Water-soluble dopamine resin flame retardant and preparation method thereof

Abstract

The invention provides a water-soluble dopamine resin flame retardant and a preparation method thereof. The water-soluble dopamine resin flame retardant is obtained by carrying out addition reaction on dopamine and formaldehyde. The water-soluble dopamine resin prepared in the invention has a phenol structure and a specific high-crosslinking-density network crosslinking network of phenolic resin, and can release more flame-retardant gases while forming a compact carbon layer at a high temperature, thereby diluting combustible gases and playing a role in physical heat insulation and oxygen isolation on a base material.

Description

Technical Field

[0001] The present invention belongs to the field of flame retardants, and particularly relates to a water-soluble dopamine resin flame retardant and a preparation method thereof. Background Art

[0002] Regarding the development and research of phenolic resins, the work mainly focuses on enhancement, flame retardancy, low smoke, and molding applicability, and develops towards functionalization and refinement. Researchers in various countries take phenolic resin materials with high added value as the research and development objects. However, phenolic resins are insoluble in water and soluble in organic solvents such as acetone and ethanol. This greatly increases the danger during the production process, poses a greater threat to life and property safety, and is not conducive to safe production. In addition, phenolic resins are extremely difficult to degrade under natural conditions, which pollutes the environment to a certain extent and affects the ecological environment. Currently, the field of flame retardants is undergoing a technological revolution from halogen-based to halogen-free transformation, and bio-based materials show unique advantages. As an important part of human neurotransmitters, dopamine contains both catechol and primary amine functional groups in its molecular structure, showing good flame retardant performance, environmental compatibility, and strong interfacial modification ability. Therefore, dopamine, as a multifunctional material, has been widely studied in the field of flame retardants. Summary of the Invention

[0003] Technical problems to be solved: The present invention provides a water-soluble dopamine resin flame retardant and a preparation method thereof. By using the addition and condensation reaction of dopamine and formaldehyde, a water-soluble dopamine resin is obtained, avoiding the use of organic solvents.

