Novel halogen-free flame retardant and preparation method and application thereof

Abstract

The application belongs to the field of organic polymer compounds, and relates to a novel halogen-free flame retardant and a preparation method and application thereof. Specifically disclosed is a flame retardant with a structure of formula I, wherein R1 is an aryl phosphine-containing fragment formed by nucleophilic ring-opening addition reaction of an epoxy group and a P-H bond on an aryl phosphine derivative, R2 is a boric acid group-containing fragment formed by nucleophilic ring-opening addition reaction of an epoxy group and a boric acid derivative, and R3 is R1 or R2. Compared with the prior art, the application provides a novel halogen-free flame retardant containing phosphorus macromolecules with a structure of formula I, which has good flame retardant effect when applied in a flame-retardant polymer material. The flame retardant of the application can be used for flame-retardant modification of a thermoplastic resin composition, and can achieve a V-0 flame-retardant grade of 3.2 mm. Since the flame retardant of formula I belongs to a macromolecular flame retardant, the activity space is limited in the thermoplastic resin composition, the diffusion rate is low, and the flame retardant is difficult to migrate to the surface, so the precipitation problem in the processing process can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of organic polymer compounds, specifically relating to novel halogen-free flame retardants, their preparation methods, and applications. Background Technology

[0002] Among halogen-free flame retardants, phosphorus-based flame retardants have relatively low flame retardant efficiency when used alone, and are usually used in combination with synergists. Synergists can significantly reduce the amount of phosphorus-based flame retardant added, improve flame retardant efficiency, optimize char layer structure, and suppress dripping and smoke generation. Common synergists include nitrogen-based, silicon-based, sulfur-based, and metal salts. Among them, nitrogen-based synergists are the most commonly used synergistic system for phosphorus-based flame retardants, such as melamine, melamine polyphosphate (MPP), and melamine cyanurate (MCA). Their synergistic mechanism is gas-phase dilution and foaming enhancement. The nitrogen source decomposes upon heating, releasing non-combustible gases, diluting the oxygen concentration in the combustion zone, and simultaneously synergistically forming an expanded char layer with the phosphorus source, improving the char layer thickness and thermal insulation.

[0003] However, this type of compound system is a physical compound. Although it can improve performance, the inherent properties of different flame retardant components, such as polarity, particle size, and thermal stability, are very different. This can easily lead to uneven dispersion, poor compatibility, and interface defects, which in turn can cause problems such as decreased mechanical properties, reduced migration resistance, and insufficient long-term stability of the material. At the same time, some flame retardants are prone to precipitation and decomposition of some components during processing, which affects the appearance and service life of the material and makes it difficult to meet the stringent requirements of high-end fields for the comprehensive performance of flame retardant materials.

[0004] Therefore, there is a need to develop new halogen-free flame retardants. Summary of the Invention

[0005] To address one of the technical problems existing in the aforementioned physically compounded flame retardant systems, the present invention aims to provide a novel halogen-free flame retardant with good flame retardant effect, its preparation method, and its application. This is specifically achieved through the following technical solution: Novel halogen-free flame retardants, including flame retardants with Formula I structure: Formula I In the formula, R1 is an arylphosphine-containing fragment formed by a nucleophilic ring-opening addition reaction between an epoxy group and a PH bond on an arylphosphine derivative, R2 is a borate-containing fragment formed by a nucleophilic ring-opening addition reaction between an epoxy group and a boric acid derivative, and R3 is either R1 or R2.

[0006] Optionally, R1 is selected from one of formulas II (1) to (3). Formula II In the formula, • ​​represents the connection site.

[0007] Optionally, R2 is selected from one of formulas II (4) to (7). Formula III In the formula, • ​​represents the connection site.

[0008] Optionally, the intermediate formed by the nucleophilic ring-opening addition reaction of triglycidyl isocyanurate (TGIC, also known as 1,3,5-triglycidyl-S-triazinetrione) and the PH bond on an arylphosphine derivative is prepared by the nucleophilic ring-opening addition reaction of the intermediate with a boric acid derivative.

[0009] Optionally, the arylphosphine derivative includes one or more of diphenylphosphine oxide (DPO), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and 6H-dibenzo[c,e][1,2]azaphosphacyclohexene-6-oxide (DPPA).

