Preparation method of polysulfone with stable color and reduced yellowness

Abstract

The invention discloses a preparation method of polysulfone with stable color and reduced yellowness, which comprises the following steps: by using N-methyl pyrrolidone as a reaction solvent, reacting bisphenol A with 4, 4 '-dichlorodiphenyl sulfone in the presence of an acid-binding agent to generate polysulfone; wherein the N-methyl pyrrolidone contains N-methyl pyrrolidone peroxide, and the molar content of the N-methyl pyrrolidone peroxide in the N-methyl pyrrolidone is less than or equal to 0.05%. The polysulfone with stable color and reduced yellowness value can be synthesized by controlling the content of peroxide impurities in the N-methyl pyrrolidone.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials and relates to a method for preparing polysulfone, in particular to a method for preparing polysulfone with stable color and reduced yellowness. Background Art

[0002] Polysulfone plastics are amorphous thermoplastics. They have strong mechanical properties, excellent heat resistance, oxidation resistance, water resistance, and flame retardancy. They are widely used in water treatment membranes, medical equipment, food utensils and other fields. Polysulfone generally refers to bisphenol A type polysulfone, which is prepared by Farnham nucleophilic reaction of bisphenol A and 4,4-dichlorodiphenyl sulfone under the action of alkali. Commonly used reaction solvents include N,N-dimethylacetamide, N,N-dimethylformamide, cyclopentane, dimethyl sulfoxide, N-methylpyrrolidone, etc. Usually, in order to remove the water generated by the reaction, it is necessary to add water-carrying agents such as xylene, toluene, and chlorobenzene. After the reaction is completed, it is precipitated and crushed in water. The obtained polymer powder is purified and dried, and extruded and granulated to obtain polysulfone particles.

[0003] Compared with polycarbonate, the physical and chemical properties of polysulfone are similar, but the commercial use of polycarbonate is more extensive, part of which is that the color of polysulfone is unstable, usually yellow or amber. The oxidation of phenolate end groups to quinones during the synthesis process is a major cause of polysulfone yellowing. US 6420514B1 has announced that reducing ortho-ortho isomers and ortho-para isomers in bisphenol A can reduce the coloring of polysulfone, because the ortho phenolic hydroxyl group is more easily oxidized to dark quinones than the para phenolic hydroxyl group. In addition, under the acceptable reaction rate, the amount of alkali and alkalinity should be controlled to be minimum during the reaction, such as using weak base potassium carbonate, sodium carbonate can reduce the formation of quinone coloring substances. AU2001241824B2 has announced a method for preparing low-color polyphenyl sulfone using anhydrous potassium carbonate with small particle size. End-capping after the reaction is completed to reduce the content of phenolate end groups, or acidifying the phenolate end groups to phenolic hydroxyl groups that are not easy to oxidize by acidification can also reduce the coloring of polysulfone. Most patents use methyl chloride as a capping agent. In addition, WO2023019862A1 discloses a method for preparing light-colored polysulfone using p-hydroxybenzenesulfonic acid, p-aminophenol, etc. as capping agents. CN115010926A discloses a method for preparing polysulfone with better optical properties using water-soluble sodium 2-bromoethylsulfonate, 1,3-propane sultone, etc. as capping agents. CN115894923A discloses a method for preparing polysulfone with low color and high transparency by washing polysulfone powder with dilute hydrochloric acid.

[0004] Compared with N,N-dimethylacetamide, N,N-dimethylformamide, sulfolane, dimethyl sulfoxide and other solvents for the synthesis of polysulfone, N-methylpyrrolidone has many advantages, such as fast reaction rate, no need for additional water-carrying agent, lower residual monomer content, etc. However, it is also found that when N-methylpyrrolidone is used to synthesize polysulfone, there are also disadvantages such as darker color during the reaction process, darker color of the final polymer, and large color difference between different batches.

