WO2006027110A1

WO2006027110A1 - Method for the production of polycarbonate

Info

Publication number: WO2006027110A1
Application number: PCT/EP2005/009162
Authority: WO
Inventors: Peter Fischer; Melanie MÖTHRATH; Bernd Willenberg; Johann Rechner; Marc Buts; Lydia Simon
Original assignee: Bayer Materialscience Ag
Priority date: 2004-09-07
Filing date: 2005-08-25
Publication date: 2006-03-16
Also published as: DE102004043114A1

Abstract

The invention relates to a method for producing polycarbonate according to the transesterification of molten mass method, by reacting at least one aromatic dihydroxyaryl compound and a diarylcarbonate in the melt, at least in the presence of a catalyst. A carbonate forming reagent is used, said reagent containing: at least 99.9 % of a diarylcarbonate of general formula ArO(C=O)OAr 0.5 to 500 ppm of a hydroxyaromate of general formula ArOH - 2 to 300 ppm of arylurethanes of general formula ArO(C=O)NR1R2 - 2 to 100 ppm in the sum of (methylaryl)arylcarbonates of general formula (CH3Ar1)O(C=O)OAr a maximum of 100 ppm in the sum of (aryloxy)aryl carboxylic acid derivatives of general formula Ar2O-Ar3COOZ1 a maximum of 100 ppm in the sum of hydroxyaryl carboxylic acid derivatives of general formula Z2O-Ar4COOAr a maximum of 10 ppm in the sum of o,o`-biphenylene carbonate, dibenzofuran and biphenyldiol derivatives of general formula Z3OAr5-Ar5OZ4 a maximum of 10 ppm in the sum of aryloxyhydroxyaryl derivatives of general formula Ar6OArOZ5 a maximum of 10 ppm in the sum of halogenhydroxyaromate derivatives of general formula (X)mAr7OZ6 a maximum of 10 ppm in the sum of o-arylencarbonate, dihydroxyaromates and derivatives of general formula Ar(OZ7)2 a maximum of 10 ppm of alkylarylcarbonates of general formula ArO(C=O)OR3 - a maximum of 10 ppm in the sum of ethers of general formula ArOR4 a maximum of 5 ppm chloroformic acid ester of general formula Cl(C=O)OAr respectively, a maximum of 1 ppm of benzofuran-1.3-dione, diphenyloxalate and p-Chlorbenzoate a maximum of 10 ppm total content of chlorine respectively, a maximum of 1 ppm of Pb, Cu, Zn, Pd, Sn and Ti, wherein Z1 to Z7 independently represent one or several elements from the group -H, -Ar or -(C=O)OAr, Ar, Ar1 to Ar7 independently represent an aryl radial, X represents -Cl or -Br, m represents a whole number from 1 to 3 and R1 to R4 independently represent a linear, cyclic or branched alkyl radial having 1-20 C-atoms, wherein R1 and R2 form, optionally together, a cycle.

Description

Process for the production of polycarbonate

The invention relates to a process for the preparation of polycarbonate by the transesterification process by reacting an aromatic dihydroxyaryl compound and a diaryl carbonate in the melt.

In melt transesterification for the production of polycarbonate on an industrial scale, diphenyl carbonate is predominantly used. For the synthesis of diphenyl carbonate (DPC) various technical routes are known. Many of the known methods dispense with the use of phosgene.

A newer, phosgene-free method for the production of diphenyl carbonate is the oxidative direct carbonylation, in which phenol is reacted with oxygen and carbon monoxide. Here, complex catalyst systems are used, which are typically a palladium compound, at least one transition or main group metal compound and an inorganic or

Have quaternary salt bromide. In side reactions in this less selective process, oxidation products of phenol such as dihydroxybiphenyls, phenoxyphenols and bromine compounds such as mono- or dibromophenols are produced here. The complete removal of traces of these by-products, as well as of volatile organometallic species or thermal

Decomposition products is difficult to accomplish on an industrial scale.

A number of DPC production processes use dialkyl carbonates such as dimethyl carbonate (DMC) or dibutyl carbonate (DBC) or dialkyl oxalates as starting materials. These reactions also produce by-products such as salicylic compounds, alkylaryl carbonates, alkylphenyl derivatives (eg (methylphenyl) phenylcarbonates), dialkyl and alkylaryl ethers which, together with volatile derivatives of the metals used as transesterification catalysts (eg Zn, Ti, Sn, Pb, Tl) can contaminate the generated diphenyl carbonate.

As an impurity of the dialkyl carbonates or oxalates further substances can get into the DPC used. Commercial processes for their preparation are based on the carbonylation of

Alcohols under copper catalysis in the presence of hydrochloric acid. Here can be chloro-organic or

Copper organyl be introduced. In synthetic routes via the transesterification of ethylene carbonate, traces of ethylene glycol, ethylene carbonate or derivatives thereof such as (2-hydroxyethyl) methyl carbonate, 1,2-ethylene (bismethyl carbonate) or 2-phenoxyethanol can be introduced into the product.

A blatant disadvantage of all these processes is a low selectivity compared to phosgenation, ie the generation of by-products, and often the use of metalloids. metallic catalysts. The manufacturing process is generally followed by only a distillative purification of the product, so that separation of impurities on a trace scale is difficult to accomplish. This means that impurities are generated in the DPC via these synthetic routes, which have a very disturbing effect on the transparency and quality of the melt polycarbonate. A complete separation of these impurities often turns out to be too costly in economic terms, as shown in, for example, EP 592 900 A and EP 677 545 A prior art.

It is desirable to avoid the occurrence of contaminants in general and those described in particular. At the same time, however, the claim is made to provide an economical process for the production of diphenyl carbonate. In this context, impurities are tolerable as long as the quality of the melt polycarbonate, e.g. Color, mechanics, weather resistance and thermal stability is not significantly affected.

Starting from the prior art, therefore, the object is to provide a process for the preparation of polycarbonate, in which the quality of the polycarbonate is not impaired by impurities of the diaryl carbonate.

The invention provides a process for preparing polycarbonate by the melt transesterification process by reacting at least one aromatic dihydroxyaryl compound and a diaryl carbonate in the melt, at least in the presence of a catalyst, using a carbonate formation reagent which contains at least

- At least 99.9% of a diaryl carbonate of the general formula ArO (C = O) OAr

0.5 to 500 ppm of a hydroxyaromatic of the general formula ArOH

2 to 300 ppm of arylurethanes of the general formula ArO (C =O) NR ¹ R ²

2 to 100 ppm in total of (methylaryl) arylcarbonates of the general formula (CH ₃ Ar ¹ P (C = O) OAr

- A maximum of 100 ppm in total of (aryloxy) arylcarbonsäurederivaten the general formula Ar ² O-Ar ³ COOZ. ¹

not more than 100 ppm in total of hydroxyarylcarboxylic acid derivatives of the general formula Z ² O-Ar ⁴ COOAr

not more than 10 ppm in total of o, o ^Λ- biphenylene carbonate, dibenzofuran and biphenyl diol derivatives of the general formula Z ³ OAr ⁵ -Ar ⁵ OZ ⁴ - A maximum of 10 ppm in total of Aiyloxyhydroxyatylderivaten the general formula Ar ⁶ OArOZ. ⁵

not more than 10 ppm in total of Halogenhydroxyaromatenderivaten the general formula (X) _1n Ar ⁷ OZ. ⁶

- A maximum of 10 ppm in total of o-arylene carbonate, of dihydroxyaromatics and derivatives of the general Formel.Ar (OZ ⁷ ) ₂

a maximum of 10 ppm of alkylaryl carbonates of the general formula ArO (C =O) OR ³

- a maximum of 10 ppm in total of ethers of the general formula ArOR ⁴

- A maximum of 5 ppm of aryl chloroformate of the general formula Cl (C = O) OAr

in each case not more than 1 ppm of benzofuran-1,3-dione, diphenyl oxalate and p-chlorobenzoate

- maximum 10 ppm total chlorine content

in each case at most 1 ppm of Pb, Cu, Zn, Pd, Sn and Ti,

where Z ¹ to Z ⁷ each independently of one another represent one or more elements of the group -H, -Ar or - (C =O) OAr,

Ar, Ar ¹ to Ar ^{7 are} each independently an aryl radical,

X is -Cl or -Br, m is an integer from 1 to 3 and

R ¹ to R ⁴ each independently represent a linear, cyclic or branched alkyl radical having 1-20 C atoms, where R ¹ and R ² optionally together form a cycle, stand.

