Modified phenolic resin and preparation method thereof

Abstract

The invention discloses a modified phenolic resin and a preparation method thereof, and belongs to the technical field of phenolic resins, the modified phenolic resin comprises the following raw materials by mass: 100 parts of phenol, 140-145 parts of a formaldehyde aqueous solution, 25-30 parts of gradient topology phosphonate, 15-17 parts of hyperbranched siloxane, 12-14 parts of a dynamic borate cross-linking agent, and 3-4 parts of hexamethylenetetramine. Through the synergistic effect of the gradient topology phosphonate, the hyperbranched siloxane and the dynamic boric acid ester cross-linking agent, the flame retardance, the thermal stability, the mechanical property and the dynamic function of the phenolic resin are comprehensively improved, and the environmental protection property of the phenolic resin is remarkably superior to that of a traditional technology. The experimental data fully verifies the inseparability and synergistic interaction among innovation points, and the technical combination and effect are non-obvious and accord with the creativity requirement of the patent. In addition, the application potential of the resin in the fields of aerospace, electronic packaging and the like further highlights the industrial value of the resin.

Description

Technical Field

[0001] The present invention belongs to the technical field of phenolic resins, and particularly relates to a modified phenolic resin and a preparation method thereof. Background Art

[0002] Phenolic resin (PF) is an important thermosetting polymer material. Due to its excellent mechanical strength, heat resistance, chemical corrosion resistance and flame retardancy, it is widely used in fields such as electronic packaging, aerospace, building insulation, and flame retardant materials. In recent years, with the strictness of environmental protection regulations and the growth of demand for high-performance materials, the modification research of phenolic resins has become a hot topic. For example, in the field of flame retardancy, introducing benzoxazine (BZ) or cardanol can improve the char residue rate and thermal stability of the resin; in composite materials, adding nano-fillers (such as carbon fiber, silica) can enhance the mechanical properties. However, there are still significant problems in existing modification technologies: although a single modifier can improve a certain property, it often leads to a decline in other properties. For example, although benzoxazine modification can reduce the curing shrinkage rate, the brittleness of the resin increases; cardanol can improve toughness but may reduce thermal stability. In addition, traditional flame retardant modification mostly relies on halogen-containing or heavy metal additives, which pose an environmental pollution risk.

[0003] Currently, the simultaneous improvement of flame retardancy and mechanical properties of phenolic resins remains a technical challenge. In the prior art, although intumescent flame retardants (IFR) can inhibit combustion through char formation, their compatibility with the resin is poor, easily leading to interfacial defects and reducing mechanical strength. For example, Patent CN106046671B improves the hydrophobicity by compounding epoxy-modified phenolic resin with inorganic fillers, but the flame retardant effect is limited. In addition, composite flame retardants such as pentaerythritol phosphate melamine salt (PPMS) can improve the flame retardancy, but the synthesis process is complex and toxic solvents (such as toluene) are required. Therefore, there is an urgent need for an environmentally friendly and efficient multifunctional modification method to achieve the simultaneous improvement of the flame retardancy, thermal stability and toughness of phenolic resins without sacrificing mechanical properties. Summary of the Invention

[0004] Aiming at the problem that it is difficult to simultaneously improve the flame retardancy, thermal stability and mechanical properties of phenolic resins in the prior art, the present invention proposes a modified phenolic resin with a gradient topological structure and dynamic bonding.

[0005] The object of the present invention can be achieved by the following technical solutions:

[0006] A modified phenolic resin, comprising the following raw materials in parts by mass:

[0007] 100 parts of phenol, 140 - 145 parts of aqueous formaldehyde solution, 25 - 30 parts of gradient topological phosphonate, 15 - 17 parts of hyperbranched siloxane, 12 - 14 parts of dynamic borate crosslinking agent, 3 - 4 parts of hexamethylenetetramine.

[0008] Further, the gradient topological phosphonate is prepared by the following steps:

[0009] A1. Mix and stir tris(2-carboxyethyl)phosphine and cyclic pentaerythritol phosphate in N,N-dimethylformamide, then add zinc acetate thereto, heat up to 100-110°C, and then keep stirring at a constant temperature for 6-8 h. After completion, a prepolymer is obtained.

[0010] A2. Dropwise add 30 g of epichlorohydrin to 100 g of the prepolymer. After completion, protect with nitrogen, then heat up to 55-60°C, and then keep reacting at a constant temperature for 4-5 h. After completion, a reaction solution is obtained. Add 500 mL of ice ether to the reaction solution, filter and wash with pure water to obtain a crude product. Then dissolve the crude product in tetrahydrofuran at a mass ratio of 1:10 to obtain a solution. Then treat the solution with an ultrafiltration membrane package with a cut-off molecular weight of 10,000 Da, collect the permeate, and then treat the permeate with an ultrafiltration membrane package with a cut-off molecular weight of 5,000 Da, collect the retentate. Concentrate the retentate by rotary evaporation to 1 / 5 of the original volume, then add acetone thereto at a volume ratio of 1:4, stir, and then concentrate by rotary evaporation to 1 / 10 of the original volume. Then add acetone thereto at a volume ratio of 1:1 to obtain a concentrated solution. Dropwise add 25 mL of n-hexane to the concentrated solution, stir and let stand, then remove the precipitate. Continue to dropwise add 50 mL of n-hexane, stir and let stand, then remove the precipitate. Continue to dropwise add 150 mL of n-hexane, stir and let stand, and collect the precipitate. The precipitate is washed and dried to obtain the gradient topological phosphonate.

