DOPO derivative flame retardant containing α-hydroxyl and having cyclic structure as bridge chain, preparation method for DOPO derivative flame retardant, and use of DOPO derivative flame retardant

Abstract

The present invention provides a DOPO derivative flame retardant containing α-hydroxyl and having a cyclic structure as a bridge chain. The DOPO derivative flame retardant has a structure represented by formula (I). In formula (I), R1 and R2 are independently selected from C1-C18 alkylene; R3 and R4 are independently selected from hydrogen, C1-C18 alkyl, C3-C18 heteroaryl, and C6-C24 aryl; and x and y are independently selected from 0, 1, 2, 3, and 4. The DOPO derivative flame retardant has a simple and convenient preparation method, high atom efficiency and good flame retardance, and can retain excellent physical properties of a polymer material.

Description

A DOPO derivative flame retardant containing α-hydroxyl and having a cyclic structure as a bridge chain, and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of flame retardant preparation, and relates to a DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain, and a preparation method and application thereof. Background Art

[0002] With the rapid rise of polymer materials science, polymers have become widely used in human production and daily life. Since most polymers are flammable, fires caused by their ignition are increasing, and therefore the flame retardant properties of polymers have garnered widespread attention. Polymers themselves cannot meet the requirements of flame retardant regulations, and flame retardants are often added to achieve this. Recently, due to environmental protection needs, halogen-free flame retardants, such as phosphorus-based flame retardants, have seen significant development. In particular, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives have attracted attention due to their high flame retardant efficiency, low toxicity, and minimal impact on polymer performance.

[0003] Currently reported DOPO derivatives can be structurally divided into reactive and additive types: reactive derivatives have reactive groups such as carboxyl and hydroxyl groups on the phosphorus atom substituents, while additive derivatives are structurally inert and lack reactive functional groups.

[0004] Chinese patent publication CN100366627C reports on a DiDOPO with a hydroxyalkyl-substituted vinylene bridge structure. The hydroxyl group is far away from the phosphorus atom and has high reactivity, allowing it to undergo ester exchange reactions with carboxylic acids or esters. Chinese patent publication CN104086593B reports on the preparation of DiDOPO with a phenylene bridge structure by the addition of semi-aryl ketones and DOPO. The reaction process first involves the reaction of DOPO and the ketone group to form an α-hydroxyphosphine compound, which is then dehydrated under heat to form a vinylphosphonate, thereby introducing a second DOPO. Chinese patent publication CN106366128B uses the hydroxyl group of the α-hydroxyphosphine compound to introduce an allyloxy group. The hydroxyl group is highly reactive, and the patent specifically points out that phosphophananthenanthrene compounds containing hydroxyl groups are not suitable for low dielectric systems (dielectric loss less than 0.010). From this patent, it can be seen that introducing a hydroxyl group is not an option unless it is for the purpose of reaction.

[0005] Japanese patent publications JPH11-106619, JP2001270993, and Chinese patent publication CN102428091B report on DiDOPO with an inert bridge structure that lacks reactive functional groups. PCT patent WO2013020696A2 and Chinese patent publication CN109851639B report on DOPO derivatives containing P-N bonds. These derivatives can be used as additive flame retardants.

[0006] Existing reactive DOPO derivatives need to be further reacted with polymers or monomers before use, which is not conducive to the flame retardant modification of existing polymer materials. Moreover, due to the different reactivity between polymers or monomers, the performance is difficult to control and the cost is high. Additive DOPO derivatives have a greater impact on the physical properties of flame retardant polymer materials. For example, US Patent US8536256B2 mentions that the introduction of DiDOPO with a vinylidene bridge structure can increase the T g Reducing the temperature from 163-172°C to 126-131°C makes it difficult to meet the requirements of lead-free welding, limiting its application areas; Chinese patent CN106366128B mentions that the presence of hydroxyl groups is detrimental to the dielectric loss factor (Df) of flame-retardant polymer materials, making them difficult to use in low dielectric loss copper-clad laminates.

[0007] Based on the above analysis, existing reactive and additive DOPO derivatives still struggle to meet the requirements for thermal and chemical stability, as well as minimal impact on the physical properties of flame-retardant polymers. Furthermore, the preparation process for existing DOPO derivatives is complex and costly. There is a continued desire to develop a flame retardant with a simple preparation process, high atom efficiency, excellent flame retardancy, minimal impact on the physical properties of flame-retardant polymers, and even the ability to improve the electrical properties of the flame-retardant system.

[0008] Summary of the Invention

[0009] The present invention aims to address the shortcomings of the prior art by providing a DOPO derivative flame retardant containing an α-hydroxyl group and a cyclic structure as a bridge, a preparation process, and flame-retardant applications in polymer materials. The preparation method for the DOPO derivative flame retardant containing an α-hydroxyl group and a cyclic structure as a bridge is simple, exhibits high atom efficiency, exhibits excellent flame retardancy, and retains the excellent physical properties of the polymer material.

[0010] The first object of the present invention is achieved through the following technical solutions:

[0011] A DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain has a structure shown in the following formula (I):

[0012] Wherein, R1 and R2 are independently selected from C1 to C 18The alkylene group, any hydrogen atom on the alkylene group can be independently replaced by a C1 to C8 alkyl group, a C6 to C 18 aromatic substitution;

[0013] R3 and R4 are independently selected from hydrogen, C1-C 18 Alkyl, C3~C 18 Heteroaryl, C6~C 24 Any hydrogen atom on the aromatic ring of the aromatic or heteroaryl group can be independently replaced by any C1 to C 18 Alkyl substitution;

[0014] x and y are independently selected from 0, 1, 2, 3, and 4.

[0015] Preferably, R1 and R2 are independently selected from C1-C8 alkylene groups, and any hydrogen atom on the alkylene group may be independently substituted with a C1-C8 alkyl group. Further preferably, R1 and R2 are independently selected from methylene, ethylene, propylene, butylene, methyl-substituted methylene, dimethyl-substituted methylene, ethyl-substituted methylene, methyl-substituted ethylene, dimethyl-substituted ethylene, methyl-substituted propylene, dimethyl-substituted propylene, or propyl-substituted propylene.

[0016] Preferably, R3 and R4 are independently selected from hydrogen, C1-C8 alkyl, C3-C 18 Heteroaryl, C6~C 18 Further preferably, R3 and R4 are independently hydrogen, methyl, or ethyl. Alternatively, R3 and R4 are hydrogen.

[0017] Preferably, x=y=0.

[0018] The second object of the present invention is achieved through the following technical solutions:

[0019] A method for preparing a DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain comprises the following steps:

[0020] reacting a compound having a structure of formula (II) with an aliphatic cyclic diketone compound having a structure of formula (III); and, after the reaction is completed, purifying to obtain a DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain;

[0021] Wherein, R3 and R4 have the same meaning as R3 and R4 in formula (I), that is, they are independently selected from hydrogen, C1-C 18 Alkyl, C3~C 18 Heteroaryl, C6~C 24Any hydrogen atom on the aromatic ring of the aromatic or heteroaryl group can be independently replaced by any C1 to C 18 Alkyl substitution;

[0022] x and y have the same meanings as those defined in formula (I), i.e., they are independently selected from 0, 1, 2, 3, 4;

[0023] Wherein, R1 and R2 have the same meaning as R1 and R2 in formula (I), that is, they are independently selected from C1 to C 18 The alkylene group, any hydrogen atom on the alkylene group can be independently replaced by a C1 to C8 alkyl group, a C6 to C 18 of aromatic substitution.

[0024] Preferably, the compound having the structure of formula (II) is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. That is, in formula (II), x and y are 0.

[0025] Optionally, the aliphatic cyclic diketone compound with the structure of formula (III) includes but is not limited to one or more of cyclohexanedione, cyclobutanedione, cyclopentanedione, cycloheptanedione, cyclooctanedione, methylcyclohexanedione, dimethylcyclohexanedione, propylcyclohexanedione, tetramethylcyclobutanedione, methylcyclopentanedione, dimethylcyclopentanedione, and ethylcyclopentanedione. Preferably, the aliphatic cyclic diketone compound with the structure of formula (III) is one or more of cyclohexanedione, methylcyclohexanedione, dimethylcyclohexanedione, cyclopentanedione, and cycloheptanedione. Further preferably, the aliphatic cyclic diketone compound with the structure of formula (III) is one or more of 1,4-cyclohexanedione, 1,3-cyclohexanedione, 5,5-dimethyl-1,3-cyclohexanedione, and cyclopentanedione. Most preferably, it is 1,4-cyclohexanedione.

[0026] The present invention controls the molar ratio of the aliphatic cyclic diketone compound having the structure of formula (III) to the compound having the structure of formula (II), the reaction time, the purification method, and the like, so that the product is a pure DOPO derivative having the structure shown in formula (I).

[0027] Preferably, when the compound having the structure of formula (II) and the aliphatic cyclic diketone compound having the structure of formula (III) are reacted, the molar ratio of the compound having the structure of formula (II) to the aliphatic cyclic diketone compound having the structure of formula (III) is 2 to 20:1. More preferably, it is 2 to 10:1, and even more preferably, it is 2.5 to 7:1. If the molar ratio of the two compounds is too large, the compound having the structure of formula (II) will be excessive, resulting in low raw material utilization; if the molar ratio is too small, the product yield will decrease.

