Method for producing polyetherketoneketone

Abstract

The present invention relates to a method for producing polyetherketoneketone (PEKK). The method for producing PEKK includes the steps of: a) mixing 1,4-EKKE, terephthaloyl chloride (TCL) and isophthaloyl chloride (ICL) with an aprotic solvent under cooling to obtain a reaction solution; b) mixing a Lewis acid and the reaction solution to obtain a product mixture containing a PEKK-Lewis acid complex; c) deactivating the PEKK-Lewis acid complex by contacting the product mixture obtained in step b) with an aliphatic alcohol and subsequently adding water to obtain PEKK, where the amount of water in step c) is not less than 25 wt% of the total amount of aprotic solvent and aliphatic alcohol; d) isolating the PEKK obtained in step c) by washing with a protic solvent and drying. The method provides for the production of recyclable PEKK under conditions in which the reaction medium formed during synthesis has low corrosivity, thus making it possible to reduce the likelihood of metals from the material of the reaction equipment being incorporated into the resulting polymer powder.

Description

[0001] METHOD FOR PRODUCING POLYETHERKETONE KETONE

[0002] Field of technology to which the invention relates

[0003] The present invention relates to the chemical industry, specifically to a method for synthesizing polyaryletherketones, which are used, for example, as structural materials characterized by high deformation resistance, high thermal stability, low moisture absorption, and resistance to fire, chemicals, and radiation. Polyaryletherketones are used as materials in electronics and electrical engineering, mechanical engineering, and medicine. More specifically, the present invention relates to a method for synthesizing polyetherketone ketone (PEKK), one of the most widely used polyaryletherketones.

[0004] State of the art

[0005] The main requirement for the processes of producing polyether ketone ketone (PEKK) is to ensure the possibility of producing recyclable polymer products with high stability, which is largely determined by their purity, namely, a low content of residual materials, such as residual monomers, catalyst residues or other reaction components or impurities, for example, xanthan hydrol compounds.

[0006] WO2019025579 (Arkema, published 07.02.2019) and WO2019016121 (Arkema, published 24.01.2019) disclose a method for producing PECK by deactivating the formed PECK-Lewis acid complex using a protic solvent at the PECK isolation stage. The protic solvent used was an organic solvent such as methanol, ethanol, isopropanol, or acetic acid. An alternative protic solvent for deactivating the PECK-Lewis acid complex is an aqueous solution, including water or an aqueous solution of hydrochloric acid.

[0007] The essence of the invention

[0008] The objective of the present invention is to develop a method for producing polyether ketone ketone (PEKK) that ensures low corrosivity of the reaction system and efficient separation of PEKK from the product mixture, resulting in a polymer with the desired rheological properties. The technical result consists of producing PEKK with an initial complex melt viscosity ranging from 40 to 900 Pa s, and a melt viscosity increase of no more than 40% of the initial value after 10 minutes.

[0009] Another technical result is an increase in the service life of the reaction equipment used for the synthesis of PECK, and a reduction in the content of metals, including the material of the reaction equipment, in the composition of the PECK obtained according to the claimed invention, which makes it possible to maintain the necessary rheological characteristics of PECK.

[0010] An additional technical result consists in improving the technological efficiency of the process of obtaining PECK by reducing the filtration time of the obtained PECK powder at the isolation stage and reducing the stages of washing the polymer from residual aluminum.

[0011] This technical problem is solved, and the technical result is achieved, through the sequential addition of protic solvents, namely, an aliphatic alcohol to deactivate the PECK-Lewis acid complex formed during the synthesis stage in order to isolate PECK, and water in an amount of at least 25% by weight of the total amount of aprotic solvent and aliphatic alcohol to reduce the corrosive activity of the product mixture.

[0012] The present inventors have discovered that adding water during the PECK isolation step reduces the corrosivity of the product mixture and shortens the filtration time of the PECK powder obtained by deactivation with an aliphatic alcohol. Implementation of the present invention also increases the efficiency of washing away aluminum compounds by reducing the aluminum content in the PECK during the deactivation of the PECK-Lewis acid complex, which subsequently reduces the number of times the PECK powder needs to be washed with a protic solvent during the isolation step.

