Acenaphthene phosphorus flame retardant and preparation method thereof
By designing acenaphthene-based phosphorus flame retardants and employing a stereoselective synthesis method, structurally regular acenaphthene-DOPO derivatives were generated. This solved the problems of insufficient heat resistance and dielectric properties of existing DOPO derivatives during high-temperature flame retardancy, achieving efficient char formation and flame retardancy. This method is suitable for high-frequency and high-speed copper-clad laminates based on PPO resin and hydrocarbon resin substrates.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGDONG UNIV OF TECH
- Filing Date
- 2026-01-30
- Publication Date
- 2026-05-12
AI Technical Summary
Existing DOPO derivatives exhibit poor heat resistance and char formation at high temperatures, their flexible structure leads to insufficient dielectric properties, and existing synthesis methods suffer from poor atom economy and demanding conditions.
Phosphorus-based flame retardants of acenaphthene are used. Through the phase transfer catalyst and activator formed by organic amine/organic ammonium salt and high-concentration hydrogen halide, the reaction conditions are controlled to generate trans-addition dihaloacenaphthene, which then reacts with DOPO to form acenaphthene-DOPO derivatives, ensuring stereoselectivity and molecular symmetry.
It achieves efficient carbonization and flame retardancy, high heat resistance, and excellent dielectric properties, meeting the requirements of 5G communication for high-frequency and high-speed substrate materials. It also has good compatibility with the substrate and does not impair mechanical properties.
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Figure CN122011032A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of flame retardant preparation technology, and in particular to a phosphorus-based flame retardant of acenaphthene and its preparation method. Background Technology
[0002] 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives are a class of novel flame retardants that are currently under extensive research. They are non-toxic, harmless, and possess excellent flame-retardant properties. Among DOPO derivatives, those containing P-C bonds have a greater advantage in high-temperature flame retardancy than P-O derivatives due to their better temperature resistance and water absorption.
[0003] Early methods for constructing P-C bonds primarily involved Arbuzov or Arbuzov-like reactions. These methods used tricoordinated phosphorus compounds to react with alkyl halides, resulting in poor atom economy (requiring the elimination of one molecule of a haloalkane) and a relatively limited substrate selection, especially when constructing organophosphorus compounds with specific structures, where the conditions were quite demanding.
[0004] Patents US9522927B2, CN102428092A, and CN105153233B disclose the structure of a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-derived compound and its preparation method, involving the preparation of DOPO-derived compounds by reacting DOPO with a diol compound in the presence of a catalyst. Patent CN201610601334.3 discloses a method for preparing a double DOPO derivative, which involves reacting a DOPO derivative with an alcohol, with the DOPO atoms linked by ether bonds. In this type of flame retardant structure, the DOPO atoms are linked by flexible structures such as aliphatic hydrocarbons or ether bonds, resulting in insufficient heat resistance and poor char formation during combustion, requiring large amounts to achieve a satisfactory flame retardant effect.
[0005] Patent CN201410333261.5 describes a phosphorus-based flame retardant with a double DOPO structure, which is prepared by aryl ketones and DOPO compounds under the action of an acidic catalyst. The DOPOs are formed by vinyl bridge chains with aromatic group substitution. The DOPOs are also connected by flexible chains. The substitution of aromatic groups destroys the symmetry of the molecular structure, resulting in insufficient dielectric properties of the flame retardant. Summary of the Invention
[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a novel compound structure and its preparation method.
[0007] To achieve the above objectives, the present invention adopts the following technical solution:
[0008] This invention first proposes a phosphorus-based flame retardant compound of acenaphthene, having the following structure:
[0009] .
[0010] This invention also proposes a method for preparing the aforementioned acenaphthene-based phosphorus flame retardant, comprising the following steps:
[0011] S1, Preparation of dihaloacenaphthene
[0012] Under a nitrogen atmosphere, add organic amines or organic ammonium salts to an organic solvent, then slowly add high-concentration hydrohalic acid, control the temperature to <55℃, and cool down to 0℃ after reacting for 0.5-6 hours.
