Flame-retardant cyclotriphosphazene epoxy compound as well as preparation method and application thereof

Abstract

The invention relates to the technical field of thermosetting resin materials, and discloses a flame-retardant cyclotriphosphazene epoxy compound as well as a preparation method and application thereof. The epoxy resin provided by the invention is a halogen-free flame-retardant epoxy system, an epoxy curing cross-linked network contains rich phosphazene ring structures, DOPO and Schiff base can improve the flame retardance of the epoxy resin, and meanwhile, due to the existence of a large number of rigid benzene ring structures and six-functional-group epoxy structures, the cross-linking density is high, so that the flame retardance of the epoxy resin is improved. The flame retardant property is excellent, and the mechanical strength is relatively high. # imgabs0 #

Description

Technical Field

[0001] The invention relates to the technical field of thermosetting resin materials, and in particular to a flame retardant cyclotriphosphazene epoxy compound and a preparation method and application thereof. Background Art

[0002] Epoxy resin has excellent mechanical properties, bonding properties, chemical corrosion resistance, electrical insulation and other advantages, and is widely used in composite materials, adhesives, coatings, electronic packaging and other fields. However, epoxy resin is a flammable material with a limiting oxygen index of about 19.8%, and it is accompanied by molten droplets when burning, which poses a serious fire safety hazard and limits its application field. Flame retardants are usually used to modify epoxy resins for flame retardancy. Commonly used flame retardants are additive and reactive. The amount of additive flame retardant is large. Although organic flame retardants have good compatibility with epoxy resins and can be evenly dispersed in the resin matrix, the molecular weight of the flame retardant is small, resulting in reduced mechanical properties of the resin matrix; reactive flame retardants can react chemically with the epoxy resin matrix or curing agent, and introduce flame retardant structural units into the cross-linked network structure of epoxy resin in the form of chemical bonds, which can improve its flame retardant properties and can improve or maintain high mechanical properties. Therefore, improving or maintaining high mechanical properties while modifying epoxy resins for flame retardancy has become one of the research hotspots of flame retardant epoxy resins.

[0003] Phosphazene compounds and phosphaphenanthrene compounds are widely used in the field of epoxy resin flame retardancy due to their high flame retardant efficiency and halogen-free and low toxicity. The flame retardant mechanism is the combined effect of condensed phase flame retardancy and gas phase flame retardancy. In the condensed phase, the phosphorus-containing structural unit degrades to generate phosphoric acid and metaphosphoric acid after heating to promote the formation of a carbon layer in the resin matrix, which plays a role in oxygen isolation and heat insulation; in the gas phase, the flame retardant structural unit decomposes after heating to produce non-flammable gases such as nitrogen and ammonia, dilute the concentration of combustible gases such as oxygen, and release phosphorus oxygen free radicals to quench active flammable free radicals, terminating the combustion chain reaction. The Schiff base structure has high-temperature self-crosslinking characteristics, and can form a highly thermally stable nitrogen heterocyclic structure at high temperature to strengthen the carbon layer and further improve the flame retardant effect of the condensed phase. Therefore, Schiff base, phosphazene and phosphaphenanthrene groups are highly potential synergistic flame retardant structural units.

[0004] The patent application with publication number CN118344705A discloses a halogen-free flame-retardant epoxy resin and a preparation method thereof, wherein hydroxyaldehyde and hexachlorocyclotriphosphazene are used as raw materials to synthesize an aldehyde-containing cyclotriphosphazene intermediate, and then DOPO is reacted with the aldehyde group to obtain an additive halogen-free flame retardant based on phosphazene and phosphaphenanthrene groups, which can be used for flame retardancy of epoxy resin. However, the flame retardant does not form a chemical bond with the epoxy resin matrix, which will reduce the mechanical properties of the flame-retardant epoxy resin.

[0005] The patent application with publication number CN117820605A discloses a method for preparing a flame retardant epoxy resin, in which a flame retardant is prepared using hydroxy aldehyde and hexachlorocyclotriphosphazene as raw materials. A diamine curing agent is used, and the aldehyde group of the flame retardant reacts with the amino group of the curing agent to undergo a Schiff base reaction, thereby embedding the cyclotriphosphazene and Schiff base flame retardant structural units into the polymer long chain to achieve flame retardancy of the epoxy resin. However, when the aldehyde group of the flame retardant reacts with the amino group of the curing agent to undergo a Schiff base reaction, small molecules of water are released, and dehydration treatment is required during the preparation process, which easily generates pores in the resin, thereby affecting the mechanical properties of the resin.

