Phosphorus-containing phenolic multifunctional curing agent, preparation method and heat-resistant flame-retardant epoxy resin thereof

Abstract

The invention relates to the technical field of epoxy resin curing agents and functional epoxy resin, and discloses a phosphorus-containing phenolic multifunctional curing agent, a preparation method of the phosphorus-containing phenolic multifunctional curing agent and heat-resistant flame-retardant epoxy resin of the phosphorus-containing phenolic multifunctional curing agent. The preparation method comprises the following steps: preparing modified phenolic aldehyde amine by taking a DOPO type phenol monomer containing a flexible ether chain, phenol, paraformaldehyde and triethylene tetramine as raw materials; based on an amino-chlorine nucleophilic substitution reaction mechanism, modified phenolic aldehyde amine and chloropropyl heptaisobutyl POSS are subjected to reactive compounding to obtain the phosphorus-containing phenolic aldehyde multifunctional curing agent, and the curing agent is used for carrying out curing reaction on epoxy resin to obtain the phosphorus-containing phenolic aldehyde multifunctional curing agent. The epoxy resin cured product prepared by the method has high heat resistance, excellent toughness balance and efficient phosphorus-silicon-nitrogen synergistic intrinsic flame retardant property.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin curing agents and functional epoxy resins, specifically to phosphorus-containing phenolic multifunctional curing agents, their preparation methods, and their heat-resistant and flame-retardant epoxy resins. Background Technology

[0002] Epoxy resins are widely used in adhesives, coatings, electronic packaging, engineering composites, and civil engineering materials due to their excellent adhesive strength, low curing shrinkage, high mechanical strength, good electrical insulation, and processability. As the core component of the epoxy curing system, the structure and properties of the curing agent directly determine the quality of the final cured product. Among them, phenolic amine curing agents, prepared by the Mannich reaction of phenols, aldehydes, and lower aliphatic amines, are one of the most widely used epoxy resin curing agents.

[0003] The phenolic hydroxyl groups introduced into the molecular structure of phenolic amine curing agents can significantly activate the curing reaction, giving them the ability to cure rapidly in low-temperature and humid environments, effectively reducing construction difficulty and cost. At the same time, the phenolic skeleton structure introduced into the molecule can significantly improve the rigidity and thermal stability of the epoxy crosslinking network, and overcome the defects of traditional low-grade aliphatic amine curing agents (ethylenediamine, diethylenetriamine, triethylenetetramine, etc.) such as high volatility, high irritation and high toxicity.

[0004] However, existing phenolic amine curing agents contain a large number of rigid benzene rings in their molecular structure, resulting in high crosslinking density and poor molecular chain flexibility in the cured products. This high rigidity structure causes the cured products to have problems such as high brittleness, insufficient flexibility, poor fatigue resistance and impact resistance. When subjected to external impact or long-term vibration load, cracks are easily generated and propagated, which seriously restricts their service life and reliability in high-end fields.

[0005] While there are reports in the prior art of toughening epoxy curing products by introducing flexible segments into phenolic amine curing agents, simply introducing flexible segments can improve impact toughness, but it will significantly reduce the mechanical strength (such as tensile strength) and heat resistance of epoxy curing products, making it difficult to achieve a synergistic balance between mechanical properties and heat resistance.

[0006] Furthermore, the molecular skeleton of general-purpose epoxy resins such as bisphenol A is rich in carbon-hydrogen bonds, making them flammable materials that easily release large amounts of smoke and toxic gases when burned. Currently, the mainstream flame-retardant modification method is physical blending, which involves adding flame retardants to the resin matrix. While this process is simple, flame retardants are prone to migration and precipitation during processing or use, leading to a decrease in flame-retardant effectiveness. Moreover, the addition of large amounts of flame retardants may degrade the mechanical properties and heat resistance of the resin matrix, failing to meet the demands of high-end applications. Summary of the Invention

[0007] This invention develops a multifunctional phenolic amine curing agent grafted with flexible ether chains, flame-retardant DOPO groups, and nano-reinforced POSS structures through molecular structure design and a flexible-rigid synergistic regulation strategy. The curing agent is used to cure epoxy resin, and the resulting epoxy resin cured product has high heat resistance, excellent strength-toughness balance, and efficient phosphorus-silicon-nitrogen synergistic intrinsic flame retardant properties.

