Disubstituted phosphinic acid ester compounds, processes for their preparation and use

Abstract

This invention provides a disubstituted phosphonate compound, its preparation method, and its applications, belonging to the technical field of organophosphorus flame retardants. The disubstituted phosphonate compound provided by this invention exhibits excellent flame retardant properties. It is synthesized in a one-step process using phosphonates and halogenated compounds as raw materials. Compared to existing traditional synthesis methods, this method offers higher yields, fewer and easier-to-separate byproducts, a simpler process, shorter processing time, greater safety and environmental friendliness, lower cost, and easier implementation. The flame-retardant epoxy resin cured products prepared using the disubstituted phosphonate compound as a raw material exhibit excellent flame retardant properties and are transparent and clear. The flame-retardant epoxy resin cured product specimens prepared in Examples 1-3 of this invention show significantly better flame retardant effects than those in Comparative Examples 1-2. Furthermore, the flame-retardant epoxy resin cured products prepared in Examples 1-3 are all clear and transparent with superior physical properties.

Description

Technical Field

[0001] This invention relates to the field of organophosphorus flame retardant technology, and in particular to a disubstituted phosphonate compound, its preparation method, and its application. Background Technology

[0002] With social progress and development, synthetic polymer materials are widely used in production and daily life. Because polymer materials are rich in carbon and hydrogen, they are highly flammable. To date, fires caused by the combustion of polymer materials have resulted in significant losses. Phosphate esters are versatile chemicals; among them, phosphites and alkyl phosphates are the main types of organophosphorus flame retardants, possessing advantages such as long-lasting flame retardancy, good compatibility with polymer substrates, water resistance, and weather resistance. Therefore, they are widely used in polyurethane, epoxy resins, polycarbonate, unsaturated resins, and other polymer materials. Furthermore, disubstituted phosphinate esters, due to the presence of hypophosphite in their molecular structure, also exhibit good flame retardant properties. Moreover, disubstituted phosphinate esters do not contain monoalkyl structures and are not controlled chemicals by the OPCW, showing broad prospects for future development. Current technologies for synthesizing disubstituted phosphinate esters involve lengthy and complex processes, high reaction pressures, demanding equipment, expensive monomers, and high costs. They also produce large quantities of highly polluting halogen acids and flammable and explosive organic compounds as byproducts, making the process environmentally unfriendly and unsafe. Therefore, it is necessary to develop novel processes for the synthesis of disubstituted phosphonates to address the problems faced by existing processes.

[0003] Furthermore, due to its excellent properties, epoxy resin is widely used in the bonding and potting of electronic components, as well as in the preparation and bonding of components in the new energy industry. However, the low oxygen index of cured epoxy resin makes it inherently flammable, thus requiring corresponding flame-retardant modification for these applications. Currently, achieving transparent flame-retardant modification of epoxy resin remains difficult, limiting its further application development. Existing technologies for flame-retardant modification of epoxy resin mainly involve adding powdered flame retardants. However, powders can only be dispersed in epoxy resin and cannot achieve transparency. Adding industrially available liquid phosphate flame retardants can achieve a certain degree of transparency, but phosphorus-containing liquid phosphate flame retardants have poor compatibility with epoxy resin. During the curing process, these flame retardants migrate to the surface, forming a hazy surface that affects appearance and transparency. Moreover, adding large amounts of these phosphates alone is insufficient to achieve good flame-retardant effects. The addition of large amounts of liquid phosphates significantly impacts the curing efficiency and softening point of the cured epoxy resin, directly affecting its physical properties. If a transparent flame retardant that can be made from epoxy resin can be produced and is a simple additive, it will allow for a direct view of the internal structure when used for potting electronic components and fabricating structural parts. This will enable timely detection of faults and defects, facilitating prompt problem-solving and preventing more serious consequences. Summary of the Invention

[0004] The purpose of this invention is to provide a disubstituted phosphonate compound, its preparation method, and its application. The disubstituted phosphonate compound provided by this invention has excellent flame retardant properties. It is synthesized in one step using phosphonates and halogenated compounds as raw materials. Compared with existing traditional synthesis methods, it has a high yield, fewer and easier-to-separate byproducts, a simple process, short processing time, safe and environmentally friendly process, lower cost, and is easier to implement. The flame-retardant epoxy resin cured product prepared using the disubstituted phosphonate compound as a raw material has excellent flame retardant properties and is transparent and clear.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a disubstituted phosphonate compound having the structure shown in Formula I:

[0007]

[0008] In Formula I: R1, R2, R3 and R4 are independently selected from hydrogen, C1 to C8 alkyl, cycloalkyl, aryl or alkenyl, and n is an integer from 1 to 3.