[0013] The corrosive activity of the product mixture containing the PECK-Lewis acid complex is due to the main chemical reaction of polymer formation—Friedel-Crafts acylation—in the presence of a Lewis acid as a catalyst. A suitable Lewis acid can be selected, in particular, from the group of compounds including: aluminum(III) chloride, aluminum(III) bromide, antimony(V) chloride, antimony(V) fluoride, indium(III) chloride, gallium(III) chloride, boron(III) chloride, boron(III) fluoride, zinc chloride, iron(III) chloride, tin(IV) chloride, and titanium(IV) chloride. The use of aluminum(III) chloride is preferred. Hydrogen halide is released during the synthesis, for example, as shown in the scheme below, when using aluminum(III) chloride as a catalyst.

[0014] The hydrogen chloride formed during the reaction is removed from the reaction zone by a continuous supply of inert gas, thereby shifting the chemical equilibrium toward the formation of the PECK-Lewis acid complex. However, some hydrogen chloride may remain in the reaction zone, leading to increased acidity of the resulting product mixture containing the PECK-Lewis acid complex.

[0015] At the stage of isolating PECK by deactivating the PECK-Lewis acid complex with an aliphatic alcohol, aluminum salts are formed, which are mainly represented by aluminum hydroxochlorides of the general formula Al(OH) пC1m, where n ranges from 1 to 2 and w ranges from 1 to 2, also maintains an acidic environment in the reaction system during the PECK isolation stage. Adding water after deactivation of the catalyst complex dilutes the resulting product mixture containing PECK, thereby reducing the acidity and corrosivity of the environment. The interaction of aluminum hydroxychloride with water also results in the formation of aluminum(III) chloride crystalline hydrates with the formula AICI3 6H2O. Thus, the corrosive catalyst (AlCl3) is isolated by a shell of water molecules within the crystalline hydrate structure, which also reduces the corrosivity of the environment. Reducing the corrosivity of the environments formed during polymer synthesis reduces the risk of metals from the equipment material entering the PECK, which could lead to failure to achieve the required rheological properties.

[0016] Detailed description of the invention

[0017] The following is a detailed description of various aspects and embodiments of the present invention.

[0018] According to the present invention, a method for producing PECK includes a step of synthesizing polyether ketone ketone (PECK) using 1,4-bis(4-phenoxybenzoyl)benzene (1,4-EKKE) as a monomer, followed by isolating and purifying PECK.

[0019] More specifically, the method for producing PECK powder includes the following steps:

[0020] SUBSTITUTE SHEET (RULE 26) a) mixing 1,4-ECCE, terephthaloyl chloride (TPC), isophthaloyl chloride (IPC) with an aprotic solvent upon cooling to obtain a reaction solution; b) mixing a Lewis acid and the reaction solution to obtain a product mixture containing a PECC-Lewis acid complex; c) deactivating the PECC-Lewis acid complex by bringing the product mixture obtained in step b) into contact with an aliphatic alcohol, followed by adding water, to obtain a PECC powder, wherein the amount of water in step c) is at least 25 wt. % of the total amount of aprotic solvent and aliphatic alcohol; d) purifying the PECC powder obtained in step c) by washing with a protic solvent and drying.

[0021] 1,4-Bis(4-phenoxybenzoyl)benzene (1,4-ECCE) is a reaction product of TPC and DPE as starting reactants in the presence of a Lewis acid as a catalyst in an aprotic solvent to produce a 1,4-ECCE-Lewis acid catalytic complex. A protic solvent or a pre-prepared aqueous-protic solvent mixture, preferably methanol, is typically used to isolate 1,4-ECCE. 1,4-ECCE is used as a monomer to produce the PECC according to the present invention.

