Aromatic polyoxadiazole film with high solubility and high flame retardancy and preparation method thereof

Abstract

The present invention relates to the technical field of polymer synthesis and processing, and particularly relates to an aromatic polyoxadiazole film with high solubility and high flame retardancy and a preparation method thereof. The preparation method is as follows: a condensation reaction and a sulfonation reaction are carried out on biphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid and a flame retardant dicarboxylic acid monomer to obtain an aromatic polyoxadiazole solution; the aromatic polyoxadiazole solution is cast into filaments, washed, pulverized and dried to obtain polyoxadiazole powder; after the polyoxadiazole powder is dissolved in a solvent, it is coated and dried to obtain the polyoxadiazole film. The flame retardant dicarboxylic acid monomer is at least one of 2-(diphenylphosphoryl) terephthalic acid and 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide. The polyoxadiazole film has high flame retardancy, and after using the flame retardant dicarboxylic acid monomer to participate in the condensation reaction to prepare the film, it has good solubility, high solid content and is easier to process.

Description

Technical Field

[0001] The invention relates to a highly soluble and highly flame retardant aromatic polyoxadiazole film and a preparation method thereof, belonging to the technical field of polymer synthesis and processing. Background Art

[0002] With the rapid development of modern science and technology, polymer materials are widely used in all aspects of life and production. Since polymer materials generally have the advantages of high mechanical strength, light weight, good heat resistance, and easy large-scale production, these materials are widely used in the fields of automobiles, construction, semiconductors, electronics, aerospace, etc., thus replacing traditional materials such as steel, wood, and cotton and linen. However, considering the inherent aromatic structure of polymer materials, most of them are flammable or combustible. The widespread use of these polymer materials in life or production also poses certain security threats to humans.

[0003] Aromatic polyoxadiazole (POD) is a polymer containing benzene rings and oxadiazole heterocyclic rings in the molecular chain. Due to its good high temperature resistance, corrosion resistance, and electrical insulation, aromatic polyoxadiazole is used in various fields, such as high temperature resistance and electrical insulation protection. As we all know, POD and aramid are both aromatic polymers with high carbon and nitrogen contents. The LOI of halogen-free polymers can be estimated according to the Krevelen empirical formula. The limiting oxygen index (LOI) of POD and aramid should be above 33%. The estimated value of aramid is close to the actual value, but the actual value of POD is less than 25%, which is still flammable.

[0004] In order to obtain flame-retardant POD polymers, relevant scientific researchers have introduced halogen-based, phosphorus-based and other flame-retardant monomers into the molecular structure from the perspective of molecular design. Halogen-based flame retardants usually have better effects with brominated flame retardants. Although brominated flame retardants have the advantages of good heat resistance, high flame retardant efficiency, and can meet the processing requirements of a variety of polymer materials, they are prone to generate more smoke, toxic gases and corrosive gases when burning, causing serious secondary damage to on-site personnel and the environment, which greatly limits the wide application of this series of flame retardants. With the implementation of a series of laws and regulations in various countries around the world to restrict and prohibit the addition of certain toxic and harmful substances and elements to electronic and electrical equipment, as well as people's increasing attention to environmental protection and health and safety, finding suitable substitutes for halogen-based flame retardants has become a severe challenge facing the flame retardant industry, and accelerating the research and development of its substitutes has also become an important topic in related scientific research fields. Phosphoric anhydride or phosphoric acid generated by phosphorus-based flame retardants when heated can promote the dehydration and carbonization of polymer materials and prevent or reduce the generation of combustible gases to achieve the purpose of flame retardancy. More importantly, phosphorus-based flame retardants have the advantages of low toxicity, low smoke, and halogen-free, and are one of the most promising high-efficiency flame retardants that meet environmental protection requirements.

[0005] Traditional POD polymers are polymerized from terephthalic acid and isophthalic acid as the main carboxylic acid monomers. The linear arrangement and rigid connection of aromatic heterocycles result in very poor solubility of the polymer. Except for concentrated sulfuric acid, it is almost insoluble in other solvents. There are generally problems such as low solid content, strong corrosiveness, poor thickness uniformity, and difficulty in processing and forming when using the concentrated sulfuric acid system polymerization solution for film making.

[0006] Based on this, in view of the above characteristics of polyoxadiazole, it is very necessary to research and prepare a phosphorus-based aromatic polyoxadiazole film material with high solid content, good solubility, easy processing, and non-sulfuric acid solubility for the flame retardant field. Summary of the Invention

[0007] In view of the deficiencies of the existing technology, the present invention provides a highly soluble and highly flame-retardant aromatic polyoxadiazole film and a preparation method thereof. The polyoxadiazole film has high flame retardancy, and has the advantages of low toxicity, less smoke, and halogen-free. Moreover, after using a flame-retardant dicarboxylic acid monomer to participate in the polycondensation reaction to prepare the film, it has good solubility, high solid content, and is easier to process.

[0008] The technical solution of the present invention to solve the above technical problems is as follows: A preparation method of a highly soluble and highly flame-retardant aromatic polyoxadiazole film, and the preparation method is:

[0009] S1. Carry out a polycondensation reaction and a sulfonation reaction on diphenic acid, diphenyl ether dicarboxylic acid, and a flame-retardant dicarboxylic acid monomer to obtain an aromatic polyoxadiazole solution;

[0010] S2. Cast the aromatic polyoxadiazole solution into filaments, and after washing, pulverizing, and drying, obtain polyoxadiazole powder;

[0011] S3. Dissolve the polyoxadiazole powder in a solvent, and then coat and dry to obtain the polyoxadiazole film.

