Polyimide resin containing epoxy group on side chain, polyimide adhesive and preparation method thereof

Abstract

The invention belongs to the field of advanced functional materials, and particularly relates to polyimide resin with a side chain containing an epoxy group, a polyimide adhesive and a preparation method of the polyimide adhesive. The adhesive is composed of polyimide resin with a side chain containing an epoxy group, polysiloxane, a polyphenol compound and a Lewis alkali substance. Wherein the epoxy group-containing polyimide resin is synthesized by oxidizing unsaturated double bonds in a polyimide molecular chain through peracetic acid or hydrogen peroxide. Under the catalysis of Lewis base, an epoxy group is subjected to ring opening and is quickly subjected to cross-linking reaction with phenolic hydroxyl at 80-130 DEG C, and a cured product contains a large number of ether bonds, hydroxyl and hydrogen bonds, so that the adhesion of the cured product can be effectively improved; meanwhile, a polyimide cross-linked network and polysiloxane form a semi-interpenetrating network structure, so that the impact toughness of the cured resin can be improved. The adhesive has the characteristics of low curing temperature, strong adhesive force, excellent mechanical properties and the like, and has wide application prospects in the fields of chip packaging, aerospace, electronics and electrics, composite materials and the like.

Description

Technical Field

[0001] This application belongs to the field of advanced functional materials, and specifically relates to a polyimide resin with epoxy groups in its side chain, a polyimide adhesive, and a method for preparing the same. Background Technology

[0002] Polyimide (PI) adhesives are a class of high-performance polymer materials containing imide ring structures. Due to their outstanding high-temperature resistance, excellent dimensional stability, good physical and chemical stability, and superior dielectric and adhesive properties, they have become an important component in the field of high-performance adhesives. These properties enable polyimide adhesives to play an irreplaceable role in high-tech fields such as aerospace, electronics, and composite materials. With the advancement of science and technology and the increasing demand for high-temperature stability, significant progress has been made in the research and application of high-temperature resistant polyimide adhesives.

[0003] Traditional polyimide adhesives typically introduce unsaturated units, such as maleimide, phenylcyclobutene, norbornene, ethynyl, or phenylethynyl groups, and utilize the thermal crosslinking reaction of these active groups to form a three-dimensional crosslinked network, thereby imparting excellent adhesive properties. However, the crosslinking and curing reaction temperatures of these active functional groups are high (250 ℃-400 ℃), and the curing reaction time is long, which greatly limits the application of this type of adhesive in microelectronics, chip packaging, and other fields. In addition, the cured products contain a large number of aromatic units such as benzene rings and imide rings, resulting in high rigidity, high brittleness, and poor impact resistance. To solve these problems, methods such as molecular structure design (e.g., introducing flexible segments) or catalytic low-temperature curing reaction mechanisms have been gradually developed. For example, the invention patent with application number CN202411150177.X discloses a method for catalyzing the low-temperature imidization reaction of polyimide adhesives by adding catalysts such as N-N' carbonyl diimidazole (CDI), 6-aminoquinoline (AQL), ​​and benzotriazole (BTA), but does not mention the method for controlling the crosslinking reaction of the adhesive; the invention patent with application number CN200880114990.4 discloses a method for achieving low-temperature curing of polyimide adhesives by introducing acrylic unsaturated units and catalysts, but the introduction of a large number of flexible acrylic structural units will impair the excellent adhesion and heat resistance stability of the material itself. To address the problem of high brittleness in traditional polyimide adhesives, invention patent application number CN201010621313.0 discloses a method for synergistically toughening a thermosetting adhesive mixture of polyimide and epoxy resin by adding SiO2, Al(OH)3 and rubber elastomer. However, this method faces challenges in ensuring uniform dispersion of inorganic nanoparticles in the matrix and compatibility between the rubber elastomer and the resin matrix.