[0005] Therefore, it is necessary to develop a new method for preparing polysulfone using N-methylpyrrolidone as a solvent to obtain batches of polysulfone products with stable and light colors, and expand its application in the optical field. Summary of the invention

[0006] In view of the problem that when N-methylpyrrolidone is used as a solvent for synthesizing polysulfone, the reaction process and the product have dark colors and a large color difference between batches, the present invention aims to provide a method for preparing polysulfone with stable color and reduced yellowness.

[0007] The technicians of the present invention unexpectedly found in the experiment of synthesizing polysulfone that there are some peroxides in N-methylpyrrolidone, and the presence of the peroxide is the main influencing factor of the product color. Further analysis found that this may be due to the fact that N-methylpyrrolidone is easily oxidized in the air, producing N-methylpyrrolidone peroxide with strong oxidizing property, which will oxidize the phenolate end group of polysulfone to dark quinone in the reaction of synthesizing polysulfone, resulting in a higher yellowness of polysulfone, and different batches of N-methylpyrrolidone have different peroxide contents due to different storage environments and storage times, resulting in unstable color of the prepared polysulfone, and the yellowness value of polysulfone can be increased from 10 to 30 or even higher. Therefore, by controlling the content of the peroxide within a certain range, the color problem existing when N-methylpyrrolidone is used as a polysulfone synthesis solvent can be effectively solved.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solution:

[0009] The invention provides a method for preparing polysulfone with stable color and reduced yellowness, comprising using N-methylpyrrolidone as a reaction solvent, reacting bisphenol A (i.e. 2,2-bis(4-hydroxyphenyl)propane) with 4,4'-dichlorodiphenyl sulfone in the presence of an acid binding agent to generate polysulfone;

[0010] The N-methylpyrrolidone contains N-methylpyrrolidone peroxide, and the molar content of the N-methylpyrrolidone peroxide in the N-methylpyrrolidone is denoted as m, m≤0.05%, such as 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, preferably 0<m≤0.05%, more preferably 0.01%≤m≤0.02%.

[0011] In the present invention, the yellowness index (YI) of the polysulfone is between 6-9.

[0012] In the present invention, the yellowness can be tested by referring to a common method such as ASTM E313 standard; the content of N-methylpyrrolidone peroxide can be obtained by conventional methods such as nuclear magnetic resonance hydrogen spectrum, chromatography and the like.

[0013] In some specific examples of the present invention, the N-methylpyrrolidone peroxide comprises a structure as shown in formula (1):

[0014]

[0015] Generally, the lower the content of N-methylpyrrolidone peroxide in N-methylpyrrolidone, the better. However, since N-methylpyrrolidone is easily oxidized in the air, a certain amount of N-methylpyrrolidone peroxide will inevitably exist, and its content will hardly be 0. In addition, a certain amount of peroxide will continue to be generated due to the mixing of a small amount of air during the storage process, which will continue to increase with the extension of the storage time, resulting in a higher yellowness of the polysulfone and a large color difference between different batches.

[0016] In the method described in the present invention, the N-methylpyrrolidone solvent used needs to control the molar content of N-methylpyrrolidone peroxide therein to be ≤0.05%. The N-methylpyrrolidone product within this ratio range can be directly purchased or prepared by any feasible method. The present invention has no special restrictions on its source. For example, it can be obtained by conventional physical separation methods such as adsorption and distillation, or by chemical conversion methods such as reduction. Among them, the control of N-methylpyrrolidone peroxide by methods such as adsorption or distillation mainly involves purifying the raw materials by means of adsorption, distillation, etc. to improve its purity. The specific process can refer to the prior art; the control of N-methylpyrrolidone peroxide by chemical conversion methods such as reduction is to purify it by adding peroxide reactive substances to improve its purity.

[0017] Based on existing research, the present invention has found a preferred solution for controlling the peroxide content in N-methylpyrrolidone solvent, by adding a small amount of reducing compound to N-methylpyrrolidone, the molar content of peroxide in N-methylpyrrolidone can be reduced to below 0.05%.