The carbonate formation reagent used in the process according to the invention for the production of polycarbonate contains no impurities which affect the quality of the melt polycarbonate prepared according to the invention, e.g. in terms of color, mechanics, weather resistance and thermal stability, significantly reduce.

In a preferred embodiment, the carbonate forming reagent which is erfϊndungsgem according to used for the production of polycarbonate, prepared by a process comprising at least the following steps: (a) reacting an alkaline aqueous solution of a compound ArOH with a solution of phosgene in an inert organic solvent, if appropriate in the presence of an organic catalyst, at least to form a diaryl carbonate

(b) at least one simple, preferably multiple, extraction of the reaction mixture obtained according to step (a) with an aqueous solution

(c) treating said in step (b) the resulting organic extract containing the Lösungs¬ medium with a residual moisture content of at least 0.5 wt.%, by distillation and / or steam distillation with introduction of water or steam at temperatures from 40 to 180 ⁰ C, preferably 50 to 150 ⁰ C _{5, more} preferably 60 to 135 ° C.

(d) Distillative purification of the reaction mixture obtained according to step (c), which is optionally concentrated, the diaryl carbonate being taken off as top product or in the side stream and at least 0.2% by weight, preferably at least 0.3% by weight, more preferably at least 0.5% by weight (based on the ArOH mass used) is taken from the bottom product.

A carbonate-forming reagent prepared by this process contains no impurities, by-products or the like, which substantially impair the quality of a melt polycarbonate produced therefrom. The quality of the carbonate-forming reagent produced by means of phosgene is sufficient to produce a melt polycarbonate of excellent quality and transparency. Existing impurities or the like. do not impair the quality of the molten polycarbonate. On the other hand, it has been found that in the phosgene-free diphenyl carbonate or diaryl carbonate processes, systemic by-products are formed which limit the use of a phosgene-free diphenyl carbonate mixture or diaryl carbonate mixture in polycarbonate synthesis or reduce the quality of the polycarbonate produced.

In addition, the carbonate forming reagent is economically very efficient to produce by this method due to its relatively simple technical implementation.

The preparation of carbonic acid diaryl esters (diaryl carbonates) by the phase boundary process is known in principle from the literature (eg EP-A 12 16 981, EP-A 12 16 982 or EP-A 12 19 589). Hereinafter, the carbonate forming reagent in the context of the present invention is also referred to simply as carbonic acid diarylester. The alkali used in step (a) may be an alkali metal hydroxide solution (Na, K, Li, Ca hydroxide), preferably sodium hydroxide solution and is preferably used in the process according to the invention as 20 to 55% by weight, more preferably 30 to 50% by weight. -% solution used.

Phosgene can be used liquid, gaseous or dissolved in an inert solvent.

Suitable monophenols ArOH for use in the reaction are phenols of the formula (I) or (H)

Herein, R represents hydrogen, tert-butyl, halogens, a branched or unbranched CrQ ₂ -alkyl, C 7 -C ₄₂ -alkylaryl or a C 6 -C 10 -aryl radical, a car-boxyalkyl or -aryl radical (τCO ₂ R ⁶ ). The substituents R ^1, R ^2, R ^3, R ^4, R ⁵ and R ⁶ are independently members of the set of moieties defined by R, except that R ⁶ should not be H or halogen. Also suitable are therefore phenol itself, alkylphenols such as cresols, xylenols, p-tert-butylphenol, p-cumylphenol, pn-octylphenol, p-iso-octylphenol, pn-nonylphenol and p-iso-nonylphenol, halophenols such as p-chlorophenol, 2,4-dichlorophenol, p-bromophenol and 2,4,6-tribromophenol, arylphenols such as 4-phenylphenol, hydroxybenzoic acid esters such as methyl, isopropyl or phenyl salicylate or p-hydroxy (benzoic acid methyl ester). The cresols and hydroxybenzoic acid esters are preferred, phenol being particularly preferred.

Inert organic solvents used in this process are, for example, dichloromethane, toluene, the various dichloroethanes and chloropropane compounds, chlorobenzene and chlorotoluene, preferably dichloromethane is used.

The reaction procedure according to step (a) is preferably carried out continuously and preferably in a plug flow without much back-mixing. This can thus be done for example in tubular reactors. The mixing of the two phases (aqueous and organic phase) can be realized by built-in tube diaphragms, static mixers and / or pumps, for example. The reaction procedure is divided into two successive stages.

In the first stage, the aqueous phase is mixed with the organic phase in an orifice, nozzle or dynamic mixer. Preferably, a nozzle is to be used, for example a confused-difrusor combination provided with bores or a suddenly narrowed tube. Behind the mixing element is a cooler, preferably with a liquid distributor, for cooling the reaction mixture to a maximum of 50 ⁰ C, preferably a maximum of 40 ⁰ C provided.

If the mixing power is too low, the reaction is incomplete, i. the monophenol is not completely reacted with the phosgene, so that, on the one hand, monophenol enters the wastewater and, on the other hand, the intermediate product of the aryl chloroformate is dragged into the end product. If the mixing performance is too high, a higher saponification and cleavage of the phosgene and the carbonic diaryl ester occurs, so that, on the one hand, monophenol enters the wastewater and, on the other hand, a significantly increased phosgene excess is required.

The reaction of the first stage is started by bringing the reaction components phosgene, inert solvent, which preferably serves first as a solvent for the phosgene, and phenol, which is preferably already previously dissolved in the alkali, are brought into contact. The residence time in the continuous process of the first stage is in the range of 2 seconds to 300 seconds, preferably in the range of 4 seconds to 200 seconds. Preferably, the pH of the first stage is adjusted by the ratio of Älkalilauge / Pheήol / phosgene, that the pH in the range of 11.0 to 12.0, preferably 11.2 to 11.8, particularly preferably 11 , 4 to 11.6. The reaction temperature in the first stage is maintained by cooling to a maximum of 40 ⁰ C, preferably a maximum of 35 ° C.

In the second stage of the continuous process according to step (a), the reaction is completed to the carbonic acid diaryl ester. The mixing of the two phases (aqueous and organic phase) in the second stage takes place at regular intervals by means of preferably static or dynamic dispersing agents. As static elements are preferably diaphragms, nozzles or narrowed pipe sections are used. In the latter, additional installations (static mixers) can be used for stream splitting and mixing. The pressure drop per dispersing element is preferably 0.1 to 0.5 bar. The velocity in the narrowest cross-section of the element is typically 2 to 10 m / s, preferably 3 to 9 m / s, most preferably 4 at 7 m / s. The mixing time (residence time in the dispersing) is at most 0.5 s, preferably 0.01 to 0.1 s. The residence time between two successive dispersing agents is 3 to 12 s, preferably 5 to 10 s. Suitable dynamic mixers are, for example, pumps or generally rotor-stator systems. The residence times of the second stage are 1 minute to 2 hours, preferably 2 minutes to 20 minutes, most preferably 3 minutes to 15 minutes.

