A modified phenol-formaldehyde resin and a method for producing the same

Abstract

The application discloses a modified phenolic resin and a preparation method thereof, and belongs to the technical field of phenolic resin.The modified phenolic resin comprises the following raw materials in mass parts: 100 parts of phenol, 140-145 parts of a formaldehyde aqueous solution, 25-30 parts of gradient topological phosphonate, 15-17 parts of hyperbranched siloxane, 12-14 parts of a dynamic borate ester crosslinking agent and 3-4 parts of hexamethylenetetramine.The synergistic effect of the gradient topological phosphonate, the hyperbranched siloxane and the dynamic borate ester crosslinking agent is utilized, so that the overall improvement of the flame retardancy, the thermal stability, the mechanical property and the dynamic function of the phenolic resin is realized, and the environmental protection property is obviously better than that of the traditional technology.The experimental data fully verify the indivisibility and the synergistic effect of the innovation points, the technical combination and the effect are non-obvious, and the application meets the requirement of patent creativity.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] This invention belongs to the field of phenolic resin technology, specifically relating to a modified phenolic resin and its preparation method. Background Technology

[0002] Phenolic resin (PF) is an important thermosetting polymer material, widely used in electronic packaging, aerospace, building insulation, and flame-retardant materials due to its excellent mechanical strength, heat resistance, chemical corrosion resistance, and flame retardancy. In recent years, with increasingly stringent environmental regulations and growing demand for high-performance materials, the modification of phenolic resins has become a hot topic. For example, in the flame-retardant field, the introduction of benzoxazine (BZ) or cardanol can improve the resin's char residue and thermal stability; in composite materials, the addition of nanofillers (such as carbon fibers and silica) can enhance mechanical properties. However, existing modification techniques still have significant problems: while a single modifier can improve a certain property, it often leads to a decline in other properties. For example, while benzoxazine modification can reduce curing shrinkage, it increases resin brittleness; cardanol can improve toughness but may reduce thermal stability. Furthermore, traditional flame-retardant modifications often rely on additives containing halogens or heavy metals, posing environmental pollution risks.

[0003] Currently, achieving a synergistic improvement in the flame retardancy and mechanical properties of phenolic resins remains a technical challenge. In existing technologies, while intumescent flame retardants (IFRs) can inhibit combustion through char formation, their poor compatibility with resins easily leads to interfacial defects and reduces mechanical strength. For example, patent CN106046671B, which combines epoxy-modified phenolic resin with inorganic fillers, improves hydrophobicity but has limited flame retardant effect. Furthermore, while composite flame retardants such as pentaerythritol phosphate melamine salt (PPMS) can improve flame retardancy, their synthesis processes are complex and require the use of toxic solvents (such as toluene). Therefore, there is an urgent need for an environmentally friendly, efficient, and multifunctional modification method to achieve a synergistic improvement in the flame retardancy, thermal stability, and toughness of phenolic resins without sacrificing mechanical properties. Summary of the Invention

[0004] To address the problem that it is difficult to synergistically improve the flame retardancy, thermal stability and mechanical properties of phenolic resins in existing technologies, this invention proposes a modified phenolic resin with a gradient topology and dynamic bonding.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A modified phenolic resin comprises the following raw materials in parts by weight:

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

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

[0009] A1. Tris(2-carboxyethyl)phosphine and cyclic pentaerythritol phosphate are mixed and stirred in N,N-dimethylformamide, and then zinc acetate is added. The mixture is heated to 100-110°C and stirred at a constant temperature for 6-8 hours. After the mixture is stirred, the prepolymer is obtained.

[0010] A2. Add 30g of epichlorohydrin dropwise to 100g of prepolymer. After completion, purge with nitrogen for protection, then heat to 55-60℃ and maintain the temperature for 4-5 hours. After completion, obtain the reaction solution. Add 500mL of icy diethyl ether to the reaction solution, filter, and wash with pure water to obtain the crude product. 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 10000Da, collect the permeate, and then treat the permeate with an ultrafiltration membrane with a molecular weight cutoff of 5000Da. The retentate was collected and concentrated by rotary evaporation to 1 / 5 of its original volume. Acetone was then added to the retentate at a volume ratio of 1:4, and the mixture was stirred. The mixture was then concentrated by rotary evaporation to 1 / 10 of its original volume. Acetone was then added to the retentate at a volume ratio of 1:1 to obtain a concentrated solution. 25 mL of n-hexane was added dropwise to the concentrated solution, and the mixture was stirred and allowed to stand. The precipitate was then removed. 50 mL of n-hexane was added dropwise to the concentrated solution, and the mixture was stirred and allowed to stand. The precipitate was then removed. 150 mL of n-hexane was added dropwise to the concentrated solution, and the mixture was stirred and allowed to stand. The precipitate was collected, washed, and dried to obtain a gradient topof-topophosphonate.

