High-temperature-resistant adhesive and preparation method thereof

Abstract

The invention relates to the technical field of high-temperature-resistant adhesives, discloses a high-temperature-resistant adhesive and a preparation method thereof, and solves the problem that the existing high-temperature-resistant adhesive cannot effectively dissipate dynamic stress to maintain structural integrity on the premise of not sacrificing heat resistance due to a single energy dissipation channel caused by a static covalent network structure of the existing high-temperature-resistant adhesive. Comprises: a polyimide resin having a side chain containing a carboxyl functional group and a hydrophobic side chain at the same time; the invention relates to a high-temperature-resistant covalent skeleton and a metal ion source with a variable oxidation state, in the process that a polyamide acid precursor is cured into polyimide, metal ions and carboxyl are coordinated in situ to form an energy-consuming ion network, and meanwhile, hydrophobic side chains are spontaneously enriched to form a shielding layer. A graded energy dissipation mechanism is constructed, and the inherent contradiction between heat resistance and toughness of the adhesive is effectively decoupled.

Description

Technical Field

[0001] This invention relates to a high-temperature resistant adhesive and its preparation method, belonging to the technical field of high-temperature resistant adhesives. Background Technology

[0002] With the increasing demands for reliability in extreme operating conditions from industries such as aerospace, high-power semiconductors, and new energy, developing adhesives that can maintain structural stability in high-temperature environments remains a core issue. To this end, after long-term development, a mature and widely followed technical approach has been formed in this field: achieving the heat resistance of materials by constructing static covalent networks with high crosslinking density and high glass transition temperature, represented by epoxy resins, phenolic resins, or polyimides. This approach deeply binds the upper limit of the material's temperature resistance to the rigidity of the network structure, demonstrating its due value in dealing with static high-temperature environments.

[0003] However, when such adhesives are placed in dynamic stress scenarios dominated by material thermal expansion mismatch and severe temperature cycling, the inherent contradictions of the above-mentioned technical approaches begin to emerge. The fundamental reason is that static covalent networks have a single defect in energy response. That is, when the adhesive structure is subjected to thermal shock or mechanical stress, energy is rapidly transferred in the rigid network. Once the accumulated energy at the stress concentration point exceeds the bond energy of the covalent bond, the only consequence is the irreversible breakage of the chemical bond, which in turn triggers the initiation and propagation of microcracks. To alleviate this problem, the industry has also conducted many explorations, such as toughening by adding rubber elastomers or thermoplastic resins. However, the introduction of these low-softening-point flexible components inevitably sacrifices the overall high-temperature resistance and modulus of the material, constituting a performance compromise.

[0004] Specifically, existing technologies suffer from the following shortcomings: 1. Lack of energy dissipation mechanism: Traditional covalent cross-linked networks are essentially pure stress-bearing structures, not energy management systems. Before covalent bond breakage, they lack reversible energy dissipation channels with low energy thresholds. 2. Inherent contradiction between heat resistance and toughness: Any toughening modification within the existing technological framework inevitably sacrifices the glass transition temperature or high-temperature modulus of the material, failing to simultaneously improve both core properties. Therefore, simply increasing cross-linking density or introducing conventional toughening agents—linear improvement approaches—is insufficient to address the current demands for dynamic structural integrity of the adhesive layer under extreme operating conditions. The root of this contradiction has shifted from the selection of material components to the design philosophy of the adhesive network's energy response mechanism. Therefore, how to implant a novel, non-destructive dynamic energy dissipation mechanism within the material without sacrificing its high-temperature resistance, transforming it from a passive stress-bearing body into an active energy manager, is the technical problem this invention aims to solve. Summary of the Invention

[0005] This invention provides a high-temperature resistant adhesive and its preparation method. Its main purpose is to solve the problem that existing high-temperature resistant adhesives, due to their static covalent network structure, have a single energy dissipation channel, thus failing to effectively dissipate dynamic stress and maintain structural integrity without sacrificing heat resistance.

[0006] To achieve the above objectives, the present invention provides a high-temperature resistant adhesive comprising:

[0007] A polyimide resin, wherein the polymer backbone of the polyimide resin is formed by reacting at least three different diamine monomers with dianhydride monomers, wherein the at least three different diamine monomers include a diamine monomer containing a carboxyl functional group and a diamine monomer having a hydrophobic side chain in its molecular structure.

[0008] A metal ion source with a variable oxidation state; a solution containing a polyamic acid precursor formed by the reaction of a diamine monomer and a dianhydride monomer and a metal ion source with a variable oxidation state is cured by heating, causing the polyamic acid precursor to cyclize into a polyimide. At the same time, the metal ions with a variable oxidation state coordinate with the carboxyl functional groups of the side chains, forming an ionic cross-linked network in situ in the polyimide covalent network. Furthermore, during the heating and curing process, the hydrophobic side chains spontaneously accumulate around the ionic cross-linked network to form a hydrophobic isolation layer.

[0009] Preferably, the molar fraction of the diamine monomer containing the carboxyl functional group in all diamine monomers is 5% to 15%; and the molar equivalent of the metal ion source having a variable oxidation state is 0.3 to 0.8 relative to the carboxyl functional group in the side chain.

[0010] Preferably, the diamine monomer containing a carboxyl functional group is 3,5-diaminobenzoic acid; the metal ion with a variable oxidation state is one of the group consisting of cerium ions, manganese ions and iron ions.

[0011] Preferably, when the composition is subjected to dynamic mechanical loads, its internal energy dissipation follows a graded response mechanism, wherein when the value of the strain energy absorbed by a local micro-region reaches and exceeds the value of the average dissociation energy of a single coordination bond in the ionic cross-linked network, the ionic cross-linked network undergoes reversible dissociation to dissipate the strain energy, and the value of the strain energy is lower than the average bond energy of the covalent bonds constituting the polyimide covalent network.

[0012] Preferably, metal ions with variable oxidation states serve as physical crosslinking points in the ionic bond crosslinking network, while simultaneously constituting an in-situ free radical quenching center. This free radical quenching center reduces the free radicals generated by the polyimide chain through changes in its own valence state under high temperature and oxygen-rich conditions.