[0011] Further, the dosage ratio of tris(2-carboxyethyl)phosphine, cyclic pentaerythritol phosphate, N,N-dimethylformamide and zinc acetate in A1 is 45-50 g:75-80 g:500 mL:1-2 g.

[0012] Further, the hyperbranched siloxane is prepared by the following steps:

[0013] Mix and stir γ-aminopropyltrimethoxysilane and octamethylcyclotetrasiloxane in toluene, then stir and add potassium hydroxide thereto, protect with nitrogen, heat up to 78-80°C, and then keep polymerizing at a constant temperature for 6-8 h. After completion, stir and add perfluorooctyltriethoxysilane thereto, then heat up to 100-110°C. After completion, keep reacting at a constant temperature for 12 h. After completion, add deionized water thereto, then place the system at 80°C and stir for 1 h. Then, after rotary evaporation, washing and vacuum drying, the hyperbranched siloxane is obtained.

[0014] Further, the dosage ratio of γ-aminopropyltrimethoxysilane, octamethylcyclotetrasiloxane, toluene, potassium hydroxide, perfluorooctyltriethoxysilane, and deionized water is 100 g: 50 - 60 g: 500 mL: 1 g: 50 g: 5 mL.

[0015] Further, the dynamic borate crosslinking agent is prepared by the following steps:

[0016] Mix phenylboronic acid and 1,4-butanediol diglycidyl ether in tetrahydrofuran, then stir and add boron trifluoride diethyl ether thereto, charge nitrogen for protection, heat the system to 50 - 60 °C, and then keep stirring and reacting for 5 - 6 h. After completion, cool to room temperature, and then rotary evaporate to remove tetrahydrofuran to obtain the dynamic borate bond crosslinking agent.

[0017] Further, the dosage ratio of phenylboronic acid, 1,4-butanediol diglycidyl ether, tetrahydrofuran, and boron trifluoride diethyl ether is 20 g: 30 - 40 g: 500 mL: 0.5 - 1 g.

[0018] Further, the preparation method of the modified phenolic resin includes the following steps:

[0019] S1. Weigh raw materials phenol, formaldehyde aqueous solution, gradient topological phosphonate, hyperbranched siloxane, dynamic borate crosslinking agent, and hexamethylenetetramine according to mass parts. Stir and mix phenol, gradient topological phosphonate, hyperbranched siloxane, and dynamic borate crosslinking agent for 1 - 2 h, then heat the system to 80 - 90 °C, and keep stirring and pre-polymerizing for 50 - 60 min. After completion, an intermediate is obtained.

[0020] S2. Then, dropwise add the formaldehyde aqueous solution to the intermediate, heat the system to 85 - 95 °C, keep stirring for 2 h, then heat to 120 - 125 °C, keep stirring for 1 h, then heat to 150 - 155 °C, keep stirring for 30 min. After completion, cool to 100 °C, then stir and add hexamethylenetetramine thereto, stir for 20 - 30 mn, and after vacuum dehydration, the modified phenolic resin is obtained.

[0021] Advantages of the present invention:

[0022] The present invention provides a modified phenolic resin and its preparation method. Through the improvement of three core technologies of introducing gradient topological phosphonate, hyperbranched siloxane, and dynamic borate crosslinking agent, the industry problem that it is difficult to synergistically improve the flame retardancy, thermal stability, and mechanical properties in the existing phenolic resin modification technology is successfully solved.

[0023] First, the existing phenolic resin modification technology has the following limitations: imbalance between flame retardancy and mechanical properties, insufficient environmental protection, and lack of dynamic performance. Compared with the existing technology, the present invention has the following innovation points:

[0024] (1) Gradient topological phosphonate: In the present invention, a gradient branched structure (branching degree 0.30 - 0.35) is constructed through transesterification and epoxidation reactions, forming a dense and continuous carbon layer during combustion (char residue rate ≥ 50%), significantly improving the flame retardancy (LOI ≥ 37.5%, UL-94 V-0 grade).

[0025] (2) Hyperbranched siloxane: In the present invention, a hyperbranched structure with both flexibility and interface enhancement is formed through ring-opening polymerization and fluorination grafting. Its flexible chain segments disperse stress and inhibit brittle fracture (impact strength ≥ 12.2 kJ / m 2 ), and at the same time, the fluorinated groups improve the stability of the carbon layer.

[0026] (3) Dynamic borate crosslinking agent: Based on the reversibility of the borate bond, the present invention endows the resin with dynamic crosslinking ability, releasing stress through bond breakage and recombination at high temperature or under stress (flexural strength ≥ 120 MPa), and achieving self-healing of microcracks.

[0027] Then, the above innovative components are not simply stacked, but form a synergistic system through molecular structure design and functional complementarity, as follows:

[0028] (1) Synergistic improvement of flame retardancy and thermal stability: The branched structure of the gradient topological phosphonate forms carbon rapidly in the initial stage of combustion, creating a physical barrier; the fluorinated chain segments of the hyperbranched siloxane stabilize the carbon layer through interface enhancement, preventing cracking (the char residue rate in Comparative Example 2 decreased by 10%); the dynamic borate crosslinking agent dynamically adjusts the crosslinking density at high temperature, delaying thermal decomposition (initial decomposition temperature ≥ 340 °C). The synergy of the three significantly improves the LOI value and the char residue rate.