[0004] Technical solutions: A water-soluble dopamine resin flame retardant, characterized in that: the water-soluble dopamine resin is obtained by the addition and condensation reaction of dopamine and formaldehyde. Preferably, the preparation method comprises the following steps: S1. Add formaldehyde to an alkaline solution and stir to obtain a homogeneous solution, and then dropwise add dopamine hydrochloride to the homogeneous solution. After heating and reacting, a water-soluble dopamine resin mixture is obtained; S2. Rotate and evaporate the water-soluble dopamine resin mixture obtained in S1 to obtain a water-soluble dopamine resin. Preferably, the mass ratio of dopamine hydrochloride to formaldehyde in S1 is 3 - 8:5 - 20. Preferably, the alkaline solution in S1 is an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution. Preferably, the concentration of the alkaline solution in S1 is 0.001 - 0.005 mol / L. Preferably, the heating reaction temperature in S1 is 60 - 100 °C, and the heating reaction time is 2 - 8 h. Preferably, in S2, the temperature of rotary evaporation is 50 - 60 °C, the vacuum degree is 0.1 - 0.3 bar, and the temperature of the condensed water used for rotary evaporation is 2 - 6 °C. Preferably, the method for using the water-soluble dopamine resin comprises the following steps: S11. Add the water-soluble dopamine resin into water to prepare a flame retardant solution with a mass fraction of 15 - 30 wt%; S12. Immerse the substrate in the flame retardant solution for 2 - 5 min and then dry it at 90 - 110 °C for 4 - 8 min to obtain the flame retardant treated substrate. Beneficial effects: The present invention has the following advantages: 1. The flame retardant mechanism of the water-soluble dopamine resin prepared in the present invention is through the phenolic structure (-OH) and the unique high cross-linking density network cross-linking network of phenolic resin. The high cross-linking density network can form a dense carbon layer at high temperature, and its monomer contains an amino group and two phenolic hydroxyl groups, which can release more flame retardant gases (H 2 O, NH 3 and CO 2 ), thereby diluting the combustible gas and playing a physical heat insulation and oxygen isolation role for the matrix; 2. The dopamine resin prepared in the present invention has strong adhesion performance. Due to the presence of a catechol group composed of two ortho-hydroxy (-OH) groups, this functional group can form strong bonds with the surfaces of various materials (such as silicon, metal oxides, organic polymers, etc.) through hydrogen bonds, electrostatic interactions, π-π interactions, etc. It also contains a primary amine (-NH 2 ), and this group can undergo covalent bond reactions (such as Schiff base or Michael addition reactions) with other molecules or active groups on the surface of the substrate (such as carbonyl, carboxyl) under strong alkaline conditions, further enhancing its adhesion ability, especially showing good performance on multifunctional matrices (such as metals, glass fibers, carbon fibers), and can also maintain good adhesion strength at high temperature or in harsh environments, being suitable for structural applications; 3. The water-soluble dopamine resin prepared in the present invention can be directly dissolved in water, avoiding the use of organic solvents such as acetone and ethanol during the dissolution process of traditional resins. It has environmental protection characteristics and is easy to operate, and has good application prospects in the field of flame retardants. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is the reaction flow chart of the water-soluble dopamine resin flame retardant prepared in Example 1 of the present invention; Figure 2 It is the nuclear magnetic resonance H spectrum of the water-soluble dopamine resin flame retardant prepared in Example 1 of the present invention; Figure 3 It is the nuclear magnetic resonance C spectrum of the water-soluble dopamine resin flame retardant prepared in Example 1 of the present invention; Figure 4 Photographs of the products obtained under different pH reaction conditions; Figure 5 Comparison diagrams of air filter paper impregnated with water-soluble dopamine resin flame retardant, ordinary alcohol-soluble phenolic resin impregnated filter paper, and air filter paper before and after combustion; Figure 6 Comparison diagram of the viscous flow and adhesion of the water-soluble dopamine resin prepared in Example 1 of the present invention and ordinary phenolic resin on a plastic plate; Figure 7 Diagram of the marks after using tape to tear off the air filter paper impregnated with the water-soluble dopamine resin prepared in Example 1 of the present invention and ordinary phenolic resin; Figure 8 Products prepared with NaOH solution (concentration 3×10 -6 mol / L) at pH = 8.5, products prepared with Na 2 CO 3 (concentration 0.005 mol / L) at pH = 11, and products prepared by reacting with NaOH solution (concentration 0.001 mol / L) at pH = 11 with a reaction temperature of 50°C. Detailed implementation manners The present invention will be further described below in conjunction with embodiments. The following embodiments are explanations of the present invention and the present invention is not limited to the following embodiments: Example 1 S1. Add formaldehyde to a sodium hydroxide solution with a concentration of 0.001 mol / L (pH = 11). Subsequently, dissolve dopamine hydrochloride in 20 mL of deionized water, and gradually add the dopamine solution dropwise to the sodium hydroxide formaldehyde solution system. Stir and heat. The mass ratio of dopamine hydrochloride to formaldehyde is 5:20. The temperature for stirring and heating is 80°C and the time is 4 h to obtain a water-soluble dopamine resin mixture; S2. Perform rotary evaporation on the water-soluble dopamine resin mixture obtained in S1 to obtain a water-soluble dopamine resin. The temperature of the rotary evaporation is 55°C, the vacuum degree is 0.1 bar, and the