[0004] Therefore, the key prerequisite for expanding the application of such materials and meeting the increasingly demanding needs of different fields is to develop novel adhesives that combine low-temperature curing properties, excellent adhesion, good toughness, and adaptability to various substrate surfaces through macromolecular structure design and multiple action mechanisms. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a polyimide mixture adhesive that has the advantages of low-temperature curing, high bonding strength, good toughness and excellent performance, and can be used on a variety of substrates.

[0006] In one aspect, a polyimide resin with epoxy groups in its side chains is obtained by condensing a dianhydride monomer with a carboxylic acid-containing aromatic diamine monomer, followed by a grafting reaction with a hydroxyl compound containing a double bond, and finally epoxidizing the double bond with an oxidant.

[0007] The dianhydride monomer is selected from one or more of the following: 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), hexafluorodianhydride (6FDA), bisphenol A type diether dianhydride (BPADA), 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride (DSDA), and cyclobutane tetracarboxylic dianhydride (CBDA); The carboxylic acid-containing aromatic diamine monomer is selected from one or more combinations of 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and 3,5-diaminobenzoic acid; The hydroxyl group in the hydroxyl compound containing the double bond is a primary hydroxyl group, and the hydroxyl group is located on the α-carbon or β-carbon of the double bond; Preferably, the hydroxyl compound containing a double bond further comprises at least one aromatic ring; More preferably, the hydroxyl compound containing a double bond is selected from cinnamyl alcohol; Preferably, the oxidant is selected from peracetic acid or hydrogen peroxide.

[0008] Preferably, the grafting reaction is an esterification reaction between hydroxyl groups and carboxyl groups in a carboxylic acid aromatic diamine monomer.

[0009] Furthermore, the preparation method of polyimide resin with epoxy groups in the side chain specifically includes the following steps: S1. Dissolve dianhydride and diamine monomer in a polar aprotic solvent, stir evenly at room temperature, and then heat to react, thereby synthesizing a polyimide solution; S2. After the polyimide solution prepared in step S1 is cooled to room temperature, a dehydrating agent and a hydroxyl compound containing double bonds are added to the reaction solution and stirred at room temperature. After the reaction is completed, an alcohol solvent is poured in to precipitate the product, which is then crushed and filtered to obtain a solid product. S3. Dissolve the solid product synthesized in step S2 in a polar aprotic solvent, and add an oxidant to the solution to react at room temperature; after the reaction is complete, remove the solvent and oxidant by rotary evaporation to obtain a polyimide resin containing epoxy groups.

[0010] Preferably, step S1 involves stirring and heating the reaction under nitrogen or inert gas protection. Preferably, step S1 involves stirring at room temperature for 12-24 hours; Preferably, in step S1, the temperature is raised to 180-200°C and the reaction is carried out for 12-18 hours; Preferably, the total mass fraction of dianhydride and diamine monomers in step S1 is (10-25) wt%. Preferably, in step S1, the molar ratio of dianhydride to diamine monomer is (1.1-1):1; Preferably, the polar aprotic solvent in step S1 is selected from any one of N-methylpyrrolidone, N-vinyl-2-pyrrolidone, or hexamethylphosphoric triamine; Preferably, the dehydrating agent in step S2 is selected from N,N'-diisopropylcarbodiimide; Preferably, the reaction in step S2 is carried out under nitrogen or inert gas protection and in the dark. Preferably, the reaction time for step S2 is 4-8 hours; Preferably, the solid product of step S2 is dried in a vacuum oven at 100 °C for 12 hours to obtain light yellow granules; Preferably, in step S2, the dehydrating agent and the hydroxyl compound containing double bonds each account for (10-15) wt% of the solid matter. Preferably, the alcohol solvent in step S2 is selected from either methanol or ethanol; Preferably, the reaction time for step S3 is 4-8 hours; Preferably, the polar aprotic solvent in step S3 is selected from any one of N,N-dimethylformamide or N,N-dimethylacetamide; Preferably, in step S3, the molar ratio of oxidant to polyimide resin is (1.5-1):1.

