A phosphorus-containing dopamine flame retardant and its preparation method and application

Abstract

A phosphorus-containing dopamine flame retardant and its preparation method and application of the present invention belong to the technical field of flame retardants. The technical scheme is: a protective group is connected to a dopamine catechol group through a nucleophilic reaction; a phosphorus-containing compound is connected to the amino group of protected DA-R through a grafting reaction; finally, the protective group is removed to obtain a new type of phosphorus-containing dopamine flame retardant. The reaction process uses an organic solvent as a reaction solvent, and the reaction is carried out in a reactor through a solution reaction, and the reaction temperature is room temperature. The beneficial effects of the present invention are: this type of flame retardant retains the catechol group of DA itself, and can be self-oxidatively polymerized on a variety of substrates to produce a flame-retardant nano-coating, which is particularly suitable for open-porous materials with a large specific surface area such as flexible polyurethane, and has a significant flame retardant effect.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardants, and in particular relates to the synthesis and flame retardant application of a phosphorus-containing dopamine flame retardant. Background Art

[0002] Traditional flame retardants, halogen flame retardants, have a fairly high flame retardant efficiency, but they generate toxic substances when burned, which affect human health and cause environmental pollution and are therefore restricted in use. In recent years, the exploration and preparation of new flame retardants have received increasing attention. Biomass materials such as dopamine (DA) are environmentally friendly and degradable, and the flame retardants prepared from them meet the requirements of the green strategy, so related research has become a hot topic. However, biomass materials are often difficult to meet flame retardant requirements when used alone as flame retardants.

[0003] As an alternative to halogenated flame retardants, organic phosphorus compounds can play a flame retardant role in both the condensed phase and the gas phase. The combination of phosphorus-nitrogen (PN) compounds can be regarded as one of the most promising synergists for halogen-free flame retardants. Therefore, it is necessary to introduce the flame retardant element phosphorus into the molecular structure of dopamine.

[0004] Compared with the method of physically adding flame retardants, weak interfacial interaction is one of the main challenges. In recent years, the surface coating strategy has attracted widespread attention because it can improve the flame retardancy of the substrate without basically affecting the mechanical properties of the substrate, and has better application conditions on substrates with large specific surface areas. Studies have shown that dopamine has a catechol structure and can self-oxidize and polymerize on a variety of substrates to form nanocoatings. The process of preparing the coating by this deposition method is relatively simple and the conditions are mild.

[0005] Therefore, in order to form a highly efficient flame-retardant coating on the surface of the substrate, it has become a difficult problem that needs to be solved urgently while introducing the flame-retardant element phosphorus to form a phosphorus-nitrogen (PN) flame-retardant system while retaining the catechol structure. Summary of the invention

[0006] In order to solve the above problems, the present invention synthesizes a phosphorus-containing dopamine flame retardant, which has mild reaction conditions and simple operation during preparation, and the product can achieve a high flame retardant effect at a very low loading amount. At the same time, the flame retardant retains the catechol group and has the ability of self-oxidative polymerization on the substrate, and can form a coating containing a phosphorus-nitrogen (PN) flame retardant system on the surface of different substrates.

[0007] The specific technical scheme of the phosphorus-containing dopamine flame retardant of the present invention is as follows.

[0008] A phosphorus-containing dopamine flame retardant, characterized in that the phosphorus-containing dopamine flame retardant has a structural formula of

[0009]

[0010] Wherein: R1 is an organic functional group, which is hydrogen, C1-C20 alkyl, C1-C20 phenyl, C1-C20 substituted phenyl or C1-C20 aralkyl; R2 is an organic functional group, which is C1-C20 alkyl, C1-C20 phenyl, oxyphenyl, C1-C20 aralkyl or a halogen element.

[0011] Preferred organic functional groups R1 are hydrogen, methyl, ethyl, propyl, isopropyl, sec-butyl, tert-butyl, and phenyl; preferred organic functional groups R2 are methyl, ethyl, propyl, isopropyl, sec-butyl, tert-butyl, phenyl, and oxyphenyl.

[0012] The specific technical scheme of the preparation method of the phosphorus-containing dopamine flame retardant of the present invention is as follows.

