Nitrogen-rich doPO-based flame retardant and synthesis and application thereof

Abstract

The present application relates to the technical fields of flame retardant and flame retardant composite material, and particularly relates to a nitrogen-rich DOPO-based flame retardant and synthesis and application thereof. The conventional phosphorus-based flame retardant and the epoxy resin have poor polarity matching degree, and are prone to phase separation or migration and precipitation, resulting in unstable flame retardancy of the flame-retardant epoxy resin, and the flame-retardant effect needs to be further improved. In view of the above technical problems, the present application provides a nitrogen-rich DOPO-based flame retardant, which belongs to the reaction-type phosphorus-nitrogen flame retardant. The secondary amine group in the molecular structure of the nitrogen-rich DOPO-based flame retardant can form a chemical bond with the epoxy group in the structure of the epoxy resin. Compared with the conventional phosphorus-based flame retardant, the nitrogen-rich DOPO-based flame retardant has better compatibility with the epoxy resin, is not prone to falling off, has less influence on the mechanical properties and transparency of the epoxy resin, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of flame retardants, in particular to a nitrogen-rich DOPO-based flame retardant and a synthesis and application thereof. BACKGROUND

[0002] Epoxy resin, as an important kind of thermosetting polymer material, has been widely used in the fields of electronics and electrical appliances, home appliance manufacturing, aerospace, etc. due to its excellent chemical corrosion resistance, insulation performance and thermal stability. However, the limiting oxygen index (LOI) of general epoxy resin is usually lower than 24%, which shows significant flammable characteristics. In the combustion process, not only a large amount of heat is released, but also the phenomenon of melt dripping occurs, which easily causes secondary fire risk. Therefore, improving the intrinsic flame retardant performance of epoxy resin has become a key problem to be solved in the field.

[0003] In the traditional flame retardant technology, halogen-based flame retardants (such as brominated epoxy resin) have been used for a long time due to their high flame retardant effect. However, such flame retardants will produce toxic gases such as hydrogen halide and dioxin and corrosive smoke during thermal decomposition or combustion, which poses a serious threat to the ecological environment and human health. With the increasing strictness of green chemistry and environmental protection regulations worldwide, the development of efficient halogen-free flame retardant systems has become an industry consensus.

[0004] Among halogen-free flame retardant systems, phosphorus-based flame retardants show significant advantages due to their low toxicity, high flame retardant efficiency and multiple flame retardant mechanisms (gas phase quenching, condensed phase carbonization, etc.). However, the application of existing phosphorus-based flame retardants in epoxy resin matrix still faces many technical bottlenecks:

[0005] Compatibility defects: Most phosphorus-based flame retardants have low polarity matching degree with epoxy resin, which easily causes phase separation or migration and precipitation, resulting in the decrease of long-term stability of the material;

[0006] Performance compromise: In order to achieve UL-94 V-0 level flame retardation, more than 15 wt.% of flame retardant is usually added, which will significantly deteriorate the mechanical strength (such as tensile modulus reduction > 20%) and optical transparency (transmittance loss > 30%) of the composite material;

[0007] Reaction inertness: Some flame retardants lack the chemical bonding ability with epoxy groups, only through physical blending dispersion, which is difficult to form stable interfacial interaction, further aggravating the compatibility problem.

[0008] Taking the prior art CN 102428091A as an example, it discloses a flame retardant based on DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) derivative, which improves the flame retardant efficiency through halogen end group modification. However, this technology has the following limitations:

[0009] The active functional groups (such as amino, hydroxyl) in the flame retardant molecules are not designed to react with epoxy groups, resulting in only physical adsorption between the flame retardant and the resin matrix, and weak interfacial bonding force;

[0010] Although the high halogen content improves the flame retardancy, it aggravates the combustion toxicity, which is contrary to the trend of halogen-free;

[0011] The addition amount needs to reach more than 10 wt.% to meet the V-0 level requirement, and the bending strength of the composite material decreases by about 18%.

[0012] Based on the above technical problems, it is urgent to develop a new phosphorus-nitrogen synergistic flame retardant system, which needs to have the following characteristics:

[0013] By introducing reactive groups through molecular structure design, chemical bonding with epoxy resin is achieved, and the compatibility and dispersion stability are improved;

[0014] With low addition amount (≤5 wt.%), high flame retardant grade (LOI≥30%, UL-94 V-0 level) is achieved, and the mechanical and optical properties of the matrix are maximized;

[0015] Avoiding halogen elements meets the green environmental protection requirements.

[0016] The present application aims at the above-mentioned needs, and provides a nitrogen-rich DOPO-based flame retardant and its composite material, which effectively overcomes the core defects of the prior art by precisely controlling the molecular structure and reaction path of the flame retardant, and provides an innovative solution for the development of high-performance flame-retardant epoxy resin. SUMMARY

[0017] The existing problems in the prior art are that the conventional phosphorus-based flame retardant and the epoxy resin have poor polarity matching, and are prone to phase separation or migration and precipitation, resulting in unstable flame retardancy of the flame-retardant epoxy resin, and the flame-retardant effect needs to be further improved. In view of the above technical problems, the present application provides a nitrogen-rich DOPO-based flame retardant, and its chemical structural formula is as follows:

[0018]

[0019] The R group in the above chemical structure includes at least one of hydrogen atom, C1-C3 straight chain alkyl, hydroxyl, hydroxymethyl, nitro group, dimethylamino, boric acid group, acetoxy, methoxy.

