Flame retardant maleimide copolymer resin and method of making same

Abstract

The application belongs to the technical field of flame-retardant high polymer materials, and particularly relates to a kind of flame-retardant maleimide copolymer resin and a preparation method thereof, the resin takes phenyl maleimide, styrene monomer and glycidyl methacrylate as the main body of copolymerization, introduces phosphorus nitrogen silane grafted maleimide base cyclic phosphorus chalcide and boron nitrogen phosphorus triazine aryl ether vinyl monomer, and cooperates initiator, solvent and antioxidant, is prepared through segmented reaction under nitrogen protection, cooling, sedimentation, filtration, washing and drying. The application improves the flame retardancy, heat resistance, charring property and mechanical stability of the resin through the synergistic effect of cyclic phosphorus chalcide, phosphorus heteroheptacyclic, silane, triazine, aryl ether borate and maleimide structure, and is suitable for electronic and electrical enclosures, connectors and new energy electrical components.

Description

Technical Field

[0001] This invention belongs to the field of flame-retardant polymer materials technology, specifically relating to a flame-retardant maleimide copolymer resin and its preparation method. Background Technology

[0002] Flame-retardant polymer materials are widely used in electronic and electrical appliance housings, connectors, relays, circuit breakers, new energy electrical components, and heat-resistant insulating structural parts. As electronic devices develop towards lighter weight, smaller size, and higher power density, resin materials not only need good processing and molding properties and dimensional stability, but also need to maintain high flame-retardant safety under heat, short circuits, electric arcs, or external fire sources. Styrene-based resins have advantages such as moderate cost, good moldability, high rigidity, and good electrical insulation properties; however, their molecular structure has a high proportion of combustible hydrocarbon segments, making them prone to softening, dripping, and releasing significant heat during combustion. Therefore, when used alone, they are insufficient to meet the application requirements of high flame retardancy and high heat resistance scenarios.

[0003] Existing flame-retardant modification methods typically involve adding phosphorus-based flame retardants, nitrogen-based flame retardants, intumescent flame retardants, metal hydroxides, or inorganic nanofillers to the resin system. While these methods can improve the flame-retardant properties of materials to some extent, they often require high addition amounts to achieve a stable flame-retardant effect. This can easily lead to reduced resin flowability, rough product surfaces, decreased tensile strength, poor impact toughness, and problems such as flame retardant migration, precipitation, and moisture absorption during long-term use. Especially in precision electronic and electrical components, uneven dispersion or insufficient interfacial bonding of flame retardants can also affect the material's electrical insulation stability, thermal deformation stability, and long-term service reliability. Therefore, flame-retardant modification methods that rely solely on physical blending cannot simultaneously achieve high flame retardancy, high mechanical properties, heat resistance, and processing stability.

[0004] Maleimide, with its rigid imide ring structure, can improve the resin's heat resistance, dimensional stability, and char formation tendency. Copolymerizing maleimide with styrene monomers and monomers containing active functional groups can, to some extent, improve the insufficient heat resistance and flame retardancy of traditional styrene resins. However, the flame-retardant structure design in existing maleimide copolymer resins is still relatively simple. Flame-retardant elements such as phosphorus, nitrogen, silicon, and boron are difficult to form stable synergies at the molecular level, resulting in insufficient continuity, density, and crack resistance of the char layer during combustion. If the flame-retardant groups cannot be stably introduced into the resin molecular chain through a polymerizable structure, defects such as poor compatibility, migration and precipitation, and decreased flame-retardant efficiency may occur. Therefore, it is necessary to develop a reactive, multi-element synergistic flame-retardant maleimide copolymer resin that allows the flame-retardant structure to form a stable bond with the resin matrix, thereby improving the resin's flame retardancy, heat resistance, char formation, and overall mechanical stability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a flame-retardant maleimide copolymer resin and its preparation method.

[0006] A first aspect of the present invention provides a flame-retardant maleimide copolymer resin, prepared from the following raw materials in parts by weight: 15-35 parts of N-phenylmaleimide, 50-70 parts of styrene monomer, 5-20 parts of glycidyl methacrylate, 1-8 parts of phosphorus nitrogen silane grafted maleimide cyclophosphonitrile, 1-6 parts of boron nitrogen phosphorus triazine aryl ether vinyl monomer, 0.1-0.8 parts of azobisisobutyronitrile, 0.05-0.5 parts of tert-butyl peroxide, 60-160 parts of N,N-dimethylformamide, 20-80 parts of toluene, 80-200 parts of ethanol, 0.1-0.5 parts of antioxidant 1010, and 0.1-0.5 parts of antioxidant 168.

[0007] A second aspect of the present invention provides a method for preparing the flame-retardant maleimide copolymer resin, comprising the steps of: S1. Under stirring, N-phenylmaleimide, styrene monomer, glycidyl methacrylate, phosphorus nitrogen silane grafted maleimide cyclophosphonitrile, boron nitrogen phosphorus triazine aryl ether vinyl monomer, N,N-dimethylformamide and toluene are mixed to obtain a monomer mixture; under nitrogen protection, azobisisobutyronitrile is added to the monomer mixture and reacted at 60-70℃, followed by reaction at 75-85℃ to obtain a copolymer reaction solution.

[0008] S2. Add tert-butyl peroxide to the copolymerization reaction solution and react at 100-115℃. After the reaction is complete, cool and add antioxidant 1010 and antioxidant 168. Stir to obtain resin reaction solution. Add resin reaction solution to ethanol, filter, wash and dry.

