WO2022146199A1

WO2022146199A1 - Method for preparing 1,3-bis(4-phenoxybenzoyl)benzene (1,3-ekke) and method for preparing polyetherketoneketone using said 1,3-ekke

Info

Publication number: WO2022146199A1
Application number: PCT/RU2021/050457
Authority: WO
Inventors: Alexander Vladimirovich SAMAROV; Maksim Aleksandrovich POZDNIAKOV; Marina Olegovna NAGORNAYA; Diana Sergeevna DOMRACHEVA; Alexander Alexeevich KUZNETSOV
Original assignee: Public Joint Stock Company "Sibur Holding" (Pjsc "Sibur Holding")
Priority date: 2020-12-30
Filing date: 2021-12-29
Publication date: 2022-07-07

Abstract

The invention relates to the field of the production of thermostable polymers. In particular, the invention relates to the production of polyetherketoneketone (PEKK) having a solution intrinsic viscosity in concentrated H2SO4 in the range of 0.72 to 1.09 cm3/g, characterized by a minimum number of structural defects in the macromolecular chain, the presence of which eventually leads to an increase in the melt viscosity of polymer under processing conditions. The invention discloses a method for preparing PEKK through the production of 1,3-bis(4-phenoxybenzoyl)benzene (1,3-EKKE) as an intermediate, and to a method for preparing said intermediate 1,3-EKKE.

Description

METHOD FOR PREPARING 1,3-BIS(4-PHENOXYBENZOYL)BENZENE (1,3- EKKE) AND METHOD FOR PREPARING POLYETHERKETONEKETONE

USING SAID 1,3-EKKE TECHNICAL FIELD

The present invention relates to the chemical industry, particularly to a method for synthesizing polyaryletherketones useful, for example, as structural materials possessing high thermal deformation resistance, high thermal stability, low moisture absorption, fire resistance, and resistance to chemical and radiation effects. Polyaryletherketones are used as materials for articles in electronics and electrical engineering, in mechanical engineering and medicine.

BACKGROUND OF THE INVENTION

The main requirement for the processes of preparing PEKK (polyetherketoneketone) resides in allowing the production of polymer products with high stability that is largely determined by the polymer purity, namely, a low content of residual materials such as residual monomers, catalyst residues or other reaction components or impurities, for example, xanthydrol compounds.

US2019153143 (Arkema, publ. 23.05.2019) describes a method for preparing PAEK by an electrophilic substitution reaction between one or more aromatic acid chlorides and one or more aromatic esters in the presence of a Lewis acid as a catalyst. The resulting PAEK has a solvent content of less than 100 ppm and comprises aromatic esters (including l,4-bis(4-phenoxybenzoyl)benzene) in an amount of less than 1%.

US4816556 (DuPont De Nemours, publ. 28.03.1989) discloses a method for producing ordered copolymers by copolymerization of 1,4-EKKE or 1,3-EKKE and tere- and isophthaloyl halides in the presence of a Lewis acid, which are characterized by a high resistance to stress cracking and solvent at elevated temperatures and good moldability. The achievement of such properties is ensured by conducting reaction between reagents at strictly defined reagent ratios and by following the order of addition of the reagents.

Currently, PAEK and PEKK are usually produced by polycondensation of nucleophilic and electrophilic reagents in the presence of a Friedel-Crafts catalyst with use of a structuring agent, l,4-bis(4-phenoxybenzoyl)benzene (1,4-EKKE), as an electrophilic reagent to obtain PEKK, the synthesis of which proceeds by the reaction of electrophilic substitution in the benzene ring under interaction of diphenyl ether (DPE) and terephthaloyl chloride (TPC) in the presence of a Lewis acid as a catalyst in aprotic solvents, in particular, orthodichlorobenzene or dichloromethane (o-DCB or DCM). Said preparation method is described, in particular, in WO2018210959 (Arkema, publ. 22.11.2018), US4816556 (DU PONT DE NEMOURS, publ. 28.03.1989), US4826947 (Raychem, publ. 02.05.1989), and WO9523821 (Victrex Manufacturing, publ. 08.09.1995).

W02020094820 (Arkema, publ. 14.05.2020) describes a method for manufacturing 1,4-EKKE by reacting DPE and TPC in the presence of a Lewis acid. Wherein, the 1,4-EKKE-Lewis acid complex so obtained is partially in the form of a precipitate. Disadvantages of this technical solution are a limited solubility of the 1,4- EKKE-Lewis acid complex in a supersaturated state in a solvent at certain temperatures, and its relatively low reactivity, which is due to uncontrolled chemical reactions in heterogeneous regions of the PEKK synthesis system, in particular, an uncontrolled increase in the molecular weight of the polymer associated with simultaneous running of the process in homogeneous and heterogeneous phases and a wrong rati o/stoi chi om etry of the polycondensation reaction, as well as with a decrease in the rate of the polycondensation reaction during PEKK preparation. The indicated disadvantages do not allow obtaining PEKK with desired high stability.

WO201 1004164 (Ketonex, publ. 13.01.2011) describes a method for preparing PEKK. The method ensures obtaining a high stability polymer consisting of spherical particles of 0.1 to 3000 pm size, wherein at least 25% of the particles are less than 100 pm. This result is achieved due to the control of the ratio of tere-/isophthalic units in a polymer chain by partial replacement of the used 1,4-EKKE with l,3-bis(4- phenoxyb enzoy l)b enzene ( 1 , 3 -EKKE) .

Thus, there is a need to develop improved methods for preparing PEKK characterized by high stability and purity by using a suitable structuring agent.

SUMMARY OF THE INVENTION

The objective of the present invention is to obtain PEKK characterized by a minimum number of structural defects in the macromolecular chain, eventually leading to an increase in the melt viscosity of the polymer under processing conditions, and to develop a method for its production. The technical result resides in providing PEKK with a better processability and a reduced amount of xanthydrol groups, wherein an intrinsic viscosity of the polymer solution in concentrated sulfuric acid is in the range of 0.72 to 1.09 cm³/g. At the same time, the complex dynamic viscosity of the polymer melt changes insignificantly over a long time (up to 45 minutes) and ranges from 500 to 1750 Pa-s. An additional technical result of the method according to the invention is a high rate of polycondensation reaction leading to the formation of PEKK with desired properties.

This technical objective is solved, and the technical result is achieved by using 1,3-EKKE as a structuring agent. The synthesis of 1,3-EKKE runs in an inert atmosphere by using isophthalic acid dichloroanhydride (IPC) and DPE (Fig. 1). At the end of the process, the reaction product is deactivated and purified, which further decreases the content of xanthydrol groups in the polymer based thereon, see Table 1. After purification of 1,3-EKKE, TPC is used in the polycondensation reaction to obtain the target PEKK polymer.