[0020] The preparation method of the nitrogen-rich DOPO-based flame retardant comprises the following steps:

[0021] (1) 2-thiophene formaldehyde or 2-thiophene formaldehyde derivative reacts with 5-amino tetrazole to generate a Schiff base intermediate, and the structure formula of the Schiff base intermediate is as follows:

[0022]

[0023] In the above chemical formula, the R group includes at least one of hydrogen atom, C1-C3 straight chain alkyl, hydroxyl, hydroxymethyl, nitro, dimethylamino, boronic acid group, acetoxy, methoxy;

[0024] (2) The Schiff base intermediate reacts with DOPO to obtain the nitrogen-rich DOPO-based flame retardant.

[0025] Preferably, the 2-thiophene formaldehyde derivative includes at least one of 5-hydroxy-2-thiophene formaldehyde, 5-nitro-2-thiophene formaldehyde, 5-methyl-2-thiophene formaldehyde, 5-ethyl-2-thiophene formaldehyde, 5-propyl-2-thiophene formaldehyde, 5-hydroxymethyl-2-thiophene formaldehyde, 5-dimethylamino-2-thiophene formaldehyde, formaldehyde thienyl-2-boronic acid, 5-acetyl methyl-2-thiophene formaldehyde, 5-methoxy-2-thiophene formaldehyde.

[0026] Preferably, the solvent used in the reaction in step (1) includes one or a combination of two or more of anhydrous ethanol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, dichloromethane, dichloroethane, chloroform, ethyl acetate, benzene, toluene, 1,4-dioxane.

[0027] Preferably, the temperature of the reaction in step (1) is 40-100℃, and the reaction time is 8-12h.

[0028] Preferably, the molar ratio of 2-thiophene formaldehyde or 2-thiophene formaldehyde derivative to 5-amino tetrazole in step (1) is 1-1.1:1.

[0029] Preferably, the molar ratio of the Schiff base intermediate to DOPO in step (2) is 1:1-1.1.

[0030] Preferably, the temperature of the reaction in step (2) is 40-100℃, and the reaction time is 12-24h.

[0031] A preparation method of a flame-retardant epoxy resin includes the following steps:

[0032] (1) Heating the epoxy resin to 140-160℃, adding the above-mentioned nitrogen-rich DOPO-based flame retardant, stirring until the nitrogen-rich DOPO-based flame retardant is completely dissolved in the epoxy resin, and keeping the temperature for 8-20min to obtain a mixed solution;

[0033] (2) After cooling the mixed solution obtained in step (1) to 90-100℃, adding an epoxy curing agent to the reaction system, stirring at constant temperature until the epoxy curing agent is completely dissolved, quickly pouring the reaction system into a mold preheated to the curing temperature, and performing thermal curing to obtain the flame-retardant epoxy resin.

[0034] Preferably, the epoxy curing agent is selected from one or more of an amine curing agent, an amide curing agent and an imidazole curing agent.

[0035] Further preferably, the selected amine curing agent can be one or more of meta-phenylenediamine, m-toluenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, meta-aminomethylamine, p-phenylenediamine and methylene bisphenylenediamine.

[0036] Further preferably, the amide curing agent can be one or both of polyamide 650 and polyamide 651.

[0037] Further preferably, the imidazole curing agent can be one or more of imidazole, 2-methylimidazole, 2-ethylimidazole and 2-ethyl-4-methylimidazole.

[0038] The present application has the following beneficial effects:

[0039] (1) The present application obtains a nitrogen-rich DOPO-based flame retardant, which belongs to a reactive phosphorus-nitrogen flame retardant. The secondary amine group in the molecular structure of the flame retardant can form a chemical bond with the epoxy group in the epoxy resin structure. Compared with conventional phosphorus-based flame retardants, the nitrogen-rich DOPO-based flame retardant has better compatibility with the epoxy resin, is not easy to fall off, and has less influence on the mechanical properties and transparency of the epoxy resin.

[0040] (2) The nitrogen-rich DOPO-based flame retardant obtained by the present application is obtained by a simple two-step one-pot synthesis reaction of 2-thiophenecarboxaldehyde or a 2-thiophenecarboxaldehyde derivative, 5-5-amino tetrazole and DOPO. The raw materials used are easy to obtain, the reaction conditions are mild, the purification is simple, the reaction solvent can be recycled, the molecular structure of the product is simple, the steric hindrance is small, and the purity and yield of the product are relatively high.

[0041] (3) The present application uses the nitrogen-rich DOPO-based flame retardant as a flame-retardant additive in the preparation process of the flame-retardant epoxy resin. The obtained flame-retardant epoxy resin has good flame-retardant properties. The addition amount of the nitrogen-rich DOPO-based flame retardant is relatively small (not higher than 4 wt%), but the flame-retardant property of the obtained flame-retardant epoxy resin can reach V-0 level (UL-94), has better market prospects, and the economic benefit is more considerable.

[0042] (4) The 2-thiophenecarboxaldehyde derivatives selected in the present application are all 2-thiophenecarboxaldehyde derivatives with good compatibility with the epoxy resin and small steric hindrance. The transparency and flame-retardant property of the obtained flame-retardant epoxy resin are better. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 : is the infrared spectrum of THAMP obtained in Example 1 of the present application.

[0044] Figure 2: are the carbon residue morphology and SEM images of EP, EP / THAMP (2wt.%), EP / THAMP (4wt.%) after cone calorimeter test in Example 1 of the present application.