[0009] In this invention, the flame-retardant maleimide copolymer resin is prepared using N-phenylmaleimide, styrene monomer, and glycidyl methacrylate as the main comonomers, while phosphorus-nitrogen silane-grafted maleimide-based cyclophosphonitrile and boron-nitrogen-phosphorus triazine aryl ether vinyl monomers are introduced as reactive flame-retardant modifying components. N,N-dimethylformamide and toluene enable the raw materials to fully dissolve and form a homogeneous monomer mixture. Nitrogen protection removes oxygen from the system, preventing oxygen from abstracting free radicals and inhibiting polymerization. Upon addition of azobisisobutyronitrile (AIB), the azo bonds in the system thermally decompose at a lower temperature to form isobutyronitrile free radicals. These radicals initiate the free radical chain growth process, involving the cis-unsaturated double bonds on the N-phenylmaleimide molecule, the vinyl groups of the styrene monomer, the acryloyloxy double bonds of glycidyl methacrylate, and the maleimide double bonds and vinyl groups on the two modified components. The electron-attracting double bonds of N-phenylmaleimide and the electron-donating double bonds of styrene exhibit a strong alternation tendency, resulting in a stable alternating segment structure in the main chain. Glycidyl methacrylate introduces suspended epoxy groups into the main chain, yielding a copolymerization solution containing a phosphorus-nitrogen silane-grafted maleimide-based cyclophosphonitrile structure and a boron-nitrogen-phosphorus triazine aryl ether vinyl monomer structure. Further heating to the copolymerization temperature allows the remaining double bonds to participate in chain growth. Adding tert-butyl peroxide to the copolymerization reaction solution leads to the thermal decomposition of peroxide bonds at higher temperatures, forming new acyloxy radicals and tert-butyloxy radicals. This initiates further reactions of the remaining polymerizable double bonds in the system, increasing monomer conversion and copolymer molecular weight. After cooling following the reaction, antioxidants 1010 and 168 are added. Antioxidant 1010 captures peroxide radicals through its hindered phenolic structure, while antioxidant 168 decomposes hydrogen peroxide through its phosphite structure. Together, they synergistically improve the thermo-oxidative stability of the resin. Finally, the resin reaction solution is added to ethanol for precipitation. The copolymerized resin precipitates from the solution, and after filtration, washing, and drying, flame-retardant maleimide copolymer resin is obtained. In this resin, the two modified components are covalently fixed to the main chain, reducing the risk of migration and precipitation of small-molecule flame-retardant components. Furthermore, the synergistic effect of the cyclophosphonitrile, phosphenanthrene, silane, triazine, borate, and maleimide structures enhances the resin's flame retardancy, charring ability, heat resistance, and mechanical stability.

[0010] According to a preferred embodiment of the present invention, in step S1, the reaction time at 60-70°C is 2-4 hours.

[0011] According to a preferred embodiment of the present invention, in step S2, the reaction time at 100-115°C is 1-3 hours.

[0012] According to a preferred embodiment of the present invention, the method for preparing the phosphorus-nitrogen silane grafted with maleimide cyclophosphonitrile includes: A1. By weight, 8.0-14.0 parts of hexachlorocyclotriphosphazene, 3.0-8.0 parts of 3-aminopropyltriethoxysilane, 22.0-38.0 parts of potassium carbonate, and 120.0-220.0 parts of anhydrous acetonitrile are mixed and reacted at 0-5°C under nitrogen protection; then the temperature is raised to 25-30°C, and 6.0-12.0 parts of N-(4-hydroxyphenyl)maleimide are added to react; then the temperature is raised to 65-78°C, and 10.0-20.0 parts of 4-hydroxybenzaldehyde are added to react. The mixture is filtered to obtain an aldehyde-silane-maleimide-cyclophosphazene intermediate solution.

[0013] A2. Add 18.0-34.0 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), 0.2-0.8 parts of triethylamine, and 60.0-120.0 parts of toluene to the aldehyde-silane-maleimide-cyclophosphonitrile intermediate solution, and react at 75-82℃; after the reaction is completed, cool, precipitate, wash, dry, pulverize, and vibrate sieve.

[0014] In this invention, the preparation of maleimide-based cyclophosphonitriles grafted onto phosphorus-nitrogen silanes uses hexachlorocyclotriphosphonitrile as the cyclic reaction core. The phosphorus-chlorine bonds on the hexachlorocyclotriphosphonitrile molecular skeleton are highly reactive and can accept nucleophilic substitution. Since different nucleophiles exhibit varying reactivity, the order of addition and reaction temperature can be controlled to allow the three substituent groups to sequentially enter the cyclophosphonitrile skeleton. The primary amino group at the end of the 3-aminopropyltriethoxysilane molecular chain exhibits the strongest nucleophilicity. Under nitrogen protection and low-temperature conditions, the lone pair electrons on the amino group preferentially attack the phosphorus-chlorine sites on the hexachlorocyclotriphosphonitrile skeleton, causing the chlorine atom to leave and forming a phosphorus-nitrogen covalent bond. This allows the silane structure to enter the cyclophosphonitrile molecule. Potassium carbonate absorbs the hydrogen chloride generated in the reaction, preventing the primary amino group from being protonated and deactivated. Subsequently, the temperature was raised and N-(4-hydroxyphenyl)maleimide was added. Under the action of potassium carbonate, its phenolic hydroxyl group was deprotonated to form a phenolic oxygen active site, significantly enhancing its nucleophilicity. This site then continued to replace the remaining chlorine site on the hexachlorocyclotriphosphazene, forming a stable phosphoro-oxyaryl ring bond. This allowed the maleimide structure to be incorporated into the cyclophosphazene skeleton, bringing the terminal double bond into the product. The temperature was then raised further and 4-hydroxybenzaldehyde was added. The phenolic hydroxyl group of 4-hydroxybenzaldehyde was also converted to a phenolic oxygen active site under the action of potassium carbonate, replacing the remaining chlorine site on the cyclophosphazene skeleton. The aldehyde group did not participate in this substitution process and remained at the para position of the aromatic ring. After filtration, a solution of aldehyde-silane maleimide-cyclophosphazene intermediate containing potassium chloride precipitate was obtained. Subsequently, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and triethylamine were added to the intermediate solution. Triethylamine abstracts a hydrogen proton from the phosphorus-hydrogen bond, activating the lone pair electrons on the phosphorus group. These electrons then attack the suspended aldehyde carbonyl carbon in the intermediate molecule, resulting in nucleophilic addition. This causes the phosphaphenanthrene structure to be stably attached to the intermediate molecule via a carbon-phosphorus bond, simultaneously forming a benzyl alcohol hydroxyl group. After cooling, precipitation, washing, drying, pulverizing, and vibrating sieving, a phosphorus-nitrogen silane-grafted maleimide-based cyclophosphonitrile was obtained.