[0029] (2) Comprehensive improvement of mechanical properties: The rigid skeleton of the gradient topological phosphonate provides support and disperses stress concentration; the flexible chain segments of the hyperbranched siloxane absorb impact energy and improve toughness; the dynamic borate crosslinking agent relieves local stress through reversible bonding, avoiding brittle fracture. The data shows that the flexural strength and impact strength of Example 11 far exceed those of Comparative Examples 1 - 3, proving that none of the three can be missing.

[0030] (3) Combination of dynamic function and environmental protection: The dynamic borate endows the material with self-healing potential, expanding its application in harsh environments such as aerospace; at the same time, the entire system abandons halogen-containing flame retardants and toxic solvents, meeting the requirements of green chemistry.

[0031] In summary, through the synergistic effect of gradient topological phosphonates, hyperbranched siloxanes and dynamic borate crosslinkers, the present invention has comprehensively improved the flame retardancy, thermal stability, mechanical properties and dynamic functions of phenolic resins, and its environmental friendliness is significantly better than that of traditional technologies. The experimental data fully verify the inseparability and synergistic effect among the innovation points. The technical combination and its effects are non-obvious and meet the requirements for patent creativity. In addition, the application potential of this resin in the fields of aerospace, electronic packaging, etc. further highlights its industrial value. Detailed implementation manners

[0032] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0033] Example 1

[0034] Preparation of gradient topological phosphonate:

[0035] A1. Mix 45 g of tris(2-carboxyethyl)phosphine (TCEP) and 75 g of cyclic pentaerythritol phosphate (CPP) in 500 mL of N,N-dimethylformamide (DMF) and stir for 10 min, then stir and add 1 g of the catalyst zinc acetate (Zn(OAc) 2 ) to the mixture. Heat the system to 100 °C and then stir and react at a constant temperature for 6 h. After the reaction is completed, cool it to room temperature to obtain a prepolymer containing phosphonate. During the above reaction process, the carboxyl group of TCEP and the phosphate group of CPP undergo transesterification under the catalysis of Zn 2+ to form a branched skeleton;

[0036] A2. 30 g of epichlorohydrin was added dropwise to 100 g of prepolymer. After the addition was complete, nitrogen was introduced into the system for protection. The system was then heated to 55 °C and subjected to an epoxidation reaction at a constant temperature for 4 h. After the reaction was completed, it was cooled to room temperature to obtain a reaction solution. 500 mL of ice-cold diethyl ether was added to the reaction solution to precipitate the polymer. The solid was collected by filtration, washed three times with pure water, and the washed solid was collected to obtain the crude product. The crude product was then dissolved in tetrahydrofuran at a mass ratio of 1:10, and ultrasonic treatment was carried out for 30 min (40 kHz) to ensure complete dissolution to obtain a solution. The solution was then treated with an ultrafiltration membrane package with a molecular weight cut-off of 10,000 Da, and the permeate (components with a molecular weight ≤ 10,000 Da) was collected. The permeate was then treated with an ultrafiltration membrane package with a molecular weight cut-off of 5,000 Da, and the retentate (components with a molecular weight of 5,000 - 10,000 Da) was collected. The retentate was rotary evaporated and concentrated to 1 / 5 of the original volume, and then acetone was added to it at a volume ratio of 1:4, stirred for 10 min, and then rotary evaporated and concentrated to 1 / 10 of the original volume. Then acetone was added to it at a volume ratio of 1:1 to obtain a concentrated solution. 25 mL of n-hexane was added dropwise to the concentrated solution, stirred for 10 min, and left to stand for 30 min to remove the precipitate (branching degree > 0.4). 50 mL of n-hexane was continuously added dropwise to it, stirred for 10 min, and left to stand for 30 min to remove the precipitate (branching degree 0.35 - 0.4). 150 mL of n-hexane was continuously added dropwise to it, stirred for 10 min, and left to stand for 60 min to collect the precipitate (branching degree 0.30 - 0.35). The precipitate was washed three times with n-hexane and then freeze-dried to obtain gradient topological phosphonate. By GPC measurement (THF as the mobile phase, PS standard sample), Mn ≈ 8000 Da, PDI = 1.3. Then, 1 The branching degree was calculated by ¹H-NMR (through the integral ratio of terminal epoxy groups) to be 0.35 ± 0.02. During the above reaction process, the epoxy group of epichlorohydrin reacted with the hydroxyl group in the prepolymer to introduce epoxy end groups, and finally gradient topological phosphonate was obtained by constructing a gradient branching degree.

[0037] Example 2

[0038] Preparation of gradient topological phosphonate:

[0039] A1. 50 g of tris(2-carboxyethyl)phosphine (TCEP) and 75 g of cyclic pentaerythritol phosphate (CPP) were mixed and stirred in 500 mL of N,N-dimethylformamide (DMF) for 30 min, and then 2 g of catalyst zinc acetate (Zn(OAc) 2 ) was added thereto with stirring. The system was heated to 100 °C and stirred at a constant temperature for 8 h. After the reaction was completed, it was cooled to room temperature to obtain a prepolymer containing phosphonate. During the above reaction process, the carboxyl group of TCEP and the phosphate group of CPP underwent transesterification under the catalysis of Zn 2+ to form a branched skeleton;

