A phosphorus-nitrogen synergistic flame retardant containing flexible nitrile group, and a preparation method and application thereof

Abstract

The application discloses a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups and a preparation method thereof, and comprises the following steps: mixing hexanediamine and vanillin into an organic solvent, heating, refluxing and stirring until completely dissolved; heating and refluxing the solution; after the reaction is completed, vacuum filtering the reaction solution, washing with water and drying to obtain a powder precursor; mixing the precursor and 4-nitrophthalonitrile into an organic solvent, stirring under heating until completely dissolved; then adding a catalyst, heating and refluxing again; adding DOPO and supplementing the solvent, and continuing to reflux; after the reaction is completed, washing the reaction product with water and ethanol, filtering and drying to obtain the phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups. The one-pot method for preparing the phosphorus-nitrogen synergistic flame retardant monomer containing flexible nitrile groups has the characteristics of simple operation, low-toxicity solvent, mild reaction condition, easy realization and low by-product, and is beneficial to industrial production.

Description

Technical Field

[0001] This invention relates to the field of flame retardant technology for polymer materials, specifically to a method for preparing a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups and its application in epoxy resins. Background Technology

[0002] Epoxy resins possess excellent mechanical properties, dimensional stability, chemical resistance, and heat resistance, and have been widely used in coatings, composite materials, casting materials, adhesives, and injection molding materials, making them an indispensable engineering material in modern industry.

[0003] Like other engineering materials, flammability is a significant factor limiting the application of epoxy resins, posing a high fire risk in applications such as aircraft, trains, and ships. Epoxy resins release a large amount of heat when burning, and a fire could have extremely serious consequences. Furthermore, the combustion of epoxy resins produces large amounts of smoke, which poses a serious threat to human health and hinders escape in a fire. Therefore, improving the flame-retardant properties of epoxy resins and reducing safety hazards in practical applications is of great practical significance. Traditional flame-retardant methods involve adding halogen-containing flame retardants. While halogen-containing flame retardants have high flame-retardant efficiency, they produce highly toxic and difficult-to-degrade toxic byproducts during combustion, causing severe harm to human health and the environment. Therefore, halogen-free, highly efficient, and environmentally friendly flame retardants are the development trend.

[0004] In recent years, DOPO and its derivatives have attracted widespread attention from researchers as a novel, highly efficient phosphorus-containing flame retardant due to their halogen-free and highly effective flame retardancy. Furthermore, the presence of active pH bonds in their molecules facilitates reactions with other nitrogen-containing functional groups, forming different types of phosphorus / nitrogen synergistic flame retardant materials. The introduction of flexible nitrile groups allows for self-crosslinking at high temperatures, forming an interpenetrating network structure with the macromolecular chains in the polymer matrix, increasing the degree of crosslinking and thus enhancing the flexural strength of epoxy composites. Simultaneously, the use of phosphorus-nitrogen synergistic flame retardancy can further improve its flame retardant efficiency.

[0005] Therefore, how to provide a flame retardant containing flexible nitrile-based phosphorus and nitrogen synergy and use it to improve the flame retardant properties of epoxy resin is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups that is simple and convenient to operate and has excellent flame retardant effect, as well as its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A phosphorus-nitrogen synergistic flame retardant containing a flexible nitrile group, wherein the phosphorus-nitrogen synergistic flame retardant containing the flexible nitrile group is a compound having the structure of Formula I:

[0009]

[0010] This invention also provides a method for preparing the above-mentioned phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups, comprising the following steps:

[0011] (1) Mix hexamethylenediamine and vanillin and add them to an organic solvent, then heat and reflux and stir until completely dissolved;

[0012] (2) Heat the solution and reflux it again;

[0013] (3) After the reaction is complete, the reaction solution is vacuum filtered, washed with water and dried to obtain a powdered precursor.

[0014] (4) The precursor and 4-nitrophthalonitrile (4-PN) are mixed and added to an organic solvent, and the mixture is refluxed and stirred under heating conditions until completely dissolved; then the catalyst is added, and the temperature is raised to carry out the reflux reaction again;

[0015] (5) After the reflux reaction, add DOPO and continue the reflux reaction;

[0016] (6) After the reaction is complete, the reaction product is washed with water and ethanol, then filtered and dried to obtain a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups.

