Sulfathiazolyl P / N / S-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 relates to a sulfathiazolyl P / N / S-containing halogen-free flame retardant as well as a preparation method and application thereof. The halogen-free flame retardant containing phosphorus, nitrogen and sulfur elements is obtained 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 forming a Schiff base structure by the intermediate and sulfathiazole, and finally performing addition reaction with DOPO (9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide). The flame retardant can play a synergistic flame-retardant role of phosphorus-nitrogen-sulfur elements, and has a good flame-retardant effect. When the flame retardant disclosed by the invention is used for modifying epoxy resin, the UL-94V-0 level can be reached when the addition amount is less than 5% of the total mass. The influence on Tg of an epoxy resin cured product is small, and the smoke suppression and char formation performance and the mechanical property of the epoxy resin cured product can be remarkably improved. The prepared flame-retardant epoxy resin has good smoke suppression property and char forming property, has good compatibility with epoxy resin, and improves the stability of cured epoxy resin in processing.

Description

Technical Field

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

[0002] As one of the most important thermosetting polymers, epoxy resin has a variety of applications due to its excellent adhesion, chemical resistance, mechanical and dielectric properties, such as in coatings, adhesives, electronic appliances and high-performance composite materials. Despite the excellent properties of epoxy resin, its high flammability and the release of a large amount of toxic gases and smoke during combustion still limit its application. In order to broaden its application areas, the flame retardant properties of epoxy resin must be improved by introducing flame retardants. In the past, halogenated compounds were widely used to improve the flame retardancy of epoxy resin. However, their use will lead to a series of environmental problems because they will 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] Among the halogen-free flame retardants for epoxy resin (EP), phosphorus-based flame retardants have the advantages of low toxicity and long-lasting flame retardant effect. They have low ignition rate during degradation and good ability to prevent re-ignition, and are widely used in epoxy resin. Phosphorus-based flame retardants have been widely used as environmentally friendly halogen-free flame retardants for epoxy resin due to their high efficiency and low generation of corrosive and toxic gases during combustion. They can interrupt the combustion reaction by scavenging active free radicals in the gas phase, or play a flame retardant role by changing the decomposition pathway of the matrix and promoting carbonization in the condensed phase.

[0004] 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is an important intermediate of phosphorus-based flame retardants. It has attracted widespread attention due to its high thermal stability, antioxidant properties, flame retardant efficiency, and the ability to achieve multiple structures through functionalization. The structure contains active PH bonds, which can react with various functional groups such as double bonds, amino groups, epoxy groups, carbonyl groups, and halogens to convert into different types of bonds, such as PC, PO, PN, etc. These different chemical bonds have different thermal properties and flame retardant properties and are used as raw materials for epoxy resin flame retardants. DOPO is regarded as one of the most promising flame retardants because of its high flame retardant efficiency and environmental friendliness.

[0005] However, existing halogen-containing flame retardants produce toxic gases and a large amount of smoke, and DOPO-based flame retardants have poor flame retardant effects. The amount added is large and will have a significant impact on the mechanical properties of the resin.

[0006] Therefore, it is necessary to develop a new flame retardant to solve the problems existing in the prior art. Summary of the invention

[0007] 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 sulfathiazole-based P / N / S halogen-free flame retardant. The sulfathiazole-based P / N / S halogen-free flame retardant of the present invention combines the two structures of DOPO and sulfathiazole, and has a high charring rate, excellent flame retardant effect, and significantly improved smoke suppression performance and mechanical properties.

[0008] In order to solve the problems of the prior art, the first aspect of the present invention provides a sulfathiazole-based P / N / S halogen-free flame retardant, the molecular structure of which is shown in formula (I):

[0009]

[0010] X 1 , X 2 Independently selected from H, methoxy or ethoxy.

