Synthesis method of flame-retardant hyperbranched polymer with side group grafted with P-N group

Abstract

The invention relates to the field of synthesis of hyperbranched polymers, and discloses a synthesis method of a flame-retardant hyperbranched polymer with a side group grafted with a P-N group, and the synthesis method comprises the following steps: dissolving phenyl dichlorophosphate and triethylamine in tetrahydrofuran, dropwise adding hydroxyethyl acrylate dissolved in tetrahydrofuran, carrying out a stirring reaction for 3 h, dropwise adding N, N-dimethylethanolamine dissolved in tetrahydrofuran, carrying out a stirring reaction for 2 h, and carrying out a reaction for 3 h; stirring and reacting for 3h; raising the temperature to 20 DEG C, continuously reacting for 10 hours, and ending the reaction; filtering the product in the previous step, extracting and separating liquid, and carrying out reduced pressure distillation to remove the solvent to obtain yellow viscous liquid DPHP; the preparation method comprises the following steps: dissolving DPHP and a catalyst Pd-diimine in dichloromethane, carrying out shading reaction for 24 hours under the ethylene pressure of 0.1 Mpa, and removing excessive solvent to obtain a product HBPE (at) PDPHP; then, the HBPE-coated PDPHP is added into a PI matrix, and through vertical combustion and limit oxygen index tests, it is found that the flame retardant effect of the PI composite material added with 10% of HBPE-coated PDPHP reaches the V-0 level. The preparation method is mild in preparation condition and environment-friendly, can be used as an additive to be added into engineering plastics for modification, and has the advantages of harmlessness, smoke suppression, environment friendliness and the like.

Description

Technical Field

[0001] The present invention relates to the field of synthesis of hyperbranched polymers, and particularly to a method for synthesizing a flame-retardant hyperbranched polymer grafted with P-N groups on the side chains. Background Art

[0002] With the wide application of polymer materials in daily life and industrial production, their flammability has become a major safety hazard. Especially in the fields of building materials, electronic devices, textiles, and transportation, the combustion of polymer materials not only leads to the rapid spread of fires but also generates a large amount of toxic smoke, endangering human health. Therefore, improving the flame retardancy of polymer materials has always been one of the research hotspots in the field of materials science.

[0003] Currently, common flame retardants are mainly divided into two categories: organic and inorganic. Organic flame retardants include halogen-containing flame retardants, phosphorus-based flame retardants, nitrogen-based flame retardants, etc., while inorganic flame retardants include aluminum hydroxide, magnesium hydroxide, expanded graphite, etc. Among them, halogen-containing flame retardants were widely used due to their excellent flame retardant effects, but they produce a large amount of toxic and corrosive gases and smoke during combustion, causing serious harm to the environment and human health. Therefore, the development of halogen-free flame retardants has become one of the main research directions in the current flame retardant technology field.

[0004] In recent years, phosphorus-nitrogen (P-N) based flame retardants have become an important halogen-free flame retardant material because they generate non-volatile polyphosphoric acid and nitrogen during the combustion process, which can effectively form a carbon layer to protect the matrix material and inhibit the release of heat and combustible gases. However, conventional P-N based flame retardants have poor compatibility with polymer matrices and are prone to migration and loss in the matrix material, thus greatly reducing their flame retardant efficiency.

[0005] To solve these problems, researchers have proposed a strategy of introducing P-N groups into the main chain or side chain of polymers, thereby firmly binding the flame retardant to the polymer matrix through chemical bonds and improving the durability of the flame retardant and the overall flame retardant performance of the material.

[0006] Hyperbranched polymers (HBPs) have received extensive attention in recent years due to their unique spherical structure, low melting point, high solubility, and abundant end-group functionalization sites. By grafting phosphorus-nitrogen groups on the side chains of hyperbranched polymers, the flame retardancy of the polymer and the thermal stability of the material can be effectively improved. In addition, the presence of the hyperbranched structure can also increase the free volume and intermolecular voids of the material, further improving the physical properties of the material.