[0009] This invention also provides a method for preparing the disubstituted phosphonate compound described in the above technical solution, comprising the following steps:

[0010] A phosphonate having the structure of formula II, a halogenated compound having the structure of formula III, an organic solvent and a catalyst are mixed and a substitution reaction is carried out in an inert atmosphere to obtain a disubstituted phosphonate.

[0011]

[0012] In Formula II, R1 and R2 are independently selected from hydrogen, C1-C8 alkyl, cycloalkyl, aryl or alkenyl, and M is a metal ion;

[0013] In Formula III, R3 and R4 are independently selected from hydrogen, C1-C8 alkyl, cycloalkyl, aryl or alkenyl, X is a halogen atom, and n is an integer from 1 to 3.

[0014] Preferably, the organic solvent is one or more of toluene, xylene, dioxane, acetonitrile, and tetrahydrofuran.

[0015] Preferably, the catalyst is at least one of a phase transfer catalyst and an amphoteric compound.

[0016] The present invention also provides the application of the disubstituted phosphonate compound described in the above technical solution or the disubstituted phosphonate compound prepared by the above preparation method in the preparation of flame-retardant epoxy resin cured products.

[0017] Preferably, the method for preparing the flame-retardant epoxy resin cured product includes the following steps:

[0018] After mixing disubstituted phosphonate compounds and epoxy resin, an anhydride curing agent and a tertiary amine accelerator are added and cured to obtain a flame-retardant epoxy resin cured product.

[0019] Preferably, the mass of the disubstituted phosphonate compound is 7% to 45% of the mass of the epoxy resin.

[0020] Preferably, the anhydride curing agent is at least one of methyltetrahydrophthalic anhydride and methylhexahydrophthalic anhydride.

[0021] Preferably, the tertiary amine promoter is at least one of triethylamine, triethylhydroxyamine, dimethylaminomethylphenol, and tris(dimethylaminomethyl)phenol.

[0022] Preferably, the curing temperature is 110℃~170℃, and the curing time is 1~4h.

[0023] This invention provides a disubstituted phosphonate compound having the structure shown in Formula I:

[0024]

[0025] In Formula I, R1, R2, R3, and R4 are independently selected from hydrogen, C1-C8 alkyl, cycloalkyl, aryl, or alkenyl groups, and n is an integer from 1 to 3. The disubstituted phosphonate compounds provided by this invention exhibit excellent flame retardant properties. Furthermore, they are synthesized in a one-step process using phosphonates and halogenated compounds as raw materials. Compared to existing traditional synthesis methods, this method offers higher yields, fewer and easier-to-separate byproducts, a simpler process, shorter processing time, greater safety and environmental friendliness, lower cost, and easier implementation. The flame-retardant epoxy resin cured products prepared using the disubstituted phosphonate compounds as raw materials exhibit excellent flame retardant properties and are transparent and clear. The results of the examples show that the flame-retardant epoxy resin cured product specimens prepared using Examples 1-3 of this invention have significantly better flame retardant effects than those using Comparative Examples 1-2. Moreover, the flame-retardant epoxy resin cured products prepared using Examples 1-3 are all clear and transparent with superior physical properties. This indicates that using the disubstituted hypophosphite compound provided by the present invention as a flame retardant can produce a transparent and clear flame-retardant epoxy resin cured product with excellent flame retardant properties, thereby achieving transparency of the flame-retardant epoxy resin cured product and reducing the adverse effects on the physical properties of the flame-retardant foamed polyurethane material. Attached Figure Description

[0026] Figure 1 The 1H NMR spectrum of the disubstituted phosphonate compound prepared in Example 1 of this invention;

[0027] Figure 2 The p-NMR spectrum of the disubstituted phosphonate compound prepared in Example 1 of this invention. Detailed Implementation

[0028] Unless otherwise specified, all raw materials used in this invention are commercially available products in the art.

[0029] This invention provides a disubstituted phosphonate compound having the structure shown in Formula I:

[0030]

[0031] In Formula I: R1, R2, R3 and R4 are independently selected from hydrogen, C1 to C8 alkyl, cycloalkyl, aryl or alkenyl, and n is an integer from 1 to 3.

