A dynamic cross-linked polyimine material based on bio-based solvent with flexible side chains, preparation method and application

Abstract

A kind of dynamic flexible side chain containing cross-linked polyimine material based on bio-based solvent, preparation method and application, the method uses GVL, 2-MeTHF and other bio-based sustainable solvents or its mixture with NMP, DMF as reaction system, solventing ability is excellent, polarity adaptability is good, can realize the complete dissolution of all monomers and auxiliary agent, ensure the uniformity of polymerization reaction and product performance stability, and solvent can be regenerated, low toxicity and easy to degrade, avoid the pollution and residual problem of traditional petroleum-based solvent from the source.The material is prepared by copolymerization of TA and FFDA with a molar ratio of 2:1, Y12D and TREN with constant total molar mass and adjustable ratio.The main chain is constructed with a continuous cross-linked skeleton containing dynamic imine bond and bridged benzene ring, and the side chain fluorene group accounts for 60 wt.%~75 wt.%It has the characteristics of high self-repairing and recyclability.In addition, the hydrophobic stability of polyester fabric modified by its dilute solution is good, the contact angle is up to 125°, and the hydrophobic performance is outstanding in polyimine film material.

Description

Technical Field

[0001] This invention belongs to the field of dynamic polymer materials technology, specifically relating to a dynamic cross-linked polyimide material with flexible side chains based on bio-based solvents, its preparation method, and its application. Background Technology

[0002] Dynamically cross-linked polymers have broad application prospects in additive manufacturing, biomedical carriers, and fiber composite materials due to their unique properties of being repairable, recyclable, and remodelable. The key to their preparation is to achieve structural regulation by constructing dynamic covalent bonds (such as imines, disulfide bonds, borate esters, acylhydrazones, etc.) or dynamic non-covalent interactions (hydrogen bonds, metal coordination, host-guest interactions, etc.), which has become a research hotspot for next-generation polymer materials.

[0003] It is worth noting that solvent selection is crucial in the preparation of dynamic polymers, ensuring adequate dispersion of monomers and auxiliaries, smooth polymerization, and stable product performance. Currently, researchers in dynamic polymer fabrication generally employ... N 2-Methylpyrrolidone (NMP) N,N Traditional petroleum-based organic solvents such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), and chloroform, as well as acetonitrile used as a reaction solvent in patent application CN202610015946 and DMF used as a reaction solvent in patent application CN202510732688.0, while meeting the preparation requirements and achieving good material properties, still have many insurmountable drawbacks. These traditional solvents, such as DMF and NMP, are mainly derived from petroleum, are non-renewable, and their large-scale use results in high costs. Furthermore, many are volatile and flammable, easily causing environmental pollution, which is inconsistent with the "dual-carbon" green development concept. Simultaneously, some solvents are highly toxic, posing operational safety hazards and threatening the health of operators. Their separation and purification processes are complex, recovery costs are high, and they are prone to leaving residues in the product, limiting the further application of dynamic polymers.

[0004] γ Valproic acid lactone (GVL), 2-methyltetrahydrofuran (2-MeTHF), ethyl lactate (EL), furfural (Fur), acetic acid (HAc), tetraethylene glycol (4-EG), tetrapropylene glycol (4-PG), and dihydroglucosidone (Cyrene™) are bio-based sustainable solvents, mainly derived from corn, sugarcane, and wood. They are renewable, have low toxicity, good biodegradability, and suitable boiling points, showing promising potential in organic synthesis and biomass conversion. However, there are insufficient reports on their application in dynamic polymer preparation to replace traditional organic solvents, and the field of dynamic polymers still lacks suitable sustainable solvent systems. Therefore, developing dynamic polymer preparation processes that use sustainable bio-based solvents such as GVL to replace traditional organic solvents is of great significance for promoting the sustainable industrialization of dynamic polymers.