[0007] In summary, this flame-retardant hyperbranched polymer with side-chain grafted P-N groups can not only effectively introduce flame-retardant groups into polymer materials, thereby enhancing the flame-retardant performance of the materials, but also improve the mechanical properties and thermal stability of the materials, and has important application prospects. Based on this, the present invention provides a method for synthesizing a flame-retardant hyperbranched polymer with side-chain grafted P-N groups. Summary of the Invention

[0008] The purpose of this application is to provide a method for synthesizing a flame-retardant hyperbranched polymer with side-chain grafted P-N groups. The advantages of this method are simple process, easy operation, low cost, mild preparation conditions, environmental friendliness, and the ability to apply to a variety of polymer materials. Its structural formula is:

[0009]

[0010] To achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions:

[0011] A method for synthesizing a flame-retardant hyperbranched polymer with side-chain grafted P-N groups, comprising the following steps:

[0012] (1) Dissolve phenyl dichlorophosphate and triethylamine (TEA) in tetrahydrofuran (THF) to form a blended solution, and control the temperature at about 0 °C.

[0013] (2) Dropwise add 2-hydroxyethyl acrylate dissolved in tetrahydrofuran, stir and react at 600 rpm for 3 h, and then dropwise add N,N-dimethylethanolamine dissolved in tetrahydrofuran, stir and react at 600 rpm for 3 h;

[0014] (3) Raise the temperature to 20 °C and continue to react for 10 h, and then end the reaction.

[0015] (4) Filter the product in step (3), extract and separate the liquid, and remove the solvent by vacuum distillation to obtain a yellow viscous liquid, which is the product DPHP.

[0016] (5) Dissolve the product in step (4) and the catalyst Pd-diimine in dichloromethane, react under an ethylene pressure of 0.1 Mpa for 24 h in the dark, and then remove the excess solvent to obtain the final product HBPE@PDPHP.

[0017] Among them, the molar ratio of added 2-hydroxyethyl acrylate to phenyl dichlorophosphate is 0.5:1, the molar ratio of N,N-dimethylethanolamine to phenyl dichlorophosphate is 0.5:1, and the molar ratio of added triethylamine to phenyl dichlorophosphate is 1:1.

[0018] The operations of filtration, extraction and liquid separation, and solvent removal by vacuum distillation in step (4) are to wash with saturated NaCl solution three times, then add anhydrous sodium sulfate to remove the moisture in the product, and finally rotary evaporate to dryness to obtain a yellow viscous liquid DPHP.

[0019] The removal of the excess solvent in step (5) means that after drying the product, add THF to just dissolve the product, add 6 drops of concentrated HCl and 6 drops of H2O2, stir until the solution turns orange-yellow (about 3 h), then transfer it to a centrifuge tube, add methanol to completely precipitate the product, remove the supernatant, and blow-dry the product with cold air (repeat the above operations three times). The product is vacuum dried at 60 °C to dryness (about 72 h) to obtain a yellow semi-fluid product HBPE@PDPHP.

[0020] Preferably, the solvent in step (1) can be anhydrous dichloromethane.

[0021] Preferably, the molar ratio of triethylamine to phenyl dichlorophosphate added in step (1) can be 1.2:1.

[0022] Preferably, in step (3), the final reaction temperature can be set at 25 °C to make the reaction more active.

[0023] In step (5) of the present invention, preferably, after the product is completely precipitated, it can be centrifuged (4000 rpm) for 5 min, and then the supernatant is removed, which can improve the yield.

[0024] Preferably, the optimal feeding ratio of DPHP in step (5) is 0.3 mol / L.

