A method for preparing a polyetherimide

Abstract

The application relates to the technical field of high polymer synthesis, and discloses a preparation method of polyetherimide, which comprises the following steps: carrying out imidization reaction on a mixture of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride, m-phenylenediamine and a water-carrying agent in an organic solvent to obtain a solid-liquid mixture, filtering and drying the solid-liquid mixture, and then washing the solid-liquid mixture with anhydrous ethanol until the purity of the solid-liquid mixture is higher than 99.5% to obtain bis(chlorophthalimide); carrying out salt reaction on bisphenol A, a water-carrying agent, sodium hydroxide and potassium carbonate in an organic solvent to obtain a bisphenol salt slurry; and adding the bis(chlorophthalimide) into the bisphenol salt slurry, and carrying out polymerization under the action of a catalyst to obtain the polyetherimide. The bis(chlorophthalimide) is washed with hot ethanol to improve the purity of the bis(chlorophthalimide), and the bisphenol salt is directly prepared in an organic solvent, so that water is avoided from being introduced as a solvent, high-molecular-weight polyetherimide is finally prepared, the yield is high, and the thermal stability of the product is higher.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polymer synthesis, and particularly relates to a preparation method of polyetherimide. BACKGROUND

[0002] The main chain of polyetherimide (PEI) is formed by imide ring and ether bond connecting benzene ring, which has excellent high-temperature resistance, low dielectric constant, high strength, thermoplasticity and easy processing, and is widely used in the fields of electronic and electrical, automobile transportation, aerospace, etc. At present, the PEI is mainly produced by the route of nucleophilic substitution of nitro-phthalic anhydride (such as patent US3838097A), but the preparation of nitro-phthalic anhydride monomer is difficult, and the by-product of nitrite in the polymerization process has great pollution to the environment. In the route of nucleophilic substitution of chloro-phthalic anhydride, the chloro-phthalic anhydride monomer is widely available, and the by-product of chloride in the polymerization process is harmless to the environment, so the route of nucleophilic substitution of chloro-phthalic anhydride for preparing PEI has a more extensive prospect.

[0003] However, the route of nucleophilic substitution of chloro-phthalic anhydride also has some defects, such as incomplete imidization in the reaction, and more impurities of imide or chloro-phthalic anhydride. The patent US6235866A1 uses liquid chromatography to detect the content of impurities (monobasic imide or chloro-phthalic anhydride) in the imidization product, and according to the spectrum, the corresponding monomer is added to reduce the impurities, but this method usually needs to repeat the steps of "adding monomer-HPLC testing" for many times, and it is difficult to control the degree of imidization, and there are monobasic imide and amide acid impurities which are not completely imidized, and a long reaction time is needed to achieve a high conversion rate.

[0004] On the other hand, the bisphenol salt is usually prepared in water, and the bisimide monomer is sensitive to water and is easily hydrolyzed in water, so how to reduce the water content of the bisphenol salt is also very important. The patent US20140099510A1 reports a method for preparing bisphenol A salt, which uses bisphenol A and sodium hydroxide to form salt in aqueous solution, then the aqueous solution is added to high-temperature o-dichlorobenzene to remove water, and finally the solvent is evaporated and vacuum dried to obtain bisphenol A sodium salt. The preparation process is very complicated, and the drying process is long.

[0005] The patent CN1560113A uses bisphenol and alkali to form salt in a reflux process, and polymerizes with the imidization product to obtain PEI, but the addition of excessive strong alkali in this method will cause the hydrolysis of the imidization product, and it is difficult to control the equimolar ratio of the imidization product and the bisphenol salt.

[0006] Therefore, it is very urgent to develop a green manufacturing process which has less imide impurities, low water content of bisphenol salt, simple preparation steps, low cost and is friendly to the environment. SUMMARY

[0007] The present application is directed to the problems of high water content and many impurities in the preparation process of polyetherimide in the prior art, and provides a preparation method of polyetherimide, aiming to obtain high-purity bisimide monomer and low-water-content bisphenol salt monomer, so as to polymerize to obtain high-molecular-weight polyetherimide resin.