[0013] Preferably, the hydrophobic side chain is a fluorinated alkyl side chain; the molar fraction of the diamine monomer with the hydrophobic side chain in its molecular structure is 5% to 20% of the total diamine monomer.

[0014] Preferably, the composition further comprises multi-walled carbon nanotubes as thermally conductive fillers and silica nanoparticles with heavy metal-modified surfaces. The multi-walled carbon nanotubes and silica nanoparticles with heavy metal-modified surfaces work synergistically to construct a phonon bridging network at the bonding interface. This phonon bridging network alleviates the interfacial thermal resistance caused by the mismatch of the lattice vibration modes of the two bonded materials.

[0015] Preferably, the composition further comprises a semi-crystalline thermoplastic polymer dispersed in an amorphous form in the polyimide resin, which undergoes thermal crystallization when the ambient temperature is higher than the glass transition temperature of the polyimide resin, forming a physical cross-linked network to anchor the polyimide segments and inhibit creep. The composition also comprises an ion-exchange treated porous zeolite molecular sieve, the pores of which are preloaded with the same metal ions as a metal ion source with a variable oxidation state. In the chemical environment in which the composition is located, the molecular sieve releases the loaded metal ions to the ionic cross-linked network while adsorbing impurities in the chemical environment.

[0016] Preferably, the composition further comprises a plurality of microcapsules dispersed therein, each microcapsule containing a force-sensitive color-changing dye or its precursor, the shell of the microcapsule rupturing at an energy threshold higher than the average dissociation energy of a single coordination bond in an ionic crosslinking network and lower than the average bond energy of the covalent bonds constituting the polyimide covalent network, thereby releasing the force-sensitive color-changing dye or its precursor to produce a color change.

[0017] A method for preparing a high-temperature resistant adhesive includes the following steps:

[0018] Step a, at least three different diamine monomers and dianhydride monomers are subjected to a polycondensation reaction in a solvent to obtain a solution containing a polyamic acid precursor;

[0019] Step b: Add a metal ion source with a variable oxidation state to a solution containing a polyamic acid precursor, and mix to obtain the composition to be cured;

[0020] Step c: Coat the composition to be cured onto the substrate;

[0021] Step d involves heating and curing the substrate coated with the composition to be cured. During the heating and curing process, the polyamic acid precursor is dehydrated and cyclized to form a polyimide covalent network. At the same time, metal ions with variable oxidation states coordinate with the carboxyl functional groups of the side chains to form an ionic crosslinking network. Furthermore, hydrophobic side chains spontaneously accumulate around the ionic crosslinking network to form a hydrophobic isolation layer.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. This invention provides an adhesive composition in which a polyimide resin containing carboxyl functional groups on its polymer backbone forms a high-temperature resistant continuous phase skeleton, while a divalent or polyvalent metal ion source forms an ionic crosslinking network distributed throughout the skeleton with the carboxyl functional groups. Under external force, since the bond energy of the ionic bonds is lower than that of the covalent bonds constituting the polyimide skeleton, the stress preferentially acts on the ionic bond network and causes it to undergo large-scale reversible dissociation. This process absorbs external energy and avoids irreversible breakage of the polyimide covalent skeleton. After the stress is removed, the dissociated ionic bonds can reform crosslinking under the retraction of molecular chain segments. In this way, the destructive energy input from the outside is not passively borne by the material, but is converted into a recoverable conformational adjustment within the network, so that the heat resistance and structural integrity of the adhesive, which are mutually constrained in the long term, can be synergistically improved.

[0024] 2. When the metal ions provided by the metal ion source are metal ions with variable oxidation states, the adhesive composition exhibits another operating mechanism in a high-temperature and oxygen-rich environment. At this time, the ionic bond crosslinking points, while acting as physical anchors to restrict chain segment movement, also constitute in-situ cyclical free radical quenching centers. When the polymer chain generates free radicals due to thermo-oxygen reactions, the neighboring metal ions reduce the polymer free radicals through changes in their own valence states, repairing the chemical structure of the molecular chain and thus avoiding the collapse of the covalent network caused by chain degradation reactions. This design reuses the ion network, which was originally only used to dissipate mechanical stress, as a reaction center to inhibit chemical degradation. This allows the material to suppress the aging paths of physical durability and chemical stability at different levels when facing extreme conditions of combined force, heat, and oxygen under the same technical element.

[0025] 3. This invention also introduces multi-walled carbon nanotubes and silica nanoparticles with heavy metal-modified surfaces into the composition. These two types of particles work synergistically in the polyimide matrix to construct a composite phonon transport pathway. When bonding two heterogeneous materials with significantly different thermal conductivity, low-frequency phonons on the substrate side couple with the heavy metal-modified layer, while high-frequency phonons on the chip side couple with the carbon nanotubes. Energy is effectively transferred through the broad-spectrum characteristics of these two mediators, establishing an effective transport bridge at the heterogeneous interface. This alleviates the interfacial thermal resistance caused by the mismatch of the lattice vibration modes of the two materials, reducing the additional thermal stress caused by local heat accumulation from the source. This mechanism, combined with the aforementioned dynamic dissipation mechanism of ionic bond networks, enables the adhesive layer not only to effectively dissipate the generated stress but also to actively manage the heat flow distribution to suppress excessive stress generation, forming a full-link management structure from energy generation to dissipation. Attached Figure Description

[0026] Figure 1 This is a block diagram showing the component structure and functional relationship of the high-temperature resistant adhesive of the present invention;

[0027] Figure 2 This is a schematic diagram of the covalent ion composite network and functional units of the adhesive of the present invention;

[0028] Figure 3 This is a schematic diagram illustrating the multi-mechanism synergistic protection of the adhesive of the present invention in encapsulation applications;

[0029] Figure 4 This is a time-series diagram of the graded energy dissipation and structural self-recovery process of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] This invention provides a high-temperature resistant adhesive and its preparation method. The composition comprises an interpenetrating crosslinking system formed by a high-temperature resistant covalent network and a dynamic ionic bond network in its molecular structure. Polyimide resin constitutes the covalent network skeleton providing high-temperature resistance and basic mechanical strength. Side-chain carboxyl functional groups react in situ with a metal ion source with variable oxidation states during curing, forming an ionic crosslinking network that serves as a reversible energy dissipation unit. Simultaneously, hydrophobic side chains introduced by copolymerization migrate and accumulate during curing, forming a molecular-level hydrophobic shielding layer for the ionic bond crosslinking points. Optionally, the composition may further include a composite thermally conductive filler for regulating interfacial thermal resistance, a semi-crystalline thermoplastic polymer for inhibiting high-temperature creep, a porous zeolite molecular sieve for stabilizing the chemical environment of the ionic network, and force-sensitive microcapsules for enabling damage visualization. These functional units work synergistically to achieve an adhesive material that combines high heat resistance, dynamic toughness, chemical stability, and multifunctional integration.

