DOPO-based compound and preparation method thereof, epoxy resin curing agent, flame retardant and flame-retardant epoxy resin composition

Abstract

The invention discloses a DOPO-based compound and a preparation method thereof, an epoxy resin curing agent, a flame retardant and a flame-retardant epoxy resin composition. The DOPO-based compound has the following structure: # imgabs0 #, in which R is at least one of alkylene, arylene, arylene alkyl, alkylene aryl, cycloalkylene, alkylene cycloalkyl and cycloalkylene alkyl. From the perspective of low cost, environmental friendliness, excellent flame retardant property and comprehensive performance, the organic nitrogen / phosphorus flame retardant is developed, and is used as an epoxy curing agent at the same time. The nitrogen-phosphorus flame retardant simultaneously contains two structures of DOPO and secondary amine, a generated cured product is good in flame retardant property, the flame retardant does not migrate to the surface of resin, the mechanical property is not reduced, and the flame retardant property, the limit oxygen index and the heat resistance of the epoxy resin can be effectively improved by modifying the epoxy resin with the nitrogen-phosphorus flame retardant.

Description

Technical Field

[0001] The invention relates to the technical field of flame retardants, and in particular to a DOPO-based compound and a preparation method thereof, an epoxy resin curing agent, a flame retardant and a flame retardant epoxy resin composition. Background Art

[0002] Epoxy resin is an epoxy oligomer that can form a three-dimensional network of thermosetting plastics when reacting with a curing agent. Because its cured product has excellent adhesion, heat resistance, chemical resistance, mechanical properties and electrical properties, it is a widely used variety of thermosetting resins and is widely used in coatings, adhesives, composite materials and other fields.

[0003] Epoxy resin is a flammable material. After being ignited in the air, epoxy resin can burn quickly and release a large amount of heat during the combustion process. The flame spreads rapidly and produces molten droplets, thick smoke and harmful gases, which cause great harm to life and property. These shortcomings limit the use of epoxy resin in fields with flame retardant requirements. Therefore, flame retardant modification of epoxy resin is conducive to broadening its application range. Most of the research on halogen-free flame retardants at home and abroad focuses on the development of organic phosphorus-containing flame retardants, organic nitrogen-containing flame retardants, and phosphorus / nitrogen synergistic flame retardants (CN102838778A, CN107056840A, CN106279771A, CN105950188A, CN105153228A). Among them, the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) structure is an important flame retardant intermediate. Its molecule contains a PH bond and can undergo addition reactions with unsaturated bonds, carbonyl groups, oxazine rings, etc. Compared with inorganic phosphorus additives (red phosphorus, phosphates, phosphate oxides, phosphate compounds, phosphates, etc.), this type of organophosphorus flame retardant has better compatibility and binding ability with the matrix resin and is not prone to agglomeration and exudation. However, since DOPO has only one PH reaction site, when DOPO is directly mixed with epoxy resin, the crosslinking density of the epoxy resin will be significantly reduced, resulting in a decrease in heat resistance.

[0004] Therefore, there is an urgent need for a flame retardant compound that, when mixed with an epoxy resin, does not significantly reduce the crosslinking density of the epoxy resin, resulting in a decrease in its heat resistance, and has a good flame retardant effect. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a DOPO-based compound and a preparation method, an epoxy resin curing agent, a flame retardant and a flame retardant epoxy resin composition. The present invention develops an organic nitrogen / phosphorus flame retardant from the perspective of low cost, environmental friendliness, excellent flame retardancy and comprehensive performance, and is also used as an epoxy curing agent. This nitrogen-phosphorus flame retardant contains both DOPO and secondary amine structures, and the generated cured product has good flame retardancy, the flame retardant does not migrate to the resin surface, and the mechanical properties are not reduced. Modifying the epoxy resin with it can effectively improve the flame retardancy, limiting oxygen index and heat resistance of the epoxy resin.

[0006] One of the purposes of the present invention is to provide a DOPO-based compound having the following structure:

[0007]

[0008] Wherein, R is at least one of alkylene, arylene, arylenealkyl, alkylenearyl, cycloalkylene, alkylenecycloalkylene, and cycloalkylenealkyl, preferably C 1 ~C 10 Alkylene, C 6 ~C 10 Arylene, C 6 ~C 10 Arylene alkyl, C 6 ~C 10 Alkylene aryl, C 3 ~C 10 Cycloalkylene, C 6 ~C 10 Alkylenecycloalkyl, C 6 ~C 10 at least one of cycloalkylenealkyl;

[0009] In the present invention, the cycloalkyl group may be cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, etc., preferably cyclohexyl; more preferably,

[0010] R is At least one of , wherein * represents a connection position.

