How to make polycarbonate - when to add chain terminators

Abstract

The present invention relates to a method for producing polycarbonates by the phase boundary process from at least one dihydroxydiarylalkane, phosgene, at least one catalyst, and at least one chain terminator, which produces polycarbonates having a low proportion of oligomers and a low proportion of two chain terminator carbonates. The method according to the present invention is characterized in that the chain terminator is added to the reaction system at a predetermined time.

Description

[Technical field]

[0001] The present invention relates to a process for producing polycarbonates by an interfacial process from at least one dihydroxydiarylalkane, phosgene, at least one catalyst, and at least one chain terminator, the process having a polycarbonate with a low proportion of oligomers and a low proportion of di-chain terminator carbonate. [Background technology]

[0002] The production of polycarbonates by the interfacial method has been previously described in (1), (2), (3) and finally (4).

[0003] The interfacial process for producing polycarbonates is further described in US Pat. No. 5,399,633.

[0004] The process generally involves the phosgenation of the disodium salt of a bisphenol or a mixture of different bisphenols, initially placed in an aqueous alkaline solution or suspension, in the presence of an inert organic solvent or solvent mixture which forms a second organic phase in addition to the aqueous phase. The resulting oligocarbonates, present mainly in the organic phase, are condensed by suitable catalysts to give polycarbonates of high molecular weight dissolved in the organic phase, the molecular weight of which can be controlled by suitable chain terminators (e.g. monofunctional phenols). The organic phase is finally separated from which the polycarbonate is isolated through various processing steps.

[0005] The properties of the resulting polycarbonate (PC) are influenced by the proportion of oligomers in the PC and also by the proportion of double chain terminator carbonate. In the present invention, "double chain terminator carbonate" is understood to mean a compound formed by reacting two chain terminator molecules with phosgene to form a carbonate. The properties of the PC affected thereby include impact strength, glass transition temperature, and behavior at high temperatures. Low molecular weight compounds can also lead to bleaching during CD production. It should also be noted that the formation of double chain terminator carbonate results in the loss of chain terminator, which is necessary for the actual reaction itself and its viscosity control. Thus, the higher the proportion of double chain terminator in the polycarbonate, the higher the amount of chain terminator required, which is neither economically nor environmentally advantageous, and also makes viscosity control during the process more difficult. It is therefore desirable to keep the content of double chain terminator carbonate as low as possible.

[0006] The double chain stopper carbonate is produced by the reaction of phosgene with a chain stopper. Therefore, it is common to add the chain stopper to the reaction system only when the phosgene has completely reacted. This can be achieved, for example, by using a multi-stage process including a first stage in which oligomers are initially produced, followed by a second stage of further condensation, or by adding the chain stopper very late in the process, at a high conversion, i.e. when the molecular weight of the polycarbonate is already high. However, the conventional theory is that if the chain stopper is not added before the high conversion, the oligomer content in the resulting polycarbonate will increase. It has been reported that a high proportion of oligomers leads to brittleness of low molecular weight PC, and the molecular weight may be reduced by transesterification during extrusion, resulting in a decrease in impact strength. Therefore, in the prior art, the process is usually carried out to find a compromise between a high content of oligomers and a low content of double chain stopper carbonate in the polycarbonate, or between a low content of oligomers and a high content of double chain stopper carbonate.

[0007] Patent document 2 describes the production of low molecular weight polycarbonates with a narrow molecular weight distribution, i.e. a low proportion of oligomers. To achieve such a narrow distribution, this prior art proposes a two-stage process in which a phosgene-free bischloroformate with a degree of polymerization of 0-6 is capped, for example with phenol, and then the resulting capped bischloroformate is condensed by adding a catalyst and a base. Here too, phenol is added as a chain terminator to the bischloroformate solution at the point when phosgene is no longer present in the solution. Patent document 3 likewise relates to the production of polycarbonates with a low proportion of oligomers. It likewise starts from a bischloroformate with a degree of polymerization of 0-6. According to example 2, this bischloroformate is first produced in a reaction with an excess of phosgene (739.3 mmol of phosgene for 250 mmol of bisphenol A). The unreacted phosgene is then decomposed by the addition of NaOH. Only afterwards is the chain terminator pt-butylphenol added. This again means that the chain terminator is added to the reaction system once phosgene is no longer present.

[0008] US Patent No. 5,399,633 describes a two-stage process in which bisphenol A is first reacted continuously with an excess of phosgene. In a further step which follows this, the organic and aqueous phases are separated and then further bisphenol A and NaOH are added to the organic phase, thereby reacting any still remaining phosgene. Only afterwards are catalysts and chain terminators added.

[0009] In both of the above cases, an excess amount of phosgene is used at the beginning, which is then destroyed again. Not only is it uneconomical, since not all of the phosgene is utilized in the actual reaction, but it is also unsustainable from an environmental point of view, since the previously produced product is destroyed "unused". Moreover, in the described process, after the production of bischloroformates, a new solution needs to be produced, which entails corresponding costs. This has the consequence, among other things, that the described process cannot be easily carried out as a continuous process. For this reason, additional, corrosion-resistant equipment is required, which involves additional residence time of highly corrosive materials.

[0010] Patent document 5 describes a method that can reduce the phosgene excess in the interfacial process for producing polycarbonate. However, this prior art is silent about the formation of oligomers and two chain terminator carbonates. It also does not state whether phosgene is still present in the reaction mixture at the time of adding the chain terminator. The same can be inferred from Patent document 6. Both described processes optimize the phosgene excess, but do not pay any attention to optimizing the product properties by good molecular weight distribution. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] European Patent Application Publication No. 0517044 [Patent Document 2] European Patent Application Publication No. 0408924 [Patent Document 3] European Patent Application Publication No. 0289826 [Patent Document 4] European Patent Application Publication No. 0640639 [Patent Document 5] European Patent Application Publication No. 2098553 [Patent Document 6] International Publication No. 2015 / 110447 [Non-patent literature]

[0012] [Non-Patent Document 1] Schnell, "Chemistry and Physics of Polycarbonates", Polymer Reviews, volume 9, Interscience Publishers, New York, London, Sydney 1964, pp. 33-70 [Non-Patent Document 2] DC Prevorsek, BT Debona and Y. Kesten, Corporate Research Center, Allied Chemical Corporation, Morristown, New Jersey 07960: "Synthesis of Poly(ester Carbonate) Copolymers" in Journal of Polymer Science, Polymer Chemistry Edition, vol. 18, (1980); pp. 75-90 [Non-Patent Document 3] D. Freitag, U. Grigo, PR Mueller, N. Nouverne', BAYER AG, "Polycarbonates" in Encyclopedia of Polymer Science and Engineering, volume 11, second edition, 1988, pp. 651-692 [Non-Patent Document 4] Dres U. Grigo, K. Kircher and PR Mueller "Polycarbonate" [Polycarbonates] in Becker / Braun, Kunststoff Handbuch [Plastics handbook], volume 3 / 1, Polycarbonates, polyacetals, polyesters, cellulose esters, Crul Hanser Verlag Munich, Vienna 1992, pp. 118-145 Summary of the Invention [Problem to be solved by the invention]

