Preparation method of ultrahigh length-diameter ratio polyesterimide nanocrystal fiber

Abstract

The invention relates to a preparation method of ultrahigh length-diameter ratio polyesterimide nanocrystal fibers, which comprises the following steps: S1, in a dichloromethane solvent system, mixing trimellitic anhydride and fatty amine for reaction, and heating for cyclization to obtain an end-capping reagent; s2, in an inert atmosphere, trimellitic anhydride and ethanolamine are subjected to a prepolymerization reaction, then an end-capping reagent is added, a full reaction is performed, and semi-aromatic polyester imide is obtained; s3, dissolving the semi-aromatic polyester imide in a tetrahydrofuran solvent, standing and crystallizing to obtain a crystallized gel product; and S4, carrying out centrifugal separation on the crystallized gel-like product, and removing free impurities which do not participate in crystallization, so as to obtain the polyesterimide nanofiber with the ultrahigh length-diameter ratio. Compared with the prior art, the method has the advantages that the polyesterimide nanocrystal fiber with the ultrahigh length-diameter ratio is successfully prepared in the single-phase polar solvent, and excellent structural controllability and potential application value are shown.

Description

Technical Field

[0001] This invention belongs to the field of controlled synthesis and self-assembly technology of functional polymers, and relates to a method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers. Background Technology

[0002] The crystallization behavior of polymers has a decisive influence on their properties. Key parameters such as crystallinity, crystal morphology (e.g., spherulite size and distribution, crystal structure), and molecular chain orientation formed during crystallization directly dominate the overall performance of the material. In terms of mechanical properties, increased crystallinity enhances the strength and rigidity of the material, but excessively high crystallinity may lead to decreased toughness, while crystal orientation enables fibrous materials to exhibit significant anisotropic strengthening effects. Regarding thermal properties, the regular arrangement of crystalline regions increases the melting temperature and thermal stability of the material, expanding its high-temperature application range. In terms of optical properties, the refractive index difference between crystalline and amorphous regions induces light scattering, and precise control of crystal morphology can optimize the transparency of the material. Processing performance is closely related to crystallization kinetics; the crystallization rate and grain size distribution directly affect the parameter selection and finished product quality stability of molding processes such as injection molding and extrusion. Therefore, achieving precise control over polymer crystallization behavior is significant not only for overcoming the uncontrollability of traditional crystallization behavior but also for providing a new paradigm for the rational design of high-performance functional materials. This has always been an important research goal in materials science and one of the core challenges in polymer materials science.

[0003] Crystallization-driven self-assembly, as a flexible and efficient self-assembly method, has wide applications in nanomedicine and nanoelectronics. Currently, applicable systems for crystallization-driven self-assembly include polyferrocene silane, polycaprolactone, and polythiophene systems. There are two main methods for controlling crystallization assembly behavior: one is phase separation-driven, such as adding a poor solvent to a good solvent, utilizing the solvent affinity / relativity effect to drive assembly; the other is temperature-driven, such as first heating to above the polymer's crystallization temperature and then cooling to room temperature to obtain different crystal nuclei and micelles. However, both of these methods are traditional crystallization control techniques, belonging to passive crystallization, and cannot reflect the original state of the system. They rely heavily on the passive adjustment of macroscopic environmental parameters, making it difficult to achieve directional control of crystal nucleation, growth direction, and crystal structure at the molecular scale, thus becoming a bottleneck restricting the research and application of polymer crystallization self-assembly. Therefore, effectively controlling the spontaneous crystallization behavior of polymers is an urgent problem to be solved.