Table 1 : The content of xanthydrol groups depending on the type of EKKE and its processing features

The process of synthesis of PEKK can be divided into several stages: i. Synthesis of a 1,3-EKKE oligomer; ii. Isolation and purification of 1,3-EKKE; iii. Synthesis of PEKK; iv. Isolation and purification of PEKK

In the stage of synthesis of a 1,3-EKKE oligomer, a reactor is fed with an aprotic halogenated organic solvent resistant to acylation in the Friedel-Crafts reaction, IPC, and DPE. In a preferred embodiment of the invention, ortho-dichlorobenzene is used as a solvent. A Lewis acid is used as a catalyst for the reaction. In a preferred embodiment of the invention, the Lewis acid is anhydrous aluminum trichloride (or a solution thereof). The Lewis acid can be loaded batchwise or all at once. The components are added to the reactor in any sequence under constant purging of an inert gas through its volume to completely remove traces of water, oxygen, and remove hydrogen chloride formed during the reaction.

In the stage of isolation and purification of 1,3-EKKE, the reaction mass is deactivated with monohydric liquid alcohol (C1-C12), resulting in the precipitation of the formed 1,3-EKKE as a powder, which is quite convenient to separate. Even a simple washing of such a powder enables a high degree of separation of impurities. The separation of the powder by any method gives crude 1,3-EKKE that is further recrystallized for purification. The powder is dried at elevated temperature and under reduced pressure to constant weight.

In the stage of PEKK synthesis, o-DCB, 1,3-EKKE powder, TPC, a Lewis acid, and benzoyl chloride (BC) are introduced into the reactor. The reaction mixture is heated and maintained at a desired temperature under vigorous stirring, then cooled, and the contents of the reactor are directed to the next stage.

The stage of isolation and purification of PEKK comprises the following sequential steps: a) isolation of solid PEKK by sequential washing in an aqueous inorganic acid solution; b) removal of the residual content of the inorganic acid in an aqueous solution of a neutralizing agent, followed by filtration; c) purification of the obtained solid PEKK by washing, followed by filtration; d) drying of the obtained solid PEKK under a reduced pressure to constant weight.

Before processing PEKK in the melt, a phosphorus-comprising thermal stabilizer is optionally introduced into the polymer to prevent macromolecules from destruction under high temperature exposure.

DESCRIPTION OF DRAWINGS

Figures 1-3 are presented to explain the technical solutions disclosing the essence of the present invention.

FIG. 1 represents a reaction scheme of the condensation reaction between IPC and DPE, which is an acylation reaction (Friedel-Crafts reaction) leading to the formation of l,3-bis(4-phenoxybenzoyl)benzene (1,3-EKKE). FIG. 2 shows UV absorption spectra of the solutions of polymers obtained in Examples 1-3. The absorption intensities of the solutions of polymers 4-8 have values below 0.05-0.06.

FIG. 3 shows photographs of samples of polymers subjected to heat treatment to assess their processability, wherein photo "a" represents an infusible and charred polymer sample, photo "b" represents a fusible polymer sample that does not form melt droplets, photo "c" represents a polymer that is fused with the formation of large melt droplets.

DETAILED DESCRIPTION OF THE INVENTION

Various aspects and embodiments of the present invention are described in detail below.

In accordance with the present invention, a method for preparing PEKK includes the synthesis of 1,3-EKKE followed by its isolation and purification; and the synthesis of polyetherketoneketone (PEKK) followed by its isolation and purification.

More specifically, the method for preparing 1,3-EKKE includes the following steps: a) mixing isophthalic acid dichloroanhydride (IPC) and diphenyl ether (DPE) with a solvent to obtain a reaction solution; b) adding a Lewis acid as a catalyst to the reaction solution to obtain a reaction mixture, wherein the catalyst is added at a temperature of -30 to 10°C; c) heating the reaction mixture to a reaction temperature of 10 to 40°C; d) maintaining the reaction mixture at the reaction temperature to obtain a product mixture comprising 1,3-EKKE.

A solvent, IPC and DPE are mixed at a DPE to IPC molar ratio that is typically in the range of 1.0 to 5.0, preferably 2.0 to 4.0, most preferably 2.5 to 3.5. The range of the DPE to IPC molar ratio is selected based on the specificity of the reactions: at a ratio of less than 1 condensation reactions producing linear oligomers begin to proceed, while at a ratio of more than 5, unreacted monomers begin to accumulate. According to the stoichiometry of the reaction, to obtain the target product 1,3-EKKE, the DPE to IPC ratio has to be equal to 2. A lower DPE to IPC molar ratio will not enable a predominant production of 1,3-EKKE; in this case, the reaction products will be represented by a mixture of 1,3-EKKE and low molecular weight products. In the case of accumulation of an excessive amount of unreacted monomers (starting reagents), it may require more labor-intensive steps of purification of 1,3-EKKE, including the use of large volumes of deactivating reagents, namely, a solvent in the isolation step, which significantly reduces the resource efficiency of the method for preparing 1,3-EKKE.

The used solvent is an aprotic solvent for the Friedel-Crafts acylation reaction, selected from the group consisting of dichloromethane, di chloroethane, dichlorobenzenes, tetrachlorethylene, chloroform, and nitrobenzene. The most preferred solvent is orthodi chlorobenzene (o-DCB).

It should be noted that the maximum water content in an undried solvent should not exceed 500 ppm (ppm by weight is kept in mind hereinbelow if otherwise is not specified) since this has a negative effect on the reaction of the formation of an active complex TPC/IPC with a Lewis acid. However, to obtain a product with controlled properties, the water content has to be in the range of 1 to 100 ppm, preferably 5 to 50 ppm, most preferably 15 to 25 ppm. The added catalyst reacts with the contained water and is hydrolyzed thereby, with a partial reduction in its activity, and forms insoluble hydrolysis products that can act as crystallization centers of EKKE and, subsequently, PEKK during their synthesis. In addition, the hydrolysis reactions of the Lewis acids listed below are exothermic, which obstructs introducing them into a system with a high moisture content while simultaneously controlling the reaction temperature. It should be noted that the presence of a small number of crystallization centers, which are hydrolysis products, is important in the synthesis of PEKK - it is these centers on which a gel-like precipitate is formed, in which the growth of macromolecules and partial crystallization of the polymer continue. The seeds in the system, which are formed due to the presence of traces of moisture in it, can influence the moment of the onset of the formation of a precipitate and its morphology (friability), and, ultimately, the growth rate of macromolecules and their molecular weight. Thus, the presence of an uncontrolled number of crystal seeds - that are chloride hydrolysis products - can lead to irreproducibility of the results in terms of the molecular weight of the product. Therefore, it is important to control the drying degree of the solvent. An excess of such sites formed when a wetter solvent is used will lead to the formation of a difficult-to- mix system and, as a result, a product with a reduced molecular weight. A Lewis acid is used as a catalyst for the reaction. 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 most preferably the Lewis acid is aluminum (III) chloride. The amount of the catalyst is calculated so that the molar ratio of Lewis acid (for example, A1C1₃) to carbonyl groups in the system is from 1.0 to 1.7, preferably from 1.1 to 1.5, most preferably from 1.2 to 1.4.