[0017] Furthermore, the molar ratio of hexamethylenediamine and vanillin in step (1) is (0.8-1.2):(2-2.22), preferably 1:2;

[0018] The organic solvent is dimethylacetamide;

[0019] The heating temperature is 50-75℃.

[0020] The beneficial effects of adopting the above-mentioned further solutions are as follows:

[0021] Currently synthesized nitrile resins are characterized by high melting points and poor solubility (as disclosed in patents such as "An Additive Crosslinkable Flame Retardant and Its Preparation Method" ZL202011509590.2 and "A Crosslinkable Flame Retardant Containing Di(DOPO) Di(phthalonitrile) and Its Preparation Method and Application" ZL2021110703643.2). The flexible nitrile epoxy composite material synthesized in this invention introduces flexible chains, which improves the solubility of the flexible nitrile flame retardant in the epoxy resin matrix and lowers the melting point of the flexible nitrile resin. At the same time, the flexible chain segments can also effectively improve the toughness of the interpenetrating network formed by the nitrile crosslinking and the epoxy matrix, thereby improving the mechanical properties of the epoxy resin composite material with added flexible nitrile flame retardant.

[0022] Furthermore, the heating in step (2) is to raise the temperature to 75-85℃, and the reflux reaction time is 4-5h.

[0023] The beneficial effects of adopting the above-mentioned further scheme are as follows: the above-mentioned scheme of the present invention can effectively maintain the activity of aldehyde-amine condensation reaction and ensure that the reaction is as complete as possible. The reaction temperature is generally controlled between 75-85℃ and the reaction time is generally controlled between 4-5h.

[0024] Furthermore, the drying in step (3) is vacuum drying, with a temperature of 60-80℃ and a drying time of 20-24h.

[0025] The advantages of adopting the above-mentioned further solutions are as follows: the vacuum environment greatly reduces the boiling point of the liquid that needs to be expelled; for samples that are not easy to dry, such as powder or other granular samples, vacuum drying can effectively shorten the drying time; vacuum drying is safer to use - under vacuum or inert conditions, the possibility of oxides exploding when heated is eliminated; compared with ordinary drying that relies on air circulation, powdered samples will not be blown or moved by flowing air.

[0026] Furthermore, the molar ratio of the precursor, 4-nitrophthalonitrile (4-PN) in step (4) to DOPO in step (5) is (0.8-1.2):(2-2.22):(2-2.22), preferably 1:2:2;

[0027] The beneficial effect of adopting the above-mentioned further scheme is that: the required molar ratio of reactants can be determined according to the reactive groups of the reactants to ensure that they react fully. Since the precursor contains two phenolic hydroxyl groups and two C=N bonds, it can react with two 4-PN and two DOPO.

[0028] Furthermore, the organic solvent mentioned in step (4) is dimethylformamide; the heating temperature is 50-60℃;

[0029] Furthermore, the catalyst mentioned in step (4) is potassium carbonate;

[0030] The heating is performed by raising the temperature to 70-75°C, and the reflux reaction time is 4-5 hours.

[0031] The beneficial effects of adopting the above-mentioned further scheme are as follows: The purpose of adding a catalyst in this invention is to promote the reaction between the nitro group and the phenolic hydroxyl group of 4-PN, thereby improving the reaction efficiency. After comprehensive consideration from the perspectives of volatility and cost, potassium carbonate is determined to be the best catalyst.

[0032] Furthermore, the drying in step (6) is vacuum drying, with a temperature of 60-80℃ and a drying time of 20-24h.

[0033] The beneficial effect of adopting the above-mentioned further scheme is that it has the same optimization effect as step (3) above.

[0034] Furthermore, all reflux reactions in the above preparation process were carried out under a nitrogen atmosphere.

[0035] The beneficial effect of adopting the above-mentioned further scheme is that nitrogen is an inert gas, and maintaining a nitrogen atmosphere during the reaction process plays a protective role in improving the reaction quality.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] 1) The "one-pot method" used in this invention for preparing phosphorus-nitrogen synergistic flame retardant monomers containing flexible nitrile groups has the advantages of simple operation, low solvent toxicity, mild and easy-to-achieve reaction conditions, and low by-products, which is conducive to industrial production.