[0004] For example, Chinese patent CN113563587A provides a method for preparing a polyester imide polymer. The first step involves premixing trimellitic anhydride and ethanolamine in a low-oxygen or inert gas atmosphere for a period of time to carry out an amidation reaction. The second step involves raising the temperature and simultaneously carrying out a melt polyester reaction and an imide reaction under certain temperature and pressure conditions. After the reaction is complete, the polyester imide polymer is obtained. However, the polyester imide polymer in this patent cannot produce nanofibers. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers, aiming to solve the technical problems of traditional crystal self-assembly preparation process relying on complex block copolymer design, adding unsuitable solvents or relying on affinity-reluctance solvent effect control, resulting in cumbersome preparation process and poor controllability of crystal morphology.

[0006] The objective of this invention can be achieved through the following technical solutions: This invention provides a method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers. By introducing small molecule alkane groups at the ends of the polyesterimide polymer molecular chains, precise site-specific modification of the molecular chains is achieved through covalent bonds. The synergistic effect of the π-π conjugation of the benzoimide ring in the polymer molecule and the volume exclusion effect of the long-chain alkane end-capping groups is utilized. This synergistic effect can serve as the core driving force to guide the orderly stacking of crystals along the one-dimensional direction, thereby achieving precise control of the crystal morphology. The entire preparation process is completed in a single-phase polar solvent system, eliminating the need for adding undesirable solvents, constructing complex block copolymers, or relying on affinity-reluctance solvent effects for control. This significantly simplifies the preparation process, reduces the complexity of the process, and effectively improves the uniformity and controllability of the product's crystal morphology. Ultimately, polyesterimide nanocrystalline fibers with ultra-high aspect ratios can be stably prepared.

[0007] The technical problem to be solved by the present invention is to achieve efficient control of the spontaneous crystallization morphology of polyesterimide polymers through precise design and modification of terminal groups, breaking through the dependence of traditional methods on complex systems.

[0008] Specifically, the preparation method of the present invention includes the following steps: S1. In a dichloromethane solvent system, trimellitic anhydride and aliphatic amine are mixed and reacted, and then cyclized by heating to obtain a capping agent; S2. Under an inert atmosphere, trimellitic anhydride and ethanolamine are first prepolymerized, and then the end-capping agent in S1 is added. After the reaction is complete, the product is purified to obtain a long-chain alkane-terminated semi-aromatic polyesterimide. S3. Dissolve the long-chain alkane-terminated semi-aromatic polyesterimide obtained in S2 in tetrahydrofuran solvent to prepare a certain concentration, and let it stand at room temperature to crystallize, so that the system gradually changes from a clear solution to a gel, and obtains a crystalline gel product. S4. Centrifuge the crystalline gel product from S3, and redisperse the resulting precipitate in tetrahydrofuran solvent. Then centrifuge again and repeat the process three times to remove free impurities that did not participate in crystallization. The collected precipitate is the polyesterimide nanofiber with an ultra-high aspect ratio.

[0009] Furthermore, in S1, the alkyl chain of the aliphatic amine has 8 to 18 carbon atoms, and for example, it can be at least one of stearylamine, n-dodecylamine, n-octylamine, etc. Here, the end-capping agent synthesized using aliphatic amines of a specific length can utilize its own steric hindrance effect to suppress isotropy during the crystallization process, restricting the crystallization orientation of the polyesterimide to a one-dimensional direction. When its own volume is not large enough, this suppression effect will disappear.

[0010] Furthermore, in S1, the molar ratio of trimellitic anhydride to fatty amine is 1:(0.8~1.2), and for example, it can be 1:1.

[0011] Furthermore, in S1, the temperature of the mixed reaction is 0~30℃, and the time is 12~36h; The temperature for circulation is 150~170℃, and the time is 1~2h.

[0012] Furthermore, in S1, the chemical structural formula of the capping agent is: , where m is 7~17.

[0013] Furthermore, in S2, the molar ratio of trimellitic anhydride, ethanolamine, and plugging agent is 1:(0.8~1.2):(0.1~0.5), for example, it can be 1:1:0.1, or 1:1:0.5, or 1:1:0.3, etc.

