Halogen-free alkyl phosphate oligomer organic flame retardant and synthesis method thereof

Abstract

The invention discloses a halogen-free alkyl phosphate oligomer organic flame retardant and a synthesis method, the halogen-free alkyl phosphate oligomer flame retardant (PNX) is a phosphate oligomer, is often used as an additive flame retardant of polyurethane foam, and has the advantages of no halogen, high phosphorus content, high flame retardant efficiency, low VOC (volatile organic compound) value and the like. The flame retardant is synthesized by the following method: firstly, pre-cooling phosphorus oxychloride, then slowly dropwise adding ethanol in a negative pressure state, and heating for reaction to obtain an ethyl dichlorophosphate intermediate; slowly dropwise adding the ethyl dichlorophosphate intermediate into one third of precooled ethylene glycol, stirring, heating and reacting for a period of time, continuously dropwise adding the rest ethyl dichlorophosphate, reacting for a period of time, and dropwise adding ethanol for blocking to obtain a PNX product. The method has the advantages of simple synthesis process, mild conditions, fast reaction, common and easily available raw materials, no use of a catalyst, no introduction of metal ions, and no need of post-treatment. The large-scale industrial production is easy to realize.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of synthesis process of flame retardant, in particular to a synthesis method of halogen-free alkyl phosphate oligomer organic flame retardant (PNX). BACKGROUND

[0002] Polyurethane foam is widely used as thermal insulation, structural or decorative material in many fields of national economy, such as building, petroleum, chemical pipeline, refrigerator, refrigerated container, aerospace, etc. However, polyurethane foam is extremely flammable and decomposes to release toxic smoke in the air, and its large use also brings a very serious fire situation. In recent years, many fire accidents are related to polyurethane foam. Therefore, it is necessary to flame retard polyurethane foam. At present, the flame retardant of polyurethane foam is mainly small molecule chlorinated phosphate or halogen-based flame retardant, which has the problems of high volatile organic compounds (VOC), large amount of smoke and toxic substances during combustion, low flame retardant performance, large amount of addition, and fog influence on use performance. In comparison, the halogen-free alkyl phosphate oligomer organic flame retardant (PNX) of the present application is a new type of halogen-free flame retardant with high efficiency, environmental protection and low migration, which has broad development prospects.

[0003] At present, the flame retardant applied to polyurethane foam mainly includes halogen-based flame retardant and phosphorus-based flame retardant. Among them, although the halogen-based flame retardant has good flame retardant effect, it has the defects of easy migration, dispersion, and non-persistent flame retardancy, and is easy to produce corrosive gas such as hydrogen halide during combustion. With the improvement of environmental protection requirements, halogen-free, environmental protection and low toxicity have become the trend of development of flame retardant, and the application of halogen-based flame retardant is limited.

[0004] In comparison, phosphorus-based flame retardant has the advantages of low dosage, persistent and stable flame retardancy, and no release of corrosive gas during combustion, and is a good choice for modification of polyurethane foam. However, the existing phosphorus-based flame retardant still has some problems, such as easy migration and precipitation in the base material, resulting in reduced flame retardant performance, or poor compatibility with polymers, affecting the overall performance of the composite material. Therefore, developing a high-efficiency, environmentally friendly, low-migration halogen-free alkyl phosphate oligomer organic flame retardant to replace the halogen-based flame retardant which is easy to migrate and has non-persistent flame retardant effect has become an important research direction for the modification of polyurethane foam.

[0005] The existing technology has the problems of easy migration of halogen-based flame retardant, non-persistent flame retardancy, easy production of corrosive gas, and poor compatibility with polyurethane foam. Therefore, in order to solve the above problems, the present application provides a synthesis method of high-efficiency, environmentally friendly, low-migration halogen-free alkyl phosphate oligomer organic flame retardant (PNX).

[0006] However, there is very little available information on the synthesis of halogen-free alkyl phosphate oligomer organic flame retardants (PNX) in the prior art. To address the shortcomings of the prior art, the purpose of this invention is to provide a method for synthesizing a highly efficient, environmentally friendly, and low-migration halogen-free alkyl phosphate oligomer organic flame retardant. The structural formula of this halogen-free alkyl phosphate oligomer organic flame retardant is as follows: Summary of the Invention

[0007] The purpose of this invention is to provide a method for synthesizing a high-efficiency, environmentally friendly, and low-migration halogen-free alkyl phosphate oligomer organic flame retardant (PNX). The structural formula of this halogen-free alkyl phosphate oligomer organic flame retardant is as follows:

[0008] The design reaction principle of this halogen-free alkyl phosphate oligomer organic flame retardant:

