A method for preparing polyimide materials by aqueous phase polymerization

Abstract

This invention relates to a method for preparing polyimide materials via aqueous phase polymerization. The method includes acidifying anhydride with deionized water as a solvent to obtain an acid; after half of the carboxyl groups in the acid react with a secondary amine and are occupied, a diamine is added to react with the remaining carboxyl groups to generate a nylon salt; then, polyetherimide is added to obtain a mixed precipitate of nylon salt and polyetherimide; the resulting mixed precipitate is dried, molded, and thermally imidized to obtain the polyimide material. This invention uses deionized water as a solvent, avoiding the large amounts of organic solvents required in traditional polyimide synthesis processes. It synthesizes nylon salt powder and uses the nylon salt powder as the processing target. Compared to polyimide powder, nylon salt powder has better processability, enabling rigid structures to be molded at lower temperatures. Furthermore, the molding process is separated from the thermal imidization process, achieving high-efficiency, low-energy consumption, and low-cost green production of polyimide materials, which has great application potential in aerospace and other fields.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and specifically relates to a method for preparing polyimide materials by aqueous phase polymerization. Background Technology

[0002] Polyimide (PI) is a high-performance polymer material with excellent overall properties, including superior resistance to high and low temperatures, good chemical corrosion resistance, and high dimensional stability. It has been widely used in aerospace, microelectronics, and other fields. However, the synthesis of polyimide requires the use of large quantities of expensive and environmentally harmful organic solvents, such as N-methylpyrrolidone (NMP) and dimethylacetamide (DMAc). To reduce the production cost of polyimide and minimize its environmental impact, using alternative green solvents is crucial.

[0003] Research on the synthesis of polyimide (PI) using green solvents is relatively limited both domestically and internationally. Monomer reactive polymerization (PMR) methods utilize low-boiling-point alcohols as solvents to synthesize PI and prepare its composites, while research on PI synthesis using water as a solvent is even rarer. Traditional PI synthesis methods use organic solvents, increasing the production and application costs of PI materials. Furthermore, the extensive use of organic solvents leads to air pollution, damages aquatic ecosystems, and ultimately impacts human health. Synthesizing polyamic acid salt precursors using water as a solvent can avoid the adverse environmental impacts of these organic solvents and reduce PI production costs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing polyimide materials by aqueous phase polymerization, which solves the problems of traditional polyimide synthesis requiring a large amount of organic solvents and high processing costs. The polyimide materials prepared by this invention have a green and healthy production process, low processing costs, and good mechanical properties.

[0005] This invention provides a method for preparing polyimide materials by aqueous phase polymerization, comprising the following steps:

[0006] An acid is obtained by acidifying anhydride with deionized water as a solvent. Half of the carboxyl groups in the acid react with a secondary amine and are occupied. Then, a diamine is added to react with the remaining carboxyl groups to generate a nylon salt. Polyetherimide is then added to obtain a mixed precipitate of nylon salt and polyetherimide. The resulting mixed precipitate is dried, molded, and thermally imidized to obtain a polyimide material. The pKa value of the conjugate acid of the secondary amine is in the range of 6-11.

[0007] Preferably, the acid anhydride has one or more of the following structures:

[0008] , , , , , .

[0009] Preferably, the secondary amine is at least one selected from morpholine, piperazine, dipropylamine, and 4-methylmorpholine.

[0010] Preferably, the diamine is one or more of the following structures:

[0011] , , , , , .

[0012] Furthermore, in the thermosetting system with controlled degree of polymerization, the end-capping agent is one of the following structures, and the final molar ratio of amino group to acid anhydride is controlled to be 1:1 by the amount of end-capping agent used:

[0013] , , .

[0014] Preferably, the pKa of the conjugate acid of the secondary amine is in the range of 6-11. A pKa value greater than 11 leads to an overly vigorous reaction, preventing the yield of high molecular weight products; conversely, a pKa value that is too low results in insufficient basicity for catalysis. Polyimides prepared using aromatic diamines as monomers exhibit superior heat resistance and mechanical properties compared to aliphatic diamines, and since aromatic diamines generally have pKa values ​​less than 6, they are suitable for using moderately basic secondary amines as catalysts.

