Polymeric spirocyclic phosphorus-nitrogen intumescent flame retardant and preparation method thereof

Abstract

The application relates to a polymeric spirocyclic phosphorus-nitrogen intumescent flame retardant and a preparation method thereof, and belongs to the technical field of flame retardants. The polymeric spirocyclic phosphorus-nitrogen intumescent flame retardant is a kind of highly symmetrical flame retardant with a cage structure, which is obtained by the following steps: reacting pentaerythritol with phosphorus oxychloride to obtain spirocyclic phosphate diacyl chloride, then reacting the spirocyclic phosphate diacyl chloride with 4,6-dihydroxypyrimidine to obtain a crude product, and then purifying the crude product to obtain the flame retardant. The flame retardant can achieve UL-94 V-0 grade flame-retardant epoxy resin only with an addition amount of 0.5% to 2.5%, realizes high-efficiency and environment-friendly flame-retardant effect, and the mechanical property of the material itself does not decrease, and the tensile strength is still kept above 54.9 MPa.

Description

Technical Field

[0001] The invention relates to a polymeric spirophosphorus nitrogen expansion flame retardant and a preparation method thereof, belonging to the technical field of flame retardants. Background Art

[0002] Epoxy resin (EP) is widely used in chemical corrosion protection, small electronic devices, building materials, and lightweight structures of spacecraft due to its excellent chemical resistance, low shrinkage, insulation, and mechanical properties. However, epoxy resin is currently very flammable and emits a large amount of toxic smoke into the air during combustion, making it difficult to protect human life and property. For this reason, it is extremely necessary to study and prepare new flame retardants that improve the flame retardancy of EP and reduce the harm of smoke. However, most of the traditional high-efficiency flame retardants require the introduction of halogen elements, such as decabromodiphenyl ether, chlorinated paraffin, and tetrabromophthalic anhydride, which are extremely harmful to the ecological environment. In recent years, environmentally friendly halogen-free flame retardants have gradually replaced this type of flame retardant, injecting new impetus into the sustainable development of flame retardant solutions.

[0003] Over the past decade, halogen-free flame retardants, such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), boron nitride, carbon nanomaterials, SiO2, and organic-inorganic hybrid compounds (such as polyhedral siloxanes and metal-organic frameworks), have been widely used to flame-retard polymer materials. Among these materials, phosphorus-nitrogen intumescent flame retardants, as a type of green flame retardant, are a new type of flame retardant with potential development advantages due to their excellent free radical scavenging effect. DOPO, as one of these flame retardants, possesses a unique phosphaphenanthrene structure that imparts excellent fire resistance and antioxidant properties to epoxy resins. The active PH bond in DOPO enables a variety of modifications, such as substitution, oxidation, and addition. However, DOPO derivatives primarily exhibit a gas-phase flame retardant mechanism, which is not conducive to suppressing smoke release. Furthermore, they often require the addition of large amounts of DOPO flame retardants, which is detrimental to maintaining the mechanical properties of the polymer material.

[0004] Spirocyclic phosphorus oxychloride (SPDPC) is a type of phosphorus flame retardant. It has a stable heterocyclic structure and high thermal stability. Thanks to the presence of pentaheptanol in its spirocyclic structure, SPDPC has good carbonization performance, can inhibit the further combustion of polymer materials, and exert a flame retardant effect in gas-phase free radical capture and condensed phase carbonization. In addition, this type of flame retardant also has an active P-Cl bond, which can realize a variety of modification methods (introduction of amino groups) on this functional group, and prepare many new intumescent flame retardants that integrate three sources. However, at present, such flame retardants (such as a polymeric intumescent flame retardant disclosed in CN109096492A) often require a high addition amount (more than 5%) to achieve the ideal flame retardant effect, and there is little research on new polymeric flame retardants with good compatibility with the matrix, which needs further research. Summary of the Invention

[0005] In light of this, the present invention aims to provide a polymeric spirocyclic phosphorus-nitrogen intumescent flame retardant and its preparation method. This highly symmetrical polymeric phosphorus-nitrogen intumescent flame retardant not only exhibits excellent compatibility with substrates but also achieves excellent flame retardancy at relatively low addition levels, significantly preserving the material's inherently superior mechanical properties. This is of great significance for green flame retardancy and broadens the material's application range.

[0006] To achieve the above objectives, the technical solutions of the present invention are as follows.