[0015] According to a preferred embodiment of the present invention, in A1, the reaction time at 0-5°C is 1-2 hours.

[0016] According to a preferred embodiment of the present invention, in A2, the reaction time at 75-82°C is 6-10 hours.

[0017] According to a preferred embodiment of the present invention, the method for preparing the boron-nitrogen-phosphorus triazine aryl ether vinyl monomer includes: B1. By weight, mix 10.0-18.0 parts of cyanuric chloride, 120.0-220.0 parts of acetone and 0.05-0.20 parts of hydroquinone, cool to 0-5℃, add 18.0-32.0 parts of anhydrous potassium carbonate and 8.0-15.0 parts of 4-hydroxybenzaldehyde to react; heat to 25-35℃, add 4.0-8.0 parts of 4-vinylphenol to react, filter, and distill under reduced pressure to obtain a chloroaldehyde-based vinyl triazine ether intermediate; add 12.0-26.0 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 0.1-0.5 parts of triethylamine and 80.0-160.0 parts of N,N-dimethylformamide to the chloroaldehyde-based vinyl triazine ether intermediate, and react at 85-95℃ to obtain a chloroDOPO addition vinyl triazine ether intermediate.

[0018] B2. Add 8.0-15.0 parts of 4-hydroxyphenylboronic acid, 8.0-16.0 parts of anhydrous potassium carbonate and 60.0-120.0 parts of N,N-dimethylformamide to the vinyl triazine ether intermediate of chloroDOPO, and react at 95-110℃; after the reaction is completed, precipitate, filter, wash, dry, grind and vibrate sieve.

[0019] In this invention, the preparation of boron-nitrogen-phosphorus triazine aryl ether vinyl monomers uses cyanuric chloride as the core of the triazine reaction. The three chlorine sites on cyanuric chloride exhibit significantly different activities, following a stepwise substitution pattern, allowing for the sequential incorporation of different aryloxy groups through temperature control. After mixing cyanuric chloride, acetone, and hydroquinone, the mixture is cooled to a low temperature. Hydroquinone acts as a polymerization inhibitor to suppress free radical side reactions of the subsequently added vinyl monomers. Anhydrous potassium carbonate is added, followed by the batch addition of 4-hydroxybenzaldehyde. The phenolic hydroxyl groups of 4-hydroxybenzaldehyde undergo deprotonation under the action of anhydrous potassium carbonate to form phenolic oxygen active sites, which nucleophilically attack the most reactive chlorine site on the triazine ring, generating an aryl ether linkage. This allows the aryl oxygen structure with a free aldehyde group to be incorporated into the triazine ring, while the aldehyde group does not participate in this step and remains intact. After heating to room temperature, 4-vinylphenol is added. The phenolic hydroxyl group of 4-vinylphenol is converted into a phenolic oxygen active site under the action of potassium carbonate, which continues to replace the second chlorine site on the triazine ring. The vinyl group in the molecule is completely retained at the para position of the aromatic ring due to the polymerization inhibition protection of hydroquinone. After filtration to remove potassium chloride salt and vacuum distillation to remove acetone, a chloroaldehyde-vinyltriazine aryl ether intermediate is obtained. Then, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, triethylamine, and N,N-dimethylformamide are added to the chloroaldehyde-vinyltriazine aryl ether intermediate. Triethylamine abstracts a hydrogen proton from the phosphorus-hydrogen bond, activating the lone pair electrons on the phosphorus, and undergoes nucleophilic addition to the aldehyde carbonyl carbon suspended on the intermediate molecule. The phosphaphenanthrene structure is stably attached to the intermediate backbone through a carbon-phosphorus bond, and a benzyl alcohol hydroxyl group is formed, resulting in a chloroaddition vinyltriazine aryl ether intermediate. Finally, 4-hydroxyphenylboronic acid and anhydrous potassium carbonate are added. 4-hydroxyphenylboronic acid undergoes deprotonation of the phenolic hydroxyl group in the molecule and replaces the last remaining chlorine site on the triazine ring. The borate group is completely retained at the para position of the aromatic ring due to its extremely weak nucleophilicity and the absence of a palladium catalytic system. After precipitation, filtration, washing, drying, grinding, and vibrating sieving, the boron-nitrogen-phosphorus triazine aryl ether vinyl monomer is obtained. This monomer molecule simultaneously contains a triazine structure, a phosphorus-phenanthroline structure, an aryl ether bond, a borate group, and a vinyl group.

[0020] According to a preferred embodiment of the present invention, in B1, the reaction time for adding 4-hydroxybenzaldehyde is 1-3 hours, and the reaction time for adding 4-vinylphenol is 3-5 hours.

[0021] According to a preferred embodiment of the present invention, in B2, the reaction time at 95-110°C is 4-8 hours.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses N-phenylmaleimide, styrene monomer, and glycidyl methacrylate as the main copolymer raw materials, so that the flame-retardant maleimide copolymer resin has both rigidity, moldability, and reactivity. N-phenylmaleimide is beneficial to improving the heat resistance and dimensional stability of the resin, styrene monomer is beneficial to maintaining the processing fluidity and molding performance of the resin, and glycidyl methacrylate can improve the internal bonding of the copolymer system, so that the obtained flame-retardant maleimide copolymer resin maintains good mechanical stability and processing adaptability while being flame-retardant modified.