[0009] A method for synthesizing a high-efficiency, environmentally friendly, low-migration halogen-free alkyl phosphate oligomer organic flame retardant (PNX) includes the following steps: (1) Phosphorus oxychloride was pre-cooled to below 5°C and then ethanol was added dropwise under negative pressure. The temperature was increased to carry out the reaction. After the reaction was completed, ethyl dichlorophosphate intermediate S1 was obtained for later use. (2) After precooling ethylene glycol to below 10°C, add ethyl dichlorophosphate intermediate S1 dropwise under negative pressure, and heat up to carry out the reaction. After the reaction is completed, intermediate S2 is obtained. (3) After precooling intermediate S2 to below 20°C, intermediate S1 is added dropwise under negative pressure. Under heating conditions, S1 reacts with S2 to obtain intermediate S3. (4) After precooling intermediate S3 to below 20°C, ethanol is added dropwise under negative pressure to seal the end, and the temperature is raised to carry out the reaction. After the reaction is completed, excess ethanol is evaporated under reduced pressure to obtain PNX product.

[0010] In step (1), below 5℃ refers to any value or any range between -10℃ and 5℃.

[0011] In step (1), ethanol is added dropwise under a negative pressure of 0.02-0.055 MPa; after the addition is completed, the temperature is raised to 25-50℃ and the reaction is carried out under a pressure of 0.08-0.1 MPa.

[0012] The negative pressure condition of 0.02-0.055MPa is any value or any range of this pressure condition.

[0013] The temperature and pressure conditions of 25-50℃ and 0.08-0.1MPa are any values ​​or any ranges of these conditions.

[0014] Low-temperature dropwise addition is used because the reaction is significantly exothermic, and there is a risk of violent boiling and material overflow in the reaction system. Furthermore, it is necessary to control the reaction concentration to avoid excessive reaction, resulting in gel formation and increased degree of polymerization.

[0015] Reaction temperatures exceeding 50°C will cause the product to over-react, forming a gel with increased polymerization degree, making it unable to flow or be stirred; and under negative pressure conditions, some of the product will decompose to form triethyl phosphate as a byproduct.

[0016] Negative pressure is used to promptly vent the byproduct HCl gas during the reaction process, so as to avoid affecting subsequent reactions, product quality, and acid value.

[0017] In step (2), below 10℃ refers to any value or any range between -10℃ and 10℃, such as -10℃ to 5℃ or -10℃ to 0℃.

[0018] In step (2), intermediate S1 is added dropwise under a negative pressure of 0.02-0.055 MPa; after the addition is completed, the temperature is raised to 25-50℃ and the reaction is carried out under a pressure of 0.08-0.1 MPa.

[0019] The negative pressure condition of 0.02-0.055MPa is any value or any range of this pressure condition.

[0020] The temperature and pressure conditions of 25-50℃ and 0.08-0.1MPa are any values ​​or any ranges of these conditions.

[0021] In step (3), below 20℃ refers to any value or any range between -10℃ and 20℃, such as -10℃ to 10℃ or -10℃ to 5℃.

[0022] In step (3), ethanol is added dropwise under a negative pressure of 0.02-0.055 MPa; after the addition is completed, the temperature is raised to 25-50℃ and the reaction is carried out under a pressure of 0.08-0.1 MPa.

[0023] The negative pressure condition of 0.02-0.055MPa is any value or any range of this pressure condition.

[0024] The temperature and pressure conditions of 25-50℃ and 0.08-0.1MPa are any values ​​or any ranges of these conditions.

[0025] Low-temperature dropwise addition is used because the reaction is significantly exothermic, and there is a risk of violent boiling and material overflow in the reaction system. Furthermore, it is necessary to control the reaction concentration to avoid excessive reaction, resulting in gel formation and increased degree of polymerization.

[0026] Reaction temperatures exceeding 50°C will cause the product to over-react, forming a gel with increased polymerization degree, making it unable to flow or be stirred; and under negative pressure conditions, some of the product will decompose to form triethyl phosphate as a byproduct.

[0027] Negative pressure is used to promptly vent the byproduct HCl gas during the reaction process, so as to avoid affecting subsequent reactions, product quality, and acid value.

[0028] In step (4), below 20℃ refers to any value or any range between -10℃ and 20℃, such as -10℃ to 10℃ or -10℃ to 5℃.

[0029] In step (4), intermediate S1 is added dropwise under a negative pressure of 0.02-0.055 MPa; after the addition is completed, the temperature is raised to 25-30℃ and the reaction is carried out under a pressure of 0.08-0.1 MPa.