All components are mixed with constant bubbling of an inert gas through the volume of the reaction mixture to completely remove oxygen and hydrogen chloride formed during the reaction. The used inert gas is nitrogen, helium, argon, neon, xenon, krypton, or their mixture.

The Lewis acid catalyst is added to a preliminarily prepared mixture comprising DPE, TPC, and a solvent. The catalyst is added to the reaction mixture batchwise or all at once under conditions that prevent the heating of the reaction mixture and side reactions. Such conditions include a reduced temperature of -30 to 10°C, preferably -15 to 5°C, most preferably -10 to 5°C, to reduce the possibility of the interaction between the Lewis acid and diphenyl ether at ortho positions.

Once the entire portion of the catalyst is added, the resulting reaction mixture is vigorously stirred and heated to a reaction temperature of 10 to 40°C, preferably 20 to 35°C, most preferably 25 to 30°C. In this case, the reaction mixture is heated at a rate of 2.5 to 10°C/min, most preferably 3 to 6°C/min, to shorten the step of reaching a desired reaction temperature. The stirring rate is usually from 60 to 500 rpm.

The interaction of the components of the reaction mixture - the condensation reaction - is performed for 0.5 to 3.0 hours, preferably 0.5 to 2.0 hours, depending on the reaction temperature, thereby providing the formation of a 1,3-EKKE-Lewis acid complex with a yield of more than 90%.

Thus, the obtained product mixture comprises 1,3-EKKE, more particularly, the product mixture comprises 1,3-EKKE in the form of the 1,3-EKKE-Lewis acid complex.

To isolate the reaction product, 1,3-EKKE, the product mixture comprising 1,3- EKKE is deactivated and purified. Deactivation is carried out using a protic solvent known in the prior art, which is preferably an alcohol. During deactivation, the 1,3- EKKE-Lewis acid complex is decomposed and 1,3-EKKE is precipitated. The resulting 1,3-EKKE precipitate is separated by a method selected from the group of methods including sedimentation, filtration, and centrifugation, to obtain crude 1,3-EKKE.

Thus, in accordance with the present invention, further steps for preparing 1,3- EKKE include: e) isolation of crude 1,3-EKKE by deactivation of the product mixture comprising 1,3-EKKE; f) purification of the crude 1,3-EKKE by recrystallization followed by filtration; and g) drying of the resulting solid 1,3-EKKE.

In the step of isolation and purification of 1,3-EKKE, the reagent for deactivation of the product mixture is mainly an alcohol. The type of the alcohol is selected in such a way that its addition leads to precipitation of 1,3-EKKE during the deactivation of the product mass. The resulting precipitate is sufficiently pure after one washing on a filter with a portion of the alcohol and, unlike large precipitate particles, does not contain an occluded reaction mixture. As the alcohol, a linear monoalcohol having Ci to Ci₂, preferably Ci to C₈, most preferably Ci to C₅, or a mixture thereof is used. The resulting precipitate is separated by a method known in the prior art, such as, for example, centrifugation, sedimentation, and filtration.

In the step of purification of the resulting 1,3-EKKE solid residue, the 1,3- EKKE is recrystallized in a solvent selected from the group of aprotic solvents, including: benzene, toluene, di chlorobenzene, dimethylformamide, dimethylacetamide, or mixtures thereof. Orthodi chlorobenzene is preferably used as the aprotic solvent. Recrystallization is carried out at the solvent boiling point, followed by cooling and separation of the 1,3-EKKE precipitated crystals. The obtained crystals are separated by a method known in the prior art, such as, for example, centrifugation, sedimentation, and filtration.

The resulting residue of pure 1,3-EKKE is then dried in a vacuum drying oven at a residual pressure of 500 to 900 Torr, preferably 600 to 800 Torr, most preferably 650 to 750 Torr, at a temperature of 50 to 100°C, preferably 60 to 90°C, most preferably from 70 to 80°C, to constant weight. The obtained 1,3-EKKE is further sent to the stage of synthesis of a PEKK polymer. Further steps for preparing PEKK in accordance with the present invention include: b) mixing terephthalic acid dichloroanhydride (TPC) and benzoyl chloride (BC) with 1,3-EKKE obtained in accordance with the present invention to obtain a reaction solution; c) adding a Lewis acid as a catalyst to the reaction solution to obtain a reaction mixture, wherein the catalyst is added at a temperature of -30 to 10°C; d) heating the reaction mixture formed in step (c) to the reaction temperature; and e) maintaining the reaction mixture formed in step (c) to obtain a product mixture comprising PEKK.

TPC and BC are mixed with 1,3-EKKE in a solvent, wherein the resulting reaction solution is pre-cooled to a temperature of -30 to 10°C, preferably -20 to 5°C, most preferably -10 to 0°C. TPC is added as a dry powder or as a solution in an aprotic solvent in an amount necessary to achieve a desired molar ratio of tere- to iso-phthalic units in the final polymer, in the range of 50/50 to 80/20, in particular, 50/50, 60/40, 70/30, or 80/20.

The solvent used is an aprotic solvent used for the Friedel-Crafts acylation reaction, which is selected from the following: dichloromethane, di chloroethane, dichlorobenzenes, tetrachlorethylene, chloroform, and nitrobenzene. Orthodi chlorobenzene (o-DCB) is the most preferred solvent.

BC is introduced as a compound that controls the polymer molecular weight. As a rule, the amount of BC ranges from 1 to 5 mol.%, preferably 1 to 3 mol.%, most preferably 1 to 2 mol.% based on the amount of phenyl-comprising monomers. The use of an increased BC content of more than 5 mol.% leads to the formation of a low molecular weight polymer, and in a BC deficiency in the reactor, such as less than 1 mol.%, agglomeration of the reaction complex precipitate is observed.

A Lewis acid as a catalyst is further added to the resulting reaction solution comprising TPC, BC, and 1,3-EKKE. The amount of the Lewis acid is determined in such a way that the amount of the catalyst in the system per 1 mol of carbonyl groups is in the range of 1.0 to 1.6 mol, preferably 1.01 to 1.5 mol, to compensate for the possible low purity of the catalyst and/or moisture accidentally falling into the reaction mass.