[0023] (2) In this invention, maleimide-grafted cyclophosphonitrile and boron-phosphonitrile-triazine aryl ether vinyl monomers are introduced into the resin system as reactive flame-retardant modifying components. This allows the flame-retardant structure to be fixed in the resin molecular chain through copolymerization, reducing the problems of easy migration, precipitation, and uneven dispersion of additive flame-retardant components. The cyclophosphonitrile, phosphaphenanthrene, silane, and maleimide structures in the phosphorus-phosphonitrile-grafted maleimide-cyclophosphonitrile are beneficial to improving char formation ability and char layer stability. The triazine, phosphaphenanthrene, borate group, and aryl ether structures in the boron-phosphonitrile-triazine aryl ether vinyl monomers are beneficial to enhancing the density of the char layer and its heat and oxygen insulation capabilities, thereby improving the flame-retardant safety of the flame-retardant maleimide copolymer resin.

[0024] (3) This invention uses azobisisobutyronitrile and tert-butyl peroxide to initiate the copolymerization reaction, which is beneficial to improving the conversion degree of raw materials and reducing the impact of residual polymerizable components on resin stability; N,N-dimethylformamide and toluene are beneficial to forming a uniform reaction system of raw materials; ethanol is used for resin precipitation and purification, which is beneficial to obtaining a flame-retardant maleimide copolymer resin with a relatively uniform composition; antioxidant 1010 and antioxidant 168 can improve the thermo-oxidative stability of the resin during processing and use. The obtained flame-retardant maleimide copolymer resin has good flame retardancy, heat resistance, char formation, dimensional stability and mechanical retention, and is suitable for electronic appliances and new energy electrical components and other scenarios with high requirements for flame retardancy and heat resistance. Detailed Implementation

[0025] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0026] Example 1 This embodiment provides a method for preparing a flame-retardant maleimide copolymer resin, the steps of which include: S1. 25.0g N-phenylmaleimide, 60.0g styrene monomer, 12.5g glycidyl methacrylate, 4.5g phosphorus-nitrogen silane-grafted maleimide-based cyclophosphonitrile, 3.5g boron-nitrogen-phosphorus triazine aryl ether vinyl monomer, 110.0g N,N-dimethylformamide, and 50.0g toluene were added to a reaction vessel equipped with a mechanical stirrer, temperature control device, reflux condenser, and nitrogen protection device. The stirring rate was 250r / min, and the mixture was stirred at 25℃ for 30min to obtain a monomer mixture. Nitrogen gas was introduced into the monomer mixture for 30min at a flow rate of 60mL / min. Then, under nitrogen protection, 0.45g azobisisobutyronitrile was added, and the mixture was reacted at 65.0℃ for 3h. Subsequently, the temperature was raised to 80.0℃ and reacted for 5h. The stirring rate was maintained at 250r / min during the reaction to obtain a copolymer reaction solution.

[0027] S2. Add 0.275g of tert-butyl peroxide to the copolymer reaction solution obtained in step S1, and react at 107.5℃ for 2h with a stirring rate of 250r / min. After the reaction is completed, cool the reaction system to 40℃, add 0.3g of antioxidant 1010 and 0.3g of antioxidant 168, and stir for 30min to obtain a resin reaction solution. Slowly add 140.0g of ethanol to the resin reaction solution for precipitation. During the precipitation process, the stirring rate is 200r / min and the precipitation time is 30min. After the precipitation is completed, filter and collect the solid. Wash with ethanol 3 times, each time using 80.0g of ethanol. Place the washed solid in a vacuum drying oven and dry at 70℃ for 12h to obtain flame-retardant maleimide copolymer resin.

[0028] Preparation steps of grafting maleimide-based cyclophosphonitriles onto phosphorus nitrogen silanes: A1. Add 11.0 g of hexachlorocyclotriphosphazene, 5.5 g of 3-aminopropyltriethoxysilane, 30.0 g of potassium carbonate, and 170.0 g of anhydrous acetonitrile to a reaction vessel equipped with a mechanical stirrer, temperature control device, reflux condenser, and nitrogen protection device. Start stirring at a rate of 300 r / min, purge with nitrogen for 30 min, and maintain nitrogen protection at a flow rate of 60 mL / min. Control the reaction temperature at 2.5 °C and react for 1.5 h. Then raise the temperature to 27.5 °C, add 9.0 g of N-(4-hydroxyphenyl)maleimide, and react at 27.5 °C for 4 h. Finally, raise the temperature to 71.5 °C and add 15.0 g of... 4-Hydroxybenzaldehyde was reacted at 71.5℃ for 8 hours with a stirring rate of 300 r / min during the reaction. After the reaction was completed, the reaction system was cooled to 25℃ and filtered by vacuum filtration to remove inorganic salts. The filtrate was collected to obtain an aldehyde-silane maleimide-cyclophosphonitrile intermediate solution.

[0029] A2. Add 26.0 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 0.5 g of triethylamine, and 90.0 g of toluene to the aldehyde-silane maleimide-cyclophosphonitrile intermediate solution obtained in step A1. Stir at 300 r / min and react at 78.5 °C for 8 h. After the reaction is complete, cool the reaction system to 25 °C and slowly add 500.0 g of ethanol to precipitate the mixture. Stir at 200 r / min and precipitate for 30 min. After precipitation, filter and collect the precipitate. Wash the precipitate three times with 100.0 g of ethanol each time, and then wash it twice with 100.0 g of deionized water each time. Place the washed solid in a vacuum drying oven and dry at 60 °C for 12 h. After drying, pulverize and sieve using a 200 mesh sieve to obtain phosphorus-nitrogen silane grafted maleimide-cyclophosphonitrile.