[0011] Secondly, the application of the polyimide resins with epoxy groups in the side chains described above in the preparation of adhesives.

[0012] Thirdly, a polyimide adhesive comprises: the polyimide resin with epoxy groups in its side chains as described above, a polymer containing polysiloxane segments, a polyphenolic compound containing at least two phenolic hydroxyl groups, a Lewis base compound, and a solvent. The polymer containing polysiloxane segments is selected from one or more combinations of: polydimethylsiloxane, polysiloxane-15, poly(dimethylsiloxane-co-methylphenylsiloxane), poly[dimethylsiloxane-co-(3-aminopropyl)methylsiloxane] and poly(dimethylsiloxane-co-diphenylsiloxane); The polyphenolic compound containing at least two phenolic hydroxyl groups is selected from one or more combinations of tannic acid, quercetin, apigenin, resveratrol, kaempferol, rosin, dopamine, or polydopamine; The Lewis base compound is selected from one or more combinations of benzotriazole, pyrazole, isoquinoline, quinoline, pyridine, benzimidazole, imidazole, 2-methylimidazolium, piperazine, triethylamine, piperidine, and 2,6-dimethylpiperidine; The solvents include: polar aprotic solvents and low-boiling-point solvents with a boiling point not exceeding 130°C; The polar aprotic solvent is selected from one or a combination of two of N,N-dimethylformamide or N,N-dimethylacetamide; Low-boiling-point solvents with a boiling point not exceeding 130℃ are selected from one or more combinations of solvents such as toluene, tetrahydrofuran, ethanol, methanol, acetone, ethyl acetate, isopropanol, n-butanol, and butyl acetate. Preferably, the low-boiling-point solvent with a boiling point not exceeding 130°C accounts for (10-40)% of the total solvent volume. Furthermore, by mass fraction, the polyimide resin containing epoxy groups in the side chain accounts for (50-70) wt% of the total solid mass, the polymer containing polysiloxane segments accounts for (10-25) wt% of the solid mass, the polyphenolic compound containing at least two phenolic hydroxyl groups accounts for (10-20) wt% of the solid mass, and the Lewis base compound accounts for (5-10) wt% of the solid mass. Preferably, the total mass fraction of solids in the polyimide adhesive composition is (15-30) wt%.

[0013] Fourthly, the preparation method of the polyimide adhesive described above includes: dissolving the polyimide resin with epoxy groups in the side chain, the polymer containing polysiloxane segments, the polyphenol compound containing at least two phenolic hydroxyl groups, and the Lewis base compound in a solvent and mixing them evenly, and then obtaining the polyimide adhesive by degassing and filtration.

[0014] Fifthly, a cured product is obtained by curing the polyimide adhesive described above at 80-130°C.

[0015] Sixthly, the above-mentioned polyimide adhesives are used for bonding between organic polymer materials, inorganic non-metallic materials and metallic materials.

[0016] Preferably, the organic polymer material is selected from polyimide, the inorganic non-metallic material is selected from glass, and the metallic material is selected from copper.

[0017] The beneficial effects of the technical solution in this application are: 1. This invention synthesizes polyimides with unsaturated double bond units in the side chains, and synthesizes polyimide resins with epoxy side groups through the oxidation reaction of unsaturated double bonds. This provides active sites for the low-temperature crosslinking reaction of polyimides and solves the compatibility problem existing in traditional physical blending methods. At the same time, the main chain of the polyimide resin still has a high rigidity structure, so the excellent comprehensive properties of the resin itself are not lost.

[0018] 2. By adding Lewis base and polyphenols as catalysts and curing agents, the epoxy groups and phenolic hydroxyl groups can undergo rapid cross-linking and curing reactions at relatively low temperatures; the cured product contains a large number of ether bonds, hydroxyl groups and hydrogen bonds, which can effectively improve the adhesion of the cured product.

