An intrinsically flame-retardant nylon 66 and its preparation method

Abstract

This invention relates to the field of flame-retardant polymer materials technology, and in particular to an intrinsically flame-retardant nylon 66 and its preparation method. This invention embeds a furan-phosphorus synergistic flame-retardant structure into the molecular backbone of nylon 66. This design achieves dual-dimensional synergistic flame retardancy at the molecular level, encompassing both the gas-phase and condensed-phase phases. The furan ring can catalyze char formation at high temperatures, providing a high-quality char source for the system; while the phosphorus-containing units decompose and release free radicals in the gas phase, interrupting the chain combustion reaction, and simultaneously promote the formation of a dense char layer in the condensed phase. The synergistic effect of these two factors significantly improves the flame-retardant efficiency.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant polymer materials technology, and in particular to an intrinsically flame-retardant nylon 66 and its preparation method. Background Technology

[0002] Nylon 66 (PA66) is widely used in electronics, automobiles, textiles and other fields due to its excellent mechanical properties, heat resistance and processability. However, PA66 has a limiting oxygen index of only about 20-22%, making it extremely flammable and producing severe molten dripping during combustion, which limits its application in scenarios with stringent flame retardant requirements.

[0003] Traditional methods for improving the flame retardant properties of PA66 mainly rely on additive flame retardants, such as phosphorus-containing, nitrogen-containing, or inorganic flame retardants. However, additive flame retardants have poor compatibility with the PA66 matrix and are prone to migration and precipitation during long-term use or in humid and hot environments, leading to a decrease in flame retardant performance and deterioration of the material's mechanical properties and surface quality. To address this issue, researchers have attempted to introduce flame-retardant elements (such as phosphorus) into the PA66 main chain through copolymerization to prepare intrinsically flame-retardant nylon. Existing technologies often employ direct salt formation of phosphorus-containing dicarboxylic acids (such as phenylphosphonic acid and DOPO derivatives) with hexamethylenediamine, followed by copolymerization with adipic acid, or the use of phosphorus-containing diamines. However, these methods still have significant shortcomings: on the one hand, the flame retardant efficiency of a single phosphorus structure is limited, making it difficult to achieve the ideal flame retardant level at low addition levels; on the other hand, the introduction of phosphorus-containing monomers often disrupts the regularity of nylon chain segments, leading to decreased crystallinity, lower melting point, and loss of mechanical properties.

[0004] In recent years, furan-based bio-based monomers have attracted attention due to their rigid oxygen-containing heterocyclic structure, excellent char-forming ability, and sustainability. Among them, 2,5-di(aminomethyl)furan (BAMF) is a furan diamine monomer. Its furan ring can undergo ring-opening rearrangement at high temperatures, promoting cross-linking and char formation, and exhibiting a condensed-phase flame-retardant effect. However, when BAMF is introduced into PA66 as a comonomer alone, the low polarity of the furan ring leads to poor compatibility with the amide segment, easily resulting in uneven polymerization and a low molecular weight. More importantly, BAMF itself does not contain flame-retardant elements, and its use alone cannot impart highly efficient flame-retardant properties to the material. Summary of the Invention

[0005] The purpose of this invention is to provide an intrinsically flame-retardant nylon 66 and its preparation method. By using a "pre-salt-copolymerization" strategy, 2,5-di(aminomethyl)furan and phosphorus-containing dicarboxylic acid are introduced into the main chain of nylon 66 to construct an intrinsically flame-retardant structure with "furan-phosphorus" synergy. This enables the material to maintain good mechanical and processing properties while endowing it with efficient and long-lasting flame-retardant properties.

[0006] To achieve the above objectives, the present invention provides a method for preparing intrinsically flame-retardant nylon 66, comprising the following preparation steps: After mixing the flame retardant salt with hexamethylenediamine adipic acid salt, a condensation reaction was carried out under a protective atmosphere to obtain intrinsically flame retardant nylon 66. The flame-retardant salt includes at least one of the following compounds: .

[0007] Preferably, the mass ratio of the flame retardant salt to hexamethylenediamine adipic acid salt is 1:0.01-20.

