Polyimide diamine chain extender as well as preparation method and application thereof

Abstract

The invention discloses a polyimide diamine chain extender as well as a preparation method and application thereof. The preparation method comprises the following steps: adding 2, 2 '-diaminodiphenyl disulfide powder into a solvent, adding hexafluorodianhydride after the 2, 2'-diaminodiphenyl disulfide powder is completely dissolved, and reacting for 24-48 hours in a nitrogen atmosphere of an ice-water bath to obtain a polyamide acid solution; a dehydrating agent and a catalyst are mixed and then dropwise added into a polyamide acid solution, the mixture is placed in a nitrogen atmosphere at the temperature of 45-65 DEG C and kept at the constant temperature for 24-48 h, and after a solvent is removed, the diamine chain extender of polyimide is obtained. The high-solubility polyimide diamine chain extender provided by the invention can be used for remarkably improving the mechanical property of a material after heat treatment. The photo-thermal dual-curing 3D printing resin is low in viscosity and good in stability, the printing requirement of a photo-curing 3D printer can be met at the normal temperature, and a printed product of the photo-thermal dual-curing 3D printing resin has the self-repairing performance, the low dielectric performance and the electromagnetic shielding performance.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, and relates to a polyimide diamine chain extender, its preparation method and application. Background Technology

[0002] Photopolymer 3D printing technology has become a key technology in advanced manufacturing due to its high precision, high speed, and high design freedom. Its core principle lies in using light of a specific wavelength to excite a photoinitiator, causing a photopolymerization reaction in liquid photosensitive resin, and precisely constructing a three-dimensional solid through layer-by-layer curing. This technology significantly overcomes the limitations of traditional manufacturing in forming complex geometric structures, providing strong support for product innovation. However, traditional photopolymerization technology has an inherent drawback: the photopolymerization reaction is often incomplete, leading to limited molecular chain growth, and the mechanical properties (such as strength and toughness) of the final product are difficult to meet the requirements of high-performance applications. Although increasing the proportion of high molecular weight oligomers in the resin system can improve mechanical properties, this inevitably causes a sharp increase in resin viscosity, severely impairing its rheological properties and molding quality during the printing process.

[0003] To overcome the limitations of single-stage photopolymerization and improve material properties, dual-curing technology combining photopolymerization and thermopolymerization has emerged. This technology cleverly combines the rapid prototyping advantages of photopolymerization with the deep cross-linking and strengthening capabilities of thermopolymerization: first, photopolymerization is used to quickly construct the basic shape of the part, followed by heat treatment to drive deeper reactions (such as thermally initiated chain extension and cross-linking), significantly improving the mechanical properties, thermal stability, and dimensional stability of the final product. A representative technology from Carbon Corporation (such as patent CN201680050991.1) employs a two-component system containing blocked polyurethane acrylate and a polyol / amine chain extender. The process involves first photopolymerization, followed by heating to deblock and release isocyanate groups for thermal cross-linking. However, this two-component system suffers from poor storage stability: the two components react slowly during storage, leading to a continuous increase in viscosity and even gelation, forcing the resin to be mixed before use. More importantly, the viscosity of the mixed resin is usually too high, failing to meet the stringent requirements of conventional photopolymer 3D printers for resin flowability at room temperature, greatly limiting its convenience and versatility.

[0004] Against the backdrop of the deep integration of materials and manufacturing technologies, the development of novel resin systems that combine excellent performance with good processability has become a research hotspot. Polyimide (PI), as a star high-performance polymer material, exhibits outstanding comprehensive properties: excellent heat resistance (long-term operating temperature -200 to 300°C, short-term operating temperature above 400°C), outstanding mechanical strength (tensile strength of unfilled plastics generally >100 MPa), excellent electrical insulation, self-extinguishing properties, low smoke and non-toxicity, and good chemical resistance, making it highly promising in aerospace, microelectronics, and medical device fields. However, the introduction of polyimide into the field of photopolymerization 3D printing currently mainly relies on photosensitive polyimide (PSPI). Although PSPI can be photopolymerized, its application faces significant challenges: its solubility is generally poor, making it difficult to formulate high-solids-content, homogeneous, and stable photosensitive resin slurries; at the same time, its synthesis routes are usually complex and cumbersome, increasing costs and limiting large-scale production and application promotion. Summary of the Invention

[0005] One object of the present invention is to provide a polyimide diamine chain extender, the structural formula of which is as follows: ; Where n represents the number of polyimide segments, n = 3 to 20.

