High temperature resistant adhesive and method for preparing the same

Abstract

The present application relates to the technical field of high-temperature-resistant adhesive, and discloses a high-temperature-resistant adhesive and a preparation method thereof, which solves the problem that the existing high-temperature-resistant adhesive cannot effectively dissipate dynamic stress without sacrificing heat resistance to maintain structural integrity due to the single energy dissipation channel caused by the static covalent network structure, and comprises: a polyimide resin, the side chain of which contains a carboxyl functional group and a hydrophobic side chain at the same time; and a source of metal ions with variable oxidation states, in the process of curing the polyamide acid precursor into polyimide, the metal ions are coordinated with the carboxyl group to form an energy-consuming ionic network in situ, and the hydrophobic side chain spontaneously accumulates to form a shielding layer, the present application implants a reversible dissociation ionic network in the high-temperature-resistant covalent skeleton, constructs a hierarchical energy dissipation mechanism, and effectively decouples the inherent contradiction between the heat resistance and toughness of the adhesive.

Description

TECHNICAL FIELD

[0001] The present application relates to a high-temperature-resistant adhesive and a preparation method thereof, and belongs to the technical field of high-temperature-resistant adhesives. BACKGROUND

[0002] At present, with the continuous improvement of the reliability requirements of extreme working conditions in the aerospace high-power semiconductor and new energy industries, the development of adhesives that can maintain structural stability in high-temperature environments has always been one of the core topics. Therefore, through long-term development, the field has formed a mature and widely followed technical path, that is, by constructing a static covalent network with high cross-linking density and high glass transition temperature represented by epoxy resin, phenolic resin or polyimide, the heat resistance of the material is realized. This way deeply binds the upper limit of the material's temperature resistance with the rigidity of the network structure, and shows its due value when dealing with static high-temperature environments.

[0003] However, when such adhesives are placed in a dynamic stress scenario dominated by material thermal expansion mismatch and severe temperature cycling, the inherent contradictions of the above technical path begin to appear. The fundamental reason is that the static covalent network has a single defect in energy response. That is, when the adhesive structure is subjected to thermal shock or mechanical stress, energy is rapidly transmitted 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 rupture of the chemical bond, which in turn initiates the initiation and propagation of microcracks. To alleviate this problem, the industry has also made many explorations, such as adding rubber elastomers or thermoplastic resins for toughening. However, the introduction of such low-softening-point flexible components inevitably sacrifices the overall high-temperature resistance and modulus of the material, constituting a compromise in performance.

[0004] Specifically, the existing technology mainly has the following deficiencies: 1. Lack of energy dissipation mechanism. The traditional covalent cross-linked network is essentially a pure stress-bearing structure, not an energy management system. It lacks a reversible energy dissipation channel with a low energy threshold before the covalent bond breaks. 2. Inherent contradiction between heat resistance and toughness. Any toughening modification under the existing technical framework inevitably sacrifices the glass transition temperature or high-temperature modulus of the material, making it impossible to simultaneously improve both core performances. In view of this, simply increasing the cross-linking density or introducing conventional toughening agents, such as linear improvement ideas, cannot meet the demand for the dynamic structural integrity of the adhesive layer in extreme working conditions. The root of this contradiction has risen from the selection of material components to the design philosophy of the adhesive network energy response mechanism. Therefore, how to implant a completely new non-destructive dynamic energy dissipation mechanism into the material without sacrificing its high-temperature resistance, and make it change from a passive stress bearer to an active energy manager, has become a technical problem to be solved by the present application. SUMMARY

[0005] The present application provides a high-temperature-resistant adhesive and a preparation method thereof, and the main purpose is to solve the problem that the existing high-temperature-resistant adhesive cannot effectively dissipate dynamic stress without sacrificing heat resistance due to the single energy dissipation channel caused by the static covalent network structure.