[0014] Furthermore, in S2, the prepolymerization reaction process is as follows: first, the temperature is raised to 100~160℃ and reacted for 0.5~1h, then the temperature is raised to 200~240℃ and reacted for 1~2h; After adding the capping agent, the temperature for a complete reaction is 200~240℃, and the time is 2~3h.

[0015] Furthermore, in S2, the purification process involves dissolving the reaction product in... N In a methylpyrrolidone solution, add anhydrous ethanol to control... NThe volume ratio of methylpyrrolidone to anhydrous ethanol is 1:10 to 1:30, causing a precipitate to form. This precipitate is then thoroughly washed with anhydrous ethanol and dried. Specifically, the reaction product is... N The concentration of methylpyrrolidone in the solution can be 30~60 mg / mL.

[0016] Furthermore, the inert atmosphere is provided by nitrogen, argon, helium, etc.

[0017] Furthermore, in S2, the chemical structural formula of the long-chain alkane-terminated semi-aromatic polyesterimide is: Where m is 7~17 and n is 6~8.

[0018] Furthermore, in S3, the concentration range of the semi-aromatic polyesterimide in the tetrahydrofuran solvent is 0.5~100 mg / ml.

[0019] Compared with the prior art, the present invention has the following advantages: (1) By introducing terminal groups of small molecule alkane, the polymer molecular chain is modified at specific sites through covalent bonds, resulting in a simple molecular structure design. (2) The crystal morphology can be controlled in a single-phase polar solvent without the need to add undesirable solvents, construct complex block copolymers, or rely on the affinity-reluctance solvent effect for regulation. The π-π conjugation of the benzoimide ring and the size exclusion effect of the long-chain alkane end-capping groups work together as the driving force for the orderly stacking of crystals in the one-dimensional direction. (3) The resulting crystal morphology is controlled to be nanofibers with an ultra-high aspect ratio. Attached Figure Description

[0020] Figure 1 This is the 1H NMR spectrum of the capping agent T-OA from Example 1 of the present invention (… 1 H NMR spectrum); Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the intermediate product PEIs-OA from Example 1 of the present invention. 1 H NMR spectrum); Figure 3 This is a matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF MS) spectrum of PEIs-OA, the intermediate product of Example 1 of the present invention. Figure 4 This is a transmission electron microscope (TEM) image of the PEIs-OA crystallization product in Example 1 of the present invention; Figure 5 This is a scanning electron microscope (SEM) image of the PEIs-OA crystallization product in Example 1 of the present invention; Figure 6It is the end-capping agent T-12A of Example 4 of the present invention. 1 H NMR spectrum; Figure 7 It is PEIs-12A in Embodiment 4 of the present invention. 1 H NMR spectrum; Figure 8 This is the MALDI-TOF MS spectrum of PEIs-12A in Example 4 of the present invention; Figure 9 This is a TEM image of the PEIs-12A crystallized product in Example 4 of the present invention; Figure 10 This is an SEM image of the PEIs-12A crystallized product in Example 4 of the present invention; Figure 11 It is the end-capping agent T-8A of Example 5 of the present invention. 1 H NMR spectrum; Figure 12 It is PEIs-8A in Embodiment 5 of the present invention. 1 H NMR spectrum; Figure 13 This is the MALDI-TOF MS spectrum of PEIs-8A in Example 5 of the present invention; Figure 14 This is a TEM image of the PEIs-8A crystallized product in Example 5 of the present invention; Figure 15 This is a SEM image of the PEIs-8A crystallized product in Example 5 of the present invention; Figure 16 This is a TEM image of the PEIs-OA crystallization product in Example 6 of the present invention; Figure 17 This is a TEM image of the uncapped PEIs crystallization product in Comparative Example 1 of the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0023] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0024] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0025] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0026] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0027] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5°C, ±4°C, ±3°C, ±2°C, or ±1°C.

[0028] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0029] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0030] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0031] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0032] Unless otherwise specified, all preparations and tests described herein took place at 25°C.

