Preparation of DOPO-based hollow polymer microspheres and application of DOPO-based hollow polymer microspheres in flame-retardant polymers

Abstract

The invention discloses preparation of DOPO-based hollow polymer microspheres and application of the DOPO-based hollow polymer microspheres in flame-retardant polymers, and belongs to the technical field of high polymer materials. The preparation method of the DOPO-based hollow polymer microspheres comprises the following steps: preparing a template core through self-stable precipitation polymerization, then polymerizing a DOPO-based flame-retardant monomer, an anhydride monomer and a cross-linking agent on the surface of the template core to construct a cross-linking shell layer in situ to obtain copolymer microspheres with a core-shell structure, and finally removing the template through solvent etching to obtain the DOPO-based hollow polymer microspheres. And the DOPO-based hollow polymer microspheres are prepared. The compatibility between the DOPO-based hollow polymer microspheres and a polymer matrix is greatly improved through rich anhydride groups on the surfaces of the DOPO-based hollow polymer microspheres, the flame retardant property of the polymer composite material is improved, the mechanical property of the polymer composite material is greatly improved, and due to the unique hollow structure of the polymer composite material, the flame retardant property of the polymer composite material is greatly improved. The polymer material is endowed with excellent transparency and low dielectric property.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to the preparation of DOPO-based hollow polymer microspheres and their application in flame-retardant polymers. Background Art

[0002] Polymers such as epoxy resin (EP) are widely used in the fields of electronic packaging, coatings, composite materials, and structural adhesives due to their excellent mechanical properties, electrical insulation, chemical corrosion resistance, and adhesion properties. However, polymers such as EP themselves are highly flammable polymer materials, and are prone to decomposition and generate a large amount of combustible gases under the action of high temperature or fire sources, which can easily cause fires. Therefore, how to improve the flame retardancy of polymers such as EP has become a research topic widely concerned by the academic and industrial circles.

[0003] At present, the main flame retardants include halogen-based flame retardants, phosphorus-nitrogen-based flame retardants, etc. Halogen-based flame retardants are the most effective flame retardants for reducing the flammability of polymers. Among them, bromine and chlorine-based flame retardants are the most widely used. They have the advantages of low addition amount and good effect, and cause less damage to the mechanical properties of polymer composites. Polymer composites containing halogen flame retardants will decompose and generate HX (X refers to Br, Cl) during the combustion process, which can combine with the free radicals generated by the pyrolysis of polymers to dilute the concentration of combustible free radicals and achieve the flame retardant effect. Of course, halogen flame retardancy is also accompanied by a series of problems. Since its main action occurs in the gas phase, halogen-based flame retardants will generate a large amount of smoke during the combustion process. The hydrohalic acid formed by the combination of hydrogen halide vapor and water in the air is highly corrosive and will cause relatively great harm to the environment. In addition, with the continuous development of technology, people have gradually realized that the use of halogen-based flame retardants will have a certain impact on the ecological system and human health. With the gradual penetration of the concept of green sustainability, the replacement of halogen-based flame retardants with halogen-free flame retardants will be the future development trend.

[0004] Phosphorus-based flame retardants are one of the most commonly used halogen-free flame retardant systems at present. The flame retardant effect of phosphorus-nitrogen flame retardants is mainly reflected in two aspects: the gas phase and the condensed phase. Gas-phase flame retardant mechanism: During the combustion process, phosphorus-nitrogen flame retardants decompose and release phosphorus- and nitrogen-containing free radicals (such as PO·, HPO·, NH3, etc.). These free radicals can interfere with the combustion chain reaction and capture high-energy active free radicals (H·, OH·), thereby inhibiting combustion and reducing the flame propagation speed. In addition, the decomposition of nitrogen generates non-combustible gases (such as NH3, N2), effectively diluting the oxygen concentration and reducing the flammability of the material. Condensed-phase flame retardant mechanism: Under the action of high temperature, phosphorus-nitrogen flame retardants promote the carbonization reaction and form a stable phosphorus-rich carbon layer. This carbon layer can isolate oxygen, prevent heat transfer, and reduce the release of combustible gases at the same time, thereby improving the fire resistance of the material. In addition, the presence of nitrogen can enhance the compactness of the carbon layer and improve the carbonization efficiency, further improving the flame retardant performance. The synergistic effect of phosphorus-nitrogen flame retardants can significantly increase the limiting oxygen index (LOI) of epoxy resins, reduce the heat release rate (HRR) and the total heat release (THR), achieving the purpose of high-efficiency flame retardancy.

[0005] 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is an efficient phosphorus-containing flame retardant. Due to its excellent thermal stability, low smoke, low toxicity characteristics and good compatibility, it has become one of the important choices for halogen-free flame retardancy of epoxy resins. As an efficient flame retardant, DOPO has a special phosphaphenanthrene ring system. The phosphorus element in its structure can promote carbonization during the combustion process, and the presence of the oxygen bridge and aromatic ring endows it with high thermal stability. The molecular formula of DOPO is C 12H9O2P has a relatively small relative molecular mass, which enables it to have good dispersibility in the epoxy resin system. As an additive flame retardant, DOPO can be directly doped into the epoxy resin to improve its flame retardant performance. However, as a small molecule compound, DOPO is prone to migration in the material, resulting in the phenomenon of flame retardant precipitation and affecting the long-term stability of EP. Therefore, researchers have developed DOPO derivatives to improve their compatibility and flame retardant efficiency in the epoxy system. For example, by introducing amino groups or amine groups into the DOPO structure, its chemical bonding in the epoxy resin can be enhanced, improving the thermal stability. DOPO reacts with m-phenylenediamine (m-PDA) to form DOPO-PDA, which exhibits good flame retardant performance in the epoxy resin system and the mechanical properties are not significantly affected. Although significant progress has been made in the halogen-free flame retardant research of DOPO and its derivatives in epoxy resins, the following key problems still need to be solved to improve the flame retardant efficiency: optimizing the structural design of DOPO derivatives to improve their flame retardant effect at low addition amounts. Enhancing compatibility: developing covalently bondable DOPO derivatives to improve the mechanical properties and long-term stability of the material. Green environmental protection: exploring renewable bio-based DOPO derivatives to reduce environmental pollution. Functional composite: developing DOPO composite materials with flame retardant, heat-resistant and mechanical strengthening functions to meet the needs of high-end applications. Summary of the Invention

[0006] The object of the present invention is to provide the preparation of DOPO-based hollow polymer microspheres and their application in flame retardant polymers to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention: A method for preparing DOPO-based hollow polymer microspheres, comprising the following steps:

[0009] Mix a DOPO-based flame retardant monomer (abbreviated as FAFD), an acid anhydride monomer, a crosslinking agent, a polymer microsphere template, an initiator, and a solvent 1, and perform self-stabilized precipitation polymerization to obtain DOPO-based core-shell polymer microspheres; subject the DOPO-based core-shell polymer microspheres to solvent etching to obtain the DOPO-based hollow polymer microspheres.

