Hyperbranched flame retardant, preparation method thereof and flame-retardant epoxy resin

Abstract

The invention belongs to the technical field of flame-retardant materials, and particularly relates to a hyperbranched flame retardant, a preparation method thereof and flame-retardant epoxy resin. The specific preparation method comprises the following steps: in a solvent system, placing itaconic anhydride and phosphaphenanthrene at 80-110 DEG C, and carrying out an addition reaction to obtain a first intermediate; mixing phosphorus oxychloride and 1, 3, 5-tris (2-ethoxyl) cyanuric acid in a solvent system, and carrying out nucleophilic substitution reaction under the action of an acid-binding agent to obtain a second intermediate; carrying out esterification reaction on the first intermediate and the second intermediate at 80-120 DEG C to obtain a phosphorus-nitrogen intermediate; and under a protective atmosphere, placing the phosphorus-nitrogen intermediate and boric acid at 120-160 DEG C, and carrying out a condensation reaction to obtain the hyperbranched flame retardant. The flame-retardant epoxy resin prepared by using the hyperbranched flame retardant prepared by the invention not only has excellent flame retardant property, but also has the characteristics of high strength and high toughness.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame retardant materials, and particularly relates to a hyperbranched flame retardant, a preparation method thereof, and a flame retardant epoxy resin. Background Art

[0002] As one of the three major traditional thermosetting resins, epoxy resin is widely used in fields such as aviation materials, electronic component bonding materials, coatings, and composite materials due to its high strength and chemical resistance. However, similar to most polymer materials, epoxy resin has high flammability, with an oxygen index of only 23.7%, and generates a large amount of heat and toxic smoke during combustion, resulting in serious fire hazards, which greatly limits its application in high-safety requirement scenarios such as precision electronic devices.

[0003] Currently, for the flame retardant modification of epoxy resin, the main method is to add intumescent flame retardants to the epoxy resin matrix to improve its flame retardant performance. Although traditional halogen-based flame retardants have significant flame retardant effects, they generate toxic gases such as hydrogen halide and environmental pollutants such as polybrominated dibenzodioxins during combustion, causing certain harm to the ecological environment. Therefore, the development of halogen-free flame retardants suitable for epoxy resin has become an inevitable trend in the industry. Compared with halogen-containing flame retardants, phosphorus-nitrogen flame retardants can carry out flame retardancy in both the condensed phase and the gas phase, and have the advantages of low toxicity, high efficiency, and smoke suppression, and are widely used in various halogen-free flame retardant polymer materials.

[0004] Patent CN113621217A discloses a halogen-free flame retardant epoxy resin and a preparation method thereof, which uses halogen-free phosphorus-containing flame retardants, coupling agents, defoamers and other additives to achieve the flame retardancy of epoxy resin, but the total filler addition amount is as high as 10wt%, which leads to a significant decrease in the transparency of the material.

[0005] Patent CN110760163A discloses a halogen-free flame retardant epoxy resin composite, and the addition amount of its flame retardant needs to reach 16wt% to reach the UL-94V-0 grade, which inevitably causes a significant attenuation of the mechanical properties of the material.

[0006] Therefore, existing halogen-free flame retardants need to be added in relatively high amounts to meet the V-0 grade. However, due to the poor compatibility between the flame retardant and the polymer resin matrix, excessive addition is likely to cause a significant deterioration of the mechanical properties of the material. Summary of the Invention

[0007] In order to solve the above technical problem that the excessive addition of existing halogen-free flame retardants leads to the deterioration of mechanical properties, the present invention provides a hyperbranched flame retardant, a preparation method thereof, and a flame retardant epoxy resin.

[0008] The present invention integrates phosphorus, nitrogen, and boron elements into the structure of a hyperbranched flame retardant, utilizes the ternary synergistic flame retardancy of phosphorus, nitrogen, and boron, and significantly improves the flame retardant performance of the hyperbranched flame retardant through three mechanisms: gas-phase quenching, char expansion, and char layer strengthening, which is conducive to reducing the dosage of the flame retardant. At the same time, the transparency and mechanical properties of the material itself are maintained.

