Thermosetting polyimide with intrinsic self-repairing and low-friction characteristics and preparation method thereof

Abstract

The invention provides thermosetting polyimide with intrinsic self-repairing and low-friction characteristics and a preparation method thereof, and belongs to the technical field of self-repairing materials. The prepared thermosetting polyimide contains dynamic imine bonds and thiourea groups, the double decomposition reaction of the dynamic imine bonds and the synergistic effect of strong and weak hydrogen bonds generated by thiourea and urea groups enable the polyimide to have a low friction coefficient and also have a self-repairing capability, and a polyimide film is endowed with a hot-pressing response self-repairing performance. In addition, due to the existence of dynamic covalent bonds, the polyimide also has recoverable potential. Unification of intrinsic self-repairing performance and friction performance of the thermosetting polyimide is realized for the first time, the service life of the thermosetting polyimide is greatly prolonged, a thought is provided for realizing low friction performance of intrinsic self-repairing polyimide, and the application of the self-repairing material in engineering is expanded.

Description

Technical Field

[0001] The invention relates to the technical field of self-repairing materials, and in particular to a thermosetting polyimide with intrinsic self-repairing and low friction properties and a preparation method thereof. Background Art

[0002] Self-healing materials have the characteristics of stimulus response, and they can complete the repair of cracks under environmental stimulation, such as acid-base stimulation, heat pressure stimulation, light stimulation, etc. According to the classification method, they are divided into two types: external aid repair and intrinsic repair. However, self-healing materials generally have the defect of low mechanical properties, which limits their application in engineering, especially the research on intrinsic self-healing materials, which is currently limited to thermoplastic polymer elastomers. There is little research on intrinsic self-healing thermosetting polymers, especially polyimides with rigid structures. In addition, traditional polyimides are inevitably mechanically damaged during use, which limits their use in high-end working environments. For example, when traditional polyimide seals are damaged, they cannot be repaired under environmental stimulation, which greatly reduces the sealing performance.

[0003] Introducing self-healing function into polyimide materials can solve the problem that polyimide cannot be repaired and extend its service life. However, most current research relies on external repair agents, and there is no research on solving the self-healing and low friction problems of thermosetting polyimide from the perspective of intrinsic self-healing. Therefore, balancing the relationship between the intrinsic self-healing and friction performance of thermosetting polyimide from the root is of great significance for extending the service life of polyimide and expanding its application in engineering. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a thermosetting polyimide with intrinsic self-healing and low friction properties and a preparation method thereof. The thermosetting polyimide provided by the present invention has both good friction performance and intrinsic self-healing properties, and can greatly extend the service life of the thermosetting polyimide.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a thermosetting polyimide having intrinsic self-healing and low friction properties, comprising the following steps:

[0007] Mixing BPADA, 6FODA and an organic solvent to carry out a first polycondensation reaction to obtain a polyimide precursor solution;

[0008] Adding toluene to the polyimide precursor solution, and performing chemical imidization and thermal imidization synergistic treatment under heating conditions to obtain a polyimide oligomer;

[0009] The polyimide oligomer and terephthalaldehyde undergo a second polycondensation reaction to obtain a polyimide oligomer containing dynamic imine;

[0010] The dynamic imine-containing polyimide oligomer is mixed with hexamethylene diisocyanate trimer and an organic solvent to carry out a third polycondensation reaction, and benzyl isothiocyanate is added to the obtained third polycondensation reaction system to carry out a capping reaction to obtain a thermosetting polyimide with intrinsic self-healing and low friction properties.

[0011] Preferably, the molar ratio of 6FODA to BPADA is 1.5 to 2.5:1;

[0012] The first condensation reaction is carried out in an ice-water bath, and the time of the first condensation reaction is 10 to 20 hours.

[0013] Preferably, the mass of the toluene is 1 / 10 to 1 / 5 of the mass of the organic solvent in the first polycondensation reaction liquid;

[0014] The temperature of the chemical imidization and thermal imidization synergistic treatment is 200-240° C. and the time is 3-7 hours.

[0015] Preferably, the molar ratio of the polyimide oligomer to terephthalaldehyde is 1:0.4-2.6;

[0016] The temperature of the second polycondensation reaction is 40 to 90° C., and the time is 2 to 6 hours.

[0017] Preferably, the molecular weight of the dynamic imide-containing polyimide oligomer is 1,000 to 20,000.

[0018] Preferably, the molar ratio of the dynamic imine-containing polyimide oligomer to the hexamethylene diisocyanate trimer is 1:0.3-0.6;

[0019] The temperature of the third polycondensation reaction is 60-100° C., and the time is 1-4 hours.

[0020] Preferably, the molar ratio of the dynamic imine-containing polyimide oligomer to benzyl isothiocyanate is 0.5 to 1:1;

[0021] The temperature of the end-capping reaction is 30-60° C. and the time is 10-48 hours.

[0022] The invention provides a thermosetting polyimide prepared by the above preparation method and having intrinsic self-repairing and low friction properties.

[0023] The invention provides a thermosetting polyimide film with intrinsic self-repairing and low friction properties, which is obtained by sequentially casting and stepwise thermal curing the thermosetting polyimide film with intrinsic self-repairing and low friction properties.

[0024] Preferably, the temperature rise program of the step thermal curing includes:

[0025] First keep warm at 40-60°C for 2-4h;

[0026] Second insulation at 70-80°C for 2-4h;

[0027] The third heat preservation is at 100-120°C for 1-2 hours;

[0028] The fourth heat preservation is at 130-150°C for 1-2 hours;

[0029] The fifth heat preservation is carried out at 200-250°C for 5-8 hours.

