Method for producing polyethersulfone

Abstract

The invention relates to polyethersulfones which can be used as engineering thermoplastics and also as polymers suitable for use in membrane technologies. A method for producing a polyethersulfone includes carrying out a nucleophilic polycondensation between 4,4'dioxydiphenyl sulfone and 4,4'dichlorodiphenyl sulfone in the presence of potassium carbonate in an aprotic solvent environment in two steps of: a) obtaining a dipotassium salt of 4,4'dioxydiphenyl sulfone and b) adding 4,4'dichlorodiphenyl sulfone to the salt obtained in the first step, then holding the resulting mixture while controlling the viscosity thereof to provide a mixture containing a polyethersulfone in a dissolved form in which the mass fraction of the polymer is from 50.5 to 53.3%, isolating the polyethersulfone and drying same. The invention makes it possible to produce a high-molecular-weight polyethersulfone having a controlled set mass-average molecular mass of from 85340 to 104300 g / mol, rendering the polymer suitable for use in the production of finished articles.

Description

[0001] METHOD FOR PRODUCING POLYETHERSULFONE

[0002] FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0003] The invention relates to a method for producing aromatic polyethersulfones, specifically polyethersulfone (PESU), which belongs to a class of polymeric materials with high performance characteristics, enabling its use as an engineering structural thermoplastic in industries such as aerospace, electronics, automotive, and others. PESU also possesses chemical and hydrolytic resistance, enabling its use in acidic and alkaline environments, as well as for the production of membranes for separating solution mixtures at temperatures up to 180°C.

[0004] LEVEL OF TECHNOLOGY

[0005] The synthesis of aromatic polysulfones, including their variety—polyethersulfones (PESUs), is carried out by nucleophilic polycondensation in one or two stages. In the two-stage process known from GB1153035 (ICI LTD, published May 21, 1969) and US4108837 (UNION CARBIDE CORP., published August 22, 1978), a phenolate is formed in the first stage by the interaction of aqueous alkali solutions with bisphenols. This phenolate then reacts with a dihaloaromatic compound in the second stage to form a polymer.

[0006] From US4156068 (ICI Americas Inc., published 22.05.1979) a one-stage process for the preparation of high-molecular polyethersulfones is also known under conditions of simultaneous loading of dihalogendiphenylsulfone monomer, 3,3',5,5'-tetraalkyl-4,4'-dihydroxybiphenyl and from 0 to 30% stoichiometric excess of alkali metal carbonate in an aprotic solvent medium under conditions of a stepwise increase in temperature to the synthesis temperature and holding until the required viscosity value is achieved. The synthesis temperature depends on the solvent used and the reactivity of the monomers, where the solvents are compounds selected from the group consisting of dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), dimethyl sulfone (DMS), dimethylacetamide (DMAA).

[0007] RU2005737 (Artemov Sergey Vasilyevich, published 15.01.1994) describes a method for producing PESU by reacting aromatic bisphenols and halogenaromatic sulfones in a solvent medium in the presence of an alkaline agent, in particular 4,4'-dioxydiphenyl sulfone with 4,4'-dichlorodiphenyl sulfone in an equimolar ratio in the presence of a mixture of potassium carbonate and potassium hydrogen carbonate in dimethyl sulfone at a reaction temperature of 230 to 235°C. The resulting polymer is characterized by a reduced viscosity in dimethylformamide equal to 0.47 dl / g.However, while solving the technical problem of eliminating the need for precise dosing of the alkaline agent and using a single solvent at all stages of the process, this invention has the following drawbacks: the need for new technological operations to grind the solid polymer solution, lengthy washing of the resulting polymer from the solvent and formed salts, and the difficulty of regenerating the solid solvent—dimethyl sulfone. RU2440381 (BASF SE, published 20.01.2012) discloses a method for producing polysulfones and PESU, which are characterized by a reduced yellowness index: less than 19 for polysulfones and less than 30 for PESU, respectively, as well as increased light transmittance of more than 85% inclusive and turbidity of less than 3%, and can be used to produce dialyzer membranes.The method according to this invention is implemented by nucleophilic polycondensation of equimolar amounts of dihydroxydiphenylsulfone, dichlorodiphenylsulfone, and potassium carbonate, dried, in N-methylpyrrolidone solvent at a reaction temperature of 190°C, followed by chain termination by cooling the reaction mixture to 140°C and treating it with methyl chloride (10 l / h) using a forced-flow anchor stirrer with a d / D ratio greater than 0.9, ensuring cross-flow. These conditions lead to the achievement of the technical effect. However, disadvantages of the process include the high reaction temperature and the use of gaseous chloromethane, which is toxic to humans, which complicates the technical equipment of the process.

