A polyamide-imide composite nanofiber and its preparation method

Abstract

The present invention relates to the technical field of spinning fibers, and discloses a polyamide-imide composite nanofiber and a preparation method thereof. The polyamide-imide composite nanofiber in this application uses dianhydride monomers, diamine monomers, and functional monomers as the main synthesis raw materials, and is synthesized by a wet spinning process; this composite nanofiber not only combines the advantages of traditional polyamide fibers and polyimide fibers, but also improves the flexibility, mechanical properties, and heat resistance of the fibers by introducing functional monomers. Therefore, the polyamide-imide composite nanofiber in the present invention has broad application prospects in the fields of high-temperature filtration, protective clothing, aerospace, electronics and electrical, automotive industry, industrial seals, composite materials, medical materials, and environmental protection materials.

Description

Technical Field

[0001] The present invention relates to the technical field of spinning fibers, and particularly to a polyamide-imide composite nanofiber and a preparation method thereof. Background Art

[0002] Polyamide-imide fiber (abbreviated as PAI fiber) is a kind of high-performance fiber. The PAI molecular chain contains both relatively flexible amide groups and heat-resistant imide units. Due to its excellent mechanical properties and chemical stability, it shows its unique advantages in many demanding applications. Therefore, this kind of polymer not only has excellent heat stability of polyimide, low constant and dielectric loss, good mechanical properties, anti-creep properties, radiation resistance and solvent corrosion resistance, but also has excellent mechanical properties and processability of aromatic polyamide. It has a wide range of applications in the fields of aerospace industry, electrical and electronic industries, high-temperature cables, automotive industry, high-temperature filtration and ocean engineering, etc.

[0003] However, there are a large number of rigid benzene ring structures in the molecular chain of this kind of polymer, which will lead to poor toughness of the fiber material synthesized by the spinning process. This limits the application of the fiber material in some fields. For example, in the textile field, polyamide-imide has a unique macromolecular chain structure, so that PAI fiber and its fabric do not melt and continue to burn at high temperatures, and have excellent flame retardancy. It is widely used in protective clothing such as fire-fighting suits and anti-riot police uniforms. However, the flexibility of this kind of fabric is poor, and the clothes will be damaged after long-term wearing and it is difficult to restore to the initial state. Therefore, it is necessary to improve the toughness of PAI fiber by modification to meet the actual needs. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a polyamide-imide composite nanofiber and a preparation method thereof.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A preparation method of a polyamide-imide composite nanofiber, comprising the following steps:

[0007] Step S1: Mix and stir a dianhydride monomer, a diamine monomer and a functional monomer in an organic solvent, and keep the temperature at 0 °C and react for 5-6 h to obtain a polyamide-acid solution;

[0008] Step S2: Add acetic anhydride and triethylamine to the above polyamide-acid solution, stir evenly, react at 25-35 °C for 4-6 h, then perform vacuum degassing and filtration treatment, spray out through a spinneret, enter the treatment liquid to obtain primary fibers, and then through a coagulation bath, hot water drawing, washing, drying, thermal cyclization, and winding to obtain a polyamide-imide composite nanofiber;

[0009] Further, the molar ratio of the dianhydride monomer, diamine monomer, and functional monomer in step S1 is 1:0.96 - 1:0.02 - 0.05, and the solid content of the polyamide-acid solution is 15% - 25%;

[0010] Further, the dianhydride monomer in step S1 is one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, or 3,3',4,4'-diphenylether tetracarboxylic dianhydride;

[0011] Further, the diamine monomer in step S1 is one of p-phenylenediamine or diphenyl ether diamine;

[0012] Further, the organic solvent in step S1 is one of N,N-dimethylformamide or N,N-dimethylacetamide;

[0013] Further, the volume ratio of acetic anhydride and triethylamine in step S2 is 2 - 3:1, and the molar ratio of acetic anhydride and the dianhydride monomer in step S1 is 0.3 - 0.5:1;

[0014] Further, the treatment liquid in step S2 is a mixed solution of acetic anhydride and triethylamine with a volume ratio of 1:3;

[0015] Further, the coagulation bath in step S2 is a mixed solution of N,N-dimethylacetamide and water with a volume ratio of 4:6;

[0016] Further, the hot water drawing temperature in step S2 is 90°C, the drawing ratio is 2.4, and the thermal cyclization temperature is 320°C.

