Rigid photocurable flame-retardant compound as well as preparation method and application thereof

Abstract

The invention provides a rigid photocurable flame-retardant compound as well as a preparation method and application thereof. The rigid photocurable flame-retardant compound is synthesized by taking pentaerythritol, phosphorus oxychloride and hydroxyethyl acrylate as raw materials through two steps of nucleophilic substitution reaction: firstly, enabling the pentaerythritol to react with the phosphorus oxychloride, and then enabling a phosphoryl chloride intermediate to further react with the hydroxyethyl acrylate. The method is simple in process and environment-friendly. The obtained light-cured resin monomer has a rigid spiro structure, a phosphate group and a polymerizable double bond, and has a rapid light-curing characteristic and an excellent flame retardant property. The cured material is high in hardness, excellent in flame retardant property, high in thermal stability, excellent in mechanical property and wide in application prospect. The monomer not only can be independently used as flame-retardant light-cured resin, but also can be applied to various flame-retardant light-cured formulas as a reactive flame retardant.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photocurable flame-retardant materials. Specifically, it relates to a rigid photocurable flame-retardant compound, a preparation method and application thereof, and a bulk flame-retardant resin comprising the rigid photocurable flame-retardant compound. The rigid photocurable flame-retardant compound contains a rigid spirocyclic structure, a phosphate group and a polymerizable double bond at the same time, and has both rapid photocuring characteristics and bulk flame-retardant performance, and has a wide application prospect. BACKGROUND

[0002] Photocuring technology, as an efficient and environmentally friendly molding technology, has been widely used in the fields of coatings, inks, adhesives and 3D printing. The core component of photocurable materials is photocurable resin, which can rapidly change from liquid to solid under ultraviolet light irradiation, and has the advantages of low energy consumption, high efficiency, and low emission of volatile organic compounds (VOC). However, most conventional photocurable resins, such as epoxy acrylate and polyurethane acrylate, have a molecular backbone mainly composed of carbon, hydrogen and oxygen elements, and belong to inherently flammable materials. They are prone to release a large amount of heat and produce spreading fire droplets during combustion, which poses a significant fire safety hazard, greatly limiting their application in fields such as electronic packaging and aerospace that have stringent requirements for flame retardancy.

[0003] In order to endow photocurable materials with flame-retardant properties, the most commonly used method is to add an additive flame retardant, such as phosphorus-based, nitrogen-based or inorganic nano flame retardant, to the formulation. However, such flame retardants have poor compatibility with the resin matrix, and are prone to migration and precipitation during long-term use or curing process, not only leading to the attenuation of flame-retardant properties over time, but also causing serious deterioration of the mechanical properties, thermal stability and transparency of the material.

[0004] In order to overcome the defects of additive flame retardants, researchers have turned their attention to reactive flame retardants, that is, by chemical methods to bond flame-retardant units (such as phosphorus, nitrogen, silicon, etc.) to the molecular backbone of polymerizable monomers or oligomers. Among them, phosphorus-based flame retardants are favored due to their high efficiency, low toxicity and low smoke generation. They can promote the formation of char during combustion, and isolate oxygen and heat, thereby achieving good flame-retardant effect. Currently, the reported phosphorus-containing UV monomers are mostly phosphate or phosphonate structures, but these structures often sacrifice the rigidity of the molecule itself in order to maintain reactivity, resulting in difficulty in balancing the high thermal stability and excellent mechanical strength (such as hardness and modulus) required for the cured material while effectively improving the flame retardancy of the material. In addition, the existing synthesis methods are sometimes complicated in steps, or use toxic solvents, which are not environmentally friendly.

[0005] Therefore, there is an urgent need in this field to develop a new type of photocurable flame retardant material that can integrate a highly efficient flame retardant structure with polymerizable groups through stable chemical bonds, and can endow the cured product with excellent rigidity, thermal stability and mechanical properties through ingenious molecular design. At the same time, its preparation process should be as simple and environmentally friendly as possible.