[0022] The reaction solution obtained as a result of mixing in step a), comprising IFC, TPC, 1,4-ECCE, is typically cooled to a temperature of -30 to 10°C, preferably -20 to 5°C, most preferably -10 to 0°C. In order to adjust the composition of the final polymer, IFC is added in the form of a dry powder or in the form of a solution in an amount necessary to achieve the desired molar ratio of "terephthalic:isophthalic units" in the final polymer from 50 / 50 to 80 / 20, in particular 50 / 50, 60 / 40, 70 / 30 or 80 / 20. Mixing in step a) is carried out in any sequence, preferably initially mixing in a solvent of TPC, IFC followed by the addition of 1,4-ECCE.

[0023] In one embodiment of the invention, benzoyl chloride (BC) is used to control the molecular weight of the polymer. The amount of benzoyl chloride typically ranges from 1 to 10 mol.%, preferably from 1 to 7 mol.%, and most preferably from 2 to 5 mol.% of the amount of phenyl-containing monomers. Using a higher benzoyl chloride content (greater than 6 mol.%) can lead to the formation of a low-molecular-weight polymer, while a benzoyl chloride deficiency (less than 1 mol.%) in the reactor can lead to agglomeration of the reaction complex precipitate.

[0024] The aprotic reaction solvent used is a solvent used for the Friedel-Crafts acylation reaction, specifically selected from the following series: dichloromethane, dichloroethane, dichlorobenzenes, tetrachloroethylene, chloroform, and nitrobenzene. The most preferred solvent is ortho-dichlorobenzene (o-DCB).

[0025] A Lewis acid is then added as a catalyst to the resulting reaction solution comprising IFC, TFC, 1,4-ECCE and benzoyl chloride. A suitable Lewis acid, in one embodiment of the invention, may be selected, in particular, from the group of compounds containing: aluminum (III) chloride, aluminum (III) bromide, antimony (V) chloride, antimony (V) fluoride, indium (III) chloride, gallium (III) chloride, boron (III) chloride, boron (III) fluoride, zinc chloride, iron (III) chloride, tin (IV) chloride, titanium (IV) chloride. Most preferably, in one embodiment of the invention, anhydrous aluminum (III) chloride is used as the Lewis acid.

[0026] The amount of Lewis acid is generally determined so that for every 1 mol of carbonyl groups in the system there is from 1.0 to 2.0 mol of catalyst, preferably from 1.01 to 1.8 mol, which compensates for the possible low purity of the catalyst and / or moisture accidentally introduced into the reaction mixture.

[0027] After the addition of the Lewis acid, the reaction mixture is typically heated to a reaction temperature of 45 to 100°C, preferably 60 to 90°C. In one embodiment, the reaction mixture is maintained under stirring for 1 to 8 hours, preferably 1.5 to 6 hours, and most preferably 1.5 to 5 hours, depending on the reaction temperature. After maintaining the reaction mixture under constant stirring, the reaction solution is cooled to room temperature. Exceeding the reaction temperature results in the formation of a cross-linked product with a very high melting point, which prevents the processing of PECK for use in various fields.

[0028] In this way, a product mixture is obtained that contains PECK, more specifically, the product mixture contains a PECK-Lewis acid complex.

[0029] To isolate the final product—PECC powder—the PECC-Lewis acid complex is destroyed (or deactivated) in step c), followed by separation of the PECC. This process is accomplished by mixing the product mixture with an aliphatic alcohol to destroy the complex and then adding water to the product mixture containing solid PECC to dilute it. Separation of the solid PECC precipitate from the liquid is accomplished using methods known in the art, such as centrifugal filtration, vacuum filtration, sedimentation, or centrifugation.

[0030] As an aliphatic alcohol, alcohols from the series from C1 to C3 are generally used, more preferably methanol is used. The aliphatic alcohol from the series from C1 to C3 according to this invention is a colorless liquid. The destruction (deactivation) of the PECK-Lewis acid complex in step c) is generally carried out at a temperature of from 10 to 80°C, preferably from 20 to 75°C, most preferably from 25 to 70°C with constant stirring, usually for from 5 to 20 hours, preferably from 8 to 18 hours, most preferably from 10 to 16 hours.