[0030] The negative pressure condition of 0.02-0.055MPa is any value or any range of this pressure condition.

[0031] The temperature and pressure conditions of 25-30℃ and 0.08-0.1MPa are any values ​​or any ranges of these conditions.

[0032] Low-temperature dropwise addition is used because the reaction is significantly exothermic, and there is a risk of violent boiling and material overflow in the reaction system. Furthermore, it is necessary to control the reaction concentration to avoid excessive reaction, resulting in gel formation and increased degree of polymerization.

[0033] Reaction temperatures exceeding 50°C will cause the product to over-react, forming a gel with increased polymerization degree, making it unable to flow or be stirred; and under negative pressure conditions, some of the product will decompose to form triethyl phosphate as a byproduct.

[0034] Negative pressure is used to promptly vent the byproduct HCl gas during the reaction process, so as to avoid affecting subsequent reactions, product quality, and acid value.

[0035] In step (1), the molar ratio of phosphorus oxychloride to ethanol is 1:1-3.

[0036] In the preferred embodiment, the molar ratio of phosphorus oxychloride to ethanol in step (1) is 1:1.

[0037] In step (2), the molar ratio of ethylene glycol to ethyl dichlorophosphate intermediate S1 is 1.5:1-2.5:1.

[0038] In the preferred embodiment, the molar ratio of ethylene glycol to ethyl dichlorophosphate intermediate S1 in step (2) is 2:1.

[0039] In step (3), the molar ratio of intermediate S2 to ethyl dichlorophosphate intermediate S1 is 1:1.5-1:2.5.

[0040] In the preferred embodiment, the molar ratio of intermediate S2 to ethyl dichlorophosphate intermediate S1 is 1:2.

[0041] In step (4), the molar ratio of intermediate S3 to ethanol is 1:2-1:4.

[0042] In the preferred embodiment, the molar ratio of intermediate S3 to ethanol is 1:4.

[0043] The synthesis of PNX can be broken down into the following steps: (1) Phosphorus oxychloride was precooled to below 5°C and placed in a reaction vessel. Ethanol was slowly added dropwise under a negative pressure of 0.02-0.055 MPa. The temperature was raised to 50°C and the reaction was carried out under a negative pressure of 0.08-0.1 MPa to obtain ethyl dichlorophosphate intermediate.

[0044] (2) Pre-cool ethylene glycol to below 10°C, place it in a reaction vessel, and slowly add the ethyl dichlorophosphate intermediate S1 obtained in step (1) under a negative pressure of 0.02-0.055 MPa. Heat the mixture to 30°C and react it under a negative pressure of 0.08-0.1 MPa to obtain intermediate S2.

[0045] (3) Pre-cool intermediate S2 to below 10°C, place it in a reaction vessel, and continue to slowly add the ethyl dichlorophosphate intermediate obtained in step (1) under a negative pressure of 0.02-0.055 MPa. At the same time, the reaction is carried out at 50°C and the negative pressure is reduced to 0.08-0.1 MPa to obtain intermediate S3.

[0046] (4) Pre-cool intermediate S3 to below 5°C, place it in a reaction vessel, slowly add ethanol as a capping agent under a negative pressure of 0.02-0.055 MPa, heat to 50°C, and react under a negative pressure of 0.08-0.1 MPa. Distill off excess ethanol under reduced pressure to obtain PNX product.

[0047] This invention also provides a halogen-free alkyl phosphate oligomer organic flame retardant, PNX, prepared by the above method. The molecular structure of PNX is as follows: The n is an integer ≤ 6, preferably between 2 and 4. The phosphorus content is ≥ 18%, the acid value is ≤ 0.5 mg KOH / g, the water solubility is good, and the viscosity is between 1000-1100 mPa.s.

[0048] The preferred formulation has a phosphorus content between 19-19.7%, a viscosity between 1000-1100 mPa.s, an acid value ≤0.1 mg KOH / g, and good water solubility.

[0049] In this invention, phosphorus oxychloride, ethanol, and ethylene glycol are all of analytical grade, and the temperature control accuracy of the reaction vessel is ±5℃, and the pressure control accuracy is ±10mbar.

[0050] The method for synthesizing PNX does not require a catalyst and solvent, or the reactants themselves can act as solvents.

[0051] The reaction temperature should be controlled to not exceed 50℃, the reaction pressure should be controlled to be between 50-900mbar, and the reaction time should not exceed 8h.

[0052] The synthesis method of PNX maintains an internal temperature of no more than 20°C during the reaction dropwise addition process and a final temperature of no more than 50°C.