[0008] To achieve the above-mentioned object, the technical scheme adopted by the present application is:

[0009] A preparation method of polyetherimide, the structure of the polyetherimide is as follows:

[0010]

[0011] Wherein n≥70;

[0012] The preparation method of the polyetherimide comprises the following steps:

[0013] Step 1, a mixture of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride, m-phenylenediamine and a water-carrying agent are imidized in an organic solvent to obtain a solid-liquid mixture, which is discharged into anhydrous ethanol, filtered and vacuum dried to obtain a crude bis(chlorophthalimide) product; due to the different positions of chlorine on the benzene ring in chlorophthalic anhydride, the imidization product synthesized has three isomers, the structures of which are as follows:

[0014]

[0015] Step 2, the crude bis(chlorophthalimide) product prepared in step 1 is crushed and washed with anhydrous ethanol until the purity is above 99.5% to obtain bis(chlorophthalimide); the purpose of this step is to reduce the content of unreacted raw materials, and by repeatedly washing with hot ethanol until the purity reaches above 99.5% as detected by liquid chromatography, the molecular weight of the final polyetherimide can be effectively improved. If the purity is not above 99.5%, repeat the washing with hot ethanol until the purity is above 99.5%.

[0016] Step 3, bisphenol A, a water-carrying agent, sodium hydroxide and potassium carbonate are reacted in an organic solvent to form a salt; in the present application, bisphenol A is directly salted with sodium hydroxide in an organic solvent, which avoids the introduction of water, and potassium carbonate is added. The alkalinity of potassium carbonate is not as strong as that of sodium hydroxide, and a slight excess of potassium carbonate is not enough to cause ring-opening hydrolysis side reactions of bis(chlorophthalimide) while salt formation with bisphenol A. Finally, the water content in the slurry of bisphenol salt is very low, which avoids the influence of water on the hydrolysis of bis(chlorophthalimide) during polymerization.

[0017] Step 4, the bis(chlorophthalimide) is added to the slurry of bisphenolate, and polymerization is carried out under the action of a catalyst to obtain the polyetherimide. Based on the previous purification and anhydrous treatment, the molecular weight of the polyetherimide obtained by polymerization can be significantly improved.

[0018] Preferably, in step 1, the molar ratio of both 3-chlorophthalic anhydride and 4-chlorophthalic anhydride is any value; the total molar amount of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride to the molar ratio of m-phenylenediamine is 2.0-2.5:1;

[0019] In step 1, the imidization reaction temperature is 100-200℃, and the reaction time is 0.2-2h. Appropriate temperature rise can improve the rate of imidization reaction.

[0020] Preferably, in step 1, the anhydrous ethanol is 1-10 times the volume of the solid-liquid mixture; the greater the amount of anhydrous ethanol, the more complete the discharge of bis(chlorophthalimide).

[0021] In step 2, the washing temperature is 60-85℃, the washing time is more than 1h, and the washing is 1-3 times. Hot ethanol has a good effect on the dissolution of chlorophthalic anhydride and monoimide impurities in bis(chlorophthalimide).

[0022] Preferably, in step 2, the washing temperature is 60-85℃, the washing time is 1-10h, and the washing is 1-3 times. It is further preferred to wash for 3-6h, which can basically achieve a purity of bis(chlorophthalimide) of more than 99.5%.

[0023] Sodium hydroxide is a strong base with fast salting rate. In the prior art, excess sodium hydroxide is usually used to promote the complete reaction of bisphenol A, but excess sodium hydroxide can cause hydrolysis of bis(chlorophthalimide) in the polymerization process, affecting the molecular weight of the product. In step 3, the molar ratio of bisphenol A to sodium hydroxide is 1:1.95-2.0; the mass of potassium carbonate is 1-10% of the mass of sodium hydroxide. In the present application, the amount of sodium hydroxide is less than the molar ratio, which effectively avoids the problem of hydrolysis of bis(chlorophthalimide) in strong base.

[0024] Instead, a small amount of potassium carbonate is added in the present application to salt with the remaining bisphenol A, but based on its slow salting speed, the addition amount should not be too high. On the other hand, since the alkalinity of potassium carbonate is weaker than that of sodium hydroxide, it is not easy to cause ring-opening hydrolysis side reaction of bis(chlorophthalimide).

[0025] The temperature of the salting reaction is 140-200℃, and the reaction time is 0.5-5h; appropriately increasing the temperature and prolonging the reaction time is beneficial to the complete salting of bisphenol A.

[0026] The molar ratio of bis(chlorophthalimide) to bisphenolate in step 4 is 0.9-1.1:1; the polymerization temperature is 150-200℃, and the polymerization time is 2-20h.