temperature of the circulating cooling water used is 4°C. The usage method of the water-soluble dopamine resin obtained in this embodiment includes the following steps: S11. Add the water-soluble dopamine resin to water to prepare a flame retardant solution with a mass fraction of 20 wt%; S12. Place the original air filter paper in the flame retardant solution obtained in S11, impregnate it for 3 min, and then dry it at 105°C for 5 min to obtain a flame retardant treated air filter paper. Figure 1Reaction flow chart of the water-soluble dopamine resin flame retardant prepared in Example 1. Since the –OH groups on C1 and C2 in dopamine have a +M conjugation effect, C3, C5, and C6 are more likely to undergo an electrophilic addition reaction with formaldehyde (HCHO) because they are located at the ortho and para positions of the phenolic hydroxyl groups (C1 and C2). Formaldehyde (HCHO) is converted to methanol aldehyde (–CH 2 OH) under alkaline conditions, with enhanced electrophilicity, and can react with C3, C5, and C6 to form a hydroxymethylated (–CH 2 OH) intermediate, which then undergoes dehydration condensation to form a C–CH 2 –C cross-linked structure. Figure 2 1H NMR spectrum of the water-soluble dopamine resin flame retardant prepared in Example 1. The H at positions 4 - 6 in the dopamine spectrum is replaced by formaldehyde to form a new 1H spectrum. Due to the successful incorporation of formaldehyde, a new H peak appears at position 4 in the dopamine resin, thus proving that the water-soluble dopamine resin was successfully synthesized in this example; Figure 3 13C NMR spectrum of the water-soluble dopamine resin flame retardant in Example 1. The peak intensities at positions 3 and 4 in dopamine decrease from the original 115 ppm, and a new C peak appears at position 1 in the PDAF spectrum. This is due to the addition reaction of formaldehyde with the C atoms at the original positions 3, 4, and 5 of the benzene ring, proving the successful synthesis of the water-soluble dopamine resin. Example 2 S1. Add formaldehyde to a sodium hydroxide solution with a concentration of 0.001 mol / L. Subsequently, dissolve dopamine hydrochloride in 20 mL of deionized water, and gradually add the dopamine solution dropwise to the sodium hydroxide - formaldehyde solution system. Stir and heat. The mass ratio of dopamine hydrochloride to formaldehyde is 3:5. The temperature for stirring and heating is 70 °C, and the time is 3 h to obtain a water-soluble dopamine resin mixture; S2. Subject the water-soluble dopamine resin mixture obtained in S1 to rotary evaporation to obtain a water-soluble dopamine resin. The temperature for rotary evaporation is 60 °C, the vacuum degree is 0.3 bar, and the temperature of the circulating cooling water used is 4 °C. The usage method of the water-soluble dopamine resin obtained in this example includes the following steps: S11. Add the water-soluble dopamine resin to water to prepare a flame retardant solution with a mass fraction of 18 wt%; S12. Immerse the original air filter paper in the flame retardant solution obtained in S11 for 2 min and then dry it at 90 °C for 5 min to obtain the flame-retardant treated air filter paper. Example 3 S1. Add formaldehyde to a sodium hydroxide solution with a concentration of 0.001 mol / L. Subsequently, dissolve dopamine hydrochloride in 20 mL of deionized water, and gradually add the dopamine solution dropwise to the sodium hydroxide - formaldehyde solution system. Stir and heat. The mass ratio of dopamine hydrochloride to formaldehyde is 4:7. The temperature of stirring and heating is 90 °C, and the time is 5 h to obtain a water - soluble dopamine resin mixture; S2. Perform rotary evaporation on the water - soluble dopamine resin mixture obtained in S1 to obtain a water - soluble dopamine resin. The temperature of rotary evaporation is 55 °C, the vacuum degree is 0.2 bar, and the temperature of the circulating cooling water used is 4 °C. The usage method of the water - soluble dopamine resin obtained in this example includes the following steps: S11. Add the water - soluble dopamine resin to water to prepare a flame - retardant solution with a mass fraction of 20 wt%; S12. Immerse the original air filter paper in the flame - retardant solution obtained in S11 for 3 min and then dry it at 100 °C for 5 min to obtain a flame - retardant - finished air filter paper. Example 4 S1. Add formaldehyde to a sodium hydroxide solution with a concentration of 0.001 mol / L. Subsequently, dissolve dopamine hydrochloride in 20 mL of deionized water, and gradually add the dopamine solution dropwise to the sodium hydroxide - formaldehyde solution system. Stir and heat. React at 70 °C for 5 h. The mass ratio of dopamine hydrochloride to formaldehyde is 7:8 to obtain a water - soluble dopamine resin mixture; S2. Perform rotary evaporation on the water - soluble dopamine resin mixture obtained in S1 to obtain a water - soluble dopamine resin. The temperature of rotary evaporation is 55 °C, the vacuum degree is 0.1 bar, and the temperature of the circulating cooling water used is 4 °C. The usage method of the water - soluble dopamine resin obtained in this example includes the following steps: S11. Add the water - soluble dopamine resin to water to prepare a flame - retardant solution with a mass fraction of 20 wt%; S12. Immerse the original air filter paper in the flame - retardant solution obtained in S11 for 3 min and then dry it at 95 °C for 5 min to obtain a flame - retardant - finished air filter paper. Example 5 S1. Add formaldehyde to a sodium hydroxide solution with a concentration of 0.001 mol / L. Subsequently, dissolve dopamine hydrochloride in 20 mL of deionized water, and gradually add the dopamine solution dropwise to the sodium hydroxide - formaldehyde solution system. Stir and heat. The mass ratio of dopamine hydrochloride to formaldehyde is 6:7. The temperature of stirring and heating is 95 °C, and the time is 2 h to obtain a water - soluble dopamine resin mixture; S2. Rotate and evaporate the