Phenylboronic acid-based P / N / B-containing halogen-free flame retardant as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of flame-retardant materials, and particularly relates to a phenylboronic acid-based P / N / B-containing halogen-free flame retardant, a preparation method thereof and application of the phenylboronic acid-based P / N / B-containing halogen-free flame retardant in epoxy resin. The preparation method comprises the following steps: by taking diphenyl hypophosphorous chloride as a basis, preparing a flame-retardant intermediate through nucleophilic substitution reaction between diphenyl hypophosphorous chloride and an aldehyde group-containing phenolic compound, then reacting a phenylboronic acid structure with 3-amino-1, 2-propylene glycol to obtain an amino group-containing phenylboronic acid compound, and finally reacting the phenylboronic acid compound with 3-amino-1, 2-propylene glycol to obtain the amino group-containing phenylboronic acid compound. And finally, carrying out a Schiff base reaction on the flame-retardant intermediate and an amino-containing phenylboronic acid compound to obtain the halogen-free flame retardant containing phosphorus, nitrogen and boron elements. The flame retardant provided by the invention can significantly improve the flame retardant property and mechanical property of epoxy resin. A flame-retardant epoxy resin prepared based on the flame retardant; the influence on Tg of an epoxy resin cured product is small, the smoke suppression and char formation performance and the mechanical performance of the cured product can be remarkably improved, and meanwhile, the flame retardant has excellent flame retardant efficiency; the limit oxygen index of the flame-retardant epoxy resin can reach 31%; the vertical combustion grade is V-0 or above, and the carbon residue amount can reach 18% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant materials, and particularly relates to a phenylboronic acid-based P / N / B-containing halogen-free flame retardant, a preparation method thereof, and application of the flame retardant in epoxy resin. Background Art

[0002] Thermosetting epoxy resin (EP) has been widely used in electronics, construction, transportation and other fields due to its excellent properties, such as chemical resistance, corrosion resistance, mechanical properties and excellent adhesion. However, EP is flammable and produces a lot of toxic smoke when burning. In order to meet the requirements of environmentally friendly principles, the development of halogen-free flame retardants for epoxy resins has received more and more attention. The most convenient solution to improve the fire safety of EP is to blend the flame retardant with the epoxy monomer and curing agent before curing. Halogenated compounds have been widely used in the past to improve the flame retardancy of epoxy resins. However, halogen-containing chemicals have negative effects on the environment and human health because they produce toxic and corrosive smoke during combustion. In order to meet the requirements of environmentally friendly principles, the development of halogen-free flame retardants for epoxy resins has received more and more attention.

[0003] As a promising alternative to halogen-free flame retardants, phosphorus-containing flame retardants have attracted increasing attention due to their structural diversity and low toxicity. Phosphorus-containing flame retardants exhibit significant flame retardant properties due to the gas phase capture mechanism of phosphorus radicals, promoting rapid flame extinguishing. However, phosphorus-containing flame retardants have limited smoke suppression effects during epoxy resin combustion and often require a high addition amount to achieve good flame retardant properties. The addition of a large amount of phosphorus-containing flame retardants usually reduces mechanical properties.

[0004] Therefore, it is necessary to develop a new flame retardant to solve the problems existing in the prior art. Summary of the invention

[0005] In order to solve the problems that existing halogen-containing flame retardants produce toxic gases and a large amount of smoke, and phosphorus-containing flame retardants have limited smoke suppression effect on epoxy resin combustion and require a higher addition amount to achieve good flame retardant properties, which has a greater impact on mechanical properties, etc., a new and efficient preparation method of a phenylboronic acid-based P / N / B halogen-free flame retardant and its application are provided.

[0006] The purpose of the present invention is to solve the problems existing in the existing flame retardants, and to provide a novel and efficient preparation method and application of a phenylboronic acid-based P / N / B-containing halogen-free flame retardant. The phenylboronic acid-based P / N / B-containing halogen-free flame retardant of the present invention combines the two structures of phosphorus oxychloride and phenylboric acid, and has a high carbonization rate, excellent flame retardant effect, and significantly improved smoke suppression performance and mechanical properties.

[0007] In order to solve the problems of the prior art, the present invention provides the following technical solutions:

[0008] The first aspect of the present invention is to provide a phenylboronic acid-based P / N / B-containing halogen-free flame retardant, the molecular structure of which is shown in formula (I):

[0009]

[0010] X 1 , X 2 Independently selected from H or methoxy; X 3 Independently selected from H, saturated or unsaturated alkyl groups of 1 to 4 carbon atoms, and phenyl groups.