[0045] Figure 3 : are the digital photos of the transmittance of 3mm thick EP, THAMP (2wt.%), THAMP (4wt.%) in Example 1 of the present application.

[0046] Figure 4 : are the transmittance test figures of EP, EP / THAMP (2wt.%), EP / THAMP (4wt.%) in Example 1 of the present application. DETAILED DESCRIPTION

[0047] The present application is described in detail below with reference to the examples. It should be understood, however, that the following examples are merely illustrative of the present application and should not be construed as limiting the scope of the present application.

[0048] Example 1

[0049] A synthesis method of the nitrogen-rich DOPO-based flame retardant is as follows:

[0050] Into a 500mL four-necked flask, 23.53g of 2-thiophene formaldehyde and 17.85g of 5-amino tetrazole were added, and 200mL of anhydrous ethanol was added to the four-necked flask as a solvent, and the temperature was raised to 80°C under stirring, and constant temperature stirring was carried out for 8h, and after the complete conversion of 2-thiophene formaldehyde, 45g of DOPO was added to the system, and constant temperature stirring was carried out for 12h, and then the reaction system was cooled to precipitate the solid product, which was then filtered and washed with anhydrous ethanol for 3 times, and the obtained solid product was vacuum dried at 80°C for 24h to obtain the nitrogen-rich DOPO-based flame retardant, which is recorded as THAMP, and the yield was 86.20%.

[0051] As shown in the accompanying drawings of the specification, Figure 1 is the infrared spectrum of the flame retardant THAMP, and the spectrum analysis results are: -NH- (3321cm -1 ); P=O (1239cm -1 ); P-O-Ar (1211cm -1 ); P-C (758cm -1 ).

[0052] Specific application:

[0053] The epoxy resin (E51, epoxy equivalent weight 0.51) was heated to 160°C, then the THAMP obtained in Example 1 was added, stirred until the THAMP was completely dissolved in the epoxy resin, then constant temperature stirring was carried out for 8 min, then cooled to 90°C, while stirring, the curing agent 4,4'-diaminodiphenyl methane was added, stirred until the 4,4'-diaminodiphenyl methane was completely dissolved in the reaction system, then quickly transferred to a mold preheated to 100°C, cured in a forced air oven at 100°C for 2h, then cured at 150°C for 3h, to obtain a flame-retardant epoxy resin.

[0054] When the mass percentage content of THAMP in the above-mentioned epoxy resin reaction system was 2wt.%, and the mass percentage content of 4,4'-diaminodiphenyl methane in the epoxy resin reaction system was 19.57wt.%, the obtained flame-retardant epoxy resin was recorded as EP / THAMP(2wt.%), and the flame-retardant properties of the transparent flame-retardant epoxy resin were as shown in Table 1, and the mechanical properties were as shown in Table 2.

[0055] When the mass percentage content of THAMP in the above-mentioned epoxy resin reaction system was 4wt.%, and the mass percentage content of 4,4'-diaminodiphenyl methane in the epoxy resin reaction system was 18.97wt.%, the obtained flame-retardant epoxy resin was recorded as EP / THAMP(4wt.%), and the flame-retardant properties of the transparent flame-retardant epoxy resin were as shown in Table 1, and the mechanical properties were as shown in Table 2.

[0056] The flame-retardant properties of the pure epoxy resin were also as shown in Table 1, and the mechanical properties were as shown in Table 2.

[0057] Table 1

[0058]

[0059] None in Table 1 represents that the sample burned to the clamp and did not reach the UL-94 grade standard; the flame-retardant grade NO represents that there was no dripping phenomenon during the burning process, and Yes represents that there was dripping phenomenon during the burning process.

[0060] As shown in Table 1, the pure epoxy resin showed dripping, but it was found that the dripping disappeared after the addition of the flame retardant THAMP, the flame-retardant grade reached V-1 level after the addition of 2wt% THAMP in the epoxy resin, and the standard test reached V-0 level after the addition of 4wt% THAMP in the epoxy resin, which indicated that THAMP could achieve high flame retardancy of the epoxy resin at a very low addition amount.

[0061] In Table 1, the limiting oxygen index standard: ASTM D2863, the sample size was 130x6.5x3mm 3 . Vertical burning test standard: ASTM D3801, sample size: 130x13x3mm 3 .

[0062] The mechanical property test results of EP, EP / THAMP (2 wt.%) and EP / THAMP (4 wt.%) are shown in Table 2.

[0063] Mechanical property: the test standard is ASTM D638 (tensile property) and ASTM D790 (flexural stiffness and strength property of materials).

[0064] Table 2

[0065]

[0066] From the analysis of Table 2, it can be seen that the addition of 2 wt.% or 4 wt.% THAMP in the epoxy resin has little effect on the mechanical properties of the epoxy resin.

[0067] Figure 1 Figure 2 are the pictures of combustion char residue and SEM images of CCT test, wherein a1-a3, b1-b3, c1-c3 belong to pure EP, EP / THAMP (2 wt.%), EP / THAMP (4 wt.%), respectively. The images show that the morphology of residual carbon and the expansion height of carbon layer of EP / THAMP (2 wt.%), EP / THAMP (4 wt.%) are better than those of pure EP, and with the increase of the amount of THAMP added in the epoxy resin, the carbon layer integrity and expansion height of the obtained flame-retardant epoxy resin are better. The SEM images further confirm that the introduction of THAMP significantly improves the compactness and continuity of the carbon layer of the obtained flame-retardant epoxy resin after combustion. Therefore, after the addition of THAMP, the obtained flame-retardant epoxy resin can form a more stable carbon layer after combustion, which can effectively block oxygen and prevent the escape of flammable gas generated by pyrolysis to the combustion zone, thereby achieving better flame-retardant effect.