[0012] Further, the flame-retardant dicarboxylic acid monomer is at least one of 2-(diphenylphosphoryl)terephthalic acid and 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide.

[0013] Further, in step S1, diphenic acid, diphenyl ether dicarboxylic acid, a flame-retardant dicarboxylic acid monomer, and a hydrazine salt are added to fuming sulfuric acid, stirred, heated for a polycondensation reaction and a sulfonation reaction, and then a capping agent is added to terminate the chain growth, and finally an aromatic polyoxadiazole solution is obtained.

[0014] Further, the hydrazine salt is at least one of hydrazine sulfate, hydrazine acetate, or hydrazine hydrochloride;

[0015] The capping agent is at least one of 4-methylbenzoic acid, 4-ethylbenzoic acid, or 4-propylbenzoic acid.

[0016] Furthermore, the molar ratio of the fuming sulfuric acid, diphenic acid, diphenyl ether dicarboxylic acid, flame retardant dicarboxylic acid monomer, and hydrazine salt is (4 - 7):(0.20 - 0.50):(0.40 - 0.70):(0.02 - 0.20):(1.05 - 1.40), and the molar amount of the fuming sulfuric acid is calculated based on the molar amount of SO3 contained in the fuming sulfuric acid;

[0017] The addition amount of the end-capping agent is 3% - 8% of the molar amount of the hydrazine salt.

[0018] Furthermore, the reaction process of step S1 is as follows: in the first stage of the polycondensation reaction, the pre-polymerization reaction temperature is 80 - 100°C, and the reaction time is 2 - 4 h; in the second stage of the chain growth reaction, the reaction temperature is 115 - 130°C, and the reaction time is 2 - 4 h; in the third stage of the cyclization and sulfonation reaction, the reaction temperature is 135 - 160°C, and the reaction time is 1 - 5 h.

[0019] Furthermore, in step S2, the polyoxadiazole solution is passed through a spinneret hole and pressed into ice water to form a film, and after being washed with water and alkali several times respectively, when the pH = 7 - 8, the acid-free wet polyoxadiazole filaments are crushed and then dried to obtain polyoxadiazole powder.

[0020] Furthermore, in step S3, the polyoxadiazole powder is added to a solvent and heated to dissolve, and a co-solvent is added. After the dissolved polymerization solution is degassed under vacuum, a coating operation is carried out;

[0021] The solvent is at least one of DMSO, DMAc, DMF, and NMP;

[0022] The mass content of polyoxadiazole in the polymerization solution is 10% - 40%.

[0023] Furthermore, in step S3, the coating operation is as follows: the uniform polymerization solution is transferred to a glass plate or stainless steel plate substrate at 50 - 120°C, the moving speed of the scraper is 0.2 - 15 mm / min, the coating thickness is 50 - 1000 μm, the coated substrate is dried, the drying temperature is 80 - 200°C, and the time is 5 - 10 h. After drying, peeling and trimming are carried out to finally obtain the polyoxadiazole film.

[0024] The present invention also discloses a highly soluble and highly flame-retardant aromatic polyoxadiazole film, and the polyoxadiazole film is prepared by the preparation method described in the present invention.

[0025] The beneficial effects of the present invention are:

[0026] The polyoxadiazole film of the present invention has high flame retardancy. After copolymerizing with a phosphorus-based flame retardant monomer, the phosphoric anhydride or phosphoric acid generated when heated can promote the dehydration and carbonization of the polymer material, prevent or reduce the generation of combustible gases, achieving a good flame retardant effect. The LOI value can reach up to more than 45%, and it has the advantages of low toxicity, less smoke, and halogen-free, meeting the environmental protection requirements.

[0027] The aromatic polyoxadiazole powder obtained by the preparation method of the present invention is soluble in common solvents such as DMSO, DMAc, DMF, or NMP, and the solid content can reach up to 40%, avoiding the problems of strong corrosion and low solid content caused by dissolving with concentrated sulfuric acid (the solid content of conventional concentrated sulfuric acid dissolution is generally ≤10%), and it is more convenient for subsequent film coating processing.

[0028] The polyoxadiazole film of the present invention has high mechanical strength, and the fracture strength can reach more than 200 MPa. While being flame retardant, it can better protect the service life of application scenarios such as electronic and electrical appliances, transportation vehicles, and furniture products.

[0029] In the preparation method of the present invention, by adjusting the addition ratio of the carboxylic acid monomer and the capping agent, as well as the solid content of the dissolved polyoxadiazole powder, films with different thicknesses of 10 - 150 μm can be obtained. Detailed Description of the Invention

[0030] The following provides a detailed description of the specific embodiments of the present invention. The present invention can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used are only for describing specific embodiments and do not limit the present invention.

[0032] A preparation method of a highly soluble and highly flame - retardant aromatic polyoxadiazole film, and the preparation method is as follows:

[0033] S1. Carry out a polycondensation reaction and a sulfonation reaction on diphenic acid, diphenyl ether dicarboxylic acid, and a flame - retardant dicarboxylic acid monomer to obtain an aromatic polyoxadiazole solution;

[0034] S2. Cast the aromatic polyoxadiazole solution into filaments, and after washing, pulverizing, and drying, obtain polyoxadiazole powder;

[0035] S3. Dissolve the polyoxadiazole powder in a solvent, and then coat and dry to obtain the polyoxadiazole film.