[0008] Preferably, the polycondensation reaction process includes sequential dehydration, preliminary melt polycondensation, and depressurization; the dehydration temperature is 205-215℃, the holding time is 0.5-1h, and the rate of heating to the dehydration temperature is 2-5℃ / min; the preliminary melt polycondensation temperature is 255-265℃, the holding time is 0.5-1h, the pressure is 1.5-2.0MPa, and the rate of heating to the preliminary melt polycondensation temperature is 1-3℃ / min; the depressurization process includes releasing the pressure value of the preliminary melt polycondensation to atmospheric pressure, and then evacuating to 0.05-0.1kPa; the depressurization rate is 0.01-0.05MPa / min.

[0009] In an optional embodiment of the present invention, the polycondensation reaction includes: mixing a flame-retardant salt with hexamethylenediamine adipate and placing the mixture in a polymerization reactor; heating the system to 205-215°C at a rate of 2-5°C / min under a protective atmosphere and holding at this temperature for 0.5-1 h for dehydration; then heating to 255-265°C at a rate of 1-3°C / min and holding at this temperature for 0.5-1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation is maintained at 1.5-2.0 MPa); then depressurizing the pressure to atmospheric pressure at a rate of 0.01-0.05 MPa / min and then evacuating to 0.05-0.1 kPa. The protective atmosphere includes nitrogen.

[0010] Preferably, the preparation process of the flame retardant salt includes: mixing an aqueous solution of a phosphorus diacid monomer with an aqueous solution of 2,5-bis(aminomethyl)furan to carry out a salt formation reaction to obtain a salt solution, and evaporating and dehydrating the salt solution to obtain the flame retardant salt.

[0011] Preferably, the concentration of the aqueous solution containing the phosphorus dicarboxylic acid monomer is 0.15-0.25 mol / L, and the concentration of the aqueous solution of 2,5-bis(aminomethyl)furan is 0.15-0.25 mol / L.

[0012] In an optional embodiment of the present invention, the preparation process of the phosphorus-containing dicarboxylic acid monomer aqueous solution includes: placing the phosphorus-containing dicarboxylic acid monomer in deionized water and mixing to obtain the phosphorus-containing dicarboxylic acid monomer aqueous solution. The mixing temperature is 25-80℃ and the time is 0.05-1h.

[0013] In this invention, the preparation process of the 2,5-bis(aminomethyl)furan aqueous solution includes: placing 2,5-bis(aminomethyl)furan in deionized water and mixing to obtain the 2,5-bis(aminomethyl)furan aqueous solution. The mixing temperature is 25-80℃, and the time is 0.05-1h.

[0014] In an optional embodiment of the present invention, the concentration of the aqueous solution of the phosphorus-containing dicarboxylic acid monomer is 0.20 mol / L, and the concentration of the aqueous solution of 2,5-bis(aminomethyl)furan is 0.20 mol / L.

[0015] Preferably, in the aqueous solution of the phosphorus-containing dicarboxylic acid monomer, the phosphorus-containing dicarboxylic acid monomer includes: 5-((diphenoxyphosphoryl)amino)isophthalic acid, 5-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)amino)isophthalic acid, 5-((diphenylphosphoryl)amino)isophthalic acid, 2-((diphenoxyphosphoryl)methyl)succinic acid, 2-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)methyl)succinic acid, 2-((diphenylphosphoryl)methyl)succinic acid, 4-(((4-carboxyphenyl)(diphenyl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)methyl)succinic ... At least one of the following: phenoxyphosphoryl)methyl)amino)benzoic acid, 4-(((4-carboxyphenyl)(6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)methyl)amino)benzoic acid, 4-(((4-carboxyphenyl)(diphenylphosphoryl)methyl)amino)benzoic acid, 5-(bis((diphenoxyphosphoryl)methyl)amino)isophthalic acid, 5-(bis((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)methyl)amino)isophthalic acid, and 5-(bis((diphenylphosphoryl)methyl)amino)isophthalic acid.

[0016] The structural formula of the 5-((diphenoxyphosphoryl)amino)isophthalic acid is as follows: .

[0017] The structural formula of 5-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)amino)isophthalic acid is as follows: .

[0018] The structural formula of the 5-((diphenylphospho)amino)isophthalic acid is as follows: .

[0019] The structural formula of 2-((diphenoxyphosphoryl)methyl)succinic acid is as follows: .

[0020] The structural formula of 2-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)methyl)succinic acid is as follows: .

[0021] The structural formula of 2-((diphenylphospho)methyl)succinic acid is as follows: .

[0022] The structural formula of 4-(((4-carboxyphenyl)(diphenoxyphosphoryl)methyl)amino)benzoic acid is as follows: .