[0068] Figure 2 Figure 3 From the visual observation, it can be seen that the transparency of EP / THAMP (2 wt.%), EP / THAMP (4 wt.%) has little difference compared with that of pure EP, and from the Figure 4 From the UV-visible transmission spectrum, it can be seen that the transmittance of EP / THAMP (2 wt.%), EP / THAMP (4 wt.%) slightly decreases compared with that of pure EP in the range of 300-800 nm, but still maintains a high transmittance, which indicates that the addition of THAMP in the epoxy resin has little effect on its transparency.

[0069] Example 2

[0070] A synthesis method of a nitrogen-rich DOPO-based flame retardant is as follows:

[0071] Into a 500 mL four-necked flask, 160.45 g of 5-hydroxy-2-thiophenecarboxaldehyde and 17.85 g of 5-amino tetrazole were added, and 200 mL of anhydrous ethanol was added as a solvent into the four-necked flask, and the temperature was raised to 80°C under stirring, and the reaction was kept at constant temperature for 8 h. After the 5-hydroxy-2-thiophenecarboxaldehyde was completely converted, 45 g of DOPO was added into the system, and the reaction was kept at constant temperature for 12 h under stirring. After the solid product in the reaction liquid was completely precipitated, it was filtered, and washed with anhydrous ethanol for 3 times. The obtained solid product was dried at 80°C under vacuum for 24 h, to obtain a nitrogen-rich DOPO-based flame retardant, recorded as THAMP-1, with a yield of 84.78%.

[0072] Specific application

[0073] The epoxy resin was heated to 160°C, and then the THAMP-1 obtained in Example 2 was added. After the THAMP-1 was completely dissolved in the epoxy resin under stirring, the temperature was kept constant for 8 min under stirring. Then, the temperature was lowered to 90°C, and 4,4’-diaminodiphenyl methane was added under stirring. After the 4,4’-diaminodiphenyl methane was completely dissolved in the reaction system, it was quickly transferred into a mold preheated to 100°C. The mold was cured in a blast oven at 100°C for 2 h, and then cured at 150°C for 3 h, to obtain a flame-retardant epoxy resin.

[0074] When the mass percentage content of the THAMP-1 in the above-mentioned epoxy resin reaction system was 2 wt.%, and the mass percentage content of the 4,4’-diaminodiphenyl methane in the above-mentioned epoxy resin reaction system was 19.58 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-1(2 wt.%). The flame-retardant properties of the obtained transparent flame-retardant epoxy resin were shown in Table 3, and the mechanical properties were shown in Table 4.

[0075] When the mass percentage content of the THAMP-1 in the above-mentioned epoxy resin reaction system was 4 wt.%, and the mass percentage content of the 4,4’-diaminodiphenyl methane in the above-mentioned epoxy resin reaction system was 18.99 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-1(4 wt.%). The flame-retardant properties of the obtained transparent flame-retardant epoxy resin were shown in Table 3, and the mechanical properties were shown in Table 4.

[0076] Table 3

[0077]

[0078] In Table 3, the limiting oxygen index standard: ASTM D2863, the sample size: 130 x 6.5 x 3 mm 3 . Vertical burning test standard: ASTM D3801, sample size: 130 x 13 x 3 mm 3 .

[0079] The results of the mechanical property tests of EP, EP / THAMP-1 (2 wt.%), and EP / THAMP-1 (4 wt.%) are shown in Table 2.

[0080] Mechanical properties: The test standards are ASTM D638 and ASTM D790.

[0081] Table 4

[0082]

[0083] Example 3

[0084] A method for synthesizing a nitrogen-rich DOPO-based flame retardant is as follows:

[0085] Into a 500 mL four-necked flask, 16.09 g of 5-nitro-2-thiophenecarboxaldehyde and 17.85 g of 5-amino tetrazole were added, and 200 mL of anhydrous ethanol was added to the four-necked flask as a solvent. The mixture was stirred and heated to 80°C, and constant temperature reaction was carried out for 8 h. After sampling analysis showed that the 5-nitro-2-thiophenecarboxaldehyde was completely converted, 45 g of DOPO was added to the reaction system, and constant temperature stirring reaction was carried out for 12 h. After the reaction liquid was cooled and the solid product was completely precipitated, it was filtered and washed with anhydrous ethanol for 3 times. The obtained solid product was vacuum dried at 80°C for 24 h to obtain a nitrogen-rich DOPO-based flame retardant, which is recorded as THAMP-2, with a yield of 85.23%.

[0086] Specific application

[0087] The epoxy resin was heated to 160°C, and then the THAMP-2 obtained in Example 3 was added. The mixture was stirred until the THAMP-2 was completely dissolved in the epoxy resin. Then, constant temperature stirring was carried out for 8 min. After that, the temperature was lowered to 90°C, and 4,4'-diaminodiphenylmethane was added while stirring. The mixture was stirred until the 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. Then, the mixture was quickly transferred to a mold preheated to 100°C. The mixture was cured in a blast oven at 100°C for 2 h, and then cured at 150°C for 3 h to obtain a flame-retardant epoxy resin.