[0027] Preferably, the catalyst comprises any one or more of hexaethylguanidinium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, benzyltriethylammonium bromide, benzyltriethylammonium chloride, cetyltrimethylammonium bromide, cetyltrimethylammonium chloride;

[0028] The organic solvent comprises any one or more of o-dichlorobenzene, N-methylpyrrolidone, N,N-dimethylacetamide;

[0029] The water-carrying agent comprises toluene and / or xylene; the action is to remove moisture in the system, reducing the hydrolysis side reaction of bis(chlorophthalimide) monomers.

[0030] The volume ratio of the water-carrying agent to the organic solvent is 0.1-1:1.

[0031] Preferably, the product obtained by polymerization in step 4 is discharged into anhydrous methanol, and the polyetherimide is obtained after filtration, drying, and crushing and washing. Preferably, the washing uses ethanol and / or water, and further preferably, water and ethanol are each used for 1-3 times of washing.

[0032] Preferably, the moisture content in the slurry of the bisphenolate prepared in step 3 is not higher than 1000ppm. Preferably, it is not higher than 500ppm, and further preferably, the moisture content in the slurry of the bisphenolate is below 300ppm. The lower the water content in the slurry, the smaller the influence on the imide, and the more conducive to the high molecular weight of the product.

[0033] In the prior art, the chlorophthalic anhydride and monomeric imide impurities in the imide will act as end-capping agents in the polymerization process, hindering the growth of the molecular chain, and water will cause the imide to undergo ring-opening hydrolysis side reactions in the polymerization process, affecting the preparation of high molecular weight polyetherimide. The present application separates and purifies bis(chlorophthalimide) and directly prepares bisphenolate in an organic solvent, effectively reducing the chlorophthalic anhydride and monomeric imide impurities in the imide raw material and the water content in the bisphenolate, and the high molecular weight polyetherimide prepared by polymerization has a molecular weight of up to 3.0*10 4 or more.

[0034] Preferably, the molecular weight of the polyetherimide is 4.0*10 4 or more, and further preferably, the molecular weight of the polyetherimide is 4.5*10 4 or more.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] In one aspect of the present application, the bis(chloro-phthalimide) is washed with hot ethanol to improve its purity. In another aspect, the bisphenolate salt is directly prepared in an organic solvent, avoiding the introduction of water as a solvent. The final product has a molecular weight of 3.0*10 4 The above polyetherimide has a high yield and higher thermal stability. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Infrared spectrum of the polyetherimide prepared in the examples. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application. Those skilled in the art can modify or replace the equivalent without departing from the spirit and scope of the present application, which should be covered within the protection scope of the present application.

[0039] The raw materials used in the following specific embodiments are purchased from the market, and the main raw material sources and purity are shown in Table 1.

[0040] Table 1 Raw material sources and purity

[0041] Raw materials Source Purity 4-chlorophthalic anhydride Shanghai Dibo 99.0％ 3-chlorophthalic anhydride Shanghai Dibo 99.0％ o-dichlorobenzene Mcclin 99.0％ m-phenylenediamine Mcclin 99.5％ toluene Guo Yao 99.0％ Bisphenol A Mcclin 99.0％ Sodium hydroxide Mcclin 99.0％ Potassium carbonate Mcclin 99.99％ Hexaethylguanidinium chloride Suzhou Haofan 99.9％

[0042] The relevant analysis and test methods in the following specific embodiments are as follows:

[0043] Gel permeation chromatography analysis uses a US Agilent 1260 Infinity II gel chromatograph (GPC), two 300*7.5mm, 5μm PLgel Mixed-D chromatographic columns and a 50*7.5mm, 5μm PLgel Mixed guard column are used, polystyrene is used as a standard sample, chloroform is used as a mobile phase, the sample concentration is 3mg / mL, the column temperature and differential detector temperature are both 35℃, the flow rate is 1mL / min, the sample injection amount is 50μL, and the PEI molecular weight and its distribution are tested.

[0044] Differential scanning calorimetry analysis uses a DSC 214Polyma differential scanning calorimeter from Germany Mettler, under a nitrogen atmosphere, first quickly scan the thermal history at a temperature rising rate of 20℃ / min, then raise the temperature from 25℃ to 400℃ at a temperature rising rate of 10℃ / min to test the glass transition temperature (T g ) of PEI.