[0013] It is therefore an object of the present invention to provide a method for producing polycarbonate by an interfacial process, in which at least one of the drawbacks of the prior art is remedied. A particular object of the present invention was to provide a method for producing polycarbonate by an interfacial process, in which the amount of phosgene excess can be reduced. In addition, and preferably at the same time, it was desired to obtain polycarbonate with a low oligomer content and therefore a narrow molecular weight distribution. It is also desirable, and preferably at the same time, that said method provides polycarbonate with a low content of double chain terminator carbonate. A particular object of the present invention was to provide a method for producing polycarbonate by an interfacial process, which obtains polycarbonate with a low proportion of oligomers and a low proportion of double chain terminator carbonate at the same time. [Means for solving the problem]

[0014] At least one, preferably all of the above-mentioned objectives have been achieved by the present invention. Surprisingly, it has been found that the addition of a chain terminator to the reaction system can be carried out even when phosgene is still present in the reaction system. However, this is only possible if the chain terminator is introduced into the reaction system at a very early time. Here, "very early" is understood to mean that only oligomeric compounds with a degree of polymerization of at least one unit on average and at most 5 or 6 units from the reaction of at least one dihydroxydiarylalkane with phosgene are present. The polycarbonate obtained surprisingly has a low proportion of two chain terminator carbonates, despite the introduction of a chain terminator into a system containing phosgene. At the same time, the polycarbonate obtained has a narrow molecular weight distribution and therefore a low oligomer proportion. The polycarbonate obtained therefore also has the above-mentioned improved properties due to the low proportion of two chain terminator carbonates and the low proportion of oligomers. Thus, the process according to the present invention is more economical and environmentally friendly than the processes described in the prior art. The process according to the invention not only allows the phosgene excess to be reduced, but also allows the amount of chain terminator required to be reduced, since less is lost due to the formation of double chain terminator carbonates.

[0015] Accordingly, the present invention provides a process for producing polycarbonates by an interfacial process from at least one dihydroxydiarylalkane, phosgene, at least one catalyst, and at least one chain terminator, comprising the steps of: (i) A process is provided in which at least one chain terminator is introduced into a reaction system comprising at least at least one dihydroxydiarylalkane, phosgene, and a reaction product R of the at least one dihydroxydiarylalkane and phosgene, at a time when the reaction product R is a mixture of compounds having, on average, a degree of polymerization of at least one unit and up to 5 or 6 units formed from the at least one dihydroxydiarylalkane by reaction with phosgene.

[0016] According to the present invention, at the time of adding at least one chain terminator, the reaction system comprises at least one dihydroxydiarylalkane, phosgene, and reaction product R. The system may also comprise at least one catalyst at this time. However, this is not preferred. At the time of adding at least one chain terminator, the reaction system preferably comprises at least one dihydroxydiarylalkane, phosgene, reaction product R, and a solvent necessary for carrying out the interfacial process, and very particularly preferably consists of these. The solvent is preferably an aqueous alkali metal hydroxide solution and at least one organic solvent.

[0017] As already mentioned above, according to the present invention, the chain terminator is introduced "early" into the reaction system, which is defined according to the present invention as the time when the reaction product R is a mixture of compounds, which have an average degree of polymerization of at least 1 unit and at most 6 units.

[0018] The term "degree of polymerization" is known to those skilled in the art. It preferably indicates the number of units in the oligomeric reaction product R formed from at least one dihydroxydiarylalkane by reaction with phosgene. The specified degree of polymerization is an average value. This means that the degree of polymerization is preferably determined by the number-average molar mass M n This is because the M of the oligomer / polymer is determined based on n and the molar mass of the repeating units (units formed from at least one dihydroxydiarylalkane by reaction with phosgene; preferably units represented by general chemical formula (I)). On the other hand, according to the present invention, the number-average molar mass M n is preferably determined by gel permeation chromatography (GPC). nIt is particularly preferred that the molecular weights Mw (weight average), Mn (number average) and Mv (viscosity average) are determined by GPC according to DIN 55672-1:2016-03, calibrated against bisphenol A polycarbonate standards with dichloromethane as eluent. According to the invention, it is very particularly preferred that the molecular weights Mw (weight average), Mn (number average) and Mv (viscosity average) are determined by gel permeation chromatography according to DIN 55672-1:2007-08 with BPA polycarbonate calibration. Calibration was carried out with linear polycarbonates of known molar mass distribution (for example from PSS Polymer Standards Service Gmbh, Germany). Method 2301-0257502-09D (German version of 2009) from Currenta Gmbh & Co. OHG, Leverkusen, was used. Dichloromethane was used as eluent. The column combination consisted of crosslinked styrene-divinylbenzene resin. The GPC may comprise one or more serially connected commercially available GPC columns for size exclusion chromatography, selected to allow sufficient separation of the molar masses of the polymers, in particular of aromatic polycarbonates with weight-average molar masses Mw between 2000 g / mol and 100000 g / mol. The analytical column generally has a diameter of 7.5 mm and a length of 300 mm. The particle size of the column material ranges from 3 μm to 20 μm. The concentration of the solution to be analyzed was 0.2% by weight. The flow rate was adjusted to 1.0 ml / min and the temperature of the solution was 30° C. A refractive index (RI) detector was used for detection.

[0019] The process according to the invention preferably comprises the steps of: [ka] (In the formula, R1 and R2 independently represent H, C1-C18 alkyl, C1-C18 alkoxy, halogen, for example Cl or Br, or in each case optionally substituted aryl or aralkyl, preferably H or C1-C12 alkyl, particularly preferably H or C1-C8 alkyl, very particularly preferably H or methyl, R3 represents H, (C=O)-Cl or (C=O)-OH; R4 represents OH or Cl; X represents a single bond, -SO2-, -CO-, -O-, -S-, C1-C6 alkylene, C2-C5 alkylidene or C5-C6 cycloalkylidene, optionally substituted with C1-C6 alkyl, preferably methyl or ethyl, or represents a C6-C12 arylene, optionally fused to a further aromatic ring containing a heteroatom; n represents the degree of polymerization and therefore the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene and may have a value on average of 1 to 6, preferably 1 to 5, particularly preferably 1 to 4 and very particularly preferably 1 to 3.