[0088] When the mass percentage content of THAMP-2 in the above epoxy resin reaction system was 2 wt.% and the mass percentage content of 4,4'-diaminodiphenylmethane in the above epoxy resin reaction system was 19.59 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-2 (2 wt.%). The flame-retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 5, and the mechanical properties are shown in Table 6.

[0089] When the mass percentage of THAMP-2 in the above-mentioned epoxy resin reaction system is 4wt.%, and the mass percentage of 4,4'-diaminodiphenyl methane in the above-mentioned epoxy resin reaction system is 19.01wt.%, the flame-retardant epoxy resin is recorded as EP / THAMP-2(4wt.%), and the flame-retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 5, and the mechanical properties are shown in Table 6.

[0090] Table 5

[0091]

[0092] In Table 5, the limiting oxygen index standard is ASTM D2863, and the sample size is 130x6.5x3mm. 3 The vertical burning test standard is ASTM D3801, and the sample size is 130x13x3mm. 3 .

[0093] The mechanical properties are tested according to the standards of ASTM D638 and ASTM D790.

[0094] Table 6

[0095]

[0096] Example 4

[0097] A synthesis method of the nitrogen-rich DOPO-based flame retardant is as follows:

[0098] Into a 500mL four-necked flask, 16.09g of 5-methyl-2-thiophenecarboxaldehyde and 17.85g of 5-aminotetrazole were added, and 200mL of anhydrous ethanol was added as a solvent into the four-necked flask, and the mixture was stirred and heated to 80℃, and then the reaction was carried out at constant temperature for 8h, and the sample was analyzed in the middle control, and after the complete conversion of 5-methyl-2-thiophenecarboxaldehyde, 45g of DOPO was added into the system; the reaction was carried out at constant temperature for 12h, and then the reaction liquid was cooled to room temperature, and the solid product was filtered, and washed with anhydrous ethanol for 3 times, and the obtained solid product was dried at 80℃ under vacuum for 24h, to obtain the nitrogen-rich DOPO-based flame retardant, recorded as THAMP-3, with a yield of 82.23%.

[0099] Specific application

[0100] The epoxy resin was heated to 160°C, then THAMP-3 obtained in Example 4 was added, stirred until THAMP-3 was completely dissolved in the epoxy resin, then constant temperature stirring was carried out for 8 min, then cooled to 90°C, 4,4'-diaminodiphenyl methane was added while stirring, stirred until 4,4'-diaminodiphenyl methane was completely dissolved in the reaction system, then quickly transferred to a mold preheated to 100°C, cured in a forced air oven at 100°C for 2 h, then cured at 150°C for 3 h, to obtain a flame-retardant epoxy resin.

[0101] When the mass percentage content of THAMP-3 in the above-mentioned epoxy resin reaction system was 2 wt.%, and the mass percentage content of 4,4'-diaminodiphenyl methane in the above-mentioned epoxy resin reaction system was 19.58 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-3(2 wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin were as shown in Table 7, and the mechanical properties were as shown in Table 8.

[0102] When the mass percentage content of THAMP-3 in the above-mentioned epoxy resin reaction system was 4 wt.%, and the mass percentage content of 4,4'-diaminodiphenyl methane in the above-mentioned epoxy resin reaction system was 18.98 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-3(4 wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin were as shown in Table 7, and the mechanical properties were as shown in Table 8.

[0103] Table 7

[0104]

[0105] In Table 7, the limiting oxygen index standard: ASTM D2863, the sample size: 130 x 6.5 x 3 mm 3 .

[0106] The vertical burning test standard: ASTM D3801, the sample size: 130 x 13 x 3 mm 3 .

[0107] Mechanical properties: test standards are ASTM D638 and ASTM D790.

[0108] Table 8

[0109]

[0110] Example 5

[0111] A synthesis method of a nitrogen-rich DOPO-based flame retardant is as follows:

[0112] Into a 500 mL four-necked flask, 20.72 g of 5-dimethylamino-2-thiophenecarboxaldehyde and 17.85 g of 5-amino-tetrazole were added, and 200 mL of anhydrous ethanol was added as a solvent into the four-necked flask, and the temperature was raised to 80°C under stirring, and the reaction was kept at constant temperature for 8 h. After the 5-dimethylamino-2-thiophenecarboxaldehyde was completely converted, 45 g of DOPO was added into the system, and the reaction was kept at constant temperature for 12 h under stirring. After the solid product in the reaction liquid was completely precipitated, it was filtered, and washed with anhydrous ethanol for 3 times. The obtained solid product was dried at 80°C under vacuum for 24 h, to obtain a nitrogen-rich DOPO-based flame retardant, which was recorded as THAMP-4, and the yield was 80.58%.

[0113] Specific application

[0114] The epoxy resin was heated to 160°C, and then the THAMP-4 obtained in Example 5 was added. After the THAMP-4 was completely dissolved in the epoxy resin under stirring, the temperature was kept constant for 8 min under stirring. Then, the temperature was lowered to 90°C, and 4,4’-diaminodiphenylmethane was added under stirring. After the 4,4’-diaminodiphenylmethane was completely dissolved in the reaction system, it was quickly transferred into a mold preheated to 100°C, and cured at 100°C for 2 h in a blast oven, and then cured at 150°C for 3 h, to obtain a flame-retardant epoxy resin.

[0115] When the mass percentage content of the THAMP-4 in the above-mentioned epoxy resin reaction system was 2 wt.%, and the mass percentage content of the 4,4’-diaminodiphenylmethane in the above-mentioned epoxy resin reaction system was 19.59 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-4(2 wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin were shown in Table 9, and the mechanical properties were shown in Table 10.