[0011] The second object of the present invention is to provide a method for preparing the DOPO-based compound of the first object of the present invention, comprising the step of reacting components including 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), formaldehyde and diamine to obtain the DOPO-based compound. In the present invention, DOPO, diamine and formaldehyde undergo a Mannich reaction, wherein formaldehyde reacts to form a methylene group, which acts as a bridge; the DOPO-based compound of the present invention has a diamine as a skeleton, and the nitrogen on the amine group is covalently bonded to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO).

[0012] In a preferred embodiment of the present invention,

[0013] The method comprises:

[0014] 1) adding a formaldehyde aqueous solution into a diamine solution to react to obtain a mixture solution;

[0015] 2) Adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to the mixture solution obtained in step 1) to react and obtain the DOPO-based compound.

[0016] In a preferred embodiment of the present invention,

[0017] In step 1),

[0018] The diamine is at least one of an aromatic diamine, an alicyclic diamine, and an aliphatic diamine, preferably at least one of 1,2-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 1,3-cyclohexanedimethylamine, and 1,4-cyclohexanedimethylamine; and / or,

[0019] The solvent in the diamine solution is at least one of N,N'-dimethylformamide, N,N'-dimethylacetamide and N-methylpyrrolidone; and / or,

[0020] The mass ratio of the diamine to the solvent in the diamine solution is 1:(1-10), preferably 1:(3-6); and / or,

[0021] The concentration of formaldehyde in the formaldehyde aqueous solution is 37-40%; and / or,

[0022] The molar ratio of the diamine to formaldehyde is 1:(2.0-3.0), preferably 1:(2.0-2.4).

[0023] In a preferred embodiment of the present invention,

[0024] In step 1),

[0025] The formaldehyde aqueous solution is added to the diamine solution by dropwise addition, and the dropwise addition time is preferably 10 to 120 minutes, more preferably 10 to 60 minutes; and / or,

[0026] The reaction temperature is 20 to 60° C., preferably 20 to 30° C.; and / or the reaction time is 20 to 60 min, preferably 20 to 40 min.

[0027] In a preferred embodiment of the present invention,

[0028] In step 2),

[0029] The molar ratio of the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to the diamine is (2-3):1, preferably (2-2.2):1.

[0030] In a preferred embodiment of the present invention,

[0031] In step 2),

[0032] The reaction temperature is 70-100° C., preferably 75-85° C.; and / or the reaction time is 1-12 h, preferably 5-12 h.

[0033] In a preferred embodiment of the present invention,

[0034] Step 2) further comprises the steps of precipitating the reaction solution obtained by the reaction into a poor solvent after the reaction, precipitating the solid, and washing and drying the solid; preferably,

[0035] The poor solvent is at least one of ethanol, methanol and water; and / or,

[0036] The drying conditions include: a drying temperature of 60 to 80° C.; and / or a drying time of 12 to 24 hours.

[0037] The present invention can adopt the following specific technical solutions:

[0038] The preparation method of the DOPO-based compound comprises the following steps:

[0039] 1) dissolving a diamine in a solvent at room temperature, wherein the mass ratio of the diamine to the solvent is 1:(1-10), adding dropwise a 37% formaldehyde aqueous solution at room temperature, and the formaldehyde aqueous solution is added dropwise over 30-120 minutes, wherein the molar ratio of the diamine to the formaldehyde is 1:(2.0-3.0), and stirring the mixture at 20-60° C. and 100-500 rpm / min for 20-60 minutes; in this step, the formaldehyde and the diamine undergo an aminomethylation reaction to generate aminomethyl alcohol;

[0040] 2) Add DOPO to the solution in step 1) in a molar ratio of diamine to DOPO of 1:(2-2.2), react at 70-100° C. for 1-12 hours, and then precipitate the reaction solution into a poor solvent to precipitate a white or yellow powder. After washing the powder with the poor solvent for 1-3 times, dry it in a vacuum oven at 60-80° C. for 12-24 hours to obtain the DOPO-based compound.

