METHOD FOR THE PRODUCTION OF A POLYCARBONATE USING A HALOGENED DIARYLCARBONATE

Description

[0001] The present invention relates to a process for producing a polycarbonate from one or more diaryl alcohols and a diaryl carbonate by the melt transesterification process. At least part of the diaryl carbonate is obtained by reacting a fully or partially halogenated monophenol with a carbonyl halide. The process according to the invention is characterized in that a halogenated diaryl carbonate offers significant advantages in the reaction procedure.

[0002] Both polycarbonates and their production by the melt transesterification process are known from the state of the art.

[0003] In the production of polycarbonate by melt transesterification, dihydroxyaryl compounds are reacted with diaryl carbonates, whereby the monohydroxyaryl compound is cleaved from the diaryl carbonates in a transesterification reaction. The condensation initially leads to the formation of low-molecular-weight polycarbonate oligomers, which react further with continued cleavage of the monohydroxyaryl compound to form high-molecular-weight polycarbonate. The reaction progress can be promoted by the use of suitable catalysts.

[0004] The production of aromatic polycarbonates by the melt transesterification process is known and described, for example, in "Schnell", Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney 1964, in D.C. Prevorsek, B.T. Debona and Y. Kersten, Corporate Research Center, Allied Chemical Corporation, Moristown, New Jersey 07960, "Synthesis of Poly(ester)carbonate Copolymers" in Journal of Polymer Science, Polymer Chemistry Edition, Vol. 19, 75-90 (1980), in D. Freitag, U. Grigo, P.R. Müller, N. Nouvertne, BAYER AG, "Polycarbonates" in Encyclopedia of Polymer Science and Engineering, Vol. 11, Second Edition, 1988, pages 648-718 and finally in Drs. U. Grigo, K. Kircher and P.R. Müller "Polycarbonates" in Becker / Braun, Kunststoff-Handbuch, Volume 3 / 1, Polycarbonates, Polyacetals, Polyesters, Cellulose Esters, Carl Hanser Verlag Munich, Vienna 1992, pages 117-299.

[0005] DE60202691T2 discloses a process for producing an aromatic polycarbonate by a melt transesterification process from an aromatic dihydroxy compound and a carbonic acid diester, wherein the carbonic acid diester may be bis(chlorophenyl) carbonate.

[0006] Of technical importance is the production of high-molecular polycarbonate from 2,2-bis(4-hydroxyphenyl)propane (also called bisphenol A or BPA) and diphenyl carbonate (also called DPC).

[0007] Polycarbonates within the meaning of the present invention include both homopolycarbonates and copolycarbonates and / or polyestercarbonates; the polycarbonates can be linear or branched in a known manner. Mixtures of polycarbonates can also be used according to the invention.

[0008] The thermoplastic polycarbonates, including the thermoplastic aromatic polyester carbonates, have average molecular weights M w (determined by measuring the relative solution viscosity with an Ubbelohde viscometer at 25°C in CH 2 Cl 2 and a concentration of 0.5 g per 100 ml CH 2 Cl 2 ) of 20,000 g / mol to 32,000 g / mol, preferably of 23,000 g / mol to 31,000 g / mol, in particular of 24,000 g / mol to 31,000 g / mol.

[0009] A portion, up to 80 mol%, preferably from 20 mol% to 50 mol%, of the carbonate groups in the polycarbonates used according to the invention can be replaced by aromatic dicarboxylic acid ester groups. Such polycarbonates, which contain both carbonic acid residues and acid residues of aromatic dicarboxylic acids incorporated into the molecular chain, are referred to as aromatic polyester carbonates. For the purposes of the present invention, they are subsumed under the generic term of thermoplastic aromatic polycarbonates.

[0010] The polycarbonates are produced in a basically known manner from diaryl alcohols, carbonic acid derivatives, optionally chain terminators and optionally branching agents, whereby to produce the polyester carbonates, some of the carbonic acid derivatives are replaced by aromatic dicarboxylic acids or derivatives of dicarboxylic acids, depending on the carbonate structural units to be replaced in the aromatic polycarbonates by aromatic dicarboxylic acid ester structural units.