[0053] This invention achieves rapid and efficient reaction by controlling reaction temperature, pressure, and other conditions, utilizing readily available raw materials and facilitating large-scale industrial production, thus overcoming the shortcomings of insufficient reaction condition optimization in existing technologies. The PNX flame retardant of this invention is halogen-free, has a high phosphorus content, exhibits high flame retardant efficiency, and does not release corrosive gases during combustion, improving the product's environmental performance and meeting increasingly stringent environmental requirements. The use of ethanol as a capping agent effectively prevents poor compatibility between the flame retardant and the polyurethane foam matrix material, improving the stability of the flame retardant in the matrix. The synthesis method of this invention is simple, uses readily available raw materials, is convenient to operate, easy to control, and produces stable product quality, solving the problem of complex flame retardant preparation processes in existing technologies.

[0054] The key technical point of this application lies in the fact that the reaction can proceed without using a catalyst, by promptly venting the byproduct HCl gas under negative pressure, and the venting of HCl gas during the reaction effectively controls the acid value of the subsequent products to be less than or equal to 1. The absence of a catalyst prevents the introduction of metal ions or other impurities, allowing for polyurethane applications without post-treatment. A key technical point is the increase in chain length through the reaction of intermediates S1 and S2, effectively utilizing existing raw material technology.

[0055] In traditional processes, the synthesis of PNX typically employs a reaction system of ethylene oxide, triethyl phosphate, and phosphorus pentoxide. This method relies on high-cost catalysts such as stannous isooctanoate, dimethylaminoethyl ether, or organobismuth compounds, and the intermediate pyrophosphate generated during the reaction is highly toxic. Furthermore, ethylene oxide itself is a hazardous chemical, requiring high-pressure reactions, which not only exacerbates the risk of explosions caused by ethylene oxide self-polymerization but also increases the difficulty of process control, leading to a high risk of runaway reactions. The method proposed in this invention features mild reaction conditions suitable for industrial application, avoiding the use of hazardous raw materials and high-cost catalysts. In contrast, by introducing intermediates S1 and S2 to gradually extend the molecular chain, the degree of polymerization can be effectively controlled, allowing for more selective acquisition of target products with a degree of polymerization between 2 and 4. The resulting product exhibits significant water solubility and good water solubility. Attached Figure Description

[0056] Figure 1 This is the mass spectrum of the product from Example 2. Detailed Implementation

[0057] The present invention will be further illustrated below through embodiments. It is worth noting that the given embodiments should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention should still fall within the scope of protection of the present invention.

[0058] Example 1 A method for synthesizing a high-efficiency, environmentally friendly, low-migration halogen-free alkyl phosphate oligomer organic flame retardant (PNX) includes the following steps: (1) Pre-cool phosphorus oxychloride to below 5°C, place it in a reaction vessel, slowly add ethanol under a negative pressure of 0.02 MPa, raise the temperature to 30°C, and carry out the reaction under a negative pressure of 0.1 MPa until no bubbles are generated in the system, and obtain colorless transparent liquid S1 intermediate of ethyl dichlorophosphate for later use. (2) Pre-cool ethylene glycol to below 5°C, place it in a reaction vessel, and slowly add the intermediate S1 of ethyl dichlorophosphate obtained in step (1) under a negative pressure of 0.03 MPa. Heat the mixture to 30°C and react it under a negative pressure of 0.1 MPa until no bubbles are generated in the system. Obtain intermediate S2 as a colorless, transparent, viscous liquid for later use. (3) Pre-cool intermediate S2 to below 5°C, place it in a reaction vessel, and slowly add ethyl dichlorophosphate intermediate S1 obtained in step (1) under a negative pressure of 0.02 MPa. At the same time, carry out the reaction at 30°C and a negative pressure reduced to 0.1 MPa until no bubbles are generated in the system, and obtain intermediate S3 as a colorless, transparent, viscous liquid for later use. (4) Pre-cool intermediate S3 to below 5°C, place it in a reaction vessel, slowly add ethanol as a capping agent under a negative pressure of 0.02 MPa, heat to 30°C, and react under a negative pressure of 0.1 MPa until no bubbles are generated in the system. Then remove excess ethanol to obtain PNX product, which is a colorless, clear, transparent, viscous liquid.

[0059] In step (1), the amount of phosphorus oxychloride used is 1406.53 g (8.94 mol), and the amount of ethanol used is 411.86 g (8.94 mol). In step (2), the amount of ethylene glycol used is 362.56 g (5.84 mol), and the amount of ethyl dichlorophosphate intermediate used is 476.05 g (2.92 mol). In step (3), the amount of intermediate S2 used is the same as all products in step (2), the amount of ethyl dichlorophosphate intermediate used is 772.11 g (5.84 mol), the amount of intermediate S3 used is the same as all products in step (3), and the amount of ethanol used is 270 g (5.94 mol). The above molar relationships can also be converted into corresponding molar ratios.

