Reactive phosphorus-containing flame retardant containing self-crosslinking structure as well as preparation method and application of reactive phosphorus-containing flame retardant

Abstract

The invention relates to a reactive phosphorus-containing flame retardant containing a self-crosslinking structure as well as a preparation method and application of the reactive phosphorus-containing flame retardant. The phosphorus-containing flame retardant is obtained by taking a monoaminophenoxy phthalonitrile compound and phenylphosphoryl dichloride as raw materials and carrying out nucleophilic substitution reaction by utilizing amino and chlorine atoms. The preparation method comprises the following steps: respectively mixing phenyl phosphoryl dichloride and a monoaminophenoxy phthalonitrile compound with tetrahydrofuran to form a solution A and a solution B; under the stirring and inert gas atmosphere, dropwise adding the solution B into the solution A, and completely dropwise adding within 1 hour; continuously reacting at room temperature for 1.5 to 3h; reacting for 10 to 15 hours under a reflux temperature condition; and cooling, filtering, removing the solvent from the filtrate, and washing to obtain the reactive phosphorus-containing flame retardant with the self-crosslinking structure. The monoaminophenoxy phthalonitrile compound with the high-temperature self-crosslinking characteristic is introduced into phosphorus flame retardant molecules, so that the phosphorus flame retardant has the characteristics of efficient flame retardance and excellent heat resistance in the epoxy resin.

Description

Technical Field

[0001] The present invention relates to the technical field of epoxy resins, and particularly to a reactive phosphorus-containing flame retardant with a self-crosslinking structure, its preparation method and application. Background Art

[0002] Epoxy resins have been widely used in fields such as coatings, adhesives, laminates, and the electronics industry due to their excellent mechanical properties, adhesive strength, chemical corrosion resistance, electrical insulation, and dimensional stability. Ordinary epoxy resins are limited in application in some scenarios with high safety requirements due to their inherent flammability. Therefore, flame retardant modification of epoxy resins to improve their fire resistance has become a necessary means to meet actual needs.

[0003] Currently, phosphorus-based flame retardants have become the main choice for flame retardant modification of epoxy resins due to their high flame retardancy efficiency and relatively environmental friendliness.

[0004] However, to meet the flame retardant standards required for actual use, a relatively high content of phosphorus-based flame retardants usually needs to be added, which often leads to a significant decrease in the mechanical properties of the cured resin. In addition, the flame retardant effect of phosphorus-based flame retardants depends on the gas-phase flame retardant mechanism. The phosphorus-containing free radicals generated by their decomposition can capture the active free radicals released by the thermal decomposition of epoxy resins, interrupt the combustion chain reaction, and thus inhibit flame propagation. However, during the process, the unburned small molecules are prone to aggregate into smoke in the gas phase, resulting in a relatively high smoke density. This situation is particularly significant in application scenarios such as electronic packaging or enclosed spaces.

[0005] Therefore, how to achieve efficient flame retardancy at a low addition amount while maintaining the comprehensive properties of the resin (such as mechanical strength and thermal stability) remains the focus and difficulty of current research. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a reactive phosphorus-containing flame retardant with a self-crosslinking structure, its preparation method and application. By introducing a monoaminophenoxyphthalonitrile compound with high-temperature self-crosslinking characteristics into the phosphorus-based flame retardant molecule, it has the characteristics of high efficiency in flame retardancy and excellent heat resistance in epoxy resins.

[0007] The technical solution adopted by the present invention to solve its technical problems is: a reactive phosphorus-containing flame retardant with a self-crosslinking structure, whose molecular structural formula is

[0008]

[0009] wherein, R1, R2, R3, R4, and R5 are each selected from one of hydrogen or alkyl.

[0010] Further, the phosphorus-containing flame retardant is obtained by using a monoaminophenoxyphthalonitrile compound and phenylphosphonic dichloride as raw materials and performing a nucleophilic substitution reaction between the amino group in the monoaminophenoxyphthalonitrile compound and the chlorine atom of phenylphosphonic dichloride; the molar ratio of phenylphosphonic dichloride to the monoaminophenoxyphthalonitrile compound is 1:(2 - 2.2); the molecular structural formula of phenylphosphonic dichloride is The molecular structural formula of the monoaminophenoxyphthalonitrile compound is

[0011]

[0012] wherein, R1, R2, R3, R4, and R5 are each independently selected from one of hydrogen or an alkyl group.

