A perfluoroether bond network and carbon dot node enhanced self-lubricating polyimide resin, a preparation method and application thereof

Abstract

This invention belongs to the field of polymer composite materials technology, specifically relating to a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement, its preparation method, and applications. The invention involves mixing carboxyl-functionalized carbon dots, an ether-containing aromatic diamine, and a polar aprotic solvent to obtain a carbon dot-diamine pre-assembled system, which is then polymerized with a perfluoroaromatic dianhydride to obtain a linear polyamic acid solution. This linear polyamic acid solution is then reacted with a phenylacetylene-containing active end-capping agent to obtain a polyamic acid solution with a three-dimensional network structure. Finally, the polyamic acid solution with the three-dimensional network structure is cured in a protective gas atmosphere to obtain a self-lubricating polyimide resin. The self-lubricating polyimide resin provided by this invention achieves a synergistic improvement in load-bearing capacity, wear resistance, and structural stability under high temperature and high load conditions, and can be widely applied in aerospace high-temperature bearings, high-load sealing rings, wear-resistant coatings for extreme conditions, and high-temperature sliding components.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, specifically relating to a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement, its preparation method, and its application. Background Technology

[0002] Polyimide resins are often used in friction components in high-temperature environments due to their excellent thermal stability and mechanical properties. However, under extreme high temperatures (such as above 350 °C) and high load conditions (18 N), the molecular chain segment movement of traditional polyimides intensifies, making the material prone to plastic deformation and rapid wear. This leads to a sharp increase in the coefficient of friction and a rapid decrease in load-bearing capacity. This limits its further application in high-end aerospace, precision machinery, and other fields.

[0003] Existing technologies have attempted to reinforce polyimides with nanofillers (such as graphene and carbon nanotubes), but due to weak interfacial bonding and uneven dispersion, interfacial debonding easily occurs under high temperature and high shear, resulting in limited reinforcement effects. For example, a graphene-modified polyimide composite material still has a high coefficient of friction above 300 °C, and its load-bearing capacity is not sufficiently improved. Summary of the Invention

[0004] The purpose of this invention is to provide a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement, its preparation method, and its application. The self-lubricating polyimide resin provided by this invention achieves a synergistic improvement in load-bearing capacity, wear resistance, and structural stability under high temperature and high load conditions. It can maintain structural stability, low friction, and ultra-high load-bearing capacity under high temperature and high load conditions, and can be widely used in aerospace high-temperature bearings, high-load sealing rings, wear-resistant coatings for extreme working conditions, and high-temperature sliding components.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement, comprising the following steps: (1) A carbon dot-diamine pre-assembled system is obtained by mixing carboxyl-functionalized carbon dots, an aromatic diamine containing ether bonds, and a polar aprotic solvent, and adjusting the pH value to >7. The carboxyl-functionalized carbon dots are carboxyl-functionalized doped and / or undoped carbon dots. The doped carbon dots include one or both of nitrogen-doped carbon dots and nitrogen-boron co-doped carbon dots. The mass percentage of the carboxyl-functionalized carbon dots to the total mass of the aromatic diamine containing ether bonds, the perfluoroaromatic dianhydride, and the active end-capping agent containing phenylacetylene groups is <0.75 wt.%. (2) The carbon dot-diamine pre-assembly system is polymerized with perfluoroaromatic dianhydride to obtain a linear polyamic acid solution; the polymerization includes the following steps: heating the carbon dot-diamine pre-assembly system to a first temperature and reacting it with a portion of the perfluoroaromatic dianhydride to obtain a star-shaped prepolymer; further heating the star-shaped prepolymer to a second temperature and reacting it with the remaining perfluoroaromatic dianhydride to obtain a linear polyamic acid solution, wherein the first temperature is ≥40 °C and the first temperature is < the second temperature; (3) The linear polyamic acid solution is reacted with an active end-capping agent containing phenylacetylene groups to obtain a polyamic acid solution with a three-dimensional network structure; (4) The polyamic acid solution with a three-dimensional network structure is cured in a protective gas atmosphere to obtain the self-lubricating polyimide resin; the curing includes a first stage curing, a second stage curing and a third stage curing in sequence; the temperature of the first stage curing is ≤120 ℃; the second stage curing is carried out in a cycle of 1 to 3 times "cooling down from the first temperature to the second temperature, holding at the second temperature and then heating up from the second temperature to the first temperature" under a pressure ≥0.5 MPa, wherein the first temperature is 220~250 ℃, the second temperature is 20~40 ℃ lower than the first temperature, and the holding time is 30~90 min; the temperature of the third stage curing is ≥300 ℃.

[0006] Preferably, in step (1), the surface carboxyl group density of the carboxyl functionalized carbon dots is not less than 0.5 mmol / g; the particle size of the carboxyl functionalized carbon dots is 2~5 nm; the mass percentage of the carboxyl functionalized carbon dots to the total mass of the ether-containing aromatic diamine, perfluoroaromatic dianhydride and the phenylacetylene-containing active end-capping agent is 0.01~0.5 wt.%; the ether-containing aromatic diamine is at least one of the aromatic diamines containing a diphenyl ether unit, a trifluoromethyl-substituted diphenyl ether unit or a diphenyl ether unit in its structure; and the pH value is 7.5~9.

[0007] Preferably, in step (2), the first temperature is 40~60 ℃; the second temperature is 60~80 ℃; the mass of the partial perfluoro aromatic dianhydride accounts for 30~60% of the total mass of the perfluoro aromatic dianhydride; the perfluoro aromatic dianhydride is at least one of the perfluoro aromatic tetracarboxylic dianhydrides whose structure contains hexafluoroisopropyl or octafluorobiphenyl as a linking group.

[0008] Preferably, in step (3), the active capping agent containing phenylacetylene is at least one of aromatic anhydride capping agents having phenylacetylene substituents; the reaction temperature is 50~80 ℃ and the time is 8~20 h.

[0009] Preferably, in step (4), the curing temperature of the first stage is 80~120 ℃, and the heat preservation time is 1~3 h; The heating rate from the first stage curing temperature to the first temperature is 2~5 ℃ / min, the cooling rate from the first temperature to the second temperature is 1~2 ℃ / min, the heating rate from the second temperature to the first temperature is 2~5 ℃ / min, and the pressure for the second stage curing is 0.5~1 MPa. The curing temperature for the third stage is 300~400 ℃, the pressure is 0.5~1 MPa, and the holding time is 1~3 h.

[0010] Preferably, the ether-containing aromatic diamine is at least one of 4,4'-diaminodiphenyl ether (ODA) and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA); the perfluoroaromatic dianhydride is at least one of 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA) and 4,4'-(octafluorobiphenyl)phthalic anhydride (8FDA); and the phenylethynyl-containing active end-capping agent is at least one of 4-phenylethynyl phthalic anhydride (4-PEPA) and 3-phenylethynyl phthalic anhydride (3-PEPA).

[0011] Preferably, the method for preparing the carboxyl-functionalized carbon dots includes the following steps: The raw materials are mixed with water and subjected to microwave pulse treatment and hydrothermal reaction sequentially to obtain the carboxyl-functionalized carbon dots. The raw materials are a carbon source or a carbon source and a dopant. The dopant is a nitrogen source or a nitrogen source and a boron source. The carbon source includes citric acid and / or benzoic acid, the nitrogen source includes benzenetetramine and / or urea, and the boron source is boric acid. The pulse period of the microwave pulse treatment is 5-10 s, and the total duration is 3-5 min. The hydrothermal reaction includes a first stage hydrothermal reaction, a second stage hydrothermal reaction, and a third stage hydrothermal reaction sequentially. The temperature of the first stage hydrothermal reaction is < the temperature of the second stage hydrothermal reaction is < the temperature of the third stage hydrothermal reaction. The temperature of the first stage hydrothermal reaction is 160-180 ℃, the temperature of the second stage hydrothermal reaction is 180-220 ℃, and the temperature of the third stage hydrothermal reaction is 220-240 ℃.