In a preferred embodiment, a catalyst is fed zuge¬ at the beginning of the second stage. Directly after or during the addition of the catalyst, the reaction of the process is preferably cooled. The reaction temperature is maintained by cooling to a maximum of 50 ° C, preferably a maximum of 40 ⁰ C, most preferably a maximum of 35 ° C. It may be advantageous to add the catalyst at several, preferably at two, points in the second stage of the reaction in the continuous process. Between the first and the second stage, an intermediate buffering can also be carried out, for example, in a stirred residence vessel while maintaining the mixed phases.

Suitable catalysts are, for example, tertiary amines, N-alkylpiperidines or onium salts. Among onium salts, the scope of the present invention is understood to mean compounds such as PR ₄ X and NR ₄ X, where R can be an alkyl and / or aryl radical and / or an H and X is an anion. Tributylamine, triethylamine and N-ethylpiperidine are preferably used. Very particular preference is given to N-ethylpiperidine. The concentration of the catalysts is 0.0001 mol% to 0.1 mol%, preferably 0.01 mol% to 0.075 mol%, based on the phenol used.

Preferably, in the second stage of the process, the pH is controlled by measuring the pH (preferably measured online in the continuous process by methods known in the art) and adjusting the pH accordingly by adding the caustic. The amount of added alkali metal hydroxide solution is adjusted so that the pH after the second process stage is in the range of 7.5 to 10.5, preferably 8 to 10, particularly preferably 8.2 to 9.5.

Phosgene is run relative to the phenol in the ratio of 1.01 to 1.14 mol%, preferably 1.05 to 1.10 mol%. The solvent is mixed in such a way that the carbonic acid diphenyl ester is present in a 5 to 60% strength solution, preferably 20 to 45% strength solution, after the reaction.

After the reaction, the organic phase containing the carbonic acid diarylester is customarily washed with an aqueous liquid and separated from the aqueous phase as far as possible after each washing operation (extraction with an aqueous solution according to step (b)). The laundry is preferably carried out with desalinated water. The carbonic acid diarylester solution is usually cloudy after washing and separation of the washing liquid. The washing liquid used is aqueous liquids for separating off the catalyst, for example dilute mineral acids such as HCl or H 3 PO ₄ , and deionized water for further purification. The concentration of HCl or H ₃ PO ₄ in the washing liquid may be, for example, 0.5 to 1.0% by weight. The extraction takes place at least twice.

As phase separation devices for separating the washing liquid from the organic phase it is possible in principle to use known separating devices, such as separating vessels, phase separators, centrifuges and coalescers, or else combinations of these devices.

In the subsequent step (c), the organic extract containing the solvent having a residual moisture content of at least 0.5% by weight of step (b) is thermally treated with water. This step is carried out at temperatures of 40 ⁰ C to 180 ⁰ C, preferably 50 to 150 ⁰ C, particularly preferably 70 to 135 ° C, by means of distillation and / or steam distillation with introduction of water or steam (steam stripping). The residual moisture contained in the organic extract or the optionally added liquid water or the added water vapor act as a drag gas (stripping gas) to remove the solvent, residues of the phenol and impurities.

A first possible embodiment is the distillation of the organic extract with a residual moisture content of at least 0.5% by weight in the temperature range mentioned. In this case, the organic extract, which is optionally concentrated, freed of solvent and residual phenol. A second, preferred embodiment is the steam distillation of the optionally concentrated organic extract while introducing water or steam.

Subsequently, the distillate is preferably condensed and the resulting solvent-water mixture, preferably without prior phase separation, recycled into the reaction.

The treatment according to step (c) may be carried out in one or more temperature and pressure stages, e.g. in different distillation columns and / or stripping vessels. If several stages are used, it is preferred to work with a temperature profile rising in the direction of flow and / or a decreasing pressure profile.

Subsequently, according to step (d), a distillative purification (fine distillation) of the diaryl carbonate remaining in the bottom in step (c). Characteristic of this step is that at least 0.2 wt.%, Preferably at least 0.3 wt.%, Particularly preferably at least 0.5 wt.%, (Based on the ArOH mass used) is taken from the bottom product. The diaryl carbonate obtained from the bottom product is not returned to the process. Step (d) can be one or more stages. Various methods of distillation known in principle can be used. For example, the distillation can be carried out in two stages, wherein in a first column first ArOH and other lower-boiling compounds are taken overhead and the diaryl carbonate remains in the bottom. If necessary, the high boiler fraction can be returned to the process. In a second column at a higher temperature and / or lower pressure than in the first column, the diaryl carbonate can then be removed as top product or on one of the upper separation trays. The bottoms of this column circulated, for example, by means of a circulation evaporator, are then taken off a corresponding subset as purges.

An alternative variant is the use of a dividing wall column, in which high boilers are taken as Kopφrodukt, a circulating bottom product, from which a purge stream is diverted, and diaryl carbonate is taken as a side stream.

A preferred variant is based on the embodiment of EP 784 048 A developed for a substance phosgenation process. The fine distillation of the diaryl carbonate takes place here in a single distillation column. The reaction mixture from step (c) is fed to one of the upper trays, at the top of the column, a product is withdrawn, the bottom is circulated by means of a circulation evaporator, wherein a purge stream is removed and the diaryl carbonate in the side stream preferably on a bottom below the Height of feed feed taken. Before the removal of the purge stream, a further separation step can be carried out, in which, by known methods, such as distillation, extraction, membrane separation or precipitation, an enrichment of the high boilers to be separated from the present in high concentration diaryl carbonate is made. For example, a stream comprising about 0.5 to 5% of the feed stream from step (c) may be withdrawn from the bottoms and subjected to further distillation, eg, in a column or a falling film evaporator. The bottom of this distillation, the said portion is removed as purge, while the distillate can be recycled to the Feindestillationskolonne or to another point in the process. These purification steps may be, for example, continuously guided such that the bottom temperature in the distillation of at least 150 ⁹ C to 310 ⁰ C, preferably at least 160 located to 230 ⁰ C. The pressure necessary to carry out the distillation is from 1 to 1000 mbar, preferably from 5 to 100 mbar.

The carbonic acid diaryl esters prepared by the preferred method using phosgene are distinguished by a very high purity with GC purities (cool on column method) of at least 99.99%, preferably at least 99.9925%, very particularly preferably at least 99.995%, and extremely good transesterification behavior, so that a polycarbonate can be produced in excellent quality. The carbonate forming reagent which is used in the process according to the invention for the production of polycarbonate is characterized by a content of

At least 99.9%, preferably at least 99.95%, particularly preferably at least 99.97% (detection by cool-on-column GC method) of a diaryl carbonate of the general formula ArO (C =O) OAr, which consists of the phenols of formula (I) or (II) is prepared, wherein

Diphenyl carbonate is particularly preferred.

0.5 to 500 ppm, preferably 1 to 300 ppm, more preferably 2 to 150 ppm, of a hydroxyaromatic of the general formula ArOH, preferably of the formula (I) or (II), with phenol being particularly preferred.

2 to 300 ppm, preferably 4 to 150 ppm, particularly preferably 5 to 100 ppm, of aryl urethanes of the general formula ArO (C =O) NR ¹ R ² . Important representatives of this group are dealkylation products of the trialkylamines and alkylpiperidines used as catalysts. In particular phenylpiperidylurethane should be mentioned here.

• 2 to 100 ppm, preferably 3 to 80 ppm, particularly preferably 4 to 60 ppm, in the sum of (methylaryl) arylcarbonates (CH ₃ Ar ¹ ) O (C = O) OAr. Examples of this group are o-, m- and p -resol as well as cresylaryl carbonates and mixed or uniform dicresylcarbonates. Most important are the o-cresol derivatives. On the one hand, it is important to use a phenol which is as low in cresol as possible, ie preferably a phenol having less than 300 ppm of cresols, more preferably less than 100 ppm of cxesols. In addition, it is important to keep the reaction mixture free of alkylaryl carbonates or dialkyl carbonates in the case of phosgene processes or at least not to decompose these substances at high temperatures, since otherwise the rresol derivatives can be formed.

