Preparation method and application of low-cost symmetric imine type epoxy resin

Abstract

The application discloses a low-cost symmetric imine type epoxy resin preparation method and application, belongs to the field of material science and technology, and uses beta-resorcylic acid and p-phenylenediamine which are widely applied in the field of organic synthesis as raw materials. A low-cost symmetric imine type epoxy resin is prepared by firstly condensing aldehyde amine to generate a double imine tetraphenol precursor containing a highly symmetric structure and then reacting with epichlorohydrin to close a ring. The raw material cost of the reaction is low, a more simple and efficient preparation process is adopted to reduce the complexity of the synthesis process, and various curing agents are selected in the subsequent curing process to provide more diverse epoxy resin structures. The epoxy resin has high strength, high elastic modulus and good insulation after curing, and the cost is much lower than that of special imine epoxy resins containing a sulfonyl group and a heterocyclic ring. The epoxy resin can be widely applied in the fields of high-performance structural composites, industrial anticorrosive coatings and low-cost electronic potting, and solves the technical problems of high cost and poor universality of existing imine epoxy resins.

Description

Technical Field

[0001] This invention belongs to the field of materials science and technology, and relates to a low-cost method for preparing symmetrical imine epoxy resin and its application. Background Technology

[0002] Epoxy resin, as a thermosetting polymer material with excellent comprehensive properties, is widely used in key fields such as high-performance structural composite materials, industrial anti-corrosion coatings, electronic device potting, rail transportation, and aerospace, thanks to its good mechanical strength, adhesion, processability, and chemical stability. As downstream applications increasingly demand lightweight, high-reliability, and low-cost materials, more stringent requirements are being placed on the mechanical properties, structural rigidity, production economy, and process adaptability of epoxy resin.

[0003] In recent years, to improve the heat resistance and mechanical properties of epoxy resins, the field has often used imine bonds to construct an aromatic rigid framework in the molecular backbone to prepare imine-modified epoxy resins. These resins, through the conjugated structure of the imine bonds and the rigidity of the aromatic rings, can effectively improve the glass transition temperature, tensile strength, and modulus, demonstrating significant advantages in the field of high-performance materials.

[0004] However, existing imine-type epoxy resin technologies generally suffer from the following technical drawbacks: First, the aromatic diamine monomers used in the existing technologies for synthesizing imine precursors mostly involve long synthesis routes and are expensive, directly leading to high raw material costs for epoxy resins and limiting their application in general-purpose high-performance structural materials and large-scale industrial coatings. Second, most reported imine-type epoxy resins use asymmetric diamines as raw materials, resulting in resin molecules with poor symmetry and loose packing, making it difficult to form a highly ordered condensed structure. This leads to poor mechanical properties of the cured product, failing to meet the long-term service requirements of high-strength structural components. Finally, the synthesis process is complex and difficult to industrialize. Existing imine epoxy precursors often suffer from poor reaction selectivity, low product solubility, and cumbersome purification steps, requiring the use of high-boiling-point special solvents and complex post-processing. This not only increases production energy consumption and processes but also easily causes solvent residues and a decrease in product purity, affecting batch stability and curing performance.

[0005] p-Phenylenediamine (PDA), as the simplest symmetrical aromatic diamine, is characterized by readily available raw materials, low price, high molecular symmetry, and moderate reactivity. It can undergo a highly selective condensation reaction with β-resol, ultimately forming a centrosymmetric, highly regular diimide epoxy resin through a series of reactions. The symmetrical rigid skeleton endows the resin with excellent mechanical strength and heat resistance, while significantly reducing raw material and process costs. Summary of the Invention

[0006] To address the technical problems of expensive raw materials, asymmetrical structure, insufficient mechanical properties, and high difficulty in industrialization of existing imine-type epoxy resins, this invention provides a symmetrical imine-type epoxy resin precursor, epoxy resin, and preparation method that are structurally regular, use inexpensive raw materials, and are easy to prepare, achieving a synergistic balance between high rigidity, high strength, and low cost.