[0010] Optionally, the boric acid derivative includes one or more of boric acid, phenylboronic acid, methylboronic acid, and phenylethylboronic acid.

[0011] The present invention also provides a method for preparing a flame retardant according to any of the above technical solutions, comprising the following steps: The intermediate formed by the nucleophilic ring-opening addition reaction of triglycidyl isocyanurate and the PH bond on the arylphosphine derivative is then reacted with a boric acid derivative via a nucleophilic ring-opening addition reaction to obtain the flame retardant described in Formula I.

[0012] Optionally, the molar ratio of the triglycidyl isocyanurate to the arylphosphine derivative is 1:(1~2).

[0013] Optionally, the molar ratio of the intermediate to the boric acid derivative is 1:(1~2).

[0014] Optionally, the nucleophilic ring-opening addition reaction is carried out at a temperature of 150~170℃ for 3~6 hours.

[0015] Optionally, the nucleophilic ring-opening addition reaction temperature is 75~95℃, and the reaction time is 4~6h.

[0016] The present invention also provides the application of the flame retardant according to any of the above technical solutions, as a non-reactive flame retardant for flame-retardant polymer materials.

[0017] Optionally, the flame-retardant polymer material is a thermoplastic resin composition, which includes one or more compositions with polyamide resin, polyester resin, and polyolefin resin as the matrix.

[0018] Optionally, the thermoplastic resin composition may further include one or more of antioxidants, lubricants, toughening agents, antistatic agents, laser marking agents, and color powders.

[0019] Optionally, the thermoplastic resin composition further includes a compounded flame retardant, which includes one or more of the following: nitrogen-based, phosphorus-based, boron-based, silicon-based, and sulfur-based flame retardants, excluding those of Formula I. Those skilled in the art can reduce the amount of Formula I flame retardant and increase the amount of the compounded flame retardant as needed to obtain the desired flame retardant effect. For example, if gas-phase flame retardancy is required, it can be compounded with a nitrogen-based flame retardant; if charring flame retardancy is required, it can be compounded with a silicon-based flame retardant.

[0020] Optionally, the thermoplastic resin composition comprises, by weight, the following components: 45-85 parts of thermoplastic resin; 0-30 parts of reinforcing filler; Formula I flame retardant 15-25 parts; The sum of the above components in the composition is 100 parts by weight, and the 3.2mm flame retardant rating of the thermoplastic resin composition is V-0. Those skilled in the art may add other additives as needed, such as antioxidants, lubricants, toughening agents, antistatic agents, laser marking agents, color powders, etc. It is emphasized here that the aforementioned three components only need to be 100 parts by weight.

[0021] Optionally, the polyamide resin includes one or more of PA6, PA66, PA6 / 66 copolymer, PA66 / 6 copolymer, PA46, PA610, PA612, PA1010, PA6T, PA9T, PA10T, PA4T, PA11T, PA56, PA11, PA12, MXD6, etc.

[0022] Optionally, the polyester resin includes one or more of PBT, PET, PC, etc., and copolymers containing one of them.

[0023] Optionally, the polyolefin resin includes one or more of PP, PE, POE, EVA, etc., and copolymers containing one of them.

[0024] Optionally, the thermoplastic resin composition may further include a composition with ABS as the resin matrix.

[0025] Compared with the prior art, the present invention provides a novel halogen-free flame retardant with a phosphorus-containing macromolecule of Formula I, which has good flame retardant effect when applied to flame-retardant polymer materials.

[0026] The "wick effect" in fiber-reinforced composites refers to the phenomenon where fibers act like the wick in a candle, igniting and guiding the flame. When heated, the surface of the material melts, and the molten liquid moves along the fibers towards higher temperatures. Upon reaching the fiber tips, it vaporizes, generating combustible molecules that burn. The heat of combustion further promotes the melting of the matrix material and its movement towards the flame, creating a continuous cycle that sustains combustion. Therefore, in fiber-reinforced composites, the fibers promote combustion, making it more difficult to achieve high flame retardancy ratings. Research on flame retardancy in fiber-reinforced composites requires not only determining the flame retardant and retardant method based on the properties of the matrix material but also considering ways to eliminate the "wick effect" of the fibers to better achieve the desired flame retardant effect.

