A flame-retardant epoxy resin with thiophene basic properties and its preparation method

Abstract

This invention discloses a thiophene-based intrinsic flame-retardant epoxy resin and its preparation method, belonging to the field of flame-retardant materials technology. The invention uses thiophene derivatives as raw materials and reacts with epichlorohydrin in the presence of a phase transfer catalyst and alkaline substances via an epoxidation reaction to obtain the target epoxy resin. The sulfur-containing thiophene ring is directly embedded into the main chain framework of the epoxy resin molecule, achieving intrinsic flame-retardant modification at the molecular level. This invention solves the core problems of traditional bisphenol A type epoxy resins being flammable, existing additive flame-retardant modification techniques easily degrading the mechanical properties of the resin, and insufficient environmental friendliness. The prepared epoxy resin does not require the addition of additional flame retardants and possesses excellent flame retardancy, mechanical properties, and environmental friendliness, making it suitable for electronic and electrical packaging, composite material matrices, and other fields, with broad prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials technology, specifically to a thiophene-based flame retardant epoxy resin and its preparation method. Background Technology

[0002] Epoxy resins, due to their excellent mechanical properties, adhesive properties, chemical stability, electrical insulation, and molding processability, have been widely used in electronic and electrical packaging, composite material matrices, aerospace structural components, and high-end adhesives. They are an indispensable core basic polymer material in the high-end manufacturing field. With the rapid development of industries such as new energy, electronic information, and aerospace, the industry has put forward increasingly stringent requirements for the flame retardancy, environmental protection, and comprehensive mechanical properties of epoxy resins. Traditional bisphenol A type epoxy resins, as the mainstream product in the market, lack flame-retardant functional groups in their molecular chains. Their limiting oxygen index is typically below 25%, and their vertical burning rating is only UL94HB. These significant flammability defects make them highly susceptible to fires, and the combustion process releases large amounts of heat and toxic fumes, severely limiting their application in high-end fields. To address the flammability issue of epoxy resins, the industry mainstream adopts additive flame-retardant modification schemes, mainly including three categories: inorganic flame retardants, halogenated flame retardants, and phosphorus-based flame retardants. However, all three schemes have insurmountable industry pain points: inorganic flame retardants require high addition levels to achieve a flame-retardant effect, which can seriously... The mechanical and processing properties of epoxy resins are degraded; although halogenated flame retardants have high flame retardant efficiency, they release highly toxic and corrosive gases and carcinogenic dioxins during combustion, which does not comply with global RoHS, REACH and other environmental regulations, and has been restricted in many fields; phosphorus-based additive flame retardants have poor compatibility with epoxy resin matrices, are prone to migration and precipitation during long-term use, have poor flame retardant durability, and also have irreversible negative impacts on the mechanical and electrical insulation properties of the resin; in summary, existing additive flame retardant modification technologies have always been unable to overcome the long-standing technical bottleneck in the industry where flame retardant performance, mechanical performance and environmental protection are mutually exclusive. Thiophene compounds, as sulfur-containing aromatic heterocyclic derivatives, possess excellent char-forming properties and free radical scavenging capabilities. The sulfur element within the framework can achieve gas-phase-condensed-phase synergistic flame retardancy, effectively interrupting the combustion chain reaction. Simultaneously, the rigid conjugated structure of the thiophene ring can provide excellent mechanical property support for polymer materials. Theoretically, it is an ideal solution to address the pain points in the epoxy resin flame retardant modification industry. However, most existing related technologies only add thiophene derivatives as auxiliary flame retardant additives to epoxy resins, failing to fundamentally solve the core defects of poor compatibility and easy migration and precipitation of additive flame retardants. The few technical solutions involving thiophene-based epoxy resins suffer from cumbersome synthesis routes, harsh reaction conditions, high raw material costs, low product conversion rates, and inability to achieve large-scale production, and have failed to achieve a dual improvement in flame retardant and mechanical properties. Therefore, it is necessary to design a thiophene-based flame-retardant epoxy resin and its preparation method. Summary of the Invention