[0041] The third object of the present invention is to provide an epoxy curing agent, including the DOPO-based compound of the first object of the present invention or the DOPO-based compound obtained by the preparation method of the second object of the present invention.

[0042] Preferably, the epoxy curing agent also includes any other epoxy resin curing agent disclosed in the prior art.

[0043] A fourth object of the present invention is to provide an epoxy flame retardant, comprising the DOPO-based compound of one of the objects of the present invention or the DOPO-based compound obtained by the preparation method of the second object of the present invention.

[0044] The fifth object of the present invention is to provide a flame retardant epoxy resin composition, comprising an epoxy resin and the DOPO-based compound of the present invention and / or a mixed cured product of an epoxy resin and the DOPO-based compound of the present invention; preferably, based on 100 parts by weight of the epoxy resin, the amount of the DOPO-based compound is 1 to 50 parts by weight, preferably 10 to 30 parts by weight, and more preferably 20 to 30 parts by weight; further preferably, the phosphorus content in the flame retardant epoxy resin composition is above 1.0 wt%, preferably 1.9 to 3.0 wt%.

[0045] The type of epoxy resin in the present invention is not particularly limited, and it can be any epoxy resin in the prior art.

[0046] The present invention has no particular limitation on the composition of the flame retardant epoxy resin composition. The components and their amounts are all commonly used components and conventional amounts in the art, or can be adjusted according to the requirements of actual conditions. For example, conventional components such as curing agents in the art can also be added, and their amounts are also conventional amounts. Those skilled in the art can adjust according to actual conditions.

[0047] The sixth object of the present invention is to provide a method for preparing the flame retardant epoxy resin composition of the fifth object of the present invention, comprising mixing components including epoxy resin and DOPO-based compounds, and optionally comprising a curing step after mixing.

[0048] The curing process and curing conditions can adopt the common processes and conditions in the prior art. The equipment used is also the equipment used in the processing of epoxy resin compositions in the prior art.

[0049] The DOPO-based compound of the present invention is a flame retardant that does not contain halogen elements, has nitrogen and phosphorus synergy, is low in smoke, low in toxicity, and is environmentally friendly. It can participate in the curing reaction of epoxy resin and can significantly improve the vertical combustion performance, limiting oxygen index, and heat resistance of epoxy resin.

[0050] The DOPO-based compound provided by the present invention is used as a flame retardant, which improves the shortcomings of poor compatibility and easy migration of traditional flame retardants, has good compatibility with epoxy resin, and participates in the curing reaction of epoxy resin. By adding it to epoxy resin through physical blending, the flame retardant performance and heat resistance of epoxy resin can be significantly improved.

[0051] The raw materials diamine, formaldehyde and DOPO used in the preparation method of the DOPO-based compound of the present invention are widely available and inexpensive, and the process is simple and efficient, and is convenient for industrial mass production.

[0052] The preparation method of the DOPO-based compound of the present invention has cheap raw materials, a wide range of sources, a simple process, high efficiency, safety, environmental protection, and is conducive to mass production. The flame retardant overcomes the shortcomings of traditional flame retardants such as large combustion smoke, environmental pollution, poor compatibility, and easy precipitation. The DOPO-based compound is used as a flame retardant and added to epoxy resin to significantly improve the flame retardant properties of epoxy resin cured products. When the P addition amount in the epoxy resin reaches 2.0wt%, the vertical combustion grade reaches UL94 V-0, the limiting oxygen index reaches 36-39, the charring rate at 800°C reaches 26-28%, and the glass transition temperature reaches 125-135°C. DETAILED DESCRIPTION

[0053] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0054] The limiting oxygen index test in the embodiments and comparative examples of the present invention is carried out according to the ASTM D2863 standard and is tested on an HC-2C oxygen index meter; the UL94 vertical burning test is carried out according to the ASTM D3801 standard; the glass transition temperature is determined on a TAQ10 DSC instrument, and the test conditions are: a heating rate of 10°C / min, a test range of 40°C to 200°C, and a nitrogen atmosphere; the charring rate is carried out on a METTLER TGA / SDTA851 thermal analysis instrument, and the test temperature range is 30°C to 800°C, a heating rate of 20°C / min, and a nitrogen atmosphere; the phosphorus content in the epoxy cured product is obtained by theoretical calculation.