[0028] Preferably, the reaction time of the compound having the structure of formula (II) and the aliphatic cyclic diketone compound having the structure of formula (III) is 0.01 to 25 hours. More preferably, it is 0.1 to 20 hours, and even more preferably, it is 0.5 to 10 hours. If the reaction time is too short, the reaction is incomplete and the product yield is low; while if the reaction time is too long, the production efficiency is low and the production cost is increased.

[0029] Preferably, when reacting the compound having the structure of formula (II) and the aliphatic cyclic diketone compound having the structure of formula (III), the reaction temperature is room temperature to 250°C. More preferably, it is 50 to 220°C, and even more preferably, it is 80 to 200°C. If the reaction temperature is too high, the compound having the structure of formula (II) tends to thermally degrade; while if the reaction temperature is too low, the reaction rate is too slow, resulting in poor economic efficiency.

[0030] When the compound having the structure of formula (II) and the aliphatic cyclic diketone compound having the structure of formula (III) react, the reaction can be carried out in the absence of a solvent or in an inert solvent. Solvent-free means that no other solvent is added to the reactants, but the excess reactants are used as solvents. For example, when a large amount of the compound having the structure of formula (II) is added, in addition to a portion of it reacting with the aliphatic cyclic diketone compound having the structure of formula (III), the excess compound having the structure of formula (II) can be used as a solvent. The inert solvent can be listed as one or more conventional solvents including aromatic hydrocarbons, alkanes, alcohols, esters, etc.; optionally, the inert solvent is selected from at least one of toluene, xylene, and trimethylbenzene.

[0031] When the compound having the structure of formula (II) and the aliphatic cyclic diketone compound having the structure of formula (III) react, the reaction can be carried out under normal pressure, positive pressure or negative pressure.

[0032] When the compound with formula (II) structure and the aliphatic cyclic diketone compound with formula (III) structure react, it is unexpected that the reaction can be carried out without an external catalyst. The phosphine hydrogenation reaction of the general pH bond addition to the ketone group, i.e., the Pudovik reaction, requires an alkaline or acidic catalyst. However, when the aliphatic cyclic diketone compound with formula (III) structure reacts with the compound with formula (II), an external catalyst is unnecessary, which greatly reduces the cost of removing the catalyst and greatly improves economic efficiency. Of course, the reaction can also be carried out in the presence of a catalyst, and the catalyst can be any catalyst applied to the Pudovik reaction, such as one or more of titanate, organic amine, inorganic base, fatty alcohol aluminum, etc. Preferably, the reaction is carried out without an external catalyst.

[0033] After the reaction is completed, it can be purified by conventional methods such as solvent washing and recrystallization to remove unreacted products, intermediates and impurities to obtain a high-purity DOPO derivative having a structure as shown in formula (I). Optionally, after the reaction is completed, the product is subjected to solvent washing. Optionally, the solvent used in the solvent washing is a good solvent for the compound having the structure of formula (II) and / or the aliphatic cyclic diketone compound having the structure of formula (III). Optionally, the solvent used in the solvent washing is selected from at least one of alcohols, esters, ethers, alkanes, and aromatic hydrocarbons. Optionally, the solvent used in the solvent washing is selected from at least one of ethanol, isopropanol, toluene, and p-xylene.

[0034] Specifically, the preparation method of the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain comprises the following steps:

[0035] The compound having the structure of formula (II) is added to an inert solvent for dissolution, or the compound having the structure of formula (II) is heated and melted, and then an aliphatic cyclic diketone compound having the structure of formula (III) is added to react. After the reaction is completed, the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain is purified.

[0036] The third object of the present invention is achieved through the following technical solutions:

[0037] A flame retardant polymer material comprises the DOPO derivative flame retardant containing α-hydroxyl and having a cyclic structure as a bridge chain and the polymer material.

[0038] Preferably, the flame retardant polymer material comprises 1 to 50 wt% of the DOPO derivative flame retardant containing α-hydroxyl groups and having a cyclic structure as a bridge chain and 50 to 99 wt% of a polymer material.

[0039] Optionally, the mass fraction of the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain in the flame retardant polymer material is 1 to 50 wt%, further 1 to 45 wt%, further 1 to 40 wt%, further 2 to 50 wt%, further 2 to 45 wt%, further 2 to 40 wt%, further 3 to 50 wt%, further 3 to 45 wt%, further 3 to 40 wt%, further 5 to 35 wt%, further 3 to 30 wt%, further 5 to 30 wt%, further 5 to 25 wt%, further 8 to 30 wt%, further 10 to 30 wt%, further 12 to 30 wt%. All values ​​not listed within the above numerical ranges are applicable.

[0040] Specifically, the amount of the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain depends on the structure of the polymer material and the flame retardant effect to be achieved.

[0041] The polymer material is selected from one or more of thermoplastic resins and thermosetting resins.

[0042] The thermoplastic resin is at least one selected from polybutadiene, polyamide, polyester, polyphenylene ether, acrylonitrile-butadiene-styrene copolymer, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyimide, polyphenylene sulfide, and polyetheretherketone.

[0043] The thermosetting resin is selected from at least one of vinyl polyphenylene ether resin, epoxy resin, cyanate resin, BT resin, bismaleimide resin, phenolic resin, polyurethane resin, thermosetting polyimide, unsaturated polyester resin, vinyl resin, benzoxazine resin, arylacetylene resin, and furan resin. Preferably, the thermosetting resin is at least one of vinyl polyphenylene ether resin, epoxy resin, cyanate resin, BT resin, bismaleimide resin, and thermosetting polyimide. More preferably, the thermosetting resin is at least one of vinyl polyphenylene ether resin and epoxy resin.

[0044] The vinyl polyphenylene ether resin refers to a polyphenylene ether resin having an unsaturated double bond in the end-capping group. Optionally, the vinyl polyphenylene ether resin is selected from at least one of Mitsubishi Gas's OPE-2st and SABIC's SA-9000.

[0045] Preferably, the epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, dicyclopentadiene epoxy resin, biphenyl epoxy resin or naphthol epoxy resin.

[0046] Optionally, the mass fraction of the polymer material in the flame retardant polymer material is 50-99wt%, further 50-90wt%, further 50-80wt%, further 50-70wt%, further 50-60wt%, further 55-99wt%, further 55-90wt%, further 55-80wt%, further 55-70wt%, further 60-90wt%, further 65-85wt%. All values ​​not listed within the above numerical ranges are applicable.

[0047] Optionally, the flame retardant polymer material further includes functional additives, which can be selected from at least one of a reinforcing agent, an anti-dripping agent, a stabilizer, a pigment, a dye, a carbonizing catalyst, a dispersant, a nucleating agent, an inorganic filler, an organic filler, and an antioxidant.

[0048] The reinforcing agent may be exemplified by glass fiber.

[0049] The anti-dripping agent may be a polytetrafluoroethylene-based anti-dripping agent.

[0050] Optionally, the inorganic filler is selected from at least one of silicon dioxide, mica, calcium carbonate, aluminum oxide, aluminum nitride, talc, calcium oxide, calcium silicate, glass fiber powder, and silica. Preferably, the inorganic filler is silicon dioxide. Further preferably, the median particle size D of the silicon dioxide is 50 1~15μm.

[0051] Optionally, the organic filler is selected from at least one of polytetrafluoroethylene powder, polyphenylene sulfide powder, and polyethersulfone powder.

[0052] Optionally, the mass fraction of the functional additive in the flame retardant polymer material is 5-40 wt %, further 5-35 wt %, further 5-30 wt %, further 5-25 wt %, further 5-20 wt %, further 10-35 wt %, further 15-35 wt %, further 20-35 wt %. All values ​​not listed in the above numerical ranges are applicable.

[0053] Optionally, the flame retardant polymer material further includes a flame retardant Q, and the flame retardant Q is selected from at least one of a phosphorus-based flame retardant, a nitrogen-based flame retardant, and a boron-based flame retardant.

[0054] Preferably, the phosphorus-based flame retardant is selected from at least one of bisphosphate flame retardants, phosphazene flame retardants, dialkyl phosphinates, DOPO derivatives, and phosphine oxide compounds.

[0055] Furthermore, the bisphosphate flame retardant is selected from at least one of bisphenol A bisdiphenyl phosphate, resorcinol bisdiphenyl phosphate, and 1,3-phenylene (2,6-xylyl) tetraphosphate.

[0056] Furthermore, the phosphazene flame retardant is selected from at least one of hexaphenoxycyclotriphosphazene, cyanophenoxyphosphazene (such as FP-300 of Fushimi Pharmaceutical Co., Ltd. of Japan), allyl cyclophosphazene (such as SPV-100 of Otsuka of Japan), and cyclic biphenyloxyphosphazene (such as BP-PZ of Otsuka of Japan).

[0057] Furthermore, the dialkyl phosphinate is at least one selected from the group consisting of aluminum diethylphosphinate, aluminum diisobutylphosphinate, aluminum dipropylphosphinate, and zinc diethylphosphinate.

