Purification method of cast film grade polyethersulfone resin and the obtained product

Abstract

The present invention provides a method for purifying a cast-grade polyethersulfone resin and the resulting product, and belongs to the technical field of organic compound purification. The present invention improves the traditional polyethersulfone purification process, and removes most of the polymers in the polymer through three steps of high-temperature dissolution of the polymer and addition of a precipitating agent, low-temperature precipitation, and boiling and washing. The mixed solvent (waste liquid generated by dissolution and precipitation and waste liquid generated by washing) can be recovered by molecular distillation equipment, which optimizes the production process, reduces production costs, improves polymer quality, and can realize industrial production. In addition, the present invention can separate polymers of different molecular weights by using the above process, so that the prepared polyethersulfone product has the advantages of low content of polymers, high purity, narrow molecular weight distribution, etc., and the prepared membrane material can have excellent optical and mechanical properties, and has good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of organic compound purification, and in particular relates to a purification method of a cast-grade polyethersulfone resin and the obtained product. Background Art

[0002] Polyethersulfone resin is a special engineering material with good application prospects. Due to its good chemical stability, excellent heat resistance and mechanical stability, it can be processed into various types of profiles, synthetic fibers, composite materials, metal and ceramic material substitutes, and can be effectively used in hemodialysis, sewage treatment and other fields.

[0003] The commonly used polyethersulfone synthesis method is the high-temperature solution polycondensation method. The raw materials are bisphenol S, 4,4'-dichlorodiphenyl sulfone, potassium carbonate or sodium carbonate, etc. In addition to polyethersulfone, the polymerization also contains by-products such as inorganic salts, organic solvents and oligomers. Therefore, the crude polyethersulfone needs to be purified before the next processing and application.

[0004] Traditional polyethersulfone purification mostly adopts the forward precipitation method, that is, deionized water is added to the polymer solution to precipitate polyethersulfone through phase separation, but this purification method still causes the polymer to wrap a large amount of byproduct inorganic salts, and it is impossible to separate low molecular weight polymers, which easily leads to the problem of low purity and wide molecular weight distribution of polyethersulfone. Further, due to the poor solubility of polymers, they are easy to crystallize and precipitate during the dissolution and processing of polyethersulfone, causing machine blockage, which is also very easy to affect the overall performance of polyethersulfone membrane. In addition, traditional polyethersulfone purification mostly uses a large amount of deionized water for multiple high-temperature boiling and washing to remove the solvent and inorganic salts wrapped in the polymer, but this will undoubtedly produce a large amount of sewage, consume a lot of energy, high cost and pollute the environment. Therefore, it is necessary to design and develop a new and simplified purification method for polyethersulfone polymers, so that the obtained polyethersulfone product has low polymer content, high purity and narrow molecular weight distribution, so as to effectively improve the performance of polyethersulfone products. Summary of the invention

[0005] The invention provides a method for purifying a cast-grade polyethersulfone resin and a product obtained therefrom. The method adopts a method in which a precipitating agent is added after the polymer is dissolved at high temperature and the polymer is naturally precipitated at low temperature, so that polymers with different molecular weights can be separated, and the prepared polyethersulfone product has the advantages of low oligomer content, high purity, narrow molecular weight distribution, etc. The prepared membrane material can have excellent optical and mechanical properties and has good application prospects.

[0006] In order to achieve the above object, the present invention provides a method for purifying a cast-grade polyethersulfone resin, comprising the following steps:

[0007] The polyethersulfone polymer is dissolved in a solvent at 130°C to 150°C, and a precipitating agent is added dropwise into the system while stirring and the system is kept homogeneous, and then the system is allowed to stand and gradually cooled to room temperature to precipitate crystals;

[0008] After the crystals are completely precipitated, the obtained polyethersulfone polymer is separated from the system solvent by filtration, and the collected polymer is repeatedly soaked, boiled and washed with methanol, and dried to obtain a casting grade polyethersulfone resin.

[0009] Preferably, the polyethersulfone polymer is heated and dissolved in a solvent under nitrogen protection to obtain a homogeneous polymer solution with a polyethersulfone solution concentration of 12% to 15%.

[0010] Preferably, the solvent is selected from at least one of dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide and sulfolane.