[0011] In some preferred embodiments, X 3 Independently selected from H, methyl or ethyl.

[0012] In one example, X 1 All of them are replaced by H, and the molecular structure of the phenylboronic acid group-containing P / N / B halogen-free flame retardant is shown in formula (I-1):

[0013]

[0014] X 2 Independently selected from H or methoxy; X 3 Independently selected from H, methyl or ethyl.

[0015] The second aspect of the present invention provides a method for preparing the phenylboronic acid-based P / N / B-containing halogen-free flame retardant, comprising the following steps:

[0016] S1: In an inert atmosphere, a flame retardant intermediate is obtained by nucleophilic substitution between diphenylphosphinoyl chloride and aldehyde-containing phenolic compounds;

[0017] S2: In an inert atmosphere, a phenylboronic acid compound containing an amino group is obtained by reacting a phenylboronic acid structure with 3-amino-1,2-propanediol;

[0018] S3: In an inert atmosphere, the flame retardant intermediate obtained in step S1 and the amino-containing phenylboronic acid compound obtained in step S2 form a Schiff base structure to obtain a phenylboronic acid-based P / N / B-containing halogen-free flame retardant;

[0019] Furthermore, the order of step S1 and step S2 is adjustable; the numbers are for illustration only and do not limit the order of the reaction steps.

[0020] Further, in step S1, the aldehyde group and the phenolic hydroxyl group in the aldehyde-containing phenolic compound are in the para position. In some preferred embodiments, in step S1, the aldehyde-containing phenolic compound is selected from p-hydroxybenzaldehyde, vanillin, ethyl vanillin or syringaldehyde.

[0021] In some embodiments, in step S1, the nucleophilic substitution reaction uses tetrahydrofuran as a solvent, adds an acid binding agent, and reacts at 0° C. to 60° C. for 6 to 12 hours to obtain a flame retardant intermediate.

[0022] In some embodiments, in step S1, the molar ratio of diphenylphosphinoyl chloride to the aldehyde-containing phenolic compound is 1:(1-1.5);

[0023] In some preferred embodiments, in step S1, the amount of the organic solvent is 1g of raw material: 7-10mL of solvent, specifically, 1g of diphenylphosphinoyl chloride or aldehyde-containing phenolic compound is dissolved in 7-10mL of solvent; preferably, the amount of the organic solvent is 1g of raw material: 8mL of solvent.

[0024] In some embodiments of the present invention, the acid binding agent includes one or a combination of sodium hydroxide, potassium carbonate, sodium carbonate, triethylamine, and pyridine.

[0025] In one embodiment, the acid binding agent is triethylamine; the acid binding agent and the generated HCl form triethylamine hydrochloride.

[0026] In some preferred embodiments, in step S1, the molar ratio of the acid-binding agent to the aldehyde-containing phenolic compound is 1:1.

[0027] In some embodiments of the present invention, in step S2, the phenylboronic acid structure is selected from phenylboronic acid, p-methylphenylboronic acid or p-ethylphenylboronic acid, 4-biphenylboronic acid, 4-alkenylphenylboronic acid, 4-butylphenylboronic acid; further preferably, phenylboronic acid, p-methylphenylboronic acid or p-ethylphenylboronic acid.

[0028] In some embodiments, in step S2, the molar ratio of the phenylboronic acid structure to 3-amino-1,2-propanediol is (1-1.5):1;

[0029] In some embodiments, in step S2, the reaction temperature is 60-100° C., and the reaction time is 6-10 hours.

[0030] In some preferred embodiments, in step S2, the amount of organic solvent used is 1g of phenylboronic acid structure or 3-amino-1,2-propanediol dissolved in 8-15mL of solvent; preferably, the amount of the organic solvent used is 1g of raw material: 10mL of solvent.

[0031] In one embodiment, in step S2, ethanol is used as the reaction solvent.

[0032] In some embodiments of the present invention, in step S3, the molar ratio of the flame retardant intermediate to the amino-containing phenylboronic acid compound is 1:(1-1.5);

[0033] Furthermore, in step S3, the reaction temperature is 80-100° C., and the reaction time is 8-12 hours.

[0034] In some preferred embodiments, in step S3, the reaction temperature is 80-100° C., and the reaction time is 8-12 hours.