[0015] Preferably, the polyetherimide has a molecular weight range of 5000-10000 g / mol.

[0016] Specifically, the present invention provides a method for preparing polyimide materials by aqueous phase polymerization, comprising the following steps:

[0017] (1) Prepare an aqueous solution of acid by heating the acid anhydride in deionized water;

[0018] (2) Add a secondary amine to the aqueous solution of the above acid to react and obtain a clear salt solution;

[0019] (3) Add diamine to water, stir, and then sonicate in an ultrasonic machine to obtain a clear diamine solution or dispersion;

[0020] (4) Add the obtained diamine solution or dispersion dropwise into the clear salt solution to continue the reaction;

[0021] (5) Continue to add polyetherimide, cool down and stir continuously to obtain a mixed precipitate of polyetherimide and nylon salt;

[0022] (6) After filtering and drying the above mixed precipitate, it is molded in a mold to obtain the molded polyetherimide nylon salt material;

[0023] (7) The formed polyetherimide nylon salt material is thermally imidized to obtain a polyimide material.

[0024] Preferably, the heating temperature in step (1) is 80-100 ℃ and the heating time is 3-5 h.

[0025] Preferably, in step (2), the molar ratio of secondary amine to acid anhydride is 2:1; the reaction temperature is 60-80 °C; and the reaction time is 1-3 h.

[0026] Preferably, in step (3), the molar ratio of diamine to anhydride is 1:1 or the degree of polymerization n is controlled to be 1-20 by an excess of one of the anhydride and diamine, and the final molar ratio of amino to anhydride is controlled to be 1:1 by the amount of end-capping agent; the stirring temperature is 30-50 ℃, the stirring time is 0.5-1 h; the ultrasonic frequency is 20 kHz, and the ultrasonic time is 0.5-1 h.

[0027] Preferably, the dripping rate in step (4) is 10-50 mmol / min, the reaction temperature is 45-60 ℃, and the reaction time is 1-3 h.

[0028] Preferably, the amount of polyetherimide added in step (5) is 1-5% of the mass of nylon salt; the stirring temperature is 0-5℃ and the stirring time is 0.5-1 h.

[0029] Preferably, the drying temperature in step (6) is 50-60 ℃ and the drying time is 12-24 h.

[0030] Preferably, the molding pressure in step (6) is 50-80 MPa, the molding temperature is 40-80 ℃, the molding time is 3-5 min, and the mold direction needs to be changed each time pressure is applied. The pressure is applied 3-5 times to ensure complete compression.

[0031] Preferably, the thermal imidization conditions in step (7) are constant temperatures of 100, 200, 300, and 400 °C for 1 h each.

[0032] Beneficial effects

[0033] This invention uses deionized water as a solvent, avoiding the large amount of organic solvents required in the traditional synthesis process of polyimide. It synthesizes nylon salt powder and uses nylon salt powder as the processing object. Compared with polyimide powder, nylon salt powder has better processability, enabling rigid structures to be formed at lower temperatures. Moreover, the forming process is separated from the thermal imidization process, realizing high-efficiency, low-energy consumption, low-cost, and green production of polyimide materials, which has great application potential in aerospace and other fields. Attached Figure Description

[0034] Figure 1 Photograph of the dried nylon salt and polyetherimide mixed powder from Example 1.

[0035] Figure 2 This is a photograph of the polyetherimide nylon salt material formed in Example 1.

[0036] Figure 3 This is a photograph of the polyimide material formed in Example 1.

[0037] Figure 4 This is a scanning electron microscope image of the polyimide material in Example 1. Detailed Implementation

[0038] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0039] The dianhydride, diamine, and end-capping agent were provided by Tianjin Zhongtai Materials Technology Co., Ltd., the secondary amine was provided by Shanghai Maclean Biochemical Technology Co., Ltd., and the polyetherimide, brand name Ultem 1000R, was purchased from Saudi Basic Innovation Plastics Co., Ltd.