[0005] Meanwhile, in the field of fabric hydrophobic modification, traditional processes often rely on petroleum-based organic solvents to formulate coating solutions, which suffer from problems such as high toxicity, environmental pollution, and solvent residue. Furthermore, some modified fabrics exhibit poor hydrophobic stability and their contact angles are prone to decay. Currently, there is a lack of efficient and environmentally friendly fabric hydrophobic modification technologies based on bio-based sustainable solvent systems, and research on combining dynamically cross-linked polyimide materials with sustainable solvents for fabric hydrophobic modification is insufficient. Therefore, developing dynamic polymer preparation processes and fabric hydrophobic modification technologies that use sustainable solvents to replace traditional organic solvents is of great significance for promoting the green industrialization of dynamic polymers and expanding their application scenarios. Summary of the Invention

[0006] The purpose of this invention is to design a dynamic cross-linked polyimide material with flexible side chains based on bio-based solvents, its preparation method, and its application. The main chain of the material includes dynamic imine bonds (-CH=N-), bridging benzene rings, short aliphatic chains (-CH2CH2-), and tertiary amine nitrogen atoms to form a continuous cross-linked backbone. The side chains are fluorene-substituted fluorinated aromatic groups (60 wt.% to 75 wt.% by mass), which are connected to the main chain through imine bonds. At the same time, the performance is optimized by the hydrogen bonding between molecular chains. After curing, a soluble and recyclable dynamic cross-linked polyimide membrane material is obtained. The contact angle of this membrane material is higher than that of similar materials prepared by traditional petroleum-based organic solvents under the same conditions. When the sustainable solvent is GVL, the contact angle reaches 125° and remains above 105° for 10 minutes. It exhibits excellent hydrophobicity, antifouling ability, and interfacial stability. At the same time, the sustainable solvent system has moderate polarity and complete dissolution characteristics, which enables all monomers, polymers, and additives to form a homogeneous and transparent solution, ensuring uniform polymerization reaction and consistent material properties. It is suitable for scenarios with requirements for material stability and environmental protection, such as humid environments and complex media contact.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A dynamically crosslinked polyimide material with flexible side chains based on a bio-based solvent includes a main chain and side chains. The main chain comprises dynamic imine bonds (-CH=N-), bridging benzene rings, short aliphatic chains (-CH2CH2-), and tertiary amine nitrogen atoms, forming a continuous crosslinked backbone. The side chains are fluorene-substituted monofluoroaromatic groups connected to the main chain via imine bonds. The mass percentage of the side chains is 60 wt.% to 75 wt.% of the total mass of the dynamically crosslinked polyimide material. The structural formula of the material is: .

[0008] Select a sustainable solvent, wherein the sustainable solvent is selected from... γ-At least one of the following: valproic acid (GVL), 2-methyltetrahydrofuran (2-MeTHF), ethyl lactate (EL), furfural (Fur), cycloallyl alcohol (Cy), dimethyl isosorbide (DMI), acetic acid (HAc), tetraethylene glycol (4-EG), tetrapropylene glycol (4-PG), and dihydrol-glucosidone (Cyrene™), or any one or more of the above combined with... N -Methylpyrrolidone NMP or dimethylacetamide DMAc or N , N A mixture of dimethylformamide (DMF) was prepared; then, terephthalaldehyde (TA), difluorodiamine fluorene (FFDA), and tris(2-aminoethyl)amine (TREN) or amino-terminated trimethylolpropane tripropylene glycol ether (T-403), laurylamine dipropylenediamine (Y12D) were copolymerized in a sustainable solvent to obtain a dynamically crosslinked polyimide material with flexible side chains. The material exhibited a high glass transition temperature, with the glass transition temperature of the membrane sample reaching 150 °C.