[0060] The phosphorus oxychloride, ethanol, and ethylene glycol used are all of analytical grade. The temperature control accuracy of the reactor is ±5℃, and the pressure control accuracy is ±0.005MPa.

[0061] The PNX has a degree of polymerization n between 1 and 4, a molecular weight mainly around 790, a phosphorus content of 19.4%, a viscosity of 1089.56 mPa·s, and an acid value of 0.1 mg KOH / g.

[0062] Example 2 A method for synthesizing a high-efficiency, environmentally friendly, low-migration halogen-free alkyl phosphate oligomer organic flame retardant (PNX) includes the following steps: (1) Pre-cool phosphorus oxychloride to below 5°C, place it in a reaction vessel, slowly add ethanol under a negative pressure of 0.02 MPa, raise the temperature to 30°C, and carry out the reaction under a negative pressure of 0.1 MPa until no bubbles are generated in the system, and obtain colorless transparent liquid S1 intermediate of ethyl dichlorophosphate for later use. (2) Pre-cool ethylene glycol to below 10°C, place it in a reaction vessel, and slowly add the intermediate S1 of ethyl dichlorophosphate obtained in step (1) under a negative pressure of 0.03 MPa. Heat the mixture to 35°C and react it under a negative pressure of 0.1 MPa until no bubbles are generated in the system. Obtain intermediate S2 as a colorless, transparent, viscous liquid for later use. (3) Pre-cool intermediate S2 to below 10°C, place it in a reaction vessel, and slowly add ethyl dichlorophosphate intermediate S1 obtained in step (1) under a negative pressure of 0.02 MPa. At the same time, carry out the reaction at 35°C and a negative pressure reduced to 0.1 MPa until no bubbles are generated in the system, and obtain intermediate S3 as a colorless, transparent, viscous liquid for later use. (4) Pre-cool intermediate S3 to below 10°C, place it in a reaction vessel, slowly add ethanol as a capping agent under a negative pressure of 0.02 MPa, heat to 40°C, and react under a negative pressure of 0.1 MPa until no bubbles are generated in the system. Then remove excess ethanol to obtain PNX product, which is a colorless, clear, transparent, viscous liquid.

[0063] In step (1), the amount of phosphorus oxychloride used is 1406.53g (8.94mol) and the amount of ethanol used is 411.86g (8.94mol). In step (2), the amount of ethylene glycol used is 362.56g (5.84mol) and the amount of ethyl dichlorophosphate intermediate used is 476.05g (2.92mol). In step (3), the amount of intermediate S2 used is all the products in step (2), the amount of ethyl dichlorophosphate intermediate used is 772.11g (5.84mol), the amount of intermediate S3 used is all the products in step (3), and the amount of ethanol used is 270g (5.94mol).

[0064] The phosphorus oxychloride, ethanol, and ethylene glycol used are all of analytical grade. The temperature control accuracy of the reactor is ±5℃, and the pressure control accuracy is ±0.005MPa.

[0065] The PNX has a degree of polymerization n between 2 and 5, a phosphorus content of 19.5%, a viscosity of 1093.78 mPa·s, and an acid value of 0.2 mg KOH / g.

[0066] Example 3 A method for synthesizing a high-efficiency, environmentally friendly, low-migration halogen-free alkyl phosphate oligomer organic flame retardant (PNX) includes the following steps: (1) Pre-cool phosphorus oxychloride to below 5°C, place it in a reaction vessel, slowly add ethanol under a negative pressure of 0.03 MPa, raise the temperature to 30°C, and carry out the reaction under a negative pressure of 0.09 MPa until no bubbles are generated in the system, and obtain colorless transparent liquid S1 intermediate of ethyl dichlorophosphate for later use. (2) Pre-cool ethylene glycol to below 10°C, place it in a reaction vessel, and slowly add the intermediate S1 of ethyl dichlorophosphate obtained in step (1) under a negative pressure of 0.03 MPa. Heat the mixture to 35°C and react it under a negative pressure of 0.09 MPa until no bubbles are generated in the system. Obtain intermediate S2 as a colorless, transparent, viscous liquid for later use. (3) Pre-cool intermediate S2 to below 10°C, place it in a reaction vessel, and slowly add ethyl dichlorophosphate intermediate S1 obtained in step (1) under a negative pressure of 0.03 MPa. At the same time, react under the conditions of 35°C and negative pressure reduced to 0.09 MPa until no bubbles are generated in the system, and obtain intermediate S3 as a colorless, transparent, viscous liquid for later use. (4) Pre-cool intermediate S3 to below 10°C, place it in a reaction vessel, slowly add ethanol as a capping agent under a negative pressure of 0.03 MPa, heat to 40°C, and react under a negative pressure of 0.09 MPa until no bubbles are generated in the system. Then remove excess ethanol to obtain PNX product, which is a colorless, clear, transparent, viscous liquid.