[0020] In addition, according to the invention, it is also possible for the reaction product R to be in at least partially hydrolyzed form. The chlorine of the chloroformate group is liberated and carbonate is formed. However, according to the invention, this side reaction is undesirable. This means that the reaction product R is a mixture which contains hydrolysis products of this type. However, this is less preferred. The compounds of the mixture of reaction products R are preferably: R1 and R2 each independently represent H or C1-C12 alkyl, particularly preferably H or C1-C8 alkyl, very particularly preferably H or methyl, R3 represents H or (C=O)-Cl; R4 represents Cl; X represents a single bond, a C1-C6 alkylene, a C2-C5 alkylidene, or a C5-C6 cycloalkylidene, which may be substituted by methyl or ethyl; It is represented by the general chemical formula (I), in which n represents the degree of polymerization and therefore the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene and may have, on average, a value of 1 to 6, preferably 1 to 5, particularly preferably 1 to 4 and very particularly preferably 1 to 3.

[0021] The compounds of the mixture of reaction products R are very particularly preferably R1 and R2 each independently represent H or methyl; R3 represents H or (C=O)-Cl; R4 represents OH; X represents isopropylidene or 3,3,5-trimethylcyclohexylidene; It is represented by the general chemical formula (I), in which n represents the degree of polymerization and therefore the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene and may have, on average, a value of 1 to 6, preferably 1 to 5, particularly preferably 1 to 4 and very particularly preferably 1 to 3.

[0022] The use of bisphenol A as dihydroxydiarylalkane in the process according to the invention preferably results in average molar masses Mn (number average) ranging from 352 g / mol (BPA with two chlorocarbonate end groups) to 1623 g / mol (n=average 6), depending on the nature of the end groups R3 and / or R4 (OH or Cl) in the general chemical formula (I). Particular preference here is given to molar masses below 1000 g / mol.

[0023] It has been found to be advantageous if the at least one chain terminator is first thoroughly mixed before it can react. The at least one chain terminator is preferably uniformly distributed. This can be achieved, for example, by using a static mixer after adding the at least one chain terminator and before it reacts.

[0024] It has also proven to be advantageous if the at least one chain terminator is fed to the reaction system as an organic phase rather than as an aqueous phase.

[0025] It is preferred if the method according to the invention is characterized in that it comprises at least one step of adding an aqueous alkali metal hydroxide solution. Here, the term "addition" is preferably understood to mean an active step of additional addition. It is also possible, in particular, to initially dissolve at least one dihydroxyarylalkane in the aqueous alkali metal hydroxide solution before feeding it to the reaction system. Such an initial step is preferably not, according to the invention, an addition of an aqueous alkali metal hydroxide solution. However, it is further preferred to understand that any addition of an aqueous alkali metal hydroxide solution (whether or not accompanied by at least one dihydroxyarylalkane) after this initial step of dissolving at least one dihydroxyarylalkane constitutes an addition of an aqueous alkali metal hydroxide solution.

[0026] The method according to the invention comprises the steps of: (ii) It has been found to be particularly advantageous when the addition of at least one chain terminator to the reaction system in process step (i) is characterised in that it takes place before the first of the one or more additions of the aqueous alkali metal hydroxide solution.

[0027] It is obvious to the skilled person that in principle an aqueous alkali metal hydroxide solution can be added before the addition of at least one chain extender. However, it has been found according to the invention that this amount should not be too high, since this would lead to too high a degree of polymerization of the reaction product R. This means that before the addition of at least one chain extender, the skilled person can only add an aqueous alkali metal hydroxide solution in such an amount that it is still ensured that the requirements for the reaction product R according to the invention are respected.

[0028] However, it has proven to be advantageous if the at least one chain terminator is added at a pH between 8 and 11, preferably between 9 and 10. At higher pH values ​​(above 11), it has been found that the distribution of the at least one chain terminator between the organic and aqueous phase is unfavourable. In this case, a large proportion is present in the aqueous phase and is unable to react with the chloroformate end groups. It is therefore preferred according to the invention if the process according to the invention does not involve the addition of an aqueous alkali metal hydroxide solution before the addition of the at least one chain terminator. This is in particular the case when the at least one chain terminator comprises a phenol. For this reason, it is advantageous to add the aqueous alkali metal hydroxide solution only after the addition of the at least one chain terminator.

[0029] The method according to the invention preferably comprises the following steps: (a) forming a dispersion from an organic phase and an aqueous phase, the organic phase comprising at least one solvent suitable for polycarbonates and at least a portion of the phosgene, and the aqueous phase comprising at least one dihydroxydiarylalkane, water and 1.8 to 2.2 mol, preferably 1.95 to 2.05 mol, of an aqueous alkali metal hydroxide solution per mol of dihydroxydiarylalkane; (b) reacting the at least one dihydroxydiarylalkane with phosgene to produce a reaction system comprising at least a reaction product R from the at least one dihydroxydiarylalkane and phosgene in the dispersion obtained from step (a); (c) adding at least one chain terminator to the reaction system of step (b) while unreacted phosgene is still present in the reaction system of step (b); (d) optionally, performing at least one addition of an alkali metal hydroxide solution to the mixture resulting from step (c); The present invention is characterized by comprising:

[0030] Dispersion of the two phases (aqueous and organic) in step (a) can preferably be achieved by built-in pipe baffles, static mixers, dispersers and / or, for example, pumps. The reaction is preferably carried out in plug flow with little back mixing. That is, it can be carried out, for example, in a tubular reactor. As already mentioned above, according to the present invention, the presence of an aqueous alkali metal hydroxide solution in step (a) is preferably not understood to mean the addition of an aqueous alkali metal hydroxide solution. This is an aqueous alkali metal hydroxide solution, preferably an aqueous sodium hydroxide solution, used to dissolve BPA in the aqueous phase. During the phosgenation step (a), it is preferred that the available amount of free aqueous alkali metal hydroxide solution is as small as possible in order to avoid hydrolysis of phosgene to sodium carbonate (i.e. loss of phosgene). In step (a) of the present invention, therefore, 1.80 mol to 2.20 mol, preferably 1.95 mol to 2.05 mol, of an aqueous alkali metal hydroxide solution per mol of dihydroxydiarylalkane is used.

[0031] Dispersion of an organic phase into an aqueous phase or dispersion of an aqueous phase into an organic phase, preferably using a disperser, can produce an oil-in-water (ow) dispersion or a water-in-oil (wo) dispersion, oil being understood to mean the organic phase. Preferably, in the dispersion, a water-in-oil dispersion is produced. The organic phase is preferably continuously dispersed in the aqueous phase using a disperser.

[0032] An oil-in-water dispersion is, by definition, one in which water forms the external (continuous) phase and oil forms the internal (dispersed) phase, i.e. oil droplets are dispersed in water. A water-in-oil dispersion is therefore one in which oil forms the external phase and water forms the internal phase.

[0033] The organic phase comprises one or more solvents.