[0011] Preferably, the precipitation agent is selected from at least one of acetonitrile, methanol, ethanol and acetone; the amount of the precipitation agent added is 10% to 15% of the mass of the polymer solution. It is understandable that if the amount of precipitation agent added is too much, a large amount of polymer will be precipitated, resulting in a high content of oligomers; while if the amount of precipitation agent added is too little, the polymer precipitation is insufficient, resulting in the loss of part of the polymer.

[0012] Preferably, the precipitation agent has a dropping speed of 20-40 ml / min. It is understood that if the dropping speed of the precipitation agent is too fast, the polymer will be precipitated quickly, and the separation of polymers with different molecular weights cannot be achieved; while if the dropping speed is too slow, the overall precipitation time will be slowed down.

[0013] Preferably, the static cooling is performed by cooling with ice water or natural cooling.

[0014] The collected polymer is soaked and boiled in methanol at 45°C to 55°C for 30 to 50 minutes, and the boiling and washing is repeated 3 to 5 times; the drying temperature is 100°C to 120°C, and the drying time is 6h to 10h.

[0015] Preferably, the method further comprises the steps of separating the remaining system solvent by fractional distillation using a molecular distillation device and recovering the solvents separately.

[0016] The present invention provides a casting-grade polyethersulfone resin obtained by the purification method described in any one of the above technical solutions.

[0017] Preferably, the oligomer content is ≤0.24%, the purity is ≥99.969%, the molecular weight distribution is between 1.6 and 2.0, and the ash content is ≤0.031%.

[0018] The present invention provides a membrane material, which is prepared by using the casting-grade polyethersulfone resin prepared by the purification method described in any one of the above technical solutions or the casting-grade polyethersulfone resin described in any one of the technical solutions.

[0019] Compared with the prior art, the advantages and positive effects of the present invention are:

[0020] 1. The present invention improves the traditional polyethersulfone purification process. Most of the polymers in the polymer are removed through three steps: high-temperature dissolution of the polymer and addition of a precipitating agent, low-temperature precipitation, and boiling and washing. The mixed solvent (waste liquid generated by dissolution and precipitation and waste liquid generated by washing) can be recovered by molecular distillation equipment, which optimizes the production process, reduces production costs, improves polymer quality, and can realize industrial production.

[0021] 2. The present invention adopts a method in which a precipitating agent is added after the polymer is dissolved at high temperature and the precipitating agent is naturally precipitated at low temperature, which can achieve the separation of polymers with different molecular weights and low molecular weight oligomers are not easy to precipitate, so that the prepared polyethersulfone product has the advantages of low oligomer content, high purity, narrow molecular weight distribution, etc. In this way, when it is used for subsequent processing, the clogging of the film casting machine can be effectively avoided, and various problems that occur when the traditional polyethersulfone resin is cast can be solved quickly. A casting solution with high transparency can be obtained, and the film material prepared based on it has excellent optical and mechanical properties and has good application prospects. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1

[0024] In a four-necked flask with a stirrer, a condenser, and a nitrogen inlet, 50 g of Solvay 3000 p polyethersulfone resin and 360 g of NMP solvent were added, and heated to 130 ° C under nitrogen protection to fully dissolve it. 50 g of acetonitrile precipitant was added to the solution at a rate of 40 ml / min, and the system always maintained a homogeneous system. After the acetonitrile was added, it was stirred for 10 min, and then the polymerization solution was allowed to stand and cool. When it dropped to room temperature, polyethersulfone gradually crystallized from the system. After it was completely precipitated, the polymer was filtered and separated from the mixed solvent with a filter, and soaked and washed with methanol solution at 45 ° C for 50 min, and the washing was repeated 5 times. After drying in an oven at 120 ° C for 6 h, a high-purity polyethersulfone resin was obtained. The mixed solvent produced during the purification process and the methanol solvent after washing were separated by molecular distillation equipment, and methanol, acetonitrile, NMP and oligomers were recovered respectively, so as to realize the reuse of methanol, acetonitrile and NMP solvents.

[0025] The polyethersulfone before and after purification was tested by gel permeation chromatography (GPC) using the method in GB / T 21863, and the ash content was tested using the method in GB / T 9345.1. The test results showed that the polymer content of the polyethersulfone was reduced from 2.5% before purification to 0.24%, the molecular weight distribution was reduced from 2.5 before purification to 1.8, and the ash content was reduced from 0.3% before purification to 0.025%.