[0040] A2. Gradually add 30 g of epichlorohydrin dropwise to 100 g of prepolymer. After the addition is complete, introduce nitrogen protection into the system, heat the system to 55 °C, and then carry out the epoxidation reaction at a constant temperature for 5 h. After the reaction is completed, cool to room temperature to obtain a reaction solution. Add 500 mL of ice-cold diethyl ether to the reaction solution to precipitate the polymer, filter and collect the solid, wash the solid three times with pure water, and then collect the washed solid to obtain the crude product. Then dissolve the crude product in tetrahydrofuran at a mass ratio of 1:10, and perform ultrasonic treatment for 30 min (40 kHz) to ensure complete dissolution to obtain a solution. Then treat the solution with an ultrafiltration membrane package with a molecular weight cut-off of 10,000 Da, and collect the permeate (components with a molecular weight ≤ 10,000 Da). Then treat the permeate with an ultrafiltration membrane package with a molecular weight cut-off of 5,000 Da, and collect the retentate (components with a molecular weight of 5,000 - 10,000 Da). Concentrate the retentate by rotary evaporation to 1 / 5 of the original volume, then add acetone to it at a volume ratio of 1:4, stir for 30 min, and then concentrate it by rotary evaporation to 1 / 10 of the original volume. Then add acetone to it at a volume ratio of 1:1 to obtain a concentrated solution. Add 25 mL of n-hexane dropwise to the concentrated solution, stir for 10 min, let it stand for 30 min, and remove the precipitate (branching degree > 0.4). Continue to add 50 mL of n-hexane dropwise to it, stir for 10 min, let it stand for 30 min, and remove the precipitate (branching degree 0.35 - 0.4). Continue to add 150 mL of n-hexane dropwise to it, stir for 10 min, let it stand for 60 min, and collect the precipitate (branching degree 0.30 - 0.35). Wash the precipitate three times with n-hexane, and then perform freeze-drying to obtain gradient topological phosphonate. Determined by GPC (THF as the mobile phase, PS standard sample), Mn ≈ 8000 Da, PDI = 1.3, and then by 1 1H-NMR calculation (through the integral ratio of terminal epoxy groups), the branching degree is 0.35 ± 0.02. In the above reaction process, the epoxy group of epichlorohydrin reacts with the hydroxyl group in the prepolymer to introduce epoxy end groups, and then by constructing a gradient branching degree, gradient topological phosphonate is finally obtained.

[0041] Example 3

[0042] Preparation of gradient topological phosphonate:

[0043] A1. Mix 50 g of tris(2-carboxyethyl)phosphine (TCEP) and 80 g of cyclic pentaerythritol phosphate (CPP) in 500 mL of N,N-dimethylformamide (DMF) and stir for 30 min, then stir and add 2 g of the catalyst zinc acetate (Zn(OAc) 2 ) to it. Heat the system to 110 °C, and then carry out the stirring reaction at a constant temperature for 8 h. After the reaction is completed, cool to room temperature to obtain a prepolymer containing phosphonate. In the above reaction process, the carboxyl group of TCEP and the phosphate group of CPP react in the presence of Zn2+ Transesterification occurs under catalysis to form a branched backbone;

[0044] A2. Gradually add 30 g of epichlorohydrin dropwise to 100 g of the prepolymer. After the addition is complete, introduce nitrogen protection into the system, then heat the system to 60 °C, and carry out the epoxidation reaction at a constant temperature for 5 h. After the reaction is completed, cool it to room temperature to obtain a reaction solution. Add 500 mL of ice ether to the reaction solution to precipitate the polymer, filter and collect the solid, wash the solid three times with pure water, then collect the washed solid to obtain a crude product. Then dissolve the crude product in tetrahydrofuran at a mass ratio of 1:10, and perform ultrasonic treatment for 30 min (40 kHz) to ensure complete dissolution to obtain a solution. Then treat the solution with an ultrafiltration membrane package with a cut-off molecular weight of 10,000 Da, and collect the permeate (components with a molecular weight ≤ 10,000 Da). Then treat the permeate with an ultrafiltration membrane package with a cut-off molecular weight of 5,000 Da, and collect the retentate (components with a molecular weight of 5,000 - 10,000 Da). Concentrate the retentate by rotary evaporation to 1 / 5 of the original volume, then add acetone to it at a volume ratio of 1:4, stir for 30 min, and then concentrate it by rotary evaporation to 1 / 10 of the original volume. Then add acetone to it at a volume ratio of 1:1 to obtain a concentrated solution. Dropwise add 25 mL of n-hexane to the concentrated solution, stir for 10 min, let it stand for 30 min, and remove the precipitate (branching degree > 0.4). Continue to dropwise add 50 mL of n-hexane to it, stir for 10 min, let it stand for 30 min, and remove the precipitate (branching degree 0.35 - 0.4). Continue to dropwise add 150 mL of n-hexane to it, stir for 10 min, let it stand for 60 min, and collect the precipitate (branching degree 0.30 - 0.35). Wash the precipitate three times with n-hexane, and then carry out freeze-drying to obtain gradient topological phosphonate. Determined by GPC (THF as the mobile phase, PS standard sample), Mn ≈ 8000 Da, PDI = 1.3, and then by 1 1H-NMR calculation (through the integral ratio of terminal epoxy groups), the branching degree is 0.35 ± 0.02. During the above reaction process, the epoxy group of epichlorohydrin reacts with the hydroxyl group in the prepolymer to introduce epoxy end groups, and finally gradient topological phosphonate is obtained by constructing a gradient branching degree.