[0067] In step (1), the amount of phosphorus oxychloride used is 1406.53g (8.94mol) and the amount of ethanol used is 411.86g (8.94mol). In step (2), the amount of ethylene glycol used is 362.56g (5.84mol) and the amount of ethyl dichlorophosphate intermediate used is 476.05g (2.92mol). In step (3), the amount of intermediate S2 used is all the products in step (2), the amount of ethyl dichlorophosphate intermediate used is 772.11g (5.84mol), the amount of intermediate S3 used is all the products in step (3), and the amount of ethanol used is 270g (5.94mol).

[0068] The phosphorus oxychloride, ethanol, and ethylene glycol used are all of analytical grade. The temperature control accuracy of the reactor is ±2℃, and the pressure control accuracy is ±0.005MPa.

[0069] The PNX has a degree of polymerization n between 2 and 4, a phosphorus content of 19.3%, a viscosity of 1080 mPa·s, and an acid value of 0.3 mg KOH / g.

[0070] Example 4 A method for synthesizing a high-efficiency, environmentally friendly, low-migration halogen-free alkyl phosphate oligomer organic flame retardant (PNX) includes the following steps: (1) Pre-cool phosphorus oxychloride to below 5°C, place it in a reaction vessel, slowly add ethanol under a negative pressure of 0.03 MPa, raise the temperature to 30°C, and carry out the reaction under a negative pressure of 0.09 MPa until no bubbles are generated in the system, and obtain colorless transparent liquid S1 intermediate of ethyl dichlorophosphate for later use. (2) Pre-cool ethylene glycol to below 5°C, place it in a reaction vessel, and slowly add the intermediate S1 of ethyl dichlorophosphate obtained in step (1) under a negative pressure of 0.03 MPa. Heat the mixture to 30°C and react it under a negative pressure of 0.09 MPa until no bubbles are generated in the system. Obtain intermediate S2 as a colorless, transparent, viscous liquid for later use. (3) Pre-cool intermediate S2 to below 5°C, place it in a reaction vessel, and slowly add ethyl dichlorophosphate intermediate S1 obtained in step (1) under a negative pressure of 0.03 MPa. At the same time, react under the conditions of 30°C and negative pressure reduced to 0.09 MPa until no bubbles are generated in the system, and obtain intermediate S3 as a colorless, transparent, viscous liquid for later use. (4) Pre-cool intermediate S3 to below 5°C, place it in a reaction vessel, slowly add ethanol as a capping agent under a negative pressure of 0.03 MPa, heat to 30°C, and react under a negative pressure of 0.09 MPa until no bubbles are generated in the system. Then remove excess ethanol to obtain PNX product, which is a colorless, clear, transparent, viscous liquid.

[0071] In step (1), the amount of phosphorus oxychloride used is 1406.53g (8.94mol) and the amount of ethanol used is 411.86g (8.94mol). In step (2), the amount of ethylene glycol used is 362.56g (5.84mol) and the amount of ethyl dichlorophosphate intermediate used is 476.05g (2.92mol). In step (3), the amount of intermediate S2 used is all the products in step (2), the amount of ethyl dichlorophosphate intermediate used is 772.11g (5.84mol), the amount of intermediate S3 used is all the products in step (3), and the amount of ethanol used is 270g (5.94mol).

[0072] The phosphorus oxychloride, ethanol, and ethylene glycol used are all of analytical grade. The temperature control accuracy of the reactor is ±2℃, and the pressure control accuracy is ±0.005MPa.

[0073] The PNX has a degree of polymerization n between 1 and 4, a phosphorus content of 19.1%, a viscosity between 1030 mPa·s, and an acid value of 0.5 mg KOH / g.