[0031] The molar ratio of aliphatic alcohol to carbonyl groups in the system is from 20 to 30, preferably from 23 to 26. This amount allows for the complete destruction of the bonds between the carbonyl groups (C=O) and the Lewis acid formed in step b).

[0032] Thus, the final product is obtained - PECK powder, while the PECK-Lewis acid complex is absent from the composition of the product mixture.

[0033] In the resulting product mixture, which contains PECK powder and an organic phase containing an aprotic solvent and an aliphatic alcohol, aluminum salts in the form of hydroxyhalides of the general formula Al(OH)nCL m, where n is from 1 to 2, and w is from 1 to 2, demineralized water is added, followed by separation of the wet precipitate of PECK. The amount of water is at least 25 wt.%, preferably at least 37 wt.%, most preferably at least 50 wt.% of the total amount of the initial aprotic solvent and aliphatic alcohol. In one embodiment of the invention, at the stage of isolating the PECK to reduce corrosion of the reactor equipment, water was added to the reaction mass and maintained at a temperature of 30 to 70°C, preferably 40 to 60°C, most preferably 45 to 55°C, for 0.5 to 5 hours, preferably 1 to 3 hours. The resulting PECK powder is typically separated from the original aprotic solvent, aliphatic alcohol and water by a method known from the prior art, such as, for example, centrifugal filtration, vacuum filtration, sedimentation, centrifugation.

[0034] Additionally, the resulting PECK powder is typically washed with a protic solvent to remove aluminum salts formed during synthesis. In one embodiment, the protic solvent used is an aliphatic alcohol from C1 to C3, with methanol being more preferred. The optimal number of washes is typically 1 to 5, preferably 1 to 3. The resulting washed PECK is separated from the aliphatic alcohol using a method known in the art, such as centrifugal filtration, vacuum filtration, sedimentation, or centrifugation.

[0035] In order to remove residual protic solvent used for washing PECK, in one embodiment of the invention, one or more azeotropic washings of PECK powder are carried out using water until the aluminum salt content reaches no more than 0.02 wt.%, preferably no more than 0.01 wt.%. Azeotropic washing is typically carried out at a temperature of 30 to 60°C, preferably 40 to 50°C, and a pressure of 200 to 290 mbar, preferably 220 to 280 mbar.

[0036] The resulting raw PECK is then dried in a vacuum oven at temperatures above the glass transition temperature (T g ) and below the crystallization temperature (T с ) until a constant weight is achieved, yielding the target PECK polymer. The drying temperature is typically between 150 and 240°C, preferably between 155 and 185°C.

[0037] Implementation of the invention

[0038] Residual content of aluminum salts in terms of the Al ion 3+The aluminum content of PECK polymer samples was determined using inductively coupled plasma mass spectrometry (ICP-MS), which combines the use of inductively coupled plasma as an ion source with a quadrupole mass spectrometer acting as a mass analyzer (filter) and a discrete diode detector used to record individual ions and their fluxes. The measurement range for determining the mass fraction of aluminum is 0.00001 to 2.0%. The PECK samples were prepared for aluminum content determination by acid digestion in a fluoroplastic autoclave in a microwave oven with nitric acid. The sample was then transferred to a 50 ml volumetric flask and diluted with deionized water to the mark. The sample was then filtered and prepared for analysis. The mass spectrometer was calibrated by external calibration using standard samples of aluminum ion solutions.The influence of non-spectral (matrix) interference on the determination result is neutralized by introducing an internal standard (rhodium).

[0039] The complex viscosity of the PECK melt is determined by rotational viscometry in oscillation mode using an Anton Paar MCR 102e rotational rheometer and a CTD 600 high-temperature attachment according to GOST Plastics 57950-2017 (ISO

[0040] 6721-10:2015).

[0041] The method is applicable to determining the viscosity of high-melting-point polymer melts. Studying the time dependence of complex viscosity is used to determine the thermal stability of PECK samples during processing at high temperatures.