[0013] Further, the monoaminophenoxyphthalonitrile compound is obtained by using 4-nitrophthalonitrile and a monoaminophenol compound as raw materials and performing a substitution reaction between the nitro group of 4-nitrophthalonitrile and the phenolic group of the monoaminophenol compound; the molar ratio of 4-nitrophthalonitrile to the monoaminophenol compound is 1:(1 - 1.2);

[0014] The molecular structural formula of 4-nitrophthalonitrile is The monoaminophenol compound is wherein, R1, R2, R3, R4, and R5 are each independently selected from one of hydrogen or an alkyl group.

[0015] The monoaminophenol compound is selected from one of, but not limited to, 4-aminophenol, 2-aminophenol, 2-methyl-5-aminophenol, or 2-aminop-cresol.

[0016] The preparation method of the above reaction-type phosphorus-containing flame retardant with a self-crosslinking structure is specifically prepared according to the following steps:

[0017] S1. Mix phenylphosphonic dichloride and tetrahydrofuran to form solution A; mix the monoaminophenoxyphthalonitrile compound and tetrahydrofuran to form solution B;

[0018] S2. Under stirring and in an inert gas atmosphere, slowly add solution B dropwise to solution A within 1 h; then, continue to react at room temperature for 1.5 - 3 h, and then reflux for 10 - 15 h; after the reaction is completed, cool to room temperature; filter the reaction product, take the filtrate, remove the solvent, and wash with deionized water to obtain the reaction-type phosphorus-containing flame retardant with a self-crosslinking structure.

[0019] Further, the monoaminophenoxyphthalonitrile compound in step S1 is prepared through the following steps: Mix 4-nitrophthalonitrile, monoaminophenol compound, potassium carbonate, and dimethyl sulfoxide, and react at 55-65°C for 6-8 h under an inert gas atmosphere; after the reaction is completed, cool to room temperature; add the reaction product to sodium hydroxide solution and soak for 10-15 h, wash and filter with distilled water multiple times until the pH value of the filtrate is neutral, and dry the obtained solid to obtain the monoaminophenoxyphthalonitrile compound.

[0020] The above reactive phosphorus-containing flame retardant with a self-crosslinking structure is applied to the intrinsically flame-retardant epoxy resin system.

[0021] Advantages of the present invention: 1. The present invention integrates a flame-retardant phosphoryl group and a phthalonitrile group with a high-temperature self-crosslinking function into the same molecular structure; compared with traditional phosphorus-based flame retardants, when achieving the same flame-retardant effect, the required phosphorus content is lower, and the combustion smoke volume is significantly reduced; 2. In the flame retardant synthesized by the present invention, the phthalonitrile group can crosslink to form a triazine and phthalocyanine structure at high temperature, improving the heat resistance of the residual carbon and effectively blocking the heat and oxygen exchange during the combustion of epoxy resin, thereby significantly improving the flame-retardant efficiency; 3. By introducing a rigid phthalonitrile group into the epoxy resin crosslinking network, the present invention utilizes its steric hindrance effect to restrict the movement of epoxy resin molecular chains, thereby enhancing the rigidity and heat resistance of the cured product. Detailed implementation manners

[0022] To deepen the understanding of the present invention, the following will further describe the present invention in detail with reference to embodiments. These embodiments are only used to explain the present invention and do not limit the protection scope of the present invention.

[0023] Example 1

[0024] This embodiment provides a reactive phosphorus-containing flame retardant with a self-crosslinking structure, and its molecular structural formula is

[0025]

[0026] This embodiment also provides a preparation method of the reactive phosphorus-containing flame retardant with a self-crosslinking structure:

[0027] Preparation of monoaminophenoxyphthalonitrile compound: Add 4-nitrophthalonitrile, 4-aminophenol, and potassium carbonate into a four-necked flask filled with dimethyl sulfoxide, introduce nitrogen, heat in an oil bath at 60°C for 6-8 h, cool to room temperature after the reaction is completed, pour it into sodium hydroxide solution and soak for 12 h, then wash and filter with distilled water multiple times until the filtrate is neutral, and finally dry in an oven at 70°C for 12 h to obtain the monoaminophenoxyphthalonitrile compound, and its molecular structural formula is as follows:

[0028]