[0009] Sustainable solvents (including single solvent systems and blended systems) have moderate polarity, which can effectively dissolve the monomers and prepolymers required for the preparation of dynamically cross-linked polymers, ensuring the smooth progress of monomer dispersion and polymerization reactions. At the same time, their physical parameters such as boiling point and viscosity are adapted to the polymerization, dip coating, impregnation, and drying processes, supporting the stability of material properties. Their contact angle is higher than that of polyimide film materials prepared with traditional petroleum-based organic solvents (such as NMP) under the same monomer ratio and process conditions. Due to the higher contact angle, the material has better hydrophobicity, antifouling ability and interfacial stability, and its reliability is significantly improved in humid environments and complex media contact scenarios. When the sustainable solvent is GVL, the contact angle of the membrane material reaches 125°, and this contact angle remains above 105° within 10 minutes. After 10 minutes, it remains stable without significant decrease. Compared with the instantaneous water contact angle of dynamically cross-linked polyimide prepared by traditional petroleum-based organic solvents, which can reach 118.3°, the hydrophobicity is significantly improved, while the water absorption rate can be less than 3%. Moreover, in the sustainable solvent system, the material prepared with GVL as the solvent has more advantages in contact angle performance and overall reliability.

[0010] The polymerization system constructed with sustainable solvents has complete dissolution characteristics. The sustainable solvents can completely dissolve monomers such as TA, FFDA, TREN, and Y12D, as well as polymers generated during the reaction and required additives, to form a homogeneous and transparent solution without residual precipitates or insoluble components. This can ensure that the polymerization reaction proceeds uniformly and provide support for the consistency of material properties.

[0011] A method for preparing the aforementioned bio-based solvent-based dynamically crosslinked polyimide material with flexible side chains, the method being as follows: Step 1: Weigh TA and FFDA in a certain molar ratio. First, add TA to a magnetically stirred beaker containing sustainable solvent GVL and stir for 10 min to dissolve it completely. Then, add FFDA to the mixed solution and stir for 2 h to mix it completely. Step 2: Weigh out Y12D and TREN in different ratios, keeping the total molar amount of the two constant, and add them to the mixed solution one after the other, stirring for 1 min to ensure thorough mixing; Step 3: Pour the polyimide solution into a polytetrafluoroethylene mold, heat it in a 50-100 °C forced-air oven for 48 h, and finally heat it in a 50-120 °C vacuum oven for 6-24 h to obtain a dynamic cross-linked polyimide material with flexible side chains.

[0012] Furthermore, in step 1, the molar ratio of TA to FFDA is 2:1.

[0013] Application of a dynamically cross-linked polyimide material with flexible side chains based on a bio-based solvent in the preparation of hydrophobic coatings or hydrophobic modified fabrics.

[0014] Furthermore, the surface water contact angle of the hydrophobic modified fabric is 125°, and this contact angle remains above 120° for 10 minutes. A hydrophobic modification treatment solution is prepared by diluting the solution to 0.1–10 wt.% using a sustainable solvent system; the alkali-treated fabric is then soaked and cured according to the drying process of claim 3 to obtain the hydrophobic modified fabric.

[0015] The modified fabric surface has a water contact angle of 125°, and this contact angle remains above 120° within 10 minutes, exhibiting outstanding hydrophobic stability. It also possesses good anti-fouling properties and strong interfacial bonding between the coating and the fabric fibers. During the preparation process, the bio-based sustainable solvent system does not release any toxic or harmful substances, has excellent biodegradability, and leaves no residue of traditional petroleum-based solvents, thus meeting the environmental protection and usage requirements in fields such as waterproof fabrics and anti-fouling fabrics.

[0016] The above technical solution can achieve the following beneficial effects: This method utilizes bio-based sustainable solvents such as GVL and 2-MeTHF, or mixtures thereof with NMP and DMF, as the reaction system. It exhibits excellent solvation capability and good polarity compatibility, ensuring complete dissolution of all monomers and additives, guaranteeing the uniformity of the polymerization reaction and the stability of product performance. Furthermore, the solvent is regenerable, low-toxicity, and easily degradable, avoiding the pollution and residue problems of traditional petroleum-based solvents from the source. The material is prepared by copolymerizing TA and FFDA in a 2:1 molar ratio with a constant total molar amount and adjustable proportion of Y12D and TREN. The main chain constructs a continuous cross-linked framework containing dynamic imine bonds and bridging benzene rings, with fluorene substituents accounting for 60 wt.%~75 wt.% of the side chains, exhibiting both high self-healing and recyclability. In addition, the diluted solution modifies polyester fabrics with excellent hydrophobic stability, with a contact angle of up to 125°, demonstrating outstanding hydrophobic performance among polyimide film materials. This process is simple and controllable, effectively expanding the application of dynamic polyimide materials in waterproof fabrics and other fields, aligning with the green industrialization development under the "dual carbon" background. Attached Figure Description