[0006] The information disclosed in this background section is only for enhancing the understanding of the background technology of the present invention, and therefore may include information that does not constitute prior art. Summary of the Invention

[0007] To overcome the problems of flammability of existing photocurable resins and low flame retardant efficiency, poor compatibility with the matrix, easy migration of flame retardants, and damage to the thermal stability and mechanical properties of materials caused by conventional additive flame retardant methods, this invention provides a rigid photocurable flame retardant compound that combines rapid photocuring characteristics with inherent flame retardant properties, its preparation method and applications, and a bulk flame retardant resin including this rigid photocurable flame retardant compound. The rigid photocurable flame retardant compound is prepared from pentaerythritol, phosphorus oxychloride, and hydroxyethyl acrylate through two nucleophilic substitution reactions. The molecule of the rigid photocurable flame retardant compound has a rigid spirocyclic structure, phosphate groups, and polymerizable double bonds. The rigid spirocyclic structure and diphosphate units in this monomer can significantly improve the mechanical properties of photocurable materials while enhancing their flame retardant properties, showing broad application prospects.

[0008] However, the present invention is not limited to the above aspects, but can be extended in various ways without departing from the technical spirit of the present invention.

[0009] One aspect of the present invention provides a rigid photocurable flame retardant compound, said rigid photocurable flame retardant compound being represented by the following structural formula 1: Structural Formula 1 .

[0010] Another aspect of the present invention provides a method for preparing a rigid photocurable flame retardant compound, the method comprising the following steps: Step 1: subjecting pentaerythritol to a nucleophilic substitution reaction with phosphorus oxychloride to obtain intermediate SPDPC; Step 2: subjecting the SPDPC intermediate to a nucleophilic substitution reaction with hydroxyethyl acrylate to obtain the compound.

[0011] In an embodiment of the present invention, in step 1, pentaerythritol and phosphorus oxychloride are added to a reaction vessel and reacted at a first reaction temperature for a first reaction time, and then reacted at a second reaction temperature for a second reaction time to obtain intermediate SPDPC; in step 2, intermediate SPDPC, hydroxyethyl acrylate, polymerization inhibitor, and solvent are added to a reaction vessel, mixed, and then an acid-binding agent is added, reacting at a third reaction temperature for a third reaction time, and then reacting at a fourth reaction temperature for a fourth reaction time to obtain the compound. Through the above steps, a rigid photocurable flame-retardant compound possessing a rigid spirocyclic structure, phosphate groups, and polymerizable double bonds in its molecule can be successfully prepared. This compound combines rapid photocuring properties with bulk flame-retardant performance.

[0012] In an embodiment of the present invention, in step 1, the first reaction temperature is in the range of 70°C to 90°C, and the first reaction time is in the range of 2 hours to 4 hours; the second reaction temperature is in the range of 100°C to 120°C, and the second reaction time is in the range of 6 hours to 8 hours; in step 2, the third reaction temperature is in the range of 0°C to 5°C, and the third reaction time is in the range of 1 hour to 3 hours; the fourth reaction temperature is room temperature, and the fourth reaction time is in the range of 6 hours to 10 hours. With the above process conditions, the target compound can be prepared efficiently.

[0013] In an embodiment of the present invention, in step 1, the molar ratio of pentaerythritol to phosphorus oxychloride is 1:5~7; in step 2, the molar ratio of SPDPC to hydroxyethyl acrylate is 1:2~2.5. By setting the above feed amounts, the raw material utilization rate can be maximized, raw material waste can be avoided, and the desired target product can be prepared.

[0014] In embodiments of the present invention, the solvent is one or more selected from dichloromethane, trichloromethane, acetonitrile, diethyl ether, and acetone.

[0015] In embodiments of the present invention, the polymerization inhibitor is one or more selected from p-hydroxyanisole, p-methoxyphenol, hydroquinone, 2,5-di-tert-butylhydroquinone, and 2,6-di-tert-butyl-p-cresol, and the amount of the polymerization inhibitor added is from 50 ppm to 500 ppm. By adjusting the amount of polymerization inhibitor added, the reaction can proceed smoothly and the generation of side reactions can be effectively avoided.

[0016] In embodiments of the present invention, the acid-binding agent is one of pyridine, triethylamine, N,N-diisopropylethylamine, sodium carbonate, potassium carbonate, and sodium acetate.

[0017] In embodiments of the present invention, the molar ratio of SPDPC to the acid-binding agent is 1:2 to 2.6. By adjusting the amount of acid-binding agent added, side reactions can be effectively avoided, and the reaction rate and yield can be improved.

