Dop-based halogen-free reactive flame retardant with terminal dicarboxyl and preparation method thereof

Abstract

The application provides a terminal dicarboxyl DOPO-based halogen-free reactive flame retardant and a preparation method thereof. The flame retardant has a structure as shown in formula I: wherein -R is selected from C1-C8 alkyl, phenol group, furan group, aryl group, heteroaryl group, alkyl / alkoxy-substituted aryl group and alkyl / alkoxy-substituted phenol group; the preparation process of the flame retardant with the structure as shown in formula I is as follows: 5-amino isophthalic acid and aldehyde compounds are mixed under an inert atmosphere, then the mixture is heated, continuously stirred for a period of time, cooled, continuously stirred, DOPO is added into the mixture, the mixture is heated and stirred again to obtain the terminal dicarboxyl DOPO-based halogen-free reactive flame retardant with the structure as shown in formula I; the above scheme is simple in steps and does not generate toxic and harmful substances in the preparation process; the terminal dicarboxyl DOPO-based halogen-free reactive flame retardant prepared by using the above scheme has high flame retardant efficiency, can be combined in a polymer molecular chain through reaction, and realizes intrinsic flame retardation of the polymer.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant materials technology, specifically relating to a DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups and its preparation method. Background Technology

[0002] Traditional flame retardants are mainly classified according to the type of flame-retardant element, including halogenated flame retardants, phosphorus-based flame retardants, nitrogen-based flame retardants, silicon-based flame retardants, inorganic nanofiller flame retardants, and compound flame retardants combining multiple flame retardants. Halogenated flame retardants were widely used in the last century due to their high flame-retardant efficiency. However, halogenated flame retardants release toxic gases such as hydrogen halides during combustion, and with increasing environmental awareness, their use has gradually decreased.

[0003] Among halogen-free flame retardants, phosphorus-based and nitrogen-based flame retardants are the most widely used. Phosphorus-based flame retardants primarily function in the condensed phase. When combustion occurs, they decompose upon heating to generate free radicals, which quench the active free radicals needed for the combustion reaction chain, thus achieving flame retardancy. Furthermore, phosphorus-based flame retardants often produce phosphoric acid, which promotes the formation of a dense, non-combustible char layer on the polymer surface. This protective film prevents the exchange of matter and energy between the inside and outside of the film, achieving flame retardancy. Nitrogen-based flame retardants primarily function in the gas phase. During combustion, nitrogen-based flame retardant molecules decompose into non-combustible gases, diluting the concentration of oxygen and combustible gases on the burning surface of the material, thereby preventing combustion. Simultaneously, the free radicals generated by polymer combustion can be combined with N2, interrupting the combustion chain reaction and preventing further combustion and decomposition of the material. However, traditional additive flame retardants are added to nylon materials through blending. Phosphorus-based flame retardants have poor compatibility with polyamide materials, often leading to uneven dispersion or precipitation of the flame retardant during material use, reducing its flame-retardant effect. Therefore, developing intrinsic flame retardants has become the mainstream trend in the development of flame retardants.

[0004] DOPO is a common reactive phosphorus-based flame retardant. Its CP bond, together with biphenyl, forms a phosphaphenanthrene structure, exhibiting high thermal stability. To address this, Chinese Patent Publication No. CN105061711B describes a DOPO-type reactive flame retardant with epoxy groups at the end, its preparation method, and its applications. This flame retardant is prepared through a ring-opening addition reaction between DOPO and epoxy groups, possessing two active end groups. The synthesis process is simple and yields high results. However, its active end groups are epoxy groups and hydroxyl groups, limiting its application to intrinsic flame retardancy of polyurethanes and not to polymers such as polyamides, polyesters, and polyetheramides. Chinese Patent Application Publication No. CN106928278A introduces a novel DOPO-based flame retardant with readily available raw materials and a simple process. However, it contains a large amount of fluorine, which is not environmentally friendly and cannot achieve intrinsic flame retardancy. Furthermore, the flame retardant is prone to migration and precipitation, making long-term flame retardancy difficult to guarantee.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to address the problems in the prior art by providing a halogen-free reactive flame retardant with a terminal dicarboxyl group and DOPO group. This invention utilizes the high thermal stability of the DOPO group, and the introduced terminal dicarboxyl group is directly attached to the benzene ring. In the process of introducing the DOPO group, N atoms are introduced, which further improves the thermal stability and flame retardant performance of the flame retardant. Due to the presence of the terminal dicarboxyl group, the flame retardant can enter other molecules through reaction, thereby achieving intrinsic flame retardancy in various materials.

[0007] Another objective of this invention is to provide a method for preparing a halogen-free reactive flame retardant with a terminal dicarboxyl group DOPO, wherein the amino group on 5-aminoisophthalic acid is converted into an imine through a reaction, and then linked to the P group on the DOPO group through an imine bond; the preparation process is simple and easy to control, and no toxic or harmful substances are generated during the reaction, thus ensuring high safety.

[0008] To achieve the above objectives, the first aspect of the present invention provides a DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group, the structure of which is shown in Formula I:

[0009]

[0010] Wherein, -R is selected from one of the following C1-C8 alkyl, phenolic, furanyl, aryl, heteroaryl, alkyl / alkoxy-substituted aryl, and alkyl / alkoxy-substituted phenolic groups.

[0011] Preferably, -R is selected from phenolic, furanyl, aryl, heteroaryl, alkyl / alkoxy-substituted aryl, and alkyl / alkoxy-substituted phenolic.

[0012] More preferably, -R is selected from Where X is C1-C 10 Alkyl groups.

[0013] In a further preferred embodiment, X is methyl.