[0058] Furthermore, the DOPO derivative is selected from at least one of 6H-dibenzo[c,e][1,2]oxophosphoglycerate, 6,6'-(1,2-ethanediyl)bis-6,6'-dioxide, 6H-dibenzo[c,e][1,2]oxane-6,6'-(1,4-ethanediyl)bis-,6,6'-dioxide, and 6H-dibenzo[c,e][1,2]oxane-6,6'-(1,4-phenylethanediyl)bis-6,6'-dioxide (such as HTP-6123 of Guizhou Yuanyi Group).

[0059] Furthermore, the phosphine oxide compound is p-xylylbisdiphenylphosphine oxide (such as PQ-60 from Jinyi Chemical).

[0060] Preferably, the nitrogen-based flame retardant is at least one selected from melamine cyanurate, melamine polyphosphate, and ammonium polyphosphate;

[0061] Preferably, the boron-based flame retardant is selected from zinc borate.

[0062] Optionally, the mass fraction of the flame retardant Q in the flame retardant polymer material is 0.5-20 wt %, further 0.5-15 wt %, further 0.5-10 wt %, further 1-20 wt %, further 1-18 wt %, further 1-13 wt %, further 2-19 wt %, further 2-14 wt %, further 3-16 wt %, further 4-17 wt %, further 5-12 wt %. All values ​​not listed within the above numerical ranges are applicable.

[0063] Preferably, the flame-retardant polymer material includes the DOPO derivative flame retardant containing an α-hydroxyl group and a cyclic structure as a bridge chain and a phosphorus-based flame retardant, and the mass ratio of the DOPO derivative flame retardant containing an α-hydroxyl group and a cyclic structure as a bridge chain to the phosphorus-based flame retardant is 1 to 20:1. The use of the DOPO derivative flame retardant containing an α-hydroxyl group and a cyclic structure as a bridge chain and the phosphorus-based flame retardant of the present invention together helps to improve the flame retardant properties of the polymer material and simultaneously reduce the dielectric loss factor (Df) of the polymer material.

[0064] The fourth object of the present invention is achieved through the following technical solutions:

[0065] A low-dielectric flame-retardant resin composition comprises 2 to 150 parts by weight of a DOPO derivative flame retardant containing alpha-hydroxyl groups and having a cyclic structure as a bridge chain and 100 parts by weight of a vinyl polyphenylene ether resin.

[0066] The low-dielectric flame-retardant resin composition of the present invention further comprises a crosslinking agent and an initiator. Optionally, 1-200 parts by weight of the crosslinking agent and 0.1-15 parts by weight of the initiator are added to every 100 parts by weight of the vinyl polyphenylene ether resin.

[0067] Preferably, the dielectric loss factor of the low-dielectric flame-retardant resin composition is lower than that of a composition comprising the vinyl polyphenylene ether resin but excluding the DOPO derivative flame retardant containing an α-hydroxy group and having a cyclic structure as a bridge chain.

[0068] Preferably, the dielectric loss factor of the low-dielectric flame retardant resin composition is lower than that of a composition comprising the vinyl polyphenylene ether resin, a crosslinking agent and an initiator but excluding the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain.

[0069] It is known that compounds containing hydroxyl groups are detrimental to the dielectric loss factor, that is, the introduction of hydroxyl groups will increase the dielectric loss factor. However, surprisingly, although the DOPO derivative flame retardant containing α-hydroxyl groups and having a cyclic structure as a bridge chain also contains hydroxyl groups, their introduction can significantly reduce the dielectric loss factor of polymer materials such as vinyl polyphenylene ether resin systems. This is completely contrary to traditional knowledge and is unexpected. This unexpected result may be because the α-hydroxyl group of the DOPO derivative flame retardant containing α-hydroxyl groups and having a cyclic structure as a bridge chain can form intramolecular hydrogen bonds with adjacent P=O groups. The presence of the cyclic bridge chain restricts the conformation of the α-hydroxyl group, making the strength of this intramolecular hydrogen bond stronger than the hydrogen bond formed by the hydroxyl group on the non-cyclic structure, thereby significantly reducing the effect of this hydroxyl group on the dielectric loss. At the same time, this intramolecular hydrogen bond also significantly reduces the chemical activity of this hydroxyl group. As a result, the DOPO derivative flame retardant containing an α-hydroxyl group and a cyclic structure as a bridge chain, despite containing a hydroxyl group, exhibits an inert nature, making it different from traditional hydroxyl-containing reactive flame retardants and a new type. In addition, the presence of hydroxyl groups also increases the melting point of the DOPO derivative containing an α-hydroxyl group and a cyclic structure as a bridge chain. The increase in melting point helps reduce the expansion coefficient of the copper clad laminate. The presence of hydroxyl groups also increases the bonding strength with the metal, making the copper clad laminate less likely to peel.

[0070] In the low-dielectric flame-retardant resin composition, 2 to 150 parts by weight of a DOPO derivative flame retardant containing an α-hydroxyl group and a cyclic structure as a bridge is added per 100 parts by weight of vinyl polyphenylene ether resin. Too little of the DOPO derivative flame retardant containing an α-hydroxyl group and a cyclic structure as a bridge may result in insufficient flame retardancy; too much may adversely affect the mechanical properties of the flame-retardant resin composition. Alternatively, the amount of the DOPO derivative flame retardant containing an α-hydroxyl group and a cyclic structure as a bridge is within the range of 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, or 150 parts by weight per 100 parts by weight of vinyl polyphenylene ether resin, or within the range of any two of these values.

[0071] Preferably, in the formula (I) of the DOPO derivative flame retardant containing an α-hydroxy group and having a cyclic structure as a bridge chain, R1 and R2 are ethylene groups, R3=R4=H, and x=y=0.

[0072] The vinyl polyphenylene ether resin refers to a polyphenylene ether resin having an unsaturated double bond in the end-capping group. Optionally, the vinyl polyphenylene ether resin is selected from at least one of Mitsubishi Gas's OPE-2st and SABIC's SA-9000.

[0073] In the described low dielectric constant flame retardant resin composition, comprise crosslinking agent.Alternatively, the consumption of crosslinking agent is the usage amount of 1-200 weight parts of per 100 weight parts of vinyl polyphenylene ether resin.Alternatively, crosslinking agent includes but is not limited to olefin compound, alternatively, crosslinking agent is selected from polybutadiene, polyisoprene, triallyl isocyanurate, triallyl cyanurate, styrene-butadiene-styrene polymer, styrene-butadiene polymer, bismaleimide.Preferably, crosslinking agent is selected from triallyl isocyanurate.

[0074] The low-dielectric flame-retardant resin composition includes an initiator. Optionally, the amount of the initiator is 0.1-15 parts by weight per 100 parts by weight of the vinyl polyphenylene ether resin. Optionally, one or more initiators can be selectively added to promote the curing rate of the resin. Preferably, the initiator comprises a peroxide that can generate free radicals, including but not limited to dicumyl peroxide, di-tert-butyl peroxide dicumyl benzene, tert-butyl perbenzoate, benzoyl peroxide, dibenzoyl peroxide and tert-butyl peroxyisopropyl carbonate. Most preferably, the initiator is dicumyl peroxide.

[0075] Optionally, the low-dielectric flame retardant resin composition includes a polymer resin and / or a functional additive.

[0076] The polymer resin is selected from one or more of thermoplastic polymer resins and thermosetting polymer resins.

[0077] The thermoplastic polymer resin is selected from at least one of polybutadiene, polyamide, polyester, polyphenylene ether, acrylonitrile-butadiene-styrene copolymer, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyimide, polyphenylene sulfide, and polyetheretherketone.

[0078] The thermosetting polymer resin is selected from at least one of epoxy resin, cyanate resin, BT resin, bismaleimide resin, phenolic resin, polyurethane resin, thermosetting polyimide, unsaturated polyester resin, vinyl resin, benzoxazine resin, arylacetylene resin, and furan resin. Preferably, the polymer resin is at least one of epoxy resin, cyanate resin, BT resin, bismaleimide resin, and thermosetting polyimide.

[0079] Optionally, in the low-dielectric flame-retardant resin composition, 1 to 300 parts by weight of the polymer resin are added per 100 parts by weight of the vinyl polyphenylene ether resin. The amount of the polymer resin can be any one of 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 150, 180, 200, 230, 260, and 300 parts by weight, or a range between any two of these values.

[0080] The functional additive can be selected from at least one of a reinforcing agent, an anti-dripping agent, a stabilizer, a pigment, a dye, a carbon-forming catalyst, a dispersant, a nucleating agent, an inorganic filler, an organic filler, and an antioxidant.

[0081] The reinforcing agent may be exemplified by glass fiber.

[0082] The anti-dripping agent may be a polytetrafluoroethylene-based anti-dripping agent.

[0083] Preferably, the inorganic filler is selected from at least one of silicon dioxide, mica, calcium carbonate, aluminum oxide, aluminum nitride, talc, calcium oxide, calcium silicate, glass fiber powder, and silica. Preferably, the inorganic filler is silicon dioxide. Further preferably, the median particle size D of the silicon dioxide is 50 1~15μm.

[0084] Preferably, the organic filler is selected from at least one of polytetrafluoroethylene powder, polyphenylene sulfide powder and polyethersulfone powder.