[0013] Simultaneously add elemental halogen and acenaphthene, control the reaction temperature at 0-25℃, continue the reaction for 3-9 hours until the color of the elemental halogen disappears, raise the temperature to 55-85℃ until the acenaphthene is completely consumed, purify, and obtain dihaloacenaphthene with two substituted carbon atoms in the configuration of (R, S).
[0014] Acenamethane (molecular formula C) 12 H8) undergoes an electrophilic addition reaction with halogen elements (such as Cl2, Br2, or I2) in the presence of organic amines / organoammonium salts and hydrohalic acids to form dihaloacenaphthenes. Taking bromine as an example:
[0015]
[0016] Organic amines (such as triethylamine) or organic ammonium salts (such as tetrabutylammonium bromide) react with high concentrations of hydrohalic acids (such as hydrobromic acid) to form quaternary ammonium salts or protonated amine species (such as R3NH). + X - These species act as phase-transfer catalysts or activators, promoting the polarization and dissociation of halogen elements.
[0017]
[0018] The five-membered double bond in the acenaphthene molecule, located at the 1,2-position, is attacked by a halide cation, forming a halonium ion intermediate. Due to the rigid planar structure of acenaphthene, the attack mainly occurs from the reverse side of the double bond, leading to trans-addition. Subsequently, the halide anion (X... - The reaction proceeds from the back side, forming dihaloacenaphthene. Low temperatures favor the kinetic control of trans-addition, primarily producing the (R,S) diastereomeric form. This is because the planarity of the acenaphthene double bond makes the two carbon atoms after addition chiral centers, but reaction conditions (such as steric hindrance of the organic amine and solvent polarity) promote the dominance of the (R,S) configuration. Heating to 55-85℃ ensures complete reaction without significantly altering stereoselectivity.
[0019] S2. Preparation of DOPO derivatives with acenaphthene structure
[0020] The monomer of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, i.e., DOPO, was added to a polar organic solvent and stirred at 50°C until DOPO was completely dissolved. Then, dihaloacenaphthene was added, followed by the slow addition of an organic amine. After the addition was completed, the reaction temperature was raised to >120°C and the reaction was continued for 18-36 hours. After purification, DOPO derivatives with acenaphthene structure were obtained, i.e., acenaphthene-based phosphorus flame retardants.
[0021] Dihaloacenaphthene undergoes a nucleophilic substitution reaction with DOPO in the presence of an organic amine to generate acenaphthene-DOPO derivatives;
[0022]
[0023] (R,S) configuration
[0024] In polar organic solvents, the pH bond of DOPO is deprotonated by an organic amine, forming a DOPO anion. The organic amine acts as a base, capturing the released proton. The DOPO anion attacks the carbon-halogen bond in the dihaloacenaphthene, undergoing an SN2 reaction. Since the dihaloacenaphthene has two halogen sites, two DOPO molecules are successively substituted, forming a bis-DOPO-substituted acenaphthene derivative. The two chiral carbon atoms of the dihaloacenaphthene may undergo configuration inversion during the substitution reaction. Initially, the dihaloacenaphthene is predominantly (R, S) in configuration, but the attack of DOPO is influenced by the steric hindrance of the acenaphthene skeleton, preferentially attacking sites with less steric hindrance, resulting in the (R, S) configuration still being dominant in the product.
[0025] Preferably, the organic solvent is a weakly polar saturated organic solvent, such as cyclohexane, n-hexane, n-heptane, or carbon tetrachloride.
[0026] The organic amine is selected from at least one of aliphatic amines or heterocyclic organic amines; the preferred aliphatic amines are ethylenediamine, triethylamine, n-butylamine, tri-n-butylamine, 1,4-butanediamine, N,N-diisopropylethylamine, and trimethylenetetramine; the preferred heterocyclic organic amines are pyridine, 4-(dimethylamino)pyridine, and 3-methylimidazole; the preferred organic ammonium salts are tetrabutylammonium bromide, tetramethylammonium bromide, octyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and octadecylmethylammonium bromide.
