A PCN-bonded functional group-substituted α-aminocaprolactam flame retardant, preparation method and application thereof

Abstract

The present invention discloses an α-aminocaprolactam flame retardant containing a substituted P-C-N functional group, and a preparation method and application thereof. The flame retardant is prepared by a two-step reaction of three components, namely, α-aminocaprolactam, an aldehyde-containing compound, and an organophosphorus compound containing a P-H bond. First, the aldehyde-containing compound is reacted with the α-aminocaprolactam to obtain a Schiff base intermediate, which is then subjected to nucleophilic addition with the organophosphorus compound containing a P-H bond to obtain an α-aminocaprolactam substituted with a P-C-N functional group. The flame retardant of the present invention can introduce a variety of flame retardant elements including phosphorus, nitrogen, halogen, silicon and the like through the aldehyde-containing compound and the organophosphorus compound containing a P-H bond, thereby giving it good flame retardant properties; at the same time, the caprolactam group contained can be copolymerized with a variety of monomers or exchanged with a variety of polymers to prepare a variety of intrinsic flame-retardant polymers, and has broad application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of reactive flame retardants, and particularly relates to an alpha-aminocaprolactam flame retardant containing a PCN bond functional group substitution, a preparation method and an application thereof. Background Art

[0002] With the development of society, a variety of polymer materials have entered people's daily lives. However, most polymer materials are flammable or combustible, which limits the application range of their products. In order to reduce the flammability of polymer materials and reduce the occurrence of fires, flame retardants are usually added to polymer materials in industrial production.

[0003] Flame retardants can be divided into additive and reactive flame retardants based on their operating principles. Additive flame retardants are typically physically incorporated into polymers, but they generally have poor compatibility with polymers, requiring large addition amounts to achieve effective flame retardancy. They also have drawbacks such as reduced mechanical properties. Unlike additive flame retardants, reactive flame retardants can act as a monomer in polymerization reactions or undergo grafting reactions on polymers, becoming chemically bonded to form a part of the polymer and imparting durable flame retardancy. Reactive flame retardants also require only small additions to achieve effective flame retardancy, with minimal impact on the mechanical properties of polymer materials. They are currently a hot topic in flame retardant research.

[0004] In recent years, research on reactive flame retardants has generally linked flame-retardant compounds with compounds having reactive groups through a chemical reaction to produce reactive flame retardants that both exhibit flame retardancy and react with polymers. For example, Chinese patent application CN117229323A discloses a latent reactive flame retardant containing DOPO. This is prepared by reacting DOPO with a nitrogen-containing monomer and then capping it with a hydroxyl-containing compound (capping agent). This latent reactive flame retardant exhibits excellent flame retardancy and char-forming properties. Adding 8 wt% to polylactic acid (PLA) can achieve a UL94 V-0 flame retardancy rating. However, the preparation of flame-retardant polymer materials using DOPO and its derivatives currently presents several challenges. The primary issue is that copolymerization or modification of reactive DOPO derivatives with polymers can result in cleavage of the main molecular chain, resulting in a low molecular weight that cannot meet the requirements for spinning, injection molding, and application.

[0005] Chinese patent application CN112368318A discloses a method for preparing flame-retardant polyamide 6 copolymers and filaments. This method synthesizes a closed-loop, recyclable, flame-retardant functionalized comonomer containing a phosphoramide bond (based on ε-caprolactam), which is then copolymerized with caprolactam to produce recyclable flame-retardant (FR) polyamide 6 fibers. The resulting flame-retardant copolyamide 6, obtained by copolymerizing caprolactam with a flame retardant (DOPO-CL) synthesized from DOPO and α-amino-ε-caprolactam at a weight ratio of 90:10, achieves a UL94 V-0 rating. However, the relative viscosity of the flame-retardant copolyamide 6 is relatively low, primarily due to the fact that the phosphoramide bonds (P-NH) in the flame retardant (DOPO-CL) undergo an exchange reaction with the amide bonds in the polyamide 6 during polymerization, disrupting the molecular chain structure of the polyamide 6 and hindering its polymerization. Dai Lixing's research group used [(6-oxo-6H-dibenzo[c,e][1,2]oxaphosphorin-6-yl)methyl]succinic acid (DDP), hexamethylenediamine and caprolactam to copolymerize to prepare a series of copolymer nylon 6 resins. When the DDP content was 1.6%, the limiting oxygen index of the polymer increased from the initial 22% to 26%. When the DDP content was above 2.4%, the polymer oxygen index increased to more than 30%. However, further increasing the DDP content did not significantly increase the polymer oxygen index, and the viscosity decreased significantly, which had a great impact on the spinnability of the polymer chips and the strength of the spun fibers. Summary of the Invention