[0010] First, the present invention prepares polymer microspheres as templates through self-stabilized precipitation polymerization. Subsequently, a cross-linked shell layer is in-situ constructed on the surface of the template core by polymerizing a DOPO-based flame retardant monomer (FAFD), an anhydride monomer, and a cross-linking agent to obtain copolymer microspheres with a core-shell structure. Finally, the template is removed by solvent etching to prepare DOPO-based hollow polymer microspheres with different sizes. As a multifunctional filler, the DOPO-based hollow polymer microspheres can not only endow polymers such as epoxy resins with excellent flame retardant properties, but also largely retain the original mechanical properties of polymers such as epoxy resins, and endow them with excellent dielectric properties and transparency.

[0011] Specifically, compared with commercial DOPO flame retardants, the DOPO-based hollow polymer microspheres prepared in the present invention have very obvious advantages. The DOPO-based hollow polymer microspheres combine the phosphorus-nitrogen synergistic flame retardant mechanism of DOPO, and at the same time, the special structure of the microspheres can form a stable char layer, which helps to improve the fire resistance and smoke suppression performance of the material. Secondly, the DOPO-based hollow polymer microspheres improve the compatibility of the flame retardant with polymers such as epoxy resins: due to its structural characteristics, traditional DOPO has poor compatibility in polymer matrices such as epoxy resins, and phase separation is likely to occur, resulting in uneven dispersion, which affects the flame retardant effect and the mechanical properties of the material. The DOPO-based hollow polymer microspheres introduce anhydride monomers, and improve the interfacial interaction with polymers such as epoxy resins through their active anhydride groups, making the dispersion of the microspheres in the matrix better, improving the overall uniformity and processing stability, and significantly enhancing the mechanical properties of polymers such as epoxy resins. As a molecular-level flame retardant, traditional DOPO often reduces the mechanical strength of materials in polymer matrices, such as tensile strength and impact toughness. The DOPO-based hollow polymer microspheres are hollow microspheres with regular morphologies, which can not only act as reinforcing fillers to improve the strength and toughness of composite materials, but also significantly enhance the impact resistance of materials through the stress dispersion effect of the microsphere structure, avoiding the problem of mechanical property degradation caused by traditional flame retardant additives. The DOPO-based hollow polymer microspheres endow polymers such as epoxy resins with excellent dielectric properties. Due to the existence of the hollow structure, a gas-phase medium is formed inside the microspheres, and this structure with a low dielectric constant can effectively reduce the overall dielectric constant of polymer composites and improve the electrical insulation performance. Traditional DOPO flame retardants often affect the optical properties of polymers such as epoxy resins, making the composite materials show strong opacity or yellowing. The addition of the DOPO-based hollow polymer microspheres greatly improves the related problems.

[0012] Furthermore, the FAFD is a monomer prepared by copolymerizing furfurylamine, furfural, and DOPO, and the structural formula of the FAFD is

[0013] Further, the polymer microsphere template is an olefin - anhydride copolymer microsphere, an olefin - maleimide copolymer microsphere, a homopolymer microsphere of styrene - type monomers, or a homopolymer microsphere of (meth)acrylate - type monomers.

[0014] Further, the cross - linker includes divinylbenzene (DVB), diallylbenzene, diallylamide, diacrylamide, allyl glycidyl ether, triethylene glycol divinyl ether, diethylene glycol divinyl ether, diallylphenol, divinyldimethylsiloxane, ethylene glycol diacrylate, ethylene glycol dimethacrylate, or trimethylolpropane triacrylate.

[0015] Further, the initiator is an azo - type initiator or a peroxide initiator.

[0016] Further, the solvent 1 includes one of organic acid alkyl esters and a mixed solution of alkane and organic acid alkyl ester.

[0017] Further, the molar ratio of the anhydride - type monomer to FAFD is 1:2 - 4.

[0018] Further, the molar amount of the cross - linker is 30 - 60% of the sum of the molar amounts of the anhydride - type monomer and FAFD, preferably 35%.

[0019] Further, the mass of the polymer microsphere template is the sum of the masses of the anhydride - type monomer and FAFD.

[0020] Further, the mass of the initiator is 0.5 - 10% of the sum of the masses of FAFD, the anhydride - type monomer, and the cross - linker.

[0021] The DOPO - based hollow polymer microspheres have a clear hollow structure, and the shell layer (the remaining part after etching) has a cross - linked structure. The cross - linked shell layer of the DOPO - based hollow polymer microspheres is formed by FAFD, the anhydride - type monomer, and the cross - linker.

[0022] Further, the preparation steps of the olefin - anhydride copolymer microspheres include: mixing the anhydride - type monomer, olefin, initiator, and solvent 2, and carrying out self - stabilized polymerization to obtain the olefin - anhydride copolymer microspheres.

[0023] Further, the preparation steps of the olefin - maleimide copolymer microspheres include: mixing the maleimide - type monomer, olefin, initiator, and solvent 2, and carrying out self - stabilized polymerization to obtain the olefin - anhydride copolymer microspheres.

[0024] Further, the anhydride - type monomer includes one or more of maleic anhydride (Ma) and itaconic anhydride (Ia).

[0025] Further, the maleimide monomer includes one or more of N,N'-(4,4'-methylenediphenyl) bismaleimide, N,N'-(4-methyl-1,3-phenylene) bismaleimide, 2,2'-bis[4-(4-maleimidophenoxy)phenyl] propane, N,N'-m-phenylene bismaleimide, N,N'-(1,4-phenylene) bismaleimide, 1,2-bis(maleimidyl) ethane, 1,3-bis(maleimidyl) propane, 1,4-bis(maleimidyl) butane, bis[4-(3-maleimidophenoxy)phenyl] sulfone, 1,4-bis(4-maleimidophenoxy) benzene, 1,4-bis(3-maleimidophenoxy) benzene, 3,4'-diphenyl ether bismaleimide, and 4,4'-diphenyl ether bismaleimide.

[0026] Further, the olefin includes one or more of styrene monomers, (meth)acrylate monomers, vinyl acetate, α-olefins, dicyclopentadiene, and ethylidene norbornene.

[0027] Further, the solvent 2 is one of an organic acid alkyl ester, a mixed solution of a ketone and an organic acid alkyl ester, a mixed solution of a ketone and an alkane, and a mixed solution of an alkane and an organic acid alkyl ester.

[0028] Further, the initiator is an azo initiator or a peroxide initiator.

[0029] Further, the mixing of the acid anhydride monomer, the olefin, the initiator, and the solvent 2 includes: the molar ratio of the acid anhydride monomer to the olefin is 1:1, and the mass of the initiator is 0.5-10% of the sum of the masses of the acid anhydride monomer and the olefin.

[0030] Further, the mixing of the maleimide monomer, the olefin, the initiator, and the solvent 2 includes: the molar ratio of the maleimide monomer to the olefin is 1:1, and the mass of the initiator is 0.5-10% of the sum of the masses of the maleimide monomer and the olefin.

[0031] Further, the styrene monomer includes styrene.