[0014] In the above scheme, the presence of the DOPO group gives the flame retardant excellent flame retardant properties. At the same time, due to the presence of the dicarboxyl group, the flame retardant molecule does not simply achieve flame retardant modification of the material through mixing, but enters the molecule through reaction to achieve intrinsic flame retardancy of the material, effectively avoiding compatibility issues and ensuring stable performance of flame retardant properties.

[0015] Furthermore, the flame retardant molecule is prepared by an addition reaction of DOPO with an imine bond on an amine compound having the structure shown in Formula II;

[0016]

[0017] Wherein, -R is selected from one of the following C1-C8 alkyl, phenolic, furanyl, aryl, heteroaryl, alkyl / alkoxy-substituted aryl, and alkyl / alkoxy-substituted phenolic groups.

[0018] Preferably, -R is selected from phenolic, furanyl, aryl, heteroaryl, alkyl / alkoxy-substituted aryl, and alkyl / alkoxy-substituted phenolic.

[0019] More preferably, -R is selected from Where X is C1-C 10 Alkyl groups.

[0020] In a further preferred embodiment, X is methyl.

[0021] In the above scheme, since DOPO is linked by an addition reaction with an imine bond, it ensures that only two carboxyl groups participate in the reaction during use, making the flame retardant molecule as a whole stable and preventing the flame retardant performance from being affected by incorrect reaction sites.

[0022] Furthermore, amine compounds with the structure shown in Formula II are prepared by a Schiff base reaction between the amino group on 5-aminoisophthalic acid and the aldehyde group of an aldehyde compound. The structure of the aldehyde compound is shown in Formula III.

[0023]

[0024] Wherein, -R is selected from one of the following C1-C8 alkyl, phenolic, furanyl, aryl, heteroaryl, alkyl / alkoxy-substituted aryl, and alkyl / alkoxy-substituted phenolic groups.

[0025] Preferably, -R is selected from phenolic, furanyl, aryl, heteroaryl, alkyl / alkoxy-substituted aryl, and alkyl / alkoxy-substituted phenolic.

[0026] More preferably, -R is selected from Where X is C1-C 10 Alkyl groups.

[0027] In a further preferred embodiment, X is methyl.

[0028] A second aspect of the present invention provides a method for preparing the above-mentioned DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group, comprising the following steps:

[0029] S1. Under an inert atmosphere, a solution of 5-aminoisophthalic acid and a solution of an aldehyde compound having the structure shown in Formula III are mixed and reacted at a preset temperature to obtain a mixture.

[0030] S2. Add DOPO to the mixture obtained in step S1 and react to obtain a DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group as shown in Formula I.

[0031] The specific synthesis route is as follows:

[0032]

[0033] Furthermore, step S1 specifically includes:

[0034] Under an inert atmosphere, a solution of 5-aminoisophthalic acid and a solution of an aldehyde compound having the structure shown in Formula III are mixed, heated to a preset first temperature and stirred continuously, and then cooled to a preset second temperature and stirred continuously.

[0035] Preferably, the solvents for the 5-aminoisophthalic acid solution and the aldehyde compound solution in step S1 are selected from at least one of anhydrous ethanol, diethyl ether, acetone, and ethyl acetate.

[0036] Furthermore, in step S1, the preset first temperature is 5-20°C higher than the boiling point of the solvent; the preset second temperature is 10-50°C lower than the boiling point of the solvent.

[0037] Preferably, the reaction time is 1-5 hours at a preset first temperature and 5-9 hours at a preset second temperature.

[0038] The above scheme controls the reaction process by first raising the temperature to above the boiling point of the solvent and then lowering it to below the boiling point of the solvent. This ensures the reaction rate while reducing side reactions by lowering the temperature in the later stage, thereby increasing the yield. Limiting the reaction time ensures that the reaction can proceed fully, further improving the yield.

[0039] Furthermore, in step S2, the reaction temperature is 5-20°C higher than the boiling point of the solvent.

[0040] By controlling the reaction temperature to be higher than the boiling point of the solvent, DOPO-based halogen-free reactive flame retardants with terminal dicarboxyl groups can be synthesized with higher efficiency.

[0041] Preferably, the reaction time is 1-8 hours.

[0042] Furthermore, in the mixture of step S1, the molar ratio of 5-aminoisophthalic acid to aldehyde compounds is 1:(0.5-2).

[0043] Furthermore, in step S2, the molar ratio of DOPO to the amine compounds in the mixture is (0.5-2):1.

[0044] The present invention also provides the application of the DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups prepared by the above preparation method, specifically, as an intrinsic polyamide flame retardant.

[0045] Furthermore, the process for preparing flame-retardant polyamide using a DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups is as follows:

[0046] S1. A flame retardant salt is prepared by mixing a DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group having the structure shown in Formula I with hexamethylenediamine.

[0047] S2. The flame retardant salt and nylon 66 salt are mixed and polymerized to obtain DOPO-based halogen-free intrinsic flame retardant nylon 66.

[0048] The molar ratio of nylon 66 salt to flame retardant salt is (90-99):(10-1).

[0049] Preferably, the molar ratio of nylon 66 salt to flame retardant salt is (94-96):(6-4).

[0050] The beneficial effects of this invention are as follows:

[0051] 1. The DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group as shown in Formula I contains a DOPO group. The DOPO group is connected to an imine group through a C=N bond, which facilitates preparation and introduces N atoms. In addition, the DOPO molecule has CP bonds, which have excellent flame retardant properties and stability. Furthermore, this flame retardant does not contain halogens and meets environmental protection requirements.