[0011] Dihydroxyaryl compounds suitable for the production of polycarbonates are those of the structural formula (1) HO-Z-OH (1), in which Zein aromatic radical having 6 to 30 C atoms, which may contain one or more aromatic nuclei, may be substituted and may contain aliphatic or cycloaliphatic radicals or alkylaryls or heteroatoms as bridge members. Preferably, Z in structural formula (2) represents a radical of structural formula (2) in the R 6< and R 7< independently of one another represent H, C 1 - to C 18 -alkyl-, C 1 - to C 18 -alkoxy, halogen such as Cl or Br or represent in each case optionally substituted aryl- or aralkyl, preferably H or C 1 - to C 12 -alkyl, particularly preferably H or C 1 - to C 8 -alkyl and very particularly preferably H or methyl, and X represents a single bond, -SO 2 -, -CO-, -O-, -S-, C 1 - to C 6 -alkylene, C 2 - to C 5 -alkylidene or C 5 - to C 6 -cycloalkylidene, which may be substituted by C 1 - to C 6 -alkyl, preferably methyl or ethyl, and furthermore represents C 6 - to C 12 -arylene, which may optionally be condensed with further aromatic rings containing heteroatoms. Preferably X represents a single bond, C 1 - to C 3 -alkylene, C 2 - to C 3 -alkylidene, C 3 - to C 6 -Cycloalkylidene, -O-, -SO-, -CO-, -S-, -SO 2 - or for a residue of the structural formula (2a)

[0012] Examples of diaryl alcohols (dihydroxyaryl compounds) are: dihydroxybenzenes, dihydroxydiphenyls, bis-(hydroxyphenyl)-alkanes, bis-(hydroxyphenyl)-cycloalkanes, bis-(hydroxyphenyl)-aryls, bis-(hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones, bis-(hydroxyphenyl)-sulfides, bis-(hydroxyphenyl)-sulfones, bis-(hydroxyphenyl)-sulfoxides, 1,1'-bis-(hydroxyphenyl)-diisopropylbenzenes and their nuclear alkylated and nuclear halogenated compounds.

[0013] Diaryl alcohols suitable for the production of the polycarbonates to be used according to the invention are, for example, hydroquinone, resorcinol, dihydroxydiphenyl, bis-(hydroxyphenyl)-alkanes, bis-(hydroxyphenyl)-cycloalkanes, bis-(hydroxyphenyl)-sulfides, bis-(hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones, bis-(hydroxyphenyl)-sulfones, bis-(hydroxyphenyl)-sulfoxides, α,α'-bis-(hydroxyphenyl)-diisopropylbenzenes and their alkylated, nuclear alkylated and nuclear halogenated compounds.

[0014] Preferred diaryl alcohols are 4,4'-dihydroxydiphenyl, 2,2-bis-(4-hydroxyphenyl)-1-phenylpropane, 1,1-bis-(4-hydroxyphenyl)-phenylethane, 2,2-bis-(4-hydroxyphenyl)-propane, 2,4-bis-(4-hydroxyphenyl)-2-methylbutane, 1,3-Bis-[2-(4-hydroxyphenyl)-2-propyl]benzene (Bisphenol M), 2,2-Bis-(3-methyl-4-hydroxyphenyl)-propane, Bis-(3,5-dimethyl-4-hydroxyphenyl)-methane, 2,2-Bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, Bis-(3,5-dimethyl-4-hydroxyphenyl)-sulfone, 2,4-Bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane, 1,3-bis-[2-(3,5-dimethyl-4-hydroxyphenyl)-2-propyl]-benzene and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (also called bisphenol TMC for short).