[0027] In this invention, a nucleophilic ring-opening addition reaction between a boric acid derivative and an intermediate is further utilized to introduce the boric acid derivative group into a macromolecular flame retardant of formula I. Through the synergistic effect of phosphorus, nitrogen, and boron—especially the synergistic effect of phosphorus, nitrogen, and boron within the same molecular structure—the flame retardant decomposes to generate phosphorus-oxygen free radicals with quenching activity and nitrogen-containing gases with diluting activity. It also generates borophosphates with a glassy capping layer effect. The simultaneous action of phosphorus and boron promotes the conversion of the substrate into residual char with a POB cross-linked network structure, which helps to construct a denser and stronger carbon skeleton. A glassy carbon protective layer is formed on the substrate surface, improving the high-temperature resistance of the individual phosphorus-containing carbon layer, isolating oxygen and combustible gas concentrations, and restricting melt flow on the glass fiber surface. This restricts melt flow and reduces mass loss, further improving flame retardant performance and achieving anti-dripping properties. Compared to simple physical compounding, it exhibits better condensed phase and gas phase activity. Simultaneously, phosphorus and nitrogen elements are transformed into phosphorus-oxygen free radicals with quenching activity and nitrogen-containing gases with diluting effects, extinguishing the flame at the fiber location and thus reducing the "wick effect" caused by fiber-reinforced thermoplastic resin compositions. This allows for a V-0 flame retardant rating even in high-component fiber-reinforced thermoplastic resin compositions. Furthermore, the boric acid derivative groups introduce boron and nitrogen / powder elements into the same molecular structure, resulting in closer spatial proximity and easier synergistic effects with nitrogen / powder, leading to even better results.

[0028] This invention introduces boric acid derivative groups into the macromolecular flame retardant of formula I through a nucleophilic ring-opening addition reaction, so that the epoxy group is ring-opened but the hydroxyl group is retained, which has the following advantages: (1) Catalytic dehydration and carbonization: When heated, the hydroxyl groups undergo a condensation reaction to dehydrate, which promotes the cross-linking and carbonization of the polymer chain, and quickly forms a dense and porous carbon layer, which isolates oxygen and heat transfer and inhibits the escape of combustible gases; (2) Heat absorption and cooling: The process of hydroxyl dehydration and release of crystal water absorbs a large amount of heat, reduces the surface temperature of the material, and slows down the thermal decomposition rate; (3) Enhanced interfacial compatibility: The hydroxyl group is a reactive functional group, which can undergo condensation or grafting reaction with the amide group or terminal amino / carboxyl group on the polyamide molecular chain, so that the flame retardant is chemically bonded to the matrix, preventing precipitation, improving heat resistance and long-lasting flame retardancy; (4) Improved processing dispersion: The polar hydroxyl group increases the affinity between the flame retardant and the polar polyamide matrix, optimizes the dispersion uniformity, and reduces the decline in mechanical properties caused by poor compatibility.

[0029] This invention, a flame retardant of Formula I, exhibits higher thermal stability (specifically manifested in a higher melting temperature and a higher initial decomposition temperature), and has a wider range of applications. It can be used not only in thermosetting epoxy resin compositions with lower requirements but is also suitable for thermoplastic resins with higher thermal stability requirements (such as PA66, whose processing temperature is typically around 270°C). Thermoplastic resins are conventionally processed using high-temperature melt processing techniques such as extrusion and injection molding, with processing temperatures generally above 200°C. Liquid / viscous additives are highly volatile and decompose at these high temperatures, even producing toxic gases and compromising processing stability. Such additives are difficult to disperse uniformly with molten thermoplastic resins, easily leading to localized agglomeration, clogging the injection molding machine's feed inlet and mold runner, and significantly increasing the scrap rate.

[0030] The flame retardant of Formula I of this invention is used for flame retardant modification of thermoplastic resin compositions, achieving a flame retardant rating of V-0 at a thickness of 3.2 mm. Since the Formula I flame retardant is a macromolecular flame retardant, its activity space in the thermoplastic resin composition is limited, resulting in a low diffusion rate and difficulty in migrating to the surface, thus reducing precipitation problems during processing.