[0036] Specifically, the flame-retardant dicarboxylic acid monomer is at least one of 2-(diphenylphosphoryl) terephthalic acid and 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide.

[0037] The 2-(diphenylphosphoryl) terephthalic acid and 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide are obtained by self-preparation, and the preparation method is as follows.

[0038] The synthesis route and steps of 2-(diphenylphosphoryl) terephthalic acid are as follows:

[0039] 。

[0040] Add 1.86 kg of 2-iodoterephthalic acid, 1.21 kg of compound 1 (diphenylphosphine), 1.12 g of palladium acetate, and 200 mL of triethylamine into the reaction kettle, and add 3 L of anhydrous methanol to dissolve. React overnight under nitrogen protection and reflux conditions. After the reaction is completed, distill off methanol under reduced pressure. The residue is extracted with dichloromethane (200 mL×3), and the combined organic phases are washed 3 times with saturated sodium chloride aqueous solution (300 mL), dried with anhydrous sodium sulfate for 5 h, and then the solvent is distilled off under reduced pressure to obtain the crude product. The obtained crude product is separated by a silica gel chromatographic column (the volume ratio of petroleum ether to ethyl acetate used in column separation is 1:1) to obtain a yellow solid compound 2 (1.23 kg, yield 70%). Mass spectrum: m / z = 366.07; hydrogen spectrum: 1 H NMR (400 MHz, Chloroform-d) δ12.75 (s, 2H), 8.9 (s, 1H), 8.58 (d , J = 8.4Hz, 1H), 8.34 (d, J = 8.4Hz, 1H),7.91-7.81 (m, 4H), 7.62-7.49 (m, 6H).

[0041] Place 1 kg of compound 2 in the reaction kettle, add 2 L of chloroform to dissolve, and then add 20 L of hydrogen peroxide. React at room temperature for 6 h. After the reaction is completed, distill off the solvent under reduced pressure to obtain 2-(diphenylphosphoryl) terephthalic acid (1.02 kg, yield 98%).

[0042] The synthesis route and steps of 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide are as follows:

[0043] ;

[0044] Add 1.50 kg of 2-iodoterephthalic acid, 1.1 kg of Compound 3 (phosphaphenanthrene), 29.41 g of tetrakis(triphenylphosphine)palladium, and 1.99 kg of potassium acetate into a reaction kettle, and dissolve them in 2.5 L of 1,4-dioxane. React overnight under nitrogen protection and reflux conditions. After the reaction is completed, distill off methanol under reduced pressure. The residue is extracted with dichloromethane (200 mL × 3). After combining the organic phases, wash them 3 times with saturated sodium chloride aqueous solution (200 mL), dry over anhydrous sodium sulfate for 5 h, and then distill off the solvent under reduced pressure to obtain a crude product. The obtained crude product is separated by silica gel chromatography column (the volume ratio of petroleum ether to ethyl acetate used in column separation is 1:1) to obtain 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (1.27 kg, yield 65%). Mass spectrum: m / z = 380.05; hydrogen spectrum: 1 H NMR (400 MHz, Chloroform-d) δ12.74 (s, 2H), 8.87 (s,1H), 8.58 (d, J J = 8.4Hz, 1H), 8.34 (d, J J = 8.4Hz, 1H), 8.12 - 7.95 (m, 3H), 7.65 - 7.25 (m, 5H).

[0045] Specifically, in step S1, add diphthalic acid, diphenylether dicarboxylic acid, flame-retardant dicarboxylic acid monomer, and hydrazine salt into fuming sulfuric acid, stir, heat up for polycondensation reaction and sulfonation reaction, then add a capping agent to terminate chain growth, and finally obtain an aromatic polyoxadiazole solution.

[0046] Specifically, the hydrazine salt is at least one of hydrazine sulfate, hydrazine acetate, or hydrazine hydrochloride;

[0047] The capping agent is at least one of 4-methylbenzoic acid, 4-ethylbenzoic acid, or 4-propylbenzoic acid.

[0048] Specifically, the molar ratio of the fuming sulfuric acid, diphthalic acid, diphenylether dicarboxylic acid, flame-retardant dicarboxylic acid monomer, and hydrazine salt is (4 - 7):(0.20 - 0.50):(0.40 - 0.70):(0.02 - 0.20):(1.05 - 1.40), and the molar number of the fuming sulfuric acid is calculated based on the molar number of SO3 contained in the fuming sulfuric acid;

[0049] The addition amount of the capping agent is 3% - 8% of the molar number of the hydrazine salt.

[0050] Preferably, the molar ratio of the fuming sulfuric acid, diphenic acid, diphenyl ether dicarboxylic acid, flame-retardant dicarboxylic acid monomer, and hydrazine salt is (6-7):(0.20-0.40):(0.50-0.60):(0.10-0.20):(1.20-1.30), and the molar number of the fuming sulfuric acid is based on the molar number of SO3 contained in the fuming sulfuric acid;

[0051] The addition amount of the end-capping agent is 5-8% of the molar number of the hydrazine salt.

[0052] Specifically, the reaction process of step S1 is carried out in three stages:

[0053] The first stage (prepolymerization reaction): The reaction temperature is 80-100 °C, and the reaction time is 2-4 h;

[0054] The second stage (chain growth reaction): The reaction temperature is 115-130 °C, the reaction time is 2-4 h, and the end-capping agent is added when the second stage is completed;

[0055] The third stage (cyclization and sulfonation reaction): The reaction temperature is 135-160 °C, and the reaction time is 1-5 h.