[0006] To achieve the above-mentioned purpose, the present application provides a high-temperature-resistant adhesive, which comprises:

[0007] A polyimide resin, the polymer main chain 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 comprise a carboxyl functional group-containing diamine monomer and a diamine monomer with a hydrophobic side chain in its molecular structure;

[0008] A source of metal ions with variable oxidation states; a solution containing polyamic acid precursors formed by reacting diamine monomers with dianhydride monomers and a source of metal ions with variable oxidation states is subjected to temperature curing to cyclize the polyamic acid precursors into polyimides, at the same time, the metal ions with variable oxidation states coordinate with the side chain carboxyl functional groups, forming an ionic bond crosslinking network in the polyimide covalent network in situ, and the hydrophobic side chains spontaneously accumulate around the ionic bond crosslinking network to form a hydrophobic isolation layer during the temperature curing process.

[0009] Preferably, the molar fraction of the carboxyl functional group-containing diamine monomer in all diamine monomers is 5% to 15%; the molar equivalent of the source of metal ions with variable oxidation states relative to the side chain carboxyl functional groups is 0.3 to 0.8.

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

[0011] Preferably, when the composition is subjected to dynamic mechanical load, the internal energy dissipation thereof follows a hierarchical response mechanism, wherein when the value of the strain energy absorbed by a local microzone reaches and exceeds the value of the average dissociation energy of a single coordination bond in the ionic bond crosslinking network, the ionic bond crosslinking network reversibly dissociates 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, the metal ion with variable oxidation states, while serving as a physical crosslinking point of the ionic bond crosslinking network, constitutes an in-situ free radical quenching center which reduces the free radicals generated by the polyimide chain under a high-temperature oxygen-rich environment through its own valence state change.

[0013] Preferably, the hydrophobic side chains are fluorine-containing alkyl side chains; the mole fraction of the diamine monomers with hydrophobic side chains in the total diamine monomers is 5% to 20%.

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

[0015] Preferably, the composition further comprises a semi-crystalline thermoplastic polymer, the thermoplastic polymer is dispersed in the polyimide resin in an amorphous state and undergoes thermal crystallization to form a physical crosslinking network to anchor the segments of the polyimide when the ambient temperature is higher than the glass transition temperature of the polyimide resin, thereby inhibiting creep; the composition further comprises a porous zeolite molecular sieve treated by ion exchange, the pores of the molecular sieve are pre-loaded with metal ions of the same type as the metal ion source with variable oxidation states, and the molecular sieve releases the loaded metal ions to the ionic crosslinking network while adsorbing impurities in the chemical environment of the composition.

[0016] Preferably, the composition further comprises a plurality of microcapsules dispersed in the composition, the microcapsules contain a force-sensitive color-changing dye or its precursor inside, the shell of the microcapsules ruptures at an energy threshold, the energy threshold is higher than the average dissociation energy of the single coordination bond in the ionic crosslinking network and lower than the average bond energy of the covalent bonds constituting the polyimide covalent network, and the rupture releases the force-sensitive color-changing dye or its precursor to produce a color change.

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

[0018] Step a, polycondensation reaction of at least three different diamine monomers and dianhydride monomers in a solvent to obtain a solution containing polyamide acid precursors;

[0019] Step b, adding a metal ion source with variable oxidation states to the solution containing polyamide acid precursors, and mixing to obtain a to-be-cured composition;

[0020] Step c, coating the to-be-cured composition on a substrate;

[0021] Step d, subjecting the substrate coated with the to-be-cured composition to a temperature rising curing process, in which the polyamide acid precursor is dehydrated and cyclized to form a polyimide covalent network, while the metal ions with variable oxidation states are coordinated with the side chain carboxyl functional groups to form an ionic bond crosslinking network, and the hydrophobic side chains spontaneously enrich around the ionic bond crosslinking network to form a hydrophobic isolation layer.