[0026] Example 2

[0027] Add 50 g of Solvay 3000 p polyethersulfone resin and 360 g of DMAC solvent to a four-necked flask with a stirrer, a condenser and a nitrogen inlet, heat to 135 ° C under nitrogen protection to fully dissolve it, and drop 50 g of methanol precipitant into the solution at a rate of 30 ml / min. The system always maintains a homogeneous system. After the methanol is added, continue to stir for 10 min, then let the polymer solution stand and cool down. When it drops to room temperature, polyethersulfone gradually crystallizes from the system. After the precipitation is complete, filter and separate the polymer from the mixed solvent with a filter, soak and boil with methanol solution at 50 ° C for 40 min, repeat boiling and washing 4 times, and dry in an oven at 100 ° C for 12 h to obtain a high-purity polyethersulfone resin. The mixed solvent produced during the purification process and the methanol solvent after boiling and washing are separated by molecular distillation equipment, and methanol, NMP and oligomers are recovered respectively, so as to realize the reuse of methanol and NMP solvents.

[0028] The polyethersulfone before and after purification was tested by gel permeation chromatography (GPC) using the method in GB / T 21863, and the ash content was tested using the method in GB / T 9345.1. The test results showed that the polymer content of the polyethersulfone was reduced from 2.5% before purification to 0.20%, the molecular weight distribution was reduced from 2.5 before purification to 1.6, and the ash content was reduced from 0.3% before purification to 0.010%.

[0029] Example 3

[0030] In a four-necked flask with a stirrer, a condenser, and a nitrogen inlet, 50 g of Solvay 3000 p polyethersulfone resin and 360 g of DMSO solvent were added, and the mixture was heated to 140 ° C under nitrogen protection to fully dissolve it. 60 g of ethanol precipitant was added to the solution at a rate of 25 ml / min, and the system always maintained a homogeneous system. After the ethanol was added, the stirring was continued for 10 min, and then the polymerization solution was allowed to stand and cool. When it dropped to room temperature, polyethersulfone gradually crystallized from the system. After the precipitation was complete, the polymer was filtered and separated from the mixed solvent with a filter, and the mixture was soaked and washed with methanol solution at 55 ° C for 30 min, and the washing was repeated 3 times. After drying in an oven at 110 ° C for 10 h, a high-purity polyethersulfone resin was obtained. The mixed solvent produced during the purification process and the methanol solvent after washing were separated by molecular distillation equipment, and methanol, ethanol, NMP and oligomers were recovered respectively, so as to realize the reuse of methanol, ethanol and NMP solvents.

[0031] The polyethersulfone before and after purification was tested by gel permeation chromatography (GPC) using the method in GB / T 21863, and the ash content was tested using the method in GB / T 9345.1. The test results showed that the oligomer content of the polyethersulfone was reduced from 2.5% before purification to 0.23%, the molecular weight distribution was reduced from 2.5 before purification to 1.8, and the ash content was reduced from 0.3% before purification to 0.020%.

[0032] Example 4

[0033] In a four-necked flask with a stirrer, a condenser, and a nitrogen inlet, 50 g of Solvay 3000 p polyethersulfone resin and 360 g of cyclopentane solvent were added, and heated to 150 ° C under nitrogen protection to fully dissolve it. 60 g of acetone precipitant was added to the solution at a rate of 20 ml / min, and the system always maintained a homogeneous system. After the acetone was added, it was stirred for 10 minutes, and then the polymerization solution was allowed to stand and cool. When it dropped to room temperature, polyethersulfone gradually crystallized from the system. After it was completely precipitated, the polymer was filtered and separated from the mixed solvent with a filter, and soaked and washed with methanol solution at 50 ° C for 30 minutes, and the washing was repeated 4 times. After drying in an oven at 120 ° C for 6 hours, a high-purity polyethersulfone resin was obtained. The mixed solvent produced during the purification process and the methanol solvent after washing were separated by molecular distillation equipment, and methanol, acetone, NMP and oligomers were recovered respectively, so as to realize the reuse of methanol, acetone and NMP solvents.

[0034] The polyethersulfone before and after purification was tested by gel permeation chromatography (GPC) using the method in GB / T 21863, and the ash content was tested using the method in GB / T 9345.1. The test results showed that the polymer content of the polyethersulfone was reduced from 2.5% before purification to 0.24%, the molecular weight distribution was reduced from 2.5 before purification to 2.0, and the ash content was reduced from 0.3% before purification to 0.031%.