[0018] Another aspect of the present invention provides the application of a rigid photocurable flame retardant compound in a photocurable bulk flame retardant resin, including forming a bulk flame retardant resin by photocuring the compound alone, or forming a bulk flame retardant resin by mixing the compound with other photocurable materials and then photocuring the mixture.

[0019] Another aspect of the present invention provides a bulk flame retardant resin, which may comprise only a rigid photocurable flame retardant compound as a main component and optional additives, or may include a rigid photocurable flame retardant compound and other photocurable flame retardant materials and optional additives.

[0020] The bulk flame-retardant resin can be formed by photocuring a rigid photocurable flame-retardant compound, or by photocuring a mixture of a rigid photocurable flame-retardant compound and other photocurable flame-retardant materials. Other photocurable flame-retardant materials may include (meth)acrylate monomers or oligomers.

[0021] Compared with the prior art, the beneficial effects of the present invention may include: 1. The photocurable monomer synthesized through molecular design contains rigid spirocyclic units, phosphate ester groups, and polymerizable double bonds. This structure endows the monomer with both photocurable activity and inherent flame retardant properties, significantly enhancing the mechanical properties of photocurable materials while improving their flame retardancy.

[0022] 2. This monomer is prepared by a two-step nucleophilic substitution reaction. The reaction intermediates do not require complex post-processing, and the synthesis process is simple and environmentally friendly.

[0023] 3. The obtained flame-retardant UV-curable product can be used directly as a flame-retardant UV-curable resin, or as a reactive flame retardant in other UV-curable flame-retardant formulations.

[0024] The effects of this invention are not limited to those mentioned herein, and those skilled in the art will clearly understand other effects from the description of the claims. Attached Figure Description

[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide further explanation of the invention. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0026] Figure 1 The reaction equation for the preparation process of the rigid photocurable flame retardant compound according to an embodiment of the present invention is shown.

[0027] Figure 2 Infrared spectral analysis of rigid photocurable flame retardant compounds according to embodiments of the present invention.

[0028] Figure 3 This is a TG / DTG thermal stability analysis diagram of a rigid photocurable flame retardant compound according to an embodiment of the present invention. Detailed Implementation

[0029] In the following description, embodiments of the invention will be described in more detail with reference to the accompanying drawings. However, the invention may be embodied in various different forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided as examples so that the invention will be thorough and complete, and will fully convey aspects and features of the invention to those skilled in the art. Therefore, unnecessary processes, steps, and techniques for fully understanding aspects and features of the invention by those skilled in the art are not described. The terms or words used in this specification and claims should not be construed as limited to their ordinary or dictionary meaning, but should be interpreted as meaning and concept consistent with the technical concept of the invention, based on the principle that the inventors can appropriately define the concepts of the terms to best describe the invention.

[0030] It is understood that the present invention can be modified in many alternative forms. It should be understood that the present invention is not limited to the specific forms disclosed, but is intended to cover all modifications, equivalents, and alternatives falling within the scope of the present invention.

[0031] Embodiments of the invention are described in more detail below. However, these embodiments are merely examples, and the invention is not limited thereto; rather, it is defined by the scope of the claims. The terminology used herein is for descriptive purposes only and is not intended to limit the invention.

[0032] As used herein, the terms “substantially,” “about,” and similar terms are used as approximate terms rather than as terms of degree, and are intended to take into account the inherent biases of measurements or calculations that would be recognized by one of ordinary skill in the art.

[0033] Furthermore, any numerical range described herein is intended to include all subranges containing the same numerical precision within the described range. For example, the range "1.0 to 10.0" is intended to include all subranges between the described minimum value of 1.0 and the described maximum value of 10.0 (and includes both the described minimum value of 1.0 and the described maximum value of 10.0), i.e., having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as 2.4 to 7.6. Any maximum numerical limit described herein is intended to include all lower numerical limits contained therein, while any minimum numerical limit described in this specification is intended to include all higher numerical limits contained therein. Therefore, the applicant reserves the right to amend this specification (including the claims) to expressly describe any subranges contained within the scope expressly described herein.

[0034] The rigid photocurable flame retardant compound of the present invention, its preparation method and application, and bulk flame retardant resin including the same will be described in detail below.