[0013] A method for preparing a phosphorus-containing dopamine flame retardant comprises a process for preparing a protected product, a process for preparing a phosphorus-containing intermediate product and a deprotection process;

[0014] The process of preparing the protection product is to dissolve the functionalized dopamine and chlorosilane in an organic solvent, use imidazole (IM) as a salt-forming agent, and react at room temperature for 12 to 30 hours; the reaction causes the catechol position of the functionalized dopamine to be substituted, and a silyl ether protection group is introduced, and the silyl ether protection group is used to protect the catechol group of DA; after extraction, the excess solvent is removed by rotary evaporation, and the protection product DA-R is obtained by drying; wherein the molar ratio of the functionalized dopamine to the chlorosilane in the chlorosilane is 1:2-3, and the molar ratio of the functionalized dopamine to the imidazole (IM) is 1:3-5; the organic functional group R1 of the functionalized dopamine is hydrogen, C The alkyl group is C1-C20, the phenyl group is C1-C20, the substituted phenyl group is C1-C20 or the aralkyl group is C1-C20; the chlorosilane is trimethylchlorosilane (TMS-Cl), triethylchlorosilane (TES-Cl), tert-butyldimethylchlorosilane (TBDMS-Cl), tert-butyldiphenylchlorosilane (TBDPS-Cl) or triisopropylchlorosilane (TIPS-Cl); the silyl ether protecting group is trimethylsilyl group (TMS), triethylsilyl group (TES), tert-butyldimethylsilyl group (TBDMS), tert-butyldiphenylsilyl group (TBDPS) or triisopropylsilyl group (TIPS);

[0015] The structural formula (II) of the obtained protected product DA-R is as follows

[0016]

[0017] R3 is a silyl ether protecting group.

[0018] The process of preparing the phosphorus-containing intermediate product is to react the secondary amine group of the protected product DA-R (II) with the chlorinated phosphorus-containing compound to connect the phosphorus-containing compound to the amino position of the protected product DA-R; specifically, the protected product DA-R and the chlorinated phosphorus-containing compound are used as raw materials, and an organic base is used as an acid-binding agent, dissolved in an organic solvent, reacted at room temperature for 12 to 30 hours, and then the excess solvent is removed by rotary evaporation after extraction, and dried to obtain the phosphorus-containing intermediate product; wherein the molar ratio of the protected product DA-R to the chlorinated group in the chlorinated phosphorus-containing compound is 1:1, and the molar ratio of the protected product DA-R to the acid-binding agent is 1:1 to 2; the chlorinated phosphorus-containing compound is diphenylphosphine chloride (DPC), diphenyl chlorophosphate (DPPC), diisopropyl chlorophosphate, phenyl dichlorophosphate or methyl dichlorophosphate; the organic base is pyridine (PY), triethylamine (TEA), N,N-diisopropylethylamine (DIPEA) or potassium carbonate (K2CO3);

[0019] The structural formula (III) of the obtained phosphorus-containing intermediate product is as follows:

[0020]

[0021] The deprotection process comprises dissolving the phosphorus-containing intermediate product in an organic solvent, adding a deprotecting agent, reacting for 12 to 24 hours, extracting or centrifuging to remove impurities and the organic solvent, and drying to obtain a phosphorus-containing dopamine flame retardant; wherein the molar ratio of the phosphorus-containing intermediate product to the deprotecting agent is 1:2 to 4; and the deprotecting agent is 1M tetrabutylammonium fluoride (TBAF), hydrochloric acid (HCl), trimethylsilyl iodide (TMS-I) or concentrated potassium hydroxide (KOH) solution.

[0022] The structural formula (I) of the obtained phosphorus-containing dopamine flame retardant is as follows

[0023]

[0024] The organic solvent in the preparation process can be anhydrous ethanol, dichloromethane, tetrahydrofuran, petroleum ether, ethyl acetate, acetone, dimethylformamide (DMF), and the amount of organic solvent accounts for 30-90wt% of the total system. When selecting, pay attention to the solubility of the reactants in different solvents. In order to improve the reaction efficiency and enhance the reaction stability, in the process of preparing the phosphorus-containing intermediate product, the protected product DA-R having the structure of general formula (II) is preferably dissolved in the organic solvent tetrahydrofuran.

[0025] In the process of preparing the protected product, the molar ratio of functionalized dopamine to imidazole (IM) is preferably 1:4.

[0026] In the process of preparing the phosphorus-containing intermediate product, the chlorinated phosphorus-containing compound is preferably diphenylphosphine chloride (DPC) or diphenyl chlorophosphate (DPPC).

[0027] In the process of preparing structures (II) and (III), the solid salt produced in the solution can be filtered after reacting for 12 to 30 hours to further purify the product.

[0028] To further improve the yield and purity, preferably after the compounds having structures (II) and (III) are reacted for 12 to 30 hours, an extractant can be added and then extracted and washed using a separatory funnel; the present invention has no particular restrictions on the selection of the extractant, preferably dichloromethane, ethyl acetate, toluene, hexane or cyclohexane; the washing liquid includes an aqueous solution of NaHCO3, NH4Cl, and NaCl, and its concentration is above 1M. The present invention has no particular restrictions on other requirements for extraction and concentration, and the extraction and concentration methods well known to those skilled in the art can be used.