[0027] High-concentration hydrohalic acid is one of the following: 36.5% concentrated hydrochloric acid, hydrobromic acid with a mass fraction >45% or hydroiodic acid aqueous solution;
[0028] The molar ratio of hydrohalic acid to organic amine or organic ammonium salt is 1-1.3:1;
[0029] Preferably, in S1, the halogen element is selected from the same type of halogen as the high-concentration hydrohalic acid, and the molar ratio of the halogen element to the organic amine or ammonium salt is 1-1.2:1;
[0030] The molar ratio of halogen to acenaphthene is 1.05-1.5:1.
[0031] Preferably, in S2, the polar organic solvent is a polar solvent with a boiling point >120℃, including xylene, cyclohexanone, dimethyl sulfoxide, formamide, and N-methylpyrrolidone.
[0032] The molar ratio of DOPO to dihaloacenaphthene is 2-2.1:1;
[0033] The organic amines can be any of aliphatic amines, aromatic amines, or heterocyclic organic amines; for aliphatic amines, triethylamine, n-butylamine, tri-n-butylamine, and N,N-diisopropylethylamine are preferred; for aromatic amines, diphenylamine, p-methylaniline, dimethylaniline, o-ethoxyaniline, 2,6-diethylaniline, and N-butylaniline with electron-donating activity are preferred; for heterocyclic organic amines, pyridine, 4-(dimethylamino)pyridine, and 3-methylimidazole are preferred.
[0034] The molar ratio of organic amines to DOPO is 1.3-2:1.
[0035] Preferably, in S2, the two chiral carbon atoms of the DOPO derivative with an acenaphthene structure synthesized are predominantly of the (R, S) configuration, and the sum of the (R, R) and (S, S) configurations accounts for less than 50%.
[0036] The acenaphthene-based phosphorus flame retardant proposed in this invention has efficient charring and flame retardant effects, and can be used as a flame retardant for high-performance applications, especially suitable for high-frequency and high-speed copper-clad laminates based on PPO resin and hydrocarbon resin substrates.
[0037] Compared with the prior art, the beneficial effects of the present invention are:
[0038] 1. Based on the above molecular design mechanism, the phosphorus compounds of this invention exhibit unparalleled advantages in high-frequency, high-speed copper-clad laminates based on PPO resin and hydrocarbon resin substrates. The rigid planar structure of acenaphthene and DOPO, along with the high symmetry of the entire molecule, results in low polarizability and difficulty in dipole orientation under electromagnetic fields, achieving high heat resistance, low dielectric loss, and high flame retardancy. The advantageous configuration obtained through stereoselective synthesis ensures that the molecules are tightly stacked and have a small free volume in the copper-clad laminate matrix resin, reducing the polarizable "air gaps." The extremely low dielectric constant (Dk) and dielectric loss factor (Df) are crucial for signal integrity and transmission speed, fully meeting the stringent requirements of 5G / 6G communication for high-frequency, high-speed substrate materials.
[0039] 2. The in-situ formation of the organic amine / ammonium salt and hydrohalic acid system acts as both a phase transfer catalyst and an acid catalyst, enabling the formation of halide anions (X... - The transfer from the aqueous phase to the organic phase allows it to form more reactive "halonium ion pairs" with halogen elements, greatly enhancing the electrophilic attack ability of halogens on the acenaphthene double bond. Low-temperature control suppresses side reactions such as over-halogenation and free radical substitution, ensuring that the reaction specifically occurs on the most reactive five-membered ring double bond of acenaphthene, achieving high site selectivity and laying the foundation for the subsequent precise reaction with DOPO.
[0040] The addition of halogens to the double bond of acenaphthene is a trans-addition. While the acenaphthene molecule itself has a planar rigid structure, the microenvironments on both sides of the double bond are not perfectly symmetrical. Under the influence of the "chiral environment" provided by organic amines / ammonium salts or steric hindrance, the reaction tends to generate the (R,S) dihaloacenaphthene, a dihaloacenaphthene with a predominantly (R,S) configuration. Obtaining a dihaloacenaphthene with a predominantly (R,S) configuration means that the subsequent product also has a predominantly single configuration. This regularity of molecular structure is crucial for its compatibility and dispersibility in polymer matrices, such as PPO resins or hydrocarbon resins. It effectively prevents phase separation or crystallization defects caused by disordered stacking of molecules with different configurations, thereby avoiding the deterioration of the material's mechanical and dielectric properties.