[0017] Figure 1 This is the total reflectance infrared spectrum (ATR-FTIR) of the dynamically cross-linked polyimide material obtained in Example 1 of this invention, used to characterize the chemical structure and characteristic functional groups of the material. The 1626 cm⁻¹ value is shown in the image. -1 The wavenumber likely corresponds to the formed imine bond, 1760 cm⁻¹ -1 The functional group corresponding to the wavenumber may be a residual solvent in the system. γ -Ester bond in valproic acid lactone.

[0018] Figure 2 The diagram shows the contact angle of the dynamically cross-linked polyimide material prepared using the sustainable solvent GVL in Example 1 of this invention, which is used to characterize the surface wetting and hydrophobic properties of the material in the sustainable solvent system.

[0019] Figure 3 The image shows the contact angle of the dynamically cross-linked polyimide material prepared using the conventional solvent NMP in Comparative Example 1, used to compare its hydrophobic properties with those of a sustainable solvent system.

[0020] Figure 4 This is a water absorption rate diagram of the dynamically cross-linked polyimide film obtained in Example 1 of the present invention, used to evaluate the water resistance of the material.

[0021] Figure 5 The image shown is a scanning electron microscope image of the hydrophobic modified fabric obtained in Example 2, used to observe the coating state, morphology, and interfacial bonding of the coating on the surface of the fabric fibers.

[0022] Figure 6 The image shows a physical picture of the water droplets on the hydrophobic modified fabric obtained in Example 2 of this invention. It visually demonstrates the excellent hydrophobic and stain-resistant properties of the modified fabric. The water droplets are spherical on the fabric surface and do not wet or penetrate.

[0023] Figure 7 This is a photograph of the appearance of the dynamically cross-linked polyimide film material obtained from sample No. 2 of Example 1 of the present invention after being cut up, used to present the initial shape and color of the material.

[0024] Figure 8 This is a photograph of the appearance of the shredded membrane material obtained from sample No. 2 of Embodiment 1 of the present invention after hot pressing and reshaping treatment, used to demonstrate the material's hot reshaping capability.

[0025] Figure 9 The graph shows the storage modulus and loss factor of the dynamically cross-linked polyimide material obtained in Example 1 of this invention, used to characterize that the glass transition temperature peak of the sample reaches 150 °C.

[0026] Figure 10 The ATR-FTIR of the dynamically cross-linked polyimide material obtained in Example 4 of this invention is used to characterize the chemical structure and characteristic functional groups of the material. Detailed Implementation

[0027] Combined with appendix Figure 1-10 The embodiments of the present invention will be described in detail below. These embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0028] A dynamic cross-linked polyimide material with flexible side chains based on a bio-based solvent is disclosed. This membrane material uses a bio-based sustainable solvent system (selected from at least one of GVL, 2-MeTHF, EL, etc., or a mixture of any of the above with NMP, DMAc, etc.) as the medium. It is prepared by copolymerizing terephthalaldehyde (TA) and difluorodiamine fluorene (FFDA) at a controlled molar ratio of 2:1, along with TREN / laurylamine dipropylenediamine (Y12D) in varying proportions with a constant total molar amount. The main chain of the material contains dynamic imine bonds (-CH=N-), bridging benzene rings, short aliphatic chains (-CH2CH2-), and tertiary amine nitrogen atoms, forming a continuous cross-linked framework. The side chains are fluorene-substituted fluorinated aromatic groups (60 wt.%–75 wt.%), connected to the main chain via imine bonds. Simultaneously, the performance is optimized through hydrogen bonding between molecular chains. After curing, a soluble and recyclable dynamic cross-linked polyimide membrane material is obtained. The contact angle of this membrane material is higher than that of similar materials prepared by traditional petroleum-based organic solvents under the same conditions. When the sustainable solvent is GVL, the contact angle reaches 125° and remains above 105° for 10 minutes. It exhibits excellent hydrophobicity, antifouling ability, and interfacial stability. At the same time, the sustainable solvent system has moderate polarity and complete dissolution characteristics, which enables all monomers, polymers, and additives to form a homogeneous and transparent solution, ensuring uniform polymerization reaction and consistent material properties. It is suitable for scenarios with requirements for material stability and environmental protection, such as humid environments and complex media contact.