[0029] The present invention also claims to protect the use of phosphorus-containing dopamine flame retardants, which is characterized in that the phosphorus-containing dopamine flame retardants are self-oxidatively polymerized on the surface of the substrate in an alkaline solution to form a coating, thereby improving the thermal stability and flame retardant properties of the substrate.

[0030] In the use of phosphorus-containing dopamine flame retardants, the substrate is polyurethane foam (FPUF), polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE) materials.

[0031] The beneficial effects of the present invention are as follows: the prepared phosphorus-containing dopamine flame retardant structure (I) retains the catechol group in the DA structure, can be completely dissolved in an alkaline solution, and self-oxidatively polymerizes to form a polymer similar to polydopamine (PDA). The flame retardant belongs to a PN synergistic flame retardant system and can be used as a flame retardant coating after self-oxidative polymerization. The preparation conditions are mild, and a high flame retardant effect can still be achieved when the flame retardant loading rate is low. At the same time, in addition to being used alone, the phosphorus-containing flame retardant can also be used in combination with other organic or inorganic flame retardants. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The NMR spectrum of the phosphorus-containing dopamine flame retardant DPP-DA prepared in Example 9 includes 1 H and 31 P NMR images.

[0033] Figure 2 TGA (left) and DTG (right) analysis results of original flexible polyurethane foam (FPUF) and coated FPUF in N2 atmosphere.

[0034] Figure 3 Heat release rate (HRR) analysis results of original flexible polyurethane foam (FPUF) and coated FPUF in N2 atmosphere. DETAILED DESCRIPTION

[0035] In order to clearly illustrate the technical features of this solution, the preferred implementation scheme of the present invention is described below in conjunction with examples. These descriptions are only to further illustrate the technical features and practical application characteristics of the present invention.

[0036] Example 1 Process for obtaining protected product (1)

[0037] The present invention provides a method for preparing a catechol structure compound in dopamine with protected functionalization in structure (II). Under anhydrous conditions, different types of chlorosilanes and DA with different substituents are mixed and reacted in an organic solvent to obtain a protected product with structure (II), namely DA-R.

[0038] Specific implementation process: add 200 mL of dichloromethane, an organic solvent from which water has been removed, to a 500 mL single-necked flask, add dopamine hydrochloride (4.00 g, 0.021 mol) and imidazole (5.74 g, 0.084 mol), and stir evenly with a magnetic stirrer at room temperature. Then add TMS-Cl (5.76 g, 0.053 mol) to the flask and react for 12 h at room temperature; sequentially use aqueous solutions of NaHCO3, NH4Cl, and NaCl with concentrations exceeding 1 M to extract and wash, remove excess solvent by rotary evaporation, and obtain the protected product DA-R after drying, as shown in reaction formula (IV)

[0039]

[0040] In this example, only the amount of TMS-Cl was changed, and the experiment was repeated without changing the process. The inventors used TMS-Cl (4.56 g, 0.042 mol) and TMS-Cl (6.84 g, 0.063 mol) to replace TMS-Cl (5.76 g, 0.053 mol), respectively, which had little effect on the obtained protected product DA-R.

[0041] Example 2 Process for obtaining protected product (2)

[0042] The protected product DA-R was obtained by the same process as in Example 1 except that TES-Cl (7.98 g, 0.053 mol) was used instead of TMS-Cl (5.76 g, 0.053 mol) and the organic solvent chloroform was used instead of dichloromethane.

[0043] Example 3 Process for obtaining protected product (3)

[0044] Except that TBDMS-Cl (7.95 g, 0.053 mol) was used instead of TMS-Cl (5.76 g, 0.053 mol) and the reaction time was 24 h, the implementation process was the same as that of Example 1, and the protected product DA-R was also obtained.

[0045] Example 4 Process for obtaining protected product (4)

[0046] Except that TBDPS-Cl (14.56 g, 0.053 mol) was used instead of TMS-Cl (5.76 g, 0.053 mol), the implementation process was the same as that of Example 1, and the protected product DA-R was also obtained.

[0047] Example 5 Process for preparing phosphorus-containing intermediates (1)

[0048] The present invention provides a method for preparing a phosphorus-containing intermediate product of structure (III). Under anhydrous conditions, a protected product DA-R having structure (II) and a chlorinated phosphorus-containing compound containing different substituents R3 are subjected to a substitution reaction in an organic solvent to obtain a phosphorus-containing intermediate product of structure (III). The substituents R3 may be the same or different.