[0029] In a three-necked flask equipped with a reflux condenser and mechanical stirring, phenylphosphoryl dichloride and tetrahydrofuran were added; the monoaminophenoxyphthalonitrile compound was dissolved in tetrahydrofuran, and under mechanical stirring and a nitrogen atmosphere, the addition was completed within 1 h; after the addition was completed, the reaction was continued at room temperature for 2 h, then the temperature of the reaction system was adjusted to 75 °C, and the reflux reaction was carried out for 12 h; after the reaction was completed, the reaction system was cooled to room temperature, and the filtrate was taken for rotary evaporation to obtain the crude product; it was washed three times with deionized water to obtain a reactive phosphorus-containing flame retardant (No.: A) containing a self-crosslinked structure.

[0030] The synthetic route of the reactive phosphorus-containing flame retardant containing a self-crosslinked structure in this example is as follows:

[0031]

[0032] Example 2

[0033] This example provides a reactive phosphorus-containing flame retardant containing a self-crosslinked structure, and its molecular structural formula is

[0034]

[0035] This example also provides a preparation method of the reactive phosphorus-containing flame retardant containing a self-crosslinked structure:

[0036] Preparation of the monoaminophenoxyphthalonitrile compound: 4-Nitrophthalonitrile, 2-aminophenol, and potassium carbonate were added to a four-necked flask equipped with dimethyl sulfoxide, nitrogen was introduced, and the reaction was carried out in an oil bath at 60 °C for 6 - 8 h. After the reaction was completed, it was cooled to room temperature, poured into sodium hydroxide solution and soaked for 12 h, then washed and filtered with distilled water several times until the filtrate was neutral, and finally dried in an oven at 70 °C for 12 h to obtain the monoaminophenoxyphthalonitrile compound, and its molecular structural formula is as follows:

[0037]

[0038] In a three-necked flask equipped with a reflux condenser and mechanical stirring, phenylphosphoryl dichloride and tetrahydrofuran were added; the monoaminophenoxyphthalonitrile compound was dissolved in tetrahydrofuran, and under mechanical stirring and a nitrogen atmosphere, the addition was completed within 1 h; after the addition was completed, the reaction was continued at room temperature for 2 h, then the temperature of the reaction system was adjusted to 75 °C, and the reflux reaction was carried out for 12 h; after the reaction was completed, the reaction system was cooled to room temperature, and the filtrate was taken for rotary evaporation to obtain the crude product; it was washed three times with deionized water to obtain a reactive phosphorus-containing flame retardant (No.: B) containing a self-crosslinked structure.

[0039] Example 3

[0040] This example provides a reactive phosphorus-containing flame retardant with a self-crosslinking structure, and its molecular structural formula is

[0041]

[0042] This example also provides a preparation method of a reactive phosphorus-containing flame retardant with a self-crosslinking structure:

[0043] Preparation of monoaminophenoxyphthalonitrile compounds: Add 4-nitrophthalonitrile, 2-methyl-5-aminophenol, and potassium carbonate into a four-necked flask filled with dimethyl sulfoxide, introduce nitrogen, heat in an oil bath at 60 °C for 6 - 8 h. After the reaction is completed, cool to room temperature, pour it into sodium hydroxide solution and soak for 12 h. Then wash and filter with distilled water multiple times until the filtrate is neutral. Finally, dry in an oven at 70 °C for 12 h to obtain monoaminophenoxyphthalonitrile compounds, and the molecular structural formula is as follows:

[0044]

[0045] In a three-necked flask equipped with a reflux condenser and mechanical stirring, add phenylphosphoryl dichloride and tetrahydrofuran; dissolve the monoaminophenoxyphthalonitrile compounds in tetrahydrofuran, and under mechanical stirring and nitrogen atmosphere, finish dropping within 1 h; after dropping, continue to react at room temperature for 2 h, then adjust the temperature of the reaction system to 75 °C and reflux for 12 h; after the reaction is completed, cool the reaction system to room temperature, take the filtrate and perform rotary evaporation to obtain the crude product; wash three times with deionized water to obtain a reactive phosphorus-containing flame retardant with a self-crosslinking structure (No.: C).