[0018] In some specific examples of the present invention, the present invention provides a method for controlling the peroxide content in N-methylpyrrolidone, which is to add a reducing compound to N-methylpyrrolidone with a high peroxide content to react so that the molar content of peroxide in N-methylpyrrolidone m≤0.05%, for example 0.01%, 0.02%, 0.03%, 0.04%, 0.05%.

[0019] In the present invention, the molar content of peroxide in the N-methylpyrrolidone with a high peroxide content may be above 0.05%, such as 0.06%, 0.1%, 0.5%, 1.0%, preferably 0.06-0.5%.

[0020] In the present invention, the reducing compound is a reducing salt compound;

[0021] Preferably, the reducing salt compound is selected from one or more of sodium dithionite, ferrous sulfate, lithium aluminum hydride, sodium bis(2-methoxyethoxy)aluminum hydride, sodium borohydride, and potassium borohydride;

[0022] Preferably, the ratio of the amount of the reducing compound added to the molar amount of peroxide in N-methylpyrrolidone is 0.1-0.5:1, such as 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, preferably 0.2-0.3:1.

[0023] In the present invention, the reaction temperature is 90-170°C, such as 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, preferably 110-150°C, and the reaction time is 1-3h, such as 1h, 2h, 3h, preferably 2-3h;

[0024] After the reaction is completed, operations such as vacuum distillation and purification are also included, which belong to the conventional separation technology available in the field and are not required in detail.

[0025] It should be noted that the above method disclosed in the present invention is only an exemplary description of controlling the peroxide content in N-methylpyrrolidone, and the source of the N-methylpyrrolidone raw material described in the present invention should not be limited by the above method.

[0026] In some specific examples of the present invention, the molar ratio of bisphenol A to 4,4'-dichlorodiphenyl sulfone is 0.98-1.02:1, such as 0.98:1, 0.99:1, 1.00:1, 1.005:1, 1.01:1, 1.02:1, preferably 1-1.005:1.

[0027] In some specific examples of the present invention, the acid-binding agent is selected from inorganic alkaline compounds, preferably one or more of potassium carbonate, sodium carbonate, potassium hydroxide, and sodium hydroxide, more preferably potassium carbonate.

[0028] In some specific examples of the present invention, the amount of the acid binding agent is 1-1.3 times the molar amount of bisphenol A, such as 1.0 times, 1.1 times, 1.2 times, 1.3 times, preferably 1.1-1.2 times.

[0029] In some specific examples of the present invention, the amount of N-methylpyrrolidone used is 280-2000 g, for example, 280 g, 300 g, 400 g, 600 g, 800 g, 1000 g, 1500 g, 2000 g, preferably 400-1000 g, based on each mole of bisphenol A.

[0030] In some specific examples of the present invention, bisphenol A is reacted with 4,4-dichlorodiphenyl sulfone in N-methylpyrrolidone solvent, and the reaction temperature is 180-200°C, such as 180°C, 185°C, 190°C, 195°C, 200°C, preferably 190-200°C, and the reaction time is 2-5h, such as 2h, 3h, 4h, 5h, preferably 3-4h;

[0031] Preferably, the reaction process is carried out in stages. In the first stage, the system temperature is raised to 180-190°C, such as 180°C, 185°C, 190°C, and the reaction is carried out for 0.5-2h, such as 0.5h, 1.0h, 1.5h, 2.0h. In the second stage, the system temperature is raised to 190-200°C, such as 190°C, 195°C, 200°C, and the reaction is continued for 1.5-3h, such as 1.5h, 2.0h, 2.5h, 3.0h.

[0032] Since small molecules of water are generated during polymerization in the reaction process, removing water from the reaction process is more conducive to continuous polymerization. The water can be removed by conventional methods such as azeotropy and distillation, and there are no special requirements. For example, the water can be removed by azeotropy with N-methylpyrrolidone solvent. Preferably, after the first stage reaction is completed, the water is removed by azeotropy with part of the N-methylpyrrolidone solvent, and then the second stage reaction is carried out. More preferably, the removed part of N-methylpyrrolidone accounts for 5-10% of the total amount of N-methylpyrrolidone, such as 5%, 6%, 7%, 8%, 9%, 10%.