[0034] Suitable solvents are aromatic and / or aliphatic chlorinated hydrocarbons, preferably dichloromethane, trichloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane and chlorobenzene, and mixtures thereof. However, it is also possible to use aromatic hydrocarbons, such as benzene, toluene, m- / p- / o-xylene, or aromatic ethers, such as anisole, alone, in mixtures, or in addition to or in mixtures with chlorinated hydrocarbons, with dichloromethane and chlorobenzene and mixtures thereof being preferred. Another embodiment of the process according to the invention uses a solvent that does not dissolve the polycarbonate, but merely swells it. It is therefore also possible to use a non-solvent for polycarbonate in combination with the solvent. Solvents that are also soluble in the aqueous phase, such as tetrahydrofuran, 1,3- or 1,4-dioxane, or 1,3-dioxolane, can be used as solvents, in the case where the solvent partner forms a second organic phase.

[0035] Suitable dihydroxydiarylalkanes (also referred to above and below specifically as diphenols) have the general formula: HO-Z-OH where Z is a divalent organic radical having 6 to 30 carbon atoms containing one or more aromatic groups. Examples of such compounds that can be used in the process according to the invention are dihydroxydiarylalkanes, such as hydroquinone, resorcinol, dihydroxydiphenyl, bis(hydroxyphenyl)alkanes, bis(hydroxyphenyl)cycloalkanes, bis(hydroxyphenyl)sulfides, bis(hydroxyphenyl)ethers, bis(hydroxyphenyl)ketones, bis(hydroxyphenyl)sulfones, bis(hydroxyphenyl)sulfoxides, 4,4'-bis(hydroxyphenyl)diisopropylbenzene, and alkylated, ring-alkylated and ring-halogenated compounds thereof.

[0036] Preferred dihydroxydiarylalkanes are 4,4'-dihydroxydiphenyl, 2,2-bis(4-hydroxyphenyl)-1-phenylpropane, 1,1-bis(4-hydroxyphenyl)phenylethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A (BPA)), 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- Bis(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, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC).

[0037] Particularly preferred dihydroxydiarylalkanes are 4,4'-dihydroxydiphenyl, 1,1-bis(4-hydroxyphenyl)phenylethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A (BPA)), 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 (bisphenol TMC).

[0038] These and other suitable dihydroxydiarylalkanes can be found, for example, in U.S. Pat. Nos. 2,999,835, 3,148,172, 2,991,273, 3,271,367, 4,982,014, and 2,999,846, DE-A-1,570,703, DE-A-2,063,050, DE-A-2,036,052, DE-A-2,211,956, and DE-A-3,832,396, FR-A-1,561,518, H. Schnell, monographs in "Chemistry and Physics of Polycarbonates", Interscience Publishers, New York 1964, pp. 28 ff., 102 ff., and in DG Legrand, JT Endler, "Handbook of Polycarbonate Science and Technology", Marcel Dekker New York, This is described in the monograph, 2000, p. 72 et seq.

[0039] Polycarbonates are understood according to the invention to mean both homopolycarbonates and copolycarbonates. In the case of the inventive production of homopolycarbonates, only one dihydroxydiarylalkane is used, in the case of the inventive production of copolycarbonates, two or more dihydroxydiarylalkanes are used, it being self-evident that the dihydroxydiarylalkanes used, as well as all other chemicals and auxiliaries added to the synthesis, can be contaminated with impurities resulting from their own synthesis, handling and storage, although it is desirable to use the purest possible raw materials.

[0040] Aqueous alkali metal hydroxide solution is understood in the context of the present invention to mean preferably aqueous sodium hydroxide, aqueous potassium hydroxide or mixtures thereof, particularly preferably aqueous sodium hydroxide.

[0041] The aqueous phase in the interfacial process for producing polycarbonates comprises an aqueous alkali metal hydroxide solution, one or more dihydroxydiarylalkanes and water, the concentration of which, calculated as free dihydroxydiarylalkanes and not as alkali metal salts, is preferably 1% to 30% by weight, particularly preferably 3% to 25% by weight, very particularly preferably 15% to 18% by weight, based on the total weight of the aqueous phase. The alkali metal hydroxides, for example sodium hydroxide or potassium hydroxide, used to dissolve the dihydroxydiarylalkanes can be used in solid form or as the corresponding aqueous alkali metal hydroxide solution. The concentration of the aqueous alkali metal hydroxide solution is determined depending on the target concentration of the desired dihydroxydiarylalkane solution, but is usually 5% to 25% by weight, preferably 5% to 10% by weight, based on 100% by weight of the aqueous alkali metal hydroxide solution, or a more concentrated solution is selected which is then diluted with water. In the method with subsequent dilution, an aqueous alkali metal hydroxide solution with a concentration of 15% to 75% by weight, preferably 25% to 55% by weight, is used, which is optionally thermally equilibrated. The alkali content per mole of dihydroxydiarylalkane depends on the structure of the dihydroxydiarylalkane, but is usually 1.5 mol alkali / mol dihydroxydiarylalkane to 2.5 mol alkali / mol dihydroxydiarylalkane, preferably 1.8 mol alkali / mol dihydroxydiarylalkane to 2.2 mol alkali / mol dihydroxydiarylalkane, and in the particularly preferred case where bisphenol A is used as the only dihydroxydiarylalkane, 1.85 mol to 2.5 mol alkali, very particularly preferably 2.00 mol alkali. If two or more dihydroxydiarylalkanes are used, they may be dissolved together.However, since the solubility of dihydroxydiarylalkanes depends very strongly on the amount of alkali used, it may be advantageous to dissolve two solutions, each containing one dihydroxydiarylalkane, in the appropriate aqueous alkali metal hydroxide solution, instead of one solution containing two dihydroxydiarylalkanes, which are separately metered to the correct mixing ratio. Furthermore, it may be advantageous to dissolve the dihydroxydiarylalkane(s) not in an aqueous alkali metal hydroxide solution, but in a dilute dihydroxydiarylalkane solution containing additional alkali. The dissolution process may proceed from solid dihydroxydiarylalkane, usually in flake or prill form, or from molten dihydroxydiarylalkane. The alkali metal hydroxide or aqueous alkali metal hydroxide solution used may be produced, for example, by the amalgam process or the so-called membrane process, in the case of sodium hydroxide / aqueous sodium hydroxide. Both methods are old and well known to the skilled person. If an aqueous sodium hydroxide solution is used, it is preferably produced by the membrane process.

[0042] In such aqueous solutions and / or phases the dihydroxydiarylalkane(s) are completely or partly in the form of the corresponding alkali metal / dialkali metal salts.

[0043] The optional actual metered addition of dihydroxydiarylalkane(s) after or during the introduction of phosgene can be carried out as long as phosgene or the chlorocarbonate formed directly therefrom is present in the reaction solution.