[0032] In a specific application scenario, such as the packaging and bonding of high-power semiconductor IGBT modules, the difference in the coefficient of thermal expansion between the chip and the heat dissipation substrate can induce cyclic thermal stress under temperature cycling. This stress requires the adhesive not only to withstand high temperatures but also to effectively dissipate dynamic stress to inhibit the initiation and propagation of microcracks. To address this challenge, the high-temperature resistant adhesive of this invention is configured to contain a polyimide resin whose polymer backbone is formed by a condensation reaction of at least three different diamine monomers and dianhydride monomers, followed by thermal dehydration and cyclization. The polyimide covalent network provides high-temperature resistance due to its aromatic heterocyclic structure, ensuring that the main load-bearing framework of the adhesive does not undergo thermal degradation or softening at operating temperatures of 300°C or higher. Furthermore, among the at least three different diamine monomers, the first is a conventional aromatic diamine used to construct the rigidity of the polyimide backbone. To clarify the composition of the polymer backbone, the conventional aromatic diamine can be... -Diaminodiphenyl ether or p-phenylenediamine, the dianhydride monomer may be pyromellitic dianhydride or The first type is a diamine monomer with a hydrophobic side chain, specifically 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane. The selection of these monomers forms the basis of the polyimide covalent network. The second type is a diamine monomer containing a carboxyl functional group, preferably 3,5-diaminobenzoic acid, which introduces a side chain carboxyl functional group (-COOH) on the polymer backbone. The third type is a diamine monomer with a hydrophobic side chain, preferably a diamine with a fluorinated alkyl side chain. The introduced hydrophobic segment provides the material basis for the subsequent construction of a humid and hot environment shielding layer.

[0033] Accordingly, to introduce a dynamic energy dissipation mechanism into this rigid covalent network, the composition of the present invention further comprises a metal ion source having a variable oxidation state, such as cerium(III) acetate. ), or manganese acetate, ferric acetate; in the preparation process, a metal ion source is added to the polyamic acid precursor solution generated by the reaction of diamine monomer and dianhydride monomer. In the subsequent temperature curing process, the polyamic acid precursor undergoes dehydration and cyclization to form a polyimide covalent network, while metal ions, such as It undergoes a coordination reaction with the carboxyl functional groups of the side chain, forming an ionic cross-linked network with metal ions as cross-linking centers in situ. This composition thus forms a hierarchical energy dissipation internal structure, whose energy response follows a predetermined hierarchical mechanism. That is, when the adhesive is subjected to dynamic mechanical load, if the strain energy absorbed by a local micro-region is lower than the average bond energy of the covalent bonds constituting the polyimide covalent network, then... However, it reached and exceeded the average dissociation energy of a single coordination bond in an ionic cross-linked network. In this process, the ionic network with lower bond energy will undergo large-scale reversible dissociation first. This process absorbs and dissipates a large amount of external strain energy, thereby avoiding irreversible breakage of the main covalent network. When the stress is removed, the pulled polymer chain segments retract under the action of intermolecular forces, and the dissociated ionic bonds can be reorganized in situ or in a nearby location, restoring the network performance. In this way, the destructive mechanical stress is transformed into a recoverable conformational adjustment inside the network, achieving a synergy between stress dissipation and high-temperature resistance.

[0034] The molar fraction of carboxyl-functionalized diamine monomers in all diamine monomers was set within a working window of 5% to 15% (5-15 mol%). This range was determined because when the molar fraction is below 5%, the density of the resulting ionic crosslinking network is insufficient, resulting in too few ionic bonds available for energy dissipation per unit volume and an insignificant dynamic toughening effect. Conversely, when the molar fraction is above 15%, excessive polar carboxyl side chains may cause over-association of the polyamic acid precursor in solution, increasing viscosity. Furthermore, excessively high ionic crosslinking density after curing may also restrict polymer chain movement to some extent, affecting toughness. Therefore, 5-15 mol% was identified as a range for synergistically achieving processability and dynamic toughness. Similarly, the molar equivalent of the metal ion source with variable oxidation state relative to the side chain carboxyl functional groups was set to 0.3 to 0.8. This is because when the equivalent is below 0.3, the number of metal ions is insufficient to allow most carboxyl groups to form effective ionic crosslinks, resulting in poor network integrity. When the equivalent is above 0.8, excessive free metal ions may act as plasticizers in the system, lowering the glass transition temperature of the material, or become stress concentration points. Therefore, the range of 0.3 to 0.8 ensures that the ionic network forms effective connections without excessive crosslinking.

[0035] Furthermore, under the coupled force-heat-oxygen conditions of high temperature and oxygen enrichment, the covalent backbone of traditional adhesives will undergo chemical degradation due to thermo-oxidative aging. Therefore, this solution selects metal ions with variable oxidation states, so that the ionic bond crosslinking points they construct not only serve as physical energy dissipation units but also constitute an in-situ free radical quenching center. The specific mechanism lies in the fact that when the polymer chain generates a highly reactive polymer free radical in a high-temperature, oxygen-rich environment due to thermo-oxidative action (…),… When ), neighboring metal ions in a lower valence state, such as It will be immediately oxidized to a higher valence state. Simultaneously, the polymer free radicals are reduced, thereby repairing the chemical structure of the molecular chain and terminating the chain degradation reaction; trace amounts of reducing substances present in the system, or through cycling with other redox pairs, can... Regenerated This forms a catalytic cycle; this design allows the metal ion component to simultaneously function as a physical crosslinking point and a chemical reaction center, enabling the material's physical durability and chemical stability to be maintained through the same technical element.