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

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

[0013] γ-aminopropyltrimethoxysilane and octamethylcyclotetrasiloxane were mixed and stirred in toluene, and then potassium hydroxide was added while stirring. Nitrogen gas was introduced for protection, and the temperature was raised to 78-80°C. Polymerization was carried out at this temperature for 6-8 hours. After polymerization, perfluorooctyltriethoxysilane was added while stirring, and the temperature was raised to 100-110°C. After polymerization, the reaction was carried out at this temperature for 12 hours. After polymerization, deionized water was added, and the system was stirred at 80°C for 1 hour. After rotary evaporation, washing, and vacuum drying, hyperbranched siloxane was obtained.

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

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

[0016] Phenylboronic acid and 1,4-butanediol diglycidyl ether were mixed in tetrahydrofuran, and boron trifluoride ethyl ether was added to the mixture while stirring. The mixture was then purged with nitrogen for protection, and the system was heated to 50-60°C and stirred at a constant temperature for 5-6 hours. After the reaction was completed, the mixture was cooled to room temperature, and the tetrahydrofuran was removed by rotary evaporation to obtain a dynamic borate ester crosslinking agent.

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

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

[0019] S1. Weigh the raw materials phenol, formaldehyde aqueous solution, gradient topological phosphonate, hyperbranched siloxane, dynamic borate crosslinking agent and hexamethylenetetramine according to the mass parts. Stir and mix phenol, gradient topological phosphonate, hyperbranched siloxane and dynamic borate crosslinking agent for 1-2 hours. Then heat the system to 80-90℃ and stir at a constant temperature for 50-60 minutes for prepolymerization. After completion, the intermediate is obtained.

[0020] S2. Add formaldehyde aqueous solution dropwise to the intermediate, heat the system to 85-95℃, stir at constant temperature for 2 hours, then heat to 120-125℃, stir at constant temperature for 1 hour, then heat to 150-155℃, stir at constant temperature for 30 minutes. After completion, cool down to 100℃, add hexamethylenetetramine to the mixture, stir for 20-30 minutes, and after vacuum dehydration, obtain modified phenolic resin.

[0021] The beneficial effects of this invention are:

[0022] This invention provides a modified phenolic resin and its preparation method. By introducing three core technologies—gradient topological phosphonates, hyperbranched siloxanes, and dynamic borate ester crosslinking agents—it successfully solves the industry problem of the difficulty in synergistically improving flame retardancy, thermal stability, and mechanical properties in existing phenolic resin modification technologies.

[0023] First, traditional phenolic resin modification technology has the following limitations: an imbalance between flame retardancy and mechanical properties, insufficient environmental friendliness, and lack of dynamic performance. Compared with existing technologies, this invention has the following innovations:

[0024] (1) Gradient topological phosphonates: The present invention constructs a gradient branched structure (branching degree 0.30-0.35) through transesterification and epoxidation reaction, which forms a dense and continuous char layer (char residue ≥50%) during combustion, significantly improving flame retardancy (LOI ≥37.5%, UL-94V-0 rating).

[0025] (2) Hyperbranched siloxanes: This invention forms a hyperbranched structure with both flexibility and interface reinforcement through ring-opening polymerization and fluorination grafting. Its flexible chain segments disperse stress and suppress brittle fracture (impact strength ≥12.2kJ / m). 2 Meanwhile, the fluorinated groups enhance the stability of the carbon layer.

[0026] (3) Dynamic borate ester crosslinking agent: Based on the reversibility of borate ester bonds, this invention endows the resin with dynamic crosslinking ability, which releases stress (flexural strength ≥120MPa) through bond breaking and recombination when under high temperature or stress, and realizes self-repair of microcracks.

[0027] Furthermore, the aforementioned innovative components are not simply superimposed, but rather form a synergistic system through molecular structure design and functional complementarity, as detailed below:

[0028] (1) Synergistic improvement of flame retardancy and thermal stability: The branched structure of gradient topological phosphonates rapidly forms char in the early stage of combustion, creating a physical barrier; the fluorinated segments of hyperbranched siloxanes stabilize the char layer through interfacial reinforcement, preventing cracking (comparative example 2 showed a 10% decrease in char residue); the dynamic borate ester crosslinking agent dynamically adjusts the crosslinking density at high temperatures, delaying thermal decomposition (initial decomposition temperature ≥340℃). The synergistic effect of these three factors significantly improves the LOI value and char residue.

[0029] (2) Comprehensive improvement in mechanical properties: The rigid framework of the gradient topological phosphonate provides support and disperses stress concentration; the flexible segments of the hyperbranched siloxane absorb impact energy and improve toughness; the dynamic borate ester crosslinking agent relieves local stress through reversible bonding and avoids brittle fracture. The data shows that the bending strength and impact strength of Example 11 are far superior to those of Comparative Examples 1 to 3, proving that all three are indispensable.