water-soluble dopamine resin mixture obtained in S1 to obtain water-soluble dopamine resin. The temperature of the rotary evaporation is 58°C, the vacuum degree is 0.1 bar, and the temperature of the circulating cooling water used is 4°C. The usage method of the water-soluble dopamine resin obtained in this example includes the following steps: S11. Add the water-soluble dopamine resin to water to prepare a flame retardant solution with a mass fraction of 15 wt%. S12. Immerse the original air filter paper in the flame retardant solution obtained in S11 for 3 minutes and then dry it at 105°C for 5 minutes to obtain the flame retardant treated air filter paper. Comparative Example 1 The difference between this comparative example and Example 1 is that an acidic solution is used instead of an alkaline solution. The specific steps are as follows: S1. Add formaldehyde to a sulfuric acid solution with a concentration of 0.01 mol / L and a pH of 2. Then dissolve dopamine hydrochloride in 20 mL of deionized water, and gradually add the dopamine solution dropwise to the sodium hydroxide formaldehyde solution system, stir and heat. The mass ratio of dopamine hydrochloride to formaldehyde is 5:20, the temperature of stirring and heating is 80°C, and the time is 4 h to obtain a mixture. S2. Rotate and evaporate the mixture obtained in S1 to obtain a product. The temperature of the rotary evaporation is 55°C, the vacuum degree is 0.1 bar, and the temperature of the circulating cooling water used is 4°C. Comparative Example 2 The difference between this comparative example and Example 1 is that a neutral solution is used instead of an alkaline solution. The specific steps are as follows: S1. Add formaldehyde to deionized water with a pH of 7. Then dissolve dopamine hydrochloride in 20 mL of deionized water, and gradually add the dopamine solution dropwise to the sodium hydroxide formaldehyde solution system, stir and heat. The mass ratio of dopamine hydrochloride to formaldehyde is 5:20, the temperature of stirring and heating is 80°C, and the reaction time is 4 h to obtain a mixture. S2. Rotate and evaporate the water-soluble mixture obtained in S1 to obtain a product. The temperature of the rotary evaporation is 55°C, the vacuum degree is 0.1 bar, and the temperature of the circulating cooling water used is 4°C. From Figure 4 it can be seen that when the pH is 2, 7, and 11 respectively, the obtained products are different. When pH = 7, the reaction is unsuccessful, and the mixed system is in a dilute fluid state. When adding a sulfuric acid solution with pH = 2, the reactant is a paste, without viscosity and fluidity. Only when pH = 11, the obtained product meets the expectation, and the resin presents a black viscous liquid. Comparative Example 3 The difference between this comparative example and Example 1 is further that a common alcohol-soluble phenolic resin is used. The specific steps are as follows: S1. Take 20 ml of formaldehyde and place it in a beaker. Under stirring conditions, take 30 ml of sodium hydroxide solution by volume fraction and add it to the beaker. Then stir at 400 r / min to mix evenly. S2. Take 20 mL of phenol solution (99%) and add it to the system, stir and mix evenly. While dropping, heat and stir. After all are dropped, stir at 120 °C and 400 r / min for 4 h. S3. In a room temperature environment, take the mixed solution after the reaction in S2 and perform vacuum rotary evaporation into a collection bottle until no more water drips in. The temperature of the rotary evaporation is 55 °C and the vacuum degree is 0.1 bar. The usage method of the ordinary alcohol-soluble phenolic resin obtained in this comparative example includes the following steps: S11. Add the ordinary alcohol-soluble phenolic resin into ethanol to prepare a flame retardant solution with a mass fraction of 20 wt%. S12. Immerse the original air filter paper in the flame retardant solution obtained in S11 for 3 min and then dry it at 105 °C for 5 min to obtain the flame retardant treated air filter paper. Comparative Example 4 The difference between this comparative example and Example 1 is that the original air filter paper is not impregnated with any resin and is directly burned. Figure 5 It is a comparison chart before and after burning of the air filter paper impregnated with the water-soluble dopamine resin flame retardant prepared in Example 1 of the present invention, the filter paper impregnated with the ordinary alcohol-soluble phenolic resin prepared in Comparative Example 3, and the air filter paper in Comparative Example 4. As can be seen from the figure, the ordinary air filter paper burns rapidly and completely after being ignited; the flame does not go out after the filter paper impregnated with the ordinary resin forms a carbon layer, and there are sparks; the air filter paper impregnated with the dopamine resin has stable char formation, self-extinguishes quickly, does not have flame spread, and the carbon layer is complete, which can achieve the effect of isolating air. This shows that the water-soluble dopamine resin obtained in Example 1 of the present invention has good flame retardant performance. Comparative Example 5 The difference between this comparative example and Example 1 is that the alkaline solution used is sodium hydroxide solution with a pH of 8.5. S1. Add formaldehyde to sodium hydroxide solution with a concentration of 3×10 -6 mol / L (pH = 8.5). Then dissolve hydrochloric acid dopamine in 20 mL of deionized water, and drop the dopamine solution into the sodium hydroxide formaldehyde solution system drop by drop, stir and heat. The mass ratio of hydrochloric acid dopamine to formaldehyde is 5:20, the temperature of stirring and heating is 80 °C, and the time is 4 h to obtain a mixture. S2. Rotate and evaporate the water-soluble dopamine resin mixture obtained in S1 to obtain a product. The temperature of the rotary evaporation is 55°C, the vacuum degree is 0.1 bar, and the temperature of the circulating cooling water used is 4°C. Comparative