[0052] 2. The preparation steps of the DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups provided by the present invention are simple, the reaction conditions are easy to achieve, and it is easy to promote industrialization. Moreover, no toxic or harmful substances are generated during the preparation process, and the production safety is high.

[0053] 3. DOPO-based halogen-free reactive flame retardants with terminal dicarboxyl groups as shown in Formula I can enter the molecular chains of other materials through the two carboxyl groups, thereby achieving intrinsic flame retardancy without the problem of poor compatibility. In actual use, they can react with other molecules with active end groups to change the type of active end groups, so as to adapt to the molecular chains of different materials. Furthermore, although the two terminal carboxyl groups are directly connected to the benzene ring, they can further improve the flame retardant performance, although they have some impact on the polymerization performance of the flame retardant. Attached Figure Description

[0054] Figure 1 The halogen-free reactive flame retardant with terminal dicarboxyl groups and DOPO group prepared in Example 1 of this invention. 1 H-NMR spectrum.

[0055] Figure 2 The image shows the TGA diagram of the DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups prepared in Example 1 of this invention and DOPO.

[0056] In the picture:

[0057] BADO represents a DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group having the structure shown in Formula I, prepared by the method described in this invention. Detailed Implementation

[0058] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. Those skilled in the art will understand that the following embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0059] It should be noted first that, in the experimental examples section of the specific implementation method, the performance testing methods for the DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups and the flame retardant copolymer prepared using the flame retardant of the present invention are as follows:

[0060] Limiting Oxygen Index (LOI) testing was conducted according to ASTM D 2863 on a Fire Testing Technology instrument (FTT, West Sussex, UK). The sample size was 80.0 × 10.0 × 4.0 mm. 3 .

[0061] The UL-94 vertical burning test was conducted according to ASTM D 3801 on a CZF-5 instrument (Jiangning Analytical Instruments Co., Ltd., Jiangning, China). The specimen size was 80.0 × 13.0 × 3.2 mm. 3 .

[0062] Tensile properties were tested using a tensile testing machine (Instron 3365). Test samples with a thickness of approximately 0.5-0.8 mm were cut into dumbbell shapes. The test conditions for all samples were as follows: strain rate of 100 mm / min, spacing of 4 mm, testing at room temperature, and relative humidity of 60 ± 3%. Each sample was tested five times, and the average value was taken as the final test result for the sample.

[0063] Impact performance was tested using an impact testing machine (XJC-25D); cantilever beam notched impact test, test temperature 23℃, relative humidity 60±3%, according to standard GB1043-2008.

[0064] The melt flow index was tested on a melt flow meter according to ISO 1133; the sample mass was 6g and the test temperature was 230℃.

[0065] This invention provides a halogen-free reactive flame retardant with a terminal dicarboxyl group and a DOPO-based structure, the structure of which is shown in Formula I:

[0066]

[0067] Wherein, -R is selected from one of C1-C8 alkyl, phenolic, furanyl, aryl, heteroaryl, alkyl / alkoxy-substituted aryl, and alkyl / alkoxy-substituted phenolic groups;

[0068] Preferably, -R is selected from one of phenolic, furanyl, aryl, heteroaryl, alkyl / alkoxy-substituted aryl, and alkyl / alkoxy-substituted phenolic groups;

[0069] More preferably, -R is selected from Where X is C1-C 10 Alkyl groups;

[0070] In a further preferred embodiment, X is methyl.

[0071] The present invention will now be described in further detail with reference to specific embodiments.

[0072] Example 1

[0073] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 13.11 g (0.1 mol) of benzaldehyde were added to 250 mL beakers respectively, and 150 mL of anhydrous ethanol was added to each beaker. The mixtures were stirred thoroughly to dissolve the solids.

[0074] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, slowly heated to 85 °C, and stirred at 200 rpm for 2 h.

[0075] The solution was cooled to 50°C under a nitrogen atmosphere and stirred at 200 rpm for 8 hours.

[0076] After the reaction was complete, 21.62 g (0.1 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 5 h.

[0077] After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. Then, it was dried in a vacuum oven at 60 °C for 24 h to obtain 44.23 g of DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, with a yield of 87%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is phenyl.

[0078] The NMR results of the DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups prepared in this embodiment are as follows: Figure 1 As shown, the results are as follows:

[0079] 1 H-NMR (400MHz, DMSO-d6, 25℃) δ12.87(s,2H),8.20(d,J=8Hz,1H),8.16(t,J=8Hz,1H),7.95(t,J=12Hz,1H),7.76(t,J=12Hz,1H),7.6 4(s,1H),7.54(t,J=12Hz,1H),7.45(s,2H),7.43-7.40(d,t,J=12Hz,3H),7.35-7.20(d,t,5H),7.04(d,J=8Hz,1H),5.32(d,J=8,1H).

[0080] Figure 2 The figures show the halogen-free reactive flame retardant with terminal dicarboxyl groups (DOPO) prepared in this embodiment and its thermogravimetric analysis (TGA) curve. It can be seen that under N2 atmosphere, the decomposition temperature of DOPO is below 260°C, which cannot meet the polymerization process requirements of PA66. In contrast, the initial decomposition temperature (T0) of the halogen-free reactive flame retardant with terminal dicarboxyl groups (DOPO) prepared in this embodiment in N2 is significantly higher. 5％ The polymerization temperature was 287℃. Therefore, the DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups can meet the polymerization conditions of PA66. Furthermore, the residual amount of the DOPO-based halogen-free reactive flame retardant at 800℃ (50.4%) is much higher than that of DOPO (0.3%), indicating that the DOPO-based halogen-free reactive flame retardant has a much greater char-forming effect than DOPO, which is more conducive to improving the flame retardant effect.