[0025] The basic reaction principle of the present invention is:

[0026]

[0027]

[0028]

[0029]

[0030] The purpose of the present invention is to graft P-N groups on the side chains of hyperbranched polyethylene to form a flame-retardant hyperbranched polymer. This synthesis method can not only effectively introduce flame-retardant groups into polymer materials, thereby enhancing the flame-retardant performance of the materials, but also improve the mechanical properties and thermal stability of the materials, and has very important application prospects.

[0031] In the above technical scheme, the main functions of HBPE@PDPHP are: hyperbranched polymer has a three-dimensional macromolecule with high branching, which is spherical and has low melt viscosity. Doping and blending with engineering plastics can significantly improve the melt fluidity of the material and make it easy to process and shape.

[0032] The HBPE@PDPHP in the present invention is a spherical polymer with a flame retardant group at the end, which has excellent flame retardant properties and thermal conductivity. Due to the PN structure, HBPE@PDPHP releases N gas when it is heated and decomposes. The N-containing compound reduces the volatilization of P and increases the oxidation of P, generating a carbon layer and flame-retardant and non-flammable gases such as NH3 and H2O in the condensed phase and gas phase respectively. It can effectively dilute the O2 content in the air and weaken the combustion-supporting effect of O2. P is converted into polyphosphoric acid, polymetaphosphoric acid, etc. when heated, which can effectively promote carbonization and generate a dense carbonized layer. It has a good barrier effect, can prevent heat exchange, the spread of O2, suppress smoke, etc., and can prevent molten droplets from dripping and stop the spread of flames. And the PN structure unique to the hyperbranched copolymer has a synergistic flame retardant effect.

[0033] In the present invention, due to the positive effect of HBPE@PDPHP, the addition amount will also affect the yield of the final product. Preferably, the optimal addition amount of DPHP is 0.3 mol / L, and the addition amount of anhydrous dichloromethane is 20 mL. At this time, the grafting rate and yield of the final product obtained are the best.

[0034] Compared with the prior art, the advantages and beneficial effects of the present invention are: the method is simple, easy to operate, the preparation conditions are mild, it is environmentally friendly, and a hyperbranched polyethylene copolymer with flame retardant function can be produced, so that it can be used as an auxiliary agent in the processing field and the field of improving flame retardancy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 This is the DPHP NMR 1H spectrum obtained in Example 1 of the present invention.

[0037] Figure 2 This is the infrared absorption spectrum of DPHP obtained in Example 1 of the present invention.

[0038] Figure 3 This is the 1H NMR spectrum of HBPE@PDPHP obtained in Example 1 of the present invention.

[0039] Figure 4 This is the infrared absorption spectrum of HBPE@PDPHP obtained in Example 1 of the present invention.

[0040] Figure 5 This is the nuclear magnetic phosphorus spectrum of HBPE@PDPHP obtained in Example 1 of the present invention.

[0041] Figure 6 This is the comparison chart of the vertical burning tests of Example 2 of the present invention and Comparative Example 3.

[0042] Figure 7 This is the limiting oxygen index test of Example 2 of the present invention and Comparative Example 3.

[0043] Figure 8 This is the comparison chart of the vertical burning tests of Example 2 of the present invention and Comparative Example 4.

[0044] Figure 9 This is the limiting oxygen index test of Example 2 of the present invention and Comparative Example 4. Detailed implementation manners

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. For those conditions not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0046] 1. Sample preparation

[0047] Example 1

[0048] a: Dissolve phenyl dichlorophosphate (0.1 mol) in 40 ml of anhydrous tetrahydrofuran, and then inject it into a three-necked flask equipped with a thermometer, a constant-pressure dropping funnel, and a magnetic stirrer using a syringe. After cooling the mixture to about 0 °C in an ice-methanol bath, add triethylamine (0.12 mol) to the reaction system, and stir for 30 min to mix evenly. Dissolve 2-hydroxyethyl acrylate (0.05 mol) in 10 ml of anhydrous tetrahydrofuran, then inject it into the constant-pressure dropping funnel, control the dropping rate, and finish dropping within 2 h, and then stir at a constant temperature for 3 h. Subsequently, dissolve N,N-dimethylethanolamine (0.05 mol) in 10 ml of anhydrous tetrahydrofuran, then inject it into the constant-pressure dropping funnel, and then react at a constant temperature for 3 h. Finally, heat the system to 20 °C and stir for another 10 h to ensure complete reaction. After suction filtration, extraction, and solvent removal under reduced pressure, wash with saturated sodium chloride solution to obtain a very viscous yellow liquid DPHP.