[0045] Example 4

[0046] Prepare hyperbranched siloxane:

[0047] Mix 100 g of γ-aminopropyltrimethoxysilane (KH540) with 50 g of octamethylcyclotetrasiloxane (D4) in 500 mL of toluene and stir for 10 min. Then, add 1 g of potassium hydroxide to it while stirring, fill with nitrogen for protection, heat the system to 78 °C, and then carry out ring-opening polymerization at a constant temperature for 6 h. During the reaction process, D4 undergoes ring-opening to form linear polysiloxane, and condenses with the amino group of KH540 to form a hyperbranched skeleton. After completion, add 50 g of perfluorooctyltriethoxysilane to the system while stirring, heat the system to 100 °C, and after completion, carry out grafting reaction at a constant temperature for 12 h. During the reaction process, Si - OCH 2 CH 3 condenses with Si - OH of the hyperbranched skeleton to graft C8F17 chains. After completion, add 5 mL of deionized water to the system to quench the unreacted siloxane groups, then place the system at 80 °C and stir for 1 h, then remove toluene by rotary evaporation, wash with n-hexane, and then place it in a vacuum drying oven at 50 °C for 24 h. After completion, hyperbranched siloxane is obtained.

[0048] Example 5

[0049] Preparation of hyperbranched siloxane:

[0050] Mix 100 g of γ-aminopropyltrimethoxysilane (KH540) with 55 g of octamethylcyclotetrasiloxane (D4) in 500 mL of toluene and stir for 30 min. Then, add 1 g of potassium hydroxide to it while stirring, fill with nitrogen for protection, heat the system to 78 °C, and then carry out ring-opening polymerization at a constant temperature for 8 h. During the reaction process, D4 undergoes ring-opening to form linear polysiloxane, and condenses with the amino group of KH540 to form a hyperbranched skeleton. After completion, add 50 g of perfluorooctyltriethoxysilane to the system while stirring, heat the system to 105 °C, and after completion, carry out grafting reaction at a constant temperature for 12 h. During the reaction process, Si - OCH 2 CH 3 condenses with Si - OH of the hyperbranched skeleton to graft C8F17 chains. After completion, add 5 mL of deionized water to the system to quench the unreacted siloxane groups, then place the system at 80 °C and stir for 1 h, then remove toluene by rotary evaporation, wash with n-hexane, and then place it in a vacuum drying oven at 50 °C for 24 h. After completion, hyperbranched siloxane is obtained.

[0051] Example 6

[0052] Preparation of hyperbranched siloxane:

[0053] Mix 100 g of γ-aminopropyltrimethoxysilane (KH540) with 60 g of octamethylcyclotetrasiloxane (D4) in 500 mL of toluene and stir for 30 min. Then, add 1 g of potassium hydroxide to it while stirring, fill with nitrogen for protection, heat the system to 80 °C, and then carry out ring-opening polymerization at a constant temperature for 8 h. During the reaction process, D4 undergoes ring-opening to form linear polysiloxane, and condenses with the amino group of KH540 to form a hyperbranched skeleton. After completion, add 50 g of perfluorooctyltriethoxysilane to the system while stirring, heat the system to 110 °C, and after completion, carry out grafting reaction at a constant temperature for 12 h. During the reaction process, the Si-OCH 2 CH 3 of siloxane condenses with the Si-OH of the hyperbranched skeleton to graft the C8F17 chain. After completion, add 5 mL of deionized water to the system to quench the unreacted siloxane groups, then place the system in a stirrer at 80 °C for 1 h, then remove toluene by rotary evaporation, wash with n-hexane, and then place it in a vacuum dryer at 60 °C for 24 h. After completion, hyperbranched siloxane is obtained.

[0054] Example 7

[0055] Prepare a dynamic borate crosslinking agent:

[0056] Mix 20 g of phenylboronic acid with 30 g of 1,4-butanediol diglycidyl ether in 500 mL of tetrahydrofuran for 10 min. Then, add 0.5 g of the catalyst boron trifluoride diethyl etherate (BF 3 ·Et 2 O) to it while stirring, fill with nitrogen for protection, heat the system to 50 °C, and then carry out stirring reaction at a constant temperature for 5 h. During the reaction process, phenylboronic acid (PhB(OH) 2 ) reacts with the epoxy group of 1,4-butanediol diglycidyl ether under acidic conditions to undergo ring-opening reaction to form a borate bond (Ph-B-O-(CH 2 ) 4 -O-B-Ph). After completion, cool to room temperature, and then remove tetrahydrofuran by rotary evaporation to obtain a pale yellow viscous liquid, that is, a dynamic borate bond crosslinking agent.

[0057] Example 8

[0058] Prepare a dynamic borate crosslinking agent:

[0059] Mix 20 g of phenylboronic acid with 35 g of 1,4-butanediol diglycidyl ether in 500 mL of tetrahydrofuran for 30 min. Then, add 1 g of the catalyst boron trifluoride diethyl etherate (BF 3 ·Et 2 O) to it while stirring, fill with nitrogen for protection, heat the system to 55 °C, and then carry out stirring reaction at a constant temperature for 6 h. During the reaction process, phenylboronic acid (PhB(OH) 2) undergoes a ring-opening reaction with the epoxy groups of 1,4-butanediol diglycidyl ether under acidic conditions to form a borate ester bond (Ph-B-O-(CH 2 ) 4 -O-B-Ph). After completion, it is cooled to room temperature, and then tetrahydrofuran is removed by rotary evaporation to obtain a pale yellow viscous liquid, i.e., the dynamic borate ester bond crosslinking agent.