[0032] This invention also provides a method for preparing the disubstituted phosphonate compound described in the above technical solution, comprising the following steps:

[0033] A phosphonate having the structure of formula II, a halogenated compound having the structure of formula III, an organic solvent and a catalyst are mixed and a substitution reaction is carried out in an inert atmosphere to obtain a disubstituted phosphonate.

[0034]

[0035] In Formula II, R1 and R2 are independently selected from hydrogen, C1-C8 alkyl, cycloalkyl, aryl or alkenyl, and M is a metal ion;

[0036] In Formula III, R3 and R4 are independently selected from hydrogen, C1-C8 alkyl, cycloalkyl, aryl or alkenyl, X is a halogen atom, and n is an integer from 1 to 3.

[0037] In this invention, in Formula II, R1 is preferably one of ethyl, phenyl, propyl, isopropyl, butyl, cyclopropyl, and cyclopentyl; R2 is preferably at least one of ethyl, phenyl, propyl, isopropyl, butyl, cyclopropyl, and cyclopentyl; and M is preferably at least one of sodium ion and potassium ion. In this invention, in Formula III, R3 is preferably one of hydrogen, methyl, ethyl, and cyclopropyl; R4 is preferably at least one of ethyl, phenyl, cyclopropylalkyl, and cyclopentyl; and X is preferably a chlorine atom. In this invention, the molar ratio of the phosphonate having the structure of Formula II to the halogenated compound having the structure of Formula III is preferably 1:(0.8–2.5), more preferably 1:(1–2), and even more preferably 1:1.6.

[0038] In this invention, the organic solvent is preferably one or more of toluene, xylene, dioxane, acetonitrile, and tetrahydrofuran; the catalyst is at least one of phase transfer catalysts and amphoteric compounds, more preferably at least one of ionic polyalkyl quaternary ammonium salts, cationic haloalkyl polyalkyl quaternary ammonium salts, alkyl ammonium chlorides, alkyl ammonium bromides, anionic alkyl sulfates, alkyl sulfonates, alkylbenzene sulfonates, nonionic surfactants, and quaternary phosphine salts, more preferably at least one of 15-Crown-5, 18-Crown-6, and tetrabutylammonium bromide. In this invention, the mass of the catalyst is preferably 2-7% of the mass of the phosphonate having the structure of Formula II, more preferably 5%.

[0039] In this invention, the inert atmosphere is preferably nitrogen protection; the substitution reaction is preferably a heating reflux reaction for 8 to 18 hours.

[0040] After the substitution reaction is completed, the product of the substitution reaction is preferably subjected to cooling, extraction, drying and rotary evaporation in sequence to obtain a disubstituted phosphonate compound.

[0041] In this invention, the extraction is preferably performed by adding water and ethyl acetate to the cooled product. This invention does not impose any particular limitation on the drying method; any technique well-known in the art can be used to remove water from the extracted organic phase. This invention also does not impose any particular limitation on the rotary evaporation method; any technique well-known in the art can be used to remove organic solvents from the dried product by rotary evaporation.

[0042] The present invention also provides the application of the disubstituted phosphonate compound described in the above technical solution or the disubstituted phosphonate compound prepared by the above preparation method in the preparation of flame-retardant epoxy resin cured products.

[0043] In this invention, the method for preparing the flame-retardant epoxy resin cured product preferably includes the following steps:

[0044] After mixing disubstituted phosphonate compounds and epoxy resin, an anhydride curing agent and a tertiary amine accelerator are added and cured to obtain a flame-retardant epoxy resin cured product.

[0045] In this invention, the mass of the disubstituted phosphonate compound is preferably 7% to 45% of the mass of the epoxy resin, more preferably 10% to 40%; the epoxy resin is preferably at least one of liquid epoxy resin E51, waterborne epoxy resin, two-component epoxy resin, and one-component epoxy resin; the anhydride curing agent is preferably at least one of methyltetrahydrophthalic anhydride and methylhexahydrophthalic anhydride; and the tertiary amine accelerator is preferably at least one of triethylamine, triethylhydroxyamine, dimethylaminomethylphenol, and tris(dimethylaminomethyl)phenol.

[0046] In this invention, the curing temperature is preferably 110℃~170℃, and the curing time is preferably 1~4h.

