A cage type silicon phosphorus polymer flame retardant and a preparation method and application thereof

Abstract

The application discloses a cage type silicon-phosphorus polymer flame retardant and a preparation method and application thereof, and belongs to the technical field of flame retardant preparation. The preparation method comprises the following steps: dissolving a side chain phosphorus source, an epoxy silane and a skeleton phosphorus source in a solvent to obtain a mixed monomer solution; adding the mixed monomer solution into an acidic aqueous solution reaction medium to perform hydrolysis polycondensation reaction, thereby obtaining a flame retardant precursor; and adding a chain extender into the flame retardant precursor to perform chain extension reaction, thereby obtaining the cage type silicon-phosphorus polymer flame retardant. The application further discloses the cage type silicon-phosphorus polymer flame retardant prepared by the method and application thereof. The cage type silicon-phosphorus polymer flame retardant solves the problems of the existing fluorine-free flame retardant, such as insufficient load capacity, carbonization, mechanical property, optical transparency and anti-dripping effect, and has good practical value.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant preparation technology, specifically relating to a cage-type silicon-phosphorus polymer flame retardant, its preparation method, and its application. Background Technology

[0002] With the rapid development of industrial technology, high-performance engineering plastics such as polycarbonate (PC) and epoxy resin (EP) have become key basic materials in the fields of electronics and electrical engineering (E&E), aerospace, rail transportation, and new energy vehicles due to their excellent mechanical strength, heat resistance, and optical transparency. However, these carbon-chain polymers are inherently flammable materials, and their combustion is accompanied by severe melt dripping. Melt dripping not only accelerates the spread of fire, forming flowing fires, but also easily ignites underlying combustibles, making it one of the main culprits causing fires to escalate. To meet stringent flame retardant standards such as UL-94 V-0, the industry has developed a mature "flame retardant + anti-dripping agent" compound system. Among them, polytetrafluoroethylene (PTFE) and its derivatives, such as potassium perfluorobutane sulfonate and Rimar salts, are the absolute dominant anti-dripping agents. At extremely low addition levels (0.1~0.5 wt.%), PTFE can significantly increase melt viscosity by forming a fibrous physical network structure in the polymer melt, thereby effectively suppressing dripping. However, perfluorinated and polyfluorinated alkyl substances (PFAS) are known as permanent chemicals because of their extremely stable carbon-fluorine bonds (CF), which are difficult to degrade in the natural environment and pose a persistent threat to human health and ecosystems.

[0003] Currently, fluorine-free alternatives on the market mainly fall into two categories: phosphorus-based flame retardants and inorganic nanofillers. However, these solutions still have significant shortcomings in high-performance applications: First, to compensate for the lack of PTFE and its anti-dripping ability, it is usually necessary to significantly increase the amount of phosphate esters, such as bisphenol A bis(diphenyl phosphate) (BDP) and resorcinol bis(diphenyl phosphate) (RDP), to 15-30%. At a high filler content of wt.%, this strong plasticizing effect causes a sharp drop in the glass transition temperature of the plastic substrate, making it unable to meet the requirements of electronic device housings in terms of heat distortion temperature. Furthermore, it significantly deteriorates impact strength and tensile modulus, resulting in substantial loss of mechanical properties. Secondly, for applications requiring high transparency, such as display back panels and optical lenses, traditional inorganic anti-drip agents, such as nano-clay and fumed silica, cannot meet the actual requirements. This is because the refractive indices of inorganic fillers and organic resin matrices are mismatched, and nano-agglomeration is highly likely, leading to strong light scattering. This causes the originally transparent plastic substrate to become milky white or opaque, with a sharp decrease in light transmittance. In addition, while current fluorine-free flame retardant systems (such as sulfonates) can promote charring, the resulting char layer is often loose and porous, lacking sufficient mechanical strength to support molten polymer droplets. Without the support of a PTFE fiber network, relying solely on chemical charring makes it difficult to pass the stringent UL-94 vertical burning test.