[0035] Comparative Example 1

[0036] 50g brand Solvay 3000p polyethersulfone resin is added to the funnel body of the constant pressure dropping funnel, and the lower end of the constant pressure dropping funnel is sealed and connected with the 250mL three-necked flask below, and 100mL of 15-crown ether-5 is contained in the three-necked flask, and zeolite is put into it. The upper end of the constant pressure dropping funnel is sealed and connected with the condenser tube. The solvent in the three-necked flask is heated by a heating jacket, and the steam enters the condenser tube through the balance tube of the constant pressure dropping funnel and liquefies. The condensate drips into the funnel body of the constant pressure dropping funnel, and the resin is purified and cleaned. By adjusting the rotary switch at the lower end of the funnel body, the liquid level is always above the polyethersulfone resin and does not overflow to the condenser tube. After 5 hours of reflux, the filtrate is collected by filtering with filter paper. The obtained filtrate is evaporated to dryness. The steamed 15-crown ether-5 is added to the aforementioned three-necked flask again, and the above steps are repeated to extract the extracted polyethersulfone resin for the second time. Repeat the above steps again to extract for the third time.

[0037] The polyethersulfone oligomer content and molecular weight distribution of the examples and comparative examples are shown in Table 1 below.

[0038] Table 1

[0039]

[0040] From the above experimental results, it can be seen that the purification method of adding a precipitating agent after dissolving the polyethersulfone polymer at high temperature and precipitating it naturally at low temperature can effectively reduce the content of oligomers in the polymer and obtain polyethersulfone with high purity and narrow molecular weight distribution. Among them, the effect of using methanol as a precipitating agent is the best, and the obtained polymer has the lowest oligomer content and the narrowest molecular weight distribution. Compared with Comparative Example 1, CN113648678 A, etc., the polyethersulfone is purified by multiple organic solvents and extracted multiple times. The operation process is complicated, the solvent types are many, the amount is large and the toxicity is high. The content of oligomers in the purified polyethersulfone is 0.25% to 2.12%. The content of oligomers in the purified polyethersulfone of the present invention is not higher than 0.24%, which can be effectively separated.

Claims

1. Casting grade polyethersulfone resin, characterized in that: Its oligomer content is ≤0.24%, purity is ≥99.969%, and molecular weight distribution is between 1.6-2.0; It is prepared by the following steps: The polyethersulfone polymer is dissolved in a solvent at 130°C to 150°C, and a precipitating agent is added dropwise into the system at a dropping speed of 20 to 40 ml / min while stirring and maintaining a homogeneous system, and then the system is allowed to stand and gradually cooled to room temperature to precipitate crystals; After the crystals are completely precipitated, the obtained polyethersulfone polymer is separated from the system solvent by filtration, and the collected polymer is repeatedly soaked, boiled and washed with methanol, and dried to obtain a casting grade polyethersulfone resin.

2. The casting grade polyethersulfone resin according to claim 1, characterized in that The polyethersulfone polymer is heated and dissolved in a solvent under nitrogen protection to obtain a homogeneous polymer solution with a polyethersulfone solution concentration of 12% to 15%.

3. The casting grade polyethersulfone resin according to claim 1 or 2, characterized in that: The solvent is selected from at least one of dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide and sulfolane.

4. The casting grade polyethersulfone resin according to claim 1, characterized in that: The precipitation agent is selected from at least one of acetonitrile, methanol, ethanol and acetone; The addition amount of the precipitation agent is 10% to 15% of the mass of the polymerization liquid.

5. The casting grade polyethersulfone resin according to claim 1, characterized in that: The static cooling is performed by cooling with ice water or by natural cooling.

6. The casting grade polyethersulfone resin according to claim 1, characterized in that: The collected polymer was soaked and washed with methanol at 45℃~55℃ for 30~50min, and the washing was repeated 3~5 times; The drying temperature is 100°C to 120°C, and the drying time is 6h to 10h.

7. The casting grade polyethersulfone resin according to claim 1, characterized in that: The method also includes the steps of using molecular distillation equipment to perform graded distillation separation on the remaining system solvent and recovering the solvents respectively.

8. The casting grade polyethersulfone resin according to any one of claims 1 to 7, characterized in that: Its ash content is ≤0.031%.

9. A casting solution and a membrane material, characterized in that: The polyethersulfone resin is prepared by using the casting grade polyethersulfone resin described in any one of claims 1 to 8.

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