[0015] Particularly preferred diaryl alcohols are 4,4'-dihydroxydiphenyl, 1,1-bis-(4-hydroxyphenyl)-phenylethane, 2,2-bis-(4-hydroxyphenyl)-propane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)-propane, 1,1-bis-(4-hydroxyphenyl)-cyclohexane and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

[0016] These and other suitable diaryl alcohols are described, for example, in US 2 999 835 A, US 3 148 172 A, US 2 991 273 A, US 3 271 367 A, US 4 982 014 A and US 2 999 846 A, in the German laid-open specifications DE 1 570 703 A, DE 2 063 050 A, DE 2 036 052 A, DE 2 211 956 A and DE 3 832 396 A, the French patent FR 1 561 518 A1, in the monograph "H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964, p. 28 ff.; p. 102 ff.", and in "DG Legrand, JT Bendler, Handbook of Polycarbonate Science and Technology, Marcel Dekker New York 2000, p. 72ff.".

[0017] In the case of homopolycarbonates, only one diaryl alcohol is used; in the case of copolycarbonates, two or more different diaryl alcohols are used. The diaryl alcohols used, as well as all other chemicals and auxiliaries added to the synthesis, may be contaminated with impurities arising from their own synthesis, handling, and storage. However, it is desirable to work with the purest raw materials possible.

[0018] In the same way, any branching agents or branching agent mixtures that may be used are added to the synthesis. Typically, trisphenols, quaternphenols, or acid chlorides of tri- or tetracarboxylic acids are used, or mixtures of polyphenols or acid chlorides.

[0019] Some of the compounds which can be used as branching agents and which have three or more than three phenolic hydroxyl groups are, for example, phloroglucinol, 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-2-heptene, 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane, 1,3,5-tris-(4-hydroxyphenyl)-benzene, 1,1,1-tri-(4-hydroxyphenyl)-ethane, tris-(4-hydroxyphenyl)-phenylmethane, 2,2-bis-[4,4-bis-(4-hydroxyphenyl)-cyclohexyl]-propane, 2,4-bis-(4-hydroxyphenyl-isopropyl)-phenol, tetra-(4-hydroxyphenyl)-methane.

[0020] Some of the other trifunctional compounds are 2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and 3,3-bis-(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.

[0021] Preferred branching agents are 3,3-bis-(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole and 1,1,1-tri-(4-hydroxyphenyl)ethane.

[0022] The amount of branching agents to be used, if appropriate, is 0.05 mol% to 2 mol%, again based on the moles of diaryl alcohols used, the branching agents being initially introduced with the diaryl alcohols.

[0023] All of these measures for producing polycarbonates are familiar to the person skilled in the art.

[0024] Both diaryl carbonates, their preparation and their use in a melt transesterification process for the production of polycarbonate are known from the prior art.

[0025] In Applied Catalysis A: General, Volume 316 (2007), pp. 1-21, Gong, Ma, and Wang provide an overview of methods for preparing diaryl carbonates using diphenyl carbonate as an example. Methods are described starting from phosgene and phenol, or carbon monoxide, oxygen, and phenol, as well as starting from carbon monoxide, oxygen, and methanol with subsequent transesterification of dimethyl carbonate to diphenyl carbonate with phenol, or starting from methyl nitrite and carbon monoxide via dimethyl oxalate and dimethyl carbonate by transesterification. Further methods for preparing dimethyl carbonate for transesterification with aryl alcohols to form diaryl carbonates are described by Delledonne, Rivetti, and Romano in Appl. Catal. A: Gen., 221 (2001), p. 241.Here, methods are described starting from phosgene and methanol, urea and methanol, carbon dioxide and methanol, carbon dioxide and ethylene oxide via ethylene carbonate as an intermediate for transesterification with methanol, and also the previously reported reactions starting from carbon monoxide, oxygen and methanol, as well as methyl nitrite and carbon monoxide.

[0026] On a laboratory scale, the preparation of diaryl carbonates via phosgene and an aryl alcohol is preferred due to the one-step, rapid, and efficient reaction at low temperatures and pressures. The diaryl carbonates used in the examples of the present invention have also been prepared using phosgene and phenol or substituted phenol, but this should not limit the applicability of the described diaryl carbonates in melt transesterification to polycarbonates to this method of preparing diaryl carbonates.