[0116] When the mass percentage content of the THAMP-4 in the above-mentioned epoxy resin reaction system was 4 wt.%, and the mass percentage content of the 4,4’-diaminodiphenylmethane in the above-mentioned epoxy resin reaction system was 19.01 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-4(4 wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin were shown in Table 9, and the mechanical properties were shown in Table 10.

[0117] Table 9

[0118]

[0119] In Table 9, the limiting oxygen index standard: ASTM D2863, the sample size: 130 x 6.5 x 3 mm 3 . Vertical burning test standard: ASTM D3801, sample size: 130 x 13 x 3 mm 3 .

[0120] Mechanical properties: test standards are ASTM D638 and ASTM D790.

[0121] Table 10

[0122]

[0123] Example 6

[0124] A method for synthesizing a nitrogen-rich DOPO-based flame retardant is as follows:

[0125] Into a 500 mL four-necked flask, 20.39 g of 5-acetyloxy-2-thiophenecarboxaldehyde and 17.85 g of 5-amino tetrazole were added, and 200 mL of anhydrous ethanol was added to the four-necked flask as a solvent, and the temperature was raised to 80°C under stirring, and constant temperature reaction was carried out for 8 h, and after the complete conversion of 5-dimethylamino-2-thiophenecarboxaldehyde, 45 g of DOPO was added to the system, and constant temperature stirring reaction was carried out for 12 h, and then the reaction liquid was cooled to room temperature, and the solid product was filtered, and washed with anhydrous ethanol for 3 times, and the obtained solid product was vacuum dried at 80°C for 24 h, to obtain a nitrogen-rich DOPO-based flame retardant, which is recorded as THAMP-5, and the yield is 80.58%.

[0126] Specific application

[0127] The epoxy resin was heated to 160°C, and then THAMP-5 obtained in Example 5 was added, and stirred until THAMP-5 was completely dissolved in the epoxy resin, and then constant temperature stirring was carried out for 8 min, and then the temperature was lowered to 90°C, and 4,4'-diaminodiphenylmethane was added under stirring, and stirred until 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system, and then quickly transferred to a mold preheated to 100°C, and cured in a blast oven at 100°C for 2 h, and then cured at 150°C for 3 h, to obtain a flame-retardant epoxy resin.

[0128] When the mass percentage content of THAMP-5 in the above-mentioned epoxy resin reaction system is 2 wt.%, and the mass percentage content of 4,4'-diaminodiphenylmethane in the above-mentioned epoxy resin reaction system is 19.41 wt.%, the flame-retardant epoxy resin is recorded as EP / THAMP-5(2 wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin are shown in Table 9, and the mechanical properties are shown in Table 10.

[0129] When the mass percentage content of THAMP-5 in the above-mentioned epoxy resin reaction system is 4 wt.%, and the mass percentage content of 4,4'-diaminodiphenylmethane in the above-mentioned epoxy resin reaction system is 19.00 wt.%, the flame-retardant epoxy resin is recorded as EP / THAMP-4(4 wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin are shown in Table 11, and the mechanical properties are shown in Table 12.

[0130] Table 11

[0131]

[0132] In Table 11, the limiting oxygen index standard: ASTM D2863, sample size: 130 x 6.5 x 3mm 3 . Vertical burning test standard: ASTM D3801, sample size: 130 x 13 x 3mm 3 .

[0133] Mechanical properties: test standards are ASTM D638 and ASTM D790.

[0134] Table 12

[0135]

[0136] Example 7

[0137] A method for synthesizing a nitrogen-rich DOPO-based flame retardant is as follows:

[0138] Into a 500 mL four-necked flask, 18.64 g of 5-hydroxymethyl-2-thiophenecarboxaldehyde and 17.85 g of 5-amino tetrazole were added, and 200 mL of anhydrous ethanol was added to the four-necked flask as a solvent, and the temperature was raised to 80°C under stirring, and constant temperature reaction was carried out for 8 h, and sample analysis was carried out in the middle control, and after the complete conversion of 5-dimethylamino-2-thiophenecarboxaldehyde, 45 g of DOPO was added to the system, and constant temperature stirring reaction was carried out for 12 h, and then the reaction liquid was cooled to room temperature, and the solid product was completely precipitated, and then filtration was carried out, and the solid product was washed with anhydrous ethanol for 3 times, and the obtained solid product was vacuum dried at 80°C for 24 h, and a nitrogen-rich DOPO-based flame retardant was obtained, which was recorded as THAMP-6, and the yield was 84.5%.

[0139] Specific application

[0140] The epoxy resin was heated to 160°C, and then THAMP-6 obtained in Example 5 was added, and stirring was carried out until THAMP-6 was completely dissolved in the epoxy resin, and then constant temperature stirring was carried out for 8 min, and then the temperature was lowered to 90°C, and 4,4'-diaminodiphenylmethane was added under stirring, and stirring was carried out until 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system, and then it was quickly transferred to a mold preheated to 100°C, and cured in a blast oven at 100°C for 2 h, and then cured at 150°C for 3 h, and a flame-retardant epoxy resin was obtained.

[0141] When the mass percentage content of THAMP-6 in the above-mentioned epoxy resin reaction system is 2wt.%, and the mass percentage content of 4,4'-diaminodiphenyl methane in the above-mentioned epoxy resin reaction system is 19.59wt.%, the flame-retardant epoxy resin is recorded as EP / THAMP-6(2wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin are shown in Table 9, and the mechanical properties are shown in Table 10.