[0033] The terms “comprising,” “including,” “containing,” “having,” “comprising,” or other variations thereof are intended to cover non-closed inclusion, and no distinction is made between these terms. The term “comprising” means that other steps and ingredients may be added without affecting the final result. The compositions and methods / processes of the present invention comprise, consist of, and substantially consist of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein. No distinction is made between the terms “efficacy,” “performance,” “effect,” and “potency” herein.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0036] Example 1: (1) 29.49 g stearamine was dissolved in an appropriate amount of dichloromethane, and then stirred with 20.20 g trimellitic anhydride in dichloromethane solvent at room temperature (25℃) for 24 h to complete the acylation reaction. Subsequently, the temperature was raised to 160℃ and held for 2 h to carry out the cyclization reaction, directionally generating the end-capping agent T-OA. (1H NMR spectrum) Figure 1 The results show that the peak at δ=8.5-9.5 corresponds to the proton on the benzene ring, and the peak near δ=4.4 corresponds to the proton on the methylene group attached to nitrogen (marked as a in the figure). The integral area of ​​the two peaks at δ=8.6 and δ=4.4 is 1:2. The above results prove the correctness of the T-OA structure.

[0037] (2) In a nitrogen atmosphere, 25.25 g trimellitic anhydride and 7.94 g ethanolamine were reacted at 160 °C for 30 min under molten conditions, and then the temperature was increased to 220 °C for 1 h. Subsequently, 19.22 g T-OA was added and reacted at 220 °C for 2 h to complete the molecular chain end capping and obtain the crude product.

[0038] (3) Dissolve 1 g of crude product in 20 mL N A 50 mg / mL solution was prepared in methyl-2-pyrrolidone and then added dropwise to 400 mL of vigorously stirred anhydrous ethanol to induce precipitation. After discarding the supernatant, the residue was resuspended in 400 mL of anhydrous ethanol and stirred for 30 min. This process was repeated twice for purification. After filtration and vacuum drying, the target product PEIs-OA was obtained. (1H NMR spectroscopy) Figure 2 The results showed that the peak at δ=8.0-9.0 corresponds to the proton on the benzene ring, and the two peaks in the range of δ=4.3-5.0 correspond to the protons on the two methylene groups on the polymer backbone (labeled a and b in the figure). The integral area ratio of the two peaks is 1:1. The peak near δ=3.9 corresponds to the proton on the methylene group bonded to nitrogen (labeled c in the figure). These results prove the correctness of the PEIs-OA structure. MALDI-TOF results show that the number average molecular weight of the prepared PEIs-OA is approximately 1300 Da. Figure 3 ).

[0039] (4) The purified PEIs-OA was dissolved in tetrahydrofuran to prepare a solution with a concentration of 0.5 mg / mL. The solution was sonicated until it was clear and transparent. When irradiated with a laser pen, there was no obvious Tyndall effect. The solution was then placed at room temperature (25℃) for crystallization.

[0040] (5) A portion of the above-mentioned crystalline gel sample was transferred to a centrifuge tube, centrifuged, and the supernatant was discarded. The precipitate obtained by centrifugation was collected, redispersed in tetrahydrofuran solvent, diluted, and then vortexed. The mixed solution was dropped onto a copper grid and observed under transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. Polyesterimide nanofibers with ultra-high aspect ratios were observed. The average diameter of the fibers was about 6 nm, and the fiber length exceeded the field of view. Based on the length of the field of view, the fiber length was predicted to exceed 3 µm, and the aspect ratio of the fibers was >500.

[0041] Example 2: (1) 29.49 g stearamine was dissolved in an appropriate amount of dichloromethane and stirred with 20.20 g trimellitic anhydride in dichloromethane solvent at room temperature (25℃) for 24 h to complete the acylation reaction. Then the temperature was raised to 160℃ and kept for 2 h to carry out the cyclization reaction, and the end-capping agent T-OA was generated in a directional manner.