[0031] Furthermore, when diphenylphosphine oxide (DPO) is selected as the arylphosphine derivative, the problem of DPO's inability to be used as a flame retardant in thermoplastic resins can be solved. The reasons are as follows: DPO is a single-component organophosphorus flame retardant with high phosphorus content and good flame retardant effect. It exhibits high gas-phase activity, but due to its low melting temperature (approximately 56°C), it typically exists in a liquid / solid state, making it inconvenient to handle and limiting its use to epoxy resin flame retardancy. It cannot be used in thermoplastic resins for the following reasons: 1) In the thermoplastic resin processing environment, if the processing site temperature is high, or the frictional heat during the mixing process causes DPO to exist in a liquid state with a certain viscosity, it will cause particle agglomeration, resulting in uneven dispersion. It is also easy to bridge during the feeding process and is easy to remain on the mixing equipment, making cleaning difficult. 2) DPO is a secondary phosphine oxide. Its PH bond is highly reactive and readily reacts with oxygen in the air. For example, at 165°C, its oxidation products are corresponding phosphoric acid derivatives (phenylphosphine acid or its anhydrides) and diphenylphosphine, etc. The introduction of oxygen atoms macroscopically results in an increase in mass. Epoxy resins typically have curing temperatures below 100°C and generally do not undergo oxidation reactions. Therefore, in the prior art, DPO is only used as a flame retardant in epoxy resins. However, at the high processing temperatures of commonly used thermoplastic resins (polyamides are typically above 220°C, polyesters above 210°C, and polypropylene above 190°C), it may have already reacted and lost its original high flame retardant properties. Those skilled in the art can judge from common sense that it cannot be used in thermoplastic resin flame retardant systems. 3) DPO’s P=O is very easy to adsorb environmental moisture through hydrogen bonds or van der Waals forces. It will become damp when placed in the air under normal conditions. Even without considering thermal stability and processing decomposition, when used in thermoplastic resins, the parts will absorb water, which will promote the migration and precipitation of flame retardants, resulting in a decrease in flame retardant performance, unstable part dimensions or part deformation, and difficulty in subsequent assembly. For the reasons mentioned above, those skilled in the art may have technical biases and generally believe that DPO cannot be used in flame-retardant polymer materials, especially in thermoplastic resin systems.

[0032] When diphenylphosphine oxide (DPO) is selected as the arylphosphine derivative, the present invention, as a flame retardant of Formula I, has the following advantages compared with DPO: higher melting temperature, significantly increased thermal decomposition temperature, solid state during feeding and mixing, easy dispersion, less prone to oxidation during processing, less susceptible to moisture and water absorption in processed parts, and stable performance. Attached Figure Description

[0033] Figure 1 For flame retardant 1 in Example 1 1 H NMR spectrum; Figure 2 For flame retardant 1 in Example 1 31 P NMR spectrum; Figure 3 The FT-IR spectra of intermediate 2 and flame retardant 2 in Example 2 are shown below. Figure 4 For flame retardant 3 in Example 3 1 H NMR spectrum; Figure 5 For flame retardant 4 in Example 4 31P NMR spectrum. Detailed Implementation

[0034] The specific implementation of this application is described in detail below through examples. However, the specific implementation of this application is not intended to limit the technical solution of this application. Any non-substantial changes, such as replacing common technical solutions in the field, using the technical solutions described in the embodiments of this application are within the protection scope of this application.

[0035] The raw materials used in the embodiments and comparative examples of this invention are as follows, but are not limited to these materials. Unless otherwise specified, the raw materials in the embodiments and comparative examples of this application can be obtained by commercial use or by preparing them according to the disclosed technology: DPO (diphenylphosphine oxide), CAS: 4559-70-0; DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), CAS: 35948-25-5; DPPA (6H-dibenzo[c,e][1,2]azaphosphacyclohexene-6-oxide), CAS: 53778-28-2; TGIC (triglycidyl isocyanurate or 1,3,5-triglycidyl-S-triazinetrione), CAS: 2451-62-9; Boric acid, CAS: 10043-35-3; Benzylboronic acid, CAS: 98-80-6; Methylboric acid, CAS: 13061-96-6; Phenylacetic acid, CAS: 34420-17-2; Xylene, CAS: 1330-20-7; Ethanol, CAS: 64-17-5; PA6: Tianjin Changlu Haijing 2702BR; PA66: Tianjin Changlu Haijing YN2700; PBT: Zhejiang Changhong CH810; Reinforcing filler: chopped glass fiber, China Jushi, ECS10-4.5-568H; Antioxidant 1098, commercially available.