Once the Lewis acid is added, the reaction mixture is heated to a temperature of 45 to 120°C, preferably 50 to 100°C, most preferably 60 to 80°C, and maintained under stirring for 0.5 to 3 hours, preferably 0.5 to 2.0 hours, most preferably 0.5 to 1.5 hours, depending on the reaction temperature, to obtain a high molecular weight PEKK with a yield of 96-97%. After maintaining under constant stirring, the reaction mixture is cooled to room temperature. The stirring rate is from 60 to 500 rpm. Exceeding the reaction temperature leads to the formation of a cross-linked product with a very high melting point or with no melting point.

Thus, the product mixture is obtained, which comprises PEKK, more particularly, the reaction mixture comprises a PEKK-Lewis acid complex.

To isolate the final product, the PEKK-Lewis acid complex is subjected to destruction followed by the isolation of PEKK. This process is carried out using a protic solvent, and the precipitate is separated from the liquid by a method known in the art, for example, such as centrifugal filtration, vacuum filtration, sedimentation, and centrifugation.

In accordance with the present invention, further steps for preparing PEKK include: f) isolation of solid PEKK by successive washing in an aqueous inorganic acid solution; g) removal of a residual content of the inorganic acid in an aqueous solution of a neutralizing agent, followed by filtration; h) purification of the obtained solid PEKK by washing, followed by filtration to obtain crude PEKK; i) drying of the resulting crude PEKK to obtain the target PEKK with a solution intrinsic viscosity in concentrated H₂SO₄ of 0.72 to 1.09 cm³/g.

In the stage of separation and purification of PEKK, the powder of a PEKK- aluminum chloride complex is separated from the solution by filtration and transferred to an excess of an aqueous acid solution to deactivate the catalytic complex. The aqueous acid solution is a solution of an acid forming water-soluble aluminum salts. It is preferred to use an aqueous solution of hydrochloric acid with a concentration of 0.1 to 2.5N, preferably 0.5 to 2. ON, most preferably 1.0 to 1.5N. The resulting mixture is stirred at room temperature until the orange color of the particles disappears, more preferably under reflux. The resulting white precipitate is filtered. If the polymer particles have a residual color, it is repeatedly washed with an aqueous acid solution for deep deactivation.

The precipitate is washed with demineralized water on a filter, placed in an excess of an aqueous solution of a neutralizing agent, and stirred until the residual acid is completely neutralized. The used neutralizing agent is an aqueous alkali solution, preferably sodium hydroxide with a concentration of 0.1 to 0.5N, preferably 0.1 to 0.4N, most preferably 0.1 to 0.2N. The precipitate is washed with demineralized water until the medium pH is neutral. At the end of the process, the PEKK polymer powder is treated with alcohol to remove residual Lewis acid and organic impurities. The treatment is carried out in batch or continuous extractors with alcohol vapor at temperatures sufficient for the boiling of the extractant. The used alcohol is an aliphatic C|-C₃ alcohol, preferably methanol. The extraction is carried out at a temperature of 20°C to 160°C, preferably 50°C to 120°C, most preferably 60°C to 100°C, under constant stirring in the proposed mixture under reflux for 0.5 to 12 hours, preferably 3 to 8 hours, most preferably 5 to 6 hours.

Then the PEKK polymer is dried in a vacuum oven at a residual pressure of 1-2 Torr and temperatures above the glass transition temperature (T_g) and below the crystallization temperature (T_c) to constant weight. The drying temperature is in the range of 165 to 240°C, preferably 170 to 210°C, most preferably 175 to 185°C.

The product prepared in accordance with the present invention is PEKK with a solution intrinsic viscosity in concentrated H₂SO₄ ranging from 0.72 to 1.09 cm³/g, preferably 0.97 to 1.07 cm³/g, and a complex melt viscosity enabling the use of the product in the manufacture of products in electronics and electrical engineering, mechanical engineering, and medicine.

The synthesis of 1,4-EKKE (Example 2) is performed according to the method described in document US4816556 (DuPont De Nemours, publ. 28.03.1989).

Embodiments of the invention

The presence of xanthydrol groups is determined by UV spectroscopy of polymer solutions in trichloroacetic acid. The absorption intensity in the range of 450- 500 nm indicates the presence of defects in the polymer structure. The concentration of polymer in the solution is 1 mg/ml. 3 ml of the solution is added to a 1 cm cuvette and the absorption intensity of the solution is measured using an Evolution 600 UV spectrophotometer (Thermo Fisher Scientific).

The number of xanthydrol groups is also determined by UV spectroscopy, using a previously plotted calibration curve of the absorption intensity of commercial xanthydrol vs. its concentration. The concentration range of xanthydrol calibration solutions is from 0.01 to 1.0 wt%.

The solution intrinsic viscosity of PEKK is determined in a 94.5% sulfuric acid solution at 25°C using an Ubbelohde glass viscometer with a hanging level. The intrinsic viscosity is calculated by extrapolating the reduced viscosity values obtained for several concentrations to zero concentration. The solution concentrations for measurement are selected so that the ratio of the solution flow time to the solvent flow time (relative viscosity) is in the range of 1.1 to 1.5.

The polymer melt viscosity is analyzed on a rotary rheometer (Discovery HR-2) with a cone diameter of 25 mm, an angle between the generatrix of the cone and the plane of 2°, and a temperature of 380°C at a constant shear rate of 0.1 s’¹, wherein the duration of the melt viscosity measurements is 45 minutes. Before testing, anhydrous sodium dihydrogen pyrophosphate (which acts as a stabilizer during material processing) is added to the final product in an amount of up to 0.5 wt%.

The processability of a polymeric material is determined by visual assessment of the fusion of PEKK samples in a muffle furnace (SNOL 30/1100) at temperatures from 350 to 400°C (to assess the material capacity of forming melt drops).

Physical and mechanical properties of the material, such as tensile and flexural modulus, are determined according to ASTM D638 and ISO 527, respectively, and test samples are prepared using a Haake Mini Jet Pro injection molding machine (polymer melt temperature and mold temperature are 380°C and 220°C, respectively).

Example 1. Synthesis of PEKK from simple monomers

550 ml (717.8 g (4.88 mol)) of o-DCB, 7.95 g (0.039 mol) of IPC, 13.38 g (0.0786 mol) of DPE, 7.95 g (0.039 mol) of TPC, and 0.186 g (0.0013 mol) of BC are added to a rector under stirring and purging with nitrogen. The mixture is cooled to - 12°C and 31.3 g (0.2348 mol) of aluminum chloride are added batchwise to the mixture under stirring over 10 minutes. The mixture is maintained at this temperature for 30 minutes until the reaction mixture is completely homogenized. The mixture is heated to 60°C at a rate of 3°C/min for 25 minutes. The system is maintained at this temperature for 120 minutes, then cooled to 30°C, and transferred to the next step.