[0003] The purpose of this invention is to provide a thiophene-based intrinsic flame-retardant epoxy resin and its preparation method, so as to solve the core problems of flammability and poor flame-retardant performance of traditional bisphenol A type epoxy resin mentioned in the background art. At the same time, it solves the industry pain points of existing additive flame-retardant modification technology, such as deterioration of mechanical properties and insufficient environmental compliance, as well as the inability of existing thiophene flame-retardant technology to achieve intrinsic flame retardancy at the molecular level and the complexity of the process, which makes it difficult to achieve industrial mass production.

[0004] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, a method for preparing a thiophene-based flame-retardant epoxy resin is provided. The method uses a thiophene derivative, epichlorohydrin, a phase transfer catalyst, and an alkaline substance as initial raw materials. The molar ratio of the thiophene derivative, epichlorohydrin, phase transfer catalyst, and alkaline substance is 0.8~1.2:5~25:0.05~0.15:2.5~5. The method includes the following steps: S1 adds thiophene derivative, epichlorohydrin, and phase transfer catalyst to a reaction vessel and mixes them under nitrogen protection to obtain a mixed reaction system; S2 heats the mixed reaction system to 70~110℃, holds the temperature for 5~10 hours, cools down after the reaction is complete, adds an alkaline substance to the system, and continues the reaction to obtain the crude product; S3 purified the crude product to obtain a thiophene-based flame-retardant epoxy resin with a thiophene ring and sulfur element introduced into the molecular structure.

[0005] As a further technical solution of the present invention, the thiophene derivative is any one of 2,5-thiophene dicarboxylic acid and thiophene-2,5-dimethyldiethanol.

[0006] As a further technical solution of the present invention, the phase transfer catalyst is one or more combinations of quaternary ammonium salts, polyethers, and quaternary phosphine salts.

[0007] As a further technical solution of the present invention, the quaternary ammonium salt is one or more of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, and tetradecyltrimethylammonium chloride; the polyether is chain polyethylene glycol; and the quaternary phosphine salt is one or more of tetraphenylphosphine chloride and triphenylphosphine.

[0008] As a further technical solution of the present invention, the alkaline substance is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and sodium bicarbonate; the alkaline substance is added in the form of an aqueous solution with a concentration of 10 mol / L.

[0009] As a further technical solution of the present invention, in step S2, after the heat preservation reaction is completed, the system is cooled to 25~60℃, and an alkaline aqueous solution is added dropwise at a rate of 1~12mL / min. After the addition is completed, the heat preservation reaction continues for 1~2 hours.

[0010] As a further technical solution of the present invention, in step S3, the purification process includes a separation step and a drying step; the separation step includes vacuum filtration and solvent extraction, and the drying step includes dehydration with a desiccant, vacuum distillation, and drying in a vacuum drying oven.

[0011] As a further technical solution of the present invention, the desiccant is one or more of the following: anhydrous sodium sulfate, anhydrous sodium carbonate, anhydrous potassium carbonate, anhydrous calcium chloride, anhydrous calcium sulfate, anhydrous calcium oxide, and anhydrous magnesium sulfate.

[0012] In a second aspect, a thiophene-based flame-retardant epoxy resin is provided, prepared by any one of the preparation methods described in the first aspect.