[0004] Therefore, developing a structural fluorine-free flame retardant that integrates high flame retardancy, excellent anti-dripping properties, high transparency, and superior mechanical properties has become a challenge in the field of polymer materials science. Summary of the Invention

[0005] The problem to be solved by this invention is to provide a cage-type silicon-phosphorus polymer flame retardant, its preparation method and application, so as to solve the problems of insufficient loading capacity and char formation, poor mechanical properties, poor optical transparency and anti-dripping effect of existing fluorine-free flame retardants.

[0006] The technical solution adopted to solve its technical problem is a method for preparing a cage-type silicon-phosphorus polymer flame retardant, comprising the following steps: (1) Dissolve the side-chain phosphorus source, epoxy silane and skeletal phosphorus source in a solvent to obtain a mixed monomer solution; (2) The mixed monomer solution is added to the acidic aqueous solution reaction medium to carry out hydrolysis and polycondensation reaction to obtain the flame retardant precursor; (3) Add a chain extender to the flame retardant precursor to carry out a chain extension reaction, and a cage-type silicon-phosphorus polymer flame retardant is obtained.

[0007] The beneficial effects of the above-mentioned technical solution in this invention are as follows: In this invention, the skeletal phosphorus source provides phosphorus atoms that are directly embedded into the inorganic skeleton to form Si-OP bonds, the side-chain phosphorus source provides external gas-phase flame-retardant groups, and the epoxy silane, as a reactive site, provides the epoxy groups required for subsequent chain extension; the side-chain phosphorus source, epoxy silane, and skeletal phosphorus source are subjected to hydrolysis and condensation reaction in an acidic aqueous solution reaction medium to form a double-terminated epoxy T20 silicon-phosphorus precursor, and then the two epoxy groups retained on the T20 cage are used for chain extension to connect the dispersed T20 cages in series to form a cage-type silicon-phosphorus polymer flame retardant. It has a larger inorganic cage, can form more and more stable silica ceramic layers at high temperatures, provides a stronger physical barrier, and has 20 modifiable vertices, which is 2.5 times that of T8. It can graft a large number of intrinsic flame-retardant groups containing phosphorus and nitrogen, making a single T20 molecule a super-efficient flame-retardant node. This invention, without any fluorine content, uses molecular structure design to enable in-situ chemical cross-linking of flame retardants during combustion, providing melt strength sufficient to resist gravity, completely eliminating droplets, and replacing PTFE. It overcomes the limitation of the limited number of vertices in T8-type POSS, constructing a T20 high-dimensional cage with 20 vertices, significantly increasing the effective loading density of phosphorus and silicon per unit molecule. At the same time, it solves the problem of poor light transmittance of PC caused by traditional inorganic fillers, maintaining more than 90% light transmittance of the plastic matrix through refractive index matching and true nanoscale molecular dispersion. It also solves the problem of easy migration of small molecule flame retardants by converting cage-type monomers into high molecular weight polymers through a two-stage chain extension reaction, permanently anchoring them in the matrix network.

[0008] Preferably, in step (1), the side chain phosphorus source is a phosphorus-containing silane coupling agent; the epoxy silane is 3-glycidyloxypropyltrimethoxysilane or 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane; the skeleton phosphorus source is phenylphosphonodichloro and / or phenylphosphine dichloride; and the solvent is toluene or ethanol.

[0009] More preferably, the phosphorus-containing silane coupling agent is diethylphosphorylethyltriethoxysilane or DOPO-VTS; DOPO-VTS is prepared through the following steps: The product is obtained by mixing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and vinyltrimethoxysilane and carrying out a free radical addition reaction in the presence of an initiator.

[0010] The beneficial effects of the above-mentioned technical solution in this invention are as follows: utilizing the high reactivity of the PH bond in the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) molecule, a free radical addition reaction is carried out with vinyltrimethoxysilane (VTS) under the action of an initiator. This reaction follows the anti-Markovnikov rule, with the phosphorus atom attached to the terminal carbon of the vinyl group to form a stable PC bond.

[0011] More preferably, DOPO-VTS is prepared by the following steps: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was dissolved in a solvent at 80 °C. After adding an initiator and under an inert atmosphere, vinyltrimethoxysilane was added dropwise, followed by a free radical addition reaction to obtain the product.