[0008] Also, application EP0347669 (BAYER AG, published 27.12.1989) discloses a method for producing high-molecular-weight polyethersulfones (PES) by reacting equimolar amounts of diphenols with dihaloarylene in the presence of anhydrous alkali carbonate in an amount of 1.0 - 1.2 mol of carbonate per mol of diphenol in a polar aprotic solvent selected from the group of N-alkylated acid amides with boiling points in the range from 150 to 270 °C. In particular, N-methylpyrrolidone or N-methylcapro lactam are used as solvent. The reaction takes place under conditions of complete removal of water formed as a result of the reaction, at temperatures from 5 to 20 °C below the boiling point of the corresponding acid amide with the formation of an azeotrope in the form of a mixture of the acid amide and water. To isolate the polymer from the reaction solution, precipitation is carried out with methanol at a temperature of 60°C, followed by filtration, washing with water and drying.The reduced viscosity of the obtained polymer, measured at 0.2 g of polymer in 100 ml of chloroform and a temperature of 25°C, is 0.52 dl / g, as shown in Example 1. Similar to Example 1, PES with a viscosity of 0.49 dl / g is obtained using 4, 4-dihydroxybiphenyl as the dihydroxy compound, PES with a viscosity of 0.35 dl / g and 0.40 dl / g based on tetramethylbisphenol-A and 4,4'-dihydroxydiphenylsulfone as the bisphenol, respectively. The high process temperature and the use of large quantities of methanol complicate the implementation of the claimed invention on an industrial scale.

[0009] US4156068 (ICI Americas Inc., published 05 / 22 / 1979) describes a method for producing high-molecular polyethersulfones with a molecular weight Mw from 20,000 to 125,000 g / mol by reacting equimolecular amounts of 3,3',5,5'-tetraalkyl-4,4'-dihydroxybiphenyl

[0010] (tetramethylbiphenol) with 4,4'-dihalodiphenylsulfone in the presence of a stoichiometric excess of alkali metal carbonate or bicarbonate relative to dihydroxybiphenyl in a dipolar aprotic solvent using an entrainer to remove the resulting water. The resulting products are characterized by good solvent resistance and tensile strength. For example, according to examples 2-7, the molecular weight of the resulting polymers ranges from 46,000 to 90,000 g / mol, were obtained by the reaction of tetramethylbiphenol with 4,4'-dichlorodiphenylsulfone (DCDFS) in a mixture of dimethylacetamide (DMAA) and toluene in the presence of an excess of potassium carbonate against the stoichiometry of 5 to 26%, under inert conditions and gradual heating to a temperature of 150 to 165 °C to distill off the toluene. The resulting product is off-white, spongy solid, with low bulk density, and the reduced viscosity (0.2 g polymer in 100 ml chloroform) ranges from 0.42 to 1.08 dl / g.The disadvantages of this method include the use of tetramethylbiphenol as a biphenol - a more scarce and specific main reagent, a long reaction time, and the use of toluene (an azeotropic agent) complicates the process.

[0011] US108837 (Union Carbide Corp., published 22.08.1978) discloses a process for the preparation of polyethersulfone by reacting 2,2'-bis(4-hydroxyphenyl)propane with 4,4'-dichlorodiphenylsulfone (DCDS) in an equimolecular ratio, according to which, in the first step, bisphenol-A and a solution of potassium hydroxide in a mixture of dimethyl sulfoxide and benzene are reacted in an inert atmosphere at a temperature of from 130 to 135°C to obtain the dipotassium salt under conditions of continuous removal of water in the form of an azeotrope with benzene. In the second step, DCDS and an additional 40 ml of DMSO are added to the reaction mixture obtained in the first step, followed by maintaining at a temperature of from 130 to 140°C under conditions of sufficient stirring. The resulting polymer was isolated by adding the polymer solution to water and vacuum drying at 110°C. The polymer was purified by dissolving it in tetrachloroethane and rinsing it sequentially with acetic acid, water, and methanol.The viscosity of the resulting polyethersulfone, measured in chloroform (0.2 g polymer in 100 ml at 25°C), is 0.59 dl / g. Polyethersulfone film products obtained by compression molding of powder at 270°C and pressures from 2 to 3000 psi show the following results: tensile modulus of 293,000 psi, tensile strength of 10,200 psi, elongation at break of 7%. The disadvantages of this invention are the high consumption rates of methanol at the reprecipitation stage, as well as double filtration, which increases the process time and complicates the equipment design.

[0012] Patent RU2063404 (OJSC "G.S. Petrov Research Institute of Plastics," published July 10, 1996) proposes a method for producing aromatic polyesters, specifically polyether ketone, polyether sulfone, and their copolymers, used as superstructural polymeric materials. This method involves the nucleophilic substitution reaction of a polyaromatic nucleophilic reagent with a haloaromatic compound in an aprotic solvent in the presence of an alkaline agent upon heating. The alkaline agent used is potassium carbonate in combination with an equimolecular mixture of sodium sulfide nonaqueous and aluminum trioxide or silicon disulfide. The polyethersulfones obtained according to this invention are characterized by a high impact strength value (from 163 to 208 kJ / m2) with a narrower molecular weight distribution (about 1.8), surpassing in these indicators the polyethersulfone obtained in accordance with the prototype (control example 12).However, the main difference of this invention, which is the use of a carbonate system and a mixture of sodium sulfide nonahydrate with aluminum trioxide or silicon dioxide, also presents a drawback. Sodium sulfide nonahydrate is a difficult product to process, as it has light-sensitive hygroscopic properties, oxidizes in air, and can cause irritation when in contact with mucous membranes and skin.

[0013] As the methods presented above demonstrate, they are not without their drawbacks. Therefore, a pressing challenge is the development of technologically advanced and controlled methods for producing polyethersulfone suitable for use at high temperatures in various applications, including electronics, automotive, aerospace, carbon fiber composites, food contact products, and, especially, membranes based on it.