[0006] Another object of the present invention is to provide a method for preparing the polyimide diamine chain extender.

[0007] Step (1) Add 2,2'-diaminodiphenyl disulfide powder to a solvent and mix in a reactor. After the powder is completely dissolved, add hexafluorodianhydride to the reaction system in 3 to 6 portions, with an interval of 10 to 30 minutes between each addition. Place the system in a nitrogen atmosphere in an ice-water bath and react for 24 to 48 hours to obtain a polyamic acid solution. Add 2 to 3 ml of solvent to each gram of 2,2'-diaminodiphenyl disulfide powder. The molar ratio of the added 2,2'-diaminodiphenyl disulfide to hexafluorodianhydride is 1:1.05 to 1:1.5 to ensure that the synthesized polyimide is amino-terminated.

[0008] Step (2) After mixing the dehydrating agent and the catalyst, add them dropwise to the polyamic acid solution. Place the system under a nitrogen atmosphere at 45-65°C for 24-48 hours. After removing the solvent, the diamine chain extender of polyimide is obtained. Add 0.4 to 0.8 ml of a mixture of dehydrating agent and catalyst per milliliter of polyamic acid solution; the volume ratio of the added dehydrating agent to catalyst is 1:0.8 to 1:1.2.

[0009] The synthesis route is as follows: Furthermore, the solvent is N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-methylpyrrolidone (NMP), or dimethyl sulfoxide (DMSO). Furthermore, the dehydrating agent is acetic anhydride (C4H6O3) or propionic anhydride (C6H2O3). 10 O3) or trifluoroacetic anhydride (C4F6O3); Furthermore, the catalyst is pyridine (C5H5N) or triethylamine (C6H5N). 15 N), isoquinoline (C9H7N) or imidazole (C3H4N2).

[0010] A third objective of this invention is to provide the application of this polyimide diamine chain extender as a 3D printing material.

[0011] Blocked polyurethane, polyimide diamine chain extender, reactive diluent, and photoinitiator were mixed evenly to obtain a photothermal dual-curing 3D printing resin; the mass percentage of each substance in the composition is as follows: 40-50% of the material is closed-cell polyurethane; Polyimide diamine chain extender 10-25%; Reactive diluent 22-48%; Photoinitiator 0.5-3%.

[0012] The structural formula of closed-cell polyurethane is as follows: It is prepared using existing publicly available methods, such as the method in patent CN119823697A.

[0013] Furthermore, the active diluent is acrylomorpholine, hydroxyethyl methacrylate, isobornyl acrylate, isobornyl methacrylate, N,N-dimethylacrylamide, or 2-phenoxyethyl acrylate.

[0014] Furthermore, the photoinitiator is 2,4,6-trimethylbenzoyl diphenylphosphine oxide, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, or 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0015] The 3D printing material is photothermal dual-curing; photocuring 3D includes printing using SLA, DLP or LCD 3D printing equipment, followed by thermal curing after printing. The thermal curing temperature is 90-140℃ and the thermal curing time is 1-8 hours.

[0016] This invention is based on the principle of photothermal dual curing. It prepares a highly soluble polyimide diamine chain extender, which is combined with blocked polyurethane, reactive diluent and photoinitiator to form a photothermal dual curing 3D printing resin with low viscosity and good stability. It can meet the printing requirements of photopolymer 3D printers at room temperature. Its printed products have self-healing, low dielectric and electromagnetic shielding properties.

[0017] Compared with the prior art, the beneficial effects of the present invention include: (1) Based on the principle of photothermal dual curing, this invention prepares a highly soluble polyimide diamine chain extender, which is combined with a blocked polyurethane oligomer, an active diluent and a photoinitiator to form a photothermal dual curing 3D printing resin with low viscosity and good stability. It can meet the printing requirements of photocuring 3D printers at room temperature, and its printed products have self-healing, low dielectric and electromagnetic shielding properties.