[0009] The present invention uses phosphaphenanthrene and phosphorus oxychloride to provide phosphorus elements, and inhibits combustion through the dual effects of gas-phase free radical quenching of phosphorus and catalytic char formation in the condensed phase; at the same time, 1,3,5-tris(2-hydroxyethyl) cyanuric acid is introduced to provide a rich nitrogen source, and non-combustible gases such as NH3 and N2 are generated by the decomposition of nitrogen to dilute the concentration of combustible gases and promote the formation of an expanded char layer; at the same time, boron elements are also introduced, and boron phosphate is formed by reacting with phosphorus during combustion to participate in the char formation reaction, forming a B-O-C cross-linked network in the char layer, enhancing the thermal stability and compactness of the char layer, and thereby reducing heat and smoke release.

[0010] The first object of the present invention is to provide a preparation method of a hyperbranched flame retardant, comprising the following steps:

[0011] In a solvent system, itaconic anhydride and phosphaphenanthrene shown in Formula 1 are placed at 80°C to 110°C to cause an addition reaction between the P-H group of the phosphaphenanthrene shown in Formula 1 and the C═C group of itaconic anhydride to obtain a first intermediate;

[0012]

[0013] In a solvent system, phosphorus oxychloride and 1,3,5-tris(2-hydroxyethyl) cyanuric acid are mixed, and under the action of an acid-binding agent, a nucleophilic substitution reaction occurs between the phosphoryl chloride group in phosphorus oxychloride and the hydroxyl group of 1,3,5-tris(2-hydroxyethyl) cyanuric acid to obtain a second intermediate; the first intermediate and the second intermediate are placed at 80°C to 120°C to cause an esterification reaction between the anhydride group of the first intermediate and the hydroxyl group in the second intermediate to obtain a phosphorus-nitrogen intermediate; under a protective atmosphere, the phosphorus-nitrogen intermediate and boric acid are placed at 120°C to 160°C to cause a condensation reaction between the hydroxyl group of the phosphorus-nitrogen intermediate and the hydroxyl group of boric acid to form a three-dimensional hyperbranched network, obtaining a hyperbranched flame retardant.

[0014] The specific synthesis route is as follows:

[0015]

[0016]

[0017] Among them, M is * is the connection part.

[0018] It should be noted that the P-H bond contained in phosphaphenanthrene with excellent gas-phase free radical capture ability has high reactivity and is prone to undergo an addition reaction with the C═C in itaconic anhydride. In the present invention, itaconic anhydride is used as a linking unit. In a solvent system, after mixing itaconic anhydride and phosphaphenanthrene and heating under reflux, the P-H group of phosphaphenanthrene undergoes an addition reaction with the C═C group of itaconic anhydride to form a first intermediate containing phosphaphenanthrene.

[0019] Preferably, the molar ratio of the C═C group of itaconic anhydride to the P-H group of the phosphaphenanthrene shown in Formula 1 is 1:1.

[0020] Preferably, the time for the addition reaction is 8 h to 16 h.

[0021] In the present invention, the triazine trione unit of 1,3,5-tris(2-hydroxyethyl)cyanuric acid is introduced to provide a rich nitrogen source to promote the formation of an expanded carbon layer; meanwhile, phosphorus element is provided by phosphorus oxychloride. Phosphorus oxychloride undergoes a nucleophilic substitution reaction with the hydroxyl groups of 1,3,5-tris(2-hydroxyethyl)cyanuric acid to form a phosphorus-containing phosphate ester structure, obtaining a second intermediate.

[0022] Preferably, the specific preparation method of the second intermediate is as follows:

[0023] After mixing 1,3,5-tris(2-hydroxyethyl)cyanuric acid, an acid-binding agent and a solvent, phosphorus oxychloride is slowly added dropwise to enable the phosphorus oxychloride to undergo a nucleophilic substitution reaction with the hydroxyl groups of 1,3,5-tris(2-hydroxyethyl)cyanuric acid, obtaining the second intermediate.

[0024] Preferably, the molar ratio of the hydroxyl group of 1,3,5-tris(2-hydroxyethyl)cyanuric acid to the phosphoryl chloride group of phosphorus oxychloride is 3:1.

[0025] Preferably, the acid-binding agent is potassium carbonate.

[0026] Preferably, the temperature of the nucleophilic substitution reaction is room temperature and the time is 6 h to 10 h.

[0027] Preferably, the solvent is all tetrahydrofuran.

[0028] Preferably, the molar ratio of the anhydride group of the first intermediate to the hydroxyl group of the second intermediate is 1:2.

[0029] Preferably, the time for the esterification reaction is 8 h to 16 h.