[0033] In some specific examples of the present invention, the reaction is carried out in a nitrogen atmosphere.

[0034] In the present invention, after the reaction is completed, conventional post-treatment operations such as solid precipitation, filtration, and washing are also included. Preferably, after the reaction system is cooled to room temperature, it is added into pure water to precipitate polysulfone solid, which is crushed into powder, filtered, and then added with pure water for washing and desalting, filtered, and dried. For details, reference may be made to the prior art.

[0035] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0036] The present invention uses N-methylpyrrolidone as the polymerization solvent, has the advantages of fast reaction rate, no need to add additional water-carrying agents such as xylene, toluene, chlorobenzene, etc., lower residual monomer content, etc., simplifies the polymerization process, and reduces the cost of waste liquid recovery.

[0037] The invention controls the peroxide content in N-methylpyrrolidone to be lower than 0.05 mol %, so as to obtain a polysulfone product with stable color between different batches and low yellowness value, thereby expanding its application in the optical field. DETAILED DESCRIPTION

[0038] The method provided by the present invention is further described below by way of examples, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0039] The sources of the main raw materials in the examples and comparative examples of the present invention are as follows. Unless otherwise specified, other raw materials and reagents were purchased from commercial sources:

[0040] 4,4'-Dichlorodiphenyl sulfone: Hebei Xulong, high purity (≥99.5%);

[0041] Bisphenol A: Inokai, high purity (≥99.5%);

[0042] N-Methylpyrrolidone: Binzhou Yuneng, electronic grade (≥99.9%);

[0043] Potassium carbonate: Uni-Dex, superior quality (≥99.0%);

[0044] Sodium dithionite: Inokane, purity 85%.

[0045] The main test methods used in the embodiments of the present invention and the comparative examples are as follows:

[0046] Yellowness value: tested according to ASTM E313 standard, measured by molding polysulfone powder at 300°C to form a 2mm thick sample.

[0047] The content of N-methylpyrrolidone peroxide was measured by hydrogen nuclear magnetic spectroscopy: the testing instrument was Bruker AVANCENeo 600 MHz, the solvent was deuterated DMSO-d6, the characteristic chemical shifts were 1.91 ppm and 11.45 ppm (see the formula below), and the content of N-methylpyrrolidone peroxide was obtained by integrating the two characteristic hydrogen area ratios.

[0048]

[0049] Example 1

[0050] 1) reducing the molar content of N-methylpyrrolidone peroxide in the N-methylpyrrolidone solvent, the steps are:

[0051] Take N-methylpyrrolidone (990g, 10mol), wherein the peroxide content is 0.40mol%, add sodium dithionite (1.74g, 0.01mol) thereto, react at 120°C for 2h, and then distill under reduced pressure to obtain N-methylpyrrolidone, wherein the peroxide content of N-methylpyrrolidone is reduced to 0.02mol%.

[0052] 2) Preparation of polysulfone, the steps are:

[0053] In a 5L reactor protected by nitrogen, 4,4'-dichlorodiphenyl sulfone (574.32g, 2mol) and bisphenol A (456.58g, 2mol) were added in sequence, and then 800g of N-methylpyrrolidone in step 1) was added, and stirred until the solid dissolved. Potassium carbonate (304.04g, 2.2mol) was added to the reactor, and the system temperature was stirred and heated to 180°C, and the reaction was kept warm for 0.5h. 78g of N-methylpyrrolidone solvent was removed by distillation to azeotropically remove water, and then the temperature was raised to 200°C and the reaction was continued for 3h. After the reaction was completed, the system was cooled to room temperature, added to pure water to precipitate polysulfone solid, crushed into powder, filtered, and then washed three times with pure water to remove salt, filtered and dried to obtain polysulfone powder, and its yellowness value YI=7.6 was tested by tableting.

