A kind of thermoplastic polyimide resin and preparation method thereof

Abstract

The present invention discloses a thermoplastic polyimide resin and a preparation method thereof, wherein the preparation method of the thermoplastic polyimide resin comprises the following steps: S1, mixing a dianhydride monomer with a polar solvent, adding a diamine monomer, stirring, and obtaining a polyamic acid solution; S2, adding an organic base to the polyamic acid solution, adding a dehydrating agent, stirring, adding the reaction solution to an alcohol solvent to precipitate a precipitate, collecting the precipitate, washing, and drying, and obtaining a thermoplastic polyimide resin. The diamine monomer is a large sterically hindered biphenyl diaryl ether diamine monomer. The present invention introduces a twisted non-coplanar biphenyl diaryl ether skeleton to reduce the intermolecular stacking density, thereby effectively improving the T of the thermoplastic polyimide resin. g , T m and melt fluidity, effectively improving the melt processing performance of the material.

Description

Technical Field

[0001] The invention relates to the technical field of polyimide materials, and in particular to a thermoplastic polyimide resin and a preparation method thereof. Background Art

[0002] Thermoplastic polyimide (TPI) is developed based on traditional thermosetting polyimide PI. Compared with thermosetting PI, TPI has many potential advantages. First, TPI has excellent thermal stability, corrosion resistance, toughness and damage resistance, as well as short production cycle, simple operation and low manufacturing cost. Secondly, TPI can be melted and reprocessed, so damaged structures can be repaired by heating and pressurizing. Finally, TPI has the advantage of being environmentally friendly. It is a fully imidized polymer that does not contain any reactive chemicals, so its toxicity is very low. Due to its heating and melting characteristics and re-solubility in solvents, TPI can be recycled or combined with other recycled materials on the market to make new products.

[0003] In order to improve the melt processability of TPI, people have explored the relationship between its chemical structure and properties (such as glass transition temperature, melting ability, etc.) and proposed the following methods:

[0004] The first is to introduce flexible groups (ether bonds, ketone bonds, hexafluoroisopropyl, etc.) into the main chain. Flexible groups can improve the flexibility of the molecular chain, increase the free volume between molecules, and improve the solubility of TPI. The second is to introduce large side groups on the main chain to reduce the regularity of the main chain and improve the solubility of TPI. The third is to introduce fluorine-containing groups, such as trifluoromethyl. Its large volume will reduce the regularity of the molecular chain and increase the gaps between the molecular chains, thereby effectively improving the solubility of TPI. In addition, fluorine-containing groups have an affinity for a variety of solvents, so the synthesized TPI has excellent solubility. The fourth is to use a copolymerization method to use different diamine and dianhydride monomers for random copolymerization. Due to the different monomer structures, the regularity and flexibility of the molecular chain will be reduced, thereby reducing the interaction force and rigidity of the molecular chain and enhancing the solubility. The fifth is to introduce a twisted non-coplanar structure to destroy the symmetry of the molecular chain, increase the rotation resistance of the molecular chain, and increase the glass transition temperature.

[0005] Although the first method mentioned above can effectively improve thermoplasticity and solubility, it is at the expense of lowering the glass transition temperature of the polymer. The second and third methods have high synthesis costs and complex processes and cannot be mass-produced. It can be seen that introducing a twisted non-coplanar structure is an effective method to improve the various properties of TPI. The current common strategy is to use a spirofluorene structure to introduce an asymmetric structure, but the synthesis cost of the spirofluorene structure is relatively high. Summary of the invention

[0006] In order to overcome the above disadvantages, one of the objectives of the present invention is to provide a thermoplastic polyimide resin, which uses a large sterically hindered biphenyl structure to achieve the deflection of the polyimide structural unit, thereby achieving better thermoplasticity.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention is: a thermoplastic polyimide resin, the thermoplastic polyimide resin has the following structural formula:

[0008]

[0009] Among them, n≥5;

[0010] R 1 and R 2 is any one of carboxyl, carbonyl, ester, benzyl, tert-butyl, tert-pentyl, tert-hexyl, isopropyl, diisopropylmethyl, di-tert-butylmethyl, diisopropylamino, cyclohexyl, cyclopentyl, phenyl, substituted phenyl, naphthalene, and anthracene, and R 1 and R 2 The same or independent and unrelated;

[0011] Ar is an aromatic structure.

[0012] Preferably, n≥50.

[0013] More preferably, n≥100.

[0014] Further, the imide structure where Ar is located is one of the following structures:

[0015]

[0016] Furthermore, the thermoplastic polyimide resin has a glass transition temperature of 240-270° C., a melting temperature of 365-405° C., a melt index of 9-10 g / 10 min, a tensile strength of 80-105 MPa, and an elongation at break of 80%-95%.

[0017] Furthermore, the raw materials for preparing the thermoplastic polyimide resin include dianhydride monomers and large sterically hindered biphenyl diaryl ether diamine monomers.

[0018] The biphenyl diaryl ether skeleton in the thermoplastic polyimide resin is not a planar structure, and will undergo spatial deflection, so that the polyimide polymer structural units are in different planes. It can be seen that by introducing a twisted non-coplanar biphenyl diaryl ether skeleton, the intermolecular stacking density can be reduced and the T of the thermoplastic polyimide can be improved. g , T m and melt fluidity, effectively improving the melt processing performance of the material.

[0019] Exemplarily, when the imide structure where Ar is located is , R 1 , R 2 When all are phenyl groups, the resulting biphenyl diaryl ether skeleton will undergo spatial deflection as shown in the following structural formula.

[0020]

[0021] Further, the dianhydride monomer is one of the following structures:

[0022] .

[0023] Furthermore, the structure of the large sterically hindered biphenyl diaryl ether diamine monomer is as follows:

[0024]

[0025] Among them, R 1 and R 2 is any one of carboxyl, carbonyl, ester, benzyl, tert-butyl, tert-pentyl, tert-hexyl, isopropyl, diisopropylmethyl, di-tert-butylmethyl, diisopropylamino, cyclohexyl, cyclopentyl, phenyl, substituted phenyl, naphthalene, and anthracene, and R 1 and R 2 The same or independent and unrelated.