[0036] The electrostatic attraction of ionic bonds is easily shielded by strongly polar water molecules under humid and hot conditions, leading to a reduction in the effectiveness of the dynamic toughening mechanism. To address this challenge, this solution introduces a third type of diamine monomer with hydrophobic side chains in its molecular structure. The molar fraction of this third monomer is 5% to 20% (5-20 mol%) of the total diamine monomers, preferably containing fluorinated alkyl side chains. Based on the principle of minimizing surface energy in polymer systems, during the temperature curing process, these low-surface-energy fluorinated segments spontaneously migrate and accumulate around the strongly polar ionic cross-linked network, forming a nanoscale hydrophobic isolation layer. This isolation layer physically prevents water molecules from approaching and acting on the ionic bonds, ensuring the effectiveness of the dynamic toughening mechanism in humid and hot environments, thereby broadening the working environment range for maintaining stable adhesive performance. The formation and effectiveness of the hydrophobic isolation layer are verified through a standardized post-curing process parameter determination procedure, which uses the final post-curing temperature as the basis for the verification. With duration Using the parameter as the independent variable, samples were prepared and treated at a series of parameter combinations, and then the static contact angle of deionized water for each sample was measured. And calculate its hydrophobic shielding effectiveness index according to the following formula. , in, The contact angle is the reference sample without the addition of hydrophobic diamine monomers, and the final combination of parameters selected for the curing process. It is capable of making that The index reached its maximum value, corresponding to the 5% thermogravimetric temperature of the sample. Not less than The combination of parameters.

[0037] When bonding two heterogeneous materials with significantly different thermal conductivity, the interfacial thermal resistance formed at the interface due to the mismatch of lattice vibration modes can induce local hot spots, thereby generating additional thermal stress. Therefore, the composition of this invention may further include multi-walled carbon nanotubes (MWCNTs) as thermally conductive fillers and a surface coated with a heavy metal (such as bismuth). ) modified silica ( Nanoparticles; these two types of nanoparticles work synergistically to construct a phonon bridging network at the bonding interface. Carbon nanotubes, due to their broad phonon spectrum, can couple with phonons from various materials, responsible for broadband energy transfer; while the heavy metal atoms on the surface of silica nanospheres have large atomic masses, and their low-frequency vibration modes can match the low-frequency phonon spectrum of the metal substrate, responsible for capturing low-frequency phonons from the metal substrate. This composite filler system alleviates the interfacial phonon mismatch problem, improves interfacial heat flow, and suppresses the generation of additional thermal stress caused by interfacial thermal resistance from the source. For scenarios requiring continuous high temperature and constant static load operation, the dynamic ionic bond network of this invention may allow polymer segments to undergo... Slow slippage, or creep, can cause problems. To address this, the composition may also include a semi-crystalline thermoplastic polymer, such as polyetheretherketone (PEEK). Under conventional curing processes and at most operating temperatures, PEEK is dispersed in the polyimide matrix as amorphous molecular chains. When the ambient temperature continues to rise and enters a high-risk creep region, such as above the glass transition temperature of the polyimide resin, the mobility of the PEEK molecular chain segments increases, resulting in thermally induced crystallization and the formation of numerous nanoscale microcrystalline regions. These in-situ formed PEEK microcrystals act as physical crosslinking points, interpenetrating and anchoring between the polyimide network, limiting the slippage ability of the polymer backbone and thus improving the material's creep resistance.

[0038] To enhance the stability of the ionic network under complex chemical environments, the composition may also contain an ion-exchange treated porous zeolite molecular sieve, such as ZSM-5 molecular sieve; before addition, the molecular sieve is ion-exchange treated in a concentrated solution of the metal salt used in the composition, such as cerium acetate, so that its pores and framework are pre-loaded with the same metal ions as the ionic network. During service, when impurities in the external environment consume metal ions in the ionic bond network, the metal ions stored in the molecular sieve channels are released according to the principle of chemical equilibrium, replenishing the ionic bond network and maintaining its cross-linking density. Simultaneously, the specific surface area and pore structure of the molecular sieve enable it to adsorb small-molecule acidic or alkaline impurities in the environment, purifying the microenvironment of the ionic bond network and thus maintaining its working efficiency in a chemically corrosive environment. To visualize the cumulative damage inside the material, the composition may also contain a plurality of dispersed microcapsules containing a mechanosensitive color-changing dye or its precursor. The key to this approach lies in setting the energy threshold, i.e., the fracture energy of the microcapsule shell. Designed to have a dissociation energy higher than that of ionic bond networks However, it is lower than the fracture energy of covalent networks. ,Right now When the adhesive is subjected to stress, the ionic bonds dissociate first, consuming energy. If the stress level and the degree of deformation increase, it means that a large number of ionic bond networks have dissociated, and the deformation energy of the matrix will exceed the required energy. This causes the microcapsule shell to rupture; the dye precursor released from the rupture reacts with specific components in the matrix, producing an irreversible color change in the damaged area, thus presenting the invisible microscopic damage history as a visual signal.