[0036] The test methods and standards used in each comparative example and embodiment are as follows: Nuclear magnetic resonance (NMR) spectrometer, 400 MHz, testing standard ASTM E2977-15(2023); Fourier transform infrared spectroscopy (FT-IR) was performed using the potassium bromide pellet method, according to the standard ASTM E1252-98 (2021). Differential scanning calorimetry (DSC), test standard: ISO 11357-3-2018; Thermogravimetric analysis (TG), test standard: ISO 11358-1:2014; The structure of the flame retardant was characterized by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FT-IR), and its thermal properties were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). Flame retardancy rating: Injection-molded 3.2mm thick standard test strips, tested according to ASTM-D3801-26, which is equivalent to the ANSI / UL 94 20 mm (50W) vertical burning test (V-0, V-1, V-2); The limiting oxygen index (LOI) was tested according to ASTM D2863-17 standard, with a sample size of 100mm × 6.5mm × 3.2mm.

[0037] The preparation methods for the flame retardants of Formula I in Examples 1-4 are as follows: An intermediate formed by the nucleophilic ring-opening addition reaction of triglycidyl isocyanurate with the PH bond of an arylphosphine derivative is then reacted with a boric acid derivative via a nucleophilic ring-opening addition reaction to obtain the flame retardant described in Formula I. It should be noted that the intermediate is one or two of the three epoxy groups on the triglycidyl isocyanurate molecule undergoing a nucleophilic ring-opening addition reaction with the PH bond. The formation of the intermediate is primarily controlled by adjusting the feed ratio, experimental temperature, and reaction time, rather than ensuring the complete reaction of all three epoxy groups. When one epoxy group undergoes a nucleophilic ring-opening addition reaction with the PH bond, a subsequent nucleophilic ring-opening addition reaction with the boric acid derivative occurs. The complete reaction of the other two epoxy groups is controlled by adjusting the feed ratio, experimental temperature, and reaction time.

[0038] It should be noted that the mechanism of nucleophilic ring-opening addition reaction is common knowledge, and those skilled in the art can obtain flame retardants of Formula I by controlling the raw materials and reaction conditions according to specific embodiments.

[0039] In addition, in this preparation method, TGIC cannot be reacted with boric acid derivatives first. The reasons include: (1) If the product after the reaction of boric acid derivatives with TGIC is subjected to high temperature (such as 150 °C) for subsequent nucleophilic ring-opening addition reaction with arylphosphine derivatives, it will react violently, causing the excess hydroxyl groups on the boric acid derivatives to preferentially react with the epoxy groups on other TGICs, which easily leads to condensation and makes it impossible to prepare the flame retardant of Formula I structure; (2) The steric hindrance of the boric acid derivatives is relatively small compared with that of the arylphosphine derivatives, and the subsequent reaction is more likely to insert into the macromolecular intermediate after the reaction of arylphosphine derivatives with TGIC.

[0040] Example 1 0.2 mol DPO was added to the reaction vessel, and nitrogen gas was continuously purged to replace the air. The system was heated to 150 °C, and 0.1 mol TGIC was added. The nucleophilic ring-opening addition reaction was continued for 4 hours. After the reaction was completed, the melt was transferred while hot, washed with xylene, and dried to obtain intermediate 1.

[0041] 0.1 mol of intermediate 1, 0.1 mol of boric acid and an appropriate amount of ethanol were added to the reaction vessel. After heating to 95°C, the nucleophilic ring-opening addition reaction was continued for 4 h. Subsequently, the ethanol was removed by rotary evaporation, and the mixture was washed and dried with deionized water to obtain flame retardant 1 with a yield of 94.4%.

[0042] In this embodiment, intermediate 1 is one or two of the three epoxy groups on the TGIC molecule that undergo a nucleophilic ring-opening addition reaction with the PH bond. The following reaction formula is only an example of two nucleophilic ring-opening addition reactions with the PH bond. By controlling the feed ratio, experimental temperature, reaction time, and other conditions, the primary formation of intermediate 1 is controlled, rather than the complete reaction of all three epoxy groups. A specific reaction formula example is as follows:

[0043] Thermal performance test results: The melting temperature of this flame retardant is 136.7 ℃, and the initial decomposition temperature is 315 ℃.