Isolation and purification of PEKK. In the previous reaction step, an insoluble PEKK precipitate is formed, which is separated by filtration on a Schott filter, and transferred from the filter into 0.5 L of a IN aqueous HC1 solution. The mixture is stirred at room temperature (RT) for 1 hour until the orange color of the particles disappears. The wet precipitate is washed with demineralized water on a filter and placed into 0.5 L of a 0.1N aqueous NaOH solution and stirred until the residual HC1 is completely neutralized. The precipitate is filtered and washed with demineralized water until the medium pH is neutral. At the end of the process, the polymer powder is transferred into 100 ml of methanol heated to 50°C for 30 minutes to remove the residual Lewis acid and organic impurities, then filtered, and washed with methanol on a filter. The final product is dried in a vacuum drying oven at a residual pressure of 1-2 Torr and a temperature of 180°C to a constant weight. The UV absorption intensity of the polymer solution is 0.3, the concentration of xanthydrol groups is 2.1 wt%, the intrinsic viscosity is 1.02 cm³/g, the change in the complex viscosity of the polymer melt at the initial and final time points is in the range of 453 to 2735 Pa-s. The tensile and flexural modulus values are 2.1 and 2.5 GPa, respectively. The photography of the polymer after heating is shown in Fig. 3, photo "a".

Example 2, Synthesis of PEKK from L4-EKKE

Synthesis of L4-EKKE. 6.53 g (0.0322 mol) of TPC, 13.74 g (0.0807 mol) of DPE, and 65 ml (84.83 g (0.577 mol)) of o-DCB are added to a round-bottomed flask at RT and under purging with nitrogen. The residual moisture content of the solvent is 23 ppm. The reaction mass is cooled under stirring to a temperature of -5 °C. 19.714 g of anhydrous A1C1₃ (0.1479 mol) are slowly added to the reaction mixture by using a granular auger screw feeder under a constant nitrogen flow and stirring the reaction mass. At the beginning of the catalyst feed, the color of the solution changes from yellow to orange. After complete addition of the catalyst, the mixture is heated to 25°C at a heating rate of 3°C/min. The reaction mixture is maintained at this temperature for 15 minutes under 150 rpm stirring. 114 ml of methanol cooled to -50°C are added to the reaction mixture so that the temperature does not exceed 70°C. The whole mass is cooled to RT and stirred for 30 minutes. The powder is again placed into 114 ml of pure methanol and filtered. The product is purified by recrystallization from boiling N,N- dimethylacetamide, dried at 120°C in a vacuum drying oven, and used in the next step.

Synthesis of PEKK. 9.94 g (0.0211 mol) of 1,4-EKKE, 4.23 g (0.0208 mol) of IPC, 0.118 g (0.0008 mol, 1 mol.%) of BC are added to 150 ml (195.8 g (1.33 mol)) of o-DCB and cooled to -10°C. 16.78 g (0.1259 mol, 1.5-fold excess) of aluminum chloride are added batchwise to the mixture under stirring and the mixture is heated to a temperature of 90°C under 300 rpm stirring, maintained at this temperature for 30 minutes, then cooled to 30°C, and transferred to the next step.

Isolation and purification of PEKK. Isolation and purification are carried out as described in Example 1. The UV absorption intensity of the polymer solution is 0.16, the concentration of xanthydrol groups is 1.1 wt.%, the solution intrinsic viscosity is 0.72 cm³/g, the change in the complex viscosity of the polymer melt at the initial and final moment of time is in the range of 691 to 2043 Pa-s. The tensile and flexural modulus values are 2.9 and 3.1 GPa, respectively. The photography of the polymer after heating is shown in Fig. 3, photo "b".

Example 3, Synthesis of PEKK from E3-EKKE

Synthesis of 1,3-EKKE. 3.64 g (0.018 mol) of IPC, 10.185 g (0.060 mol) of DPE, and 117 ml (152.7 g (1.04 mol)) of o-DCB are added to a round-bottomed flask at RT under purging with nitrogen. The residual moisture content of the solvent is 35 ppm. The reaction mass is cooled under stirring to a temperature of -5°C. 7.74 g (0.058 mol) of anhydrous A1C1₃ are slowly added to the reaction mixture by using a granular auger screw feeder under a constant nitrogen flow and stirring the reaction mass. At the beginning of the catalyst feed, the color of the solution changes from yellow to orange. After the complete addition of the catalyst, the mixture is heated to 15°C at a rate of 6°C/min and kept at this temperature for 30 minutes under 140 rpm stirring. 114 ml of isopropyl alcohol cooled to -50°C are added to the reaction mixture so that the temperature does not exceed 70°C. The whole mass is cooled to RT and stirred for 30 minutes. The powder is again placed in 114 ml of pure isopropyl alcohol and filtered. The product is purified by recrystallization from boiling N,N-dimethylacetamide, then dried at 100°C in a vacuum drying oven, and used in the next step. Synthesis of PEKK. 9.94 g (0.0211 mol) of 1,3-EKKE, 4.23 g (0.0208 mol) of TPC, and 0.118 g (0.0008 mol, 1 mol.%) of BC are added to 150 ml (195.8 g (1.33 mol)) of o-DCB and cooled to -10°C. The residual moisture content of the solvent is 42 ppm. 16.78 g (0.1259 mol, 1.5-fold excess) of aluminum chloride is added batchwise to the mixture under stirring, and the mixture is heated to a temperature of 90°C under 300 rpm stirring. The system is maintained at this temperature for 30 minutes, then cooled to 30°C, and transferred to the next stage.

Isolation and purification of PEKK. Isolation and purification are carried out as described in Example 1, but the time of holding in methanol is 5 hours. The UV absorption intensity of the polymer solution is 0.07, the concentration of xanthydrol groups is 0.49 wt%, the solution intrinsic viscosity is 0.72 cm³/g, the change in the complex viscosity of the polymer melt at the initial and final moment of time is in the range of 789 to 971 Pa-s. The tensile and flexural modulus values are 3.1 and 3.5 GPa, respectively. The photography of the polymer after heating is shown in Fig. 3, photo "c".

Example 4, Synthesis of PEKK from E3-EKKE

The synthesis is carried out as described in Example 3, but in the stage of "synthesis of 1,3-EKKE", 7.31 g (0.036 mol) of IPC, 15.28 g (0.060 mol) of DPE, and 175.5 ml (229, 1 g (1.56 mol)) of o-DCB, at a DPE to IPC ratio of 1.67, are added to a flask and cooled to -15°C. The residual moisture content of the solvent is 15 ppm. The mass of aluminum chloride is 13.44 g (0.101 mol), and the ratio A1C1₃/IPC carbonyl groups is 1.4. The mixture is heated to 40°C at a heating rate of 5°C/min and maintained for 1.5 hours under 140 rpm stirring, after that the catalytic complex is destructed with n-butanol, and purification is carried out as described in Example 3.