[0018] (2) The highly soluble polyimide diamine chain extender provided by the present invention can significantly improve the mechanical properties of materials after heat treatment. Its advantages are as follows: On the one hand, disulfide bonds and trifluoromethyl groups are introduced during the synthesis process, which greatly enhances the intermolecular forces of polyimide and enhances its solubility. At the same time, according to different feed ratios, it can ensure that the polyimide is amino-terminated, so that it can act as a diamine chain extender. The polyimide groups participate in the reaction during the heat curing process to form soft and hard embedded polymer segments, which can avoid the oligomer from having excessive viscosity due to the connection of small molecule hard segments during the synthesis process, further reducing the overall viscosity of the resin composition, so that it can meet the printing requirements of photopolymer 3D printers at room temperature. On the other hand, it is not necessary to prepare photosensitive polyimide, which greatly reduces the difficulty of synthesis. In addition, polyimide can endow 3D printing resin with self-healing, low dielectric and electromagnetic shielding properties. Attached Figure Description

[0019] Figure 1 This is a comparison chart of tensile property tests between the examples and the comparative examples; Figure 2 A comparison chart of dielectric constant tests for the examples and comparative examples; Figure 3 This is a demonstration image of the self-healing properties of 3D printed resin materials. Detailed Implementation

[0020] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0021] Example 1. Step (1) Add 24.837 g (0.1 mol) of 2,2'-diaminodiphenyl disulfide powder to 50 mL of N,N-dimethylformamide solvent and mix in a reactor; after complete dissolution, add 46.645 g (0.105 mol) of hexafluorodianhydride to the reaction system in 3 portions, with an interval of 20 minutes each time; place the system in a nitrogen atmosphere in an ice-water bath and react for 24 hours to obtain a polyamic acid solution; Step (2) Take 50 mL of polyamic acid solution, mix 10 mL of acetic anhydride and 10 mL of pyridine and add them dropwise to the polyamic acid solution. Place the system at 45 °C under a nitrogen atmosphere for 48 h. After removing the solvent, polyimide diamine chain extender is obtained.

[0022] Example 2. Step (1) Add 24.837 g (0.1 mol) of 2,2'-diaminodiphenyl disulfide powder to 74 mL of N,N-dimethylacetamide solvent and mix in a reactor; after complete dissolution, add 66.636 g (0.15 mol) of hexafluorodianhydride to the reaction system in 6 portions, with an interval of 10 minutes between each addition; place the system in a nitrogen atmosphere under an ice-water bath and react for 48 hours to obtain a polyamic acid solution; Step (2) Take 70 mL of polyamic acid solution, mix 26 mL of propionic anhydride and 29 mL of triethylamine and add them dropwise to the polyamic acid solution. Place the system at 65 °C under a nitrogen atmosphere for 24 h. After removing the solvent, polyimide diamine chain extender is obtained.

[0023] Example 3. Step (1) Add 24.837 g (0.1 mol) of 2,2'-diaminodiphenyl disulfide powder to 60 mL of N-Methylpyrrolidone solvent and mix in a reactor; after complete dissolution, add 53.308 g (0.12 mol) of hexafluorodianhydride to the reaction system in 4 portions, with an interval of 30 minutes each time; place the system in a nitrogen atmosphere in an ice-water bath and react for 40 hours to obtain a polyamic acid solution; Step (2) Take 60 mL of polyamic acid solution, mix 20 mL of trifluoroacetic anhydride and 16 mL of isoquinoline and add them dropwise to the polyamic acid solution. Place the system at 50 °C under a nitrogen atmosphere for 36 h. After removing the solvent, polyimide diamine chain extender is obtained.

[0024] Example 4. Step (1) Add 24.837 g (0.1 mol) of 2,2'-diaminodiphenyl disulfide powder to 68 mL of dimethyl sulfoxide solvent and mix in a reactor; after complete dissolution, add 48.866 g (0.11 mol) of hexafluorodianhydride to the reaction system in 5 portions, with an interval of 10 minutes each time; place the system in a nitrogen atmosphere in an ice-water bath and react for 36 hours to obtain a polyamic acid solution; Step (2) Take 60 mL of polyamic acid solution, mix 20 mL of acetic anhydride and 24 mL of imidazole and add them dropwise to the polyamic acid solution. Place the system at 55 °C under a nitrogen atmosphere for 40 h. After removing the solvent, polyimide diamine chain extender is obtained.

