High-strength high-modulus electrospun polypyrrolone nanofiber and preparation method thereof

文档序号：1885180 发布日期：2021-11-26 浏览：23次中文

阅读说明：本技术 一种高强高模电纺聚吡咙纳米纤维及其制备方法 (High-strength high-modulus electrospun polypyrrolone nanofiber and preparation method thereof ) 是由侯豪情胡添赵永丽江昱轩彭慧珍于 2021-06-08 设计创作，主要内容包括：本申请涉及聚吡咙材料技术领域,具体涉及到一种高强高模电纺聚吡咙纳米纤维及其制备方法。本发明中采用了含两个隐形氨基(乙酰氨基)的四氨基联苯(4,4’-二乙酰氨基-3,3’-二氨基联苯)为单体先合成聚酰亚胺的前聚体(聚乙酰氨基酰胺酸),后者在空气气氛中亚胺化(300-350℃的高温)形成聚乙酰氨基酰亚胺(聚吡咙的前聚体),再在空气气氛中高温吡咙化(450-500℃的高温)得到拉伸强度高达3.0GPa,拉伸膜量高达200GPa及以上,高玻璃化转变温度、高分解温度等高性能聚吡咙纳米纤维。这个方案比直接采用3,3’,4,4’-四氨基联苯作为单体合成聚吡咙的优点就在于：在空气气氛中高温亚胺化和吡咙化,而不会破坏聚合物的化学结构,因为乙酰氨基比氨基更能耐高温和耐空气氧化。(The application relates to the technical field of polypyrrolone materials, in particular to a high-strength high-modulus electrospun polypyrrolone nanofiber and a preparation method thereof. The invention adopts tetramino biphenyl (4,4 '-diacetamido-3, 3' -diaminobiphenyl) containing two invisible amino groups (acetamido) as a monomer to synthesize a polyimide prepolymer (polyacetylaminoamic acid), the polyimide prepolymer (polyacetylaminoimide) is imidized in the air atmosphere (at the high temperature of 300-350 ℃) to form polyacetylaminoimide (polypyrrolone prepolymer), and then the polyacetylamimide prepolymer is subjected to high-temperature networking in the air atmosphere (at the high temperature of 450-500 ℃) to obtain the polypyrrolone nanofiber with the tensile strength of 3.0GPa, the tensile film thickness of 200GPa and above, high glass transition temperature, high decomposition temperature and the like. Compared with the scheme that 3,3 ', 4, 4' -tetramino biphenyl is directly adopted as a monomer to synthesize polypyrrolone, the scheme has the advantages that: imidization and imidation are carried out at high temperature in an air atmosphere without destroying the chemical structure of the polymer, because the acetamido group is more resistant to high temperature and air oxidation than the amino group.)

1. The utility model provides a high-strength high-modulus electrospun polypyrrolone nanofiber, which is characterized in that the polypyrrolone of the polypyrrolone nanofiber has the following structure:

the diameter of the polypyrrolone nanofiber is 100-400 nm.

2. The high-strength high-mode electrospun polypyrrolone nanofiber according to claim 1, wherein said polypyrrolone nanofiber has a tensile strength of not less than 2.0 GPa.

3. The high-strength high-mode electrospun polypyrrolone nanofiber according to claim 1, wherein the amount of stretched film of polypyrrolone nanofiber is not less than 80 GPa.

4. The high-strength high-mode electrospun polypyrrolone nanofiber according to claim 1, wherein said polypyrrolone nanofiber has a glass transition temperature of not less than 350 ℃.

5. The high-strength high-modulus electrospun polypyrrolone nanofiber according to any one of claims 1 to 4, wherein the polypyrrolone nanofiber is prepared from raw materials comprising substituted biphenyldiamine; the substituted biphenyldiamine has the following structure:

wherein the substituent R₁And a substituent R₂Each independently a hydrogen atom or an acetamido group.