[0055] The raw materials used in the examples of the present invention are all conventional commercially available raw materials.

[0056] [Example 1]

[0057] The synthesis steps of DOPO-based compounds are as follows:

[0058] 1) Add 10.8 g (0.1 mol) of 1,3-phenylenediamine (commercially available) and 50 g of N,N'-dimethylformamide into a three-necked flask with a stirring device, and add dropwise 16.22 g (containing 0.2 mol of formaldehyde) of formaldehyde solution (commercially available) for 30 minutes, and stir at 25°C (stirring rate 300 rpm / min) for 30 minutes.

[0059] 2) Add 43.2 g (0.2 mol) of DOPO to the reaction solution of the first step, react at 80° C. for 6 h, and then precipitate the reaction solution into water to precipitate a white powder. The powder is washed with water three times and dried in a vacuum oven at 80° C. for 12 h to obtain the DOPO-based compound.

[0060] The test and analysis results of the above DOPO-based compounds are as follows:

[0061] 1H-NMR(ppm,DMSO-d6),2.51(2H,–NH–),4.31(4H,–N–CH2–P–),6.35–8.62(16H,Aromatic H).

[0062] 13C-NMR (DMSO-d6), δ = 48.6, 51.2, 113.6, 119.2, 119.5, 121.1, 123.2, 123.4, 123.7, 124.2, 124.8, 126.9, 129.7, 130.8, 131.2, 132.9, 134.8.

[0063] 31P-NMR (DMSO-d6, ppm): 38.62.

[0064] FTIR(KBr):1225cm -1 (P–O stretch), 1347cm -1 (–C–N–C–stretch),1731cm -1 (P = Ostretch).

[0065] From the above analysis, it can be seen that a DOPO-based compound with the following structure was successfully synthesized:

[0066] in

[0067] Add the above 27g DOPO-based compound to 100g epoxy resin E-51 (commercially available), add 20.5g 4,4'-diaminodiphenylmethane as curing agent, mix evenly by mechanical stirring, and then pour into the mold. The mold is placed in a blast oven and heated and cured according to the curing process of 140℃ / 2h+180℃ / 2h, and then cooled to room temperature to obtain an epoxy resin cured product. At this time, the phosphorus content in the epoxy cured product is 2.0wt%, the vertical burning grade reaches UL94 V-0, the limiting oxygen index reaches 38, the charring rate at 800℃ reaches 28%, and the glass transition temperature is 132℃.

[0068] [Example 2]

[0069] The synthesis steps of DOPO-based compounds are as follows:

[0070] 1) Add 13.6 g (0.1 mol) of 1,3-phenylenediamine (commercially available) and 50 g of N,N'-dimethylformamide into a three-necked flask with a stirring device, and add dropwise 16.22 g (containing 0.2 mol of formaldehyde) of formaldehyde solution (commercially available) over a period of 50 min. Stir at 25°C (stirring rate 300 rpm / min) and react for 20 min.

[0071] 2) Add 43.2 g (0.2 mol) of DOPO to the reaction solution of the first step, react at 80° C. for 10 h, and then precipitate the reaction solution into water to precipitate a white powder. The powder is washed with water three times and dried in a vacuum oven at 80° C. for 12 h to obtain the DOPO-based compound.

[0072] The test and analysis results of the above DOPO-based compounds are as follows:

[0073] 1H-NMR(ppm,DMSO-d6),2.46(2H,–NH–),4.21(4H,Ar–CH2–N),4.35(4H,N–CH2–P),6.35–8.62(16H,Aromatic H).

[0074] 13C-NMR (DMSO-d6), δ = 45.2, 47.2, 51.2, 51.6, 112.5, 119.1, 119.8, 121.7, 1 23.1,123.9,124.5,123.8,124.8,126.9,128.2,130.8,130.1,131.7,133.8.

[0075] 31P-NMR (DMSO-d6, ppm): 39.12.

[0076] FTIR(KBr):1222cm-1 (P–O stretch), 1351cm -1 (–C–N–C–stretch),1738cm -1 (P = Ostretch).