[0044] The organic phase in step (a) additionally contains at least phosgene, besides at least one solvent. The organic phase here already contains all or part of the required phosgene before the formation of the mixture. Before the formation of the mixture, the organic phase preferably contains the total amount of phosgene required, including the excess amount of phosgene used. Phosgene can be introduced into the organic phase in gaseous or liquid form. It is preferred if the reaction system contains an excess amount of phosgene of 3 mol% to 20 mol%, particularly preferably 5 mol% to 18 mol%, very particularly preferably 7.5 mol% to 15.0 mol%, based on the total amount of dihydroxydiarylalkane used, at the start of the reaction.

[0045] The addition of at least one chain terminator to the reaction system of step (b) is carried out in step (c). The reaction system of step (b) still contains unreacted phosgene. The at least one chain terminator is usually monofunctional. The at least one chain terminator is preferably selected from the group consisting of phenol, alkylphenol, and its chlorocarbonate or acid chloride of monocarboxylic acid, preferably selected from phenol, tert-butylphenol, and isooctylphenol, cumylphenol. Any desired mixture of the listed chain terminators can be used.

[0046] In a particularly preferred embodiment of the process according to the invention, phenol is used as a chain terminator. In step (c), phenol is preferably used in the form of a solution comprising at least one organic solvent and phenol in a concentration of 5% to 40% by weight, preferably 10% to 25% by weight. In this embodiment, the aqueous phase is adjusted to a pH of preferably 11.3 to 11.6 at the end of the reaction (i.e. step (c)). The addition of phenol and the adjustment of the pH to 11.3 to 11.6 are preferably carried out before the addition of the catalyst.

[0047] In another preferred embodiment of the process according to the invention, p-tert-butylphenol is used as a chain terminator. The p-tert-butylphenol in step (c) is preferably used in the form of a solution comprising at least one organic solvent and p-tert-butylphenol in a concentration of 2% to 25% by weight, preferably 3% to 15% by weight. In this embodiment, the aqueous phase is adjusted to a pH of preferably 11.5 to 11.8 at the end of the reaction (i.e. step (c)). The addition of p-tert-butylphenol and the adjustment of the pH to 11.5 to 11.8 are preferably carried out before the addition of the catalyst.

[0048] In step (c), one or more branching agents or a mixture of branching agents may be optionally added to the synthesis. However, such branching agents are preferably added before the chain terminator(s). Very particularly preferably, such branching agents are added to the aqueous phase in process step (a) together with a solution of at least one dihydroxydiarylalkane. Examples of branching agents used include trisphenols, quaterphenols, acid chlorides of tri- or tetracarboxylic acids, or polyphenols, or mixtures of acid chlorides.

[0049] Examples of compounds suitable as branching agents having three or more phenolic hydroxyl groups are phloroglucinol, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)hept-2-ene, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptane, 1,3,5-tri(4-hydroxyphenyl)benzene, 1,1,1-tri(4-hydroxyphenyl)ethane, tri(4-hydroxyphenyl)phenylmethane, 2,2-bis[4,4-bis(4-hydroxyphenyl)cyclohexyl]propane, 2,4-bis(4-hydroxyphenyl-isopropyl)phenol, tetra(4-hydroxyphenyl)methane.

[0050] Examples of other trifunctional compounds suitable as branching agents include 2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride, and 3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole. Particularly preferred branching agents are 3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole and 1,1,1-tri(4-hydroxyphenyl)ethane.

[0051] At least one addition of an aqueous alkali metal hydroxide solution to the mixture obtained from step (c) is carried out in an optional step (d). The process according to the invention preferably comprises this step (d). This step is an exothermic reaction. According to the invention, it is preferably carried out in a temperature range of from -5°C to 100°C, particularly preferably from 15°C to 80°C, very particularly preferably from 25°C to 65°C, and depending on the solvent or solvent mixture, it may have to be carried out under positive pressure. Depending on the reactor used, different pressures can be used. For example, pressures of 0.5 bar (absolute) to 20 bar (absolute) can be preferably used.

[0052] It has been found to be advantageous if at least one addition of aqueous alkali metal hydroxide solution is carried out when the dispersion is still an oil-in-water dispersion. The addition of aqueous alkali metal hydroxide solution to a water-in-oil emulsion generally results in a non-ideal molecular weight distribution. Since at least one chain terminator is preferably added beforehand, this also means that at least one chain terminator is preferably added to the oil-in-water dispersion. According to the present invention, it is also possible to change the dispersion from a water-in-oil dispersion to an oil-in-water dispersion during the process.

[0053] Furthermore, the method according to the present invention may optionally further comprise the steps of: (e) providing at least one addition of at least one catalyst; Includes.

[0054] The method according to the present invention preferably comprises this step.The method according to the present invention preferably comprises step (e) after step (d).

[0055] It is preferred if the at least one catalyst is selected from the group consisting of tertiary amines, organic phosphines, and any desired mixtures. Very particularly preferably, the at least one catalyst is a tertiary amine or a mixture of at least two tertiary amines.

[0056] The tertiary amine is likewise preferably triethylamine, tributylamine, trioctylamine, N-ethylpiperidine, N-methylpiperidine or N-isopropyl / Nn-propylpiperidine, which compounds are described in the literature as typical interfacial catalysts, are commercially available and are well known to the person skilled in the art. The catalysts can be added to the synthesis individually, in a mixture or simultaneously or successively, optionally also before the phosgenation, but are preferably metered in after the introduction of phosgene. The metering of the catalyst(s) can be carried out as a pure substance, in an inert solvent, preferably in the solvent of the organic phase in the polycarbonate synthesis or in one of the solvents, or as an aqueous solution. When a tertiary amine is used as catalyst, its metering can be carried out in aqueous solution, for example in the form of an ammonium salt with an acid, preferably a mineral acid, in particular hydrochloric acid. When using two or more catalysts or when metering in portions of the total amount of catalyst, it is of course also possible to carry out different modes of metered addition at different places or at different times. The total amount of the catalyst used is preferably 0.001 mol % to 10 mol %, more preferably 0.01 mol % to 8 mol %, particularly preferably 0.05 mol % to 5 mol %, based on the number of moles of the dihydroxydiarylalkane used.

[0057] The process according to the invention is preferably characterised in that it is carried out continuously. As already explained above, the advantages of the invention are particularly great in continuous processes.

[0058] Thus, the entire reaction, i.e. the reaction and further condensation, may be carried out in a stirred tank reactor, a tubular reactor, a pumped-circulation reactor or a cascade of stirred tank reactors or a combination thereof, the use of said mixing devices ensuring that the aqueous and organic phases are ideally demixed only when the synthesis mixture has reacted completely, i.e. when no hydrolysable chlorine of phosgene or chlorocarbonate is any more present.