[0060] Example 9

[0061] Preparation of dynamic borate crosslinking agent:

[0062] 20 g of phenylboronic acid and 40 g of 1,4-butanediol diglycidyl ether are mixed in 500 mL of tetrahydrofuran for 30 min, and then 1 g of the catalyst boron trifluoride diethyl etherate (BF 3 ·Et 2 O) is added thereto with stirring. Nitrogen is filled for protection, and the system is then heated to 60 °C and stirred at a constant temperature for 6 h. During the reaction, phenylboronic acid (PhB(OH) 2 ) undergoes a ring-opening reaction with the epoxy groups of 1,4-butanediol diglycidyl ether under acidic conditions to form a borate ester bond (Ph-B-O-(CH 2 ) 4 -O-B-Ph). After completion, it is cooled to room temperature, and then tetrahydrofuran is removed by rotary evaporation to obtain a pale yellow viscous liquid, i.e., the dynamic borate ester bond crosslinking agent.

[0063] Example 10

[0064] Preparation of modified phenolic resin:

[0065] First, the modified phenolic resin includes the following raw materials in parts by mass:

[0066] 100 parts of phenol (industrial grade, purity ≥ 99%);

[0067] 140 parts of formaldehyde aqueous solution (37%; analytical pure);

[0068] 25 parts of gradient topological phosphonate (prepared in Example 1);

[0069] 15 parts of hyperbranched siloxane (prepared in Example 4);

[0070] 12 parts of dynamic borate ester crosslinking agent (prepared in Example 7);

[0071] 3 parts of hexamethylenetetramine (analytical pure).

[0072] Then, weigh the raw materials phenol, aqueous formaldehyde solution, gradient topological phosphonate, hyperbranched siloxane, dynamic borate crosslinking agent and hexamethylenetetramine according to parts by mass. Stir and mix phenol, gradient topological phosphonate, hyperbranched siloxane and dynamic borate crosslinking agent for 1 h. Then, heat the system to 80 °C and carry out a constant-temperature stirring prepolymerization reaction for 50 min. After completion, an intermediate is obtained. Then, drip the aqueous formaldehyde solution (37%) into the intermediate, heat the system to 85 °C, carry out a constant-temperature stirring for 2 h, then heat it to 120 °C, carry out a constant-temperature stirring for 1 h, then heat it to 150 °C, carry out a constant-temperature stirring for 30 min. After completion, cool it to 100 °C, then stir and add hexamethylenetetramine thereto, stir for 20 mn, and carry out vacuum dehydration until the gel time reaches 40 s (monitor the viscosity through a gel time tester, and stop dehydration when the gel time reaches 40 s, corresponding resin viscosity ≈ 10 4 cP), and a modified phenolic resin is obtained.

[0073] Example 11

[0074] Preparation of modified phenolic resin:

[0075] First, the modified phenolic resin includes the following raw materials in parts by mass:

[0076] 100 parts of phenol (industrial grade, purity ≥ 99%);

[0077] 142 parts of aqueous formaldehyde solution (37%; analytical pure);

[0078] 28 parts of gradient topological phosphonate (self-made in Example 2);

[0079] 16 parts of hyperbranched siloxane (self-made in Example 5);

[0080] 14 parts of dynamic borate crosslinking agent (self-made in Example 8);

[0081] 4 parts of hexamethylenetetramine (analytical pure).

[0082] Then, weigh the raw materials phenol, aqueous formaldehyde solution, gradient topological phosphonate, hyperbranched siloxane, dynamic borate crosslinking agent and hexamethylenetetramine according to parts by mass. Stir and mix phenol, gradient topological phosphonate, hyperbranched siloxane and dynamic borate crosslinking agent for 2 h. Then, heat the system to 85 °C and carry out a constant-temperature stirring prepolymerization reaction for 60 min. After completion, an intermediate is obtained. Then, drip the aqueous formaldehyde solution (37%) into the intermediate, heat the system to 90 °C, carry out a constant-temperature stirring for 2 h, then heat it to 120 °C, carry out a constant-temperature stirring for 1 h, then heat it to 150 °C, carry out a constant-temperature stirring for 30 min. After completion, cool it to 100 °C, then stir and add hexamethylenetetramine thereto, stir for 30 mn, and carry out vacuum dehydration until the gel time reaches 40 s (monitor the viscosity through a gel time tester, and stop dehydration when the gel time reaches 40 s, corresponding resin viscosity ≈ 10 4By using (cP), a modified phenolic resin is obtained.

[0083] Example 12

[0084] Preparation of modified phenolic resin:

[0085] First, the modified phenolic resin includes the following raw materials in parts by mass:

[0086] 100 parts of phenol (industrial grade, purity ≥ 99%);

[0087] 145 parts of aqueous formaldehyde solution (37%; analytical pure);

[0088] 30 parts of gradient topological phosphonate (self-made in Example 3);

[0089] 17 parts of hyperbranched siloxane (self-made in Example 6);

[0090] 14 parts of dynamic borate crosslinking agent (self-made in Example 9);

[0091] 4 parts of hexamethylenetetramine (analytical pure).