[0013] Compared with existing technologies, the beneficial effects of this thiophene-based flame-retardant epoxy resin and its preparation method are: Through molecular structure design, sulfur-containing thiophene rings are fully integrated into the molecular backbone of epoxy resin. The sulfur element is fixed in the resin molecular structure in the form of covalent bonds, which can endow epoxy resin with excellent flame retardant properties without the addition of any exogenous flame retardants. This fundamentally solves the industry pain points of traditional additive flame retardants, such as poor compatibility with the resin matrix, easy migration and precipitation, insufficient flame retardant durability, and performance degradation over long-term use. At the same time, it avoids the negative impact of adding flame retardants on the resin processing performance. This invention breaks through the common technical prejudice in the field that flame retardant modification inevitably leads to the deterioration of mechanical properties. By utilizing the rigid conjugated structure of the thiophene ring, it provides excellent mechanical support for the epoxy resin crosslinking system while achieving efficient flame retardant modification. Compared with traditional bisphenol A type epoxy resin, the epoxy resin prepared by this invention has improved tensile strength and elongation at break after curing, solving the long-standing technical bottleneck in the industry where flame retardancy and mechanical properties cannot be achieved simultaneously. It achieves synergistic flame retardancy solely by sulfur elements within the thiophene ring skeleton, and its molecular structure contains no halogens or phosphorus elements, making it a completely environmentally friendly halogen-free flame retardant system. When the cured resin system burns, the peak heat release rate, total heat release, and total smoke production all decrease significantly, with no release of toxic or harmful gases, meeting the environmental regulations of global electronics, aerospace, and other fields, and adapting to the application needs of high-end scenarios in enclosed spaces. The one-step phase-transfer catalytic synthesis process utilizes widely available and inexpensive raw materials, with mild and controllable reaction conditions, eliminating the need for stringent requirements such as high temperature and high pressure, and achieving high product conversion rates. It eliminates the need for complex column chromatography purification processes, allowing for the acquisition of high-purity products through conventional washing, extraction, distillation, and drying. The process is highly operable, efficient, and batch-stable, making it easy to scale up for industrial production and possessing significant market promotion and industrial application value. The prepared thiophene-based flame-retardant epoxy resin also possesses excellent flame retardant properties, mechanical properties, environmental friendliness, electrical insulation, and processing performance. It is perfectly suited for high-end fields with stringent requirements for comprehensive material performance, such as electronic and electrical packaging, composite matrix, aerospace structural components, and high-end adhesives, effectively expanding the application boundaries of epoxy resin. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of the molecular structure of the thiophene-based flame-retardant epoxy resin in this invention. Figure 3 Infrared spectra of thiophene-based flame-retardant epoxy resin compounds; Figure 4 This is a schematic diagram of the molecular structure of the thiophene-based flame-retardant epoxy resin in the examples. Figure 5 Tensile stress-tensile strain diagrams of thiophene-based flame-retardant epoxy resin system and comparative example DGEBA epoxy resin after curing with 4,4-diaminodiphenylmethane as curing agent. Figure 6 This is a comparison graph of the heat release rate (HRR) curves of the embodiments and comparative examples in this invention; Figure 7 This is a comparison chart of the total heat release (THR) curves of the embodiments and comparative examples in this invention; Figure 8 This is a comparison chart of the total smoke production (TSP) curves of the embodiments and comparative examples in this invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Please see Figure 1The present invention provides an embodiment of a method for preparing a thiophene-based flame-retardant epoxy resin, wherein the preparation method uses thiophene derivatives, epichlorohydrin, a phase transfer catalyst, and an alkaline substance as initial raw materials; wherein the molar ratio of thiophene derivatives, epichlorohydrin, phase transfer catalyst, and alkaline substance is 0.8~1.2:5~25:0.05~0.15:2.5~5; The thiophene derivative is any one of 2,5-thiophene dicarboxylic acid and thiophene-2,5-dimethyldiethanol; The phase transfer catalyst is one or more of quaternary ammonium salts, polyethers, and quaternary phosphine salts; the quaternary ammonium salt is one or more of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, and tetradecyltrimethylammonium chloride; the polyether is chain polyethylene glycol; and the quaternary phosphine salt is one or more of tetraphenylphosphine chloride and triphenylphosphine. The alkaline substance is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and sodium bicarbonate; the alkaline substance is added in the form of an aqueous solution with a concentration of 10 mol / L; The method includes the following steps: S1 adds thiophene derivative, epichlorohydrin, and phase transfer catalyst to a reaction vessel and mixes them under nitrogen protection to obtain a mixed reaction system; S2 heats the mixed reaction system to 70~110℃ and keeps it at that temperature for 5~10 hours. After the reaction is completed, the temperature is lowered, an alkaline substance is added to the system, and the reaction is continued to obtain the crude product. Further, after the reaction is completed, the system is cooled to 25~60℃, and an aqueous solution of an alkaline substance is added dropwise at a rate of 1~12mL / min. After the addition is completed, the reaction is kept at that temperature for 1~2 hours. S3 purifies the crude product to obtain a thiophene-based flame-retardant epoxy resin with a thiophene ring and sulfur element introduced into the molecular structure; further, the purification process includes separation and drying steps; the separation steps include vacuum filtration and solvent extraction, and the drying steps include dehydration with a desiccant, vacuum distillation, and drying in a vacuum drying oven; the desiccant is one or a combination of anhydrous sodium sulfate, anhydrous sodium carbonate, anhydrous potassium carbonate, anhydrous calcium chloride, anhydrous calcium sulfate, anhydrous calcium oxide, and anhydrous magnesium sulfate.