[0074] Example 5 A method for synthesizing a high-efficiency, environmentally friendly, low-migration halogen-free alkyl phosphate oligomer organic flame retardant (PNX) includes the following steps: (1) Pre-cool phosphorus oxychloride to below 5°C, place it in a reaction vessel, slowly add ethanol under a negative pressure of 0.03 MPa, raise the temperature to 30°C, and carry out the reaction under a negative pressure of 0.1 MPa until no bubbles are generated in the system, and obtain colorless transparent liquid S1 intermediate of ethyl dichlorophosphate for later use. (2) Pre-cool ethylene glycol to below 10°C, place it in a reaction vessel, and slowly add the intermediate S1 of ethyl dichlorophosphate obtained in step (1) under a negative pressure of 0.03 MPa. Heat the mixture to 50°C and react it under a negative pressure of 0.1 MPa until no bubbles are generated in the system. Obtain intermediate S2 as a colorless, transparent, viscous liquid for later use. (3) Pre-cool intermediate S2 to below 20°C, place it in a reaction vessel, and slowly add ethyl dichlorophosphate intermediate S1 obtained in step (1) under a negative pressure of 0.03 MPa. At the same time, carry out the reaction at 50°C and a negative pressure reduced to 0.1 MPa until no bubbles are generated in the system, and obtain intermediate S3 as a colorless, transparent, viscous liquid for later use. (4) Pre-cool intermediate S3 to below 20°C, place it in a reaction vessel, slowly add ethanol as a capping agent under a negative pressure of 0.03 MPa, heat to 50°C, and react under a negative pressure of 0.1 MPa until no bubbles are generated in the system. Then remove excess ethanol to obtain PNX product, which is a colorless, clear, transparent, viscous liquid.

[0075] In step (1), the amount of phosphorus oxychloride used is 1406.53g (8.94mol) and the amount of ethanol used is 411.86g (8.94mol). In step (2), the amount of ethylene glycol used is 362.56g (5.84mol) and the amount of ethyl dichlorophosphate intermediate used is 476.05g (2.92mol). In step (3), the amount of intermediate S2 used is all the products in step (2), the amount of ethyl dichlorophosphate intermediate used is 772.11g (5.84mol), the amount of intermediate S3 used is all the products in step (3), and the amount of ethanol used is 270g (5.94mol).

[0076] The phosphorus oxychloride, ethanol, and ethylene glycol used are all of analytical grade. The temperature control accuracy of the reactor is ±2℃, and the pressure control accuracy is ±0.005MPa.

[0077] The PNX has a degree of polymerization n between 1 and 5, a phosphorus content of 19.7%, a viscosity between 1100 mPa·s, and an acid value of 0.1 mg KOH / g.

[0078] Comparative Example 1 (1) Pre-cool phosphorus oxychloride to below 5°C, place it in a reaction vessel, slowly add ethanol under a negative pressure of 0.02 MPa, raise the temperature to 30°C, and carry out the reaction under a negative pressure of 0.1 MPa until no bubbles are generated in the system, and obtain colorless transparent liquid S1 intermediate of ethyl dichlorophosphate for later use. (2) Pre-cool ethylene glycol to below 10°C, place it in a reaction vessel, and slowly add the intermediate S1 of ethyl dichlorophosphate obtained in step (1) under a negative pressure of 0.03 MPa. Heat the mixture to 35°C and react it under a negative pressure of 0.1 MPa until no bubbles are generated in the system. Obtain intermediate S2 as a colorless, transparent, viscous liquid for later use. (3) Pre-cool intermediate S2 to below 10°C, place it in a reaction vessel, and slowly add ethyl dichlorophosphate intermediate S1 obtained in step (1) under a negative pressure of 0.02 MPa. At the same time, carry out the reaction at 65°C and a negative pressure of 0.1 MPa until no bubbles are generated in the system, and obtain intermediate S3 as a colorless, transparent, viscous liquid (very viscous and poor fluidity) for later use. The inventor found that when the reaction temperature increases, it will lead to over-reaction, increase the degree of polymerization of the product, and eventually form a gel state, which cannot continue to react.

[0079] (4) Pre-cool intermediate S3 to below 10°C, place it in a reaction vessel, slowly add ethanol as a capping agent under a negative pressure of 0.02 MPa, heat to 70°C, and react under a negative pressure of 0.1 MPa until no bubbles are generated in the system. Then remove excess ethanol to obtain PNX product, which is a colorless, clear, transparent, viscous liquid.

[0080] In step (1), the amount of phosphorus oxychloride used is 1406.53g (8.94mol) and the amount of ethanol used is 411.86g (8.94mol). In step (2), the amount of ethylene glycol used is 362.56g (5.84mol) and the amount of ethyl dichlorophosphate intermediate used is 476.05g (2.92mol). In step (3), the amount of intermediate S2 used is all the products in step (2), the amount of ethyl dichlorophosphate intermediate used is 772.11g (5.84mol), the amount of intermediate S3 used is all the products in step (3), and the amount of ethanol used is 270g (5.94mol).