6. The high-strength high-mode electrospun polypyrrolone nanofiber according to claim 5, wherein said substituent R is₁And a substituent R₂The same; preferably, the substituent R₁And a substituent R₂Is an acetylamino group.

7. The preparation method of the high-strength high-modulus electrospun polypyrrolone nanofiber according to any one of claims 1 to 4, characterized by comprising the following steps:

(1) preparation of raw material monomers: dissolving acetic anhydride in an organic solvent A to obtain a reaction material A, adding the reaction material A into a solution B of an organic solvent for substituting diphenyldiamine, and reacting at a reaction temperature of not higher than 5 ℃ for 2-6 hours to obtain an intermediate crude product; adding calcium oxide into the intermediate crude product for precipitation, filtering and concentrating to obtain a crude product; then recrystallizing the crude product to obtain the raw material monomer;

(2) synthesis of intermediate polyacetylaminoacid: adding the raw material monomer into a reactor, and carrying out condensation reaction with binary acid anhydride in a solvent to obtain a poly (acetylamino-amide) acid solution;

(3) spinning and forming: adding the organic solvent A or the organic solvent B into the poly-acetamido-amic acid solution to dilute the concentration of the poly-acetamido-amic acid solution, adding a conductivity regulator to obtain a spinning solution, and then performing electrospinning to form nanofibers with the diameter of 100-500 nm;

(4) decarboxylation: and then drying the nano-fiber at the temperature of 150-.

8. The method for preparing the high-strength and high-modulus electrospun polypyrrolone nanofiber according to claim 7, wherein the conductivity of the spinning solution obtained after the conductivity regulator is added in the step (3) is 3.5-4.5 mS/cm.

9. The method for preparing the high-strength and high-modulus electrospun polypyrrolone nanofiber according to claim 7, wherein the absolute viscosity of the spinning solution in the step (3) is 2.0-3.6 Pa.s.

10. The method for preparing the high-strength and high-modulus electrospun polypyrrolone nanofiber according to claim 7, wherein the solid content of the polyacetylamide acid solution is 10-20 wt%.

Technical Field

The application relates to the technical field of polypyrrolone materials, in particular to a high-strength high-modulus electrospun polypyrrolone nanofiber and a preparation method thereof.

Background

The polypyrrolone is a rigid trapezoidal or semi-trapezoidal polyaromatic heterocyclic macromolecular polymer, has good high temperature resistance and oxidation resistance, and the decomposition temperature of part of polypyrrolone exceeds 700 ℃. The polymer fiber is not only a high-temperature resistant flame-retardant fiber, but also a high-strength high-modulus high-performance fiber. Since the sixties of the last century, the polymers have been widely studied and are generally polymerized in high-boiling solvents such as polyphosphoric acid at high temperatures. Since polypyrrolones are neither melted nor dissolved in common organic solvents, their processability is greatly limited and their application development is greatly hindered. Moreover, their insoluble and infusible nature makes it impossible to prepare nanofibers of such polymers by melt electrospinning or solution electrospinning. In addition, the traditional preparation method of polypyrrolone crude fiber or film is to dissolve the polypyrrolone crude fiber or film in ultra-strong protonic acid such as methanesulfonic acid, chlorosulfonic acid and the like for processing, and the solvents have strong toxicity and high boiling point, are difficult to remove cleanly from the prepared fiber or film material, and are easy to cause environmental pollution. Therefore, it is necessary to change the synthesis path of polypyrrolone and to perform a two-step synthesis method similar to the preparation of polyimide by synthesizing a pre-polymer of high molecular weight polypyrrolone soluble in common organic solvents, preparing a pre-polymer fiber (or nanofiber) or a pre-polymer film from the pre-polymer solution, and then conducting the polypyrrolone fiber (or nanofiber) or polypyrrolone film through the pre-polymer solution.