[0056] Preferably, the reaction process of step S1 is carried out in three stages:

[0057] The first stage (prepolymerization reaction): The reaction temperature is 80-90 °C, and the reaction time is 3 h;

[0058] The second stage (chain growth reaction): The reaction temperature is 120-125 °C, the reaction time is 3 h, and the end-capping agent is added when the second stage is completed;

[0059] The third stage (cyclization and sulfonation reaction): The reaction temperature is 150 °C, and the reaction time is 3 h.

[0060] Specifically, in step S2, the polyoxadiazole solution is passed through the spinneret holes and pressed into ice water to form filaments by casting. After being washed with water and alkali several times respectively, when the pH = 7-8, the acid-free wet polyoxadiazole filaments are crushed and then dried to obtain polyoxadiazole powder.

[0061] More specifically, in step S2, the spinneret plate is made of 904L stainless steel, 316L stainless steel, TA2 titanium alloy or Hastelloy, the spinneret plate pressure is 0.3-1.5 MPa, and the crushing speed is 3500-5000 rpm.

[0062] More specifically, in step S2, the drying temperature is 60-120 °C, and the drying time is 5-10 h.

[0063] Specifically, in step S3, the polyoxadiazole powder is added to a solvent and heated to dissolve, and a cosolvent is added. After the dissolved polymerization solution is degassed under vacuum, a coating operation is carried out;

[0064] The solvent is at least one of DMSO, DMAc, DMF, and NMP;

[0065] The mass content of polyoxadiazole in the polymerization solution is 10% - 40%.

[0066] More specifically, the cosolvent is at least one of lithium chloride, calcium chloride, and potassium chloride.

[0067] Preferably, the solvent is DMSO; the cosolvent is lithium chloride.

[0068] More specifically, the addition amount of the cosolvent is 0.5 - 2% of the total mass of the polymerization solution, the heating dissolution temperature is 70 - 130 °C, the stirring speed is 50 - 150 rpm, the stirring time is 3 - 8 h. After dissolution, degassing treatment is carried out. During degassing treatment, the vacuum degree is 500 - 1000 Pa, and the degassing time is 3 - 6 h. Reducing the vacuum degassing time will lead to an increase in film bubbles, and reducing the substrate coating temperature will cause a decrease in the fluidity of the polyoxadiazole solution, an increase in viscosity, affecting the uniform flatness of the polyoxadiazole film, and thus affecting the flame retardant effect.

[0069] Specifically, in step S3, the coating operation is as follows: the uniform polymerization solution is transferred to a glass plate or stainless steel plate substrate at 50 - 120 °C, the moving speed of the doctor blade is 0.2 - 15 mm / min, the coating thickness is 50 - 1000 μm. The coated substrate is dried, the drying temperature is 80 - 200 °C, and the time is 5 - 10 h. After drying, peeling and edge trimming are carried out to finally obtain the polyoxadiazole film.

[0070] More specifically, the stainless steel substrate is made of 904L stainless steel, and the doctor blade is made of any one of TA2 titanium alloy, Hastelloy alloy, or 904L stainless steel.

[0071] Example 1

[0072] The preparation of a highly soluble and highly flame - retardant aromatic polyoxadiazole film, the preparation method comprising the following steps:

[0073] S1. Mix biphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, 2-(diphenylphosphoryl) terephthalic acid, and hydrazine sulfate evenly, and then add them to fuming sulfuric acid (the mass content of sulfur trioxide is 20 wt%). The molar ratio of fuming sulfuric acid, biphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, 2-(diphenylphosphoryl) terephthalic acid, and hydrazine sulfate is 6:0.4:0.5:0.1:1.2. React at 80 °C for 3 h with stirring at 100 rpm. After heating to 120 °C and reacting for 3 h, add 4-propylbenzoic acid (the addition amount of 4-propylbenzoic acid is 5% of the molar amount of hydrazine sulfate), then raise the temperature to 150 °C and react for 3 h to stop the reaction, and cool the temperature to 100 °C.

[0074] S2. Transfer the polyoxadiazole solution after the reaction to a mold with spinnerets, extrude it into an ice-water bath at a pressure of 1 MPa to solidify into filaments. After washing with water three times and alkali washing respectively, add the acid-free wet polyoxadiazole filaments to a pulverizer and pulverize at a speed of 4000 rpm. Place the pulverized mush in an oven, dry at a temperature of 100 °C for 8 h to obtain dried polyoxadiazole powder.

[0075] S3. Add polyoxadiazole powder, DMSO, and the co-solvent lithium chloride to a stirring kettle and mix evenly. The polyoxadiazole powder accounts for 25% of the total mass of the polymerization solution, and the co-solvent lithium chloride accounts for 1% of the total mass of the polymerization solution. The dissolution temperature is 110 °C, the stirring speed is 100 rpm, and the stirring time is 4 h. After dissolution, carry out degassing treatment to obtain a polymerization solution with a vacuum degree of 600 Pa and a degassing time of 5 h. The substrate coating temperature is 100 °C, the moving speed of the doctor blade is 0.5 mm / min, the coating thickness is 500 μm, the drying temperature is 150 °C, and the time is 6 h. Then carry out peeling and trimming to finally obtain the polyoxadiazole film.