[0035] In one example, an excess amount of an amino-containing phenylboronic acid compound is used to react with a flame retardant intermediate, that is, the molar ratio of the two is higher than 1:1, such as a molar ratio of 1.1:1. At this time, the reaction is fully complete, and all hydroxyl groups are replaced. The molecular structure of the obtained phenylboronic acid-based P / N / B halogen-free flame retardant is shown in the above formula (I-1).

[0036] In some preferred embodiments, in step S3, the amount of organic solvent used is 1g of flame retardant intermediate or amino-containing phenylboronic acid compound dissolved in 10-20mL of solvent; preferably, the amount of organic solvent used is 1g of raw material: 15mL of solvent.

[0037] In one embodiment, in step S3, the reaction is carried out using ethanol as solvent.

[0038] The third aspect of the present invention provides a flame retardant epoxy resin, comprising a phenylboronic acid-based P / N / B-containing halogen-free flame retardant, or a phenylboronic acid-based P / N / B-containing halogen-free flame retardant prepared by the method;

[0039] Furthermore, the amount of the halogen-free flame retardant added to the flame-retardant epoxy resin is 2%-8% of the total mass of the epoxy resin prepolymer and the curing agent; preferably 3%-7%.

[0040] Furthermore, the flame retardant epoxy resin comprises an epoxy resin prepolymer, a curing agent and a P / N / B halogen-free flame retardant;

[0041] Furthermore, the mass ratio of the epoxy resin prepolymer, the curing agent and the phenylboronic acid-based P / N / B-containing halogen-free flame retardant is 100:(20-26):(3-10).

[0042] In some embodiments, the epoxy resin prepolymer is selected from one or a combination of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin or alicyclic epoxy resin;

[0043] In some embodiments, the curing agent is selected from one or a combination of anhydride, polyamine, dicyandiamide or phenolic resin.

[0044] Another aspect of the present invention provides the use of the phenylboronic acid-based P / N / B-containing halogen-free flame retardant in flame retardant materials.

[0045] Another aspect of the present invention is to provide a method for preparing the flame-retardant epoxy resin mentioned above, comprising the following steps: stirring a phenylboronic acid-based P / N / B halogen-free flame retardant and an epoxy resin prepolymer to form a uniform liquid, then adding a curing agent and stirring until dissolved, and then performing a curing treatment, to obtain a flame-retardant epoxy resin cured product after curing.

[0046] Furthermore, the phenylboronic acid-based P / N / B-containing halogen-free flame retardant and the epoxy resin prepolymer are stirred at 70 to 100° C. for 15 to 30 minutes to form a uniform liquid.

[0047] Furthermore, the curing treatment includes adding a curing agent to a uniform liquid and pouring the mixture into a mold, placing the mold in a drying oven, and curing the mixture at 100° C., 120° C., 140° C., 160° C., and 180° C. for 1 to 2 hours respectively.

[0048] In some embodiments, the prepared phenylboronic acid-based P / N / B-containing halogen-free flame retardant and epoxy resin prepolymer are stirred at 80°C for 30 minutes to form a uniform liquid, and then a curing agent is added and stirred until dissolved, and then quickly poured into a preheated stainless steel mold, and then the mold is placed in a blast drying oven and cured at 100°C, 120°C, 140°C, 160°C, and 180°C for 1 to 2 hours. Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The phenylboronic acid-based P / N / B-containing halogen-free flame retardant provided by the present invention can exert the synergistic flame retardant effect of phosphorus-nitrogen-boron elements, and when applied to epoxy resin, it has a good flame retardant effect, and has good smoke suppression and charring properties;

[0050] (2) The flame retardant prepared by the present invention has good compatibility with epoxy resin, is easy to disperse in the resin matrix, improves the stability of epoxy resin cured product during processing, and can be used to control the T of epoxy cured product. g Improve the mechanical properties of epoxy cured products with less impact;

[0051] (3) The preparation method of the phenylboronic acid-based P / N / B-containing halogen-free flame retardant provided by the present invention has simple steps and the yield can reach 85%;

[0052] (4) The flame retardant epoxy resin provided by the present invention has good flame retardancy and can maintain a high T g ; Limiting oxygen index can reach 31%; Vertical combustion level is V-0 or above; Vertical combustion test time is less than 5+2s; T g Above 165°C, the residual carbon content of flame retardant epoxy resin can reach more than 18%. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. The preferred embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings;

[0054] Figure 1 This is a hydrogen nuclear magnetic resonance spectrum of the flame retardant intermediate prepared in Example 1 of the present invention;

