A green and environmentally friendly preparation process for polyimide monomers

Abstract

The present invention discloses a preparation process of a green and environment-friendly polyimide monomer, which comprises the following steps: Step 1, preparing a Cu-Al2O3 catalyst: mixing copper powder, iodine, nano-aluminum oxide and DMSO, stirring at 5-25 °C for 2-10 h, filtering by suction, washing the filter cake with water and acetone respectively, and then drying to obtain the Cu-Al2O3 catalyst for standby; Step 2, reacting 4-halophthalic anhydride with an inorganic base in water to prepare an aqueous solution of disodium 4-halophthalate for use; using water as a solvent, mixing bisphenol AF and an inorganic base, reacting to prepare disodium bisphenol AF, then adding the Cu-Al2O3 catalyst and a phase transfer catalyst prepared in Step 1, carrying out a condensation reaction, then filtering to recover the catalyst, and acidifying the filtrate with an acid to obtain S1-tetracarboxylic acid; Step 3, subjecting the S1-tetracarboxylic acid in Step 2 to high-temperature dehydration to obtain bisphenol AF diether dianhydride, that is, the polyimide monomer.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical raw materials, and particularly relates to a preparation process of a green and environment-friendly polyimide monomer. Background Art

[0002] Polyimide (abbreviation: PI) is a polymer formed by the polycondensation of a dianhydride monomer and a diamine monomer. Due to its excellent high and low temperature resistance (-250°C to 450°C), good mechanical processing performance, radiation resistance, flame retardancy, outstanding insulation properties, and no release of harmful gases, it is increasingly applied in high-tech fields such as aerospace, national defense, and microelectronics. Therefore, polyimide is a new material with great development potential and application value.

[0003] Introducing fluorine-containing groups, especially trifluoromethyl groups, into the molecular main chain can obtain a PI material with great development potential. The trifluoromethyl group can disrupt the regularity of the main chain, making the molecular chain in a three-dimensional twisted state. Therefore, fluorine-containing PI can be dissolved in a variety of organic solvents. In addition, fluorine atoms have strong polarity, which can increase the polarity of the chain, thereby improving the solubility of PI in polar solvents. In addition, the high C-F bond energy makes the heat resistance and thermal oxygen stability of PI improved, and fluorine atoms can disrupt the electronic conjugation of the chromogenic functional groups in the PI molecular structure, thus making PI have good light transmittance.

[0004] Bisphenol AF diether dianhydride is a polyimide dianhydride monomer. Compared with bisphenol A diether dianhydride, due to the introduction of -CF3 groups in its structure, based on the above discussion, bisphenol AF diether dianhydride has better solubility and higher heat resistance, and is expected to replace bisphenol A diether dianhydride, having good application prospects.

[0005] Currently, the synthesis of bisphenol AF diether dianhydride generally has the following problems. First, expensive raw materials are used. Second, organic solvents are used as the medium in the condensation stage, increasing the material cost and being unfriendly to the environment. Third, a large amount of strong base is used in the hydrolysis stage, generating a large amount of wastewater. For example: Patent US20170260334 and the literature (Macromolecules, Vol. 39, NO. 22, 2006) both use 4-nitrophthalonitrile and bisphenol AF as raw materials, and are prepared through steps such as condensation, hydrolysis, and acetic anhydride dehydration to form a ring. In this process, expensive 4-nitrophthalonitrile is used; dimethyl sulfoxide is used as a solvent in the condensation stage, increasing the material and environmental protection costs; in addition, a large amount of sodium hydroxide is required to hydrolyze four cyano groups, generating a large amount of wastewater. The reaction formula is as follows:

[0006]

[0007] In the preparation of bisphenol A diether dianhydride as described in patents CN1336364A and CN108148029A, during the condensation stage, toluene and mesitylene are respectively used as solvents. First, diphenol sodium salt is generated through reaction, and then the methanol and water generated by the reaction are removed by distillation using an organic solvent. This not only increases the operation procedures, but also increases the material cost and has an impact on the environment. The reaction formula is as follows:

[0008] 。 Summary of the Invention

[0009] To solve the problems mentioned in the above background art, the present invention provides a new method for synthesizing a green and environmentally friendly polyimide monomer. Firstly, the use of expensive 4-nitrophthalonitrile is avoided; secondly, the use of organic solvents is avoided during the condensation stage to reduce the emission of organic gases; thirdly, no hydrolysis reaction is introduced, which not only reduces the operation procedures and shortens the production cycle, but also reduces the emission of waste water and solid waste.