[0011] In some preferred embodiments of the present invention, X 1 All of them are replaced by H, and the molecular structure of the sulfathiazole-based P / N / S halogen-free flame retardant is shown in formula (I-1):

[0012]

[0013] Where X 2 is selected from H, methoxy or ethoxy.

[0014] Furthermore, the sulfathiazole-based P / N / S halogen-free flame retardant T g In a preferred embodiment, T g Up to 165°C.

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

[0016] S1: Under an inert atmosphere, flame retardant intermediates are obtained by nucleophilic substitution between diphenylphosphinoyl chloride and aldehyde-containing phenolic compounds;

[0017] S2: Under an inert atmosphere, the flame retardant intermediate obtained in step S1 and sulfathiazole form a Schiff base structure compound;

[0018] S3: Under an inert atmosphere, the Schiff base structure compound obtained in step S2 and DOPO undergo an addition reaction to obtain a sulfathiazole-based P / N / S-containing halogen-free flame retardant.

[0019] In some embodiments of the present invention, 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.

[0020] In some embodiments of the present invention, in step S1, the nucleophilic substitution reaction is carried out by using tetrahydrofuran as an organic solvent and adding an acid binding agent, and reacting at 0°C-60°C for 6-12 hours.

[0021] In some embodiments of the present invention, in step S1, the molar ratio of diphenylphosphinoyl chloride to the aldehyde-containing phenolic compound is 1:(1-1.5).

[0022] Furthermore, 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.

[0023] 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.

[0024] In one embodiment, the acid binding agent is triethylamine; the acid binding agent and the generated HCl form triethylamine hydrochloride.

[0025] In some preferred embodiments, in step S1, the molar ratio of the acid-binding agent to the aldehyde-containing phenolic compound is 1:1.

[0026] In some embodiments of the present invention, in step S2, the reaction temperature is 90 to 120° C., and the reaction time is 8 to 12 hours;

[0027] In some embodiments of the present invention, in step S2, the molar ratio of the flame retardant intermediate to sulfathiazole is 1:(1-1.5).

[0028] Further, in step S2, the amount of organic solvent used is 1g of flame retardant intermediate or sulfathiazole dissolved in 10-20mL of solvent, specifically, the amount of organic solvent used is 1g of flame retardant intermediate or sulfathiazole dissolved in 10-20mL of solvent; preferably, the amount of the organic solvent used is 1g of raw material: 15mL of solvent.

[0029] In some embodiments of the present invention, in step S2, the solvent is dimethylformamide.

[0030] In some embodiments of the present invention, in step S3, the reaction temperature is 100 to 120° C., and the reaction time is 12 to 18 hours;

[0031] In some embodiments of the present invention, in step S3, the molar ratio of the Schiff base structure compound to DOPO is 1:(1-1.5). In one example, an excess of DOPO is used to react with the Schiff base structure compound, that is, the molar ratio of the two is higher than 1:1, such as a molar ratio of 1.2:1. At this time, the reaction is fully complete, all double bonds are added, and the molecular structure of the obtained sulfathiazole-based P / N / S halogen-free flame retardant is shown in the above formula (I-1).

[0032] Furthermore, in step S3, the amount of organic solvent used is 1g of Schiff base structure compound or DOPO dissolved in 10-20mL of solvent; specifically, the amount of organic solvent used is 1g of Schiff base structure compound or DOPO dissolved in 10-20mL of solvent; preferably, the amount of the organic solvent used is 1g of raw material: 10mL of solvent.

[0033] In some embodiments of the present invention, in step S3, the solvent is dimethylformamide.

[0034] In some embodiments of the present invention, the yield of the preparation method of the sulfathiazolyl-based P / N / S halogen-free flame retardant is greater than 80%; preferably, the yield is greater than 82%; more preferably, the yield is 82% to 86%.

[0035] The third aspect of the present invention provides a flame retardant epoxy resin, wherein the flame retardant epoxy resin comprises the halogen-free flame retardant as described above, or the halogen-free flame retardant prepared by the method;

[0036] In some embodiments of the present invention, the amount of the halogen-free flame retardant added to the flame-retardant epoxy resin is 3%-8%, preferably 3%-7%.