[0054] Example 2

[0055] 1) reducing the molar content of N-methylpyrrolidone peroxide in the N-methylpyrrolidone solvent, the steps are:

[0056] Take N-methylpyrrolidone (990g, 10mol), wherein the peroxide content is 0.25mol%, add ferrous sulfate (1.9g, 0.0125mol) thereto, react at 90°C for 3h, and then distill under reduced pressure to obtain N-methylpyrrolidone, wherein the peroxide content of N-methylpyrrolidone is reduced to 0.01mol%.

[0057] 2) Preparation of polysulfone, the steps are:

[0058] In a 500mL reaction bottle filled with nitrogen protection, 4,4'-dichlorodiphenyl sulfone (58.58g, 0.204mol) and bisphenol A (45.66g, 0.2mol) were added in sequence, and then 160g of N-methylpyrrolidone in step 1) was added, and stirred until the solid was dissolved. Potassium carbonate (33.16g, 0.24mol) was added to the reaction bottle, and the system temperature was stirred and heated to 190°C, and the reaction was kept warm for 1.5h. 11g of N-methylpyrrolidone solvent was removed by distillation to azeotropically remove water, and then the temperature was raised to 200°C and the reaction was continued for 1.5h. After the reaction was completed, the system was cooled to room temperature, added to pure water to precipitate polysulfone solid, crushed into powder, filtered, and then washed three times with pure water to remove salt, filtered and dried to obtain polysulfone powder, and its yellowness value YI=6.5 was tested by tableting.

[0059] Example 3

[0060] 1) reducing the molar content of N-methylpyrrolidone peroxide in the N-methylpyrrolidone solvent, the steps are:

[0061] Take N-methylpyrrolidone (990g, 10mol), wherein the peroxide content is 0.45mol%, add sodium borohydride (0.17g, 0.0045mol) thereto, react at 170°C for 1h, and then distill under reduced pressure to obtain N-methylpyrrolidone, wherein the peroxide content of N-methylpyrrolidone is reduced to 0.05mol%.

[0062] 2) Preparation of polysulfone, the steps are:

[0063] In a 500mL reaction bottle filled with nitrogen protection, 4,4'-dichlorodiphenyl sulfone (56.28g, 0.196mol) and bisphenol A (45.66g, 0.2mol) were added in sequence, and then 200g of N-methylpyrrolidone in step 1) was added, and stirred until the solid was dissolved. Potassium carbonate (33.16g, 0.24mol) was added to the reaction bottle, and the system temperature was stirred and heated to 180°C, and the reaction was kept warm for 2h. 12g of N-methylpyrrolidone solvent was removed by distillation to azeotropically remove water, and then the temperature was raised to 190°C to continue the reaction for 1.5h. After the reaction was completed, the system was cooled to room temperature, added to pure water to precipitate polysulfone solid, crushed into powder, filtered, and then washed three times with pure water to remove salt, filtered and dried to obtain polysulfone powder, and its yellowness value YI=8.1 was tested by tableting.

[0064] Example 4

[0065] 1) reducing the molar content of N-methylpyrrolidone peroxide in the N-methylpyrrolidone solvent, the steps are:

[0066] Take N-methylpyrrolidone (990g, 10mol), wherein the peroxide content is 0.40mol%, add it into a distillation column for fractionation, the distillation column is 30cm high, the filler is 2*2mm triangular spiral ring, the oil temperature is 120℃, the distillation temperature is 78℃, the pressure is 20mbar, and N-methylpyrrolidone is obtained, wherein the peroxide content of N-methylpyrrolidone is reduced to 0.03mol%.

[0067] 2) Preparation of polysulfone, the steps are similar to those of Example 3, and the yellowness value of the prepared polysulfone is YI=7.8 after tableting test.

[0068] Comparative Example 1

[0069] Polysulfone was prepared by referring to the method of Example 3, except that: N-methylpyrrolidone directly purchased was used, wherein the content of N-methylpyrrolidone peroxide was 0.15 mol %, and other operations and conditions remained unchanged to obtain polysulfone powder, and its yellowness value YI was tested to be 15.