Disclosure of Invention

In view of the above technical problems, a first aspect of the present invention provides a high-strength high-mode electrospun polypyrrolone nanofiber, wherein the polypyrrolone of the polypyrrolone nanofiber has the following structure:

the diameter of the polypyrrolone nanofiber is 100-400 nm.

As a preferable technical scheme of the invention, the tensile strength of the polypyrrolone nano fiber is not less than 2.0 GPa.

As a preferable technical scheme of the invention, the amount of the drawn film of the polypyrrolone nano fiber is not less than 80 GPa.

As a preferable technical scheme of the invention, the glass transition temperature of the polypyrrolone nano fiber is not lower than 350 ℃.

As a preferable technical scheme, the raw materials for preparing the polypyrrolone nano fiber comprise substituted biphenyldiamine; the substituted biphenyldiamine has the following structure:

wherein the substituent R₁And a substituent R₂Each independently a hydrogen atom or an acetamido group.

As a preferred embodiment of the present invention, the substituent R is₁And a substituent R₂The same; preferably, the substituent R₁And a substituent R₂Is an acetylamino group.

The second aspect of the present invention provides a method for preparing the high-strength and high-modulus electrospun polypyrrolone nanofiber, which comprises the following steps:

(4) decarboxylation: and then drying the nano-fiber at the temperature of 150-.

As a preferable technical scheme of the invention, the conductivity of the spinning solution obtained after the conductivity regulator is added in the step (3) is 3.5-4.5 mS/cm.

As a preferable technical scheme of the invention, the absolute viscosity of the spinning solution in the step (3) is 2.0-3.6 Pa.s.

As a preferable technical scheme of the invention, the solid content of the poly-acetamido-acid solution is 10-20 wt%.

Has the advantages that: the invention adopts tetramino biphenyl (4,4 '-diacetamido-3, 3' -diaminobiphenyl) containing two invisible amino groups (acetamido) as a monomer to synthesize a polyimide prepolymer (polyacetylaminoamic acid), the polyimide prepolymer (polyacetylaminoimide) is imidized in the air atmosphere (at the high temperature of 300-350 ℃) to form polyacetylaminoimide (polypyrrolone prepolymer), and then the polyacetylamimide prepolymer is subjected to high-temperature networking in the air atmosphere (at the high temperature of 450-500 ℃) to obtain the polypyrrolone polymer with the tensile strength of 3.0GPa, the tensile film thickness of 200GPa and above, the glass transition temperature, the high decomposition temperature and the like. Compared with the scheme that 3,3 ', 4, 4' -tetramino biphenyl is directly adopted as a monomer to synthesize polypyrrolone, the scheme has the advantages that: imidization and imidation are carried out at high temperature in an air atmosphere without destroying the chemical structure of the polymer, because the acetamido group is more resistant to high temperature and air oxidation than the amino group. If 3,3 ', 4, 4' -tetraaminobiphenyl is directly used as a monomer to synthesize polyaminoamic acid (polyimide precursor), and is imidized in high-temperature air, amino groups can be oxidized into nitrogen-oxygen compounds, and the nitrogen-oxygen compounds cannot react with carbonyl on an imide ring in the subsequent imidation reaction to form a polypyrrolone structure containing carbon-nitrogen double bonds, so that the polypyrrolone compound cannot be obtained. In addition, the free amino groups in the polyaminoamic acid are so reactive that the prepolymer polymer is not stable enough and is liable to gel, which seriously affects the flowability of the solution and prevents smooth spinning.

Detailed Description

The technical features of the technical solutions provided by the present invention will be further clearly and completely described below with reference to the specific embodiments, and it should be apparent that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The words "preferred", "preferably", "more preferred", and the like, in the present invention, refer to embodiments of the invention that may provide certain benefits, under certain circumstances. However, other embodiments may be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.

It should be understood that other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

The invention provides a high-strength high-mode electrospun polypyrrolone nanofiber, wherein a polypyrrolone of the polypyrrolone nanofiber has the following structure:

the diameter of the polypyrrolone nanofiber is 100-400 nm.