[0037] Furthermore, the flame retardant epoxy resin comprises an epoxy resin prepolymer, a curing agent and a halogen-free flame retardant; in some embodiments of the present invention, in the flame retardant epoxy resin, the mass ratio of the epoxy resin prepolymer, the curing agent and the halogen-free flame retardant is 100:(20-26):(5-10).

[0038] In some embodiments of the present invention, the epoxy resin is selected from one or a combination of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin or alicyclic epoxy resin;

[0039] In some embodiments of the present invention, the curing agent is selected from one or a combination of anhydrides, polyamines, dicyandiamide or phenolic resins.

[0040] In some embodiments of the present invention, the limiting oxygen index of the flame retardant epoxy resin cured product is not less than 27%.

[0041] In some preferred embodiments, the limiting oxygen index of the flame retardant epoxy resin is 27% to 32%, preferably 29% to 32%.

[0042] Furthermore, the vertical combustion grade of the flame retardant epoxy resin is V-0 or above.

[0043] Furthermore, the vertical burning test time of the flame retardant epoxy resin is less than 8+3s.

[0044] Furthermore, the flame retardant epoxy resin has a T g Higher than 163°C, preferably 163°C to 165°C.

[0045] Furthermore, the residual carbon content of the flame retardant epoxy resin is higher than 18%, preferably higher than 19%.

[0046] Another aspect of the present invention provides a method for preparing the flame retardant epoxy resin, comprising the following steps: stirring the sulfathiazole-based P / N / S halogen-free flame retardant and epoxy resin prepolymer to form a uniform liquid, then adding a curing agent and stirring until dissolved, then performing a curing treatment, and obtaining a flame retardant epoxy resin cured product after cooling.

[0047] Furthermore, the halogen-free flame retardant and the epoxy resin prepolymer are stirred at 120 to 160° C. for 15 to 30 minutes to form a uniform liquid.

[0048] 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.

[0049] In a preferred embodiment, the sulfathiazole-based P / N / S halogen-free flame retardant and epoxy resin prepolymer are stirred at 140°C for 30 minutes to form a uniform liquid, and then a curing agent is added and stirred until dissolved, and then the mixture is quickly poured into a preheated mold, and then the mold is placed in a forced air drying oven and cured at 100°C, 120°C, 140°C, 160°C, and 180°C for 1 to 2 hours respectively, and a flame-retardant epoxy resin cured product is obtained after cooling.

[0050] Another aspect of the present invention provides the use of the sulfathiazole-based P / N / S-containing halogen-free flame retardant in the preparation of flame-retardant epoxy resin.

[0051] Compared with the prior art, the beneficial effects of the present invention are at least:

[0052] (1) The sulfathiazole-based P / N / S halogen-free flame retardant provided by the present invention can exert the synergistic flame retardant effect of phosphorus-nitrogen-sulfur elements. The epoxy resin cured product prepared by applying the sulfathiazole-based P / N / S halogen-free flame retardant to epoxy resin has good flame retardant effect. When the addition amount is less than 5%, the UL-94 V-0 grade can be achieved.

[0053] (2) The flame retardant epoxy resin has good smoke suppression and charring properties; the vertical burning grade is V-0 or above, and the vertical burning test time is less than 8+3s. The residual carbon content reaches more than 19%;

[0054] (3) 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 has a good thermal stability. g Improve the mechanical properties of epoxy cured products with less impact;

[0055] (4) The flame retardant preparation method of the present invention is simple and the yield can reach 86%. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings:

[0057] The preferred embodiments of the present invention are described in further detail below in conjunction with the accompanying drawings.