[0030] (3) Combining dynamic functionality with environmental friendliness: Dynamic borate esters endow materials with self-healing potential, expanding their application in harsh environments such as aerospace; at the same time, the entire system eliminates halogenated flame retardants and toxic solvents, meeting the requirements of green chemistry.

[0031] In summary, this invention achieves a comprehensive improvement in the flame retardancy, thermal stability, mechanical properties, and dynamic functions of phenolic resin through the synergistic effect of gradient topological phosphonates, hyperbranched siloxanes, and dynamic borate crosslinking agents, while also exhibiting significantly better environmental performance than traditional technologies. Experimental data fully validates the indivisibility and synergistic effect between the innovative points, and the combination of technologies and their effects are non-obvious, meeting the requirements for patent inventiveness. Furthermore, the resin's application potential in aerospace, electronic packaging, and other fields further highlights its industrial value. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] Preparation of gradient topological phosphonates:

[0035] A1. 45g of tris(2-carboxyethyl)phosphine (TCEP) and 75g of cyclic pentaerythritol phosphate (CPP) were mixed and stirred in 500mL of N,N-dimethylformamide (DMF) for 10min. Then, 1g of zinc acetate (Zn(OAc)2) catalyst was added to the mixture. The system was heated to 100℃ and stirred at a constant temperature for 6h. After the reaction was complete, the mixture was cooled to room temperature to obtain a prepolymer containing phosphonate esters. During the above reaction, the carboxyl groups of TCEP and the phosphate groups of CPP reacted in the Zn... 2+ Under catalysis, transesterification occurs, forming a branched framework;

[0036] A2. Add 30g of epichlorohydrin dropwise to 100g of prepolymer. After the addition is complete, purge the system with nitrogen for protection. Then heat the system to 55℃ and perform an epoxidation reaction at this temperature for 4 hours. After the reaction is complete, cool to room temperature to obtain a reaction solution. Add 500mL 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 collect the washed solid to obtain a crude product. Dissolve the crude product in tetrahydrofuran at a mass ratio of 1:10 and sonicate for 30 minutes (40kHz) to ensure complete dissolution. Obtain a solution. Pass the solution through an ultrafiltration membrane with a molecular weight cutoff of 10000Da and collect the permeate (molecular weight ≤10000Da). Then pass the permeate through an ultrafiltration membrane with a molecular weight cutoff of 5000Da and collect the retentate (molecular weight 5000~10000Da). Rotate the retentate... The solution was concentrated to 1 / 5 of its original volume by evaporation. Acetone was then added at a volume ratio of 1:4, and the mixture was stirred for 10 minutes. The solution was then concentrated again by rotary evaporation to 1 / 10 of its original volume. Acetone was added again at a volume ratio of 1:1 to obtain a concentrated solution. 25 mL of n-hexane was added dropwise to the concentrated solution, and the mixture was stirred for 10 minutes. The solution was allowed to stand for 30 minutes to remove the precipitate (branching degree > 0.4). 50 mL of n-hexane was added dropwise, and the mixture was stirred for 10 minutes. The solution was allowed to stand for 30 minutes to remove the precipitate (branching degree 0.35–0.4). 150 mL of n-hexane was added dropwise, and the mixture was stirred for 10 minutes. The solution was allowed to stand for 60 minutes 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 a gradient topof-topophosphonate. GPC analysis (THF as mobile phase, PS standard) showed Mn ≈ 8000 Da and PDI = 1.3. 1 H-NMR calculation (by the integral ratio of terminal epoxy groups) shows that the degree of branching is 0.35±0.02. In the above reaction process, the epoxy groups of epichlorohydrin react with the hydroxyl groups in the prepolymer to introduce epoxy end groups. Then, by constructing a gradient degree of branching, a gradient topological phosphonate is finally obtained.

[0037] Example 2

[0038] Preparation of gradient topological phosphonates:

[0039] A1. 50g of tris(2-carboxyethyl)phosphine (TCEP) and 75g of cyclic pentaerythritol phosphate (CPP) were mixed and stirred in 500mL of N,N-dimethylformamide (DMF) for 30min. Then, 2g of zinc acetate (Zn(OAc)2) catalyst was added to the mixture. The system was heated to 100℃ and stirred at a constant temperature for 8h. After the reaction was complete, the mixture was cooled to room temperature to obtain a prepolymer containing phosphonate esters. During the above reaction, the carboxyl groups of TCEP and the phosphate groups of CPP reacted in the Zn... 2+ Under catalysis, transesterification occurs, forming a branched framework;