In some embodiments, the polypyrrolone nanofibers have a tensile strength of not less than 2.0 GPa; further preferably, the tensile strength is not less than 2.2 GPa; further preferably, the amount of the drawn film of the polypyrrolone nanofibers is not less than 80 GPa. The tensile strength and the tensile film amount of the fiber are obtained by adopting a Shanghai Zhongchen superfine fiber monofilament tensile tester JQ03B, and can be tested according to the ISO 11566-. In some preferred embodiments, the glass transition temperature of the polypyrrolone nanofibers is not less than 350 ℃; preferably 380 to 500 ℃.

In some embodiments, the polypyrrolone nanofibers are prepared from starting materials comprising substituted biphenyldiamines; the substituted biphenyldiamine has the following structure:

wherein the substituent R₁And a substituent R₂Each independently a hydrogen atom or an acetamido group. The amino group in the polyacetylaminoimide monomer of the invention may be the same substituent R on any of the 2-position, 3-position or 4-position carbon atoms₁And a substituent R₂Or on any of the carbon atoms in positions 2, 3 and 4. Preferably, the substituent R₁And a substituent R₂Each independently a hydrogen atom or an acetamido group. Wherein the substituent R₁And a substituent R₂The substituents may be the same or different.

Further, the substituent R₁And a substituent R₂The same; preferably, the substituent R₁And a substituent R₂Is an acetylamino group; further preferably, the amino group in the polyacetylaminoimide monomer is substituted with the carbon atom at position 3, and the acetamido group is substituted with the carbon atom at position 4, having the chemical name 3,3 '-diamino-4, 4' -diacetylaminobiphenyl, having the structure:

the second aspect of the present invention provides a method for preparing the high-strength and high-modulus electrospun polypyrrolone nanofiber, which comprises the following steps:

(4) decarboxylation: and then drying the nano-fiber at the temperature of 150-200 ℃, and then annealing at the temperature of 450-500 ℃ for 15-30 minutes to obtain the high-strength high-modulus electrospun polypyrrolone nano-fiber.

In some embodiments, the 3,3 ' -diamino-4, 4 ' -diacetoxybiphenyl is obtained by reacting 3,3 ' -diaminobenzidine with acetic anhydride at low temperature. Because the 3,3 '-diaminobenzidine structure contains four amino groups, and the activity of each amino group is different, the reaction needs to be carried out at low temperature, and the acetic anhydride is ensured to react with the high-activity diamino at the 4.4' -position only to form the 3,3 '-diamino-4, 4' -diacetoxybiphenyl. In some embodiments, the temperature of the reaction is no greater than 5 degrees celsius; preferably, the reaction temperature is not higher than 0 ℃; further, the reaction temperature is-5-0 ℃. In addition, in order to avoid the reaction of acetic anhydride with all amino groups on the 3,3 '-diaminobenzidine and generate unnecessary byproducts, the adding speed of the acetic anhydride is further controlled, and the content of the acetic anhydride in the system is ensured to be kept less than the content of the 3, 3' -diaminobenzidine in the reaction process.

In some embodiments, the above reaction is carried out in a liquid phase; preferably, 3 '-diaminobenzidine is dissolved in an organic solvent B to prepare a solution with the weight percent of 10-20%, acetic anhydride is prepared into a solution with the weight percent of 5-15% by adopting the organic solvent A, and the solution of acetic anhydride is added into the solution of 3, 3' -diaminobenzidine for reaction. In some preferred embodiments, the dropping speed of the reactant A into the organic solvent B solution of substituted biphenyldiamine is 1-3 mL/min.

In the present invention, the specific types of the organic solvent a and the organic solvent B are not particularly limited, and various organic solvents capable of dissolving acetic anhydride, which are well known to those skilled in the art, may be selected, including but not limited to tetrahydrofuran, ethylene glycol dimethyl ether, methyl carbonate, dimethyl sulfoxide, DMF, DMAc, and the like. In some preferred embodiments, the organic solvent a and the organic solvent B are the same; further preferably, the organic solvent a and the organic solvent B are tetrahydrofuran.