[0076] The obtained finished film has a thickness of 70 μm and is a flame-retardant film with a LOI value of 40%.

[0077] Example 2

[0078] Preparation of a highly soluble and highly flame-retardant aromatic polyoxadiazole film, the preparation method comprising the following steps:

[0079] S1. Mix biphenyl dicarboxylic acid, biphenyl ether dicarboxylic acid, 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, and hydrazine sulfate evenly, and then add them to fuming sulfuric acid (the mass content of sulfur trioxide is 20 wt%). The molar ratio of fuming sulfuric acid, biphenyl dicarboxylic acid, biphenyl ether dicarboxylic acid, 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, and hydrazine sulfate is 7:0.3:0.5:0.2:1.3. React at 90 °C for 3 h with stirring at 100 rpm, raise the temperature to 125 °C and react for 3 h, then add 4-propylbenzoic acid (the addition amount of 4-propylbenzoic acid is 5% of the molar amount of hydrazine sulfate), raise the temperature to 150 °C and react for 3 h to stop the reaction, and lower the temperature to 100 °C.

[0080] S2. Transfer the polyoxadiazole solution after the reaction to a mold with spinnerets, extrude it into an ice-water bath at a pressure of 0.8 MPa to solidify into filaments. After washing three times with water and once with alkali respectively, add the acid-free wet polyoxadiazole filaments to a crusher and crush at a speed of 5000 rpm. Place the crushed mush in an oven, dry at 120 °C for 6 h to obtain dried polyoxadiazole powder.

[0081] S3. Add polyoxadiazole powder, DMSO, and the co-solvent lithium chloride to a stirring kettle and mix evenly. The polyoxadiazole powder accounts for 35% of the total mass of the polymerization solution, and the co-solvent lithium chloride accounts for 1.5% of the total mass of the polymerization solution. The dissolution temperature is 120 °C, the stirring speed is 100 rpm, and the stirring time is 5 h. After dissolution, perform degassing treatment to obtain a polymerization solution with a vacuum degree of 600 Pa and a degassing time of 6 h. The substrate coating temperature is 100 °C, the moving speed of the scraper is 0.8 mm / min, the coating thickness is 700 μm, the drying temperature is 150 °C, and the time is 8 h. Then perform peeling and edge trimming to finally obtain the polyoxadiazole film.

[0082] The obtained finished film has a thickness of 110 μm and is a flame-retardant film with a LOI value of 46%.

[0083] Example 3

[0084] Preparation of a highly soluble and highly flame-retardant aromatic polyoxadiazole film, the preparation method comprising the following steps:

[0085] In step S1, use the same method as in Example 1, and change the molar ratio of fuming sulfuric acid, biphenyl dicarboxylic acid, biphenyl ether dicarboxylic acid, 2-(diphenylphosphoryl)terephthalic acid, and hydrazine sulfate in step S1 of Example 1 to 6:0.3:0.6:0.1:1.2;

[0086] Step S2 is the same as in Example 1;

[0087] In step S3, the polyoxadiazole powder accounts for 30% of the total mass of the polymerization solution, and the co-solvent lithium chloride accounts for 1% of the total mass of the polymerization solution.

[0088] The obtained finished film has a thickness of 80 μm and a limiting oxygen index (LOI) value of 37% for the flame-retardant film.

[0089] Example 4

[0090] Preparation of a highly soluble and highly flame-retardant aromatic polyoxadiazole film, the preparation method comprising the following steps:

[0091] In step S1, the same method as in Example 2 is adopted, and the molar ratio of fuming sulfuric acid, diphenic acid, diphenylether dicarboxylic acid, 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, and hydrazine sulfate in step S1 of Example 2 is 7:0.2:0.6:0.2:1.3;

[0092] Step S2 is the same as in Example 2;

[0093] In step S3, the polyoxadiazole powder accounts for 38% of the total mass of the polymerization solution, and the co-solvent lithium chloride accounts for 1.5% of the total mass of the polymerization solution.

[0094] The obtained finished film has a thickness of 120 μm and a limiting oxygen index (LOI) value of 45% for the flame-retardant film.

[0095] Example 5

[0096] Preparation of a highly soluble and highly flame-retardant aromatic polyoxadiazole film, the preparation method comprising the following steps:

[0097] The process of step S1 is as follows: After mixing diphenic acid, diphenylether dicarboxylic acid, 2-(diphenylphosphoryl)terephthalic acid, and hydrazine sulfate evenly, add them to fuming sulfuric acid (the mass content of sulfur trioxide is 20 wt%), wherein the molar ratio of fuming sulfuric acid, diphenic acid, diphenylether dicarboxylic acid, 2-(diphenylphosphoryl)terephthalic acid, and hydrazine sulfate is 4:0.5:0.4:0.02:1.4, stir at a rotation speed of 100 rpm and react at 100 °C for 2 h, raise the temperature to 115 °C and react for 4 h, then add 4-methylbenzoic acid (the addition amount of 4-methylbenzoic acid is 8% of the molar number of hydrazine sulfate), and then raise the temperature to 160 °C and react for 1 h to stop the reaction, and lower the temperature to 120 °C.

[0098] Step S2 is the same as in Example 1;

[0099] In step S3, the polyoxadiazole powder accounts for 27% of the total mass of the polymerization solution, and the co-solvent lithium chloride accounts for 1% of the total mass of the polymerization solution.