[0030] After mixing the phosphorus-nitrogen intermediate and boric acid, the hydroxyl group of the phosphorus-nitrogen intermediate undergoes a condensation reaction with boric acid at high temperature to form a B-O-C bond, forming a three-dimensional hyperbranched network, obtaining a hyperbranched flame retardant.

[0031] Preferably, the molar ratio of the hydroxyl group of the phosphorus-nitrogen intermediate to the hydroxyl group of boric acid is 3:2.

[0032] Preferably, the condensation reaction time is 2 h to 6 h.

[0033] The second object of the present invention is to provide a hyperbranched flame retardant prepared by the above preparation method.

[0034] Preferably, the hyperbranched flame retardant has the following structural general formula:

[0035]

[0036] wherein M is * is the connecting part.

[0037] The third object of the present invention is to provide a flame retardant epoxy resin.

[0038] Preferably, the specific preparation method of the flame retardant epoxy resin is as follows:

[0039] After mixing the epoxy resin monomer, the curing agent and the hyperbranched flame retardant, injection molding and curing are carried out to obtain the flame retardant epoxy resin.

[0040] Preferably, the molar ratio of the epoxy group in the epoxy resin monomer to the active hydrogen on the amine in the curing agent is 1:1.

[0041] Preferably, the mass percentage of the hyperbranched flame retardant in the flame retardant epoxy resin is 1% to 5%.

[0042] Preferably, the mixing temperature is 80 °C.

[0043] Preferably, the curing conditions are: curing at 120 °C for 2 h and then curing at 160 °C for 3 h.

[0044] Preferably, the epoxy resin monomer is bisphenol A epoxy resin, and the epoxy value is 0.42 to 0.58.

[0045] Preferably, the curing agent is an amine-based flame retardant; the curing agent is one or two of 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylether and m-phenylenediamine.

[0046] Compared with the prior art, the present invention has the following technical effects:

[0047] 1. The present invention integrates phosphorus, nitrogen and boron elements into the structure of the hyperbranched flame retardant, utilizes the triple synergistic flame retardancy of phosphorus, nitrogen and boron, and through the triple mechanisms of gas-phase quenching, intumescent char formation and char layer strengthening, the heat release rate of combustion is significantly reduced, the flame retardant performance is significantly improved, which is beneficial to reducing the dosage of the flame retardant, and at the same time, maintaining the transparency and mechanical properties of the material itself.

[0048] 2. The hyperbranched flame retardant molecules formed by the present invention contain a phosphaphenanthrene rigid structure, a phosphate flexible segment, and a hyperbranched structure with boron as the node. Through the toughening of the flexible segment and microphase separation, the interaction between the hyperbranched flame retardant and the epoxy resin molecular chain is improved, and the compatibility is enhanced. At the same time, the carboxyl functional groups at the ends of the hyperbranched flame retardant can participate in the curing reaction of the epoxy resin, enabling the hyperbranched flame retardant to be embedded in the epoxy resin in a covalent bond manner. This not only avoids the precipitation of traditional additive flame retardants on the surface of the product but also significantly improves the compatibility between the flame retardant and the epoxy matrix, enhances the interfacial bonding force, and thus significantly improves the overall performance of the epoxy resin.

[0049] 3. The flame-retardant epoxy resin prepared by the present invention not only has excellent flame retardant properties but also has the characteristics of high strength and high toughness. This is mainly because the designed hyperbranched flame retardant and the epoxy resin can react and be compatible at the molecular scale, and its molecules contain a phosphaphenanthrene rigid structure, a phosphate flexible segment, and a hyperbranched structure with boron as the node, which can enhance the mechanical properties of the epoxy resin through the toughening of the flexible segment and the enhancement of microphase separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 1H NMR spectrum of the hyperbranched flame retardant prepared in Example 1.

[0051] Figure 2 Heat release rate diagrams of the epoxy resins prepared in Application Example 1 and Application Comparative Examples 1 - 3.

[0052] Figure 3 Total heat release diagrams of the epoxy resins prepared in Application Example 1 and Application Comparative Examples 1 - 3.

[0053] Figure 4 Smoke release rate diagrams of the epoxy resins prepared in Application Example 1 and Application Comparative Examples 1 - 3.

[0054] Figure 5 Total smoke release diagrams of the epoxy resins prepared in Application Example 1 and Application Comparative Examples 1 - 3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings.

[0056] In the description of the present invention, unless otherwise specified, the reagents used are commercially available, and the methods used are conventional techniques in the art.