[0010] The reaction formula of the present invention is as follows:

[0011]

[0012] To achieve the above object, the present invention adopts the following technical solutions:

[0013] A green and environmentally friendly process for preparing polyimide monomers, comprising the following steps:

[0014] Step 1: Prepare a Cu-Al2O3 catalyst

[0015] Mix copper powder, iodine, nano-aluminum oxide and DMSO (dimethyl sulfoxide), stir at 5 - 25 °C for 2 - 10 h, perform suction filtration, wash the filter cake with water and acetone respectively, and then dry to obtain the Cu-Al2O3 catalyst for standby; the particle size of the nano-aluminum oxide is 30 - 50 nm;

[0016] Step 2: Prepare S1-tetracarboxylic acid

[0017] React 4-halophthalic anhydride with an inorganic base in water to prepare an aqueous solution of 4-halophthalic acid disodium salt for use;

[0018] Using water as a solvent, mix bisphenol AF and an inorganic base, react to prepare bisphenol AF disodium salt, then add the Cu-Al2O3 catalyst and a phase transfer catalyst prepared in Step 1, perform a condensation reaction, then filter, recover the catalyst, and acidify the filtrate with an acid to obtain S1-tetracarboxylic acid;

[0019] Step 3: Prepare bisphenol AF diether dianhydride

[0020] The S1-tetracarboxylic acid in Step 2 is subjected to high-temperature dehydration to obtain bisphenol AF diether dianhydride, which is the polyimide monomer.

[0021] Preferably, the preparation method of S1-tetracarboxylic acid specifically includes the following steps:

[0022] Mix 4-halophthalic anhydride, inorganic base, and water, then raise the temperature to 50 - 100 °C and react for 1 - 4 h to obtain a colorless and transparent solution of disodium 4-halophthalate for standby.

[0023] Mix bisphenol AF, water, and inorganic base, displace with nitrogen, then raise the temperature to 95 - 100 °C and react for 3 - 6 h to obtain a colorless and transparent solution of disodium bisphenol AF.

[0024] Then add the solution of disodium 4-halophthalate to the solution of disodium bisphenol AF, add Cu - Al2O3 catalyst and phase transfer catalyst, raise the temperature to reflux, carry out the condensation reaction, then filter to recover the catalyst; acidify the filtrate with acid to obtain S1-tetracarboxylic acid.

[0025] Preferably, the preparation method of bisphenol AF diether dianhydride specifically includes the following steps:

[0026] Put S1-tetracarboxylic acid into a vacuum oven, heat to 200 - 250 °C, control the vacuum ≤ -0.05 MPa, and dry for 3 - 10 h to obtain bisphenol AF diether dianhydride, which is the polyimide monomer.

[0027] Preferably, in the preparation of Cu - Al2O3 catalyst, the molar ratio of copper powder to iodine is 100:1 - 8.

[0028] Preferably, in the preparation of Cu - Al2O3 catalyst, the weight ratio of copper powder to nanoscale aluminum oxide is 1:3 - 10.

[0029] Preferably, in the preparation of Cu - Al2O3 catalyst, the weight ratio of copper powder to DMSO is 1:5 - 12.

[0030] Preferably, in the preparation of Cu - Al2O3 catalyst, the drying temperature is 200 - 250 °C and the drying time is 3 - 5 h.

[0031] Preferably, in the preparation of S1-tetracarboxylic acid, 4-halophthalic anhydride can be 4-chlorophthalic anhydride, 4-bromophthalic anhydride, etc.; the inorganic base can be sodium hydroxide, potassium hydroxide, cesium hydroxide, etc.

[0032] Preferably, in the preparation of S1-tetracarboxylic acid, the molar ratio of 4-halophthalic anhydride to inorganic base is 1:2 - 2.5, and the molar ratio of bisphenol AF to inorganic base is 1:2 - 2.5.

[0033] Preferably, in the preparation of S1-tetracarboxylic acid, the weight ratio of 4-halophthalic anhydride to water is 1:2 - 6, and the weight ratio of bisphenol AF to water is 1:5 - 10.

[0034] Preferably, in the preparation of S1-tetracarboxylic acid, based on the weight of bisphenol AF, the addition amount of Cu-Al2O3 catalyst is 3% - 10%.