[0042] (2) In a nitrogen atmosphere, 25.25 g trimellitic anhydride and 7.94 g ethanolamine were reacted at 160 °C for 30 min under molten conditions, and then the temperature was increased to 220 °C for 1 h. Subsequently, 5.82 g T-OA was added and the reaction was carried out at 220 °C for 2 h to complete the molecular chain end capping and obtain the crude product.

[0043] (3) Dissolve 1 g of crude product in 20 mL N A 50 mg / mL solution was prepared in methyl-2-pyrrolidone and then added dropwise to 400 mL of anhydrous ethanol under vigorous stirring to induce precipitation. After discarding the supernatant, the residue was resuspended in anhydrous ethanol (400 mL) and stirred for 30 min. This process was repeated twice for purification. After filtration and vacuum drying, the target product PEIs-OA was obtained.

[0044] (4) The purified PEIs-OA was dissolved in tetrahydrofuran to prepare a solution with a concentration of 0.5 mg / mL. The solution was sonicated until it was clear and transparent. When irradiated with a laser pen, there was no obvious Tyndall effect. The solution was then placed at room temperature (25℃) for crystallization.

[0045] (5) Take a portion of the above-mentioned crystalline gel sample and transfer it to a centrifuge tube. After centrifugation, discard the supernatant. Collect the precipitate obtained by centrifugation, redisperse it in tetrahydrofuran solvent and dilute it, and then perform vortex mixing. Take the mixed solution and drop it onto a copper grid. Observe it under a transmission electron microscope (TEM) and a scanning electron microscope (SEM) respectively. Polyesterimide nanofibers with ultra-high aspect ratio can be observed.

[0046] Example 3: (1) 29.49 g stearamine was dissolved in an appropriate amount of dichloromethane and stirred with 20.20 g trimellitic anhydride in dichloromethane solvent at 0℃ for 36 h to complete the acylation reaction. Then the temperature was raised to 160℃ and kept for 2 h to carry out the cyclization reaction, and the end-capping agent T-OA was generated in a directional manner.

[0047] (2) In a nitrogen atmosphere, 25.25 g trimellitic anhydride and 7.94 g ethanolamine were reacted at 100°C for 1 h under molten conditions, and then the temperature was increased to 200°C for 2 h. Subsequently, 19.22 g T-OA was added and reacted at 200°C for 3 h to complete the molecular chain capping and obtain the crude product.

[0048] (3) Dissolve 1 g of crude product in 20 mL NA 50 mg / mL solution was prepared in methyl-2-pyrrolidone and then added dropwise to 400 mL of anhydrous ethanol under vigorous stirring to induce precipitation. After discarding the supernatant, the residue was resuspended in anhydrous ethanol (400 mL) and stirred for 30 min. This process was repeated twice for purification. After filtration and vacuum drying, the target product PEIs-OA was obtained.

[0049] (4) The purified PEIs-OA was dissolved in tetrahydrofuran to prepare a solution with a concentration of 0.5 mg / mL. The solution was sonicated until it was clear and transparent. When irradiated with a laser pen, there was no obvious Tyndall effect. The solution was then placed at room temperature (25℃) for crystallization.

[0050] (5) Take a portion of the above-mentioned crystalline gel sample and transfer it to a centrifuge tube. After centrifugation, discard the supernatant. Collect the precipitate obtained by centrifugation, redisperse it in tetrahydrofuran solvent and dilute it, and then perform vortex mixing. Take the mixed solution and drop it onto a copper grid. Observe it under a transmission electron microscope (TEM) and a scanning electron microscope (SEM) respectively. Polyesterimide nanofibers with ultra-high aspect ratio can be observed.