[0142] When the mass percentage content of THAMP-5 in the above-mentioned epoxy resin reaction system is 4wt.%, and the mass percentage content of 4,4'-diaminodiphenyl methane in the above-mentioned epoxy resin reaction system is 19.00wt.%, the flame-retardant epoxy resin is recorded as EP / THAMP-6(4wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin are shown in Table 13, and the mechanical properties are shown in Table 14.

[0143] Table 13

[0144]

[0145] In Table 13, the limiting oxygen index standard is ASTM D2863, and the sample size is 130x6.5x3mm. 3 The vertical burning test standard is ASTM D3801, and the sample size is 130x13x3mm. 3 .

[0146] The mechanical properties are tested according to the standards of ASTM D638 and ASTM D790.

[0147] Table 14

[0148]

[0149] Example 8

[0150] A synthesis method of a nitrogen-rich DOPO-based flame retardant is as follows:

[0151] Into a 500mL four-necked flask, 24.82g of 5-formyl-2-thiophene boronic acid and 17.85g of 5-amino tetrazole are added, and 200mL of anhydrous ethanol is added as a solvent into the four-necked flask, and the temperature is increased to 80°C under stirring, and the reaction is kept at constant temperature for 8h, and after the complete conversion of 5-dimethylamino-2-thiophenecarboxaldehyde, 45g of DOPO is added into the system, and the reaction is kept at constant temperature for 12h, and then the reaction liquid is cooled to room temperature, and the solid product is filtered, and washed with anhydrous ethanol for 3 times, and the obtained solid product is vacuum dried at 80°C for 24h, to obtain a nitrogen-rich DOPO-based flame retardant, recorded as THAMP-7, and the yield is 84.5%.

[0152] Specific application

[0153] The epoxy resin was heated to 160°C, then THAMP-7 obtained in Example 5 was added, stirred until THAMP-7 was completely dissolved in the epoxy resin, then constant temperature stirring was carried out for 8 min, then cooled to 90°C, 4,4'-diaminodiphenyl methane was added while stirring, stirred until 4,4'-diaminodiphenyl methane was completely dissolved in the reaction system, then quickly transferred to a mold preheated to 100°C, cured at 100°C in a blast oven for 2 h, then cured at 150°C for 3 h, to obtain a flame-retardant epoxy resin.

[0154] When the mass percentage content of THAMP-7 in the above-mentioned epoxy resin reaction system was 2 wt.%, and the mass percentage content of 4,4'-diaminodiphenyl methane in the above-mentioned epoxy resin reaction system was 19.26 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-7(2 wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin were as shown in Table 9, and the mechanical properties were as shown in Table 10.

[0155] When the mass percentage content of THAMP-6 in the above-mentioned epoxy resin reaction system was 4 wt.%, and the mass percentage content of 4,4'-diaminodiphenyl methane in the above-mentioned epoxy resin reaction system was 18.35 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-7(4 wt.%), and the flame-retardant properties of the obtained flame-retardant epoxy resin were as shown in Table 15, and the mechanical properties were as shown in Table 16.

[0156] Table 15

[0157]

[0158] In Table 15, the limiting oxygen index standard: ASTM D2863, the sample size: 130 x 6.5 x 3 mm 3 The vertical burning test standard: ASTM D3801, the sample size: 130 x 13 x 3 mm 3 .

[0159] Mechanical properties: test standards are ASTM D638 and ASTM D790.

[0160] Table 16

[0161]

[0162] Example 9

[0163] A synthesis method of a nitrogen-rich DOPO-based flame retardant is as follows:

[0164] Into a 500 mL four-necked flask, 18.48 g of 5-methoxy-2-thiophene carboxaldehyde and 17.85 g of 5-amino tetrazole were added, and 200 mL of anhydrous ethanol was added as a solvent into the four-necked flask, and the temperature was raised to 80°C under stirring, and the reaction was kept at constant temperature for 8 h. After the 5-dimethylamino-2-thiophene carboxaldehyde was completely converted, 45 g of DOPO was added into the system, and the reaction was kept at constant temperature for 12 h under stirring. After the solid product in the reaction liquid was completely precipitated, it was filtered and washed with anhydrous ethanol for 3 times. The obtained solid product was dried at 80°C under vacuum for 24 h to obtain a nitrogen-rich DOPO-based flame retardant, which was recorded as THAMP-8, and the yield was 84.5%.

[0165] Specific application

[0166] The epoxy resin was heated to 160°C, and then the THAMP-8 obtained in Example 5 was added. After the THAMP-8 was completely dissolved in the epoxy resin, the temperature was kept constant and stirred for 8 min. Then, the temperature was lowered to 90°C, and 4,4'-diaminodiphenylmethane was added under stirring. After the 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system, it was quickly transferred to a mold preheated to 100°C, and cured at 100°C for 2 h in a blast oven, and then cured at 150°C for 3 h to obtain a flame-retardant epoxy resin.

[0167] When the mass percentage content of THAMP-8 in the above-mentioned epoxy resin reaction system was 2 wt.%, and the mass percentage content of 4,4'-diaminodiphenylmethane in the above-mentioned epoxy resin reaction system was 19.59 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-8 (2 wt.%). The flame-retardant properties of the obtained flame-retardant epoxy resin were shown in Table 9, and the mechanical properties were shown in Table 10.