[0035] Preferably, in the preparation of S1-tetracarboxylic acid, the phase transfer catalyst is quaternary ammonium salt, polyether, or cyclic crown ether. The quaternary ammonium salt is selected from one of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogensulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, and tetradecyltrimethylammonium chloride;

[0036] The polyether is polyethylene glycol; the cyclic crown ether is 18-crown-6 or 15-crown-5;

[0037] Based on the weight of bisphenol AF, the addition amount of the phase transfer catalyst is 1% - 5%.

[0038] Preferably, in the preparation of S1-tetracarboxylic acid, the molar ratio of bisphenol AF to 4-halophthalic anhydride is 1:2 - 3.

[0039] Preferably, in the preparation of S1-tetracarboxylic acid, the condensation reaction temperature is 95 - 100 °C, and the reaction time is 8 - 15 h.

[0040] Preferably, in the preparation of S1-tetracarboxylic acid, the acidification uses hydrochloric acid with a concentration of more than 30% or sulfuric acid with a concentration of more than 95%.

[0041] In the present invention, when preparing the Cu-Al2O3 catalyst, using water as the medium, the condensation reaction of disodium 4-halophthalate and disodium bisphenol AF is carried out, and then acidification is carried out to obtain S1-tetracarboxylic acid. Compared with the existing literature and patent reports, this scheme replaces the organic solvent with water, and S1-tetracarboxylic acid can be obtained without going through the hydrolysis reaction. The traditional preparation of S1-tetracarboxylic acid requires two-step reactions of condensation - hydrolysis, while this scheme can be achieved in one step, which not only reduces the generation of wastewater and solid waste but also helps to shorten the production cycle.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] 1. The present invention provides a method for synthesizing polyimide monomers. The prepared product has a purity of more than 99% and a good yield. The key to promoting the success of this experiment lies in the addition of the Cu-Al2O3 catalyst. The nano-scale aluminum oxide has a high specific surface area, large pore volume, and good pore size distribution, making it a good catalyst carrier; in addition, the copper powder activated with iodine has high catalytic activity and is evenly attached to the surface of the nano-scale aluminum oxide, improving the catalytic efficiency and promoting chemical reactions.

[0044] 2. This solution uses water to replace organic solvents, avoids using expensive 4-nitrophthalonitrile, and can obtain S1-tetracarboxylic acid without hydrolysis reaction. The traditional preparation of S1-tetracarboxylic acid requires two-step condensation-hydrolysis reaction, while this solution can achieve it in one step. This not only reduces the generation of wastewater and solid waste, but also helps to shorten the production cycle. The obtained product has a lower cost, has the prospect of industrial scale-up, and has high social use value and application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0046] Figure 1 1H NMR spectrum of the product in Example 1 of the present invention;

[0047] Figure 2 HPLC chromatogram of the product in Example 1 of the present invention;

[0048] Figure 3 HPLC chromatogram of the product in Example 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Example 1

[0050] Step 1. Preparation of Cu-Al2O3 catalyst

[0051] Add 110 g of DMSO to a clean and dry 250 mL four-neck reaction flask, start stirring, and then add 6.4 g (0.1 mol) of copper powder, 1.27 g (0.005 mol) of iodine, and 23 g of nano-aluminum oxide with a particle size of 30 nm to the reaction flask. After adding, control the temperature at 20 °C and stir for 5 h;

[0052] After stirring, filter, and wash the filter cake with a small amount of water and acetone respectively, and then dry at 220 °C for 3 h to obtain 28.8 g of light pink powder;

[0053] Step 2. Preparation of S1-tetracarboxylic acid

[0054] In a clean 250 ml reaction flask, add 41.97 g (0.23 mol) of 4-chlorophthalic anhydride and 100 g of water. Start stirring and add 18.4 g (0.46 mol) of sodium hydroxide portionwise at room temperature. After addition, raise the temperature to 80 °C and keep the reaction for 2 h to obtain a colorless, transparent and clear solution, namely the disodium 4-chlorophthalate solution, for standby.