[0055] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the amino-containing phenylboronic acid compound prepared in Example 2 of the present invention;

[0056] Figure 3 This is a hydrogen nuclear magnetic resonance spectrum of the phenylboronic acid-based P / N / B halogen-free flame retardant prepared in Example 3 of the present invention;

[0057] Figure 4 The dynamic thermal analysis curves of the flame retardant epoxy resin cured products obtained in Examples 8-10 and Comparative Example 1 of the present invention;

[0058] Figure 5 The thermal weight loss curves of the flame retardant epoxy resin cured products obtained in Examples 8-10 and Comparative Example 1 of the present invention;

[0059] Figure 6 The bending strength and impact strength diagram of the epoxy resin cured products prepared in Examples 8-10 and Comparative Example 1 of the present invention (A: bending strength and bending modulus; B: impact strength). DETAILED DESCRIPTION

[0060] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described below in conjunction with embodiments and drawings, but the present invention is not limited in any way. Any changes or substitutions made based on the present invention belong to the protection scope of the present invention.

[0061] It should be noted that the embodiments of the present application use an excess of amino-containing phenylboronic acid compounds to fully react with flame-retardant intermediates to obtain phenylboronic acid-based P / N / B halogen-free flame retardants. However, those skilled in the art will know that when the structure of the phenylboronic acid compound is changed, phenylboronic acid-based P / N / B halogen-free flame retardants with different phenylboronic acid structures will be obtained, and this application will not go into details one by one.

[0062] The epoxy resin prepolymer used in the examples is a glycidyl ether epoxy resin.

[0063] Example 1

[0064] The preparation of one of the intermediates of the phenylboronic acid-based P / N / B halogen-free flame retardant of the present invention comprises the following steps:

[0065] Weigh 16.74g (0.11mol) of vanillin and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200mL of tetrahydrofuran and stir to dissolve, then add 11.13g (0.11mol) of triethylamine and stir at room temperature for 10 minutes. Then dissolve 27.67g (0.10mol) of diphenylphosphinoyl chloride in 100mL of tetrahydrofuran, and add the solution dropwise to the reaction system at 0°C, stir well for 0.5 hours, and then heat to 60°C and stir for 6 hours. After the reaction is completed, the solution is cooled to room temperature, the obtained solution is concentrated by rotary evaporation, 300mL of dichloromethane is added to the concentrated solution, and then extracted with 1mol / L sodium hydroxide solution several times until the upper liquid becomes transparent, and the obtained lower liquid is concentrated by rotary evaporation, and vacuum dried to obtain a white solid with a yield of 84.3%, which is a flame retardant intermediate. The molecular structure of the flame retardant intermediate is shown below and is named DV. The hydrogen nuclear magnetic resonance spectrum is shown as follows Figure 1 As shown; it proves that DV was successfully produced.

[0066] The reaction equation is as follows:

[0067]

[0068] Example 2

[0069] The preparation of one of the amino-containing phenylboronic acid compounds of the present invention specifically comprises the following steps:

[0070] Weigh 6.47g (0.11mol) of phenylboric acid and add it to a three-necked flask equipped with mechanical stirring and nitrogen, then add 150mL of ethanol and stir to dissolve. Then dissolve 9.10g (0.10mol) of 3-amino-1,2-propanediol in 50mL of ethanol, and add the solution dropwise to the reaction system, raise the temperature to 60°C and stir for 12 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is evaporated to remove the solvent. The crude product is washed with ethyl acetate and vacuum dried to obtain a white solid product with a yield of 86.6%, which is an amino-containing phenylboric acid compound. The molecular structure of the amino-containing phenylboric acid compound is shown below and is named PBMA. The hydrogen nuclear magnetic resonance spectrum is shown below Figure 2 As shown; it proves that PBMA was successfully prepared.

[0071] The reaction equation is as follows:

[0072]

[0073] Example 3

[0074] The preparation of the phenylboronic acid-based P / N / B-containing halogen-free flame retardant specifically comprises the following steps:

[0075] Weigh 0.033 mol of the amino-containing phenylboronic acid compound prepared in Example 2 and add it to a three-necked flask equipped with mechanical stirring and nitrogen, and add 200 mL of ethanol to stir and dissolve. Then dissolve 0.03 mol of the flame-retardant intermediate prepared in Example 1 in 50 mL of ethanol, and add the solution dropwise to the reaction system, raise the temperature to 80°C and stir for 8 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is evaporated to remove the solvent. The crude product is washed with a large amount of hot water and vacuum dried to constant weight to obtain a white solid product with a yield of 82.4%, which is a phenylboronic acid-containing P / N / B halogen-free flame retardant. The molecular structure of the phenylboronic acid-containing P / N / B halogen-free flame retardant is shown below and is named DVB. The hydrogen nuclear magnetic resonance spectrum is shown in Figure 3 As shown; it proves that DVB was successfully produced.