[0025] The simplified structural formulas of the polyimide diamine chain extenders obtained in Examples 1-4 are as follows: Among them, the product of Example 1 has n=15-20 (average molecular weight of 12000), the product of Example 2 has n=3-8 (average molecular weight of 3000), the product of Example 3 has n=10-15 (average molecular weight of 8000), and the product of Example 4 has n=12-17 (average molecular weight of 9000).

[0026] Example 5. Preparation of blocked polyurethane (IPDI-PCL2000): 500g of dehydrated polycaprolactone diol (PCL, Mn=2000) and 111.15g of isophorone diisocyanate (IPDI) were mixed evenly in a reactor. After adding 0.01g of dibutyltin dilaurate (DBTDL), the reaction was kept at 80℃ for 4h under a nitrogen atmosphere to obtain the isocyanate prepolymer. The reaction temperature was lowered to 50°C, and 91.65g of 2-(tert-butylamino)ethyl methacrylate (TBAEMA) was slowly added dropwise to the above isocyanate prepolymer. 0.21g of 4-methoxyphenol (MEHQ) was also added, and the reaction was continued at a constant temperature for 6 hours to finally obtain the blocked polyurethane IPDI-PCL2000.

[0027] Example 6. Take 50g of the polyimide diamine chain extender prepared in Example 1, 100g of the blocked polyurethane prepared in Example 5, 44g of acryloylmorpholine and 6g of 2,4,6-trimethylbenzoyl diphenylphosphine oxide and mix them evenly to obtain a photothermal dual-curing 3D printing resin.

[0028] The printing process is performed using SLA equipment. After printing, the product undergoes thermosetting at a temperature of 90°C for 8 hours.

[0029] Example 7. Take 80g of the polyimide diamine chain extender prepared in Example 2, 184g of the blocked polyurethane prepared in Example 5, 128g of hydroxyethyl methacrylate and 8g of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and mix them evenly to obtain a photothermal dual-curing 3D printing resin.

[0030] The printing process is performed using DLP equipment. After printing, the product undergoes thermosetting at 100℃ for 6 hours.

[0031] Example 8. Take 70g of the polyimide diamine chain extender prepared in Example 3, 280g of the blocked polyurethane prepared in Example 5, 336g of isobornyl acrylate and 14g of 2-hydroxy-2-methyl-1-phenyl-1-propanone and mix them evenly to obtain a photothermal dual-curing 3D printing resin.

[0032] The printing process is performed using an LCD device. After printing, the product undergoes a heat curing process at a temperature of 120℃ for 4 hours.

[0033] Example 9. Take 60g of the polyimide diamine chain extender prepared in Example 4, 175g of the blocked polyurethane prepared in Example 5, 160g of isobornyl methacrylate and 2g of 2,4,6-trimethylbenzoyl diphenylphosphine oxide and mix them evenly to obtain a photothermal dual-curing 3D printing resin.

[0034] The printing process is performed using DLP equipment. After printing, the product undergoes a heat curing process at a temperature of 130℃ for 2 hours.

[0035] Example 10. Take 48g of the polyimide diamine chain extender prepared in Example 1, 168g of the blocked polyurethane prepared in Example 5, 180g of N,N-dimethylacrylamide and 4g of 2,4,6-trimethylbenzoyl diphenylphosphine oxide and mix them evenly to obtain a photothermal dual-curing 3D printing resin.

[0036] The printing process is performed using DLP equipment. After printing, the product undergoes thermosetting at a temperature of 140℃ for 1 hour.

[0037] Example 11. (1) Prepare the blocked polyurethane oligomer (IPDI-PCL2000) using the same method as in Example 5.

[0038] (2) Preparation of highly soluble polyimide diamine chain extender (NH2-SPI-6500).

[0039] Weigh 5.322 g of 2,2'-diaminodiphenyl disulfide and 30 mL of N,N-dimethylformamide (DMF) and mix them evenly in a reactor. After the powder is completely dissolved, add 8.975 g of hexafluorodianhydride to the reaction system in batches, purge with nitrogen gas, and place the reaction in an ice-water bath for 24 h to obtain a polyamic acid solution.

[0040] Chemical imidization: 6 ml of acetic anhydride and 6 ml of pyridine were measured and mixed evenly, and then slowly added dropwise to the above polyamic acid solution. Nitrogen gas was introduced and the reaction was placed in an ice-water bath. After the addition was completed, the reaction was placed at 65°C for 24 hours under a nitrogen atmosphere to obtain a polyimide solution.