[0007] A polymeric spirophosphorus nitrogen intumescent flame retardant (DHPPC), the structural formula of the flame retardant is as follows:

[0008]

[0009] Among them, the repeating unit is C9O8N2H 10 P2, the degree of polymerization n is an integer of 8 to 12.

[0010] Preferably, the molecular weight of the flame retardant is 3000-4000.

[0011] A method for preparing the polymeric spirophosphorus nitrogen intumescent flame retardant of the present invention comprises the following steps:

[0012] Step 1: In a closed system without water or oxygen, pentaerythritol is added to solvent A, stirred until the system is uniformly mixed, and then the temperature is raised to temperature 1, phosphorus oxychloride is added, nitrogen is introduced, and the reaction is maintained at this temperature for 2 to 4 hours, and then the temperature is raised to temperature 2, stirred, and reacted for 8 to 16 hours, washed, and dried to obtain an intermediate spirocyclic phosphate dichloride; wherein the molar ratio of pentaerythritol to phosphorus oxychloride is 1:2 to 7; temperature 1 is 40 to 70° C., and temperature 2 is 80 to 120° C.;

[0013] Step 2: In an anhydrous and oxygen-free environment, 4,6-dihydroxypyrimidine is added to solvent B, stirred until the solution is clear and transparent, the intermediate spirocyclic phosphate dichloride and the acid binding agent are added, and pre-reacted at temperature 3 for 1 to 2 hours, then heated to temperature 4 and stirred and refluxed for 6 to 16 hours. After the reaction is completed, the mixture is washed and dried to obtain a crude flame retardant as a yellow-brown powdery solid; wherein the molar ratio of 4,6-dihydroxypyrimidine to spirocyclic phosphate dichloride is 1:1 to 1.5, temperature 3 is 30 to 55° C., and temperature 4 is 60 to 100° C.;

[0014] Step 3: Grind the crude flame retardant, reflux and purify it, and then dry it to obtain a polymeric spirophosphorus nitrogen intumescent flame retardant.

[0015] Preferably, in step 1, the molar ratio of pentaerythritol to phosphorus oxychloride is 1:3-5.

[0016] Preferably, in step 1, the stirring rate is 220-300 rpm.

[0017] Preferably, in step 1, the flow rate of nitrogen is 5 to 20 mL / min.

[0018] Preferably, in step 1, temperature 1 is 55-65° C. Under this temperature condition, the reaction is more gentle and the yield is higher.

[0019] Preferably, in step 1, temperature 2 is 90-110°C.

[0020] Preferably, in step 1, the solvent A is one or more of anhydrous acetonitrile, acetone, dichloromethane and dioxane.

[0021] Preferably, in step 1, one or more of acetone, chloroform and dichloromethane are used for washing.

[0022] Preferably, in step 2, the solvent B is one or more of acetone, tetrahydrofuran, xylene, anhydrous acetonitrile and N,N-dimethylformamide.

[0023] Preferably, in step 2, the acid binding agent is one or more of triethylamine, cerium chloride, anhydrous potassium carbonate and pyridine.

[0024] Preferably, in step 2, the molar ratio of the 4,6-dihydroxypyrimidine to the acid-binding agent is 1:1.5-2.2.

[0025] Preferably, in step 2, temperature 4 is 70-85°C.

[0026] Preferably, in step 2, one or more of deionized water, ether, anhydrous methanol, anhydrous ethanol, dichloromethane and acetonitrile are used for washing.

[0027] Preferably, in step 3, during the reflux purification, the solvent is one or more of acetone, dichloromethane, anhydrous ethanol and tetrahydrofuran.

[0028] Preferably, in step 3, during the reflux purification, the temperature is 60-90° C., and the cooling reflux is carried out for 3-12 hours.

[0029] Preferably, in step 1, step 2 and step 3, the drying is performed under vacuum at 80-100° C. for 12-24 hours.

[0030] Beneficial effects

[0031] 1. The present invention provides a polymeric phosphorus-nitrogen intumescent flame retardant, which is a type of polymeric phosphorus-nitrogen intumescent flame retardant with a highly symmetrical structure and a cage structure. It can achieve UL-94 V-0 grade flame retardant epoxy resin with an addition amount of only 0.5% to 2.5%, achieving a high-efficiency and environmentally friendly flame retardant effect, and the mechanical properties of the material itself are not reduced, and the tensile strength is still maintained above 54.9 MPa.