[0085] Optionally, in the low-dielectric flame-retardant resin composition, 1 to 500 parts by weight of the functional additive are added per 100 parts by weight of vinyl polyphenylene ether resin. The amount of the functional additive can be any one of 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 150, 180, 200, 230, 260, 300, 350, 400, 450, or 500 parts by weight, or a range between any two of the values.

[0086] Optionally, the low-dielectric flame-retardant resin composition further comprises a flame retardant Q, and the flame retardant Q is selected from at least one of a phosphorus-based flame retardant, a nitrogen-based flame retardant, and a boron-based flame retardant.

[0087] Preferably, the phosphorus-based flame retardant is selected from at least one of bisphosphate flame retardants, phosphazene flame retardants, dialkyl phosphinates, DOPO derivatives, and phosphine oxide compounds.

[0088] Furthermore, the bisphosphate flame retardant is selected from at least one of bisphenol A bisdiphenyl phosphate, resorcinol bisdiphenyl phosphate, and 1,3-phenylene (2,6-xylyl) tetraphosphate.

[0089] Furthermore, the phosphazene flame retardant is selected from at least one of hexaphenoxycyclotriphosphazene, cyanophenoxyphosphazene (such as FP-300 of Fushimi Pharmaceutical Co., Ltd. of Japan), allyl cyclophosphazene (such as SPV-100 of Otsuka of Japan), and cyclic biphenyloxyphosphazene (such as BP-PZ of Otsuka of Japan).

[0090] Furthermore, the dialkyl phosphinate is at least one selected from the group consisting of aluminum diethylphosphinate, aluminum diisobutylphosphinate, aluminum dipropylphosphinate, and zinc diethylphosphinate.

[0091] Furthermore, the DOPO derivative is selected from at least one of 6H-dibenzo[c,e][1,2]oxophosphoglycerate, 6,6'-(1,2-ethanediyl)bis-6,6'-dioxide, 6H-dibenzo[c,e][1,2]oxane-6,6'-(1,4-ethanediyl)bis-6,6'-dioxide, and 6H-dibenzo[c,e][1,2]oxane-6,6'-(1,4-phenylethanediyl)bis-6,6'-dioxide.

[0092] Furthermore, the phosphine oxide compound is p-xylylbisdiphenylphosphine oxide (such as PQ-60 from Jinyi Chemical).

[0093] Preferably, the nitrogen-based flame retardant is at least one selected from melamine cyanurate, melamine polyphosphate, and ammonium polyphosphate;

[0094] Preferably, the boron-based flame retardant is selected from zinc borate.

[0095] Optionally, in the low-dielectric flame-retardant resin composition, 1 to 30 parts by weight of the flame retardant Q are added per 100 parts by weight of vinyl polyphenylene ether resin. The amount of the flame retardant Q can be any one of 1, 2, 3, 4, 5, 8, 10, 12, 15, 18, 20, 25, and 30 parts by weight, or a range between any two of these values.

[0096] Preferably, the low-dielectric flame-retardant resin composition comprises the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain and a phosphorus-based flame retardant, and the mass ratio of the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain to the phosphorus-based flame retardant is 1 to 20:1. The use of the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain and the phosphorus-based flame retardant of the present invention together helps to improve the flame retardant properties of the polymer material and reduce the dielectric loss factor (Df) of the low-dielectric flame-retardant resin composition.

[0097] The fifth object of the present invention is achieved through the following technical solutions:

[0098] A flame retardant epoxy resin comprises the DOPO derivative flame retardant containing α-hydroxyl groups and having a cyclic structure as a bridge chain, an epoxy compound and a curing agent.

[0099] Preferably, in the flame retardant epoxy resin, the mass proportion of the DOPO derivative flame retardant containing α-hydroxyl and having a cyclic structure as a bridge chain is 1 to 30 wt%, and the mass proportion of the epoxy compound and the curing agent is 70 to 99 wt%.

[0100] The weight percentage of the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain is any one of 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, and 30wt%, or a range between any two of them. When the weight percentage is less than 1wt%, the flame retardant performance decreases; when it is greater than 30wt%, the physical properties of the flame retardant epoxy resin decrease.

[0101] The epoxy compound in the flame-retardant epoxy resin contains at least two epoxy groups and is selected from at least one of bisphenol or polyphenol glycidyl ethers (such as bisphenol A epoxy resins E44 and E51), aliphatic chain glycidyl ethers (such as polyethylene glycol diglycidyl ether), aliphatic ring glycidyl ethers (1,3- or 1,4-cyclohexanedimethanol diglycidyl ether), glycidyl esters (such as tetrahydrophthalic acid diglycidyl ester and phthalic acid diglycidyl ester), and heterocyclic epoxy compounds (such as triglycidyl isocyanurate). Preferably, the epoxy compound is selected from commercially available bisphenol glycidyl ethers (such as Baling Petrochemical's E44 and E51).

[0102] Preferably, the curing agent is an amine curing agent, selected from at least one of trimethylenediamine, tetramethylenediamine, hexamethylenediamine, p-phenylenediamine, m-phenylenediamine, p-phenylenediamine, m-phenylenediamine, 4,4-diaminodiphenylmethane, 4,4-diaminodiphenylsulfone, 4,4-diaminodiphenyl ether, dicyandiamide, and 1,4-cyclohexanediamine. Preferably, the curing agent is selected from at least one of trimethylenediamine, tetramethylenediamine, hexamethylenediamine, 4,4-diaminodiphenylmethane, and 4,4-diaminodiphenylsulfone.

[0103] The preparation method of the flame retardant epoxy resin specifically comprises the following steps:

[0104] The epoxy compound, curing agent, and a DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain are melt-stirred at room temperature to 120°C for 0.1 to 4 hours, cured at 70 to 90°C, 110 to 130°C, and 160 to 180°C for 0.5 to 8 hours, respectively, and naturally cooled to obtain a flame-retardant epoxy resin. Preferably, the melt-stirring time is 0.5 to 2 hours, and the curing time at different temperatures is 0.5 to 4 hours.

[0105] The DOPO derivative flame retardant having a structure of formula (I) and containing an α-hydroxyl group and a cyclic structure as a bridge chain (hereinafter referred to as the "flame retardant having a structure of formula (I)") described in the present invention, compared with DOPO derivatives that do not contain hydroxyl groups, such as 6H-dibenzo[c,e][1,2]oxyphosphoric acid glyceride and 6,6'-(1,2-ethanediyl)bis-6,6'-dioxide prepared from DOPO and ethylene glycol, the flame retardant having a structure of formula (I) can better improve the compatibility of the flame retardant with the epoxy resin through the hydroxyl group, and unexpectedly better maintains the glass transition temperature of the flame-retardant epoxy resin, reducing the loss of physical properties of the epoxy resin caused by the introduction of the DOPO derivative that does not contain hydroxyl groups. Equally surprising is that compared to DOPO derivatives containing α-hydroxyl groups but lacking a cyclic bridge structure, such as the reaction products of DOPO and formaldehyde or acetone, flame retardants with Formula (I) exhibit significantly improved thermal and chemical stability, allowing them to be cured at high temperatures in epoxy resins. Compared to DOPO derivatives with hydroxyl groups not in the α position, such as DiDOPO with a hydroxyalkyl-substituted vinylidene bridge structure, flame retardants with Formula (I) possess intramolecular hydrogen bonding, resulting in stronger inertness and improved electrical properties. Furthermore, the cyclic aliphatic bridge structure imparts molecular rigidity, resulting in improved physical properties for flame-retardant epoxy resins.

[0106] Compared with the prior art, the present invention has the following beneficial effects:

[0107] 1. The preparation method of the DOPO derivative flame retardant having the structure of formula (I) and containing an α-hydroxyl group and a cyclic structure as a bridge chain is simple, does not require a catalyst, and essentially all reactants are converted into products, with high atomic efficiency and good economic benefits;

[0108] 2. By controlling the reaction time, reaction molar ratio, reaction temperature and other process conditions, as well as through subsequent purification steps, a DOPO derivative flame retardant having a structure of formula (I) and containing an α-hydroxyl group and having a cyclic structure as a bridge chain can be effectively obtained;

[0109] 3. The DOPO derivative flame retardant of the present invention, which contains an α-hydroxyl group and a cyclic structure as a bridge chain and has a structure of formula (I), exhibits chemical inertness and high thermal and chemical stability, which is completely different from traditional DOPO additive and reactive derivatives. This property enables it to provide effective flame retardancy while also helping to maintain or even improve the physical properties of polymer materials.