[0081] The phosphorus oxychloride, ethanol, and ethylene glycol used are all of analytical grade. The temperature control accuracy of the reactor is ±5℃, and the pressure control accuracy is ±0.005MPa.

[0082] The PNX has a degree of polymerization n between 2 and 9, a phosphorus content of 20.0%, a viscosity of 1293.78 mPa.s, and an acid value of 1.2 mgKOH / g.

[0083] Comparative Example 2 450g of tributyl phosphate was added to the reactor, followed by the slow addition of 300g of phosphorus pentoxide. During the addition process, vigorous stirring was maintained to prevent clumping. The reaction was continued for 3 hours at approximately 60°C to generate the intermediate pyrophosphate ester (highly toxic). 70g of stannous isooctanoate catalyst was added to the reaction system, followed by the slow introduction of 240g of ethylene oxide (a highly toxic and hazardous chemical with a risk of explosion due to its exothermic self-polymerization) into the reactor under high pressure. After the introduction of EO, the temperature of the reaction system was controlled and maintained at 100°C. The reaction was stopped when the acid value of the product reached 5.5 mg·KOH / g. Nitrogen gas was introduced into the reaction system at 120°C to remove residual phosphate ester and ethylene oxide. After cooling, the product was a yellow, viscous liquid.

[0084] The inventors discovered that the raw material ethylene oxide is difficult to control, and it is prone to self-polymerization, which causes the product to be dark in color, sometimes even black.

Claims

1. A method for synthesizing a halogen-free alkyl phosphate oligomer organic flame retardant PNX, characterized in that, Includes the following steps: (1) Phosphorus oxychloride was pre-cooled to below 5°C and then ethanol was added dropwise under negative pressure. The temperature was increased to carry out the reaction. After the reaction was completed, ethyl dichlorophosphate intermediate S1 was obtained for later use. (2) After precooling ethylene glycol to below 10°C, add ethyl dichlorophosphate intermediate S1 dropwise under negative pressure, and heat up to carry out the reaction. After the reaction is completed, intermediate S2 is obtained. (3) After precooling intermediate S2 to below 20°C, intermediate S1 is added dropwise under negative pressure. Under heating conditions, S1 reacts with S2 to obtain intermediate S3. (4) After precooling intermediate S3 to below 20°C, ethanol is added dropwise under negative pressure to seal the end, and the temperature is raised to carry out the reaction. After the reaction is completed, excess ethanol is evaporated under reduced pressure to obtain PNX product.

2. The method for synthesizing PNX according to claim 1, characterized in that, In step (1), ethanol is added dropwise under a negative pressure of 0.02-0.055 MPa; after the addition is completed, the temperature is raised to 25-50℃ and the reaction is carried out under a pressure of 0.08-0.1 MPa.

3. The method for synthesizing PNX according to claim 1, characterized in that, In step (2), intermediate S1 is added dropwise under a negative pressure of 0.02-0.055 MPa; after the addition is completed, the temperature is raised to 25-50℃ and the reaction is carried out under a pressure of 0.08-0.1 MPa.

4. The method for synthesizing PNX according to claim 1, characterized in that, In step (3), ethanol is added dropwise under a negative pressure of 0.02-0.055 MPa; after the addition is completed, the temperature is raised to 25-50℃ and the reaction is carried out under a pressure of 0.08-0.1 MPa.

5. The method for synthesizing PNX according to claim 1, characterized in that, In step (4), intermediate S1 is added dropwise under a negative pressure of 0.02-0.055 MPa; after the addition is completed, the temperature is raised to 25-30℃ and the reaction is carried out under a pressure of 0.08-0.1 MPa.

6. The method for synthesizing PNX according to claim 1, characterized in that, In step (1), the molar ratio of phosphorus oxychloride to ethanol is 1-3:

1.

7. The method for synthesizing PNX according to claim 1, characterized in that, In step (2), the molar ratio of ethylene glycol to ethyl dichlorophosphate intermediate S1 is 1.5:1-2.5:

1.

8. The method for synthesizing PNX according to claim 1, characterized in that, In step (3), the molar ratio of intermediate S2 to ethyl dichlorophosphate intermediate S1 is 1.5:1-2.5:

1.

9. The method for synthesizing PNX according to claim 1, characterized in that, In step (4), the molar ratio of intermediate S3 to ethanol is 1:2-1:

4.

10. A halogen-free alkyl phosphate oligomer organic flame retardant, characterized in that, The halogen-free alkyl phosphate oligomer organic flame retardant PNX, prepared by the method according to any one of claims 1-9, has the following molecular structure: , n≤6 integers; phosphorus content≥18%, acid value≤0.5mg KOH / g.

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