[0057] It should be noted that the full English name of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide is 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-oxide, which is abbreviated as phosphaphenanthrene in Chinese and DOPO in English; the full English name of itaconic anhydride is Itaconic anhydride, abbreviated as IA.

[0058] Example 1

[0059] A preparation method of a hyperbranched flame retardant includes the following steps:

[0060] Add 11.2 g of itaconic anhydride and 21.6 g of phosphaphenanthrene to 200 mL of tetrahydrofuran, heat under reflux at 80 °C for 10 h, remove the solvent under vacuum decompression to obtain a first intermediate, denoted as DOPO-IA.

[0061] Mix 26.1 g of 1,3,5-tris(2-hydroxyethyl) cyanuric acid, 15 g of potassium carbonate and 300 mL of tetrahydrofuran, and then dropwise add 5.5 g of phosphorus oxychloride, and react at room temperature for 6 h to obtain a second intermediate.

[0062] Add 9 g of DOPO-IA to the second intermediate, heat under reflux at 80 °C for 8 h, filter and dry to obtain a phosphorus-nitrogen intermediate, denoted as P-DOPO-N.

[0063] Add 12 g of P-DOPO-N and 1 g of boric acid to a round-bottom flask, react at 140 °C for 2 h under nitrogen protection, cool, add ethanol for washing, filter and dry to obtain a hyperbranched flame retardant, denoted as BPN.

[0064] Example 2

[0065] A preparation method of a hyperbranched flame retardant includes the following steps:

[0066] Add 11.2 g of itaconic anhydride and 21.6 g of phosphaphenanthrene to 200 mL of tetrahydrofuran, heat under reflux at 110 °C for 8 h, remove the solvent under vacuum decompression to obtain a first intermediate, denoted as DOPO-IA.

[0067] Mix 26.1 g of 1,3,5-tris(2-hydroxyethyl) cyanuric acid, 15 g of potassium carbonate and 300 mL of tetrahydrofuran, and then dropwise add 5.5 g of phosphorus oxychloride, and react at room temperature for 10 h to obtain a second intermediate.

[0068] Add 9 g of DOPO-IA to the second intermediate, heat under reflux at 120 °C for 8 h, filter and dry to obtain a phosphorus-nitrogen intermediate, denoted as P-DOPO-N.

[0069] Add 12 g of P-DOPO-N and 1 g of boric acid into a round-bottom flask, react at 160 °C for 2 h under nitrogen protection, add ethanol for washing, filtration, and drying after cooling to obtain a hyperbranched flame retardant, denoted as BPN.

[0070] Example 3

[0071] A preparation method of a hyperbranched flame retardant, comprising the following steps:

[0072] Add 11.2 g of itaconic anhydride and 21.6 g of phosphaphenanthrene into 200 mL of tetrahydrofuran, heat under reflux at 90 °C for 16 h, remove the solvent under vacuum to obtain a first intermediate, denoted as DOPO-IA.

[0073] Mix 26.1 g of 1,3,5-tris(2-hydroxyethyl) cyanuric acid, 15 g of potassium carbonate and 300 mL of tetrahydrofuran, and then dropwise add 5.5 g of phosphorus oxychloride, react at room temperature for 8 h to obtain a second intermediate.

[0074] Add 9 g of DOPO-IA into the second intermediate, heat under reflux at 100 °C for 16 h, filter and dry to obtain a phosphorus-nitrogen intermediate, denoted as P-DOPO-N.

[0075] Add 12 g of P-DOPO-N and 1 g of boric acid into a round-bottom flask, react at 120 °C for 6 h under nitrogen protection, add ethanol for washing, filtration, and drying after cooling to obtain a hyperbranched flame retardant, denoted as BPN.

[0076] Comparative Example 1

[0077] A preparation method of a flame retardant, comprising the following steps:

[0078] Add 11.2 g of itaconic anhydride and 21.6 g of phosphaphenanthrene into 200 mL of tetrahydrofuran, heat under reflux at 80 °C for 10 h, remove the solvent under vacuum to obtain a flame retardant, denoted as DOPO-IA.

[0079] Comparative Example 2

[0080] A preparation method of a flame retardant, comprising the following steps:

[0081] Add 11.2 g of itaconic anhydride and 21.6 g of phosphaphenanthrene into 200 mL of tetrahydrofuran, heat under reflux at 80 °C for 10 h, remove the solvent under vacuum to obtain a first intermediate, denoted as DOPO-IA.