[0041] 2. The organic amine first reacts with the pH bond of DOPO to generate a highly nucleophilic DOPO anion. In a polar solvent, the DOPO anion performs S_N2 nucleophilic substitution on the two CX bonds of the dihaloacenaphthene. Since the S1 step already provides a high-purity dihalo precursor, and DOPO is in excess, it ensures that both DOPO groups can be efficiently and quantitatively attached to the acenaphthene skeleton, generating a target product with a well-defined structure and a single molecular weight.
[0042] Mechanistically, the final product is a rigid planar acenaphthene unit connected on both sides by two large DOPO phosphenanthrene rings via CP bonds. Both the fused-ring structure of acenaphthene and the aromatic heterocycles of DOPO are highly thermally stable structural units. Their stable CP bond connection forms a large, rigid conjugated molecular system, resulting in a very high decomposition temperature, perfectly matching the high-temperature resistance requirements of copper-clad laminates such as PPO or hydrocarbon resins. During combustion, the rigid acenaphthene skeleton acts as an excellent char-forming agent, while DOPO is a highly efficient acid source. Through synergistic chemical bonding, they rapidly form a dense and stable char layer in the condensed phase, isolating oxygen and heat, achieving a perfect synergy between the "char layer-gas mechanism," resulting in flame-retardant efficiency far exceeding that of physically mixed flame-retardant systems.
[0043] In summary, the beneficial effects of this invention lie in the design of novel phosphorus-containing acenaphthene compounds and the preparation of structurally regular acenaphthene-DOPO flame retardants through stereoselective synthesis. This molecule possesses both a rigid acenaphthene framework and highly efficient phosphorus-based flame-retardant groups, exhibiting significant synergistic effects, high heat resistance, and good char formation. When applied to high-frequency, high-speed copper-clad laminates based on PPO resin or hydrocarbon resin substrates, it demonstrates excellent thermal stability and halogen-free flame-retardant efficiency while maintaining extremely low dielectric constant and losses. Simultaneously, it exhibits good compatibility with the matrix, does not impair the mechanical properties of the matrix, and meets the stringent requirements for comprehensive material performance in applications such as 5G communication. Attached Figure Description
[0044] Figure 1 This is the infrared spectrum of acenaphthene-based phosphorus flame retardants. Detailed Implementation
[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0046] The purity and manufacturers of the various drugs used in the experiment are shown in Table 1.
[0047] Table 1. Raw Material Drug Information
[0048]
[0049] Example 1:
[0050] 1. Under a nitrogen atmosphere, add 200g of cyclohexane to a 1000mL three-necked flask, then add 0.2mol of tri-n-butylamine, stir well, and then slowly add 0.2mol of 47% HBr dropwise. Control the temperature at 25℃ and react for 6h, then cool down to 0℃.
[0051] 2. Using a constant pressure dropping funnel, measure 0.22 mol of elemental Br2 and 0.186 mol of acenaphthene, respectively, controlling the dropping rate so that the temperature does not exceed 25℃. After the dropping is completed, continue the reaction for a period of time until the color of elemental Br2 in the solution disappears.
[0052] 3. The temperature was raised to 75℃ and the reaction continued until the acenaphthene was completely consumed. The product was then extracted and purified to obtain 0.18 mol of dihaloacenaphthene with (R, S) configurations for the two substituted carbon atoms. The proportion of the two chiral carbon atoms with (R, S) configurations in the product was 89%.
[0053] 4. Add 0.205 mol of DOPO monomer to 300 g of xylene, an organic solvent, and stir at 50°C until the DOPO is completely dissolved;
[0054] 5. Add 0.1 mol of the stereochemically structured halide prepared in S1, and slowly add 0.28 mol of the organic amine N,N-diisopropylethylamine, controlling the addition time to 3 h;
[0055] 6. After the addition was completed, the reaction temperature was raised to 125℃ and the reaction was continued for 36 hours. After slurrying and purification, 38.9 g of acenaphthene-based phosphorus flame retardant was obtained, with a yield of 67%.