[0041] The above polyimide solution was slowly added dropwise to 500 ml of ethanol solution, allowed to stand and precipitate, and then centrifuged. The solid powder was washed three times with anhydrous ethanol and dried in a vacuum oven at 50°C for 8 hours to obtain a highly soluble polyimide diamine chain extender with a molecular weight of 6500.

[0042] (3) Prepare a photothermal dual-curing resin composition.

[0043] The above-mentioned blocked polyurethane oligomer IPDI-PCL2000, highly soluble polyimide diamine chain extender NH2-SPI-6500, N,N-dimethylacrylamide (DMAA), 2-phenoxyethyl acrylate (PHEA) and 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) were weighed according to the amounts in Table 1 and mixed evenly to obtain photothermal dual-curing 3D printing resin.

[0044] The photothermal dual-curing resin composition obtained in Example 11 was placed in a photopolymer 3D printer and cured layer by layer to obtain a three-dimensional product. After cleaning the surface of the three-dimensional product with alcohol to remove residual resin, it was transferred to a constant temperature oven at 110°C for 6 hours to obtain the final product. The product was tested for tensile strength, elongation at break, etc., and the results are shown in the table below. Example 12. (1) Prepare the blocked polyurethane oligomer (IPDI-PCL2000) using the same method as in Example 5.

[0045] (2) Preparation of highly soluble polyimide diamine chain extender (NH2-SPI-4500).

[0046] Weigh 6.336 g of 2,2'-diaminodiphenyl disulfide and 30 mL of N,N-dimethylformamide (DMF) and mix them evenly in a reactor. After the powder is completely dissolved, add 8.975 g of hexafluorodianhydride to the reaction system in batches, purge with nitrogen gas, and place the reaction in an ice-water bath for 24 h to obtain a polyamic acid solution.

[0047] Chemical imidization: 6 ml of propionic anhydride and 6 ml of triethylamine were measured and mixed evenly, and then slowly added dropwise to the above polyamic acid solution. Nitrogen gas was introduced and the reaction was placed in an ice-water bath. After the addition was completed, the reaction was placed at 65°C for 24 hours under a nitrogen atmosphere to obtain a polyimide solution.

[0048] The above polyimide solution was slowly added dropwise to 500 mL of ethanol solution, allowed to stand and precipitate, and then centrifuged. The solid powder was washed three times with anhydrous ethanol and dried in a vacuum oven at 50 °C for 8 h to obtain a highly soluble polyimide diamine chain extender with a molecular weight of 4500.

[0049] (3) Prepare a photothermal dual-curing resin composition.

[0050] The above-mentioned blocked polyurethane oligomer IPDI-PCL2000, highly soluble polyimide diamine chain extender NH2-SPI-4500, N,N-dimethylacrylamide (DMAA), 2-phenoxyethyl acrylate (PHEA) and 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) were weighed according to the amounts in Table 2 and mixed evenly to obtain photothermal dual-curing 3D printing resin.

[0051] The photothermal dual-curing resin composition obtained in Example 12 was placed in a photopolymer 3D printer and cured layer by layer to obtain a three-dimensional product. After cleaning the surface of the three-dimensional product with alcohol to remove residual resin, it was transferred to a constant temperature oven at 110°C for 6 hours to obtain the final product. The tensile strength, elongation at break and other tests were performed on the product, and the results are shown in the table below. Example 13. (1) Prepare the blocked polyurethane oligomer (IPDI-PCL2000) using the same method as in Example 5.

[0052] (2) Preparation of highly soluble polyimide diamine chain extender (NH2-SPI-2500).

[0053] Weigh 6.336 g of 2,2'-diaminodiphenyl disulfide and 30 mL of N,N-dimethylformamide (DMF) and mix them evenly in a reactor. After the powder is completely dissolved, add 8.975 g of hexafluorodianhydride to the reaction system in batches, purge with nitrogen gas, and place the reaction in an ice-water bath for 24 h to obtain a polyamic acid solution.

[0054] Chemical imidization: 6 ml of propionic anhydride and 6 ml of triethylamine were measured and mixed evenly, and then slowly added dropwise to the above polyamic acid solution. Nitrogen gas was introduced and the reaction was placed in an ice-water bath. After the addition was completed, the reaction was placed at 65°C for 24 hours under a nitrogen atmosphere to obtain a polyimide solution.