[0019] 3. High molecular weight polysiloxane polymers are introduced as modifiers, forming a semi-interpenetrating network with the polyimide crosslinking structure. The flexible Si-O-Si structure and semi-interpenetrating network can solve the problem of high brittleness of polyimide cured products and improve the impact toughness of cured resins. On the other hand, they can improve the adhesion of adhesives to inorganic substrates such as glass and ceramics.

[0020] In summary, the polyimide adhesive proposed in this application has three major advantages: low-temperature curing capability, high impact resistance and toughness, and applicability to multiple substrates. Attached Figure Description

[0021] Figure 1 Epoxidation reaction of the cinnamyl alcohol-containing polyimide synthesized in Example 1; Figure 2 Schematic diagram of the semi-interpenetrating network structure formed by the cured material in Example 1; Figure 3 Example 1: DSC test curve of the adhesive. Detailed Implementation

[0022] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0023] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0024] Unless otherwise specified, the experimental conditions used in the examples are generally in accordance with conventional conditions in the art or the conditions recommended by the reagent company. Unless otherwise specified, the materials and reagents used in the examples can be purchased commercially.

[0025] The aforementioned dianhydride and diamine monomers were purchased from Tianjin Zhongtai Materials Technology Co., Ltd., N,N'-diisopropylcarbodiimide, cinnamyl alcohol, hydrogen peroxide and peracetic acid were purchased from Sinopharm Group, and polysiloxanes and polyphenols were purchased from Merck GmbH, Germany.

[0026] The adhesive properties were tested by lap shear test (GB / T 33334-2016), in which the tensile rate of the tensile testing machine was 50 mm·min. -1 .

[0027] The curing behavior of the adhesive was determined by differential scanning calorimetry (DSC) at a heating rate of 5 °C / min over a temperature range of 25–300 °C.

[0028] Example 1 Under nitrogen protection, equimolar amounts of hexafluorodianhydride 6FDA and 3,5-diaminobenzoic acid were dissolved in N-methyl-pyrrolidone solvent. The mixture was stirred at room temperature for 12 h, and then the temperature of the reaction solution was raised to 180 °C, and the reaction was continued for another 12 h to synthesize a viscous polyimide solution. After cooling to room temperature, the same mass of N,N'-diisopropylcarbodiimide and cinnamyl alcohol were added to the above reaction solution, and the mass fraction of the two substances was controlled to be uniform at 10 wt%. The mixture was stirred at room temperature for 4 h under nitrogen protection and in the dark. After the reaction was completed, the mixture was poured into methanol to precipitate the solid product, which was then crushed and filtered to obtain a solid product. The solid product was dried in a vacuum oven at 100 °C for 12 h to obtain a pale yellow granule. The above resin was redissolved in N,N-dimethylformamide solvent, and peracetic acid was slowly added dropwise to the solution, controlling the molar ratio of peracetic acid to polyimide resin to be 1:1. The reaction was carried out at room temperature for 4 h. After the reaction was completed, the solvent and oxidant were removed by rotary evaporation to obtain polyimide resin containing epoxy groups. A mixed solvent of N,N-dimethylformamide / tetrahydrofuran with a volume fraction of 20% tetrahydrofuran was prepared. Under nitrogen atmosphere and in the dark, the synthesized polyimide resin containing epoxy groups, polydimethylsiloxane, tannic acid, and triethylamine were dissolved together in the mixed solvent, controlling the total mass fraction of polyimide containing epoxy groups to be 60%, polydimethylsiloxane 15%, tannic acid 20 wt%, and triethylamine 5%. After dissolution, the solution was degassed and set aside for later use.