[0017] The functional monomer is prepared by the following steps:

[0018] Step A1: Stir p-nitrobenzoyl chloride in tetrahydrofuran, transfer it to an ice-water bath, add pyridine and stir for 1 h, then add 1-amino-5-hexene and stir for 3.5 - 4.5 h, add water and stir for 30 min, filter by suction, recrystallize, and dry to obtain nitro-benzamide derivative;

[0019] Further, in step A1, the dosage ratio of p-nitrobenzoyl chloride, tetrahydrofuran, 1-amino-5-hexene, pyridine, and water is 0.01 - 0.03 mol:100 mL:0.01 - 0.03 mol:0.01 - 0.03 mol:200 mL;

[0020] Step A2: Stir the nitro-benzamide derivative, ethanol, and catalyst Pt / SnO2-Sb2O3 at 50°C for 15 min, then introduce 4 MPa of hydrogen and stir for 3 h, and extract to obtain amino-benzamide derivative;

[0021] Further, in step A2, the dosage ratio of the nitro-benzamide derivative, ethanol, and the catalyst Pt / SnO2-Sb2O3 is 0.5-1.5 g: 10-30 mL: 0.3-0.9 g;

[0022] Further, in step A2, Pt in the catalyst Pt / SnO2-Sb2O3 accounts for 0.5 wt% of the total amount of the catalyst, and the molar ratio of Sn and Sb is 0.1:1;

[0023] In step A3, mix toluene-2,4-diisocyanate, sodium hydroxide, toluene, and the amino-benzamide derivative, heat up to 60-70 °C, introduce nitrogen and react for 10-15 h, then carry out rotary evaporation and drying to obtain the isocyanate-benzamide derivative;

[0024] Further, in step A3, the dosage ratio of toluene-2,4-diisocyanate, sodium hydroxide, toluene, and the amino-benzamide derivative is 0.01-0.02 mol: 0.02-0.04 g: 100 mL: 0.01-0.02 mol;

[0025] In step A4, add sodium hydroxide, toluene, and ethylenediamine to the isocyanate-benzamide derivative, stir evenly, react at 70 °C under nitrogen for 6-8 h, then carry out rotary evaporation and drying to obtain the double bond-benzamide derivative;

[0026] Further, in step A4, the molar ratio of ethylenediamine to toluene-2,4-diisocyanate in step A3 is 1:1, and the dosage of sodium hydroxide is 0.015-0.03 g;

[0027] In step A5, under nitrogen conditions, mix the double bond-benzamide derivative, KARSTEDT catalyst, and toluene evenly, then slowly dropwise add hydrogen-terminated polydimethylsiloxane, and heat up to 80-100 °C to react for 20-24 h, then carry out rotary evaporation, purification, and drying to obtain the functional monomer;

[0028] Further, in step A5, the molar ratio of hydrogen-terminated polydimethylsiloxane to the double bond-benzamide derivative is 1:1-1.02, and the KARSTEDT catalyst accounts for 0.002 wt% of the total amount of the reactants.

[0029] Another object of the present invention is to provide a polyamideimide composite nanofiber prepared by the above method.

[0030] The beneficial effects of the present invention:

[0031] The polyamide-imide composite nanofibers in this application are synthesized by a wet spinning process using dianhydride monomers, diamine monomers, and functional monomers as the main raw materials for synthesis; these composite nanofibers not only incorporate the advantages of traditional polyamide fibers and polyimide fibers but also improve the flexibility, mechanical properties, and heat resistance of the fibers by introducing functional monomers. Therefore, the polyamide-imide composite nanofibers in this invention have broad application prospects in fields such as high-temperature filtration, protective clothing, aerospace, electronics and electrical engineering, automotive industry, industrial seals, composite materials, medical materials, and environmental protection materials.