[0012] The present invention provides a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement prepared by the preparation method described above.

[0013] Preferably, the self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement has a friction coefficient of no more than 0.1 under extreme working conditions of no less than 300 °C and no less than 18 N, and a wear rate of no more than 1.0 × 10⁻⁶. -13 m 3 / (N·m).

[0014] The present invention provides the application of the self-lubricating polyimide resin based on perfluoroether bond network and carbon dot node reinforcement described above in bearings, sealing rings, wear-resistant coatings or sliding parts.

[0015] This invention provides a method for preparing a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot node reinforcement. The preparation method provided by this invention employs a combined approach of "carboxyl-directed induced hierarchical self-assembly polymerization - programmed topological locking." First, under alkaline conditions (pH > 7), the carboxyl groups on the surface of the carboxyl-functionalized carbon dots are deprotonated to form negatively charged carboxylate groups, which then react with the protonated primary amine groups (-NH3) in an ether-containing aromatic diamine. + Through strong electrostatic attraction and hydrogen bonding, a dynamic and reversible "carbon dot-diamine ion complex" is spontaneously formed, resulting in a carbon dot-diamine pre-assembled system. Then, this invention achieves in-situ node anchoring and network growth through hierarchical polymerization. Under the first temperature condition, some perfluoroaromatic dianhydride molecules preferentially react with the highly reactive, free or weakly bound diamine amino groups in the carbon dot-diamine pre-assembled system. This reaction is exothermic and alters the local chemical environment, weakening the electrostatic interaction of the original complex, thereby driving the diamine molecules already "pre-positioned" around the carbon dot to preferentially condense with the dianhydride. Thus, the growth starting point of the newly generated polyamic acid chain segments is directly "chemically locked" to the carbon dot surface, forming a "star-shaped prepolymer" with a single carbon dot as the core and radiating multiple short polyamic acid chains. Under the second temperature condition, the amino groups (from unreacted diamine) or carboxyl groups (from the chain ends) at the ends of the "star-shaped prepolymer" on the carbon dot surface become more reactive, serving as new growth points to continue polymerization with the remaining diamine and dianhydride. Polyamic acid chains extend outward from carbon dot "nodes" and couple and entangle with chains from other carbon dots, ultimately constructing a linear polyamic acid solution with carbon dots as covalent cross-linking points and long polyamic acid chains as a three-dimensional interconnected network. This invention uses a phenylacetylene-containing active end-capping agent for end-capping followed by curing. The curing process is divided into three stages, with the second stage employing a "thermo-mechanical coupled programmed curing method," the core of which lies in the dynamic temperature cycling of the second stage curing. This design simulates the complex stress states that polyimide materials may experience during high-temperature service. Through "pre-training" during the polyimide material preparation process, it actively induces carbon dot nodes to achieve a more thermodynamically stable and mechanically optimized distribution and bonding state within the polyimide network. Compared to traditional static step-curing, this significantly reduces residual stress within the polyimide material, avoiding early failure due to node agglomeration or interface defects, thereby enabling the polyimide material to achieve excellent high-temperature and high-load performance. In summary, the preparation method provided by this invention has the following superior effects: This invention is the first to propose a composite reinforcement model of "a flexible network of perfluoroether bonds combined with rigid carbon nodes of covalent bonds", which solves the contradiction between high-temperature toughness and load-bearing capacity of polyimide at the molecular scale.

[0016] This invention achieves enhanced interfacial bonding: carbon dots are anchored by chemical bonds, preventing interfacial failure at high temperatures, and ensuring uniform node distribution. This invention employs a phased curing process: the proposed "thermal-mechanical coupled programmed curing process" significantly reduces residual stress within the material, preventing early failure caused by node agglomeration or interfacial defects, and is a key process guarantee for achieving excellent high-temperature and high-load performance.

[0017] The preparation method provided by this invention is controllable and widely applicable: the raw materials are readily available and the process parameters are well-defined. By adjusting the type of carbon dots, the amount added, and the curing procedure, a series of graded materials with adjustable properties can be prepared, which is easy to scale up and promote application.

[0018] This invention provides a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot node reinforcement, prepared by the method described in the above technical solution. The self-lubricating polyimide resin provided by this invention is a polyimide resin based on a perfluoroether bond "fishnet-carbon dot node" reinforcement. The self-lubricating polyimide resin consists of a flexible three-dimensional skeleton composed of a polyimide network containing perfluoroether bonds, and nano-carbon dots are anchored as rigid nodes at the crosslinking points of the perfluoroether bond-containing polyimide network through chemical bonds, forming a "fishnet-node" reinforcement structure. The self-lubricating polyimide resin prepared by this invention exhibits excellent tribological properties at high temperatures. Experiments show that when the CDs addition amount is 0.5 wt.%, as... Figure 3 As shown, the obtained CDs-FOPI resin exhibits a friction coefficient as low as 0.006 and a wear rate as low as 5.82 × 10⁻⁶ under extreme conditions of 350 °C, 18 N load, and 0.05 m / s sliding speed. -14 m 3 / N·m, reaching a super-lubricated state. Attached Figure Description

[0019] Figure 1 The 1H NMR spectra of the FOPI prepared in Comparative Example 1 and the CDs-FOPI prepared in Example 1 of this invention; Figure 2 AFM phase map of CDs-FOPI prepared in Example 1 of this invention; Figure 3 The high-temperature load-bearing friction resistance of CDs-FOPI prepared in Example 1 of this invention. Detailed Implementation

[0020] This invention provides a method for preparing a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement, comprising the following steps: (1) A carbon dot-diamine pre-assembled system is obtained by mixing carboxyl-functionalized carbon dots, an aromatic diamine containing ether bonds, and a polar aprotic solvent, and adjusting the pH value to >7. The carboxyl-functionalized carbon dots are carboxyl-functionalized doped and / or undoped carbon dots. The doped carbon dots include one or both of nitrogen-doped carbon dots and nitrogen-boron co-doped carbon dots. The mass percentage of the carboxyl-functionalized carbon dots to the total mass of the aromatic diamine containing ether bonds, the perfluoroaromatic dianhydride, and the active end-capping agent containing phenylacetylene groups is <0.75 wt.%. (2) The carbon dot-diamine pre-assembly system is polymerized with perfluoroaromatic dianhydride to obtain a linear polyamic acid solution; the polymerization includes the following steps: heating the carbon dot-diamine pre-assembly system to a first temperature and reacting it with a portion of the perfluoroaromatic dianhydride to obtain a star-shaped prepolymer; further heating the star-shaped prepolymer to a second temperature and reacting it with the remaining perfluoroaromatic dianhydride to obtain a linear polyamic acid solution, wherein the first temperature is ≥40℃ and the first temperature is < the second temperature; (3) The linear polyamic acid solution is reacted with an active end-capping agent containing phenylacetylene groups to obtain a polyamic acid solution with a three-dimensional network structure; (4) The polyamic acid solution with a three-dimensional network structure is cured in a protective gas atmosphere to obtain the self-lubricating polyimide resin; the curing includes a first stage curing, a second stage curing and a third stage curing in sequence; the temperature of the first stage curing is ≤120 ℃; the second stage curing is carried out in a cycle of 1 to 3 times "cooling down from the first temperature to the second temperature, holding at the second temperature and then heating up from the second temperature to the first temperature" under a pressure ≥0.5 MPa, wherein the first temperature is 220~250 ℃, the second temperature is 20~40 ℃ lower than the first temperature, and the holding time is 30~90 min; the temperature of the third stage curing is ≥300 ℃.