[0035] Rigid photocurable flame retardant compounds This invention provides a rigid, photocurable flame retardant compound synthesized from pentaerythritol, phosphorus oxychloride, and hydroxyethyl acrylate via a two-step nucleophilic substitution reaction. The intermediates require no complex post-processing, making the synthesis process simple and environmentally friendly. The two steps are the reaction between pentaerythritol and phosphorus oxychloride, and the reaction between hydroxyethyl acrylate and phosphoryl chloride groups. Specifically, pentaerythritol is first subjected to a nucleophilic substitution reaction with phosphorus oxychloride to obtain the intermediate bis(chlorophosphoryl)pentaerythritol (SPDPC). Subsequently, a nucleophilic substitution reaction between hydroxyethyl acrylate and the phosphoryl chloride groups of SPDPC yields a rigid, photocurable flame retardant compound containing a rigid spirocyclic structure, phosphate groups, and polymerizable double bonds. This rigid, photocurable flame retardant compound combines rapid photocuring with excellent intrinsic flame retardant properties.

[0036] The rigid, photocurable flame-retardant compound of the present invention is represented by the following structural formula 1: Structural Formula 1 .

[0037] As shown in Structural Formula 1 above, the rigid photocurable flame-retardant compound of this invention has a rigid spirocyclic structure at its center, connected to two phosphate ester groups, and then capped with acrylate, thus containing two photocurable polymerizable double bonds within a single molecule. Based on this structure, the rigid photocurable flame-retardant compound of this invention can simultaneously achieve an organic combination of flame-retardant properties, rigid structural units, and photocurable active groups. Therefore, the rigid photocurable flame-retardant compound of this invention can possess both rapid photocuring characteristics and excellent inherent flame-retardant properties. Furthermore, the rigid spirocyclic structure and diphosphate ester units can significantly improve the mechanical properties of the photocurable material while enhancing its flame-retardant properties.

[0038] Use of rigid photocurable flame retardant compounds This invention also provides an application of a rigid photocurable flame-retardant compound. Specifically, the rigid photocurable flame-retardant compound of this invention can be used alone as a flame-retardant photocurable resin, that is, it can form a bulk flame-retardant resin by photocuring alone. Furthermore, the rigid photocurable flame-retardant compound of this invention can also be added as a reactive flame retardant to a photocurable resin formulation. For example, it can be blended with general photocurable materials (e.g., acrylate monomers or oligomers) and then photocured to form a bulk flame-retardant resin. Moreover, since each molecule contains two polymerizable double bonds, the rigid photocurable flame-retardant compound of this invention can form a highly cross-linked three-dimensional network during photocuring, significantly improving the mechanical properties of the material and imparting rapid curing characteristics.

[0039] Bulk flame retardant resins comprising rigid photocurable flame retardant compounds The present invention also provides a bulk flame-retardant resin comprising the rigid photocurable flame-retardant compound. The bulk flame-retardant resin may comprise only the rigid photocurable flame-retardant compound as a main component and optional additives. The bulk flame-retardant resin may also comprise the rigid photocurable flame-retardant compound and other photocurable flame-retardant materials and optional additives.

[0040] In other words, the bulk flame-retardant resin of the present invention can be a bulk flame-retardant resin formed by photocuring the rigid photocurable flame-retardant compound of the present invention. Specifically, the bulk flame-retardant resin can be formed solely by photocuring the rigid photocurable flame-retardant compound of the present invention, or it can be formed by photocuring the rigid photocurable flame-retardant compound of the present invention together with other photocurable flame-retardant materials.

[0041] In other words, the bulk flame-retardant resin according to the present invention can be a flame-retardant resin obtained by photocuring only a rigid photocurable flame-retardant compound, or a flame-retardant resin obtained by photocuring a mixture of a rigid photocurable flame-retardant compound and other photocurable flame-retardant materials. Here, other photocurable flame-retardant materials can be monomers or oligomers having polymerizable carbon-carbon double bonds, for example, (meth)acrylate monomers or oligomers.

[0042] In this article, "(meth)acrylate" means "methacrylate" or "acrylate".