[0007] To achieve the above objectives, the present invention employs the following technical solution: Firstly, this invention provides a low-cost method for preparing symmetrical imine-type epoxy resin, the steps of which are as follows: (1) Mix β-resolaldehyde and p-phenylenediamine at a molar ratio of 1:(0.48-0.5) and add a solvent at a molar ratio of 1:(10-20) to β-resolaldehyde. React for 3-10 minutes in a microwave environment of 800-1000W and 50-80℃. Monitor the reaction by thin-layer chromatography. After the reaction is complete, cool the system to room temperature and concentrate it. After the solid precipitates, filter it to obtain a low-cost symmetrical imine-type aromatic tetraphenol precursor. (2) The symmetrical aromatic tetraphenol precursor based on dual dynamic imine bonds prepared in step (1) and epichlorohydrin are mixed in a molar ratio of 1:(14-20), and a phase transfer catalyst with a molar ratio of 1:(0.05-0.15) to the tetraphenol precursor is added. The mixture is stirred continuously at 70-100℃ under N2 atmosphere for 1-2 hours. After adding 25wt.% NaOH solution to the system, the reaction is continued for 2-3 hours, wherein the molar ratio of tetraphenol precursor to NaOH is 1:(2-3). The reaction is monitored by thin-layer chromatography. After the reaction is complete, the system is cooled to room temperature, deionized water is added, and the mixture is extracted with an organic solvent. The organic phase is then washed with water and saturated brine, dried with anhydrous MgSO4, filtered and concentrated to obtain the low-cost symmetrical imine epoxy resin precursor. (3) After uniformly mixing the low-cost symmetrical imine epoxy resin precursor prepared in step (2) with the curing agent and vacuum degassing, the resin is poured into a mold and thermoset to obtain low-cost symmetrical imine epoxy resin.

[0008] Preferably, the solvent in step (1) is glacial acetic acid.

[0009] Preferably, the phase transfer catalyst in step (2) includes benzyltriethylammonium chloride, benzyltrimethylammonium chloride, tetramethylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride or tetrabutylammonium hydrogen sulfate.

[0010] Preferably, the phase transfer catalyst in step (2) includes benzyltriethylammonium chloride, benzyltrimethylammonium chloride, tetramethylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride or tetrabutylammonium hydrogen sulfate.

[0011] Preferably, the organic solvent used for extraction in step (2) includes dichloromethane, chloroform, 1,2-dichloroethane, toluene, and ethyl acetate.

[0012] Preferably, the curing agent in step (3) is a polyamine. Under the condition of 80-100℃, the epoxy curing agent is added to the epoxy resin, mixed evenly and vacuum degassed, poured into the mold and kept at 100-120℃ for 1-3 hours, then kept at 120-140℃ for 1-3 hours, then kept at 140-160℃ for 1-3 hours, and finally cured at 160-200℃ for 1-4 hours.

[0013] On the other hand, the present invention provides a low-cost symmetrical imine epoxy resin having the following structure: The cured epoxy resin has a Young's modulus of approximately 2158 MPa, while maintaining a low and stable dielectric constant and dielectric loss, ranging from 3.71 to 3.86 and 0.01 to 0.025, respectively; the AC breakdown field strength at room temperature is 75.64 kV / mm. -1 .

[0014] Finally, this invention provides an application of a low-cost symmetrical imine epoxy resin, characterized in that it is applied in the fields of high-performance structural composite materials, industrial anti-corrosion coatings, and low-cost electronic potting.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses β-resolaldehyde and p-phenylenediamine, which are widely used in the field of organic synthesis, as raw materials to generate a tetraphenol precursor containing an imine bond in a microwave environment. Then, it reacts with epichlorohydrin to close the ring and prepare a low-cost symmetrical imine epoxy resin. Compared with the existing synthesis methods, the experimental operation and post-processing are simpler and more efficient. At the same time, a variety of polyamines are selected as curing agents in the subsequent curing process, providing epoxy resin final products with more diverse structures.

[0016] (2) The present invention provides a low-cost method for preparing a symmetrical imine-type epoxy resin. The cured epoxy resin has a maximum Young's modulus of approximately 2158 MPa, while maintaining a low and stable dielectric constant and dielectric loss, which are between 3.71 and 3.86 and 0.01 and 0.025, respectively. The maximum AC breakdown field strength at room temperature is 77.4 KV / mm. -1 It possesses excellent rigidity and insulation properties, and can be widely used in high-performance structural composite materials, industrial anti-corrosion coatings, low-cost electronic potting, and other fields. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope.