[0014] DISCLOSURE OF THE INVENTION

[0015] The objective of the invention is to develop a method for producing polyethersulfone (PESU) for the manufacture of membranes based on it, which makes it possible to achieve the required molecular weight characteristics of the polymer under conditions of a controlled polycondensation reaction.

[0016] The technical result consists of obtaining a PESU whose viscosity index in dimethylacetaminophen (DMAA) at 40°C ranges from 58.6 to 71.6 ml / g. Another technical result is obtaining a PESU characterized by a weight-average molecular weight of 85,340 to 104,300 g / mol. This technical task and the achievement of the technical result are ensured by carrying out nucleophilic polycondensation between 4,4'-dioxydiphenyl sulfone (DODFS) and 4,4'-dichlorodiphenyl sulfone (DCDS) in the presence of potassium carbonate in an aprotic solvent in two stages: 1. obtaining the dipotassium salt of DODFS, 2. adding the required amount of DCDS to the salt obtained in the first stage to obtain PESU under conditions of constant bubbling of the system with an inert gas, distillation and addition of the required amount of aprotic solvent to provide a mixture essentially containing PESU in dissolved form, in which the mass fraction of the polymer is from 50.5 to 53.5%.

[0017] PESU is isolated by pre-diluting the mixture to a PESU content of 20 to 24%, followed by polymer isolation using any known method. The resulting PESU is typically vacuum-dried to remove residual solvent and water.

[0018] The present inventors have unexpectedly discovered that by synthesizing PESU through the intermediate production of the dipotassium salt of DODPS, controlling the mass fraction of the polymer in the resulting mixture during the reaction, as well as controlling the viscosity of the mixture during the holding stage, it is possible to obtain a high-molecular-weight PESU, the value of the specified weight-average molecular weight of which is controlled, which in turn ensures the applicability of the polymer for the manufacture of finished products, in particular membranes for various purposes. DESCRIPTION OF FIGURES

[0019] To explain the technical solutions that reveal the essence of the present invention, Fig. 1 is presented.

[0020] Fig. 1 shows the curves of viscosity versus time during the holding of mixture 3 to obtain a mixture including PESU.

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0022] The following is a description of various embodiments of the present invention.

[0023] To eliminate the disadvantages indicated in the prior art, a method according to the present invention is proposed.

[0024] In accordance with the present invention, the method for producing PESU comprises the following stages:

[0025] Obtaining mixture 1 by mixing a pre-prepared mixture containing 4,4'-dioxydiphenyl sulfone (DODPS) and potassium carbonate in an aprotic solvent;

[0026] Obtaining mixture 2 at a reaction temperature equal to the boiling point of the aprotic solvent, under conditions of distillation of the solvent and water;

[0027] Mixing mixture 2 with 4,4'-dichloro diphenyl sulfone (DCDS) and DMAA at the reaction temperature to obtain mixture 3;

[0028] Maintaining mixture 3 at the reaction temperature under conditions of distillation of the solvent and water to obtain a PESU solution;

[0029] Isolation of PESU from PESU solution to obtain PESU;

[0030] Drying of PESU to obtain PESU. 4,4'-dihydroxy diphenyl sulfone (DODPS) and 4,4'- dichlorodiphenyl sulfone (DCHDPS) are used as monomers to obtain polyethersulfone, which has the following repeating unit structure:

[0031] Potassium carbonate is used as an alkaline agent to produce the dipotassium salt of DODPS for the subsequent production of PESU under the conditions of the present invention. The potassium carbonate according to the present invention does not contain any hydrocarbonates. The presence of hydrocarbonates in potassium carbonate reduces the rate of the nucleophilic polycondensation reaction, as it has lower activity than carbonate, which in turn does not ensure the achievement of the technical result. In one embodiment of the invention, potassium carbonate is obtained by preliminary heat treatment at a temperature of 270 to 455°C, preferably 445 to 455°C.

[0032] In one embodiment of the invention, the potassium carbonate is characterized by an average particle size of no more than 50 μm, preferably no more than 35 μm.

[0033] An aprotic solvent is used as the reaction solvent, typically selected from the group consisting of dimethyl sulfoxide, dimethylacetamide (DMAA), N-methylpyrrolidone, dimethyl sulfone, diphenyl sulfone, preferably DMAA. The term "mixture 1" in the context of this invention means a mixture of 4,4'-dioxydiphenyl sulfone (DODPS), potassium carbonate and an aprotic solvent until it is heated to a reaction temperature at which the dipotassium salt of DODPS is essentially not yet formed.

[0034] The term "mixture 2" in the context of the present invention means a mixture which essentially contains the insoluble dipotassium salt of DODPS in the reaction solvent.

[0035] The term "blend 3" in the context of this invention means a mixture that essentially contains nucleophilic polycondensation products between the dipotassium salt of DODPS and DCHDPS, including PESU. Blend 3 is characterized in that the mass fraction of PESU in said mixture is from 50.5 to 53.5%.

[0036] The term “mixture” means that the mixture obtained during the nucleophilic polycondensation reaction of DODPS and DCHDPS under the conditions of the present invention before the isolation step is essentially PESU dissolved in the reaction solvent, as well as possibly minor amounts of potassium salts insoluble in the reaction solvent.

[0037] The difference between mixture 3 and mixture is the different viscosity, the values ​​of which are disclosed below.

[0038] To obtain mixture 1, DODFS and potassium carbonate are used.