[0032] When the functional monomers in this application are used as raw materials to synthesize polyamide-imide fiber molecules, an Si-O-Si structure is introduced into their main chain. This structure has excellent flexibility, can improve the toughness of the fibers, making them easier to process and apply. At the same time, the Si-O-Si structure will undergo an oxidative cross-linking reaction at high temperatures, increasing the cross-linking density of the polyamide-imide fibers. The increase in cross-linking density enhances the intermolecular interaction between the molecular chains of the fibers, thereby improving the heat resistance of the fibers and enabling them to remain stable at high temperatures. In addition, the introduction of urea bonds enhances the intermolecular force of the fibers, improves the strength and toughness of the fibers, and can also protect them using the benzene ring structure with a large steric hindrance to reduce the impact of high temperatures on them. Detailed implementation manners

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0034] Example 1: The functional monomer is prepared by the following steps:

[0035] Step A1: Stir 0.01 mol of p-nitrobenzoyl chloride in 100 mL of tetrahydrofuran, transfer it to an ice-water bath, add 0.01 mol of pyridine and stir for 1 h, then add 0.01 mol of 1-amino-5-hexene and stir for 3.5 h. Add 200 mL of water and stir for 30 min, then filter, recrystallize, and dry to obtain the nitro-benzamide derivative.

[0036] Step A2: Stir 0.5 g of the nitro-benzamide derivative, 10 mL of ethanol, and 0.3 g of the catalyst Pt / SnO2-Sb2O3 at a constant temperature of 50 °C for 15 min, then introduce 4 MPa of hydrogen and stir for 3 h, and extract to obtain the amino-benzamide derivative. In the catalyst Pt / SnO2-Sb2O3, Pt accounts for 0.5 wt% of the total amount of the catalyst, and the molar ratio of Sn to Sb is 0.1:1.

[0037] Step A3: Mix 0.01 mol of toluene-2,4-diisocyanate, 0.02 g of sodium hydroxide, 100 mL of toluene, and 0.01 mol of amino-benzamide derivative, heat up to 60 °C, introduce nitrogen gas and react for 10 h, then perform rotary evaporation and drying to obtain the isocyanate-benzamide derivative;

[0038] Step A4: Add sodium hydroxide, toluene, and ethylenediamine to the isocyanate-benzamide derivative, stir evenly, react at 70 °C under nitrogen gas for 6 h, then perform rotary evaporation and drying to obtain the double bond-benzamide derivative. The molar ratio of ethylenediamine to toluene-2,4-diisocyanate in Step A3 is 1:1, and the amount of sodium hydroxide used is 0.015 g;

[0039] Step A5: Under nitrogen gas condition, mix the double bond-benzamide derivative, KARSTEDT catalyst, and toluene evenly, then slowly dropwise add hydrogen-terminated polydimethylsiloxane, heat up to 80 °C and react for 20 h, then perform rotary evaporation, purification, and drying to obtain the functional monomer. The molar ratio of hydrogen-terminated polydimethylsiloxane to the double bond-benzamide derivative is 1:1, and the KARSTEDT catalyst accounts for 0.002 wt% of the total amount of reactants.

[0040] Example 2: The functional monomer is prepared by the following steps:

[0041] Step A1: Stir 0.02 mol of p-nitrobenzoyl chloride evenly in 100 mL of tetrahydrofuran, transfer it to an ice-water bath, add 0.02 mol of pyridine and stir for 1 h, then add 0.02 mol of 1-amino-5-hexene and stir for 4 h, add 200 mL of water and stir for 30 min, then perform suction filtration, recrystallization, and drying to obtain the nitro-benzamide derivative;

[0042] Step A2: Stir 1 g of the nitro-benzamide derivative, 20 mL of ethanol, and 0.6 g of the catalyst Pt / SnO2-Sb2O3 at a constant temperature of 50 °C for 15 min, then introduce 4 MPa of hydrogen gas and stir for 3 h, and perform extraction to obtain the amino-benzamide derivative. In the catalyst Pt / SnO2-Sb2O3, Pt accounts for 0.5 wt% of the total amount of the catalyst, and the molar ratio of Sn to Sb is 0.1:1;