[0058] Figure 1 This is a hydrogen nuclear magnetic resonance spectrum of the flame retardant intermediate prepared in Example 1 of the present invention;

[0059] Figure 2 This is a hydrogen nuclear magnetic resonance spectrum of the sulfathiazole-based P / N / S halogen-free flame retardant prepared in Example 3 of the present invention;

[0060] Figure 3 The thermal weight loss curves of the flame retardant epoxy resin cured products obtained in Examples 7-9 and Comparative Example 1 of the present invention;

[0061] Figure 4 The dynamic thermal analysis curves of the epoxy resin cured products obtained in Examples 7-9 and Comparative Example 1 of the present invention;

[0062] Figure 5 The bending strength and impact strength diagram of the epoxy resin cured products prepared in Examples 7-9 and Comparative Example 1 of the present invention (A: bending strength and bending modulus; B: impact strength). DETAILED DESCRIPTION

[0063] 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.

[0064] It should be noted that the embodiments of the present application use an excess of DOPO to fully react with a Schiff base structure compound as an example to obtain a sulfathiazolyl-based P / N / S halogen-free flame retardant. However, those skilled in the art will know that when the structure of the flame retardant intermediate is changed, different sulfathiazolyl-based P / N / S halogen-free flame retardants will be obtained, and this application will not go into details one by one.

[0065] The epoxy resin prepolymer used in the examples is a glycidyl ether epoxy resin.

[0066] Example 1

[0067] S1. Preparation of one of the intermediates of sulfathiazole-based P / N / S halogen-free flame retardant, comprising the following steps:

[0068] 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, cool the solution to room temperature, concentrate the obtained solution by rotary evaporation, add 300mL of dichloromethane to the concentrated solution, and then extract it with 1mol / L sodium hydroxide solution several times until the upper liquid becomes transparent, and concentrate the obtained lower liquid by rotary evaporation, and vacuum dry to obtain a white solid with a yield of 84.3%, which is a flame retardant intermediate. Its nuclear magnetic resonance hydrogen spectrum is shown as follows: Figure 1 The molecular structure of the flame retardant intermediate is shown below, denoted as DV.

[0069] The reaction equation is as follows:

[0070]

[0071] Example 2

[0072] S2. Preparation of one of the Schiff base structure compounds, comprising the following steps:

[0073] Weigh 0.03 mol of the prepared flame retardant intermediate and add it to a three-necked flask equipped with magnetic stirring and nitrogen, add 200 mL of dimethylformamide solution and stir to dissolve. Then add 8.43 g (0.033 mol) of sulfathiazole dissolved in 50 mL of dimethylformamide solution dropwise to the reaction system at room temperature, stir thoroughly for 0.5 hours at room temperature, then heat to 90 ° C and stir for 8 hours. After the reaction is completed, the solution is concentrated by rotary evaporation, the concentrated solution is washed with a large amount of acetone, and vacuum dried to obtain a light brown solid product with a yield of 87.5%, which is a Schiff base structure compound. The molecular structure of the Schiff base structure compound is shown below, named DVS. The reaction equation is as follows:

[0074]

[0075] Example 3

[0076] S3. The preparation method of the sulfathiazole-based P / N / S halogen-free flame retardant comprises the following steps:

[0077] Weigh 0.033 mol of the Schiff base structure compound prepared in Example 2 and add it to a three-necked flask equipped with mechanical stirring and nitrogen, and add 200 mL of dimethylformamide solution and stir to dissolve. Then, 7.14 g (0.033 mol) of DOPO dissolved in 50 mL of dimethylformamide solution was added dropwise to the reaction system at room temperature, and the temperature was raised to 110°C and stirred for 12 hours. After the reaction, the solution was cooled to room temperature, and the filtrate was concentrated by rotary evaporation. The concentrated solution was washed with acetone and ethanol respectively, and vacuum dried to obtain a brown solid product with a yield of 86.4%, which is a sulfathiazole-based P / N / S halogen-free flame retardant. Its hydrogen nuclear magnetic resonance spectrum is shown as follows: Figure 2 The molecular structure of the sulfathiazole-based P / N / S halogen-free flame retardant is shown below and is named DVSD.