[0059] Despite the small phosgene excess, the process according to the invention allows a good phase separation at the end of the reaction, achieving both a low water content in the organic phase and a low residual monomer content in the aqueous phase, and also avoiding contamination of the product with catalyst components.

[0060] For workup, the reacted at least two-phase reaction mixture, which contains at most trace amounts, preferably less than 2 ppm, of chlorocarbonates, is left to undergo phase separation. The alkaline aqueous phase is optionally fully or partially recycled as aqueous phase to the polycarbonate synthesis or sent to a wastewater workup, where the solvent and catalyst fractions are separated and optionally recycled to the polycarbonate synthesis. In another workup variant, separation of organic impurities, in particular solvent and polymer residues, and optionally adjustment to a specific pH, for example by addition of aqueous sodium hydroxide, is followed by separation of salts, which may for example be sent to chloralkali electrolysis, and the aqueous phase can optionally be recycled to the polycarbonate synthesis.

[0061] The organic phase containing the polycarbonate may then be purified by a variety of methods known to those skilled in the art to remove alkali metal, ionic, or catalytic contaminants.

[0062] After one or more precipitation processes, optionally via settling tanks, stirred tank reactors, coalescers or separators and / or combinations of these means (optionally with active or passive mixing devices, possibly with the addition of water in each or several separation steps), the organic phase generally still contains part of the catalyst(s) as well as part of the alkaline aqueous phase in fine droplet form. After this crude separation of the alkaline aqueous phase, the organic phase can be washed one or more times with dilute acids, mineral acids, carboxylic acids, hydroxycarboxylic acids and / or sulfonic acids. Aqueous mineral acids are preferred, in particular hydrochloric acid, phosphorous acid, phosphoric acid or mixtures of these acids. The concentration of these acids should preferably be between 0.001% and 50% by weight, preferably between 0.01% and 5% by weight. The organic phase can further be repeatedly washed with demineralized or distilled water. After each washing step, separation of the organic phase, optionally dispersed with a portion of the aqueous phase, is carried out using a settling tank, a stirred tank reactor, a coalescer or a separator or a combination of these means, and the metered addition of washing water between the washing steps can be carried out optionally using an active or passive mixing device. During or after these washing steps, an addition of an acid, preferably dissolved in the solvent used in the polymer solution, can be optionally carried out. Here, it is preferred to use hydrogen chloride gas, phosphoric acid or phosphorous acid, which can also be used optionally as a mixture. After the final separation process, the resulting purified polycarbonate solution should preferably contain less than 5% by weight of water, preferably less than 1% by weight, very particularly preferably less than 0.5% by weight.

[0063] Isolation of the polycarbonate from the solution can be accomplished by evaporation of the solvent by temperature, vacuum, or heated entrained gas. Other isolation methods include, for example, crystallization and precipitation.

[0064] Concentration of the polycarbonate solution, and possibly further isolation of the polycarbonate, is carried out by distillative removal of the solvent, optionally by heating and expansion, which is called the "flash process". Such processes are known to the person skilled in the art and are described, for example, in "Thermische Trennverfahren [Thermal Separation Processes]", VCH Verlagsanstalt 1988, page 114. If a heated carrier gas is instead sprayed together with the solution to be concentrated, this is called "spray evaporation / spray drying" and is described, for example, by Vauck, "Grundoperationen chemischer Verfahrenstechnik [Basic operations of chemical engineering]", Deutscher Verlag fuer Grundstoffindustrie 2000, 11th edition, page 690. All these processes are described in the patent literature and textbooks and are well known to the person skilled in the art.

[0065] Highly concentrated polycarbonate melts are obtained by removing the solvent by temperature (distillative removal) or by the technically more efficient flash process, in which the polymer solution is repeatedly heated under a slight positive pressure to a temperature above the boiling point at atmospheric pressure, and then these solutions superheated to atmospheric pressure are decompressed in a vessel at lower pressure, for example at atmospheric pressure. It may be advantageous to make the concentration stage, or in other words the temperature stage of superheating, less extensive, but rather to choose a two- to four-stage process.

[0066] From the resulting highly concentrated polycarbonate melt, the solvent residues can be removed by means of vented extruders (see, for example, BE 866991, EP 0 411 510, U.S. Pat. No. 4,980,105, DE 3 332 065), thin-film evaporators (see, for example, EP 0 267 025), falling-film evaporators, strand evaporators, foam evaporators (see, for example, U.S. 2012 / 015763) directly from the melt or by friction compression. It can also be removed by compaction (see, for example, EP-A-0 460 450), optionally with further addition of entraining agents such as nitrogen or carbon dioxide or by using a vacuum (see, for example, EP-A-0 03 996, EP-A-0 256 003, US-A-4 423 207), alternatively by subsequent crystallization (see, for example, DE-A-3 429 960) and / or by baking out the residues of the solvent in the solid phase (see, for example, US-A-3 986 269, DE-A-2 053 876). These processes and the apparatus required therefor are described in the literature and are well known to the skilled person.

[0067] Polycarbonate granules can be obtained, if possible, by direct spinning of the melt followed by granulation or by using melt extruders from which they are spun in air or in liquid (usually water). If extruders are used, the polycarbonate melt can be mixed with additives upstream of the extruder, optionally using static mixers or side extruders of said extruders.

[0068] Alternatively, the polycarbonate solution may be spray-evaporated. During spraying, the optionally heated polycarbonate solution is atomized into a vessel under reduced pressure or into a vessel under atmospheric pressure through a nozzle with a heated carrier gas, such as nitrogen, argon or steam. In either case, depending on the concentration of the polymer solution, a polymer powder (dilute) or flakes (concentrated) are obtained, from which it may also be necessary to remove the last residues of solvent as described above. Granules can then be obtained by a compounding extruder followed by spinning. Here too, the additives described herein above can be added to the peripheral equipment or to the extruder itself. The polymer powder may often need to undergo a compaction step before extrusion due to the low bulk density of the powder and flakes.

[0069] The addition of a non-solvent to the polycarbonate allows the polymer to be largely precipitated from the washed and optionally further concentrated polycarbonate solution. The non-solvent acts here as a precipitant. Here, it is advantageous to add a small amount of the non-solvent first and, optionally, also provide a waiting period between the addition of each portion of the non-solvent. Furthermore, it is also advantageous to use different non-solvents. Examples of precipitants used here include aliphatic or cycloaliphatic hydrocarbons, in particular heptane, isooctane or cyclohexane, alcohols such as methanol, ethanol or isopropanol, ketones such as acetone, or mixtures thereof. During precipitation, the polymer solution is generally added slowly to the precipitant. The polycarbonate obtained is processed into granules as described in spray evaporation and, optionally, additives are added (additized).