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

[0023] 1. The present application provides an adhesive composition, wherein a polyimide resin containing carboxyl functional groups on the polymer main chain constitutes a continuous phase skeleton resistant to high temperature, and a divalent or multivalent metal ion source forms an ionic bond crosslinking network throughout the skeleton; under external force, due to the lower bond energy of ionic bonds than covalent bonds constituting the polyimide skeleton, stress will preferentially act on the ionic bond network and cause large-scale reversible dissociation, which absorbs external energy and avoids irreversible fracture of the polyimide covalent skeleton, and after the stress is removed, the dissociated ionic bonds can be reformed into crosslinks under the retraction of molecular chain segments, in this way, the externally input destructive energy is not passively borne by the material, but is converted into internal conformation adjustment that can be restored, so that the heat resistance of the adhesive and the structural integrity of the bearing structure, which have been long-term mutually restrictive properties, can be coordinated.

[0024] 2. When the metal ion source provides metal ions with variable oxidation states, the adhesive composition exhibits another operating mechanism in a high-temperature oxygen-rich environment; at this time, the ionic bond crosslinking points, while limiting chain segment movement as physical anchor points, also constitute in-situ recyclable free radical quenching centers, when polymer chains produce free radicals due to thermal oxidation, adjacent metal ions reduce the polymer free radicals by changing their own valence states, repairing the chemical structure of the molecular chain, and further avoiding the collapse of the covalent network caused by chain degradation reactions; this design reuses the ionic network originally only used to dissipate mechanical stress as a reaction center to inhibit chemical degradation, so that when the material is subjected to force, heat, and oxygen complex extreme conditions, its physical durability and chemical stability, two different aspects of aging paths, are inhibited by the same technical element.

[0025] 3、The present application also introduces multi-walled carbon nanotubes and heavy metal modified silica nanoparticles in the composition, the two particles synergistically act in the polyimide matrix to construct a composite phonon transmission path; when bonding two heterogeneous materials with significantly different thermal conductivities, the low-frequency phonons on the substrate side couple with the heavy metal modification layer, while the high-frequency phonons on the chip side couple with the carbon nanotubes, and the energy is transmitted through the broadband transmission characteristics of the two mediators, establishing an effective transmission bridge at the heterogeneous interface, which relieves the interface thermal resistance formed due to the mismatch of the two materials' lattice vibration modes, and reduces the additional thermal stress caused by local heat accumulation from the source; this mechanism cooperates with the aforementioned dynamic dissipation mechanism of the ionic bond network, so that the bonding layer not only can effectively dissipate the generated stress, but also can actively manage the heat flow distribution to inhibit the excessive generation of stress, forming a full-link management structure from energy generation to dissipation. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The component structure and functional relationship diagram of the high-temperature resistant adhesive of the present application;

[0027] Figure 2 The covalent ionic composite network and functional unit diagram of the adhesive of the present application;

[0028] Figure 3 The multi-mechanism synergistic protection diagram of the adhesive of the present application in packaging applications;

[0029] Figure 4 The timing diagram of the hierarchical energy dissipation and structure self-recovery process of the present application. DETAILED DESCRIPTION

[0030] To make the technical solutions and advantages of the present application clearer, the present application will be further described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[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 in the rigid covalent network, the composition of the present application further comprises a source of metal ions with variable oxidation states, such as cerium (III) acetate , or manganese acetate, iron acetate; during the preparation process, the source of metal ions is added to the polyamic acid precursor solution formed by the reaction of diamine monomers with dianhydride monomers, and during the subsequent thermal curing process, the polyamic acid precursor undergoes dehydration and cyclization to form a polyimide covalent network, while the metal ions, such as , coordinate with the carboxyl functional groups of the side chains to form an ionic bond crosslinked network with the metal ions as the crosslinking center in situ; the composition thus forms a hierarchical energy dissipation internal structure, and the energy response follows a predetermined hierarchical mechanism, i.e. when the adhesive is subjected to dynamic mechanical loading, the value of the strain energy absorbed by a local microzone is lower than the average bond energy of the covalent bonds constituting the polyimide covalent network , but reaches and exceeds the average dissociation energy of a single coordination bond in the ionic bond crosslinked network , then the ionic bond network with lower bond energy will undergo large-scale reversible dissociation first, which absorbs and dissipates a large amount of external strain energy, thereby avoiding irreversible rupture of the main covalent network; after the stress is removed, the polymer segments that have been pulled apart will shrink under the action of intermolecular forces, and the dissociated ionic bonds will recombine in situ or adjacent positions, restoring the network performance; in this way, the destructive mechanical stress is converted into recoverable conformational adjustment within the network, achieving the synergy of stress dissipation and high temperature resistance.