[0043] Step A3: Mix 0.015 mol of toluene-2,4-diisocyanate, 0.03 g of sodium hydroxide, 100 mL of toluene, and 0.015 mol of amino-benzamide derivative, heat up to 65 °C, introduce nitrogen gas and react for 12 h, then perform rotary evaporation and drying to obtain the isocyanate-benzamide derivative;

[0044] Step A4: Add sodium hydroxide, toluene and ethylenediamine to the isocyanate-benzamide derivative, stir evenly, react at 70 °C for 7 h under nitrogen, rotary evaporate and dry to obtain the double bond-benzamide derivative. The molar ratio of ethylenediamine to toluene-2,4-diisocyanate in Step A3 is 1:1, and the amount of sodium hydroxide used is 0.022 g;

[0045] Step A5: Under nitrogen conditions, mix the double bond-benzamide derivative, KARSTEDT catalyst and toluene and stir evenly, then slowly dropwise add hydrogen-terminated polydimethylsiloxane, and raise the temperature to 90 °C and react for 22 h, rotary evaporate, purify and dry to obtain the functional monomer. The molar ratio of hydrogen-terminated polydimethylsiloxane to double bond-benzamide derivative is 1:1.01, and the KARSTEDT catalyst accounts for 0.002 wt% of the total amount of reactants.

[0046] Example 3: The functional monomer is prepared by the following steps:

[0047] Step A1: Stir 0.03 mol of p-nitrobenzoyl chloride in 100 mL of tetrahydrofuran, transfer it to an ice-water bath, add 0.03 mol of pyridine and stir for 1 h, then add 0.03 mol of 1-amino-5-hexene and stir for 4.5 h, add 200 mL of water and stir for 30 min, filter by suction, recrystallize and dry to obtain the nitro-benzamide derivative;

[0048] Step A2: Stir 1.5 g of nitro-benzamide derivative, 30 mL of ethanol and 0.9 g of catalyst Pt / SnO2-Sb2O3 at a constant temperature of 50 °C for 15 min, then introduce 4 MPa of hydrogen and stir for 3 h, and extract to obtain the amino-benzamide derivative. Pt in the catalyst Pt / SnO2-Sb2O3 accounts for 0.5 wt% of the total amount of the catalyst, and the molar ratio of Sn to Sb is 0.1:1;

[0049] Step A3: Mix 0.02 mol of toluene-2,4-diisocyanate, 0.04 g of sodium hydroxide, 100 mL of toluene and 0.02 mol of amino-benzamide derivative, raise the temperature to 70 °C, introduce nitrogen and react for 15 h, rotary evaporate and dry to obtain the isocyanate-benzamide derivative;

[0050] Step A4: Add sodium hydroxide, toluene and ethylenediamine to the isocyanate-benzamide derivative, stir evenly, react at 70 °C for 8 h under nitrogen, rotary evaporate and dry to obtain the double bond-benzamide derivative. The molar ratio of ethylenediamine to toluene-2,4-diisocyanate in Step A3 is 1:1, and the amount of sodium hydroxide used is 0.03 g;

[0051] Step A5: Under nitrogen conditions, mix the double bond-benzamide derivative, KARSTEDT catalyst, and toluene and stir evenly. Then slowly dropwise add hydrogen-terminated polydimethylsiloxane and heat to 100 °C for reaction for 24 h. Rotate and evaporate, purify, and dry to obtain the functional monomer. The molar ratio of hydrogen-terminated polydimethylsiloxane to the double bond-benzamide derivative is 1:1.02, and the KARSTEDT catalyst accounts for 0.002 wt% of the total amount of reactants.