[0029] Example 2 Under nitrogen protection, equimolar amounts of hexafluorodianhydride 6FDA and 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid were dissolved in N-methyl-pyrrolidone solvent. The mixture was stirred at room temperature for 12 h, and then the temperature of the reaction solution was raised to 180 °C, and the reaction was continued for another 12 h to synthesize a viscous polyimide solution. After cooling to room temperature, the same mass of N,N'-diisopropylcarbodiimide and cinnamyl alcohol were added to the above reaction solution, and the mass fraction of the two substances was controlled to be uniform at 10 wt%. The mixture was stirred at room temperature for 4 h under nitrogen protection and in the dark. After the reaction was completed, the mixture was poured into methanol to precipitate the solid product, which was then crushed and filtered to obtain a solid product. The solid product was dried in a vacuum oven at 100 °C for 12 h to obtain a pale yellow granule. The above resin was redissolved in N,N-dimethylformamide solvent, and peracetic acid was slowly added dropwise to the solution, controlling the molar ratio of peracetic acid to polyimide resin to be 1:1. The reaction was carried out at room temperature for 4 h. After the reaction was completed, the solvent and oxidant were removed by rotary evaporation to obtain polyimide resin containing epoxy groups. A mixed solvent of N,N-dimethylformamide / tetrahydrofuran with a volume fraction of 20% tetrahydrofuran was prepared. Under nitrogen atmosphere and in the dark, the synthesized polyimide resin containing epoxy groups, polydimethylsiloxane, tannic acid, and triethylamine were dissolved together in the mixed solvent, controlling the total mass fraction of polyimide containing epoxy groups to be 60%, polydimethylsiloxane 15%, tannic acid 20 wt%, and triethylamine 5%. After dissolution, the solution was degassed and set aside for later use.

[0030] Example 3 Under nitrogen protection, equimolar amounts of hexafluorodianhydride 6FDA and 3,5-diaminobenzoic acid were dissolved in N-methyl-pyrrolidone solvent and stirred at room temperature for 24 h. The reaction solution was then heated to 180 °C and reacted for another 24 h to synthesize a viscous polyimide solution. After cooling to room temperature, equal masses of N,N'-diisopropylcarbodiimide and cinnamyl alcohol were added to the reaction solution, maintaining a uniform mass fraction of 15 wt%. The reaction was stirred at room temperature for 4 h under nitrogen protection and in the dark. After the reaction was complete, the precipitate was poured into methanol, crushed, and filtered to obtain a solid product. This solid product was dried in a vacuum oven at 100 °C for 12 h to obtain pale yellow granules. The above resin was redissolved in N,N-dimethylformamide solvent, and peracetic acid was slowly added dropwise to the solution, controlling the molar ratio of peracetic acid to polyimide resin to be 1:1. The reaction was carried out at room temperature for 4 h. After the reaction was completed, the solvent and oxidant were removed by rotary evaporation to obtain polyimide resin containing epoxy groups. A mixed solvent of N,N-dimethylformamide / tetrahydrofuran with a volume fraction of 20% tetrahydrofuran was prepared. Under nitrogen atmosphere and in the dark, the synthesized polyimide resin containing epoxy groups, polydimethylsiloxane, tannic acid, and triethylamine were dissolved together in the mixed solvent, controlling the total mass fraction of polyimide containing epoxy groups to be 60%, polydimethylsiloxane 15%, tannic acid 20 wt%, and triethylamine 5%. After dissolution, the solution was degassed and set aside for later use.