[0032] Further, the azo initiator includes azodiisobutyronitrile (AIBN), azodiisovaleronitrile, or dimethyl azodiisobutyrate; the peroxide initiator includes benzoyl peroxide, diisopropylbenzene peroxide, bis(2,4-dichlorobenzoyl) peroxide, di-tert-butyl peroxide, lauroyl peroxide, tert-butyl perbenzoate, diisopropyl peroxydicarbonate, or dicyclohexyl peroxydicarbonate. The initiator is mainly used to provide primary free radicals, and different types of initiators play the same role in the polymerization process.

[0033] Further, the structural formula of the organic acid alkyl ester in Solvent 1 or Solvent 2 is wherein, R1 is H, an alkyl group with 1 - 8 carbon atoms, a benzyl group, a phenyl group or a substituted phenyl group, and R2 is an alkyl group with 1 - 5 carbon atoms.

[0034] More preferably, the organic acid alkyl esters include ethyl formate, propyl formate, isobutyl formate, pentyl formate, ethyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isoamyl acetate, benzyl acetate, phenyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, isobutyl butyrate, isoamyl butyrate, ethyl isobutyrate, ethyl isovalerate, isoamyl isovalerate, methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate, isoamyl benzoate, methyl phenylacetate, ethyl phenylacetate, propyl phenylacetate, butyl phenylacetate or isoamyl phenylacetate.

[0035] Further, the alkanes in Solvent 1 or Solvent 2 include n - pentane, n - hexane, cyclohexane, n - heptane, n - octane or isooctane.

[0036] Further, when Solvent 1 or Solvent 2 is a mixed solution of an alkane and an organic acid alkyl ester, the volume fraction of the alkane in the mixed solution is 5 - 40%.

[0037] The organic acid alkyl ester is a good solvent. FAFD, cross - linker, acid anhydride monomers, initiators, etc. can be well dissolved in the organic acid alkyl ester, and the polymerization product is insoluble in the organic acid alkyl ester. Therefore, it can be well separated from the solvent by centrifugation. For the same type of organic acid alkyl esters, their monomer reaction processes are similar when used as solvents. They have similar structural compositions as organic acid alkyl esters, so they can all be used as solvents for self - stabilized precipitation polymerization. The mixed solution of an alkane and an organic acid alkyl ester is used to further adjust the overall solubility parameter of the solvent to prepare copolymer microspheres with different particle sizes.

[0038] Further, the solvent etching of the DOPO - based core - shell polymer microspheres includes: the solvents used include ketones.

[0039] Further, the ketones include acetone, butanone, cyclohexanone, methyl isobutyl ketone or methyl isopropyl ketone.

[0040] Further, the temperature of the self - stabilized precipitation polymerization is all 55 - 75 °C, and the time is all 5 - 10 h.

[0041] The second technical solution of the present invention: the DOPO - based hollow polymer microspheres prepared by the above - mentioned preparation method.

[0042] The third technical solution of the present invention: the application of the above-mentioned DOPO-based hollow polymer microspheres in the preparation of flame-retardant polymers.

[0043] The fourth technical solution of the present invention: a flame-retardant polymer composite material, which is a flame-retardant thermosetting polymer composite material or a flame-retardant thermoplastic polymer composite material; the raw materials of the flame-retardant polymer composite material include the above-mentioned DOPO-based hollow polymer microspheres.

[0044] Further, by mass percentage, the raw materials of the flame-retardant thermosetting polymer composite material include: 74-78% of thermosetting polymer, 18-20% of curing agent, and the balance of the above-mentioned DOPO-based hollow polymer microspheres.

[0045] Or, by mass percentage, the raw materials of the flame-retardant thermoplastic polymer composite material include: 70-95% of thermoplastic polymer and the balance of the above-mentioned DOPO-based hollow polymer microspheres.

[0046] The fifth technical solution of the present invention: the preparation method of the above-mentioned flame-retardant polymer composite material, including the following steps:

[0047] Mix the DOPO-based hollow polymer microspheres, thermosetting polymer and curing agent, perform defoaming treatment, and then carry out pre-curing and curing in sequence to obtain the flame-retardant thermosetting polymer composite material;

[0048] Or, mix the DOPO-based hollow polymer microspheres and thermoplastic polymer by internal mixing and blending, and then form to obtain the flame-retardant thermoplastic polymer composite material.

[0049] Further, the thermosetting polymer includes epoxy resin (EP).

[0050] Further, the temperature of the pre-curing is 100 °C and the time is 3 h; the temperature of the curing is 150 °C and the time is 4 h.

[0051] Further, the thermoplastic polymer includes nylon 66 (PA66), polyethylene (PE) or polypropylene (PP).

[0052] Further, the temperature of the internal mixing and blending is 165-220 °C, the rotation speed is 75 rpm, and the time is 6 min.

[0053] The present invention discloses the following technical effects:

[0054] Compared with traditional DOPO, the DOPO-based hollow polymer microspheres of the present invention not only solve the compatibility problem, but also can improve the mechanical properties, transparency and dielectric properties of polymers such as epoxy resin, while still maintaining excellent flame-retardant effects. This new type of flame retardant with a novel structure has broad application prospects in the field of high-performance flame-retardant composite materials. Brief Description of the Drawings

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0056] Figure 1 1H NMR test results of the Schiff base and FAFD monomer prepared in step (1) of Example 1, where a is the Schiff base and b is the FAFD monomer; 1 1H NMR test results of the Schiff base and FAFD monomer prepared in step (1) of Example 1, where a is the Schiff base and b is the FAFD monomer;

[0057] Figure 2 TEM image of the DOPO-based hollow polymer microspheres (FADM) prepared in Example 1;

[0058] Figure 3 Vertical burning test results (photos during two combustion processes) of the flame-retardant EP composites of Application Example 1 (E-51 / 5wt% APP), Application Example 2 (E-51 / 4wt% FAFD), Comparative Application Example 1 (E-51 / 5wt% FAFD), Comparative Application Example 2 (E-51 / 4wt% FADM), Comparative Application Example 3 (E-51 / 5wt% FADM) and pure E-51 (Comparative Application Example 4);

[0059] Figure 4 Cone calorimeter test results of the flame-retardant EP composites of Application Example 2 and Comparative Application Example 2 and pure E-51, where a is the maximum heat release rate and b is the total heat release;

[0060] Figure 5 Mechanical property (tensile strength) test results of the flame-retardant EP composites of pure E-51, Application Examples 1-2 and Comparative Application Examples 1-3;

[0061] Figure 6 Test results of the dielectric properties and transparency of the flame-retardant EP composites of pure E-51, Application Example 2 and Comparative Application Example 2, where a is the dielectric constant, b is the dielectric loss, and c is the transmittance. Detailed Description of the Embodiments

[0062] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0063] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0064] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0065] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0066] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0067] It should be noted that the aspects not described in detail in the present invention are all conventional operating means in the art and are not the focus of the present invention.