[0023] The structural formula of 4-(((4-carboxyphenyl)(6-oxodibenzo[c,e][1,2]oxaphosphacyclohexene-6-yl)methyl)amino)benzoic acid is as follows: .

[0024] The structural formula of 4-(((4-carboxyphenyl)(diphenylphosphomethyl)amino)benzoic acid is as follows: .

[0025] The structural formula of the 5-(bis((diphenoxyphosphoryl)methyl)amino)isophthalic acid is as follows: .

[0026] The structural formula of 5-(bis((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)methyl)amino)isophthalic acid is as follows: .

[0027] The structural formula of the 5-(bis((diphenylphospho)methyl)amino)isophthalic acid is as follows: .

[0028] Preferably, the salt-forming reaction is carried out at a temperature of 40-80°C for a time of 0.5-5 hours.

[0029] In one optional embodiment of the present invention, the salt formation reaction is carried out at a temperature of 70°C for 2 hours.

[0030] In an optional embodiment of the present invention, the temperature of the evaporation and dehydration is 80°C.

[0031] The present invention also provides intrinsic flame-retardant nylon 66 prepared by the above-described method for preparing intrinsic flame-retardant nylon 66.

[0032] Preferably, the intrinsic flame-retardant nylon 66 provided by the present invention can be applied in the fields of electronics, automobiles, or textiles.

[0033] The present invention has the following beneficial effects: This invention involves pre-reacting 2,5-bis(aminomethyl)furan with a phosphorus-containing diacid to form a flame-retardant salt, followed by a condensation reaction with hexamethylenediamine adipic acid salt, thereby embedding a "furan-phosphorus" synergistic flame-retardant structure into the molecular backbone of nylon 66. This design achieves synergistic flame retardancy in both the gas-phase and condensed-phase dimensions at the molecular level. The furan ring in 2,5-bis(aminomethyl)furan can be catalytically converted into char at high temperatures, providing a high-quality char source for the system; while the phosphorus-containing unit decomposes and releases free radicals in the gas phase, interrupting the chain combustion reaction, and promotes the formation of a dense char layer in the condensed phase. The synergistic effect of these two factors significantly improves the flame-retardant efficiency.

[0034] To address the mismatch in polymerization activity between furan diamine and nylon 66 salt, this invention employs a pre-salt copolymerization strategy. Through covalent bonding and reactivity regulation, it ensures the synthesis of high molecular weight polymers, endowing PA66 with intrinsic flame-retardant properties while maintaining its mechanical properties, and achieving uniform distribution and long-lasting stability of flame-retardant units in the main chain.

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0036] Figure 1 This is a comparison diagram of the thermal stability of the flame retardant salt (Formula I) prepared in Example 1 of the present invention, the white PA66 salt prepared in Comparative Example 1, and the phosphate salt-A prepared in Comparative Example 2. Figure 2 This is a comparison chart of the combustion heat release rates of intrinsic flame-retardant nylon 66 prepared in Example 1 of the present invention, pure nylon 66 prepared in Comparative Example 1, and flame-retardant nylon 66 prepared in Comparative Example 2. Figure 3 This is a comparison diagram of the thermal stability of the flame retardant salt (Formula V) prepared in Example 5 of the present invention, the white PA66 salt prepared in Comparative Example 1, and the phosphate salt-B prepared in Comparative Example 3. Figure 4 This is a comparison chart of the combustion heat release rates of intrinsic flame-retardant nylon 66 prepared in Example 5 of the present invention, pure nylon 66 prepared in Comparative Example 1, and flame-retardant salt prepared in Comparative Example 3. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0038] Example 1 The phosphorus-containing dicarboxylic acid monomer is 5-((diphenoxyphosphoryl)amino)isophthalic acid, with the following structural formula: .

[0039] 10.0 mmol of 5-((diphenoxyphosphoryl)amino)isophthalic acid (a phosphorus dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0040] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame retardant salt (Formula I), with the following structure: Formula I.

[0041] 5.0 g of flame-retardant salt of Formula I and 45.0 g of hexamethylenediamine adipate (PA66 salt) were mixed and placed in a polymerization reactor. The system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration under a nitrogen atmosphere. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). The pressure was then released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame-retardant nylon 66.

[0042] Example 2 The phosphorus-containing dicarboxylic acid monomer is 5-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)amino)isophthalic acid, with the following structural formula: .