Since acetic acid is produced as a by-product in the above reaction, an appropriate amount of calcium oxide is added to the reaction product to precipitate calcium acetate from acetic anhydride in the system, unreacted acetic anhydride in the system is removed by filtration, and then the filtrate is concentrated by rotary evaporation or the like to remove the solvent therein to obtain a crude product. The amount of the calcium oxide is not particularly limited, and can be determined according to actual conditions, and in some preferred embodiments, the content of the calcium oxide is 0.3-0.8 times of the molar amount of the acetic anhydride; further preferably, the content of the calcium oxide is 0.5 times of the molar amount of the acetic anhydride. In the invention, the coarse product obtained by calcium oxide precipitation and filtration is recrystallized to further purify the coarse product. The recrystallization step is not particularly limited in the present invention, and may be performed according to a manner known to those skilled in the art. In some preferred embodiments, the solvent used for recrystallization is a mixed solvent of ethanol and tetrahydrofuran; preferably, the volume ratio of ethanol to tetrahydrofuran is 1: 1.

The intermediate of the invention, namely the poly-acetamido-amic acid, is prepared by condensing the raw material monomer prepared in the step 1 and dibasic acid anhydride. The specific type of anhydride reacted with the polyamidoamide monomer is not particularly limited in this application, and various types of dibasic anhydrides known to those skilled in the art can be used. The molar ratio of the raw material monomer to the dibasic acid anhydride in the above reaction is 1: (0.8-1.2), preferably the molar ratio is 1: 1. In some embodiments, the condensation reaction temperature is 5 to 15 ℃. Stirring the reaction raw materials under the reaction conditions, wherein the stirring speed is 150-250 r/min, and reacting for 4-9 hours to obtain a viscous intermediate poly (acetamido amic acid) (PAAA) solution with a solid content of 8-20 wt% (preferably 10-20 wt%).

In the invention, the spinning solution prepared according to the steps is subjected to electrostatic spinning to obtain the nano-fiber. Wherein the organic solvent A or the organic solvent B is added into the poly-acetamido-amic acid solution to dilute the concentration of the poly-acetamido-amic acid solution to obtain the electrostatic spinning solution, and the electrostatic spinning solution is subjected to electrostatic spinning to form the nano-fiber with the diameter of 100-500 nm.

Because the electrostatic spinning is that the spinning solution is extruded and then is drawn into filaments under the action of an electric field, the concentration of the spinning solution during the extrusion is correspondingly adjusted, the extrusion difficulty caused by overlarge concentration is avoided, and the extruded nano-fibers cannot be effectively drawn to form nano-fibers with specific sizes. In some embodiments, the polyaminoamic acid solution of step 2 is diluted to provide a dope. The diluting solvent may be the organic solvent A or the organic solvent B, or a mixed solvent of the two. In some embodiments, the viscosity of the spinning solution is 1.5 to 4pa.s, wherein the viscosity is an absolute viscosity and can be measured according to a method known to those skilled in the art. Further preferably, the absolute viscosity of the spinning solution is 2.0 to 3.6 pa.s.

In order to ensure that the spinning solution can be smoothly spread and stretched under the action of an electrostatic field, in some preferred embodiments, a conductivity regulator is added into the spinning solution to regulate the conductivity of the spinning solution. In some embodiments, the conductivity of the spinning solution is 2-6 mS/cm; further preferably, the conductivity of the spinning solution is 3.5-4.5 mS/cm.