[0110] 4. In particular, the DOPO derivative flame retardant having a structure of formula (I) and containing an α-hydroxyl group and having a cyclic structure as a bridge chain can significantly reduce the dielectric loss factor of polymer materials despite containing hydroxyl groups, which is completely unexpected;

[0111] 5. The DOPO derivative flame retardant having a structure of formula (I) and a cyclic structure as a bridge chain is used together with a phosphorus-based flame retardant to help improve the flame retardant properties of the material and reduce the dielectric loss factor (Df) of the material;

[0112] 6. Although the DOPO derivative flame retardant with a structure of formula (I) containing α-hydroxyl groups and a cyclic structure as a bridge chain has a lower phosphorus content, its flame retardant efficiency for polymers is higher than that of the flame retardant with a corresponding structure without hydroxyl groups, and the usage amount is smaller. BRIEF DESCRIPTION OF THE DRAWINGS

[0113] FIG1 is a nuclear magnetic phosphorus spectrum of Example 1 of the present invention;

[0114] FIG2 is a hydrogen NMR spectrum of Example 1 of the present invention;

[0115] FIG3 is an infrared spectrum of Example 1 of the present invention. DETAILED DESCRIPTION

[0116] Below by specific embodiment and accompanying drawing, technical scheme of the present invention is further described explanation, it should be understood that specific embodiment described herein is only for helping to understand the present invention, is not used for specific limitation of the present invention.And accompanying drawing used herein, is only for better illustrating the disclosure of the present invention, does not have limiting effect on protection scope.If no special instructions, the raw materials adopted in the embodiment of the present invention are all raw materials commonly used in this area, and the method adopted in the embodiment is all conventional method in this area.

[0117] The chemical reagents used in the following examples and comparative examples are as follows:

[0118] (A) E44 bisphenol A epoxy resin, purchased from Baling Petrochemical, epoxy value 0.44.

[0119] (B) 4,4-Diaminodiphenylmethane (DDM), a curing agent, was purchased from Aladdin Reagents.

[0120] (C) Vinyl polyphenylene ether resin, manufactured by Sabic Corporation, trade name SA9000.

[0121] (D) Triallyl isocyanurate (TAIC), a cross-linking agent, was purchased from Aladdin Reagents.

[0122] (E1) The flame retardant prepared by Example 1 or 2 or 3 or 4.

[0123] (E2) Vinylene-bridged DiDOPO-A was prepared according to Chinese patent application CN110885344 A. The specific preparation method is as follows: 32.4 g DOPO (0.15 mol), 25 g diphenylmethane, and 20 g xylene were added to a four-necked flask equipped with a thermometer, a water separator, a mechanical stirrer, and a constant pressure funnel. Under nitrogen, the mixture was heated to 195°C. A mixed solution of 6.6 g ethylene carbonate (0.075 mol) and 0.34 g sodium iodide (0.0023 mol) was then added dropwise at a constant rate over 2.5 hours. The mixture was then incubated at 195°C for 2 hours to complete the reaction. After cooling, 38 g isopropyl alcohol was added, and the mixture was stirred under reflux for 20 minutes. After cooling, the mixture was filtered. The solid product was washed with isopropyl alcohol and then three times with an appropriate amount of deionized water. The mixture was then dried in vacuo at 180°C to obtain a white solid powder, namely, vinylene-bridged DiDOPO-A.

[0124] (E3) Aluminum diethylphosphinate, purchased from Klein Corporation with the trade name OP935.

[0125] (E4) Product of DOPO and formaldehyde; Specific preparation method: 43.20 g DOPO (0.20 mol) and 60 g xylene were added to a four-necked flask equipped with a thermometer, magnetic stirring, and reflux. Under nitrogen, the mixture was heated to 95°C. 6.01 g paraformaldehyde (0.20 mol) was then added in multiple portions. The reaction was then continued at 95°C for 4 hours to complete. After cooling, the mixture was filtered, the solid product was washed with toluene, and vacuum dried at 100°C to obtain a white solid powder product, which is the addition product of DOPO and formaldehyde.

[0126] (E5) Product of DOPO and acetone; Preparation method: 21.60 g DOPO (0.10 mol) and 46.4 g acetone (0.40 mol) were added to a four-necked flask equipped with a thermometer, magnetic stirring, and reflux. Under nitrogen, the mixture was heated to reflux temperature and then refluxed for 4 hours to complete the reaction. After cooling, the mixture was filtered and the solid product was washed with acetone and then three times with an appropriate amount of deionized water. The product was then dried in vacuo at 80°C to obtain a white solid powder, which is the addition product of DOPO and acetone.

[0127] (F1) Polybutadiene (PB), purchased from MacLean's reagent.

[0128] (F2) BT resin was obtained by curing N,N′-4,4′-diphenylmethane bismaleimide (BMI) and cyanate ester resin (CE), both of which were purchased from Aladdin Reagents.

[0129] (G) Dicumyl peroxide (DCP), initiator, was purchased from Aladdin Reagents.

[0130] (H) Spherical silica, an inorganic filler, was purchased from Qinghe County Andy Metal Materials Co., Ltd., with a particle size of 2 μm.

[0131] (I) 1,4-cyclohexanedione, 1,3-cyclopentanedione, and 5,5-dimethyl-1,3-cyclohexanedione were purchased from Aladdin Reagent.

[0132] (J) 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was purchased from MacLean's reagent.

[0133] The characterization methods in the embodiments and comparative examples are as follows:

[0134] (1) Nuclear magnetic resonance spectroscopy (NMR): performed on a Bruker AVANCE III 400M NMR spectrometer (Bruker, USA) using deuterated dimethyl sulfoxide as the solvent.

[0135] (2) Fourier transform infrared spectroscopy (FTIR): performed on a Nicolet 6700 infrared spectrometer (Thermo-Fisher, USA) using the KBr method.

[0136] The performance testing methods of the flame retardant resin materials prepared in the examples and comparative examples are as follows:

[0137] (1) Flame retardant test: UL-94 vertical combustion test was carried out on a 5400 horizontal / vertical combustion apparatus according to ASTM D3801.

[0138] [Corrected 14.08.2023 according to Rule 26] (2) Mechanical property test: Tensile and bending tests were carried out on a 5567 universal tensile tester (Instron, USA) in accordance with GB / T 1040.1-2006 and GB / T 9341-2000 standards, respectively; notched impact tests were carried out on a GT-7045-HML impact tester (GOTECH, Taiwan, China) in accordance with ISO179-1:98.

[0139] (3) Glass transition temperature (T g ): T of the polyphenylene ether resin composition g The T values ​​of epoxy resin materials were obtained by TMA 402 F3 thermomechanical analyzer (NETZSCH, Germany). g The measurements were carried out on DSC (METTLER, Sweden).

[0140] (4) Dielectric constant (Dk) and dielectric loss factor (Df): The dielectric constant (Dk) and dielectric loss factor (Df) of the flame retardant resin material were measured on a ZNA Vector Network Analyzer (ROHDE & SCHWARZ, Germany) using the stripline method. Df was taken as the average value of 9-12 GHz.

[0141] (5) Coefficient of thermal expansion (CTE): Thermomechanical analysis (TMA) was used to test the CTE on a TMA 402 F3 thermomechanical analyzer (NETZSCH, Germany).

[0142] Example 1

[0143] The DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain in this embodiment has the following structure:

[0144] Wherein, R1 and R2 are ethylene (-CH2CH2-), R3 and R4 are hydrogen, and x=y=0.

[0145] The DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain is prepared by the following steps:

[0146] Under nitrogen, 0.15 mol of DOPO was placed in a 250 mL four-necked round-bottom flask equipped with a thermometer, reflux, and magnetic stirring. 120 mL of p-xylene was added and the mixture was heated to 120°C until completely dissolved. 0.05 mol of 1,4-cyclohexanedione was added in two batches and the reaction continued at 120°C for 5 hours. After the reaction, the mixture was filtered while hot and washed five times with hot isopropanol. The washed solid product was vacuum-dried at 100°C to obtain a white product with a yield of 99.0% based on 1,4-cyclohexanedione.

[0147] The NMR phosphorus spectrum of the DOPO derivative flame retardant prepared in Example 1 is shown in Figure 1, and the NMR hydrogen spectrum is shown in Figure 2. NMR: 31 PNMR, 35 ppm; 1 HNMR, 7-8.5ppm is benzene ring hydrogen, 5.37ppm is hydroxyl hydrogen, 1.0-2.5ppm is aliphatic ring hydrogen. Its infrared spectrum is shown in Figure 3, and a strong hydroxyl absorption peak (3263cm -1 ). Melting point: greater than 300℃.

[0148] Example 2

[0149] The DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain in this embodiment has the following structure:

[0150] Wherein, R1 and R2 are ethylene (-CH2CH2-), R3 and R4 are hydrogen, and x=y=0.

[0151] The DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain is prepared by the following steps:

[0152] Under nitrogen, 0.25 mol of DOPO was placed in a 250 mL four-necked round-bottom flask equipped with a thermometer, reflux, and magnetic stirring. The temperature was raised to 180°C until completely melted. 0.05 mol of 1,4-cyclohexanedione was added in two portions and the reaction was continued at 180°C for 2 hours before terminating. The reaction product was added to a large amount of isopropanol, hot-washed at 60°C, and filtered while hot. This process was repeated three times before drying in a vacuum oven at 80°C to yield a white powder. The yield based on 1,4-cyclohexanedione was 93.7%. Nuclear magnetic resonance spectroscopy confirmed the white powder to have the structure described above.

[0153] Example 3

[0154] The DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain in this embodiment has the following structure:

[0155] Among them, R1 is a methylene group (-CH2-), R2 is a dimethyl-substituted propylene group (-CH2-C(CH3)2-CH2-), R3 and R4 are hydrogen, and x=y=0.