[0017] Please see Figure 2 The present invention provides an embodiment of a thiophene-based flame-retardant epoxy resin, which is prepared by any one of the preparation methods described in the above-mentioned embodiments of the preparation method of a thiophene-based flame-retardant epoxy resin. Figure 2 In this context, R represents either H or O atoms.

[0018] Furthermore, in another embodiment provided, a method for preparing a thiophene-based flame-retardant epoxy resin includes the following steps: 17.2 g of 2,5-thiophene dicarboxylic acid was added to a three-necked flask, followed by 92.56 g of epichlorohydrin and 1.75 g of tetrabutylammonium bromide. The mixture was stirred for 30 min at room temperature under nitrogen protection, then heated to 110 °C and maintained at this temperature for 6 h. The reaction temperature was then lowered to 40 °C, and 25 ml of 10 mol / L sodium hydroxide solution was slowly added dropwise at a rate of 1 ml / min using a peristaltic pump. The reaction was allowed to proceed for 2 h. After the reaction was complete, the mixture was washed four times with 200 ml of deionized water. The lower organic phase was collected, dried with anhydrous magnesium sulfate, and the solid was removed by vacuum filtration. Excess epichlorohydrin was then removed by vacuum distillation. The mixture was then vacuum dried in an 80 °C vacuum oven for 5 h. The resulting light yellow transparent liquid was the thiophene-based flame-retardant epoxy resin. Figure 3 As can be seen from the data, the epoxidized 2,5-thiophene dicarboxylic acid is located at 2795 cm⁻¹. -1 The characteristic peak of the carboxyl group at [location] disappears, and after epoxidation, it is located at 965 cm⁻¹. -1 The presence of characteristic peaks for epoxy functional groups indicates the successful preparation of 2,5-thiophene dicarboxylic acid epoxy resin, with a yield of approximately 93.8%. The molecular structure is shown below. Figure 4 As shown.

[0019] Furthermore, in another embodiment provided, a method for preparing a thiophene-based flame-retardant epoxy resin includes the following steps: 17.2 g of 2,5-thiophene dicarboxylic acid was added to a three-necked flask, followed by 102.37 g of epichlorohydrin and 1.9 g of tetrabutylammonium bromide. The mixture was stirred for 30 min at room temperature under nitrogen protection, then heated to 80 °C and maintained at this temperature for 10 h. The reaction temperature was then lowered to 60 °C, and 40 ml of sodium hydroxide solution (10 mol / L) was slowly added dropwise at a rate of 3 ml / min using a peristaltic pump. The reaction was allowed to proceed for 1 h. After the reaction was complete, the mixture was washed four times with 200 ml of deionized water. The lower organic phase was collected, dried with anhydrous magnesium sulfate, and the solid was removed by vacuum filtration. Excess epichlorohydrin was then removed by vacuum distillation. The mixture was then vacuum dried in an 80 °C vacuum drying oven for 5 h. The resulting light yellow transparent liquid was the thiophene-based flame-retardant epoxy resin, with a yield of approximately 92.2%.