[0168] When the mass percentage content of THAMP-8 in the above-mentioned epoxy resin reaction system was 4 wt.%, and the mass percentage content of 4,4'-diaminodiphenylmethane in the above-mentioned epoxy resin reaction system was 18.99 wt.%, the flame-retardant epoxy resin was recorded as EP / THAMP-8 (4 wt.%). The flame-retardant properties of the obtained flame-retardant epoxy resin were shown in Table 17, and the mechanical properties were shown in Table 18.

[0169] Table 17

[0170]

[0171] In Table 17, the limiting oxygen index standard: ASTM D2863, the sample size: 130 x 6.5 x 3 mm 3 . Vertical burning test standard: ASTM D3801, sample size: 130 x 13 x 3 mm 3 .

[0172] Mechanical properties: test standards are ASTM D638 and ASTM D790.

[0173] Table 18

[0174]

[0175]

[0176] Comparative Example 1 is the same as Example 1, except that in Comparative Example 1, 2-thiophene formaldehyde is replaced with the same molar amount of 5-(4-(diphenylamine)phenyl)thiophene-2-formaldehyde, and the reaction solvent is chloroform. The obtained flame retardant is denoted as THAMP-9. Although 5-(4-(diphenylamine)phenyl)thiophene-2-formaldehyde is also a thiophene formaldehyde derivative, THAMP-9 obtained in Comparative Example 1 cannot be completely dissolved in the epoxy resin, and the EP / THAMP-9 flame-retardant epoxy resin formed by processing exhibits an opaque state. Compared with pure EP, the flame-retardant performance and the mechanics both appear a relatively large decline. The possible reason is that the flame retardant has a large molecular structure and a large steric hindrance, and has poor compatibility with the epoxy resin, which affects its many properties. The flame-retardant performance is shown in Table 19, and the mechanical properties are shown in Table 20. The specific test results are shown in Tables 19 and 20:

[0177] Table 19

[0178]

[0179] Table 20

[0180]

[0181] Comparative Example 2 is the same as Example 1, except that in Comparative Example 2, 2-thiophene formaldehyde is replaced with the same molar amount of 5-[bis(4-methylphenyl)amino]-2-thiophene formaldehyde, and the reaction solvent used is chloroform. The obtained flame retardant is denoted as THAMP-10. THAMP-10 cannot be completely dissolved in the epoxy resin, and the EP / THAMP-10 flame-retardant epoxy resin exhibits an opaque state. Compared with pure EP, the flame-retardant performance and the mechanics both appear a relatively large decline. The flame-retardant performance is shown in Table 21, and the mechanical properties are shown in Table 22. The specific test results are as follows:

[0182] Table 21

[0183]

[0184]

[0185] Table 22

[0186]

[0187] With the above ideal embodiments according to the present application as the inspiration, through the above description, relevant staff can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims

1. A nitrogen-rich DOPO-based flame retardant, characterized by, The chemical structural formula is as follows: ， The R group in the above chemical structure is a boronic acid group.

2. The nitrogen-rich DOPO-based flame retardant according to claim 1, characterized in that, The preparation method comprises the following steps: (1) 2-thiophene formaldehyde or 2-thiophene formaldehyde derivative reacts with 5-amino tetrazole to generate a Schiff base intermediate, and the structural formula of the Schiff base intermediate is as follows: ， The R group in the above chemical structure is a boronic acid group; (2) The Schiff base intermediate reacts with DOPO to generate a nitrogen-rich DOPO-based flame retardant through phosphorus-hydrogen addition reaction.

3. The nitrogen-rich DOPO-based flame retardant according to claim 2, characterized in that, The solvent used in the reaction in step (1) is one or a combination of two or more of anhydrous ethanol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, dichloromethane, dichloroethane, chloroform, ethyl acetate, benzene, toluene, and 1,4-dioxane.

4. The nitrogen-rich DOPO-based flame retardant according to claim 2, characterized in that, The temperature of the reaction in step (1) is 40-100°C, and the reaction time is 8-12h.

5. The nitrogen-rich DOPO-based flame retardant according to claim 2, characterized in that, The molar ratio of 2-thiophene formaldehyde or 2-thiophene formaldehyde derivative to 5-amino tetrazole in step (1) is 1-1.1:

1.

6. The nitrogen-rich DOPO-based flame retardant according to claim 2, characterized in that, The molar ratio of the Schiff base intermediate to DOPO in step (2) is 1:1-1.

1.

7. The nitrogen-rich DOPO-based flame retardant according to claim 2, characterized in that, The temperature of the reaction in step (2) is 40-100°C, and the reaction time is 12-24h.

8. A flame retardant epoxy resin characterized by comprising: The nitrogen-rich DOPO-based flame retardant according to any one of claims 1-7 is used as a flame retardant additive.

9. A flame retardant epoxy resin according to claim 8, characterised in that, The preparation method comprises the following steps: (1) The epoxy resin is heated to 140-160°C, the nitrogen-rich DOPO-based flame retardant is added, and stirring is performed until the nitrogen-rich DOPO-based flame retardant is completely dissolved in the epoxy resin, and the mixture is kept at a constant temperature for 8-20min to obtain a mixed solution; (2) After the mixed solution obtained in step (1) is cooled to 90-100°C, an epoxy curing agent is added to the reaction system, constant temperature stirring is performed until the epoxy curing agent is completely dissolved, the reaction system is quickly poured into a mold preheated to a curing temperature, and heat curing is performed, thereby obtaining a flame-retardant epoxy resin.

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