[0034] The mole fraction of the diamine monomer containing carboxyl functional groups in all diamine monomers is set in the working window of 5-15 mol%; the range is determined based on the fact that when the mole fraction is lower than 5%, the density of the ionic bond crosslinked network formed is insufficient, the number of ionic bonds per unit volume for energy dissipation is too small, and the dynamic toughening effect is not obvious; when the mole fraction is higher than 15%, too many polar carboxyl side chains may cause excessive association of the polyamic acid precursor in solution, increasing the viscosity, and at the same time, too high an ionic crosslinking density after curing may limit the movement of polymer segments to some extent, affecting the toughness, so 5-15 mol% is confirmed as an interval for achieving the synergy of processability and dynamic toughness; similarly, the mole equivalent of the source of metal ions with variable oxidation states relative to the carboxyl functional groups of the side chains is set to 0.3-0.8, because when the equivalent is lower than 0.3, the number of metal ions is insufficient to form effective ionic bond crosslinking for most carboxyl groups, resulting in poor network integrity; when the equivalent is higher than 0.8, the excess free metal ions may act as a plasticizer in the system to reduce the glass transition temperature of the material, or become stress concentration points, therefore the range of 0.3-0.8 ensures that the ionic bond 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 reaches the maximum value, and the 5% thermal weight loss temperature of the corresponding sample No less than The parameter combination.

[0037] When bonding two heterogeneous materials with significantly different thermal conductivities, the interfacial thermal resistance formed at the interface due to the mismatch of lattice vibration modes will cause local hot spots, thereby generating additional thermal stress; therefore, the composition of the present application can further comprise multi-walled carbon nanotubes (MWCNTs) as a thermal conductive filler and silica ) nanoparticles with surface modification by heavy metals (such as bismuth ); the two nanoparticles work synergistically to construct a phonon bridging network at the bonding interface, wherein the carbon nanotubes, due to their wide phonon spectrum, can couple with the phonons of various materials and are responsible for wide-band energy transfer; and the heavy metal atoms on the surface of the silica nanospheres have a large mass, 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 problem of interfacial phonon mismatch, improves the interfacial heat flow, and inhibits the generation of additional thermal stress caused by interfacial thermal resistance from the source; for scenarios that need to serve under continuous high temperature and constant static load, the dynamic ionic bond network of the present application may allow the polymer chain segments to slowly slip, i.e. creep; to solve this problem, the composition can also contain a semi-crystalline thermoplastic polymer, such as polyether ether ketone (PEEK); under conventional curing processes and most working temperatures, PEEK is dispersed in the polyimide matrix in the form of amorphous molecular chains; when the ambient temperature continues to rise and enters the high-risk area of creep, such as above the glass transition temperature of the polyimide resin, the activity of the PEEK molecular segments increases, and thermal-induced crystallization occurs, forming a large number of nanoscale crystalline regions; these in-situ formed PEEK microcrystals act as physical crosslinking points, penetrating and anchoring between the polyimide networks, limiting the slip ability of the polymer main chain, thereby improving the anti-creep performance of the material.