[0006] In view of the technical problems in the prior art of reactive flame retardants copolymerized with polymer monomers or reactively blended with polymer materials, such as large structural differences between the flame retardant and the polymer monomer, which have an adverse effect on polymerization, poor structural stability of the flame retardant and easy decomposition, low flame retardant efficiency of single-element flame retardants, complex synthesis of flame retardants, and expensive raw materials, the present invention provides an α-aminocaprolactam flame retardant containing a PCN bond functional group substitution and its preparation method and application. The α-aminocaprolactam flame retardant containing a PCN bond functional group substitution synthesized by the present invention is mainly obtained by the reaction of three components: α-aminocaprolactam, an aldehyde-containing compound (R1-CHO), and an organophosphorus compound containing a PH bond (R2R3P(O)H). The reactive flame retardant involved in the present invention is mainly synthesized by the Kabachnik-Fields reaction, with simple synthesis steps, easy purification, and abundant, cheap and easy-to-obtain raw material sources. The flame retardant involved in the present invention can introduce various flame retardant elements including phosphorus, nitrogen, halogen, silicon and other elements through aldehyde-containing compounds and organic phosphorus compounds containing pH bonds, giving it good flame retardant properties; at the same time, the caprolactam group contained can be copolymerized with various monomers or exchanged with various polymers to prepare various intrinsic flame retardant polymers, and has broad application prospects.

[0007] The technical solutions of the present invention are as follows:

[0008] An α-aminocaprolactam flame retardant containing a PCN bond functional group substitution, the general chemical structure of which is shown in formula (I):

[0009]

[0010] The preparation method of the above-mentioned α-aminocaprolactam flame retardant containing a PCN bond functional group substitution is synthesized from three components: α-aminocaprolactam, an aldehyde-containing compound (R1-CHO), and an organophosphorus compound containing a PH bond (R2R3P(O)H). The general synthesis formula is shown in formula (II):

[0011]

[0012] Furthermore, the structural formula of the α-aminocaprolactam is shown in formula (III):

[0013]

[0014] Furthermore, the aldehyde-containing compound (R1CHO) is an aldehyde compound containing an R1 group.

[0015] Furthermore, the R1 group is any one of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted arylalkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroarylalkyl group or a substituted or unsubstituted alkylheteroaryl group.

[0016] Furthermore, the substitution includes hydrogen atom substitution, heteroatom substitution, and hydrogen atom and heteroatom substitution.

[0017] Furthermore, the aldehyde compound containing the R1 group is paraformaldehyde, hexanal, octanal, benzaldehyde, p-bromobenzaldehyde, p-hydroxybenzaldehyde, terephthalaldehyde, p-trifluoromethylbenzaldehyde, syringaldehyde, 2-butyl-5-chloro-1H-imidazole-4-carboxaldehyde, etc.

[0018] Furthermore, the organophosphorus compound containing a PH bond is preferably one of the following structures:

[0019]

[0020] Furthermore, the preparation method specifically comprises the following steps:

[0021] The synthesis is carried out in two steps via the Kabachnik-Fields reaction. The first step is the reaction of α-aminocaprolactam with an aldehyde-containing compound to synthesize a Schiff base intermediate. The second step is the reaction of DOPO with the Schiff base intermediate synthesized in the first step to obtain a reactive flame retardant containing DOPO and PCN bond functional group substitutions.

[0022] Furthermore, the first step, i.e., the synthesis of the Schiff base intermediate, is carried out according to the reaction formula (VIII):

[0023]

[0024] The aldehyde compound containing the R1 group and α-aminocaprolactam are dissolved in an organic solvent, and after complete dissolution, a catalyst and a water absorbent are added, and the reaction is carried out under heating conditions. After the reaction is completed, the reaction liquid is filtered and the solvent is removed by distillation under reduced pressure. The solvent is used for post-processing for recrystallization or pulping, and the solvent is removed by filtration to obtain a Schiff base intermediate.

[0025] Furthermore, the molar ratio of the aldehyde compound containing the R1 group to α-aminocaprolactam is 1:1 to 1.2, preferably 1:1 to 1.1, the molar ratio of the aldehyde compound containing the R1 group to the catalyst is 1:0.01 to 0.1, preferably 1:0.01 to 0.05, the molar ratio of the aldehyde compound containing the R1 group to the water absorbent is 1:1 to 3, preferably 1:1 to 2, and the amount of organic solvent used is 5 to 50 times the mass of the aldehyde compound containing the R1 group, preferably 15 to 25 times.