[0018] Figure 1 The 1H NMR spectra of the imine-bonded epoxy resin tetraphenol precursors prepared in different embodiments 1 H-NMR; Figure 2 Carbon NMR spectra of imine-bonded epoxy resin tetraphenol precursors prepared in different embodiments 13 C-NMR; Figure 3 Tensile strength diagrams of the low-cost symmetrical imine epoxy resin (Example 1 and Comparative Example 1). Figure 4 The graph shows the relative permittivity of the low-cost symmetrical imine epoxy resin as a function of frequency (Example 1 and Comparative Example 1). Figure 5 The dielectric loss of this low-cost symmetrical imine epoxy resin varies with frequency (Example 1 and Comparative Example 1). Figure 6 The breakdown field strength diagrams of this low-cost symmetrical imine epoxy resin (Example 1 and Comparative Example 1). Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on this embodiment, a low-cost symmetrical imine epoxy resin preparation method and the positional relationship of the various components are described in detail.

[0023] A low-cost method for preparing symmetrical imine-type epoxy resin, comprising the following steps: (1) Mix β-resolaldehyde and p-phenylenediamine at a molar ratio of 1:(0.48-0.5) and add a solvent at a molar ratio of 1:(10-20) to β-resolaldehyde. React for 3-10 minutes in a microwave environment of 800-1000W and 50-80℃. Monitor the reaction by thin-layer chromatography. After the reaction is complete, cool the system to room temperature and concentrate it. After the solid precipitates, filter it to obtain a low-cost symmetrical imine-type aromatic tetraphenol precursor. (2) The symmetrical aromatic tetraphenol precursor based on dual dynamic imine bonds prepared in step (1) and epichlorohydrin are mixed in a molar ratio of 1:(14-20), and a phase transfer catalyst with a molar ratio of 1:(0.05-0.15) to the tetraphenol precursor is added. The mixture is stirred continuously at 70-100℃ under N2 atmosphere for 1-2 hours. After adding 25wt.% NaOH solution to the system, the reaction is continued for 2-3 hours, wherein the molar ratio of tetraphenol precursor to NaOH is 1:(2-3). The reaction is monitored by thin-layer chromatography. After the reaction is complete, the system is cooled to room temperature, deionized water is added, and the mixture is extracted with an organic solvent. The organic phase is then washed with water and saturated brine, dried with anhydrous MgSO4, filtered and concentrated to obtain the low-cost symmetrical imine epoxy resin precursor. (3) After uniformly mixing the low-cost symmetrical imine epoxy resin precursor prepared in step (2) with the curing agent and vacuum degassing, the resin is poured into a mold and thermoset to obtain low-cost symmetrical imine epoxy resin.

[0024] Further specifying, the solvent in step (1) is glacial acetic acid.

[0025] Further specifying, the phase transfer catalyst in step (2) includes benzyltriethylammonium chloride, benzyltrimethylammonium chloride, tetramethylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride or tetrabutylammonium hydrogen sulfate.

[0026] Further specifying, the phase transfer catalyst in step (2) includes benzyltriethylammonium chloride, benzyltrimethylammonium chloride, tetramethylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride or tetrabutylammonium hydrogen sulfate.

[0027] Further specifying, the organic solvents used for extraction in step (2) include dichloromethane, chloroform, 1,2-dichloroethane, toluene, and ethyl acetate.

[0028] Further specifying, the curing agent in step (3) is a polyamine. Under the condition of 80-100℃, the epoxy curing agent is added to the epoxy resin, mixed evenly and vacuum degassed, poured into the mold and kept at 100-120℃ for 1-3 hours, then kept at 120-140℃ for 1-3 hours, then kept at 140-160℃ for 1-3 hours, and finally cured at 160-200℃ for 1-4 hours.

[0029] The above method can be implemented in the following specific ways: Example 1 (1) Synthesis of symmetrical imine-type epoxy resin DHB-PDA tetraphenol precursor: 2.8 g β-resolaldehyde, 1.08 g p-phenylenediamine and 5 ml glacial acetic acid were successively added to a three-necked flask. Under a nitrogen atmosphere, the mixture was placed in a microwave environment at 1000 W and 75 °C for 15 minutes. The reaction was monitored by thin-layer chromatography. After the starting materials disappeared, the system was cooled to room temperature, and excess solvent was removed by rotary evaporation. After the solid precipitated, it was filtered and washed several times with anhydrous ethanol. Then, it was dried in a high-temperature forced-air oven to obtain the symmetrical imine-type epoxy resin tetraphenol precursor.