[0039] In the preparation of the polyamic acid precursor, at least three different diamine monomers and dianhydride monomers undergo a polycondensation reaction in an aprotic polar solvent. To ensure the target molecular weight is obtained and to facilitate subsequent processing, the ratio of the total molar amount of all diamine monomers to the molar amount of dianhydride monomers is controlled within the range of 0.98:1 to 1.05:1. The reaction is carried out under inert gas protection, the reaction temperature is controlled between 0°C and 50°C, and the reaction time is 4 to 24 hours until the viscosity of the system reaches stability. The resulting solution containing the polyamic acid precursor has a solid content, preferably 10% to 30% by weight, more preferably 15% to 25%, to obtain a viscosity suitable for coating processes. To support a wider range of material choices, conventional aromatic diamines, in addition to... In addition to diaminodiphenyl ether or p-phenylenediamine, m-phenylenediamine can also be used. -Diaminodiphenylmethane or One or more combinations of -(9-fluorene-1,2-diphenylamine), dianhydride monomers, other than pyromellitic dianhydride or 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, may also be selected. -Benzenone tetracarboxylic dianhydride, -Oxyphthalic anhydride or One or more combinations of biphenyltetracarboxylic dianhydrides, diamine monomers with hydrophobic side chains in their molecular structure, including diamines containing organosiloxane segments such as bis(3-aminopropyl)polydimethylsiloxane, can achieve the same hydrophobic shielding function; for optional functional fillers, the amount added can be adjusted within a certain range to achieve the target performance. The total amount of multi-walled carbon nanotubes and silica nanoparticles with heavy metal modified surfaces as thermally conductive fillers in the composition is 0.5% to 15% by weight of the composition; the amount of semi-crystalline thermoplastic polymers added is 1% to 15% by weight of the composition; in addition to polyetheretherketone, polyetherketone or polyphenylene sulfide can also be selected; porous zeolite molecular sieves treated by ion exchange are added at 0.5% to 5% by weight of the composition; and multiple microcapsules used to achieve damage visualization are added at 0.1% to 5% by weight of the composition.

[0040] Example 1: In a high-power gallium nitride (GaN) system for airborne radar In the packaging of RF power amplifier modules, the core chip and copper-tungsten (CT) alloy are used. The heat dissipation substrate is bonded using a high-temperature resistant adhesive. During operation, the module's junction temperature undergoes frequent and significant cycling between -55°C and 225°C, while the entire component is placed in an environment continuously containing high temperature, oxygen, and trace amounts of moisture. In the initial stage of module operation, as the junction temperature rapidly rises, shear stress caused by the mismatch in thermal expansion coefficients between the chip and the heat dissipation substrate begins to accumulate within the adhesive layer. When the strain energy in the stress concentration region reaches and exceeds the average dissociation energy of the ionic bonds... At this time, the ionic cross-linked network composed of cerium ions and side-chain carboxyl functional groups undergoes large-scale reversible dissociation. This process dissipates most of the initial thermal shock energy through the breaking and recombination of ionic bonds, thus causing the actual stress borne by the polyimide covalent network, which serves as the main load-bearing structure, to be lower than the average bond energy of its covalent bonds. The initiation of microcracks is thus suppressed.

[0041] As thousands of temperature cycles continue, the high temperature and oxygen-rich environment begin to chemically erode the polyimide covalent network, generating polymer free radicals on the polymer backbone due to thermo-oxidative effects. Under these conditions, cerium ions, which serve as cross-linking points for ionic bonds ( It also functions as a quenching center for chemical free radicals, adjacent to polymer free radicals. The ions will reduce it, and they themselves will be oxidized to... This process repairs the chemical damage to the covalent network at the molecular scale. The operation of this chemical repair mechanism relies on the physical toughness provided by the ionic network, which inhibits the propagation of microcracks and reduces the continuous exposure of new polymer surfaces to the oxidative environment. Thus, the physical dissipation mechanism and the chemical repair mechanism are interdependent, enabling the material to withstand mechanical stress while resisting chemical degradation. During this process, trace amounts of water vapor in the environment penetrate into the adhesive and hydrate with the polar ionic bonds, thereby reducing the energy dissipation capacity of the ionic network. Meanwhile, the fluorinated alkyl side chains that have spontaneously accumulated around the ionic network during the curing stage form a low-surface-energy hydrophobic barrier layer. This barrier layer prevents the intrusion of water molecules at the molecular scale, maintaining the non-polar microenvironment around the ionic crosslinking points. This hydrophobic shield preserves the non-polar environment of the ionic network, thus maintaining the operational efficiency of the physical dissipation and chemical repair mechanisms in a humid and hot environment.

[0042] After undergoing a complete accelerated aging life cycle test, the gallium nitride RF power amplifier module was cross-sectionally analyzed. The results showed that the bonding interface was free of delamination and cracks, the thermal resistance of the module did not increase significantly compared to the initial state, and no obvious signs of degradation were observed in the internal chemical structure of the adhesive. Through the aforementioned energy dissipation and chemical structure repair mechanism, the adhesive maintained the structural integrity of the bonding interface under the dual conditions of dynamic stress and chemical erosion.

[0043] Example 2: To objectively verify the effect of introducing an ionic crosslinking network into the polyimide covalent network on the structural integrity of the material under dynamic thermal stress, this example prepared two samples, the present invention sample group and the control group, for comparative testing. The present invention sample group was prepared by polycondensing a conventional aromatic diamine, 3,5-diaminobenzoic acid containing a carboxyl functional group, and a diamine monomer with a fluorinated alkyl side chain with a dianhydride monomer. Cerium acetate (III) was added to the resulting polyamic acid precursor solution, followed by coating to form a film and curing under gradient temperature. The control group was prepared using the exact same monomer components and process parameters except for the absence of 3,5-diaminobenzoic acid and cerium acetate (III), thus forming a sample containing only a pure polyimide covalent network. The system ensures that the only variable between the two groups of samples is the presence or absence of an ionic cross-linking network. The test procedure is as follows: First, according to the ASTM D1002 standard, the initial shear strength of the two groups of samples is measured at a high temperature of 250°C. The results show that the initial performance of the sample group of this invention is comparable to that of the control group, which are 24.8 MPa and 25.1 MPa, respectively. Then, the two groups of samples are placed in the same thermal shock test chamber and subjected to repeated thermal cycling treatment in the temperature range of -55°C to 175°C. The cycle period of each cycle is set to 60 minutes. This parameter setting is intended to simulate a harsh service environment while effectively accelerating the fatigue damage process of the material. At different stages of thermal cycling treatment, samples are taken out in batches for retesting of high-temperature shear strength and observation of microstructure.