[0026] Furthermore, when R 1 and R 2 When aryl or alkyl, and R 1 and R 2 For the same substituent, the synthetic route of the heavily hindered biphenyl diaryl ether diamine monomer is as follows:

[0027]

[0028] The specific synthesis steps are as follows:

[0029] Step 1: Add the raw material 2-bromo-6-fluoroiodobenzene, alkali and copper powder into a polar solvent, heat and stir to react, and after the reaction is completed, crystallize and filter to obtain intermediate 1;

[0030] Step 2: adding intermediate 1, p-aminophenol and a base to a polar solvent, heating and stirring to react, and after the reaction is completed, crystallizing and filtering to obtain a solid, and then washing and drying to obtain intermediate 2;

[0031] Step 3: adding intermediate 2, halogenated hydrocarbon, catalyst and reducing agent to a polar solvent, heating and stirring to react under the protection of inert gas, and separating and obtaining the target large sterically hindered biphenyl diaryl ether diamine monomer after the reaction is completed;

[0032] Preferably, the specific synthesis steps are as follows:

[0033] Step 1: Add the raw material 2-bromo-6-fluoroiodobenzene, alkali and copper powder to a polar solvent, stir at high temperature for 2 to 24 hours, and determine the progress of the reaction by TLC. After the reaction is completed, filter through diatomaceous earth and silica gel respectively, add water, and the precipitated solid is obtained by filtration to obtain intermediate 1.

[0034] Step 2: Add intermediate 1, p-aminophenol and base to a polar solvent and stir at high temperature for 2 to 24 hours. After the reaction is completed, pour the reaction solution into water, filter to obtain a solid, and obtain intermediate 2 after washing and drying.

[0035] Step 3: Add intermediate 2, halogenated hydrocarbon (RX), catalyst, and reducing agent to a polar solvent, replace argon or nitrogen, and react at high temperature for 2 to 24 hours. After the reaction is completed, separate the target large sterically hindered biphenyl diaryl ether diamine monomer by column chromatography.

[0036] The above preparation steps of the large sterically hindered biphenyl diaryl ether diamine monomer containing aromatic or alkyl groups are simple and easy to purify. Compared with the currently common method of introducing an asymmetric structure using a spirofluorene structure, this method has low synthesis cost and is easy to prepare.

[0037] Furthermore, the base in steps 1 and 2 is one or more of potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, potassium tert-butoxide, and sodium hydride.

[0038] Furthermore, the polar solvent in steps 1, 2 and 3 is one or more of DMF, DMAc, DMSO and NMP.

[0039] Furthermore, the high temperature in steps 1, 2 and 3 is any temperature between 80 and 200°C.

[0040] Furthermore, the molar ratio of 2-bromo-6-fluoroiodobenzene to the base in step 1 is any value between 1:1 and 5.

[0041] Furthermore, the molar ratio of the intermediate 1 in step 2 to p-aminophenol is any value between 1:1 and 5.

[0042] Furthermore, the molar ratio of the intermediate 1 to the base in step 2 is any value between 1:1 and 5.

[0043] Furthermore, the halogenated hydrocarbon in step 3 is any one of iodinated aromatic hydrocarbons, iodinated alkanes, brominated aromatic hydrocarbons and brominated alkanes.

[0044] Furthermore, the molar ratio of the halogenated hydrocarbon in step 3 to the intermediate 2 is any value between 2 and 6:1.

[0045] Furthermore, the catalyst in step 3 can be any metal salt or complex of Pd, Ni, or Cu.

[0046] Furthermore, the molar ratio of the catalyst to the intermediate 2 in step 3 can be any value between 1:5 and 1000.

[0047] Furthermore, the reducing agent in step 3 is any one of Mg metal powder, Mn metal powder, Zn metal powder and Al metal powder.

[0048] Furthermore, when R 1 and R 2 When it is an ester group, that is, R 1 and R 2 It is the -COOR group in the following structural formula. The synthetic route of the large sterically hindered biphenyl diaryl ether diamine monomer is as follows:

[0049]

[0050] The specific synthesis steps are as follows:

[0051] Step (1): adding 2-iodo-3-fluorobenzoic acid, R-OH and an acid catalyst to a solvent, heating and reflux with stirring, and after the reaction is completed, removing the solvent by rotary evaporation, and obtaining intermediate 3 by recrystallization;

[0052] Step (2): adding intermediate 3, alkali and copper powder into a polar solvent, heating and stirring, and after the reaction is completed, crystallizing and filtering to obtain intermediate 4;

[0053] Step (3): adding intermediate 4, p-aminophenol and a base to a polar solvent, heating and stirring, and after the reaction is completed, crystallizing and filtering to obtain a solid, and then washing and drying to obtain the target large sterically hindered biphenyl diaryl ether diamine monomer.

[0054] Preferably, the specific synthesis steps are as follows:

[0055] Step (1): 2-iodo-3-fluorobenzoic acid, R-OH and an acid catalyst are added to toluene, and the mixture is refluxed at high temperature with stirring for 2 to 24 hours. After the reaction is completed, the toluene is removed by rotary evaporation, and the intermediate 3 is obtained by recrystallization.

[0056] Step (2): Add intermediate 3, alkali and copper powder to a polar solvent, stir at high temperature for 2 to 24 hours, and determine the progress of the reaction by TLC. After the reaction is completed, filter through diatomaceous earth and silica gel respectively, add water, and filter the precipitated solid to obtain intermediate 4.

[0057] Step (3): Add intermediate 4, p-aminophenol and base to a polar solvent and stir at high temperature for 2 to 24 hours. After the reaction is completed, pour the reaction solution into water, filter to obtain a solid, and then wash and dry to obtain the target large sterically hindered biphenyl diaryl ether diamine monomer.

[0058] The above preparation steps of the ester-containing large sterically hindered biphenyl diaryl ether diamine monomer are simple and easy to purify. Compared with the currently common method of introducing an asymmetric structure using a spirofluorene structure, the synthesis cost of this method is low.

[0059] Furthermore, the acid catalyst in step (1) is one or more of sulfuric acid, methanesulfonic acid, and p-toluenesulfonic acid.

[0060] Furthermore, the base in step (2) and step (3) is one or more of potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, potassium tert-butoxide, and sodium hydride.