[0038] 2) The flame retardant prepared by this invention contains phosphorus and nitrogen, two flame retardant elements, which work synergistically to exhibit a more efficient flame retardant effect;

[0039] 3) The monomer containing flexible nitrile groups prepared by this invention has phthalonitrile structures at both ends, which can carry out more free self-crosslinking reaction, further increasing the crosslinking density inside the composite material, so that the composite material can improve its mechanical properties while improving its flame retardant properties.

[0040] This invention also provides the application of the above-mentioned phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups in improving the flame retardancy of epoxy resins. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0042] Figure 1 The infrared spectra of VDH, DOPO, 4-PN, and VDHPD in Embodiment 1 of the present invention are shown below.

[0043] Figure 2 The VDHPD NMR hydrogen spectrum and phosphorus spectrum prepared in Example 1 of this invention. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] A phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups

[0047] Its synthetic route is as follows:

[0048]

[0049] Its preparation method is as follows:

[0050] (1) Mix 11.62g hexamethylenediamine (0.1mol) and 30.43g vanillin (0.2mol) and add them to 100ml dimethylacetamide. Then heat to 70℃ and reflux under nitrogen atmosphere until completely dissolved.

[0051] (2) Heat the solution to 80°C and reflux it again under nitrogen atmosphere for 5 hours;

[0052] (3) After the reaction is complete, the reaction solution is vacuum filtered, washed with water, and vacuum dried at 70°C for 24 hours to obtain powdered bisphenol precursor (VDH).

[0053] (4) 38.45 g of bisphenol precursor (VDH) (0.1 mol) and 34.63 g of 4-nitrophthalonitrile (0.2 mol) were mixed and added to 75 g of dimethylformamide. The mixture was heated to 60 °C and stirred under nitrogen atmosphere until completely dissolved. Then 15.2 g of potassium carbonate (0.11 mol) was added and the mixture was heated to 75 °C and refluxed again for 4 h.

[0054] (5) After reflux reaction, add 43.2g DOPO and continue reflux reaction for 8h;

[0055] (6) After the reaction is complete, the reaction product is washed with water and ethanol, then filtered and dried under vacuum at 70°C for 24 hours to obtain a phosphorus-nitrogen synergistic flame retardant (VDHPD) containing flexible nitrile groups.

[0056] Example 2

[0057] (1) Mix 17.43g hexamethylenediamine (0.15mol) and 45.65g vanillin (0.3mol) and add them to 150ml dimethylacetamide. Then heat to 75℃ and reflux under nitrogen atmosphere until completely dissolved.

[0058] (2) Heat the solution to 85°C and reflux it again under nitrogen atmosphere for 5 hours;

[0059] (3) After the reaction is complete, the reaction solution is vacuum filtered, washed with water, and vacuum dried at 70°C for 24 hours to obtain powdered bisphenol precursor (VDH).

[0060] (4) 57.68 g of bisphenol precursor (VDH) (0.15 mol) and 51.95 g of 4-nitrophthalonitrile (0.3 mol) were mixed and added to 120 g of dimethylformamide. The mixture was heated to 62 °C and stirred under nitrogen atmosphere until completely dissolved. Then 22.8 g of potassium carbonate (0.165 mol) was added and the mixture was heated to 75 °C and refluxed again for 4 h.

[0061] (5) After reflux reaction, add 64.8g DOPO and continue reflux reaction for 8h;

[0062] (6) After the reaction is complete, the reaction product is washed with water and ethanol, then filtered and dried under vacuum at 70°C for 24 hours to obtain a phosphorus-nitrogen synergistic flame retardant (VDHPD) containing flexible nitrile groups.

[0063] Example 3

[0064] (1) Mix 5.81g hexamethylenediamine (0.05mol) and 15.22g vanillin (0.1mol) and add them to 70ml dimethylacetamide. Then heat to 70℃ and reflux under nitrogen atmosphere until completely dissolved.

[0065] (2) Heat the solution to 80°C and reflux it again under nitrogen atmosphere for 5 hours;

[0066] (3) After the reaction is complete, the reaction solution is vacuum filtered, washed with water, and vacuum dried at 70°C for 24 hours to obtain powdered bisphenol precursor (VDH).