Not more than 100 ppm, preferably not more than 50 ppm, particularly preferably not more than 25 ppm in total of aryloxyarylcarboxylic acid derivatives of the general formula Ar ² O-Ar ³ COOZ ¹ . Important representatives are the p- and especially the o-Phenoxybenzoesäurederivate and here again especially the phenyl esters.

At most 100 ppm, preferably at most 10 ppm, particularly preferably at most 5 ppm, in total of hydroxyarylcarboxylic acid derivatives of the general formula Z ² O-Ar ⁴ COOAr. Important representatives are the p- and especially the o-Hydroxybenzoesäurephenylester and their carbonates. Due to the similar boiling point, the separation of phenyl salicylate from

Diphenyl carbonate by distillation particularly difficult. However, it can be significantly depleted by the extraction according to step (b). • Maximum of 10 ppm, preferably at most 5 ppm, particularly of the formula Z is preferably more than 1 ppm, in sum of o, o ^Λ -Biphenylencarbonat, dibenzofuran and Biphenyldiolderivaten ³ OAr ⁵ - Ar ⁵ OZ. ⁴ Important representatives are the o, o \ o, p ^Λ - and p, p ^{^} -Dihydroxybiphenyle, and their mono- and diaryl carbonates. In order to minimize their content it is important to use a phenol which is as low in biphenyl diol as possible and to avoid oxidative conditions such as the presence of oxygen during the process. This can be achieved by methods known to the person skilled in the art, for example by blowing or passing inert gases, degassing the educt streams or adding reducing agents.

At most 10 ppm, preferably at most 5 ppm, more preferably at most 1 ppm in total of Aryloxyhydroxyarylderivaten the general formula Ar ⁶ OArOZ. ⁵ Important representatives are the o and p-Phenoxyphenole and their carbonates. In order to minimize their content, it is important to use a Phenoxyphenolarmes phenol which is as low as possible and to avoid oxidative conditions, such as the presence of oxygen, during the process. This can be achieved by methods known to the person skilled in the art, for example by blowing or passing inert gases, degassing the educt streams or adding reducing agents.

At most 10 ppm, preferably at most 5 ppm, particularly preferably at most 1 ppm, in total of Halogenhydroxyaromatenderivaten the general formula (X) _1n Ar ⁷ OZ. ⁶ Important representatives are the o- and p-halophenols, the 2,4- and 2,6-Dihalogenphenole and their carbonates. Important here is the use of a low-chlorine and (C = O) ClBr-poor phosgene.

At most 10 ppm, preferably at most 5 ppm, particularly preferably at most 1 ppm, in total of o-arylene carbonate, of dihydroxyaromatics and derivatives of the formula Ar (OZ ⁷ ) ₂ . Preferably, therefore, a phenol is used for the synthesis of diphenyl carbonate which contains less than 500 ppm, preferably less than 200 ppm, more preferably less than 100 ppm, of dihydroxybenzenes.

At most 10 ppm, preferably at most 5 ppm, particularly preferably at most 1 ppm, of alkyl aryl carbonates of the general formula ArO (C =O) OR ³

A maximum of 10 ppm, preferably a maximum of 5 ppm, more preferably a maximum of 1 ppm in total of Ethern AxOR ⁴

At most 5 ppm, preferably at most 3 ppm, particularly preferably at most 1 ppm, aryl chloroformate of the general formula Cl (C =O) OAr. Chloroformic acid phenyl ester is known to be a strong inhibitor of the reaction. He can reaction as well as by the in the extraction according to step (b) proceeding hydrolysis and subsequent steam treatment and / or steam distillation are largely ent removed.

• A maximum of 1 ppm of benzofuran-l, 3-dione, diphenyl oxalate, p-chlorobenzoate

• Maximum 10 ppm total chlorine content

1 ppm maximum of Pb, Cu, Zn, Pd, Sn and Ti,

Ar, Ar ¹ to Ar ^{7 are} each independently an aryl radical, preferably in each case a phenyl radical,

X for -Cl or -Br

m for an integer from 1 to 3 and

R ¹ to R ⁴ each independently represent a linear, cyclic or branched alkyl radical having 1-20 C atoms, wherein R ¹ and R ^{2 may} together form a cycle.

Preferably, the carbonate forming reagent contains no further organic impurities in an amount of more than 100 ppm and no further elements except C, H, N, P, Cl and O in the scale of more than 5 ppm. Possibly. existing metals are particularly preferably contained only in amounts of at most 1 ppm.

The carbonate forming reagent is used in the production of polycarbonate by the melt transesterification method by reacting at least one aromatic dihydroxyaryl compound and the carbonate forming reagent containing a diaryl carbonate in the melt at least in the presence of a catalyst. The melt transesterification process is basically known from the prior art. The implementation of the method is described for example in WO 02/077067.

For the preparation of polycarbonates, suitable dihydroxyaryl compounds are those of the formula

HO-Z-OH in which Z is an 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.

Examples of 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, l, r-bis (hydroxyphenyl) diisopropylbenzenes, and their ring-alkylated and ring-halogenated compounds.

Preferred dihydroxyaryl compounds are, for example: resorcinol, 4,4'-dihydroxydiphenyl, bis (4-hydroxyphenyl) methane, bis (3,5-dimethyl-4-hydroxyphenyl) methane, bis (4-hydroxyphenyl) - diphenylmethane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,1-bis (4-hydroxyphenyl) -1- (1-naphthyl) ethane, 1,1-bis- (4-hydroxyphenyl) -1- (2-naphthyl) ethane, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (3-methyl-4-hydroxyphenyl) -propane, 2,2-bis- (3,5-dimethyl-4-hydroxyphenyl) -propane, 2,2-bis (4-hydroxyphenyl) -1-phenyl-propane, 2,2-bis (4-hydroxyphenyl ) -hexa-fluoropropane, 2,4-bis- (4-hydroxyphenyl) -2-methyl-butane, 2,4-bis (3,5-dimethyl-4-hydroxyphenyl) -

2-methyl-butane, 1,1-bis (4-hydroxyphenyl) -cyclohexane, 1,1-bis (3,5-dimethyl-4-hydroxyphenyl) -cyclohexane, 1,1-bis- (4-hydroxyphenyl) -4 -methylcyclohexane, 1,1-bis- (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 1,3-bis- [2- (4-hydroxyphenyl) -2-propyl] -benzene, 1 '1'-Bis (4-hydroxyphenyl) -3-diisopropylbenzene, 1'-bis (4-hydroxyphenyl) -4-diisopropylbenzene, 1,3-bis- [2- (3 , 5-dimethyl-4-hydroxyphenyl) -2-propyl] -benzene, bis (4-hydroxyphenyl) ether, bis (4-hydroxyphenyl) sulfide, bis (4-hydroxyphenyl) sulfone, bis - (3,5-dimethyl-4-hydroxyphenyl) sulfone and

2,2 ', 3,3'-tetrahydro-3,3,3 ^I , 3 ^I -tetramethyl-1, 1'-spirobi- [1H-indene] -5 ₅ 5'-diol.

Particularly preferred dihydroxyaryl compounds are: resorcinol, 4,4'-dihydroxydiphenyl, bis- (4-hydroxyphenyl) -diphenyl-methane, 1,1-bis- (4-hydroxyphenyl) -1-phenyl-ethane, bis- (4-hydroxy - phenyl) -1- (1-naphthyl) ethane, bis (4-hydroxyphenyl) -1- (2-naphthyl) ethane, 2,2-bis- (4-hydroxyphenyl) -propane, 2, 2-bis (3,5-dimethylo-4-hydroxyphenyl) -propane, 1,1-bis (4-hydroxyphenyl) -cyclohexane, 1,1-bis (3,5-dimethyl-4-hydroxyphenyl) -cyclohexane 1,1-Bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 1,1'-bis (4-hydroxyphenyl) -3-diisopropylbenzene and 1,1 * - bis ( 4-hydroxyphenyl) -4-diisopropylbenzene.