[0030] Preparation steps of boron, nitrogen, phosphorus, triazine, aromatic ether, vinyl monomers: B1. 14.0 g of cyanuric chloride, 170.0 g of acetone, and 0.125 g of hydroquinone were added to a reaction vessel equipped with a mechanical stirrer, temperature control device, and reflux condenser. The stirring speed was 300 r / min. The mixture was cooled to 2.5 °C, and 25.0 g of anhydrous potassium carbonate was added, followed by 11.5 g of 4-hydroxybenzaldehyde. The reaction was carried out at 2.5 °C for 2 h. Subsequently, the temperature was raised to 30.0 °C, and 6.0 g of 4-vinylphenol was added. The reaction was carried out at 30.0 °C for 4 h, maintaining a stirring speed of 300 r / min throughout the reaction. After the reaction was completed, the mixture was filtered, and the filtrate was collected. Acetone was removed by vacuum distillation at 35 °C and -0.08 MPa to obtain a chloroaldehyde-based vinyl triazine ether intermediate. 19.0 g of [unspecified ingredient] was added to the chloroaldehyde-based vinyl triazine ether intermediate. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 0.3 g triethylamine, and 120.0 g N,N-dimethylformamide were reacted at 90.0 °C for 8 h with a stirring rate of 300 r / min to obtain a chloroDOPO addition vinyltriazine aryl ether intermediate.

[0031] B2. Add 11.5 g of 4-hydroxyphenylboronic acid, 12.0 g of anhydrous potassium carbonate, and 90.0 g of N,N-dimethylformamide to the chloroDOPO addition vinyl triazine aryl ether intermediate obtained in step B1. Stir at 300 r / min and react at 102.5 °C for 6 h. After the reaction is complete, cool the reaction system to 25 °C and add 500.0 g of ethanol to precipitate the mixture. Stir at 200 r / min and precipitate for 30 min. After precipitation, filter and collect the solid. Wash the solid three times with ethanol (100.0 g each time) and twice with deionized water (100.0 g each time). Place the washed solid in a vacuum drying oven and dry at 60 °C for 12 h. After drying, grind the solid and sieve it using a 200-mesh sieve to obtain the boron-nitrogen-phosphorus triazine aryl ether vinyl monomer.

[0032] Example 2 The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a flame-retardant maleimide copolymer resin, the steps of which include: S1. Add 15.0g N-phenylmaleimide, 50.0g styrene monomer, 5.0g glycidyl methacrylate, 1.0g phosphorus nitrogen silane grafted maleimide cyclophosphonitrile, 1.0g boron nitrogen phosphorus triazine aryl ether vinyl monomer, 60.0g N,N-dimethylformamide and 20.0g toluene to a reaction vessel equipped with a stirrer, a temperature control device and a nitrogen protection device. Mix under stirring to obtain a monomer mixture. Under nitrogen protection, add 0.1g azobisisobutyronitrile to the monomer mixture and react at 60℃ for 2h, followed by reaction at 75℃ for 4h to obtain a copolymer reaction solution.

[0033] S2. Add 0.05g of tert-butyl peroxide to the copolymer reaction solution obtained in step S1, and react at 100℃ for 1h. After the reaction is completed, cool, add 0.1g of antioxidant 1010 and 0.1g of antioxidant 168, stir, and obtain resin reaction solution. Add the resin reaction solution to 80.0g of ethanol, filter, wash, and dry to obtain flame-retardant maleimide copolymer resin.

[0034] Preparation steps of grafting maleimide-based cyclophosphonitriles onto phosphorus nitrogen silanes: A1. 8.0 g of hexachlorocyclotriphosphazene, 3.0 g of 3-aminopropyltriethoxysilane, 22.0 g of potassium carbonate and 120.0 g of anhydrous acetonitrile were added to a reaction vessel equipped with a stirrer, temperature control device and nitrogen protection device. The reaction was carried out at 0 °C for 1 h under nitrogen protection. Then the temperature was raised to 25 °C and 6.0 g of N-(4-hydroxyphenyl)maleimide was added and the reaction was carried out for 3 h. The temperature was then raised to 65 °C and 10.0 g of 4-hydroxybenzaldehyde was added and the reaction was carried out for 6 h. After the reaction was completed, the mixture was filtered to obtain an intermediate solution of aldehyde-based silane-maleimide-based cyclophosphazene.

[0035] A2. Add 18.0 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 0.2 g of triethylamine and 60.0 g of toluene to the aldehyde-silane maleimide-cyclophosphonitrile intermediate solution obtained in step A1, and react at 75 °C for 6 h. After the reaction is completed, cool, precipitate the reaction solution, collect the precipitate, wash, dry, pulverize and vibrate sieve the precipitate to obtain phosphorus-nitrogen silane grafted maleimide-cyclophosphonitrile.

[0036] Preparation steps of boron, nitrogen, phosphorus, triazine, aromatic ether, vinyl monomers: B1. Add 10.0g cyanuric chloride, 120.0g acetone and 0.05g hydroquinone to a reaction vessel equipped with a stirrer, temperature control device and cooling device, cool to 0℃, add 18.0g anhydrous potassium carbonate, and then add 8.0g 4-hydroxybenzaldehyde and react for 1h; then raise the temperature to 25℃, add 4.0g 4-vinylphenol and react for 3h. After the reaction is completed, filter and distill under reduced pressure to obtain a chloroaldehyde-based vinyltriazine ether intermediate; add 12.0g 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 0.1g triethylamine and 80.0g N,N-dimethylformamide to the chloroaldehyde-based vinyltriazine ether intermediate, and react at 85℃ for 6h to obtain a chloroDOPO addition vinyltriazine ether intermediate.

[0037] B2. Add 8.0 g of 4-hydroxyphenylboronic acid, 8.0 g of anhydrous potassium carbonate and 60.0 g of N,N-dimethylformamide to the chloroDOPO addition vinyl triazine aryl ether intermediate obtained in step B1, and react at 95 °C for 4 h. After the reaction is completed, precipitate the reaction solution, filter it, collect the solid, wash the solid, dry it, grind it and vibrate it to obtain the boron nitrogen phosphorus triazine aryl ether vinyl monomer.

[0038] Example 3 The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a flame-retardant maleimide copolymer resin, the steps of which include: S1. 35.0g N-phenylmaleimide, 70.0g styrene monomer, 20.0g glycidyl methacrylate, 8.0g phosphorus-nitrogen silane-grafted maleimide-based cyclophosphonitrile, 6.0g boron-nitrogen-phosphorus triazine aryl ether vinyl monomer, 160.0g N,N-dimethylformamide, and 80.0g toluene were added to a reaction vessel equipped with a stirrer, a temperature control device, and a nitrogen protection device. The mixture was stirred to obtain a monomer mixture. Under nitrogen protection, 0.8g azobisisobutyronitrile was added to the monomer mixture, and the reaction was carried out at 70°C for 4 hours, followed by a reaction at 85°C for 6 hours to obtain a copolymerization reaction solution.