[0068] As a first aspect of the present invention, the present invention provides a method for preparing DOPO-based hollow polymer microspheres, comprising the following steps:

[0069] Mix a DOPO-based flame retardant monomer (abbreviated as FAFD, FAFD is a monomer prepared by copolymerization of furfurylamine, furfural and DOPO, and the structural formula is )), an acid anhydride monomer, a crosslinking agent, a polymer microsphere template, an initiator and a solvent 1, and carry out self-stabilized precipitation polymerization to obtain DOPO-based core-shell polymer microspheres; perform solvent etching on the DOPO-based core-shell polymer microspheres to obtain the DOPO-based hollow polymer microspheres.

[0070] As a preferred embodiment of the present invention, the polymer microsphere template is an olefin - acid anhydride copolymer microsphere, an olefin - maleimide copolymer microsphere, a homopolymer microsphere of a styrene monomer or a homopolymer microsphere of a (meth)acrylate monomer.

[0071] As a preferred embodiment of the present invention, the preparation method of the DOPO-based hollow polymer microspheres further specifically comprises the following steps:

[0072] (1) Preparation of the FAFD monomer

[0073] Dissolve furfural in absolute ethanol (the dosage ratio of furfural to absolute ethanol is 0.5 - 1 mol: 80 - 180 mL) to obtain a furfural solution; dissolve furfurylamine in absolute methanol (the dosage ratio of furfurylamine to absolute methanol is 0.5 - 1 mol: 30 - 60 mL) to obtain a furfurylamine solution; under nitrogen protection, drop the furfurylamine solution into the furfural solution (the molar ratio of furfurylamine contained in the furfurylamine solution to furfural contained in the furfural solution is 1:1), and react at room temperature for 1 - 5 h to obtain a Schiff base;

[0074] Mix DOPO, absolute ethanol and the Schiff base (the dosage ratio of DOPO, absolute ethanol and the Schiff base is 0.1 mol: 100 mL: 0.1 - 0.2 mol), and continue to react under nitrogen protection at 60 °C for 6 - 10 h to obtain the FAFD monomer;

[0075] (2) Preparation of the polymer microsphere template

[0076] Mix an acid anhydride monomer, an olefin, an initiator and a solvent 2 (the molar ratio of the acid anhydride monomer to the olefin is 1:1; the mass of the initiator is 0.5 - 10% of the sum of the masses of the acid anhydride monomer and the olefin), and carry out self-stabilized polymerization (the temperature is 55 - 75 °C, and the time is 5 - 10 h) to obtain an olefin - acid anhydride copolymer microsphere;

[0077] Or, mix a maleimide monomer, an olefin, an initiator and a solvent 2 (the molar ratio of the maleimide monomer to the olefin is 1:1; the mass of the initiator is 0.5 - 10% of the sum of the masses of the maleimide monomer and the olefin), and carry out self-stabilized polymerization (the temperature is 55 - 75 °C, and the time is 5 - 10 h) to obtain the olefin - acid anhydride copolymer microsphere;

[0078] (3) Preparation of the DOPO-based core-shell polymer microspheres

[0079] Mix FAFD, an acid anhydride monomer, a crosslinking agent, a polymer microsphere template, an initiator, and a solvent 1 (the molar ratio of the acid anhydride monomer to FAFD is 1:2 - 4, preferably 1:4; the molar amount of the crosslinking agent is 30 - 60% of the sum of the molar amounts of the acid anhydride monomer and FAFD, preferably 35%; the mass of the polymer microsphere template is the sum of the masses of the acid anhydride monomer and FAFD; the mass of the initiator is 0.5 - 10% of the sum of the masses of FAFD, the acid anhydride monomer, and the crosslinking agent), and perform self-stabilized precipitation polymerization (temperature is 55 - 75 °C, time is 5 - 10 h) to obtain DOPO-based core-shell polymer microspheres;

[0080] (4) Remove the template

[0081] Perform solvent etching on the DOPO-based core-shell polymer microspheres (to remove the template) to obtain the DOPO-based hollow polymer microspheres.

[0082] As a preferred embodiment of the present invention, in steps (2) and (3):

[0083] The acid anhydride monomer includes one or more of maleic anhydride (Ma) and itaconic anhydride (Ia).

[0084] As a preferred embodiment of the present invention, in step (3):

[0085] The crosslinking agent includes divinylbenzene (DVB), diallylbenzene, diallyl acrylamide, diallyl amide, allyl glycidyl ether, triethylene glycol divinyl ether, diethylene glycol divinyl ether, diallyl phenol, divinyldimethylsiloxane, ethylene glycol diacrylate, ethylene glycol dimethacrylate, or trimethylolpropane triacrylate;

[0086] And / or, the initiator is an azo initiator or a peroxide initiator.

[0087] As a preferred embodiment of the present invention, in step (2):

[0088] The maleimide monomers include one or more of N,N'-(4,4'-methylenediphenyl)bismaleimide, N,N'-(4-methyl-1,3-phenylene)bismaleimide, 2,2'-bis[4-(4-maleimidophenoxy)phenyl]propane, N,N'-m-phenylene bismaleimide, N,N'-(1,4-phenylene)bismaleimide, 1,2-bis(maleimidyl)ethane, 1,3-bis(maleimidyl)propane, 1,4-bis(maleimidyl)butane, bis[4-(3-maleimidophenoxy)phenyl]sulfone, 1,4-bis(4-maleimidophenoxy)benzene, 1,4-bis(3-maleimidophenoxy)benzene, 3,4'-diphenylether bismaleimide, and 4,4'-diphenylether bismaleimide;

[0089] And / or, the olefins include one or more of styrene monomers (preferably styrene), (meth)acrylate monomers, vinyl acetate, α-olefins, dicyclopentadiene, and ethylidene norbornene;

[0090] And / or, the initiator is an azo initiator or a peroxide initiator.

[0091] As a preferred embodiment of the present invention, the azo initiators in steps (2) and (3) include azobisisobutyronitrile (AIBN), azobisisoheptanenitrile, or dimethyl azobisisobutyrate; the peroxide initiators include benzoyl peroxide, dicumyl peroxide, bis(2,4-dichlorobenzoyl)peroxide, di-tert-butyl peroxide, lauroyl peroxide, tert-butyl perbenzoate, diisopropyl peroxydicarbonate, or dicyclohexyl peroxydicarbonate; the initiator is preferably AIBN, and the addition amount of AIBN is preferably 5% of the total mass of all monomers (in step (2), it is the acid anhydride monomer + olefin or maleimide monomer + olefin; in step (3), it is FAFD + acyl-containing monomer + crosslinking agent).

[0092] As a preferred embodiment of the present invention, the solvent 1 includes one of organic acid alkyl esters and a mixed solution of alkane and organic acid alkyl ester (the volume fraction of alkane in the mixed solution is 5 - 40%);

[0093] And / or, the solvent 2 is one of organic acid alkyl esters, a mixed solution of ketone and organic acid alkyl ester, a mixed solution of ketone and alkane, and a mixed solution of alkane and organic acid alkyl ester (the volume fraction of alkane in the mixed solution is 5 - 40%).

[0094] As a preferred embodiment of the present invention, the structural formula of the organic acid alkyl ester in the solvent 1 or solvent 2 is Among them, R1 is H, an alkyl group with 1-8 carbon atoms, benzyl, phenyl or substituted phenyl, and R2 is an alkyl group with 1-5 carbon atoms.