[0044] Figure 1 For flame retardant 1 1 The 1H NMR spectrum showed that the peaks at 7.51–8.01 ppm corresponded to the benzene ring group in DPO, and the peak at 3.39 ppm corresponded to -OH, formed by the ring-opening reaction of the epoxy group, indicating that the epoxy group successfully participated in the reaction. The peaks at 2.74–2.95 ppm corresponded to hydrogen on the O=CN-CH structure. The peak at 4.31 ppm corresponded to hydrogen on the P-CH structure, indicating that the PH bond successfully reacted with the epoxy group. The peak at 5.23 ppm referred to hydrogen on the methine group in the CH-OH structure, while the peaks at 3.85–3.95 ppm referred to hydrogen on the CH-OB structure, indicating that boric acid grafting was successful and flame retardant 1 was successfully synthesized.

[0045] Figure 2 For flame retardant 1 31 P NMR spectrum. The results showed a peak at 28.62 ppm, indicating that phosphorus in this structure has only one chemical environment, and flame retardant 1 was successfully synthesized.

[0046] Example 2 0.2 mol DOPO was added to the reaction vessel, and nitrogen gas was continuously introduced to replace the air. The system was heated to 155°C, and after the DOPO melted, 0.1 mol TGIC was added, and the nucleophilic ring-opening addition reaction was continued for 5 hours. After the reaction was completed, the melt was transferred while hot, washed with xylene, and dried to obtain intermediate 2.

[0047] 0.1 mol of intermediate 2, 0.1 mol of phenylboronic acid and an appropriate amount of ethanol were added to the reaction vessel. After heating to 80 °C, the nucleophilic ring-opening addition reaction was continued for 4.5 h. Subsequently, the ethanol was removed by rotary evaporation, and the mixture was washed and dried with deionized water to obtain flame retardant 2 with a yield of 91.3%.

[0048] Thermal performance test results: The melting temperature of this flame retardant is 147.8 ℃, and the initial decomposition temperature is 323 ℃.

[0049] Figure 3 The image shows the FT-IR spectra of intermediate 2 and flame retardant 2. The 1688 cm⁻¹ spectrum is shown. -1 and 1464 cm -1 The peaks at 1170 cm⁻¹ correspond to the C=O and CN bonds in the triazine trione ring of TGIC, respectively. -1 and 959 cm -1 The peak at 1370 cm⁻¹ is attributed to the P=O and PO structures of the phosphane-amorphous groups. Additionally, the peak at 1370 cm⁻¹... -1 The peak at that position corresponds to a phosphorus-related BOC bond, indicating that the boric acid group and the epoxy group reacted, and flame retardant 2 was successfully synthesized.

[0050] Example 3 0.3 mol DPO was added to the reaction vessel, and nitrogen gas was continuously purged to replace the air. The system was heated to 160°C, and after the DPO melted, 0.3 mol TGIC was added, and the nucleophilic ring-opening addition reaction was continued for 5 hours. After the reaction was completed, the melt was transferred while hot, washed with xylene, and dried to obtain intermediate 3.

[0051] 0.15 mol of intermediate 3, 0.3 mol of methylboric acid and an appropriate amount of ethanol were added to the reaction vessel. After heating to 75°C, the nucleophilic ring-opening addition reaction was continued for 3 hours. Subsequently, the ethanol was removed by rotary evaporation, and the mixture was washed with deionized water and dried to obtain flame retardant 3 with a yield of 92%.

[0052] Thermal performance test results: The melting temperature of this flame retardant is 144.5 ℃, and the initial decomposition temperature is 308 ℃.

[0053] Figure 4 For flame retardant 3 1¹H NMR spectra. The results show that the peak at 7.44–7.77 ppm corresponds to the benzene ring group in DPO, the peak at 3.34 ppm corresponds to -OH, and the peak at 2.74–2.89 ppm corresponds to hydrogen on the O=CN-CH structure. The peak at 4.25 ppm corresponds to hydrogen on the P-CH structure, indicating that the PH bond has successfully reacted with the epoxy group. The peak at 5.19 ppm refers to hydrogen on the methine group in the CH-OH structure, while the peak at 3.82–3.97 ppm refers to hydrogen on the CH-OB structure, indicating that methylboronic acid grafting was successful and flame retardant 3 was successfully synthesized.