[0038] To enhance the stability of the ionic bond network in complex chemical environments, the composition can also contain a porous zeolite molecular sieve, such as ZSM-5 molecular sieve, which has been ion-exchanged; before adding, the molecular sieve is ion-exchanged in a concentrated solution of metal salt used in the composition, such as cerium acetate, so that it is pre-loaded with the same metal ions ); during service, when the metal ions in the ionic network are consumed by impurities in the external environment, the metal ions stored in the molecular sieve channels will be released according to the principle of chemical equilibrium to supplement the ionic network, maintaining its crosslinking density; at the same time, the specific surface area and channel structure of the molecular sieve enable it to adsorb small molecular acidic or basic impurities in the environment, playing a role in purifying the microenvironment of the ionic network, thereby maintaining the working efficiency of the ionic network in a chemically corrosive environment; to realize the visualization of the cumulative damage inside the material, the composition can also contain a plurality of microcapsules dispersed therein, the inside of which contains a force-sensitive color-changing dye or its precursor; the key to this scheme is the setting of the energy threshold, i.e. the breaking energy of the microcapsule shell designed to be higher than the dissociation energy of the ionic network but lower than the breaking energy of the covalent network , i.e. ; when the adhesive is subjected to stress, the ionic bonds are first dissociated to dissipate energy, and if the stress level and degree of deformation increase, it means that the ionic network has been largely dissociated, and the deformation energy of the matrix will exceed , causing the microcapsule shell to rupture; the released dye precursor reacts with specific components in the matrix to produce irreversible color changes in the damaged area, thereby presenting the invisible microscopic damage history as a visual signal.

[0039] In the preparation process of the polyamic acid precursor, at least three different diamine monomers and dianhydride monomers are subjected to polycondensation reaction in an aprotic polar solvent, in order to ensure that the target molecular weight is obtained and facilitate subsequent processing, the total molar amount of all diamine monomers to the molar amount of dianhydride monomers is controlled in 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 to 50°C, and the reaction time is 4 to 24 hours until the system viscosity reaches stable; the solution containing the polyamic acid precursor obtained therefrom has a solid content of 10% to 30% by weight, preferably 15% to 25%, to obtain a suitable viscosity for coating process; to support a wider selection of materials, in addition to -diamino diphenyl ether or p-phenylenediamine, one or more combinations of -diamino diphenyl methane or -(9-fluorenyl) diphenylamine, dianhydride monomers, in addition to pyromellitic dianhydride or 4,4'-(hexafluoroisopropylidene) phthalic anhydride, one or more combinations of -diphenone tetraacid dianhydride, -oxo phthalic 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... Thus, the chemical damage of covalent network is repaired at molecular scale; the operation of this chemical repair mechanism relies on the physical toughness provided by ionic network, which inhibits the propagation of micro-cracks and in turn reduces the continuous exposure of new polymer surface to oxidative environment; in this way, the physical dissipation mechanism and chemical repair mechanism are interdependent, enabling the material to resist chemical degradation while bearing mechanical stress; in this process, trace amount of water vapor in the environment penetrates into the adhesive and hydrates with the polar ionic bonds, thus reducing the energy dissipation capacity of ionic network; the fluorine-containing alkyl side chains, which have been spontaneously enriched around the ionic network during the curing stage, form a low-surface-energy hydrophobic barrier layer, which hinders the intrusion of water molecules at the molecular scale and maintains the non-polar micro-environment around the ionic cross-linking points; this hydrophobic shielding preserves the non-polar environment of ionic network, thus maintaining the operational efficiency of physical dissipation and chemical repair mechanisms in a humid and hot environment.

[0042] After going through the complete accelerated aging life cycle test, the gallium nitride radio frequency power amplifier module is analyzed by sectioning, and the results show that the adhesive interface has no delamination or cracks, the thermal resistance of the module has no significant increase compared to the initial state, and there is no obvious degradation of the internal chemical structure of the adhesive; the adhesive maintains the structural integrity of the adhesive interface under the dual working conditions of dynamic stress and chemical attack through the aforementioned energy dissipation and chemical structure repair mechanisms.