The selection of specific components of the conductivity modifier in the present invention is not particularly limited, and ionic compounds known to those skilled in the art, including but not limited to organic ionic compounds, inorganic ionic compounds, etc., may be selected; further preferably, organic ionic compounds are used, including but not limited to anionic compounds, cationic compounds; it is further preferred to employ cationic compounds including, but not limited to, trimethyl dodecyl ammonium chloride and the like. The electrostatic field intensity in the electrostatic spinning process is not particularly limited in the invention, and can be adjusted according to the actual situation, and in some embodiments, the electrostatic field intensity in the electrostatic spinning process is 300-800 kV/m.

Drying the fiber obtained by electrostatic spinning, removing the solvent (about 15 percent of the weight of the fiber) in the fiber, avoiding the problems of fiber adhesion and connection and the like caused by the existence of the solvent, then drying at the temperature of 150-; further annealing at 450-500 ℃ for 15-30 minutes.

In the invention, tetraaminobiphenyl (4,4 '-diacetamido-3, 3' -diaminobiphenyl) containing two invisible amino groups (acetamido) is adopted as a monomer to synthesize a polyimide prepolymer (polyacetylaminoamic acid), the polyimide prepolymer is imidized (at the high temperature of 300-350 ℃) in the air atmosphere to form polyacetylaminoimide (polypyrrolone prepolymer), and then is imidized at high temperature (at the high temperature of 450-500 ℃) in the air atmosphere to form a high-performance polypyrrolone polymer. Compared with the scheme that 3,3 ', 4, 4' -tetramino biphenyl is directly adopted as a monomer to synthesize polypyrrolone, the scheme has the advantages that: imidization and imidation are carried out at high temperature in an air atmosphere without destroying the chemical structure of the polymer, because the acetamido group is more resistant to high temperature and air oxidation than the amino group. If 3,3 ', 4, 4' -tetraaminobiphenyl is directly used as a monomer to synthesize polyaminoamic acid (polyimide precursor), and is imidized in high-temperature air, amino groups can be oxidized into nitrogen-oxygen compounds, and the nitrogen-oxygen compounds cannot react with carbonyl on an imide ring in the subsequent imidation reaction to form a polypyrrolone structure containing carbon-nitrogen double bonds, so that the polypyrrolone compound cannot be obtained. In addition, the free amino groups in the polyaminoamic acid are so reactive that the prepolymer polymer is not stable enough and is liable to gel, which seriously affects the flowability of the solution and prevents smooth spinning.

The present invention will be specifically described below by way of examples. It should be noted that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention, and that the insubstantial modifications and adaptations of the present invention by those skilled in the art based on the above disclosure are still within the scope of the present invention.

The reaction equation is shown in the following schematic structure:

example 1

(1) Placing 10 g (46.67mmol) of 3,3 '-diaminobenzidine into a reactor, adding 56.7 g of THF (tetrahydrofuran) for dissolving to prepare a solution with the concentration of 15%, then dropwise adding 95.29 g (2 x 46.67mmol of acetic anhydride (M ═ 102.09) and 9.53 g of acetic anhydride) of 10% THF solution of acetic anhydride into the THF solution of the 3, 3' -diaminobenzidine (M ═ 214.27) at the speed of 1-3g/min, controlling the reaction temperature within the range of-5-0 ℃ for reacting for 4 hours, then adding 2.26g (46.67mmol) of dried calcium oxide (M ═ 56.077), reacting with acetic acid to form calcium acetate precipitate, and precipitating from the THF solution; calcium acetate in the system was removed by filtration, and the filtrate was concentrated by rotary evaporation to give 13.6 g (theoretical yield 13.92 g) of a crude product of 3,3 '-diamino-4, 4' -diacetoxybiphenyl (M ═ 298.27); the crude 3,3 '-diamino-4, 4' -diacetoxybiphenyl product was added with an ethanol/THF solvent in a volume ratio of 1/1, and recrystallization was carried out to obtain 13.1 g of 3,3 '-diamino-4, 4' -diacetoxybiphenyl product having a purity of 99%, with a final yield of 94.1%.