[0051] Example 4: (1) 19.66 g of n-dodecylamine was dissolved in an appropriate amount of dichloromethane, and then stirred with 20.20 g of trimellitic anhydride in dichloromethane solvent at room temperature (25℃) for 24 h to complete the acylation reaction. Subsequently, the temperature was raised to 160℃ and held for 2 h to carry out the cyclization reaction, directionally generating the end-capping agent T-12A. (1H NMR spectrum) Figure 6 The results show that the peak at δ=8.0-9.0 corresponds to the proton on the benzene ring, and the peak near δ=3.9 corresponds to the proton on the methylene group attached to nitrogen (marked as a in the figure). The integral area of ​​the two peaks at δ=8.6 and δ=4.4 is 1:2. The above results prove the correctness of the T-12A structure.

[0052] (2) In a nitrogen atmosphere, 25.25 g trimellitic anhydride and 7.94 g ethanolamine were reacted at 160 °C for 30 min under molten conditions, and then the temperature was increased to 220 °C for 1 h. Subsequently, 15.58 g T-12A was added and reacted at 220 °C for 2 h to complete the molecular chain end capping and obtain the crude product.

[0053] (3) Dissolve 1 g of crude product in 20 mL NA 50 mg / mL solution was prepared in methyl-2-pyrrolidone and then added dropwise to 400 mL of vigorously stirred anhydrous ethanol to induce precipitation. After discarding the supernatant, the residue was resuspended in 400 mL of anhydrous ethanol and stirred for 30 min. This process was repeated twice for purification. After filtration and vacuum drying, the target product PEIs-12A was obtained. (1H NMR spectroscopy) Figure 7 The results showed that the peak at δ=8.0-9.0 corresponds to the proton on the benzene ring, and the two peaks in the range of δ=4.3-5.0 correspond to the protons on the two methylene groups on the polymer backbone (labeled a and b in the figure). The integral area ratio of the two peaks is 1:1. The peak near δ=3.9 corresponds to the proton on the methylene group bonded to nitrogen (labeled c in the figure). These results prove the correctness of the PEIs-12A structure. MALDI-TOF results show that the number average molecular weight of the prepared PEIs-12A is approximately 1400 Da. Figure 8 ).

[0054] (4) The purified PEIs-OA was dissolved in tetrahydrofuran to prepare a solution with a concentration of 0.5 mg / mL. The solution was sonicated until it was clear and transparent. When irradiated with a laser pen, there was no obvious Tyndall effect. The solution was then placed at room temperature (25℃) for crystallization.

[0055] (5) A portion of the above-mentioned crystalline gel sample was transferred to a centrifuge tube, centrifuged, and the supernatant was discarded. The precipitate obtained by centrifugation was collected, redispersed in tetrahydrofuran solvent, diluted, and then vortexed. The mixed solution was dropped onto a copper grid and observed under a transmission electron microscope (TEM) and a scanning electron microscope (SEM), respectively. Polyesterimide nanofibers with ultra-high aspect ratios were observed. The average diameter of the fibers was about 6 nm, and the fiber length exceeded the field of view. Based on the length of the field of view, the fiber length was predicted to be more than 3 µm, and the aspect ratio of the fibers was greater than 500.

[0056] Example 5: (1) 13.45 g of n-octylamine was dissolved in an appropriate amount of dichloromethane, and then stirred with 20.20 g of trimellitic anhydride in dichloromethane solvent at room temperature (25℃) for 24 h to complete the acylation reaction. Subsequently, the temperature was raised to 160℃ and held for 2 h to carry out the cyclization reaction, directionally generating the end-capping agent T-8A. (1H NMR spectrum) Figure 11 The results show that the peak at δ=8.0-9.0 corresponds to the proton on the benzene ring, and the peak near δ=3.9 corresponds to the proton on the methylene group attached to nitrogen (marked as a in the figure). The integral area of ​​the two peaks at δ=8.6 and δ=4.4 is 1:2. The above results prove the correctness of the T-8A structure.