[0012] More preferably, the molar ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, vinyltrimethoxysilane and initiator is 100:(70~80):(0.2~1).

[0013] More preferably, the molar ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, vinyltrimethoxysilane and initiator is 100:71.97:0.23.

[0014] More preferably, the solvent is toluene; the initiator is azobisisobutyronitrile or diisopropylbenzene peroxide.

[0015] More preferably, the dropping time is 3 h; the free radical addition reaction time is 18 h.

[0016] Preferably, the molar ratio of the side-chain phosphorus source, epoxy silane, and skeletal phosphorus source is (5.4~6.6):(1.8~2.2):(10.8~13.2); and the mass concentration of the mixed monomer solution is 2~10%.

[0017] More preferably, the molar ratio of the side-chain phosphorus source, the epoxy silane, and the skeletal phosphorus source is 6:2:12; and the mass concentration of the mixed monomer solution is 10%.

[0018] The beneficial effects of the above-mentioned technical solution in this invention are as follows: In order to form the T20 structure, the total silicon / phosphorus atom count of the reaction system is set to 20 equivalents; this ratio ensures that the cage framework contains up to 60% phosphorus, and that the cage surface has two active epoxy functional groups. The mixed monomer solution has a mass concentration of 10%, which is key to inhibiting random network condensation and promoting intramolecular ring-closed cage formation.

[0019] Preferably, step (2) includes the following steps: under stirring conditions and at -2~2℃, the mixed monomer solution is added dropwise to the acidic aqueous solution reaction medium, kept at -2~2℃ for 22~26 h, and then heated to 65~80℃ for reflux reaction for 4~6 h to obtain the flame retardant precursor.

[0020] The beneficial effects of the above-mentioned technical solution in this invention are as follows: the dropwise addition under low temperature conditions can significantly reduce the hydrolysis and condensation rate, allowing the intermediate sufficient time for conformational adjustment, and assembling into a cage-like structure according to the principle of minimum thermodynamic energy, rather than a kinetically controlled random polymer; after the dropwise addition is completed, low-temperature aging is carried out, followed by a reflux reaction at 65~80℃, in order to overcome steric hindrance and promote the condensation of the last unclosed hydroxyl groups in the cage, thus completing the final construction of the T20 cage.

[0021] More preferably, step (2) includes the following steps: under stirring conditions and at 0°C, the mixed monomer solution is added dropwise to the acidic aqueous solution reaction medium, kept at 0°C for 24 h, and then heated to 65°C and refluxed for 4 h to obtain the flame retardant precursor.

[0022] More preferably, the dropping rate is 500 mL / h.

[0023] More preferably, the acidic aqueous solution reaction medium is a mixture of butanone, concentrated hydrochloric acid and water; the volume ratio of butanone, concentrated hydrochloric acid and water is 1000:(10~20):(250~350).

[0024] More preferably, the volume ratio of butanone, concentrated hydrochloric acid and water is 1000:15:300.

[0025] The beneficial effects of the above technical solution adopted in this invention are as follows: in the acidic aqueous solution reaction medium, butanone serves as a good solvent, water serves as a hydrolyzing agent, and concentrated sulfuric acid serves as a catalyst to jointly form the reaction substrate for the hydrolysis and polycondensation reaction.

[0026] Preferably, in step (3), the chain extender is a monoamine compound with a benzene ring; the mass ratio of the flame retardant precursor to the chain extender is 100:(1~5); the chain extension reaction temperature is 30~80℃ and the time is 5.5~6.5 h.

[0027] The beneficial effects of the above-mentioned technical solution in this invention are as follows: This invention also carries out a chain extension reaction for the flame retardant precursor - silicon-phosphorus polymer. A monoamine compound with a benzene ring is used as a chain extender to undergo a linear chain extension reaction with the epoxy group of the silicon-phosphorus polymer, thereby increasing the molecular weight and enhancing the anti-drop performance. The benzene ring of the chain extender can impart compatibility and heat resistance to plastics. The monoamine group ensures that only a chain extension reaction will occur with the silicon-phosphorus polymer, without cross-linking, so that the synthesized polymer is infusible and insoluble and will not disperse in the plastic matrix.