[0021] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0022] Step (1): In this invention, carboxyl-functionalized carbon dots, ether-containing aromatic diamines, and a polar aprotic solvent are mixed and the pH value is adjusted to >7 to obtain a carbon dot-diamine pre-assembled system. The carboxyl-functionalized carbon dots are carboxyl-functionalized doped and / or undoped carbon dots, and the doped carbon dots include one or both of nitrogen-doped carbon dots and nitrogen-boron co-doped carbon dots. The mass percentage of the carboxyl-functionalized carbon dots to the total mass of the ether-containing aromatic diamine, perfluoroaromatic dianhydride, and phenylacetylene-containing active end-capping agent (i.e., CDs addition amount) is <0.75 wt.%. In this invention, the carboxyl-functionalized carbon dots have a Janus structure. The surface carboxyl group density of the carboxyl-functionalized carbon dots is preferably not less than 0.5 mmol / g, more preferably 0.50~1 mmol / g, and in the examples it can be 0.85 mmol / g, 0.68 mmol / g, or 0.50 mmol / g. The particle size of the carboxyl-functionalized carbon dots (CDs) is preferably 2-5 nm, and in the embodiments, it can be 3 nm, 2 nm, or 3.2 nm. The carboxyl-functionalized carbon dots can be carboxyl-functionalized nitrogen-boron co-doped carbon dots. Alternatively, the carboxyl-functionalized carbon dots can be carboxyl-functionalized nitrogen-doped carbon dots. Or, the carboxyl-functionalized carbon dots can be carboxyl-functionalized undoped carbon dots. This invention uses carboxyl-functionalized nitrogen-boron co-doped carbon dots as rigid nanonodes, which can be further covalently anchored at the network crosslinking points through strong amide bonds, greatly enhancing the nodes' resistance to deformation and stress dispersion capabilities.

[0023] In this invention, the percentage of the mass of the carboxyl functionalized carbon dots relative to the total mass of the ether-containing aromatic diamine, the perfluoro aromatic dianhydride, and the phenylacetylene-containing active end-capping agent is preferably 0.01 to 0.5 wt.%, more preferably 0.1 to 0.5 wt.%, and in the examples it can be 0.25 wt.% or 0.5 wt.%.

[0024] In this invention, the carboxyl-functionalized carbon dots are preferably prepared by a programmed microwave pulse-hydrothermal gradient annealing method. The carboxyl-functionalized carbon dots are carboxyl-functionalized carbon dots with a "hard core-soft shell" Janus structure.

[0025] In this invention, the method for preparing the carboxyl-functionalized carbon dots preferably includes the following steps: mixing the raw materials and water, and sequentially performing microwave pulse treatment and hydrothermal reaction to obtain the carboxyl-functionalized carbon dots. The raw materials are preferably a carbon source or a carbon source and a dopant. The dopant is preferably a nitrogen source or a nitrogen source and a boron source. The carbon source preferably includes citric acid and / or phenyltetracarboxylic acid. The nitrogen source preferably includes benzenetetramine and / or urea. The boron source is preferably boric acid. This invention first induces precursor pre-assembly and local carbonization through microwave pulse treatment to form sp-rich... 2 Rigid aromatic nuclei of carbon.

[0026] In this invention, the water can be deionized water. The microwave pulse treatment is carried out in a microwave reactor. The power of the microwave pulse treatment can be 800~850 W. The pulse period of the microwave pulse treatment is preferably 5~10 s, and the total duration is preferably 3~5 min. The hydrothermal reaction is carried out in a high-pressure reactor. The hydrothermal reaction includes a first-stage hydrothermal reaction, a second-stage hydrothermal reaction, and a third-stage hydrothermal reaction in sequence, and the temperature of the first-stage hydrothermal reaction is < the temperature of the second-stage hydrothermal reaction is < the temperature of the third-stage hydrothermal reaction. The temperature of the first-stage hydrothermal reaction is 160~180 ℃, and in the embodiment, it can be 160 ℃. The holding time of the first-stage hydrothermal reaction is preferably 2~4 h. The temperature of the second-stage hydrothermal reaction is preferably 180~220 ℃, and in the embodiment, it can be 200 ℃. The holding time of the second-stage hydrothermal reaction is preferably 2~4 h. The temperature of the third-stage hydrothermal reaction is preferably 220~240 ℃, and in the embodiment, it can be 240 ℃. The holding time of the third-stage hydrothermal reaction is preferably 2~4 h. This invention preferably employs the aforementioned gradient hydrothermal reaction method to epitaxially grow a carboxyl-rich polymer-like shell on the surface of a rigid aromatic core, forming Janus-structured carbon dots with a particle size of 2-5 nm and a surface carboxyl density ≥0.5 mmol / g. In this invention, after the hydrothermal reaction is completed, the temperature is lowered to room temperature to obtain a hydrothermal reaction solution. Preferably, this invention further processes the hydrothermal reaction solution to obtain the carboxyl-functionalized carbon dots. The post-processing preferably includes sequential dialysis and drying. The dialysis bag used for dialysis preferably has a molecular weight cutoff of 1000 Da. The drying can be freeze-drying.

[0027] In this invention, the ether-containing aromatic diamine is preferably at least one of the aromatic diamines containing a diphenyl ether unit, a trifluoromethyl-substituted diphenyl ether unit, or a diphenyl ether unit in its structure; more preferably, it is at least one of the aromatic diamines containing a diphenyl ether unit, a trifluoromethyl-substituted diphenyl ether unit, or a diphenyl ether unit as a core structure. The ether-containing aromatic diamine is more preferably at least one of 4,4'-diaminodiphenyl ether (ODA) and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA). In this invention, the polar aprotic solvent is preferably a weakly basic polar solvent, which in the examples can be N,N-dimethylacetamide (DMAc). The mixing is carried out in a protective gas atmosphere, which can be nitrogen. The pH value is preferably 7.5~9, which in the examples can be 8.5, 8, or 7.8. This invention mixes carboxyl-functionalized carbon dots, an ether-containing aromatic diamine, and a polar aprotic solvent, and adjusts the pH value to >7 to obtain a carbon dot-diamine pre-assembled system. The carbon dot-diamine pre-assembled system is prepared under ultrasonic or stirring conditions, preferably for 1-4 hours. By optimizing the ultrasonic or stirring time, this invention enables a more uniform distribution of components in the carbon dot-diamine pre-assembled system and achieves preliminary ordered arrangement at the molecular level, laying a spatial foundation for subsequent directional polymerization.

[0028] The preparation of the carbon dot-diamine pre-assembled system is carried out under a protective gas atmosphere and an ice-water bath. The preferred preparation method includes: dispersing the carboxyl-functionalized carbon dots in a polar aprotic solvent under a protective gas atmosphere, performing a first-stage ultrasonic treatment to obtain a dispersion; mixing the dispersion with an ether-containing aromatic diamine, then adding a pH adjuster to adjust the pH value, followed by a second-stage ultrasonic treatment or stirring treatment to obtain the carbon dot-diamine pre-assembled system. The preferred ratio of the carboxyl-functionalized carbon dots to the polar aprotic solvent is (0.03~0.06) g: 5 mL. The pH adjuster can be an organic base, and in the examples, it can be triethylamine. The first-stage ultrasonic treatment is performed in an ice-water bath. The preferred duration of the first-stage ultrasonic treatment or stirring treatment is 0.5~2 h. The second-stage ultrasonic treatment is performed in an ice-water bath, and the preferred duration of the second-stage ultrasonic treatment or stirring treatment is 0.5~2 h, more preferably 1~1.5 h. Under the condition that the pH value is preferably 7.5-9, the carboxyl group on the surface of the carboxyl-functionalized carbon dot is deprotonated to form a negatively charged carboxylate group, which reacts with the protonated primary amine group (-NH3) in the diamine monomer. +Through strong electrostatic attraction and hydrogen bonding, a dynamic and reversible "carbon dot-diamine ion complex" spontaneously forms. The invention employs a second-stage ultrasonic or stirring treatment lasting 0.5–2 hours, which allows for a more uniform distribution of the complex and achieves preliminary molecular-level ordered arrangement, laying the spatial foundation for subsequent directional polymerization.