[0030] (2) Synthesis of symmetrical imine-type epoxy resin DHB-PDA-EP: 3.48 g of symmetrical imine-type epoxy resin tetraphenol precursor, 30 ml of cyclochloropropane, and 0.348 g of benzyltriethylammonium chloride were successively added to a three-necked flask. Under a nitrogen atmosphere, the mixture was heated to 80 °C and reacted for 1 hour. Then, 0.8 g of sodium hydroxide was prepared into a 25 wt.% sodium hydroxide methanol solution, which was added dropwise to the reaction system, and the reaction was continued for 2 hours. The reaction was monitored by thin-layer chromatography. After the starting material disappeared, the system was cooled to room temperature, deionized water was added, and the mixture was extracted with an organic solvent. The organic phase was then washed with water and saturated brine, dried with anhydrous MgSO4, filtered, and concentrated to obtain the symmetrical imine-type epoxy resin precursor.

[0031] (3) Curing of symmetrical imine epoxy resin DHB-PDA-EP: Take 5g of symmetrical imine epoxy resin precursor and mix it evenly with 2.4g of curing agent 4,4'-diaminodiphenyl sulfone (DDS). Place the mixture in a vacuum oven at 100℃ to remove bubbles under reduced pressure until no bubbles are generated. Pour the mixture into a mold and cure it according to the following curing procedure: 120℃ / 2h + 140℃ / 2h + 160℃ / 2h + 180℃ / 2h. The properties of the cured epoxy resin are as follows: Young's modulus is about 2158MPa, while maintaining a low and stable dielectric constant and dielectric loss, which are between 3.71-3.86 and 0.01-0.025, respectively; the AC breakdown field strength at room temperature is 75.64KV / mm. -1 .

[0032] Example 2 Unlike Example 1, in (3), 4,4'-diaminodiphenylmethane and the symmetrical imine epoxy resin precursor were mixed uniformly at a molar ratio of epoxy:NH = 1:1. The mixture was placed in an 85°C vacuum oven for degassing until no bubbles were generated. The mixture was then poured into a mold and cured according to the following curing procedure: 105°C / 2h + 125°C / 2h + 145°C / 2h + 175°C / 2h. The properties of the cured symmetrical imine epoxy resin were as follows: the Young's modulus of the cured epoxy resin was approximately 1985 MPa, while maintaining a low and stable dielectric constant and dielectric loss, which were between 3.75-3.91 and 0.01-0.025, respectively; the AC breakdown field strength at room temperature was 77.4 KV / mm. -1 .

[0033] Example 3 Unlike Example 1, in (3), 4,4'-diaminodiphenyl ether and the symmetrical imine epoxy resin precursor were mixed uniformly at a molar ratio of epoxy:NH=1:1. The mixture was placed in an 85°C vacuum oven for degassing until no bubbles were generated. The mixture was then poured into a mold and cured according to the following curing procedure: 105°C / 2h + 120°C / 2h + 140°C / 2h + 165°C / 2h. The properties of the cured symmetrical imine epoxy resin were as follows: Young's modulus was approximately 1820 MPa, while maintaining a low and stable dielectric constant and dielectric loss, which were between 3.70-3.89 and 0.01-0.03, respectively; the AC breakdown field strength at room temperature was 68.5 KV / mm. -1 .

[0034] Example 4 Unlike Example 1, in (3), isophorone diamine and the symmetrical imine epoxy resin precursor were mixed uniformly at a molar ratio of epoxy:NH=1:1. The mixture was placed in an 85°C vacuum oven for degassing until no bubbles were generated. The mixture was then poured into a mold and cured according to the following curing procedure: 105°C / 2h + 120°C / 2h + 140°C / 2h + 165°C / 2h. The properties of the cured symmetrical imine epoxy resin were as follows: Young's modulus was approximately 1420 MPa, while maintaining a low and stable dielectric constant and dielectric loss, which were between 3.79-3.95 and 0.01-0.03, respectively; the AC breakdown field strength at room temperature was 60.2 KV / mm. -1 .