[0028] More preferably, the mass ratio of flame retardant precursor to chain extender is 100:(2~5); the chain extension reaction temperature is 80°C and the time is 6 h.

[0029] More preferably, the flame retardant precursor is dissolved in toluene and then a chain extender is added to carry out a chain extension reaction.

[0030] More preferably, the chain extender is at least one selected from aniline, o-toluidine, m-toluidine, p-toluidine, 1-naphthylamine, and 2,6-dimethylaniline.

[0031] The present invention also provides a cage-type silicon-phosphorus polymer flame retardant prepared by the above preparation method.

[0032] The beneficial effects of the above-mentioned technical solution of the present invention are as follows: The cage-type silicon-phosphorus polymer flame retardant obtained by the present invention is a T20 cage-type silicon-phosphorus polymer flame retardant, which is a phosphorus-containing organosilicon polymer with a phosphorus-containing inner skeleton, phosphorus-attached outer branches, and double-ended epoxy active chain extenders. Its inorganic cage skeleton is composed of Si-O-Si bonds and Si-OP bonds. The cage body is grafted with organophosphorus side chains containing DOPO structure. The cage bodies are connected by organic chain segments formed by the reaction of chain extenders and epoxy groups, and it is in the form of a linear polymer.

[0033] This invention also provides the application of cage-type silicon-phosphorus polymer flame retardants in engineering plastics as fluorine-free flame retardants or fluorine-free anti-dripping agents, or in the preparation of V-0 grade flame retardant materials.

[0034] Preferably, the engineering plastic is polycarbonate, epoxy resin or polybutylene terephthalate.

[0035] Preferably, the amount of cage-type silicon-phosphorus polymer flame retardant added to the engineering plastic is 2 wt.%.

[0036] The present invention has the following beneficial effects: (1) The cage-type silicon-phosphorus polymer flame retardant of the present invention achieves spatial differential distribution of phosphorus through molecular engineering. The condensed phase (internal skeleton phosphorus) is directly formed by phosphorus atoms introduced from the skeleton phosphorus source to form the cage skeleton (Si-OP). At high temperature, this structure is transformed in situ into an extremely stable phosphosilicate glass. This ceramic layer is more dense and has lower porosity than traditional siloxane (silicon dioxide), and has the ability to heal cracks at high temperature flow, and can perfectly isolate oxygen and heat. Its gas phase (external branched phosphorus) is connected by the side chain phosphorus source groups on the outside through relatively weak PC bonds. In the early stage of fire (300~350℃), it breaks and releases PO· free radicals, which efficiently capture H· and OH· free radicals in the flame and cut off the combustion chain reaction. This mechanism enables the cage-type silicon-phosphorus polymer flame retardant of the present invention to achieve UL-94 V-0 rating for 0.8mm thin-walled PC when the addition amount is only 1.5~3.0 wt.%, and the flame retardant efficiency is far superior to T8 type POSS (usually >5~8 wt.%).

[0037] (2) Traditional fluorine-free flame retardants drip because they cannot form a network structure. The cage-type silicon-phosphorus polymer flame retardant of the present invention is in the form of a linear polymer in the plastic substrate. Due to the strong physical entanglement and anchoring effect between the huge T20 side groups (nanocages), it has a high melt viscosity enhancement effect. More importantly, the reserved terminal epoxy groups trigger chemical cross-linking at high combustion temperature, causing the melt to instantly change from thermoplastic to partially thermosetting, forming an elastic carbon capsule that firmly locks the melt, achieving drip-free or even completely drip-free performance, perfectly replacing the function of traditional polytetrafluoroethylene anti-dripping agents.

[0038] (3) A large number of phenyl groups are introduced into the molecular design of this invention, which adjusts the refractive index of the flame retardant to be extremely close to that of the plastic substrate. Combined with the inherent nanoscale of the side chain phosphorus source (such as POSS), the Rayleigh scattering source is eliminated. The plastic substrate with this flame retardant has better light transmittance, which solves the problem of opacity caused by traditional inorganic fillers.

[0039] (4) The cage-type silicon-phosphorus polymer flame retardant of the present invention is completely free of fluorine, bromine and chlorine (the finished product has a Cl content of <50ppm), which fully complies with the latest restrictions on PFAS under the EU REACH regulation and the RoHS directive. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of this invention, and not all of them.