(2) Synthesis of intermediate polyacetylaminoacid: the method comprises the steps of carrying out condensation polymerization reaction on 3,3 '-diamino-4, 4' -diacetamido biphenyl and biphenyltetracarboxylic dianhydride monomers serving as raw materials, controlling the molar ratio of diamine to dianhydride to be 1:1 and the solid content of the solution to be 15 wt% by taking DMAc as a solvent, and carrying out condensation polymerization for 8 hours at the temperature of 10-15 ℃ to form a viscous polyacetylamide acid solution.

(3) Electrostatic spinning: adding a proper amount of DMAc into the 15 wt.% of the polyacetylaminoacid solution, diluting the viscous polyamic acid solution to an absolute viscosity of 2.5Pa.s, and adding a trace amount of trimethyl dodecyl ammonium chloride to ensure that the conductivity of the solution reaches 3.8 mS/cm; electrostatic spinning is carried out in an electrostatic field of 300-800kV/m to form the polyacetylaminoacid nanofibers with the diameter;

(4) and then drying the solvent of the electrospun nanofiber at about 150 ℃, annealing for 25 minutes at 480 ℃, enabling nitrogen elements in the acetamido group to react with imide ring carbonyl at high temperature to form carbon-nitrogen double bonds, and removing acetic acid molecules to obtain the high-strength and high-modulus electrospun polypyrrolone nanofiber.

Example 2

(2) Synthesis of intermediate polyacetylaminoacid: the method comprises the steps of carrying out condensation polymerization reaction on 3,3 '-diamino-4, 4' -diacetamido biphenyl and pyromellitic anhydride monomers as raw materials, controlling the molar ratio of diamine to dianhydride to be 1:1 and the solid content of the solution to be 15 wt% by taking DMAc as a solvent, and carrying out condensation polymerization for 8 hours at the temperature of 10-15 ℃ to form a viscous polyacetylamide acid solution.

Example 3

(2) Synthesis of intermediate polyacetylaminoacid: the method comprises the steps of carrying out condensation polymerization reaction on 3,3 '-diamino-4, 4' -diacetoxybiphenyl and benzophenone dianhydride monomers serving as raw materials, controlling the molar ratio of diamine to dianhydride to be 1:1 and the solid content of the solution to be 15 wt% by taking DMAc as a solvent, and carrying out condensation polymerization for 8 hours at the temperature of 10-15 ℃ to form a viscous polyacetylamide acid solution.

Example 4

(2) Synthesis of intermediate polyacetylaminoacid: the method comprises the steps of carrying out condensation polymerization reaction on 3,3 '-diamino-4, 4' -diacetamido biphenyl and diphenyl ether dianhydride monomers serving as raw materials, controlling the molar ratio of diamine to dianhydride to be 1:1 and the solid content of a solution to be 15 wt.% by taking DMAc as a solvent, and carrying out condensation polymerization for 8 hours at the temperature of 10-15 ℃ to form a viscous polyacetylamide acid solution.

Example 5

(2) Synthesis of intermediate polyacetylaminoacid: the method comprises the steps of carrying out condensation polymerization reaction on 3,3 '-diamino-4, 4' -diacetamido biphenyl and naphthalene tetracarboxylic dianhydride monomers serving as raw materials, controlling the molar ratio of diamine to dianhydride to be 1:1 and the solid content of the solution to be 15 wt% by taking DMAc as a solvent, and carrying out condensation polymerization for 8 hours at the temperature of 10-15 ℃ to form a viscous polyacetylamide acid solution.

Example 6

(2) Synthesis of intermediate polyacetylaminoacid: the method comprises the steps of carrying out condensation polymerization reaction on 3,3 '-diamino-4, 4' -diacetamido biphenyl and triphenyl diphenyl ether dianhydride monomers serving as raw materials, controlling the molar ratio of diamine to dianhydride to be 1:1 and the solid content of the solution to be 15 wt.% by taking DMAc as a solvent, and carrying out condensation polymerization for 8 hours at the temperature of 10-15 ℃ to form a viscous polyacetylamide acid solution.