[0092] Then, weigh the raw materials of phenol, aqueous formaldehyde solution, gradient topological phosphonate, hyperbranched siloxane, dynamic borate crosslinking agent and hexamethylenetetramine according to parts by mass. Stir and mix phenol, gradient topological phosphonate, hyperbranched siloxane and dynamic borate crosslinking agent for 2 h, then raise the temperature of the system to 90 °C and carry out a constant-temperature stirring prepolymerization reaction for 60 min. After completion, an intermediate is obtained. Then, dropwise add aqueous formaldehyde solution (37%) to the intermediate, raise the temperature of the system to 95 °C, carry out a constant-temperature stirring for 2 h, then raise the temperature to 125 °C, carry out a constant-temperature stirring for 1 h, then raise the temperature to 155 °C, carry out a constant-temperature stirring for 30 min. After completion, cool down to 100 °C, then stir and add hexamethylenetetramine to it, stir for 30 mn, and carry out vacuum dehydration until the gel time is 40 s (monitor the viscosity through a gel time tester, and stop dehydration when the gel time reaches 40 s, corresponding to a resin viscosity ≈ 10 4 cP), a modified phenolic resin is obtained.

[0093] Comparative Example 1

[0094] Comparative Example 1 is the control group of Example 11. Replace the raw material gradient topological phosphonate (self-made in Example 2) in the modified phenolic resin of Example 11 with linear phosphonate bisphenol A bis(diphenyl phosphate), and keep the other raw materials, raw material dosages and preparation methods unchanged, and finally obtain a modified phenolic resin.

[0095] Comparative Example 2

[0096] Comparative Example 2 was the control group of Example 11. 16 parts of the hyperbranched silicone oxygen alkane (self-made in Example 5) in the modified phenolic resin of Example 11 was removed, and the remaining raw materials, the amounts of raw materials, and the preparation method remained unchanged, and finally a modified phenolic resin was obtained.

[0097] Comparative Example 3

[0098] Comparative Example 3 was the control group of Example 11. 14 parts of the dynamic borate cross-linking agent (self-made in Example 8) in the modified phenolic resin of Example 11 was removed, and the remaining raw materials, the amounts of raw materials, and the preparation method remained unchanged, and finally a modified phenolic resin was obtained.

[0099] Test Example 1

[0100] The modified phenolic resins prepared in Examples 10 to 12 and Comparative Examples 1 to 3 were subjected to performance tests. The performance test process was as follows, and the test results are shown in Table 1:

[0101] (1) Flame retardancy test:

[0102] a. Limiting oxygen index (LOI): Referring to the ASTM D2863 standard, an oxygen index meter was used to test the limiting oxygen index of the modified phenolic resin.

[0103] b. UL-94 vertical burning test: Referring to the UL-94 standard, the modified phenolic resin was subjected to a vertical burning test, and the burning time, dripping substances, and self-extinguishing property were recorded.

[0104] (2) Thermal stability test:

[0105] a. Thermogravimetric analysis (TGA): Under a nitrogen atmosphere, the temperature was raised from 30 °C to 800 °C at a heating rate of 10 °C / min, and the initial decomposition temperature (temperature at 5% weight loss) and the char residue rate at 800 °C of the modified phenolic resin were recorded.

[0106] (3) Mechanical property test

[0107] a. Flexural strength: Referring to the ASTM D790 standard, a universal material testing machine was used to test the flexural strength of the modified phenolic resin (span / thickness ratio = 16:1).

[0108] b. Notched impact strength: Referring to the ASTM D256 standard, a pendulum impact testing machine was used to test the notched impact strength of the modified phenolic resin.

[0109] Table 1 Test results

[0110] Project Example 10 Example 11 Example 12 Comparative Example 1 Comparative Example 2 Comparative Example 3 LOI (%) 37.5 38.1 37.8 28.5 32.9 30.7 UL-94 Rating V-0 V-0 V-0 V-2 V-1 V-2 Initial Decomposition Temperature (°C) 340 345 345 290 315 305 Residual Carbon Ratio (%) 51 55 54 38 45 42 Flexural Strength (MPa) 120 128 125 95 105 98 <![CDATA[Impact strength (kJ / m 2 )]]> 12.2 12.5 12.4 6.8 8.2 7.5

[0111] As can be seen from Table 1;

[0112] Flammability and Thermal Stability: The LOI value (38.1%) and UL-94 V-0 rating of Example 11 are significantly better than those of Comparative Example 1 (LOI 28.5%, V-2), indicating that the branched structure of the gradient topological phosphonate can form a denser carbon layer during combustion compared to the linear phosphonate bisphenol A bis(diphenyl phosphate), which can effectively isolate heat and oxygen. Its char yield (55%) is also much higher than that of Comparative Example 1 (38%), further verifying the carbon layer strengthening effect of the gradient topological structure. The char yield of Comparative Example 2 (without hyperbranched siloxane) decreased (45%), indicating that siloxane promoted the stability of the carbon layer by enhancing the interfacial bonding; the LOI and char yield of Comparative Example 3 (without borate ester) are lower than those of Example 11, indicating that the reversible crosslinking of the dynamic borate ester helps the dynamic repair of the carbon layer.

[0113] Mechanical Properties: The flexural strength (128 MPa) and impact strength (12.5 kJ / m 2 ) of Example 11 are much higher than those of Comparative Example 1 (95 MPa, 6.8 kJ / m 2 ), proving that the branched network of the gradient topological phosphonate can disperse stress and avoid brittle fracture. The mechanical properties of Comparative Example 2 decreased (impact strength 8.2 kJ / m 2 ) indicating that the hyperbranched siloxane improved toughness through flexible chain segments; the decrease in the mechanical properties of Comparative Example 3 indicates that the dynamic borate ester crosslinking agent can relieve stress concentration through reversible bonding.

[0114] Summary: The branched structure of the gradient topological phosphonate provides a rigid framework, the flexible chains of the hyperbranched siloxane enhance the interfacial bonding, and the dynamic borate ester crosslinking agent balances rigidity and toughness through dynamic bonding. The three work together to achieve a comprehensive improvement in flame retardancy, thermal stability, and mechanical properties.