[0070] Comparative Example 2

[0071] Polysulfone was prepared by referring to the method of Example 3, except that: the N-methylpyrrolidone used was the N-methylpyrrolidone used in Comparative Example 1 which was opened and left for 2 weeks before use, wherein the content of N-methylpyrrolidone peroxide was increased to 0.40 mol %, and other operations and conditions remained unchanged, to obtain polysulfone powder, and its yellowness value YI was tested to be 22.

[0072] Comparative Example 3

[0073] Polysulfone was prepared by referring to the method of Example 3, except that fresh N-methylpyrrolidone was used as raw material, wherein the content of N-methylpyrrolidone peroxide was 0.06 mol %, and other operations and conditions remained unchanged to obtain polysulfone powder, and its yellowness value YI was tested to be 10.

Claims

1. A method for preparing polysulfone with stable color and reduced yellowness, characterized in that: The method comprises using N-methylpyrrolidone as a reaction solvent, reacting bisphenol A with 4,4'-dichlorodiphenyl sulfone in the presence of an acid binding agent to generate polysulfone; The N-methylpyrrolidone contains N-methylpyrrolidone peroxide, and the molar content of the N-methylpyrrolidone peroxide in the N-methylpyrrolidone is denoted as m, m≤0.05%, preferably 0<m≤0.05%, and more preferably 0.01%≤m≤0.02%.

2. The preparation method according to claim 1, characterized in that: The N-methylpyrrolidone peroxide comprises a structure as shown in formula (1):

3. The preparation method according to claim 1 or 2, characterized in that: The method comprises adding a reducing compound to N-methylpyrrolidone with a high peroxide content to carry out a reaction so that the molar peroxide content of N-methylpyrrolidone is less than or equal to 0.05%.

4. The preparation method according to claim 3, characterized in that: The N-methylpyrrolidone with a high peroxide content has a molar peroxide content of more than 0.05%, preferably 0.06-0.5%.

5. The preparation method according to claim 3, characterized in that: The reducing compound is a reducing salt compound; Preferably, the reducing salt compound is selected from one or more of sodium dithionite, ferrous sulfate, lithium aluminum hydride, sodium bis(2-methoxyethoxy)aluminum hydride, sodium borohydride, and potassium borohydride; Preferably, the ratio of the amount of the reducing compound added to the molar amount of the peroxide in N-methylpyrrolidone is 0.1-0.5:1, preferably 0.2-0.3:1; and / or The reaction temperature is 90-170°C, preferably 110-150°C, and the reaction time is 1-3h, preferably 2-3h.

6. The preparation method according to claim 1, characterized in that: The molar ratio of bisphenol A to 4,4'-dichlorodiphenyl sulfone is 0.98-1.02:1, preferably 1-1.005:

1.

7. The preparation method according to claim 1, characterized in that: The acid-binding agent is selected from inorganic alkaline compounds, preferably one or more of potassium carbonate, sodium carbonate, potassium hydroxide, and sodium hydroxide, more preferably potassium carbonate; and / or The amount of the acid binding agent used is 1-1.3 times the molar amount of bisphenol A, preferably 1.1-1.2 times.

8. The preparation method according to claim 1, characterized in that: The amount of N-methylpyrrolidone used is 280-2000 g, preferably 400-1000 g, based on each mole of bisphenol A.

9. The preparation method according to claim 1, characterized in that: The reaction temperature is 180-200°C, preferably 190-200°C, and the time is 2-5h, preferably 3-4h; Preferably, the reaction process is carried out in stages. In the first stage, the system temperature is raised to 180-190°C and the reaction is carried out for 0.5-2h. In the second stage, the system temperature is raised to 190-200°C and the reaction is continued for 1.5-3h. Preferably, after the first stage reaction is completed, water is removed by azeotropic removal of part of the N-methylpyrrolidone solvent, and then the second stage reaction is carried out; more preferably, the part of N-methylpyrrolidone removed accounts for 5-10% of the total amount of N-methylpyrrolidone.

10. The preparation method according to claim 1, characterized in that: The reaction was carried out under nitrogen atmosphere.

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