[0078] The reaction equation is as follows:

[0079]

[0080] Example 4

[0081] The preparation of sulfathiazole-based P / N / S halogen-free flame retardant specifically comprises the following steps:

[0082] Step 1, weigh 0.1 mol of p-hydroxybenzaldehyde and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200 mL of tetrahydrofuran and stir to dissolve, then add 0.1 mol of triethylamine and stir at room temperature for 10 minutes. Then dissolve 0.10 mol of diphenylphosphinoyl chloride in 100 mL 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 8 hours. After the reaction is completed, the solution is cooled to room temperature, the obtained solution is rotary evaporated to remove tetrahydrofuran, and vacuum dried to obtain a white solid with a yield of 88.3%, which is a flame retardant intermediate.

[0083] Step 2, weigh 0.03 mol of the flame retardant intermediate prepared in this embodiment and add it to a three-necked flask equipped with magnetic stirring and nitrogen, add 200 mL of dimethylformamide solution and stir to dissolve. Then 8.43 g (0.033 mol) of sulfathiazole dissolved in 50 mL of dimethylformamide solution is added dropwise to the reaction system at room temperature, fully stirred for 0.5 hours at room temperature, and then heated to 100 ° C and stirred for 8 hours. After the reaction is completed, the solution is concentrated by rotary evaporation, the concentrated solution is washed with a large amount of acetone, and vacuum dried to obtain a light brown solid product with a yield of 85.2%, which is a Schiff base structure compound.

[0084] Step 3, weigh 0.033 mol of the Schiff base structure compound prepared in step 2 and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200 mL of dimethylformamide solution and stir to dissolve. Then, 7.14 g (0.033 mol) of DOPO dissolved in 50 mL of dimethylformamide solution is added dropwise to the reaction system at room temperature, heated to 110 ° C and stirred for 14 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is concentrated by rotary evaporation. The concentrated solution is washed with a large amount of acetone and ethanol respectively, and vacuum dried to obtain a brown solid product with a yield of 84.4%, which is a sulfathiazole-based P / N / S halogen-free flame retardant.

[0085] Example 5

[0086] The preparation of sulfathiazole-based P / N / S halogen-free flame retardant specifically comprises the following steps:

[0087] Step 1, weigh 0.1 mol of p-syringaldehyde and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200 mL of tetrahydrofuran and stir to dissolve, then add 0.1 mol of triethylamine and stir at room temperature for 10 minutes. Then dissolve 0.10 mol of diphenylphosphinoyl chloride in 100 mL of tetrahydrofuran, and add the solution dropwise to the reaction system at 0°C, stir well for 0.5 hours, and then heat to 70°C and stir for 8 hours. After the reaction is completed, the solution is cooled to room temperature, the obtained solution is evaporated to remove tetrahydrofuran, and vacuum dried to obtain a white solid with a yield of 86.8%, which is a flame retardant intermediate.

[0088] Step 2, weigh 0.03 mol of the flame retardant intermediate prepared in step 1 and add it to a three-necked flask equipped with magnetic stirring and nitrogen, add 200 mL of dimethylformamide solution and stir to dissolve. Then 8.43 g (0.033 mol) of sulfathiazole dissolved in 50 mL of dimethylformamide solution is added dropwise to the reaction system at room temperature, fully stirred for 0.5 hours at room temperature, and then heated to 110 ° C and stirred for 8 hours. After the reaction is completed, the solution is concentrated by rotary evaporation, the concentrated solution is washed with a large amount of acetone, and vacuum dried to obtain a light brown solid product with a yield of 82.6%, which is a Schiff base structure compound.