[0056] A portion of a acenaphthene-based phosphorus flame retardant was dispersed in dimethyl sulfoxide and subjected to infrared spectroscopy. The results are as follows: Figure 1 As shown;
[0057] Figure 1 Medium, 1000-1250cm -1 The strong absorption peaks in the 1400-1600 cm⁻¹ range are characteristic of P=O bonds (strong polarity, large dipole moment variation, and high absorption intensity); -1 The multiplets in the range correspond to the double bond vibrations of the benzene ring (diphenylphosphonoyl benzene ring) and the naphthalene ring (binaphthyl skeleton); 500-1000 cm⁻¹ -1 Complex peaks in the range, including 700 and 750 cm⁻¹ peaks of monosubstituted benzene rings (the benzene ring of the diphenylphosphonoyl group is monosubstituted). -1 Characteristic peaks, and out-of-plane bending vibrations of the naphthalene ring; 2000-3000 cm⁻¹ -1 The flat range and lack of significant absorption indicate that the molecule does not contain alkyl groups and conforms to the structure of a fully aromatic ring / phosphine oxide, proving that the expected phosphorus-based flame retardant molecule of acenaphthene has been successfully prepared through this invention.
[0058] The synthesis reactions of Examples 2-4, which used a similar process to Example 1, are shown in Table 2.
[0059] Table 2. Summary of Reaction Ratios and Product Yields
[0060]
[0061] Dissolve 66g of polyphenylene ether resin in 100g of toluene, then add 16g of hydrocarbon resin, 30g of synthesized acenaphthene-based phosphorus flame retardant, 12g of tripropylene isocyanurate, and 0.5g of 1,4-di-tert-butylperoxyisopropylbenzene, and stir until homogeneous to prepare a resin solution. Impregnate fiberglass cloth in the resin solution, first gel at 135℃ for 15min, then increase the temperature to 175℃ at 5℃ / min and cure for 30min. Finally, increase the temperature to 210℃ at 5℃ / min and cure for 2h, then slowly lower to room temperature. Cut the fiberglass composite board into appropriately sized test samples for further testing.
[0062] Based on this, the following design was also created:
[0063] Comparative Example 1: The composite material formulation and experimental methods were the same as in Example 1, but the acenaphthene-based phosphorus flame retardant was replaced with an aromatic-substituted vinyl bridged flame retardant. The structure of the aromatic-substituted vinyl bridged flame retardant was as follows:
[0064] ;
[0065] Comparative Example 2: The composite material and experimental method were the same as in Example 1, but the acenaphthene-based phosphorus flame retardant was replaced with an aromatic-substituted vinyl bridged flame retardant. The structure of the aromatic-substituted vinyl bridged flame retardant was as follows:
[0066] ;
[0067] For each embodiment and comparative example, specific performance tests were conducted according to IPC-TM-650 2.4.25, IPC-TM-650 2.4.24, IPC-TM-650 2.5.5.9, and UL 94, including tests for glass transition temperature, coefficient of thermal expansion, dielectric constant, and flame retardancy rating. The corresponding results are shown in the table below.
[0068] Table 3. Performance testing of three DOPO derivative structures in composite materials for copper clad laminates
[0069]
[0070] Data Analysis:
[0071] In the synthesis of halideneenes, the ion pairs formed by organic amines / ammonium salts and high-concentration hydrohalic acids, such as the nucleophilic complex formed by tri-n-butylamine and HBr in Example 1, regulate the electrophilic addition pathway of halogens to the acenaphthene double bonds through phase transfer catalysis and steric hindrance effects in the weakly polar solvent cyclohexane. During this process, the electronic effects and steric hindrance of the ion pairs work together to make the bromium ion intermediate more inclined to generate dihaloacenaphthenes with a (R,S) configuration predominant, as shown in Example 1 where the (R,S) configuration accounts for 89%, providing a structural basis for subsequent coupling reactions.