[0115] It should be noted that in this article, terms such as "including", "comprising", or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device including a series of elements not only includes those elements but also includes other elements not explicitly listed, or also includes elements inherent to such a process, method, article, or device.

[0116] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A modified phenolic resin, characterized in that: Including the following raw materials by weight: 100 parts of phenol, 140-145 parts of formaldehyde aqueous solution, 25-30 parts of gradient topology phosphonate, 15-17 parts of hyperbranched siloxane, 12-14 parts of dynamic borate crosslinking agent, and 3-4 parts of hexamethylenetetramine.

2. A modified phenolic resin according to claim 1, characterized in that: The gradient topology phosphonate is prepared by the following steps: A1. Mix tri(2-carboxyethyl)phosphine and cyclic pentaerythritol phosphate in N,N-dimethylformamide, add zinc acetate, heat to 100-110° C., and stir at constant temperature for 6-8 hours to obtain a prepolymer; A2. Add 30 g of epichlorohydrin dropwise to 100 g of the prepolymer. After completion, introduce nitrogen protection, then heat to 55-60 ° C, and then react at a constant temperature for 4-5 hours. After completion, obtain a reaction solution, add 500 mL of ice ether to the reaction solution, filter, and wash with pure water to obtain a crude product, then dissolve the crude product in tetrahydrofuran at a mass ratio of 1:10 to obtain a solution, then treat the solution with an ultrafiltration membrane with a molecular weight cutoff of 10000 Da, collect the permeate, and then treat the permeate with an ultrafiltration membrane with a molecular weight cutoff of 5000 Da. , collect the retentate, concentrate the retentate by rotary evaporation to 1 / 5 of the original volume, add acetone thereto at a volume ratio of 1:4, stir, and then concentrate by rotary evaporation to 1 / 10 of the original volume, add acetone thereto at a volume ratio of 1:1 to obtain a concentrated solution, add 25 mL of n-hexane dropwise to the concentrated solution, stir and let stand, remove the precipitate, continue to add 50 mL of n-hexane dropwise thereto, stir and let stand, remove the precipitate, continue to add 150 mL of n-hexane dropwise thereto, stir and let stand, collect the precipitate, wash and dry the precipitate to obtain a gradient topology phosphonate.

3. A modified phenolic resin according to claim 2, characterized in that: The usage ratio of tri(2-carboxyethyl)phosphine, cyclic pentaerythritol phosphate, N,N-dimethylformamide and zinc acetate in A1 is 45-50g:75-80g:500mL:1-2g.

4. A modified phenolic resin according to claim 1, characterized in that: The hyperbranched siloxane is prepared by the following steps: γ-Aminopropyltrimethoxysilane and octamethylcyclotetrasiloxane are mixed and stirred in toluene, and potassium hydroxide is added thereto while stirring, nitrogen is filled in for protection, the temperature is raised to 78-80°C, and the polymerization is carried out at a constant temperature for 6-8 hours. After completion, perfluorooctyltriethoxysilane is added thereto while stirring, and the temperature is raised to 100-110°C. After completion, the reaction is carried out at a constant temperature for 12 hours. After completion, deionized water is added thereto, and the system is placed at 80°C and stirred for 1 hour. After rotary evaporation, washing, and vacuum drying, hyperbranched siloxane is obtained.

5. A modified phenolic resin according to claim 4, characterized in that: The dosage ratio of the γ-aminopropyltrimethoxysilane, octamethylcyclotetrasiloxane, toluene, potassium hydroxide, perfluorooctyltriethoxysilane and deionized water is 100g:50-60g:500mL:1g:50g:5mL.

6. A modified phenolic resin according to claim 1, characterized in that: The dynamic borate crosslinker is prepared by the following steps: Mix phenylboric acid and 1,4-butanediol diglycidyl ether in tetrahydrofuran, then add boron trifluoride ether thereto with stirring, fill with nitrogen for protection, heat the system to 50-60°C, and then stir and react at a constant temperature for 5-6 hours. After completion, cool to room temperature, and then rotary evaporate to remove tetrahydrofuran to obtain a dynamic borate ester bond crosslinker.

7. A modified phenolic resin according to claim 6, characterized in that: The usage ratio of the phenylboric acid, 1,4-butanediol diglycidyl ether, tetrahydrofuran and boron trifluoride ethyl ether is 20g:30-40g:500mL:0.5-1g.

8. A method for preparing a modified phenolic resin according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Weigh the raw materials phenol, formaldehyde aqueous solution, gradient topology phosphonate, hyperbranched siloxane, dynamic borate crosslinker and hexamethylenetetramine according to mass parts, stir and mix phenol, gradient topology phosphonate, hyperbranched siloxane and dynamic borate crosslinker for 1 to 2 hours, then heat the system to 80 to 90° C., stir and prepolymerize at constant temperature for 50 to 60 minutes, and after completion, obtain an intermediate; S2. Add formaldehyde aqueous solution dropwise to the intermediate, heat the system to 85-95°C, stir at constant temperature for 2 hours, then heat to 120-125°C, stir at constant temperature for 1 hour, then heat to 150-155°C, stir at constant temperature for 30 minutes. After completion, cool to 100°C, add hexamethylenetetramine and stir therein, stir for 20-30 minutes, and dehydrate in vacuo to obtain modified phenolic resin.