[0054] Example 4 0.2 mol DPPA was added to the reaction vessel, and nitrogen gas was continuously purged to replace the air. The system was heated to 170°C, and 0.1 mol TGIC was added. The nucleophilic ring-opening addition reaction was continued for 3 hours. After the reaction was completed, the melt was transferred while hot, washed with xylene, and dried to obtain intermediate 4.

[0055] 0.1 mol of intermediate 4, 0.1 mol of ethanol and an appropriate amount of ethanol were added to the reaction vessel. After heating to 85°C, a nucleophilic ring-opening addition reaction was carried out for 5 hours. Subsequently, the ethanol was removed by rotary evaporation, and the mixture was washed with deionized water and dried to obtain flame retardant 4 with a yield of 95.6%.

[0056] Thermal performance test results: The melting temperature of this flame retardant is 145.8 ℃, and the initial decomposition temperature is 317 ℃.

[0057] Figure 5 Flame retardant 4 31 P NMR spectrum. The results showed a peak at 28.60 ppm, indicating that phosphorus in this structure has only one chemical environment, and flame retardant 4 was successfully synthesized.

[0058] This embodiment uses a thermoplastic resin composition as an example of a flame-retardant polymer material to demonstrate its flame-retardant effect. Those skilled in the art can apply this concept to other non-thermoplastic resins, such as coatings and rubber compositions. Preparation of the thermoplastic resin: Table 1 shows the components and properties of the thermoplastic resin compositions in Examples 5-12. Flame retardants of Formula I synthesized in Examples 1-4 were selected, weighed according to the components in Table 1 (by mass; 0.2 parts by mass of antioxidant 1098 were added to each example and comparative composition, which is not shown in Table 1 again; those skilled in the art can choose whether to add antioxidant according to actual needs), mixed, melted, extruded, and granulated using a twin-screw extruder to prepare flame-retardant thermoplastic resin. The parameters such as the corresponding screw extruder temperature and speed are well known to those skilled in the art and will not be elaborated further. Short-cut glass fiber was side-fed in the components. Test specimens were injection molded according to the testing standards. The flame-retardant performance of the thermoplastic resin was characterized by its flame retardancy rating and limiting oxygen index (LOI).

[0059] Table 1. Components and properties of the thermoplastic resin compositions in Examples 5-12

[0060] As can be seen from the data in Table 1, all examples 5-12 used the prepared flame retardant of Formula 1, with a limiting oxygen index (LOI) of 28.5%-31.3%, which is considered a flame retardant material (generally, a material with an LOI of 27% or higher can be considered a flame retardant material). Furthermore, it achieved a flame retardant rating of V-0 at 3.2mm, demonstrating good flame retardant performance.

[0061] In Examples 5-12, 45-85 parts of polyamide resin / polyester resin; 0-30 parts of reinforcing filler; 15-25 parts of Formula I flame retardant; and the sum of the above components in the composition is 100 parts by mass, all of which can achieve a flame retardant rating of V-0 at 3.2mm.

[0062] Examples 5-7 use three thermoplastic resin compositions without reinforcing fillers: PA6, PA66, and PBT. Their limiting oxygen indices are 28.9%, 30.1%, and 30.8%, respectively, classifying them as flame-retardant materials. When added at amounts of 15, 18, and 20 parts by weight, a flame retardancy rating of V-0 can be achieved at a thickness of 3.2 mm.

[0063] The compositions in Examples 9-12 all contained reinforcing filler (chopped glass fiber). Although the addition of chopped glass fiber would reduce the overall flame retardant performance of the material due to the wick effect, the limiting oxygen index was 28.5%~30.2% in the presence of the flame retardant of Formula I in this application, classifying it as a flame retardant material. Furthermore, a flame retardant rating of V-0 was achieved for a 3.2mm section, demonstrating good flame retardant performance.