[0095] As a preferred embodiment of the present invention, the organic acid alkyl esters include ethyl formate, propyl formate, isobutyl formate, pentyl formate, ethyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isoamyl acetate, benzyl acetate, phenyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, isobutyl butyrate, isoamyl butyrate, ethyl isobutyrate, ethyl isovalerate, isoamyl isovalerate, methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate, isoamyl benzoate, methyl phenylacetate, ethyl phenylacetate, propyl phenylacetate, butyl phenylacetate or isoamyl phenylacetate, preferably isoamyl acetate.

[0096] As a preferred embodiment of the present invention, the alkanes in the solvent 1 or solvent 2 include n-pentane, n-hexane, cyclohexane, n-heptane, n-octane or isooctane, preferably n-heptane.

[0097] As a preferred embodiment of the present invention, the solvents used in the solvent etching in step (4) include but are not limited to ketones, and the ketones include acetone, butanone, cyclohexanone, methyl isobutyl ketone or methyl isopropyl ketone. In addition to ketones, other solvents that can dissolve the polymer microsphere template can also be used as etching solvents.

[0098] As a preferred embodiment of the present invention, the particle size range of the polymer microsphere template is 0.05-3 μm, preferably 0.2-1 μm, and more preferably 0.4-0.8 μm. Here, the "particle size" refers to the "average particle size". The specific method is to observe with a scanning electron microscope (SEM). The size of the microspheres is represented by the average particle size. According to the SEM photos of the obtained samples, the average value of at least 100 microspheres is measured and calculated as the average particle size.

[0099] As a preferred embodiment of the present invention, in step (1), the polymer microsphere template is a styrene-maleic anhydride copolymer microsphere, and its reaction route is as follows:

[0100] Among them, 2SP represents self-stabilized precipitation polymerization.

[0101] As a preferred embodiment of the present invention, in step (3), the acid anhydride monomer is maleic anhydride, the crosslinking agent is DVB, and the structural formula of the shell layer in the DOPO-based core-shell polymer microsphere is:

[0102]

[0103] As a second aspect of the present invention, the present invention provides DOPO-based hollow polymer microspheres prepared by the above preparation method.

[0104] As a third aspect of the present invention, the present invention provides the use of the above DOPO-based hollow polymer microspheres in the preparation of flame-retardant polymers.

[0105] As a fourth aspect of the present invention, the present invention provides a flame-retardant polymer composite material, which is a flame-retardant thermosetting polymer composite material or a flame-retardant thermoplastic polymer composite material; the raw materials of the flame-retardant polymer composite material include the above DOPO-based hollow polymer microspheres.

[0106] As a preferred embodiment of the present invention, by mass percentage, the raw materials of the flame-retardant thermosetting polymer composite material include: 74-78% of thermosetting polymer, 18-20% of curing agent, and the balance of the above DOPO-based hollow polymer microspheres;

[0107] Or, by mass percentage, the raw materials of the flame-retardant thermoplastic polymer composite material include: 70-95% of thermoplastic polymer and the balance of the above DOPO-based hollow polymer microspheres.

[0108] As a fifth aspect of the present invention, the present invention provides a preparation method of the above flame-retardant polymer composite material, comprising the following steps:

[0109] Mix the DOPO-based hollow polymer microspheres, thermosetting polymer and curing agent, perform defoaming treatment, and then perform pre-curing and curing in sequence to obtain the flame-retardant thermosetting polymer composite material;

[0110] Or, mix the DOPO-based hollow polymer microspheres and thermoplastic polymer by internal mixing and blending, and then form to obtain the flame-retardant thermoplastic polymer composite material.

[0111] As a preferred embodiment of the present invention, the thermosetting polymer includes epoxy resin, and the curing agent includes 4,4-diaminodiphenylmethane.

[0112] As a preferred embodiment of the present invention, the temperature of the pre-curing is 100 °C and the time is 3 h; the temperature of the curing is 150 °C and the time is 4 h.

[0113] As a preferred embodiment of the present invention, the thermoplastic polymer includes nylon 66 (PA66), polyethylene (PE) or polypropylene (PP).

[0114] As a preferred embodiment of the present invention, the temperature of the internal mixing and blending is 165-220 °C, the rotation speed is 75 rpm, and the time is 6 min.

[0115] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0116] In the specific embodiments of the present invention, the room temperature specifically refers to 25 ± 2 °C.

[0117] All raw materials used in the specific embodiments of the present invention are ordinary commercially available products.

[0118] Example 1

[0119] A preparation method of DOPO-based hollow polymer microspheres is as follows:

[0120] (1) Preparation of FAFD monomer

[0121] Dissolve 0.5 mol of furfural in 85 mL of absolute ethanol, mix well and add it to a three-necked flask protected by nitrogen (N2). Then dissolve 0.5 mol of furfurylamine in 50 mL of absolute methanol and add it dropwise to the three-necked flask within 0.5 h. Then react at room temperature for 3 h. After the reaction is completed, filter the mixed liquid by suction to obtain a brown transparent solution; then perform rotary evaporation to remove absolute methanol and absolute ethanol in the solution, and obtain a Schiff base after cooling;

[0122] Add 0.1 mol of DOPO and 100 mL of absolute ethanol to a three-necked flask protected by N2, then add 0.1 mol of Schiff base, and continue to react at 60 °C for 8 h. After the reaction is completed, wait for the solution to cool to room temperature, wash the solution three times with 2 wt% NaOH solution, then wash it with deionized water until neutral, and dry it to obtain the bio-based flame retardant monomer FAFD;

[0123] The 1H NMR test results of the Schiff base and FAFD monomer prepared in this step are as 1 shown, where a is the Schiff base and b is the FAFD monomer. Figure 1 shown, where a is the Schiff base and b is the FAFD monomer.

[0124] (2) Preparation of olefin - anhydride copolymer microsphere template

[0125] First, add 0.1 mol (10.4 g) of styrene and 0.1 mol (9.8 g) of maleic anhydride (Ma) to 200 mL of isoamyl acetate, add initiator AIBN according to 1% of the monomer mass (i.e., the total mass of styrene and maleic anhydride), ultrasonically dissolve the monomers completely, react at 75 °C for 7 h, and then use ethanol for centrifugal washing to remove the residual isoamyl acetate to obtain 19.2 g of olefin - anhydride copolymer microspheres (abbreviated as SMA), with a yield of about 95% and an average particle size of the microspheres of 400 nm;

[0126] (3) Preparation of DOPO-based core-shell polymer microspheres

[0127] Disperse 15.4 g of SMA into 220 mL of isopentyl acetate, then add 0.02 mol (7.56 g) of FAFD, 0.08 mol (7.84 g) of Ma, and DVB with a molar amount of 35% of the total molar amount of FAFD and Ma, and add initiator AIBN according to 5% of the monomer mass (i.e., the total mass of FAFD, Ma, and DVB); then add 70 mL of n - heptane, ultrasonicate until the monomers are completely dissolved, react at 75 °C for 7 h, and then perform centrifugal separation. The resulting precipitate product is the DOPO - based core - shell polymer microspheres;

[0128] (4) Remove the template

[0129] Add 200 mL of acetone to the DOPO - based core - shell polymer microspheres obtained in step (3) and soak at room temperature for 1 h. Repeat three times (to remove the template), then wash three times with petroleum ether to remove acetone, and then dry in an oven at 45 °C to obtain the DOPO - based hollow polymer microspheres (abbreviated as FADM), with a yield of about 65%.