[0055] The above polyimide solution was slowly added dropwise to 500 mL of ethanol solution, allowed to stand and precipitate, and then centrifuged. The solid powder was washed three times with anhydrous ethanol and dried in a vacuum oven at 50 °C for 8 h to obtain a highly soluble polyimide diamine chain extender with a molecular weight of 2500.

[0056] (3) Prepare a photothermal dual-curing resin composition.

[0057] The above-mentioned blocked polyurethane oligomer IPDI-PCL2000, highly soluble polyimide diamine chain extender NH2-SPI-2500, N,N-dimethylacrylamide (DMAA), 2-phenoxyethyl acrylate (PHEA) and 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) were weighed according to the amounts in Table 3 and mixed evenly to obtain a photothermal dual-curing resin composition.

[0058] The photothermal dual-curing resin composition obtained in Example 13 was placed in a photopolymer 3D printer and cured layer by layer to obtain a three-dimensional product. After cleaning the surface of the three-dimensional product with alcohol to remove residual resin, it was transferred to a constant temperature oven at 110°C for 6 hours to obtain the final product. The product was tested for tensile strength, elongation at break, etc., and the results are shown in the table below. Comparative Example 1. (1) Prepare the blocked polyurethane oligomer (IPDI-PCL2000) using the same method as in Example 5.

[0059] (2) Preparation of highly soluble polyimide diamine chain extender (NH2-CPI-6500).

[0060] Weigh 6.824 g of 2,2'-ethylenediphenylamine and 30 mL of N,N-dimethylformamide (DMF) and mix them evenly in a reactor. After the powder is completely dissolved, add 13.599 g of hexafluorodianhydride to the reaction system in batches, purge with nitrogen gas, and place the reaction in an ice-water bath for 24 h to obtain a polyamic acid solution.

[0061] Chemical imidization: 6 ml of acetic anhydride and 6 ml of pyridine were measured and mixed evenly, and then slowly added dropwise to the above polyamic acid solution. Nitrogen gas was introduced and the reaction was placed in an ice-water bath. After the addition was completed, the reaction was placed at 65°C for 24 hours under a nitrogen atmosphere to obtain a polyimide solution.

[0062] The above polyimide solution was slowly added dropwise to 500 mL of ethanol solution, allowed to stand and precipitate, and then centrifuged. The solid powder was washed three times with anhydrous ethanol and dried in a vacuum oven at 50 °C for 8 h to obtain a polyimide diamine chain extender with a molecular weight of 6500. The structural formula is as follows: .

[0063] (3) Prepare a photothermal dual-curing resin composition.

[0064] The above-mentioned blocked polyurethane oligomer IPDI-PCL2000, highly soluble polyimide diamine chain extender NH2-CPI-6500, N,N-dimethylacrylamide (DMAA), 2-phenoxyethyl acrylate (PHEA) and 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) were weighed according to the amounts in Table 4 and mixed evenly to obtain a photothermal dual-curing resin composition.

[0065] The photothermal dual-curing resin composition obtained in Comparative Example 1 was placed in a photopolymer 3D printer and cured layer by layer to obtain a three-dimensional product. After cleaning the surface of the three-dimensional product with alcohol to remove residual resin, it was transferred to a constant temperature oven at 110℃ for 6 hours to obtain the final product. The tensile strength, elongation at break and other tests of the product were performed, and the results are shown in the table below. Comparative Example 2. (1) Prepare the blocked polyurethane oligomer (IPDI-PCL2000) using the same method as in Example 5.

[0066] (2) Preparation of photothermal dual-curing resin composition.

[0067] The above-mentioned blocked polyurethane oligomer IPDI-PCL2000, 4,4'-diaminodicyclohexylmethane (PACM), N,N-dimethylacrylamide (DMAA), 2-phenoxyethyl acrylate (PHEA) and 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO) were weighed according to the amounts in the table below and mixed evenly to obtain a photothermal dual-curing resin composition.

[0068] The photothermal dual-curing resin composition obtained in Comparative Example 2 was placed in a photopolymer 3D printer and cured layer by layer to obtain a three-dimensional product. After cleaning the surface of the three-dimensional product with alcohol to remove residual resin, it was transferred to a 90℃ constant temperature oven for heat treatment for 6 hours to obtain the final product. The tensile strength, elongation at break and other tests were performed on the product, and the results are shown in the table below. Tensile property tests of Examples 11, 12, 13, Comparative Examples 1 and 2: Figure 1 As shown, polyimide diamine chain extender can significantly enhance the mechanical properties and toughness of materials, which is something that short-chain chain extenders such as PACM currently on the market do not possess.