[0040] Mechanical properties were tested using an Instron 3400, with a tensile rate of 5 mm·min. -1 The fixture height is 5 cm, and the average value is taken from five tests.

[0041] Porosity was measured using the density method.

[0042] Example 1

[0043] Step (1): Under nitrogen deoxygenation protection, add 32.23 g (0.1 mol) of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) to a 250 mL three-necked flask, add 128 g of deionized water to adjust the solid content to 25 wt%, heat to 100 ℃ in an oil bath, reflux the distilled deionized water through a condenser, and stir for 3 h to obtain an aqueous solution of acidified 3,3',4,4'-benzophenone tetracarboxylic acid.

[0044] Step (2): Under a nitrogen atmosphere, the temperature of the system in step (1) was lowered to 60 °C, and 17.42 g (0.2 mol) of morpholine (conjugate acid pKa of 8.33) was added. The reaction was stirred for 1 h to obtain a clear salt solution.

[0045] Step (3): Control the molar ratio of dianhydride to diamine to be 1:1, add 10.81 g (0.1 mol) of p-phenylenediamine (PDA) to deionized water, stir for 0.5 h and sonicate at 20 kHz for 0.5 h to obtain a clear aqueous solution of PDA.

[0046] Step (4): Under a nitrogen atmosphere, the temperature of the system in step (2) was lowered to 45 °C. The clear aqueous solution of PDA was slowly added to the clear salt solution at a rate of 10 mmol / min using a syringe pump. Deionized water was added until the solid content was 25 wt%. The reaction was stirred for 3 h to obtain 60 g of nylon salt.

[0047] Step (5): Under a nitrogen atmosphere, add 0.6 g of polyetherimide with a molecular weight of 7500 g / mol (1% of the mass of nylon salt) to the system in step (4), lower the system temperature to 0 ℃, stir the reaction for 0.5 h, and then filter while cold to obtain a mixed precipitate of nylon salt and polyetherimide.

[0048] Step (6): The obtained mixed precipitate was dried under air purging at 50 °C for 12 h to obtain a dry mixed powder, such as... Figure 1 As shown; the mixed powder is added to the mold, the press is preheated to 60 ℃, a pressure of 80 MPa is applied, and the pressure is maintained for 3~5 min. After changing the direction and repeating the pressure application 3 times, the molded polyetherimide nylon salt material is obtained, such as Figure 2 As shown.

[0049] Step (7): The molded polyetherimide nylon salt material is subjected to thermal imidization in a nitrogen-filled high-temperature oven at constant temperatures of 100, 200, 300, and 400 °C for 1 h each, to obtain the molded polyimide material, such as... Figure 3 and 4 As shown.

[0050] Example 2

[0051] Step (1): Under nitrogen deoxygenation protection, 32.23 g (0.1 mol) of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) and 4.96 g (0.02 mol) of 4-phenylethynyl phthalic anhydride (PEPA) were added to a 250 mL three-necked flask as end-capping agents. 138 g of deionized water was added to adjust the solid content to 25 wt%. The mixture was heated to 100 °C in an oil bath. The distilled deionized water was refluxed through a condenser. After stirring for 3 h, an aqueous solution of acidified 3,3',4,4'-benzophenone tetracarboxylic acid and 4-phenylethynyl phthalic acid was obtained.

[0052] Step (2): Under a nitrogen atmosphere, the temperature of the system in step (1) was lowered to 60 °C, and 19.17 g (0.22 mol) of morpholine (conjugate acid pKa of 8.33) was added. The reaction was stirred for 1 h to obtain a clear salt solution.

[0053] Step (3): The degree of polymerization n is controlled to be 10 by the ratio of dianhydride to diamine. 11.90 g (0.11 mol) of p-phenylenediamine (PDA) is added to deionized water and stirred for 0.5 h and sonicated at 20 kHz for 0.5 h to obtain a clear aqueous solution of PDA.