[0008] A method for preparing a phosphorus-containing phenolic multifunctional curing agent includes the following steps:

[0009] (a) Preparation of modified phenolic amine: DOPO type phenol monomer containing flexible ether chain, phenol, paraformaldehyde and triethylenetetramine are prepared in a molar ratio of (0.2-0.4):(0.6-0.8):1:1. The mixture is reacted by Mannich reaction in anhydrous ethanol solvent under nitrogen protection at 80±2℃ with stirring and reflux for 4-6 h. Modified phenolic amine is obtained after post-treatment.

[0010] (b) POSS grafting reaction: The modified phenolic amine obtained in step (a) is mixed with chloropropylheptaisobutyl POSS at a mass ratio of 1:(0.05-0.15). The reaction is carried out by amino-chloro nucleophilic substitution reaction in anhydrous tetrahydrofuran solvent under nitrogen protection at 60±2℃ for 10-14h with stirring. After post-treatment, a phosphorus-containing phenolic multifunctional curing agent is obtained.

[0011] Preferably, the method for preparing the DOPO-type phenol monomer containing a flexible ether chain is as follows:

[0012] Based on the addition reaction mechanism of hydroxy-isocyanate group, an acrylate monomer containing a flexible ether chain is obtained by reacting 1 molar equivalent of polyethylene glycol monomer with 2.01-2.05 molar equivalents of ethyl isocyanate. The polyethylene glycol monomer is one of triethylene glycol, tetraethylene glycol, pentaethylene glycol, and hexaethylene glycol.

[0013] Based on the Kabachnik-Fields reaction mechanism, a DOPO-type phenol monomer containing a secondary amine group was obtained by condensation reaction of 1 molar equivalent of 4-hydroxybenzylamine, 0.95-0.99 molar equivalents of DOPO and 0.95-0.99 molar equivalents of paraformaldehyde.

[0014] Based on the addition reaction mechanism of acrylate group-secondary amine group, DOPO type phenol monomer containing flexible ether group is obtained by adding 1 molar equivalent of acrylate group monomer containing flexible ether chain to 2.01-2.05 molar equivalent of DOPO type phenol monomer containing secondary amine group.

[0015] The amine value of the phosphorus-containing phenolic multifunctional curing agent prepared according to the above method is 330-380 mgKOH / g.

[0016] The heat-resistant and flame-retardant epoxy resin is prepared by curing bisphenol A epoxy resin with the above-mentioned phosphorus-containing phenolic multifunctional curing agent.

[0017] Preferably, the formulation of the heat-resistant and flame-retardant epoxy resin is as follows:

[0018] 75-90 parts by weight of bisphenol A epoxy resin;

[0019] 3-8 parts by weight of diluent;

[0020] 30-40 parts by weight of phosphorus-containing phenolic multifunctional curing agent;

[0021] 0.2-0.7 parts by weight of curing accelerator.

[0022] Preferably, the bisphenol A epoxy resin is of type E-51.

[0023] A method for preparing heat-resistant and flame-retardant epoxy resin includes the following steps:

[0024] Step 1: According to the formula of heat-resistant and flame-retardant epoxy resin, add diluent to bisphenol A epoxy resin and stir at 400-600 r / min for 5-15 min. Then add phosphorus-containing phenolic multifunctional curing agent and curing accelerator and stir at 800-1200 r / min for 5-15 min. During the mixing process, ensure that the material temperature does not exceed 30℃. Vacuum defoaming at low speed is performed to obtain epoxy slurry.

[0025] Step 2: Pour the epoxy slurry into a polytetrafluoroethylene mold coated with a release agent, and cure it using a stepped temperature curing process: first cure at 75-85℃ for 0.8-1.2h, then raise the temperature to 110-125℃ for 0.8-1.2h, and finally cure at 130-150℃ for 0.5-1.2h. Cool and demold to obtain heat-resistant and flame-retardant epoxy resin.