[0031] Example 4 Under nitrogen protection, equimolar amounts of bisphenol A type diether dianhydride (BPADA) and 3,5-diaminobenzoic acid were dissolved in N-methyl-pyrrolidone solvent. The mixture was stirred at room temperature for 12 h, and then the temperature of the reaction solution was raised to 180 °C, and the reaction was continued for another 12 h to synthesize a viscous polyimide solution. After cooling to room temperature, the same mass of N,N'-diisopropylcarbodiimide and cinnamyl alcohol were added to the above reaction solution, and the mass fraction of the two substances was controlled to be uniform at 10 wt%. The mixture was stirred at room temperature for 4 h under nitrogen protection and in the dark. After the reaction was completed, the product was poured into methanol to precipitate, crushed and filtered to obtain a solid product, which was dried in a vacuum oven at 100 °C for 12 h to obtain a light yellow granule. The above resin was redissolved in N,N-dimethylformamide solvent, and peracetic acid was slowly added dropwise to the solution, controlling the molar ratio of peracetic acid to polyimide resin to be 1:1. The reaction was carried out at room temperature for 4 h. After the reaction was completed, the solvent and oxidant were removed by rotary evaporation to obtain polyimide resin containing epoxy groups. A mixed solvent of N,N-dimethylformamide / toluene with a toluene volume fraction of 20% was prepared. Under nitrogen atmosphere and in the dark, the synthesized polyimide resin containing epoxy groups, poly(dimethylsiloxane-co-methylphenylsiloxane), resveratrol, and pyridine were dissolved together in the mixed solvent, controlling the total mass fraction of polyimide containing epoxy groups to be 60%, poly(dimethylsiloxane-co-methylphenylsiloxane) 15%, resveratrol 20 wt%, and triethylamine 5%. After dissolution, the solution was degassed and set aside for later use.

[0032] Example 5 Under nitrogen protection, equimolar amounts of hexafluorodianhydride 6FDA and 3,5-diaminobenzoic acid were dissolved in N-methyl-pyrrolidone solvent. The mixture was stirred at room temperature for 12 h, and then the temperature of the reaction solution was raised to 180 °C, and the reaction was continued for another 12 h to synthesize a viscous polyimide solution. After cooling to room temperature, the same mass of N,N'-diisopropylcarbodiimide and cinnamyl alcohol were added to the above reaction solution, and the mass fraction of the two substances was controlled to be uniform at 10 wt%. The mixture was stirred at room temperature for 4 h under nitrogen protection and in the dark. After the reaction was completed, the mixture was poured into methanol to precipitate the solid product, which was then crushed and filtered to obtain a solid product. The solid product was dried in a vacuum oven at 100 °C for 12 h to obtain a pale yellow granule. The above resin was redissolved in N,N-dimethylformamide solvent, and peracetic acid was slowly added dropwise to the solution, controlling the molar ratio of peracetic acid to polyimide resin to be 1:1. The reaction was carried out at room temperature for 4 h. After the reaction was completed, the solvent and oxidant were removed by rotary evaporation to obtain polyimide resin containing epoxy groups. A mixed solvent of N,N-dimethylformamide / tetrahydrofuran with a volume fraction of 20% tetrahydrofuran was prepared. Under nitrogen atmosphere and in the dark, the synthesized polyimide resin containing epoxy groups, polydimethylsiloxane, tannic acid, and triethylamine were dissolved together in the mixed solvent, controlling the total mass fraction of polyimide containing epoxy groups to be 70%, polydimethylsiloxane 15%, tannic acid 10 wt%, and triethylamine 5%. After dissolution, the solution was degassed and set aside for later use.

[0033] Comparative Example 1 In Example 1, no polydimethylsiloxane was added, and the mass ratio of epoxy-containing polyimide / tannic acid / triethylamine was controlled at 12:4:1. All other conditions were the same as in Example 1.

[0034] Comparative Example 2 In Example 1, no triethylamine catalyst was added, and the mass ratio of epoxy-containing polyimide / polydimethylsiloxane / tannic acid was controlled at 12:3:4. The other conditions were the same as in Example 1.

[0035] Comparative Example 3 In Example 1, the epoxy-containing polyimide resin, polydimethylsiloxane, tannic acid, and triethylamine were ultimately dissolved in pure N,N-dimethylformamide solvent, rather than in a mixed solvent, and the remaining conditions were the same as in Example 1.

[0036] Comparative Example 4 In Example 1, the polyimide resin containing cinnamyl alcohol units was not treated with peracetic acid, and the other conditions were the same as in Example 1.