[0057] (2) In a nitrogen atmosphere, 25.25 g trimellitic anhydride and 7.94 g ethanolamine were reacted at 160 °C for 30 min under molten conditions, and then the temperature was increased to 220 °C for 1 h. Subsequently, 13.15 g T-8A was added and reacted at 220 °C for 2 h to complete the molecular chain end capping and obtain the crude product.

[0058] (3) Dissolve 1 g of crude product in 20 mL N A 50 mg / mL solution was prepared in methyl-2-pyrrolidone and then added dropwise to 400 mL of vigorously stirred anhydrous ethanol to induce precipitation. After discarding the supernatant, the residue was resuspended in 400 mL of anhydrous ethanol and stirred for 30 min. This process was repeated twice for purification. After filtration and vacuum drying, the target product PEIs-8A was obtained. (1H NMR spectroscopy) Figure 12 The results showed that the peak at δ=8.0-9.0 corresponds to the proton on the benzene ring, and the two peaks in the range of δ=4.3-5.0 correspond to the protons on the two methylene groups on the polymer backbone (labeled a and b in the figure). The integral area ratio of the two peaks is 1:1. The peak near δ=3.9 corresponds to the proton on the methylene group bonded to nitrogen (labeled c in the figure). These results prove the correctness of the PEIs-8A structure. MALDI-TOF results show that the number average molecular weight of the prepared PEIs-8A is approximately 1300 Da. Figure 8 ).

[0059] (4) The purified PEIs-8A was dissolved in tetrahydrofuran to prepare a solution with a concentration of 0.5 mg / mL. The solution was sonicated until it was clear and transparent. When irradiated with a laser pen, no obvious Tyndall effect was observed. The solution was then placed at room temperature (25°C) for crystallization.

[0060] (5) A portion of the above-mentioned crystalline gel sample was transferred to a centrifuge tube, centrifuged, and the supernatant was discarded. The precipitate obtained by centrifugation was collected, redispersed in tetrahydrofuran solvent, diluted, and then vortexed. The mixed solution was dropped onto a copper grid and observed under a transmission electron microscope (TEM) and a scanning electron microscope (SEM), respectively. Polyesterimide nanofibers with ultra-high aspect ratios were observed. The average diameter of the fibers was about 6 nm, and the fiber length exceeded the field of view. Based on the length of the field of view, the fiber length was predicted to be more than 3 µm, and the aspect ratio of the fibers was greater than 500.

[0061] Example 6 In step four, the concentration was set at 100 ml / ml, and other conditions were the same as in Example 1. TEM test results showed that the obtained crystals were still polyesterimide nanofibers with an ultra-high aspect ratio.

[0062] Comparative Example 1: (1) In a nitrogen atmosphere, 25.25 g trimellitic anhydride and 7.94 g ethanolamine were reacted at 160 °C for 30 min under molten conditions, and then the temperature was increased to 220 °C for 3 h. The mixture was poured out and cooled to obtain uncapped PEIs.

[0063] (2) After purifying the above PEIs, dissolve them in tetrahydrofuran to prepare a solution with a concentration of 0.5 mg / mL. Sonicate the solution until it is clear and transparent. Irradiate it with a laser pen and there is no obvious Tyndall effect. Then place the solution at room temperature (25°C) to crystallize.

[0064] (3) Take a portion of the above-mentioned crystallized sample and transfer it to a centrifuge tube. After centrifugation, discard the supernatant. Collect the precipitate obtained by centrifugation, redisperse it in tetrahydrofuran solvent and dilute it, and then perform vortex mixing. Take the mixed solution and drop it onto a copper grid. Observe it under TEM. The bundled spherulite structure can be observed.

[0065] Compared with Example 1, it can be seen that PEIs with long-chain alkane end caps can obtain nanofibers with ultra-high aspect ratio through solution crystallization, while the crystals obtained by PEIs without long-chain alkyl end caps are bundled spherulite structures. This comparison proves the difference in crystallization brought about by long-chain alkane modification.