[0006] Therefore, developing highly efficient flame-retardant intrinsically flame-retardant epoxy resins or reactive flame retardants and preparing halogen-free flame-retardant epoxy resins that have both highly efficient flame retardancy and can improve or maintain high mechanical properties are of great significance to expanding their application areas. Summary of the invention

[0007] The present invention aims at the flammability problem of epoxy resin and provides a flame-retardant cyclotriphosphazene epoxy compound with a completely new structure. The compound can be used alone as an intrinsic flame-retardant epoxy monomer, and can also be used as a reactive epoxy flame retardant to be cured with a curing agent to prepare a flame-retardant epoxy resin, and at the same time has both excellent flame retardancy and mechanical strength.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A flame retardant cyclotriphosphazene epoxy compound having a general formula as shown in Formula I:

[0010]

[0011] Wherein R1 to R6 are independently selected from any one of the structures shown in ① to ④:

[0012]

[0013] In formulas ① to ④, R is H, -CH3 or -OCH3.

[0014] The present invention also provides a method for preparing the flame-retardant cyclotriphosphazene epoxy compound. When R1 to R6 are all selected from ① or ③, the compound contains only cyclotriphosphazene and Schiff base structures. The preparation process comprises the steps of:

[0015] Step 1, mixing hexa(4-aminophenoxy)cyclotriphosphazene with a hydroxyaldehyde compound as shown in Formula I-1 in a solvent, and treating to obtain a hexahydroxycyclotriphosphazene containing a Schiff base structure as shown in Formula I-2;

[0016] Step 2, mixing the compound represented by formula I-2 and epichlorohydrin for reaction, adding a phase transfer catalyst to continue the reaction after the reaction system becomes a homogeneous phase, and then dropping an inorganic base to continue the reaction, and purifying to obtain the flame-retardant cyclotriphosphazene epoxy compound;

[0017] When at least one of R1 to R6 is selected from ② or ④, the compound contains cyclotriphosphazene, Schiff base and DOPO structure at the same time, and the preparation process comprises the steps of:

[0018] Step 1, mixing hexa(4-aminophenoxy)cyclotriphosphazene with a hydroxyaldehyde compound as shown in Formula I-1 in a solvent for reaction, and treating to obtain a hexahydroxycyclotriphosphazene containing a Schiff base structure as shown in Formula I-2;

[0019] Step 1-2, mixing the compound represented by formula I-2 and DOPO and subjecting them to reflux reaction, and purifying the product to obtain the compound represented by formula I-3;

[0020] Step 2, mixing the compound represented by formula I-3 and epichlorohydrin for reaction, adding a phase transfer catalyst to continue the reaction after the reaction system becomes a homogeneous phase, and then dropping an inorganic base to continue the reaction, and purifying to obtain the flame-retardant cyclotriphosphazene epoxy compound;

[0021]

[0022] R1'~R6' is selected from any one of the structures shown in ⑤~⑧, at least one of which is ⑥ or ⑧:

[0023]

[0024] Wherein, R is as described in claim 1.

[0025] The reaction in step 1 is carried out at 50-90° C. for 4-15 hours;

[0026] In step 2, after adding epichlorohydrin, the reaction is carried out at 60-110° C. until the system is in a homogeneous phase; after adding a phase transfer catalyst, the reaction is continued for 6-15 hours; after adding an inorganic base, the reaction is continued at 50-90° C. for 2-10 hours;

[0027] In step 2, the molar ratio of the compound represented by formula I-2 or I-3 to epichlorohydrin is 1:75 to 120;

[0028] In step 1-2, the molar ratio of the compound represented by formula I-2 to DOPO is 1:1-6; in this process, DOPO reactive groups are grafted onto carbon on some Schiff bases. When the molar ratio of the compound represented by formula I-2 to DOPO is 1:6, DOPO groups are grafted onto all Schiff base structures, and the compound exhibits higher flame retardant properties, but the mechanical toughness and bending strength are affected to a certain extent, and the overall performance remains excellent.

[0029] In step 1-2, the reaction temperature is 100-115° C. and the reaction time is 8-36 h.

[0030] The hydroxyaldehyde compound represented by formula I-1 is one of p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, vanillin, syringaldehyde, and 2-methyl-4-hydroxybenzaldehyde;

[0031] At least one of the solvents used in the reaction process: 1,4-dioxane, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and methyl pyrrolidone;

[0032] The phase transfer catalyst is tetrabutylammonium bromide, benzyltriethylammonium chloride, hexadecyltrimethylammonium bromide or triphenylphosphine.