[0046] Example 4

[0047] This example provides a reactive phosphorus-containing flame retardant with a self-crosslinking structure, and its molecular structural formula is

[0048]

[0049] This example also provides a preparation method of a reactive phosphorus-containing flame retardant with a self-crosslinking structure:

[0050] Preparation of monoaminophenoxyphthalonitrile compounds: Add 4-nitrophthalonitrile, 2-aminop-cresol, and potassium carbonate into a four-necked flask filled with dimethyl sulfoxide, introduce nitrogen, heat in an oil bath at 60 °C for 6 - 8 h. After the reaction is completed, cool to room temperature, pour it into sodium hydroxide solution and soak for 12 h. Then wash and filter with distilled water multiple times until the filtrate is neutral. Finally, dry in an oven at 70 °C for 12 h to obtain monoaminophenoxyphthalonitrile compounds, and the molecular structural formula is as follows:

[0051]

[0052] In a three-necked flask equipped with a reflux condenser and mechanical stirring, phenylphosphonic dichloride and tetrahydrofuran were added; the monoaminophenoxyphthalonitrile compound was dissolved in tetrahydrofuran, and under mechanical stirring and nitrogen atmosphere, the addition was completed within 1 h; after the addition was completed, the reaction was continued at room temperature for 2 h, then the temperature of the reaction system was adjusted to 75 °C, and the reflux reaction was carried out for 12 h; after the reaction was completed, the reaction system was cooled to room temperature, and the filtrate was taken for rotary evaporation to obtain the crude product; it was washed three times with deionized water to obtain a reactive phosphorus-containing flame retardant with a self-crosslinked structure (No.: D).

[0053] Application Example

[0054] According to the phosphorus content of the system being 0.5 wt%, the reactive phosphorus-containing flame retardants with self-crosslinked structures prepared in Examples 1 to 4 in corresponding proportions were respectively mixed with bisphenol A epoxy resin (E-51, brand CYD-127, Yueyang Baling Huaxing Petrochemical Co., Ltd.), and then 4,4'-diaminodiphenylmethane (DDM) calculated according to the epoxy equivalent was added as a curing agent, denoted as EP / DDM / A, EP / DDM / B, EP / DDM / C, and EP / DDM / D respectively.

[0055] Comparative Example

[0056] Bisphenol A epoxy resin (E-51, brand CYD-128) was mixed with 4,4'-diaminodiphenylmethane (DDM) calculated according to the epoxy equivalent, denoted as EP / DDM.

[0057] The Application Example and Comparative Example The prepared epoxy resin systems were respectively injected into a preheated mold and placed in an oven for curing according to the following process: cured at 160 °C for 2 h and at 180 °C for 5 h. The obtained cured products were subjected to the following performance tests:

[0058] The limiting oxygen index (LOI) was determined according to ASTM D2863 standard;

[0059] The UL-94 vertical burning rating was evaluated according to ASTM D3801 standard;

[0060] The combustion smoke density rating was determined using an XP-2 building material smoke density tester according to ASTM D2843 standard;

[0061] The glass transition temperature (T g ) was determined by dynamic thermomechanical analysis;

[0062] The mechanical properties were tested using an electronic universal testing machine according to ASTM D3039 standard, and the loading rate was 1 mm / min.

[0063] The above test results are shown in Table 1 and Table 2 respectively.

[0064] Table 1 Flame retardant performance parameters of epoxy resin cured products

[0065] Cured Product LOI(%) UL-94 Vertical Burning Rating Smoke Density Rating System Phosphorus Content (wt%) EP / DDM 24.2 No Rating 94 0 EP / DDM / A 29.5 V-0 68 0.5 EP / DDM / B 28.7 V-0 66 0.5 EP / DDM / C 30.5 V-0 75 0.5 EP / DDM / D 31.4 V-0 70 0.5

[0066] Table 2 Glass transition temperature and mechanical property parameters of epoxy resin cured products

[0067] Cured Product <![CDATA[T g (℃)]]> Tensile Strength (MPa) Tensile Modulus (MPa) EP / DDM 174 65.2 2792 EP / DDM / A 170 74.5 2996 EP / DDM / B 176 79.8 3043 EP / DDM / C 180 77.1 2976 EP / DDM / D 174 70.2 2856

[0068] As can be seen from the data in Table 1, for the cured products prepared from the reactive phosphorus-containing flame retardants A-D of the present invention and epoxy resin, when the phosphorus content is only 0.5 wt%, the LOI values all exceed 28%, the vertical burning rating reaches UL-94 V-0, and the combustion smoke density drops below 75, showing more excellent flame retardant efficiency and smoke suppression effect compared with traditional phosphorus-based flame retardants. As can be seen from the data in Table 2, compared with the comparative example EP / DDM, the T of the cured products of the four application examples g is maintained, and the T of EP / DDM / B and EP / DDM / C g even increases; at the same time, the tensile strength and modulus of the four modified cured products are all enhanced to a certain extent. This indicates that the flame retardant of the present invention significantly improves the flame retardant performance while effectively improving the heat resistance and mechanical properties of the epoxy resin cured products.