Very particularly preferred are: 4,4'-dihydroxydiphenyl, 2,2-bis (4-hydroxyphenyl) -propane and bis (4-hydroxyphenyl) -3,3,5-trimethyl-cyclohexane. Both a dihydroxyaryl compound to form homopolycarbonates and several dihydroxyaryl compounds to form copolycarbonates can be used.

Instead of the monomeric Dihydroxyarylverbindungen and low molecular weight, predominantly OH-endgruppengestoppte oligocarbonates can be used as the starting compound.

The dihydroxyaryl compounds can also be used with residual contents of the monohydroxyaryl compounds from which they have been prepared, or the low molecular weight oligocarbonates with residual contents of the monohydroxyaryl compounds which have been removed in the preparation of the oligomers. The contents may be up to 20%, preferably 10%, more preferably up to 5% and most preferably up to 2%.

Based on the dihydroxyaryl compound, the diphenyl carbonate is admixed with 1.02 to 1.30 mol, preferably with 1.04 to 1.25 mol, particularly preferably with 1.06 to 1.22 mol, very particularly preferably with 1.06 to 1, 20 moles per mole of dihydroxyaryl used.

To influence or change the end groups, it is additionally possible to use a monohydroxyaryl compound which was not used for the preparation of the diphenyl carbonate used. It is represented by the following general formula:

where R, R ¹ and R "independently of one another are H, optionally branched C ₁ -C ₃₄ alkyl / cycloalkyl, C ₇ -C ₃₄ -alkylaryl or C ₆ -C ₃₄ -aryl R can also be -COO-R '" where R '''may be H, optionally branched C ₁ -C ₃₄ alkyl / cycloalkyl, C ₇ -C ₃₄ -AhCyIaTyI or C ₀ -C ₃₄ aryl In this particular case, R may not be H, but R' and R ".

Examples of such monohydroxyaryl compounds are: 1-, 2- or 3-methylphenol, 2,4-dimethylphenol 4-ethylphenol, 4-n-propylphenol, 4-iso-propylphenol, 4-n-butylphenol, 4-isobutylphenol, 4- tert-butylphenol, 4-n-peniylphenol, 4-n-hexylphenol, 4-iso-octylphenol, 4-n-nonylphenol, 3-pentadecylphenol, 4-cyclohexylphenol, 4- (1-methyl-1-phenylethyl) -phenol, 4-phenylphenol, 4-phenoxyphenol, 4- (1-naphthyl) -phenol, 4- (2-naphthyl) -phenol, 4-trirylphenol, methyl salicylate, ethyl salicylate, n-propyl salicylate, iso-propyl salicylate, n-butyl salicylate, iso- Butyl salicylate, tert-butyl salicylate, phenyl salicylate and benzyl salicylate. Preference is given to 4-tert-butylphenol, 4-iso-octylphenol and 3-pentadecylphenol.

A monohydroxyaryl compound whose boiling point is above that of the monohydroxyaryl compound used to prepare the diaryl carbonate used must be chosen. The monohydroxyaryl compound can be added at any time in the course of the reaction. It is preferably added at the beginning of the reaction or else at any point in the course of the process. The proportion of free monohydroxyaryl compound may be 0.2-20 mol%, preferably 0.4-10 mol%, based on the dihydroxyaryl compound.

The end groups can also be altered by concomitant use of a diaryl carbonate whose base mono-hydroxyaryl compound has a higher boiling point than the base monohydroxyaryl compound of the main diaryl carbonate used. Again, the diaryl carbonate can be added at any time during the course of the reaction. It is preferably added at the beginning of the reaction or else at any point in the course of the process. The proportion of the diaryl carbonate with the higher-boiling base monohydroxyaryl compound in the total amount of diaryl carbonate used can be 1 to 40 mol%, preferably 1 to 20 mol% and particularly preferably 1 to 10 mol%.

Catalysts which are used in the melt transesterification process for preparing polycarbonates are the basic catalysts known in the literature, such as, for example, alkali metal and alkaline earth oxides and oxides, but also ammonium or phosphonium salts, referred to below as onium salts. Onium salts, more preferably phosphonium salts, are preferably used in the synthesis. Phosphonium salts in the context of the invention are those of the general formula:

where R ^{1 "4 are the} same or different Q-Cio-alkyls, C ₆ -C ₁₄ -aryls, C ₇ -C ₁₅ -arylalkyls or C ₅ -C ₆ -cycloalkyls, preferably methyl or C ₆ -C ₁₄ -aryls, are particularly preferred May be methyl or phenyl, and X ^{"may be} an anion such as hydroxide, sulfate, hydrogensulfate, bicarbonate, carbonate or a halide, preferably chloride or an alkylate or arylate of the formula -OR, where R is a Cβ-Cu-aryl , C ₇ -C ₅ -Arylalkyl or Cs-Cβ-cycloalkyl, preferably phenyl. Preferred catalysts are tetraphenylphosphonium chloride, tetraphenylphosphonium hydroxide and tetraphenylphosphonium phenolate, particular preference is given to tetraphenylphosphonophenolate.

They are preferably used in amounts of from ^10.sup.-8 to 10.sup.- ³ mol, based on 1 mol of dihydroxyaryl compound, more preferably in amounts of 10.sup.- ⁷ to 10.sup.- ⁴ mol.

Other catalysts may be used alone or in addition to the onium salt as cocatalyst to increase the rate of polycondensation.

These include the alkaline salts of alkali metals and alkaline earth metals, such as hydroxides, alkoxides and acryloxyde of lithium, sodium and potassium, preferably hydroxides, alkoxides or acryloxyde of sodium. Most preferred are sodium hydroxide and sodium phenolate, as well as the disodium salt of 2,2-bis- (4-hydroxyphenyl) -propane.

The amounts of alkaline salts of alkali metals and alkaline earth metals alone or as co-catalyst may range from 1 to 500 ppb, preferably from 5 to 300 ppb, and most preferably from 5 to 200 ppb, each calculated as sodium and based on polycarbonate to be formed.

The alkaline salts of alkali metals and alkaline earth metals can already be used in the preparation of the oligocarbonates, that is to say at the beginning of the synthesis, or else be added only before the polycondensation in order to suppress undesirable side reactions.

Furthermore, it is also possible to add additional amounts of onium catalysts of the same type or another before the polycondensation.

The addition of the catalysts takes place in solution in order to avoid harmful overconcentration during the metering. The solvents are system and process inherent compounds such as dihydroxyaryl compounds, diaryl carbonates or monohydroxyaryl compounds. Particular preference is given to monohydroxyaryl compounds because it is familiar to the person skilled in the art that the dihydroxyaryl compounds and diaryl carbonates readily change and decompose at already slightly elevated temperatures, in particular under the action of a catalyst. These include polycarbonate grades. In the technically significant transesterification process for the production of polycarbonate, the preferred compound is phenol. That's why phenol is already available mandatory, because the preferably used catalyst tetraphenylphosphonium phenolate is isolated in the production as a mixed crystal with phenol.

The thermoplastic polycarbonates are represented by the formula

described. The bracket denotes a n-times repeating structural unit, where Z is as defined above.

is in this case as a whole group also H.

The polycarbonates have an extremely low content of cations and anions of in each case not more than 60. ppb, preferably not more than 40 ppb and especially preferably not more than 20 ppb (as sodium).