[0045] Thermogravimetric analysis (TGA) was performed on a TA Instruments TGA 55 thermogravimetric analyzer. The temperature program was 50-800 °C at 20 °C / min under a nitrogen flow of 50 mL / min. The thermal decomposition temperature (T 5％ ) of PEI was determined.

[0046] Infrared spectroscopy (IR) was performed on a Nicolet iS 20 infrared spectrometer from Thermo Fisher. The mode was attenuated total reflectance (ATR). The wave number range was 4000-500 cm -1 . The number of scans was 32. The resolution was 4 cm -1 . The atmospheric background was automatically subtracted.

[0047] Moisture content was determined using an AKF-C6 moisture analyzer from Mettler Toledo. At least 5 sets of parallel tests were performed for each sample.

[0048] Liquid chromatography (LC) was performed on an Agilent 1260 Infinity II high-performance liquid chromatograph (HPLC). One InfinityLab Poroshell 120 EC-C18 column (150 x 4.6 mm, 4 μm) was used. The mobile phase was pure acetonitrile. The sample concentration was 50 mg / L. The column temperature was 25 °C. The flow rate was 0.3 mL / min. The injection volume was 10 μL. The UV detector wavelength was the maximum absorption wavelength of UV-vis. The area normalization method was used for ClPAMI purity analysis.

[0049] Example 1

[0050] Step 1, synthesis of bis-imide: 25.0 g of 3-chlorophthalic anhydride, 25.0 g of 4-chlorophthalic anhydride, 14.5 g of m-phenylenediamine, 300 mL of o-dichlorobenzene, and 100 mL of toluene were added to a 1000 mL three-necked flask under N2 atmosphere, heated to 160 °C for 0.5 h, and the solution was slightly cooled. The product was discharged into 1500 mL of anhydrous ethanol, filtered, dried, and crushed. The yellowish powder was washed with boiling ethanol for 5 h, filtered, and dried to obtain bis(chlorophthalimide) with a yield of 96.0% and a liquid chromatography purity of 99.7%.

[0051] Step 2, synthesis of bisphenol sodium salt: 22.1 g of bisphenol A, 7.7 g of sodium hydroxide, 0.5 g of potassium carbonate powder, 300 mL of o-dichlorobenzene, and 100 mL of toluene were added to a 1000 mL four-necked flask under N2 atmosphere, heated to 160 °C for 4 h to obtain a white slurry of bisphenol sodium salt. The moisture content of the system was measured to be 200 ppm.

[0052] Step 3, Polymerization reaction: 41.7 g of bis(chlorophthalimide) and 0.5 g of hexaethylguanidine chloride were added to the white bisphenol sodium salt slurry from Step 2, and the mixture was heated to 180°C for 12 h to obtain a viscous brownish-red solution. The solution was discharged into anhydrous methanol, filtered, dried, pulverized, and washed three times each with ethanol and deionized water, and dried to obtain brown PEI powder. The yield was 95.8%, and the molecular weight (Mw) was determined to be 4.8 × 10⁻⁶. 4 The polymer molecular weight distribution (PDI) is 3.6, T g The temperature is 225℃, T 5％ It is 510℃.

[0053] The infrared spectrum of the PEI prepared in this embodiment is as follows: Figure 1 As shown, 1777cm -1 1718cm -1 The peak at 1351 cm⁻¹ is a characteristic peak of the stretching vibration of C=O. -1 The peak at 1085 cm⁻¹ is the characteristic peak of the stretching vibration of CN. -1 The peak at 741 cm⁻¹ is the characteristic peak of the stretching vibration of the ROR. -1 The peak at that position is a characteristic peak of the bending vibration of C=O. The absence of carboxyl and imino signals in this spectrum indicates a high imidization rate of PEI.

[0054] Example 2

[0055] Step 1, Synthesis of bis(chlorophthalimide): Under a nitrogen atmosphere, 25.0 g of 3-chlorophthalic anhydride, 25.0 g of 4-chlorophthalic anhydride, 14.5 g of m-phenylenediamine, 300 ml of o-dichlorobenzene, and 100 ml of toluene were added to a 1000 ml three-necked flask. The mixture was heated to 150 °C and reacted for 1 h. After the solution cooled slightly, it was discharged into 1500 ml of anhydrous ethanol, filtered, dried, pulverized, and washed with boiling ethanol for 5 h. After further filtration and drying, a pale yellow powder of bis(chlorophthalimide) was obtained. The yield was 95.9%, and the purity according to liquid chromatography was 99.6%.