[0055] Under nitrogen protection, in another clean 500 ml reaction flask, add 250 g of water, add 8.4 g (0.21 mol) of sodium hydroxide with stirring to prepare a solution, then add 33.6 g (0.1 mol) of bisphenol AF, raise the temperature to 95 °C and keep the reaction for 5 h. During the reaction process, the solid slowly dissolves and finally becomes completely clear to obtain the disodium bisphenol AF solution. Cool it to below 80 °C, add the above-obtained disodium 4-chlorophthalate solution into it, then add 1.7 g of Cu - Al2O3 catalyst and 1.7 g of tetrabutylammonium bromide, continue to raise the temperature to 95 °C and keep the reaction for 12 h;

[0056] After the reaction is completed, cool it to room temperature, filter, collect the filtrate, acidify the filtrate with 36% hydrochloric acid to pH ≤ 1, a large amount of white solid precipitates, perform suction filtration, wash the filter cake with water, and after drying, obtain 58.5 g of white S1-tetracarboxylic acid solid, with a yield of 88%;

[0057] Step 3: Preparation of bisphenol AF diether dianhydride

[0058] Put 58.5 g of S1-tetracarboxylic acid into a vacuum oven, set the temperature to 220 °C, turn on the vacuum pump and dry for 4 h to obtain 53.1 g of white solid, with a purity of 99.38% and a yield of 96%. Example 2

[0059] Step 1: Preparation of Cu - Al2O3 catalyst

[0060] Add 150 g of DMSO to a clean and dry 250 mL four-necked reaction flask, start stirring, and then add 6.4 g (0.1 mol) of copper powder, 2.0 g (0.008 mol) of iodine and 35 g of nanoscale aluminum oxide with a particle size of 50 nm to the reaction flask. After addition, control the temperature at 20 - 25 °C and stir for 5 h;

[0061] After stirring, filter, wash the filter cake with a small amount of water and acetone respectively, and then dry at 230 °C for 5 h to obtain 40.8 g of light pink powder;

[0062] Step 2: Preparation of S1-tetracarboxylic acid

[0063] In a clean 500 ml reaction flask, add 56.75 g (0.25 mol) of 4-bromophthalic anhydride and 200 g of water. Start stirring and add 28.0 g (0.5 mol) of potassium hydroxide in portions at room temperature. After addition, heat up to 100 °C and keep the reaction for 1 h to obtain a colorless, transparent and clear solution, namely the solution of dipotassium 4-bromophthalate, for standby.

[0064] Under nitrogen protection, in another clean 1000 ml reaction flask, add 250 g of water. Add 11.76 g (0.21 mol) of potassium hydroxide with stirring to prepare a solution, and then add 33.6 g (0.1 mol) of bisphenol AF. Heat up to 100 °C and keep the reaction for 3 h. During the reaction process, the solid slowly dissolves and finally becomes completely clear to obtain the solution of dipotassium bisphenol AF. Cool it to below 80 °C, add the above-obtained solution of dipotassium 4-bromophthalate into it, then add 3.0 g of Cu - Al2O3 catalyst and 3.0 g of polyethylene glycol, continue to heat up to 100 °C and keep the reaction for 10 h;

[0065] After the reaction is completed, cool it to room temperature, filter, collect the filtrate, acidify the filtrate with 36% hydrochloric acid to pH ≤ 1, a large amount of white solid precipitates, perform suction filtration, wash the filter cake with water again, and after drying, obtain 53.7 g of white S1-tetracarboxylic acid solid, with a yield of 80.8%;

[0066] Step three: Prepare bisphenol AF diether dianhydride

[0067] Put 53.7 g of S1-tetracarboxylic acid into a vacuum oven, set the temperature to 200 °C, turn on the vacuum pump, and dry for 7 h to obtain 47.7 g of white solid, with a purity of 99.24% and a yield of 94%.

[0068] Comparative example 1

[0069] The difference between this comparative example and Example 1 lies in:

[0070] Preparation of S1-tetracarboxylic acid

[0071] In a clean 250 ml reaction flask, put in 41.97 g (0.23 mol) of 4-chlorophthalic anhydride and 100 g of water. Start stirring and add 18.4 g (0.46 mol) of sodium hydroxide in portions at room temperature. After addition, heat up to 80 °C and keep the reaction for 2 h to obtain the solution of disodium 4-chlorophthalate, for standby.

[0072] Under nitrogen protection, in another clean 500 ml reaction flask, add 250 g of water, add 8.4 g (0.21 mol) of sodium hydroxide under stirring to form a solution, then add 33.6 g (0.1 mol) of bisphenol AF, heat up to 95 °C, keep the temperature for reaction for 5 h to obtain a disodium salt solution of bisphenol AF, cool it to below 80 °C, add the above-obtained disodium salt solution of 4-chlorophthalic acid thereto, without adding a catalyst, heat up to 95 °C, and keep the temperature for reaction for 12 h;

[0073] At the end of heat preservation, no solid precipitates in the reaction flask, and it is a clear and transparent solution, indicating that the two raw materials do not react.