Calculated cation), wherein as cations are those of alkali and alkaline earth metals, which may originate, for example, as an impurity from the raw materials used and the phosphonium and ammonium salts. Other ions such as Fe, Ni, Cr, Zn, Sn, Mo, Al ions and their homologues can be contained in the raw materials or originate from the materials of the plant used by removal or corrosion. The content of these ions is in the sum a maximum of 2 ppm, preferably at most 1 ppm and more preferably at most 0.5 ppm.

As anions are those of inorganic acids and organic acids in equivalent amounts (e.g., chloride, sulfate, carbonate, phosphate, phosphite, oxalate).

The aim is thus the smallest amounts that can be achieved only by using pure raw materials. Such pure raw materials are e.g. only available after purification processes such as recrystallization, distillation, topping with washes.

The weight average molecular weights (M _w ) obtained are from 15,000 to 40,000, preferably from 17,000 to 36,000, particularly preferably from 17,000 to 34,000 g / mol, where M _{w is determined} by the relative Viscosity according to the Mark-Houwink correlation (JMG Cowie, Chemistry and Physics of synthetic polymers, Vieweg textbook, Braunschweig / Wϊesbaden, 1997, page 235) is determined.

The polycarbonates can be selectively branched. Suitable branching agents are the compounds known for polycarbonate preparation having three or more functional groups, preferably those having three or more hydroxyl groups.

Some of the useful compounds having three or more phenolic hydroxyl groups include, for example, phloroglucinol, 4,6-dimethyl-2,4,6-tri- (4-hydroxyphenyl) -heptene-2, 4,6-dimethyl-2,4,6- tri- (4-hydroxyphenyl) heptane, 1, 3, 5-tri- (4-hydroxyphenyl) -benzene, 1,1,1-tris (4-hydroxyphenyl) -ethane, tri- (4-hydroxyphenyl ) -phenylmethane, 2,2-bis (4,4-bis (4-hydroxyphenyl) -cyclohexyl] -propane, 2,4-bis (4-hydroxyphenyl-isopropyl) -phenol and tetra- (4 hydroxyphenyl) methane.

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.

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

The branching agents are used in amounts of from 0.02 to 3.6 mol%, based on the Dihydroxyaryl- connection.

The process for the production of polycarbonate by the transesterification process can be designed discontinuously or else continuously. After the dihydroxyaryl compounds and the diphenyl carbonate, optionally with other compounds, are in the form of a melt, the reaction is started in the presence of suitable catalysts. The conversion or the molecular weight is increased with increasing temperatures and falling pressures in suitable apparatuses and devices by removing the monohydroxyaryl compound which has split off until the desired final state has been reached. By selecting the ratio of dihydroxyaryl compound to diphenyl carbonate, the loss rate of the diphenyl carbonate via the vapors and optionally added compounds, such as, for example, a higher-boiling monohydroxyaryl compound, given by the choice of the method or plant for preparing the polycarbonate, the end groups are characterized in type and concentration.

Regarding the way in which plant and according to which procedure the process is carried out, there is no limitation and restriction. Further, there is no specific limitation and limitation on the temperatures, pressures and catalysts used to perform the melt transesterification reaction between the dihydroxyaryl compound and the diphenyl carbonate, optionally also other added reactants. Each condition is possible, as long as the selected temperatures, pressures and catalysts allow a melt transesterification with correspondingly rapid removal of the cleaved Monohydroxyarylverbindung.

The temperatures over the entire process are 180 to 330 ⁰ C, the pressures at 15 bar absolute to 0.01 mbar absolute.

Mostly, a continuous procedure is chosen because it is beneficial to product quality.

Preferably, the continuous process for the preparation of polycarbonates is characterized in that one or more Dihydroxyarylverbindungen with the diphenyl carbonate, optionally also other added reactants, using catalysts, after a precondensation without separating the Monohydroxyarylverbindung formed in then then connected to several reaction evaporator Step by step increasing temperatures and gradually decreasing pressures, the molecular weight is built up to the desired size.

The apparatus, apparatuses and reactors suitable for the individual reaction-evaporator stages are, according to the process course, heat exchangers, expansion apparatuses, separators, columns, evaporators, stirred vessels and reactors or other commercially available apparatuses which provide the necessary residence time at selected temperatures and pressures. The chosen devices must provide the necessary heat input and be designed to meet the ever-increasing melt viscosities.

All devices are connected by pumps, piping and valves. The pipelines between all devices should, of course, be as short as possible and the curvatures of the lines should be kept as low as possible in order to avoid unnecessarily extended residence times. Here, the external, that is technical Rahmen¬ conditions and concerns for assemblies of chemical plants to be considered.

To carry out the process according to a preferred continuous procedure, the reactants can either be melted together or the solid Dihydroxy¬ arylverbindung in the Diphenylcarbonatschmelze or the solid diphenyl carbonate in the melt the dihydroxyaryl compound are dissolved or both raw materials are melted together, preferably directly from the production. The residence times of the separate melts of the raw materials, in particular those of the melt of the dihydroxyaryl compound, are adjusted as short as possible. On the other hand, the melt mixture can linger longer due to the reduced melting point of the raw material mixture compared to the individual raw materials at correspondingly lower temperatures without sacrificing quality.

Thereafter, the catalyst, preferably dissolved in phenol, admixed and the melt is heated to the reaction temperature. This is at the beginning of the technically significant process for the production of polycarbonate from 2,2-bis (4-hydroxyphenyl) propane and diphenyl 180 to 220 ⁰ C, preferably 190 to 210 ° C, most preferably 190 ° C. At residence times of 15 to 90 minutes, preferably 30 to 60 minutes, the reaction equilibrium is adjusted without the hydroxyaryl compound formed being removed. The reaction can be run at atmospheric pressure, but for technical reasons even at overpressure. The preferred pressure in technical systems is 2 to 15 bar absolute.

The melt mixture is expanded in a first vacuum chamber whose pressure is set to 100 to 400 mbar, preferably to 150 to 300 mbar, and then directly heated to the inlet temperature in a suitable device at the same pressure. In the relaxation process, the resulting hydroxyaryl compound is evaporated with remaining monomers. After a residence time of 5 to 30 minutes in a sump original, if necessary with pumping at the same pressure and temperature, the reaction mixture is in a second vacuum chamber whose pressure is 50 to 200 mbar, preferably 80 to 150 mbar, relaxed and then directly in a suitable Device at the same pressure to a temperature of 190 to 250 ⁰ C, preferably 210 to 240 ⁰ C, particularly preferably 210 to 230 ⁰ C, heated. Again, the resulting Hydroxyarylverbindung is evaporated with remaining monomers. After a residence time of 5 to 30 minutes in a sump, possibly with pumping, at the same pressure and temperature, the reaction mixture in a third vacuum chamber whose pressure is 30 to 150 mbar, preferably 50 to 120 mbar, relaxed and directly afterwards in a suitable device at the same pressure to a temperature of 220 to 280 ⁰ C, preferably 240 to 270 ⁰ C, particularly preferably 240 to 260 ⁰ C, heated. Again, the resulting Hydroxyarylverbindung is evaporated with remaining monomers. After a residence time of 5 to 20 minutes in a sump original, possibly with pumping at the same pressure and temperature, the reaction mixture is in a further vacuum chamber whose pressure at 5 to 100 mbar, preferably 15 to 100 mbar, particularly preferably 20 to 80 mbar , relaxed and directly afterwards in a suitable device at the same pressure to a temperature of 250 to 300 ⁰ C, preferably 260 to 290 ° C, particularly preferably 260 to 280 ° C, heated. Again, the resulting Hydroxyarylverbindung is evaporated with remaining monomers.

The number of these stages, here exemplarily 4, can vary between 2 and 6. The temperatures and pressures are to be adjusted accordingly when changing the step, in order to obtain comparable results. The achieved in these stages rel. Viscosity of the oligomeric carbonate is 1.04 to 1.20, preferably 1.05 to 1.15, particularly preferably 1.06 to 1.10.