[0082] Mix 26.1 g of 1,3,5-tris(2-hydroxyethyl) cyanuric acid, 15 g of potassium carbonate and 300 mL of tetrahydrofuran, and then dropwise add 5.5 g of phosphorus oxychloride, react at room temperature for 6 h to obtain a second intermediate.

[0083] 9 g of DOPO-IA was added to the second intermediate, and the mixture was heated under reflux at 80 °C for 8 h, filtered and dried to obtain a flame retardant denoted as P-DOPO-N.

[0084] In Examples 1 to 3 of the present invention, hyperbranched flame retardants that solve the problem of deterioration of mechanical properties caused by excessive addition of halogen-free flame retardants were prepared. The flame retardancy data of the hyperbranched flame retardants prepared in Examples 2 to 3 were similar to those in Example 1. Taking the hyperbranched flame retardants prepared in Example 1 and Comparative Examples 1 to 3 as examples, the preparation of flame-retardant epoxy resins was studied, and the specific research methods and results are as follows:

[0085] Application Example 1

[0086] A method for preparing a flame-retardant epoxy resin, comprising the following steps:

[0087] 5.2 g of BPN prepared in Example 1, 25 g of 4,4'-diaminodiphenylmethane and 100 g of bisphenol A epoxy resin were mixed, stirred at 80 °C for 30 min, degassed under vacuum for 10 min, and then quickly injected into a mold. The mixture was cured at 120 °C for 2 h and then at 160 °C for 3 h to obtain a flame-retardant epoxy resin.

[0088] Application Example 2

[0089] A method for preparing a flame-retardant epoxy resin, comprising the following steps:

[0090] 2.6 g of BPN prepared in Example 1, 25 g of 4,4'-diaminodiphenylmethane and 100 g of bisphenol A epoxy resin were mixed, stirred at 80 °C for 30 min, degassed under vacuum for 10 min, and then quickly injected into a mold. The mixture was cured at 120 °C for 2 h and then at 160 °C for 3 h to obtain a flame-retardant epoxy resin.

[0091] The difference from Application Example 1 is:

[0092] The mass percentage of BPN in the flame-retardant epoxy resin is 2%.

[0093] Application Example 3

[0094] A method for preparing a flame-retardant epoxy resin, comprising the following steps:

[0095] 3.1 g of BPN prepared in Example 1, 25 g of 4,4'-diaminodiphenylmethane and 100 g of bisphenol A epoxy resin were mixed, stirred at 80 °C for 30 min, degassed under vacuum for 10 min, and then quickly injected into a mold. The mixture was cured at 120 °C for 2 h and then at 160 °C for 3 h to obtain a flame-retardant epoxy resin.

[0096] The difference from Application Example 1 is as follows:

[0097] The mass percentage of BPN in the flame-retardant epoxy resin is 3%.

[0098] Application Comparative Example 1

[0099] A preparation method of a flame-retardant epoxy resin includes the following steps:

[0100] Mix 25 g of 4,4'-diaminodiphenylmethane and 100 g of bisphenol A epoxy resin, stir at 80 °C for 30 min, then perform vacuum defoaming for 10 min and quickly inject into a mold. The mixture is cured at 120 °C for 2 h and then cured at 160 °C for 3 h to obtain the flame-retardant epoxy resin.

[0101] The difference from Application Example 1 is as follows:

[0102] The BPN prepared in Example 1 was not added.

[0103] Application Comparative Example 2

[0104] A preparation method of a flame-retardant epoxy resin includes the following steps:

[0105] Mix 2.6 g of DOPO-IA prepared in Comparative Example 1, 25 g of 4,4'-diaminodiphenylmethane and 100 g of bisphenol A epoxy resin, stir at 80 °C for 30 min, then perform vacuum defoaming for 10 min and quickly inject into a mold. The mixture is cured at 120 °C for 2 h and then cured at 160 °C for 3 h to obtain the flame-retardant epoxy resin.

[0106] The difference from Application Example 1 is as follows:

[0107] The DOPO-IA prepared in Comparative Example 1 was added.

[0108] Application Comparative Example 3

[0109] A preparation method of a flame-retardant epoxy resin includes the following steps:

[0110] Mix 2.6 g of P-DOPO-N prepared in Comparative Example 2, 25 g of 4,4'-diaminodiphenylmethane and 100 g of bisphenol A epoxy resin, stir at 80 °C for 30 min, then perform vacuum defoaming for 10 min and quickly inject into a mold. The mixture is cured at 120 °C for 2 h and then cured at 160 °C for 3 h to obtain the flame-retardant epoxy resin.