[0032] 2. The present invention provides a polymeric phosphorus-nitrogen intumescent flame retardant. When the addition amount is only 1% in flame-retardant epoxy resin, the limiting oxygen index can reach 29.8%, and when the addition amount is 2.5%, the limiting oxygen index can reach 31.8%. After adding 1% of this flame retardant, the peak heat release rate can be reduced by 42.3%, the carbon dioxide production can be reduced by 32.5%, and the carbon monoxide production can be reduced by 38.3%, with an outstanding smoke suppression effect.

[0033] 3. The polymeric phosphorus-nitrogen intumescent flame retardant provided by the present invention is a new type of green and environmentally friendly flame retardant. The product has a small amount of smoke and no molten droplet phenomenon, and has high fire safety.

[0034] 4. The polymeric phosphorus-nitrogen intumescent flame retardant provided by the present invention has a symmetrical structure and, thanks to its pentaerythritol spirocyclic structure, has a decomposition temperature in the range of 250 to 300°C, which is lower than the decomposition temperature of epoxy resin. During the combustion process, it can preferentially decompose and flame retardant, and has a good catalytic carbonization effect.

[0035] 5. The present invention provides a polymeric phosphorus-nitrogen intumescent flame retardant, which has a simple preparation method and easily controllable reaction conditions, and a yield of more than 98.5%. A high purity can be ensured through simple purification, and the production can be scaled up to achieve industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the infrared spectrum of the flame retardant described in Example 1.

[0037] Figure 2 This is the nuclear magnetic phosphorus spectrum of the flame retardant described in Example 1.

[0038] Figure 3This is the H NMR spectrum of the flame retardant described in Example 1. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below with reference to specific embodiments.

[0040] A method for preparing a polymeric spirophosphorus nitrogen intumescent flame retardant, comprising the following steps:

[0041] Step 1. In a closed system without water or oxygen, fully ground pentaerythritol is added to solvent A, and the mixture is stirred at room temperature until the system is evenly mixed. After the system temperature is raised to temperature 1, freshly distilled phosphorus oxychloride is added, nitrogen is introduced, and the reaction is carried out under this temperature condition until the system is stable (this process takes 2 to 4 hours), and the temperature is further slowly raised to temperature 2. The reaction is stirred until no gas is generated (this process takes 8 to 16 hours), and the product is washed several times with solvent B, filtered, and vacuum dried to obtain the intermediate spirocyclic phosphate dichloride.

[0042] In some embodiments, the molar ratio of pentaerythritol to phosphorus oxychloride in step 1 is preferably 1:(2-7), and more preferably 1:(3-5);

[0043] In some embodiments, the solvent A in step 1 is one of anhydrous acetonitrile, acetone, dichloromethane, dioxane, or a mixed solvent. All solvents need to be dried before use to prevent the introduction of moisture.

[0044] In some embodiments, the flow rate of nitrogen in step 1 is 5 to 20 mL / min;

[0045] In some embodiments, the temperature 1 in step 1 is 40-70° C., more preferably 55-65° C., under which the reaction is more moderate and the yield is higher;

[0046] In some embodiments, the temperature 2 in step 1 is 80-120° C., more preferably 90-110° C.;

[0047] In some embodiments, the stirring rate in step 1 is 220-300 rpm;

[0048] In some embodiments, the solvent B in step 1 is acetone, chloroform, or dichloromethane, and the order of washing is not distinguished.

[0049] Step 2: In an anhydrous and oxygen-free environment, 4,6-dihydroxypyrimidine was added to solvent C and stirred at room temperature until the solution became clear. The intermediate spirocyclic phosphate dichloride synthesized in step 1 was added, and an acid-binding agent was added to facilitate the nucleophilic substitution reaction. The reaction was pre-reacted at temperature 3, and the temperature was slowly increased. Stirring and refluxing were performed at temperature 4. After the reaction, the mixture was washed alternately with solvent D multiple times, filtered, and vacuum dried to obtain a crude flame retardant as a yellow-brown powdery solid.

[0050] In some embodiments, the solvent C in step 2 is one of acetone, tetrahydrofuran, xylene, anhydrous acetonitrile, and N,N-dimethylformamide. All solvents are of analytical grade and are soaked in molecular sieves to remove water for 48 hours before use.