[0130] Figure 2 This is the TEM image of the DOPO - based hollow polymer microspheres prepared in this example. It can be clearly seen that it indeed has a hollow structure.

[0131] Example 2

[0132] A preparation method of DOPO - based hollow polymer microspheres is as follows:

[0133] (1) Prepare FAFD monomer

[0134] The preparation steps of FAFD are the same as those in Example 1;

[0135] (2) Prepare the olefin - anhydride copolymer microsphere template

[0136] The preparation steps of the olefin - anhydride copolymer microsphere template are the same as those in Example 1;

[0137] (3) Prepare DOPO - based core - shell polymer microspheres

[0138] Disperse 15.4 g of SMA into 220 mL of isopentyl acetate, then add 0.02 mol (7.56 g) of FAFD, 0.08 mol (7.84 g) of Ma, and DVB with a molar amount of 35% of the total molar amount of FAFD and Ma, and add initiator AIBN according to 5% of the monomer mass (i.e., FAFD, Ma, and DVB), ultrasonicate until the monomers are completely dissolved, react at 75 °C for 7 h, and then perform centrifugal separation. The resulting precipitate product is the DOPO - based core - shell polymer microspheres;

[0139] (4) Remove the template

[0140] 200 mL of acetone was added to the DOPO-based core-shell polymer microspheres obtained in step (3), and the mixture was soaked at room temperature for 1 h. After repeating this three times, the mixture was washed three times with petroleum ether to remove the acetone, and then dried in an oven at 45 °C to obtain DOPO-based hollow polymer microspheres (abbreviated as FADM), with a yield of about 53%.

[0141] Application Example 1

[0142] A flame-retardant EP composite material was prepared as follows:

[0143] 95 g of E-51 was weighed and added to a beaker, and the mixture was heated to 80 °C on a heating table with magnetic stirring. After E-51 became less viscous, 5 g of FADM (prepared in Example 1) was added, and stirring was continued at 80 °C until FADM was uniformly dispersed in E-51. Subsequently, 25 g of 4,4-diaminodiphenylmethane (DDM) curing agent was added and completely dissolved to obtain a mixture.

[0144] The above mixture was placed in a vacuum oven at 80 °C, and the vacuum was applied to remove the bubbles in the mixture. Subsequently, pre-curing was carried out in an oven at 100 °C for 3 h, and then the temperature was raised to 150 °C for curing for 4 h. After that, the flame-retardant EP composite material was taken out and denoted as E-51 / 5wt% FADM.

[0145] Application Example 2

[0146] A flame-retardant EP composite material was prepared as follows:

[0147] 96 g of E-51 was weighed and added to a beaker, and the mixture was heated to 80 °C on a heating table with magnetic stirring. After E-51 became less viscous, 4 g of FADM (prepared in Example 1) was added, and stirring was continued at 80 °C until FADM was uniformly dispersed in E-51. Subsequently, 25 g of DDM was added and completely dissolved to obtain a mixture.

[0148] The above mixture was placed in a vacuum oven at 80 °C, and the vacuum was applied to remove the bubbles in the mixture. Subsequently, pre-curing was carried out in an oven at 100 °C for 3 h, and then the temperature was raised to 150 °C for curing for 4 h. After that, the flame-retardant EP composite material was taken out and denoted as E-51 / 4wt% FADM.

[0149] Comparative Application Example 1

[0150] A flame-retardant EP composite material was prepared as follows:

[0151] 95 g of E-51 was weighed and added to a beaker, and the mixture was heated to 80 °C on a heating table with magnetic stirring. After E-51 became less viscous, 5 g of FAFD was added, and stirring was continued at 80 °C until FAFD was uniformly dispersed in E-51. Subsequently, 25 g of DDM was added and completely dissolved to obtain a mixture.

[0152] Put the above mixture into a vacuum oven at 80 °C, evacuate the air to remove the bubbles in the mixture. Subsequently, pre-cure it in an oven at 100 °C for 3 h, then raise the temperature to 150 °C and cure for 4 h, and then take it out to obtain the flame-retardant EP composite material, denoted as E-51 / 5 wt% FAFD.

[0153] Comparative Application Example 2

[0154] A flame-retardant EP composite material is prepared as follows:

[0155] Weigh 96 g of E-51 and add it to a beaker, and heat it to 80 °C on a heating table with a magnetic stirrer. After E-51 becomes thinner from viscous, add 4 g of FAFD, and continue to stir at 80 °C until FAFD is uniformly dispersed in E-51. Then add 25 g of DDM and dissolve it completely to obtain a mixture.

[0156] Put the above mixture into a vacuum oven at 80 °C, evacuate the air to remove the bubbles in the mixture. Subsequently, pre-cure it in an oven at 100 °C for 3 h, then raise the temperature to 150 °C and cure for 4 h, and then take it out to obtain the flame-retardant EP composite material, denoted as E-51 / 4 wt% FAFD.

[0157] Comparative Application Example 3

[0158] A flame-retardant EP composite material is prepared as follows:

[0159] Weigh 95 g of E-51 and add it to a beaker, and heat it to 80 °C on a heating table with a magnetic stirrer. After E-51 becomes thinner from viscous, add 5 g of APP (ammonium polyphosphate), and continue to stir at 80 °C until APP is uniformly dispersed in E-51. Then add 25 g of DDM and dissolve it completely to obtain a mixture.

[0160] Put the above mixture into a vacuum oven at 80 °C, evacuate the air to remove the bubbles in the mixture. Subsequently, pre-cure it in an oven at 100 °C for 3 h, then raise the temperature to 150 °C and cure for 4 h, and then take it out to obtain the flame-retardant EP composite material, denoted as E-51 / 5 wt% APP.

[0161] Comparative Application Example 4

[0162] The preparation of pure EP material is as follows:

[0163] Weigh 100 g of E-51 and add it to a beaker, and heat it to 80 °C on a heating table with a magnetic stirrer. After E-51 becomes thinner from viscous, add 25 g of DDM and dissolve it completely to obtain a mixture.

[0164] Put the above mixture into a vacuum oven at 80 °C, evacuate the air to remove the bubbles in the mixture. Subsequently, pre-cure it in an oven at 100 °C for 3 h, then raise the temperature to 150 °C and cure for 4 h, and then take it out to obtain the pure EP material, denoted as E-51.

[0165] Test Example 1

[0166] (1) UL-94 test

[0167] Perform UL-94 tests (refer to "ASTM D3801-2010", the same below) on the flame-retardant EP composites prepared in Application Examples 1-2 and Comparative Application Examples 1-3, as well as pure EP (prepared in Comparative Application Example 4). The results are shown in Table 1 and Figure 2 as follows.