[0037] The adhesives prepared in the above examples and comparative examples were used to adhere polyimide films, copper sheets, and glass plates, and cured for 2 hours at different curing temperatures. The curing temperature for Example 1 was 98 °C, for Example 2 it was 125 °C, for Example 3 it was 127 °C, for Example 4 it was 91 °C, for Example 5 it was 126 °C, for Comparative Example 1 it was 140 °C, for Comparative Example 2 it was 171 °C, for Comparative Example 3 it was 93 °C, and for Comparative Example 4 it was 175 °C.

[0038] The performance tests of the adhesives prepared in the above embodiments and comparative examples are summarized in Table 1.

[0039] Table 1

[0040] Examples 1-5 prepared polyimide adhesives. Compared with Example 1, Comparative Example 1 did not add polysiloxane substances, so it could not form a semi-interpenetrating network, resulting in low elongation at break and poor adhesion strength to peel, with a significant decrease in adhesion strength to glass plates mainly composed of silica; Comparative Example 2 did not add Lewis base catalysts, so the adhesive had a high curing temperature and decreased adhesion strength, possibly related to an imperfect cross-linking network structure; Comparative Example 3 did not use a mixed solvent containing low boiling points, which resulted in slow solvent evaporation in the adhesive, with most of the curing reaction occurring in solution or gel state, leading to poor adhesion between the adhesive and substrates such as PI film, copper sheet, and glass; Comparative Example 4 did not contain epoxy functional groups, therefore, its adhesion was poor.

[0041] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. Furthermore, it should be understood that after reading the above teachings of this application, those skilled in the art can make various alterations or modifications to this application, and the equivalent forms obtained also fall within the scope of protection of this application. It should also be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A polyimide resin with epoxy groups in its side chains, characterized in that, A polyimide resin with epoxy groups on the side chain is obtained by condensing a dianhydride monomer with a carboxylic acid-containing aromatic diamine monomer, followed by grafting with a hydroxyl compound containing a double bond, and finally epoxidizing the double bond with an oxidant. The dianhydride monomer is selected from one or more of the following: 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), hexafluorodianhydride (6FDA), bisphenol A type diether dianhydride (BPADA), 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride (DSDA), and cyclobutane tetracarboxylic dianhydride (CBDA); The carboxylic acid-containing aromatic diamine monomer is selected from one or more combinations of 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and 3,5-diaminobenzoic acid; The hydroxyl group in the hydroxyl compound containing the double bond is a primary hydroxyl group, and the hydroxyl group is located on the α-carbon or β-carbon of the double bond.

2. The polyimide resin with epoxy groups in its side chains according to claim 1, characterized in that, The hydroxyl compound containing a double bond also includes at least one aromatic ring; And / or, the oxidant is selected from peracetic acid or hydrogen peroxide; And / or, the grafting reaction is an esterification reaction of hydroxyl groups with carboxyl groups in a carboxylic acid aromatic diamine monomer.

3. The polyimide resin with epoxy groups in its side chains according to claim 1, characterized in that, The method for preparing the polyimide resin with epoxy groups in the side chain includes the following steps: S1. Dissolve dianhydride and diamine monomer in a polar aprotic solvent, stir evenly at room temperature, and then heat to react, thereby synthesizing a polyimide solution; S2. After the polyimide solution prepared in step S1 is cooled to room temperature, a dehydrating agent and a hydroxyl compound containing double bonds are added to the reaction solution and stirred at room temperature. After the reaction is completed, an alcohol solvent is poured in to precipitate the product, which is then crushed and filtered to obtain a solid product. S3. Dissolve the solid product synthesized in step S2 in a polar aprotic solvent, and add an oxidant to the solution to react at room temperature; after the reaction is complete, remove the solvent and oxidant by rotary evaporation to obtain a polyimide resin containing epoxy groups.