[0054] Step (4): Under a nitrogen atmosphere, the temperature of the system in step (2) was lowered to 45 °C. The clear aqueous solution of PDA was slowly added to the clear salt solution at a rate of 10 mmol / min using a syringe pump. Deionized water was added until the solid content was 25 wt%. The reaction was stirred for 3 h to obtain 68 g of nylon salt.

[0055] Step (5): Under a nitrogen atmosphere, add 0.68 g of polyetherimide with a molecular weight of 7500 g / mol (1% of the mass of nylon salt) to the system in step (4), lower the system temperature to 0 ℃, stir the reaction for 0.5 h, and then filter while cold to obtain a mixed precipitate of nylon salt and polyetherimide.

[0056] Step (6): The obtained mixed precipitate is dried under air purging at 50 ℃ for 12 h to obtain a dry mixed powder. The mixed powder is added to the mold, the press is preheated to 60 ℃, a pressure of 80 MPa is applied, and the pressure is maintained for 3~5 min. The direction is changed and the pressure is applied repeatedly 3 times to obtain the molded polyetherimide nylon salt material.

[0057] Step (7): The shaped polyetherimide nylon salt material is thermally imidized in a nitrogen-filled high-temperature oven at constant temperatures of 100, 200, 300, and 400 °C for 1 h each to obtain the shaped polyimide material.

[0058] Example 3

[0059] Step (1): Under nitrogen deoxygenation protection, add 29.42 g (0.1 mol) of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) to a 250 mL three-necked flask, add 125 g of deionized water to adjust the solid content to 25 wt%, heat to 100 ℃ in an oil bath, reflux the distilled deionized water through a condenser, and stir for 3 h to obtain an acidified aqueous solution of 3,3',4,4'-biphenyltetracarboxylic acid.

[0060] Step (2): Under a nitrogen atmosphere, the temperature of the system in step (1) was lowered to 60 °C, and 17.42 g (0.2 mol) of morpholine (conjugate acid pKa of 8.33) was added. The reaction was stirred for 1 h to obtain a clear salt solution.

[0061] Step (3): Control the molar ratio of dianhydride to diamine to be 1:1, add 10.81 g (0.1 mol) of p-phenylenediamine (PDA) to deionized water, stir for 0.5 h and sonicate at 20 kHz for 0.5 h to obtain a clear aqueous solution of PDA.

[0062] Step (4): Under a nitrogen atmosphere, the temperature of the system in step (2) was lowered to 45 °C. The clear aqueous solution of PDA was slowly added to the clear salt solution at a rate of 10 mmol / min using a syringe pump. Deionized water was added until the solid content was 25 wt%. The reaction was stirred for 3 h to obtain 57 g of nylon salt.

[0063] Step (5): Under a nitrogen atmosphere, add 0.57 g of polyetherimide with a molecular weight of 7500 g / mol (1% of the mass of nylon salt) to the system in step (4), lower the system temperature to 0 ℃, stir the reaction for 0.5 h, and then filter while cold to obtain a mixed precipitate of nylon salt and polyetherimide.

[0064] Step (6): The obtained mixed precipitate is dried under air purging at 50 ℃ for 12 h to obtain a dry mixed powder. The mixed powder is added to the mold, the press is preheated to 60 ℃, a pressure of 80 MPa is applied, and the pressure is maintained for 3~5 min. The direction is changed and the pressure is applied repeatedly 3 times to obtain the molded polyetherimide nylon salt material.

[0065] Step (7): The polyetherimide nylon salt material is thermally imidized in a nitrogen-filled high-temperature oven at constant temperatures of 100, 200, 300, and 400 °C for 1 h each to obtain the shaped polyimide material.

[0066] Example 4

[0067] Step (1): Under nitrogen deoxygenation protection, 29.42 g (0.1 mol) of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) and 4.96 g (0.02 mol) of 4-phenylethynyl phthalic anhydride (PEPA) were added to a 250 mL three-necked flask as end-capping agents. 135 g of deionized water was added to adjust the solid content to 25 wt%. The mixture was heated to 100 °C in an oil bath. The distilled deionized water was refluxed through a condenser. After stirring for 3 h, an aqueous solution of acidified 3,3',4,4'-biphenyltetracarboxylic acid and 4-phenylethynyl phthalic acid was obtained.