[0069] Dielectric constant tests of Examples 11, 12, 13, Comparative Examples 1 and 2: Figure 2 As shown, the polyimide diamine chain extender imparts a low dielectric constant and electromagnetic shielding properties to the material, giving it certain functionalities.

[0070] The self-healing demonstration of Example 11 is as follows: Figure 3 As shown, it can be seen that polyimide diamine chain extender can achieve self-healing properties. At the same time, compared with Comparative Example 1, it can be seen that disulfide bonds are the key to giving the material self-healing ability.

[0071] The above are merely preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any simple substitutions or improvements made based on the above embodiments should be covered within the protection scope of the present invention.

Claims

1. A polyimide diamine chain extender, characterized in that, The simplified structure is as follows: Where n represents the number of polyimide segments, n = 3 to 20.

2. A method for preparing the polyimide diamine chain extender as described in claim 1, characterized in that: Step (1) Add 2,2'-diaminodiphenyl disulfide powder to a solvent and mix in a reactor. After the powder is completely dissolved, add hexafluorodianhydride to the reaction system in 3 to 6 portions, with an interval of 10 to 30 minutes between each addition. Place the system in a nitrogen atmosphere in an ice-water bath and react for 24 to 48 hours to obtain a polyamic acid solution. Add 2 to 3 ml of solvent to each gram of 2,2'-diaminodiphenyl disulfide powder. The molar ratio of the added 2,2'-diaminodiphenyl disulfide to hexafluorodianhydride is 1:1.05 to 1:1.5 to ensure that the synthesized polyimide is amino-terminated. Step (2) After mixing the dehydrating agent and the catalyst, add them dropwise to the polyamic acid solution. Place the system under a nitrogen atmosphere at 45-65°C for 24-48 hours. After removing the solvent, the polyimide diamine chain extender is obtained. Add 0.4 to 0.8 ml of a mixture of dehydrating agent and catalyst per milliliter of polyamic acid solution; the volume ratio of the added dehydrating agent to catalyst is 1:0.8 to 1:1.

2.

3. The method for preparing polyimide diamine chain extender according to claim 2, characterized in that: The solvent is N,N-dimethylformamide, N,N-dimethylacetamide, N,N-methylpyrrolidone, or dimethyl sulfoxide; The dehydrating agent is acetic anhydride, propionic anhydride, or trifluoroacetic anhydride; The catalyst is pyridine, triethylamine, isoquinoline, or imidazole.

4. The application of the polyimide diamine chain extender as described in claim 1 as a 3D printing material.

5. The application of the polyimide diamine chain extender as described in claim 4 as a 3D printing material, characterized in that: Blocked polyurethane, polyimide diamine chain extender, reactive diluent, and photoinitiator were mixed evenly to obtain a photothermal dual-curing 3D printing resin; the mass percentage of each substance in the composition is as follows: 40-50% of the material is closed-cell polyurethane; Polyimide diamine chain extender 10-25%; Reactive diluent 22-48%; Photoinitiator 0.5-3%.

6. The application of the polyimide diamine chain extender as described in claim 5 as a 3D printing material, characterized in that: The structural formula of the closed-cell polyurethane is as follows: 。 7. The application of the polyimide diamine chain extender as described in claim 5 as a 3D printing material, characterized in that: The active diluent is acrylomorpholine, hydroxyethyl methacrylate, isobornyl acrylate, isobornyl methacrylate, N,N-dimethylacrylamide, or 2-phenoxyethyl acrylate. The photoinitiator is 2,4,6-trimethylbenzoyl diphenylphosphine oxide, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, or 2-hydroxy-2-methyl-1-phenyl-1-propanone.

8. The application of the polyimide diamine chain extender as described in any one of claims 4-7 as a 3D printing material, characterized in that: The 3D printing material is photothermal dual-curing; photothermal 3D includes printing using SLA, DLP or LCD 3D printing equipment, followed by thermal curing after printing, with a thermal curing temperature of 90-140℃ and a thermal curing time of 1-8 hours.

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