[0027] A disadvantage of the melt transesterification processes for producing polycarbonate according to the prior art is that an excess of diaryl carbonate is used compared to bisphenol. Despite this excess, some of the polymer's end groups are not terminated and thus end in reactive OH groups, and the unreacted bisphenol remains in the resulting polycarbonate. In addition to the increased use of diaryl carbonate, another disadvantage is a longer reaction time in the production of the polycarbonate, since increased use of diaryl carbonate slows the reaction to form the polycarbonate.

[0028] The object of the present invention was to overcome the disadvantages of the prior art. In particular, the object of the present invention was to provide a process for producing a polycarbonate from one or more diaryl alcohols and a diaryl carbonate by the melt transesterification process, in which a smaller excess of diaryl carbonate relative to the diaryl alcohol is required compared to conventional processes, without increasing the amount of reactive OH groups or leaving more unreacted bisphenol in the resulting polycarbonate.

[0029] Surprisingly, it has been found that the object is achieved by a process according to the main claim as a first embodiment, namely by a process for producing polycarbonate by melt transesterification of at least one diaryl carbonate and at least one diaryl alcohol, wherein 0.1 to 10 wt.% of the amount of diaryl carbonates used is a halogenated diaryl carbonate or wherein 95 to 99 wt.% of the amount of diaryl carbonates used is a halogenated diaryl carbonate.

[0030] According to the invention, it is preferred that 0.2 to 3 wt.%, preferably 0.3 to 1 wt.%, of the amount of diaryl carbonates used is a halogenated diaryl carbonate.

[0031] This preferred embodiment of the method according to the invention represents a second embodiment after the first embodiment presented above.

[0032] It is further preferred according to the invention that 96 to 98 wt.% of the amount of diaryl carbonates used is a halogenated diaryl carbonate.

[0033] This further preferred embodiment of the method according to the invention represents a third embodiment after the first embodiment presented above.

[0034] It is further preferred according to the invention that the halogenated diaryl carbonate is selected from the group comprising the members di-(halophenyl) carbonate and halophenyl phenyl carbonate, as well as any mixtures of a di-(halophenyl) carbonate and a halophenyl phenyl carbonate.

[0035] This further preferred embodiment of the method according to the invention represents a fourth embodiment according to one of the embodiments presented above, in particular this fourth embodiment represents an embodiment according to the first embodiment presented above or the second embodiment presented above or the third embodiment presented above.

[0036] It is particularly preferred according to the invention that the di-(halophenyl) carbonate is a di-(2-halophenyl) carbonate.

[0037] This particularly preferred embodiment of the method according to the invention represents a fifth embodiment after the fourth embodiment presented above.

[0038] It is also particularly preferred according to the invention that the halophenyl phenyl carbonate is a 2-halophenyl phenyl carbonate.

[0039] This particularly preferred embodiment of the method according to the invention represents a sixth embodiment after the fourth embodiment presented above.

[0040] It is particularly preferred according to the invention that the di-(halophenyl) carbonate is di-(2-fluorophenyl) carbonate or di-(2-chlorophenyl) carbonate.

[0041] This particularly preferred embodiment of the method according to the invention represents a seventh embodiment after the fifth embodiment presented above.

[0042] It is also particularly preferred according to the invention that the 2-halophenyl phenyl carbonate is 2-fluorophenyl phenyl carbonate or 2-chlorophenyl phenyl carbonate.

[0043] This particularly preferred embodiment of the method according to the invention represents an eighth embodiment after the sixth embodiment presented above.

[0044] It is further preferred according to the invention that the at least one diaryl alcohol is bisphenol A.

[0045] This further preferred embodiment of the method according to the invention represents a ninth embodiment after the first embodiment presented above.

[0046] A further subject of the present invention is also a polycarbonate produced by a process as described in one of the embodiments listed above.

[0047] In particular, it has been found that the object is achieved by the melt transesterification process according to the invention for producing polycarbonate using certain substituted diaryl carbonates (structural formula X, where R1 and R2 can independently of one another be a substituent other than hydrogen), which on the one hand reduces the excess of diaryl carbonate and on the other hand reduces the amount of residual monomers remaining after the reaction, without the mass fraction of end groups that are not terminated, i.e. end on reactive OH groups, increasing.