[0044] The experimental results revealed significant differences in the performance evolution of the two samples. The mechanical properties of the control group sample continuously deteriorated with increasing thermal cycling cycles. After 1000 cycles, its high-temperature shear strength decreased to 15.3 MPa, and after 3000 cycles, the strength further decreased to 4.8 MPa, only 19.1% of its initial strength. Simultaneous scanning electron microscopy observations showed high-density microcracks at the bonding interface. In contrast, the sample of this invention exhibited high performance stability. After 1000 thermal cycles, its high-temperature shear strength remained at 23.5 MPa, and after 3000 cycles, its strength remained at 20.6 MPa, maintaining 83.1% of its initial strength. Furthermore, no significant microcracks were observed to initiate at the bonding interface throughout the entire testing period. The direct reason for this performance difference lies in the internal stress distribution of the two materials. Due to the different force dissipation mechanisms, in the sample group of this invention, the internal stress generated by thermal expansion mismatch is effectively dissipated by the low-bond-energy ionic cross-linked network within the system through a large-scale reversible dissociation and recombination process, thereby avoiding cumulative damage to the main covalent network. In contrast, the control group, lacking this low-energy-threshold dissipation channel, has cyclic stress passively borne by the rigid covalent network, which is ultimately released in the form of irreversible chemical bond breakage and microcrack propagation, leading to a continuous decline in its mechanical properties. Through direct comparison of the mechanical property stability of the two sample groups under long-term thermal cycling conditions, the data from this experiment show that introducing an ionic cross-linked network formed by metal ions and side-chain carboxyl groups into the polyimide covalent network can effectively improve the material's resistance to thermal fatigue damage. This provides objective verification of the role of the graded energy dissipation mechanism in improving the service reliability of the bonded structure in the specific implementation.

[0045] To verify the composition of multi-walled carbon nanotubes and their surface treated with heavy metal bismuth ( The composite thermally conductive filler composed of bismuth-modified silica nanoparticles plays a role in reducing the interfacial thermal resistance of heterogeneous material bonding. In this embodiment, three additional sets of samples were prepared for interfacial thermal conductivity testing. The first set was the reference adhesive of this invention without any thermally conductive filler; the second set was an adhesive with only 2 wt% multi-walled carbon nanotubes added to the reference adhesive; and the third set was an adhesive with both 2 wt% multi-walled carbon nanotubes and 1 wt% bismuth-modified silica nanoparticles added to the reference adhesive. The interfacial thermal resistance of standard components consisting of silicon chips and copper substrates bonded by these three sets of adhesives was measured using a laser flare method. The measurement results showed that the interfacial thermal resistance of the first set of reference samples was [missing information]. The second group of samples, containing only multi-walled carbon nanotubes, showed a decrease in interfacial thermal resistance to [missing value]. The third group of samples, containing composite thermally conductive fillers, showed a further decrease in interfacial thermal resistance. This data indicates that the synergistic effect of multi-walled carbon nanotubes and silica nanoparticles with heavy metal-modified surfaces, through a phonon bridging mechanism, is superior to that of a single thermally conductive filler in improving interfacial heat transfer efficiency.

[0046] Example 3: This example combines Figures 1 to 4 This describes a high-temperature resistant adhesive and its preparation method, such as... Figure 1 As shown, it uses a polyimide resin precursor formed by the reaction of three different functional diamine monomers and dianhydride monomers, and a metal ion source providing metal ions with variable oxidation states as core raw materials. Functional fillers can be selectively added to achieve multifunctional integration. During the temperature curing process, the above components undergo a synergistic effect of multiple physicochemical processes, ultimately forming a composite network structure. This structure consists of a polyimide covalent network providing high-temperature resistance and basic mechanical strength, an ionic cross-linked network formed by the coordination of metal ions and carboxyl groups and serving as a reversible energy dissipation unit, and a network formed by the spontaneous enrichment of hydrophobic side chains. The adhesive is composed of a molecular-level hydrophobic shielding layer formed by the ionic bonds. This composite network structure endows the adhesive with a hierarchical energy dissipation mechanism. Under the action of external force, the ionic bond network with lower bond energy preferentially undergoes large-scale reversible dissociation to absorb and dissipate energy, thereby protecting the rigid covalent network skeleton from damage. At the same time, this structure also gives rise to the dual functions of in-situ free radical quenching center, chemical self-healing and protection against humid and hot environments. Among them, metal ions reduce polymer free radicals through their own valence state changes, inhibit the chain degradation reaction in high temperature and oxygen-rich environment, and realize chemical stability and environmental adaptability by utilizing the dual functions of the ionic network.

[0047] like Figure 2 As shown, the thick solid line represents the main framework of the polyimide covalent network, on which side-chain carboxyl functional groups are grafted. Metal ions Coordination with the carboxyl functional groups of the side chains forms an ionic cross-linked network centered on metal ions. These ionic cross-linking sites also constitute the chemical self-healing reaction centers. Around these ionic cross-linking sites, hydrophobic side chains introduced by the hydrophobic diamine monomer... Spontaneous enrichment occurs, forming a hydrophobic shield against ionic bonds. Multi-walled carbon nanotubes and silica with heavy metal-modified surfaces can also be dispersed within the system. With functional fillers such as nanoparticles, the entire system achieves a hierarchical energy dissipation mechanism through hierarchical responses between ionic and covalent networks.

[0048] like Figure 3 As shown, in high-power gallium nitride RF chips and copper-tungsten In the packaging of the heat dissipation substrate, the application mechanism of the adhesive is demonstrated. Due to the mismatch of the thermal expansion coefficients between the chip and the substrate, the high-temperature adhesive layer is challenged under the combined action of high temperature and oxygen-rich environment and cyclic thermal stress. At this time, the ion network inside the adhesive absorbs thermal stress through reversible dissociation and realizes dynamic energy release, thereby inhibiting the initiation of microcracks. At the same time, metal ions, as free radical quenching centers, perform chemical self-repair of the material and inhibit the thermo-oxidative aging of the material. In addition, the composite thermally conductive filler improves thermal conductivity by constructing phonon bridging, alleviates interfacial thermal resistance, and reduces thermal stress caused by local heat accumulation, thereby ensuring that the heat of the chip can be effectively transferred to the heat dissipation substrate.