[0043] For example, other photocurable flame retardant materials may include monofunctional monomers such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, isooctyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and glycidyl methacrylate; difunctional monomers such as 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, and ethylene glycol di(meth)acrylate; and polyfunctional monomers such as trimethylolpropane triacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate; as well as their oligomers.

[0044] As described above, since the rigid photocurable flame retardant compound of the present invention contains two polymerizable double bond structures in a single molecule, a high cross-linking density three-dimensional network can be formed in the resulting photocurable bulk flame retardant resin, whether it is photocured alone or photocured together with other photocurable flame retardant materials. This significantly improves the mechanical properties of the flame retardant resin and endows it with the characteristic of rapid curing.

[0045] Process for the preparation of rigid photocurable flame retardant compounds Figure 1 The reaction equations for the preparation process of a rigid photocurable flame retardant compound according to an embodiment of the present invention are shown.

[0046] Reference Figure 1 As can be seen, the method for producing the rigid photocurable flame retardant compound of the present invention mainly includes the following two reactions.

[0047] Reaction 1: The nucleophilic substitution reaction between pentaerythritol and phosphorus oxychloride yields the intermediate bis(chlorophosphoryl)pentaerythritol (SPDPC). That is, one pentaerythritol molecule undergoes a nucleophilic substitution reaction with two phosphorus oxychloride molecules to produce a spirocyclic phosphate ester.

[0048] Reaction 2: A nucleophilic substitution reaction between SPDPC and hydroxyethyl acrylate yields the rigid, photocurable flame retardant compound. Specifically, one SPDPC molecule undergoes a nucleophilic substitution reaction with two hydroxyethyl acrylates, resulting in a rigid, photocurable flame retardant compound containing a rigid spirocyclic structure, phosphate groups, and polymerizable double bonds.

[0049] According to an embodiment of the present invention, the preparation method of the rigid photocurable flame retardant compound of the present invention may include the following specific steps: (1) Synthesizing phosphoryl dichloride with a helical structure: In a three-necked flask, a certain amount of pentaerythritol and phosphorus oxychloride are added, and the temperature is slowly raised to 70~90℃ and kept at a constant temperature for 2-4h; then the temperature is raised to 100~120℃ and kept at a constant temperature for 6-8h until no HCl gas is released. After the reaction is completed, the system is cooled to room temperature, the precipitate is collected by filtration and washed three times with solvent. Finally, the obtained white solid is dried in a vacuum drying oven to obtain intermediate 1: SPDPC; (2) Synthesizing a flame retardant UV curable monomer with a helical structure: A certain amount of SPDPC, hydroxyethyl acrylate and reaction solvent are added to a three-necked flask. After stirring for 30min, a certain amount of acid-binding agent is added to the mixture, and then stirred at room temperature. After the reaction is completed, the white solid is filtered and the reaction solvent is removed to obtain a pale yellow transparent viscous liquid as a rigid, flame retardant UV curable monomer product: DP-HA.

[0050] In step (1), the molar ratio of pentaerythritol to phosphorus oxychloride can be 1:5~7, for example, 1:5.1~6.7, 1:5.2~6.3, 1:5.3~6.1, 1:5.4~5.9, 1:5.5~5.8 or 1:5.6~5.7.

[0051] In step (2), the molar ratio of SPDPC to hydroxyethyl acrylate is 1:2 to 2.5, for example, it can be 1:2.2 to 2.5, 1:2.05 to 2.45, 1:2.1 to 2.4, 1:2.15 to 2.35, or 1:2.2 to 2.3. By setting the above feed amounts, the utilization rate of raw materials can be maximized, waste of raw materials can be avoided, and the desired target product can be prepared.

[0052] The solvent added in step (2) can be one or more of dichloromethane, chloroform, acetonitrile, diethyl ether, and acetone.

[0053] The polymerization inhibitor added in step (2) can be one or more of p-hydroxyanisole, p-methoxyphenol, hydroquinone, 2,5-di-tert-butylhydroquinone, and 2,6-di-tert-butyl-p-cresol, and the amount of polymerization inhibitor added can be from 50 ppm to 500 ppm. By adjusting the amount of polymerization inhibitor added, the reaction can proceed smoothly and the generation of side reactions can be effectively avoided.

[0054] The acid-binding agent added in step (2) can be one of pyridine, triethylamine, N,N-diisopropylethylamine, sodium carbonate, potassium carbonate and sodium acetate.