[0026] Beneficial effects:

[0027] This invention uses a polyethylene glycol monomer (tetraethylene glycol) as a flexible molecular framework to synthesize a phenol monomer (a DOPO-type phenol monomer containing a flexible ether chain) through molecular design, which combines a flexible ether chain and a flame-retardant DOPO group. First, a modified phenolic amine is prepared by reacting this phenol monomer with conventional phenol, paraformaldehyde, and triethylenetetramine via the Mannich reaction. Then, it is compounded with chloropropylheptaisobutyl POSS, which has a nano-reinforcing effect, through an amino-chlorine nucleophilic substitution reaction to obtain a multifunctional phenolic amine curing agent (a phosphorus-containing phenolic multifunctional curing agent) grafted with a flexible ether chain, a flame-retardant DOPO group, and a nano-reinforcing POSS structure.

[0028] Epoxy resin was cured using a phosphorus-containing phenolic multifunctional curing agent, resulting in a cured epoxy resin with a tensile strength >65MPa and an impact toughness >25kJ / m. 2 After treatment at 150℃ for 24 hours, the tensile strength change rate is less than 5%, the limiting oxygen index reaches a maximum of 35.1%, and the flame retardancy reaches V-0 level, achieving a synergistic improvement effect of heat resistance, flame retardancy and mechanical properties. Detailed Implementation

[0029] Example 1:

[0030] The preparation process for DOPO-type phenol monomers containing flexible ether chains is as follows:

[0031] Step 1: Preparation of acrylate monomers containing flexible ether chains: Based on the addition reaction mechanism of hydroxy-isocyanate groups, an addition reaction is carried out between 1 molar equivalent of polyglycol monomer and 2.02 molar equivalents of ethyl isocyanate to obtain acrylate monomers containing flexible ether chains. The chemical structural formula of the monomer is as follows:

[0032] ;

[0033] The polyglycol monomer can be selected from the following raw materials:

[0034] Triethylene glycol: ;

[0035] Tetraethylene glycol: ;

[0036] Pentylene: ;

[0037] Hexadecimal: ;

[0038] Step 2: Preparation of DOPO-type phenol monomers containing secondary amine groups: Based on the Kabachnik-Fields reaction mechanism, a condensation reaction is carried out between 1 molar equivalent of 4-hydroxybenzylamine, 0.99 molar equivalents of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), and 0.99 molar equivalents of paraformaldehyde to obtain DOPO-type phenol monomers containing secondary amine groups. The chemical structural formula of this monomer is as follows:

[0039] ;

[0040] Step 3: Preparation of DOPO-type phenol monomers containing flexible ether chains: Based on the addition reaction mechanism of acrylate-secondary amine groups, 1 molar equivalent of acrylate monomers containing flexible ether chains is reacted with 2.01 molar equivalents of DOPO-type phenol monomers containing secondary amine groups to obtain DOPO-type phenol monomers containing flexible ether chains. The chemical structural formula of this product is as follows:

[0041] ;

[0042] When tetraethylene glycol is used as the polyethylene glycol monomer, a DOPO-type phenol monomer M containing a flexible ether chain is synthesized, and its chemical structural formula is as follows:

[0043] ;

[0044] The specific preparation steps for DOPO-type phenol monomer M containing a flexible ether chain are as follows:

[0045] Under nitrogen protection, 1.9 g tetraethylene glycol, 2.8 g ethyl isocyanate acrylate and 50 mL anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 2 drops of DBTDL catalyst were added dropwise to the three-necked flask, the temperature was raised to 60 °C and stirred for 10 h, cooled to room temperature, 0.5 g activated carbon particles were added to adsorb the catalyst, filtered, the filtrate was subjected to rotary evaporation under reduced pressure to remove the solvent, and dried under vacuum at 60 °C for 2 h to obtain acrylate monomer M containing flexible ether chains.

[0046] Under nitrogen protection, 2.5 g of 4-hydroxybenzylamine, 4.3 g of DOPO, 0.6 g of paraformaldehyde and 50 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature until completely dissolved. The mixture was then heated to 70 °C and stirred for 4 h. After cooling to room temperature, the solvent was removed by rotary evaporation under reduced pressure and dried under vacuum at 60 °C for 2 h to obtain DOPO-type phenol monomer M containing a secondary amine group.