[0052] Example 4: A preparation method of polyamide-imide composite nanofibers, comprising the following steps:

[0053] Step S1: Mix 3,3’,4,4’-benzophenone tetracarboxylic dianhydride, p-phenylenediamine, and the functional monomer prepared in Example 1 in N,N-dimethylformamide and stir, and keep the temperature at 0 °C for reaction for 5 h to obtain a polyamide-acid solution. The molar ratio of 3,3’,4,4’-benzophenone tetracarboxylic dianhydride, p-phenylenediamine, and the functional monomer prepared in Example 1 is 1:1:0.02, and the solid content of the polyamide-acid solution is 15%;

[0054] Step S2: Add acetic anhydride and triethylamine to the above polyamide-acid solution and stir evenly. React at 25 °C for 4 h, then perform vacuum degassing and filtration treatment, and extrude through a spinneret into the treatment liquid to obtain primary fibers. Then, through a coagulation bath, hot water drawing, water washing, drying, thermal cyclization, and winding, polyamide-imide composite nanofibers are obtained. The volume ratio of acetic anhydride to triethylamine is 2:1, the molar ratio of acetic anhydride to the dianhydride monomer described in Step S1 is 0.3:1, the treatment liquid is a mixed liquid of acetic anhydride and triethylamine with a volume ratio of 1:3, the coagulation bath is a mixed liquid of N,N-dimethylacetamide and water with a volume ratio of 4:6, the hot water drawing temperature is 90 °C, the drawing ratio is 2.4, and the thermal cyclization temperature is 320 °C.

[0055] Example 5: A preparation method of polyamide-imide composite nanofibers, comprising the following steps:

[0056] Step S1: Mix pyromellitic dianhydride, diphenyl ether diamine, and the functional monomer prepared in Example 2 in N,N-dimethylacetamide and stir, and keep the temperature at 0 °C for reaction for 5.5 h to obtain a polyamide-acid solution. The molar ratio of pyromellitic dianhydride, diphenyl ether diamine, and the functional monomer prepared in Example 2 is 1:0.98:0.04, and the solid content of the polyamide-acid solution is 20%;

[0057] Step S2: Add acetic anhydride and triethylamine to the above polyamide-acid solution, stir well, react at 30 °C for 5 h, then perform vacuum degassing and filtration, extrude through a spinneret, and enter the treatment liquid to obtain primary fibers. Then, through a coagulation bath, hot water drawing, water washing, drying, thermal cyclization, and winding, polyamide-imide composite nanofibers are obtained. The volume ratio of acetic anhydride to triethylamine is 2.5:1, the molar ratio of acetic anhydride to the dianhydride monomer described in Step S1 is 0.4:1, the treatment liquid is a mixed solution of acetic anhydride and triethylamine with a volume ratio of 1:3, the coagulation bath is a mixed solution of N,N-dimethylacetamide and water with a volume ratio of 4:6, the hot water drawing temperature is 90 °C, the drawing ratio is 2.4, and the thermal cyclization temperature is 320 °C.

[0058] Example 6: A preparation method of polyamide-imide composite nanofibers, comprising the following steps:

[0059] Step S1: Mix 3,3’,4,4’-diphenyl ether tetracarboxylic dianhydride, diphenyl ether diamine, and the functional monomer prepared in Example 3 in N,N-dimethylacetamide, stir, and react at 0 °C for 6 h to obtain a polyamide-acid solution. The molar ratio of 3,3’,4,4’-diphenyl ether tetracarboxylic dianhydride, diphenyl ether diamine, and the functional monomer prepared in Example 3 is 1:0.96:0.05, and the solid content of the polyamide-acid solution is 25%.

[0060] Step S2: Add acetic anhydride and triethylamine to the above polyamide-acid solution, stir well, react at 35 °C for 6 h, then perform vacuum degassing and filtration, extrude through a spinneret, and enter the treatment liquid to obtain primary fibers. Then, through a coagulation bath, hot water drawing, water washing, drying, thermal cyclization, and winding, polyamide-imide composite nanofibers are obtained. The volume ratio of acetic anhydride to triethylamine is 3:1, the molar ratio of acetic anhydride to the dianhydride monomer described in Step S1 is 0.5:1, the treatment liquid is a mixed solution of acetic anhydride and triethylamine with a volume ratio of 1:3, the coagulation bath is a mixed solution of N,N-dimethylacetamide and water with a volume ratio of 4:6, the hot water drawing temperature is 90 °C, the drawing ratio is 2.4, and the thermal cyclization temperature is 320 °C.