[0039] The amount of potassium carbonate used is typically in excess, determined relative to the amount of DODFS. In one embodiment of the invention, the molar excess of potassium carbonate relative to DODFS is at least 20 mol%, preferably at least 25 mol%. The order of mixing the components to obtain mixture 2 can generally be any; preferably, the premixed DODFS and potassium carbonate are added to an aprotic solvent.

[0040] Next, the resulting mixture 1 is used to obtain mixture 2.

[0041] The temperature for obtaining mixture 2 depends on the aprotic solvent used and is, as a rule, the boiling point of the corresponding solvent.

[0042] In one embodiment of the invention, the reaction time for obtaining mixture 2 essentially consists of the time it takes to maintain mixture 1 under stirring at the boiling point of the reaction solvent and distill off the mixture of the selected solvent and the water formed during the reaction. The time it takes to maintain the mixture at the reaction temperature typically ranges from 2 to 4 hours, preferably from 2.5 to 3 hours.

[0043] The stirring speed at the stage of obtaining mixture 2 is not less than 200 rpm, preferably not less than 150 rpm.

[0044] To effectively remove aprotic solvent vapor and water from the reaction medium, the system is continuously purged with an inert gas. The inert gas is selected from a group including argon, nitrogen, and helium, preferably nitrogen.

[0045] Then the resulting mixture 2 is used to obtain mixture 3.

[0046] For this purpose, DCDF and an aprotic solvent are added to the resulting mixture 2 at the boiling point of the aprotic solvent under conditions of distillation of the mixture of solvent and water.

[0047] In one embodiment of the invention, the distillation time of the aprotic solvent and water mixture ranges from 2 to 3 hours. Typically, the amount of DCDFS is calculated as a stoichiometric amount relative to DOPDS, so the molar ratio of DCDFS to DODFS is 1.

[0048] The molar ratio of DCDF to aprotic solvent at the stage of obtaining mixture 3 is from 1.0:1.35 to 1.0:1.40.

[0049] The temperature for obtaining mixture 3 depends on the aprotic solvent used and is, as a rule, the boiling point of the corresponding solvent.

[0050] The resulting mixture 3 includes PESU and is essentially a solution of PESU in an aprotic solvent.

[0051] The mass fraction of PESU in mixture 3 ranges from 50.5 to 53.5%.

[0052] The resulting mixture 3 is then used to obtain a mixture according to the claimed invention.

[0053] The reaction temperature for obtaining the mixture depends on the aprotic solvent used and is usually equal to the boiling point of the corresponding solvent.

[0054] To obtain a mixture essentially containing PESU, the obtained mixture 3 is maintained at the reaction temperature under conditions of distillation of the mixture of aprotic solvent with water.

[0055] During the curing process, a nucleophilic polycondensation reaction occurs, forming a mixture. This curing process is performed to achieve the desired molecular weight characteristics of the PESU. This is achieved by controlling the polymer mass fraction in the mixture and the viscosity during the curing stage.

[0056] Maintaining the mixture of an aprotic solvent and water under distillation conditions is typically accomplished by adding the required amount of aprotic solvent to dilute the mixture and ensure that the mass fraction of PESU in the mixture is between 50.5 and 53.5%, preferably between 52 and 52.5%. When the mass fraction of PESU in the solvent is less than 50.5% and the synthesis conditions according to the claimed invention are met, the molecular weight required for producing membranes from PESU is not achieved and is less than 85,000 g / mol. Moreover, when the mass fraction of PESU in the solvent is greater than 53.5%, the viscosity of the mixture including PESU reaches high values, which impede effective mixing of the system. This results in stagnant zones in the mixture and an uneven accumulation of molecular weight, which ultimately leads to failure to achieve the required molecular weight characteristics of the product.

[0057] In one embodiment of the invention, the required amount of aprotic solvent is added during the aging process by periodically adding a portion of the solvent during the aging stage, ensuring that the mass fraction of the PESU in the mixture is between 50.5 and 53.5%. The moment of adding the next portion of aprotic solvent is determined by the amount (mass) of the distilled mixture of aprotic solvent and water under the aging conditions.

[0058] The required amount of solvent is determined based on the formula for calculating the mass fraction of PESU in the mixture, equal to 50.5 to 53.5%, which is determined by the following ratio: where shpol is the mass fraction of the polymer in the mixture; shpol is the mass of the polymer; mp-lya is the mass of the aprotic solvent; wKCl is the mass of potassium chloride formed during the synthesis; mK2CO3 is the mass of potassium carbonate; wH2O is the mass of water formed during the synthesis; mCO2 is the mass of carbon dioxide formed during the synthesis.

[0059] The reaction flow diagram for obtaining PESU according to the present invention is presented in Figure 1, on the basis of which the values ​​of the masses of the compounds are calculated, as determined by the formula for calculating the mass fraction of PESU in the mixture:

[0060] Figure 1 - Scheme of the reaction for obtaining PESU

[0061] The holding time, in one embodiment of the invention, is from 5 to 20 hours, preferably from 10 to 20 hours, most preferably from 17 to 20 hours, with the formation of the mixture according to the invention. The holding time, in the context of this invention, is the total amount of time the mixture 3 is held in step d), determined in hours, which is sufficient for the reaction to produce PESU in the selected aprotic solvent.