[0033] The present invention also provides an intrinsic flame retardant epoxy resin, which is composed of the flame retardant cyclotriphosphazene epoxy compound and a curing agent. The flame retardant cyclotriphosphazene epoxy compound is an epoxy compound containing a Schiff base and a cyclotriphosphazene group, or an epoxy compound containing a Schiff base, a cyclotriphosphazene and a DOPO group, or an epoxy compound containing a cyclotriphosphazene and a DOPO group, all of which exhibit excellent intrinsic flame retardancy and can be directly used as an epoxy resin after curing.

[0034] The present invention also provides a flame retardant epoxy resin, comprising epoxy resin, the flame retardant cyclotriphosphazene epoxy compound and a curing agent; in the flame retardant cyclotriphosphazene epoxy compound, at least one of R1 to R6 is selected from the structure shown in ② or ④.

[0035] The epoxy compound that is not grafted with DOPO contains only Schiff base and cyclotriphosphazene groups. It shows excellent performance after curing as an intrinsic epoxy resin alone, but when mixed with a conventional non-flame-retardant epoxy resin matrix as a flame retardant additive, the material has average flame retardant performance when the addition amount is less than 15%. However, when the epoxy compound is grafted with DOPO, a resin material with both flame retardant and mechanical properties can be obtained at the same addition amount.

[0036] In terms of flame retardant mechanism, when the epoxy compound of the present invention is burned, in the gas phase, the phosphazene and phosphaphenanthrene groups release phosphorus-containing free radicals under heat, which combine with active flammable free radicals in the flame to terminate the combustion chain reaction, and at the same time, non-combustible gases such as ammonia and nitrogen are generated during the pyrolysis process to dilute the concentration of oxygen and combustible gases. In the condensed phase, phosphoric acid and metaphosphoric acid generated by the pyrolysis of the phosphazene and phosphaphenanthrene structures have a catalytic carbonization effect on the epoxy resin matrix to form a carbon layer, and the Schiff base structure self-crosslinks at high temperature to form a high thermal stability nitrogen heterocyclic structure, which can further strengthen the carbon layer, isolate oxygen and heat transfer, and inhibit the volatilization of pyrolysis products, thereby improving the flame retardant efficiency.

[0037] The epoxy resin includes common epoxy resins in the prior art, including bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, hydrogenated bisphenol A epoxy resin, novolac epoxy resin, etc.

[0038] The curing agent includes one or more of 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, dinitrile amine, maleic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, etc.;

[0039] The curing agent is added in an amount according to a molar ratio of 1:0.5-1.5 between the epoxy group in the epoxy compound and the active hydrogen in the curing agent.

[0040] The mass of the flame retardant cyclotriphosphazene epoxy compound accounts for 5-30% of all raw materials.

[0041] The present invention also provides a method for preparing the intrinsic flame retardant epoxy resin or the flame retardant epoxy resin, comprising the steps of: dissolving the flame retardant cyclotriphosphazene epoxy compound, epoxy resin and curing agent in a solvent, removing the solvent by reduced pressure distillation, and obtaining the flame retardant epoxy resin by degassing and curing.

[0042] Preferably, the curing temperature is 120-200°C.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The epoxy resins provided by the present invention are all halogen-free flame-retardant epoxy systems. The epoxy curing network contains rich phosphazene ring structures, DOPO and Schiff bases, which can improve the flame retardant properties of the epoxy resin. At the same time, due to the presence of a large number of rigid benzene ring structures and hexafunctional epoxy structures, the cross-linking density is high, and it has excellent flame retardant properties and high mechanical strength.

[0045] (3) The epoxy resin cross-linked network provided by the present invention contains abundant phosphorus and nitrogen elements, and the synergistic flame retardant effect of phosphorus and nitrogen makes the epoxy curing system have excellent flame retardant properties, including oxygen index, vertical combustion and anti-dripping multi-angles. The method for preparing cyclotriphosphazene epoxy compound is simple to operate, easy to control and has high yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the Schiff base-containing cyclotriphosphazene epoxide CH3O-HCCP-6CN-EP prepared in Example 1.

[0047] Figure 2 This is the nuclear magnetic resonance phosphorus spectrum of the Schiff base-containing cyclotriphosphazene epoxide CH3O-HCCP-6CN-EP prepared in Example 1. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0049] The raw materials used in the following specific embodiments are all purchased from the market, bisphenol A epoxy resin, brand EP CYD-128, epoxy value 0.51 mol / 100 g, China Petrochemical Corporation; 4,4'-diaminodiphenyl sulfone (DDS), analytical grade, purity 99.0%, Sinopharm Chemical Reagent Co., Ltd. Example 1 Preparation of cyclotriphosphazene epoxy compound containing Schiff base structure (CH3O-HCCP-6CN-EP) and flame retardant epoxy resin (CH3O-HCCP-6CN-EP / DDS and DGEBA / CH3O-HCCP-6CN-EP (15%) / DDS).