[0074] Examples 1 and 2 are mainly to illustrate the feasibility of the present invention, and Comparative Example 1 is mainly to illustrate that without adding the Cu-Al2O3 catalyst, the substrate cannot complete the reaction only in water, and the Cu-Al2O3 catalyst is indispensable.

[0075] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A green and environmentally friendly polyimide monomer preparation process, characterized in that: The following steps are involved: Step 1: Preparation of Cu-Al2O3 catalyst Copper powder, iodine, nano-aluminum oxide and DMSO are mixed, stirred at 5-25°C for 2-10 hours, filtered, the filter cake is washed with water and acetone respectively, and then dried to obtain a Cu-Al2O3 catalyst for use; Step 2: Preparation of S1-tetraacid React 4-halophthalic anhydride with an inorganic base in water to prepare a 4-halophthalic acid disodium salt aqueous solution for standby use; Using water as solvent, bisphenol AF and an inorganic base are mixed and reacted to prepare bisphenol AF disodium salt, and then the Cu-Al2O3 catalyst and phase transfer catalyst prepared in step 1 are added to carry out condensation reaction, and then filtered and acidified to obtain S1-tetraacid; Step 3: Preparation of bisphenol AF diether dianhydride Dehydrating the S1-tetraacid in step 2 at high temperature to obtain bisphenol AF diether dianhydride, i.e., a polyimide monomer; In the preparation of Cu-Al2O3 catalyst, the molar ratio of copper powder to iodine is 100:1-8; The weight ratio of copper powder to nano-aluminum oxide is 1:3-10; The weight ratio of copper powder to DMSO is 1:5-12; The preparation method of the S1-tetraacid specifically comprises the following steps: Mix 4-halophthalic anhydride, inorganic base and water, raise the temperature to 50-100°C, and react for 1-4 hours to obtain a colorless and transparent 4-halophthalic acid disodium salt solution for later use; Mix bisphenol AF, water and inorganic base, replace with nitrogen, and heat to 95-100°C for 3-6 hours to obtain a colorless and transparent bisphenol AF disodium salt solution; Then, the disodium salt solution of 4-halophthalic acid is added to the disodium salt solution of bisphenol AF, and then a Cu-Al2O3 catalyst and a phase transfer catalyst are added, the temperature is raised to reflux, the reaction is carried out for a period of time, and S1-tetraacid is obtained after filtering and acidification; In the preparation of S1-tetraacid, the molar ratio of 4-halophthalic anhydride to inorganic base is 1:2-2.5, and the molar ratio of bisphenol AF to inorganic base is 1:2-2.5; In the preparation of S1-tetraacid, the amount of Cu-Al2O3 catalyst added is 3%-10% based on the weight of bisphenol AF; In the preparation of S1-tetraacid, the phase transfer catalyst is a quaternary ammonium salt, a polyether, or a cyclic crown ether; the amount of the phase transfer catalyst added is 1%-5% based on the weight of bisphenol AF; In the preparation of S1-tetraacid, 4-halophthalic anhydride is 4-chlorophthalic anhydride; The inorganic base is sodium hydroxide; The reaction formula is as follows: 。 2. A green and environmentally friendly polyimide monomer preparation process according to claim 1, characterized in that: The preparation method of bisphenol AF diether dianhydride specifically comprises the following steps: Put S1-tetraacid into a vacuum oven, heat to 200-250°C, control the vacuum to ≦-0.05MPa, and dry for 3-10h to obtain bisphenol AF diether dianhydride, i.e., polyimide monomer.

3. The green and environmentally friendly polyimide monomer preparation process according to claim 1, characterized in that: In step 1, the drying temperature is 200-250°C and the drying time is 3-5h.

4. The green and environmentally friendly polyimide monomer preparation process according to claim 1, characterized in that: The quaternary ammonium salt is selected from one of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride and tetradecyltrimethylammonium chloride; The polyether is polyethylene glycol; the cyclic crown ether is 18-crown-6 or 15-crown-5.

5. The green and environmentally friendly polyimide monomer preparation process according to claim 1, characterized in that: In the preparation of S1-tetraacid, the condensation reaction temperature is 95-100°C and the reaction time is 8-15h; The acidification uses hydrochloric acid with a concentration of more than 30% or sulfuric acid with a concentration of more than 95%.

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