[0067] (4) 19.23 g of bisphenol precursor (VDH) (0.05 mol) and 17.32 g of 4-nitrophthalonitrile (0.1 mol) were mixed and added to 60 g of dimethylformamide. The mixture was heated to 60 °C and stirred under nitrogen atmosphere until completely dissolved. Then 7.6 g of potassium carbonate (0.055 mol) was added and the mixture was heated to 75 °C and refluxed again for 4 h.

[0068] (5) After reflux reaction, add 21.6g DOPO and continue reflux reaction for 8h;

[0069] (6) After the reaction is complete, the reaction product is washed with water and ethanol, then filtered and dried under vacuum at 70°C for 24 hours to obtain a phosphorus-nitrogen synergistic flame retardant (VDHPD) containing flexible nitrile groups.

[0070] Characterization of VDHPD in Experiment 1

[0071] like Figure 1 As shown, the P=O double bond can be clearly observed in the infrared spectrum of VDHPD (1238 cm⁻¹). -1 ), P-Ph key (1591cm) -1 ), PO-Ph bond (947cm) -1 757cm -1 ), and at the same time, the C≡N triple bond (2241cm) -1 2234cm -1 It appeared simultaneously in the infrared of both 4-PN and VDHPD, along with the PH bond in DOPO (2439cm). -1 The disappearance of ) and the C=N bond in VDH (1585cm) -1 ) and -OH (3334cm) -1 ) disappeared, and the CH bond (830cm) -1 ), NH bond (1563cm) -1 ) and CN bond (1465cm -1 The appearance of ) indicates that the expected flame retardant monomer has been successfully synthesized.

[0072] exist Figure 2 In the image, the hydrogen NMR spectrum of VDHPD is as follows: Figure 2As shown in (a), the peaks from 6.9 ppm to 8.4 ppm belong to hydrogen atoms on the benzene ring in VDHPD, the doublets at 9.87 ppm and 10.11 ppm both belong to hydrogen atoms in the CH structure, and the appearance of the doublets is attributed to the presence of chiral carbon atoms in VDHPD. The peak at 6.35 ppm belongs to hydrogen atoms in NH; 3.74 ppm and 2.98 ppm are hydrogen atoms in -CH2 and -CH3. In addition, the overall area ratio of these four types of hydrogen atoms is 1:1:9:14, which is consistent with the theoretical value. Figure 2 (b) shows the NMR phosphorus spectrum of VDHPD. Phosphorus atoms in DOPO show two peaks of 15.73 ppm and 13.22 ppm, while phosphorus atoms in VDHPD also show two peaks of 33.35 ppm and 22.91 ppm. Therefore, the NMR characterization results further prove that the flame retardant VDHPD has been successfully synthesized.

[0073] Preparation of basic flame-retardant composite materials

[0074] Bisphenol A type E51 epoxy resin was placed at 120°C until it flowed. Diaminodiphenylmethane (DDM) was used as the sole epoxy resin curing agent at a ratio of E51:DDM = 100:25. Then, the phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups prepared according to the previous mixture was added at weight ratios of 5%, 7%, and 10%. After the temperature dropped to 50°C, the flame retardant powder was slowly added to a beaker. After the flame retardant powder was completely dissolved, DDM was added, and stirring continued until fully dispersed. Finally, the thoroughly stirred mixture was quickly poured into a polytetrafluoroethylene mold coated with a release agent, and heat-treated at 120°C / 2h, 140°C / 2h, and 180°C / 2h to allow the phthalonitrile of the flame retardant uniformly dispersed in the epoxy resin matrix to completely crosslink.

[0075] Comparative Example 1: Pure epoxy resin

[0076] A pure epoxy resin was prepared using bisphenol A type E51 epoxy resin as a comparative example.

[0077] Flame retardant performance comparison test between Example 1 and Comparative Example 1:

[0078] In this invention, the UL-94 vertical burning test adopts the GB / T 2408-2008 standard; the limiting oxygen index test adopts the GB / T 2406-93 standard. The basic flame-retardant composite material prepared in Example 1 of this invention and pure epoxy resin are tested and compared, and the results are shown in the table below.

[0079] Table 1 Performance Test Results

[0080]

[0081] In the table, NR represents unrated material, which is flammable.