[0111] The difference from Application Example 1 is as follows:

[0112] The P-DOPO-N prepared in Comparative Example 2 was added.

[0113] Experimental test:

[0114] 1. Flame retardancy test.

[0115] The present invention tests the limiting oxygen index according to the ASTM D2863-97 standard. The full English name of the limiting oxygen index is limiting oxygen index, and the English abbreviation is LOI. The vertical burning UL-94 rating is tested according to the ASTM D3801 standard.

[0116] Table 1 Oxygen index and vertical burning rating of flame-retardant epoxy resin

[0117]

[0118] Note: t1 represents the first burning time; t2 represents the second burning time; t1 + t2 represents the total burning time of the two times; P represents phosphorus; Yes represents having drips; No represents having no drips; "-" represents burning out and not continuing the test.

[0119] It can be seen from Table 1 that for the characterization data of the flame retardancy of the modified epoxy resin, compared with the pure epoxy resin without flame retardant modification, just adding 4% of BPN increases the oxygen index from 24.8% to 30.4%, and the vertical burning rating successfully reaches the highest level V-0. This is mainly due to the fact that the hyperbranched flame retardant contains the highly efficient flame retardant unit DOPO and phosphate esters, which not only have highly efficient flame retardant effects in both the condensed phase and the gas phase, but also can produce a synergistic flame retardant effect with the N and B elements in BPN. At the same time, the hyperbranched flame retardant can participate in the curing reaction of the epoxy resin, which embeds the flame retardant elements into the epoxy resin matrix in the form of covalent bonds, greatly enhancing the flame retardant efficiency of BPN. By comparing Examples 1, 2, and 3, it can be seen that as the addition amount of the hyperbranched flame retardant gradually increases from 2% to 4%, the oxygen index increases from the original 29.3% to 30.4%, and t1 in the vertical burning test gradually shortens. Finally, Example 1 containing 4% BPN successfully passes the V-0 level.

[0120] From the oxygen index and vertical burning test data of Application Comparative Example 2 and Application Comparative Example 3, it can be seen that when adding a phosphorus-based flame retardant alone or a flame retardant containing both phosphorus and nitrogen elements, the improvement of the flame retardant effect is limited under the condition of a small addition amount. And from the data of Application Example 1, it can be seen that when introducing the B element into the flame retardant to form a hyperbranched flame retardant with a phosphorus / nitrogen / boron ternary system, the flame retardant effect of the epoxy resin is greatly improved. This is mainly because the presence of the B element forms a low-melting glass protective layer such as borate and boron phosphate on the surface of the material during combustion. This protective layer can cover the surface of the material, prevent the contact of oxygen with the material, and cut off the oxygen supply required for the combustion reaction, thereby achieving the purpose of highly efficient flame retardancy.

[0121] In terms of heat and smoke suppression, from Figures 2 to 5It can be clearly seen that: whether compared with pure epoxy resin, or with flame-retardant epoxy resin containing DOPO-IA and phosphorus / nitrogen binary flame-retardant epoxy resin, the epoxy resin containing the ternary hyperbranched flame retardant has significantly reduced heat release rate, total heat release, smoke generation rate and total smoke production. This indicates that the ternary hyperbranched flame retardant designed in the present invention has excellent flame retardancy, smoke suppression and heat suppression effects.

[0122] 2. Mechanical property test.

[0123] The present invention conducts tensile strength, flexural strength and impact strength tests according to national standards GB / T 1040.2 - 2006, GB / T 9341 - 2008 and GB / T 1843 - 2008.

[0124] It can be seen from the characterization data of the mechanical properties of the modified epoxy resin in Table 2 that compared with the unmodified epoxy resin, the epoxy resin incorporating the ternary hyperbranched flame retardant has significantly improved tensile strength, flexural strength and impact strength. Among them, for the modified epoxy resin with 4% BPN added, its tensile strength, flexural strength and impact strength are increased by 20%, 17% and 40% respectively. For the epoxy resins containing only P flame retardant and only P and N flame retardants, although their tensile and flexural strengths are improved, their impact strength (toughness) deteriorates significantly.