[0041] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0042] The features and performance of the present invention will be further described in detail below with reference to the embodiments. The reagents used in this description are analytical grade reagents and high-purity electronic grade solvents.

[0043] Example 1 A method for preparing a cage-type silicon-phosphorus polymer flame retardant includes the following steps: (1) 216.2 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 500 mL of toluene were added to a 1 L three-necked flask and heated to 80 °C to dissolve. Then 0.5 g of azobisisobutyronitrile (AIBN) was added. Under nitrogen protection, 155.6 g of vinyltrimethoxysilane (VTS) was added dropwise over 3 h. The free radical addition reaction was then carried out for 18 h to obtain the phosphorus-containing silane precursor, namely DOPO-VTS (molecular weight 364.41). (2) Take 0.6 mol DOPO-VTS (218.64 g) and add 47.3 g (0.2 mol) of 3-glycidyloxypropyltrimethoxysilane (GPTMS) and 234 g (1.2 mol) of phenylphosphonodichloro (PPDC). Add toluene to a total mass of 5000 g to obtain a mixed monomer solution with a mass concentration of 10%. (3) Add 1000 mL of butanone, 300 mL of deionized water, and 15 mL of concentrated hydrochloric acid to a 5 L reactor. Cool to 0 °C. Under stirring, add the mixed monomer solution dropwise to the reactor over 6 h. After the addition is complete, keep the reactor at 0 °C for 24 h, then raise the temperature to 65 °C and reflux for 4 h. Cool, separate the liquids, wash the organic phase with water until neutral, and dry to obtain the flame retardant precursor. The synthesis route is as follows: ; (4) Add 200 g of toluene to 100 g of flame retardant precursor, dissolve and clarify at 80°C, add 5 g of aniline, carry out chain extension reaction at 80°C for 6 h, remove all solvents by vacuum drying, and obtain a pale yellow solid product, cage-type silicon-phosphorus polymer flame retardant, with a yield of 95%, denoted as FR-1.

[0044] Example 2 A method for preparing a cage-type silicon-phosphorus polymer flame retardant includes the following steps: (1) Add 216.2 g DOPO and 500 mL toluene to a 1 L three-necked flask, heat to 80 °C to dissolve, then add 0.5 g AIBN, and under nitrogen protection, add 155.6 g VTS dropwise over 3 h. Then carry out a free radical addition reaction for 18 h to obtain the phosphorus-containing silane precursor, namely DOPO-VTS. (2) Take 0.6 mol DOPO-VTS (218.64 g) and add 49.3 g (0.2 mol) of 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane (ECETS) and 234 g (1.2 mol) of PPDC, and add toluene to a total mass of 5000 g to obtain a mixed monomer solution with a mass concentration of 10%. (3) Add 1000 mL of butanone, 300 mL of deionized water and 15 mL of concentrated hydrochloric acid to a 5 L reactor, cool to 0°C, and add the mixed monomer solution dropwise into the reactor over 6 h under stirring. After the addition is complete, keep the temperature at 0°C for 24 h, then raise the temperature to 65°C and reflux for 4 h. Cool, separate the liquids, wash the organic phase with water until neutral, and dry to obtain the flame retardant precursor. (4) Add 200 g of toluene to 100 g of flame retardant precursor, dissolve and clarify at 80°C, add 3 g of o-toluidine, carry out chain extension reaction at 80°C for 6 h, remove all solvents by vacuum drying, and obtain a pale yellow solid product, cage-type silicon-phosphorus polymer flame retardant, denoted as FR-2.