[0042] The complex viscosity of PECK samples is measured using a parallel-plate rheometer. The high-temperature chamber is heated to 360°C. A sample loading ring is placed on the bottom plate, into which PECK powder or granules are placed in a uniform layer. The sample weight ranges from 0.3 to 0.7 grams. When the gap between the upper and lower plates reaches 0.5 mm, the sample loading ring is removed, and any polymer leaking from the gap is trimmed with an aluminum spatula. The test is conducted at a constant shear frequency of 10 Hz and an amplitude of 5 mrad in an oxidizing environment for 10 minutes. The average of the two measurements is taken as the measurement result.

[0043] Example 1 (according to the invention). Synthesis of PECK using 25 wt.% water in step d).

[0044] In step a), 22,500 ml of o-DCB, 120 g of TPC (0.591 mol), 505.2 g of IPC (2.488 mol), 21.862 g of BC (0.154 mol), and 1,551 g of 1,4-ECCE (3.297 mol) are introduced into a 50 l reactor at room temperature and under nitrogen purging. The reaction mixture is cooled with stirring to a temperature of -10°C. In step b), 2,720 g of anhydrous AlCl3 (20.40 mol) are added at once to the reaction mixture under a constant flow of nitrogen and stirring of the reaction mixture, while the catalyst / carbonyl groups molar ratio in the system is 1.58. When the catalyst is added, the color of the solution changes from yellow to dark orange. After the catalyst has been completely added, the mixture is kept at a temperature of -10°C for 30 min. The mixture is then heated to 65°C and maintained at this temperature for 210 minutes to obtain the PECK-Lewis acid complex.

[0045] Then, in step c), the resulting product mixture containing the PECK-Lewis acid complex is cooled to room temperature and deactivated by adding 9800 g of methanol so that the temperature of the mixture does not exceed 50°C, resulting in a solid insoluble PECK precipitate. After complete deactivation, the mixture is maintained at 65°C for 15 hours. The mixture is cooled to room temperature, and 25 wt. % of water based on the total amount of o-DCB and methanol are added, and the mixture is maintained at 55°C for 1 hour. The resulting insoluble precipitate is then separated by filtration for further purification. The residual aluminum salt content in the PECK sample after the first filtration is 4 wt. %, indicating increased efficiency at the isolation stage and leading to a reduction in the number of washing stages. The filtration time was 50 min.

[0046] To purify, the wet PECK is washed with methanol for 1 hour at room temperature and filtered through a Nutsche filter. This process is repeated. 9800 g of water is added to the same container and azeotropically distilled with water under constant stirring for 1 hour at 50°C and 230 mbar. The finished product is dried in a vacuum oven at 155°C until constant weight is reached.

[0047] The values ​​of the complex viscosity of the polymer melt at the initial moment of time and after 10 min were 73.51 and 83.42 Pa s, respectively.

[0048] Example 2 (comparative). Synthesis of PECK using 12.5 wt.% water in step c).

[0049] The process for producing PECK is carried out according to the procedure described in Example 1, except that after deactivation of the PECK-acid complex in step c), water is added to the resulting product mixture containing PECK powder in an amount of 12.5 wt.% of the total amount of o-DCB and methanol. Filtration time was 120 min. The residual aluminum salt content in the PECK sample after the first filtration was 7 wt.%, indicating a deterioration in efficiency. The increase in complex viscosity from the initial value after 10 minutes was more than 40%, which may be due to the high content of metal impurities in the resulting PECK.

[0050] The PECK obtained according to this example does not have thermal stability at high temperatures, since during the measurements of the complex viscosity, high values ​​are achieved, caused by the process of cross-linking of the polymer during its study under these conditions, which subsequently leads to the impossibility of its use through processing.

[0051] Example 3 (comparative). Synthesis of PECK using 18.75 wt.% water in step c).