[0081] Example 2

[0082] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 2.91 g (0.05 mol) of propionaldehyde were added to 250 mL beakers, and 150 mL of anhydrous ethanol and 50 mL of diethyl ether were added to each beaker, and the mixture was stirred thoroughly to dissolve.

[0083] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, slowly heated to 50 °C, and stirred at a stirring rate of 200 rpm for 1 h.

[0084] The solution was cooled to 25°C under a nitrogen atmosphere and stirred at 200 rpm for 9 hours.

[0085] After the reaction was complete, 10.81 g (0.05 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 50 °C and refluxed for 1 h.

[0086] After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. Then, it was dried in a vacuum oven at 60 °C for 24 h to obtain 9.56 g of white powder of DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, with a yield of 44%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is ethyl.

[0087] Example 3

[0088] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 7.11 g (0.05 mol) of nonanal were added to 250 mL beakers respectively, and 150 mL of anhydrous ethanol was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0089] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, and the mixture was slowly heated to 85 °C and stirred at 200 rpm for 1 h.

[0090] The solution was cooled to 50°C under a nitrogen atmosphere and stirred at 200 rpm for 9 hours.

[0091] After the reaction was complete, 10.81 g (0.05 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 3 h.

[0092] After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. Then, it was dried in a vacuum oven at 60 °C for 24 h to obtain 17.02 g of white powder of DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, with a yield of 65%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is octyl.

[0093] Example 4

[0094] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 6.11 g (0.05 mol) of m-hydroxybenzaldehyde were added to 250 mL beakers respectively, and 150 mL of acetone was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0095] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, and the mixture was slowly heated to 75 °C and stirred at 200 rpm for 5 h.

[0096] The solution was cooled to 40°C under a nitrogen atmosphere and stirred at 200 rpm for 5 hours.

[0097] After the reaction was complete, 10.81 g (0.05 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 75 °C and refluxed for 5 h.

[0098] After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. Then, it was dried in a vacuum oven at 60 °C for 24 h to obtain 19.88 g of white powder of DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, with a yield of 79%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is phenol.

[0099] Example 5

[0100] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 5.35 g (0.05 mol) of 3-pyridinecarboxaldehyde were added to 250 mL beakers respectively, and 150 mL of ethyl acetate was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0101] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, and the mixture was slowly heated to 85 °C and stirred at 200 rpm for 3 h.

[0102] The solution was cooled to 50°C under a nitrogen atmosphere and stirred at 200 rpm for 7 hours.

[0103] After the reaction was complete, 10.81 g (0.05 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 8 h.

[0104] After the reaction was completed and cooled to room temperature, the mixture was filtered and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. This powder was then dried in a vacuum oven at 60 °C for 24 h to obtain 17.54 g of a DOPO-based halogen-free reactive flame retardant powder with terminal dicarboxyl groups, yielding 72%. In this example, the flame retardant with the structure shown in Formula I has an R group of...

[0105] Example 6

[0106] At room temperature, 9.06 g (0.05 mol) of 5-aminoisophthalic acid and 13.61 g (0.1 mol) of p-methoxybenzaldehyde were added to 250 mL beakers respectively, and 150 mL of acetone was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0107] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, and the mixture was slowly heated to 75 °C and stirred at 200 rpm for 1 h.

[0108] The solution was cooled to 40°C under a nitrogen atmosphere and stirred at 200 rpm for 9 hours.

[0109] After the reaction was complete, 21.62 g (0.1 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 75 °C and refluxed for 6 h.

[0110] After the reaction was completed and cooled to room temperature, the mixture was filtered and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. This powder was then dried in a vacuum oven at 60 °C for 24 h to obtain 20.18 g of a DOPO-based halogen-free reactive flame retardant powder with terminal dicarboxyl groups, yielding 78%. In this example, the flame retardant with the structure shown in Formula I has an R group of...

[0111] Example 7

[0112] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 7.61 g (0.05 mol) of 3-methoxy-4-hydroxybenzaldehyde were added to 250 mL beakers respectively, and 150 mL of anhydrous ethanol was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0113] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, and the mixture was slowly heated to 85 °C and stirred at 200 rpm for 2 h.

[0114] The solution was cooled to 50°C under a nitrogen atmosphere and stirred at 200 rpm for 8 hours.

[0115] After the reaction was complete, 10.81 g (0.05 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 5 h.

[0116] After the reaction was completed and cooled to room temperature, the mixture was filtered and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. This powder was then dried in a vacuum oven at 60 °C for 24 h to obtain 21.55 g of a DOPO-based halogen-free reactive flame retardant powder with terminal dicarboxyl groups, yielding 81%. In this example, the flame retardant with the structure shown in Formula I has an R group of...

[0117] Example 8

[0118] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 4.80 g (0.05 mol) of furfural were added to 250 mL beakers respectively, and 150 mL of anhydrous ethanol was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0119] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, and the mixture was slowly heated to 85 °C and stirred at 200 rpm for 5 h.

[0120] The solution was cooled to 50°C under a nitrogen atmosphere and stirred at 200 rpm for 5 hours.

[0121] After the reaction was complete, 10.81 g (0.5 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 4 h.

[0122] After the reaction was completed and cooled to room temperature, the mixture was filtered and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. This powder was then dried in a vacuum oven at 60 °C for 24 h to obtain 11.61 g of a DOPO-based halogen-free reactive flame retardant powder with terminal dicarboxyl groups, yielding 49%. In this example, the flame retardant with the structure shown in Formula I has an R group of...