[0156] The DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain is prepared by the following steps:

[0157] Under nitrogen, 0.20 mol of DOPO was placed in a 250 mL four-necked round-bottom flask equipped with a thermometer, reflux, and magnetic stirring. 150 mL of toluene was added and the temperature was raised to 100°C until complete dissolution. 0.1 mol of 5,5-dimethyl-1,3-cyclohexanedione was then added in two batches. The reaction was continued at 100°C for 6 hours. After the reaction, the mixture was filtered while hot and washed six times with hot isopropanol. The washed solid product was vacuum-dried at 90°C to obtain a light yellow product with a yield of 92.0% based on 5,5-dimethyl-1,3-cyclohexanedione.

[0158] Example 4

[0159] The DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain in this embodiment has the following structure:

[0160] Wherein, R1 is a methylene group (-CH2-), R2 is an ethylene group (-CH2CH2-), R3 and R4 are hydrogen, and x=y=0.

[0161] The DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain is prepared by the following steps:

[0162] Under nitrogen, 0.2 mol of DOPO was placed in a 250 mL four-necked round-bottom flask equipped with a thermometer, reflux, and magnetic stirring. The temperature was raised to 160°C until completely melted. 0.1 mol of 1,3-cyclopentanedione was added in two batches, and the reaction was continued at 160°C for 2 hours. After the reaction, the solid product was washed three times with hot isopropanol and dried in vacuo at 100°C to obtain a brown product with a yield of 95.3% based on 1,3-cyclopentanedione.

[0163] Example 5

[0164] 77 parts of bisphenol A epoxy resin E44 and 6 parts of the flame retardant obtained in Example 1 were weighed and mixed uniformly at 90°C with magnetic stirring. 17 parts of DDM were weighed and added thereto, and the mixture was completely melted at 90°C. The mixture was degassed in a vacuum oven at 80°C for 3 minutes, and then quickly poured into a preheated mold. The mixture was allowed to stand for 5 minutes, heated to 120°C and cured for 2 hours, then heated to 170°C and cured for 4 hours. Finally, the mixture was naturally cooled to room temperature to obtain specimens for UL-94 vertical burning, tensile, bending, and notched impact tests. The results are shown in Table 1.

[0165] Example 6

[0166] 66 parts of bisphenol A epoxy resin E44 and 20 parts of the flame retardant obtained in Example 1 were weighed and mixed uniformly at 90°C with magnetic stirring. 14 parts of DDM were weighed and added thereto, and the mixture was completely melted at 90°C. The mixture was degassed in a vacuum oven at 80°C for 3 minutes, and then quickly poured into a preheated mold. The mixture was allowed to stand for 5 minutes, heated to 120°C and cured for 2 hours, then heated to 170°C and cured for 4 hours. Finally, the mixture was naturally cooled to room temperature to obtain specimens for UL-94 vertical burning, tensile, bending, and notched impact tests. The results are shown in Table 1.

[0167] Example 7

[0168] 75.5 parts of bisphenol A epoxy resin E44 and 8 parts of the flame retardant obtained in Example 3 were weighed and mixed uniformly at 95°C with magnetic stirring. 16.5 parts of DDM were weighed and added thereto. The mixture was completely melted at 95°C and degassed in a vacuum oven at 85°C for 3 minutes. The mixture was quickly poured into a preheated mold and allowed to stand for 5 minutes. The mixture was then heated to 120°C and cured for 2 hours. The mixture was then heated to 180°C and cured for 4 hours. The mixture was then naturally cooled to room temperature to obtain specimens for UL-94 vertical burning, tensile, bending, and notched impact tests. The results are shown in Table 1.

[0169] Example 8

[0170] 77 parts of bisphenol A epoxy resin E44 and 6 parts of the flame retardant obtained in Example 4 were weighed and mixed uniformly at 90°C with magnetic stirring. 17 parts of DDM were weighed and added thereto, and the mixture was completely melted at 90°C. The mixture was degassed in a vacuum oven at 85°C for 3 minutes, and then quickly poured into a preheated mold. The mixture was allowed to stand for 5 minutes, heated to 120°C and cured for 2 hours, then heated to 180°C and cured for 4 hours. Finally, the mixture was naturally cooled to room temperature to obtain specimens for UL-94 vertical burning, tensile, bending, and notched impact tests. The results are shown in Table 1.

[0171] Example 9

[0172] 100 parts SA9000, 50 parts TAIC, and 200 parts toluene were weighed and completely dissolved under magnetic stirring at room temperature. 50 parts of the flame retardant prepared in Example 1 were added, the mixture was heated to 70°C and stirred until no bubbles were present. 4 parts DCP were added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene and obtain a precured resin. The solvent-free precured resin was placed in a mold preheated at 100°C and cured in a flat-plate vulcanizer using the following curing schedule: 1 hour at 150°C, 2 hours at 170°C, 1 hour at 190°C, and 1 hour at 220°C. The mixture was then cooled naturally to room temperature to obtain samples for UL-94 vertical combustion, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0173] Example 10

[0174] 100 parts SA9000, 50 parts TAIC, and 200 parts toluene were weighed and completely dissolved under magnetic stirring at room temperature. 70 parts of the flame retardant prepared in Example 2 were added, the mixture was heated to 70°C and stirred until no bubbles were present. 4 parts DCP were added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene and obtain a precured resin. The solvent-free precured resin was placed in a mold preheated at 100°C and cured in a flat-plate vulcanizer using the following curing schedule: 1 hour at 150°C, 2 hours at 170°C, 1 hour at 190°C, and 1 hour at 220°C. The mixture was then cooled naturally to room temperature to obtain samples for UL-94 vertical combustion, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0175] Example 11

[0176] 100 parts SA9000, 50 parts TAIC, and 200 parts toluene were weighed and completely dissolved under magnetic stirring at room temperature. 45 parts of the flame retardant prepared in Example 1 and 5 parts OP935 were added, the mixture was heated to 70°C and stirred until no bubbles were present. 4 parts DCP was added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene and obtain a precured resin. The solvent-free precured resin was placed in a mold preheated at 100°C and cured in a flat-bed vulcanizer at the following curing schedule: 1 hour at 150°C, 2 hours at 170°C, 1 hour at 190°C, and 1 hour at 220°C. The resin was then cooled naturally to room temperature to obtain samples for UL-94 vertical combustion, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0177] Example 12

[0178] 100 parts SA9000, 50 parts TAIC, 72 parts polybutadiene PB, and 200 parts toluene were weighed and completely dissolved under magnetic stirring at room temperature. 80 parts silica and 112 parts flame retardant prepared in Example 2 were added, respectively. The mixture was heated to 70°C and stirred until uniform and free of bubbles. 4 parts DCP was added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene and obtain a precured resin. The solvent-free precured resin was placed in a mold preheated at 100°C and cured in a flat-plate vulcanizer at the following curing schedule: 1 hour at 150°C, 2 hours at 170°C, 1 hour at 190°C, and 1 hour at 220°C. The mixture was then cooled naturally to room temperature. Samples for UL-94 vertical combustion, dielectric properties, and thermal expansion coefficient testing were obtained. The results are shown in Table 2.

[0179] Example 13

[0180] 100 parts SA9000, 50 parts TAIC, 57.6 parts CE, 14.4 parts BMI, and 200 parts toluene were weighed and magnetically stirred at room temperature. 80 parts silica and 112 parts flame retardant prepared in Example 2 were added, respectively. The mixture was heated to 70°C and stirred until bubbles disappeared. 4 parts DCP was added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene and obtain a precured resin. The solvent-free precured resin was placed in a mold preheated at 100°C and cured in a flatbed vulcanizer at the following curing schedule: 150°C for 1 hour, 170°C for 2 hours, 190°C for 1 hour, and 220°C for 1 hour. The mixture was then cooled naturally to room temperature. Samples for UL-94 vertical burning, dielectric properties, and thermal expansion coefficient testing were obtained. The results are shown in Table 2.

[0181] Example 14

[0182] 100 parts SA9000, 50 parts TAIC, and 200 parts toluene were weighed and completely dissolved under magnetic stirring at room temperature. 70 parts of the flame retardant prepared in Example 3 were added, the mixture was heated to 70°C and stirred until no bubbles were present. 4 parts DCP were added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene and obtain a precured resin. The solvent-free precured resin was placed in a mold preheated at 100°C and cured in a flat-plate vulcanizer using the following curing schedule: 1 hour at 150°C, 2 hours at 170°C, 1 hour at 190°C, and 1 hour at 220°C. The mixture was then cooled naturally to room temperature to obtain samples for UL-94 vertical combustion, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0183] Example 15

[0184] 100 parts SA9000, 50 parts TAIC, and 200 parts toluene were weighed and completely dissolved under magnetic stirring at room temperature. 50 parts of the flame retardant prepared in Example 4 were added, the mixture was heated to 70°C and stirred until uniformly free of bubbles. 4 parts DCP were added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene, yielding a precured resin. The desolventized precured resin was placed in a mold preheated at 100°C and cured in a flat-bed vulcanizer using the following curing schedule: 1 hour at 150°C, 2 hours at 170°C, 1 hour at 190°C, and 1 hour at 220°C. The mixture was then cooled naturally to room temperature. This yielded samples for UL-94 vertical combustion, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0185] Example 16

[0186] Under nitrogen protection, 5.44 g of the flame retardant prepared in Example 1 (0.01 mol) and 10.20 g of acetic anhydride (0.10 mol) were placed in a 100 mL four-necked round-bottom flask equipped with a thermometer, reflux condenser and magnetic stirring, and the temperature was raised to 140 ° C. and refluxed for 6 h. After the white turbid liquid was naturally cooled, it was filtered and the precipitate was washed three times with anhydrous ethanol and dried in a vacuum oven at 80 ° C. After infrared testing, it was completely consistent with the product obtained in Example 1, indicating that the hydroxyl group of the flame retardant having the structure of formula (I) has strong chemical stability, does not degrade at high temperatures, and does not react with acetic anhydride.