[0077] From the above analysis, it can be seen that a DOPO-based compound with the following structure was successfully synthesized:

[0078] in

[0079] Add the above 28.4g DOPO-based compound to 100g epoxy resin E-51 (commercially available), add 20.5g 4,4'-diaminodiphenylmethane as curing agent, mix evenly by mechanical stirring, and then pour into the mold. The mold is placed in a blast oven and heated and cured according to the curing process of 140℃ / 2h+180℃ / 2h, and then cooled to room temperature to obtain an epoxy resin cured product. At this time, the phosphorus content in the epoxy cured product is 2.0wt%, the vertical burning grade reaches UL94 V-0, the limiting oxygen index reaches 39, the charring rate at 800℃ reaches 27%, and the glass transition temperature is 128℃.

[0080] [Example 3]

[0081] The synthesis steps of DOPO-based compounds are as follows:

[0082] 1) 11.4 g (0.1 mol) of 1,3-cyclohexanediamine (commercially available) and 50 g of N,N'-dimethylformamide were added to a three-necked flask with a stirring device, and 16.22 g (containing 0.2 mol of formaldehyde) of formaldehyde solution (commercially available) was added dropwise over 15 min, and the mixture was stirred at 25 °C (stirring rate 300 rpm / min) for 30 min.

[0083] 2) Add 47.52 g (0.22 mol) of DOPO to the reaction solution of the first step, react at 80° C. for 8 h, and then precipitate the reaction solution into water to precipitate a white powder. The powder is washed twice with water and dried in a vacuum oven at 60° C. for 12 h to obtain the DOPO-based compound.

[0084] The test and analysis results of the above DOPO-based compounds are as follows:

[0085] 1H-NMR(ppm,DMSO-d6),2.48(2H,–NH–),3.15,3.22,3.41(6H,–CH2–),3.28(2H,–CH–),4.31(4H,–N–CH2–P–),6.33–8.68(16H,Aromatic H).

[0086] 13C-NMR (DMSO-d6), δ = 47.6, 48.2, 111.6, 119.1, 125.5, 125.1, 125.8, 125.9, 126.1, 126.2, 126.8, 127.1, 129.6, 131.7, 131.2, 132.7, 134.1.

[0087] 31P-NMR (DMSO-d6, ppm): 38.78.

[0088] FTIR(KBr):1225cm -1 (P–O stretch), 1327cm -1 (–C–N–C–stretch),1715cm -1 (P = Ostretch).

[0089] From the above analysis, it can be seen that a DOPO-based compound with the following structure was successfully synthesized:

[0090] in

[0091] Add the above 27.3g DOPO-based compound to 100g of epoxy resin E-51 (commercially available), add 20.5g 4,4'-diaminodiphenylmethane as curing agent, mix evenly by mechanical stirring, and then pour into the mold. The mold is placed in a blast oven and heated and cured according to the curing process of 140℃ / 2h+180℃ / 2h, and then cooled to room temperature to obtain an epoxy resin cured product. At this time, the phosphorus content in the epoxy cured product is 2.0wt%, the vertical burning grade reaches UL94 V-0, the limiting oxygen index reaches 36, the charring rate at 800℃ reaches 27%, and the glass transition temperature is 125℃.

[0092] [Example 4]

[0093] The synthesis steps of DOPO-based compounds are as follows:

[0094] 1) 14.2 g (0.1 mol) of 1,3-cyclohexanedimethylamine (commercially available) and 50 g of N,N'-dimethylacetamide were added to a three-necked flask with a stirring device, and 16.22 g (containing 0.2 mol of formaldehyde) of formaldehyde solution (commercially available) was added dropwise over 30 min, and the mixture was stirred at 25 °C (stirring rate: 300 rpm / min) for 30 min.

[0095] 2) Add 47.52 g (0.22 mol) of DOPO to the reaction solution of the first step, react at 80° C. for 10 h, and then precipitate the reaction solution into water to precipitate a white powder. The powder is washed three times with ethanol and dried in a vacuum oven at 60° C. for 12 h to obtain the DOPO-based compound.

[0096] The test and analysis results of the above DOPO-based compounds are as follows:

[0097] 1H-NMR(ppm,DMSO-d6),2.52(2H,–NH–),3.12,3.25,3.47,4.53(8H,–CH2–),3.29(2H,–CH–),4.35(4H,–N–CH2–P–),6.41–8.82(16H,Aromatic H).

[0098] 13C-NMR (DMSO-d6), δ = 47.5, 48.2, 115.1, 120.3, 124.5, 124.2, 124.5, 125.2, 126.3, 126.5, 126.7, 127.5, 129.8, 131.5, 132.7, 132.7, 135.8.