[0061] Furthermore, in step (2) and step (3), the polar solvent is one or more of DMF, DMAc, DMSO, and NMP.

[0062] Furthermore, in the above steps (1) to (3), the high temperature is any temperature between 80°C and 200°C.

[0063] Furthermore, the molar ratio of the intermediate 3 to the base in step (2) is 1:1-5.

[0064] Furthermore, the molar ratio of the intermediate 4 to p-aminophenol in step (3) is 1:1-5.

[0065] Furthermore, the molar ratio of the intermediate 4 to the base in step (3) is 1:1-5.

[0066] Furthermore, the raw materials for preparing the thermoplastic polyimide resin also include an organic base, a dehydrating agent, and an alcohol solvent.

[0067] Furthermore, the organic base is one or more of triethylamine, ethylenediamine, diisopropylethylamine, diethylamine, pyridine, 2,6-lutidine, 2,4,6-trimethylpyridine, 2,6-di-tert-butylpyridine, 4-dimethylaminopyridine, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).

[0068] Furthermore, the dehydrating agent is one or more of acetic anhydride, propionic anhydride, acetyl chloride, dicyclohexylcarbocyanine, trifluoroacetic anhydride and thionyl chloride.

[0069] Furthermore, the alcohol solvent is one or more of methanol, ethanol, propanol, isopropanol, hexafluoroisopropanol, butanol, tert-butanol, and acetone.

[0070] A second object of the present invention is to provide a method for preparing a thermoplastic polyimide resin, comprising the following steps:

[0071] S1, mixing the dianhydride monomer and the polar solvent, adding the diamine monomer, stirring, and obtaining a polyamic acid solution;

[0072] S2. Add an organic base and a dehydrating agent to the polyamic acid solution, stir, add the reaction solution to an alcohol solvent to precipitate a precipitate, collect the precipitate, wash, and dry to obtain a thermoplastic polyimide resin.

[0073] Preferably, a method for preparing a thermoplastic polyimide resin comprises the following steps:

[0074] S1: At room temperature, mix the dianhydride monomer and polar solvent until they are completely dissolved; then cool down and replace with inert gas, wait for the system to stabilize and reach the set low temperature environment, slowly add diamine monomer in an inert gas atmosphere, continue to stir at low temperature for 2 to 24 hours, and obtain a polyamic acid (PAA) solution.

[0075] S2: After adding an organic base to the PAA solution, slowly drop the dehydrating agent. After the addition is completed, heat and stir for 2 to 24 hours, and the solution turns from transparent to light yellow. After the reaction is completed, slowly drop the obtained light yellow solution into an alcohol solvent, and a light yellow precipitate will immediately precipitate. The light yellow resin powder is obtained by vacuum filtration, and finally the light yellow powder is further washed, filtered and dried using an alcohol solvent.

[0076] Furthermore, in step S1, the solid content of the polyamic acid solution is ≥5%.

[0077] Furthermore, in step S1, the molar ratio of the diamine monomer to the dianhydride monomer is 1:1.05-2.

[0078] Furthermore, in step S1, the polar solvent is one or more of DMF, DMAc, NMP, and DMSO.

[0079] Furthermore, in step S1, the low temperature environment is ≤5°C.

[0080] Furthermore, in step S1, the inert gas is any one of argon or nitrogen.

[0081] Furthermore, in step S2, the molar ratio of the organic base to the dehydrating agent is 1:1-2.

[0082] Furthermore, the molar ratio of the dehydrating agent to the diamine monomer is 2 to 8:1.

[0083] Furthermore, in step S2, the temperature is raised to 120-170°C.

[0084] Furthermore, in step S2, the amount of the alcohol solvent used is 5 to 50 times the volume of the reaction solvent.

[0085] The beneficial effects of the present invention are:

[0086] (1) The present invention introduces a twisted non-coplanar biphenyl diaryl ether skeleton to reduce the intermolecular stacking density, thereby effectively improving the T of the thermoplastic polyimide resin. g , T m and melt fluidity, effectively improving the melt processing performance of the material.

[0087] (2) The present invention uses a large steric hindrance biphenyl structure to achieve the deflection of the polyimide structural unit, thereby achieving better thermoplasticity and avoiding the loss of mechanical properties of the material due to the introduction of too many flexible units.

[0088] (3) The preparation of large sterically hindered biphenyl diaryl ether diamine monomers containing ester groups, aromatic groups or alkyl groups has simple synthesis steps and is easy to purify. Compared with the currently common method of introducing an asymmetric structure using a spirofluorene structure, this method has low synthesis cost and is easy to prepare.

[0089] (4) The large sterically hindered biphenyl structure used in the present invention can achieve different structural deflection rates by changing the steric hindering group, which provides a greater room for regulating structural properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0091] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0092] Figure 1 The hydrogen nuclear magnetic resonance spectrum of the phenyl-substituted hindered diamine monomer prepared in Preparation Example 1;

[0093] Figure 2 The hydrogen nuclear magnetic resonance spectrum of the ester-substituted sterically hindered diamine monomer prepared in Preparation Example 2;

[0094] Figure 3 The hydrogen nuclear magnetic resonance spectrum of the thermoplastic polyimide prepared in Example 1;

[0095] Figure 4 The hydrogen nuclear magnetic resonance spectrum of the thermoplastic polyimide prepared in Example 2;

[0096] Figure 5 The hydrogen nuclear magnetic resonance spectrum of the thermoplastic polyimide prepared in Example 3;

[0097] Figure 6 The hydrogen nuclear magnetic resonance spectrum of the thermoplastic polyimide prepared in Example 4;

[0098] Figure 7 This is the hydrogen nuclear magnetic resonance spectrum of the thermoplastic polyimide prepared in Example 5. DETAILED DESCRIPTION

[0099] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0100] Except as shown in the operating examples or otherwise indicated, all numbers used in the specification and claims to indicate the amount of ingredients, physicochemical properties, etc. are understood to be adjusted by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters listed in the above specification and the attached claims are approximate values, and those skilled in the art can use the teachings disclosed herein to seek to obtain the desired properties and appropriately change these approximate values. The use of numerical ranges expressed as endpoints includes all numbers within the range and any range within the range, for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4 and 5, etc.