[0026] Furthermore, the catalyst is any one of hydrochloric acid, acetic acid, p-toluenesulfonic acid, etc.; the water absorbent is any one of anhydrous magnesium sulfate, anhydrous sodium sulfate, calcium oxide, etc.; the organic solvent is any one of dichloromethane, chloroform, ethanol, tetrahydrofuran, toluene, etc.; the reaction time is 4h to 72h, preferably 12h to 48h; the reaction temperature is 35°C to 115°C; the solvent used for post-reaction treatment is one or more of dichloromethane, chloroform, tetrahydrofuran, ethanol, ethyl acetate, petroleum ether, and ether.

[0027] Furthermore, the second step reaction, i.e., the synthesis of the α-aminocaprolactam flame retardant containing a PCN bond functional group substitution, is carried out according to the reaction formula shown in formula (IX):

[0028]

[0029] The Schiff base intermediate synthesized in the first step undergoes a nucleophilic addition reaction with an organic phosphorus compound containing a PH bond. After the reaction is completed, the reaction solvent is removed by distillation under reduced pressure to obtain a crude product. The crude product is recrystallized or pulped to obtain an α-aminocaprolactam flame retardant containing a PCN bond functional group substitution.

[0030] Furthermore, the molar ratio of the Schiff base intermediate to the organophosphorus compound containing a PH bond is 1:1-1.2, preferably 1:1-1.05, and the reaction is carried out under the condition of adding a reaction solvent, and the amount of the reaction solvent is 5-50 times the mass of the Schiff base monomer, preferably 15-25 times.

[0031] Furthermore, the reaction solvent is dichloromethane, chloroform, tetrahydrofuran, anhydrous ethanol, toluene, etc.; the reaction time is 4h to 72h, preferably 12h to 24h; the reaction temperature is 35°C to 115°C; the solvent used for recrystallization is one or more of dichloromethane, chloroform, ethanol, ethyl acetate, petroleum ether, ether, etc.

[0032] The application of the above-mentioned α-aminocaprolactam flame retardant containing a PCN bond functional group substitution in the preparation of flame-retardant polymer materials includes:

[0033] 1. The α-aminocaprolactam flame retardant containing a PCN bond functional group substituted and caprolactam are hydrolyzed and co-condensed to prepare an intrinsic flame retardant polyamide 6 resin;

[0034] 2. Anion polymerization of the α-aminocaprolactam flame retardant containing a PCN bond functional group and caprolactam to prepare an intrinsic flame retardant casting polyamide 6 resin;

[0035] 3. Adding the α-aminocaprolactam flame retardant containing a PCN bond functional group to the polymerization process of other polyamide resins to prepare a variety of intrinsic flame retardant polyamide resins;

[0036] 4. Anion polymerization of the α-aminocaprolactam flame retardant containing a PCN bond functional group and caprolactone to prepare an intrinsic flame retardant polycaprolactone resin;

[0037] 5. Adding the α-aminocaprolactam flame retardant containing a PCN bond functional group to the polymerization process of other polyester resins to prepare a variety of intrinsic flame retardant polyester resins;

[0038] 6. Adding the α-aminocaprolactam flame retardant containing a PCN bond functional group to the polymerization process of the epoxy resin to prepare an intrinsic flame retardant epoxy resin;

[0039] 7. Adding the α-aminocaprolactam flame retardant containing a PCN bond functional group into the polyurethane polymerization process to prepare an intrinsic flame retardant polyurethane resin;

[0040] 8. The α-aminocaprolactam flame retardant containing a PCN bond functional group substituted is reacted with a resin matrix such as a polyamide resin, a polyester resin, or a polyurethane resin to prepare an intrinsic flame retardant resin material.

[0041] The beneficial effects of the present invention are:

[0042] The α-aminocaprolactam flame retardant obtained by the present invention, which contains a PCN bond functional group substitution, is formed by the reaction of three components: α-aminocaprolactam, an aldehyde-containing compound (R1-CHO), and a PH bond-containing organophosphorus compound (R2R3P(O)H). The caprolactam group of the α-aminocaprolactam can be copolymerized with a variety of polymer monomers or reacted to modify polymers. The aldehyde-containing compound (R1-CHO) has a wide range of raw materials to choose from. By changing the elemental composition and molecular structure of the R1 group, a flame retardant with two or more elements, including phosphorus, can be obtained, or a flame retardant-based multifunctional flame retardant can be obtained. The flame retardant has high thermal stability and flame retardant properties. The PH bond-containing organophosphorus compound (R2R3P(O)H) serves as the main flame retardant group, which not only has good flame retardant properties but also high thermal stability and chemical stability.