[0066] Comparative Example 2: When the solvent in S4 was replaced with N-methylpyrrolidone (NMP), and other conditions were the same as in Example 1, the results showed that the system could not crystallize, proving the specificity of the solvent.

[0067] In summary, this invention introduces small-molecule alkane terminal groups onto the polymer molecular chain and performs site-specific modification via covalent bonds. Utilizing the π-π conjugation of the benzoimide ring and the size exclusion effect of the long-chain alkane terminal groups, it synergistically drives the orderly stacking of crystals along a one-dimensional direction, achieving precise control over the crystal morphology. The molecular structure design is simple, requiring no addition of unsuitable solvents, nor the construction of complex block copolymers or reliance on affinity / reluctance solvent effects, significantly simplifying the preparation process and effectively avoiding the dependence on complex systems found in traditional methods. Under these conditions, polyesterimide nanocrystalline fibers with ultra-high aspect ratios were successfully prepared in a single-phase polar solvent, demonstrating excellent structural controllability and potential application value.

[0068] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers, characterized in that, Includes the following steps: S1. In a dichloromethane solvent system, trimellitic anhydride and aliphatic amine are mixed and reacted, and then cyclized by heating to obtain a capping agent; S2. Under an inert atmosphere, trimellitic anhydride and ethanolamine are first prepolymerized, and then the end-capping agent in S1 is added. After the reaction is complete, the product is purified to obtain a long-chain alkane-terminated semi-aromatic polyesterimide. S3. Dissolve the long-chain alkane-terminated semi-aromatic polyesterimide obtained in S2 in tetrahydrofuran solvent to prepare a certain concentration, and let it stand at room temperature to crystallize, so that the system gradually changes from a clear solution to a gel, and obtains a crystalline gel product. S4. Centrifuge the crystalline gel product from S3, and redisperse the resulting precipitate in tetrahydrofuran solvent. Then centrifuge again and repeat the process multiple times to remove free impurities that did not participate in crystallization. The collected precipitate is polyesterimide nanofiber with ultra-high aspect ratio.

2. The method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers according to claim 1, characterized in that, In S1, the alkyl chain of the fatty amine has 8 to 18 carbon atoms.

3. The method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers according to claim 2, characterized in that, The fatty amines include at least one of stearylamine, n-dodecylamine, and n-octylamine.

4. The method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers according to claim 1, characterized in that, In S1, the molar ratio of trimellitic anhydride to fatty amine is 1:(0.8~1.2).

5. The method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers according to claim 1, characterized in that, In S1, the temperature of the mixed reaction is 0~30℃ and the time is 12~36h; The temperature for circulation is 150~170℃, and the time is 1~2h.

6. The method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers according to claim 1, characterized in that, In S1, the chemical structural formula of the capping agent is: , where m is 7~17.

7. The method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers according to claim 1, characterized in that, In S2, the molar ratio of trimellitic anhydride, ethanolamine, and capping agent is 1:(0.8~1.2):(0.1~0.5).

8. The method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers according to claim 1, characterized in that, In S2, the prepolymerization reaction process is as follows: first, the temperature is raised to 100~160℃ and reacted for 0.5~1h, then the temperature is raised to 200~240℃ and reacted for 1~2h. After adding the capping agent, the temperature for a complete reaction is 200~240℃, and the time is 2~3h.

9. The method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers according to claim 1, characterized in that, In S2, the chemical structural formula of the long-chain alkane-terminated semi-aromatic polyesterimide is: Where m is 7~17 and n is 6~8.

10. The method for preparing ultra-high aspect ratio polyesterimide nanocrystalline fibers according to claim 1, characterized in that, In S3, the concentration of semi-aromatic polyesterimide in tetrahydrofuran solvent is 0.5~100 mg / ml.

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