[0048] Particularly suitable are halogenated diaryl carbonates selected from the group comprising the members di-(halophenyl) carbonate and halophenyl phenyl carbonate, as well as any mixtures of a di-(halophenyl) carbonate and a halophenyl phenyl carbonate. Di-(halophenyl) carbonates suitable according to the invention are, for example, di-(fluorophenyl) carbonate or di-(chlorophenyl) carbonate or any mixtures of a di-(fluorophenyl) carbonate and a di-(chlorophenyl) carbonate. Furthermore, it has been shown that the position of the halogen on the phenol ring is important for the reactivity in the process according to the invention for producing a polycarbonate. Particularly suitable for transesterification are di-(2-halophenyl) carbonates (structural formula Y, where X is a halogen atom), such as di-(2-fluorophenyl) carbonate or di-(2-chlorophenyl) carbonate or mixtures of di-(2-fluorophenyl) carbonate and di-(2-chlorophenyl) carbonate.

[0049] It is very difficult to obtain di-(2-halophenyl) carbonates with a purity of at least 99.5 wt.% because, very often, in addition to the variant halogenated in the 2-position (structural formula Y), the variant halogenated in the 4-position (structural formula Z) is also present in small amounts as an impurity in the ppm range, but always less than 1 wt.%. The presence of diaryl carbonates halogenated in the 4-position does not interfere with the process according to the invention, as long as their proportion compared to the proportion of diaryl carbonates halogenated in the 2-position is less than 1 wt.%.-% remains, but di-(4-halophenyl) carbonates (structural formula Z), although they are also effective, are in themselves less suitable for transesterification than di-(2-halophenyl) carbonates, since di-(4-halophenyl) carbonates require a higher reaction temperature and a deeper vacuum than di-(2-halophenyl) carbonates in order to achieve the same reaction progress in the production of polycarbonates as when using di-(2-halophenyl) carbonates.

[0050] Asymmetrically halogen-substituted diaryl carbonates (structural formula O, where X is a halogen atom) are also particularly suitable for melt transesterification with diaryl alcohols to produce polycarbonates. For example, even small amounts of these asymmetrically halogen-substituted diaryl carbonates compared to the amount of diphenyl carbonate added can result in a lower reaction temperature or a less deep vacuum being required to achieve the same reaction progress in the production of polycarbonate as would be achieved without the use of asymmetrically halogen-substituted diaryl carbonates.Halophenyl phenyl carbonates suitable according to the invention are, for example, fluorophenyl phenyl carbonates or chlorophenyl phenyl carbonates or any mixtures of a fluorophenyl phenyl carbonate and a chlorophenyl phenyl carbonate, with 2-fluorophenyl phenyl carbonate being particularly suitable as fluorophenyl phenyl carbonates and 2-chlorophenyl phenyl carbonate being particularly suitable as chlorophenyl phenyl carbonates.

[0051] By using these substances according to the formulas X, Z or O, the residence time in the melt transesterification process for producing polycarbonate can be shortened and thus, with unchanged reaction parameters, the throughput in the production of polycarbonate can be significantly increased with the same properties of the polycarbonate, and / or lower pressures and / or temperatures can be applied without the quality of the polycarbonate obtained deteriorating or resulting in a reduced yield. Methods used: Gel permeation chromatography:

[0052] GPC experiments were performed using the following equipment: Agilent 12 series. Agilent PLgel mixed 5µm columns (X 5) + infinity 1260 detector with a wavelength of 254 nm and methylene chloride as the mobile phase at a flow rate of 1.0 mL min-1 at 30°C.