[0055] In step (2), the molar ratio of SPDPC to the acid-binding agent is 1:2 to 2.6, for example, it can be 1:2 to 2.5, 1:2.05 to 2.45, 1:2.1 to 2.4, 1:2.15 to 2.35, or 1:2.2 to 2.3. By adjusting the amount of acid-binding agent added, the occurrence of side reactions can be effectively avoided, and the reaction rate and yield can be improved.

[0056] The rigid, flame-retardant UV-curable monomer prepared by this invention is synthesized from pentaerythritol, phosphorus oxychloride, and hydroxyethyl acrylate via a two-step nucleophilic substitution reaction. The reaction intermediates require no complex post-processing, making the synthesis process simple and environmentally friendly. The prepared product contains rigid spirocyclic units, phosphate groups, and polymerizable double bonds in its molecular structure, giving it both photocurability and inherent flame-retardant properties. While improving the flame retardancy of the photocurable material, it also significantly enhances its mechanical properties. The obtained flame-retardant UV-curable product can be used directly as a flame-retardant photocurable resin or as a reactive flame retardant in other photocurable flame-retardant formulations.

[0057] To provide a clearer understanding of the technical content of this invention, the following embodiments are provided for detailed description. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the raw materials involved in the following embodiments are all commercially available products that can be purchased from the market or prepared using existing methods.

[0058] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions.

[0059] Example 1 (1) 20.0 g (approximately 0.15 mol) of pentaerythritol and 130.0 g (approximately 0.85 mol) of phosphorus oxychloride were added to a 250 ml three-necked round-bottom flask equipped with a reflux apparatus and a magnetic stirrer. First, the mixture was heated to 80 °C and stirred for 3 h. Then, the temperature was raised to 110 °C and the reaction was continued for approximately 7 h until no HCl gas was released. After the reaction was completed, the system was cooled to room temperature, the precipitate was collected by filtration, and washed three times with a mixture of chloroform and diethyl ether (volume ratio 50 / 50). Finally, the obtained white solid was dried in a vacuum drying oven at 60 °C for 24 h to obtain the intermediate SPDPC with a yield of 75%.

[0060] (2) 4.5 g (about 0.038 mol) of hydroxyethyl acrylate, 5.0 g (about 0.017 mol) of SPDPC, 50 ppm of hydroquinone as a polymerization inhibitor, and 50 g of dichloromethane were added to a 250 ml three-necked round-bottom flask equipped with a magnetic stirrer and stirred for 30 min. 3.9 g (about 0.038 mol) of triethylamine was slowly added dropwise, and the reaction temperature was maintained at 0-5 °C during the dropwise addition. After the addition was completed, the reaction was kept at this temperature for 2 h, and then the temperature was raised to room temperature and reacted for 8 h. The solid was filtered, and 50 g of deionized water was added to the organic layer. The mixture was stirred and washed for 10 min and then separated. This process was repeated three times. The solvent was evaporated to obtain a pale yellow transparent viscous liquid with a yield of 90.5%.

[0061] Example 2 (1) 20.0 g (approximately 0.15 mol) of pentaerythritol and 130.0 g (approximately 0.85 mol) of phosphorus oxychloride were added to a 250 ml three-necked round-bottom flask equipped with a reflux apparatus and a magnetic stirrer. First, the mixture was heated to 80 °C and stirred for 3 h. Then, the temperature was raised to 110 °C and the reaction was continued for approximately 7 h until no HCl gas was released. After the reaction was completed, the system was cooled to room temperature, the precipitate was collected by filtration, and washed three times with chloroform and diethyl ether (volume ratio 50 / 50). Finally, the obtained white solid was dried in a vacuum drying oven at 60 °C for 24 h to obtain the intermediate SPDPC with a yield of 75%.