[0070] In another method, the precipitated and crystallized products or amorphously solidified products are crystallized into finely divided forms and further condensed to higher molecular weights by simultaneous heating below the glass transition temperature with the evaporation of one or more non-solvents for the polycarbonate, optionally in the presence of oligomers with different end groups (phenolic and chain terminator ends), this is called solid-phase condensation.

[0071] Additives can be added to improve shelf life or color stability (stabilizers), to facilitate processing (e.g., mold release agents, flow promoters, antistatic agents), or to tailor the properties of the polymer to specific requirements (impact modifiers, e.g., rubber; flame retardants, colorants, glass fibers).

[0072] These additives can be added to the polymer melt alone or in any desired mixture, together with or in a number of different mixtures. This can be done directly during the isolation of the polymer or after melting the granules in a so-called compounding process. These additives or mixtures thereof can be added to the polymer melt in solid form, preferably as a powder, or as a melt. Another aspect of metered addition is the use of a masterbatch or a mixture of masterbatches of the additive or additive mixture.

[0073] Examples of suitable additives are described in "Additives for Plastics Handbook" by John Murphy, Elsevier, Oxford 1999, and in "Plastics Additives Handbook" by Hans Zweifel, Hanser, Munich 2001.

[0074] The following examples are intended to be illustrative of the invention and are not to be construed as limiting. [Brief description of the drawings]

[0075] [Figure 1]Information about Figure 1: Solid line: original GPC, normalized to area = 1 Dotted line: Schulz-Flory distribution adjusted so that its maximum coincides with the maximum of the GPC Dashed line: difference between the two curves (solid and dotted) The percentage of oligomers is obtained from the integral of the difference curve from 500 g / mol to 5000 g / mol. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0076] The molecular weight distribution and the average values ​​Mn (number average) and Mw (weight average) were determined by gel permeation chromatography (GPC) using a Waters "Mixed Bed" column and methylene chloride as the eluent (using a BPA homopolycarbonate standard with Mw 31000 g / mol).

[0077] In addition to the standing evaluation, the deviation of the GPC from the ideal Schulz-Flory distribution was also measured. This was done by first normalizing the GPC and determining the area under the solid line of the diagram shown in Figure 1. This area was normalized to 1. Furthermore, the Schulz-Flory (SF) distribution was adjusted so that the maximum height and the molecular weight both match those of the measured distribution (dotted line in Figure 1). The difference between the measured and adjusted SF distribution gives the difference distribution (dashed line in Figure 1). In the present case, the Schulz-Flory distribution is narrower, which means that the difference distribution is positive (excluding measurement imprecision). At a maximum, the difference according to this method is zero, so that the difference distribution is divided into low and high molecular weight parts (see also Figure 1).

[0078] It is known from the prior art that a high oligomer content is detrimental to the quality of the product. However, it is generally only the total content of low molecular weight compounds below a certain threshold that is taken into account here, or the content that is soluble in acetone. This has the disadvantage of also registering the unavoidable oligomer content, which further varies depending on the type of polycarbonate (viscosity, Mn). The method of the present invention corrects this dependency and determines only the process-specific oligomer content.

[0079] In the following, 2,2'-bis(4-hydroxyphenyl)propane (bisphenol A, BPA) was used as the dihydroxydiarylalkane, and the organic phase solvent was a mixture of approximately 50% by weight methylene chloride and 50% by weight monochlorobenzene. All examples produced polycarbonates with the defined weight average molecular weights as determined by GPC (Waters "Mixed Bed" column, in methylene chloride, using a BPA homopolycarbonate standard of Mw 31000 g / mol).

[0080] Example 1: Different chain terminator addition times Successive laboratory tests were carried out on a combination of pump and stirred reactor. In all experiments, 70.1 g / h of gaseous phosgene was dissolved in a T-piece in 772 g / h of organic solvent (1:1 methylene chloride / chlorobenzene) at -7°C. The amount of solvent required to finally obtain a 15% by weight polycarbonate solution was calculated. The continuously fed phosgene solution was contacted in a further T-piece with 912 g / h of a 15% by weight alkaline aqueous BPA solution (2 mol NaOH per mol BPA), preheated to 30°C. This aqueous BPA solution was dispersed in the aqueous phosgene solution through a stainless steel filter (pore size 60 μm).

[0081] The reaction mixture was passed through a Fink HMR040 mixing pump, thermally equilibrated to 25° C., so that at the end of the reaction pump phosgene had reacted to the maximum possible extent, but was still present. In Examples 1a, 1c, and 1d, downstream of this pump, 3.29 g / h of p-tert-butylphenol was added as a chain terminator in the form of a 3% by weight solution in the same solvent mixture added above, and in a further HMR040 pump at 25° C., the reaction mixture was further reacted with 53.95 g / h of a 32% by weight aqueous sodium hydroxide solution, resulting in a pH of about 11.5 at the end of the reaction system. In Comparative Example 1b, 3.29 g / h of p-tert-butylphenol was added as a chain terminator in the form of a 3% by weight solution in the same solvent mixture as above.

[0082] This was followed by two stirred tank reactors, each equipped with a gear pump from Ismatec in each case. The metered addition of 0.679 g / h of catalyst (10% by weight N-ethylpiperidine dissolved in chlorobenzene) in a T-piece in a Teflon hose was carried out between the two stirred tanks (and the gear pump).

[0083] A total of 156 g of polycarbonate in organic solution was continuously obtained and sent to a phase separation vessel for phase separation together with the aqueous phase from the reaction. The polycarbonate solution was washed with 10 wt% HCl and dried at normal pressure and room temperature.

[0084] Table 1 summarizes the results obtained in Example 1.

[0085] [Table 1]

[0086] Example 1a shows the addition of a chain terminator at a point when the reaction product R comprises a mixture of compounds with an average molar mass Mn0 of 750 g / mol. In comparative example 1b, a chain terminator was added at a point when the reaction product R comprises a mixture of compounds with an average molar mass Mn0 of 3470 g / mol. In inventive examples 1c and 1d, the phosgene excess was reduced and a chain terminator was added at a point when the reaction product R comprises a mixture of compounds with average molar masses Mn0 of 660 g / mol and 730 g / mol, respectively. In each case, it can be seen that the polycarbonates obtained contain a low proportion of two chain terminator carbonates. However, the polycarbonates in the inventive examples also have significantly lower values ​​for oligomers (measured by differences in molecular weight distribution).

[0087] In Comparative Example 1b, NaOH is added before the addition of the chain terminator, but the chain terminator is added early enough so that the continued presence of phosgene in the reaction is assumed.

[0088] Addition of a chain terminator at a time when no phosgene remains in the reaction system means that the reaction product R has a higher average molecular weight and therefore a higher proportion of oligomers is to be expected.