[0047] Under nitrogen protection, 2.4 g of acrylate monomer M containing a flexible ether chain, 3.5 g of DOPO-type phenol monomer M containing a secondary amine group and 50 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask. The mixture was stirred at room temperature until completely dissolved, heated to 80 °C and stirred for 6 h. After cooling to room temperature, the solvent was removed by rotary evaporation under reduced pressure, and the mixture was dried under vacuum at 60 °C for 2 h to obtain DOPO-type phenol monomer M containing a flexible ether chain.

[0048] The 1H NMR characterization of DOPO-type phenol monomer M containing a flexible ether chain is as follows: 1H NMR (DMSO-d6, 400MHz) δ: 2.51-2.54 (t, 4H), 2.97-3.00 (t, 4H), 3.40-3.44 (m, 4H), 3.60-3.79 (m, 20H), 4.16-4.19 (t, 4H), 4.25-4.28 (t, 4H), 5.75-5.78 (t, 2H), 6.81-7.93 (m, 24H), 8.03 (s, 2H);

[0049] The molecular formula of DOPO-type phenol monomer M containing a flexible ether chain is C0 60H 68 O 17 N4P2 was tested using a Vario EL IIICHN elemental analyzer. The experimental values ​​(theoretical values, %) were: C 61.20 (61.12), H 5.78 (5.81), N 4.69 (4.75).

[0050] The actual and theoretical values ​​of C, H, and N elements are all within 0.3% of each other. Combined with the proton NMR results, it can be proven that the DOPO-type phenol monomer M containing a flexible ether chain was successfully synthesized.

[0051] Example 2:

[0052] The preparation of phosphorus-containing phenolic multifunctional curing agent I includes the following steps:

[0053] Step 1, Preparation of modified phenolic amine: Based on the Mannich reaction mechanism, using DOPO-type phenol monomer M containing flexible ether chains, phenol, paraformaldehyde, and triethylenetetramine as raw materials, and controlling the molar ratio of DOPO-type phenol monomer M containing flexible ether chains, phenol, paraformaldehyde, and triethylenetetramine to be 0.3:0.7:1:1, a modified phenolic amine is obtained. The preparation steps are as follows: Under nitrogen protection, 3.54g of DOPO-type phenol monomer M containing flexible ether chains, 0.66g of phenol, 1.46g of triethylenetetramine, and 50mL of anhydrous ethanol are added to a three-necked flask, stirred and mixed at room temperature for 30min, heated to 50℃, and 5mL of anhydrous ethanol solution containing 0.30g of paraformaldehyde is slowly added dropwise to the three-necked flask. After the addition is complete, the temperature is raised to 80℃ and stirred under reflux for 5h. After cooling to room temperature, the solvent is removed by rotary evaporation under reduced pressure, and the mixture is dried under vacuum at 60℃ for 2h to obtain the modified phenolic amine.

[0054] Step 2, Preparation of phosphorus-containing phenolic multifunctional curing agent I: Based on the nucleophilic substitution reaction mechanism of amine-chlorine, the modified phenolic amine is reactively compounded with chloropropylheptaisobutyl POSS to obtain phosphorus-containing phenolic multifunctional curing agent I. The preparation steps are as follows: Under nitrogen protection, 6g of modified phenolic amine, 0.3g of chloropropylheptaisobutyl POSS and 50mL of anhydrous tetrahydrofuran are added to a three-necked flask, stirred and mixed at room temperature for 30min, heated to 60℃ and stirred for 12h, cooled to room temperature, solvent removed by rotary evaporation under reduced pressure, and vacuum dried at 60℃ for 2h to obtain phosphorus-containing phenolic multifunctional curing agent I;

[0055] Among them, the CAS number of chloropropylheptaisobutyl POSS is 480438-84-4, and its chemical structural formula is as follows:

[0056] ;

[0057] The chemical structural formula of Bu is: ;