[0043] Example 2: To objectively verify the influence of introducing ionic crosslinking network into polyimide covalent network on the structural integrity of the material under dynamic thermal stress, two samples of the inventive sample group and the control group were prepared for comparative test in this example. The inventive sample group was prepared by condensation polymerization of conventional aromatic diamine, 3,5-diaminobenzoic acid containing carboxyl functional group and diamine monomer with fluorine-containing alkyl side chain with dianhydride monomer, and then adding cerium(III) acetate in the obtained polyamide acid precursor solution, followed by film coating and gradient temperature curing. The control group was prepared by using the same monomer components and process parameters except that 3,5-diaminobenzoic acid and cerium(III) acetate were not added, so as to form a reference system containing only pure polyimide covalent network, thereby ensuring that the only variable between the two groups of samples is whether there is an ionic crosslinking network. The test procedure was as follows: first, according to the ASTM D1002 standard, the initial shear strength of the two groups of samples was measured at 250°C high temperature condition, and the results showed that the initial performance of the inventive sample group and the control group was comparable, which was 24.8 MPa and 25.1 MPa, respectively; then, the two groups of samples were placed in the same thermal shock test chamber and subjected to repeated thermal cycle treatment in the temperature range of -55°C to 175°C, and the cycle of each cycle was set to 60 minutes. This parameter setting aims to simulate the severe service environment while effectively accelerating the fatigue damage process of the material; at different stages of thermal cycle treatment, the samples were taken out in batches for retest of high temperature shear strength and observation of micro morphology.

[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 shows that the synergistic effect of multi-walled carbon nanotubes and heavy metal modified silica nanoparticles through phonon bridging mechanism is better than that of single thermal conductive filler in improving the interface heat transfer efficiency.

[0046] Embodiment 3: This embodiment is in conjunction with Figures 1 to 4 a high-temperature-resistant adhesive and a preparation method thereof, as shown in Figure 1 , which takes a polyimide resin precursor formed by reacting three different functional diamine monomers and dianhydride monomers, and a metal ion source providing metal ions with variable oxidation states as core raw materials, and can selectively add functional fillers to achieve multifunctional integration. When the above components undergo temperature curing treatment, a synergistic effect of multiple physical and chemical processes occurs, and finally a composite network structure is formed. This structure is composed of a polyimide covalent network that provides high-temperature-resistant performance and basic mechanical strength, an ionic bond crosslinking network formed by metal ions and carboxyl coordination and serving as a reversible energy dissipation unit, and a molecular level hydrophobic shielding layer for the ionic bond formed by the spontaneous enrichment of hydrophobic side chains. This composite network structure gives the adhesive a hierarchical energy dissipation mechanism, that is, under 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 being destroyed. At the same time, this structure also derives the dual functions of in-situ free radical quenching center and chemical self-healing and wet heat environment protection. The metal ions reduce polymer radicals by changing their valence states, inhibit chain degradation reactions in high-temperature oxygen-rich environments, and realize chemical stability and environmental adaptability through the dual functions of the ionic network.

[0047] As shown in Figure 2 , the thick solid line represents the main skeleton of the polyimide covalent network, which is grafted with side chain carboxyl functional groups , and metal ions coordinate with the side chain carboxyl functional groups to form an ionic bond crosslinking network centered on metal ions. These ionic bond crosslinking points also constitute chemical self-healing reaction centers. Around the ionic bond crosslinking points, the hydrophobic side chains introduced by hydrophobic diamine monomers spontaneously enrich to form a hydrophobic shield for the ionic bond. Functional fillers such as multi-walled carbon nanotubes and heavy metal modified silica nanoparticles can also be dispersed in the system. The entire system realizes a hierarchical energy dissipation mechanism through the hierarchical response between the ionic bond network and the covalent network.

[0048] As shown in Figure 3 , in high-power gallium nitride radio frequency chips and copper-tungsten The application mechanism of the adhesive in the packaging of the heat dissipation substrate is embodied. Due to the mismatch of the thermal expansion coefficients of the chip and the substrate, the high-temperature-resistant adhesive layer is challenged under the combined action of a high-temperature oxygen-rich environment and a cyclic thermal stress. At this time, the ion network in the adhesive absorbs the thermal stress through reversible dissociation to realize dynamic energy release, thereby inhibiting the initiation of microcracks. Meanwhile, the metal ions act as free radical quenching centers to perform chemical structure self-repairing on the material and inhibit the thermal-oxidative aging of the material. In addition, the composite heat-conductive filler improves the heat conduction by constructing a phonon bridge, relieves the interface thermal resistance, and reduces the 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] As shown in Figure 4 When an external stress applies a load to the adhesive, the strain energy inside the adhesive begins to accumulate. If the value of the strain energy exceeds the dissociation energy of the ionic bond, a large-scale reversible dissociation of the ionic bond will be triggered. This process absorbs and dissipates the strain energy, thereby protecting the main covalent network from irreversible rupture, achieving structure recovery. If the strain energy does not reach the threshold of ionic bond dissociation, the adhesive will elastically deform. After the external stress removes the load, whether the energy is dissipated through ionic bond dissociation or only elastic deformation, the segments of the polymer will shrink, the dissociated ionic bonds will recombine, and finally the performance of the adhesive will recover.