[0043] 10.0 mmol of 5-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexene-6-yl)amino)isophthalic acid (a phosphorus-containing dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus-containing dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0044] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame retardant salt (Formula II), with the following structure: Formula II.

[0045] 5.0 g of flame-retardant salt of Formula II was mixed with 45.0 g of hexamethylenediamine adipate (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame-retardant nylon 66.

[0046] Example 3 The phosphorus-containing dicarboxylic acid monomer is 5-((diphenylphospho)amino)isophthalic acid, with the following structural formula: .

[0047] 10.0 mmol of 5-((diphenylphospho)amino)isophthalic acid (a phosphorus dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0048] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame retardant salt (Formula IV), with the following structure: Formula IV.

[0049] 5.0 g of flame-retardant salt of Formula IV was mixed with 45.0 g of hexamethylenediamine adipate (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame-retardant nylon 66.

[0050] Example 4 The phosphorus-containing dicarboxylic acid monomer is 2-((diphenoxyphosphoryl)methyl)succinic acid, with the following structural formula: .

[0051] 10.0 mmol of 2-((diphenoxyphosphoryl)methyl)succinic acid (a phosphorus dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0052] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame-retardant salt (Formula III), with the following structure: Formula III.

[0053] 5.0 g of flame-retardant salt of Formula III was mixed with 45.0 g of hexamethylenediamine adipate (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame-retardant nylon 66.

[0054] Example 5 The phosphorus-containing dicarboxylic acid monomer is 2-((6-oxodibenzo[c,e][1,2]oxaporhexene-6-yl)methyl)succinic acid, with the following structural formula: .

[0055] 10.0 mmol of 2-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)methyl)succinic acid (a phosphorus-containing dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 80 °C for 0.05 h to obtain a 0.2 mol / L aqueous solution of the phosphorus-containing dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 80 °C for 0.05 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0056] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 80 °C for 3 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame retardant salt (Formula V), with the following structure: Formula V.

[0057] 45.0 g of flame retardant salt of formula V was mixed with 5.0 g of hexamethylenediamine adipic acid salt (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame retardant nylon 66.

[0058] Example 6 The phosphorus-containing dicarboxylic acid monomer is 2-((diphenylphospho)methyl)succinic acid, with the following structural formula: .

[0059] 10.0 mmol of 2-((diphenylphospho)methyl)succinic acid (a phosphorus dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0060] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame-retardant salt (Formula VI), with the following structure: Formula VI.

[0061] 5.0 g of flame retardant salt of formula VI was mixed with 45.0 g of hexamethylenediamine adipic acid salt (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame retardant nylon 66.

[0062] Example 7 The phosphorus-containing dicarboxylic acid monomer is 4-(((4-carboxyphenyl)(diphenoxyphosphoryl)methyl)amino)benzoic acid, with the following structural formula: .

[0063] 10.0 mmol of 4-(((4-carboxyphenyl)(diphenoxyphosphoryl)methyl)amino)benzoic acid (a phosphorus-containing dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus-containing dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0064] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame-retardant salt (Formula VII), with the following structure: Formula VII.

[0065] 5.0 g of flame-retardant salt of formula VII was mixed with 45.0 g of hexamethylenediamine adipate (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame-retardant nylon 66.

[0066] Example 8 The phosphorus-containing dicarboxylic acid monomer is 4-(((4-carboxyphenyl)(6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)methyl)amino)benzoic acid, with the following structural formula: .

[0067] 10.0 mmol of 4-(((4-carboxyphenyl)(6-oxodibenzo[c,e][1,2]oxaphosphacyclohexene-6-yl)methyl)amino)benzoic acid (a phosphorus-containing dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus-containing dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0068] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame retardant salt (formula VIII), with the following structure: Formula VIII.

[0069] 5.0 g of flame-retardant salt of formula VIII was mixed with 45.0 g of hexamethylenediamine adipic acid salt (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame-retardant nylon 66.

[0070] Example 9 The phosphorus-containing dicarboxylic acid monomer is 4-(((4-carboxyphenyl)(diphenylphospho)methyl)amino)benzoic acid, with the following structural formula: .

[0071] 10.0 mmol of 4-(((4-carboxyphenyl)(diphenylphosphomethyl)amino)benzoic acid (a phosphorus-containing dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus-containing dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0072] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame-retardant salt (Formula IX), with the following structure: Formula IX.

[0073] 5.0 g of flame retardant salt of formula IX was mixed with 45.0 g of hexamethylenediamine adipic acid salt (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame retardant nylon 66.