[0050] Step 1: Hexa(4-aminophenoxy)cyclotriphosphazene (51 g, 0.065 mol) and vanillin (59.28 g, 0.39 mol) were mixed and dissolved in 500 mL of 1,4-dioxane, stirred, and reacted at 90°C for 10 h. After the reaction was completed, the product was precipitated with deionized water and then vacuum filtered, washed, and dried to obtain 94.34 g of hexahydroxycyclotriphosphazene containing a Schiff base structure, recorded as CH3O-HCCP-6CN-OH, with a yield of 91.4%.

[0051] Step 2: CH3O-HCCP-6CN-OH (60.34 g, 0.038 mol) was added to 266 mL of epichlorohydrin and stirred under heating conditions at 90 ° C. After the system was completely dissolved to form a uniform solution, 3 g of tetrabutylammonium bromide was added and reacted for 10 h. The temperature was then reduced to room temperature, and a 40 wt% sodium hydroxide aqueous solution (27 g, 0.675 mol) was added dropwise. After the addition was completed, the reaction mixture was reacted at 60 ° C for 6 h. After the reaction was completed, the reaction solution was washed several times with deionized water until neutral, and then the residual epichlorohydrin was removed by rotary evaporation to obtain 62 g of a cyclotriphosphazene epoxy compound containing a Schiff base structure, which was recorded as CH3O-HCCP-6CN-EP, with a yield of 85%.

[0052] Step 3: 27 g of CH3O-HCCP-6CN-EP was dissolved in 25 mL of 1,4-dioxane, 5.22 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) was added, and the mixture was mixed and heated with stirring until a uniform solution was formed, and then the solvent was removed by distillation under reduced pressure. The obtained mixture was poured into a mold for vacuum degassing, and the mixture was molded according to a curing system of 180°C / 2h and 200°C / 2h to obtain a flame retardant epoxy resin, which was recorded as CH3O-HCCP-6CN-EP / DDS.

[0053] Step 4: Dissolve 15g CH3O-HCCP-6CN-EP in 20mL 1,4-dioxane, add 64.52g bisphenol A epoxy resin (DGEBA) and 20.48g 4,4'-diaminodiphenyl sulfone (DDS), mix and heat with stirring to form a uniform solution, then remove the solvent by distillation under reduced pressure, pour the resulting mixture into a mold for vacuum degassing, and mold it according to a curing system of 180°C / 2h and 200°C / 2h to obtain a flame retardant epoxy resin with a CH3O-HCCP-6CN-EP addition amount of 15wt%, recorded as DGEBA / CH3O-HCCP-6CN-EP (15%) / DDS.

[0054] Example 2

[0055] Preparation of cyclotriphosphazene epoxy compounds (CH3O-HCCP-6DPCN-EP) containing DOPO structure and flame retardant epoxy resins (CH3O-HCCP-6DPCN-EP / DDS, DGEBA / CH3O-HCCP-6DPCN-EP (5%) / DDS, DGEBA / CH3O-HCCP-6DPCN-EP (10%) / DDS and DGEBA / CH3O-HCCP-6DPCN-EP (15%) / DDS).

[0056] Step 1: Hexa(4-aminophenoxy)cyclotriphosphazene (51 g, 0.065 mol) and vanillin (59.28 g, 0.39 mol) were mixed and dissolved in 500 mL of 1,4-dioxane, stirred, and reacted at 90°C for 10 h. After the reaction was completed, the product was precipitated with deionized water and then vacuum filtered, washed, and dried to obtain 94.34 g of hexahydroxycyclotriphosphazene containing a Schiff base structure, recorded as CH3O-HCCP-6CN-OH, with a yield of 91.4%.

[0057] Step 2: CH3O-HCCP-6CN-OH and DOPO were added at a molar ratio of 1:6, CH3O-HCCP-6CN-OH (31.76 g, 0.02 mol) and DOPO (25.92 g, 0.12 mol) were mixed and dissolved in 500 mL of 1,4-dioxane, and refluxed for 30 h at 110°C. After the reaction was completed, the product was precipitated with ethanol and then vacuum filtered, washed, and dried to obtain 54.30 g of hexahydroxycyclotriphosphazene containing DOPO structure, recorded as CH3O-HCCP-6DPCN-OH, with a yield of 94.1%.