[0029] This invention also provides applications, specifically hydrophobic modification of polyester fabrics. A hydrophobic modification treatment solution for polyester fabrics is prepared by diluting a polyimide solution before the formation of a dynamically cross-linked polyimide film material to a mass fraction of 0.1-10 wt.% using a sustainable solvent system. An alkali-treated polyester fabric is selected as the substrate and completely immersed in the above modification treatment solution. After immersion, it is cured according to a specific drying process (heating in a 70 °C forced-air oven for 48 h, and then in a 80 °C vacuum oven for 24 h) to obtain a hydrophobic modified polyester fabric. The modified polyester fabric exhibits a surface contact angle of 125 ° and maintains above 120 ° for 10 minutes, demonstrating outstanding hydrophobic stability. It also possesses good anti-fouling properties and strong interfacial bonding between the coating and the fabric fibers. During the preparation process, the sustainable solvent system does not release any toxic or harmful substances, exhibits excellent biodegradability, and leaves no residue of traditional petroleum-based solvents, meeting the environmental protection and usage requirements in fields such as waterproof fabrics and anti-fouling fabrics.

[0030] The present invention also provides a method for preparing the dynamically crosslinked polyimide, the method comprising the following steps: Step 1: Weigh a certain molar ratio of TA and FFDA. First, add TA to a magnetically stirred beaker containing sustainable solvent GVL and stir for 10 min to dissolve it completely. Then, add FFDA to the mixed solution and stir for 2 h to mix it thoroughly. Step 2: Weigh out Y12D and TREN in different ratios, keeping the total molar amount of the two constant, and add them to the mixed solution one after the other, stirring for 1 min to ensure thorough mixing; Step 3: Pour the polyimide solution evenly into the polytetrafluoroethylene mold, heat it in a 70 °C forced-air oven for 48 h, and finally heat it in an 80 °C vacuum oven for 24 h to obtain a dynamically cross-linked polyimide film.

[0031] In step 1, the sustainable solvent is selected from at least one of GVL, 2-MeTHF, EL, Fur, Cy, DMI, Acetic acid, 4-EG, 4-PG, Cyrene™, or a mixture of any of the above NMP, DMAc, or DMF, preferably GVL. The solid content of the system is controlled at 10 wt.% to 15 wt.%.

[0032] In step 1, the mass percentage of the side chain is 60 wt.% to 75 wt.% of the total mass of the dynamically cross-linked polyimide material.

[0033] In step 1, the molar ratio of TA to FFDA is 2:1.

[0034] In step 2, the molar ratio of Y12D to TREN is 2:1, 2:3, or 1:9. 2:1 is preferred because it offers the best contact angle and tensile strength.

[0035] The present invention also provides a method for preparing the modified fabric coating of the sustainable solvent system, the method comprising the following steps: Step 1: Weigh a certain molar ratio of TA and FFDA. First, add TA, preferably, to a magnetically stirred beaker containing sustainable solvent GVL and stir for 10 min to dissolve it completely. Then, add FFDA to the mixed solution and stir for 2 h to mix it thoroughly. Step 2: Weigh out Y12D and TREN in different ratios, keeping the total molar amount of the two constant, and add them to the mixed solution one after the other, stirring for 1 min to ensure thorough mixing; Step 3: Preferably, a certain amount of the mixed solution from Step 1 and Step 2 is added to a magnetically stirred beaker containing GVL and stirred for 5 minutes to ensure thorough and uniform mixing. Step 4: Immerse the alkali-treated polyester fabric completely in the solution from Step 3 and let it stand at room temperature for 18 hours to allow the fabric to fully absorb the solution. Step 5: Remove the soaked fabric from the solution, gently squeeze out the excess treatment liquid from the surface, put it into a forced-air drying oven, set the drying temperature to 80 ℃, maintain the constant temperature for 2 hours, remove it after drying, and let it cool naturally to room temperature to obtain the modified fabric product.