[0040] A2. Add 30g of epichlorohydrin dropwise to 100g of prepolymer. After the addition is complete, purge the system with nitrogen for protection. Then heat the system to 55℃ and perform an epoxidation reaction at this temperature for 5 hours. After the reaction is complete, cool to room temperature to obtain a reaction solution. Add 500mL 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 collect the washed solid to obtain a crude product. Dissolve the crude product in tetrahydrofuran at a mass ratio of 1:10 and sonicate for 30 minutes (40kHz) to ensure complete dissolution. Obtain a solution and pass it through an ultrafiltration membrane with a molecular weight cutoff of 10000Da. Collect the permeate (molecular weight ≤10000Da component). Then pass the permeate through an ultrafiltration membrane with a molecular weight cutoff of 5000Da and collect the retentate (molecular weight 5000~10000Da component). Rotate the retentate... The solution was concentrated to 1 / 5 of its original volume by evaporation. Acetone was then added at a volume ratio of 1:4, and the mixture was stirred for 30 minutes. The solution was then concentrated again by rotary evaporation to 1 / 10 of its original volume. Acetone was added again at a volume ratio of 1:1 to obtain a concentrated solution. 25 mL of n-hexane was added dropwise to the concentrated solution, and the mixture was stirred for 10 minutes. The solution was allowed to stand for 30 minutes to remove the precipitate (branching degree > 0.4). 50 mL of n-hexane was added dropwise, and the mixture was stirred for 10 minutes. The solution was allowed to stand for 30 minutes to remove the precipitate (branching degree 0.35–0.4). 150 mL of n-hexane was added dropwise, and the mixture was stirred for 10 minutes. The solution was allowed to stand for 60 minutes 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 a gradient topof-topophosphonate. GPC analysis (THF as mobile phase, PS standard) showed Mn ≈ 8000 Da and PDI = 1.3. 1 H-NMR calculation (by the integral ratio of terminal epoxy groups) shows that the degree of branching is 0.35±0.02. In the above reaction process, the epoxy groups of epichlorohydrin react with the hydroxyl groups in the prepolymer to introduce epoxy end groups. Then, by constructing a gradient degree of branching, a gradient topological phosphonate is finally obtained.

[0041] Example 3

[0042] Preparation of gradient topological phosphonates:

[0043] A1. 50g of tris(2-carboxyethyl)phosphine (TCEP) and 80g of cyclic pentaerythritol phosphate (CPP) were mixed and stirred in 500mL of N,N-dimethylformamide (DMF) for 30min. Then, 2g of zinc acetate (Zn(OAc)2) catalyst was added to the mixture. The system was heated to 110℃ and stirred at a constant temperature for 8h. After the reaction was complete, the mixture was cooled to room temperature to obtain a prepolymer containing phosphonate esters. During the above reaction, the carboxyl groups of TCEP and the phosphate groups of CPP reacted in the Zn... 2+ Under catalysis, transesterification occurs, forming a branched framework;

[0044] A2. Add 30g of epichlorohydrin dropwise to 100g of prepolymer. After the addition is complete, purge the system with nitrogen for protection. Then heat the system to 60℃ and perform an epoxidation reaction at this temperature for 5 hours. After the reaction is complete, cool to room temperature to obtain a reaction solution. Add 500mL 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 collect the washed solid to obtain a crude product. Dissolve the crude product in tetrahydrofuran at a mass ratio of 1:10 and sonicate for 30 minutes (40kHz) to ensure complete dissolution. Pass the solution through an ultrafiltration membrane with a molecular weight cutoff of 10000Da and collect the permeate (molecular weight ≤10000Da). Then pass the permeate through an ultrafiltration membrane with a molecular weight cutoff of 5000Da and collect the retentate (molecular weight 5000~10000Da). Rotate the retentate... The solution was concentrated to 1 / 5 of its original volume by evaporation. Acetone was then added at a volume ratio of 1:4, and the mixture was stirred for 30 minutes. The solution was then concentrated again by rotary evaporation to 1 / 10 of its original volume. Acetone was added again at a volume ratio of 1:1 to obtain a concentrated solution. 25 mL of n-hexane was added dropwise to the concentrated solution, and the mixture was stirred for 10 minutes. The solution was allowed to stand for 30 minutes to remove the precipitate (branching degree > 0.4). 50 mL of n-hexane was added dropwise, and the mixture was stirred for 10 minutes. The solution was allowed to stand for 30 minutes to remove the precipitate (branching degree 0.35–0.4). 150 mL of n-hexane was added dropwise, and the mixture was stirred for 10 minutes. The solution was allowed to stand for 60 minutes 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 a gradient topof-topophosphonate. GPC analysis (THF as mobile phase, PS standard) showed Mn ≈ 8000 Da and PDI = 1.3. 1 H-NMR calculation (by the integral ratio of terminal epoxy groups) shows that the degree of branching is 0.35±0.02. In the above reaction process, the epoxy groups of epichlorohydrin react with the hydroxyl groups in the prepolymer to introduce epoxy end groups. Then, by constructing a gradient degree of branching, a gradient topological phosphonate is finally obtained.