[0049] b: Add 250 mg of Pd - diimmine, 20 ml of anhydrous dichloromethane, and 0.006 mol of DPHP (concentration: 0.3 mol / L) prepared in the above step (a) into a Schlenk flask. The ethylene pressure is 0.1 Mpa, and the temperature of the water bath is 25 °C. React for 24 h. After the reaction is completed, expose the reaction solution to the air to terminate the polymerization, and blow it dry with cold air. Subsequently, add THF (about 10 mL) to just dissolve the product, add 6 drops of concentrated HCl and 6 drops of H2O2, stir until the solution turns orange - yellow (about 3 h), then transfer it to a centrifuge tube, add methanol (about 45 mL) to completely precipitate the product, remove the supernatant, and blow the product dry with cold air (repeat the above operation 3 times). Dry the product under vacuum at 60 °C until dry (about 72 h) to obtain a yellow semi - fluid product HBPE@PDPHP.

[0050] Comparative Example 1

[0051] Add 250 mg of Pd - diimmine, 20 ml of anhydrous dichloromethane, and 0.002 mol of DPHP (concentration: 0.1 mol / L) prepared in the above step (a) into a Schlenk flask. The ethylene pressure is 0.1 Mpa, and the temperature of the water bath is 25 °C. React for 24 h. After the reaction is completed, expose the reaction solution to the air to terminate the polymerization, and blow it dry with cold air. Subsequently, add THF (about 10 mL) to just dissolve the product, add 6 drops of concentrated HCl and 6 drops of H2O2, stir until the solution turns orange - yellow (about 3 h), then transfer it to a centrifuge tube, add methanol (about 45 mL) to completely precipitate the product, remove the supernatant, and blow the product dry with cold air (repeat the above operation 3 times). Dry the product under vacuum at 60 °C until dry (about 72 h) to obtain a yellow semi - fluid product HBPE@PDPHP.

[0052] Comparative Example 2

[0053] Add 250 mg of Pd - diimmine, 20 ml of anhydrous dichloromethane, and 0.004 mol of DPHP (concentration: 0.2 mol / L) prepared in the above step (a) into a Schlenk flask. The ethylene pressure is 0.1 Mpa, and the temperature of the water bath is 25 °C. React for 24 h. After the reaction is completed, expose the reaction solution to the air to terminate the polymerization, and blow it dry with cold air. Subsequently, add THF (about 10 mL) to just dissolve the product, add 6 drops of concentrated HCl and 6 drops of H2O2, stir until the solution turns orange - yellow (about 3 h), then transfer it to a centrifuge tube, add methanol (about 45 mL) to completely precipitate the product, remove the supernatant, and blow the product dry with cold air (repeat the above operation 3 times). Dry the product under vacuum at 60 °C until dry (about 72 h) to obtain a yellow semi - fluid product HBPE@PDPHP.

[0054] Example 2

[0055] Step 1: Measure 125 mg of HBPE@PDPHP (Example 1), 0.6 g of ODA (diaminodiphenyl ether), and 0.65 g of BPDA (the mass ratio of ODA to BPDA is 1:1.08), add them to a sample bottle, and finally add 20 mL of DMAc (dimethylacetamide). Stir at 0 - 5 °C for 4 h. After mixing evenly, put the mixture into a vacuum degassing machine and degas it under vacuum at a rotation speed of 1800 rpm for 5 min at room temperature to remove the bubbles and solvents in the mixture.