[0043] The α-aminocaprolactam flame retardant containing PCN bond functional group substitution obtained by the present invention has abundant raw material sources (the aldehyde-containing compound can be any compound with an aldehyde group, and the α-aminocaprolactam is prepared from L-lysine), is simple to synthesize, has good flame retardant effect, has good compatibility with many polymer materials, has excellent flame retardant properties at a relatively low addition amount, has little effect on the mechanical properties of polymer materials, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The aldehyde compound used in Example 1 of the present invention is a Schiff base intermediate containing a benzene ring, wherein the aldehyde compound is benzaldehyde. 1 HNMR spectrum.

[0045] Figure 2 The aldehyde compound used in Example 1 of the present invention is benzaldehyde, the organophosphorus compound containing a PH bond used is DOPO, and the α-aminocaprolactam flame retardant (P-Ph-NHACL) containing a PCN bond functional group substituted 1 H NMR spectrum.

[0046] Figure 3 The aldehyde compound used in Example 2 of the present invention is p-bromobenzaldehyde, the organophosphorus compound containing a PH bond used is DOPO, and the α-aminocaprolactam flame retardant (P-Ph(Br)-NHACL) containing a PCN bond functional group substituted 1 H NMR spectrum.

[0047] Figure 4This is a thermal gravimetric curve of an α-aminocaprolactam flame retardant (P-Ph-NHACL) substituted with a PCN functional group, in which the aldehyde compound used in Example 1 of the present invention is benzaldehyde and the organophosphorus compound containing a PH bond is DOPO. The flame retardant has good thermal stability.

[0048] Figure 5 This is a thermal gravimetric curve of an α-aminocaprolactam flame retardant (P-Ph(Br)-NHACL) substituted with a PCN functional group, in which the aldehyde compound used in Example 2 of the present invention is p-bromobenzaldehyde and the organophosphorus compound containing a PH bond used is DOPO. The flame retardant has good thermal stability. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto.

[0050] Flame retardant performance test

[0051] 1) Vertical burning test (UL-94 burning rating test)

[0052] The UL-94 rating test measures the burning rate of a specimen and assesses its combustion rating, which is classified into three levels: V-0, V-1, and V-2. The test conditions involve securing one end of a 130mm × 13mm × 1.6mm standard specimen with the test instrument's fixture and exposing the other end to the flame. The ignition distance is approximately 150mm, and the blue flame height is 20mm ± 2mm.

[0053] UL-94 combustion grade judgment standard

[0054]

[0055] 2) Limiting oxygen index test (National Standard GB / T 2406-2008 Plastics Combustion Performance Test Method - Oxygen Index Method)

[0056] The LOI value refers to the minimum oxygen concentration required for a polymer sample to maintain a stable combustion state in a mixture of N2 and O2 under standard test conditions. The value is expressed as the percentage of O2 in the total volume of the mixed gas.

[0057] The specific test method is to vertically fix a standard specimen measuring 80mm x 10mm x 4mm in a glass combustion tube and connect a nitrogen and oxygen flow inlet device. An igniter is used to ignite the specimen at the top. The highest oxygen percentage required to successfully ignite the specimen is the limiting oxygen index value of the material.

[0058] Example 1

[0059] The aldehyde-containing compound used in this embodiment is benzaldehyde, and the organophosphorus compound containing a PH bond used is DOPO.

[0060] The first step reaction is as follows:

[0061]

[0062] 21.20 g of benzaldehyde and 26.88 g of α-aminocaprolactam were dissolved in 350 ml of ethanol, and 0.76 g of p-toluenesulfonic acid and 24 g of anhydrous magnesium sulfate were added. The temperature was raised to reflux temperature and reacted for 24 hours. The reaction was filtered, and the filtrate was distilled under reduced pressure and slurried with 100 ml of ethyl acetate to obtain a Schiff base intermediate containing a benzene ring with a yield of 85%.

[0063] The second step reaction is as follows:

[0064]

[0065] 37 g of the phenyl-containing Schiff base intermediate obtained in the first step and 37 g of DOPO were dissolved in 300 ml of ethanol and the temperature was raised to reflux for reaction for 12 hours. The reaction solution was then distilled under reduced pressure and dried to obtain a pale yellow solid. The pale yellow solid was dissolved in 100 ml of chloroform and slowly added to 400 ml of ether. The mixture was filtered and the filter cake was collected to obtain a PCN-functional group-substituted α-aminocaprolactam flame retardant (P-Ph-NHACL) in which the aldehyde compound used was benzaldehyde and the organophosphorus compound containing a PH bond used was DOPO. The yield was 85%.