[0053] The columns were calibrated using polycarbonate standards in the range of Mp 7,000 to 63,000 g.mol-1. Infrared measurements of OH end groups:

[0054] HATR measurements were performed using a PerkinElmer Spectrum 100 with an ATR attachment using a ZnSe 45° crystal. An MCT / A detector ranging from 650 to 4000 cm -1 was used. The samples were dissolved in THF and adjusted with a THF blank. The final spectrum consists of 32 scans, each lasting 32 seconds. Residual monomers:

[0055] 10 g of polycarbonate are boiled in 25 mL of acetone under reflux for 2 h. Then, 25 mL of methanol is added and shaken out. The upper phase is injected into an HPLC system. Residual monomers are determined on this HPLC system from Agilent using a Zorbax 3.5 SB18 4.6 x 50 mm column (or: Halo 5 phenyl-hexyl 4.6 x 75 mm column). A UV6000LP (or FL3000) is used as the detector. The injected volume is 5 µL, and the mobile phase is acetonitrile. Example 1 (comparison example) a) Production and processing of diphenyl carbonate (DPC)

[0056] A sodium phenolate solution (188.23 grams of phenol in 481.96 grams of deionized water with 81.21 grams of sodium hydroxide solution) was introduced into a continuously operated laboratory system at 25 °C at a total rate of 751.4 grams per hour and mixed with 101.88 grams per hour of phosgene in 846.69 grams of a solvent mixture (1:1 weight ratio of chlorobenzene to methylene chloride). The mixture was metered into a Fink HMR040 mixing pump. Subsequently, 14.97 grams per hour of 32.09 weight percent sodium hydroxide solution in water were added and transferred to another Fink HMR040 mixing pump. The reaction mixture was transferred to a flooded stirred reactor with N-ethylpiperidine for complete conversion to diphenyl carbonate. The organic phase was separated and washed with 1 wt. % HCl solution and then with deionized water. The solvent was removed by distillation. b) Production of polycarbonate

[0057] In a three-neck flask equipped with oil heating, a stirrer, a short-path separator, and a cold trap with a vacuum connection, 79.91 grams of bisphenol A (0.35 mol) and 78.82 grams of diphenyl carbonate (0.37 mol) from a) were melted with 106.6 µl of catalyst solution (5 wt% tetraphenylphosphonium phenolate in phenol) at 205 °C under nitrogen. The molar ratio between DPC and BPA was thus adjusted to 1.048. The temperature was increased to 230 °C, and the pressure reduced to 200 mbar. Pressure and temperature were gradually adjusted to remove any phenol formed from the mixture (see Table 1 below). Table 1: Reaction course, temperature, pressure and time T (°C) P (mbar) t (min) 205 1013 40 230 200 20 245 100 20 275 50 20 285 25 20 315 4 45 330 <1 45

[0058] The resulting polycarbonate showed 33 ppm residual phenol, 15 ppm residual BPA, as well as 521 ppm OH end groups (weight ppm to mass polycarbonate). Example 2 and 3 a)

[0059] The procedure described in Example 1 a) is repeated successively with 2-fluorophenol (191.96 grams in 504.83 grams of deionized water and 69.53 grams of sodium hydroxide solution) and 2-chlorophenol (194.55 grams in 520.65 grams of deionized water and 51.45 grams of sodium hydroxide solution).

[0060] Already during the preparation of the diaryl carbonates, it became clear that the anions formed by 2-chlorophenol or 2-fluorophenol in this reaction regime were more stable than the phenolate anion, and therefore, there were more aromatic alcohols in the aqueous phase of the reaction mixture. Phenol was found to be 41 ppm (by weight), 2-fluorophenol to be 2430 ppm, and 2-chlorophenol to be 1310 ppm in the aqueous phase. Example 2 and 3 b)

[0061] The procedure from Example 1 b) was repeated with di-(2-fluorophenyl) carbonate and di-(2-chlorophenyl) carbonate. The molar ratio of di-(2-fluorophenyl) carbonate and di-(2-chlorophenyl) carbonate to bisphenol A was reduced to 1.03, i.e., 88.46 grams of di-(2-fluorophenyl) carbonate and 102.26 grams of di-(2-chlorophenyl) carbonate were used, respectively.

[0062] In Example 2 with 2-fluorophenol, the temperature / pressure profile was adjusted to compensate for the higher vapor pressure of 2-fluorophenol compared to phenol (Table 2). Table 2: Reaction course, temperature, pressure and time T (°C) P (mbar) t (min) 205 1013 40 230 650 20 245 550 20 275 200 20 285 25 20 315 4 45 330 <1 45

[0063] The resulting polycarbonate from Example 2 contained 26 ppm 2-fluorophenol, less than 0.5 ppm bisphenol A (below the detection limit), and had 194 ppm OH end groups.