[0089] Example 2 The equipment used for the individual process steps is as follows: Method step (A): A disperser in the form of a perforated-plate nozzle with a predisperser (having a perforated plate with a thickness of 2.35 and 5 holes with a diameter of 2.5 mm each, with a pressure drop of 0.2 bar at a flow rate of 5.2 m / s), a residence time in the predispersion space of 26 ms and subsequent dispersing (having a further perforated plate with a thickness of 2.35 mm and 18 holes with a diameter of 1.5 mm each, with a pressure drop of 0.8 bar at a flow rate of 8.9 m / s), whereby one liquid is dispersed in the other liquid. Process step (B): Residence time reactor with a residence time of 0.2 seconds. Process step (C): A recirculating reactor with a metering point (for example for NaOH; in comparative experiment 2b, 20% of the NaOH used was added here), a pump, a heat exchanger, an overflow vessel, a T-shaped take-off point with a volume of 140 l and equipped with a pH probe and a conductivity probe; redispersion is carried out on entering the recirculating reactor. In example 2a, a chain terminator is added to the recirculating reactor. Process step (D): A delivery pump with upstream metering points for the chain terminator (in comparative experiment 2b a chain terminator is added here; in experiment 2a nothing is added here) and for the NaOH solution, a static mixer in between and downstream of which a helical-tube reactor with a mixing zone and a dwell zone and a total volume of 60 l (first dwell reactor) and downstream of which a further helical-tube reactor with a total volume of 80 l and a metering point for the catalyst at the start of the reactor (second dwell reactor). Subsequent phase separation: separation vessel (4.15 m at 50% fill level) 3 size).

[0090] The following material flows were used in process step (A): 600 kg / h of aqueous bisphenol solution (a mixture of bisphenol A and bisphenol TMC at 15% by weight based on the total weight of the solution, 2.13 mol NaOH / mol bisphenol solution) 44.6kg / h of phosgene 520 kg / h of a solvent mixture consisting of 54% by weight of methylene chloride and 46% by weight of chlorobenzene

[0091] No further material streams were additionally used in process steps (B) and (C).

[0092] In process step (D), the following material streams were additionally used upstream of the first retention reactor: 17.8 kg / h of t-butylphenol solution (in a solvent mixture consisting of 20% by weight, 54% by weight methylene chloride and 46% by weight chlorobenzene) 35kg / h of NaOH aqueous solution containing 32% by weight of NaOH

[0093] In process step (D), the following material streams were additionally used in the second retention reactor: 22.7 kg / h of catalyst solution (3 wt.% solution, ethylpiperidine in a solvent mixture of 54 wt.% methylene chloride and 46 wt.% chlorobenzene)

[0094] The temperature in the recycle reactor was 35° C. (downstream of the heat exchanger) to 38° C. (upstream of the heat exchanger). The temperature in the helical tubular reactor in process step (D) was in each case 37° C., the temperature in the separation vessel was 35° C.

[0095] The dispersion direction was set so that the organic phase was dispersed into the aqueous phase.

[0096] Table 2 summarizes the results obtained.

[0097] [Table 2]

[0098] Example 2a shows the addition of a chain terminator when the reaction product R comprises a mixture of compounds with an average molar mass MnLoop of less than 900 g / mol.In comparative example 2b, a chain terminator is added when the reaction product R comprises a mixture of compounds with an average molar mass MnLoop of 2320 g / mol.

[0099] It can be seen that in the inventive examples, the resulting polycarbonates have a higher proportion of two chain terminator carbonates than in comparative example 2b. The content is nevertheless within an acceptable range. However, the inventive examples have significantly lower values ​​for oligomers (measured by differences in molecular weight distribution).

Claims

1. A process for producing polycarbonates by an interfacial process from at least one dihydroxydiarylalkane, phosgene, at least one catalyst, and at least one chain terminator, comprising the steps of: (i) introducing said at least one chain terminator into a reaction system comprising at least said at least one dihydroxydiarylalkane, phosgene, and a reaction product R of said at least one dihydroxydiarylalkane and phosgene, said reaction product R being a mixture of compounds having an average degree of polymerization of at least 1 unit and at most 6 units formed from said at least one dihydroxydiarylalkane by reaction with said phosgene; The method includes at least one step of adding an aqueous alkali metal hydroxide solution; and the addition of the at least one chain terminator to the reaction system in step (i) occurs prior to a first of one or more additions of the aqueous alkali metal hydroxide solution.

2. The reaction product R mixture has the general chemical formula (I): 【Chemistry 1】 (In the formula, R １ and R ２ represents independently H, C1-C18 alkyl, C1-C18 alkoxy, halogen, for example Cl or Br, or optionally substituted aryl or aralkyl, R ３ represents H, (C═O)—Cl or (C═O)—OH; R ４ represents OH or Cl, X is a single bond, -SO ２ -, -CO-, -O-, -S-, C1-C6 alkylene, C2-C5 alkylidene, or C5-C6 cycloalkylidene, which represents C1-C6 alkyl, which may be fused to a further aromatic ring optionally containing a heteroatom; 2. The process according to claim 1, characterized in that n represents the degree of polymerization and therefore the number of units formed from said at least one dihydroxydiarylalkane by reaction with said phosgene, which may have an average value of from 1 to 6.

3. The method comprises the following steps: (a) forming a dispersion from an organic phase and an aqueous phase, said organic phase comprising at least one solvent suitable for said polycarbonate and at least a portion of said phosgene, said aqueous phase comprising said at least one dihydroxydiarylalkane, water and an aqueous alkali metal hydroxide solution comprising 1.8 mol to 2.2 mol of alkali metal hydroxide per mol of dihydroxydiarylalkane; (b) reacting the at least one dihydroxydiarylalkane and the phosgene to produce the reaction system comprising at least the reaction product R from the at least one dihydroxydiarylalkane and phosgene in the dispersion obtained from step (a); (c) adding at least one chain terminator to the reaction system of step (b) while unreacted phosgene is still present in the reaction system of step (b); (d) optionally, performing at least one addition of an alkali metal hydroxide solution to the mixture resulting from step (c); 3. The method according to claim 1 or 2, characterized in that it comprises:

4. The method comprises the following steps: (e) providing at least one addition of at least one catalyst; The method of claim 3 further comprising:

5. 5. The method according to claim 1, wherein the reaction system at the start of the reaction contains 3 mol % to 20 mol % of excess phosgene relative to the total amount of the dihydroxydiarylalkane used.

6. The method according to any one of claims 1 to 5, characterized in that the method is carried out continuously.

7. The process according to any one of claims 1 to 6, characterized in that the at least one catalyst is selected from the group consisting of tertiary amines and organophosphines.

8. 8. The process according to claim 1, wherein the at least one chain terminator is selected from the group consisting of phenols, alkylphenols, and their chlorocarbonates or acid chlorides of monocarboxylic acids.

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