[0045] Example 4

[0046] Preparation of hyperbranched siloxanes:

[0047] 100g of γ-aminopropyltrimethoxysilane (KH540) and 50g of octamethylcyclotetrasiloxane (D4) were mixed and stirred in 500mL of toluene for 10min. Then, 1g of potassium hydroxide was added and the mixture was purged with nitrogen for protection. The system was then heated to 78℃ and subjected to ring-opening polymerization at this temperature for 6h. During the reaction, D4 underwent ring-opening to form a linear polysiloxane, which then condensed with the amino group of KH540 to form a hyperbranched framework. After the reaction was complete, 50g of perfluorooctyl ether was added to the system. Triethoxysilane was heated to 100°C, and then subjected to a grafting reaction at a constant temperature for 12 hours. During the reaction, the Si-OCH2CH3 of the siloxane condensed with the Si-OH of the hyperbranched framework, grafting C8F17 chains. After the reaction was completed, 5 mL of deionized water was added to the system to quench unreacted siloxane groups. The system was then stirred at 80°C for 1 hour, toluene was removed by rotary evaporation, and the system was washed with n-hexane. Finally, the system was dried under vacuum at 50°C for 24 hours to obtain hyperbranched siloxane.

[0048] Example 5

[0049] Preparation of hyperbranched siloxanes:

[0050] 100g of γ-aminopropyltrimethoxysilane (KH540) and 55g of octamethylcyclotetrasiloxane (D4) were mixed and stirred in 500mL of toluene for 30min. Then, 1g of potassium hydroxide was added and the mixture was purged with nitrogen for protection. The system was then heated to 78℃ and subjected to ring-opening polymerization at this temperature for 8h. During the reaction, D4 underwent ring-opening to form a linear polysiloxane, which then condensed with the amino group of KH540 to form a hyperbranched framework. After the reaction was complete, 50g of perfluorooctyl ether was added to the system. Triethoxysilane was heated to 105°C, and then subjected to a constant-temperature grafting reaction for 12 hours. During the reaction, the Si-OCH2CH3 of the siloxane condensed with the Si-OH of the hyperbranched framework, grafting C8F17 chains. After the reaction was completed, 5 mL of deionized water was added to the system to quench unreacted siloxane groups. The system was then stirred at 80°C for 1 hour, toluene was removed by rotary evaporation, and the system was washed with n-hexane. Finally, the system was dried under vacuum at 50°C for 24 hours to obtain hyperbranched siloxane.

[0051] Example 6

[0052] Preparation of hyperbranched siloxanes:

[0053] 100g of γ-aminopropyltrimethoxysilane (KH540) and 60g of octamethylcyclotetrasiloxane (D4) were mixed and stirred in 500mL of toluene for 30min. Then, 1g of potassium hydroxide was added and the mixture was purged with nitrogen for protection. The system was then heated to 80℃ and subjected to ring-opening polymerization at this temperature for 8h. During the reaction, D4 underwent ring-opening to form a linear polysiloxane, which then condensed with the amino group of KH540 to form a hyperbranched framework. After the reaction was complete, 50g of perfluorooctyl ether was added to the system. Triethoxysilane was heated to 110°C, and then subjected to a constant-temperature grafting reaction for 12 hours. During the reaction, the Si-OCH2CH3 of the siloxane condensed with the Si-OH of the hyperbranched framework, grafting C8F17 chains. After the reaction was completed, 5 mL of deionized water was added to the system to quench unreacted siloxane groups. The system was then stirred at 80°C for 1 hour, toluene was removed by rotary evaporation, and the system was washed with n-hexane. Finally, the system was dried under vacuum at 60°C for 24 hours to obtain hyperbranched siloxane.

[0054] Example 7

[0055] Preparation of dynamic borate ester crosslinking agent:

[0056] 20g of phenylboronic acid and 30g of 1,4-butanediol diglycidyl ether were mixed in 500mL of tetrahydrofuran for 10min. Then, 0.5g of boron trifluoride diethyl ether (BF3·Et2O) catalyst was added to the mixture under stirring. The mixture was then purged with nitrogen for protection. The system was heated to 50℃ and stirred at a constant temperature for 5h. During the reaction, the epoxy groups of phenylboronic acid (PhB(OH)2) and 1,4-butanediol diglycidyl ether under acidic conditions underwent ring-opening reaction to form borate ester bonds (Ph-BO-(CH2)4-OB-Ph). After the reaction was completed, the mixture was cooled to room temperature and the tetrahydrofuran was removed by rotary evaporation to obtain a pale yellow viscous liquid, which is the dynamic borate ester bond crosslinking agent.