[0058] Step 3: Add CH3O-HCCP-6DPCN-OH (57.7 g, 0.02 mol) to 180 mL of epichlorohydrin and stir under heating conditions at 90°C. After the system is completely dissolved to form a uniform solution, add 3 g of tetrabutylammonium bromide and react for 15 hours. Then the temperature is lowered to room temperature, and a 40 wt% sodium hydroxide aqueous solution is added dropwise. After the addition is complete, react at 60°C for 10 hours. After the reaction is completed, the reaction solution is washed several times with deionized water until it is neutral, and then the residual epichlorohydrin is removed by rotary evaporation to obtain 52 g of a cyclotriphosphazene epoxy compound containing a DOPO structure, which is recorded as CH3O-HCCP-6DPCN-EP, with a yield of 80.7%.

[0059] Step 4: 30 g of CH3O-HCCP-6DPCN-EP was dissolved in 25 mL of 1,4-dioxane, 3.5 g of 4,4'-diaminodiphenyl sulfone was added, and the mixture was mixed and heated and stirred to form a uniform solution, and then the solvent was removed by distillation under reduced pressure. The obtained mixture was poured into a mold for vacuum degassing, and the mixture was molded according to a curing system of 180°C / 2h and 200°C / 2h to obtain a flame retardant epoxy resin, which was recorded as CH3O-HCCP-6DPCN-EP / DDS.

[0060] Step 5: Dissolve 5 g of CH3O-HCCP-6DPCN-EP in 10 mL of 1,4-dioxane, add 72.12 g of DGEBA and 22.88 g of 4,4'-diaminodiphenyl sulfone, mix and heat with stirring until a uniform solution is formed, then remove the solvent by distillation under reduced pressure, pour the resulting mixture into a mold for vacuum degassing, and mold it according to a curing system of 180°C / 2h and 200°C / 2h to obtain a flame retardant epoxy resin with a CH3O-HCCP-6DPCN-EP addition amount of 5 wt%, recorded as DGEBA / CH3O-HCCP-6DPCN-EP (5%) / DDS. According to this method, flame retardant epoxy resins with CH3O-HCCP-6DPCN-EP addition amounts of 10wt% and 15wt% were prepared, and were recorded as DGEBA / CH3O-HCCP-6DPCN-EP (10%) / DDS and DGEBA / CH3O-HCCP-6DPCN-EP (15%) / DDS.

[0061] Example 3

[0062] A cyclotriphosphazene epoxy compound (CH3O-HCCP-5CN-1DPCN-EP) containing a Schiff base and DOPO structure in a molar ratio of 5:1 and a flame retardant epoxy resin (DGEBA / CH3O-HCCP-5CN-1DPCN-EP (15%) / DDS) were prepared.

[0063] Step 1: CH3O-HCCP-6CN-OH and DOPO were added in a molar ratio of 1:1. The other processes were the same as step 2 in Example 2 to obtain hexahydroxycyclotriphosphazene containing Schiff base and DOPO structure, recorded as CH3O-HCCP-5CN-1DPCN-OH, with a yield of 95.4%.

[0064] Step 2: CH3O-HCCP-5CN-1DPCN-OH was reacted with epichlorohydrin, and the preparation process was the same as step 3 in Example 2 to obtain a cyclotriphosphazene epoxy compound containing a Schiff base and a DOPO structure, which was recorded as CH3O-HCCP-5CN-1DPCN-EP, with a yield of 84.5%.

[0065] Step 3: Same as step 5 in Example 2, prepare a flame retardant epoxy resin with a CH3O-HCCP-5CN-1DPCN-EP addition amount of 15 wt%, recorded as DGEBA / CH3O-HCCP-5CN-1DPCN-EP (15%) / DDS.

[0066] Example 4

[0067] A cyclotriphosphazene epoxy compound (CH3O-HCCP-4CN-2DPCN-EP) with a molar ratio of Schiff base to DOPO structure of 4:2 and a flame retardant epoxy resin (DGEBA / CH3O-HCCP-4CN-2DPCN-EP (15%) / DDS) were prepared.

[0068] Step 1: CH3O-HCCP-6CN-OH and DOPO were added in a molar ratio of 1:2. The other processes were the same as step 2 in Example 2, and the hexahydroxycyclotriphosphazene containing Schiff base and DOPO structure was obtained, recorded as CH3O-HCCP-4CN-2DPCN-OH, with a yield of 95.1%.

[0069] Step 2: CH3O-HCCP-4CN-2DPCN-OH and epichlorohydrin are reacted, and the preparation process is the same as step 3 in Example 2 to obtain a cyclotriphosphazene epoxy compound containing a Schiff base and a DOPO structure, which is recorded as CH3O-HCCP-4CN-2DPCN-EP, with a yield of 83.7%.