[0101] The following examples describe the disclosure of the present invention in more detail, and these examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0102] The present invention provides a thermoplastic polyimide resin having the following structural formula:

[0103]

[0104] Among them, n≥5;

[0105] R 1 and R2 is any one of carboxyl, carbonyl, ester, benzyl, tert-butyl, tert-pentyl, tert-hexyl, isopropyl, diisopropylmethyl, di-tert-butylmethyl, diisopropylamino, cyclohexyl, cyclopentyl, phenyl, substituted phenyl, naphthalene, and anthracene, and R 1 and R 2 The same or independent and unrelated;

[0106] Ar is an aromatic structure.

[0107] In some embodiments, n≥50.

[0108] In some embodiments, n≥100.

[0109] In some embodiments, the imide structure where Ar is located is one of the following structures:

[0110] .

[0111] The biphenyl diaryl ether skeleton in the thermoplastic polyimide resin is not a planar structure, and will undergo spatial deflection, so that the polyimide polymer structural units are in different planes. It can be seen that by introducing a twisted non-coplanar biphenyl diaryl ether skeleton, the intermolecular stacking density can be reduced and the various properties of the thermoplastic polyimide can be improved.

[0112] In some embodiments, the raw materials for preparing the thermoplastic polyimide resin include dianhydride monomers, diamine monomers, and may also include organic bases, dehydrating agents, and alcohol solvents.

[0113] In some embodiments, the dianhydride monomer is one of the following structures:

[0114] .

[0115] In some embodiments, the diamine monomer is a bulky biphenyl diaryl ether-based diamine monomer.

[0116] In some embodiments, the structure of the bulky hindered biphenyl diaryl ether diamine monomer is as follows:

[0117]

[0118] Among them, R 1 and R 2 is any one of carboxyl, carbonyl, ester, benzyl, tert-butyl, tert-pentyl, tert-hexyl, isopropyl, diisopropylmethyl, di-tert-butylmethyl, diisopropylamino, cyclohexyl, cyclopentyl, phenyl, substituted phenyl, naphthalene, and anthracene, and R 1 and R 2 The same or independent and unrelated.

[0119] In some embodiments, when R 1and R 2 When it is an aryl or alkyl group, the synthetic route of the large sterically hindered biphenyl diaryl ether diamine monomer is as follows:

[0120]

[0121] In some embodiments, the specific synthesis steps are as follows:

[0122] Step 1: Add the raw material 2-bromo-6-fluoroiodobenzene, alkali and ultrafine copper powder to a polar solvent, stir at high temperature for 2-24 hours, and determine the progress of the reaction by TLC. After the reaction is completed, filter through diatomaceous earth and silica gel respectively, add a large amount of water, and the precipitated solid is obtained by filtration, which is intermediate 1.

[0123] Step 2: Add intermediate 1, p-aminophenol and base to a polar solvent and stir at high temperature for 2 to 24 hours. After the reaction is completed, pour the reaction solution into water, filter to obtain a solid, and obtain intermediate 2 after washing and drying.

[0124] Step 3: Add intermediate 2, halogenated hydrocarbon (RX), catalyst, and reducing agent to a polar solvent, replace argon or nitrogen, and react at high temperature for 2 to 24 hours. After the reaction is completed, separate the target sterically hindered diamine monomer by column chromatography.

[0125] In some embodiments, the base in steps 1 and 2 is one or more of potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, potassium tert-butoxide, and sodium hydride.

[0126] In some embodiments, the polar solvent in steps 1, 2, and 3 is one or more of DMF, DMAc, DMSO, and NMP.

[0127] In some embodiments, the high temperature in steps 1, 2, and 3 is any temperature between 80 and 200°C.

[0128] In some embodiments, the molar ratio of 2-bromo-6-fluoroiodobenzene to the base in step 1 is any value between 1:1 and 5.

[0129] In some embodiments, the molar ratio of intermediate 1 to p-aminophenol in step 2 is any value between 1:1 and 5.

[0130] In some embodiments, the molar ratio of the intermediate 1 to the base in step 2 is any value between 1:1 and 5.

[0131] In some embodiments, the halogenated hydrocarbon in step 3 is any one of iodinated aromatic hydrocarbons, iodinated alkanes, brominated aromatic hydrocarbons, and brominated alkanes.

[0132] In some embodiments, the molar ratio of the halogenated hydrocarbon in step 3 to the intermediate 2 is any value between 2 and 6:1.

[0133] In some embodiments, the catalyst in step 3 can be any metal salt or complex of Pd, Ni, or Cu.

[0134] In some embodiments, the molar ratio of the catalyst to the intermediate 2 in step 3 can be any value between 1:5 and 1000.

[0135] In some embodiments, the reducing agent in step 3 is any one of Mg metal powder, Mn metal powder, Zn metal powder, and Al metal powder.

[0136] The above preparation steps of the large sterically hindered biphenyl diaryl ether diamine monomer containing aromatic or alkyl groups are simple and easy to purify. Compared with the currently common method of introducing an asymmetric structure using a spirofluorene structure, this method has low synthesis cost and is easy to prepare.

[0137] In some embodiments, when R 1 and R 2 When it is an ester group, that is, R 1 and R 2 It is the -COOR group in the following structural formula. The synthetic route of the large sterically hindered biphenyl diaryl ether diamine monomer is as follows:

[0138]

[0139] In some embodiments, the specific synthesis steps are as follows:

[0140] Step (1): 2-iodo-3-fluorobenzoic acid, R-OH and an acid catalyst are added to toluene, and the mixture is refluxed at high temperature with stirring for 2 to 24 hours. After the reaction is completed, the toluene is removed by rotary evaporation, and the intermediate 3 is obtained by recrystallization.

[0141] Step (2): Add intermediate 3, alkali and ultrafine copper powder to a polar solvent, stir at high temperature for 2 to 24 hours, and determine the progress of the reaction by TLC. After the reaction is completed, filter through diatomaceous earth and silica gel respectively, add a large amount of water, and filter the precipitated solid to obtain intermediate 4.

[0142] Step (3): Add intermediate 4, p-aminophenol and base to a polar solvent and stir at high temperature for 2 to 24 hours. After the reaction is completed, pour the reaction solution into water, filter to obtain a solid, and then wash and dry to obtain the target ester-type hindered diamine monomer.