[0056] Step 2, synthesis of sodium bisphenol A: Under N2 atmosphere, 22.1g of bisphenol A, 7.6g of sodium hydroxide, 1.0g of potassium carbonate powder, 300ml of o-dichlorobenzene and 100ml of toluene were added to a 1000ml four-necked flask and heated to 160℃ for 4h to obtain a white slurry. The moisture content of the system was measured to be 220ppm.

[0057] Step 3, Polymerization: 41.7 g of bis(chlorophthalimide) and 0.5 g of hexaethylguanidinium chloride were added to the white bisphenol sodium salt slurry and heated to 180 °C for 18 h to give a thick, tan-brown solution. The solution was discharged into anhydrous methanol, filtered, dried, pulverized, and washed with ethanol and deionized water for 3 times each, and dried to give a tan PEI powder. Yield 96.2%, molecular weight determination Mw5.2*10 4 , PDI 3.9, T g 228 °C, T 5％ 514 °C.

[0058] Example 3

[0059] Step 1, Synthesis of bisimide: 37.5 g of 3-chlorophthalic anhydride, 12.5 g of 4-chlorophthalic anhydride, 14.5 g of m-phenylenediamine, 300 ml of o-dichlorobenzene, and 100 ml of toluene were added to a 1000 ml three-necked flask, heated to 150 °C for 1 h, and after the solution was slightly cooled, discharged into 1500 ml of anhydrous ethanol, filtered, dried, pulverized, and washed with boiling ethanol for 5 h, and after being filtered and dried, a light yellow powder of bis(chlorophthalimide) was obtained. Yield 96.5%, liquid chromatography purity 99.8%.

[0060] Step 2, Synthesis of bisphenol sodium salt: 22.1 g of bisphenol A, 7.7 g of sodium hydroxide, 0.5 g of potassium carbonate powder, 300 ml of o-dichlorobenzene, and 100 ml of toluene were added to a 1000 ml four-necked flask under N2 atmosphere, heated to 160 °C for 2 h to give a white slurry, and the water content of the system was measured to be 300 ppm.

[0061] Step 3, Polymerization: 41.7 g of bis(chlorophthalimide) and 0.5 g of hexaethylguanidinium chloride were added to the white bisphenol sodium salt slurry and heated to 180 °C for 12 h to give a thick, tan-brown solution. The solution was discharged into anhydrous methanol, filtered, dried, pulverized, and washed with ethanol and deionized water for 3 times each, and dried to give a tan PEI powder. Yield 95.5%, molecular weight determination Mw4.5*10 4 , PDI 3.5, T g 223 °C, T 5％ 507 °C.

[0062] Comparative Example 1

[0063] Step 1, synthesis of bisimide: 25.0 g of 3-chlorophthalic anhydride, 25.0 g of 4-chlorophthalic anhydride, 14.5 g of m-phenylenediamine, 300 ml of o-dichlorobenzene and 100 ml of toluene were added to a 1000 ml three-necked flask, heated to 160°C for 0.5 h, and the solution was slightly cooled, discharged into 1500 ml of anhydrous ethanol, filtered, dried, and pulverized to obtain a light yellow powder of crude bis(chlorophthalimide). Yield 97.5%, liquid chromatography purity 97.0%.

[0064] Step 2, synthesis of bisphenolate: the step was the same as in Example 1.

[0065] Step 3, polymerization reaction: 41.7 g of crude bis(chlorophthalimide) prepared in Step 1 and 0.5 g of hexaethylguanidinium chloride were added to a slurry of white bisphenolate sodium salt, heated to 180°C for 12 h to obtain a viscous brownish solution. The solution was discharged into anhydrous methanol, filtered, dried, and pulverized, and then washed with ethanol and deionized water for 3 times each, and dried to obtain a brown PEI powder. Yield 95.3%, molecular weight determination Mw2.3*10 4 , PDI 3.1, T g 215°C, T 5％ 490°C.

[0066] Compared with Example 1, the washing process of hot ethanol was omitted in Step 1, and the molecular weight of the final polyetherimide was significantly reduced, and the corresponding thermal stability also decreased.

[0067] Comparative Example 2

[0068] Step 1, synthesis of bis(chlorophthalimide): the step was the same as in Example 1.