[0057] Example 8

[0058] Preparation of dynamic borate ester crosslinking agent:

[0059] 20g of phenylboronic acid and 35g of 1,4-butanediol diglycidyl ether were mixed in 500mL of tetrahydrofuran for 30min. Then, 1g of boron trifluoride diethyl ether (BF3·Et2O) catalyst was added to the mixture under stirring. The mixture was then purged with nitrogen for protection, and the system was heated to 55℃ and stirred at a constant temperature for 6h. During the reaction, the epoxy groups of phenylboronic acid (PhB(OH)2) and 1,4-butanediol diglycidyl ether under acidic conditions underwent ring-opening reaction to form borate ester bonds (Ph-BO-(CH2)4-OB-Ph). After the reaction was completed, the mixture was cooled to room temperature, and the tetrahydrofuran was removed by rotary evaporation to obtain a pale yellow viscous liquid, which is the dynamic borate ester bond crosslinking agent.

[0060] Example 9

[0061] Preparation of dynamic borate ester crosslinking agent:

[0062] 20g of phenylboronic acid and 40g of 1,4-butanediol diglycidyl ether were mixed in 500mL of tetrahydrofuran for 30min. Then, 1g of boron trifluoride diethyl ether (BF3·Et2O) catalyst was added to the mixture under stirring. The mixture was then purged with nitrogen for protection, and the system was heated to 60℃ and stirred at a constant temperature for 6h. During the reaction, the epoxy groups of phenylboronic acid (PhB(OH)2) and 1,4-butanediol diglycidyl ether under acidic conditions underwent ring-opening reaction to form borate ester bonds (Ph-BO-(CH2)4-OB-Ph). After the reaction was completed, the mixture was cooled to room temperature, and the tetrahydrofuran was removed by rotary evaporation to obtain a pale yellow viscous liquid, which is the dynamic borate ester bond crosslinking agent.

[0063] Example 10

[0064] Preparation of modified phenolic resin:

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

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

[0067] 140 portions of formaldehyde aqueous solution (37%; analytical grade);

[0068] 25 portions of gradient topological phosphonates (prepared in Example 1);

[0069] 15 parts of hyperbranched siloxane (self-made in Example 4);

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

[0071] Three portions of hexamethylenetetramine (analytical grade).

[0072] Then, according to the mass percentages, weigh out the raw materials phenol, formaldehyde aqueous solution, gradient topof-topophosphonate, hyperbranched siloxane, dynamic borate crosslinking agent, and hexamethylenetetramine. Mix phenol, gradient topof-topophosphonate, hyperbranched siloxane, and dynamic borate crosslinking agent for 1 hour. Then, heat the system to 80°C and maintain the temperature for 50 minutes for prepolymerization. After completion, an intermediate is obtained. Add formaldehyde aqueous solution (37%) dropwise to the intermediate, heat the system to 85°C, and maintain the temperature for 2 hours. Then, heat to 120°C and maintain the temperature for 1 hour. Then, heat to 150°C and maintain the temperature for 30 minutes. After completion, cool to 100°C and add hexamethylenetetramine. Stir for 20 minutes and vacuum dehydrate until the gel time reaches 40 seconds (viscosity is monitored using a gel time tester; dehydration is stopped when the gel time reaches 40 seconds, corresponding to a resin viscosity ≈ 10). 4 cP) was used to obtain modified phenolic resin.

[0073] Example 11

[0074] Preparation of modified phenolic resin:

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

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

[0077] 142 portions of formaldehyde aqueous solution (37%; analytical grade);

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

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

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

[0081] Four portions of hexamethylenetetramine (analytical grade).

[0082] Then, according to the mass percentages, weigh out the raw materials phenol, formaldehyde aqueous solution, gradient topof-topophosphonate, hyperbranched siloxane, dynamic borate crosslinking agent, and hexamethylenetetramine. Mix phenol, gradient topof-topophosphonate, hyperbranched siloxane, and dynamic borate crosslinking agent for 2 hours. Then, heat the system to 85°C and maintain the temperature for 60 minutes for prepolymerization. After completion, an intermediate is obtained. Add formaldehyde aqueous solution (37%) dropwise to the intermediate, heat the system to 90°C, and maintain the temperature for 2 hours. Then, heat to 120°C and maintain the temperature for 1 hour. Then, heat to 150°C and maintain the temperature for 30 minutes. After completion, cool to 100°C and add hexamethylenetetramine. Stir for 30 minutes and vacuum dehydrate until the gel time reaches 40 seconds (viscosity is monitored using a gel time tester; dehydration is stopped when the gel time reaches 40 seconds, corresponding to a resin viscosity ≈ 10). 4 cP) was used to obtain modified phenolic resin.