[0049] Specific implementation process: add 100 mL of tetrahydrofuran, an organic solvent from which water has been removed, into a 500 mL single-necked flask, add 0.020 mol of DA-R prepared in Example 1, 2, 3 or 4 and DPPC (5.37 g, 0.020 mol), and add triethylamine (TEA) as an acid-binding agent. The preferred molar ratio of DA-R to triethylamine is 1:1.5. Stir magnetically at room temperature for uniformity. After reacting for 12 hours, extract and wash with aqueous solutions of NaHCO3, NH4Cl, and NaCl with a concentration of more than 1 M in sequence, remove excess solvent by rotary evaporation, and obtain the phosphorus-containing intermediate product after drying, as shown in reaction formula (V).

[0050]

[0051] In this example, only the amount of DPPC was changed, and the experiment was repeated without changing the implementation process. The inventors used DPPC (6.45 g, 0.024 mol) and DPPC (8.06 g, 0.030 mol) to replace DPPC (5.37 g, 0.020 mol), respectively, which had no effect on the preparation of the phosphorus-containing intermediate.

[0052] Example 6 Process for preparing phosphorus-containing intermediates (2)

[0053] Except that DPC (4.73 g, 0.020 mol) and DPC (5.68 g, 0.024 mol) were used to replace DPPC (5.37 g, 0.020 mol), the implementation process was the same as that of Example 5, and the preparation of the phosphorus-containing intermediate was completed.

[0054] Example 7 Process for preparing phosphorus-containing intermediates (3)

[0055] Except that pyridine (PY) and potassium carbonate (K2CO3) were used to replace triethylamine (TEA) as the acid-binding agent, the implementation process was consistent with that of Example 5, and the result of obtaining the phosphorus-containing intermediate product was no different from that of Example 5.

[0056] Example 8 Deprotection process (1)

[0057] The present invention provides a method for preparing a phosphorus-containing dopamine flame retardant in structure (I). Under anhydrous conditions, a phosphorus-containing intermediate product having structure (III) is dissolved in an organic solvent with different deprotection agent solutions to undergo a substitution reaction, thereby obtaining a phosphorus-containing dopamine flame retardant having structure (I);

[0058] Specific implementation process: add 100 mL of dehydrated organic solvent to a 500 mL single-necked flask, add 0.014 mol of the phosphorus-containing intermediate obtained in Example 5, 6 or 7, slowly drop 0.056 mol (2.04 g) of deprotecting agent hydrochloric acid into the flask, and stir evenly with magnetic force at room temperature. The reaction is carried out at room temperature. After 12 hours of reaction, centrifuge and wash three times using preferred organic solvents such as dichloromethane and petroleum ether, and dry to obtain a phosphorus-containing dopamine flame retardant (DPP-DA) containing structure (III), as shown in reaction formula (VI).

[0059]

[0060] In this example, only the amount of hydrochloric acid used as the deprotecting agent was changed, and the experiment was repeated without changing the implementation process. The inventors used 0.028 mol (1.02 g) of hydrochloric acid and 0.042 mol (1.53 g) of hydrochloric acid to replace 0.056 mol (2.04 g) of hydrochloric acid, respectively, and similarly prepared a phosphorus-containing dopamine flame retardant (DPP-DA) containing structure (III).

[0061] Example 9 Deprotection Process (2)

[0062] The process was the same as Example 9 except that 1 M tetrabutylammonium fluoride (TBAF) (56 mL) was used instead of hydrochloric acid (2.04 g, 0.056 mol).

[0063] Example 10 Characterization of the flame retardant DPP-DA structure and its application as a flame retardant coating

[0064] Figure 1 This is the NMR spectrum of phosphorus-containing dopamine flame retardant DPP-DA, including 1 H and 31 P NMR image. The NMR results showed that the flame retardant DPP-DA was successfully prepared.

[0065] The application of phosphorus dopamine flame retardant (DPP-DA) in flame retardant coating is given as an example. The substrate can be flexible polyurethane foam (FPUF), PET, PP, PE, etc.

[0066] Example application: Preparation of coated flexible polyurethane foam composites.

[0067] Step 1 (preparation of buffer solution): add 1 M NaOH aqueous solution to the solution, adjust the pH value to 8.5, and stir magnetically for 30 minutes until the solution becomes clear.

[0068] Step 2: Dissolve the flame retardant DPP-DA in the alkaline solution prepared in step 1. The concentration can be configured to (1-5 mg / mL), preferably 3 mg / mL.