[0143] The above preparation steps of the ester-containing large sterically hindered biphenyl diaryl ether diamine monomer are simple and easy to purify. Compared with the currently common method of introducing an asymmetric structure using a spirofluorene structure, the synthesis cost of this method is low.

[0144] In some embodiments, the acid catalyst in step (1) is one or more of sulfuric acid, methanesulfonic acid, and p-toluenesulfonic acid.

[0145] In some embodiments, the base in step (2) and step (3) is one or more of potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, potassium tert-butoxide, and sodium hydride.

[0146] In some embodiments, the polar solvent in step (2) and step (3) is one or more of DMF, DMAc, DMSO, and NMP.

[0147] In some embodiments, the high temperature in the above steps (1) to (3) is any temperature between 80 and 200°C.

[0148] In some embodiments, the molar ratio of the intermediate 3 to the base in step (2) is 1:1-5.

[0149] In some embodiments, the molar ratio of intermediate 4 to p-aminophenol in step (3) is 1:1-5.

[0150] In some embodiments, the molar ratio of intermediate 4 to base in step (3) is 1:1-5.

[0151] In some embodiments, a method for preparing a thermoplastic polyimide resin comprises the following steps:

[0152] S1, mixing the dianhydride monomer and the polar solvent, adding the diamine monomer, stirring, and obtaining a polyamic acid solution;

[0153] S2. Add an organic base and a dehydrating agent to the polyamic acid solution, stir, add the reaction solution to an alcohol solvent to precipitate a precipitate, collect the precipitate, wash, and dry to obtain a thermoplastic polyimide resin.

[0154] In some embodiments, a method for preparing a thermoplastic polyimide resin comprises the following steps:

[0155] S1: At room temperature, mix the dianhydride monomer and polar solvent until they are completely dissolved; then cool down and replace with inert gas, wait for the system to stabilize and reach the set low temperature environment, slowly add diamine monomer in an inert gas atmosphere, continue to stir at low temperature for 2 to 24 hours, and obtain a polyamic acid (PAA) solution.

[0156] S2: After adding an organic base to the PAA solution, slowly drop the dehydrating agent. After the addition is completed, heat and stir for 2 to 24 hours, and the solution turns from transparent to light yellow. After the reaction is completed, slowly drop the obtained light yellow solution into an alcohol solvent, and a light yellow precipitate will immediately precipitate. The light yellow resin powder is obtained by vacuum filtration, and finally the light yellow powder is further washed, filtered and dried using an alcohol solvent.

[0157] In some embodiments, in S1, the solid content of the polyamic acid solution is ≥5%.

[0158] In some embodiments, in S1, the molar ratio of the diamine monomer to the dianhydride monomer is 1:1.05-2.

[0159] In some embodiments, in S1, the polar solvent is one or more of DMF, DMAc, NMP, and DMSO.

[0160] In some embodiments, the low temperature environment described in S1 is ≤5°C.

[0161] In some embodiments, the inert gas described in S1 is any one of argon or nitrogen.

[0162] In some embodiments, in S2, the organic base is one or more of triethylamine, ethylenediamine, diisopropylethylamine, diethylamine, pyridine, 2,6-lutidine, 2,4,6-trimethylpyridine, 2,6-di-tert-butylpyridine, 4-dimethylaminopyridine, and 1,8-diazabicyclo[5.4.0]undec-7-ene DBU.

[0163] In some embodiments, in S2, the molar ratio of the organic base to the dehydrating agent is 1:1-2.

[0164] In some embodiments, the molar ratio of the dehydrating agent to the diamine monomer is 2 to 8:1.

[0165] In some embodiments, in S2, the dehydrating agent is one or more of acetic anhydride, propionic anhydride, acetyl chloride, dicyclohexylcarbocyanine, trifluoroacetic anhydride and thionyl chloride.

[0166] In some embodiments, in S2, the temperature is raised to 120-170°C.

[0167] In some embodiments, in S2, the alcohol solvent is one or more of methanol, ethanol, propanol, isopropanol, hexafluoroisopropanol, butanol, tert-butanol, and acetone.

[0168] In some embodiments, in S2, the amount of the alcohol solvent used is 5 to 50 times the volume of the reaction solvent.

[0169] Preparation Example 1

[0170] This embodiment provides a phenyl-substituted hindered diamine monomer:

[0171]

[0172] The synthetic route of this structure is as follows:

[0173]

[0174] Specific synthesis steps:

[0175] Step 1: Add the raw materials 2-bromo-6-fluoroiodobenzene (3 g, 10 mmol), K2CO3 (2.76 g, 20 mmol) and copper powder (3.8 g, 60 mmol) into 20 mL DMF, stir at 180 ° C for 16 h, and determine the progress of the reaction by TLC. After the reaction is completed, filter through diatomaceous earth and silica gel respectively, add a large amount of water, and the precipitated solid is filtered to obtain compound 1 (equivalent to intermediate 1 in the synthetic route).

[0176] Step 2: Compound 1 (3.48 g, 10 mmol), p-aminophenol (2.4 g, 22 mmol), and NaOH (1.2 g, 30 mmol) were added to 20 mL of NMP and stirred at 120 °C for 12 h. After the reaction, the reaction solution was poured into water and filtered to obtain a solid. After washing and drying, compound 2 (equivalent to intermediate 2 in the synthetic route) was obtained.

[0177] Step 3: Compound 2 (5.26 g, 10 mmol), iodobenzene (6.12 g, 30 mmol), NiBr2 (0.218 g, 1 mmol), and Zn powder (1.96 g, 30 mmol) were added to 20 mL of DMF, argon was replaced, and the mixture was reacted at 120°C for 16 h. After the reaction, compound 3 was obtained by column chromatography.

[0178] NMR data of compound 3: 1 H NMR (500 MHz, Chloroform- d ) δ 7.64 (dd, J = 7.6,2.0 Hz, 4H), 7.45 – 7.38 (m, 8H), 7.36 – 7.30 (m, 2H), 7.15 (ddd, J = 7.0, 2.7,1.1 Hz, 2H), 6.67 (dq, J = 8.4, 2.5 Hz, 4H), 6.56 – 6.50 (m, 4H), 4.11 (d, J =4.9 Hz, 4H).