[0029] Step (2): After obtaining the carbon dot-diamine pre-assembled system, the present invention polymerizes the carbon dot-diamine pre-assembled system with a perfluoroaromatic dianhydride to obtain a linear polyamic acid solution. In the present invention, the perfluoroaromatic dianhydride is preferably at least one of perfluoroaromatic tetracarboxylic dianhydrides containing hexafluoroisopropylidene or octafluorobiphenyl as a linking group in its structure. The perfluoroaromatic dianhydride is more preferably at least one of 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA) and 4,4'-(octafluorobiphenyl)phthalic anhydride (8FDA). The molar ratio of the perfluoroaromatic dianhydride to the ether-containing aromatic diamine is n:n+1, where n is the molar amount of the perfluoroaromatic dianhydride. In the present invention, the molar ratio of the perfluoroaromatic dianhydride to the ether-containing aromatic diamine is 2:3.

[0030] In this invention, the polymerization includes the following steps: heating the carbon dot-diamine pre-assembled system to a first temperature and reacting it with a portion of the perfluoroaromatic dianhydride to obtain a star-shaped prepolymer; heating the star-shaped prepolymer to a second temperature and reacting it with the remaining perfluoroaromatic dianhydride to obtain a linear polyamic acid solution, wherein the first temperature is ≥40 °C and the first temperature is < the second temperature. In this invention, the reaction is carried out at the first temperature to anchor polyamic acid segments to the carbon dot surface, forming a star-shaped prepolymer; then, the reaction is carried out at the second temperature to allow the polyamic acid chains to grow and interconnect, forming a linear polyamic acid solution.

[0031] In this invention, the first temperature is preferably 40-60 °C, and in some embodiments it can be 50 °C. After heating the carbon dot-diamine pre-assembled system to the first temperature, this invention preferably reacts it with a portion of the perfluoroaromatic dianhydride under the first temperature condition, and the reaction time is preferably 3-4 h. The second temperature is preferably 60-80 °C, and in some embodiments it can be 70 °C. After heating the star-shaped prepolymer to the second temperature, this invention preferably reacts it with the remaining perfluoroaromatic dianhydride under the second temperature condition, and the reaction time is preferably 4-10 h, more preferably 6-7 h. In this invention, the mass of the portion of the perfluoroaromatic dianhydride preferably accounts for 30-60% of the total mass of the perfluoroaromatic dianhydride, and in some embodiments it can be 50%.

[0032] In this invention, the polymerization is carried out in a protective gas atmosphere, which may be nitrogen. The polymerization is carried out in a reactor equipped with mechanical stirring, a protective gas inlet, and a constant-pressure dropping funnel. A portion of the perfluoroaromatic dianhydride is preferably dissolved in DMAc to form a perfluoroaromatic dianhydride solution, which is then added dropwise to the carbon dot-diamine pre-assembly system at a first temperature. After the addition is complete, the reaction continues at the first temperature for 3-4 hours to obtain the star-shaped prepolymer. The star-shaped prepolymer is then heated to a second temperature. The remaining perfluoroaromatic dianhydride is preferably dissolved in DMAc to form a perfluoroaromatic dianhydride solution, which is then added dropwise to the star-shaped prepolymer at a second temperature. After the addition is complete, the reaction continues at the second temperature for 4-10 hours, preferably 6-7 hours, to obtain the three-dimensional network precursor. In this invention, during the reaction at the first temperature, the dianhydride molecules preferentially react with the highly reactive, free or weakly bound diamine amino groups in the complex. The reaction is exothermic and alters the local chemical environment, weakening the electrostatic interactions of the existing complexes and driving the diamine molecules already pre-positioned around the carbon dots to preferentially condense with the dianhydrides. As a result, the growth starting point of the newly formed polyamic acid chain segments is directly "chemically locked" to the carbon dot surface, forming a "star-shaped prepolymer" with a single carbon dot as the core and radiating multiple short polyamic acid chains. When the reaction is carried out at a second temperature: at this higher temperature, the amino groups (from unreacted diamines) or carboxyl groups (from the chain ends) at the ends of the "star-shaped prepolymer" on the carbon dot surface become more active, serving as new growth points and continuing to polymerize with the remaining diamines and dianhydrides. The polyamic acid chains extend outward from the carbon dot "nodes," coupling and entangled with chains from other carbon dots, ultimately constructing a unified precursor solution with carbon dots as covalent cross-linking points and long polyamic acid chains as a three-dimensional interconnected network. After the dropwise addition, stirring is continued for 4–10 h to ensure sufficient molecular weight growth.

[0033] Step (3): After obtaining the linear polyamic acid solution, the present invention reacts the linear polyamic acid solution with a phenylacetylene-containing active capping agent to obtain a polyamic acid solution with a three-dimensional network structure. In the present invention, the phenylacetylene-containing active capping agent is at least one of aromatic anhydride capping agents with phenylacetylene substituents. The phenylacetylene-containing active capping agent is preferably at least one of 4-phenylacetylene phthalic anhydride (4-PEPA) and 3-phenylacetylene phthalic anhydride (3-PEPA). In the embodiments of the present invention, the molar ratio of the phenylacetylene-containing active capping agent, the perfluoroaromatic dianhydride, and the ether-containing aromatic diamine is 2:2:3.

[0034] In this invention, the reaction temperature is preferably 50-80 °C, more preferably 60-70 °C; the reaction time is preferably 8-20 h, more preferably 15-18 h. The raw materials for the reaction may also include DMAc. This invention does not have special requirements on the amount of DMAc used, as long as the subsequent molding process proceeds smoothly. This invention reacts a linear polyamic acid solution with a phenylacetylene-containing active end-capping agent to introduce crosslinkable end groups and stabilize the conformation. On the one hand, the end-capping reaction controls the polymer molecular weight; more importantly, it introduces thermally crosslinkable active sites at the phenylacetylene ends. Simultaneously, this mild heat treatment process relaxes the newly formed network segments, causing the chain conformation to tend towards a more thermodynamically stable state, equivalent to a "conformation freeze" of the "soft" network in the solution, which is beneficial for obtaining a homogeneous structure during the subsequent curing process.

[0035] Step (4): After obtaining the polyamic acid solution with a three-dimensional network structure, the present invention cures the polyamic acid solution with a three-dimensional network structure in a protective gas atmosphere to obtain the self-lubricating polyimide resin. In the present invention, the curing is carried out in a protective gas atmosphere, and the protective gas can be nitrogen. The curing includes sequentially performing a first stage curing, a second stage curing, and a third stage curing. The temperature of the first stage curing is ≤120 ℃; the second stage curing is performed under a pressure ≥0.5 MPa, where the temperature is raised from the first stage curing temperature to a first temperature and then subjected to 1 to 3 cycles of "cooling down from the first temperature to a second temperature, holding at the second temperature, and raising from the second temperature to the first temperature", wherein the first temperature is 220~250 ℃, the second temperature is 20~40 ℃ lower than the first temperature, and the holding time is 30~90 min; the temperature of the third stage curing is ≥300 ℃.

[0036] In this invention, prior to curing, the polyamic acid solution is preferably molded and then placed in a curing apparatus capable of applying external pressure for curing. The molding process can be a casting process.

[0037] In this invention, the curing temperature in the first stage is preferably 80~120 ℃, and the holding time is preferably 1~3 h. The first stage curing is carried out in a protective gas atmosphere, and the pressure of the first stage curing is atmospheric pressure. The first stage curing performs pre-crosslinking and solvent evaporation, initially locking the spatial position of carbon dot nodes in the network.

[0038] In this invention, the second stage curing involves 1-3 cycles of "cooling down from the first temperature to the second temperature, holding at the second temperature, and then heating back up from the second temperature to the first temperature" under a pressure ≥0.5 MPa. The first temperature is 220-250 °C, the second temperature is 20-40 °C lower than the first temperature, and the holding time is 30-90 min. The second stage curing induces "untangling-rearrangement" of the polyimide segments through a thermo-mechanical coupling field, simultaneously causing the carbon nodes to rotate and translate along the stress direction, achieving uniform distribution and preferred orientation within the network, and simultaneously releasing the internal stress generated by network shrinkage and node constraints. In this invention, the pressure of the second stage curing is preferably 0.5-1 MPa. The heating rate from the first stage curing temperature to the first temperature is preferably 2-5 °C / min, and in the embodiment, it can be 3 °C / min. The first temperature is preferably 220 °C. The cooling rate from the first temperature to the second temperature is preferably 1~2 °C / min. The second temperature is preferably 190 °C. The heating rate from the second temperature to the first temperature is preferably 2~5 °C / min, and in the embodiment it can be 3 °C / min. The cycle of "cooling from the first temperature to the second temperature, holding at the second temperature, and heating from the second temperature to the first temperature" is preferably performed twice.