[0076] The reaction equation is as follows:

[0077]

[0078] Example 4

[0079] The preparation of the phenylboronic acid-based P / N / B-containing halogen-free flame retardant specifically comprises the following steps:

[0080] Step 1, weigh 0.11mol p-hydroxybenzaldehyde and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200mL tetrahydrofuran to stir and dissolve, then add 11.13g (0.11mol) triethylamine and stir at room temperature for 10 minutes. Then 27.67g (0.10mol) diphenylphosphinoyl chloride is dissolved in 100mL tetrahydrofuran, and the solution is added dropwise to the reaction system at 0°C, fully stirred for 0.5 hour, and then warmed to 60°C and stirred for 8 hours. After the reaction is completed, the solution is cooled to room temperature, the obtained solution is concentrated by rotary evaporation, 300mL dichloromethane is added to the concentrated solution, and then 1mol / L sodium hydroxide solution is used for multiple extraction until the upper liquid becomes transparent, the obtained lower liquid is concentrated by rotary evaporation, and vacuum drying obtains a white solid with a yield of 82.3%, which is a flame retardant intermediate.

[0081] Step 2, weigh 0.033 mol of the amino-containing phenylboronic acid compound prepared in Example 2, add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200 mL of ethanol and stir to dissolve. Then 0.03 mol of the flame retardant intermediate prepared in this example is dissolved in 50 mL of ethanol, and the solution is added dropwise to the reaction system, heated to 80 ° C and stirred for 10 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is evaporated to remove the solvent, the crude product is washed with a large amount of hot water, and vacuum dried to constant weight to obtain a white solid product with a yield of 80.4%, which is a phenylboronic acid-containing P / N / B halogen-free flame retardant.

[0082] Example 5

[0083] The preparation of the phenylboronic acid-based P / N / B-containing halogen-free flame retardant specifically comprises the following steps:

[0084] Step 1, weigh 0.11mol of syringaldehyde and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200mL of tetrahydrofuran and stir to dissolve, then add 11.13g (0.11mol) of triethylamine and stir at room temperature for 10 minutes. Then 27.67g (0.10mol) of diphenylphosphinoyl chloride is dissolved in 100mL of tetrahydrofuran, and the solution is added dropwise to the reaction system at 0°C, fully stirred for 0.5 hours, and then heated to 70°C and stirred for 8 hours. After the reaction is completed, the solution is cooled to room temperature, the obtained solution is concentrated by rotary evaporation, 300mL of dichloromethane is added to the concentrated solution, and then 1mol / L of sodium hydroxide solution is used for multiple extraction until the upper liquid becomes transparent, the lower liquid obtained is concentrated by rotary evaporation, and vacuum dried to obtain a white solid with a yield of 82.3%, which is a flame retardant intermediate.

[0085] Step 2, weigh 0.033 mol of the amino-containing phenylboronic acid compound prepared in Example 2, add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200 mL of ethanol and stir to dissolve. Then 0.03 mol of the flame retardant intermediate prepared in this example is dissolved in 50 mL of ethanol, and the solution is added dropwise to the reaction system, heated to 90 ° C and stirred for 10 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is evaporated to remove the solvent, the crude product is washed with a large amount of hot water, and vacuum dried to constant weight to obtain a white solid product with a yield of 83.2%, which is a phenylboronic acid-containing P / N / B halogen-free flame retardant.

[0086] Example 6

[0087] The preparation of the phenylboronic acid-based P / N / B-containing halogen-free flame retardant specifically comprises the following steps:

[0088] Step 1: weigh 0.11 mol of p-methylphenylboronic acid and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 150 mL of ethanol and stir to dissolve. Then dissolve 9.10 g (0.10 mol) of 3-amino-1,2-propanediol in 50 mL of ethanol, and add the solution dropwise to the reaction system, heat to 70 ° C and stir for 12 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is evaporated to remove the solvent. The crude product is washed with ethyl acetate and vacuum dried to obtain a white solid product with a yield of 80.6%, which is an amino-containing phenylboronic acid compound.