[0047] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0048] Example 1

[0049] Disubstituted phosphinic acid ester compounds having the structure shown in Formula I-1:

[0050]

[0051] The preparation method of the above-mentioned disubstituted phosphonate compound having the structure shown in Formula I-1 includes the following steps:

[0052] 300 mL of toluene, 100 g of 1-chloro-3-cyclopropane-2-propanol, 77 g of diethyl hypophosphite and 3.8 g of 15-Crown-5 were added to a reaction vessel. After mixing, nitrogen gas was introduced and the mixture was heated to reflux for a substitution reaction for 14 h. After the reaction was complete and cooled, water and ethyl acetate were added for extraction. The organic phases were combined, dried and concentrated by rotary evaporation to obtain 88 g of a pale yellow oily liquid, which is a disubstituted phosphonate compound with the structure shown in Formula I-1, with a yield of 75%.

[0053] The molar ratio of the diethyl hypophosphite to 1-chloro-3-cyclopropane-2-propanol is 1:1.6; the mass of the catalyst 15-Crown-5 is 5.0% of the mass of the diethyl hypophosphite.

[0054] Figure 1 The 1H NMR spectrum of the disubstituted phosphonate compound prepared in Example 1 of this invention is obtained from... Figure 1 It can be seen that 0.6–0.9 ppm and 1.39–1.59 ppm are the peaks of the methyl and ethyl groups of the ethyl group in the disubstituted phosphonate compound, respectively. Figure 2 The p-NMR spectrum of the disubstituted phosphonate compound prepared in Example 1 of this invention is shown below. Figure 2 As can be seen, the P-NMR spectrum shows a single main peak without splitting, indicating that there is a phosphorus atom in a single chemical environment within the molecule of the disubstituted phosphonate compound, which shows that Example 1 of the present invention successfully prepared a disubstituted phosphonate compound with the structure shown in Formula I-1.

[0055] Example 2

[0056] The preparation method of the disubstituted phosphonate compound having the structure shown in Formula I-1 is as follows: 300 mL of toluene, 100 g of 1-chloro-3-cyclopropane-2-propanol, 77 g of diethyl hypophosphite and 3.8 g of tetrabutylammonium bromide are added to a reaction vessel, mixed, and nitrogen gas is introduced. The mixture is heated to reflux for a substitution reaction for 14 h. After the reaction is complete, the mixture is cooled, extracted with water and ethyl acetate, the organic phases are combined, dried, concentrated and evaporated to dryness to obtain 90 g of yellow oily liquid, with a yield of 77%.

[0057] The molar ratio of the diethyl hypophosphite to 1-chloro-3-cyclopropane-2-propanol is 1:1.6; the mass of the catalyst tetrabutylammonium bromide is 5% of the mass of the diethyl hypophosphite.

[0058] Example 3

[0059] The preparation method of the disubstituted phosphonate compound having the structure shown in Formula I-1 is as follows: 300 mL of toluene, 100 g of 1-chloro-3-cyclopropane-2-propanol, 77 g of diethyl hypophosphite and 3.8 g of 18-crown-6 are added to a reaction vessel, nitrogen gas is introduced, and the mixture is heated to reflux for a substitution reaction for 14 h. After the reaction is complete and cooled, water and ethyl acetate are added for extraction. The organic phases are combined, dried, concentrated and evaporated to dryness to obtain 94 g of yellow oily liquid, with a yield of 80%.

[0060] The molar ratio of the diethyl hypophosphite to 1-chloro-3-cyclopropane-2-propanol is 1:1.6; the mass of the catalyst 18-crown-6 is 5% of the mass of the diethyl hypophosphite.

[0061] Example 4

[0062] The preparation method of the disubstituted phosphonate compound having the structure shown in Formula I-1 is as follows: 300 mL of 1,4-dioxane, 100 g of 1-chloro-3-cyclopropane-2-propanol, 77 g of diethyl hypophosphite and 3.8 g of 18-crown-6 are added to a reaction vessel, nitrogen gas is introduced, and the mixture is heated to reflux for a substitution reaction for 14 h. After the reaction is complete and cooled, water and ethyl acetate are added for extraction. The organic phases are combined, dried, concentrated and evaporated to dryness to obtain 71 g of pale yellow oily liquid, with a yield of 60%.

[0063] The molar ratio of the diethyl hypophosphite to 1-chloro-3-cyclopropane-2-propanol is 1:1.6; the mass of the catalyst 18-crown-6 is 5% of the mass of the diethyl hypophosphite.

[0064] Example 5

[0065] The preparation method of the disubstituted phosphonate compound having the structure shown in Formula I-1 is as follows: 300 mL of tetrahydrofuran, 100 g of 1-chloro-3-cyclopropane-2-propanol, 77 g of diethyl hypophosphite and 3.8 g of 18-crown-6 are added to a reaction vessel, nitrogen gas is introduced, and the mixture is heated to reflux for a substitution reaction for 14 h. After the reaction is complete and cooled, water and ethyl acetate are added for extraction. The organic phases are combined, dried, concentrated and evaporated to dryness to obtain 47 g of yellow oily liquid, with a yield of 41%.