[0045] Example 3 A method for preparing a cage-type silicon-phosphorus polymer flame retardant includes the following steps: (1) Add 216.2 g DOPO and 500 mL toluene to a 1 L three-necked flask, heat to 80 °C to dissolve, then add 0.5 g AIBN, and under nitrogen protection, add 155.6 g VTS dropwise over 3 h. Then carry out a free radical addition reaction for 18 h to obtain the phosphorus-containing silane precursor, namely DOPO-VTS. (2) Take 0.6 mol DOPO-VTS (218.64 g) and add 47.3 g (0.2 mol) GPTMS and 234 g (1.2 mol) PPDC, and add toluene to a total mass of 5000 g to obtain a mixed monomer solution with a mass concentration of 10%; (3) Add 1000 mL of butanone, 300 mL of deionized water and 15 mL of concentrated hydrochloric acid to a 5 L reactor, cool to 0°C, and add the mixed monomer solution dropwise into the reactor over 6 h under stirring. After the addition is complete, keep the temperature at 0°C for 24 h, then raise the temperature to 65°C and reflux for 4 h. Cool, separate the liquids, wash the organic phase with water until neutral, and dry to obtain the flame retardant precursor. (4) Add 200 g of toluene to 100 g of flame retardant precursor, dissolve and clarify at 80°C, add 3 g of p-toluidine, heat to 80°C for chain extension reaction for 6 h, and vacuum dry to remove all solvents to obtain a pale yellow solid product, cage-type silicon-phosphorus polymer flame retardant, denoted as FR-3.

[0046] Example 4 A method for preparing a cage-type silicon-phosphorus polymer flame retardant includes the following steps: (1) Add 216.2 g DOPO and 500 mL toluene to a 1L three-necked flask, heat to 80℃ to dissolve, then add 0.5 g AIBN, and under nitrogen protection, add 155.6 g VTS dropwise over 3 h, and then carry out a free radical addition reaction for 18 h to obtain the phosphorus-containing silane precursor, namely DOPO-VTS; (2) Take 0.6 mol DOPO-VTS (218.64 g) and add 47.3 g (0.2 mol) of 3-glycidyloxypropyltrimethoxysilane (GPTMS), 195 g (1 mol) of PPDC and 35.8 g (0.2 mol) of phenylphosphine dichloride. Add toluene to a total mass of 5000 g to obtain a mixed monomer solution with a mass concentration of 10%. (3) Add 1000 mL of butanone, 300 mL of deionized water and 15 mL of concentrated hydrochloric acid to a 5 L reactor, cool to 0°C, and add the mixed monomer solution dropwise into the reactor over 6 h under stirring. After the addition is complete, keep the temperature at 0°C for 24 h, then raise the temperature to 65°C and reflux for 4 h. Cool, separate the liquids, wash the organic phase with water until neutral, and dry to obtain the flame retardant precursor. (4) Add 200 g of toluene to 100 g of flame retardant precursor, dissolve and clarify at 80°C, add 2 g of 2,6-dimethylaniline, carry out chain extension reaction at 80°C for 6 h, remove all solvents by vacuum drying, and obtain a pale yellow solid product, cage-type silicon-phosphorus polymer flame retardant, denoted as FR-4.

[0047] Example 5 A method for preparing a cage-type silicon-phosphorus polymer flame retardant includes the following steps: (1) Add 216.2 g DOPO and 500 mL toluene to a 1L three-necked flask, heat to 80℃ to dissolve, then add 0.5 g AIBN, and under nitrogen protection, add 155.6 g VTS dropwise over 3 h, and then carry out a free radical addition reaction for 18 h to obtain the phosphorus-containing silane precursor, namely DOPO-VTS; (2) Take 0.6 mol DOPO-VTS (218.64 g) and add 47.3 g (0.2 mol) GPTMS and 234 g (1.2 mol) PPDC, and add toluene to a total mass of 5000 g to obtain a mixed monomer solution with a mass concentration of 10%; (3) Add 1000 mL of butanone, 300 mL of deionized water and 15 mL of concentrated hydrochloric acid to a 5 L reactor, cool to 0°C, and add the mixed monomer solution dropwise into the reactor over 6 h under stirring. After the addition is complete, keep the temperature at 0°C for 24 h, then raise the temperature to 65°C and reflux for 4 h. Cool, separate the liquids, wash the organic phase with water until neutral, and dry to obtain the flame retardant precursor. (4) Add 200 g of toluene to 100 g of flame retardant precursor, dissolve and clarify at 80°C, add 2 g of p-toluidine, carry out chain extension reaction at 80°C for 6 h, remove all solvents by vacuum drying, and obtain a pale yellow solid product, cage-type silicon-phosphorus polymer flame retardant, denoted as FR-5.