[0089] Step 3, weigh 0.033 mol of the Schiff base structure compound prepared in step 2 and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200 mL of dimethylformamide solution and stir to dissolve. Then, 7.14 g (0.033 mol) of DOPO dissolved in 50 mL of dimethylformamide solution is added dropwise to the reaction system at room temperature, heated to 120 ° C and stirred for 12 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is concentrated by rotary evaporation. The concentrated solution is washed with acetone and ethanol respectively, and vacuum dried to obtain a brown solid product with a yield of 86.4%, which is a sulfathiazole-based P / N / S halogen-free flame retardant.

[0090] Example 6

[0091] The preparation of sulfathiazole-based P / N / S halogen-free flame retardant specifically comprises the following steps:

[0092] Step 1, weigh 0.1 mol of ethyl vanillin and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200 mL of tetrahydrofuran and stir to dissolve, then add 0.1 mol of triethylamine and stir at room temperature for 10 minutes. Then dissolve 0.10 mol of diphenylphosphinoyl chloride in 100 mL 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 10 hours. After the reaction is completed, the solution is cooled to room temperature, the obtained solution is rotary evaporated to remove tetrahydrofuran, and vacuum dried to obtain a white solid with a yield of 80.5%, which is a flame retardant intermediate.

[0093] Step 2: weigh 0.03 mol of the flame retardant intermediate obtained in step 1 and add it to a three-necked flask equipped with magnetic stirring and nitrogen, add 200 mL of dimethylformamide solution and stir to dissolve. Then, 8.43 g (0.033 mol) of sulfathiazole dissolved in 50 mL of dimethylformamide solution is added dropwise to the reaction system at room temperature, stirred for 0.5 hours at room temperature, and then heated to 100 ° C and stirred for 10 hours. After the reaction is completed, the solution is concentrated by rotary evaporation, the concentrated solution is washed with a large amount of acetone, and vacuum dried to obtain a light brown solid product with a yield of 84.4%, which is a Schiff base structure compound.

[0094] Step 3, weigh 0.033 mol of the Schiff base structure compound prepared in step 2 and add it to a three-necked flask equipped with mechanical stirring and nitrogen, add 200 mL of dimethylformamide solution and stir to dissolve. Then, 7.14 g (0.033 mol) of DOPO dissolved in 50 mL of dimethylformamide solution is added dropwise to the reaction system at room temperature, heated to 100 ° C and stirred for 14 hours. After the reaction is completed, the solution is cooled to room temperature, and the filtrate is concentrated by rotary evaporation. The concentrated solution is washed with acetone and ethanol respectively, and vacuum dried to obtain a brown solid product with a yield of 82.8%, which is a sulfathiazole-based P / N / S halogen-free flame retardant.

[0095] Example 7

[0096] The preparation of flame retardant epoxy resin comprises the following steps:

[0097] Take 3.76 g of the sulfathiazole-based P / N / S halogen-free flame retardant prepared in Example 3 and 100 g of epoxy resin prepolymer and stir them at 140°C for 30 minutes to form a uniform liquid, then add 25.28 g of curing agent (4,4'-diaminodiphenylmethane) and stir until dissolved, then pour it into a preheated stainless steel mold, and then put the mold into a blast drying oven, and cure it at 100°C, 120°C, 140°C, 160°C, and 180°C for 2 hours each, and obtain a flame retardant epoxy resin sample after cooling.

[0098] Example 8

[0099] The preparation of flame retardant epoxy resin comprises the following steps:

[0100] Take 6.26 g of the sulfathiazole-based P / N / S halogen-free flame retardant prepared in Example 3 and 100 g of epoxy resin prepolymer and stir them at 140°C for 30 minutes to form a uniform liquid, then add 25.28 g of curing agent (4,4'-diaminodiphenylmethane) and stir until dissolved, then pour it into a preheated stainless steel mold, and then put the mold into a blast drying oven, and cure it at 100°C, 120°C, 140°C, 160°C, and 180°C for 2 hours each, and obtain a flame retardant epoxy resin sample after cooling.