[0187] Example 17

[0188] Under nitrogen protection, 5.44 g of the flame retardant prepared in Example 1 (0.01 mol), 15.01 g of isopropyl acetate (0.15 mol) and 5% p-toluenesulfonic acid were placed in a 100 mL four-necked round-bottom flask equipped with a thermometer, reflux condenser and magnetic stirring, and the temperature was raised to 95 ° C and refluxed for 4 h. After the white turbid liquid was naturally cooled, it was filtered and the precipitate was washed three times with anhydrous ethanol and dried in a vacuum oven at 80 ° C. After infrared testing, it was completely consistent with the product obtained in Example 1, indicating that the hydroxyl group of the flame retardant having the structure of formula (I) has strong chemical stability, does not degrade, and does not react with isopropyl acetate.

[0189] Comparative Example 1

[0190] Under nitrogen protection, 2.74g of the addition product of DOPO and acetone (0.01mol) and 10.20g of acetic anhydride (0.10mol) were placed in a 100mL four-necked round-bottom flask equipped with a thermometer, reflux and magnetic stirring. The temperature was raised to 140℃ and refluxed for 1h to obtain a clear and transparent liquid. After natural cooling, the excess acetic anhydride was removed by vacuum distillation to obtain a yellow viscous liquid. Infrared spectroscopy showed a clear carbonyl peak (1771cm -1 and 1747cm -1 ), indicating that the hydroxyl group of the addition product of DOPO and acetone is highly active and reacts with acetic anhydride; the phosphorus spectrum of nuclear magnetic resonance testing shows that the addition product of DOPO and acetone will undergo esterification reaction, dehydration reaction and reverse reaction of deacetone to regenerate DOPO, with the three types of reactions accounting for 18%, 37% and 45% respectively.

[0191] Comparative Example 2

[0192] Under nitrogen protection, 2.46g of the addition product of DOPO and formaldehyde (0.01mol) and 10.20g of acetic anhydride (0.10mol) were placed in a 100mL four-necked round-bottom flask equipped with a thermometer, reflux and magnetic stirring. The temperature was raised to 140℃ and refluxed for 3h to obtain a clear and transparent liquid. After natural cooling, the excess acetic anhydride was removed by vacuum distillation to obtain a yellow viscous liquid. Infrared spectroscopy showed a clear carbonyl peak (1753cm -1 ), indicating that the hydroxyl group of the addition product of DOPO and formaldehyde is highly active and reacts with acetic anhydride; NMR tests show that the acetylated addition product of DOPO and formaldehyde 31 PNMR: 28ppm.

[0193] It can be concluded from Examples 16 and 17 and Comparative Examples 1 and 2 that the hydroxyl groups of the flame retardant prepared in Example 1 are chemically inert, while the hydroxyl groups of the adducts of DOPO and formaldehyde or acetone, which have similar structures but non-cyclic bridge structures, are highly chemically active. The adducts of DOPO and acetone can even degrade and revert to DOPO and acetone under heating.

[0194] Comparative Example 3

[0195] 82 parts of epoxy bisphenol A resin E44 were weighed and mixed uniformly at 90°C with magnetic stirring. 18 parts of DDM were weighed and added to the mixture. The mixture was completely melted at 90°C and degassed in a vacuum oven at 80°C for 3 minutes. The mixture was quickly poured into a preheated mold and allowed to stand for 5 minutes. The mixture was then heated to 120°C and cured for 2 hours. The mixture was then heated to 170°C and cured for 4 hours. The mixture was finally cooled naturally to room temperature to obtain specimens for UL-94 vertical burning, tensile, bending, and notched impact tests. The results are shown in Table 1.

[0196] Comparative Example 4

[0197] 77 parts of epoxy bisphenol A resin E44 and 6 parts of DiDOPO-A were weighed and mixed uniformly at 90°C with magnetic stirring. 17 parts of DDM was weighed and added to the mixture. The mixture was completely melted at 90°C and degassed in a vacuum oven at 80°C for 3 minutes. The mixture was quickly poured into a preheated mold and allowed to stand for 5 minutes. The mixture was then heated to 120°C and cured for 2 hours. The temperature was then raised to 170°C and cured for 4 hours. Finally, the mixture was naturally cooled to room temperature to obtain specimens for UL-94 vertical burning, tensile, bending, and notched impact tests. The results are shown in Table 1.

[0198] Comparative Example 5

[0199] 77 parts of epoxy bisphenol A resin E44 and 6 parts of a flame retardant prepared with DOPO and acetone were weighed and mixed uniformly at 90°C with magnetic stirring. 17 parts of DDM was weighed and added to the mixture. The mixture was completely melted at 90°C and degassed in a vacuum oven at 80°C for 3 minutes. The mixture was quickly poured into a preheated mold and allowed to stand for 5 minutes. The temperature was then raised to 120°C and cured for 2 hours. The temperature was then raised to 170°C and cured for 4 hours. Finally, the mixture was naturally cooled to room temperature to obtain specimens for UL-94 vertical burning, tensile, bending, and notched impact tests. The results are shown in Table 1.

[0200] Comparative Example 6

[0201] Weigh 100 parts of SA9000, 50 parts of TAIC, and 200 parts of toluene and completely dissolve them under magnetic stirring at room temperature. Heat the mixture to 70°C, add 4 parts of DCP, and stir at 70°C for 30 minutes. The mixture is then transferred to an 80°C vacuum oven to remove the toluene, yielding a precured resin. The desolventized precured resin is placed in a mold preheated at 100°C and cured in a flat-bed vulcanizer using the following curing schedule: 1 hour at 150°C, 2 hours at 170°C, 1 hour at 190°C, and 1 hour at 220°C. The resin is then cooled naturally to room temperature to yield samples for UL-94 vertical burning, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0202] Comparative Example 7

[0203] 100 parts SA9000, 50 parts TAIC, and 200 parts toluene were weighed and completely dissolved under magnetic stirring at room temperature. 50 parts DiDOPO-A was added, heated to 70°C, and stirred until no bubbles were present. 4 parts DCP was added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene, yielding a precured resin. The solvent-free precured resin was placed in a mold preheated at 100°C and cured in a flat-bed vulcanizer at 150°C for 1 hour, 170°C for 2 hours, 190°C for 1 hour, and 220°C for 1 hour. The resin was then cooled naturally to room temperature. This yielded samples for UL-94 vertical burning, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0204] Comparative Example 8

[0205] Weigh 100 parts of SA9000, 50 parts of TAIC, and 200 parts of toluene and dissolve them completely under magnetic stirring at room temperature. Add 50 parts of OP935, heat to 70°C, and stir until bubbles disappear. Add 4 parts of DCP and stir at 70°C for 30 minutes. Transfer the mixture to an 80°C vacuum oven to remove the toluene, yielding a precured resin. The desolventized precured resin was placed in a mold preheated at 100°C and cured in a flat-bed vulcanizer at 150°C for 1 hour, 170°C for 2 hours, 190°C for 1 hour, and 220°C for 1 hour. Cool naturally to room temperature to obtain samples for UL-94 vertical burning, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0206] Comparative Example 9

[0207] 100 parts of SA9000, 50 parts of TAIC, and 200 parts of toluene were weighed and completely dissolved under magnetic stirring at room temperature. 50 parts of the addition product of DOPO and formaldehyde were added, heated to 70°C, and stirred until no bubbles were present. 4 parts of DCP were added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene, yielding a precured resin. The solvent-free precured resin was placed in a mold preheated at 100°C and cured in a flat-bed vulcanizer at the following curing schedule: 150°C for 1 hour, 170°C for 2 hours, 190°C for 1 hour, and 220°C for 1 hour. The mixture was then cooled naturally to room temperature. Samples were obtained for UL-94 vertical burning, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0208] Comparative Example 10

[0209] 100 parts of SA9000, 50 parts of TAIC, and 200 parts of toluene were weighed and completely dissolved under magnetic stirring at room temperature. 50 parts of the addition product of DOPO and acetone were added, heated to 70°C, and stirred until no bubbles were present. 4 parts of DCP were added and stirred at 70°C for 30 minutes. The mixture was then transferred to an 80°C vacuum oven to remove the toluene, yielding a precured resin. The solvent-free precured resin was placed in a mold preheated at 100°C and cured in a flat-bed vulcanizer at the following curing schedule: 150°C for 1 hour, 170°C for 2 hours, 190°C for 1 hour, and 220°C for 1 hour. The mixture was then cooled naturally to room temperature. Samples were obtained for UL-94 vertical burning, dielectric properties, and thermal expansion coefficient testing. The results are shown in Table 2.