Example 6 The difference between this comparative example and Example 1 is that the alkaline solution used is sodium carbonate solution instead of sodium hydroxide solution. S1. Add formaldehyde to a sodium carbonate solution with a concentration of 0.005 mol / L (pH = 11). Subsequently, dissolve dopamine hydrochloride in 20 mL of deionized water, and gradually add the dopamine solution dropwise to the sodium hydroxide-formaldehyde solution system, stir and heat. The mass ratio of dopamine hydrochloride to formaldehyde is 5:20, the temperature of stirring and heating is 80°C, and the time is 4 h to obtain a mixture. S2. Rotate and evaporate the water-soluble dopamine resin mixture obtained in S1 to obtain a product. The temperature of the rotary evaporation is 55°C, the vacuum degree is 0.1 bar, and the temperature of the circulating cooling water used is 4°C. Comparative Example 7 The difference between this comparative example and Example 1 is that the temperature of the heating reaction in S1 is 50°C, and the product becomes a black solution. After rotary evaporation, it is still in the form of a black solution and does not become a viscous resin. This is because at 50°C, addition and polycondensation reactions do not occur, but self-polymerization of dopamine occurs. Comparative Example 8 The difference between this comparative example and Example 1 is that the mass ratio of dopamine hydrochloride to formaldehyde added in S1 is 5:2 S1. Add formaldehyde to a sodium hydroxide solution with a concentration of 0.001 mol / L. Subsequently, dissolve dopamine hydrochloride in 20 mL of deionized water, and gradually add the dopamine solution dropwise to the sodium hydroxide-formaldehyde solution system, stir and heat. The mass ratio of dopamine hydrochloride to formaldehyde is 5:2, the temperature of stirring and heating is 80°C, and the reaction time is 4 h to obtain a mixture. S2. Rotate and evaporate the water-soluble dopamine resin mixture obtained in S1 to obtain water-soluble dopamine resin. The temperature of the rotary evaporation is 55°C, the vacuum degree is 0.1 bar, and the temperature of the circulating cooling water used is 4°C. Figure 8For the substances obtained in Comparative Examples 5, 6, and 7, as can be seen from the figure, in a sodium hydroxide solution with a pH of 8.5, due to the extremely low concentration of sodium hydroxide, dopamine is only dissolved in it (dopamine dissolved in water is light brown) and does not react with formaldehyde. In a sodium carbonate solution with a pH of 11, a yellow liquid is formed with a pungent odor, and no resin is formed. In a sodium hydroxide solution at a temperature of 50 °C, due to temperature factors, dopamine does not react with formaldehyde and only undergoes self-polymerization. This experimental phenomenon occurs because under alkaline conditions, dopamine and formaldehyde mainly undergo an addition reaction to form hydroxymethylphenol, and then form a network-structured phenolic resin through a condensation reaction. By controlling the temperature and pH, problems such as over-crosslinking can be reduced, and the controllability of the product can be improved. This proves that NaOH helps to deprotonate phenol to activate it, improve its reactivity with formaldehyde, and accelerate the formation of the resin. Performance Test The flame retardancy of the samples prepared in Examples 1-6 and Comparative Examples 1-5 of the present invention was tested, and the results are shown in Table 1. Table 1 Flame Retardancy of Samples LOI(%) UL-94 <![CDATA[T 1 (s)]]> <![CDATA[T 2 (s)]]> Example 1 36 V-0 6 2 Example 2 32.2 V-0 9 3 Example 3 33 V-0 8.5 3 Example 4 29.6 V-1 12 5 Example 5 30 V-1 11 6 Comparative Example 1 / / / / Comparative Example 2 / / / / Comparative Example 3 26 HB 15 5 Comparative Example 4 16.8 / / / Comparative Example 5 / / / / Comparative Example 6 / / / / Comparative Example 7 / / / / Comparative Example 8 28 V-1 14 6 Note: 1. LOI test: Tested on a COI type index instrument according to ASTM D2863 standard. LOI < 22% belongs to flammable, LOI between 22 - 27% belongs to combustible, LOI between 27 - 34% belongs to difficult to burn, and LOI > 34% belongs to non-combustible; 2. Vertical combustion analysis: Tested according to ASTM D3801 standard. The UL-94 results are classified according to the combustion grades V-0, V-1, or V-2. The V-0 grade represents the material with the best flame retardancy; 3. T 1 refers to the flaming combustion time after the first application of the flame, and T 2 refers to the flaming combustion time after the second application of the flame. The adhesion of the dopamine resin obtained in Example 1 of the present invention and ordinary phenolic resin was tested, and the results are as Figure 6-7 shown: Figure 6-7 It is the attachment diagram of the same volume of dopamine resin and ordinary phenolic resin on a plastic plate and an air filter paper. The viscosity of the dopamine resin is better than that of the ordinary phenolic resin, and the adhesion is stronger. Under the same volume, the adhesion of the ordinary phenolic resin is weak. When the same volume of resin is dropped on a plastic plate with a certain slope, the dopamine resin has good adhesion, slow flow, and good attachment. Figure 7This is a trace diagram after using tape to tear off the air filter paper impregnated with the water-soluble dopamine resin prepared in Example 1 of the present invention and the ordinary alcohol-soluble phenolic resin. The air filter paper impregnated with the dopamine resin remains relatively intact after being torn by 3M tape, while the ordinary phenolic resin shows broken fibers and fluffs, proving that the dopamine resin has good adhesion. Obviously, the above examples are only illustrations for clear explanation and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A water-soluble dopamine resin flame retardant, characterized in that: The water-soluble dopamine resin is obtained by the addition and polycondensation reaction of dopamine and formaldehyde.