[0051] In some embodiments, the molar ratio of 4,6-dihydroxypyrimidine and spirocyclic phosphate dichloride in step 2 is preferably 1: (1 to 1.5);

[0052] In some embodiments, the temperature 3 in step 2 is 30-55° C., and the pre-reaction is 1-2 hours;

[0053] In some embodiments, the temperature 4 in step 2 is 60-100° C.; more preferably 70-85° C.;

[0054] In some embodiments, the reflux time in step 2 is preferably 12 to 36 hours;

[0055] In some embodiments, the acid-binding agent in step 2 is triethylamine, cerium chloride, anhydrous potassium carbonate, and pyridine. The introduction of the acid-binding agent will increase the product yield, but will produce certain ionic salts that affect the product purity; therefore, the molar ratio of 4,6-dihydroxypyrimidine to the acid-binding agent is 1:1.5-2.2;

[0056] In some embodiments, the solvent D in step 2 is one or more of deionized water, ether, anhydrous methanol, anhydrous ethanol, dichloromethane, and acetonitrile, and the order of washing is not distinguished.

[0057] Step 3: Grind the resulting crude polymeric flame retardant thoroughly, weigh it, and then transfer it to filter paper for wrapping. To prevent sample loss during purification, wrap a rubber rope around the filter paper to tighten it. Place the sample-wrapped filter paper horizontally in a Soxhlet extractor equipped with a condenser. Add solvent E to completely soak the filter paper. Raise the temperature to 5°C, cool and reflux for purification, and vacuum dry after purification to obtain a polymeric spirocyclic phosphorus nitrogen intumescent flame retardant.

[0058] In some embodiments, the solvent E in step 3 is one or more of acetone, dichloromethane, anhydrous ethanol, and tetrahydrofuran;

[0059] In some embodiments, the temperature 5 in step 3 is 60-90° C., which can be selected according to the type of purification solvent, ensuring that the selected temperature range is higher than the boiling point of the solvent;

[0060] In some embodiments, the reflux time in step 3 is preferably 3 to 12 hours, and the reflux time is adjusted according to the solubility of the solvent.

[0061] In some embodiments, the vacuum drying temperature is 80-100° C., and the drying time is 12-24 hours.

[0062] Example 1

[0063] A method for preparing a polymeric intumescent flame retardant DHPPC, comprising the following steps:

[0064] Weigh 20.4 g (0.15 mol) of thoroughly ground pentaerythritol into a 250 mL three-necked flask. Attach a magnetic stirrer, a condenser with an exhaust gas treatment system, and a constant-pressure dropping funnel. Stir at room temperature under nitrogen until the mixture is uniformly mixed. Under a nitrogen atmosphere (nitrogen flow rate of 10 mL / min), slowly raise the temperature to 65°C and rapidly add 69.3 g (0.45 mol) of freshly redistilled phosphorus oxychloride. Allow the mixture to react until the system stabilizes (this process takes 3 hours). Then, slowly increase the temperature gradually to 100°C and react until no HCl gas is produced at the exhaust gas outlet (reaction completion). Cool to room temperature, filter the resulting precipitate, wash several times with dichloromethane and acetone, and dry at 100°C under vacuum (-0.1 MPa) for 12 hours to obtain 32.4 g of the white powdery solid intermediate, spirocyclic phosphate dichloride, in an 85.8% yield.

[0065] Spirocyclic phosphate dichloride and 4,6-dihydroxypyrimidine were mixed in a 1:1 molar ratio. 1.12 g (0.01 mol) of 4,6-dihydroxypyrimidine was weighed and added to a 100 mL three-necked flask. A magnetic stirrer, condenser, and exhaust gas treatment device were connected. Under nitrogen, the mixture was stirred in 50 mL of acetonitrile until clear. 2.97 g (0.01 mol) of spirocyclic phosphate dichloride was added, and the reaction mixture was heated to 40°C for 1 hour. The reaction mixture was then heated to 65°C and stirred under reflux for 20 hours. The resulting precipitate was filtered, washed alternately with water, ether, and acetone three times, and dried in a vacuum oven at 80°C for 12 hours to obtain 2.71 g of the crude flame retardant as a yellow powder with a yield of 80.9%.

[0066] The dried crude flame retardant was tightly wrapped with filter paper and transferred to a Soxhlet extractor with a reflux condenser. Acetone was used as the purification solvent, and the temperature was raised to 65°C and refluxed for 3 hours. After drying, 2.63 g of a yellow powdery solid was obtained, which was a purified polymeric phosphorus-nitrogen intumescent flame retardant with a yield of 97.04%.