[0069] Step 2, synthesis of bisphenolate: 44.2 g of bisphenol A, 15.4 g of sodium hydroxide, 0.6 g of potassium carbonate powder and 500 ml of water were added to a 1000 ml three-necked flask under N2 atmosphere, heated to 70°C for 30 min to obtain a light yellow solution, and then the solution was poured into 800 ml of boiling o-dichlorobenzene with the addition of toluene for water removal. After no water was generated in the water trap, the solution was cooled and filtered and dried to obtain a white powder, and the water content was measured to be 3000 ppm.

[0070] Step 3, polymerization reaction: 26.4 g of bisphenolate, 41.7 g of bisimide, 0.5 g of hexaethylguanidinium chloride and 30 ml of toluene were added to a 1000 ml four-necked flask, heated to 180°C for 12 h to obtain a viscous brownish solution. The solution was discharged into anhydrous methanol, filtered, dried, and pulverized, and then washed with ethanol and deionized water for 3 times each, and dried to obtain a brown PEI powder. Yield 96.0%, molecular weight determination Mw2.0*10 4 , PDI 2.9, Tg Tm was 213°C, T 5％ Tm was 485°C.

[0071] From the present comparative example, it can be seen that water was used as solvent in step 2, and water was removed after the reaction until no water was produced in the water trap. However, the water content in the dried powder was as high as 3000 ppm, and the molecular weight of the polyetherimide was reduced to 2.0*10 4 41.7% of the product of Example 1, in other words, the use of organic solvent to prepare the sodium salt of bisphenol can increase the molecular weight of polyetherimide by more than 2 times, which is remarkable.

Claims

1. A process for the preparation of a polyetherimide, characterized in that, The structure of the polyetherimide is shown below: wherein n≥70; The preparation method of the polyetherimide comprises the steps of: Step 1, imidizing a mixture of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride, m-phenylenediamine and a water-carrying agent in an organic solvent to obtain a solid-liquid mixture, discharging in anhydrous ethanol, filtering and vacuum drying to obtain a crude bis(chlorophthalimide) product; Step 2, crushing the crude bis(chlorophthalimide) product prepared in step 1 and washing with anhydrous ethanol until the purity is above 99.5% to obtain bis(chlorophthalimide); Step 3, salifying bisphenol A, a water-carrying agent, sodium hydroxide and potassium carbonate in an organic solvent at 160-200℃ to obtain a bisphenolate slurry; the molar ratio of bisphenol A to sodium hydroxide is 1:1.95-2.0; the mass of potassium carbonate is 1-10% of the mass of sodium hydroxide; the organic solvent is any one or more of o-dichlorobenzene, N-methylpyrrolidone and N,N-dimethylacetamide; the water-carrying agent is toluene and / or xylene; the water content of the bisphenolate slurry prepared in step 3 is not higher than 1000 ppm; Step 4, the bis(chlorophthalimide) is added to a slurry of the bisphenate and polymerized at 180-200°C in the presence of a catalyst to produce the polyetherimide; the polyetherimide has a molecular weight of 4.5*10 4 above; The catalyst is hexaethyl guanidine chloride.

2. The method of making a polyetherimide according to claim 1, characterized in that, The molar ratio of the total amount of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride to m-phenylenediamine in step 1 is 2.0-2.5:

1.

3. The method of making a polyetherimide according to claim 1, wherein, The imidization reaction temperature in step 1 is 100-200℃, and the reaction time is 0.2-2h.

4. The method of making a polyetherimide according to claim 1, wherein, The anhydrous ethanol in step 1 is 1-10 times the volume of the solid-liquid mixture.

5. The method of making a polyetherimide according to Claim 1, characterized in that, The washing temperature in step 2 is 60-85℃, and the washing time is more than 1h, and the washing is 1-3 times.

6. The method of making a polyetherimide according to Claim 1, characterized in that, The reaction time of the salification reaction in step 3 is 0.5-5h.

7. The method of making a polyetherimide according to Claim 1, characterized in that, The molar ratio of bis(chlorophthalimide) to bisphenolate in step 4 is 0.9-1.1:

1.

8. The method of making a polyetherimide according to Claim 1, characterized in that, The polymerization time is 2-20h.

9. The method of making a polyetherimide according to Claim 1, characterized in that, The volume ratio of the water-carrying agent to the organic solvent is 0.1-1:1.

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