[0066] Example 2

[0067] The aldehyde-containing compound used in this embodiment is p-bromobenzaldehyde, and the organophosphorus compound containing a PH bond used is DOPO.

[0068] The first step reaction is as follows:

[0069]

[0070] 37 g of p-bromobenzaldehyde and 26.88 g of α-aminocaprolactam were dissolved in 300 ml of chloroform, and 0.76 g of p-toluenesulfonic acid and 24 g of anhydrous magnesium sulfate were added. The temperature was raised to reflux temperature and reacted for 24 hours. The mixture was filtered and the filtrate was distilled under reduced pressure. The filtrate was slurried with 100 ml of anhydrous ethanol and filtered to obtain a Schiff base intermediate containing p-bromophenyl in a yield of 80%.

[0071] The second step reaction is as follows:

[0072]

[0073] 47.2 g of the Schiff base intermediate containing a p-bromophenyl group obtained in the first step and 34.56 g of DOPO were dissolved in 300 ml of chloroform. The temperature was raised to reflux and the reaction was allowed to proceed for 12 hours. The reaction solution was then distilled under reduced pressure and slurried with 100 ml of ethyl acetate. The mixture was filtered and the filter cake was collected to obtain an α-aminocaprolactam flame retardant (P-Ph(Br)-NHACL) containing a PCN bond, wherein the aldehyde compound used was p-bromobenzaldehyde and the organophosphorus compound containing a PH bond was DOPO. The yield was 80%. This flame retardant can achieve phosphorus-bromine synergistic flame retardancy.

[0074] Example 3

[0075] The aldehyde-containing compound used in this embodiment is p-bromobenzaldehyde, and the organophosphorus compound containing a PH bond used is diphenyl phosphite.

[0076] The first step reaction is as follows:

[0077]

[0078] 37 g of p-bromobenzaldehyde and 26.88 g of α-aminocaprolactam were dissolved in 300 ml of chloroform, and 0.76 g of p-toluenesulfonic acid and 24 g of anhydrous magnesium sulfate were added. The temperature was raised to reflux temperature and reacted for 24 hours. The mixture was filtered and the filtrate was distilled under reduced pressure. The filtrate was slurried with 100 ml of anhydrous ethanol and filtered to obtain a Schiff base intermediate containing p-bromophenyl in a yield of 80%.

[0079] The second step reaction is as follows:

[0080]

[0081] 47.2 g of the p-bromophenyl-containing Schiff base intermediate obtained in the first step and 37.44 g of diphenyl phosphite were dissolved in 300 ml of chloroform, heated to reflux temperature, and reacted for 12 hours. The reaction solution was then distilled under reduced pressure, slurried with 100 ml of ethyl acetate, and filtered. The filter cake was collected to obtain a PCN-functional group-substituted α-aminocaprolactam flame retardant (DP-Ph(Br)-NHACL) in which the aldehyde compound used was p-bromobenzaldehyde and the organophosphorus compound containing a PH bond was diphenyl phosphite. The yield was 85%. This flame retardant can achieve phosphorus-bromine synergistic flame retardancy.

[0082] Example 4

[0083] The aldehyde-containing compound used in this embodiment is p-trifluoromethylbenzaldehyde, and the organophosphorus compound containing a PH bond used is DOPO.

[0084] The first step reaction is as follows:

[0085]

[0086] 34.8 g of p-trifluoromethylbenzaldehyde and 26.88 g of α-aminocaprolactam were dissolved in 300 ml of chloroform, and 0.76 g of p-toluenesulfonic acid and 24 g of anhydrous magnesium sulfate were added. The temperature was raised to reflux temperature and reacted for 24 hours. The mixture was filtered and the filtrate was distilled under reduced pressure. The filtrate was slurried with 150 ml of ethyl acetate and filtered to obtain a Schiff base intermediate containing p-trifluoromethylphenyl in a yield of 85%.

[0087] The second step reaction is as follows:

[0088]

[0089] 48.3 g of the Schiff base intermediate containing a p-trifluoromethylphenyl group obtained in the first step and 36.72 g of DOPO were dissolved in 300 ml of chloroform. The reaction was heated to reflux for 12 hours. The reaction solution was then distilled under reduced pressure to obtain a white solid. This solid was dissolved in 80 ml of chloroform and slowly added to 400 ml of ether. The mixture was filtered to obtain a flame retardant (P-Ph(3F)-NHACL) containing a PCN functional group, in which the aldehyde compound was p-trifluoromethylbenzaldehyde and the organophosphorus compound containing a PH bond was DOPO. The yield was 80%. This flame retardant exhibits both flame retardancy and hydrophobicity.