[0062] From the moment of obtaining mass 3 to the moment of obtaining the mixture, the characteristics of mixture 3 change due to the increase in the molecular weight of the PESU formed during synthesis. The increase in the molecular weight of the polymer in mixture 3 is accompanied by a consistent change in its viscosity characteristics. Effective control of achieving the desired molecular weight characteristics is only possible by adhering to the synthesis conditions according to the present invention. These conditions consist of controlling the process by maintaining the mass fraction of PESU in mixture 3 and in the resulting mixture and changing the viscosity of mixture 3 over time, i.e., during maintenance at the reaction temperature.

[0063] It will be apparent to those skilled in the art that the holding time for mixture 3 to obtain the mixture will vary depending on the aprotic solvent used. For example, in DMAA, the total holding time is up to 20 hours, as shown in the Examples, while in N-methylpyrrolidone, it is up to 7 hours. The total holding time for mixture 3 to obtain the mixture depends on the reaction rate, which in turn is determined by the varying solvating capacity of the aprotic solvent and its boiling point, which is essentially the synthesis temperature according to the present invention.

[0064] Thus, for the nucleophilic polycondensation process according to the present invention, it is important to control the viscosity of mixture 3 at certain stages of step d) under conditions of maintaining the mass fraction of PESU from 50.5 to 53.5%. According to the present invention, the viscosity of mixture 3 at step d) for up to 49% inclusive of the total holding time should be no more than 25 Pa*s, and for 50% inclusive of the total holding time - no less than 26 Pa*s. More preferably, the viscosity of mixture 3 for up to 30% inclusive of the total holding time is no more than 15 Pa*s, and for 65% inclusive of the total holding time - no less than 35 Pa*s. In the most preferred embodiment of the invention, the viscosity of mixture 3 for up to 20% inclusive of the total holding time is no more than 10 Pa* s, and for 65% inclusive of the slope of the straight line is from 7000 to 8500.

[0065] Fig. 1 shows the viscosity dependence curve during holding at stage d), from which a regular increase in the viscosity of mixture 3 can be seen.

[0066] After completing step d), a mixture containing PESU is obtained, where, according to the present invention, the PESU weight fraction ranges from 50.5 to 53.5%. Controlling the viscosity of the mixture allows for achieving the desired molecular weight characteristics. Accordingly, if the viscosity values, preferably the slope of the curve, are not met, it is advisable to terminate the synthesis by cooling the mixture and further isolating the PESU. This controls the polymer's characteristics, resulting in a PESU suitable for the manufacture of membranes based on it.

[0067] The PESU is separated from the mixture using a method known in the art, such as concentrating the mixture by thin-film evaporation and precipitating the mixture in water followed by rinsing with water. Separating the PESU by thin-film evaporation produces PESU granules, while precipitating it in water produces PESU powder. It's worth noting that the method of separating the PESU from the mixture does not affect the final properties of the product, but it does result in different product forms.

[0068] In one embodiment of the invention, to isolate the PESU, the mixture is cooled to a temperature below the boiling point of the aprotic solvent used, followed by dilution of the mixture with a mass fraction of the PESU from 50.5 to 53.5% by adding the required amount of aprotic solvent for dilution and achieving a mass fraction of the PESU in the mixture from 20 to 24%.

[0069] The amount of added aprotic solvent to dilute the mixture is calculated based on the formula for calculating the mass fraction of PESU in the mixture specified above.

[0070] The diluted mixture obtained according to the present invention is optionally treated to modify the end groups of the PESU. During such polymer treatment, the treating agent replaces potassium in the polymer end groups, which promotes polymer stabilization. Methyl chloride is typically used as a treating agent to modify end groups. In one embodiment, treatment with gaseous methyl chloride is carried out at a temperature of 110°C to 125°C while bubbling the mixture for 30 to 45 minutes at a flow rate of 10 l / h.

[0071] In order to remove insoluble reaction products, for example, carbonates, solid KCl, hydrocarbonates, in one embodiment of the invention, the resulting mixture is filtered using a method known from the prior art, using, for example, vacuum filtration, centrifugal filtration, centrifugation.

[0072] Thin-film evaporation is carried out by heating the mixture obtained according to the invention to a temperature of 285 to 320°C. Precipitation is carried out by gradually adding the mixture, which contains 20 to 24% PESU after dilution, to a protic solvent, preferably demineralized water, while stirring. This results in a suspension of white, flake-like PESU particles in a mixture of protic and aprotic solvents. The PESU particles are separated using a method known in the art to obtain crude PESU.

[0073] Additionally, in one embodiment of the invention, the resulting crude PESU is washed with boiling demineralized water under stirring to remove inorganic potassium compounds and residual aprotic solvent. The number of washes typically ranges from 3 to 5, preferably from 3 to 4. The washed PESU particles are separated using a method known in the art.

[0074] Drying of raw PESU is typically carried out at a temperature sufficient to remove the aprotic solvent, which typically ranges from 120 to 150°C. Drying is typically carried out at a residual pressure of no more than 150 mmHg until the polymer reaches a constant weight, yielding PESU.

[0075] Thus, during the implementation of the claimed method, a PESU is obtained that has the characteristics necessary for the production of membranes for various purposes, in particular, an average molecular weight from 85340 to 104300 g / mol and a viscosity number ranging from 58.6 to 71.6 ml / g.