[0062] (2) 4.9 g (about 0.042 mol) of hydroxyethyl acrylate, 5.0 g (about 0.017 mol) of SPDPC, 50 ppm of hydroquinone as a polymerization inhibitor, and 50 g of dichloromethane were added to a 250 ml three-necked round-bottom flask equipped with a magnetic stirrer and stirred for 30 min. 4.5 g (about 0.044 mol) of triethylamine was slowly added dropwise, and the reaction temperature was maintained at 0-5 °C during the dropwise addition. After the addition was completed, the reaction was kept at this temperature for 2 h, and then the temperature was raised to room temperature and reacted for 8 h. The solid was filtered, and 50 g of deionized water was added to the organic layer. The mixture was stirred and washed for 10 min and then separated. This process was repeated three times. The solvent was evaporated to obtain a pale yellow transparent viscous liquid with a yield of 91.2%.

[0063] Example 3 (1) 20.0 g (approximately 0.15 mol) of pentaerythritol and 130.0 g (approximately 0.85 mol) of phosphorus oxychloride were added to a 250 ml three-necked round-bottom flask equipped with a reflux apparatus and a magnetic stirrer. First, the mixture was heated to 80 °C and stirred for 3 h. Then, the temperature was raised to 110 °C and the reaction was continued for approximately 7 h until no HCl gas was released. After the reaction was completed, the system was cooled to room temperature, the precipitate was collected by filtration, and washed three times with chloroform and diethyl ether (volume ratio 50 / 50). Finally, the obtained white solid was dried in a vacuum drying oven at 60 °C for 24 h to obtain the intermediate SPDPC with a yield of 75%.

[0064] (2) 4.9 g (about 0.042 mol) of hydroxyethyl acrylate, 5.0 g (about 0.017 mol) of SPDPC, 50 ppm of hydroquinone as a polymerization inhibitor, and 50 g of dichloromethane were added to a 250 ml three-necked round-bottom flask equipped with a magnetic stirrer and stirred for 30 min. 4.2 g (about 0.042 mol) of triethylamine was slowly added dropwise, and the reaction temperature was maintained at 0-5 °C during the dropwise addition. After the addition was completed, the reaction was kept at this temperature for 2 h, and then the temperature was raised to room temperature and reacted for 8 h. The solid was filtered, and 50 g of deionized water was added to the organic layer. The mixture was stirred and washed for 10 min and then separated. This process was repeated three times. The solvent was evaporated to obtain a pale yellow transparent viscous liquid with a yield of 91.2%.

[0065] Figure 2 Infrared spectral analysis of a rigid photocurable flame retardant compound according to an embodiment of the present invention is shown. Figure 3 The thermal stability analysis diagram (TG / DTG) of a rigid photocurable flame retardant compound according to an embodiment of the present invention is shown.

[0066] like Figure 2 As shown in the FTIR spectrum of DP-HA, at 1700 cm⁻¹ -1 The absorption peak at 1643 cm⁻¹ is attributed to the stretching vibration of the carbonyl group (C=O); -1 The absorption peak at 1230 cm⁻¹ corresponds to the stretching vibration of the carbon-carbon double bond (C=C); -1 and 1190cm -1 The absorption peaks at these locations originate from the stretching vibrations of the phosphorus-oxygen double bond (P=O) and the phosphorus-oxygen-carbon bond (POC), respectively. The detection results of these characteristic peaks are consistent with the structural characteristics of the target product DP-HA, indicating that the compound has been successfully prepared.

[0067] like Figure 3 As shown, the initial decomposition temperature (T) of the sample under a nitrogen atmosphere 5% The temperature was 279.5℃, and the char residue at 700℃ reached 43.5wt%, demonstrating excellent thermal stability and char-forming performance.

[0068] Test examples The rigid, photocurable flame-retardant compounds prepared in Examples 1 to 3 were photocured to obtain bulk flame-retardant resins. The performance of each bulk flame-retardant resin was tested. The results are shown in Table 1.

[0069] The test conditions and basis are as follows: Functionality and phosphorus content: calculated based on chemical structural formula; Viscosity: rotational viscometer method, GB / T265-1988; Curing conditions: 5% photoinitiator TPO added, irradiation energy 800-1200 mJ / cm³ 2UV coated; film thickness 20μm; pencil hardness: GB / T6736-2006; tensile strength test: ASTM D-638 standard; thermogravimetric analysis: heating rate 20℃ / min, room temperature ~ 800℃; vertical burning: ASTM D618 standard; oxygen index (LOI) test: ASTM D2863 standard.