[0069] The above embodiments should not limit the present invention in any way, and all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A reactive phosphorus-containing flame retardant having a self-crosslinking structure, characterized in that: The molecular structure of the phosphorus-containing flame retardant is Wherein, R1, R2, R3, R4, and R5 are each selected from hydrogen or an alkyl group.

2. The reactive phosphorus-containing flame retardant having a self-crosslinking structure according to claim 1, characterized in that: The phosphorus-containing flame retardant is obtained by using monoaminophenoxyphthalonitrile compounds and phenylphosphoryl dichloride as raw materials, and utilizing the amino group in the monoaminophenoxyphthalonitrile compounds and the chlorine atom of phenylphosphoryl dichloride to undergo a nucleophilic substitution reaction; the molar ratio of phenylphosphoryl dichloride to the monoaminophenoxyphthalonitrile compounds is 1:(2-2.2); the molecular structural formula of the phenylphosphoryl dichloride is The molecular structural formula of the monoaminophenoxyphthalonitrile compound is Wherein, R1, R2, R3, R4, and R5 are each selected from hydrogen or an alkyl group.

3. The reactive phosphorus-containing flame retardant having a self-crosslinking structure according to claim 2, characterized in that: The monoaminophenoxyphthalonitrile compound is obtained by using 4-nitrophthalonitrile and monoaminophenol compounds as raw materials, and utilizing the nitro group of 4-nitrophthalonitrile and the phenol group of monoaminophenol to undergo a substitution reaction; the molar ratio of 4-nitrophthalonitrile to the monoaminophenol compound is 1:(1-1.2); the molecular structural formula of the 4-nitrophthalonitrile is The monoaminophenol compound is Wherein, R1, R2, R3, R4, and R5 are each selected from hydrogen or an alkyl group.

4. The reactive phosphorus-containing flame retardant having a self-crosslinking structure according to claim 3, characterized in that: The monoaminophenol compound is selected from one of 4-aminophenol, 2-aminophenol, 2-methyl-5-aminophenol and 2-amino-p-cresol.

5. The method for preparing a reactive phosphorus-containing flame retardant having a self-crosslinking structure according to any one of claims 1 to 4, characterized in that: Specifically prepared according to the following steps: S1, mixing phenylphosphoryl dichloride and tetrahydrofuran to form solution A; mixing monoaminophenoxyphthalonitrile compound and tetrahydrofuran to form solution B; S2. Add solution B to solution A under stirring and inert gas atmosphere, and the adding time is controlled within 1 hour; then, continue to react at room temperature for 1.5-3 hours, and then reflux to react for 10-15 hours; after the reaction is completed, cool to room temperature; filter the reaction product, take the filtrate, remove the solvent, and wash with deionized water to obtain a reactive phosphorus-containing flame retardant with a self-crosslinking structure.

6. The method for preparing a reactive phosphorus-containing flame retardant having a self-crosslinking structure according to claim 5, characterized in that: The monoaminophenoxyphthalonitrile compound in step S1 is prepared by the following steps: 4-nitrophthalonitrile, monoaminophenol compound, potassium carbonate and dimethyl sulfoxide are mixed, reacted at 55-65° C. for 6-8 hours under an inert gas atmosphere; after the reaction is completed, cooled to room temperature; the reaction product is added to a sodium hydroxide solution and soaked for 10-15 hours, washed and filtered with distilled water for multiple times until the pH value of the filtrate is neutral, and the obtained solid is dried to obtain a monoaminophenoxyphthalonitrile compound.

7. Use of a reactive phosphorus-containing flame retardant having a self-crosslinking structure as claimed in any one of claims 1 to 4, characterized in that: Application of reactive phosphorus-containing flame retardant with self-crosslinking structure in intrinsic flame retardant epoxy resin system.

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