[0076] IMPLEMENTATION OF THE INVENTION

[0077] To determine the average molecular weight of the obtained PESU, the gel permeation chromatography method is used in accordance with GOST R 57268.1-2016 "Polymer composites. Determination of the average molecular weight and molecular weight distribution of polymers by size-exclusion chromatography" and the requirements of GOST R 57268.3-2016 "Polymer composites. Determination of the average molecular weight and molecular weight distribution of polymers by size-exclusion chromatography. Part 3. Low-temperature method". The determination was carried out using a high-temperature, high-pressure chromatograph from Water, Alliance GPCV 2000, equipped with a Styragel HT 6E chromatographic column with dimensions of 300x7.8 mm. Detection is carried out with a refractometric detector. Freshly distilled N-methylpyrrolidone is used as an eluent at a flow rate of 1 cm3 / min. The concentration of the sample solutions in the eluent was approximately 1 mg / ml, the injected sample volume was 20 µl. The analysis temperature was 80°C.The chromatographic system was calibrated using polystyrene standards in NMP at 80°C. Styragel HR 5E and HR 4E columns were used to determine the cyclic dimer content.

[0078] The viscosity number in DMAA is determined according to GOST 18249-72 using the viscometric method, in which a solution of PESU in DMAA is prepared at a concentration of 1.0 g of polymer in 100 ml of DMAA.

[0079] The glass transition temperature is determined by differential scanning calorimetry on a DSC8500 Perkin Elmer instrument according to GOST R 55135-2012 with a heating rate of 20°C / min.

[0080] The viscosity of the PESU mixture during synthesis was determined viscometrically using a rotational rheometer. The measurement system consisted of parallel plates, each measuring plate having a diameter of 25 mm. For this test, the mixture viscosity was measured at different points during the holding stage. A mixture sample was placed on the lower plate heated to reaction temperature, after which the upper measuring plate was lowered, leaving a gap of 0.5 mm between the plates. The sample was then thermostatted for 60 seconds, and viscosity was measured in rotational mode at a constant shear rate of 200 s-1.

[0081] The invention is illustrated by the following examples:

[0082] Example 1 (according to the invention).

[0083] A four-necked flask equipped with a stirrer, thermometer, capillary for supplying inert gas, and a condenser is charged with 215 g of DMAA. The reaction flask is connected to an argon flow rate of 0.1 l / min to create an inert atmosphere that prevents oxidation of the monomers. Then a pre-prepared mixture of 62.57 g of 4,4'-dioxydiphenylsulfone (0.25 mol) and 43.2 g (0.3125 mol) of potassium carbonate is charged. The mixture is heated to a temperature of 165 °C and 50 g of the solvent-water mixture is distilled off for 2.5 h, after which 71.79 g of dichlorodiphenylsulfone (0.25 mol) and 30 g of DMAA are charged. The molar ratio of DODFS and DHDFS is 1. After this, another 125 g of the solvent-water mixture is distilled off over 3 hours. The mass fraction of the polymer in the mixture is 53.5%.

[0084] The reaction mixture is then maintained at reflux temperature for 17 hours, with volatile components continuously distilled off and fresh DMAA added. The polymer content in the reaction mixture at the end of the process is 52.0%. The reaction mixture is then diluted with DMAA to a polymer content of 23%, stirred until homogenized, vacuum filtered to remove the formed salts, and the polymer is isolated by precipitation in water. After rinsing four times with hot water, the product is dried at 120°C under vacuum. The polymer yield is 98%.

[0085] Polyethersulfone characteristics: viscosity number 67 ml / g (measured in DMAA at a concentration of 1.0 g polymer in 100 ml solvent), glass transition temperature 232°C, average molecular weight Mw is 103400 g / mol, polydispersity coefficient 2.7.

[0086] Example 2 (according to the invention).

[0087] A four-necked flask equipped with a stirrer, thermometer, capillary for supplying inert gas, and a condenser is charged with 215 g of DMAA. The reaction flask is connected to an argon flow rate of 0.1 l / min to create an inert atmosphere that prevents oxidation of the monomers. Then a pre-prepared mixture of 62.57 g of 4,4'-dioxydiphenylsulfone (0.25 mol) and 43.2 g (0.3125 mol) of potassium carbonate is charged. The mixture is heated to a temperature of 165 °C and 50 g of the solvent-water mixture is distilled off for 2.75 h, after which 71.79 g of dichlorodiphenylsulfone (0.25 mol) and 30 g of DMAA are charged. The molar ratio of DODFS and DHDFS is 1. After this, another 125 g of the solvent-water mixture is distilled off over 3 hours. The mass fraction of the polymer in the mixture is 53.3%.

[0088] The reaction mixture is then maintained at reflux temperature for 17 hours, with volatile components continuously distilled off and fresh DMAA added. The polymer content in the reaction mixture at the end of the process is 50.5%. The reaction mixture is then diluted with DMAA to a polymer content of 23%, stirred until homogenized, vacuum filtered to remove the formed salts, and the polymer is isolated by precipitation in water. After rinsing four times with hot water, the product is dried at 120°C under vacuum. The polymer yield is 98%.

[0089] Polyethersulfone characteristics: viscosity number 63 ml / g (measured in DMAA at a concentration of 1.0 g polymer in 100 ml solvent), glass transition temperature 232°C, average molecular weight Mw is 99000 g / mol, polydispersity coefficient 2.6.

[0090] Example 3 (according to the invention).