[0068] Step (2): Under a nitrogen atmosphere, the temperature of the system in step (1) was lowered to 60 °C, and 19.17 g (0.22 mol) of morpholine (conjugate acid pKa of 8.33) was added. The reaction was stirred for 1 h to obtain a clear salt solution.

[0069] Step (3): The degree of polymerization n is controlled to be 10 by the ratio of dianhydride to diamine. 11.90 g (0.11 mol) of p-phenylenediamine (PDA) is added to deionized water and stirred for 0.5 h and sonicated at 20 kHz for 0.5 h to obtain a clear aqueous solution of PDA.

[0070] Step (4): Under a nitrogen atmosphere, the temperature of the system in step (2) was lowered to 45 °C. The clear aqueous solution of PDA was slowly added to the clear salt solution at a rate of 10 mmol / min using a syringe pump. Deionized water was added until the solid content was 25 wt%. The reaction was stirred for 3 h to obtain 65 g of nylon salt.

[0071] Step (5): Under a nitrogen atmosphere, 0.65 g of polyetherimide with a molecular weight of 7500 g / mol was added to the system in step (4). The system temperature was lowered to 0 °C, and the reaction was stirred for 0.5 h. The mixture was then filtered while cold to obtain a mixed precipitate of nylon salt and polyetherimide.

[0072] Step (6): The obtained mixed precipitate is dried under air purging at 50 ℃ for 12 h to obtain a dry mixed powder. The mixed powder is added to the mold, the press is preheated to 60 ℃, a pressure of 80 MPa is applied, and the pressure is maintained for 3~5 min. The direction is changed and the pressure is applied repeatedly 3 times to obtain the molded polyetherimide nylon salt material.

[0073] Step (7): The polyetherimide nylon salt material is thermally imidized in a nitrogen-filled high-temperature oven at constant temperatures of 100, 200, 300, and 400 °C for 1 h each to obtain the shaped polyimide material.

[0074] Comparative Example 1

[0075] Step (1): Under nitrogen deoxygenation protection, 3.57 g (0.033 mol) of p-phenylenediamine was added to a 250 mL three-necked flask, dissolved in NMP, and stirred for 1 h. Then, 9.67 g (0.03 mol) of 3,3',4,4'-benzophenone tetracarboxylic anhydride (BTDA) was slowly added. The solid content was adjusted to 15 wt% by adding NMP. After reacting in an ice bath for 4 h, 1.49 g (0.006 mol) of 4-phenylethynyl phthalic anhydride (PEPA) was added, and stirring in an ice bath was continued for 24 h to obtain a uniform and transparent polyamic acid prepolymer.

[0076] Step (2): Add 0.3 g of isoquinoline as a catalyst and 10 g of toluene as an azeotropic dehydrating agent to the polyamic acid prepolymer obtained in step (1). Reflux at 190 °C for 12 h. After cooling, pour the obtained polyimide solution into a large amount of deionized water to obtain polyimide precipitate. After repeatedly rinsing the polyimide precipitate with deionized water, dry it in a vacuum oven at 120 °C for 4 h to obtain polyimide prepolymer powder.

[0077] Step (3): Place the polyimide prepolymer powder into the mold, apply a pressure of 80 MPa, maintain for 3~5 min, and repeat the pressure 3 times to obtain the polyimide prepolymer material.

[0078] Step (4): The polyimide prepolymer material is placed in a nitrogen-filled high-temperature oven and cured at constant temperatures of 100, 200, 300, and 400 °C for 1 hour each to obtain the polyimide material. Due to the difficulty of polyimide molecular chain movement, the continuity of the material is poor after pressure is applied, resulting in poor mechanical properties and high porosity of the cured polyimide material.