[0064] In Example 3 with 2-chlorophenol, the temperature / pressure profile was adjusted to compensate for the higher vapor pressure of 2-chlorophenol compared to phenol (Table 3). Table 3: Reaction course, temperature, pressure and time T (°C) P (mbar) t (min) 205 1013 40 230 500 20 245 400 20 275 300 20 285 200 20 315 4 45 330 <1 45

[0065] The resulting polycarbonate from Example 3 contained 38 ppm 2-chlorophenol, 3 ppm bisphenol A, and had 131 ppm OH end groups. Example 4

[0066] In a plant for the continuous production of polycarbonate using the melt transesterification process—as known, for example, from EP 2272890 A1—pure diphenyl carbonate was used (> 99.5 wt.% diphenyl carbonate, < 2 ppm chlorine content in the diphenyl carbonate). This was passed through several pressure and temperature stages as in Example 1b, using bisphenol A as the monomer and tetraphenylphosphonium phenolate as the catalyst, until a final temperature of 301 °C and an absolute pressure of approximately 2 mbar were reached. A relative solution viscosity (determined with an Ubbelohde viscometer at 25°C in CH 2 Cl 2 and a concentration of 0.5 g per 100 ml CH 2 Cl 2 ) of 1.309 was achieved at standard throughput (normalized to produced polycarbonate = 100%), and the resulting polycarbonate contained less than 20 ppm free bisphenol A and 520 ppm OH end groups. Example 5

[0067] In a process as described in Example 4, diphenyl carbonate was used which contained 0.63 wt.% 2-chlorophenyl phenyl carbonate (900 ppm chlorine content in the diphenyl carbonate). It was passed through several pressure and temperature stages as in Example 4 with bisphenol A as the monomer and tetraphenylphosphonium phenolate as the catalyst until a final temperature of 298 °C and an absolute pressure of approximately 1 mbar were reached. Due to the higher reactivity of the 2-chlorophenyl phenyl carbonate, a standardized throughput of 141% polycarbonate could be produced, with a relative solution viscosity (determined using an Ubbelohde viscometer at 25 °C in CH 2 Cl 2 and a concentration of 0.5 g per 100 ml CH 2 Cl 2 ) of 1.312, less than 20 ppm free bisphenol A and 518 ppm OH end groups were analyzed.

Claims

1. Process for producing polycarbonate by means of melt transesterification of at least one diaryl carbonate and at least one diaryl alcohol, characterized in that 0.1% to 10% by weight of the amount of diaryl carbonates used is a halogenated diaryl carbonate, or in that 95% to 99% by weight of the amount of diaryl carbonates used is a halogenated diaryl carbonate.

2. Process according to Claim 1, wherein 0.2% to 3% by weight, preferably 0.3% to 1% by weight, of the amount of diaryl carbonates used is a halogenated diaryl carbonate.

3. Process according to Claim 1, wherein 96% to 98% by weight of the amount of diaryl carbonates used is a halogenated diaryl carbonate.

4. Process according to any of Claims 1 to 3, wherein the halogenated diaryl carbonate is selected from the group comprising the members di(halophenyl) carbonate and halophenyl phenyl carbonate, and any desired mixtures of a di(halophenyl) carbonate and a halophenyl phenyl carbonate.

5. Process according to Claim 4, wherein the di(halophenyl) carbonate is a di(2-halophenyl) carbonate.

6. Process according to Claim 4, wherein the halophenyl phenyl carbonate is a 2-halophenyl phenyl carbonate.

7. Process according to Claim 5, wherein the di(halophenyl) carbonate is di(2-fluorophenyl) carbonate or di(2-chlorophenyl) carbonate.

8. Process according to Claim 6, wherein the 2-halophenyl phenyl carbonate is 2-fluorophenyl phenyl carbonate or 2-chlorophenyl phenyl carbonate.

9. Process according to Claim 1, wherein the at least one diaryl alcohol is bisphenol A.

10. Polycarbonate produced by a process according to any of Claims 1 to 9.