[0091] A four-necked flask equipped with a stirrer, thermometer, capillary for supplying inert gas, and a condenser is charged with 215 g of DMAA. The reaction flask is connected to an argon stream with a flow rate of 0.1 l / min to create an inert atmosphere that prevents oxidation of the monomers. Then a pre-prepared mixture of 62.57 g of 4,4'-dioxydiphenylsulfone (0.25 mol) and 43.2 g (0.3125 mol) of potassium carbonate is charged. The mixture is heated to a temperature of 165 °C and 50 g of the solvent-water mixture is distilled off for 3.0 h, after which 71.79 g of dichlorodiphenylsulfone (0.25 mol) and 30 g of DMAA are charged. The molar ratio of DODFS and DHDFS is 1. After this, another 125 g of solvent is distilled off with water for 3 hours. The mass fraction of the polymer in the mixture is 53.3%.

[0092] The reaction mixture is then maintained at reflux temperature for 17 hours, with volatile components continuously distilled off and fresh DMAA added. The polymer content in the reaction mixture at the end of the process is 53.5%. The reaction mixture is then diluted with DMAA to a polymer content of 23%, stirred until homogenized, vacuum filtered to remove the formed salts, and the polymer is isolated by precipitation in water. After rinsing four times with hot water, the product is dried at 120°C under vacuum. The polymer yield is 98%.

[0093] Polyethersulfone characteristics: viscosity number 67 ml / g (measured in DMAA at a concentration of 1.0 g polymer in 100 ml solvent), glass transition temperature 231 °C, average molecular weight Mw is 104000 g / mol, polydispersity coefficient 2.5.

[0094] Example 4 (comparative example).

[0095] Carry out the same procedure as in Example 1, but with simultaneous loading of all reagents.

[0096] 215 g of DMAA are charged into a four-necked flask equipped with a stirrer, thermometer, capillary for supplying inert gas and a condenser. The reaction flask is connected to an argon stream with a flow rate of 0.1 l / min to create an inert atmosphere that prevents oxidation of the monomers. Then 62.57 g of 4,4'-dioxydiphenyl sulfone (0.25 mol), 71.79 g of dichlorodiphenyl sulfone (0.25 mol) and 43.2 g (0.3125 mol) of potassium carbonate are charged. The molar ratio of DODFS and DCDFS is 1. The mixture is heated to a temperature of 165 °C and 145 g of the solvent-water mixture is distilled off for 2.75 h. The mass fraction of the polymer in the mixture is 53.3%.

[0097] The reaction mixture is then maintained at reflux temperature for 17 hours, with volatile components continuously distilled off and fresh DMAA added. The polymer content of the reaction mixture at the end of the process is 52.5%. The reaction mixture is then diluted with DMAA to a polymer content of 23%, stirred until homogenized, vacuum filtered to remove the formed salts, and the polymer is isolated by precipitation in water. After washing four times with hot water, the product is dried at 120°C under vacuum. The polymer yield is 97%.

[0098] Polyethersulfone characteristics: viscosity number 50 ml / g (measured in DMAA at a concentration of 1.0 g polymer in 100 ml solvent), glass transition temperature 232°C, average molecular weight Mw is 80200 g / mol, polydispersity coefficient 2.9.

[0099] Example 5 (comparative example).

[0100] It is carried out as in Example 1, but the value of the mass fraction of PESU in the mixture is 41%.

[0101] A four-necked flask equipped with a stirrer, thermometer, capillary for supplying an inert gas, and a condenser is charged with 215 g of DMAA. The reaction flask is connected to an argon (or nitrogen) flow rate of 0.1 l / min to create an inert atmosphere that prevents oxidation of the monomers. Then a thoroughly mixed mixture of 62.57 g of 4,4'-dioxydiphenylsulfone (0.25 mol) and 43.2 g (0.3125 mol) of potassium carbonate is charged. The mixture is heated to a temperature of 165 °C and 50 g of the solvent-water mixture is distilled off over 3.0 h. After this, 71.79 g of dichlorodiphenylsulfone (0.25 mol) and 30 g of DMAA are charged. The molar ratio of DODFS and DHDFS is 1. After this, another 60 g of the solvent-water mixture is distilled off over 2.5 hours. The mass fraction of the polymer in the mixture is 41%.

[0102] The reaction mixture is then maintained for 17 hours at boiling temperature, with volatile components continuously distilled off and fresh DMAA added. The polymer content of the reaction mixture is 41%.

[0103] The reaction mixture is then diluted with DMAA to a polymer content of 23%, stirred until homogenized, vacuum filtered to remove the formed salts, and the polymer is isolated by precipitation in water. After washing four times with hot water, the product is dried at 120°C under vacuum. The polymer yield is 98%.

[0104] Polyethersulfone characteristics: viscosity number 52 ml / g (measured in DMAA at a concentration of 1.0 g polymer in 100 ml solvent), glass transition temperature 233 °C, average molecular weight Mw is 84300 g / mol, polydispersity coefficient 3.0.

[0105] Example 6 (comparative example).

[0106] It is carried out as in Example 1, but with the simultaneous loading of all reagents, and the value of the mass fraction of PESU in the mixture is 41%.