[0056] Step 2: Pour the mixture into the sample groove of a polytetrafluoroethylene mold (the sample groove is a cuboid with dimensions of 125 mm × 13 mm × 1.6 mm and 80 mm × 10 mm × 4 mm), place it in a muffle furnace, and keep it at 100, 150, 200, 250, and 300 °C for 2 h respectively. The heating time for each temperature stage is 30 min. After the thermal imidization is completed and cooled to room temperature, a vertical combustion composite spline and a limiting oxygen index composite spline are obtained respectively.

[0057] Comparative Example 3

[0058] Step 1: Measure 0.6 g of ODA and 0.65 g of BPDA (the mass ratio of ODA to BPDA is 1:1.08), add them to a sample bottle, and finally add 20 mL of DMAc. Stir at 0 - 5 °C for 4 h. After mixing evenly, put the mixture into a vacuum degassing machine and degas it under vacuum at a rotation speed of 1800 rpm for 5 min at room temperature to remove the bubbles and solvents in the mixture.

[0059] Step 2: Pour the mixture into the sample groove of a polytetrafluoroethylene mold (the sample groove is a cuboid with dimensions of 125 mm × 13 mm × 1.6 mm and 80 mm × 10 mm × 4 mm), place it in a muffle furnace, and keep it at 100, 150, 200, 250, and 300 °C for 2 h respectively. The heating time for each temperature stage is 30 min. After the thermal imidization is completed and cooled to room temperature, a vertical combustion composite spline and a limiting oxygen index composite spline are obtained respectively.

[0060] Comparative Example 4

[0061] Step 1: Measure 65 mg of HBPE@PDPHP (Example 1), 0.6 g of ODA, and 0.65 g of BPDA (the molar ratio of ODA to BPDA is 1:1.08), add them to a sample bottle, and finally add 20 mL of DMAc. Stir for 4 h at 0 - 5 °C. After mixing evenly, put the mixture into a vacuum degassing machine and vacuum degas at a speed of 1800 rpm at room temperature for 5 min to remove the bubbles and solvents in the mixture.

[0062] Step 2: Pour the mixture into the sample groove of a polytetrafluoroethylene mold (the sample groove is a cuboid with dimensions of 125 mm × 13 mm × 1.6 mm and 80 mm × 10 mm × 4 mm), place it in a muffle furnace, and keep it at 100, 150, 200, 250, and 300 °C for 2 h respectively. The heating time for each temperature stage is 30 min. After the thermal imidization is completed and cooled to room temperature, a vertical combustion composite spline and a limiting oxygen index composite spline are obtained respectively.

[0063] 2. Characterization and Testing

[0064] (1) Nuclear Magnetic Resonance Spectroscopy Analysis ( 1 HNMR)

[0065] The test was carried out using an AVANCEIII 500 MHz nuclear magnetic resonance spectrometer (Bruker, Switzerland). The test was carried out at room temperature, the solvent used was deuterated chloroform (CDCl3), the concentration of the substance to be tested was 20 mg / mL, and the number of scans was 16 times.

[0066] (2) Fourier Transform Infrared Spectroscopy Analysis (FTIR)

[0067] Infrared spectroscopy analysis was carried out using a Nicolet iS50 Fourier transform infrared spectrometer (ThermoFisher, USA). The attenuated total reflection infrared method (ATR) was used to analyze the substance to be tested, and the scanning wavelength range was 4000–400 cm -1 , with a resolution of 4 cm -1 , and the number of scans was 32 times.

[0068] (3) Vertical Combustion (UL-94) Test

[0069] The vertical combustion test was carried out using an HVUL2 type vertical combustion test system (ATLAS, USA). During the test, refer to GB / T 2408 "Determination of Combustion Performance of Plastics - Horizontal Method and Vertical Method", the sample specification was 125 mm × 13 mm × 1.6 mm, and each sample was tested 5 times.