[0039] S2. Add 0.5g of tert-butyl peroxide to the copolymer reaction solution obtained in step S1 and react at 115℃ for 3h. After the reaction is completed, cool and add 0.5g of antioxidant 1010 and 0.5g of antioxidant 168, stir, and obtain resin reaction solution. Add the resin reaction solution to 200.0g of ethanol, filter, wash, and dry to obtain flame-retardant maleimide copolymer resin.

[0040] Preparation steps of grafting maleimide-based cyclophosphonitriles onto phosphorus nitrogen silanes: A1. 14.0 g of hexachlorocyclotriphosphazene, 8.0 g of 3-aminopropyltriethoxysilane, 38.0 g of potassium carbonate and 220.0 g of anhydrous acetonitrile were added to a reaction vessel equipped with a stirrer, temperature control device and nitrogen protection device. The reaction was carried out at 5 °C for 2 h under nitrogen protection. Then the temperature was raised to 30 °C and 12.0 g of N-(4-hydroxyphenyl)maleimide was added and the reaction was carried out for 5 h. The temperature was then raised to 78 °C and 20.0 g of 4-hydroxybenzaldehyde was added and the reaction was carried out for 10 h. After the reaction was completed, the mixture was filtered to obtain an intermediate solution of aldehyde-based silane-maleimide-based cyclophosphazene.

[0041] A2. Add 34.0 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 0.8 g of triethylamine and 120.0 g of toluene to the aldehyde-silane maleimide-cyclophosphonitrile intermediate solution obtained in step A1, and react at 82 °C for 10 h. After the reaction is completed, cool, precipitate the reaction solution, collect the precipitate, wash, dry, pulverize and vibrate sieve the precipitate to obtain phosphorus-nitrogen silane grafted maleimide-cyclophosphonitrile.

[0042] Preparation steps of boron, nitrogen, phosphorus, triazine, aromatic ether, vinyl monomers: B1. 18.0 g of cyanuric chloride, 220.0 g of acetone, and 0.20 g of hydroquinone were added to a reaction vessel equipped with a stirrer, temperature control device, and cooling device. The mixture was cooled to 5°C, and 32.0 g of anhydrous potassium carbonate was added, followed by 15.0 g of 4-hydroxybenzaldehyde, and the reaction was carried out for 3 h. Subsequently, the temperature was raised to 35°C, and 8.0 g of 4-vinylphenol was added, and the reaction was carried out for 5 h. After the reaction was completed, the mixture was filtered and distilled under reduced pressure to obtain a chloroaldehyde-based vinyltriazine ether intermediate. 26.0 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 0.5 g of triethylamine, and 160.0 g of N,N-dimethylformamide were added to the chloroaldehyde-based vinyltriazine ether intermediate, and the mixture was reacted at 95°C for 10 h to obtain a chloroDOPO addition vinyltriazine ether intermediate.

[0043] B2. Add 15.0 g of 4-hydroxyphenylboronic acid, 16.0 g of anhydrous potassium carbonate and 120.0 g of N,N-dimethylformamide to the chloroDOPO addition vinyl triazine aryl ether intermediate obtained in step B1, and react at 110 °C for 8 h. After the reaction is completed, precipitate the reaction solution, filter it, collect the solid, wash the solid, dry it, grind it and vibrate it to obtain the boron nitrogen phosphorus triazine aryl ether vinyl monomer.

[0044] Comparative Example 1 The difference between this comparative example and Example 1 is that in S1, 12.5g of glycidyl methacrylate is not added, and 12.5g of styrene monomer is used instead; otherwise, it is the same as in Example 1.

[0045] Comparative Example 2 The difference between this comparative example and Example 1 is that in S1, 4.5g of phosphorus nitrogen silane grafted maleimide cyclophosphonitrile is not added, and is replaced by 4.5g of N-phenylmaleimide, while the rest is the same as in Example 1.

[0046] Comparative Example 3 The difference between this comparative example and Example 1 is that, in S1, 3.5g of boron nitrogen phosphorus triazine aryl ether vinyl monomer is not added, and 3.5g of styrene monomer is used instead; otherwise, it is the same as in Example 1.

[0047] The performance of the flame-retardant maleimide copolymer resins obtained in Examples 1-3 and Comparative Examples 1-3 was tested in accordance with national and industry standard testing specifications.

[0048] The flame-retardant maleimide copolymer resins prepared in Examples 1-3 and Comparative Examples 1-3 were dried in a vacuum drying oven at 70°C for 12 hours. After removal, they were sealed and cooled to 23°C. The dried resins were then added to a twin-screw extruder for melt mixing. The barrel temperature was set sequentially to 180°C, 190°C, 200°C, 210°C, and 220°C, and the screw speed was set to 80 r / min. The extrudate was water-cooled, air-dried, and pelletized to obtain resin granules for testing. The resin granules for testing were placed in a drying oven at 70°C for another 6 hours. Subsequently, various test samples were prepared by injection molding using an injection molding machine. The injection barrel temperature was set sequentially to 190°C, 200°C, 210°C, and 220°C, the mold temperature was set to 60°C, the injection pressure was set to 80 MPa, the holding time was set to 20 s, and the cooling time was set to 30 s. After all samples were prepared, they were conditioned in an environment of 23°C and 50%RH for 48 hours.

[0049] The vertical flammability test uses 125mm×13mm×1.6mm strip specimens, with 5 specimens per group. The specimens are fixed vertically along their long axis, and the flame height is adjusted to 20mm. The first flame application time is 10s. After the flame is removed, the first afterflame time is recorded. Immediately after the flame is extinguished, the second flame application is performed for 10s. After the flame is removed, the second afterflame time, smoldering time, dripping condition, and whether the absorbent cotton is ignited are recorded. The vertical flammability rating is determined based on the specimen's combustion behavior.