[0107] 215 g of DMAA are charged into a four-necked flask equipped with a stirrer, thermometer, capillary for supplying inert gas and a condenser. The reaction flask is connected to an argon (or nitrogen) stream with a flow rate of 0.1 l / min to create an inert atmosphere that prevents oxidation of the monomers. Then 62.57 g of 4,4'-dioxydiphenylsulfone (0.25 mol), 71.79 g of dichlorodiphenylsulfone (0.25 mol), 43.2 g (0.3125 mol) of potassium carbonate are charged. The molar ratio of DODPS and DCDPS is 1. The mixture is heated to a temperature of 165 °C and 80 g of the solvent-water mixture is distilled off for 3.0 h. The mass fraction of the polymer in the mixture is 41%. The reaction mixture is then maintained for 17 hours at boiling temperature, with volatile components continuously distilled off and fresh DMAA added. The polymer content of the reaction mixture ranges from 39 to 41%.

[0108] The reaction mixture is then diluted with DMAA to a polymer content of 23%, stirred until homogenized, vacuum filtered to remove the formed salts, and the polymer is isolated by precipitation in water. After washing four times with hot water, the product is dried at 120°C under vacuum. The polymer yield is 98%.

[0109] Polyethersulfone characteristics: viscosity number 46 ml / g (measured in DMAA at a concentration of 1.0 g polymer in 100 ml solvent), glass transition temperature 232°C, average molecular weight Mw is 53240 g / mol, polydispersity coefficient 2.8.

[0110] Thus, as can be seen from Examples 1-6, the required characteristics of the PESU are achieved only through the following set of mandatory synthesis conditions: obtaining the PESU through the intermediate production of the dipotassium salt of DODPS, as well as controlling the mass fraction of the PESU in mixture 3 and in the mixture, equal to 50.5 to 53.5%, and the viscosity of mixture 3 at step d), which for up to 49% inclusive of the total holding time is no more than 25 Pa*s, and for 50% inclusive of the total holding time is no less than 26 Pa*s. Changing the conditions leads to a significant change in the molecular weight parameters of the polymer, which is unacceptable for cases of PESU application in the membrane industry.

Claims

CLAUSES OF THE INVENTION 1. A method for producing polyethersulfone, comprising the following steps: a. mixing 4,4'-dioxydiphenyl sulfone (DODPS), potassium carbonate and an aprotic solvent to obtain mixture 1; b. obtaining mixture 2 at the boiling point of the aprotic solvent under conditions of distillation of the mixture of solvent and water; c. mixing the mixture 2 and 4,4'-dichloro diphenyl sulfone (DCDPS) and an aprotic solvent at the boiling point of the aprotic solvent under conditions of distillation of the mixture of solvent and water to obtain mixture 3; d. maintaining mixture 3 at the boiling point of the aprotic solvent under conditions of distillation of the mixture of solvent and water at a viscosity of mixture 3 that is no more than 25 Pa*s for up to 49% inclusive of the total holding time, and no less than 26 Pa*s for 50% inclusive of the total holding time, to obtain a mixture; e. isolating the PESU from the mixture to obtain the PESU; f. drying the PESU to obtain the PESU, wherein the mass fraction of the PESU in steps c) and d) is from 50.5 to 53.5%.

2. The method according to step 1, wherein preliminary mixing of DODFS and potassium carbonate before adding to the aprotic solvent in step a) is preferred.

3. The method according to item 1, wherein in step a) the molar excess of potassium carbonate in relation to DODFS is at least 20 mol.%, preferably at least 25 mol.%.

4. The method according to claim 1, wherein the aprotic solvent is selected from the group comprising dimethyl sulfoxide, dimethylacetamide (DMAA), N- methylpyrrolidone, dimethylsulfone, diphenylsulfone, preferably DMAA.

5. The method according to claim 1, wherein the molar ratio of DODFS and DHDFS is 1.

6. The method according to claim 1, wherein the molar ratio of DCDF to the aprotic solvent in step c) is from 1.0:1.35 to 1.0:1.

40.

7. The method according to claim 1, wherein the time for distilling off the mixture of aprotic solvent and water in step c) is from 2 to 3 hours.

8. The method according to claim 1, wherein the total holding time in step d) is from 5 to 20 hours, preferably from 10 to 20 hours, most preferably from 17 to 20 hours.

9. The method according to claim 1, wherein the mixture obtained in step d) is characterized by a viscosity that is preferably no more than 15 Pa* s for up to and including 30% of the total holding time, and no less than 35 Pa* s for up to and including 65% of the total holding time.

10. The method according to claim 1, wherein the mixture obtained in step d) is characterized by a viscosity which is most preferably no more than 10 Pa* s for up to and including 20% ​​of the total holding time.

11. The method according to claim 1, wherein the mixture obtained in step d) is characterized by a viscosity, the curve of which has a slope equal to 7000 to 8500 for 65% of the total holding time.

12. The method according to claim 1, wherein the mixture obtained in step d) is cooled in step e) to a temperature equal to below the boiling point of the aprotic solvent.

13. The method according to claim 1, wherein the mass fraction of PESU in the mixture at step e) is from 20 to 24%. 30 14. The method according to claim 1, wherein the temperature of treatment of the mixture in step e) with methyl chloride is from 10 to 125 °C.

15. The method according to claim 14, wherein the time of treatment of the mixture in step e) with methyl chloride is from 30 to 45 minutes.

16. The method according to claim 1, where in step e) the mixture is isolated by a method selected from: precipitation in demineralized water with stirring followed by filtration and obtaining PESU, thin-film evaporation.

17. The method according to item 1, where the drying temperature of the PESU is from 120 to 150°C.

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