation of the mixture can be initiated as soon as the components start to melt. The system can be agitated slowly to promote better heat exchange. After the system has been allowed to thermally equilibrate, an effective amount of the catalyst of the present invention can be added, optionally in the presence of co-catalyst as described above. The co-catalyst serves to catalyze the formation of polycarbonate oligomeric material, which later further undergoes polycondensation to form the polycarbonates of the present invention. In this regard, the catalyst of the formula A x   +y [(Triazinyl-Pyridyl)B y   −x ] may be added at the beginning of the polycondensation reaction, at later stages or during the polymerization step, either in one portion or in multiple portions. An effective amount is at least about 1×10 −6  mol ratio of the catalyst, per mole of BPA, preferably from about1×10 −6  to 
     1×10 −5  mol ratio of the catalyst, per BPA. 
     The resulting solution can be stirred until the catalyst has been dispersed and the reaction temperature of the mixture can be raised to 180° C. to 210° C. while the pressure can be lowered to 175 to 250 torr. Distillation of aromatic hydroxy compound (i.e., the polycondensation by-product) can be effected and the pressure continuously reduced to further effect the separation of the aromatic hydroxy compound. The pressure of the reaction can be further reduced to 70 to 130 torr while the temperature can be increased to 220° C. to 250° C. The final stage of the reaction can be initiated by placing the condensation product under full vacuum at 0.1 to 5 torr at a temperature in the range of from 270° C. to 350° C. for 0.5 to 3 hours. Recovery of the final polycarbonate can be achieved after the theoretical amount of aromatic monohydroxy compound has been collected. 
     The reaction conditions of the melt polymerization are not particularly limited and may be conducted in a wide range of operating conditions. Hence, the term “polycarbonate melt polymerization conditions” will be understood to mean those conditions necessary to effect reaction between the diaryloxy compound and the dihydric phenol compound. 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 0.2 to about 15 torr. The reaction time is generally about 0.1 hours to about 10 hours. 
     The melt polymerization may be accomplished in one or more stages, as is known in the art with other catalysts. The catalysts of the present invention may be added in the same stage or different stages, if the melt polymerization is conducted in more than one stage. The optional co-catalyst may be added at any stage, although it is preferred that it be added early in the process. When utilized, the basic co-catalyst is preferably utilized in a 1-500×molar equivalent, based on the moles of catalyst utilized. 
     In a further preferred embodiment, the process is conducted as a two stage process. In the first stage of this embodiment, the catalyst of the present invention is introduced into the reaction system comprising the dihydric phenol compound and the diaryloxy compound. The first stage is conducted at a temperature of 270° C. or lower, preferably 80 to 250° C., more preferably 100 to 230° C. The duration of the first stage is preferably 0 to 5 hours, even more preferably 0 to 3 hours at a pressure from atmospheric pressure to 100 torr, with a nitrogen atmosphere preferred. 
     In a second stage, the catalyst is introduced into the product from the first stage and further polycondensation is conducted. The catalyst may be added in its entire amount in the second stage, or it may be added in batches in the second and subsequent stages so that the total amount is within the aforementioned ranges. 
     It is preferable in the second and subsequent stages of the polycondensation step for the reaction temperature to be raised while the reaction system is reduced in pressure compared to the first stage, thus bringing about a reaction between the dihydric phenol compound and the diaryloxy compound, and for the dihydric phenol and the diaryloxy compound finally to be subjected to a polycondensation reaction at 240 to 320° C. under reduced pressure of 5 mm Hg or less, and preferably 1 mm Hg or less. 
     If the melt polymerization is conducted in more than one stage, as noted above, it is preferable to add a co-catalyst base, such as tetramethyl ammonium hydroxide in an earlier stage than the catalyst of the present invention. In particular, it is preferable to add the base to the reactor before the temperature reaches 220° C., preferably before it reaches 200° C. 
     Thus, in a further embodiment, the present invention provides a method for preparing polycarbonates, which comprises the steps of 
     (a) melting a dihydric phenol and a diaryloxy compound for a time and period sufficient to form a melt, and thereafter introducing a catalyst composition comprising a catalytically effective amount of a compound of Formula(I): 
     
       
         A x   +y [(Triazinyl-Pyridyl)B y   −x ],  (I) 
       
     
     wherein A is an alkali metal selected from the group consisting of lithium, sodium, potassium, and cesium; 
     B is a charge balancing sulfonate, carboxylate, or phosphonate group; x is an integer of from 1 to 4; and 
     y is an integer of from 1 to 4; 
     optionally in the presence of a co-catalyst selected from tetraalkyl ammonium and tetraalkyl phosphonium salts; 
     (b) oligomerizing the product from step (a) in a reaction system comprising at least one continuous reactor in series, wherein said reactor is operated at a temperature of about 210° C. to about 290° C., and wherein the product from the reactor has a number average molecular weight of about 1000 to about 5500; and 
     (c) polymerizing the product from step (b) in a reaction system comprising at least one continuous polymerization reactor in series, wherein said reactor is operated at a temperature of about 280° C. to 315° C., wherein the product from step (c) has a number average molecular weight of at least about 6500. 
     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. 
     Experimental Section 
     We have discovered that certain catalysts with the general formula of A x   +y [(Triazinyl-Pyridyl)B y   −x ] significantly enhance the selectivity towards reducing this side branching reaction product (commonly referred to as the Fries product). 
     Compared with sodium tosylate, both triazinyl pyridyl structures shown below as compounds 1a, and 1b demonstrate a significant increase in reaction rate as indicated by their molecular weight. Both catalysts also demonstrate a significantly lower level of Fries branching as compared to sodium tosylate. Compared with results using NaOH both catalysts are slightly less active, however they demonstrate a significant decrease in Fries branching. Another attractive feature of these catalysts over NaOH is that they are neutral to slightly acidic in solution, thus avoiding the corrosive properties of NaOH. Comparisons of Fries and molecular weight for several catalysts are presented in Table 1. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Salt added 
                 Mn 
                 Fries 
               