[0036] The sustainable solvent is selected from at least one of GVL, 2-MeTHF, EL, Fur, Cy, DMI, Acetic acid, 4-EG, 4-PG, Cyrene™, or any of the above mixed with NMP, DMF or DMAc, preferably GVL. Example 1

[0037] This experimental example uses the bio-based sustainable solvent GVL as the reaction system to prepare a dynamically cross-linked polyimide membrane according to the monomer ratio specified in the instructions. The specific steps are as follows: Step 1: Weigh the corresponding amounts of TA and FFDA according to the molar ratio n(TA):n(FFDA)=2:1; first add TA to a magnetically stirred beaker containing sustainable solvent GVL, stir for 10 min to dissolve it completely, then add FFDA to the above mixed solution, and continue stirring for 2 h to ensure that the two are fully mixed and uniform, and control the solid content of the system at 12 wt.% (within the range of 10~15 wt.%).

[0038] Step 2: Weigh Y12D and TREN, keeping the total molar amount constant, and the molar ratio n(Y12D):n(TREN) = 2:1 (preferred ratio in the instruction manual). Add them to the mixed solution obtained in Step 1 one after the other, and stir for 1 min to mix them thoroughly to obtain a polyimide solution.

[0039] Step 3: Pour the above polyimide solution into a polytetrafluoroethylene mold, first place it in a 70 ℃ forced-air oven and heat for 48 h, then transfer it to an 80 ℃ vacuum oven and heat for 24 h. After taking it out and cooling it to room temperature, a dynamically cross-linked polyimide film is obtained.

[0040] The specific monomer feeding ratios for this experiment are shown in Table 1 (samples 1, 2, and 3). The resulting dynamically cross-linked polyimide membrane has a side chain fluorene substituent group mass ratio of 68 wt.% (within the range of 60~75 wt.%), a surface contact angle of 125°, and maintains a value above 105° within 10 minutes. It exhibits excellent hydrophobicity and thermal stability. The main chain contains dynamic imine bonds, which enable it to have self-healing and recyclable properties.

[0041] Table 1. Molar ratios of monomers fed into the three samples polymerized in Example 1 No. 1 6 3 2 0 No. 2 6 3 1.5 0.75 No. 3 6 3 1 1.5 Example 2

[0042] This experimental example uses the sustainable solvent system and modification process disclosed in the specification to prepare a hydrophobic modified fabric coating based on the polyimide solution of Experiment 1. The specific steps are as follows: Step 1: Weigh out the corresponding amounts of TA and FFDA according to the molar ratio n(TA):n(FFDA)=2:1; first add TA to a magnetically stirred beaker containing sustainable solvent GVL, stir for 10 min to dissolve it completely, then add FFDA to the above mixed solution and continue stirring for 2 h to ensure that the two are fully mixed and uniform.

[0043] Step 2: Weigh Y12D and TREN, keeping the total molar amount constant and the molar ratio n(Y12D):n(TREN)=1:9, and add them to the mixed solution obtained in Step 1. Stir for 1 min to mix them thoroughly to obtain a polyimide solution.

[0044] Step 3: Take an appropriate amount of the polyimide solution obtained in Step 2, add it to a magnetically stirred beaker containing GVL, stir for 5 minutes, and dilute to a mass fraction of 1% to obtain a fabric hydrophobic modification treatment solution.

[0045] Step 4: Select the alkali-treated polyester fabric as the substrate, immerse it completely in the modified treatment solution obtained in Step 3, and let it stand at room temperature for 18 hours to allow the fabric to fully absorb the treatment solution.