[0058] The amine value of phosphorus-containing phenolic multifunctional curing agent I was determined to be 374 mg KOH / g by titration with perchloric acid-acetic acid standard solution. The test procedure is as follows: Dissolve 0.1 g of phosphorus-containing phenolic multifunctional curing agent I in 50 mL of glacial acetic acid-toluene mixed solvent (the volume ratio of glacial acetic acid to toluene is 9:1), add 4 drops of methyl violet indicator, and titrate with 0.1 mol / L perchloric acid standard solution. The endpoint is reached when the sample solution changes from purple to pure blue and does not fade within 10 seconds. Calculate the amine value of phosphorus-containing phenolic multifunctional curing agent I. The specific calculation method is as follows:

[0059] Amine value (mgKOH / g) = (C×V×56.1) / m

[0060] Where C is the concentration of the perchloric acid standard solution, in mol / L;

[0061] V is the volume of perchloric acid standard solution consumed, in mL;

[0062] m is the mass of the sample, in grams;

[0063] 56.1 is the molar mass of potassium hydroxide, in g / mol.

[0064] Example 3:

[0065] A phosphorus-containing phenolic multifunctional curing agent II was prepared, which differs from phosphorus-containing phenolic multifunctional curing agent I only in that the amount of chloropropylheptaisobutyl POSS used is 0.6g.

[0066] The amine value of phosphorus-containing phenolic multifunctional curing agent II was determined to be 350 mg KOH / g by titration with perchloric acid-acetic acid standard solution.

[0067] Example 4:

[0068] A phosphorus-containing phenolic multifunctional curing agent III was prepared, which differs from phosphorus-containing phenolic multifunctional curing agent I only in that the amount of chloropropylheptaisobutyl POSS used is 0.9g.

[0069] The amine value of phosphorus-containing phenolic multifunctional curing agent III was determined to be 335 mg KOH / g by titration with perchloric acid-acetic acid standard solution.

[0070] Example 5:

[0071] The preparation of heat-resistant and flame-retardant epoxy resin includes the following steps:

[0072] Step 1: Add 5 parts by weight of diluent (model XY622) to 80 parts by weight of bisphenol A epoxy resin (model E-51), and stir at 500 r / min for 10 min. Then add 35 parts by weight of phosphorus-containing phenolic multifunctional curing agent and 0.5 parts by weight of curing accelerator (model K-54), and stir at 1000 r / min for 10 min. During the mixing process, turn on the jacket cooling water to ensure that the material temperature does not exceed 30℃. Then evacuate to -0.1 MPa, maintain the vacuum and defoam at 100 r / min for 20 min to obtain epoxy slurry.

[0073] Step 2: Pour the epoxy slurry prepared in Step 1 into a polytetrafluoroethylene mold coated with a release agent, and cure it using a stepped temperature curing process: first cure at 80℃ for 1 hour, then raise the temperature to 120℃ for 1 hour, and finally cure at 140℃ for 1 hour. After curing, cool to 60℃ and demold to obtain heat-resistant and flame-retardant epoxy resin.

[0074] Among them, the phosphorus-containing phenolic multifunctional curing agent is one of phosphorus-containing phenolic multifunctional curing agents I, II, and III;

[0075] When the phosphorus-containing phenolic multifunctional curing agents are phosphorus-containing phenolic multifunctional curing agents I, II, and III respectively, heat-resistant and flame-retardant epoxy resins I, II, and III are prepared sequentially.

[0076] Comparative Example 1:

[0077] The epoxy resin a is prepared, and its difference from the heat-resistant and flame-retardant epoxy resin I is only that: a modified phenolic amine is used to replace the phosphorus-containing phenolic multifunctional curing agent I;

[0078] The amine value of the modified phenolic amine containing a flexible ether chain was determined to be 387 mg KOH / g by titration with a perchloric acid-acetic acid standard solution.

[0079] Comparative Example 2:

[0080] The epoxy resin b is prepared in a manner that differs from the heat-resistant and flame-retardant epoxy resin I only in that it uses a conventional phenolic curing agent instead of the phosphorus-containing phenolic multifunctional curing agent I.

[0081] The preparation method of conventional phenolic curing agent is as follows: Under nitrogen protection, 0.94g of phenol, 1.46g of triethylenetetramine and 50mL of anhydrous ethanol are added to a three-necked flask and stirred at room temperature for 30min. The temperature is raised to 50℃, and 5mL of anhydrous ethanol solution containing 0.45g of paraformaldehyde is slowly added dropwise to the three-necked flask. After the addition is completed, the temperature is raised to 80℃ and stirred under reflux for 5h. The mixture is cooled to room temperature, the solvent is removed by rotary evaporation under reduced pressure, and the mixture is vacuum dried at 60℃ for 2h to obtain conventional phenolic curing agent.