[0079] Comparative Example 2

[0080] Polyimide materials were prepared according to the method in Example 1, except that a secondary amine was not added in step (2). Without a secondary amine as a catalyst, the monomer ratio in the precipitated nylon salt did not meet the conditions for forming macromolecules, and the reaction could not produce polyimide.

[0081] Comparative Example 3

[0082] Polyimide materials were prepared according to the method in Example 1, except that morpholine in step (2) was replaced with 1,5-diazabicyclo[4.3.0]non-5-ene (conjugate acid pKa value of 13.42). Due to the excessively strong basicity of 1,5-diazabicyclo[4.3.0]non-5-ene, the reaction rate was too fast, resulting in a low molecular weight and poor mechanical properties of the finished polyimide material.

[0083] Comparative Example 4

[0084] Polyimide materials were prepared according to the method in Example 1, except that morpholine in step (2) was replaced with 2,2'-bipyridine (the pKa value of the conjugate acid is 4.30). Since 2,2'-bipyridine is too weak, it cannot catalyze the reaction of aromatic diamines, resulting in poor mechanical properties of the finished product.

[0085] Comparative Example 5

[0086] Polyimide materials were prepared according to the method of Example 1, except that polyetherimide was not added in step (5). The resulting polyimide materials had excessively high rigidity and generally poor mechanical properties.

[0087] Comparative Example 6

[0088] Polyimide materials were prepared according to the method of Example 1, except that a pressure of 10 MPa was applied in step (6), resulting in polyimide materials with poor shape retention and poor mechanical properties.

[0089] The performance comparison of the polyimide materials in the examples and comparative examples is shown in Table 1.

[0090] Table 1

[0091]

[0092] (Note: "—" in the table indicates that the sample could not be formed and performance testing could not be performed.)

[0093] Examples 1-4 prepared polyimide materials with excellent mechanical properties. Compared with Example 1, Comparative Example 1, prepared using the traditional one-step polyimide method, not only used N-methylpyrrolidone as an organic solvent, but also produced polyimide with poor processability, resulting in poor mechanical properties of the final product. Comparative Examples 2-4 were samples with no secondary amine added and samples with excessively strong or weak secondary amine added, respectively. Only Comparative Example 3 could react to form polyimide, but its mechanical properties were poor. Comparative Examples 2 and 4 could not react at all to obtain the finished polyimide product. Comparative Example 5 did not add polyetherimide, resulting in excessively rigid material with weaker mechanical properties than Example 1. Comparative Example 6 used excessively low pressure for processing, resulting in poor shape retention, mediocre mechanical properties, and significantly excessive porosity.

Claims

1. A method for preparing polyimide materials by aqueous phase polymerization, characterized in that, Includes the following steps: An acid is obtained by acidifying anhydride with deionized water as a solvent. Half of the carboxyl groups in the acid react with a secondary amine and are occupied. A diamine is then added to react with the remaining carboxyl groups to generate a nylon salt. Polyetherimide is then added to obtain a mixed precipitate of nylon salt and polyetherimide. The resulting mixed precipitate is dried, molded, and thermally imidized to obtain a polyimide material. The molar ratio of the secondary amine to the acid anhydride is 2:

1. The reaction temperature of the half of the carboxyl groups in the acid with the secondary amine is 60-80 °C, and the reaction time is 1-3 h. The molding pressure is 50-80 MPa, and the temperature is 40-80 °C. The secondary amine is morpholine. The molecular weight range of the polyetherimide is 5000-10000 g / mol. The molar ratio of the diamine to the acid anhydride is 1:1, or the degree of polymerization (n) is controlled to be 1-20 by an excess of either the acid anhydride or the diamine. The amount of polyetherimide added is 1-5% of the mass of the nylon salt.

2. The method according to claim 1, characterized in that, The acid anhydride is one or more of the following structures: 、 、 、 、 、 。 3. The method according to claim 1, characterized in that, The diamine is one or more of the following structures: 、 、 、 、 、 。 4. The method according to claim 1, characterized in that, The thermal imidization conditions were constant temperature at 100, 200, 300, and 400 °C for 1 hour each.

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