[0050] The limiting oxygen index test uses 80mm×10mm×4mm strip specimens, with 5 specimens per group. The specimens are vertically fixed in an oxygen-nitrogen mixed gas flow and ignited from the top of the specimen. By adjusting the oxygen volume fraction, the specimen is kept in a stable combustion state. The oxygen volume fraction of each specimen is recorded, and the arithmetic mean of the 5 specimens is taken as the limiting oxygen index, with the unit being 0.

[0051] The tensile strength test uses dumbbell-shaped specimens, with 5 specimens tested in each group. Before the test, the width and thickness of the effective part of the specimen are measured with vernier calipers. The tensile speed is set to 50 mm / min. The maximum tensile load when the specimen breaks is recorded. The tensile strength is calculated by dividing the maximum tensile load by the original cross-sectional area of ​​the specimen. The arithmetic mean of the 5 specimens is taken, and the unit is MPa.

[0052] The notched impact strength test uses 80mm×10mm×4mm impact specimens, with 5 specimens tested per group. A V-shaped notch with a depth of 2mm is machined in the middle of the specimen. Before testing, the notch direction is confirmed to be consistent. The specimen is placed in the impact fixture, and the impact direction is applied to the back side of the notch. The energy absorbed by the specimen upon impact failure is recorded. The notched impact strength is calculated by dividing the absorbed energy by the remaining cross-sectional area at the notch, and the arithmetic mean of the 5 specimens is taken. The unit is kJ / m. 2 .

[0053] The heat distortion temperature test uses 80mm×10mm×4mm strip specimens, with 3 specimens tested in each group. The specimens are placed in a three-point bending fixture, the bending stress is set to 1.80MPa, the heating rate is set to 120℃ / h, and the temperature when the specimen reaches the specified bending deformation is recorded. The arithmetic mean of the 3 specimens is taken, and the unit is ℃.

[0054] The peak heat release rate reduction test used 100mm×100mm×3mm plate-shaped specimens, with 3 specimens per group. Before the test, the edges and back of the specimens were covered with aluminum foil, exposing only the upper surface. The thermal radiation flux was set to 35kW / m². 2 The peak heat release rate of the entire combustion process was recorded. The peak heat release rate of the blank resin without the addition of phosphorus nitrogen silane grafted maleimide cyclophosphonitrile and boron nitrogen phosphorus triazine aryl ether vinyl monomers was used as the benchmark. The peak heat release rate reduction rate was calculated by subtracting the peak heat release rate of the test sample from the peak heat release rate of the blank resin, dividing by the peak heat release rate of the blank resin, and multiplying by 100%. The arithmetic mean of the three samples was taken.

[0055] The performance test data above are shown in Table 1.

[0056] Table 1: Performance Test Results The test results in Table 1 clearly show that Examples 1-3 exhibit a more balanced improvement in flame retardancy, heat resistance, mechanical properties, and heat release inhibition compared to Comparative Examples 1-3. This demonstrates that the present invention can solve the problems of insufficient integration of flame retardant structure with resin system, unstable flame retardant efficiency, insufficient char layer protection, and easy decline in mechanical properties in existing flame retardant maleimide copolymer resins.

[0057] The vertical flammability ratings of Examples 1-3 all reached V-0, while those of Comparative Examples 2 and 3 were only V-1. This indicates that the self-extinguishing ability of the resin during combustion is significantly enhanced after simultaneously introducing phosphorus-nitrogen silane grafted maleimide-based cyclophosphonitrile and boron-nitrogen phosphonitrile triazine aryl ether vinyl monomers. The limiting oxygen indices of Examples 1-3 were 35.4%, 33.2%, and 36.3%, respectively, which were higher than those of Comparative Example 2 (29.8%) and Comparative Example 3 (30.6%). This suggests that the cyclophosphonitrile, phosphaphenanthrene, silane, and maleimide structures provided by the phosphorus-nitrogen silane grafted maleimide-based cyclophosphonitrile, together with the triazine, phosphaphenanthrene, borate, and aryl ether structures provided by the boron-nitrogen phosphonitrile triazine aryl ether vinyl monomers, form a synergistic effect, increasing the oxygen concentration required for the resin to maintain combustion, thereby improving flame retardant safety.

[0058] Comparative Example 1, without the addition of glycidyl methacrylate, still maintained a vertical flammability rating of V-0, but its tensile strength was only 59.7 MPa and its notched impact strength was only 11.8 kJ / m.2 It is significantly lower than 66.8 MPa and 15.6 kJ / m² in Example 1. 2 It is also lower than the 68.5 MPa and 16.2 kJ / m² of Example 2. 2 This indicates that glycidyl methacrylate is beneficial for improving the internal bonding and mechanical retention of the copolymer system, and avoids a decrease in the strength and toughness of the resin after flame retardant modification.

[0059] Comparative Example 2, without the addition of phosphorus-nitrogen silane-grafted maleimide-based cyclophosphonitrile, showed a decrease in limiting oxygen index, heat distortion temperature, and peak heat release rate to 29.8%, 112°C, and 41.6%, respectively. These figures were significantly lower than those of Example 1 (35.4%, 123°C, and 63.5%), indicating that phosphorus-nitrogen silane-grafted maleimide-based cyclophosphonitrile plays a crucial role in improving char formation ability, heat resistance, and heat release inhibition.

[0060] Comparative Example 3, without the addition of boron, nitrogen, phosphorus, triazine, aromatic ether, and vinyl monomers, had a vertical flammability rating of V-1, a limiting oxygen index of 30.6%, and a peak heat release rate reduction of 44.2%, which were significantly lower than those of Examples 1-3. This indicates that boron, nitrogen, phosphorus, triazine, aromatic ether, and vinyl monomers can enhance the density and flame retardant stability of the char layer and reduce the heat release intensity during combustion.