[0082] The amine value of the modified phenolic amine containing a flexible ether chain was determined to be 394 mg KOH / g by titration with a perchloric acid-acetic acid standard solution.

[0083] Performance testing:

[0084] I. Mechanical property testing: The mechanical properties of epoxy resin samples were tested in accordance with GB / T 2567-2021 "Test Methods for Properties of Resin Castings". The initial tensile strength (tensile speed of 2 mm / min) and impact toughness (size of 80 mm × 10 mm × 4 mm, unnotched, pendulum weight of 5.5 J) of the samples were recorded.

[0085] II. Heat Resistance Test: The epoxy resin sample was placed in a 150℃ oven for 24 hours, then removed and left at room temperature for 6 hours. Tensile testing was performed according to GB / T 2567-2021 "Test Methods for Properties of Resin Castings" at a tensile speed of 2 mm / min. The tensile strength of the sample was recorded, and the rate of change of tensile strength after 24 hours of treatment at 150℃ was calculated. The specific method is as follows:

[0086] Tensile strength change rate = (initial tensile strength - tensile strength after treatment at 150℃ for 24 hours) / initial tensile strength × 100%;

[0087] III. Flame retardant performance test:

[0088] (1) LOI (Limiting Oxygen Index) test: According to GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test", the test was conducted using an ATS 1004050 oxygen index meter. The sample size was 125mm×10mm×4mm.

[0089] (2) UL-94 test: According to GB / T 2408-2021 "Determination of the flammability of plastics by horizontal and vertical methods", the test method B-vertical flammability test was used. The sample size was 125mm×13mm×3mm.

[0090] The results of the above performance experiments are shown in Table 1.

[0091] Table 1. Experimental results of the performance of heat-resistant and flame-retardant epoxy resin

[0092] Product Type Curing agent type Tensile strength (MPa) <![CDATA[Impact toughness (kJ / m 2 )]]> Tensile strength change rate (%) after treatment at 150℃ for 24 hours LOI(%) UL-94 rating Heat-resistant and flame-retardant epoxy resin I Phosphorus-containing phenolic multifunctional curing agent I 65.2 26.5 4.6 31.4 V-0 Heat-resistant and flame-retardant epoxy resin II Phosphorus-containing phenolic multifunctional curing agent II 68.3 26.1 4.2 33.8 V-0 Heat-resistant and flame-retardant epoxy resin III Phosphorus-containing phenolic multifunctional curing agent III 69.5 25.8 4.0 35.1 V-0 Comparative Example 1 Modified phenolic amine 47.0 26.9 32.8 28.7 V-1 Comparative Example 2 Conventional phenolic curing agent 63.6 8.4 5.1 22.5 No grade

[0093] A comprehensive analysis of the above experimental results leads to the following conclusions:

[0094] Conclusion 1: The heat-resistant and flame-retardant epoxy resin prepared by the self-developed phosphorus-containing phenolic multifunctional curing agent of this invention achieves a significant improvement in impact toughness (3.07-3.15 times higher than that of unmodified conventional epoxy resin cured products), while also achieving a synergistic enhancement in tensile strength and heat resistance.

[0095] While epoxy resin cured products modified with simple flexible chains using modified phenolic amines can improve impact toughness, they also lead to a significant decrease in tensile strength and heat resistance, making it impossible to achieve an optimized balance of comprehensive performance.

[0096] Conclusion 2: The epoxy resin cured product prepared by the self-developed phosphorus-containing phenolic multifunctional curing agent of this invention exhibits excellent flame retardant properties.