Example 7

(2) Synthesis of intermediate polyacetylaminoacid: the method comprises the steps of carrying out condensation polymerization reaction on 3,3 '-diamino-4, 4' -diacetamido biphenyl and diphenyl sulfone dianhydride monomers serving as raw materials, controlling the molar ratio of diamine to dianhydride to be 1:1 and the solid content of the solution to be 15 wt.% by taking DMAc as a solvent, and carrying out condensation polymerization for 8 hours at the temperature of 10-15 ℃ to form a viscous polyacetylamide acid solution.

Performance testing

The applicant carried out tests on the experimental samples of the above examples for fiber diameter, mechanical strength, glass transition temperature, and decomposition temperature, as follows:

1. fiber diameter testing: the randomly cut fiber diameters (nm) in the samples of the above examples were measured mainly under a scanning electron microscope.

2. Glass transition temperature test: the samples of the above examples were tested for glass transition temperature Tg using DMA.

3. And (3) testing the decomposition temperature: the samples of the above examples were tested by TGA for their thermal decomposition temperature, where the decomposition temperature is Td/5% of the temperature at which the thermal weight loss reaches 5 wt%.

4. Tensile strength: the tensile strength of the fiber is tested by adopting a Shanghai Zhongchen superfine fiber monofilament tensile tester JQ03B to obtain parameters such as tensile strength (GPa), modulus (GPa) and elongation (%).

The results of the above performance tests are shown in tables 1 and 2 below.

TABLE 1

	Td/℃	Tensile strength	Elongation percentage	Modulus of elasticity
					Example 1	715-735	2.8-3.2	6.0-8.0	130-150
Example 2	700-720	2.1-2.5	3.5-5.0	200-230
					Example 3	680-700	2.5-3.0	6.0-8.0	100-130
Example 4	660-680	2.2-2.6	8.0-10.0	80-110
					Example 5	730-750	3.8-4.3	4.0-5.5	220-250
Example 6	630-650	2.3-2.8	10.0-12.0	60-80
					Example 7	650-670	2.5-3.0	5.0-7.0	150-180

TABLE 2

Comparative example

(1) 9.9077 g (46.24mmol) of 3, 3-diaminobenzidine is placed in a reactor, 180 g of DMAc is added to dissolve the 3, 3-diaminobenzidine to prepare a solution with the concentration of 5 percent, the reactor is placed in a cold bath, the temperature of a reaction system is controlled between-5 ℃ and 0 ℃, 10.0923g (46.24mmol) of pyromellitic dianhydride (PMDA) powder is added into the reaction system, and the reaction is carried out for 4 hours under mechanical stirring to form a 10 percent DMAc solution of polyaminoamic acid. The solution was then transferred to a 250ml reservoir bottle and allowed to warm to room temperature (25C) naturally, and the polymer was ready for intrinsic viscosity testing and electrospinning processing. However, in less than 2 hours, the solution viscosity became significantly high, and the fluidity was completely lost within 5 hours, resulting in a dark brown gel-like material, and as a result, the intrinsic viscosity of the polymer could not be measured, and the electrostatic spinning process could not be carried out. The reason for the failure is that the tetraamino monomer is used as the diamino monomer, and the polyaminoamic acid formed contains a large number of free amino groups, which can form a large number of hydrogen bonds with carboxyl groups between adjacent polymer molecules, and can also undergo an exchange reaction with amide bonds between adjacent polymer molecules to form polymer molecules with a cross-linked structure, so that the polyaminoamic acid solution slowly gels at room temperature, resulting in complete loss of solution fluidity.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in other forms, and any person skilled in the art may modify or change the technical content disclosed above into an equivalent embodiment with equivalent changes, but all those simple modifications, equivalent changes and modifications made on the above embodiment according to the technical spirit of the present invention still belong to the protection scope of the present invention.

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