[0123] Example 9

[0124] The R group of the DOPO-based halogen-free reactive flame retardant is selected as... Synthesize flame-retardant PA66.

[0125] DOPO-based halogen-free reactive flame retardant and hexamethylenediamine were mixed at a molar ratio of 1:1.2, dissolved in DMSO, heated to 50°C under nitrogen protection, kept at that temperature for 30 min and continuously stirred at a stirring speed of 50 rpm, then cooled and filtered to obtain the flame retardant salt.

[0126] By molar amount, 96% of hexamethylenediamine adipic acid salt and 4% of flame retardant salt were mixed and added to a 500 mL four-necked flask with a flange. The mixture was heated to 260 °C under a nitrogen atmosphere and stirred at 100 rpm for 1 h.

[0127] Reduce the stirring speed to 50 rpm, stop the nitrogen flow, evacuate to a pressure below 100 Pa, and heat to 265°C for 30 minutes.

[0128] Stop heating and stirring, resume nitrogen flow, let stand for 30 minutes to cool to room temperature, open the flange valve to discharge the material, and obtain a copolymer containing 4% flame retardant molar fraction.

[0129] Example 10

[0130] The R group of the DOPO-based halogen-free reactive flame retardant is selected as... Synthesize flame-retardant PA66.

[0131] DOPO-based halogen-free reactive flame retardant and hexamethylenediamine were mixed at a molar ratio of 1:1.2, dissolved in DMSO, heated to 50°C under nitrogen protection, kept at that temperature for 30 min and continuously stirred at a stirring speed of 50 rpm, then cooled and filtered to obtain the flame retardant salt.

[0132] By molar amount, 94% of hexamethylenediamine adipic acid salt and 6% of flame retardant salt were mixed and added to a 500 mL four-necked flask with a flange. The mixture was heated to 260 °C under a nitrogen atmosphere and stirred at 100 rpm for 1 h.

[0133] Reduce the stirring speed to 50 rpm, stop the nitrogen flow, evacuate to a pressure below 100 Pa, and heat to 265°C for 30 minutes.

[0134] Stop heating and stirring, resume nitrogen flow, let stand for 30 minutes to cool to room temperature, open the flange valve to discharge the material, and obtain a copolymer containing 6% flame retardant molar amount.

[0135] Example 11

[0136] The R group of the DOPO-based halogen-free reactive flame retardant is selected as... Synthesize flame-retardant PA66.

[0137] DOPO-based halogen-free reactive flame retardant and hexamethylenediamine were mixed at a molar ratio of 1:1.2, dissolved in DMSO, heated to 30°C under nitrogen protection, kept at this temperature for 2 hours with continuous stirring at a stirring speed of 100 rpm, and then cooled and filtered to obtain the flame retardant salt.

[0138] By molar ratio, 95% of hexamethylenediamine adipic acid salt and 5% of flame retardant salt were mixed and added to a 500 mL four-necked flask with a flange. The mixture was heated to 250 °C under a nitrogen atmosphere and stirred at 100 rpm for 2 h.

[0139] Reduce the stirring speed to 50 rpm, stop the nitrogen flow, evacuate to a pressure less than 100 Pa, and heat to 260°C for 10 minutes.

[0140] Stop heating and stirring, resume nitrogen flow, let stand for 30 minutes to cool to room temperature, open the flange valve to discharge the material, and obtain a copolymer containing 5% flame retardant molar fraction.

[0141] Example 12

[0142] The R group of the DOPO-based halogen-free reactive flame retardant is selected as...

[0143] DOPO-based halogen-free reactive flame retardant and hexamethylenediamine were mixed at a molar ratio of 1:1.2, dissolved in DMSO, heated to 50°C under nitrogen protection, kept at that temperature for 30 min and continuously stirred at a stirring speed of 50 rpm, then cooled and filtered to obtain the flame retardant salt.

[0144] By molar ratio, 90% of hexamethylenediamine adipic acid salt and 10% of flame retardant salt were mixed and added to a 500 mL four-necked flask with a flange. The mixture was heated to 240 °C under a nitrogen atmosphere and stirred at 100 rpm for 2 h.

[0145] Reduce the stirring speed to 50 rpm, stop the nitrogen flow, evacuate to a pressure below 100 Pa, and heat to 250°C for 10 minutes.

[0146] Stop heating and stirring, resume nitrogen flow, let stand for 30 minutes to cool to room temperature, open the flange valve to discharge the material, and obtain a copolymer containing 10% flame retardant molar fraction.

[0147] Example 13

[0148] The R group of the DOPO-based halogen-free reactive flame retardant is selected as...

[0149] DOPO-based halogen-free reactive flame retardant and hexamethylenediamine were mixed at a molar ratio of 1:1.2, dissolved in DMSO, heated to 30°C under nitrogen protection, kept at this temperature for 2 hours with continuous stirring at a stirring speed of 100 rpm, and then cooled and filtered to obtain the flame retardant salt.

[0150] On a molar basis, 99% of hexamethylenediamine adipic acid salt and 1% of flame retardant salt were mixed and added to a 500 mL four-necked flask with a flange. The mixture was heated to 260 °C under a nitrogen atmosphere and stirred at 100 rpm for 2 h.

[0151] Reduce the stirring speed to 50 rpm, stop the nitrogen flow, evacuate to a pressure less than 100 Pa, and heat to 270℃ and hold for 30 min.

[0152] Stop heating and stirring, resume nitrogen flow, let stand for 30 minutes to cool to room temperature, open the flange valve to discharge the material, and obtain a copolymer containing 1% flame retardant molar amount.

[0153] Example 14

[0154] The R group of the DOPO-based halogen-free reactive flame retardant is selected as...