[0066] The molar ratio of the diethyl hypophosphite to 1-chloro-3-cyclopropane-2-propanol is 1:1.6; the mass of the catalyst 18-crown-6 is 5% of the mass of the diethyl hypophosphite.

[0067] Example 6

[0068] Disubstituted phosphinic acid ester compounds having the structure shown in Formula I-2:

[0069]

[0070] The preparation method of the above-mentioned disubstituted phosphonate compound having the structure shown in Formula I-2 is as follows: 500 mL of toluene, 256 g of 1-chloro-3-cyclopropane-2-propanol, 217 g of diphenyl phosphite and 10.8 g of tetrabutylammonium bromide are added to a reaction vessel, nitrogen gas is introduced, and the mixture is heated to reflux for a substitution reaction for 20 h. After the reaction is complete and cooled, water and ethyl acetate are added for extraction. The organic phases are combined, dried, concentrated and evaporated to dryness to obtain 253 g of yellow solid, with a yield of 89%.

[0071] The molar ratio of the diphenyl hypophosphite to 1-chloro-3-cyclopropane-2-propanol is 1:1.6; the mass of the catalyst tetrabutylammonium bromide is 5% of the mass of the diphenyl hypophosphite.

[0072] Application Example 1

[0073] The preparation method of flame-retardant epoxy resin cured product includes the following steps:

[0074] Add 3g of the disubstituted hypophosphite compound prepared in Example 1 to 10g of epoxy resin (E51), mix well, add 9g of methyltetrahydrophthalic anhydride and 0.2g of triethylamine, mix and stir well, degas under vacuum, pour into a test piece mold with a thickness of 3mm, and finally place in an oven at a set temperature of 125℃ for curing for 1.5h to obtain a clear and transparent flame-retardant epoxy resin cured test piece.

[0075] The mass of the disubstituted phosphonate compound is 30% of the mass of the epoxy resin.

[0076] The flame-retardant epoxy resin cured specimen prepared in Application Example 1 was subjected to a vertical burning test according to UL94. The flame retardation time was within 5 to 8 seconds in both tests, reaching the V0 rating. Its softening point was about 85°C, and its hardness at room temperature was >80D.

[0077] Application Example 2

[0078] The preparation method of flame-retardant epoxy resin cured product includes the following steps:

[0079] Add 4g of the disubstituted hypophosphite compound prepared in Example 1 to 10g of epoxy resin (E51), mix well, add 9g of methylhexahydrophthalic anhydride and 0.1g of tris(dimethylaminomethyl)phenol, mix and stir well, degas under vacuum, pour into a test piece mold with a thickness of 3mm, and finally place in an oven at a set temperature of 145℃ for 2h to obtain a clear and transparent flame-retardant epoxy resin cured test piece;

[0080] The mass of the disubstituted phosphonate compound is 40% of the mass of the epoxy resin.

[0081] The flame-retardant epoxy resin cured specimen prepared in Application Example 2 was subjected to a vertical burning test according to UL94. The flame extension time was within 0 to 1 second in both tests, and it was basically extinguished immediately after being removed from the flame, reaching the V0 rating. Its softening point was about 100°C, and its hardness at room temperature was >85D.

[0082] Application Example 3

[0083] The preparation method of flame-retardant epoxy resin cured product includes the following steps:

[0084] Add 3.5g of the disubstituted hypophosphite compound prepared in Example 1 to 10g of epoxy resin (E51), mix well, add 9g of methylhexahydrophthalic anhydride and 0.1g of tris(dimethylaminomethyl)phenol, mix and stir well, degas under vacuum, pour into a test piece mold with a thickness of 2mm, and finally place in an oven at a set temperature of 145℃ for 2h to obtain a clear and transparent flame-retardant epoxy resin cured test piece;

[0085] The mass of the disubstituted phosphonate compound is 35% of the mass of the epoxy resin.

[0086] The flame-retardant epoxy resin cured specimen prepared in Application Example 3 was subjected to a vertical burning test according to UL94. The flame retardation time was within 4-5 seconds in both tests, reaching the V0 rating. Its softening point was approximately 105°C, and its hardness at room temperature was >85D.