[0046] Step 5: Remove the soaked fabric from the treatment solution, gently squeeze out the excess liquid on the surface, and place it in an 80 ℃ forced-air drying oven to dry at a constant temperature for 2 h. After drying, remove it and let it cool naturally to room temperature to obtain a hydrophobic modified fabric with a dynamic cross-linked polyimide coating on the surface.

[0047] The modified fabric obtained in this experiment has a surface contact angle of 125°, which remains above 120° for 10 minutes, demonstrating outstanding hydrophobic stability. It also possesses good anti-fouling properties and strong interfacial bonding between the coating and the fabric fibers. Example 3

[0048] This experimental example uses the bio-based sustainable solvent 2-MeTHF as the reaction system to prepare a dynamically cross-linked polyimide membrane according to the monomer ratio specified in the instructions. The specific steps are as follows: Step 1: Weigh the corresponding amounts of TA and FFDA according to the molar ratio n(TA):n(FFDA)=2:1; first add TA to a magnetically stirred beaker containing the sustainable solvent 2-MeTHF, stir for 10 min to dissolve it completely, then add FFDA to the above mixed solution, and continue stirring for 2 h to ensure that the two are fully mixed and uniform, and control the solid content of the system at 12 wt.% (within the range of 10~15 wt.%).

[0049] Step 2: Weigh Y12D and TREN, keeping the total molar amount constant, and the molar ratio n(Y12D):n(TREN) = 2:1 (preferred ratio in the instruction manual). Add them to the mixed solution obtained in Step 1 one after the other, and stir for 1 min to mix them thoroughly to obtain a polyimide solution.

[0050] Step 3: Pour the above polyimide solution into a polytetrafluoroethylene mold, first place it in a 70 ℃ forced-air oven and heat for 48 h, then transfer it to an 80 ℃ vacuum oven and heat for 24 h. After taking it out and cooling it to room temperature, a dynamically cross-linked polyimide film is obtained.

[0051] The dynamically cross-linked polyimide membrane obtained in this experiment has a side chain fluorene substituent group mass ratio of 68 wt.% (in the range of 60~75 wt.%), a surface contact angle of 125°, and maintains a value of over 105° within 10 minutes. It exhibits excellent hydrophobicity and thermal stability. The main chain contains dynamic imide bonds, which enable it to have self-healing and recyclable properties. Example 4

[0052] This experimental example uses the bio-based sustainable solvent GVL as the reaction system. The monomer ratio is exactly the same as that of sample No. 3 in Example 1. A high-temperature post-treatment step of 150 °C vacuum for 1 h is added to the original heating post-treatment process to prepare a high-performance dynamically cross-linked polyimide membrane. The specific steps are as follows: Step 1: Weigh the corresponding amounts of TA and FFDA according to the molar ratio n(TA):n(FFDA)=2:1; first add TA to a magnetically stirred beaker containing the sustainable solvent 2-MeTHF, stir for 10 min to dissolve it completely, then add FFDA to the above mixed solution, and continue stirring for 2 h to ensure that the two are fully mixed and uniform, and the solid content of the system is controlled at 12 wt.% (within the range of 10~15 wt.%).

[0053] Step 2: Weigh Y12D and TREN, keeping the total molar amount constant, and the molar ratio n(Y12D):n(TREN) = 2:1 (preferred ratio in the instruction manual). Add them to the mixed solution obtained in Step 1 one after the other, and stir for 1 min to mix them thoroughly to obtain a polyimide solution.

[0054] Step 3: Pour the above polyimide solution into a polytetrafluoroethylene mold, first place it in a 70 ℃ forced-air oven and heat for 48 h, then transfer it to an 80 ℃ vacuum oven and heat for 24 h, continue to heat in the vacuum oven to 150 ℃ (heating for 1 h), take it out and cool it to room temperature to obtain a dynamically cross-linked polyimide film.

[0055] In this comparative example, the proportions, processes, and operations remained unchanged. The traditional petroleum-based solvent NMP was used to compare the two solvent systems for preparing dynamically cross-linked polyimide membrane materials. The specific steps are as follows: Step 1: Weigh out the corresponding amounts of TA and FFDA according to the molar ratio n(TA):n(FFDA)=2:1; first add TA to a magnetically stirred beaker containing the traditional petroleum-based organic solvent NMP, stir for 10 min to dissolve it completely, then add FFDA to the above mixed solution, and continue stirring for 2 h to ensure that the two are fully mixed and uniform, and control the solid content of the system at 12 wt.% (within the range of 10~15 wt.%).