[0061] In summary, Examples 1-3, through the combined action of N-phenylmaleimide, styrene monomer, glycidyl methacrylate, phosphorus-nitrogen silane-grafted maleimide-based cyclophosphonitrile, and boron-nitrogen-phosphorus triazine aryl ether vinyl monomer, enable the resin to achieve a V-0 flame retardant rating while maintaining a tensile strength of 63.4-68.5 MPa and a tensile strength of 14.1-16.2 kJ / m². 2 The notched impact strength, heat distortion temperature of 119-126℃, and peak heat release rate reduction rate of 57.8-66.2% demonstrate that the present invention can improve flame retardancy and heat release inhibition capabilities while taking into account mechanical properties and heat resistance, thus solving the problem that it is difficult to improve flame retardancy efficiency, mechanical retention, and heat resistance stability at the same time in the prior art.

Claims

1. A flame-retardant maleimide copolymer resin, characterized in that, It is prepared from the following raw materials in parts by weight: 15-35 parts of N-phenylmaleimide, 50-70 parts of styrene monomer, 5-20 parts of glycidyl methacrylate, 1-8 parts of phosphorus nitrogen silane grafted maleimide cyclophosphonitrile, 1-6 parts of boron nitrogen phosphorus triazine aryl ether vinyl monomer, 0.1-0.8 parts of azobisisobutyronitrile, 0.05-0.5 parts of tert-butyl peroxide, 60-160 parts of N,N-dimethylformamide, 20-80 parts of toluene, 80-200 parts of ethanol, 0.1-0.5 parts of antioxidant 1010, and 0.1-0.5 parts of antioxidant 168.

2. A method for preparing the flame-retardant maleimide copolymer resin according to claim 1, characterized in that the step... include: S1. Under stirring, N-phenylmaleimide, styrene monomer, glycidyl methacrylate, phosphorus silane-grafted maleimide cyclophosphonitrile, boron nitrophosphorus triazine aryl ether vinyl monomer, N,N-dimethylformamide and toluene are mixed to obtain a monomer mixture; under nitrogen protection, azobisisobutyronitrile is added to the monomer mixture and reacted at 60-70℃, followed by reaction at 75-85℃ to obtain a copolymer reaction solution; S2. Add tert-butyl peroxide to the copolymerization reaction solution and react at 100-115℃. After the reaction is complete, cool and add antioxidant 1010 and antioxidant 168. Stir to obtain resin reaction solution. Add resin reaction solution to ethanol, filter, wash and dry.

3. The method for preparing the flame-retardant maleimide copolymer resin according to claim 2, characterized in that, In S1, the reaction time at 60-70℃ is 2-4 hours.

4. The method for preparing the flame-retardant maleimide copolymer resin according to claim 2, characterized in that, In S2, the reaction time at 100-115℃ is 1-3 hours.

5. The flame-retardant maleimide copolymer resin according to claim 1, characterized in that, The preparation method of the phosphorus nitrogen silane grafted with maleimide cyclophosphonitrile includes: A1. By weight, 8.0-14.0 parts of hexachlorocyclotriphosphazene, 3.0-8.0 parts of 3-aminopropyltriethoxysilane, 22.0-38.0 parts of potassium carbonate, and 120.0-220.0 parts of anhydrous acetonitrile are mixed and reacted at 0-5°C under nitrogen protection; then the temperature is raised to 25-30°C, and 6.0-12.0 parts of N-(4-hydroxyphenyl)maleimide are added and reacted; then the temperature is raised to 65-78°C, and 10.0-20.0 parts of 4-hydroxybenzaldehyde are added and reacted. The mixture is filtered to obtain an aldehyde-silane-maleimide-cyclophosphazene intermediate solution. A2. Add 18.0-34.0 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 0.2-0.8 parts of triethylamine and 60.0-120.0 parts of toluene to the aldehyde-silane-maleimide-cyclophosphonitrile intermediate solution, and react at 75-82℃; after the reaction is completed, cool, precipitate, wash, dry, pulverize and vibrate sieve.

6. The flame-retardant maleimide copolymer resin according to claim 5, characterized in that, In the A1, the reaction time at 0-5℃ is 1-2 hours.

7. The flame-retardant maleimide copolymer resin according to claim 5, characterized in that, In the A2, the reaction time is 6-10 hours at 75-82°C.

8. The flame-retardant maleimide copolymer resin according to claim 1, characterized in that, The preparation method of the boron-phosphorus triazine aryl ether vinyl monomer includes: B1. By weight, mix 10.0-18.0 parts of cyanuric chloride, 120.0-220.0 parts of acetone and 0.05-0.20 parts of hydroquinone, cool to 0-5℃, add 18.0-32.0 parts of anhydrous potassium carbonate and 8.0-15.0 parts of 4-hydroxybenzaldehyde to react; heat to 25-35℃, add 4.0-8.0 parts of 4-vinylphenol to react, filter, and distill under reduced pressure to obtain a chloroaldehyde-based vinyl triazine ether intermediate; add 12.0-26.0 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 0.1-0.5 parts of triethylamine and 80.0-160.0 parts of N,N-dimethylformamide to the chloroaldehyde-based vinyl triazine ether intermediate, and react at 85-95℃ to obtain a chloroDOPO addition vinyl triazine ether intermediate; B2. Add 8.0-15.0 parts of 4-hydroxyphenylboronic acid, 8.0-16.0 parts of anhydrous potassium carbonate and 60.0-120.0 parts of N,N-dimethylformamide to the chloroDOPO addition vinyl triazine aryl ether intermediate, and react at 95-110℃; after the reaction is completed, precipitate, filter, wash, dry, grind and vibrate sieve.

9. The flame-retardant maleimide copolymer resin according to claim 8, characterized in that, In B1, the reaction time for adding 4-hydroxybenzaldehyde is 1-3 hours, and the reaction time for adding 4-vinylphenol is 3-5 hours.

10. The flame-retardant maleimide copolymer resin according to claim 8, characterized in that, In the B2, the reaction time is 4-8 hours at 95-110℃.

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