[0101] Example 9

[0102] The preparation of flame retardant epoxy resin comprises the following steps:

[0103] Take 8.77 g of the sulfathiazole-based P / N / S halogen-free flame retardant prepared in Example 3 and 100 g of epoxy resin prepolymer and stir them at 140°C for 30 minutes to form a uniform liquid, then add 25.28 g of curing agent (4,4'-diaminodiphenylmethane) and stir until dissolved, then pour it into a preheated stainless steel mold, and then put the mold into a blast drying oven, and cure it at 100°C, 120°C, 140°C, 160°C, and 180°C for 2 hours each, and obtain a flame retardant epoxy resin sample after cooling.

[0104] Comparative Example 1: No flame retardant added

[0105] The preparation of epoxy resin comprises the following steps:

[0106] 100 g of epoxy resin prepolymer was mixed with 25.28 g of curing agent (4,4'-diaminodiphenylmethane) at 90°C to form a uniform liquid, which was quickly poured into a preheated stainless steel mold. The mold was then placed in a forced air drying oven and cured at 100°C, 120°C, 140°C, 160°C, and 180°C for 2 hours each. After cooling, epoxy resin samples were obtained for further comparative tests.

[0107] Test Case

[0108] The flame retardant properties of the flame retardant epoxy resins prepared by adding sulfathiazole-based P / N / S halogen-free flame retardants in Examples 7-9 and the pure epoxy resin in the comparative example were tested. The performance test data are shown in Table 1:

[0109] Table 1 Flame retardant properties test results of flame retardant epoxy resin

[0110] Component name Example 7 Example 8 Example 9 Comparative Example 1 Flame retardants 3.76g 6.26g 8.77g 0 Vertical burning level V-1 V-0 V-0 No level Limiting oxygen index (%) 27.9±0.5 29.5±0.2 31.3±0.4 22.8±0.2 <![CDATA[Total smoke yield (m 2 )]]> 19.0 19.0 21.9 27.0 <![CDATA[Vertical combustion test time t 1 +t 2 (s)]]> 9+3 3+2 2+1 Continued burning <![CDATA[T g (℃)]]> 165.0 163.5 163.7 169.3 Residual carbon content (%) 18.7 18.3 19.2 14.3

[0111] like Figure 3 As shown, the carbon residue of the flame retardant epoxy resin prepared in Examples 7-9 increased significantly, indicating that the addition of the flame retardant prepared in the present invention can promote the formation of a carbon layer in the epoxy resin and significantly improve the carbonization ability of the epoxy resin.

[0112] like Figure 4 As shown, the epoxy resin cured product (Examples 7-9) to which the flame retardant prepared by the present invention is added has a T g Basically unaffected, slightly reduced.

[0113] It can be seen from the comparison between Examples 7-9 and Comparative Example 1 (as shown in Table 1) that the addition of the sulfathiazole-based P / N / S halogen-free flame retardant (Example 1) of the present invention can significantly improve the limiting oxygen index and vertical combustion grade of the epoxy resin sample, and the residual carbon content is also increased, wherein the limiting oxygen index of the flame-retardant epoxy resin is greater than 27%, and can reach 31.3%; the vertical combustion grade is above V-1, and the vertical combustion test time is less than 9+3s, wherein the vertical combustion test time of Example 9 is as low as 2+1s; T g When the temperature is higher than 163°C, the residual carbon content is higher than 18%, reaching 19.2%, and the total smoke production is reduced by more than 26.0%, with the highest reduction being 32.6%. This indicates that the flame retardant of the present invention can effectively improve the flame retardant properties of epoxy resin.