[0070] Table 1 Group Functionality Phosphorus content wt% Viscosity mPa-s / 60°C Color (APHA) Pencil hardness H Thermal gravimetric T 5% °C 700°C residue wt% Vertical burning UL-94 Oxygen index % Example 1 2 13.6 15000 ≤240 5H 281.3 42.4 V-0 30.5% Example 2 2 13.4 17000 ≤300 4H 283.6 44.6 V-0 30.7% Example 3 2 13.3 24000 ≤320 5H 282.1 42.3 V-0 31.2% As shown in Table 1, the rigid flame-retardant UV-curable monomer prepared by this invention has the following characteristics: phosphorus content is higher than 13 wt%, viscosity at 60℃ is 15000~24000 mPa·s, and chroma (APHA) is lower than 320. The cured material exhibits excellent flame-retardant properties, passes the UL-94V-0 rating test, has a limiting oxygen index higher than 30%, and possesses good self-extinguishing and flame-retardant characteristics. Regarding thermal stability, the initial decomposition temperature (T0) of the material in a nitrogen atmosphere is [not specified]. 5% The temperature range is above 279.5℃, and the char residue at 700℃ reaches approximately 43.5wt%. Furthermore, this material also possesses excellent mechanical properties, exhibiting high tensile strength and hardness. In summary, the monomer provided by this invention has broad application prospects in the field of photocurable flame retardant materials.

[0071] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A rigid, photocurable flame-retardant compound, characterized in that, The compound is represented by the following structural formula 1: Structural Formula 1 。 2. A method for preparing the rigid photocurable flame retardant compound according to claim 1, characterized in that, The method includes the following steps: Step 1: Pentaerythritol undergoes a nucleophilic substitution reaction with phosphorus oxychloride to obtain the intermediate SPDPC; Step 2: The SPDPC intermediate is subjected to a nucleophilic substitution reaction with hydroxyethyl acrylate to obtain the compound.

3. The method according to claim 2, characterized in that: In step 1, pentaerythritol and phosphorus oxychloride are added to a reaction vessel and reacted at a first reaction temperature for a first reaction time, and then reacted at a second reaction temperature for a second reaction time to obtain intermediate SPDPC. In step 2, intermediate SPDPC, hydroxyethyl acrylate, polymerization inhibitor and solvent are added to a reaction vessel, mixed and then acid-binding agent is added. The reaction is carried out at a third reaction temperature for a third reaction time, and then at a fourth reaction temperature for a fourth reaction time to obtain the compound.

4. The method according to claim 3, characterized in that: In step 1, the first reaction temperature is in the range of 70°C to 90°C, the first reaction time is in the range of 2 hours to 4 hours, the second reaction temperature is in the range of 100°C to 120°C, and the second reaction time is in the range of 6 hours to 8 hours. In step 2, the third reaction temperature is in the range of 0°C to 5°C, the third reaction time is in the range of 1 hour to 3 hours, the fourth reaction temperature is room temperature, and the fourth reaction time is in the range of 6 hours to 10 hours.

5. The method according to claim 3, characterized in that: In step 1, the molar ratio of pentaerythritol to phosphorus oxychloride is 1:5~7; In step 2, the molar ratio of SPDPC to hydroxyethyl acrylate is 1:2~2.

5.

6. The method according to claim 3, characterized in that, The solvent is one or more of dichloromethane, trichloromethane, acetonitrile, diethyl ether, and acetone.

7. The method according to claim 3, characterized in that, The polymerization inhibitor is one or more of p-hydroxyanisole, p-methoxyphenol, hydroquinone, 2,5-di-tert-butylhydroquinone, and 2,6-di-tert-butyl-p-cresol, and the amount of the polymerization inhibitor added is from 50 ppm to 500 ppm.

8. The method according to claim 3, characterized in that, The acid-binding agent is one of pyridine, triethylamine, N,N-diisopropylethylamine, sodium carbonate, potassium carbonate, and sodium acetate.

9. The method according to claim 3, characterized in that, The molar ratio of SPDPC to acid binder is 1:2~2.

6.

10. The application of the rigid photocurable flame retardant compound according to claim 1 in a photocurable bulk flame retardant resin, characterized in that, The compound can be cured alone to form a bulk flame-retardant resin, or the compound can be mixed with other photocurable materials and then cured by light to form a bulk flame-retardant resin.

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