In the stage of "Synthesis of PEKK", a mixture of 26.35 g (0.056 mol) of 1,3- EKKE, 11.37 g (0.056 mol) of TPC, and 0.11 g (0.0008 mol, 1 mol.%) of BC in 205 ml (267.5 g (1.82 mol)) of o-DCB is cooled to -15°C and 27.87 g (0.209 mol, 1.3-fold excess) of aluminum chloride are added batchwise under 300 rpm stirring, and heated to a temperature of 80°C. The system is maintained at this temperature for 30 minutes, then cooled to 30°C. The stage of "Isolation and purification of PEKK" is carried out as described in Example 1. The UV absorption intensity of the polymer solution is 0.073, the concentration of xanthydrol groups is 0.51 wt.%, the solution intrinsic viscosity is 0.82 cm³/g, the change in the complex viscosity of the polymer melt at the initial and final time points is in the range of 836 to 1057 Pa-s. The tensile and flexural modulus values are 3.0 and 3.3 GPa, respectively.

Example 5, Synthesis of PEKK from 1,3-EKKE

The synthesis is performed as described in Example 3, but in the stage of "Synthesis of 1,3-EKKE", 4.06 g (0.020 mol) of IPC, 15.28 g (0.060 mol) of DPE, and 175.5 ml (229,1 g (1.56 mol)) of o-DCB, at a DPE to IPC ratio of 3.0, are added to a flask and cooled to -30°C. The residual moisture content of the solvent is 23 ppm. The mass of aluminum chloride is 6.93 g (0.052 mol), and the ratio A1C1₃/IPC carbonyl groups is 1.3. The mixture is heated to 40°C at a rate of 3°C/min and maintained for 1.5 hours under 140 rpm stirring, after that the catalytic complex is destructed with isobutyl alcohol, and purification is carried out as described in Example 3.

In the stage of "Synthesis of PEKK", a mixture of 36.70 g (0.078 mol) of 1,3- EKKE, 15.84 g (0.078 mol) of TPC, and 0.154 g (0.0011 mol, 1 mol.%) of BC in 287 ml (374.5 g (2.55 mol)) of o-DCB is cooled to -15°C and 42 g (0.315 mol, 1.4-fold excess) of aluminum chloride are added batchwise under 350 rpm stirring, the resulting mixture is further heated to 80°C. The system is maintained at this temperature for 30 minutes, then cooled to 30°C. The stage "Isolation and purification of PEKK" is carried out as described in Example 1. The UV absorption intensity of the polymer solution is 0.08, the concentration of xanthydrol groups is 0.56 wt.%, the solution intrinsic viscosity is 0.79 cm³/g, the change in the complex viscosity of the polymer melt at the initial and final time points is in the range of 958 to 1312 Pa-s. The tensile and flexural modulus values are 3.2 and 3.2 GPa, respectively.

Example 6, Synthesis of PEKK from 1,3-EKKE

The synthesis is performed as described in Example 3, but in the stage of "Synthesis of 1,3-EKKE", 3.05 g (0.015 mol) of IPC, 10.21 g (0.060 mol) of DPE, and 165 ml (215.3 g (1.46 mol)) of o-DCB, at a DPE to IPC ratio of 4.0, are added to a flask and cooled to 0°C. The residual moisture content of the solvent is 32 ppm. The mass of aluminum chloride is 9.06 g (0.068 mol), and the ratio AICI3/IPC carbonyl groups is 1.7. The mixture is heated to 25°C at a rate of 4°C/min and maintained for 2 hours under 150 rpm stirring, after that the catalytic complex is destructed with n-octanol at a temperature of -10°C, and purification is carried out as described in Example 3. In the stage of "Synthesis of PEKK", a mixture of 12.3 g (0.026 mol) of 1,3- EKKE, 5.3 g (0.026 mol) of TPC, and 0.051 g (0.0011 mol, 1 mol.%) of BC in 95.7 ml (374.5 g (2.55 mol)) of o-DCB is cooled to 0°C and 17 g (0.1275 mol, 1.7-fold excess) of aluminum chloride are added batchwise under 350 rpm stirring, and the resulting mixture is further heated to a temperature of 90°C. The system is maintained at this temperature for 45 minutes, then cooled to 30°C. The stage of "Isolation and purification of PEKK" is carried out as described in Example 1. The UV absorption intensity of the polymer solution is 0.07, the concentration of xanthydrol groups is 0.49 wt%, the solution intrinsic viscosity is 0.82 cm³/g, the change in the complex viscosity of the polymer melt at the initial and final time points is in the range of 851 to 1104 Pa-s. The tensile and flexural modulus values are 3.6 and 3.7 GPa, respectively.

Example 7, Synthesis of PEKK from E3-EKKE

The synthesis is performed as described in Example 3, but in the stage of "Synthesis of 1,3-EKKE" 2.03 g (0.01 mol) of IPC, 7.65 g (0.045 mol) of DPE, and 110 ml (143,5 g (0.98 mol)) of o-DCB, at a DPE to IPC ratio of 4.5, are added to a flask and cooled to 10°C. The residual moisture content of the solvent is 100 ppm. The mass of aluminum chloride is 6.93 g (0.052 mol), and the ratio A1C1₃/IPC carbonyl groups is 1.3. The mixture is heated to 35°C at a rate of 4°C/min and maintained for 0.5 hours under 145 rpm stirring, after that the catalytic complex is destructed with n-pentanol, and purification is performed as described in Example 3.

In the stage of "Synthesis of PEKK", a mixture of 16.94 g (0.036 mol) of 1,3- EKKE, 7.31 g (0.036 mol) of TPC, and 0.051 g (0.0004 mol, 1 mol.%) of BC in 133 ml (173.6 g (1.18 mol)) of o-DCB is cooled to 10°C and 14.96 g (0.1122 mol, 1.5-fold excess) of aluminum chloride are added batchwise under 150 rpm stirring, and the resulting mixture is heated to a temperature of 100°C. The system is maintained at this temperature for 2 hours, then cooled to 30°C. The stage of "Isolation and purification of PEKK" is performed as described in Example 1. The UV absorption intensity of the polymer solution is 0.08, the concentration of xanthydrol groups is 0.56 wt%, the solution intrinsic viscosity is 0.83 cm³/g, the change in the complex viscosity of the polymer melt at the initial and final time points is in the range of 1021 to 1424 Pa-s. The tensile and flexural modulus values are 3.1 and 3.4 GPa, respectively.