2. The method for preparing the water-soluble dopamine resin flame retardant according to claim 1, characterized in that: The preparation method comprises the following steps: S1. adding formaldehyde to an alkaline solution and stirring to obtain a uniform solution, then adding dopamine hydrochloride dropwise to the homogeneous solution, and heating the reaction to obtain a water-soluble dopamine resin mixture; S2. Rotary evaporate the water-soluble dopamine resin mixture obtained in S1 to obtain a water-soluble dopamine resin.

3. The method for preparing the water-soluble dopamine resin flame retardant according to claim 2, characterized in that: The mass ratio of dopamine hydrochloride to formaldehyde in S1 is 3-8:5-20.

4. The method for preparing the water-soluble dopamine resin flame retardant according to claim 2, characterized in that: The alkaline solution in S1 is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution.

5. The method for preparing the water-soluble dopamine resin flame retardant according to claim 2, characterized in that: The concentration of the alkaline solution in S1 is 0.001-0.005 mol / L.

6. The method for preparing the water-soluble dopamine resin flame retardant according to claim 2, characterized in that: The heating reaction temperature in S1 is 60-100° C., and the heating reaction time is 2-8 hours.

7. The method for preparing the water-soluble dopamine resin flame retardant according to claim 2, characterized in that: The temperature of the rotary evaporation in S2 is 50-60°C, the vacuum degree is 0.1-0.3 bar, and the temperature of the condensed water used for the rotary evaporation is 2-6°C.

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