[0072] The Tg (235-240℃) of the product in the examples was significantly higher than that of Comparative Example 1 (205℃). This is primarily due to the rigid constraint on molecular chain motion. Acenaphthene, a polycyclic aromatic hydrocarbon, is a rigid group; its large π-bond conjugated system, together with the heterocyclic structure of DOPO, forms a rigid network, significantly reducing the thermal mobility of the molecular chain segments. Simultaneously, the symmetrical PC bond connections cause the molecules to pack more tightly in the condensed state, further restricting the rotation and extension of the chain segments. In contrast, the aromatic-substituted vinyl bridging chain used in the comparative example, due to the flexibility of vinyl groups and the high degree of freedom of σ-bond rotation, coupled with the disruption of molecular symmetry by aromatic substitution, resulted in reduced resistance to chain segment motion and lower energy required for the glass transition, thus lowering the Tg.
[0073] The CTE (1.7%-1.9%, 0-260℃) of the examples is lower than that of the comparative examples, such as Comparative Example 1 which reaches 2.5%. This is due to the binding effect of the rigid structure on thermal expansion. The rigid framework composed of the acenaphthene fused ring and DOPO heterocycle makes it difficult for the molecules to undergo significant chain segment extension or conformational changes when heated. Moreover, the symmetrical structure makes the internal stress distribution of the material more uniform, and the volume change is more restricted when the temperature rises. In the comparative examples, the flexible vinyl bridge chain is prone to σ bond rotation and chain segment extension when heated, which macroscopically manifests as an increase in the coefficient of thermal expansion.
[0074] The dielectric constant of the examples (3.4-3.5) is superior to that of the comparative examples (e.g., 3.6 in Comparative Example 1). This is attributed to the synergistic effect of reduced molecular polarity and homogenization polarization of the symmetrical structure. The conjugated structure of acenaphthene has extremely low polarity, and the electron cloud distribution of the PC bonds is more uniform, with weaker polarity than the PO bonds, thus reducing the molecular dipole moment. Simultaneously, the symmetrical structure makes the molecular polarization more synchronized under an electric field, reducing dielectric loss and dielectric constant, which meets the requirement of low dielectric properties for high-frequency signal transmission in electronic circuits. In the comparative examples, if the bridging chain contains ether bonds (POC) or asymmetric aromatic substitution, the dielectric constant will increase due to the presence of polar bonds or uneven dipole moment distribution.
[0075] All examples achieved a UL 94 V-0 rating, while the comparative example only achieved a V-1 rating. This difference stems from the synergistic effect of phosphorus-based gas-phase flame retardancy and condensed-phase carbonization of polycyclic aromatic hydrocarbons. DOPO-derived phosphoric acid generates phosphoric acid / polyphosphoric acid at high temperatures, which both inhibits gas-phase combustion by capturing free radicals and enhances condensed-phase flame retardancy by promoting carbonization. Meanwhile, the high aromaticity of acenaphthene's polycyclic rings makes it prone to dehydrogenation and carbonization during combustion, providing a sufficient carbon source for the char layer. The combined effect of these two factors results in an intumescent, dense char layer that effectively isolates oxygen and heat transfer, inhibiting the spread of combustion. In the comparative example, if the bridging chain is a flexible vinyl group with a low char formation rate, or if aromatic substitution disrupts the phosphorus-carbon synergy, resulting in a loose char layer structure, it is difficult to form a highly efficient flame-retardant char layer, leading to a decrease in the flame retardancy rating to V-1.
[0076] In summary, by regulating the stereoselectivity of haloacenaphthene and the coupling pathway of DOPO, the prepared acenaphthene-based DOPO derivatives exhibit superior advantages over traditional structures in terms of thermal properties, dielectric properties, and char-forming flame retardant properties due to their rigid symmetric structure and phosphorus-carbon synergistic effect, providing theoretical and experimental support for high-temperature flame retardants for electronic circuits.