Example 8, Synthesis of PEKK from 1,3-EKKE The synthesis is performed as described in Example 3, but in the stage of "Synthesis of 1,3-EKKE", 4.06 g (0.02 mol) of IPC, 11.9 g (0.070 mol) of DPE, and 100 ml (130,5 g (0.89 mol)) of o-DCB, at a DPE to IPC ratio of 3.5, are added to a flask and cooled to -30°C. The residual moisture content of the solvent is 50 ppm. The mass of aluminum chloride is 8.1 g (0.060 mol), and the ratio A1C1₃/IPC carbonyl groups is 1.5. The mixture is heated to 35°C at a rate of 4°C/min and maintained for 2.5 hours under 150 rpm stirring, after which the catalytic complex is destructed with 2- ethylhexanol, and purification is carried out as described in Example 3.

In the stage of "Synthesis of PEKK", a mixture of 16.94 g (0.036 mol) of 1,3- EKKE, 7.31 g (0.036 mol) of TPC, and 0.051 g (0.0004 mol, 1 mol.%) of BC in 133 ml (173.6 g (1.18 mol)) of o-DCB is cooled to -10°C and 14.96 g (0.1122 mol, 1.5-fold excess) of aluminum chloride are added batchwise under 350 rpm stirring, and the resulting mixture is heated to a temperature of 100°C. The system is kept at this temperature for 2 hours, then cooled to 30°C. The stage of "Isolation and purification of PEKK" is carried out as described in Example 1, but in the step of purification of PEKK propanol is used as the alcohol at a temperature of 80°C. The UV absorption intensity of the polymer solution is 0.07, the concentration of xanthydrol groups is 0.49 wt%, the solution intrinsic viscosity is 0.93 cm³/g, the change in the complex viscosity of the polymer melt at the initial and final time points is in the range of 1157 to 1371 Pa-s. The tensile and flexural modulus values are 3.8 and 3.6 GPa, respectively.

Example 9, Synthesis of PEKK from 1,3-EKKE

The synthesis is carried out as described in Example 3, but in the stage of "Synthesis of 1,3-EKKE", 5.95 g (0.0292 mol) of IPC, 16.320 g (0.096 mol) of DPE, and 185 ml of o-DCB, at a DPE to IPC ratio of 3.3, are added to a flask. The residual moisture content of the solvent is 13 ppm. The reaction mass is cooled under stirring to a temperature of -10°C. 22.59 g (0.139 mol) of anhydrous FeCl₃ are slowly added to the reaction mixture by using a granular auger screw feeder under a constant nitrogen flow and stirring the reaction mixture, wherein the ratio of FeCl₃/IPC carbonyl groups is 1.6. After the complete addition of the catalyst, the mixture is kept at a temperature of -10°C for 10 minutes and then heated to 25°C at a rate of 3°C/min. The reaction mixture is maintained at this temperature for 60 minutes under 150 rpm stirring, and then cooled to -10°C. Then, the catalytic complex is destructed with 2-ethylhexanol, and purification is carried out as described in Example 3.

In the stage of "Synthesis of PEKK", 20.42 g (0.1008 mol) of TPC, 0.307 g (0.0021 mol, 1 mol.%) of BC, and 492 ml of o-DCB are added to the reaction mixture cooled to -10°C. After stirring, 43.39 g (0.2916 mol, 1.5-fold excess) of ferric chloride is added batchwise to the mixture, and the resulting mixture is heated to 90°C under 230 rpm stirring. The system is kept at this temperature for 60 minutes, and then cooled to 30°C. The stage of "Isolation and purification of PEKK" is carried out as described in Example 1. The UV absorption intensity of the polymer solution is 0.06, the concentration of xanthydrol groups is 0.32 wt.%, the intrinsic viscosity of the polymer is 1.09 cm³/g, the change in the complex viscosity of the polymer melt at the initial and final time points is in the range of 1241 Pa-s to 1754 Pa-s. The tensile and flexural modulus values are 3.0 and 3.3 GPa, respectively.

Example 10. Synthesis of PEKK from E3-EKKE

The synthesis is performed as described in Example 3, but in the step of "Synthesis of 1,3-EKKE", 5.36 g (0.0263 mol) of IPC, 14.69 g (0.086 mol) of DPE, and 167 ml of o-DCB are added to a flask, with the DPE to IPC ratio being 3.3. The residual moisture content of the solvent is 10 ppm. The reaction mass is cooled under stirring to a temperature of -10°C. 23.71 g (0.125 mol) of TiCl₄ are slowly added to the reaction mixture by using a drop funnel under a constant nitrogen flow and stirring the reaction mixture, wherein the ratio of TiCl₄/IPC carbonyl groups is 1.6. After the complete addition of the catalyst, the mixture is maintained at a temperature of -10°C for 10 minutes and then heated to 25°C at a rate of 3°C/min. The reaction mixture is kept at this temperature for 60 minutes under 150 rpm stirring, then cooled to -10°C, after which the catalytic complex is destructed with n-pentanol, and purification is carried out as described in Example 3.

In the stage of "Synthesis of PEKK", 18.38 g (0.0907 mol) of TPC, 0.276 g (0.0019 mol, 1 mol.%) of BC, and 443 ml of o-DCB are added to the reaction mixture cooled to -10°C. After stirring, 49.78 g (0.2624 mol, 1.5-fold excess) of titanium tetrachloride are added to the mixture batchwise, and the mixture is heated to 90°C under 230 rpm stirring. The system is maintained at this temperature for 60 minutes, and then cooled to 30°C. The stage of "Isolation and purification of PEKK" is carried out as described in Example 1. The UV absorption intensity of the polymer solution is 0.07, the concentration of xanthydrol groups is 0.42 wt%, the change in the complex viscosity of the polymer melt at the initial and final moment of time is in the range of 1316 to 1987 Pa-s. The tensile and flexural modulus values are 2.4 and 2.7 GPa, respectively.

Claims

1. A method for preparing l,3-bis(4-phenoxybenzoyl)benzene (1,3-EKKE), comprising the following steps: a. mixing isophthalic acid dichloroanhydride (IPC) and diphenyl ether (DPE) with an aprotic solvent to obtain a reaction solution; b. adding a Lewis acid as a catalyst to the reaction solution to obtain a reaction mixture, wherein the catalyst is added at a temperature of from -30 to 10°C; c. heating the reaction mixture to a reaction temperature from 10 to 40°C; d. maintaining the reaction mixture at the reaction temperature to obtain a product mixture comprising 1,3-EKKE; e. isolating crude 1,3-EKKE by deactivation of the product mixture comprising 1,3-EKKE with a protic solvent; f. purifying the crude 1,3-EKKE by recrystallization followed by filtration; and g. drying the obtained solid 1,3-EKKE.