[0179] Preparation Example 2

[0180] This embodiment provides an ester-substituted hindered diamine monomer:

[0181]

[0182] The synthesis method of this structure is as follows:

[0183]

[0184] Step (1): Add 2-iodo-3-fluorobenzoic acid (2.66 g, 10 mmol), methanol (5 mL), and methanesulfonic acid (0.096 g, 1 mmol) to 50 mL of toluene, reflux at 120°C with stirring for 20 h. After the reaction is completed, remove the toluene by rotary evaporation, and obtain compound 4 (equivalent to intermediate 3 in the synthetic route) by recrystallization.

[0185] Step (2): Compound 4 (2.8 g, 10 mmol), K2CO3 (2.76 g, 20 mmol) and copper powder (3.8 g, 60 mmol) were added to 20 mL of DMF and stirred at 200 °C for 20 h. The reaction progress was determined by TLC. After the reaction was completed, a large amount of water was added after filtering through diatomaceous earth and silica gel, and the precipitated solid was filtered to obtain compound 5 (equivalent to intermediate 4 in the synthetic route).

[0186] Step (3): Compound 5 (3.06 g, 10 mmol), p-aminophenol (2.4 g, 22 mmol), and NaOH (1.2 g, 30 mmol) were added to 20 mL of NMP and stirred at 120 °C for 20 h. After the reaction, the reaction solution was poured into water and filtered to obtain a solid, which was then washed and dried to obtain compound 6.

[0187] NMR data of compound 6: 1 H NMR (500 MHz, Chloroform- d ) δ 7.85 (dd, J = 7.3,2.0 Hz, 2H), 7.50 (t, J = 7.5 Hz, 2H), 7.28 (dd, J = 7.5, 2.0 Hz, 2H), 6.64 –6.51 (m, 8H), 4.07 (s, 4H), 3.95 (s, 6H).

[0188] Example 1

[0189] In this embodiment, the structure of the thermoplastic polyimide is as follows:

[0190]

[0191] The synthesis method of the thermoplastic polyimide resin of this structure is as follows:

[0192] S1: At room temperature, PMDA (2.4 g, 11 mmol) and N-methylpyrrolidone (100 mL) were mixed until completely dissolved; then the temperature was lowered and argon gas was replaced, and the reaction solution was tested by a thermometer. After the system temperature dropped to -5 °C, compound 3 (5.2 g, 10 mmol) prepared in Preparation Example 1 was slowly added under an inert gas atmosphere, and the mixture was stirred at low temperature (-5 °C) for 10 h, and then a capping agent (phthalic anhydride) was added and the reaction was continued for 2 h to obtain a polyamic acid (PAA) solution.

[0193] S2: Add pyridine (0.8 mL, 10 mmol) to the PAA solution, and slowly drop the dehydrating agent acetic anhydride (1.88 mL, 20 mmol). After the addition is completed, heat to 150 °C and stir for 16 hours. The solution turns from transparent to light yellow. After the reaction is completed, slowly drop the obtained light yellow solution into the rapidly stirred ethanol, and a light yellow precipitate will precipitate immediately. The light yellow resin powder is obtained by vacuum filtration, and finally the light yellow powder is washed, filtered and dried with an alcohol solvent (ethanol).

[0194] NMR data of thermoplastic polyimide resin: 1 H NMR (500 MHz, Chloroform- d ) δ 8.44(d, J = 3.7 Hz, 2H), 8.02 – 7.93 (m, 2H), 7.66 (dt, J = 7.8, 1.9 Hz, 4H), 7.54 –7.38 (m, 8H), 7.36 – 7.27 (m, 3H), 7.19 (dd, J = 7.2, 2.3 Hz, 1H), 7.16 – 7.09 (m, 2H), 6.94 – 6.88 (m, 2H), 6.84 – 6.78 (m, 2H).

[0195] Example 2

[0196] In this embodiment, the structure of the thermoplastic polyimide is as follows:

[0197]

[0198] The synthesis method of the thermoplastic polyimide resin of this structure is as follows:

[0199] S1: Mix biphenyltetracarboxylic dianhydride BPDA (3.236 g, 11 mmol) and N-methylpyrrolidone NMP (100 mL) at room temperature until they are completely dissolved; then cool down and replace with argon, check the reaction solution with a thermometer, wait for the system temperature to drop to -5 °C, and slowly add 35.2 g (10 mmol) of the compound prepared in Preparation Example 1 while maintaining an inert gas atmosphere. Continue stirring at low temperature (-5 °C) for 12 h, then add the end-capping agent (phthalic anhydride) and continue the reaction for 2 h to obtain a polyamic acid (PAA) solution.

[0200] S2: Add pyridine (0.8 mL, 10 mmol) to the PAA solution, and slowly drop the dehydrating agent acetic anhydride (1.88 mL, 20 mmol). After the addition is completed, heat to 130 °C and stir for 20 hours. The solution turns from transparent to light yellow. After the reaction is completed, slowly drop the obtained light yellow solution into the rapidly stirred ethanol, and a light yellow precipitate will precipitate immediately. The light yellow resin powder is obtained by vacuum filtration, and finally the light yellow powder is washed, filtered and dried with an alcohol solvent (ethanol).

[0201] NMR data of thermoplastic polyimide resin: 1 H NMR (500 MHz, Chloroform- d ) δ 8.38(dd, J = 4.2, 2.0 Hz, 2H), 8.25 – 8.17 (m, 3H), 8.09 (d, J = 7.4 Hz, 1H), 7.90(ddd, J = 9.7, 7.5, 1.9 Hz, 2H), 7.66 (td, J = 7.8, 2.0 Hz, 4H), 7.48 – 7.29 (m,10H), 7.27 – 7.19 (m, 3H), 7.16 – 7.11 (m, 2H), 7.06 (dd, J = 7.1, 2.4 Hz, 1H), 7.02 – 6.98 (m, 2H).