[0089] Step 2, take 0.033mol of the amino-containing phenylboronic acid compound prepared in this embodiment and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200mL of ethanol and stir to dissolve. Then 0.03mol of the flame retardant intermediate prepared in Example 1 is dissolved in 50mL of ethanol, and the solution is added dropwise to the reaction system, heated to 80°C and stirred for 10 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is evaporated to remove the solvent, the crude product is washed with a large amount of hot water, and vacuum dried to constant weight to obtain a white solid product with a yield of 85.2%, which is a phenylboronic acid-containing P / N / B halogen-free flame retardant.

[0090] Example 7

[0091] The preparation of the phenylboronic acid-based P / N / B-containing halogen-free flame retardant specifically comprises the following steps:

[0092] Step 1, weigh 0.11 mol of p-ethylphenylboronic acid and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 150 mL of ethanol and stir to dissolve. Then dissolve 9.10 g (0.10 mol) of 3-amino-1,2-propanediol in 50 mL of ethanol, and add the solution dropwise to the reaction system, heat to 80 ° C and stir for 10 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is evaporated to remove the solvent, the crude product is washed with ethyl acetate, and vacuum dried to obtain a white solid product with a yield of 84.2%, which is an amino-containing phenylboronic acid compound.

[0093] Step 2, take 0.033mol of the amino-containing phenylboronic acid compound prepared in this embodiment and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200mL of ethanol and stir to dissolve. Then dissolve 0.03mol of the flame retardant intermediate prepared in Example 1 in 50mL of ethanol, and add the solution dropwise to the reaction system, warm to 80°C and stir for 12 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is evaporated to remove the solvent, the crude product is washed with a large amount of hot water, and vacuum dried to constant weight to obtain a white solid product with a yield of 78.2%, which is a phenylboronic acid-containing P / N / B halogen-free flame retardant.

[0094] Example 8

[0095] The preparation of flame retardant epoxy resin comprises the following steps:

[0096] 3.76 g of the phenylboronic acid-containing P / N / B halogen-free flame retardant prepared in Example 3 and 100 g of epoxy resin prepolymer were stirred at 80° C. for 30 minutes to form a uniform liquid, and then 25.28 g of curing agent (4,4'-diaminodiphenylmethane) was added and stirred until dissolved, and then quickly poured into a preheated stainless steel mold, and then the mold was placed in a blast drying oven and cured at 100° C., 120° C., 140° C., 160° C., and 180° C. for 2 hours each. After cooling, a flame-retardant epoxy resin sample was obtained, and its thermomechanical properties were as follows: Figure 4 shown.

[0097] Example 9

[0098] The preparation of flame retardant epoxy resin comprises the following steps:

[0099] 6.62 g of the phenylboronic acid-containing P / N / B halogen-free flame retardant prepared in Example 3 and 100 g of epoxy resin prepolymer were stirred at 80° C. for 30 minutes to form a uniform liquid, and then 25.28 g of curing agent (4,4'-diaminodiphenylmethane) was added and stirred until dissolved, and then quickly poured into a preheated stainless steel mold, and then the mold was placed in a blast drying oven and cured at 100° C., 120° C., 140° C., 160° C., and 180° C. for 2 hours each. After cooling, a flame-retardant epoxy resin sample was obtained, and its thermomechanical properties were as follows: Figure 4 shown.

[0100] Example 10

[0101] The preparation of flame retardant epoxy resin comprises the following steps:

[0102] 8.77 g of the phenylboronic acid-containing P / N / B halogen-free flame retardant prepared in Example 3 and 100 g of epoxy resin prepolymer were stirred at 80° C. for 30 minutes to form a uniform liquid, and then 25.28 g of curing agent (4,4'-diaminodiphenylmethane) was added and stirred until dissolved, and then quickly poured into a preheated stainless steel mold, and then the mold was placed in a blast drying oven and cured at 100° C., 120° C., 140° C., 160° C., and 180° C. for 2 hours each. After cooling, a flame-retardant epoxy resin sample was obtained, and its thermomechanical properties were as follows: Figure 4 shown.

[0103] Comparative Example 1: No flame retardant added

[0104] 100g of epoxy resin prepolymer was mixed with 25.28g of curing agent (4,4'-diaminodiphenylmethane) at 90℃ to form a uniform liquid, which was quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 100℃, 120℃, 140℃, 160℃, and 180℃ for 2 hours each. After cooling, epoxy resin samples were obtained for further comparative tests. The thermomechanical properties of the samples were as follows: Figure 4 shown.