[0061] Comparative Example 1: This comparative example is a polyamide-imide composite nanofiber. The difference from Example 6 is that p-phenylenediamine is used instead of the functional monomer prepared in Example 3, and the rest are the same.

[0062] Comparative Example 2: This comparative example is a polyamide-imide composite nanofiber. The difference from Example 6 is that amino-terminated silicone is used instead of the functional monomer prepared in Example 3, and the rest are the same.

[0063] Comparative Example 3: This comparative example is a polyamide-imide composite nanofiber, which is different from Example 6 in that the functional monomer prepared in Example 3 is not added, and the rest are the same.

[0064] Perform performance tests on the polyamide-imide composite nanofibers prepared in Examples 4-6 and Comparative Examples 1-3:

[0065] Breaking strength test: According to GB / T 14344-2022 "Test Method for Tensile Properties of Chemical Fiber Filaments", test the breaking strength of the fiber before high-temperature treatment, and then conduct a heat resistance test on the fiber at a temperature of 300 °C for 48 h, and then test the breaking strength and calculate the breaking strength retention rate;

[0066] Elongation at break test: Perform single-filament strength tests on a fully automatic single-fiber universal tester FAVIMAT+. Separate single filaments with a separation length of more than 20 mm and test them at an initial stress of 0.3 cN and a tensile speed of 10 mm / min;

[0067] The test results are shown in Table 1:

[0068] Table 1: Performance test results

[0069]

[0070] As can be seen from Table 1, the polyamide-imide composite nanofibers prepared by the present invention are tested for heat resistance, breaking strength and elongation at break, and the fibers have excellent heat resistance, breaking strength and toughness.

[0071] The above content is only an example and illustration of the concept of the present invention. Those skilled in the art of the present technology make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the scope defined by the concept of the invention, they should all belong to the protection scope of the present invention.

Claims

1. A preparation method of polyamide-imide composite nanofibers, characterized in that, It is prepared by including the following steps: Step S1: Mix and stir a dianhydride monomer, a diamine monomer, and a functional monomer in an organic solvent, and keep the temperature at 0 °C for reaction for 5 - 6 h to obtain a polyamide-acid solution; Step S2: Add acetic anhydride and triethylamine to the above polyamide-acid solution, stir well, react at 25 - 35 °C for 4 - 6 h, then perform vacuum degassing and filtration treatment, spray it out through a spinneret, and enter the treatment liquid to obtain primary fibers, and then obtain polyamideimide composite nanofibers through a coagulation bath, hot water drawing, water washing, drying, thermal cyclization, and winding; The functional monomer is prepared by reacting a hydrogen-terminated polydimethylsiloxane and a double bond-benzamide derivative. The double bond-benzamide derivative is prepared by reacting an isocyanate-benzamide derivative and ethylenediamine. The isocyanate-benzamide derivative is prepared by reacting toluene-2,4-diisocyanate and an amino-benzamide derivative. The amino-benzamide derivative is prepared by a reduction reaction of a nitro-benzamide derivative. The nitro-benzamide derivative is prepared by reacting p-nitrobenzoyl chloride and 1-amino-5-hexene; The functional monomer is specifically prepared by the following steps: Step A1: Stir p-nitrobenzoyl chloride evenly in tetrahydrofuran, transfer it to an ice-water bath, add pyridine and stir for 1 h, then add 1-amino-5-hexene and stir for 3.5 - 4.5 h, add water and stir for 30 min, perform suction filtration, recrystallization, and drying to obtain a nitro-benzamide derivative; Step A2: Stir the nitro-benzamide derivative, ethanol, and a catalyst Pt / SnO2 - Sb2O3 at a constant temperature of 50 °C for 15 min, then introduce 4 MPa of hydrogen and stir for 3 h, and perform extraction to obtain an amino-benzamide derivative; Step A3: Mix toluene-2,4-diisocyanate, sodium hydroxide, toluene, and the amino-benzamide derivative, heat up to 60 - 70 °C, introduce nitrogen and react for 10 - 15 h, perform rotary evaporation and drying to obtain an isocyanate-benzamide derivative; Step A4: Add sodium hydroxide, toluene, and ethylenediamine to the isocyanate-benzamide derivative, stir well, react at 70 °C under nitrogen for 6 - 8 h, perform rotary evaporation and drying to obtain a double bond-benzamide derivative; Step A5: Under nitrogen conditions, mix and stir the double bond-benzamide derivative, a KARSTEDT catalyst, and toluene evenly, then slowly dropwise add a hydrogen-terminated polydimethylsiloxane, and heat up to 80 - 100 °C for reaction for 20 - 24 h, perform rotary evaporation, purification, and drying to obtain the functional monomer.