The oligocarbonate is required after a residence time of 5 to 20 minutes in a sump original, where appropriate with pumping at the same pressure and the same temperature as in the last flash / evaporator stage in a disk or basket reactor and at 250 to 310 ⁰ C, preferred 250 to 290 ⁰ C, more preferably 250 to 280 ⁰ C, at pressures of 1 to 15 mbar, preferably 2 to 10 mbar, at residence times of 30 to 90 minutes, preferably 30 to 60 minutes, further condensed. The product achieves a relative viscosity of 1.12 to 1.28, preferably 1.13 to 1.26, particularly preferably 1.13 to 1.24.

The melt leaving this reactor is brought to the desired final viscosity or the final molecular weight in a further disk or basket reactor. The temperatures are from 270 to 330 ^° C., preferably from 280 to 320 ^° C., particularly preferably from 280 to 310 ^° C., the pressure from 0.01 to 3 mbar, preferably from 0.2 to 2 mbar, with residence times of from 60 to 180 min, preferably 75 to 150 min. The rel. Viscosities are adjusted to the level required for the intended application and are 1.18 to 1.40, preferably 1.18 to 1.36, more preferably 1.18 to 1.34. The function of the two basket reactors can also be summarized in a basket reactor.

The vapors from all process stages are directly derived, collected and worked up. This work-up is usually carried out by distillation in order to achieve high purities of the recovered materials. This can be done, for example, according to DE-A 10 100 404. Recovery and isolation of the cleaved Monohydroxyarylverbindung in its purest form is of course from an economic and environmental point of view. The monohydroxyaryl compound can be used directly for producing a dihydroxyaryl compound or a diaryl carbonate.

The disk or basket reactors are characterized by the fact that they provide a very large, constantly renewing surface on a vacuum at high residence times. The disk or basket reactors are geometrically formed according to the melt viscosities of the products. Suitable examples are reactors, as described in EP-A 1 253 163, or two-shaft reactors, as described in WO-A 99/28 370.

The oligocarbonates, even very low molecular weight, and the finished polycarbonates are usually promoted by gear pumps, screws of various designs or positive displacement pumps special design.

In addition, the polycarbonate obtained can be provided with other customary additives and additives (for example auxiliaries and reinforcing agents) to modify properties. The addition of additives and additives serves to prolong the service life (eg hydrolysis or degradation stabilizers), to improve the color stability (eg thermal and UV stabilizers), to simplify the processing (eg demulsifiers, flow aids), to improve the performance properties (eg antistatic agents), improving the flame retardancy, influencing the visual impression (eg organic colorants, pigments) or adapting the polymer properties to specific loads (impact modifiers, finely divided minerals, fibers, quartz powder, glass and carbon fibers).

These additives and additives can be added individually or in any desired mixtures or several different mixtures of the polymer melt, namely directly in the isolation of the polymer or after melting of granules in a so-called compounding step.

Examples

Determination of the composition of the carbonate formation reagent:

The content of impurities is determined by gas chromatography (GC). In order to avoid the decomposition of DPC, the cool-on-column method is used for the determination of DPC and the phenol content. Metal determinations are carried out by ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy).

Determination of the relative viscosity:

The relative solution viscosity was determined in dichloromethane at a concentration of 5 g / l at 25 ° C. Determination of the proportion of phenolic OH groups:

The content of phenolic OH is obtained by IR measurement. For this purpose, a difference measurement is measured from a solution of 2 g of polymer in 50 ml of dichloromethane over pure dichloromethane and determines the Absin difference at 3582 cmfl.

Determination of the color number:

The color number was determined as the difference of the extinction at 420 nm and 700 nm in dichloromethane at a concentration of 2.4 g / 50 ml and a layer thickness of 10 cm.

The results are summarized in Table 1.

Comparative Example 1

In a 500 ml three-necked flask equipped with stirrer, internal thermometer and Vigreux column (30 cm, mirrored) with bridge, 0.5 mol of bisphenol A, 0.55 mol of diphenyl carbonate and 0.002 mol

Weighed in tetraphenylphosphonium phenolate. At the same time, 5 ppm of o, o'-biphenylenecarbonate, based on diphenyl carbonate, were added. The apparatus was freed from atmospheric oxygen by applying a vacuum and purging with nitrogen (three times) and the mixture was melted at 150 ^° C. The temperature was raised to 190 ⁰ C and the resulting phenol distilled off over 30 minutes. The pressure was then adjusted to 100 mbar and the phenol formed was distilled off for 20 minutes. In 10 minutes, the temperature was raised to 235 ⁰ C and

Distilled off 15 minutes, the resulting phenol. Then within 5 minutes the

Vacuum increased to 60 mbar and the temperature maintained for 15 minutes before being within

10 minutes to 250 ⁰ C was increased. At 250 ⁰ C, the phenol was distilled off over 15 minutes and then reduced within 10 minutes, the vacuum to 5 mbar. After another 15 minutes was increased to 280 ⁰ C within 10 minutes. After another 15 minutes, the vacuum was reduced to 0.5 mbar and stirred for a further 15 minutes. The mixture was then increased to 300 ^° C. in the course of 10 minutes, and the resulting phenol was distilled off for a further 30 minutes. The polycarbonate showed a pink color.

Comparative Example 2 - 12

Procedure as in Example 1. Instead of 5 ppm o, o'-biphenylene carbonate based on Diphenylcarbo- nat the impurities listed in Table 1 were added based on diphenyl carbonate.

example 1

In a 500 ml three-necked flask equipped with stirrer, internal thermometer and Vigreux column (30 cm, mirrored) with bridge, 0.5 mol of bisphenol A, 0.55 mol of diphenyl carbonate and 0.002 mol of tetraphenylphosphonium phenolate were weighed. The diphenyl carbonate used contained 0.5 ppm of phenyl salicylate, 0.5 ppm of o-phenoxybenzoic acid, 2 ppm of phenyl-o-phenoxybenzoate, 98 ppm of phenylpiperidinurethane, less than 1 ppm of phenyl chloroformate, 47 ppm of o-cresylphenyl carbonate and less than 1 ppm of chlorine. The apparatus was freed from atmospheric oxygen by applying a vacuum and purging with nitrogen (three times) and the mixture was melted at 150 ^° C. The temperature was raised to 190 ⁰ C and the resulting phenol distilled over 30 minutes. Then the pressure was regulated to 100 mbar and the resulting 20 minutes

Distilled off phenol. In 10 minutes, the temperature was raised to 235 ° C and distilled off for 15 minutes, the resulting phenol. Then the vacuum was raised to 60 mbar and the temperature maintained for 15 minutes within 5 minutes before being increased to 250 ⁰ C within 10 minutes. At 250 ⁰ C, the phenol was distilled off over 15 minutes and then reduced within 10 minutes, the vacuum to 5 mbar. After another 15 minutes was increased to 280 ⁰ C within 10 minutes. After another 15 minutes, the vacuum was reduced to 0.5 mbar and stirred for a further 15 minutes. The mixture was then increased to 300 ^° C. in the course of 10 minutes, and the resulting phenol was distilled off for a further 30 minutes.

Example 2

From a template were 9000 kg / h melt mixture consisting of 4600 kg diphenyl carbonate / h (21473 mol / h), which 0.5 ppm phenyl salicylate, 0.5 ppm o-phenoxybenzoic acid, 2 ppm phenyl-o-phenoxybenzoat, 101 ppm phenylpiperidine urethane, less than 1 ppm chloroformic acid phenyl ester, 37 ppm o-cresylphenyl carbonate and less than 1 ppm chlorine, and 4400 kg bisphenol A / h (19273 mol / h) with addition of 0.2628 kg of a phenol adduct of the tetra phenylphosphonium phenolate / h (0.771 mol / h) dissolved in 1.87 kg phenol / h pumped through a heat exchanger, heated to 190 ⁰ C and passed through a dwell at 12000 mbar and 190 ⁰ C. The mean residence time was 45 minutes.