[0020] Furthermore, in another embodiment provided, a method for preparing a thiophene-based flame-retardant epoxy resin includes the following steps: 14.4 g of thiophene-2,5-dimethyldiethanol was added to a three-necked flask, followed by 92.36 g of epichlorohydrin and 1.75 g of tetrabutylammonium bromide. The mixture was stirred for 30 min at room temperature and under nitrogen protection, then heated to 70 °C and maintained at this temperature for 10 h. The reaction temperature was then lowered to 60 °C, and 25 ml of sodium hydroxide solution (10 mol / L) was slowly added dropwise at a rate of 5 ml / min using a peristaltic pump. The reaction was allowed to proceed for 1 h. After the reaction was complete, the mixture was washed four times with 200 ml of deionized water. The lower organic phase was collected, dried with anhydrous magnesium sulfate, and the solid was removed by vacuum filtration. Excess epichlorohydrin was then removed by vacuum distillation. The mixture was then vacuum dried in a vacuum drying oven at 80 °C for 5 h. The resulting light yellow transparent liquid was the thiophene-based flame-retardant epoxy resin, with a yield of approximately 95.2%.

[0021] Furthermore, in another embodiment provided, a method for preparing a thiophene-based flame-retardant epoxy resin includes the following steps: 14.4 g of thiophene-2,5-dimethyldiethanol was added to a three-necked flask, followed by 110.39 g of epichlorohydrin and 2 g of tetrabutylammonium bromide. The mixture was stirred for 30 min at room temperature under nitrogen protection, then heated to 110 °C and maintained at this temperature for 5 h. The reaction temperature was then lowered to 25 °C, and 40 ml of sodium hydroxide solution (10 mol / L) was slowly added dropwise at a rate of 7 ml / min using a peristaltic pump. The reaction was allowed to proceed for 2 h. After the reaction was complete, the mixture was washed four times with 200 ml of deionized water. The lower organic phase was collected, dried with anhydrous magnesium sulfate, and the solid was removed by vacuum filtration. Excess epichlorohydrin was then removed by vacuum distillation. The mixture was then vacuum dried in a vacuum drying oven at 80 °C for 5 h. The resulting light yellow transparent liquid was the thiophene-based flame-retardant epoxy resin, with a yield of approximately 93.3%.

[0022] Furthermore, a comparative example is provided: 100g of E51 epoxy resin and 25g of 4,4'-diaminodiphenylmethane (DDM) were melt-mixed uniformly at 100℃, cured at 120℃ for 2 hours, and then cured at 150℃ for 2 hours to obtain the cured epoxy compound, named DGEBA. According to standard ASTM D3801-20, the UL-94 test result for this cured compound showed no rating. The flame retardant properties of DGEBA epoxy resin were tested using a cone calorimeter under a radiation intensity of 35kW / m². Figure 6-8 The peak heat release rate (HRR), total heat release (THR), and total smoke production (TSP) of DGEBA epoxy resin are 1085.54 kW / m2, 133.24 MJ / m2, and 25.14 m2, respectively. These results indicate that E51 epoxy resin is prone to combustion and generates a large amount of heat and toxic and harmful smoke during combustion.