[0052] The process for obtaining PECK is carried out according to the procedure described in Example 1, except that after deactivation of the PECK-acid complex in step c), water is added to the resulting product mixture containing PECK powder in an amount of 18.75 wt.% of the total amount of o-DCB and methanol. Filtration time was 70 min. The residual aluminum salt content in the PECK sample after the first filtration was 6 wt.%, indicating a decrease in washing efficiency. The increase in complex viscosity from the initial value after 10 minutes was more than 40%, which may be due to the high content of metal impurities in the resulting PECK.

[0053] The PECK obtained according to this example does not have thermal stability at high temperatures, since during the measurements of the complex viscosity, high values ​​are achieved, caused by the process of cross-linking of the polymer during its study under these conditions, which subsequently leads to the impossibility of its use through processing.

[0054] Example 4. Synthesis of PECK using 30 wt.% water in step c).

[0055] The process for obtaining PECK is carried out according to the method described in Example 1, except that after deactivation of the PECK-acid complex in step c), water is added to the resulting product mixture containing PECK powder in an amount of 30% by weight of the total amount of o-DCB and methanol. Filtration time was 50 min. The residual aluminum salt content in the PECK sample after the first filtration was 4% by weight, indicating increased efficiency at the extraction stage and leading to a reduction in the number of washing steps.

[0056] The values ​​of the complex viscosity of the polymer melt at the initial moment of time and after 10 min were 90.96 and 120.75 Pa-s, respectively.

[0057] Example 5 (according to the invention). Synthesis of PECK using 25 wt.% water in step c).

[0058] In step a), 22,500 ml of o-DCB, 120 g of TPC (0.591 mol), 505.2 g of IPC (2.488 mol), 8.745 g of BC (0.0616 mol), and 1522 g of 1,4-ECCE (3.2349 mol) are added to a 50 l reactor at room temperature under nitrogen purging. The reaction mixture is cooled with stirring to a temperature of -10°C. In step b), 2,674 g of anhydrous AlCl3 (20.054 mol) are added at once to the reaction mixture under a constant flow of nitrogen and stirring of the reaction mixture, while the catalyst / carbonyl groups molar ratio in the system is 1.58. When the catalyst is added, the color of the solution changes from yellow to dark orange. After the catalyst has been completely added, the mixture is held at -10°C for 30 minutes. The mixture is then heated to 65°C and held at this temperature for 210 minutes, yielding the PECK-Lewis acid complex.Then, in step c), the resulting product mixture containing the PECK-Lewis acid complex is cooled to room temperature and deactivated by adding 9800 g of methanol so that the temperature of the mixture does not exceed 50°C, resulting in a solid insoluble PECK precipitate. After complete deactivation, the mixture is maintained at 65°C for 15 hours. The mixture is cooled to room temperature, and 25 wt. % of water based on the total amount of o-DCB and methanol is added, and the mixture is maintained at 55°C for 1 hour. The resulting insoluble precipitate is then separated by filtration for further purification. The residual aluminum salt content in the PECK sample after the first filtration is 4 wt. %, indicating increased extraction efficiency and reducing the number of washing steps. The filtration time was 50 min.

[0059] For purification, the wet PECK is washed with methanol for 1 hour at room temperature, filtered using a Nutsche filter, and washed again. 9800 g of water is added to the same container and azeotropically distilled with water under constant stirring for 1 hour at 50°C and 230 mbar. The finished product is dried in a vacuum oven at 155°C until constant weight is reached.

[0060] The values ​​of the complex viscosity of the polymer melt at the initial moment of time and after 10 min were 833.9 and 862.9 Pa s, respectively.

Claims

CLAUSES OF THE INVENTION 1. A method for producing polyether ketone ketone (PEKK), comprising the following steps: a) mixing 1,4-bis(4-phenoxybenzoyl)benzene (1,4-EKKE), terephthaloyl chloride (TPC), isophthaloyl chloride (IPC) with an aprotic solvent while cooling to obtain a reaction solution; b) mixing a Lewis acid and the reaction solution to obtain a product mixture containing a PEKK-Lewis acid complex; c) deactivating the PEKK-Lewis acid complex by bringing the product mixture obtained in step b) into contact with an aliphatic alcohol, followed by adding water, to obtain PEKK, wherein the amount of water in step c) is at least 25 wt. % of the total amount of aprotic solvent and aliphatic alcohol; d) isolating the PEKK obtained in step c) by washing with a protic solvent and drying.