[0074] Example 10 The phosphorus-containing dicarboxylic acid monomer is 5-(bis((diphenoxyphosphoryl)methyl)amino)isophthalic acid, with the following structural formula: .

[0075] 10.0 mmol of 5-(bis((diphenoxyphosphoryl)methyl)amino)isophthalic acid (a phosphorus dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0076] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame-retardant salt (Formula X), with the following structure: Formula X.

[0077] 5.0 g of flame retardant salt of formula X was mixed with 45.0 g of hexamethylenediamine adipic acid salt (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame retardant nylon 66.

[0078] Example 11 The phosphorus-containing dicarboxylic acid monomer is 5-(bis((6-oxodibenzo[c,e][1,2]oxaphosphazene-6-yl)methyl)amino)isophthalic acid, with the following structural formula: .

[0079] 10.0 mmol of 5-(bis((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexene-6-yl)methyl)amino)isophthalic acid (a phosphorus-containing dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus-containing dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0080] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame retardant salt (Formula XI), with the following structure: Formula XⅠ.

[0081] 5.0 g of flame-retardant salt of formula XⅠ was mixed with 45.0 g of hexamethylenediamine adipate (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame-retardant nylon 66.

[0082] Example 12 The phosphorus-containing dicarboxylic acid monomer is 5-(bis((diphenylphosphoyl)methyl)amino)isophthalic acid, with the following structural formula: .

[0083] 10.0 mmol of 5-(bis((diphenylphosphoyl)methyl)amino)isophthalic acid (a phosphorus dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus dicarboxylic acid monomer. 10.0 mmol of 2,5-bis(aminomethyl)furan was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan.

[0084] The 0.2 mol / L aqueous solution of 2,5-bis(aminomethyl)furan prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain a flame retardant salt (Formula XII), with the following structure: Formula XII.

[0085] 5.0 g of flame-retardant salt of formula XII was mixed with 45.0 g of hexamethylenediamine adipate (PA66 salt) and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain intrinsic flame-retardant nylon 66.

[0086] Comparative Example 1 10.0 mmol hexamethylenediamine was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of hexamethylenediamine. 10.0 mmol of adipic acid was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of adipic acid.

[0087] Adipic acid aqueous solution was added dropwise to hexamethylenediamine aqueous solution, and the reaction was carried out at 70°C for 1 hour. The pH was adjusted to 7.5 to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80°C to obtain white PA66 salt, with the following structural formula: .

[0088] 50.0 g of white PA66 salt was placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min, and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain pure nylon 66.

[0089] Comparative Example 2 The phosphorus-containing dicarboxylic acid monomer is 5-((diphenoxyphosphoryl)amino)isophthalic acid, with the following structural formula: .

[0090] 10.0 mmol of 5-((diphenoxyphosphoryl)amino)isophthalic acid (a phosphorus dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus dicarboxylic acid monomer. 10.0 mmol hexamethylenediamine was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of hexamethylenediamine.

[0091] The 0.2 mol / L hexamethylenediamine aqueous solution prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and the salt formation reaction was carried out at 70 °C for 2 h to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80 °C to obtain phosphate salt-A (without furan unit), with the following structure: .

[0092] 3.87 g of phosphate salt-A and 50.0 g of hexamethylenediamine adipic acid salt (PA66 salt) were mixed and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min, and then vacuumed to 0.05 kPa to complete the polycondensation reaction and obtain flame-retardant nylon 66.

[0093] Comparative Example 3 The phosphorus-containing dicarboxylic acid monomer is 2-((6-oxodibenzo[c,e][1,2]oxaporhexene-6-yl)methyl)succinic acid, with the following structural formula: .

[0094] 10.0 mmol of 2-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexene-6-yl)methyl)succinic acid (a phosphorus dicarboxylic acid monomer) was placed in 50 mL of deionized water and mixed at 70 °C for 1 h to obtain a 0.2 mol / L aqueous solution of the phosphorus dicarboxylic acid monomer. 10.0 mmol of hexamethylenediamine was placed in 50 mL of deionized water and mixed at 80 °C for 1 h to obtain a 0.2 mol / L aqueous solution of hexamethylenediamine.

[0095] The hexamethylenediamine aqueous solution prepared above was added dropwise to an aqueous solution containing a phosphorus diacid monomer, and a salt formation reaction was carried out at 80°C for 3 hours to obtain a salt solution. The salt solution was placed in a vacuum oven and evaporated at 80°C to obtain phosphate salt-B (without furan unit), with the following structure: .