[0070] Step 3: Same as step 5 in Example 2, prepare a flame retardant epoxy resin with a CH3O-HCCP-4CN-2DPCN-EP addition amount of 15 wt%, recorded as DGEBA / CH3O-HCCP-4CN-2DPCN-EP (15%) / DDS.

[0071] Example 5

[0072] A cyclotriphosphazene epoxy compound (CH3O-HCCP-3CN-3DPCN-EP) with a molar ratio of Schiff base to DOPO structure of 3:3 and a flame retardant epoxy resin (DGEBA / CH3O-HCCP-3CN-3DPCN-EP (15%) / DDS) were prepared.

[0073] Step 1: CH3O-HCCP-6CN-OH and DOPO were added in a molar ratio of 1:3, and the other steps were the same as step 2 in Example 2, to obtain hexahydroxycyclotriphosphazene containing Schiff base and DOPO structure, recorded as CH3O-HCCP-3CN-3DPCN-OH, with a yield of 94.6%.

[0074] Step 2: CH3O-HCCP-3CN-3DPCN-OH and epichlorohydrin are reacted, and the preparation process is the same as step 3 in Example 2 to obtain a cyclotriphosphazene epoxy compound containing a Schiff base and a DOPO structure, which is recorded as CH3O-HCCP-3CN-3DPCN-EP, with a yield of 82.7%.

[0075] Step 3: Same as step 5 in Example 2, prepare a flame retardant epoxy resin with a CH3O-HCCP-3CN-3DPCN-EP addition amount of 15 wt%, recorded as DGEBA / CH3O-HCCP-3CN-3DPCN-EP (15%) / DDS.

[0076] Example 6

[0077] A cyclotriphosphazene epoxy compound (CH3O-HCCP-2CN-4DPCN-EP) with a molar ratio of Schiff base to DOPO structure of 2:4 and a flame retardant epoxy resin (DGEBA / CH3O-HCCP-2CN-4DPCN-EP (15%) / DDS) were prepared.

[0078] Step 1: CH3O-HCCP-6CN-OH and DOPO were added at a molar ratio of 1:4, and the other steps were the same as step 2 in Example 2, to obtain hexahydroxycyclotriphosphazene containing Schiff base and DOPO structure, recorded as CH3O-HCCP-2CN-4DPCN-OH, with a yield of 93.7%.

[0079] Step 2: CH3O-HCCP-2CN-4DPCN-OH and epichlorohydrin are reacted, and the preparation process is the same as step 3 in Example 2 to obtain a cyclotriphosphazene epoxy compound containing a Schiff base and a DOPO structure, which is recorded as CH3O-HCCP-2CN-4DPCN-EP, with a yield of 81.4%.

[0080] Step 3: Same as step 5 in Example 2, prepare a flame retardant epoxy resin with a CH3O-HCCP-2CN-4DPCN-EP addition amount of 15 wt%, recorded as DGEBA / CH3O-HCCP-2CN-4DPCN-EP (15%) / DDS.

[0081] Example 7

[0082] A cyclotriphosphazene epoxy compound (CH3O-HCCP-1CN-5DPCN-EP) with a molar ratio of Schiff base to DOPO structure of 1:5 and a flame retardant epoxy resin (DGEBA / CH3O-HCCP-1CN-5DPCN-EP (15%) / DDS) were prepared.

[0083] Step 1: CH3O-HCCP-6CN-OH and DOPO were added at a molar ratio of 1:5, and the other steps were the same as step 2 in Example 2, to obtain hexahydroxycyclotriphosphazene containing Schiff base and DOPO structure, recorded as CH3O-HCCP-1CN-5DPCN-OH, with a yield of 92.1%.

[0084] Step 2: CH3O-HCCP-1CN-5DPCN-OH and epichlorohydrin are reacted, and the preparation process is the same as step 3 in Example 2 to obtain a cyclotriphosphazene epoxy compound containing a Schiff base and a DOPO structure, which is recorded as CH3O-HCCP-1CN-5DPCN-EP, with a yield of 81.2%.

[0085] Step 3: Same as step 5 in Example 2, prepare a flame retardant epoxy resin with a CH3O-HCCP-1CN-5DPCN-EP addition amount of 15 wt%, recorded as DGEBA / CH3O-HCCP-1CN-5DPCN-EP (15%) / DDS.

[0086] Comparative Example 1

[0087] 25 g of bisphenol A epoxy resin and 7.9 g of 4,4'-diaminodiphenyl sulfone curing agent were heated until melted and stirred evenly, placed in an oven to evacuate and remove bubbles, then poured into a mold and formed according to a curing system of 180°C / 2h and 200°C / 2h. The cured resin was recorded as DGEBA / DDS.