[0049] like Figure 4 As shown, when external stress applies a load to the adhesive, the strain energy inside the adhesive begins to accumulate. If the strain energy exceeds the dissociation energy of the ionic bonds, it will trigger a large-scale reversible dissociation of the ionic bonds. This process absorbs and dissipates the strain energy, thereby protecting the main covalent network and preventing it from undergoing irreversible breakage, thus achieving structural recovery. If the strain energy does not reach the threshold of ionic bond dissociation, the adhesive undergoes elastic deformation. When the external stress removes the load, whether the energy is dissipated through ionic bond dissociation or only elastic deformation occurs, the polymer chain segments will retract, the dissociated ionic bonds can be reorganized, and the performance of the adhesive will eventually be restored.

[0050] Example 4: In a scenario where long-term structural bonding is provided for high-precision optical components on a deep space probe, the adhesive must not only maintain the connection under extreme temperature fluctuations but also possess extremely low thermal vacuum degassing performance to avoid contamination of the optical surface. This dual performance requirement necessitates a systematic determination of the precise proportions of each component in the adhesive formulation and the curing process. To determine the optimal molar fraction of 3,5-diaminobenzoic acid containing carboxyl functional groups, this example prepared a series of polyamic acid precursor solutions. The molar fraction of 3,5-diaminobenzoic acid in the total diamine monomers was set at five gradients: 5.0%, 7.5%, 10.0%, 12.5%, and 15.0%. The remaining components in the formulation, including conventional aromatic diamines, diamine monomers with fluorinated alkyl side chains, dianhydride monomers, and cerium(III) acetate, were also considered. The relative proportions were kept constant. Curing of all samples was performed in a programmed temperature-controlled vacuum curing oven with a temperature control accuracy of ±1°C. A multi-stage thermal curing procedure was used for sample curing: first, the sample was held at 80°C for 1 hour to remove most of the solvent; then, the temperature was increased to 150°C and held for 1 hour to complete the initial cyclization; next, the temperature was increased to 220°C and held for 1 hour to complete the imidization reaction; finally, a final post-curing was performed at 300°C for 2 hours. This final post-curing stage aimed to ensure the full maturation of the covalent and ionic networks and to provide sufficient migration time for the low surface energy fluorinated alkyl side chains to form a hydrophobic surface layer. After curing, the key properties of each group of samples were quantitatively characterized using a compact tensile testing machine, a thermogravimetric analyzer (TGA), and a contact angle measuring instrument.

[0051] The toughness of a material is characterized by measuring its fracture toughness value. The procedure was performed, and the results showed... The value first increased and then decreased with increasing molar fraction of 3,5-diaminobenzoic acid, reaching a peak in the range of 10.0% to 12.5%; the thermal stability of the material was characterized by determining its 5% thermogravimetric temperature using TGA. The test was conducted, and the results showed that all samples... All values ​​were above 480°C, but showed a slight decrease at a molar fraction of 15.0%. The formation effect of the hydrophobic shielding layer was characterized by measuring the water contact angle of the sample surface. The results showed that the water contact angle increased significantly as the molar fraction of 3,5-diaminobenzoic acid increased from 5.0% to 10.0%, and then tended to stabilize above 10.0%. Based on the quantitative data of the above three performance characteristics, in order to synergistically optimize the toughness, thermal stability and surface hydrophobicity of the material, a molar fraction of 11.0% was selected as the formulation parameter for this specific application. This systematic calibration process established the determination of adhesive formulation parameters and process specifications on a multi-dimensional performance data trade-off and reproducible engineering method, thereby obtaining an adhesive product that meets the dual performance requirements of this application.

[0052] Example 5: Before large-scale production of adhesives for aerospace applications requiring high batch-to-batch performance consistency, batch calibration of the reactivity of key raw materials is performed. Taking a new batch of dianhydride monomer as an example, a representative sample of the monomer from that batch is taken and synthesized on a small scale with a set of benchmark diamine monomer components whose performance has been calibrated under standard reaction conditions. After the reaction, the intrinsic viscosity of the resulting polyamic acid precursor solution is measured using an Ubbelohde viscometer and compared with a preset quality control window, such as 1.5 dL / g to 1.7 dL / g. If the measured intrinsic viscosity is within this window, the batch of dianhydride monomer is deemed qualified. If the intrinsic viscosity is lower than the lower limit of the window, it is compensated for in subsequent large-scale production by adjusting the reaction endpoint or monomer ratio. This measure aims to ensure the consistency of the molecular weight and chain structure of the polyamic acid precursor, which is the basis of adhesive performance, across different production batches.

[0053] To ensure that the force-sensitive color-changing microcapsules contained in the composition are triggered at a preset damage threshold, their mechanical response characteristics need to be matched and calibrated with the mechanical behavior of the adhesive matrix. This calibration process first uses dynamic mechanical analysis (DMA) and uniaxial tensile testing to obtain data such as the storage modulus, loss factor, and ultimate failure strain of the adhesive matrix material without microcapsules. This data characterizes the strain range at which the ionic bond network begins to dissipate energy on a large scale and the strain limit at which the covalent network undergoes macroscopic failure. Then, several batches of microcapsules with different shell thicknesses and crosslinking densities are dispersed in the adhesive matrix at fixed concentrations to prepare composite material strips. Tensile tests are performed on these strips, and the tensile strain corresponding to the point where the surface color of the strips begins to change significantly is recorded in real time using a high-resolution camera. Finally, a batch of microcapsules with a color-causing strain threshold higher than the strain corresponding to the energy dissipation peak of the ionic network in the matrix material, but lower than 70% of the ultimate failure strain of the matrix material, is selected. The hierarchical energy relationship corresponds to a specific material system that can be verified and selected through engineering experiments.

[0054] Example 6: In an adhesive application for long-term service of hot-end structural components of aero-engines, the engineering goal is to maximize the long-term thermo-mechanical stability of the adhesive under continuous high temperature and static load. This stability is defined by two key performance indicators: minimizing creep strain and simultaneously minimizing fracture toughness. The content needs to be maintained above 85% of the initial value. To achieve this, an offline optimization parameter search was first performed for the addition of the semi-crystalline thermoplastic polymer polyetheretherketone (PEEK). This process prepared a series of adhesive samples with the same composition as the formulation determined in Example 3, except for the different PEEK contents. The PEEK addition amounts were 2%, 5%, and 8% of the total mass, respectively. According to ASTM D2990, these samples were subjected to a constant shear stress of 20% of their room temperature shear strength at 260°C for 100 hours, and the creep strain of each sample was recorded. The results showed that the sample with 5% PEEK addition had a creep strain below the threshold required for the target application after 100 hours, and its fracture toughness value was also lower. Compared to the baseline sample without PEEK, the creep rate decreased by only 5%, while the sample with 8% PEEK showed the least creep, but its... Since the value decreased by more than 15%, 5% was determined to be the amount of PEEK added to meet the above optimization objectives.