[0048] Experimental Example The cage-type silicon-phosphorus polymer flame retardant prepared in the examples was applied to polycarbonate (PC) for performance testing.

[0049] The plastic substrate used is optical-grade PC (Covestro Makrolon 2805) with a melt flow rate (MVR) of 10. The following experiment was conducted: Blank group: Pure PC; Comparative group 1: Traditional T8 cage-type flame retardant, PC + 2 wt.% T8 type DOPO-POSS (Preparation method is from: Liu Xinghua, Zhao Xiaojuan, Li Shengnan, et al. Synthesis of phosphorus-containing cage-mesh structure polyhedral oligomeric silsesquioxane flame retardant and its flame retardant epoxy resin properties [J]. Journal of Beijing University of Chemical Technology (Natural Science Edition), 2020, 47(6): 62-72.); Comparative Group 2: Fluorinated flame retardant, PC + 10.0 wt.% BDP + 0.5 wt.% PTFE (simulating traditional opaque V-0 formulation); Comparative Group 3: Fluorinated flame retardant, PC + 5.0 wt.% BDP + 0.2 wt.% PTFE + 15 wt.% kaolin (simulating traditional opaque V-0 formulation); Experimental groups 1-3: PC + 2 wt.% of FR-1, FR-2 and FR-5 prepared in Examples 1, 2 and 5 of this invention, respectively.

[0050] The twin-screw extrusion granulation method was used, and the standard specimens were injection molded for performance testing. The test standards and test results are shown in Table 1.

[0051] Table 1. Test results of flame retardant performance

[0052] As can be seen from the results in Table 1 above, the cage-type silicon-phosphorus polymer flame retardant prepared by the present invention achieved complete non-dripping in the 0.8 mm thin-wall combustion test without the addition of PTFE. This confirms that the "double-ended epoxy chain extender + T20 large cage" structure of the present invention successfully constructed a cross-linked network that is strong enough to resist gravity at high temperature, solving the defect of traditional T8 type DOPO-POSS that cannot resist dripping.

[0053] Compared to the control group 2 (traditional PTFE solution) which resulted in completely opaque material, the light transmittance of the cage-type silicon-phosphorus polymer flame retardant of the present invention is almost the same as that of pure PC, with a decrease of only about 0.5%. This is due to the high refractive index design and nanoscale dispersion of T20 molecules, which perfectly solves the optical loss problem caused by existing inorganic filler flame retardants.

[0054] The T8 structure in comparison group 1 is a cage with a cubic geometry, offering only eight vertices for modification. The number of phosphorus elements a single nanoparticle can carry is fixed, with a maximum of eight DOPO groups. Therefore, at the same addition amount, V-0 flame retardancy cannot be achieved. Furthermore, the inorganic core of the T8 cage is relatively small. In the early stages of high-temperature combustion, the resulting silica layer is thin and discontinuous, with all phosphorus elements located on the external organic side chains. During thermal decomposition, the side-chain phosphorus groups often break and volatilize into the gas phase before the cage itself, resulting in a lack of sufficient phosphate source in the condensed phase to catalyze the formation of a dense phosphosilicate glass from the siloxane framework, failing to form a robust "ceramic armor" to block molten droplets. Additionally, T8-type DOPO-POSS is typically a crystalline powder with a high melting point, exhibiting limited compatibility with amorphous PC matrices. During injection molding or long-term use, small-molecule POSS easily migrates to the material surface, causing blooming, severely affecting the product's appearance and surface coating performance. Moreover, T8... POSS is essentially a single-molecule micro / nano filler, lacking a mechanism for chemical cross-linking or physical entanglement with the long chains of the polymer matrix. In the molten state during combustion, it cannot provide the high-viscosity network support found in PTFE, thus its anti-dripping effect is extremely limited, only reaching V-1 or V-2 levels. The cage-type silicon-phosphorus polymer flame retardant of this invention only requires an addition of 2 wt.% to achieve a V-0 level, and its LOI value is as high as 36%, significantly better than control group 1. This verifies the high efficiency of the dual-source synergistic mechanism of skeletal phosphorus and side-chain phosphorus.