2. The preparation method of a polyamide-imide composite nanofiber according to claim 1, characterized in that, In Step S1, the molar ratio of the dianhydride monomer, the diamine monomer, and the functional monomer is 1:0.96 - 1:0.02 - 0.

05. The solid content of the polyamide-acid solution is 15% - 25%. The dianhydride monomer is one of 3,3’,4,4’-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, or 3,3’,4,4’-diphenylether tetracarboxylic dianhydride. The diamine monomer is one of p-phenylenediamine or diphenyl ether diamine. The organic solvent is one of N,N-dimethylformamide or N,N-dimethylacetamide.

3. The preparation method of a polyamide-imide composite nanofiber according to claim 1, wherein In step S2, the volume ratio of acetic anhydride to triethylamine is 2 - 3:1, the molar ratio of acetic anhydride to the dianhydride monomer described in step S1 is 0.3 - 0.5:1, the treatment liquid is a mixed solution of acetic anhydride and triethylamine with a volume ratio of 1:3, the coagulation bath is a mixed solution of N,N - dimethylacetamide and water with a volume ratio of 4:6, the hot drawing temperature is 90 °C, the drawing ratio is 2.4, and the thermal cyclization temperature is 320 °C.

4. The preparation method of a polyamideimide composite nanofiber according to claim 1, characterized in that, In step A1, the dosage ratio of p - nitrobenzoyl chloride, tetrahydrofuran, 1 - amino - 5 - hexene, pyridine and water is 0.01 - 0.03 mol:100 mL:0.01 - 0.03 mol:0.01 - 0.03 mol:200 mL.

5. The preparation method of a polyamide-imide composite nanofiber according to claim 1, characterized in that, In step A2, the dosage ratio of nitro - benzamide derivative, ethanol and catalyst Pt / SnO2 - Sb2O3 is 0.5 - 1.5 g:10 - 30 mL:0.3 - 0.9 g. Pt accounts for 0.5 wt% of the total amount of the catalyst in the catalyst Pt / SnO2 - Sb2O3, and the molar ratio of Sn to Sb is 0.1:

1.

6. The preparation method of a polyamide-imide composite nanofiber according to claim 1, characterized in that, In step A3, the dosage ratio of toluene - 2,4 - diisocyanate, sodium hydroxide, toluene and amino - benzamide derivative is 0.01 - 0.02 mol:0.02 - 0.04 g:100 mL:0.01 - 0.02 mol.

7. The preparation method of a polyamideimide composite nanofiber according to claim 1, characterized in that, In step A4, the molar ratio of ethylenediamine to toluene - 2,4 - diisocyanate in step A3 is 1:1, and the dosage of sodium hydroxide is 0.015 - 0.03 g.

8. The preparation method of a polyamide-imide composite nanofiber according to claim 1, characterized in that, In step A5, the molar ratio of hydrogen - terminated polydimethylsiloxane to double - bond - benzamide derivative is 1:1 - 1.02, and the KARSTEDT catalyst accounts for 0.002 wt% of the total amount of the reactants.

9. A polyamide - imide composite nanofiber prepared by the preparation method according to any one of claims 1 - 8.

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