The melt was then passed through an expansion valve to a separator below 200 mbar. The effluent melt was in a, also below 200 mbar,

Falling film evaporator heated again to 190 ⁰ C and collected in a template. After a

Dwell time of 20 minutes, the melt was in the next three, similarly constructed

Pumped stages. The conditions in the 2nd, 3rd and 4th stages were 100, 75 and 60 mbar; 220, 255 and 270 ⁰ C as well as 20, 10 and 10 minutes. The resulting oligomer had a rel. Viscosity of 1.068. All vapors were passed through pressure controls in a column under vacuum and discharged as condensates.

The oligomer was condensed in a downstream basket reactor at 280 ⁰ C and 7.0 mbar at a residence time of 45 minutes to a higher molecular weight oligomer. The relative viscosity was 1.134. The vapors were condensed.

The oligomer was condensed in a further basket reactor at 295 ° C and 1.3 mbar to a relative viscosity of 1.278. The average residence time was determined to be 130 minutes. The vapors are condensed behind or in the vacuum system. The total residence time was 274 minutes.

Example 3

Procedure as in Example 1. Instead of 5 ppm o, o'-biphenylene carbonate based on diphenyl carbonate 2000 ppm phenylpiperidylurethane were added.

Table 1

From the comparative examples, a negative effect of the added impurities either on the color of the polycarbonate or on the molecular weight structure can clearly be seen in comparison with example 1. Example 2 illustrates that a melt polycarbonate of excellent color can be obtained by the process of the present invention using the carbonate forming reagent. Example 3 shows that there are impurities which have no negative effect.

Example 4-7

The carbonate formation reagent containing a diphenyl carbonate used in the method of the present invention was analyzed for the content of impurities to obtain the results shown in Tables 2 and 3.

Table 2

(n.g. = not measured, neg. = negative, undetectable),

^a : double determination

For example 7, the metal content was determined: TABLE 3

Claims

claims

A process for producing polycarbonate by the melt transesterification process by reacting at least one aromatic dihydroxyaryl compound and a

Carbonate formation reagent in the melt at least in the presence of a catalyst, characterized in that a carbonate formation reagent is used, which contains at least:

at least 99.9% of a diaryl carbonate of the general formula ArO (C = O) OAr

0.5 to 500 ppm of a hydroxyaromatic of the general formula ArOH

2 to 300 ppm of arylurethanes of the general formula ArO (C =O) NR ¹ R ²

- 2 to 100 ppm in total of (methylaryl) arylcarbonates of the general formula

(CH ₃ Ar ¹ P (C = O) OAr

not more than 100 ppm in total of (aryloxy) arylcarboxylic acid derivatives of the general formula Ar ² O-Ar ³ COOZ ¹

a maximum of 100 ppm in total of hydroxyarylcarboxylic acid derivatives of the general formula Z ² O-Ar ⁴ COOAr

not more than 10 ppm in total of OjO'-biphenylene carbonate, dibenzofuran and biphenyldiol derivatives of the general formula Z ³ OAr ⁵ -Ar ⁵ OZ ⁴

not more than 10 ppm in total of Aryloxyhydroxyarylderivaten the general formula Ar ⁶ OArOZ. ⁵

- A maximum of 10 ppm in total of Halogenhydroxyaromatenderivaten the allge my formula (X) _1n Ar ⁷ OZ. ⁶

not more than 10 ppm in total of o-arylene carbonate, of dihydroxyaromatics and derivatives of the general formula Ar (OZ ⁷ ) ₂

- a maximum of 10 ppm in total of ethers of the general formula ArOR ⁴

a maximum of 5 ppm of aryl chloroformate of the general formula Cl (C =O) OAr in each case not more than 1 ppm of benzofuran-1,3-dione, diphenyl oxalate and p-chlorobenzoate

maximum 10 ppm total chlorine content

in each case not more than 1 ppm of Pb, Cu ₅ Zn, Pd, Sn and Ti,

wherein Z ¹ to Z ⁷ each independently for one or more elements of

Group -H, -Ar or - (C = O) OAr,

Ar, Ar ¹ to Ar ^{7 are} each independently an aryl radical,

X is -Cl or -Br, m is an integer from 1 to 3 and

R ¹ to R ^{4 are} each independently a linear, cyclic or branched alkyl radical having 1-20 C atoms, wherein R ¹ and R optionally together form a cycle, stand.

2. The method according to claim 1, characterized in that the carbonate forming reagent is prepared by at least the following steps:

(a) reacting an alkaline aqueous solution of a compound ArOH with a solution of phosgene in an inert organic solvent, if appropriate in the presence of an organic catalyst, at least to form a diaryl carbonate

(c) treating the organic extract obtained in step (b) containing the

Solvent with a residual moisture content of at least 0.5% by weight, by Destilla¬ tion and / or steam distillation with introduction of water or steam at temperatures of 40 to 180 ° C, preferably 50 to 150 ⁰ C, particularly preferably 60 to 135 ° C.

(d) Distillative purification of the reaction mixture obtained according to step (c), which is optionally concentrated, wherein the diaryl carbonate is taken off as top product or in the side stream and at least 0.2, preferably at least 0.3, more preferably at least 0.5 wt .% (Based on the ArOH mass used) is removed from the bottom product.

3. The method according to any one of claims 1 or 2, characterized in that Ar, Ar ¹ to Ar ⁷ phenyl, R ³ and R ^{4 is} a linear Q-Cö-alkyl radical and R ¹ and R ² together represent a piperidyl radical.

4. The method according to any one of claims 1-3, characterized in that the carbonate forming reagent contains

at least 99.95% diphenyl carbonate,

0.5 to 500 ppm phenol,

4 to 150 ppm phenylpiperidyl urethane,

From 3 to 80 ppm in total of (methylphenyl) phenylcarbonates,

maximum 50 ppm phenyl-o-phenoxybenzoate,

a maximum of 10 ppm phenyl cis salicylate,

not more than 5 ppm in total of o, o ^{^} -Biphenylencarbonat, dibenzofuran and Biphenyldiolderivaten the formula Z ³ OAr ⁵ -Ar ⁵ OZ. ⁴

not more than 5 ppm in total of aryloxyhydroxyaryl derivatives of the formula Ar ⁶ OArOZ ⁵ ,

not more than 5 ppm in total of halohydroxyaromatic derivatives of the formula (X) _1n Ar ⁷ OZ ⁶ ,

not more than 5 ppm in total of o-arylene carbonate, of dihydroxyaromatics and derivatives of the formula Ar (OZ ⁷ ) ₂

maximum 5 ppm of alkylaryl carbonates ArO (C =O) OR ³ ,

maximum 5 ppm in total of Ethern ArOR ⁴ ,

maximum 3 ppm phenyl chloroformate,

not more than 1 ppm each of benzofuran-l, 3-dione, diphenyloxalate, p-chlorobenzoate,

maximum 10 ppm total chlorine content

maximum 1 ppm each of Pb, Cu, Zn, Pd, Sn and Ti, where Z ¹ to Z ⁷ each independently of one another represent one or more elements of the group -H, -Ar or - (C =O) OAr,

Ar, Ar ¹ to Ar ⁷ each independently represent an aryl radical,

-X for -Cl or -Br, m for an integer between 1 and 3 and

R ¹ to R ^{4 are} each independently a linear, cyclic or branched

Alkyl radical having 1-20 C atoms, wherein R ¹ and R ² together form a cycle, stand.

5. The method according to claim 2, characterized in that a phenol is used which contains a maximum of 100 ppm cresols, a maximum of 10 ppm dihydroxybiphenyls, a maximum of 10 ppm phenoxyphenols and a maximum of 100 ppm dihydroxybenzenes.