[0035] Comparative Example 1 5g of DGEBA epoxy resin precursor and 1.55g of curing agent 4,4'-diaminodiphenyl sulfone were mixed evenly. The mixture was then placed in a vacuum oven at 100℃ for degassing until no bubbles were generated. The mixture was then poured into a mold and cured according to the following curing procedure: 120℃ / 2h + 150℃ / 2h + 180℃ / 2h. The properties of the cured epoxy resin were as follows: Young's modulus of approximately 935MPa, dielectric constant and dielectric loss between 3.9-4.4 and 0.005-0.012, respectively; and AC breakdown field strength at room temperature of 65.16KV / mm. -1 .

[0036] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-cost method for preparing symmetrical imine-type epoxy resin, characterized in that, The steps are as follows: (1) Mix β-resolaldehyde and p-phenylenediamine at a molar ratio of 1:(0.48-0.5) and add a solvent at a molar ratio of 1:(10-20) to β-resolaldehyde. React for 3-10 minutes in a microwave environment of 800-1000W and 50-80℃. Monitor the reaction by thin-layer chromatography. After the reaction is complete, cool the system to room temperature and concentrate it. After the solid precipitates, filter it to obtain a low-cost symmetrical imine-type aromatic tetraphenol precursor. (2) The symmetrical aromatic tetraphenol precursor based on dual dynamic imine bonds prepared in step (1) and epichlorohydrin are mixed in a molar ratio of 1:(14-20), and a phase transfer catalyst with a molar ratio of 1:(0.05-0.15) to the tetraphenol precursor is added. The mixture is stirred continuously at 70-100℃ under N2 atmosphere for 1-2 hours. After adding 25wt.% NaOH solution to the system, the reaction is continued for 2-3 hours, wherein the molar ratio of tetraphenol precursor to NaOH is 1:(2-3). The reaction is monitored by thin-layer chromatography. After the reaction is complete, the system is cooled to room temperature, deionized water is added, and the mixture is extracted with an organic solvent. The organic phase is then washed with water and saturated brine, dried with anhydrous MgSO4, filtered and concentrated to obtain the low-cost symmetrical imine epoxy resin precursor. (3) After uniformly mixing the low-cost symmetrical imine epoxy resin precursor prepared in step (2) with the curing agent and vacuum degassing, the resin is poured into a mold and thermoset to obtain low-cost symmetrical imine epoxy resin.

2. The method for preparing low-cost symmetrical imine-type epoxy resin according to claim 1, characterized in that, The solvent in step (1) is glacial acetic acid.

3. The method for preparing low-cost symmetrical imine-type epoxy resin according to claim 1, characterized in that, The phase transfer catalyst in step (2) includes benzyltriethylammonium chloride, benzyltrimethylammonium chloride, tetramethylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride or tetrabutylammonium hydrogen sulfate.

4. The method for preparing low-cost symmetrical imine-type epoxy resin according to claim 1, characterized in that, The phase transfer catalyst in step (2) includes benzyltriethylammonium chloride, benzyltrimethylammonium chloride, tetramethylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride or tetrabutylammonium hydrogen sulfate.

5. The method for preparing low-cost symmetrical imine-type epoxy resin according to claim 1, characterized in that, The organic solvents used for extraction in step (2) include dichloromethane, chloroform, 1,2-dichloroethane, toluene, and ethyl acetate.

6. The method for preparing low-cost symmetrical imine-type epoxy resin according to claim 1, characterized in that, The curing agent in step (3) is a polyamine. Under the condition of 80-100℃, the epoxy curing agent is added to the epoxy resin, mixed evenly and vacuum degassed, poured into the mold and kept at 100-120℃ for 1-3 hours, then kept at 120-140℃ for 1-3 hours, then kept at 140-160℃ for 1-3 hours, and finally cured at 160-200℃ for 1-4 hours.

7. A low-cost symmetrical imine-type epoxy resin prepared by the preparation method according to any one of claims 1-6, characterized in that, This symmetrical imine-type epoxy resin has the following structure: The cured epoxy resin has a Young's modulus of approximately 2158 MPa, while maintaining a low and stable dielectric constant and dielectric loss, ranging from 3.71 to 3.86 and 0.01 to 0.025, respectively; the AC breakdown field strength at room temperature is 75.64 kV / mm. -1 .

8. An application of the low-cost symmetrical imine epoxy resin according to claim 7, characterized in that, It is applied in fields such as high-performance structural composite materials, industrial anti-corrosion coatings, and low-cost electronic potting.

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