[0105] Test Case

[0106] The flame retardant properties of the flame retardant epoxy resins prepared by adding phenylboronic acid-containing P / N / B halogen-free flame retardants in Examples 8-10 and the flame retardant epoxy resin in Comparative Example 1 were tested. The performance test data are shown in Table 1:

[0107] Table 1 Flame retardant properties test results of flame retardant epoxy resin

[0108] Component name Example 8 Example 9 Example 10 Comparative Example 1 Flame retardant addition 3.76g 6.62g 8.77g 0 Vertical burning level V-0 V-0 V-0 No level Limiting oxygen index (%) 28.5±0.5 30.4±0.2 31.7±0.4 22.8±0.2 <![CDATA[Vertical combustion test time t 1 +t 2 (s)]]> 5+2 3+2 2+1 Continued burning <![CDATA[Total smoke yield (m 2 )]]> 19.8 18.9 18.2 27.0 <![CDATA[T g (℃)]]> 166.4 165.8 165.6 169.3 Residual carbon content (%) 18.3 20.3 20.9 14.3

[0109] like Figure 4 As shown, the epoxy resin cured product (Examples 8-10) to which the flame retardant prepared by the present invention is added has a T g Slightly reduced.

[0110] As shown in Table 1, it can be seen from the comparison between Examples 8-10 and Comparative Example 1. Adding the phenylboronic acid-based P / N / B halogen-free flame retardant prepared in Example 3 of the present invention can significantly improve the limiting oxygen index and vertical combustion grade of the epoxy resin sample, and its residual carbon content is also increased. When the amount of flame retardant added is less than 3%, the limiting oxygen index of the flame retardant epoxy resin is 28% (Example 8), and the limiting oxygen index of the flame retardant epoxy resin of Example 10 can reach 31.7%. The vertical combustion grade of the flame retardant epoxy resin is above V-0, and the vertical combustion test time is less than 8+2s; T g Higher than 165℃; the amount of residual carbon is higher than 18%, up to 20.9%; the reduction in total smoke production is greater than 26.0%, with the highest reduction of 32.6%.

[0111] like Figure 5 As shown, the carbon residue of the flame retardant epoxy resin prepared in Examples 8-10 increased significantly, indicating that adding the flame retardant prepared in the present invention can promote the epoxy resin to form a carbon layer, and significantly improve the carbonization ability of the epoxy resin.

[0112] like Figure 6 -A, the flexural strength and flexural modulus of the epoxy resin cured products obtained in Examples 8-10 are significantly improved compared with those in Comparative Example 1. Figure 6 -B, the impact strength of the epoxy resin cured product obtained in Examples 8-10 is also greatly improved. The increase in flexural strength is greater than 7.6%, with a maximum increase of 37.0%, and the increase in impact strength is greater than 6.7%, with a maximum increase of 46.1%. This shows that the flame retardant of the present invention can significantly improve the flame retardant properties and mechanical properties of epoxy resin.

[0113] The phenylboronic acid-based P / N / B-containing halogen-free flame retardant provided by the present invention can exert the synergistic flame retardant effect of phosphorus-nitrogen-boron elements, and can form a glassy protective layer on the surface of the polymer during the combustion process, thereby delaying the generation of smoke and heat transfer. At the same time, non-combustible gas can be released during the combustion process to dilute the combustible pyrolysis products and oxygen, and the condensed phase and gas phase flame retardant behavior of the phosphorus-containing flame retardant can be enhanced, thereby achieving an excellent synergistic flame retardant effect.

[0114] In summary, the present invention provides a phenylboronic acid-based P / N / B-containing halogen-free flame retardant and a preparation method thereof. Based on diphenylphosphinoyl chloride, a flame retardant intermediate is prepared by a nucleophilic substitution reaction with a phenolic compound containing an aldehyde group, and then a phenylboronic acid structure and 3-amino-1,2-propanediol are reacted to obtain an amino-containing phenylboronic acid compound. Finally, the flame retardant intermediate and the amino-containing phenylboronic acid compound are reacted by a Schiff base reaction to obtain a halogen-free flame retardant containing phosphorus, nitrogen and boron elements, which can exert a synergistic flame retardant effect of phosphorus-nitrogen-boron elements and has excellent flame retardant efficiency. It is used to modify epoxy resin and has an effect on the T of epoxy resin cured product. g With less impact, it can significantly improve its smoke suppression and charring performance and mechanical properties, and has excellent flame retardant efficiency; the limiting oxygen index of the flame retardant epoxy resin can reach 31%; the vertical combustion grade is above V-0; the residual carbon content of the flame retardant epoxy resin can reach more than 18%.