4. The polyimide resin with epoxy groups in its side chains according to claim 3, characterized in that, Step S1 involves stirring and heating the reaction under nitrogen or inert gas protection. And / or, in step S1, the mixture is stirred at room temperature for 12-24 hours; And / or, in step S1, the temperature is raised to 180-200℃ and the reaction is carried out for 12-18 hours; And / or, the total mass fraction of dianhydride and diamine monomers in step S1 is (10-25) wt% And / or, in step S1, the molar ratio of dianhydride to diamine monomer is (1.1-1):1; And / or, the polar aprotic solvent in step S1 is selected from any one of N-methylpyrrolidone, N-vinyl-2-pyrrolidone or hexamethylphosphoric triamine; And / or, the dehydrating agent in step S2 is selected from N,N'-diisopropylcarbodiimide; And / or, the reaction in step S2 is carried out under nitrogen or inert gas protection and in the dark; And / or, the reaction time of step S2 is 4-8 hours; And / or, the solid product of step S2 is dried in a vacuum oven at 100 °C for 12 hours to obtain light yellow granules; And / or, in step S2, the dehydrating agent and the hydroxyl compound containing double bonds each account for (10-15) wt% of the solid matter. And / or, the alcohol solvent in step S2 is selected from either methanol or ethanol; And / or, the reaction time of step S3 is 4-8 hours; And / or, in step S3, the polar aprotic solvent is selected from any one of N,N-dimethylformamide or N,N-dimethylacetamide; And / or, in step S3, the molar ratio of oxidant to polyimide resin is (1.5-1):

1.

5. The use of the polyimide resin with epoxy groups in the side chain as described in any one of claims 1-4 in the preparation of adhesives.

6. A polyimide adhesive, characterized in that, Polyimide adhesives include: polyimide resins with epoxy groups in their side chains as described above, polymers containing polysiloxane segments, polyphenolic compounds containing at least two phenolic hydroxyl groups, Lewis base compounds, and solvents; The polymer containing polysiloxane segments is selected from one or more combinations of: polydimethylsiloxane, polysiloxane-15, poly(dimethylsiloxane-co-methylphenylsiloxane), poly[dimethylsiloxane-co-(3-aminopropyl)methylsiloxane] and poly(dimethylsiloxane-co-diphenylsiloxane); The polyphenolic compound containing at least two phenolic hydroxyl groups is selected from one or more combinations of tannic acid, quercetin, apigenin, resveratrol, kaempferol, rosin, dopamine, or polydopamine; The Lewis base compound is selected from one or more combinations of benzotriazole, pyrazole, isoquinoline, quinoline, pyridine, benzimidazole, imidazole, 2-methylimidazolium, piperazine, triethylamine, piperidine, and 2,6-dimethylpiperidine; The solvents include: polar aprotic solvents and low-boiling-point solvents with a boiling point not exceeding 130°C; The polar aprotic solvent is selected from one or a combination of two of N,N-dimethylformamide or N,N-dimethylacetamide; The low-boiling-point solvent with a boiling point not exceeding 130°C is selected from one or more combinations of solvents such as toluene, tetrahydrofuran, ethanol, methanol, acetone, ethyl acetate, isopropanol, n-butanol, and butyl acetate.

7. The polyimide adhesive according to claim 6, characterized in that, The polyimide resin containing epoxy groups in the side chain accounts for (50-70) wt% of the total solid mass, the polymer containing polysiloxane segments accounts for (10-25) wt% of the solid mass, the polyphenolic compound containing at least two phenolic hydroxyl groups accounts for (10-20) wt% of the solid mass, and the Lewis base compound accounts for (5-10) wt% of the solid mass.

8. A method for preparing the polyimide adhesive according to any one of claims 6-7, comprising: The polyimide resin with epoxy groups in the side chain as described in any one of claims 1-4, the polymer containing polysiloxane segments, the polyphenolic compound containing at least two phenolic hydroxyl groups, and the Lewis base compound are dissolved in a solvent, mixed evenly, and then degassed and filtered to obtain the polyimide adhesive.

9. A cured product obtained by curing the polyimide adhesive according to any one of claims 6-7 at 80-130°C.

10. Use of the polyimide adhesive according to any one of claims 6-7 for bonding between organic polymer materials, inorganic non-metallic materials and metallic materials.

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