[0023] Furthermore, in another embodiment provided: 100g of the successfully synthesized thiophene-based epoxy resin was mixed with DDM at a mass ratio of 100:35, cured at 120℃ for 2h, and then cured at 150℃ for 2h to obtain the epoxy cured product, named DGET; the UL94 rating of this epoxy resin system was measured to be V0 according to the standard ASTMD3801-20. Depend on Figure 5 It can be seen that the tensile strength of the thiophene-based flame-retardant epoxy resin DGET is increased by approximately 33.9% and the tensile strain is increased by approximately 278.5% compared to DGEBA; this indicates that the thiophene-based flame-retardant epoxy resin system has superior mechanical properties; Figure 6-8 It can be seen that the heat release rate (HRR), total heat release (THR), and total smoke production (TSP) of EP / DVEP-20 with the addition of intrinsic flame-retardant epoxy resin are 453.7 kW / m2, 68.1 MJ / m2, and 10.8 m2, respectively, which are reduced by 57.8%, 48.8%, and 53.9% respectively; this indicates that the system with the addition of intrinsic flame-retardant epoxy resin has better flame-retardant properties.

[0024] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a thiophene-based flame-retardant epoxy resin, characterized in that: The preparation method uses thiophene derivatives, epichlorohydrin, a phase transfer catalyst, and an alkaline substance as initial raw materials; wherein the molar ratio of the thiophene derivative, epichlorohydrin, phase transfer catalyst, and alkaline substance is 0.8~1.2:5~25:0.05~0.15:2.5~5; the method includes the following steps: S1 adds thiophene derivative, epichlorohydrin, and phase transfer catalyst to a reaction vessel and mixes them under nitrogen protection to obtain a mixed reaction system; S2 heats the mixed reaction system to 70~110℃, holds the temperature for 5~10 hours, cools down after the reaction is complete, adds an alkaline substance to the system, and continues the reaction to obtain the crude product; S3 purified the crude product to obtain a thiophene-based flame-retardant epoxy resin with a thiophene ring and sulfur element introduced into the molecular structure.

2. The method for preparing a thiophene-based flame-retardant epoxy resin according to claim 1, characterized in that: The thiophene derivative is either 2,5-thiophene dicarboxylic acid or thiophene-2,5-dimethyldiethanol.

3. The method for preparing a thiophene-based flame-retardant epoxy resin according to claim 1, characterized in that: The phase transfer catalyst is one or more combinations of quaternary ammonium salts, polyethers, and quaternary phosphine salts.

4. The method for preparing a thiophene-based flame-retardant epoxy resin according to claim 3, characterized in that: The quaternary ammonium salt is one or more of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, and tetradecyltrimethylammonium chloride; the polyether is chain polyethylene glycol; and the quaternary phosphine salt is one or more of tetraphenylphosphine chloride and triphenylphosphine.

5. The method for preparing a thiophene-based flame-retardant epoxy resin according to claim 1, characterized in that: The alkaline substance is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and sodium bicarbonate; the alkaline substance is added in the form of an aqueous solution with a concentration of 10 mol / L.

6. The method for preparing a thiophene-based flame-retardant epoxy resin according to claim 1, characterized in that: In step S2, after the heat preservation reaction is completed, the system is cooled to 25~60℃, and an alkaline aqueous solution is added dropwise at a rate of 1~12mL / min. After the addition is completed, the heat preservation reaction continues for 1~2 hours.

7. The method for preparing a thiophene-based flame-retardant epoxy resin according to claim 1, characterized in that: In step S3, the purification process includes a separation step and a drying step; the separation step includes vacuum filtration and solvent extraction, and the drying step includes dehydration with a desiccant, vacuum distillation, and drying in a vacuum drying oven.

8. The method for preparing a thiophene-based flame-retardant epoxy resin according to claim 7, characterized in that: The desiccant is one or a combination of anhydrous sodium sulfate, anhydrous sodium carbonate, anhydrous potassium carbonate, anhydrous calcium chloride, anhydrous calcium sulfate, anhydrous calcium oxide, and anhydrous magnesium sulfate.

9. A thiophene-based flame-retardant epoxy resin, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

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