[0096] 45.0 g of phosphate salt-B and 5.0 g of hexamethylenediamine adipic acid salt (PA66 salt) were mixed and placed in a polymerization reactor. Under a nitrogen atmosphere, the system temperature was raised to 210 °C at a rate of 2 °C / min and held for 1 h for dehydration. Then, the temperature was raised to 260 °C at a rate of 1 °C / min and held for 1 h for preliminary melt polycondensation (the pressure during the preliminary melt polycondensation was 2.0 MPa). Subsequently, the pressure was released to atmospheric pressure at a rate of 0.01 MPa / min, and then evacuated to 0.05 kPa to complete the polycondensation reaction and obtain the flame retardant salt.

[0097] Performance testing: The thermal stability of the flame-retardant salt (Formula I) prepared in Example 1, the white PA66 salt prepared in Comparative Example 1, and the phosphate salt-A prepared in Comparative Example 2 were tested, and the results are as follows: Figure 1 As shown. From Figure 1It can be seen that the white PA66 salt prepared in Comparative Example 1 has a char residue of 1.25 wt% at 800℃, while the char residue of phosphate salt-A in Comparative Example 2 is 36.16 wt% at 800℃. Example 1 (flame retardant salt (Formula I)) achieved a char residue of 43.94 wt% at 800℃, which is significantly higher than the 1.25 wt% of the white PA66 salt in Comparative Example 1, and also significantly better than the 36.16 wt% of the phosphorus-containing structure (without furan units) in Comparative Example 2. This result fully demonstrates that the present invention, by introducing furan rings and phosphorus-containing units into the salt-forming product, can exert a significant synergistic char-forming effect at high temperatures, forming a more stable and denser char layer, thereby endowing the material with superior thermal stability.

[0098] The combustion heat release rates of intrinsic flame-retardant nylon 66 prepared in Example 1, pure nylon 66 prepared in Comparative Example 1, and flame-retardant nylon 66 prepared in Comparative Example 2 were tested, and the results are as follows: Figure 2 As shown. From Figure 2 As can be seen, the peak heat release rate of pure nylon 66 in Comparative Example 1 is 384.7 W / g, the peak heat release rate of flame-retardant nylon 66 in Comparative Example 2 (containing only phosphorus structure, without furan units) is 159.3 W / g, while the peak heat release rate of intrinsic flame-retardant nylon 66 in Example 1 is 118.9 W / g, which is much lower than that of Comparative Example 1 (a reduction of about 69.1%), and also significantly lower than that of Comparative Example 2 (a reduction of about 25.3%). The above comparison fully demonstrates that by simultaneously introducing furan rings and phosphorus-containing units into the main chain of nylon 66, the present invention can exert a significant synergistic flame-retardant effect during combustion, more effectively suppressing heat release, thereby obtaining flame-retardant properties that are superior to those of single phosphorus-modified and unmodified nylon 66.

[0099] The thermal stability of the flame-retardant salt (Formula V) prepared in Example 5, the white PA66 salt prepared in Comparative Example 1, and the phosphate salt-B prepared in Comparative Example 3 were tested, and the results are as follows: Figure 3 As shown. From Figure 3 It can be seen that the white PA66 prepared in Comparative Example 1 has a char residue of 1.25 wt% at 800℃, the phosphate salt-B prepared in Comparative Example 3 has a char residue of 19.76 wt% at 800℃, and the flame-retardant salt (Formula V) prepared in Example 5 has a char residue of 33.98 wt% at 800℃, which is much higher than the 1.25 wt% of the white PA66 in Comparative Example 1, and also significantly better than the 19.76 wt% of the phosphorus-only structure (without furan) in Comparative Example 3. These results indicate that by introducing the furan ring and phosphorus-containing unit together into the salt-forming product, the present invention significantly improves the char-forming ability and char layer stability of the material at high temperatures. Its thermal stability is significantly better than that of single phosphorus-modified and unmodified nylon 66 salts, exhibiting excellent high-temperature residue and thermal stability.