[0039] In this invention, the curing temperature of the third stage is preferably 300~400℃, more preferably 350~370℃. The curing pressure of the third stage is preferably 0.5~1 MPa, and the holding time is preferably 1~3 h, which can be 2 h in the embodiment. The heating rate from the first temperature to the curing temperature of the third stage is preferably 2~5℃ / min, which can be 3℃ / min in the embodiment.

[0040] In this invention, the third stage of curing completes the imidization reaction and the thermal crosslinking of the end-capping agent, and finally permanently fixes the optimized "fishing net-node" topology to obtain the self-lubricating polyimide resin.

[0041] This invention provides a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot node reinforcement, prepared by the method described in the above technical solution. The self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot node reinforcement provided by this invention is a polyimide resin based on a perfluoroether bond fishing net-carbon dot node reinforcement. It consists of a flexible three-dimensional skeleton composed of a polyimide network containing perfluoroether bonds, and nano-carbon dots are anchored as rigid nodes at the cross-linking points of the polyimide network through chemical bonds, forming a "fishing net-node" reinforcement structure.

[0042] The self-lubricating polyimide resin based on a perfluorinated ether network and carbon dot nodes provided by this invention possesses excellent chemical inertness, high thermal stability, and low surface energy, while the ether bonds provide the necessary conformational freedom and chain segment mobility for the molecular chains. The synergy between these two elements enables the three-dimensional network to exhibit both stability and flexibility at high temperatures, forming an ideal "fishing net" framework. In this invention, the carboxyl-functionalized carbon dots are preferably carboxyl-functionalized nitrogen-boron co-doped carbon dots. As rigid nanonodes, they are covalently anchored to the network crosslinking points via strong amide bonds, greatly enhancing the nodes' resistance to deformation and stress dispersion. During high-temperature, high-load friction processes, this "fishing net-node" structure can absorb and dissipate energy through the flexible network while suppressing plastic flow and interfacial damage through the rigid nodes, thereby achieving a synergistic improvement in load-bearing capacity, lubrication, and wear resistance.

[0043] In this invention, the self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement has a friction coefficient of no more than 0.1 and a wear rate of no more than 1.0 × 10⁻⁶ under extreme working conditions of above 300 °C and 18 N. -13 m 3 / (N·m). The load-bearing capacity is increased by no less than 20% compared to unmodified pure perfluoroether polyimide resin.

[0044] The self-lubricating polyimide resin based on perfluoroether bond network and carbon dot node reinforcement provided by this invention is a composite material that significantly improves the load-bearing and wear-resistant properties under high temperature and high load conditions by using carbon dots (CDs) as chemical crosslinking nodes to reinforce the polyimide network.

[0045] This invention provides the application of the self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement, as described in the above-mentioned technical solution, in bearings, sealing rings, wear-resistant coatings, or sliding components. In this invention, the bearing can be an aerospace high-temperature (above 300 °C) bearing; the sealing ring can be a high-load (18 N) sealing ring; the wear-resistant coating can be an extreme condition (above 300 °C and 18 N conditions) wear-resistant coating; and the sliding component can be a high-temperature (above 300 °C) sliding component.

[0046] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1 1) Preparation of carboxyl-functionalized nitrogen-boron co-doped carbon dots: The microwave pulse-hydrothermal gradient annealing method was employed: First, 2 g of citric acid, 1 g of benzyl tetramine, and 0.5 g of boric acid were dissolved in 50 mL of deionized water and pretreated in a microwave reactor (800 W) for 5 min, with a pulse period of 10 s. The solution was then transferred to a high-pressure reactor and subjected to hydrothermal reaction at 160 ℃ / 4 h, 200 ℃ / 4 h, and 240 ℃ / 4 h. After the reaction, the solution was cooled to room temperature and dialyzed in deionized water through a 1000 Da dialysis bag for 24 hours, with the deionized water changed every 8 hours. A nitrogen-boron co-doped carboxyl-functionalized carbon dot solution was obtained in the dialysis bag. After freeze-drying, carboxyl-functionalized nitrogen-boron co-doped carbon dot powder was obtained. The particle size of the carboxyl-functionalized nitrogen-boron co-doped carbon dots was approximately 3 nm, and the surface carboxyl density was 0.85 mmol / g. 2) Preparation of carbon dot-diamine pre-assembly system: Under nitrogen protection and in an ice-water bath, 0.060 g (equivalent to 0.5 wt.% of the total mass of polyimide resin, where the total mass of polyimide resin is based on the total mass of 6FODA, 6FDA, and 4-PEPA) of the nitrogen-boron co-doped carboxyl functionalized carbon dot powder prepared in step (1) was dispersed in 5 mL of DMAc and sonicated for 30 min. 5.04 g of 6FODA was added to the dispersion and stirred to dissolve. Then, 3 drops of triethylamine were added dropwise to adjust the pH of the system to approximately 8.5. The system was further sonicated in an ice-water bath for 1 h to obtain a uniform “CDs-6FODA ion complex” dispersion, i.e., a carbon dot-diamine pre-assembled system. 3) Preparation of linear polyamic acid solution: Stepwise polymerization is employed, involving in-situ node anchoring and network growth. The carbon dot-diamine pre-assembly system obtained in step (2) was transferred to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet, and a constant-pressure dropping funnel. The carbon dot-diamine pre-assembly system was slowly heated to 50 °C. First step anchoring polymerization: 2.22 g of 6FDA was dissolved in 10 mL of DMAc to obtain a 6FDA solution. The above 6FDA solution was slowly added dropwise to the carbon dot-diamine pre-assembly system (this part of 6FDA accounts for 50% of the total mass of 6FDA) while stirring at 50 °C. After the addition was completed, the reaction was continued at 50 °C for 3 h. Second step network extension polymerization: The reaction system obtained from the first step network extension polymerization was heated to 70 °C. The remaining 6FDA (2.22 g) was dissolved in 10 mL of DMAc to obtain a 6FDA solution, and then slowly added dropwise to the reaction system obtained from the first step network extension polymerization at 70 °C. After the addition was complete, the reaction was continued at 70 °C for 6 h to obtain a carbon dot-node polyamic acid network precursor solution with moderate viscosity and a light yellow color, namely a linear polyamic acid solution. 4) In-situ end capping and conformational freezing: Add 2.48 g of 4-PEPA and 4 mL of DMAc to the reaction system obtained in step 3), and continue the reaction at 70 °C for 18 h to obtain a thermally crosslinkable carbon dot-terminated polyamic acid solution. 5) Controlled curing: "Thermo-mechanical coupled programmed curing": The polyamic acid solution prepared in step 4) is cast into a film and placed in a pressure curing oven (under N2 protection) for curing. The curing procedure is as follows: First stage: Under normal pressure (0.1 MPa), the temperature is increased from room temperature to 100 ℃ at a rate of 3 ℃ / min and held for 2 h; Second stage: Apply a pressure of 0.5 MPa, raise the temperature from 100 ℃ to 220 ℃ at a rate of 3 ℃ / min, then slowly lower the temperature to 190 ℃ at a rate of 2 ℃ / min, hold at 190 ℃ for 60 min, then slowly raise the temperature from 190 ℃ to 220 ℃ at a rate of 3 ℃ / min; then slowly lower the temperature to 190 ℃ at a rate of 2 ℃ / min, hold at 190 ℃ for 60 min, then slowly raise the temperature from 190 ℃ to 220 ℃ at a rate of 3 ℃ / min, thus completing two temperature cycles (220 ℃ → 190 ℃ for 60 min → 220 ℃). The third stage: under a pressure of 0.5 MPa, the temperature was increased from 220 ℃ to 370 ℃ at a rate of 3 ℃ / min, and held for 2 h.