[0115] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A phenylboronic acid-based P / N / B-containing halogen-free flame retardant, characterized in that: The molecular structure is shown in formula (I): X1 and X2 are independently selected from H or methoxy; X3 is independently selected from H, a saturated or unsaturated alkyl group of 1 to 4 carbon atoms, and a phenyl group.

2. The method for preparing the phenylboronic acid-based P / N / B-containing halogen-free flame retardant according to claim 1, characterized in that: The steps include: S1: In an inert atmosphere, a flame retardant intermediate is obtained by nucleophilic substitution between diphenylphosphinoyl chloride and aldehyde-containing phenolic compounds; S2: In an inert atmosphere, a phenylboronic acid compound containing an amino group is obtained by reacting a phenylboronic acid structure with 3-amino-1,2-propanediol; S3: In an inert atmosphere, the flame retardant intermediate obtained in step S1 and the amino-containing phenylboronic acid compound obtained in step S2 form a Schiff base structure to obtain a phenylboronic acid-based P / N / B-containing halogen-free flame retardant; The order of step S1 and step S2 is adjustable.

3. The method for preparing the phenylboronic acid-based P / N / B-containing halogen-free flame retardant according to claim 2, characterized in that: In step S1, the aldehyde-containing phenolic compound is selected from p-hydroxybenzaldehyde, vanillin, ethyl vanillin or syringaldehyde; And / or, in step S1, the nucleophilic substitution reaction uses tetrahydrofuran as solvent, adds an acid binding agent, and reacts at 0°C to 60°C for 6 to 12 hours to obtain a flame retardant intermediate.

4. The method for preparing the phenylboronic acid-based P / N / B-containing halogen-free flame retardant according to claim 2, characterized in that: In step S1, the molar ratio of diphenylphosphinoyl chloride to the phenolic compound containing an aldehyde group is 1:(1-1.5); And / or, the acid binding agent includes one or a combination of sodium hydroxide, potassium carbonate, sodium carbonate, triethylamine, and pyridine.

5. The method for preparing the phenylboronic acid-based P / N / B-containing halogen-free flame retardant according to claim 2, characterized in that: In step S2, the phenylboronic acid structure is selected from phenylboronic acid, p-methylphenylboronic acid or p-ethylphenylboronic acid, 4-biphenylboronic acid, 4-alkenylphenylboronic acid, and 4-butylphenylboronic acid; And / or, in step S2, the molar ratio of the phenylboronic acid structure to 3-amino-1,2-propanediol is (1-1.5):1; And / or, in step S2, the reaction temperature is 60-100° C., and the reaction time is 6-10 hours.

6. The method for preparing the phenylboronic acid-based P / N / B-containing halogen-free flame retardant according to claim 2, characterized in that: In step S3, the molar ratio of the flame retardant intermediate to the amino-containing phenylboronic acid compound is 1:(1-1.5); And / or, in step S3, the reaction temperature is 80-100° C., and the reaction time is 8-12 hours.

7. A flame retardant epoxy resin, characterized in that: The invention comprises the P / N / B halogen-free flame retardant according to claim 1, or the P / N / B halogen-free flame retardant prepared by the method according to any one of claims 2 to 6; The added amount of the halogen-free flame retardant in the flame-retardant epoxy resin is 2%-8% of the total mass of the epoxy resin prepolymer and the curing agent.

8. The flame retardant epoxy resin according to claim 7, characterized in that: Including epoxy resin prepolymer, curing agent and P / N / B halogen-free flame retardant; The mass ratio of the epoxy resin prepolymer, the curing agent and the phenylboronic acid-based P / N / B-containing halogen-free flame retardant is 100:(20-26):(3-10).

9. The flame retardant epoxy resin according to claim 8, characterized in that: The epoxy resin prepolymer is selected from one or a combination of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin or alicyclic epoxy resin; And / or, the curing agent is selected from one or a combination of acid anhydride, polyamine, dicyandiamide or phenolic resin.

10. Use of the phenylboronic acid-based P / N / B-containing halogen-free flame retardant according to claim 1 or the phenylboronic acid-based P / N / B-containing halogen-free flame retardant prepared by the preparation method according to any one of claims 2 to 6 in flame retardant materials.

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