[0155] DOPO-based halogen-free reactive flame retardant and hexamethylenediamine were mixed at a molar ratio of 1:1.2, dissolved in DMSO, heated to 80°C under nitrogen protection, held at that temperature for 60 min with continuous stirring at a stirring speed of 50 rpm, cooled and filtered to obtain the flame retardant salt.

[0156] On a molar basis, 98% of hexamethylenediamine adipic acid salt and 2% of flame retardant salt were mixed and added to a 500 mL four-necked flask with a flange. The mixture was heated to 260 °C under a nitrogen atmosphere and stirred at 100 rpm for 1 h.

[0157] Reduce the stirring speed to 50 rpm, stop the nitrogen flow, evacuate to a pressure less than 100 Pa, and heat to 270℃ and hold for 20 min.

[0158] Stop heating and stirring, resume nitrogen flow, let stand for 30 minutes to cool to room temperature, open the flange valve to discharge the material, and obtain a copolymer containing 2% flame retardant molar fraction.

[0159] Example 15

[0160] The R group of the DOPO-based halogen-free reactive flame retardant is -CH2-CH3.

[0161] DOPO-based halogen-free reactive flame retardant and hexamethylenediamine were mixed at a molar ratio of 1:1.2, dissolved in DMSO, heated to 40°C under nitrogen protection, kept at this temperature for 2 hours with continuous stirring at a stirring speed of 100 rpm, and then cooled and filtered to obtain the flame retardant salt.

[0162] On a molar basis, 94 mol% of hexamethylenediamine adipic acid salt and 6 mol% of flame retardant salt were mixed and added to a 500 mL four-necked flask with a flange. The mixture was heated to 245 °C under a nitrogen atmosphere and stirred at 100 rpm for 2 h.

[0163] Reduce the stirring speed to 50 rpm, stop the nitrogen flow, evacuate to a pressure of less than 100 Pa, and heat to 255°C for 10 minutes.

[0164] Stop heating and stirring, resume nitrogen flow, let stand for 30 minutes to cool to room temperature, open the flange valve to discharge the material, and obtain a copolymer containing 6 mol% flame retardant.

[0165] Example 16

[0166] The R group of the DOPO-based halogen-free reactive flame retardant is selected as...

[0167] DOPO-based halogen-free reactive flame retardant and hexamethylenediamine were mixed at a molar ratio of 1:1.2, dissolved in DMSO, heated to 60°C under nitrogen protection, kept at this temperature for 2 hours with continuous stirring at a stirring speed of 100 rpm, and then cooled and filtered to obtain the flame retardant salt.

[0168] On a molar basis, 94 mol% of hexamethylenediamine adipic acid salt and 6 mol% of flame retardant salt were mixed and added to a 500 mL four-necked flask with a flange. The mixture was heated to 245 °C under a nitrogen atmosphere and stirred at 100 rpm for 2 h.

[0169] Reduce the stirring speed to 50 rpm, stop the nitrogen flow, evacuate to a pressure of less than 100 Pa, and heat to 255°C for 10 minutes.

[0170] Stop heating and stirring, resume nitrogen flow, let stand for 30 minutes to cool to room temperature, open the flange valve to discharge the material, and obtain a copolymer containing 6 mol% flame retardant.

[0171] Example 17

[0172] The R group of the DOPO-based halogen-free reactive flame retardant is selected as...

[0173] DOPO-based halogen-free reactive flame retardant and hexamethylenediamine were mixed at a molar ratio of 1:1.2, dissolved in DMSO, heated to 60°C under nitrogen protection, kept at this temperature for 2 hours with continuous stirring at a stirring speed of 100 rpm, and then cooled and filtered to obtain the flame retardant salt.

[0174] On a molar basis, 95 mol% of hexamethylenediamine adipic acid salt and 5 mol% of flame retardant salt were mixed and added to a 500 mL four-necked flask with a flange. The mixture was heated to 250 °C under a nitrogen atmosphere and stirred at 100 rpm for 2 h.

[0175] Reduce the stirring speed to 50 rpm, stop the nitrogen flow, evacuate to a pressure less than 100 Pa, and heat to 260°C for 10 minutes.

[0176] Stop heating and stirring, resume nitrogen flow, let stand for 30 minutes to cool to room temperature, open the flange valve to discharge the material, and obtain a copolymer containing 5 mol% flame retardant.

[0177] Example 18

[0178] This embodiment adjusts the ratio of 5-aminoisophthalic acid and aldehyde compounds based on Example 1, as follows:

[0179] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 39.33 g (0.3 mol) of benzaldehyde were added to 250 mL beakers respectively, and 150 mL of anhydrous ethanol was added to each beaker. The mixtures were stirred thoroughly to dissolve the solids.

[0180] Under a nitrogen atmosphere, the two solutions were added sequentially to a 500 mL three-necked flask, and the mixture was slowly heated to 85 °C and stirred at 200 rpm for 2 h.

[0181] The solution was cooled to 50°C under a nitrogen atmosphere and stirred at 200 rpm for 8 hours.

[0182] After the reaction was complete, 64.86 g (0.3 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 5 h.

[0183] After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. Then, it was dried in a vacuum oven at 60 °C for 24 h to obtain 35.31 g of DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, with a yield of 69%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is phenyl.

[0184] Example 19

[0185] This embodiment adjusts the ratio of 5-aminoisophthalic acid and aldehyde compounds based on Example 1, as follows:

[0186] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 2.62 g (0.02 mol) of benzaldehyde were added to 250 mL beakers respectively, and 150 mL of anhydrous ethanol was added to each beaker. The mixtures were stirred thoroughly to dissolve the solids.