[0114] like Figure 5 As shown in Figure 1-A, the bending strength and bending modulus of the epoxy resin cured products obtained in Examples 7-9 are significantly improved compared with those in Comparative Example 1. Figure 5 -B, the impact strength of the epoxy resin cured product obtained in Example 7-9 is also greatly improved. The increase in flexural strength is greater than 17.3%, with a maximum increase of 33.9%, and the increase in impact strength is greater than 7.9%, with a maximum increase of 49.53%. This shows that the flame retardant of the present invention can effectively improve the mechanical properties of the epoxy resin cured product while improving the flame retardant properties of the epoxy resin.

[0115] In summary, the present invention provides a sulfathiazole-based P / N / S halogen-free flame retardant and its preparation method and application. Diphenylphosphinoyl chloride is used as the basis, and a flame retardant intermediate is prepared by a nucleophilic substitution reaction with a phenolic compound containing an aldehyde group. The intermediate is then reacted with sulfathiazole to form a Schiff base structure, and finally an addition reaction is carried out with DOPO to obtain a halogen-free flame retardant containing phosphorus, nitrogen, and sulfur elements. The flame retardant can exert the synergistic flame retardant effect of phosphorus-nitrogen-sulfur elements and has a good flame retardant effect. It is used to modify epoxy resin to prepare a flame-retardant epoxy resin; the T of epoxy resin cured product is g The smoke suppression and charring properties and mechanical properties can be significantly improved with less impact, and the flame retardant efficiency is excellent. The flame retardant epoxy resin has good smoke suppression and charring properties, and the flame retardant has good compatibility with the epoxy resin and is easy to disperse in the resin matrix, thereby improving the stability of the epoxy resin cured product during processing. The flame retardant preparation method is simple, and the yield can reach 86%.

[0116] 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 sulfathiazole-based P / N / S halogen-free flame retardant, characterized in that: The molecular structure is shown in formula (I): X1, X2 are independently selected from H, methoxy or ethoxy.

2. The method for preparing the sulfathiazole-based P / N / S halogen-free flame retardant according to claim 1, characterized in that: The steps include: S1: Under an inert atmosphere, flame retardant intermediates are obtained by nucleophilic substitution between diphenylphosphinoyl chloride and aldehyde-containing phenolic compounds; S2: Under an inert atmosphere, the flame retardant intermediate obtained in step S1 and sulfathiazole form a Schiff base structure compound; S3: Under an inert atmosphere, the Schiff base structure compound obtained in step S2 and DOPO undergo an addition reaction to obtain a sulfathiazole-based P / N / S-containing halogen-free flame retardant.

3. The method for preparing the sulfathiazole-based P / N / S 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 is carried out by using tetrahydrofuran as an organic solvent, adding an acid binding agent, and reacting at 0°C to 60°C for 6 to 12 hours.

4. The method for preparing the sulfathiazole-based P / N / S halogen-free flame retardant according to claim 2, characterized in that: In step S1, the molar ratio of diphenylphosphinoyl chloride to the aldehyde-containing phenolic compound 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 sulfathiazole-based P / N / S halogen-free flame retardant according to claim 2, characterized in that: In step S2, the reaction temperature is 90 to 120° C. and the reaction time is 8 to 12 hours; And / or, in step S2, the molar ratio of the flame retardant intermediate to sulfathiazole is 1:(1-1.5).

6. The method for preparing the sulfathiazole-based P / N / S halogen-free flame retardant according to claim 2, characterized in that: In step S3, the reaction temperature is 100 to 120° C., and the reaction time is 12 to 18 hours; And / or, in step S3, the molar ratio of the Schiff base structure compound to DOPO is 1:(1-1.5).

7. A flame retardant epoxy resin, characterized in that: The halogen-free flame retardant according to claim 1 or the 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 3%-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 halogen-free flame retardant; The mass ratio of the epoxy resin prepolymer, the curing agent and the halogen-free flame retardant is 100:(20-26):(5-10).

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. The flame retardant epoxy resin according to any one of claims 7 to 9, characterized in that: The limiting oxygen index of the flame retardant epoxy resin cured product is not less than 27%.

Images