[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: In an aerospace application where high batch-to-batch consistency of performance is required, the reactivity of key raw materials is calibrated in batches before the adhesive is produced on a large scale; as an example, a representative sample of a new batch of dianhydride monomer is taken, and a small-scale synthesis of polyamic acid precursor is carried out under standard reaction conditions with a set of benchmark diamine monomer components whose performance has been calibrated; after the reaction is complete, the intrinsic viscosity of the obtained polyamic acid precursor solution is determined by an Ubbelohde viscometer, and the value is compared with a pre-set 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 determined to be qualified; if the intrinsic viscosity is lower than the lower limit of the window, adjustments are made in the subsequent large-scale production by adjusting the reaction endpoint or monomer ratio, which aims to ensure the consistency of the molecular weight and chain structure of the polyamic acid precursor, which is the basis of the performance of the adhesive, among different production batches.

[0053] To trigger the force-sensitive color-changing microcapsules contained in the composition at a pre-set damage threshold, the mechanical response characteristics of the microcapsules need to be matched and calibrated with the mechanical behavior of the adhesive matrix; this calibration process first obtains the storage modulus, loss factor, and ultimate failure strain of the adhesive matrix material without microcapsules through dynamic mechanical analysis (DMA) and uniaxial tensile testing, to characterize the strain interval at which the ionic bond network begins to dissipate energy on a large scale and the strain limit at which the covalent network is macroscopically destroyed; then, several batches of microcapsules with different shell thicknesses and crosslinking densities are dispersed in the adhesive matrix at a fixed content to make composite samples, and these samples are subjected to tensile testing, and the tensile strain corresponding to the time when the color of the sample surface begins to change significantly is recorded in real time by a high-resolution camera; finally, the microcapsule batch 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 seventy percent of the ultimate failure strain of the matrix material is selected, so that the hierarchical energy relationship of the adhesive matrix and the microcapsules is matched to a specific material system that can be verified and selected through engineering experiments.

[0054] Example 6: In an adhesive application for a long-time serving structure component of a hot end of an aero-engine, the engineering goal is to maximize the long-term thermo-mechanical stability of the adhesive under continuous high temperature and static load, which is defined by two key performance indicators, i.e., the creep strain needs to be minimized, and the fracture toughness value ​The initial value is maintained at 85% or more; to achieve this goal, first, an offline optimization parameter search is performed for the addition amount of semi-crystalline thermoplastic polymer polyether ether ketone (PEEK), and a series of adhesive samples are prepared, which are consistent with the formula determined in Example 3 except that the PEEK content is different, and the addition amount of PEEK is 2%, 5% and 8% of the total mass, respectively. According to the standard of ASTM D2990, the samples are 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 is recorded. The results show that the 100-hour creep strain of the sample with 5% PEEK addition is lower than the threshold required by the target application, and the fracture toughness value compared with the reference sample without PEEK, only decreases by 5%, while the sample with 8% addition has the smallest creep, but its value decreases by more than 15%, so 5% is determined as the PEEK addition amount that meets the above optimization goal.