[0055] Furthermore, due to the extremely low addition amount and the good compatibility of the molecular structure with PC, the impact strength retention rate of experimental groups 1-3 is as high as 95% or more, which is far superior to the traditional high-filling flame retardant solution.

[0056] In summary, through unique molecular structure design, this invention has successfully developed an ideal flame retardant that simultaneously meets four stringent requirements: fluorine-free compliance, high-efficiency flame retardancy, self-drip resistance, and high transparency, and has extremely high industrial application value.

[0057] The present invention has been described according to the above embodiments. It should be understood that the above embodiments do not limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the scope of the present invention.

Claims

1. A method for preparing a cage-type silicon-phosphorus polymer flame retardant, characterized in that, Includes the following steps: (1) Dissolve the side-chain phosphorus source, epoxy silane and skeletal phosphorus source in a solvent to obtain a mixed monomer solution; (2) The mixed monomer solution is added to the acidic aqueous solution reaction medium to carry out hydrolysis and polycondensation reaction to obtain the flame retardant precursor; (3) Add a chain extender to the flame retardant precursor to carry out a chain extension reaction, and a cage-type silicon-phosphorus polymer flame retardant is obtained.

2. The preparation method of the cage-type silicon-phosphorus polymer flame retardant as described in claim 1, characterized in that, In step (1), the side-chain phosphorus source is a phosphorus-containing silane coupling agent; the epoxy silane is 3-glycidyloxypropyltrimethoxysilane or 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane; the skeleton phosphorus source is phenylphosphonodichloro and / or phenylphosphine dichloride; and the solvent is toluene or ethanol.

3. The preparation method of the cage-type silicon-phosphorus polymer flame retardant as described in claim 2, characterized in that, The phosphorus-containing silane coupling agent is diethylphosphorylethyltriethoxysilane or DOPO-VTS; The DOPO-VTS is prepared through the following steps: The product is obtained by mixing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and vinyltrimethoxysilane and carrying out a free radical addition reaction in the presence of an initiator.

4. The preparation method of the cage-type silicon-phosphorus polymer flame retardant as described in claim 1 or 3, characterized in that, The molar ratio of the side-chain phosphorus source, epoxy silane, and skeletal phosphorus source is (5.4~6.6):(1.8~2.2):(10.8~13.2); the mass concentration of the mixed monomer solution is 2~10%.

5. The preparation method of the cage-type silicon-phosphorus polymer flame retardant as described in claim 1, characterized in that, Step (2) includes the following steps: under stirring conditions and at -2~2℃, the mixed monomer solution is added dropwise to the acidic aqueous solution reaction medium, kept at -2~2℃ for 22~26 h, and then heated to 65~80℃ for reflux reaction for 4~6 h to obtain the flame retardant precursor.

6. The method for preparing the cage-type silicon-phosphorus polymer flame retardant as described in claim 1 or 5, characterized in that, The acidic aqueous solution reaction medium is composed of a mixture of butanone, concentrated hydrochloric acid and water; the volume ratio of butanone, concentrated hydrochloric acid and water is 1000:(10~20):(250~350).

7. The preparation method of the cage-type silicon-phosphorus polymer flame retardant as described in claim 1, characterized in that, In step (3), the chain extender is a monoamine compound with a benzene ring; the mass ratio of the flame retardant precursor to the chain extender is 100:(1~5); the chain extension reaction temperature is 30~80℃ and the time is 5.5~6.5 h.

8. The method for preparing the cage-type silicon-phosphorus polymer flame retardant as described in claim 7, characterized in that, The chain extender is at least one of aniline, o-toluidine, m-toluidine, p-toluidine, 1-naphthylamine, and 2,6-dimethylaniline.

9. The cage-type silicon-phosphorus polymer flame retardant prepared by the preparation method according to any one of claims 1 to 8.

10. The cage-type silicon-phosphorus polymer flame retardant of claim 9 is used in engineering plastics as a fluorine-free flame retardant or a fluorine-free anti-dripping agent, or in the preparation of V-0 grade flame retardant materials.

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