[0090] Example 5

[0091] The aldehyde-containing compound used in this embodiment is 2-butyl-5-chloro-1H-imidazole-4-carbaldehyde, and the organophosphorus compound containing a PH bond used is DOPO.

[0092] The first step reaction is as follows:

[0093]

[0094] 37.2 g of 2-butyl-5-chloro-1H-imidazole-4-carboxaldehyde and 26.88 g of α-aminocaprolactam were dissolved in 300 ml of chloroform, and 0.76 g of p-toluenesulfonic acid and 24 g of anhydrous magnesium sulfate were added. The mixture was heated to reflux temperature and reacted for 24 h. The mixture was filtered and the filtrate was distilled under reduced pressure. The filtrate was slurried with 150 ml of ethyl acetate and filtered to obtain a Schiff base intermediate containing 2-butyl-5-chloro-1H-imidazole in a yield of 90%.

[0095]

[0096] The second step reaction is as follows:

[0097] 47.4 g of the Schiff base intermediate containing 2-butyl-5-chloro-1H-imidazolyl obtained in the first step and 34.56 g of DOPO were dissolved in 300 ml of chloroform. The mixture was heated to reflux and reacted for 12 hours. The reaction solution was then distilled under reduced pressure to obtain an off-white solid. The off-white solid was dissolved in 100 ml of chloroform and slowly added to 500 ml of ether. The mixture was filtered to obtain a flame retardant (P-Ph(Imid)-NHACL) containing 2-butyl-5-chloro-1H-imidazolyl-4-carboxaldehyde as the aldehyde compound and DOPO as the organophosphorus compound containing a PH bond, with a yield of 84%. This flame retardant not only achieves phosphorus-nitrogen-chlorine synergistic flame retardancy but also exhibits effective antibacterial properties.

[0098] Example 6

[0099] The aldehyde-containing compound used in this embodiment is 3,5-dimethoxy-4-hydroxybenzaldehyde (syringaldehyde), and the organophosphorus compound containing a PH bond used is DOPO.

[0100] The first step reaction is as follows:

[0101]

[0102] 36.4 g of syringaldehyde and 26.88 g of α-aminocaprolactam were dissolved in 300 ml of anhydrous ethanol, and 0.76 g of p-toluenesulfonic acid and 24 g of anhydrous magnesium sulfate were added. The temperature was raised to reflux temperature and reacted for 24 hours. The mixture was filtered, and the filtrate was distilled under reduced pressure. It was then slurried with 100 ml of ethyl acetate and filtered to obtain a Schiff base intermediate containing 3,5-dimethoxy-4-hydroxyphenyl in a yield of 87%.

[0103] The second step reaction is as follows:

[0104]

[0105] 46.7 g of the Schiff base intermediate containing 3,5-dimethoxy-4-hydroxyphenyl obtained in the first step and 34.56 g of DOPO were dissolved in 300 ml of anhydrous ethanol. The mixture was heated to reflux and reacted for 12 hours. The reaction solution was then distilled under reduced pressure to obtain an off-white solid. This off-white solid was dissolved in 100 ml of chloroform and slowly added to 500 ml of ether. The mixture was filtered to obtain a PCN-functional group-substituted α-aminocaprolactam flame retardant (P-Syr-NHACL) in which the aldehyde compound used was 3,5-dimethoxy-4-hydroxybenzaldehyde and the organophosphorus compound containing a PH bond was DOPO. The yield was 85%. This flame retardant not only has flame retardancy but also exhibits good antioxidant properties.

[0106] Example 7

[0107] The α-aminocaprolactam flame retardant (P-Ph-NHACL) obtained in Example 1, wherein the aldehyde compound used was benzaldehyde and the organophosphorus compound containing a PH bond was DOPO, was hydrolyzed and co-condensed with caprolactam to produce a flame-retardant nylon 6 resin (FR-PA6-8). The flame retardant was added in an amount of 8 wt%. The flame-retardant nylon 6 resin (FR-PA6-8) had a limiting oxygen index of 35% and a vertical flammability rating of UL94 V-0.

[0108] Example 8

[0109] Anionic polymerization of caprolactam with an amine flame retardant (P-Ph-NHACL) containing a PCN-functional group substituted with benzaldehyde (the aldehyde compound used in Example 1) and DOPO (the organophosphorus compound containing a PH bond) was performed to obtain a flame-retardant anionic polymerized nylon 6 resin (FR-APA6-8). The flame retardant was added in an amount of 8 wt%. The flame-retardant anionic polymerized nylon 6 resin (FR-APA6-8) had a limiting oxygen index of 35% and a vertical flammability rating of UL94 V-0.