[0100] The combustion heat release rates of the intrinsic flame-retardant nylon 66 prepared in Example 5, the pure nylon 66 prepared in Comparative Example 1, and the flame-retardant salt prepared in Comparative Example 3 are as follows: Figure 4 As shown. From Figure 4 As can be seen, the peak heat release rate of the intrinsic flame-retardant nylon 66 prepared in Example 5 is 295.5 W / g, which is significantly lower than that of pure PA66 in Comparative Example 1 (384.7 W / g) and that of phosphorus-only (without furan rings) in Comparative Example 3 (327.9 W / g). This result fully demonstrates that the present invention, through a synergistic flame-retardant strategy of "furan-phosphorus," can more effectively suppress heat release during combustion. The peak heat release rate is reduced by approximately 23.2% compared to pure PA66 and by approximately 9.9% compared to the control sample containing only phosphorus, exhibiting significantly better flame-retardant performance than single phosphorus-modified and unmodified nylon 66.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing intrinsically flame-retardant nylon 66, characterized in that, The preparation steps include the following: After mixing the flame retardant salt with hexamethylenediamine adipic acid salt, a condensation reaction was carried out under a protective atmosphere to obtain intrinsically flame retardant nylon 66. The flame-retardant salt includes at least one of the following compounds: 。 2. The method for preparing intrinsically flame-retardant nylon 66 according to claim 1, characterized in that, The mass ratio of the flame retardant salt to hexamethylenediamine adipic acid salt is 1:0.01-20.

3. The method for preparing intrinsically flame-retardant nylon 66 according to claim 1, characterized in that, The polycondensation reaction includes sequential dehydration, preliminary melt polycondensation, and depressurization; The dehydration temperature is 205-215℃, the holding time is 0.5-1h, and the rate of heating to the dehydration temperature is 2-5℃ / min. The initial melting polycondensation temperature is 255-265℃, the holding time is 0.5-1h, the pressure is 1.5-2.0MPa, and the rate of heating to the initial melting polycondensation temperature is 1-3℃ / min. The depressurization process includes releasing the initial melt condensation pressure to atmospheric pressure, followed by evacuating to 0.05-0.1 kPa; the depressurization rate is 0.01-0.05 MPa / min.

4. The method for preparing intrinsically flame-retardant nylon 66 according to claim 1, characterized in that, The preparation process of the flame retardant salt includes: An aqueous solution of a phosphorus dicarboxylic acid monomer is mixed with an aqueous solution of 2,5-bis(aminomethyl)furan to form a salt solution, which is then evaporated and dehydrated to obtain a flame retardant salt.

5. The method for preparing intrinsically flame-retardant nylon 66 according to claim 4, characterized in that, The concentration of the aqueous solution containing the phosphorus dicarboxylic acid monomer is 0.15-0.25 mol / L, and the concentration of the aqueous solution of 2,5-bis(aminomethyl)furan is 0.15-0.25 mol / L.

6. The method for preparing intrinsically flame-retardant nylon 66 according to claim 4, characterized in that, In the aqueous solution of the phosphorus-containing dicarboxylic acid monomer, the phosphorus-containing dicarboxylic acid monomer includes: 5-((diphenoxyphosphoryl)amino)isophthalic acid, 5-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)amino)isophthalic acid, 5-((diphenylphosphoryl)amino)isophthalic acid, 2-((diphenoxyphosphoryl)methyl)succinic acid, 2-((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexen-6-yl)methyl)succinic acid, 2-((diphenylphosphoryl)methyl)succinic acid, 4-(((4-carboxyphenyl)(diphenoxyphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)amino)isophthalic acid, 5-(diphenylphosphoryl)methyl)succinic ... At least one of the following: (diphenylphospho)methyl)amino)benzoic acid, 4-(((4-carboxyphenyl)(6-oxodibenzo[c,e][1,2]oxaphosphacyclohexene-6-yl)methyl)amino)benzoic acid, 4-(((4-carboxyphenyl)(diphenylphospho)methyl)amino)benzoic acid, 5-(bis((diphenoxyphospho)methyl)amino)isophthalic acid, 5-(bis((6-oxodibenzo[c,e][1,2]oxaphosphacyclohexene-6-yl)methyl)amino)isophthalic acid, and 5-(bis((diphenylphospho)methyl)amino)isophthalic acid.

7. The method for preparing intrinsically flame-retardant nylon 66 according to claim 4, characterized in that, The salt formation reaction is carried out at a temperature of 40-80℃ for a time of 0.5-5 hours.

8. Intrinsically flame-retardant nylon 66 prepared by the preparation method of intrinsically flame-retardant nylon 66 according to any one of claims 1-7.

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