[0070] (4) Limiting Oxygen Index Test

[0071] The limiting oxygen index of the samples was determined using a JB-3 oxygen index meter (Jiubin, China). During the test, referring to Part 2: Room Temperature Test of GB / T 2406.2 "Determination of Burning Behavior by Oxygen Index Method", the sample specifications were 80 mm×10 mm×4 mm, and each sample was tested 5 times.

[0072] 3. Comparison and Analysis of Test Results

[0073] Figure 1 1H NMR spectrum of DPHP obtained in step (a) of Example 1 1 From the chemical shifts in the figure, it can be seen that: δ7.20 - 6.85 (5H, Ar-H), 6.25 and 5.70 (2H, vinyl), 5.95 (1H, CH=CH), 4.20 (2H, -COO-CH2-), 4.03 (2H, P-O-CH2-), 3.83 (4H, -O-CH2CH2, -N), 3.26 (6H, N-CH3).

[0074] Figure 2 Infrared absorption spectrum of DPHP obtained in step (a) of Example 1 of the present invention. From the analysis of the characteristic peaks in the figure, it can be known that 1720 cm -1 is the stretching vibration peak of C=O, and 1637 cm -1 is the stretching vibration peak of C=C, 1593 cm -1 and 1495 cm -1 are the stretching vibration peaks of C=C on the benzene ring, and the absorption peaks appearing at 1257 cm -1 and 1096 cm -1 are the stretching vibration peaks of P=O and P-O respectively.

[0075] Figure 3 1H NMR spectrum of HBPE@PDPHP obtained in step (b) of Example 1 of the present invention 1 From the chemical shifts, it can be seen that δ1.20 - 0.8 are the peaks of methyl, methylene and methine on the hyperbranched backbone, δ7.2 is the peak on the benzene ring, and δ3.83 is the peak of methylene on the copolymer.

[0076] Figure 4 Infrared absorption spectrum of HBPE@PDPHP obtained in step (b) of Example 1 of the present invention. From the analysis of the characteristic peaks in the figure, it can be known that 1745 cm -1 is the stretching vibration peak of C=O, and the absorption peaks appearing at 1240 cm -1 and 1144 cm -1 are the stretching vibration peaks of P=O and P-O respectively.

[0077] Figure 5It is the phosphorus NMR spectrum of HBPE@PDPHP obtained in step (b) of Example 1 of the present invention. It can be seen from the figure that δ - 4.15 (singlet peak).

[0078] Figure 6 It is a comparison chart of the vertical burning tests of Example 2 of the present invention and Comparative Example 3. Among them, Figure 6 (a) is the vertical burning (UL-94) test result chart of Example 2, Figure 6 (b) is the vertical burning (UL-94) test result chart of Comparative Example 3. It can be seen from the figure that the prepared HBPE@PDPHP / PI composite material can self-extinguish within 1 s after ignition, and still maintains a high self-extinguishing speed during the second ignition, without the occurrence of dripping phenomenon. The flame retardant effect is excellent and belongs to V-0 grade flame retardant.

[0079] The PI prepared in Comparative Example 3 cannot self-extinguish after ignition, and its flame retardant performance is poor. This shows that the HBPE@PDPHP polymer can significantly improve the flame retardant performance of the PI material.

[0080] Figure 7 It is a comparison chart of the limiting oxygen index of Example 2 and Comparative Example 3. It can be intuitively seen that compared with Comparative Example 3, the limiting oxygen index of Example 2 is 38.6% higher, which can also reflect from the side that the HBPE@PDPHP polymer has excellent effects as a flame retardant.

[0081] Figure 8 It is a comparison chart of the vertical burning tests of Example 2 of the present invention and Comparative Example 4. Among them Figure 8 (a) is the vertical burning (UL-94) test result chart of Example 2, Figure 8 (b) is the vertical burning (UL-94) test result chart of Comparative Example 4. It can be seen from the figure that the prepared HBPE@PDPHP / PI composite material in Example 2 can self-extinguish within 1 s after ignition, and still maintains a high self-extinguishing speed during the second ignition, without the occurrence of dripping phenomenon. The flame retardant effect is excellent and belongs to V-0 grade flame retardant.