[0088] The epoxy resin systems prepared in the examples and comparative examples were subjected to bending performance, limiting oxygen index and vertical combustion tests, and the test standards were as follows: oxygen index was tested according to GB / T 2406.2; horizontal and vertical combustion was tested according to GB / T 2408; bending strength and bending elastic modulus were tested according to GB / T9341; the test results are shown in Tables 1 and 2.

[0089] Table 1 Flame retardant and mechanical properties of epoxy resins prepared in Examples 1-2 and Comparative Example 1

[0090]

[0091]

[0092] As can be seen from Table 1, the cyclotriphosphazene epoxy compound CH3O-HCCP-6CN-EP containing a Schiff base structure in Example 1 has excellent flame retardancy and mechanical properties after being cured by DDS, but adding 15wt% to DGEBA / DDS as a reactive flame retardant does not reach the flame retardancy level, only the limiting oxygen index is slightly improved and the phenomenon of molten droplets dripping after ignition is overcome. It can be seen that the cyclotriphosphazene epoxy compound containing a Schiff base structure as an epoxy monomer and a curing agent can directly cross-link and form an epoxy resin with excellent flame retardancy and mechanical properties.

[0093] The cyclotriphosphazene epoxy compound CH3O-HCCP-6DPCN-EP containing a DOPO structure in Example 2 is obtained by introducing 6 DOPO groups on the basis of CH3O-HCCP-6CN-EP in Example 1. After CH3O-HCCP-6DPCN-EP is used as an epoxy monomer and directly cross-linked with DDS, the limiting oxygen index reaches the highest 37.5%. Because the epoxy value of CH3O-HCCP-6DPCN-EP is low and the steric hindrance of DOPO will reduce the cross-linking density of the epoxy network, the mechanical properties of CH3O-HCCP-6DPCN-EP / DDS are slightly lower than those of CH3O-HCCP-6CN-EP / DDS, but are still slightly higher than those of DGEBA / DDS. CH3O-HCCP-6DPCN-EP is added to DGEBA / DDS as a reactive flame retardant. As the amount added increases, its flame retardancy and mechanical properties are enhanced. It can be seen that cyclotriphosphazene epoxy compounds containing DOPO structure are more suitable as reactive flame retardants and are compounded with epoxy resins to prepare flame-retardant epoxy resins with excellent comprehensive properties.

[0094] Table 2 Flame retardant and mechanical properties of cyclotriphosphazene flame retardant epoxy resin system prepared in Examples 1-7

[0095]

[0096]

[0097] As can be seen from Table 2, the epoxy system prepared by compounding the epoxy resin with the cyclotriphosphazene epoxy compound containing DOPO and Schiff base structure as a reactive flame retardant has excellent flame retardant and mechanical properties when the addition amount is 15wt%. When the DOPO content in the flame retardant increases, the limiting oxygen index of the flame retardant resin increases, but the bending strength decreases. The main reason is that the steric hindrance of the DOPO structural unit is large, which reduces the crosslinking density of the crosslinking network.

[0098] In order to illustrate the relevant properties of the flame retardant epoxy resin provided by the present invention, it is described in conjunction with the accompanying drawings.

[0099] Figure 1 This is the nuclear magnetic resonance hydrogen spectrum of the Schiff base-containing cyclotriphosphazene epoxy compound CH3O-HCCP-6CN-EP provided in Example 1. The methoxy proton absorption peak is at 3.75 ppm, the proton absorption peak on the imine bond is at 8.36 ppm, the aromatic hydrogen absorption peak on the two benzene rings connected by the imine bond is at 6.79-7.48 ppm, the methylene proton absorption peak appears at 3.85 ppm and 4.34 ppm, and the proton absorption peak on the epoxy group appears at 2.73 ppm, 2.88 ppm and 3.37 ppm.

[0100] Figure 2This is the nuclear magnetic resonance phosphorus spectrum of the cyclotriphosphazene epoxide CH3O-HCCP-6CN-EP containing a Schiff base provided in Example 1. There is a single peak at the chemical shift of 9.52ppm, indicating that there is only one chemical environment of the P atom, and the nuclear magnetic resonance hydrogen spectrum and the phosphorus spectrum together indicate the successful synthesis of the cyclotriphosphazene epoxide CH3O-HCCP-6CN-EP containing a Schiff base.

[0101] The above description is only a preferred example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A flame retardant cyclotriphosphazene epoxy compound, characterized in that: It has the general formula shown in Formula I: Wherein R1 to R6 are independently selected from any one of the structures shown in ① to ④: In formulas ① to ④, R is H, -CH3 or -OCH3.