2. The method according to claim 1, wherein the aprotic solvent used is a solvent selected from dichloromethane, dichloroethane, dichlorobenzenes, tetrachloroethylene, chloroform, nitrobenzene, most preferably ortho-dichlorobenzene (o-DCB).

3. The method according to claim 1, where in step a) the mixing is carried out in any sequence, preferably initially mixing TFC and IFC in a solvent followed by the addition of 1,4-ECCE.

4. The method according to claim 1, wherein the temperature of the reaction solution obtained in step a) is from -30 to 10°C, preferably from -20 to 5°C, most preferably from -10 to 0°C.

5. The method according to claim 1, wherein in step a) benzoyl chloride is additionally used in an amount of 1 to 10 mol.%, preferably 1 to 7 mol.%, most preferably 2 to 5 mol.% of the amount of phenyl-containing monomers.

6. The method according to claim 1, wherein the catalyst used in step b) is a Lewis acid selected from the group containing aluminum (III) chloride, aluminum (III) bromide, antimony (V) chloride, antimony (V) fluoride, indium (III) chloride, gallium (III) chloride, boron(III) chloride, boron(III) fluoride, zinc chloride, iron(III) chloride, tin(IV) chloride, titanium(IV) chloride, preferably aluminum(III) chloride.

7. The method according to claim 1, wherein the Lewis acid is used in such an amount that per 1 mole of carbonyl groups in the system there is from 1.0 to 2.0 moles of Lewis acid, preferably from 1.01 to 1.8 moles.

8. The method according to claim 1, wherein the reaction temperature in step b) is from 45 to 100°C, preferably from 60 to 90°C.

9. The method according to claim 1, wherein the holding time in step b) is from 1 to 8 hours, preferably from 1.5 to 6 hours, most preferably from 1.5 to 5 hours.

10. The method according to claim 1, wherein the aliphatic alcohol in step c) is selected from alcohols of the series from C1 to C3, more preferably methanol is used.

11. The method according to claim 1, wherein the temperature in step c) when adding the aliphatic alcohol is from 10 to 80°C, preferably from 20 to 75°C, most preferably from 25 to 70°C.

12. The method according to claim 1, wherein the holding time in step c) upon addition of the aliphatic alcohol is from 5 to 20 hours, preferably from 8 to 18 hours, most preferably from 10 to 16 hours.

13. The method according to claim 1, wherein the molar ratio of aliphatic alcohol and carbonyl groups in the system in step c) is from 20 to 30, preferably from 23 to 26.

14. The method according to claim 1, wherein the amount of water in step c) is at least 37 wt.%, preferably at least 50 wt.% of the total amount of the initial aprotic solvent and aliphatic alcohol.

15. The method according to claim 1, wherein the temperature in step c) after adding water is from 30 to 70°C, preferably from 40 to 60°C, most preferably from 45 to 55°C.

16. The method according to claim 1, wherein the holding time in step c) after adding water is from 0.5 to 5 hours, preferably from 1 to 3 hours.

17. The method according to claim 1, wherein washing of the obtained PECK in step d) is carried out using an aliphatic alcohol selected from the series from C i to C3, preferably methanol is used.

18. The method according to claim 1, wherein, additionally after step c), azeotropic washing is carried out using water at a temperature of 30 to 60°C, preferably from 40 to 50°C.

19. The method according to claim 18, wherein the pressure is from 200 to 290 mbar, preferably from 220 to 280 mbar.

20. The method according to claim 1, wherein the drying temperature of the obtained PECK is from 150 to 240°C, preferably from 155 to 185°C.

Images