2. The method according to claim 1, wherein mixing the solvent, IPC, and DPE is carried out in any sequence at a DPE to IPC molar ratio in the range of 1.0 to 5.0, preferably 2.0 to 4.0, more preferably 2.5 to 3.5.

3. The method according to claim 1, wherein the solvent used in step (a) is an aprotic solvent selected from dichloromethane, di chloroethane, dichlorobenzenes, tetrachlor ethylene, chloroform, and nitrobenzene, preferably the solvent is orthodichlorobenzene.

4. The method according to claim 1, wherein the water content in the solvent is from 1 to 100 ppm, preferably 5 to 50 ppm, most preferably 15 to 25 ppm.

5. The method according to claim 1, wherein the used catalyst is a Lewis acid selected from the group comprising: 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; preferably, aluminum (III) chloride is used.

6. The method according to claim 1, wherein the Lewis acid is used in such an amount that the catalyst amount in the system per 1 mol of carbonyl groups is from 1.0 to 1.6 mol, preferably 1.1 to 1.5 mol, most preferably 1.2 to 1.4 mol.

7. The method according to claim 1, wherein the mixing of all components is carried out under constant bubbling of an inert gas through the volume of the reaction mixture.

8. The method according to claim 1, wherein the Lewis acid is added to the reaction mixture at a temperature of from -15 to 5°C, preferably from -10 to 5°C.

9. The method according to claim 1, wherein the reaction mixture is heated to a reaction temperature of 20 to 35°C, preferably 25 to 30°C.

10. The method according to claim 1, wherein the heating rate of the reaction mixture is from 2.5 to 10 °C /min, preferably 3 to 6 °C /min.

11. The method according to claim 1, wherein the stirring rate of the reaction mixture is from 60 to 500 rpm.

12. The method according to claim 1, wherein the reaction mixture maintaining time is from 0.5 to 3.0 hours, preferably 0.5 to 2.0 hours, most preferably 1.0 to 1.5 hours.

13. The method according to claim 1, wherein the protic solvent used in step (g) is an alcohol selected from linear monoalcohols Ci to Ci₂, preferably Ci to C₈, and most preferably Ci to C₅.

14. The method according to claim 1, wherein the solvent used for recrystallization in step (f) is an aprotic solvent, preferably o-dichlorobenzene.

15. The method according to claim 1, wherein 1,3-EKKE is isolated by filtration.

16. The method according to claim 1, wherein 1,3-EKKE is dried at a temperature of 50 to 100°C, preferably 60 to 90°C, most preferably 70 to 80°C.

17. A method for preparing poly etherketoneketone (PEKK), comprising: a. preparing 1,3-EKKE by the method according to any one of claims 1-16; b. mixing terephthalic acid dichloroanhydride (TPC) and benzoyl chloride (BC) with 1,3-EKKE obtained in step (a) in an aprotic solvent to obtain a reaction solution; c. adding a Lewis acid as a catalyst to the reaction solution to obtain a reaction mixture, wherein the catalyst is added at a temperature of from -30 to 10°C; d. heating the reaction mixture formed in step (c) to a reaction temperature; e. maintaining the reaction mixture formed in step (c) to obtain a product mixture comprising PEKK; f. isolating solid PEKK by sequential washing in an aqueous inorganic acid solution; g. removing a residual content of the inorganic acid in an aqueous solution of a neutralizing agent, followed by filtration; h. purifying the obtained solid PEKK by washing, followed by filtration to obtain crude PEKK; i. drying the obtained crude PEKK to obtain the target PEKK with a solution intrinsic viscosity in concentrated H₂SO₄ of 0.72 to 1.09 cm³/g.

18. The method according to claim 17, wherein step c) is carried out at a temperature of -20 to 5°C, most preferably -10 to 0°C.

19. The method according to claim 17, wherein the aprotic solvent is a solvent selected from dichloromethane, di chloroethane, dichlorobenzenes, tetrachlor ethylene, chloroform, and nitrobenzene, preferably, the solvent is orthodichlorobenzene.

20. The method according to claim 17, wherein BC is added in an amount of 1 to 5 mol.%, preferably 1 to 3 mol.%, most preferably 1 to 2 mol.%.

21. The method according to claim 17, wherein the catalyst is a Lewis acid selected from 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, the catalyst is aluminum (III) chloride.

22. The method according to claim 17, wherein the Lewis acid is added to the reaction solution batchwise or all at once.

23. The method according to claim 17, wherein the Lewis acid is added in an amount of 1.0 to 1.6 mol per 1 mol of carbonyl groups in IPC and TPC, preferably 1.01 to 1.5 mol per 1 mol of said carbonyl groups.

24. The method according to claim 17, wherein step c) is carried out at a temperature of 45 to 120°C, preferably 50 to 100°C, most preferably 60 to 80°C.

25. The method according to claim 17, wherein, in step d), the reaction solution is maintained under stirring for 0.5 to 2 hours, preferably 0.5 to 1.5 hours.

26. The method according to claim 17, wherein the stirring rate of the reaction mixture is from 60 to 500 rpm.

27. The method according to claim 17, wherein the reaction solution obtained in step d) is cooled to room temperature.

28. The method according to claim 17, wherein the inorganic acid used in step f) is hydrochloric acid.

29. The method according to claim 28, wherein the concentration of the aqueous inorganic acid solution is from 0.1 to 2.5 N, preferably from 0.5 to 2.0 N, most preferably from 1.0 to 1.5 N.

30. The method according to claim 17, wherein the neutralizing agent used in step g) is sodium hydroxide.

31. The method according to claim 30, wherein the concentration of the aqueous solution of the neutralizing agent is from 0.1 to 0.5 N, preferably 0.1 to 0.4 N, most preferably 0.1 to 0.2 N.

32. The method according to claim 17, wherein for washing in step h), aliphatic Cx-C₃ alcohols are used, preferably methanol.

33. The method according to claim 17, wherein the obtained PEKK is washed in step h) at a temperature of 20°C to 160°C, preferably 50°C to 120°C, most preferably 60°C to 100°C.

34. The method according to claim 17, wherein the obtained PEKK is washed in step h) for 0.5 to 12 hours, preferably 3 to 8 hours, most preferably 5 to 6 hours.

35. The method according to claim 17, wherein the PEKK is dried at a temperature of 165 to 240°C, preferably 170 to 210°C, most preferably 175 to 185°C.

36. The method according to claim 17, wherein the PEKK has an intrinsic viscosity of 0.97 to 1.07 cm³/g.