[0067] like Figure 1-3 As shown, the flame retardant has a new hydroxyl peak (3500cm -1 ) and P-Cl peak (550cm -1 The disappearance of the α-amino acid ...

[0068]

[0069] GPC gel chromatography tests on the flame retardant revealed that its molecular weight remained between 3000 and 4000. The flame retardant had a decomposition temperature between 250 and 350°C and a maximum weight loss temperature of 275°C, which was beneficial for timely response to flame retardancy.

[0070] When the flame retardant is applied to flame-retardant epoxy resin, when the addition amount is 0.5% to 2.5% of the epoxy resin mass, a V-0 grade test for vertical combustion can be achieved, and the flame retardant within this range does not damage the mechanical properties of the material itself, and the tensile strength remains above 54.9MPa. As the amount of flame retardant increases, its oxygen index value can reach 31.8% at an addition amount of 2.5%, showing an excellent self-extinguishing effect, and excellent smoke suppression and heat insulation effects. After adding 1% of this flame retardant, the peak heat release rate can be reduced by 42.3%, the carbon dioxide production can be reduced by 32.5%, and the carbon monoxide production can be reduced by 38.3%, with an outstanding smoke suppression effect.

[0071] Example 2:

[0072] Weigh 20.4 g (0.15 mol) of thoroughly ground pentaerythritol into a 250 mL three-necked flask. Connect a magnetic stirrer, a condenser with an exhaust gas treatment system, and a constant pressure dropping funnel. Stir at room temperature under vacuum (-0.1 MPa) until the mixture is uniformly mixed. Under a nitrogen atmosphere (nitrogen flow rate of 10 mL / min), slowly raise the temperature to 60°C and rapidly add 92.4 g (0.6 mol) of freshly redistilled phosphorus oxychloride. Once the system stabilizes (this process takes 2 hours), slowly increase the temperature to 105°C in a gradual manner. React until no HCl gas is produced at the exhaust gas outlet (reaction is complete). Cool to room temperature, filter the resulting precipitate, wash several times with dichloromethane and acetone, and vacuum dry at 105°C for 12 hours to obtain 38.6 g of the white powdery solid intermediate, spirocyclic phosphate dichloride, in a yield of 90.8%.

[0073] Spirocyclic phosphate dichloride and 4,6-dihydroxypyrimidine were mixed in a molar ratio of 1:1.1. 1.12 g (0.011 mol) of 4,6-dihydroxypyrimidine was weighed and added to a 100 mL three-necked flask. A magnetic stirrer, condenser, and exhaust gas treatment system were connected and stirred in 50 mL of acetone under nitrogen until the mixture became clear. 2.97 g (0.01 mol) of spirocyclic phosphate dichloride was added, and the reaction mixture was heated to 45°C for 2 hours. The temperature was then raised to 70°C and stirred under reflux for 22 hours. The resulting precipitate was filtered, washed three times with dichloromethane, ether, and acetone, and dried in a vacuum oven at 80°C for 16 hours to obtain 2.88 g of the crude flame retardant as a yellow powder with a yield of 85.9%.

[0074] The dried crude flame retardant was tightly wrapped with filter paper and transferred to a Soxhlet extractor with a reflux condenser. Dichloromethane was used as the purification solvent, and the temperature was raised to 55°C and refluxed for 6 hours. After drying, 2.76 g of a yellow powdery solid was obtained, which was a purified polymeric phosphorus-nitrogen intumescent flame retardant with a yield of 98.83%.

[0075] The performance of the flame retardant is similar to that of Example 1.

[0076] Example 3:

[0077] Weigh 20.4 g (0.15 mol) of thoroughly ground pentaerythritol into a 500 mL three-necked flask. Connect a magnetic stirrer, a condenser with an exhaust gas treatment system, and a constant-pressure dropping funnel. Stir at room temperature under vacuum (-0.1 MPa) until the mixture is uniformly mixed. Under a nitrogen atmosphere (nitrogen flow rate of 10 mL / min), slowly heat to 55°C and rapidly add 115.5 g (0.75 mol) of freshly redistilled phosphorus oxychloride. Once the system stabilizes (this process takes 4 hours), slowly increase the temperature to 105°C in a gradient manner. React until no HCl gas is produced at the exhaust gas outlet (reaction is complete). Cool to room temperature, filter the resulting precipitate, wash several times with dichloromethane and acetone, and dry in vacuum at 100°C for 12 hours to obtain 41.3 g of the white powdery solid intermediate, spirocyclic phosphate dichloride, in a yield of 92.8%.