[0125] Table 2 Tensile strength, flexural strength and impact strength of flame-retardant epoxy resins

[0126]

[0127] The excellent mechanical properties of the epoxy resin designed in the present invention are mainly due to the hyperbranched structure of BPN. On the one hand, the intramolecular cavity it has can provide free volume, enabling the molecular chains inside the epoxy resin to have more room for movement. When stressed, the molecular chains can better adjust their positions to avoid stress concentration. On the other hand, the active carboxylic acid groups in BPN can participate in the curing reaction of the matrix resin to increase the crosslinking density, and the phosphoric acid ester flexible chain segments it contains can be oriented and deformed when the material is subjected to external forces, absorbing and dissipating energy through the movement of the chain segments, thereby improving the overall toughness, ductility and robustness of the material.

[0128] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods adopted are the same as those in the examples, in order to prevent repetition, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept, and these changes and modifications all fall within the scope of the present invention.

[0129] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. If these modifications and variations of the present invention fall within the scope of equivalent technologies of the present invention, the present invention also intends to include these changes and modifications therein.

Claims

1. A preparation method of a hyperbranched flame retardant, characterized in that, Comprising the following steps: Under a solvent system, itaconic anhydride and the phosphaphenanthrene shown in Formula 1 are placed at 80°C to 110°C to cause an addition reaction between the P-H group of the phosphaphenanthrene shown in Formula 1 and the C═C group of itaconic anhydride, obtaining a first intermediate; Under a solvent system, phosphorus oxychloride and 1,3,5-tris(2-hydroxyethyl) cyanuric acid are mixed, and under the action of an acid-binding agent, a nucleophilic substitution reaction occurs between the phosphoryl chloride group in phosphorus oxychloride and the hydroxyl group of 1,3,5-tris(2-hydroxyethyl) cyanuric acid, obtaining a second intermediate; The first intermediate and the second intermediate are placed at 80°C to 120°C to cause an esterification reaction between the acid anhydride group of the first intermediate and the hydroxyl group of the second intermediate, obtaining a phosphorus-nitrogen intermediate; Under a protective atmosphere, the phosphorus-nitrogen intermediate and boric acid are placed at 120°C to 160°C to cause a condensation reaction between the hydroxyl group of the phosphorus-nitrogen intermediate and the hydroxyl group of boric acid, obtaining a hyperbranched flame retardant.

2. The preparation method of the hyperbranched flame retardant according to claim 1, wherein, The molar ratio of the hydroxyl group of the phosphorus-nitrogen intermediate to the hydroxyl group of boric acid is 3:

2.

3. The preparation method of the hyperbranched flame retardant according to claim 1, characterized in that, The molar ratio of the acid anhydride group of the first intermediate to the hydroxyl group of the second intermediate is 1:

2.

4. The preparation method of the hyperbranched flame retardant according to claim 1, wherein The molar ratio of the hydroxyl group of 1,3,5-tris(2-hydroxyethyl) cyanuric acid to the phosphoryl chloride group of phosphorus oxychloride is 3:

1.

5. The preparation method of the hyperbranched flame retardant according to claim 1, characterized in that, The molar ratio of the C═C group of itaconic anhydride to the P-H group of the phosphaphenanthrene shown in Formula 1 is 1:

1.

6. The preparation method of the hyperbranched flame retardant according to claim 1, wherein The time of the addition reaction is 8h to 16h; The temperature of the nucleophilic substitution reaction is room temperature, and the time is 6h to 10h; The time of the esterification reaction is 8h to 16h; The time of the condensation reaction is 2h to 6h.

7. The preparation method of the hyperbranched flame retardant according to claim 1, wherein The acid-binding agent is potassium carbonate.

8. A hyperbranched flame retardant, characterized in that, The hyperbranched flame retardant is prepared from the hyperbranched flame retardant according to any one of claims 1 to 7.

9. A flame-retardant epoxy resin, characterized in that, The flame-retardant epoxy resin is prepared using the hyperbranched flame retardant according to claim 8.

10. The flame-retardant epoxy resin according to claim 9, wherein The specific preparation method of the flame-retardant epoxy resin is as follows: After mixing an epoxy resin monomer, a curing agent, and a hyperbranched flame retardant, injection molding and curing are performed to obtain a flame-retardant epoxy resin; Among them, the molar ratio of the epoxy group of the epoxy resin monomer to the active hydrogen on the amine of the curing agent is 1:1; The mass percentage of the hyperbranched flame retardant in the flame-retardant epoxy resin is 1% to 5%.

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