[0100] The obtained finished film has a thickness of 78 μm and a limiting oxygen index (LOI) value of 37% for the flame-retardant film.

[0101] Example 6

[0102] Preparation of an aromatic polyoxadiazole film with high solubility and high flame retardancy, the preparation method comprising the following steps:

[0103] S1. After uniformly mixing diphenic acid, diphenyl ether dicarboxylic acid, 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, and hydrazine sulfate, add them to fuming sulfuric acid (the mass content of sulfur trioxide is 20 wt%). The molar ratio of fuming sulfuric acid, diphenic acid, diphenyl ether dicarboxylic acid, 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, and hydrazine sulfate is 6:0.5:0.7:0.15:1.4. React at 80°C for 4 h with stirring at 100 rpm, then raise the temperature to 130°C and react for 2 h. Then add 4-propylbenzoic acid (the addition amount of 4-propylbenzoic acid is 3% of the molar amount of hydrazine sulfate), and then raise the temperature to 135°C and react for 5 h to stop the reaction, and lower the temperature to 60°C.

[0104] S2. Transfer the polyoxadiazole solution after the reaction to a mold with a spinneret, extrude it into an ice-water bath at a pressure of 1.5 MPa to solidify into filaments. After washing three times with water and once with alkali respectively, add the acid-free wet polyoxadiazole filaments to a pulverizer, with a pulverizing speed of 5000 rpm. Place the pulverized mush in an oven, with a drying temperature of 120°C and a drying time of 6 h to obtain dried polyoxadiazole powder.

[0105] S3. Add polyoxadiazole powder, DMSO, and the co-solvent lithium chloride to a stirring kettle and mix evenly. The polyoxadiazole powder accounts for 40% of the total mass of the polymerization solution, and the co-solvent lithium chloride accounts for 2% of the total mass of the polymerization solution. The dissolution temperature is 120°C, the stirring speed is 100 rpm, and the stirring time is 5 h. After dissolution, perform defoaming treatment to obtain a polymerization solution, with a vacuum degree of 600 Pa and a defoaming time of 6 h. The substrate coating temperature is 100°C, the moving speed of the doctor blade is 0.8 mm / min, the coating thickness is 800 μm, the drying temperature is 150°C, and the time is 8 h. Then perform peeling and trimming to finally obtain the polyoxadiazole film.

[0106] The obtained finished film has a thickness of 120 μm and is a flame-retardant film with an LOI value of 47%.

[0107] Example 7

[0108] The aromatic polyoxadiazole film was prepared by the same method as in Example 2, except that: the solvent DMSO was replaced with DMAc, and the others remained unchanged. The mixture could not be completely dissolved, and there were still a small amount of solid powders.

[0109] The obtained aromatic polyoxadiazole film has a thickness of 116 μm and an LOI value of 43%. The flame retardancy of the film is slightly reduced.

[0110] Example 8

[0111] An aromatic polyoxadiazole film was prepared by the same method as in Example 2, except that: the cosolvent lithium chloride was changed to calcium chloride, and the others remained unchanged. A small amount of undissolved solid powder appeared in the mixture.

[0112] The obtained aromatic polyoxadiazole film has a thickness of 113 μm and an LOI value of 45%. The flame retardancy of the film is slightly reduced.

[0113] Comparative Example 1

[0114] An aromatic polyoxadiazole film was prepared by the same method as in Example 1, except that: the addition amount of the end-capping agent 4-propylbenzoic acid in step S1 was changed to 2%, and the others remained unchanged. In S3, the polyoxadiazole powder accounted for 25% of the total mass, and the cosolvent lithium chloride accounted for 1% of the total mass. After mixing, it could not be completely dissolved, and there was still a small amount of solid powder.

[0115] The obtained aromatic polyoxadiazole film has a thickness of 75 μm and an LOI value of 37%. The flame retardancy of the film is reduced.

[0116] Comparative Example 2

[0117] An aromatic polyoxadiazole film was prepared by the same method as in Example 2, except that: the addition ratio of 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide in S1 was reduced, and the molar ratio of fuming sulfuric acid, diphthalic acid, diphenyletherdicarboxylic acid, 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, and hydrazine sulfate was 7:0.49:0.5:0.01:1.3; the remaining steps were exactly the same.

[0118] The obtained aromatic polyoxadiazole film has a thickness of 115 μm and an LOI value of 32%. The flame retardancy of the film is reduced.

[0119] Comparative Example 3

[0120] An aromatic polyoxadiazole film was prepared by the same method as in Example 1, except that: the dosage ratio of diphenyletherdicarboxylic acid was reduced. In step S1 of this Comparative Example 3, the molar ratio of fuming sulfuric acid, diphthalic acid, diphenyletherdicarboxylic acid, 2-(diphenylphosphoryl)terephthalic acid, and hydrazine sulfate was changed to 6:0.5:0.4:0.1:1.2; the others remained unchanged. In S3, the polyoxadiazole powder accounted for 25% of the total mass, and the cosolvent lithium chloride accounted for 1% of the total mass. After mixing, it could not be completely dissolved, and there was still some solid powder.

[0121] The obtained aromatic polyoxadiazole film has a thickness of 70 μm and an LOI value of 36%. The flame retardancy of the film is reduced.