[0168] Table 1

[0169]

[0170] a: The burning time of the sample when it is ignited twice respectively. Among them, t1 is the time when the sample continues to burn after the first ignition and the heat source is removed, and t2 is the time when the sample continues to burn after the second ignition and the heat source is removed; b: Whether there is dripping during the burning process and whether it ignites the cotton wool below; c: UL-94 vertical burning test grade. In addition, it should be noted that in Table 1, the sum of the masses of EP and the flame retardant (FAFD, FADM or APP) is calculated as 100%, and the dosage of the curing agent DDM is not included.

[0171] Figure 3 The vertical burning test results (photos during the two burning processes, and the time includes the time for igniting the sample, specifically 10 s) of the flame-retardant EP composites of Application Example 1 (E-51 / 5 wt% APP), Application Example 2 (E-51 / 4 wt% FAFD), Comparative Application Example 1 (E-51 / 5 wt% FAFD), Comparative Application Example 2 (E-51 / 4 wt% FADM), and Comparative Application Example 3 (E-51 / 5 wt% FADM), as well as pure E-51 (Comparative Application Example 4). From Figure 3As can be seen from Table 1, E-51 with only 5wt% APP added did not show good flame retardant performance during combustion, that is, 5wt% APP did not significantly improve the flame retardant performance of the E-51 composite material. It did not have a rating in the UL-94 vertical burning test, mainly because APP, as an acid source, could not form carbon. After replacing APP with FAFD, with the increase in the content of FAFD, the flame retardant performance of the E-51 composite material was significantly improved, and the UL-94 rating increased from V-1 to V-0, proving that FAFD has a very large improvement in enhancing the flame retardant performance of the EP composite material. When FAFD was replaced with FADM, when only 4wt% was added, the flame retardant performance of the E-51 / FAMD composite material was significantly improved, and the UL-94 test rating reached V-0. With the increase in the addition amount, the flame retardant performance of the E-51 / FAMD composite material further increased, and the flame retardant effect of FAMD was significantly better than that of APP and FAFD.

[0172] (2) Cone calorimeter test

[0173] The cone calorimeter is the most ideal test instrument for characterizing the combustion performance of materials at present. Its test environment is close to the real combustion environment of fire materials, and the test data obtained can evaluate the combustion behavior of materials in a fire. In this test example, the size of the test sample is 10 cm × 10 cm × 3 mm, and the heat flux is 50 kW / m 2 . The cone calorimeter test results of the flame retardant EP composite materials of Application Example 2, Comparative Application Example 2, and pure E-51 (Comparative Application Example 4) are shown in Figure 4 , where a is the maximum heat release rate and b is the total heat release. It can be seen that the maximum heat release peak of the E-51 / 4wt% FADM composite material during combustion is significantly lower than that of pure E-51 and the E-51 / 4wt% FAFD composite material, proving that the addition of FADM has an obvious effect on improving the flame retardant performance of the E-51 composite material. Similarly, the total heat release in the test also has a significant decrease, proving that it has a very good flame retardant effect. This is mainly because the introduction of FADM makes the carbon layer more dense, achieving a better effect of protecting the internal matrix.

[0174] (3) Mechanical property test

[0175] The mechanical property test results (sampling and testing were carried out in accordance with ISO 527-2012) of the flame retardant EP composite materials of pure E-51 (Comparative Application Example 4), Application Examples 1-2, and Comparative Application Examples 1-3 are shown in Figure 5 , from Figure 5It can be seen that the tensile strength of pure E-51 is 53.1 MPa. When 5 wt% APP is added to E-51, the tensile strength decreases significantly to 45.1 MPa. When 5 wt% APP is replaced with 4 wt% FAFD, the tensile strength of the E-51 composite material increases to 47.7 MPa. As the content of FAFD increases, the mechanical properties of the E-51 composite material decrease to 46.2 MPa, mainly because the compatibility between FAFD and the E-51 matrix is poor, resulting in poor mechanical properties. The tensile strengths of the E-51 / 4 wt% FADM and E-51 / 5 wt% FADM composite materials are 60.3 MPa and 59.6 MPa, respectively. It can be seen that FADM has a very obvious promoting effect on improving the tensile strength of the E-51 composite material compared with FAFD and APP.

[0176] (4) Dielectric property and transparency tests

[0177] The test results of the dielectric properties and transparency of the flame-retardant EP composite materials of pure E-51 (comparative application example 4), application example 2, and comparative application example 2 are as Figure 6 shown, where a is the dielectric constant, b is the dielectric loss, and c is the transmittance. It can be seen that compared with pure E-51, the E-51 / FADM composite material has better dielectric properties, and both the dielectric constant and the dielectric loss are significantly reduced. This improvement is mainly attributed to the hollow structure of the FADM microspheres. Since the dielectric constant of air is relatively low (≈1), the cavities introduced by the FADM microspheres can effectively reduce the dielectric constant of the E-51 resin. In addition, due to the reaction between the epoxy groups and the anhydride groups and amino groups on the surface of FADM, a highly cross-linked network is formed, which effectively restricts the mobility of the molecular chains and inhibits the dipole movement. In addition, the good compatibility between FADM and the E-51 matrix can greatly reduce the interfacial polarization, thereby reducing the dielectric constant and the dielectric loss. The light transmittance is also an important factor in the practical application of the E-51 resin. The transmittances of E-51, E-51 / 4 wt% FAFD, and E-51 / 4 wt% FADM are 58.3%, 44.3%, and 53.1%, respectively. Obviously, the transmittances of all E-51 composite materials in the visible light region decrease significantly, which is mainly attributed to the light scattering effects of FAFD and FADM. More importantly, in the ultraviolet wavelength range, the transmittance of the E-51 composite material decreases sharply, indicating its excellent ultraviolet protection performance. The excellent ultraviolet shielding performance is mainly due to the presence of a high density of conjugated groups in the molecular structures of FAFD and FADM.

[0178] As can be seen from the above, FADM significantly improves the flame retardancy of E-51 composite materials, significantly reduces the heat release and smoke release of E-51 composite materials. Moreover, the rich anhydride groups on the surface of FADM also promote the compatibility between FADM and the E-51 matrix, improve its mechanical properties, and solve the problem that the poor compatibility between DOPO and the matrix leads to a decrease in mechanical properties. In addition, the regular hollow microspheres also endow the E-51 composite material with excellent dielectric properties and transparency (the transparency is improved compared with that when FAFD is added). The present invention provides an effective method for preparing multifunctional epoxy resin composite materials and expanding their application fields.

[0179] Application Example 3

[0180] A flame-retardant thermoplastic polymer composite material is prepared according to the following steps:

[0181] Take 34 g of PA66 and 6 g of FADM (prepared in Example 1), and blend them through a mixer. The temperature of the mixer is set at 220 °C, the rotation speed is 75 rpm, and the mixing time is 6 min. Then, use a flat vulcanizer to press and sample to obtain a flame-retardant thermoplastic polymer composite material, denoted as PA66 / 15wt% FADM.