[0187] Under a nitrogen atmosphere, the two solutions were added sequentially to a 500 mL three-necked flask, and the mixture was slowly heated to 85 °C and stirred at 200 rpm for 2 h.

[0188] The solution was cooled to 50°C under a nitrogen atmosphere and stirred at 200 rpm for 8 hours.

[0189] After the reaction was complete, 4.32 g (0.02 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 5 h.

[0190] After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. Then, it was dried in a vacuum oven at 60 °C for 24 h to obtain 4.53 g of DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, with a yield of 44%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is phenyl.

[0191] Example 20

[0192] This embodiment adjusts the reaction time of some steps based on Embodiment 1, as follows:

[0193] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 13.11 g (0.1 mol) of benzaldehyde were added to 250 mL beakers respectively, and 150 mL of anhydrous ethanol was added to each beaker. The mixtures were stirred thoroughly to dissolve the solids.

[0194] Under a nitrogen atmosphere, the two solutions were added sequentially to a 500 mL three-necked flask, and the mixture was slowly heated to 85 °C and stirred at a stirring speed of 200 rpm for 8 h.

[0195] The solution was cooled to 50°C under a nitrogen atmosphere and stirred at 200 rpm for 12 hours.

[0196] After the reaction was complete, 21.62 g (0.1 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 8 h.

[0197] After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. Then, it was dried in a vacuum oven at 60 °C for 24 h to obtain 41.88 g of DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, with a yield of 82%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is phenyl.

[0198] Example 21

[0199] This embodiment adjusts the reaction time of some steps based on Embodiment 5, as follows:

[0200] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 5.35 g (0.05 mol) of 3-pyridinecarboxaldehyde were added to 250 mL beakers respectively, and 150 mL of ethyl acetate was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0201] Under a nitrogen atmosphere, the two solutions were added sequentially to a 500 mL three-necked flask, and the mixture was slowly heated to 85 °C and stirred at a stirring speed of 200 rpm for 8 h.

[0202] The solution was cooled to 50°C under a nitrogen atmosphere and stirred at 200 rpm for 10 hours.

[0203] After the reaction was complete, 10.81 g (0.05 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 8 h.

[0204] After the reaction was completed and cooled to room temperature, the mixture was filtered and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. This powder was then dried in a vacuum oven at 60 °C for 24 h to obtain 16.92 g of a DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, yielding 69%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is...

[0205] Example 22

[0206] This embodiment adjusts the reaction time of some steps based on Embodiment Six, as follows:

[0207] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 13.61 g (0.1 mol) of p-methoxybenzaldehyde were added to 250 mL beakers respectively, and 150 mL of acetone was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0208] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, and the mixture was slowly heated to 75 °C and stirred at 200 rpm for 1 h.

[0209] The solution was cooled to 40°C under a nitrogen atmosphere and stirred at 200 rpm for 4 hours.

[0210] After the reaction was complete, 21.62 g (0.1 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 75 °C and refluxed for 1 h.

[0211] After the reaction was completed and cooled to room temperature, the mixture was filtered and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. This powder was then dried in a vacuum oven at 60 °C for 24 h to obtain 10.98 g of a DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group, yielding 42%. In this example, the flame retardant with the structure shown in Formula I has an R group of...

[0212]

[0213] Example 23

[0214] This embodiment adjusts the reaction time of some steps based on Embodiment Seven, as follows:

[0215] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 7.61 g (0.05 mol) of 3-methoxy-4-hydroxybenzaldehyde were added to 250 mL beakers respectively, and 150 mL of anhydrous ethanol was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0216] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, and the mixture was slowly heated to 85 °C and stirred at 200 rpm for 1 h.

[0217] Under a nitrogen atmosphere, the solution was cooled to 50°C and stirred at a stirring speed of 200 rpm for 2 hours.

[0218] After the reaction was complete, 10.81 g (0.05 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 85 °C and refluxed for 1 h.

[0219] After the reaction was completed and cooled to room temperature, the mixture was filtered and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. This powder was then dried in a vacuum oven at 60 °C for 24 h to obtain 8.62 g of a DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, yielding 49%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is...

[0220]

[0221] Example 24

[0222] This embodiment adjusts the reaction temperature of some steps based on Embodiment 5, as follows:

[0223] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 7.11 g (0.05 mol) of nonanal were added to 250 mL beakers respectively, and 150 mL of anhydrous ethanol was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0224] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, slowly heated to 100 °C, and stirred at a stirring rate of 200 rpm for 1 h.

[0225] The solution was cooled to 75°C under a nitrogen atmosphere and stirred at 200 rpm for 9 hours.

[0226] After the reaction was complete, 10.81 g (0.05 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 100 °C and refluxed for 3 h.

[0227] After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. Then, it was dried in a vacuum oven at 60 °C for 24 h to obtain 15.98 g of DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, with a yield of 61%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is octyl.

[0228] Example 25

[0229] This embodiment adjusts the reaction temperature of some steps based on Embodiment 4, as follows:

[0230] At room temperature, 18.12 g (0.1 mol) of 5-aminoisophthalic acid and 6.11 g (0.05 mol) of m-hydroxybenzaldehyde were added to 250 mL beakers respectively, and 150 mL of acetone was added to each beaker. The mixtures were stirred thoroughly to dissolve the substances.

[0231] Under a nitrogen atmosphere, the two solutions were added to a 500 mL three-necked flask, slowly heated to 50 °C, and stirred at 200 rpm for 5 h.

[0232] The solution was cooled to 30°C under a nitrogen atmosphere and stirred at 200 rpm for 5 hours.