[0083] Example 12

[0084] Preparation of modified phenolic resin:

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

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

[0087] 145 portions of formaldehyde aqueous solution (37%; analytical grade);

[0088] 30 portions of gradient topological phosphonates (prepared in Example 3);

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

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

[0091] Four portions of hexamethylenetetramine (analytical grade).

[0092] Then, according to the mass percentages, weigh out the raw materials phenol, formaldehyde aqueous solution, gradient topof-topophosphonate, hyperbranched siloxane, dynamic borate crosslinking agent, and hexamethylenetetramine. Mix phenol, gradient topof-topophosphonate, hyperbranched siloxane, and dynamic borate crosslinking agent for 2 hours. Then, heat the system to 90°C and maintain the temperature for 60 minutes for prepolymerization. After completion, an intermediate is obtained. Add formaldehyde aqueous solution (37%) dropwise to the intermediate, heat the system to 95°C, and maintain the temperature for 2 hours. Then, heat to 125°C and maintain the temperature for 1 hour. Then, heat to 155°C and maintain the temperature for 30 minutes. After completion, cool to 100°C and add hexamethylenetetramine. Stir for 30 minutes and vacuum dehydrate until the gel time reaches 40 seconds (viscosity is monitored using a gel time tester; dehydration is stopped when the gel time reaches 40 seconds, corresponding to a resin viscosity ≈ 10). 4 cP) was used to obtain modified phenolic resin.

[0093] Comparative Example 1

[0094] Comparative Example 1 served as the control group for Example 11. The gradient topological phosphonate (self-made in Example 2) in the modified phenolic resin of Example 11 was replaced with the linear phosphonate bisphenol A bis(diphenyl phosphate). The remaining raw materials, raw material amounts, and preparation methods remained unchanged, and the modified phenolic resin was finally obtained.

[0095] Comparative Example 2

[0096] Comparative Example 2 served as the control group for Example 11. 16 parts of hyperbranched siloxane (self-made in Example 5) were removed from the modified phenolic resin of Example 11, while the remaining raw materials, raw material amounts, and preparation methods remained unchanged, ultimately yielding the modified phenolic resin.

[0097] Comparative Example 3

[0098] Comparative Example 3 served as the control group for Example 11. 14 parts of the dynamic borate ester crosslinking agent (self-made in Example 8) were removed from the modified phenolic resin of Example 11, while the remaining raw materials, raw material amounts, and preparation methods remained unchanged, ultimately yielding the modified phenolic resin.

[0099] Test Example 1

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

[0101] (1) Flame retardant performance test:

[0102] a. Limiting Oxygen Index (LOI): The limiting oxygen index of modified phenolic resin is tested using an oxygen index tester in accordance with ASTM D2863 standard.

[0103] b. UL-94 Vertical Burning Test: In accordance with the UL-94 standard, a vertical burning test was conducted on the modified phenolic resin, and the burning time, drippings, and self-extinguishing properties were recorded.

[0104] (2) Thermal stability test:

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

[0106] (3) Mechanical property testing

[0107] a. Flexural strength: The flexural strength of the modified phenolic resin (span / thickness ratio = 16:1) was tested using a universal testing machine in accordance with ASTM D790 standard.

[0108] b. Notched impact strength: The notched impact strength of the modified phenolic resin was tested using a pendulum impact tester in accordance with ASTM D256 standard.

[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 Carbon residue rate (%) 51 55 54 38 45 42 Bending 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] Flame retardancy and thermal stability: The LOI value (38.1%) and UL-94 V-0 rating of Example 11 were 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 char layer during combustion compared to the linear phosphonate bisphenol A bis(diphenyl phosphate), effectively isolating heat and oxygen. Its char residue (55%) was also much higher than that of Comparative Example 1 (38%), further verifying the char layer enhancement effect of the gradient topology. The char residue of Comparative Example 2 (without hyperbranched siloxane) decreased (45%), indicating that siloxane promoted char layer stability by enhancing interfacial bonding. The LOI and char residue of Comparative Example 3 (without borate ester) were both lower than those of Example 11, indicating that the reversible crosslinking of dynamic borate esters facilitates dynamic char layer repair.

[0113] Mechanical properties: Flexural strength (128 MPa) and impact strength (12.5 kJ / m) of Example 11 2 The pressure is much higher than that of Comparative Example 1 (95 MPa, 6.8 kJ / m). 2This demonstrates that the branched network of gradient topological phosphonates can disperse stress and prevent brittle fracture. The mechanical properties of Comparative Example 2 decreased (impact strength 8.2 kJ / m). 2 The results show that hyperbranched siloxanes improve toughness through flexible segments; the decrease in mechanical properties of Comparative Example 3 indicates that dynamic borate ester crosslinking agents can alleviate stress concentration through reversible bonding.