[0056] Step 2: Weigh Y12D and TREN, keeping the total molar amount constant and the molar ratio n(Y12D):n(TREN)=2:1, and add them to the mixed solution obtained in Step 1. Stir for 1 min to mix them thoroughly to obtain a polyimide solution.

[0057] Step 3: Pour the above polyimide solution into a polytetrafluoroethylene mold, first place it in a 70 ℃ forced-air oven and heat for 48 h, then transfer it to an 80 ℃ vacuum oven and heat for 24 h. After taking it out and cooling it to room temperature, a dynamically cross-linked polyimide film is obtained.

[0058] The above descriptions are all preferred embodiments of the present invention. For those skilled in the art, any modifications to the present invention in various equivalent forms without departing from the principle of the present invention shall fall within the protection scope of the appended claims.

Claims

1. A dynamically cross-linked polyimide material with flexible side chains based on a bio-based solvent, characterized in that: The main chain comprises a dynamic imine bond (-CH=N-), a bridged benzene ring, a short aliphatic chain (-CH2CH2-) and a tertiary amine nitrogen atom, forming a continuous cross-linked skeleton; the side chain is a fluorenyl-substituted monofluoro aromatic group connected to the main chain through an imine bond; the mass proportion of the side chain is 60 wt.% to 75 wt.% of the total mass of the dynamic cross-linked polyimine material; the structural formula of the material is: ; Select a sustainable solvent, wherein the sustainable solvent is selected from... γ -At least one of the following: valproic acid (GVL), 2-methyltetrahydrofuran (2-MeTHF), ethyl lactate (EL), furfural (Fur), cycloallyl alcohol (Cy), dimethyl isosorbide (DMI), acetic acid (HAc), tetraethylene glycol (4-EG), tetrapropylene glycol (4-PG), and dihydrol-glucosidone (Cyrene™), or any one or more of the above combined with... N -Methylpyrrolidone NMP or dimethylacetamide DMAc or N , N A mixture of dimethylformamide (DMF) was prepared; then, a certain molar ratio of terephthalaldehyde (TA), difluorodiamine fluorene (FFDA), and tri(2-aminoethyl)amine (TREN) or amino-terminated trimethylolpropane tripropylene glycol ether (T-403), laurylamine dipropylenediamine (Y12D) were copolymerized in a sustainable solvent to obtain a dynamically crosslinked polyimide material with flexible side chains.

2. A method for preparing the dynamically cross-linked polyimide material with flexible side chains based on a bio-based solvent as described in claim 1, characterized in that: The method is as follows: Step 1: Weigh TA and FFDA in a certain molar ratio. First, add TA to a magnetically stirred beaker containing sustainable solvent GVL and stir for 10 min to dissolve it completely. Then, add FFDA to the mixed solution and stir for 2 h to mix it completely. Step 2: Weigh out Y12D and TREN in different ratios, keeping the total molar amount of the two constant, and add them to the mixed solution one after the other, stirring for 1 min to ensure thorough mixing; Step 3: Pour the polyimide solution into a polytetrafluoroethylene mold, heat it in a 50-100 °C forced-air oven for 48 h, and finally heat it in a 50-120 °C vacuum oven for 6-24 h to obtain a dynamic cross-linked polyimide material with flexible side chains.

3. The preparation method according to claim 2, characterized in that: In step 1, the molar ratio of TA to FFDA is 2:

1.

4. The application of the dynamically cross-linked polyimide material with flexible side chains based on bio-based solvents according to any one of claims 1 in the preparation of hydrophobic coatings or hydrophobic modified fabrics.

5. The application according to claim 4, characterized in that, The surface water contact angle of the hydrophobic modified fabric is 125°, and this contact angle remains above 120° for 10 minutes.

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