[0082] The HBPE@PDPHP / PI composite material prepared in Comparative Example 4 can self-extinguish within 13 s after the first ignition, and will self-extinguish within 11 s during the second ignition, still maintaining a high self-extinguishing speed, without the occurrence of dripping phenomenon. Its flame retardant performance is not as good as that of Example 2, but there is still a large improvement compared with Comparative Example 3, belonging to V-1 grade flame retardant.

[0083] Figure 9For the comparison chart of the limiting oxygen index of Example 2 and Comparative Example 4, it can be intuitively seen that compared with Comparative Example 4, the limiting oxygen index of Example 2 is 18.10% higher, which can also indirectly reflect that with the increase in the content of hyperbranched polymer, the improvement of the flame retardant performance of the PI composite material is more obvious.

[0084] The above are only the embodiments of the present application and are not used to limit the protection scope of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for synthesizing a flame retardant hyperbranched polymer with a side-grafted PN group, characterized in that: The steps include: (1) dissolving phenyl dichlorophosphate and triethylamine in tetrahydrofuran to form a mixed solution; (2) adding hydroxyethyl acrylate dissolved in tetrahydrofuran dropwise, stirring at 600 rpm for 3 h, then adding N,N-dimethylethanolamine dissolved in tetrahydrofuran dropwise, stirring at 600 rpm for 3 h; (3) The temperature was raised to 20°C and the reaction was continued for 10 h, after which the reaction was terminated; (4) filtering the product in step (3), extracting and separating the liquids, and removing the solvent by vacuum distillation to obtain a yellow viscous liquid, which is the product DPHP; (5) The product in step (4) and the catalyst Pd-diimine were dissolved in dichloromethane, and the reaction was carried out under shading for 24 hours at an ethylene pressure of 0.1 MPa, and then the excess solvent was removed to obtain the final product HBPE@PDPHP, whose structural formula is ； The molar ratio of the added hydroxyethyl acrylate to phenyl dichloride phosphate is 0.5:1, the molar ratio of the added N,N-dimethylethanolamine to phenyl dichloride phosphate is 0.5:1, and the molar ratio of the added triethylamine to phenyl dichloride phosphate is 1:

1.

2. The method for synthesizing a flame-retardant hyperbranched polymer with a side-grafted PN group as claimed in claim 1, characterized in that: The rate of adding hydroxyethyl acrylate in step (2) is 1 mL / min.

3. The method for synthesizing a flame-retardant hyperbranched polymer with a side-grafted PN group as claimed in claim 1, characterized in that: The rate of adding N,N-dimethylethanolamine in step (2) is 1 mL / min.

4. The method for synthesizing a flame-retardant hyperbranched polymer with a side-grafted PN group as claimed in claim 1, characterized in that: The filtering, extracting, separating and removing the solvent by distillation under reduced pressure in step (4) are performed by washing with a saturated NaCl solution for three times, then adding anhydrous sodium sulfate to remove the moisture in the product, and finally evaporating the solvent by rotary evaporation to obtain a yellow viscous liquid DPHP.

5. The method for synthesizing a flame-retardant hyperbranched polymer with a side-grafted PN group as claimed in claim 1, characterized in that: The removal of excess solvent in step (5) refers to blowing the product dry, adding tetrahydrofuran to dissolve the product, adding 6 drops of concentrated HCl and 6 drops of H2O2, stirring until the solution turns orange-yellow and then transferring it to a centrifuge tube, adding methanol to completely precipitate the product, removing the supernatant, and blowing the product to dryness with cold air. The product is vacuum dried at 60°C to dryness to obtain a yellow semi-fluid product HBPE@PDPHP.

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