[0233] After the reaction was complete, 10.81 g (0.05 mol) of DOPO was added to the reaction solution, and the mixture was stirred and heated to 50 °C and refluxed for 5 h.

[0234] After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed with anhydrous ethanol (150 mL × 3) to obtain a white powder. Then, it was dried in a vacuum oven at 60 °C for 24 h to obtain 9.11 g of DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups, with a yield of 36%. In the flame retardant with the structure shown in Formula I obtained in this example, the R group is phenol.

[0235] Experimental Example 1

[0236] This experimental example statistically analyzes the yields of Examples 1 to 8 and Examples 18 to 25 above. It should be noted that the yield of each example in this application refers to the ratio of the actual yield to the theoretical yield of the entire process from 5-aminoisophthalic acid and aldehyde compounds as raw materials to the final preparation of the flame retardant. The statistical results are shown in the table below:

[0237]

[0238]

[0239] As can be seen from Examples 1, 18, and 19, both excessively high and low ratios of 5-aminoisophthalic acid to aldehyde compounds directly lead to a decrease in the yield of the flame retardant. Furthermore, comparisons between Examples 1 and 20, and between Examples 5 and 21, show that extending the catalyst preparation step does not further increase the yield; on the contrary, it may lead to a decrease in the catalyst yield to some extent. Conversely, comparisons between Examples 6 and 22, and between Examples 7 and 23, show that shortening the catalyst preparation time directly leads to a significant decrease in yield, because the reaction is incomplete due to insufficient time.

[0240] Furthermore, a comparison of Examples 3 and 24, as well as Examples 4 and 25, shows that both exceeding and falling below the temperature range defined in this application will result in a significant decrease in yield.

[0241] Experimental Example 2

[0242] This experiment tested and statistically analyzed the flame retardant properties of the flame retardants prepared in Examples 9 to 17. The results are shown in the table below:

[0243]

[0244]

[0245] As can be seen from the table above, the DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups described in this invention has excellent flame retardant properties.

[0246] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. The implementation schemes in the above embodiments can also be further combined or replaced. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A halogen-free reactive flame retardant with a terminal dicarboxyl group and a DOPO group, characterized in that, The structure of the flame retardant is shown in Formula I: Wherein, -R is selected from phenyl, ethyl, octyl, phenol, , , or .

2. The DOPO-based halogen-free reactive flame retardant with terminal dicarboxyl groups according to claim 1, characterized in that, The flame retardant molecule is prepared by an addition reaction of DOPO with an imine bond on an imine compound having a structure as shown in Formula II. Wherein, -R is selected from phenyl, ethyl, octyl, phenol, , , or .

3. The DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group according to claim 2, characterized in that, The imine compounds with the structure shown in Formula II are prepared by a Schiff base reaction between the amino group on 5-aminoisophthalic acid and the aldehyde group of an aldehyde compound. The structure of the aldehyde compound is shown in Formula III. Wherein, -R is selected from phenyl, ethyl, octyl, phenol, , , or .

4. A method for preparing a halogen-free reactive flame retardant with a terminal dicarboxyl group (DOPO) as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Under an inert atmosphere, a solution of 5-aminoisophthalic acid and a solution of an aldehyde compound are mixed and reacted at a preset temperature to obtain a mixed solution; the structure of the aldehyde compound is shown in Formula III: Wherein, -R is selected from phenyl, ethyl, octyl, phenol, , , or ; S2. Add DOPO to the mixture obtained in step S1 and react to obtain a DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group as shown in Formula I.

5. The method for preparing the halogen-free reactive flame retardant with a terminal dicarboxyl group and DOPO group according to claim 4, characterized in that, Step S1 is as follows: Under an inert atmosphere, a solution of 5-aminoisophthalic acid and a solution of an aldehyde compound having the structure shown in Formula III are mixed, heated to a preset first temperature and stirred continuously, and then cooled to a preset second temperature and stirred continuously.

6. The method for preparing the halogen-free reactive flame retardant with a terminal dicarboxyl group and DOPO group according to claim 5, characterized in that, The solvents for the 5-aminoisophthalic acid solution and the aldehyde compound solution in step S1 are selected from at least one of anhydrous ethanol, diethyl ether, acetone, and ethyl acetate.

7. The method for preparing the halogen-free reactive flame retardant with a terminal dicarboxyl group and DOPO group according to claim 5, characterized in that, In step S1, the preset first temperature is 5-20°C higher than the boiling point of the solvent; the preset second temperature is 10-50°C lower than the boiling point of the solvent.

8. The method for preparing the halogen-free reactive flame retardant with a terminal dicarboxyl group and DOPO group according to claim 7, characterized in that, At the preset first temperature, the reaction time is 1-5 hours; at the preset second temperature, the reaction time is 5-9 hours.

9. The method for preparing the halogen-free reactive flame retardant with a terminal dicarboxyl group and DOPO group according to claim 4, characterized in that, In step S2, the reaction temperature is 5-20°C higher than the boiling point of the solvent.

10. The method for preparing the halogen-free reactive flame retardant with a terminal dicarboxyl group and DOPO group according to claim 4, characterized in that, In step S2, the reaction time is 1-8 hours.

11. The method for preparing the halogen-free reactive flame retardant with a terminal dicarboxyl group and DOPO group according to claim 4, characterized in that, In the mixture of step S1, the molar ratio of 5-aminoisophthalic acid to aldehyde compounds is 1:(0.5-2).

12. The application of a DOPO-based halogen-free reactive flame retardant with a terminal dicarboxyl group as described in any one of claims 1-3, characterized in that, Used as an intrinsic flame retardant for polyamides.

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