2. The method for preparing a flame retardant cyclotriphosphazene epoxy compound according to claim 1, characterized in that: When R1 to R6 are all selected from ① or ③, the method comprises the steps of: Step 1, mixing hexa(4-aminophenoxy)cyclotriphosphazene with a hydroxyaldehyde compound as shown in Formula I-1 in a solvent for reaction, and treating to obtain a hexahydroxycyclotriphosphazene containing a Schiff base structure as shown in Formula I-2; Step 2, mixing the compound represented by formula I-2 and epichlorohydrin for reaction, adding a phase transfer catalyst to continue the reaction after the reaction system becomes a homogeneous phase, and then dropping an inorganic base to continue the reaction, and purifying to obtain the flame-retardant cyclotriphosphazene epoxy compound; When at least one of R1 to R6 is selected from ② or ④, the method comprises the steps of: Step 1, mixing hexa(4-aminophenoxy)cyclotriphosphazene with a hydroxyaldehyde compound as shown in Formula I-1 in a solvent for reaction, and treating to obtain a hexahydroxycyclotriphosphazene containing a Schiff base structure as shown in Formula I-2; Step 1-2, mixing the compound represented by formula I-2 and DOPO and subjecting them to reflux reaction, and purifying the product to obtain the compound represented by formula I-3; Step 2, mixing the compound represented by formula I-3 and epichlorohydrin for reaction, adding a phase transfer catalyst to continue the reaction after the reaction system becomes a homogeneous phase, and then dropping an inorganic base to continue the reaction, and purifying to obtain the flame-retardant cyclotriphosphazene epoxy compound; R1'~R6' is selected from any one of the structures shown in ⑤~⑧, at least one of which is ⑥ or ⑧: Wherein, R is as described in claim 1.

3. The method for preparing the flame retardant cyclotriphosphazene epoxy compound according to claim 2, characterized in that: The reaction in step 1 is carried out at 50-90° C. for 4-15 hours; In step 2, after adding epichlorohydrin, the reaction is carried out at 60-110° C. until the system is in a homogeneous phase; after adding a phase transfer catalyst, the reaction is continued for 6-15 hours; after adding an inorganic base, the reaction is continued at 50-90° C. for 2-10 hours; In step 2, the molar ratio of the compound represented by formula I-2 or I-3 to epichlorohydrin is 1:75 to 120; In step 1-2, the molar ratio of the compound represented by formula I-2 to DOPO is 1:1-6; In step 1-2, the reaction temperature is 100-115° C. and the reaction time is 8-36 h.

4. The method for preparing the flame retardant cyclotriphosphazene epoxy compound according to claim 2, characterized in that: The hydroxyaldehyde compound represented by formula I-1 is one of p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, vanillin, syringaldehyde, and 2-methyl-4-hydroxybenzaldehyde; At least one of the solvents used in the reaction process: 1,4-dioxane, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and methyl pyrrolidone; The phase transfer catalyst is tetrabutylammonium bromide, benzyltriethylammonium chloride, hexadecyltrimethylammonium bromide or triphenylphosphine.

5. An intrinsic flame retardant epoxy resin, characterized in that: The invention is composed of the flame-retardant cyclotriphosphazene epoxy compound as claimed in claim 1 and a curing agent.

6. A flame retardant epoxy resin, characterized in that: The invention comprises epoxy resin, the flame retardant cyclotriphosphazene epoxy compound as claimed in claim 1 and a curing agent; in the flame retardant cyclotriphosphazene epoxy compound, at least one of R1 to R6 is selected from the structure shown in ② or ④.

7. The intrinsic flame retardant epoxy resin or flame retardant epoxy resin according to claim 5 or 6, characterized in that: The curing agent includes one or more of 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, dinitrile amine, maleic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride.

8. The intrinsic flame retardant epoxy resin or flame retardant epoxy resin according to claim 5 or 6, wherein the curing agent is added in an amount according to a molar ratio of epoxy groups in the epoxy compound to active hydrogen in the curing agent of 1:0.5-1.

5.

9. The intrinsic flame retardant epoxy resin or flame retardant epoxy resin according to claim 6, wherein the mass of the flame retardant cyclotriphosphazene epoxy compound accounts for 5-30% of all raw materials.

10. The intrinsic flame retardant epoxy resin or the method for preparing the flame retardant epoxy resin according to claim 7 or 8, characterized in that: The method comprises the following steps: dissolving the flame-retardant cyclotriphosphazene epoxy compound, epoxy resin and curing agent in a solvent, removing the solvent by reduced pressure distillation, and obtaining the flame-retardant epoxy resin by degassing and curing.

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