[0077] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A phosphorus-based flame retardant of acenaphthene, having the following structure: 。 2. The method for preparing the acenaphthene-based phosphorus flame retardant according to claim 1, characterized in that it comprises the following steps: S1, Preparation of dihaloacenaphthene Under a nitrogen atmosphere, add organic amines or organic ammonium salts to an organic solvent, then slowly add high-concentration hydrohalic acid, control the temperature to <55℃, and cool down to 0℃ after reacting for 0.5-6 hours. Simultaneously add elemental halogen and acenaphthene, control the reaction temperature at 0-25℃, continue the reaction for 3-9 hours until the color of the elemental halogen disappears, raise the temperature to 55-85℃ until the acenaphthene is completely consumed, purify, and obtain dihaloacenaphthene with two substituted carbon atoms in the configuration of (R, S). S2. Preparation of DOPO derivatives with acenaphthene structure The monomer of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, i.e., DOPO, was added to a polar organic solvent and stirred at 50°C until DOPO was completely dissolved. Then, dihaloacenaphthene was added, followed by the slow addition of an organic amine. After the addition was completed, the reaction temperature was raised to >120°C and the reaction was continued for 18-36 hours. After purification, DOPO derivatives with acenaphthene structure were obtained, i.e., acenaphthene-based phosphorus flame retardants.
3. The method for preparing a acenaphthene-based phosphorus flame retardant according to claim 2, characterized in that: The organic solvent is selected from weakly polar saturated organic solvents, such as cyclohexane, n-hexane, n-heptane, and carbon tetrachloride; In S1, the organic amine is selected from at least one of aliphatic amines or heterocyclic organic amines; the aliphatic amines are preferably ethylenediamine, triethylamine, n-butylamine, tri-n-butylamine, 1,4-butanediamine, N,N-diisopropylethylamine, and trimethylenetetramine; the heterocyclic organic amines are preferably pyridine, 4-(dimethylamino)pyridine, and 3-methylimidazole; the organic ammonium salts are preferably tetrabutylammonium bromide, tetramethylammonium bromide, octyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and octadecylmethylammonium bromide. High-concentration hydrohalic acid is one of the following: 36.5% concentrated hydrochloric acid, hydrobromic acid with a mass fraction >45% or hydroiodic acid aqueous solution; The molar ratio of hydrohalic acid to organic amine or organic ammonium salt is 1-1.3:
1.
4. The method for preparing a acenaphthene-based phosphorus flame retardant according to claim 2, characterized in that: In S1, the halogen element is selected from the same type of halogen as the high-concentration hydrohalic acid, and the molar ratio of the halogen element to the organic amine or ammonium salt is 1-1.2:1; The molar ratio of halogen to acenaphthene is 1.05-1.5:
1.
5. The method for preparing a acenaphthene-based phosphorus flame retardant according to claim 2, characterized in that: In S2, the polar organic solvent is a polar solvent with a boiling point >120℃, including xylene, cyclohexanone, dimethyl sulfoxide, formamide, and N-methylpyrrolidone. The molar ratio of DOPO to dihaloacenaphthene is 2-2.1:1; In S2, the organic amine can be any of aliphatic amines, aromatic amines, or heterocyclic organic amines; the preferred aliphatic amines are triethylamine, n-butylamine, tri-n-butylamine, and N,N-diisopropylethylamine; the preferred aromatic amines are diphenylamine, p-methylaniline, dimethylaniline, o-ethoxyaniline, 2,6-diethylaniline, and N-butylaniline; the preferred heterocyclic organic amines are pyridine, 4-(dimethylamino)pyridine, and 3-methylimidazole. The molar ratio of organic amines to DOPO is 1.3-2:
1.
6. The method for preparing a phosphorus-based flame retardant of acenaphthene according to claim 2, characterized in that: The two chiral carbon atoms of the DOPO derivative with an acenaphthene structure synthesized in S2 are predominantly (R, S) configurations, and the sum of the (R, R) and (S, S) configurations accounts for less than 50%.
7. The application of a phosphorus-based flame retardant of acenaphthene prepared by the preparation method according to any one of claims 2-6, characterized in that, It can be used as a flame retardant for high-performance applications, especially suitable for high-frequency and high-speed copper-clad laminates based on PPO resin and hydrocarbon resin substrates.