[0078] Spirocyclic phosphate dichloride and 4,6-dihydroxypyrimidine were prepared in a molar ratio of 1:1.2. 6.72 g (0.06 mol) of 4,6-dihydroxypyrimidine was weighed and added to a 250 mL three-necked flask. A magnetic stirrer, condenser, and exhaust gas treatment system were connected and stirred in 100 mL of tetrahydrofuran under nitrogen until the solution became clear. 14.84 g (0.05 mol) of spirocyclic phosphate dichloride was ultrasonically dispersed in a beaker containing 80 mL of tetrahydrofuran for 30 minutes, added to the three-necked flask, and stirred evenly. 20 mL of triethylamine was added and the temperature was raised to 45°C for a pre-reaction of 2 hours. The temperature was then raised to 75°C for a reaction of 20 hours. The resulting precipitate was filtered, washed three times with water, acetone, and ether, and dried in a vacuum oven at 80°C for 24 hours to obtain 15.15 g of a yellow-brown powdery solid with a yield of 90.2%.

[0079] The crude flame retardant after drying was divided into three parts, tightly wrapped with multiple layers of filter paper, and transferred to a Soxhlet extractor with a reflux condenser. Anhydrous ethanol was used as the purification solvent, and the temperature was raised to 80°C and refluxed for 8 hours. After drying, 14.72 g of a yellow powdery solid was obtained, which was a purified polymeric phosphorus-nitrogen intumescent flame retardant with a yield of 97.16%.

[0080] The performance of the flame retardant is similar to that of Example 1.

[0081] Example 4:

[0082] Weigh 20.4 g (0.15 mol) of thoroughly ground pentaerythritol into a 250 mL three-necked flask. Connect a magnetic stirrer, a condenser with an exhaust gas treatment system, and a constant pressure dropping funnel. Stir at room temperature under vacuum (-0.1 MPa) until the mixture is uniformly mixed. Under a nitrogen atmosphere (nitrogen flow rate of 10 mL / min), slowly heat to 60°C and rapidly add 115.5 g (0.75 mol) of freshly redistilled phosphorus oxychloride. After the system stabilizes (this process takes 3 hours), slowly increase the temperature to 105°C in a gradient manner. React until no HCl gas is produced at the exhaust gas outlet (reaction is complete). Cool to room temperature, filter the resulting precipitate, wash several times with dichloromethane and acetone, and dry in vacuum at 100°C for 12 hours to obtain 42.1 g of the white powdery solid intermediate, spirocyclic phosphate dichloride, with a yield of 94.6%.

[0083] Spirocyclic phosphate dichloride and 4,6-dihydroxypyrimidine were prepared in a molar ratio of 1:1.3. 24.7 g (0.065 mol) of 4,6-dihydroxypyrimidine was weighed and added to a 500 mL three-necked flask. A magnetic stirrer, condenser, and exhaust gas treatment device were connected and stirred in 200 mL of acetonitrile under nitrogen until the solution became clear. 14.84 g (0.05 mol) of spirocyclic phosphate dichloride was ultrasonically dispersed in a beaker containing 160 mL of tetrahydrofuran for 50 minutes, added to the three-necked flask, and stirred evenly. 28 mL of triethylamine was added and the temperature was raised to 50°C for a pre-reaction of 2 hours, then further raised to 80°C for a reaction of 24 hours. The resulting precipitate was filtered, washed three times with water and ether and acetone, and dried in a vacuum oven at 80°C for 24 hours to obtain 15.97 g of the crude flame retardant as a yellow-brown powder with a yield of 95.1%.

[0084] The crude flame retardant after drying was divided into three parts, tightly wrapped with multiple layers of filter paper, and transferred to a Soxhlet extractor with a reflux condenser. Tetrahydrofuran was used as the purification solvent, and the temperature was raised to 75°C and refluxed for 12 hours. After drying, 15.33 g of a yellow powdery solid was obtained, which was a purified polymeric phosphorus-nitrogen intumescent flame retardant with a yield of 95.99%.