[0055] To ensure the chemical environmental stability of the adhesive in the corrosive atmosphere, the porous zeolite molecular sieve as the ion buffer unit needs to be subjected to standardized ion exchange pretreatment and qualification verification. In this process, ZSM-5 molecular sieve is first calcined at 550°C for 4 hours, then immersed in a 1.0 mol / L cerium(III) acetate aqueous solution, and ion exchanged at 80°C for 24 hours with stirring. After ion exchange, the molecular sieve is filtered, washed and dried. Finally, the treated molecular sieve sample is quantitatively analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). Only when the cerium content is within the target window of 3wt% to 5wt%, the batch of molecular sieve is recognized as a qualified functional filler. This optimization parameter search and qualification verification process obtains a specific formula containing 5wt% PEEK and 2wt% of the qualified ion-exchanged ZSM-5 molecular sieve, and the components are determined by reproducible engineering experiments to meet the preset multidimensional performance requirements.

[0056] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application.

[0057] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application.

Claims

1. A high temperature resistant adhesive, characterized by, comprising: a polyimide resin, the polymer backbone of the polyimide resin is formed from at least three different diamine monomers and a dianhydride monomer, wherein the at least three different diamine monomers comprise a carboxyl functional group-containing diamine monomer and a diamine monomer having a hydrophobic side chain in its molecular structure; a source of metal ions with variable oxidation states; the solution comprising a polyamic acid precursor formed from the reaction of diamine monomers and dianhydride monomers and the source of metal ions with variable oxidation states is subjected to temperature elevation curing to cyclize the polyamic acid precursor into a polyimide while the metal ions with variable oxidation states coordinate with the side chain carboxyl functional groups to form an ionic crosslinking network in situ in the polyimide covalent network, and the hydrophobic side chains spontaneously enrich around the ionic crosslinking network to form a hydrophobic separation layer during the temperature elevation curing; and, the composition further comprises a semi-crystalline thermoplastic polymer dispersed in the polyimide resin in an amorphous state and undergoes thermal-induced crystallization to form a physical crosslinking network to anchor the polyimide segments when the ambient temperature is higher than the glass transition temperature of the polyimide resin to suppress creep, and the composition further comprises a porous zeolite molecular sieve subjected to ion exchange treatment, the pores of the molecular sieve are pre-loaded with the same metal ions as the source of metal ions with variable oxidation states, and the molecular sieve releases its loaded metal ions to the ionic crosslinking network while adsorbing impurities in the chemical environment of the composition.

2. The high temperature resistant adhesive according to claim 1, characterized in that, The mole fraction of the carboxyl functional group-containing diamine monomer in the total diamine monomers is 5 to 15 percent; and the mole equivalent of the source of metal ions with variable oxidation states relative to the side chain carboxyl functional groups is 0.3 to 0.

8.

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

4. The high temperature resistant adhesive according to claim 1, wherein The hydrophobic side chain is a fluorine-containing alkyl side chain; and the mole fraction of the diamine monomer having the hydrophobic side chain in its molecular structure in the total diamine monomers is 5 to 20 percent.

5. The high temperature resistant adhesive according to claim 1, wherein The composition further comprises a plurality of microcapsules dispersed in the composition, the interior of the microcapsules contains a force-sensitive color-changing dye or its precursor, the shell of the microcapsules ruptures at an energy threshold, the energy threshold is higher than the average dissociation energy of a single coordination bond in the ionic crosslinking network and lower than the average bond energy of the covalent bonds constituting the polyimide covalent network, and the rupture releases the force-sensitive color-changing dye or its precursor to produce a color change.

6. A method of producing a high-temperature-resistant adhesive according to any one of claims 1 to 5, characterized by, comprising the following steps: step a, subjecting at least three different diamine monomers and a dianhydride monomer to a polycondensation reaction in a solvent to obtain a solution comprising a polyamic acid precursor; step b, adding a source of metal ions with variable oxidation states to the solution comprising the polyamic acid precursor, and mixing to obtain a composition to be cured; step c, coating the composition to be cured on a substrate; Step d. subjecting the substrate coated with the composition to be cured to a heat-up curing process, during which the polyamic acid precursor is dehydrated and cyclized to form a polyimide covalent network while the metal ions with variable oxidation state are coordinated with the pendant carboxyl functional groups to form an ionic bond crosslinked network, and the hydrophobic side chains spontaneously enrich around the ionic bond crosslinked network to form a hydrophobic isolation layer.

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