[0110] Example 9

[0111] The α-aminocaprolactam flame retardant (P-Ph-NH ACL) obtained in Example 1, wherein the aldehyde compound used was benzaldehyde and the organophosphorus compound containing a PH bond was DOPO, substituted with hexamethylenediamine adipate, was copolymerized to produce a flame-retardant nylon 66 resin (FR-PA66-8). The flame retardant was added in an amount of 8 wt%. The flame-retardant nylon 66 resin (FR-PA66-8) had a limiting oxygen index of 36% and a vertical flammability rating of UL94 V-0.

[0112] Example 10

[0113] The α-aminocaprolactam flame retardant (P-Ph-NHACL) obtained in Example 1, wherein the aldehyde compound used was benzaldehyde and the organophosphorus compound used was DOPO containing a PH bond, substituted with a PCN bond functional group, was reactively blended and extruded with polyurethane resin chips to produce a flame-retardant polyurethane resin (FR-PU-8). The flame retardant was added in an amount of 8 wt%. The flame-retardant polyurethane resin (FR-PU-8) had a limiting oxygen index of 31% and a vertical flammability rating of UL94 V-0.

[0114] Example 11

[0115] The α-aminocaprolactam flame retardant (P-Ph-NHACL) obtained in Example 1, wherein the aldehyde compound used was benzaldehyde and the organophosphorus compound used was DOPO containing a PH bond, was reactively extruded with polyethylene terephthalate (PET) chips through a twin-screw extruder to obtain a flame-retardant PET resin (FR-PET-8). The flame retardant was added in an amount of 8 wt%. The flame-retardant PET resin (FR-PET-8) had a limiting oxygen index of 32% and a vertical flammability rating of UL94 V-0.

[0116] Example 12

[0117] The α-aminocaprolactam flame retardant (P-Ph(Br)-NHACL) obtained in Example 2, wherein the aldehyde compound used was p-bromobenzaldehyde and the organophosphorus compound containing a PH bond was DOPO, substituted with a PCN functional group, was hydrolyzed and co-condensed with caprolactam to produce a flame-retardant nylon 6 resin (FR-PA6-6(Br)). The flame retardant was added in an amount of 6 wt%. The flame-retardant nylon 6 resin (FR-PA6-6(Br)) had a limiting oxygen index of 36% and a vertical flammability rating of UL94 V-0.

Claims

1. An α-aminocaprolactam flame retardant containing a PCN bond functional group substitution, characterized in that: Its general chemical structure is shown in formula (I): （I）； Wherein, R1 is derived from an aldehyde compound containing R1 R1-CHO, R2 and R3 are derived from an organophosphorus compound containing a PH bond R2R3P(O)H, The aldehyde compound containing R1 is paraformaldehyde, hexanal, octanal, benzaldehyde, p-bromobenzaldehyde, p-hydroxybenzaldehyde, terephthalaldehyde, p-trifluoromethylbenzaldehyde, syringaldehyde or 2-butyl-5-chloro-1H-imidazole-4-carboxaldehyde; the organophosphorus compound containing a PH bond is selected from one of the following structures: (IV) (V) (VI), (VII).

2. The method for preparing the α-aminocaprolactam flame retardant containing a PCN bond functional group substitution according to claim 1, characterized in that: It is synthesized from three components: α-aminocaprolactam, an aldehyde compound containing R1, and an organic phosphorus compound containing a PH bond. The general synthesis formula is shown in formula (II): (II); The structural formula of the α-aminocaprolactam is shown in formula (III); (III); The aldehyde compound containing R1 is paraformaldehyde, hexanal, octanal, benzaldehyde, p-bromobenzaldehyde, p-hydroxybenzaldehyde, terephthalaldehyde, p-trifluoromethylbenzaldehyde, syringaldehyde or 2-butyl-5-chloro-1H-imidazole-4-carboxaldehyde; the organophosphorus compound containing a PH bond is selected from one of the following structures: (IV) (V) (VI), (VII).

3. The preparation method according to claim 2, characterized in that The preparation method specifically comprises the following steps: The synthesis is carried out in two steps through the Kabachnik-Fields reaction. The first step is to react α-aminocaprolactam with an aldehyde-containing compound to synthesize a Schiff base intermediate. The second step is to react an organophosphorus compound containing a PH bond with the Schiff base intermediate synthesized in the first step to obtain an α-aminocaprolactam flame retardant substituted with a PCN bond functional group.