[0202] Example 3

[0203] In this embodiment, the structure of the thermoplastic polyimide is as follows:

[0204]

[0205] The synthesis method of the thermoplastic polyimide resin of this structure is as follows:

[0206] S1: At room temperature, benzophenonetetracarboxylic dianhydride BTDA (3.544 g, 11 mmol) and N-methylpyrrolidone NMP (100 mL) were mixed until completely dissolved; then the temperature was lowered and argon gas was replaced, and the reaction solution was tested by a thermometer. After the system temperature dropped to -5 °C, compound 3 (5.2 g, 10 mmol) prepared in Preparation Example 1 was slowly added under an inert gas atmosphere, and the mixture was stirred at low temperature for 14 h, and then a capping agent (phthalic anhydride) was added and the reaction was continued for 2 h to obtain a polyamic acid (PAA) solution.

[0207] S2: Add pyridine (0.8 mL, 10 mmol) to the PAA solution, and slowly drop the dehydrating agent acetic anhydride (1.88 mL, 20 mmol). After the addition is completed, heat to 160 °C and stir for 13 hours. The solution turns from transparent to light yellow. After the reaction is completed, slowly drop the obtained light yellow solution into the rapidly stirred ethanol, and a light yellow precipitate will precipitate immediately. The light yellow resin powder is obtained by vacuum filtration, and finally the light yellow powder is washed, filtered and dried with an alcohol solvent (ethanol).

[0208] NMR data of thermoplastic polyimide resin: 1 H NMR (500 MHz, Chloroform- d ) δ 8.40(d, J = 2.0 Hz, 1H), 8.32 (d, J = 2.0 Hz, 1H), 8.16 – 8.08 (m, 5H), 8.02 (d, J =7.5 Hz, 1H), 7.56 – 7.52 (m, 2H), 7.52 – 7.38 (m, 9H), 7.36 – 7.30 (m, 4H), 7.20 (dd, J = 7.1, 2.4 Hz, 1H), 7.13 (dd, J = 7.5, 1.2 Hz, 2H), 7.03 – 6.96 (m, 4H).

[0209] Example 4

[0210] In this embodiment, the structure of the thermoplastic polyimide is as follows:

[0211]

[0212] The synthesis method of the thermoplastic polyimide resin of this structure is as follows:

[0213] S1: At room temperature, 4,4'-oxydiphthalic anhydride ODPA (3.412 g, 11 mmol) and N-methylpyrrolidone NMP (100 mL) were mixed until completely dissolved; then the temperature was lowered and argon gas was replaced, and the reaction solution was tested by a thermometer. After the system temperature dropped to -5 °C, compound 3 (5.2 g, 10 mmol) prepared in Preparation Example 1 was slowly added under an inert gas atmosphere, and the mixture was stirred at low temperature for 14 h, and then the end-capping agent (phthalic anhydride) was added and the reaction was continued for 2 h to obtain a polyamic acid (PAA) solution.

[0214] S2: Add 0.8 mL (10 mmol) of pyridine to the PAA solution, and slowly drop 1.88 mL (20 mmol) of acetic anhydride as a dehydrating agent. After the addition is complete, heat to 140 °C and stir for 17 hours. The solution turns from transparent to light yellow. After the reaction is complete, slowly drop the obtained light yellow solution into the rapidly stirred ethanol, and a light yellow precipitate will immediately precipitate. The light yellow resin powder is obtained by vacuum filtration, and finally the light yellow powder is washed, filtered and dried with an alcohol solvent (ethanol).

[0215] NMR data of thermoplastic polyimide resin: 1 H NMR (500 MHz, Chloroform- d ) δ 8.18 –8.12 (m, 2H), 8.06 (d, J = 8.0 Hz, 1H), 7.90 – 7.86 (m, 1H), 7.68 (ddd, J = 7.9,6.2, 2.0 Hz, 4H), 7.57 (dq, J = 4.2, 2.0 Hz, 2H), 7.51 – 7.47 (m, 2H), 7.46 –7.38 (m, 8H), 7.36 – 7.30 (m, 2H), 7.19 – 7.09 (m, 4H), 7.08 – 7.04 (m, 2H),7.03 – 6.98 (m, 2H).

[0216] Example 5

[0217] In this embodiment, the structure of the thermoplastic polyimide is as follows:

[0218]

[0219] The synthesis method of the thermoplastic polyimide resin of this structure is as follows:

[0220] S1: Mix PMDA (2.398 g, 11 mmol) and N-methylpyrrolidone NMP (100 mL) at room temperature until they are completely dissolved; then cool down and replace with argon, check the reaction solution with a thermometer, wait for the system temperature to drop to -5 °C, and slowly add compound 6 (4.845 g, 10 mmol) prepared in Preparation Example 2 under an inert gas atmosphere, continue stirring at low temperature for 10 h, then add the end-capping agent (phthalic anhydride) and continue the reaction for 2 h to obtain a polyamic acid (PAA) solution.

[0221] S2: Add pyridine (0.8 mL, 10 mmol) to the PAA solution, and slowly drop the dehydrating agent acetic anhydride (1.88 mL, 20 mmol). After the addition is completed, heat to 150 °C and stir for 16 hours. The solution turns from transparent to light yellow. After the reaction is completed, slowly drop the obtained light yellow solution into the rapidly stirred ethanol, and a light yellow precipitate will precipitate immediately. The light yellow resin powder is obtained by vacuum filtration, and finally the light yellow powder is washed, filtered and dried with an alcohol solvent (ethanol).

[0222] NMR data of thermoplastic polyimide resin: 1 H NMR (500 MHz, Chloroform- d ) δ 8.44(d, J = 9.5 Hz, 2H), 8.08 – 8.03 (m, 2H), 7.74 (dd, J = 7.5, 2.0 Hz, 1H), 7.61(dd, J = 7.4, 1.9 Hz, 1H), 7.54 (t, J = 7.5 Hz, 1H), 7.43 (dd, J = 7.5, 2.0 Hz,1H), 7.34 (t, J = 7.5 Hz, 1H), 7.13 (dq, J = 7.5, 1.1 Hz, 2H), 7.06 – 7.01 (m,2H), 6.93 – 6.89 (m, 2H), 6.87 (dd, J = 7.4, 1.9 Hz, 1H), δ 3.95 (s, 6H).