[0064] It should be noted that the flame retardants used in Examples 5-12 are all macromolecular flame retardants with Formula I structure. Individual raw materials (such as DPO, TGIC, and boric acid) cannot be directly compounded using traditional physical methods, nor can they be used as comparative experiments to verify the effectiveness of the Formula I structure flame retardants of this application. The reason is that small-molecule boric acid derivatives undergo dehydration condensation at approximately 150-160°C. Furthermore, arylphosphine derivatives containing pH bonds have low thermal stability; for example, DPO undergoes thermo-oxidative disproportionation, and DOPO begins to decompose at 213°C, making it difficult to meet the processing temperature requirements of polyamide and polyester polymers. In addition, compounds with polyepoxy groups, such as TGIC, are prone to curing at high temperatures, leading to bridging and affecting material feeding.

[0065] It should be noted that the embodiments in this application are merely examples of specific implementation methods and are not intended to limit the scope of protection of this application. Those skilled in the art can replace the same or similar components according to actual needs, and all such replacements are within the scope of protection of this application.

Claims

1. A novel halogen-free flame retardant, characterized in that, Including flame retardants with Formula I structure: Formula I In the formula, R1 is an arylphosphine-containing fragment formed by the nucleophilic ring-opening addition reaction of an epoxy group with a PH bond on an arylphosphine derivative, R2 is a boronic acid-containing fragment formed by the nucleophilic ring-opening addition reaction of an epoxy group with a boric acid derivative, and R3 is either R1 or R2.

2. The flame retardant according to claim 1, characterized in that, R1 is selected from one of formulas II (1) to (3). Formula II In the formula, • ​​represents the connection site.

3. The flame retardant according to claim 1, characterized in that, R2 is selected from one of formulas II (4) to (7). Formula III In the formula, • ​​represents the connection site.

4. The flame retardant according to claim 1, characterized in that, It is prepared by reacting an intermediate formed by the nucleophilic ring-opening addition reaction of triglycidyl isocyanurate with the PH bond of an arylphosphine derivative via a nucleophilic ring-opening addition reaction, and a boric acid derivative via a nucleophilic ring-opening addition reaction.

5. The flame retardant according to claim 1, characterized in that, The arylphosphine derivatives include one or more of diphenylphosphine oxide, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and 6H-dibenzo[c,e][1,2]azaphosphacyclohexene-6-oxide.

6. The flame retardant according to claim 1, characterized in that, The boric acid derivatives include one or more of boric acid, phenylboronic acid, methylboronic acid, and phenylethylboronic acid.

7. The method for preparing the flame retardant according to any one of claims 1 to 6, characterized in that, Includes the following steps: The intermediate formed by the nucleophilic ring-opening addition reaction of triglycidyl isocyanurate and the PH bond on the arylphosphine derivative is then reacted with a boric acid derivative via a nucleophilic ring-opening addition reaction to obtain the flame retardant described in Formula I.

8. The preparation method according to claim 7, characterized in that, The molar ratio of the triglycidyl isocyanurate to the arylphosphine derivative is 1:(1~2).

9. The preparation method according to claim 7 or 8, characterized in that, The molar ratio of the intermediate to the boric acid derivative is 1:(1~2).

10. The preparation method according to claim 7, characterized in that, The nucleophilic ring-opening addition reaction is carried out at a temperature of 150-170°C for 3-6 hours.

11. The preparation method according to claim 7 or 10, characterized in that, The nucleophilic ring-opening addition reaction is carried out at a temperature of 75-95°C for 4-6 hours.

12. The application of the flame retardant according to any one of claims 1 to 6, as a non-reactive flame retardant for flame-retardant polymer materials.

13. The application according to claim 12, characterized in that, The flame-retardant polymer material is a thermoplastic resin composition, which includes one or more compositions based on polyamide resins, polyester resins, and polyolefin resins.

14. The application according to claim 13, characterized in that, The thermoplastic resin composition further includes one or more of the following: antioxidants, lubricants, toughening agents, antistatic agents, laser marking agents, and color powders.

15. The application according to claim 13, characterized in that, The thermoplastic resin composition further includes a compound flame retardant, which includes one or more of the following: nitrogen-based, phosphorus-based, boron-based, silicon-based, and sulfur-based flame retardants, excluding the flame retardant of Formula I.

16. The application according to claim 13, characterized in that, The thermoplastic resin composition comprises, by weight, the following components: 45-85 parts of thermoplastic resin; 0-30 parts of reinforcing filler; Formula I flame retardant 15-25 parts; The sum of the above components in the composition is 100 parts by weight, and the 3.2mm flame retardant rating of the thermoplastic resin composition is V-0.

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