[0082] As can be seen from the table, the flame retardant prepared by this invention exhibits superior flame retardant performance when the phosphorus content is equal to or significantly lower than that of similar phosphorus-containing flame retardants. It can achieve a limiting oxygen index value of over 30% with an addition amount of only 5%. Due to the two phthalonitrile groups at the ends, the flame retardant structure synthesized by this invention can not only form a semi-interpenetrating network structure, but also generate a hyperbranched structure from the two phthalonitrile structures at both ends. The sample obtained after crosslinking has a significant improvement in limiting oxygen index compared with existing technologies. At the same time, when the addition amount is increased to 10%, the UL-94 reaches the V-0 level. The synthesis conditions are easy to achieve, the solvent is low in toxicity, and the yield is high.

[0083] This invention discloses a halogen-free, environmentally friendly flame retardant that can be used for flame retardancy of polymers. First, using DMF as a solvent, a phosphorus-nitrogen synergistic flame retardant monomer containing flexible nitrile groups was prepared using DOPO, vanillin, hexamethylenediamine, and 4-nitrophthalonitrile. The experimental conditions were mild, the solvent toxicity was relatively low, and it was easy to achieve industrial production. Then, the composite material containing this flame retardant was further heat-treated at high temperature, allowing the phthalonitrile groups in the flame retardant monomer to undergo a self-crosslinking reaction in the polymer matrix, achieving highly efficient flame retardancy of the composite material. Furthermore, the flame retardant synthesized in this invention does not require the powder-to-solid-block and then pulverization process of existing flame retardant synthesis. After synthesis, the flame retardant synthesized in this invention can be directly washed with ethanol and deionized water, dried, and used. Ethanol is easier to dry than water used in some existing flame retardants. This simplified synthesis and purification process greatly reduces product waste, increases yield, and improves synthesis efficiency, resulting in significant advancements and economic benefits.

[0084] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups, characterized in that, The phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups is a compound having the structure of Formula I:

2. A method for preparing a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups as described in claim 1, characterized in that, Includes the following steps: (1) Mix hexamethylenediamine and vanillin and add them to an organic solvent, then heat and reflux and stir until completely dissolved; (2) Heat the solution and reflux it again; (3) After the reaction is complete, the reaction solution is vacuum filtered, washed with water and dried to obtain a powdered precursor. (4) Add the precursor and 4-nitrophthalonitrile to an organic solvent and reflux and stir under heating until completely dissolved; then add the catalyst and reflux reaction again at higher temperature. (5) After the reflux reaction, add DOPO and continue the reflux reaction; (6) After the reaction is complete, the reaction product is washed with water and ethanol, then filtered and dried to obtain a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups.

3. The method for preparing a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups according to claim 2, characterized in that, The molar ratio of hexamethylenediamine and vanillin in step (1) is (0.8-1.2):(2-2.22); The organic solvent is dimethylacetamide; the heating temperature is 50-75℃.

4. The method for preparing a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups according to claim 2, characterized in that, The heating in step (2) is to raise the temperature to 75-85℃, and the reflux reaction time is 4-5h.

5. The method for preparing a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups according to claim 2, characterized in that, The drying process described in step (3) is vacuum drying, with a temperature of 60-80℃ and a drying time of 20-24h.

6. The method for preparing a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups according to claim 2, characterized in that, The molar ratio of the precursor, 4-nitrophthalonitrile, and DOPO in step (4) to that in step (5) is (0.8-1.2):(2-2.22):(2-2.22). The organic solvent mentioned in step (4) is dimethylformamide; the heating temperature is 50-60℃.

7. The method for preparing a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups according to claim 6, characterized in that, The catalyst mentioned in step (4) is potassium carbonate; The heating is performed by raising the temperature to 70-75°C, and the reflux reaction time is 4-5 hours.

8. The method for preparing a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups according to claim 2, characterized in that, The drying process described in step (6) is vacuum drying, with a temperature of 60-80℃ and a drying time of 20-24h.

9. The method for preparing a phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups according to claim 2, characterized in that, All reflux reactions during the preparation process were carried out under a nitrogen atmosphere.

10. The application of the phosphorus-nitrogen synergistic flame retardant containing flexible nitrile groups according to claim 1 in improving the flame retardancy of epoxy resin.

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