[0085] The performance of the flame retardant is similar to that of Example 1.

[0086] In summary, the invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention shall be deemed to be within the scope of protection of the present invention.

Claims

1. A polymeric spirophosphorus nitrogen intumescent flame retardant, characterized in that: The structural formula of the flame retardant is as follows: Among them, the repeating unit is C9O8N2H 10 P2, the degree of polymerization n is an integer of 8 to 12.

2. A polymeric spirophosphorus nitrogen intumescent flame retardant according to claim 1, characterized in that: The molecular weight of the flame retardant is 3000-4000.

3. A method for preparing a polymeric spirophosphorus nitrogen intumescent flame retardant according to claim 1 or 2, characterized in that: The method steps include: Step 1: In a closed system without water or oxygen, pentaerythritol is added to solvent A, stirred until the system is uniformly mixed, and then the temperature is raised to temperature 1, phosphorus oxychloride is added, nitrogen is introduced, and the reaction is maintained at this temperature for 2 to 4 hours, and then the temperature is raised to temperature 2, stirred, and reacted for 8 to 16 hours, washed, and dried to obtain an intermediate spirocyclic phosphate dichloride; wherein the molar ratio of pentaerythritol to phosphorus oxychloride is 1:2 to 7; temperature 1 is 40 to 70° C., and temperature 2 is 80 to 120° C.; Step 2: In an anhydrous and oxygen-free environment, 4,6-dihydroxypyrimidine is added to solvent B, stirred until the solution is clear and transparent, the intermediate spirocyclic phosphate dichloride and the acid binding agent are added, and pre-reacted at temperature 3 for 1 to 2 hours, then heated to temperature 4 and stirred and refluxed for 6 to 16 hours. After the reaction is completed, the mixture is washed and dried to obtain a crude flame retardant as a yellow-brown powdery solid; wherein the molar ratio of 4,6-dihydroxypyrimidine to spirocyclic phosphate dichloride is 1:1 to 1.5, temperature 3 is 30 to 55° C., and temperature 4 is 60 to 100° C.; Step 3: Grind the crude flame retardant, reflux and purify it, and then dry it to obtain a polymeric spirophosphorus nitrogen intumescent flame retardant.

4. The method for preparing a polymeric spirophosphorus nitrogen intumescent flame retardant according to claim 3, wherein: In step 1, the molar ratio of pentaerythritol to phosphorus oxychloride is 1:3-5.

5. The method for preparing a polymeric spirophosphorus nitrogen intumescent flame retardant according to claim 3, wherein: In step 1, the stirring rate is 220-300 rpm; the flow rate of nitrogen is 5-20 mL / min; temperature 1 is 55-65° C.; and temperature 2 is 90-110° C.

6. The method for preparing a polymeric spirophosphorus nitrogen intumescent flame retardant according to claim 3, wherein: In step 1, the solvent A is one or more of anhydrous acetonitrile, acetone, dichloromethane and dioxane; and one or more of acetone, chloroform and dichloromethane are used for washing.

7. The method for preparing a polymeric spirophosphorus nitrogen intumescent flame retardant according to claim 3, characterized in that: In step 2, the acid-binding agent is one or more of triethylamine, cerium chloride, anhydrous potassium carbonate and pyridine; the molar ratio of 4,6-dihydroxypyrimidine to the acid-binding agent is 1:1.5-2.2; and the temperature 4 is 70-85°C.

8. The method for preparing a polymeric spirophosphorus nitrogen intumescent flame retardant according to claim 3, wherein: In step 2, the solvent B is one or more of acetone, tetrahydrofuran, xylene, anhydrous acetonitrile and N,N-dimethylformamide; and the washing is performed using one or more of deionized water, ether, anhydrous methanol, anhydrous ethanol, dichloromethane and acetonitrile.

9. The method for preparing a polymeric spirophosphorus nitrogen intumescent flame retardant according to claim 3, characterized in that: In step 3, during reflux purification, the solvent is one or more of acetone, dichloromethane, anhydrous ethanol and tetrahydrofuran; the temperature is 60-90° C., and the cooling reflux is carried out for 3-12 hours.

10. The method for preparing a polymeric spirophosphorus nitrogen intumescent flame retardant according to claim 3, characterized in that: In step 1, step 2 and step 3, during drying, vacuum drying is performed at 80-100° C. for 12-24 hours.

Images