[0048] After cooling and demolding, self-lubricating polyimide resin is obtained, and the finished product is CDs-FOPI resin film.

[0049] 6) Performance Testing: Referring to "Reciprocating Friction and Wear Tests Part 2: High Temperature Test Methods" (No.: T / GMES 033—2025), under the conditions of 350 ℃, 0.05 m / s, and 18 N load, the coefficient of friction of the CDs-FOPI resin prepared in Example 1 was 0.006, and the wear rate was 5.82 × 10⁻⁶. -14 m 3 / N·m. Compared with the pure FOPI resin prepared in Comparative Example 1, the CDs-FOPI resin prepared in Example 1 achieved a super-lubricating state. Meanwhile, the CDs-FOPI resin prepared in Example 1 maintained excellent dimensional stability and mechanical strength at high temperatures, making it suitable for high-temperature friction components in aerospace applications.

[0050] Example 2 1) Preparation of carboxyl-functionalized nitrogen-doped carbon dots: A microwave pulse-hydrothermal gradient annealing method was employed: 3 g of citric acid and 2 g of urea were dissolved in 30 mL of deionized water and placed in a microwave reactor. The mixture was reacted at 800 W for 3 min, with a pulse period of 10 s. Subsequently, the solution was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 160 ℃ / 2 h, 200 ℃ / 2 h, and 240 ℃ / 2 h. After the reaction, the mixture was cooled to room temperature and dialyzed in deionized water through a 1000 Da dialysis bag for 24 hours, with the deionized water being replaced every 8 hours. Carboxyl-functionalized nitrogen-doped carbon dots were obtained in the dialysis bag. Lyophilization yielded carboxyl-functionalized nitrogen-doped carbon dots with a particle size of approximately 2 nm and a surface carboxyl density of 0.68 mmol / g. 2) Preparation of carbon dot-diamine pre-assembly system: Under nitrogen protection and in an ice-water bath, 0.0496 g (equivalent to 0.5 wt.% of the total mass of polyimide resin, where the total mass of polyimide resin is based on the total mass of ODA, 6FDA, and 4-PEPA) of the carboxyl-functionalized nitrogen-doped carbon dot powder prepared in step (1) was dispersed in 5 mL of DMAc and sonicated for 30 min. 3.00 g of ODA was added to the dispersion and stirred to dissolve. Then, 3 drops of triethylamine were added dropwise to adjust the pH of the system to approximately 8.0. The system was further sonicated in an ice-water bath for 1 h to obtain a uniform “CDs-ODA ion complex” dispersion, i.e., a carbon dot-diamine pre-assembled system. 3) Preparation of linear polyamic acid solution: Stepwise polymerization is employed, involving in-situ node anchoring and network growth. The carbon dot-diamine pre-assembly system obtained in step (2) was transferred to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet, and a constant-pressure dropping funnel. The carbon dot-diamine pre-assembly system was slowly heated to 45 °C. First step anchoring polymerization: 2.22 g of 6FDA was dissolved in 10 mL of DMAc to obtain a 6FDA solution. The above 6FDA solution was slowly added dropwise to the carbon dot-diamine pre-assembly system (this part of 6FDA accounts for 50% of the total mass of 6FDA) while stirring at 50 °C. After the addition was completed, the reaction was continued at 50 °C for 3 h. Second step network extension polymerization: The reaction system obtained from the first step network extension polymerization was heated to 70 °C. The remaining 6FDA (2.22 g) was dissolved in 10 mL of DMAc to obtain a 6FDA solution, and then slowly added dropwise to the reaction system obtained from the first step network extension polymerization at 70 °C. After the addition was complete, the reaction was continued at 70 °C for 6 h to obtain a carbon dot-node polyamic acid network precursor solution with moderate viscosity and a light yellow color, namely a linear polyamic acid solution. 4) In-situ end capping and conformational freezing: Add 2.48 g of 4-PEPA and 4 mL of DMAc to the reaction system obtained in step 3), and continue the reaction at 70 °C for 18 h to obtain a thermally crosslinkable carbon dot-terminated polyamic acid solution. 5) Controlled curing: "Thermo-mechanical coupled programmed curing": The polyamic acid obtained in step 4) is cast into a film and then placed in a pressure curing oven (under N2 protection) for curing. The curing procedure is as follows: First stage: Under normal pressure (0.1 MPa), the temperature is increased from room temperature to 100 ℃ at a rate of 3 ℃ / min and held for 2 h; Second stage: Apply a pressure of 0.5 MPa, raise the temperature from 100 ℃ to 220 ℃ at a rate of 3 ℃ / min, then slowly lower the temperature to 190 ℃ at a rate of 2 ℃ / min, hold at 190 ℃ for 60 min, then slowly raise the temperature from 190 ℃ to 220 ℃ at a rate of 3 ℃ / min; then slowly lower the temperature to 190 ℃ at a rate of 2 ℃ / min, hold at 190 ℃ for 60 min, then slowly raise the temperature from 190 ℃ to 220 ℃ at a rate of 3 ℃ / min, thus completing two temperature cycles (220 ℃ → 190 ℃ for 60 min → 220 ℃). The third stage: under a pressure of 0.5 MPa, the temperature was increased from 220 ℃ to 370 ℃ at a rate of 3 ℃ / min, and held for 2 h.

[0051] After cooling and demolding, self-lubricating polyimide resin is obtained, and the finished product is CDs-FOPI resin film.

[0052] 6) Performance Testing: Referring to "Reciprocating Friction and Wear Tests Part 2: High Temperature Test Methods" (No.: T / GMES 033—2025), under the conditions of 350 ℃, 0.05 m / s, and 18 N load, the coefficient of friction of the CDs-FOPI resin prepared in Example 2 was 0.025, and the wear rate was 9.41 × 10⁻⁶. -14 m 3 / N·m, compared with the pure FOPI resin prepared in Comparative Example 1, indicates that the carboxyl-functionalized nitrogen-doped carbon dots can still significantly improve the high-temperature friction performance.

[0053] A comparison of the performance of the CDs-FOPI resin films prepared in Examples 1 and 2 shows that the carboxyl-functionalized nitrogen-boron co-doped carbon dots used in Example 1 serve as rigid nanonodes. These carbon dots are covalently anchored to the network crosslinking points through stronger amide bonds, which greatly enhances the nodes' resistance to deformation and stress dispersion.

[0054] Example 1 uses carboxyl-functionalized nitrogen-boron co-doped carbon dots, which have higher temperature resistance and reactivity, and are relatively stable during the reaction. Example 2 uses carboxyl-functionalized nitrogen-doped carbon dots, which have lower temperature resistance, stability and reactivity than Example 1.