[0223] Comparative Example

[0224]

[0225] The synthetic route of this structure is as follows:

[0226] 4,4'-oxydiphthalic anhydride (ODPA) (1.80 g, 5.8 mmol), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB) (2.21 g, 6.0 mmol), end-capping agent phthalic anhydride (0.106 g, 0.72 mmol) and pyridine (0.916 g, 11.6 mmol) were added to 120 mL of m-cresol, stirred at 150 °C for 4 h, and poured into methanol after cooling. The precipitated polyimide was collected by filtration, then thoroughly washed with methanol, and dried in a vacuum oven at 80 °C for 12 h.

[0227] Test Case

[0228] The thermoplastic polyimide resins prepared in Examples 1-5 and Comparative Examples were subjected to performance tests, and the test results are shown in Table 1. g is the glass transition temperature, T m is the melting temperature.

[0229] Table 1

[0230]

[0231] The biphenyl diaryl ether skeleton is not a planar structure, and it will be spatially deflected, so that the polyimide polymer structural units are in different planes. As shown in the experimental data in Table 1, by introducing a twisted non-coplanar biphenyl diaryl ether skeleton, the intermolecular stacking density can be reduced and the T of the structure can be increased. g 、T m and melt fluidity, effectively improving the melt processing performance and high-temperature performance of the material. At the same time, it has little effect on the mechanical properties of the material and can effectively avoid the loss of mechanical properties of the material caused by the introduction of too many flexible units.

[0232] The present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, change of structural morphology, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0233] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0234] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0235] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

[0236] The above implementation modes are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A thermoplastic polyimide resin, characterized in that: The thermoplastic polyimide resin has the following structural formula: Among them, n≥5; R 1 and R 2 is any one of an ester group and a phenyl group, and R 1 and R 2 The same, wherein the ester group is a COOR group and R is an alkyl group; The imide structure where Ar is located is one of the following structures: 。 2. The thermoplastic polyimide resin according to claim 1, characterized in that The thermoplastic polyimide resin has a glass transition temperature of 240-270° C., a melting temperature of 365-405° C., a melt index of 9-10 g / 10 min., a tensile strength of 80-105 MPa, and an elongation at break of 80%-95%.

3. The thermoplastic polyimide resin according to claim 1, characterized in that The raw materials for preparing the thermoplastic polyimide resin include dianhydride monomers and bulky hindered biphenyl diaryl ether diamine monomers, and the bulky hindered biphenyl diaryl ether diamine monomers have the following structure: in, R 1 and R 2 is any one of an ester group and a phenyl group, and R 1 and R 2 The same, wherein the ester group is a COOR group and R is an alkyl group; The dianhydride monomer is one of the following structures: 。 4. The thermoplastic polyimide resin according to claim 3, characterized in that: The synthesis method of the large sterically hindered biphenyl diaryl ether diamine monomer is: Step 1: Add the raw material 2-bromo-6-fluoroiodobenzene, alkali and copper powder into a polar solvent, heat and stir to react, and after the reaction is completed, filter to obtain intermediate 1; Step 2: adding intermediate 1, p-aminophenol and a base to a polar solvent, heating and stirring to react, and after the reaction is completed, crystallizing and filtering to obtain a solid, and then washing and drying to obtain intermediate 2; Step 3: adding intermediate 2, halogenated hydrocarbon, catalyst and reducing agent to a polar solvent, heating and stirring to react under the protection of inert gas, and separating and obtaining the target large sterically hindered biphenyl diaryl ether diamine monomer after the reaction is completed; The synthetic route of the large sterically hindered biphenyl diaryl ether diamine monomer is as follows: Wherein, R is phenyl and X is halogen.

5. The thermoplastic polyimide resin according to claim 3, characterized in that: The synthesis method of the large sterically hindered biphenyl diaryl ether diamine monomer is: Step (1): adding 2-iodo-3-fluorobenzoic acid, R-OH and an acid catalyst to a solvent, heating and reflux with stirring, and after the reaction is completed, removing the solvent by rotary evaporation, and obtaining intermediate 3 by recrystallization; Step (2): adding intermediate 3, alkali and copper powder into a polar solvent, heating and stirring, and after the reaction is completed, crystallizing and filtering to obtain intermediate 4; Step (3): adding intermediate 4, p-aminophenol and a base to a polar solvent, heating and stirring, and after the reaction is completed, crystallizing and filtering to obtain a solid, and then washing and drying to obtain the target large sterically hindered biphenyl diaryl ether diamine monomer; The synthetic route of the large sterically hindered biphenyl diaryl ether diamine monomer is as follows: Wherein, R is an alkyl group.

6. A method for preparing a thermoplastic polyimide resin according to any one of claims 1 to 5, characterized in that: The steps include: S1, mixing the dianhydride monomer and the polar solvent, adding the diamine monomer, stirring, and obtaining a polyamic acid solution; S2. Add an organic base and a dehydrating agent to the polyamic acid solution, stir, add the reaction solution to an alcohol solvent to precipitate a precipitate, collect the precipitate, wash, and dry to obtain a thermoplastic polyimide resin.

7. The method for preparing a thermoplastic polyimide resin according to claim 6, characterized in that: In S1, the solid content of the polyamic acid solution is ≥5%.

8. The method for preparing a thermoplastic polyimide resin according to claim 6, characterized in that: The molar ratio of the diamine monomer to the dianhydride monomer is 1:1.05-2; The molar ratio of the organic base to the dehydrating agent is 1:1-2; The molar ratio of the dehydrating agent to the diamine monomer is 2 to 8:

1.

9. The method for preparing a thermoplastic polyimide resin according to claim 6, characterized in that: The organic base is one or more of triethylamine, ethylenediamine, diisopropylethylamine, diethylamine, pyridine, 2,6-lutidine, 2,4,6-trimethylpyridine, 2,6-di-tert-butylpyridine, 4-dimethylaminopyridine, and 1,8-diazabicyclo[5.4.0]undec-7-ene; The dehydrating agent is one or more of acetic anhydride, propionic anhydride, acetyl chloride, dicyclohexylcarbocyanine, trifluoroacetic anhydride, and thionyl chloride; The alcohol solvent is one or more of methanol, ethanol, propanol, isopropanol, hexafluoroisopropanol, butanol, tert-butanol, and acetone.

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