[0122] Comparative Example 4

[0123] An aromatic polyoxadiazole film was prepared by the same method as in Example 1, except that: the dosage ratio of 2-(diphenylphosphoryl)terephthalic acid was reduced, and the molar ratio of fuming sulfuric acid, diphthalic acid, diphenylether dicarboxylic acid, 2-(diphenylphosphoryl)terephthalic acid, and hydrazine sulfate in step S1 of this Comparative Example 4 was changed to 6:0.4:0.6:0.01:1.2; other conditions remained unchanged.

[0124] The obtained aromatic polyoxadiazole film has a thickness of 78 μm and an LOI value of 35%. The flame retardancy of the film is reduced.

[0125] Comparative Example 5

[0126] An aromatic polyoxadiazole film was prepared by the same method as in Example 1, except that: the capping agent 4-propylbenzoic acid in step S1 was changed to benzoic acid; other conditions remained unchanged. The mixture could not be completely dissolved, and there were still a small number of solid powders.

[0127] The obtained aromatic polyoxadiazole film has a thickness of 80 μm and an LOI value of 36%. The flame retardancy of the film is reduced.

[0128] Comparative Example 6

[0129] An aromatic polyoxadiazole film was prepared by the same method as in Example 2, except that: 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide was replaced with terephthalic acid, and the molar ratio of fuming sulfuric acid, diphthalic acid, diphenylether dicarboxylic acid, terephthalic acid, and hydrazine sulfate was 7:0.3:0.5:0.2:1.3; the rest of the steps were exactly the same.

[0130] The obtained aromatic polyoxadiazole film has a thickness of 106 μm and an LOI value of 28%. The flame retardancy of the film is significantly reduced.

[0131] Comparative Example 7

[0132] An aromatic polyoxadiazole film was prepared by the same method as in Example 1, except that: the reaction temperature in the third stage of step S1 was changed from 150 °C to 130 °C, and the rest of the steps were exactly the same.

[0133] The obtained aromatic polyoxadiazole film has a thickness of 75 μm and an LOI value of 35%. The flame retardancy of the film is significantly reduced.

[0134] Comparative Example 8

[0135] The aromatic polyoxadiazole film was prepared by the same method as in Example 1, except that: 4-propylbenzoic acid was added after reacting at 120 °C for 1 h in the second stage in Step S1, and the reaction was continued at this temperature for 2 h, and the remaining steps were exactly the same.

[0136] The obtained aromatic polyoxadiazole film had a thickness of 50 μm and an LOI value of 34%, and the flame retardancy of the film was significantly reduced.

[0137] The aromatic polyoxadiazole films prepared in the above examples and comparative examples were subjected to performance tests, and the specific measurement results are shown in Table 1 below. The test methods involved were: the thermal conductivity test was carried out with reference to GB 2406; the breaking strength test was carried out with reference to GB / T 13022.

[0138] Table 1 Performance index data of aromatic polyoxadiazole films

[0139]

[0140] As can be seen from the above table, the novel aromatic polyoxadiazole films prepared in Examples 1 - 8 by the preparation method described in the present invention have good flame retardancy and strength properties when applied in the flame retardant field. From the data comparison between Example 7 and Example 2, it can be seen that large polar solvents may have better solubility for polyoxadiazole. Since the polarity of DMAc is lower than that of DMSO, the solubility of polyoxadiazole in DMAc is slightly reduced, slightly affecting the uniformity of the distribution of polyoxadiazole in the film, thereby affecting the flame retardant effect. From the data comparison between Example 8 and Example 2, it can be seen that the solubilizing effect of lithium chloride is higher than that of calcium chloride, mainly due to the relatively small lattice energy of lithium chloride ionic compounds. This characteristic enables the ions in lithium chloride to interact with the polar groups in DMSO, thereby promoting dissolution. Therefore, when changing to calcium chloride for solubilization, the solubility of polyoxadiazole will be slightly reduced, affecting the uniformity of the distribution of polyoxadiazole in the film, thereby affecting the flame retardant effect.

[0141] From the data comparison between Comparative Example 1 and Example 1, it can be seen that the reduction in the amount of the capping agent reduces the solubility of polyoxadiazole powder in organic solvents, affects the uniformity of the distribution of polyoxadiazole in the film, and thus affects the flame retardant effect.

[0142] From the data comparison between Comparative Example 2 and Example 2, it can be seen that reducing the addition amount of the phosphorus-based flame retardant monomer reduces the generation of phosphoric anhydride, metaphosphoric acid or phosphoric acid when heated, weakens the dehydration and carbonization of polyoxadiazole, and thus affects the flame retardant effect.

[0143] From the data comparison between Comparative Example 3 and Example 1, it can be seen that since the ether bond in diphenyl ether not only increases the solubility of polyoxadiazole, but also the sulfonation of the benzene rings at both ends of the ether bond can increase the solubility of polyoxadiazole. Reducing the content of diphenyl ether will reduce the solubility of polyoxadiazole, affecting the uniformity of the distribution of polyoxadiazole in the film, and thus affecting the flame retardant effect.

[0144] From the data comparison between Comparative Example 4 and Example 1, it can be seen that reducing the addition amount of 2-(diphenylphosphoryl) terephthalic acid monomer will reduce the generation of phosphoric anhydride, metaphosphoric acid or phosphoric acid when heated, weakening the dehydration carbonization of polyoxadiazole, and thus affecting the flame retardant effect.

[0145] From the data comparison between Comparative Example 5 and Example 1, it can be seen that the propyl group in 4-propylbenzoic acid in the end-capping agent can improve the solubility of polyoxadiazole. Replacing it with benzoic acid as the end-capping agent will reduce the solubility of polyoxadiazole, affecting the uniformity of the distribution of polyoxadiazole in the film, and thus affecting the flame retardant effect.