[0087] Comparative Example 1

[0088] The preparation method of epoxy resin cured product includes the following steps:

[0089] Add 4g of dimethyl methyl phosphate (DMMP) to 10g of epoxy resin (E51), mix well, add 9g of methylhexahydrophthalic anhydride and 0.1g of tris(dimethylaminomethyl)phenol, mix and stir well, degas under vacuum, pour into a test piece mold with a thickness of 3mm, and finally place in an oven at a set temperature of 145℃ for curing for 2h to obtain an epoxy resin cured test piece with an uneven hazy surface.

[0090] The epoxy resin cured specimen prepared in Comparative Example 1 was subjected to a vertical burning test according to UL94. The specimen burned completely, with a softening point of approximately 65°C and a hardness of <85D at room temperature.

[0091] Comparative Example 2

[0092] The preparation method of epoxy resin cured product includes the following steps:

[0093] Add 4g of trichloroethyl phosphate (TCCP) to 10g of epoxy resin (E51) and mix well; add 9g of methylhexahydrophthalic anhydride and 0.1g of tris(dimethylaminomethyl)phenol, mix and stir well, degas under vacuum, pour into a test piece mold with a thickness of 3mm, and finally place in an oven at a set temperature of 145℃ for curing for 2h to obtain an epoxy resin cured test piece with an uneven hazy surface.

[0094] The epoxy resin cured specimen prepared in Comparative Example 2 was subjected to a vertical burning test according to UL94. The specimen burned completely, with a softening point of approximately 70°C and a hardness of <85D at room temperature.

[0095] In summary, the flame-retardant epoxy resin cured specimens prepared in Examples 1-3 exhibit significantly better flame-retardant effects than those in Comparative Examples 1-2. Furthermore, the flame-retardant epoxy resin cured specimens prepared in Examples 1-3 are all clear and transparent with superior physical properties. This demonstrates that using the disubstituted hypophosphite compound provided by this invention as a flame retardant can produce transparent and clear flame-retardant epoxy resin cured specimens with excellent flame-retardant properties, achieving transparency while reducing adverse effects on the physical properties of the flame-retardant foamed polyurethane material.

[0096] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A disubstituted phosphonate compound, characterized in that, It has the structure shown in Equation I: Formula I; In Formula I: R1 and R2 are independently selected from hydrogen, C1-C8 alkyl, cycloalkyl, aryl or alkenyl, R3 is hydrogen, R4 is cycloalkyl, and n is an integer from 1 to 3.

2. The method for preparing the disubstituted phosphonate compound according to claim 1, characterized in that, Includes the following steps: A phosphonate having the structure of formula II, a halogenated compound having the structure of formula III, an organic solvent and a catalyst are mixed and a substitution reaction is carried out in an inert atmosphere to obtain a disubstituted phosphonate. Formula II; Formula III; In Formula II, R1 and R2 are independently selected from hydrogen, C1-C8 alkyl, cycloalkyl, aryl or alkenyl, and M is a metal ion; In Formula III, R3 is hydrogen, R4 is cycloalkyl, X is a halogen atom, and n is an integer from 1 to 3.

3. The preparation method according to claim 2, characterized in that, The organic solvent is one or more of toluene, xylene, dioxane, acetonitrile, and tetrahydrofuran.

4. The preparation method according to claim 2, characterized in that, The catalyst is at least one of a phase transfer catalyst and an amphoteric compound.

5. The application of the disubstituted phosphonate compound of claim 1 or the disubstituted phosphonate compound prepared by the preparation method of any one of claims 2 to 4 in the preparation of flame-retardant epoxy resin cured products.

6. The application according to claim 5, characterized in that, The method for preparing the flame-retardant epoxy resin cured product includes the following steps: After mixing disubstituted phosphonate compounds and epoxy resin, an anhydride curing agent and a tertiary amine accelerator are added and cured to obtain a flame-retardant epoxy resin cured product.

7. The application according to claim 6, characterized in that, The mass of the disubstituted phosphonate compound is 7% to 45% of the mass of the epoxy resin.

8. The application according to claim 6, characterized in that, The anhydride curing agent is at least one of methyltetrahydrophthalic anhydride and methylhexahydrophthalic anhydride.

9. The application according to claim 6, characterized in that, The tertiary amine promoter is at least one of triethylamine, triethylhydroxyamine, dimethylaminomethylphenol, and tris(dimethylaminomethyl)phenol.

10. The application according to claim 6, characterized in that, The curing temperature is 110℃~170℃, and the curing time is 1~4h.

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