[0099] 31P-NMR (DMSO-d6, ppm): 39.05.

[0100] FTIR(KBr):1225cm -1 (P–O stretch), 1341cm -1 (–C–N–C–stretch),1721cm -1 (P = Ostretch).

[0101] From the above analysis, it can be seen that a DOPO-based compound with the following structure was successfully synthesized:

[0102] in

[0103] Add the above 27.3g DOPO-based compound to 100g epoxy resin E-51 (commercially available), add 20.5g 4,4'-diaminodiphenylmethane as curing agent, mix evenly by mechanical stirring, and then pour into the mold. The mold is placed in a blast oven and heated and cured according to the curing process of 140℃ / 2h+180℃ / 2h, and then cooled to room temperature to obtain an epoxy resin cured product. At this time, the phosphorus content in the epoxy cured product is 1.9wt%, the vertical burning grade reaches UL94 V-0, the limiting oxygen index reaches 38, the charring rate at 800℃ reaches 26%, and the glass transition temperature is 135℃.

[0104] [Example 5]

[0105] Will The DOPO-based compound is added to 100g of epoxy resin E-51 (commercially available), and 23.2g of 4,4'-diaminodiphenylmethane is added as a curing agent. The mixture is evenly mixed by mechanical stirring and then poured into the mold. The mold is placed in a blast oven and heated and cured according to the curing process of 140℃ / 2h+180℃ / 2h. After cooling to room temperature, an epoxy resin cured product is obtained. At this time, the phosphorus content in the epoxy cured product is 1.0wt%, the vertical burning grade reaches UL94 V-1, the limiting oxygen index reaches 29, the charring rate at 800℃ reaches 25%, and the glass transition temperature is 135℃.

[0106] [Example 6]

[0107] Will The DOPO-based compound is added to 100g of epoxy resin E-51 (commercially available), and 17.8g of 4,4'-diaminodiphenylmethane is added as a curing agent. The mixture is evenly mixed by mechanical stirring and then poured into the mold. The mold is placed in a blast oven and heated and cured according to the curing process of 140℃ / 2h+180℃ / 2h. After cooling to room temperature, an epoxy resin cured product is obtained. At this time, the phosphorus content in the epoxy cured product is 2.9wt%, the vertical burning grade reaches UL94 V-0, the limiting oxygen index reaches 35, the charring rate at 800℃ reaches 27%, and the glass transition temperature is 135℃.

[0108] [Comparative Example 1]

[0109] Add 25g 4,4'-diaminodiphenylmethane curing agent to 100g epoxy resin E-51 (commercially available), mix evenly by mechanical stirring, and then pour into the mold. The mold is placed in a blast oven and heated and cured according to the curing process of 140℃ / 2h+180℃ / 2h, and then cooled to room temperature to obtain epoxy resin cured product. It failed the vertical burning test (no grade), the limiting oxygen index reached 25, the charring rate reached 10%, and the glass transition temperature was 133℃.

[0110] [Comparative Example 2]

[0111] Add 20.68g DOPO and 5.17g m-phenylenediamine to 100g epoxy resin E-51 (commercially available), add 20.5g 4,4'-diaminodiphenylmethane as curing agent, mix evenly by mechanical stirring, and then pour into the mold. The mold is placed in a blast oven and heated and cured according to the curing process of 140℃ / 2h+180℃ / 2h, and then cooled to room temperature to obtain an epoxy resin cured product. At this time, the phosphorus content in the epoxy cured product is 2.0wt%, the vertical burning grade reaches UL94 V-1, the limiting oxygen index reaches 32, the charring rate at 800℃ reaches 20%, and the glass transition temperature is 105℃.

[0112] It can be seen from Example 1 and Comparative Example 1 that adding the DOPO-based compound of the present invention to the epoxy resin composition can not only greatly improve the flame retardant properties of the epoxy resin, but also will not reduce the heat resistance of the epoxy resin. It can be seen from Comparative Example 2 that directly adding DOPO and m-phenylenediamine (i.e., the raw materials for preparing the DOPO-based compound of Example 1 of the present invention) to the epoxy resin composition will reduce the heat resistance of the epoxy resin, and the flame retardant performance is not as good as the effect achieved by the DOPO-based compound of the present invention. In addition, it can be seen from Examples 1-4, 6 and Example 5 that in the flame retardant epoxy resin composition of the present invention, the phosphorus content is preferably 1.0wt% or more, more preferably 1.9-3.0wt%.