[0055] Example 3 1) Preparation of carboxyl-functionalized nitrogen-doped carbon dots: A microwave pulsed-hydrothermal gradient annealing method was employed: 2 g of citric acid and 1.2 g of benzyl tetramine were dissolved in 40 mL of deionized water and placed in a microwave reactor. The mixture was reacted at 800 W for 3 min, with a pulse period of 10 s. The solution was then transferred to a high-pressure reactor and subjected to hydrothermal reaction at 160 ℃ / 4 h, 200 ℃ / 4 h, and 240 ℃ / 4 h. After the reaction, the mixture was cooled to room temperature and dialyzed against deionized water through a 1000 Da dialysis bag for 24 hours, with the deionized water replaced every 8 hours. Carboxyl-functionalized nitrogen-doped carbon dots were obtained from the dialysis bag. The particle size of the carboxyl-functionalized nitrogen-doped carbon dots was 3.2 nm, and the surface carboxyl group density was 0.50 mmol / g. 2) Preparation of carbon dot-diamine pre-assembly system: Under nitrogen protection and in an ice-water bath, 0.030 g (equivalent to 0.25 wt.% of the total mass of polyimide resin, where the total mass of polyimide resin is based on the total mass of 6FODA, 6FDA, and 4-PEPA) of the nitrogen-doped carboxyl-functionalized carbon dot powder prepared in step (1) was dispersed in 5 mL of DMAc and sonicated for 30 min. 5.04 g of 6FODA was added to the dispersion and stirred to dissolve. Then, 3 drops of triethylamine were added dropwise to adjust the pH of the system to approximately 7.8. The system was further sonicated in an ice-water bath for 1 h to obtain a uniform “CDs-6FODA ion complex” dispersion, i.e., a carbon dot-diamine pre-assembled system. 3) Preparation of linear polyamic acid solution: Stepwise polymerization is employed, involving in-situ node anchoring and network growth. The carbon dot-diamine pre-assembly system obtained in step (2) was transferred to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet, and a constant-pressure dropping funnel. The carbon dot-diamine pre-assembly system was slowly heated to 55 °C. First step anchoring polymerization: 2.22 g of 6FDA was dissolved in 10 mL of DMAc to obtain a 6FDA solution. The above 6FDA solution was slowly added dropwise to the carbon dot-diamine pre-assembly system (this part of 6FDA accounts for 50% of the total mass of 6FDA) while stirring at 50 °C. After the addition was completed, the reaction was continued at 50 °C for 3 h. Second step network extension polymerization: The reaction system obtained from the first step network extension polymerization was heated to 70 °C. The remaining 6FDA (2.22 g) was dissolved in 10 mL of DMAc to obtain a 6FDA solution, and then slowly added dropwise to the reaction system obtained from the first step network extension polymerization at 70 °C. After the addition was complete, the reaction was continued at 70 °C for 6 h to obtain a carbon dot-node polyamic acid network precursor solution with moderate viscosity and a light yellow color, namely a linear polyamic acid solution. 4) In-situ end capping and conformational freezing: Add 2.48 g of 4-PEPA and 4 mL of DMAc to the reaction system obtained in step 3), and continue the reaction at 70 °C for 18 h to obtain a thermally crosslinkable carbon dot-terminated polyamic acid solution. 5) Controlled curing: "Thermo-mechanical coupled programmed curing": The polyamic acid obtained in step 4) is cast into a film and then placed in a pressure curing oven (under N2 protection) for curing. The curing procedure is as follows: First stage: Under normal pressure (0.1 MPa), the temperature is increased from room temperature to 100 ℃ at a rate of 3 ℃ / min and held for 3 h; Second stage: Apply a pressure of 1.0 MPa, raise the temperature from 100 ℃ to 220 ℃ at a rate of 3 ℃ / min, then slowly lower the temperature to 190 ℃ at a rate of 2 ℃ / min, hold at 190 ℃ for 60 min, then slowly raise the temperature from 190 ℃ to 220 ℃ at a rate of 3 ℃ / min; then slowly lower the temperature to 190 ℃ at a rate of 2 ℃ / min, hold at 190 ℃ for 60 min, then slowly raise the temperature from 190 ℃ to 220 ℃ at a rate of 3 ℃ / min, thus completing two temperature cycles (220 ℃ → 190 ℃ for 60 min → 220 ℃). The third stage: under a pressure of 1.0 MPa, the temperature was increased from 220 ℃ to 370 ℃ at a rate of 3 ℃ / min, and held for 2 h.

[0056] After cooling and demolding, self-lubricating polyimide resin is obtained, and the finished product is CDs-FOPI resin film.

[0057] 6) Performance Testing: Referring to "Reciprocating Friction and Wear Tests Part 2: High Temperature Test Methods" (No.: T / GMES 033—2025), under the conditions of 350 ℃, 0.05 m / s, and 18 N load, the coefficient of friction of the CDs-FOPI resin prepared in Example 3 was 0.012, and the wear rate was 7.15 × 10⁻⁶. -14 m 3 / N·m. In this embodiment, nitrogen-doped carboxyl functionalized carbon dots were used as raw materials. The amount of carbon dots added was reduced to 0.25 wt.% compared with Examples 1-2. The interfacial chemical bonding was weak, so although the carbon dots were present, they failed to play a truly efficient "node" enhancement role.

[0058] Comparative Example 1 Benchmark – Pure FOPI resin with zero added carbon dots 1) Preparation of polyamic acid solution: Under nitrogen protection, 4.44 g of 6FDA was dissolved in 5.9 mL of DMAc. After complete dissolution, 5.04 g of 6FODA and 4.7 mL of DMAc were added, and the mixture was stirred at 80 °C for 6 h to obtain a polyamic acid prepolymer solution.

[0059] 2) End sealing and curing: 2.48 g of 4-PEPA and 4 mL of DMAc were directly added to the polyamic acid prepolymer solution obtained in step 1). After reacting for 18 h, the solution was coated and cured without adding carbon dots. The solution was uniformly coated onto a clean glass plate and pretreated with a stepped temperature program (80℃ / 2 h, 150℃ / 2 h, 250℃ / 2 h, 320℃ / 2 h). Finally, it was cured at 370℃ for 2 h, cooled, and then demolded to obtain an FOPI resin film.

[0060] 3) Performance testing: Referring to "Reciprocating Friction and Wear Tests Part 2: High Temperature Test Methods" (No.: T / GMES 033—2025), under the conditions of 350 ℃, 0.05 m / s, and 10 N load, the coefficient of friction of FOPI resin is 0.024, and the wear rate is 1×10⁻⁶. -13 m 3 / N·m. The ultimate load-bearing capacity is only 10 N. Its performance is significantly lower than all carbon dot modified examples, highlighting the necessity of carbon dot end-capping modification.

[0061] Figure 1 The 1H NMR spectra of the FOPI prepared in Comparative Example 1 and the CDs-FOPI prepared in Example 1 of this invention are shown. Figure 2 AFM phase map of CDs-FOPI prepared in Example 1 of this invention. Figure 3The high-temperature load-bearing friction resistance of CDs-FOPI prepared in Example 1 of this invention.

[0062] Comparative Example 2 To verify the uniqueness of the curing process in Example 1 of this invention, using the same raw material formulation as Example 1, a thermally crosslinkable carbon-dot-terminated polyamic acid solution was obtained through steps 1) to 4) as in Example 1. Then, a control sample was prepared using a conventional stepped curing process (i.e., without applying external pressure (atmospheric pressure) and without temperature cycling, the thermally crosslinkable carbon-dot-terminated polyamic acid solution was only subjected to a programmed temperature increase and hold at 80 ℃ / 2 h, 150 ℃ / 2 h, 250 ℃ / 2 h, 320 ℃ / 2 h, and 370 ℃ / 2 h, with a heating rate of 3 ℃ / min). Tests showed that the control sample prepared in Comparative Example 2 had a friction coefficient of 0.028 and a wear rate of 9.87 × 10⁻⁶ under the same test conditions as Example 1 (350 ℃, 0.05 m / s, 18 N). - 14 m 3 / N·m. Compared to the control sample prepared in Comparative Example 2, the curing process provided in Example 1 of this invention reduced the coefficient of friction by 33.3% and the wear rate by 33.3%. This demonstrates the key role of the "thermo-mechanical coupled programmed curing" provided in Example 1 of this invention in optimizing the "fishing net-node" structure and releasing internal stress.

[0063] Table 1 Performance test results of samples prepared in Examples 1-3 and Comparative Examples 1-2

[0064] As shown in Table 1, this invention significantly improves the tribological properties and load-bearing capacity of polyimide resin under high temperature and high load through the "fishing net-node" reinforced structural design and thermo-mechanical coupled programmed curing process. The process is controllable and the structure is well-defined, which has important engineering application value.

[0065] Comparative Example 3 The preparation method is basically the same as that in Example 1, except that the amount of nitrogen-boron co-doped carboxyl functionalized carbon dot powder prepared in step (1) is 0.0897 g, which is equivalent to 0.75 wt.% of the total mass of polyimide resin, where the total mass of polyimide resin is based on the total mass of 6FODA, 6FDA, and 4-PEPA. The CDs-FOPI resin film prepared in Comparative Example 3 exhibited very poor high-temperature load-bearing performance; the resin cracked within one minute of testing on a friction testing machine, and no data could be collected.