4. The preparation method according to claim 3, characterized in that The first step, the synthesis of the Schiff base intermediate, is carried out according to the reaction formula (VIII): (VIII), The aldehyde compound containing the R1 group and α-aminocaprolactam are dissolved in an organic solvent, and after complete dissolution, a catalyst and a water absorbent are added, and the reaction is carried out under heating conditions. After the reaction is completed, the reaction liquid is filtered and the solvent is removed by distillation under reduced pressure. The solvent is used for post-processing for recrystallization or pulping, and the solvent is removed by filtration to obtain a Schiff base intermediate.

5. The preparation method according to claim 4, characterized in that The molar ratio of the aldehyde compound containing an R1 group to α-aminocaprolactam is 1:1-1.2, the molar ratio of the aldehyde compound containing an R1 group to the catalyst is 1:0.01-0.1, the molar ratio of the aldehyde compound containing an R1 group to the water absorbent is 1:1-3, and the amount of the organic solvent used is 5-50 times the mass of the aldehyde compound containing an R1 group; the catalyst is any one of hydrochloric acid, acetic acid, and p-toluenesulfonic acid; the water absorbent is any one of anhydrous magnesium sulfate, anhydrous sodium sulfate, and calcium oxide; the organic solvent is any one of dichloromethane, chloroform, ethanol, tetrahydrofuran, and toluene; the reaction time is 4 h-72 h; the reaction temperature is 35° C.-115° C.; and the solvent used for post-reaction treatment is one or more of dichloromethane, chloroform, tetrahydrofuran, ethanol, ethyl acetate, petroleum ether, and diethyl ether.

6. The preparation method according to claim 3, characterized in that The second step reaction is the synthesis of the α-aminocaprolactam flame retardant containing a PCN bond functional group substitution, which is carried out according to the reaction formula shown in formula (IX): (IX), The Schiff base intermediate synthesized in the first step undergoes a nucleophilic addition reaction with an organic phosphorus compound containing a PH bond. After the reaction is completed, the reaction solvent is removed by distillation under reduced pressure to obtain a crude product. The crude product is recrystallized or pulped to obtain an α-aminocaprolactam flame retardant containing a PCN bond functional group substitution.

7. The preparation method according to claim 6, characterized in that The molar ratio of the Schiff base intermediate to the organophosphorus compound containing a PH bond is 1:1-1.

2. The reaction is carried out under the condition of adding a reaction solvent, and the amount of the reaction solvent used is 5-50 times the mass of the Schiff base monomer. The reaction solvent is dichloromethane, chloroform, tetrahydrofuran, anhydrous ethanol or toluene. The reaction time is 4 hours to 72 hours. The reaction temperature is 35°C to 115°C. The solvent used for recrystallization is one or more of dichloromethane, chloroform, ethanol, ethyl acetate, petroleum ether and ether.

8. Use of the α-aminocaprolactam flame retardant containing a PCN bond functional group substituted according to claim 1 in the preparation of a flame retardant polymer material, characterized in that: Select one of the following applications: The α-aminocaprolactam flame retardant containing a PCN bond functional group substituted and caprolactam are hydrolyzed and co-condensed to prepare an intrinsic flame-retardant polyamide 6 resin; The α-aminocaprolactam flame retardant containing a PCN bond functional group substituted and caprolactam are anion polymerized to prepare an intrinsic flame retardant casting polyamide 6 resin; Adding the α-aminocaprolactam flame retardant containing a PCN bond functional group to the polymerization process of other polyamide resins to prepare a variety of intrinsic flame retardant polyamide resins; The α-aminocaprolactam flame retardant containing a PCN bond functional group substituted and caprolactone are anion polymerized to prepare an intrinsic flame retardant polycaprolactone resin; Adding the α-aminocaprolactam flame retardant containing a PCN bond functional group to the polymerization process of other polyester resins to prepare a variety of intrinsic flame retardant polyester resins; Adding the α-aminocaprolactam flame retardant containing a PCN bond functional group to the polymerization process of the epoxy resin to prepare an intrinsic flame retardant epoxy resin; Adding the α-aminocaprolactam flame retardant containing a PCN bond functional group into the polyurethane polymerization process to prepare an intrinsic flame retardant polyurethane resin; Alternatively, the intrinsic flame-retardant resin material is prepared by reactively extruding the α-aminocaprolactam flame retardant containing a PCN bond functional group substitution and a resin matrix polyamide resin, polyester resin or polyurethane resin.

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