[0146] From the data comparison between Comparative Example 6 and Example 2, it can be seen that the non-addition of 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide will lead to a reduction in the flame retardant performance of the film, because the rich phosphorus element in 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide or 2-(diphenylphosphoryl) terephthalic acid monomer will decompose to produce substances such as phosphoric anhydride, metaphosphoric acid or phosphoric acid when heated. These substances have strong dehydrating properties and can dehydrate and carbonize the surface of polyoxadiazole to form an isolation layer. This isolation layer can prevent the further pyrolysis of the polymer and prevent the internal thermal decomposition products from entering the gas phase to participate in the combustion process, which is beneficial to the improvement of the flame retardant performance of the film.

[0147] From the data comparison between Comparative Example 7 and Example 1, it can be seen that the flame retardant effect is significantly reduced after the reaction temperature in the third polymerization stage is lowered, because the decrease in temperature leads to a decrease in the degree of sulfonation, and then to a decrease in the solubility of polyoxadiazole in the solvent, resulting in incomplete dissolution in the solvent and affecting the dispersion uniformity in the film, thus affecting the flame retardant effect.

[0148] From the data comparison between Comparative Example 8 and Example 1, it can be seen that adding the end-capping agent after advancing the reaction in the second polymerization stage will lead to a decrease in the degree of polymerization and a shortening of the polyoxadiazole molecular chain, thus affecting the flame retardant effect.

[0149] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, all possible combinations of the various technical features in the above embodiments are not exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0150] For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, and these all fall within the protection scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

Claims

1. A method for preparing an aromatic polyoxadiazole film with high solubility and high flame retardancy, characterized in that, The preparation method is as follows: S1. Add diphthalic acid, diphenyl ether dicarboxylic acid, flame retardant dicarboxylic acid monomer, and hydrazine salt into fuming sulfuric acid, stir, heat up for polycondensation reaction and sulfonation reaction, then add a capping agent to terminate chain growth, and finally obtain an aromatic polyoxadiazole solution; S2. Cast the aromatic polyoxadiazole solution into filaments, wash, crush, and dry to obtain polyoxadiazole powder; S3. Dissolve the polyoxadiazole powder in a solvent, coat, and dry to obtain the polyoxadiazole film; The reaction process of step S1 is: the pre-polymerization reaction temperature in the first stage of polycondensation reaction is 80 - 100 °C, and the reaction time is 2 - 4 h; in the second stage of chain growth reaction, the temperature is 115 - 130 °C, and the reaction time is 2 - 4 h; in the third stage of cyclization and sulfonation reaction, the temperature is 135 - 160 °C, and the reaction time is 1 - 5 h; The flame retardant dicarboxylic acid monomer is at least one of 2-(diphenylphosphoryl) terephthalic acid and 10-(2,5-dicarboxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide; The capping agent is at least one of 4-methylbenzoic acid, 4-ethylbenzoic acid, and 4-propylbenzoic acid; The molar ratio of the fuming sulfuric acid, diphthalic acid, diphenyl ether dicarboxylic acid, flame retardant dicarboxylic acid monomer, and hydrazine salt is (4 - 7):(0.20 - 0.50):(0.40 - 0.70):(0.02 - 0.20):(1.05 - 1.40), and the molar number of the fuming sulfuric acid is calculated based on the molar number of SO3 contained in the fuming sulfuric acid; The addition amount of the capping agent is 3% - 8% of the molar number of the hydrazine salt.

2. The preparation method of an aromatic polyoxadiazole film with high solubility and high flame retardancy according to claim 1, characterized in that, The hydrazine salt is at least one of hydrazine sulfate, hydrazine acetate, and hydrazine hydrochloride.

3. The preparation method of an aromatic polyoxadiazole film with high solubility and high flame retardancy according to claim 1, characterized in that, In step S2, the polyoxadiazole solution is passed through a spinneret hole and pressed into ice water to form filaments. After multiple water washes and alkali washes respectively, when the pH = 7 - 8, the acid-free wet polyoxadiazole filaments are crushed and then dried to obtain polyoxadiazole powder.

4. The preparation method of an aromatic polyoxadiazole film with high solubility and high flame retardancy according to claim 1, characterized in that, In step S3, the polyoxadiazole powder is added to a solvent and heated to dissolve, and a co-solvent is added. After the dissolved polymerization solution is degassed under vacuum, the coating operation is carried out; The solvent is at least one of DMSO, DMAc, DMF, and NMP; The mass content of polyoxadiazole in the polymerization solution is 10% - 40%.

5. The preparation method of an aromatic polyoxadiazole film with high solubility and high flame retardancy according to claim 1, characterized in that, In step S3, the coating operation is as follows: the uniform polymerization solution is transferred to a glass plate or stainless steel plate substrate at 50 - 120 °C, the moving speed of the scraper is 0.2 - 15 mm / min, the coating thickness is 50 - 1000 μm. The coated substrate is dried, the drying temperature is 80 - 200 °C, and the time is 5 - 10 h. After drying, peeling and trimming are carried out to finally obtain the polyoxadiazole film.

6. A highly soluble and highly flame-retardant aromatic polyoxadiazole film, characterized in that, The polyoxadiazole film is prepared by the preparation method described in any one of claims 1 - 5.

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