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

[0115] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

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

Claims

1. A modified phenolic resin, characterized in that, Includes the following quantities of raw materials: 100 parts phenol, 140-145 parts formaldehyde aqueous solution, 25-30 parts gradient topological phosphonates, 15-17 parts hyperbranched siloxanes, 12-14 parts dynamic borate ester crosslinking agent, 3-4 parts hexamethylenetetramine; The gradient topological phosphonate is prepared by the following steps: A1. Tris(2-carboxyethyl)phosphine and cyclic pentaerythritol phosphate are mixed and stirred in N,N-dimethylformamide, and then zinc acetate is added. The mixture is heated to 100-110°C and stirred at a constant temperature for 6-8 hours. After the mixture is stirred, the prepolymer is obtained. A2. Add 30g of epichlorohydrin dropwise to 100g of prepolymer. After completion, purge with nitrogen for protection, then heat to 55-60℃ and maintain the temperature for 4-5 hours. After completion, obtain the reaction solution. Add 500mL of icy diethyl ether to the reaction solution, filter, and wash with pure water to obtain the crude product. 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 10000Da, collect the permeate, and then treat the permeate with an ultrafiltration membrane with a molecular weight cutoff of 5000Da. The retentate was collected and concentrated by rotary evaporation to 1 / 5 of its original volume. Acetone was then added to the retentate at a volume ratio of 1:4, and the mixture was stirred. The mixture was then concentrated by rotary evaporation to 1 / 10 of its original volume. Acetone was then added to the retentate at a volume ratio of 1:1 to obtain a concentrated solution. 25 mL of n-hexane was added dropwise to the concentrated solution, and the mixture was stirred and allowed to stand. The precipitate was then removed. 50 mL of n-hexane was added dropwise to the concentrated solution, and the mixture was stirred and allowed to stand. The precipitate was then removed. 150 mL of n-hexane was added dropwise to the concentrated solution, and the mixture was stirred and allowed to stand. The precipitate was collected, washed, and dried to obtain a gradient topof-topophosphonate.

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

3. The modified phenolic resin according to claim 1, characterized in that, The hyperbranched siloxane is prepared by the following steps: γ-aminopropyltrimethoxysilane and octamethylcyclotetrasiloxane were mixed and stirred in toluene, and then potassium hydroxide was added while stirring. Nitrogen gas was introduced for protection, and the temperature was raised to 78-80°C. Polymerization was carried out at this temperature for 6-8 hours. After polymerization, perfluorooctyltriethoxysilane was added while stirring, and the temperature was raised to 100-110°C. After polymerization, the reaction was carried out at this temperature for 12 hours. After polymerization, deionized water was added, and the system was stirred at 80°C for 1 hour. After rotary evaporation, washing, and vacuum drying, hyperbranched siloxane was obtained.

4. The modified phenolic resin according to claim 3, characterized in that, The ratio of γ-aminopropyltrimethoxysilane, octamethylcyclotetrasiloxane, toluene, potassium hydroxide, perfluorooctyltriethoxysilane, and deionized water is 100g:50-60g:500mL:1g:50g:5mL.

5. The modified phenolic resin according to claim 1, characterized in that, The dynamic borate ester crosslinking agent is prepared by the following steps: Phenylboronic acid and 1,4-butanediol diglycidyl ether were mixed in tetrahydrofuran, and boron trifluoride ethyl ether was added to the mixture while stirring. The mixture was then purged with nitrogen for protection, and the system was heated to 50-60°C and stirred at a constant temperature for 5-6 hours. After the reaction was completed, the mixture was cooled to room temperature, and the tetrahydrofuran was removed by rotary evaporation to obtain a dynamic borate ester crosslinking agent.

6. The modified phenolic resin according to claim 5, characterized in that, The ratio of phenylboronic acid, 1,4-butanediol diglycidyl ether, tetrahydrofuran, and boron trifluoride ethyl ether is 20g:30-40g:500mL:0.5-1g.

7. A method for preparing a modified phenolic resin according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Weigh the raw materials phenol, formaldehyde aqueous solution, gradient topological phosphonate, hyperbranched siloxane, dynamic borate crosslinking agent and hexamethylenetetramine according to the mass parts. Stir and mix phenol, gradient topological phosphonate, hyperbranched siloxane and dynamic borate crosslinking agent for 1-2 hours. Then heat the system to 80-90℃ and stir at a constant temperature for 50-60 minutes for prepolymerization. After completion, the intermediate is obtained. S2. Add formaldehyde aqueous solution dropwise to the intermediate, heat the system to 85-95℃, stir at constant temperature for 2 hours, then heat to 120-125℃, stir at constant temperature for 1 hour, then heat to 150-155℃, stir at constant temperature for 30 minutes. After completion, cool down to 100℃, add hexamethylenetetramine to the mixture, stir for 20-30 minutes, and after vacuum dehydration, obtain modified phenolic resin.