[0066] As can be seen from the above embodiments, this invention provides a polyimide resin with excellent high-temperature self-lubricating tribological properties and its preparation method, particularly a composite material that significantly improves the load-bearing and wear-resistant properties under high-temperature and high-load conditions by reinforcing the polyimide network with carbon dots (CDs) as chemical crosslinking nodes. This invention discloses a high-temperature self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot node reinforcement and its preparation method. The resin uses a polyimide containing perfluoroether bonds as a flexible three-dimensional network skeleton, and carboxyl-functionalized carbon dots are covalently anchored at the network crosslinking points as rigid reinforcing nodes through amide bonds, forming a "fishing net-node" reinforcement structure. This invention employs a synthesis process of "carboxyl-directed induced hierarchical self-assembly polymerization-programmed topology locking," achieving uniform node distribution and internal stress release through thermo-mechanical coupled programmed curing during the curing stage. The resulting resin exhibits a friction coefficient as low as 0.006 and a wear rate of only 5.82 × 10⁻⁶ under extreme conditions above 300 °C and 18 N. -14 m 3 The high-temperature self-lubricating polyimide resin exhibits significantly improved frictional properties and load-bearing capacity compared to pure perfluoroether resins, displaying super-lubricating characteristics. This invention provides a high-temperature self-lubricating polyimide resin suitable for applications such as aerospace high-temperature bearings, high-load sealing rings, and wear-resistant coatings for extreme operating conditions.

[0067] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement, characterized in that, Includes the following steps: (1) A carbon dot-diamine pre-assembled system is obtained by mixing carboxyl-functionalized carbon dots, an aromatic diamine containing ether bonds, and a polar aprotic solvent, and adjusting the pH value to >7. The carboxyl-functionalized carbon dots are carboxyl-functionalized doped and / or undoped carbon dots. The doped carbon dots include one or both of nitrogen-doped carbon dots and nitrogen-boron co-doped carbon dots. The mass percentage of the carboxyl-functionalized carbon dots to the total mass of the aromatic diamine containing ether bonds, the perfluoroaromatic dianhydride, and the active end-capping agent containing phenylacetylene groups is <0.75 wt.%. (2) The carbon dot-diamine pre-assembled system is polymerized with perfluoroaromatic dianhydride to obtain a linear polyamic acid solution; The polymerization includes the following steps: heating the carbon dot-diamine pre-assembly system to a first temperature and reacting it with a portion of the perfluoroaromatic dianhydride to obtain a star-shaped prepolymer; further heating the star-shaped prepolymer to a second temperature and reacting it with the remaining perfluoroaromatic dianhydride to obtain a linear polyamic acid solution, wherein the first temperature is ≥40 °C and the first temperature is < the second temperature. (3) The linear polyamic acid solution is reacted with an active end-capping agent containing phenylacetylene groups to obtain a polyamic acid solution with a three-dimensional network structure; (4) The polyamic acid solution with a three-dimensional network structure is cured in a protective gas atmosphere to obtain the self-lubricating polyimide resin; the curing includes a first stage curing, a second stage curing and a third stage curing in sequence; the temperature of the first stage curing is ≤120 ℃; the second stage curing is carried out in a cycle unit of "cooling down from the first temperature to the second temperature, holding at the second temperature and then heating up from the second temperature to the first temperature" 1 to 3 times under a pressure ≥0.5 MPa, wherein the first temperature is 220~250 ℃, the second temperature is 20~40 ℃ lower than the first temperature, and the holding time is 30~90 min; the temperature of the third stage curing is ≥300 ℃.

2. The preparation method according to claim 1, characterized in that, In step (1), the surface carboxyl group density of the carboxyl functionalized carbon dots is not less than 0.5 mmol / g; the particle size of the carboxyl functionalized carbon dots is 2~5 nm; the mass percentage of the carboxyl functionalized carbon dots to the total mass of the ether-containing aromatic diamine, perfluoroaromatic dianhydride and the phenylacetylene-containing active end-capping agent is 0.01~0.5 wt.%; the ether-containing aromatic diamine is at least one of the aromatic diamines containing a diphenyl ether unit, a trifluoromethyl-substituted diphenyl ether unit or a diphenyl ether unit in its structure; and the pH value is 7.5~9.

3. The preparation method according to claim 1, characterized in that, In step (2), the first temperature is 40~60℃; the second temperature is 60~80℃; the mass of the partial perfluoroaromatic dianhydride accounts for 30~60% of the total mass of the perfluoroaromatic dianhydride; the perfluoroaromatic dianhydride is at least one of the perfluoroaromatic tetracarboxylic dianhydrides whose structure contains hexafluoroisopropyl or octafluorobiphenyl as a linking group.

4. The preparation method according to claim 1, characterized in that, In step (3), the active end-capping agent containing phenylacetylene is at least one of the aromatic anhydride end-capping agents having phenylacetylene substituents; the reaction temperature is 50~80℃ and the time is 8~20 h.

5. The preparation method according to claim 1, characterized in that, In step (4), the curing temperature of the first stage is 80~120 ℃, and the heat preservation time is 1~3 h; The heating rate from the first stage curing temperature to the first temperature is 2~5 ℃ / min, the cooling rate from the first temperature to the second temperature is 1~2 ℃ / min, the heating rate from the second temperature to the first temperature is 2~5 ℃ / min, and the pressure for the second stage curing is 0.5~1 MPa. The curing temperature for the third stage is 300~400 ℃, the pressure is 0.5~1 MPa, and the holding time is 1~3 h.

6. The preparation method according to claim 1, 2, 3 or 4, characterized in that, The ether-containing aromatic diamine is at least one of 4,4'-diaminodiphenyl ether and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether; the perfluoroaromatic dianhydride is at least one of 4,4'-(hexafluoroisopropene)phthalic anhydride and 4,4'-(octafluorobiphenyl)phthalic anhydride; and the phenylacetylene-containing active end-capping agent is at least one of 4-phenylacetylenephthalic anhydride and 3-phenylacetylenephthalic anhydride.

7. The preparation method according to claim 1 or 2, characterized in that, The method for preparing the carboxyl-functionalized carbon dots includes the following steps: The raw materials are mixed with water and subjected to microwave pulse treatment and hydrothermal reaction sequentially to obtain the carboxyl functionalized carbon dots. The raw materials are a carbon source or a carbon source and a dopant. The dopant is a nitrogen source or a nitrogen source and a boron source. The carbon source includes citric acid and / or benzoic acid, the nitrogen source includes benzenetetramine and / or urea, and the boron source is boric acid. The pulse period of the microwave pulse treatment is 5-10 s, and the total duration is 3-5 min. The hydrothermal reaction includes a first stage hydrothermal reaction, a second stage hydrothermal reaction, and a third stage hydrothermal reaction sequentially. The temperature of the first stage hydrothermal reaction is < the temperature of the second stage hydrothermal reaction is < the temperature of the third stage hydrothermal reaction. The temperature of the first stage hydrothermal reaction is 160-180℃, the temperature of the second stage hydrothermal reaction is 180-220℃, and the temperature of the third stage hydrothermal reaction is 220-240℃.

8. The self-lubricating polyimide resin based on perfluoroether bond network and carbon dot node reinforcement prepared by the preparation method according to any one of claims 1 to 7.

9. The self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement according to claim 8, characterized in that, The self-lubricating polyimide resin based on a perfluoroether bond network and carbon dot reinforcement has a friction coefficient of no more than 0.1 and a wear rate of no more than 1.0 × 10⁻⁶ under extreme working conditions of no less than 300°C and no less than 18 N. -13 m 3 / (N·m).

10. The application of the self-lubricating polyimide resin based on perfluoroether bond network and carbon dot node reinforcement as described in claim 8 or 9 in bearings, sealing rings, wear-resistant coatings or sliding parts.

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