[0055] To ensure the chemical stability of the binder in corrosive atmospheres, the porous zeolite molecular sieves used as ion buffer units require standardized ion exchange pretreatment and qualification verification. This process uses ZSM-5 molecular sieves, which are first calcined at 550°C for 4 hours, then immersed in a 1.0 mol / L cerium(III) acetate aqueous solution and stirred at 80°C for 24 hours for ion exchange. After exchange, the samples are filtered, washed, and dried. Finally, the treated molecular sieve samples are quantitatively analyzed using inductively coupled plasma atomic emission spectrometry (ICP-AES). Only when the cerium content is within the target window of 3 wt% to 5 wt% is the batch of molecular sieves considered a qualified functional filler. This optimized selection and qualification verification process yielded a specific formulation containing 5 wt% PEEK and 2 wt% qualified ion-exchange ZSM-5 molecular sieves. All components were determined through reproducible engineering experiments to meet the preset multi-dimensional performance requirements.

[0056] 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 present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-temperature resistant adhesive, characterized in that, Include: A polyimide resin, wherein the polymer backbone of the polyimide resin is formed by reacting at least three different diamine monomers with dianhydride monomers, wherein the at least three different diamine monomers include a diamine monomer containing a carboxyl functional group and a diamine monomer having a hydrophobic side chain in its molecular structure. A metal ion source with a variable oxidation state; a solution containing a polyamic acid precursor formed by the reaction of a diamine monomer and a dianhydride monomer and a metal ion source with a variable oxidation state is cured by heating, causing the polyamic acid precursor to cyclize into a polyimide. At the same time, the metal ions with a variable oxidation state coordinate with the carboxyl functional groups of the side chains, forming an ionic cross-linked network in situ in the polyimide covalent network. Furthermore, during the heating and curing process, the hydrophobic side chains spontaneously accumulate around the ionic cross-linked network to form a hydrophobic isolation layer.

2. The high-temperature resistant adhesive according to claim 1, characterized in that, The molar fraction of the diamine monomer containing the carboxyl functional group in all diamine monomers is 5% to 15%; the molar equivalent of the metal ion source with variable oxidation state is 0.3 to 0.8 relative to the carboxyl functional group in the side chain.

3. The high-temperature resistant adhesive according to claim 1, characterized in that, The diamine monomer containing a carboxyl functional group is 3,5-diaminobenzoic acid; the metal ion with a variable oxidation state is one of the group consisting of cerium ions, manganese ions and iron ions.

4. The high-temperature resistant adhesive according to claim 1, characterized in that, When the composition is subjected to dynamic mechanical loads, its internal energy dissipation follows a graded response mechanism. When the strain energy absorbed by a local micro-region reaches and exceeds the average dissociation energy of a single coordination bond in the ionic cross-linked network, the ionic cross-linked network undergoes reversible dissociation to dissipate the strain energy. Furthermore, the strain energy is lower than the average bond energy of the covalent bonds constituting the polyimide covalent network.

5. The high-temperature resistant adhesive according to claim 1, characterized in that, Metal ions with variable oxidation states, while serving as physical crosslinking points in ionic bond crosslinking networks, also constitute an in-situ free radical quenching center. This free radical quenching center reduces the free radicals generated by the polyimide chain through changes in its own valence state under high temperature and oxygen-rich conditions.

6. The high-temperature resistant adhesive according to claim 1, characterized in that, The hydrophobic side chain is a fluorinated alkyl side chain; the molar fraction of the diamine monomer with the hydrophobic side chain in its molecular structure is 5% to 20% of the total diamine monomer.

7. The high-temperature resistant adhesive according to claim 1, characterized in that, The composition also includes a semi-crystalline thermoplastic polymer dispersed in an amorphous form in a polyimide resin, which undergoes thermal crystallization when the ambient temperature is above the glass transition temperature of the polyimide resin, forming a physical cross-linked network to anchor the polyimide segments and inhibit creep. The composition also includes an ion-exchange treated porous zeolite molecular sieve, the pores of which are preloaded with the same metal ions as a metal ion source with variable oxidation states. In the chemical environment in which the composition is located, the molecular sieve releases the loaded metal ions to the ionic cross-linked network while adsorbing impurities in the chemical environment.

8. The high-temperature resistant adhesive according to claim 1, characterized in that, The composition also comprises a plurality of microcapsules dispersed in the composition, each microcapsule containing a force-sensitive color-changing dye or a precursor thereof. The shell of the microcapsule ruptures at an energy threshold higher than the average dissociation energy of a single coordination bond in an ionic crosslinked network and lower than the average bond energy of the covalent bonds constituting the polyimide covalent network, releasing the force-sensitive color-changing dye or its precursor to produce a color change.

9. A method for preparing a high-temperature resistant adhesive according to any one of claims 1 to 8, characterized in that, Includes the following steps: Step a, at least three different diamine monomers and dianhydride monomers are subjected to a polycondensation reaction in a solvent to obtain a solution containing a polyamic acid precursor; Step b: Add a metal ion source with a variable oxidation state to a solution containing a polyamic acid precursor, and mix to obtain the composition to be cured; Step c: Coat the composition to be cured onto the substrate; Step d involves heating and curing the substrate coated with the composition to be cured. During the heating and curing process, the polyamic acid precursor is dehydrated and cyclized to form a polyimide covalent network. At the same time, metal ions with variable oxidation states coordinate with the carboxyl functional groups of the side chains to form an ionic crosslinking network. Furthermore, hydrophobic side chains spontaneously accumulate around the ionic crosslinking network to form a hydrophobic isolation layer.

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