[0069] Step 3: Immerse the washed and dried flexible polyurethane foam in the solution of step 2 at room temperature, fully squeeze the foam to absorb water, maintain air circulation and continuously shake and stir for 3 days.

[0070] Step 4: Freeze-dry the flame retardant coating foam in step 3 until it is completely free of moisture, and conduct thermal stability and flame retardant performance tests.

[0071] Test experiment 1: Thermal stability test, using the American Perkin-Elmer instrument to explore the thermal degradation of the material, the atmosphere is N2, the test range is 40℃ to 800℃, the heating rate is 10℃ / min, the performance test results are as follows Figure 2 shown.

[0072] pass Figure 2 It can be seen that after using the flame retardant coating of the present invention, under N2 conditions, all the tested samples showed similar second-order thermal decomposition behavior, and the coating can significantly improve the residual carbon mass of the soft polyurethane foam and reduce the rate of thermal decomposition.

[0073] Test experiment 2: Microcalorimetry test, using the American Comac instrument MCC-2 to explore the heat release of the coating composite material during combustion. The test range is from room temperature to 750℃, with a heating rate of 1℃ / s. The performance test results are as follows: Figure 3 shown.

[0074] pass Figure 3 It can be seen that under nitrogen (N2) conditions, the use of the flame retardant coating of the present invention significantly reduces the heat release rate. When the flame retardant loading is extremely low, the constructed organic flame retardant coating can effectively inhibit the generation of molten droplets and prevent the spread of flames.

[0075] The advantage of the phosphorus-containing dopamine flame retardant disclosed in the present invention is that it can form a PN flame retardant system, and the introduction of the flame retardant element P into the dopamine structure can give the material better flame retardant properties.

[0076] Analysis of flame retardant mechanism: In the gas phase, phosphorus-containing free radicals and catechol groups scavenged the active free radicals H· and OH· in the air.

[0077] In the condensed phase, PN synergism can also promote the formation of a cross-linked network with polymer chains during fire, thereby facilitating the retention of P in the condensed phase and producing a more thermally stable char layer structure.

[0078] It can be seen from the experimental data that phosphorus-containing dopamine flame retardants can form a flame retardant coating on the surface of the substrate. For the extremely flammable FPUF, adding the flame retardant synthesized by the present invention only increases the weight (5-10wt%) and has significant flame retardant properties, without adversely affecting the mechanical properties of the substrate.

Claims

1. A phosphorus-containing dopamine flame retardant, characterized in that: The phosphorus-containing dopamine flame retardant has the structural formula 。 2. A method for preparing a phosphorus-containing dopamine flame retardant as claimed in claim 1, comprising a process for preparing a protected product, a process for preparing a phosphorus-containing intermediate product and a deprotection process; The process of preparing the protection product is to add dopamine hydrochloride and imidazole to dichloromethane from which water has been removed, stir evenly with magnetic force at room temperature, then add TMS-Cl, react at room temperature for 12 hours, extract and wash with NaHCO3, NH4Cl, and NaCl aqueous solutions with a concentration exceeding 1M in sequence, remove excess solvent by rotary evaporation, and dry to obtain the protection product DA-R, as shown in reaction formula (IV): ； The process of preparing the phosphorus-containing intermediate product is to add DA-R and DPPC to tetrahydrofuran from which water has been removed, and at the same time add triethylamine as an acid-binding agent, the molar ratio of DA-R to triethylamine is 1:1.5, and stir evenly under magnetic stirring at room temperature. After reacting for 12 hours, extract and wash with NaHCO3, NH4Cl, and NaCl aqueous solutions with a concentration of more than 1M in sequence, remove excess solvent by rotary evaporation, and dry to obtain the phosphorus-containing intermediate product, as shown in reaction formula (V): ； The deprotection process is to add the phosphorus-containing intermediate product to the organic solvent from which water has been removed, slowly dropwise add the deprotection agent hydrochloric acid, stir evenly with magnetic force at room temperature, react at room temperature for 12 hours, centrifuge and wash three times with dichloromethane and petroleum ether respectively, and dry to obtain the phosphorus-containing dopamine flame retardant DPP-DA, as shown in reaction formula (VI): 。 3. A use of the phosphorus-containing dopamine flame retardant as claimed in claim 1, characterized in that In an alkaline solution, a phosphorus-containing dopamine flame retardant is self-oxidatively polymerized on the surface of a substrate to form a coating, thereby improving the thermal stability and flame retardancy of the substrate; the substrate is one or more of polyurethane foam, polyethylene terephthalate, polypropylene, and polyethylene materials.

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