Claims

1. A DOPO-based compound having the following structure: in, R is at least one of alkylene, arylene, arylenealkyl, alkylenearyl, cycloalkylene, alkylenecycloalkylene, and cycloalkylenealkyl, preferably C 1 ~C 10 Alkylene, C 6 ~C 10 Arylene, C 6 ~C 10 Arylene alkyl, C 6 ~C 10 Alkylene aryl, C 3 ~C 10 Cycloalkylene, C 6 ~C 10 Alkylenecycloalkyl, C 6 ~C 10 At least one of cycloalkylenealkyl, more preferably At least one of .

2. A method for preparing a DOPO-based compound as claimed in claim 1, comprising the step of reacting components including 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, formaldehyde and a diamine to obtain the DOPO-based compound.

3. The preparation method according to claim 2, Features The method comprises: 1) adding a formaldehyde aqueous solution into a diamine solution to react to obtain a mixture solution; 2) Adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to the mixture solution obtained in step 1) to react and obtain the DOPO-based compound.

4. The preparation method according to claim 3, Features: In step 1), The diamine is at least one of an aromatic diamine, an alicyclic diamine, and an aliphatic diamine, preferably at least one of 1,2-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 1,3-cyclohexanedimethylamine, and 1,4-cyclohexanedimethylamine; and / or, The solvent in the diamine solution is at least one of N,N'-dimethylformamide, N,N'-dimethylacetamide and N-methylpyrrolidone; and / or, The mass ratio of the diamine to the solvent in the diamine solution is 1:(1-10), preferably 1:(3-6); and / or, The concentration of formaldehyde in the formaldehyde aqueous solution is 37-40%; and / or, The molar ratio of the diamine to formaldehyde is 1:(2.0-3.0), preferably 1:(2.0-2.4).

5. The preparation method according to claim 3, Features: In step 1), The formaldehyde aqueous solution is added to the diamine solution by dropwise addition, and the dropwise addition time is preferably 10 to 120 minutes, more preferably 10 to 60 minutes; and / or, The reaction temperature is 20 to 60° C., preferably 20 to 30° C.; and / or the reaction time is 20 to 60 min, preferably 20 to 40 min.

6. The preparation method according to claim 3, Features: In step 2), The molar ratio of the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to the diamine is (2-3):1, preferably (2-2.2):

1.

7. The preparation method according to claim 3, Features: In step 2), The reaction temperature is 70-100° C., preferably 75-85° C.; and / or the reaction time is 1-12 h, preferably 5-12 h.

8. The preparation method according to claim 3, Features: Step 2) further comprises the steps of precipitating the reaction solution obtained by the reaction into a poor solvent after the reaction, precipitating the solid, and washing and drying the solid; preferably, The poor solvent is at least one of ethanol, methanol and water; and / or, The drying conditions include: a drying temperature of 60 to 80° C.; and / or a drying time of 12 to 24 hours.

9. An epoxy resin curing agent, comprising the DOPO-based compound according to claim 1 or the DOPO-based compound obtained by the preparation method according to any one of claims 2 to 8.

10. An epoxy resin flame retardant, comprising the DOPO-based compound according to claim 1 or the DOPO-based compound obtained by the preparation method according to any one of claims 2 to 8.

11. A flame retardant epoxy resin composition, comprising an epoxy resin and a DOPO-based compound according to claim 1 or a DOPO-based compound obtained by the preparation method according to any one of claims 2-8 and / or a mixed cured product of an epoxy resin and a DOPO-based compound according to claim 1 or a DOPO-based compound obtained by the preparation method according to any one of claims 2-8; preferably, based on 100 parts by weight of the epoxy resin, the amount of the DOPO-based compound is 1 to 50 parts by weight, preferably 10 to 30 parts by weight; further preferably, the phosphorus content in the flame retardant epoxy resin composition is above 1.0 wt%, preferably 1.9 to 3.0 wt%.

12. A method for preparing a flame retardant epoxy resin composition as claimed in claim 11, comprising mixing components including an epoxy resin and a DOPO-based compound, and optionally comprising a curing step after mixing.

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