               
                   
               
             
             
               
                 Catalyst Loading 5.0 × 10 −06  moles/mole BPA 
                   
                   
               
               
                 NaOH 
                 800 
                 3200  
               
               
                 Sodium Tosylate 
                 5938  
                 240 
               
               
                 3-[5-(sulfophenyl)-2-pyridyl]-1,2,4-triazin-5-yl benzenesulfonic acid, 
                 7464  
                  65 
               
               
                 disodium salt, 1a 
               
               
                 2-(5,6-bis[4-sulfophenyl]-1,2,4-triazin-3-yl)-4-(4-sulfophenyl)pyridine 
                 491 
                 163 
               
               
                 trisodium salt, 1b 
               
               
                 Catalyst Loading 1.0 × 10 −06  moles/mole BPA 
               
               
                 NaOH 
                 200 
                 380-450 
               
               
                 3-[5-(sulfophenyl)-2-pyridyl]-1,2,4-triazin-5-yl benzenesulfonic acid, 
                 194 
                 127 
               
               
                 disodium salt, 1a 
               
               
                 2-(5,6-bis[4-sulfophenyl]-1,2,4-triazin-3-yl)-4-(4-sulfophenyl)pyridine 
                 309 
                 156 
               
               
                 trisodium salt, 1b 
               
               
                   
               
               
                 Compound 1a  
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 3-[5-(sulfophenyl)-2-pyridyl]-1,2,4-triazin-5-yl benzenesulfonic acid, disodium salt  
               
               
                 Compound 1b  
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 2-(5,6-bis[4-sulfophenyl]-1,2,4-triazin-3-yl)-4-(4-sulfophenyl)pyridine trisodium salt  
               
             
          
         
       
     
     As illustrated in Table 1 a significant level of Fries reduction can be achieved by addition of catalyst of the present invention. 
     General Procedure 
     To facilitate observations and for purity, melt transesterification reactions were carried out in a 1 Liter glass batch reactor equipped with a solid nickel helical agitator. The reactor bottom had a breakaway glass nipple for removal of the final melt. To remove any sodium from the glass the reactor was soaked in 3N HCl for at least 12 hours followed by a soak in 18 Mohm water for at least 12 hours. The reactor was then dried in an oven overnight and stored covered until used. The temperature of the reactor was maintained using a fluidised sand bath with a PID controller and measured near the reactor and sand bath interface. The pressure over the reactor was controlled by a nitrogen bleed into the vacuum pump downstream of the distillate collection flasks and measured at higher pressures (760 mmHg-40 mmHg) with a mercury barometer and at lower pressures (40 mmHg-1 mmHg) with an Edwards pirani gauge. 
     The reactor was charged with solid Bisphenol-A (General Electric Plastics Japan Ltd., 0.6570 mol) and solid Diphenyl carbonate (General Electric Plastics Japan Ltd., 0.7096 mol) prior to assembly. The reactor was then assembled, sealed and the atmosphere was exchanged with nitrogen three times. With the final nitrogen exchange the reactor was brought to near atmospheric pressure and submerged into the fluidised bath which was at 180° C. After five minutes agitation was begun at 250 rpm. After an additional ten minutes the reactants were fully melted and a homogeneous mixture was assumed. Tetramethyl ammonium hydroxide (Sachem stock solution, 1.32×10 −4  mol) and the catalyst of the invention were added sequentially after being diluted to the proper concentrations, Table 2: 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Reactant Amounts in 18M Ohm water 
               
             
          
           
               
                   
                 Condition 
                 TMAH 
                 Catalyst of invention 
               
               
                   
                   
               
             
          
           
               
                   
                 Concentration/M 
                 0.220 
                 1.0-5.0 × 10 −3   
               
               
                   
                 Volume added/ul 
                 740 
                 660 
               
               
                   
                 Catalyst/BPA 
                 2.5 × 10 −4   
                 1.0-5.0 × 10 −6   
               
               
                   
                   
               
             
          
         
       
     
     After the final catalyst was added timing began and the temperature was ramped to 210° C. in five minutes. Once at temperature the pressure was reduced to 180 mmHg and phenol distillate was immediately formed. After 25 minutes the pressure was again reduced to 100 mmHg and maintained for 45 minutes. The temperature was then ramped to 240° C. in five minutes and the pressure was lowered to 15 mmHg. These conditions were maintained for 45 minutes. The temperature was then ramped to 270° C. in five minutes and the pressure was lowered to 2 mmHg. These conditions were maintained for 10 minutes. The temperature was then ramped to the final finishing temperature in five minutes and the pressure was reduced to 1.1 mmHg. The finishing temperature was 310° C. After 30 minutes the reactor was removed from the sand bath and the melt was extruded into liquid nitrogen to quench the reaction. 
     Fries determination (ppm) was obtained by the liquid chromatographic analysis of the KOH catalyzed methanolysis of polycarbonate prepared by melt condensation. 
     Mn (Number average molecular weight) was obtained by GPC analysis of polycarbonate prepared by melt polymerization. Standards of polystyrene were used to construct a universal calibration against which polycarbonate could be measured using the Mark-Houwink equation. The temperature of the columns was 25° C. and the mobile phase was chloroform.