Claims

1. A method for preparing a phosphorus-containing phenolic multifunctional curing agent, characterized in that, Includes the following steps: (a) Preparation of modified phenolic amine: DOPO type phenol monomer containing flexible ether chain, phenol, paraformaldehyde and triethylenetetramine are prepared in a molar ratio of (0.2-0.4):(0.6-0.8):1:

1. The mixture is reacted by Mannich reaction in anhydrous ethanol solvent under nitrogen protection at 80±2℃ with stirring and reflux for 4-6 h. Modified phenolic amine is obtained after post-treatment. (b) POSS grafting reaction: The modified phenolic amine obtained in step (a) is mixed with chloropropylheptaisobutyl POSS at a mass ratio of 1:(0.05-0.15). The reaction is carried out by amino-chloro nucleophilic substitution reaction in anhydrous tetrahydrofuran solvent under nitrogen protection at 60±2℃ for 10-14h with stirring. After post-treatment, a phosphorus-containing phenolic multifunctional curing agent is obtained. The chemical structural formula of the DOPO-type phenol monomer containing a flexible ether chain is as follows: 。 2. The preparation method of the phosphorus-containing phenolic multifunctional curing agent according to claim 1, characterized in that, The method for preparing the DOPO-type phenol monomer containing a flexible ether chain is as follows: Based on the addition reaction mechanism of hydroxy-isocyanate group, an acrylate monomer containing a flexible ether chain is obtained by reacting 1 molar equivalent of polyethylene glycol monomer with 2.01-2.05 molar equivalents of ethyl isocyanate. The polyethylene glycol monomer is one of triethylene glycol, tetraethylene glycol, pentaethylene glycol, and hexaethylene glycol. Based on the Kabachnik-Fields reaction mechanism, a DOPO-type phenol monomer containing a secondary amine group was obtained by condensation reaction of 1 molar equivalent of 4-hydroxybenzylamine, 0.95-0.99 molar equivalents of DOPO and 0.95-0.99 molar equivalents of paraformaldehyde. Based on the addition reaction mechanism of acrylate group-secondary amine group, DOPO type phenol monomer containing flexible ether group is obtained by adding 1 molar equivalent of acrylate group monomer containing flexible ether chain to 2.01-2.05 molar equivalent of DOPO type phenol monomer containing secondary amine group.

3. The preparation method of the phosphorus-containing phenolic multifunctional curing agent according to claim 2, characterized in that, When the polyethylene glycol monomer is tetraethylene glycol, the chemical structural formula of the DOPO-type phenol monomer containing a flexible ether chain obtained is: 。 4. The phosphorus-containing phenolic multifunctional curing agent prepared by the method according to any one of claims 1-3, characterized in that, The amine value of the phosphorus-containing phenolic multifunctional curing agent is 330-380 mg KOH / g.

5. A heat-resistant and flame-retardant epoxy resin, characterized in that, The heat-resistant and flame-retardant epoxy resin is prepared by curing bisphenol A epoxy resin with the phosphorus-containing phenolic multifunctional curing agent as described in claim 4.

6. The heat-resistant and flame-retardant epoxy resin according to claim 5, characterized in that, The formulation of the heat-resistant and flame-retardant epoxy resin is as follows: 75-90 parts by weight of bisphenol A epoxy resin; 3-8 parts by weight of diluent; 30-40 parts by weight of phosphorus-containing phenolic multifunctional curing agent; 0.2-0.7 parts by weight of curing accelerator.

7. The heat-resistant and flame-retardant epoxy resin according to claim 6, characterized in that, The type of the bisphenol A epoxy resin is E-51.

8. The method for preparing the heat-resistant and flame-retardant epoxy resin according to any one of claims 5-7, characterized in that, Includes the following steps: Step 1: According to the formula of heat-resistant and flame-retardant epoxy resin, add diluent to bisphenol A epoxy resin and stir at 400-600 r / min for 5-15 min. Then add phosphorus-containing phenolic multifunctional curing agent and curing accelerator and stir at 800-1200 r / min for 5-15 min. During the mixing process, ensure that the material temperature does not exceed 30℃. Vacuum defoaming at low speed is performed to obtain epoxy slurry. Step 2: Pour the epoxy slurry into a polytetrafluoroethylene mold coated with a release agent, and cure it using a stepped temperature curing process: first cure at 75-85℃ for 0.8-1.2h, then raise the temperature to 110-125℃ for 0.8-1.2h, and finally cure at 130-150℃ for 0.5-1.2h. Cool and demold to obtain heat-resistant and flame-retardant epoxy resin.

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