[0182] Application Example 4

[0183] A flame-retardant thermoplastic polymer composite material is prepared according to the following steps:

[0184] Take 32 g of PE and 8 g of FADM (prepared in Example 1), and blend them through a mixer. The temperature of the mixer is set at 165 °C, the rotation speed is 75 rpm, and the mixing time is 6 min. Then, use a flat vulcanizer to press and sample to obtain a flame-retardant thermoplastic polymer composite material, denoted as PE / 20wt% FADM.

[0185] Application Example 5

[0186] A flame-retardant thermoplastic polymer composite material is prepared according to the following steps:

[0187] Take 34 g of PP and 6 g of FADM (prepared in Example 1), and blend them through a mixer. The temperature of the mixer is set at 175 °C, the rotation speed is 75 rpm, and the mixing time is 6 min. Then, use a flat vulcanizer to press and sample to obtain a flame-retardant thermoplastic polymer composite material, denoted as PP / 15wt% FADM.

[0188] Test Example 2

[0189] The flame-retardant thermoplastic polymer composite materials prepared in Application Examples 3-5 are subjected to UL-94 tests, and the results are shown in Table 2.

[0190] Table 2

[0191]

[0192] As can be seen from Table 2, FADM exhibits excellent flame retardancy in both PA66, PE, and PP. The UL-94 rating of all test samples is above V-1. This is mainly due to the fact that the PO· free radicals generated by DOPO in FADM during combustion can capture the combustible free radicals generated by thermoplastic polymers, and the dense carbon layer generated by FADM during combustion can further protect the internal matrix. The test results confirm that FADM also has excellent flame retardancy for thermoplastic polymers.

[0193] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of DOPO-based hollow polymer microspheres, characterized in that, It includes the following steps: Mix a DOPO-based flame retardant monomer, an acid anhydride monomer, a crosslinking agent, a polymer microsphere template, an initiator, and a solvent 1, and perform self-stabilized precipitation polymerization to obtain DOPO-based core-shell polymer microspheres; subject the DOPO-based core-shell polymer microspheres to solvent etching to obtain the DOPO-based hollow polymer microspheres.

2. The preparation method according to claim 1, wherein, The polymer microsphere template is an olefin - acid anhydride copolymer microsphere, an olefin - maleimide copolymer microsphere, a homopolymer microsphere of a styrene monomer, or a homopolymer microsphere of a (meth)acrylate monomer; And / or, the crosslinking agent includes divinylbenzene, diallylbenzene, diallyl acrylamide, diallyl amide, allyl glycidyl ether, triethylene glycol divinyl ether, diethylene glycol divinyl ether, diallyl phenol, divinyldimethylsiloxane, ethylene glycol diacrylate, ethylene glycol dimethacrylate, or trimethylolpropane triacrylate; And / or, the initiator is an azo initiator or a peroxide initiator; And / or, the solvent 1 includes an organic acid alkyl ester or a mixed solution of an alkane and an organic acid alkyl ester; And / or, the molar ratio of the acid anhydride monomer to the DOPO-based flame retardant monomer is 1:2 - 4; And / or, the molar amount of the crosslinking agent is 30 - 60% of the sum of the molar amounts of the acid anhydride monomer and the DOPO-based flame retardant monomer; And / or, the mass of the polymer microsphere template is the sum of the masses of the acid anhydride monomer and the DOPO-based flame retardant monomer; And / or, the mass of the initiator is 0.5 - 10% of the sum of the masses of the DOPO-based flame retardant monomer, the acid anhydride monomer, and the crosslinking agent.

3. The preparation method according to claim 2, characterized in that, The preparation steps of the olefin - acid anhydride copolymer microspheres include: mixing an acid anhydride monomer, an olefin, an initiator, and a solvent 2, and performing self-stabilized polymerization to obtain the olefin - acid anhydride copolymer microspheres; Or, the preparation steps of the olefin - maleimide copolymer microspheres include: mixing a maleimide monomer, an olefin, an initiator, and a solvent 2, and performing self-stabilized polymerization to obtain the olefin - acid anhydride copolymer microspheres.

4. The preparation method according to claim 1 or 3, characterized in that, The acid anhydride monomer includes one or more of maleic anhydride and itaconic anhydride.

5. The preparation method according to claim 3, wherein, The maleimide monomers include one or more of N,N'-(4,4'-methylenediphenyl)bismaleimide, N,N'-(4-methyl-1,3-phenylene)bismaleimide, 2,2'-bis[4-(4-maleimidophenoxy)phenyl]propane, N,N'-m-phenylene bismaleimide, N,N'-(1,4-phenylene)bismaleimide, 1,2-bis(maleimidyl)ethane, 1,3-bis(maleimidyl)propane, 1,4-bis(maleimidyl)butane, bis[4-(3-maleimidophenoxy)phenyl]sulfone, 1,4-bis(4-maleimidophenoxy)benzene, 1,4-bis(3-maleimidophenoxy)benzene, 3,4'-diphenyl ether bismaleimide, and 4,4'-diphenyl ether bismaleimide; And / or, the olefin includes one or more of styrene monomers, (meth)acrylate monomers, vinyl acetate, α-olefins, dicyclopentadiene, and ethylidene norbornene; And / or, the solvent 2 is one of an organic acid alkyl ester, a mixed solution of a ketone and an organic acid alkyl ester, a mixed solution of a ketone and an alkane, and a mixed solution of an alkane and an organic acid alkyl ester; And / or, the initiator is an azo initiator or a peroxide initiator.

6. A DOPO-based hollow polymer microsphere prepared by the preparation method according to any one of claims 1-5.

7. Use of the DOPO-based hollow polymer microsphere according to claim 6 in the preparation of a flame-retardant polymer.

8. A flame-retardant polymer composite, characterized in that, The flame-retardant polymer composite is a flame-retardant thermosetting composite or a flame-retardant thermoplastic polymer composite; the raw materials of the flame-retardant polymer composite include the DOPO-based hollow polymer microsphere according to claim 6.

9. The flame-retardant polymer composite material according to claim 8, wherein, By mass percentage, the raw materials of the flame-retardant thermosetting polymer composite include: 74-78% of a thermosetting polymer, 18-20% of a curing agent, and the balance of the DOPO-based hollow polymer microsphere according to claim 6; Or, by mass percentage, the raw materials of the flame-retardant thermoplastic polymer composite include: 70-95% of a thermoplastic polymer and the balance of the DOPO-based hollow polymer microsphere according to claim 6.

10. The preparation method of the flame-retardant polymer composite according to claim 9, wherein, Comprising the following steps: Mix the DOPO-based hollow polymer microsphere, the thermosetting polymer, and the curing agent, perform defoaming treatment, and then perform pre-curing and curing in sequence to obtain the flame-retardant thermosetting composite; Or, knead and blend the DOPO-based hollow polymer microsphere and the thermoplastic polymer, and then mold to obtain the flame-retardant thermoplastic polymer composite.

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