[0210] Table 1 Flame retardant epoxy resin material formula and properties

[0211] From the comparison of Example 5 and Comparative Example 4 in Table 1, it can be seen that the flame retardant prepared in Example 1 has a comparable flame retardant effect to DiDOPO-A. However, at the same addition amount, the flame retardant prepared in Example 1 has better physical properties for the flame retardant epoxy resin than the flame retardant epoxy resin in Comparative Example 4, especially the flame retardant prepared in Example 1 has a better effect on the glass transition temperature (T g ) has little effect. Even at a high addition level (20 parts), Example 6 shows that the glass transition temperature of the flame-retardant epoxy resin is higher than that of the epoxy resin flame-retarded with 6 parts of DiDOPO-A, demonstrating the importance of the hydroxyl group of the flame retardant in maintaining the physical properties of the epoxy resin. As can be seen from Examples 7 and 8, the flame retardants prepared in Examples 3 and 4 not only exhibit high flame retardancy, but also exhibit mechanical properties and glass transition temperatures superior to those of Comparative Example 4. The mechanical properties of the flame-retardant epoxy resin obtained in Example 8 are also comparable to those of the pure epoxy resin in Comparative Example 3. A comparison of Example 5 with Comparative Example 5 shows that the flame retardant prepared in Example 1 not only has a higher flame retardancy, but also better retains the physical properties of the epoxy resin, demonstrating the significant advantages of cyclic bridge chain structures over non-cyclic substituents.

[0212] Table 2 Formula of low dielectric constant flame retardant polyphenylene ether resin composition

[0213] From Table 2, Example 9, Example 10 and Comparative Example 6, it can be concluded that the flame retardants prepared by Examples 1 and 2 not only improve the T g, and also reduced the Df value and linear expansion coefficient. The more flame retardant, the greater the reduction in Df value and linear expansion coefficient. The results of Comparative Examples 9 and 10, as well as Comparative Example 6, show that DOPO derivatives containing hydroxyl groups but no cyclic bridge structure not only have poor flame retardancy, but also significantly increase the Df value of the polyphenylene ether resin system. In contrast, Examples 9, 14, and 15 demonstrate that the flame retardants prepared from Examples 1, 3, and 4, which have cyclic bridge structures, not only have high flame retardant efficiency but also significantly reduce the Df value of the polyphenylene ether resin system, which is quite surprising. Examples 9, 14, and 15, along with Comparative Example 7, demonstrate that the flame retardants prepared from Examples 1, 3, and 4, despite having lower phosphorus contents than DiDOPO-A, have higher flame retardant efficiency. A comparison of Examples 9, 11, and Comparative Example 8 demonstrates that the combined use of the flame retardant prepared from Example 1 and aluminum dialkylphosphinate not only achieves the same V0 flame retardancy rating for the polyphenylene ether resin system, but also unexpectedly results in a lower Df value than when either is used alone.

[0214] The various aspects, embodiments, and features of the present invention should be considered in all respects as illustrative and not limiting, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0215] In the preparation method of the present invention, the order of the steps is not limited to the order listed. Persons skilled in the art will appreciate that variations in the order of the steps are within the scope of the present invention without inventive effort. Furthermore, two or more steps or actions may be performed simultaneously.

[0216] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit its implementation. Persons skilled in the art may make various modifications, additions, or substitute similar methods for the described specific embodiments. It is not necessary and impossible to provide comprehensive examples of all implementations here. However, obvious variations or modifications arising from the essential spirit of the present invention remain within the scope of protection of the present invention, and interpreting them as any additional limitations would be contrary to the spirit of the present invention.

Claims

1. A DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain, characterized in that: It has the structure shown in the following formula (I): Wherein, R1 and R2 are independently selected from C1 to C 18 An alkylene group, any hydrogen atom on the alkylene group can be independently replaced by a C1-C8 alkyl group, a C6-C 18 Aromatic substitution; R3 and R4 are independently selected from hydrogen, C1-C 18 Alkyl, C3~C 18 Heteroaryl, C6~C 24 Any hydrogen atom on the aromatic ring of the aromatic or heteroaryl group can be replaced independently by any C1 to C 18 Alkyl substitution; x and y are independently selected from 0, 1, 2, 3, 4.

2. A DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain according to claim 1, characterized in that: R1 and R2 are independently selected from C1-C8 alkylene groups, and any hydrogen atom on the alkylene group can be independently replaced by a C1-C8 alkyl group; R3 and R4 are independently selected from hydrogen, C1-C8 alkyl, C3-C 18 Heteroaryl, C6~C 18 Aromatic base.

3. A DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain according to claim 1 or 2, characterized in that: R1 and R2 are independently selected from methylene, ethylene, propylene, butylene, methyl-substituted methylene, dimethyl-substituted methylene, ethyl-substituted methylene, methyl-substituted ethylene, dimethyl-substituted ethylene, methyl-substituted propylene, dimethyl-substituted propylene, and propyl-substituted propylene; R3 and R4 are independently hydrogen, methyl or ethyl.

4. The method for preparing a DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain according to claim 1, characterized in that: The following steps are involved: The compound having the structure of formula (II) and the aliphatic cyclic diketone compound having the structure of formula (III) are reacted to obtain a DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain; Wherein, R3 and R4 are independently selected from hydrogen, C1-C 18 Alkyl, C3~C 18 Heteroaryl, C6~C 24 Any hydrogen atom on the aromatic ring of the aromatic or heteroaryl group can be replaced independently by any C1 to C 18 Alkyl substitution; x and y are independently selected from 0, 1, 2, 3, 4; Wherein, R1 and R2 are independently selected from C1 to C 18 An alkylene group, any hydrogen atom on the alkylene group can be independently replaced by a C1-C8 alkyl group, a C6-C 18 of aromatic substitution.

5. The preparation method according to claim 4, characterized in that: The compound having the structure of formula (II) is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

6. The preparation method according to claim 4, characterized in that: The aliphatic cyclic dione compound having the structure of formula (III) includes one or more of cyclohexanedione, cyclobutanedione, cyclopentanedione, cycloheptanedione, cyclooctanedione, methylcyclohexanedione, dimethylcyclohexanedione, propylcyclohexanedione, tetramethylcyclobutanedione, methylcyclopentanedione, dimethylcyclopentanedione, and ethylcyclopentanedione.

7. The preparation method according to claim 4, characterized in that: The molar ratio of the compound having the structure of formula (II) to the aliphatic cyclic dione compound having the structure of formula (III) is 2 to 20:

1.

8. The preparation method according to claim 4, characterized in that: The reaction time is 0.01 to 25 hours, and the reaction temperature is 5 to 250°C.

9. A flame retardant polymer material, characterized in that: The invention comprises a polymer material and the DOPO derivative flame retardant containing α-hydroxyl group and having a cyclic structure as a bridge chain as claimed in claim 1.

10. The flame retardant polymer material according to claim 9, characterized in that: The mass fraction of the DOPO derivative flame retardant containing α-hydroxyl group and having a cyclic structure as a bridge chain in the flame retardant polymer material is 1 to 50 wt %.

11. The flame retardant polymer material according to claim 9, characterized in that: The flame retardant polymer material includes the DOPO derivative flame retardant containing α-hydroxyl and having a cyclic structure as a bridge chain and a phosphorus flame retardant, and the mass ratio of the DOPO derivative flame retardant containing α-hydroxyl and having a cyclic structure as a bridge chain to the phosphorus flame retardant is 1 to 20:

1.

12. A low-dielectric flame-retardant resin composition, characterized in that: The invention comprises 100 parts by weight of vinyl polyphenylene ether resin and 2 to 150 parts by weight of the DOPO derivative flame retardant containing α-hydroxyl group and having a cyclic structure as a bridge chain as claimed in claim 1.

13. A low-dielectric flame-retardant resin composition according to claim 12, characterized in that: The dielectric loss factor of the low-dielectric flame-retardant resin composition is lower than that of a composition including the vinyl polyphenylene ether resin but not including the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain.

14. A low-dielectric flame-retardant resin composition according to claim 12, characterized in that: The low-dielectric flame-retardant resin composition includes the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain and a phosphorus-based flame retardant, and the mass ratio of the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain to the phosphorus-based flame retardant is 1 to 20:

1.

15. A flame retardant epoxy resin, characterized in that: The invention comprises the DOPO derivative flame retardant containing α-hydroxyl group and having a cyclic structure as a bridge chain as claimed in claim 1, an epoxy compound and a curing agent.

16. The method for preparing a flame retardant epoxy resin according to claim 15, characterized in that: The following steps are involved: The epoxy compound, the curing agent and the DOPO derivative flame retardant containing an α-hydroxyl group and having a cyclic structure as a bridge chain are melt-stirred at room temperature to 120°C for 0.1 to 4 hours, and cured at 70 to 90°C, 110 to 130°C and 160 to 180°C for 0.5 to 8 hours, respectively, and a flame-retardant epoxy resin is obtained after natural cooling.

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