[0030] The present invention provides a method for preparing a thermosetting polyimide having intrinsic self-repairing and low friction properties. The present invention uses 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA), bisphenol A dianhydride (BPADA) and terephthalaldehyde (TA) as raw materials to prepare a polyimide oligomer containing dynamic imine (denoted as DFBPO); then uses a polyimide oligomer containing dynamic imine, hexamethylene diisocyanate trimer and benzyl isothiocyanate as raw materials to introduce a thiourea group into a polyimide containing a dynamic covalent bond. The thermosetting polyimide prepared by the present invention contains a dynamic imine bond and a thiourea group. The reversible metathesis reaction of the dynamic imine bond at high temperature and the hydrogen bond breakage of the thiourea and urea groups at high temperature give the thermosetting polyimide a repairing property; secondly, while having self-repairing properties, it also has a low friction coefficient, which is attributed to the toughening effect of the dynamic imine bond and the strong and weak hydrogen bonds, so that the material has a certain ability to resist friction shear force. In addition, the presence of dynamic covalent bonds makes polyimide potentially recyclable. This invention realizes the unification of the intrinsic self-healing properties and friction properties of thermosetting polyimide for the first time, greatly prolonging the service life of thermosetting polyimide, providing ideas for achieving low friction of intrinsic self-healing polyimide, and expanding the application of self-healing materials in engineering.

[0031] In addition, the preparation method provided by the present invention is simple to operate and can be easily implemented in industrialized batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A synthetic route for polyimide oligomers containing dynamic imine;

[0033] Figure 2 A synthetic route for thermosetting polyimides with intrinsic self-healing and low friction properties;

[0034] Figure 3The infrared spectra of conventional polyimide oligomer powder (FBPO), dynamic imide-containing polyimide oligomer powder (DFBPO) and thermosetting polyimide with intrinsic self-healing and low friction properties (DFBSPI);

[0035] Figure 4 Dynamic thermomechanical analysis test results for thermosetting polyimide films with intrinsic self-healing and low friction properties;

[0036] Figure 5 The reciprocating friction test results of thermosetting polyimide film with intrinsic self-healing and low friction properties are shown;

[0037] Figure 6 Scratch self-healing results of thermosetting polyimide film with intrinsic self-healing and low friction properties. DETAILED DESCRIPTION

[0038] The present invention provides a method for preparing a thermosetting polyimide having intrinsic self-healing and low friction properties, comprising the following steps:

[0039] Mixing BPADA, 6FODA and an organic solvent to carry out a first polycondensation reaction to obtain a polyimide precursor solution;

[0040] Adding toluene to the polyimide precursor solution, and performing chemical imidization and thermal imidization synergistic treatment under heating conditions to obtain a polyimide oligomer;

[0041] The polyimide oligomer and terephthalaldehyde undergo a second polycondensation reaction to obtain a polyimide oligomer containing dynamic imine;

[0042] The dynamic imine-containing polyimide oligomer is mixed with hexamethylene diisocyanate trimer and an organic solvent to carry out a third polycondensation reaction, and benzyl isothiocyanate is added to the obtained third polycondensation reaction system to carry out a capping reaction to obtain a thermosetting polyimide with intrinsic self-healing and low friction properties.

[0043] Unless otherwise specified, the raw materials used in the present invention are all commercially available.

[0044] The present invention mixes BPADA, 6FODA and an organic solvent to perform a first polycondensation reaction to obtain a polyimide precursor solution. In the present invention, the organic solvent is preferably one or more of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Before the mixing, the present invention preferably performs reduced pressure distillation on the organic solvent to remove water from the organic solvent.

[0045] As a specific embodiment of the present invention, the mixing method is preferably: BPADA and 6FODA are dissolved in an organic solvent respectively to obtain a BPADA solution and a 6FODA solution, the 6FODA solution is poured into a closed three-necked flask with a stirrer and nitrogen, and dried for 2 to 6 hours under nitrogen purge and stirring, and the stirring speed is preferably 260 to 285 rpm, and then the BPADA solution is added to the 6FODA solution in three batches under an ice water bath, with an interval of 1 hour.

[0046] In the present invention, the molar ratio of 6FODA to BPADA is preferably 1.5 to 2.5:1. As a specific embodiment of the present invention, the molar ratio of 6FODA to BPADA is 1.5:1, 2:1 or 2.5:1. In the present invention, the temperature of the first polycondensation reaction is preferably carried out under ice-water bath conditions, and the time of the first condensation reaction is preferably 10 to 20 hours, specifically 10 hours, 12 hours, 14 hours, 16 hours, 18 hours or 20 hours, more preferably 12 hours. In the present invention, the solid content of the first polycondensation reaction system is preferably 10 to 30%, specifically 10%, 15%, 20, 25% or 30%, more preferably 25%.

[0047] After obtaining the first polycondensation reaction liquid, the present invention adds toluene to the polyimide precursor solution, and performs chemical imidization and thermal imidization synergistic treatment under heating conditions to obtain a polyimide oligomer. As a specific embodiment of the present invention, the structural formula of the polyimide oligomer is shown in formula a:

[0048]

[0049] In the present invention, the mass of the toluene is preferably 1 / 10 to 1 / 5 of the mass of the organic solvent in the first polycondensation reaction liquid. After adding toluene, the present invention preferably performs stirring, and the stirring time is preferably 0.5 h.

[0050] In the present invention, the chemical imidization and thermal imidization synergistic treatment is preferably carried out under closed conditions. In the present invention, the temperature of the chemical imidization and thermal imidization synergistic treatment is preferably 200-240°C, and the time is preferably 3-7h; as a specific embodiment of the present invention, the temperature of the chemical imidization and thermal imidization synergistic treatment is 200°C, 210°C, 220°C, 230°C or 240°C, and the time is 3h, 4h, 5h, 6h or 7h. The present invention can greatly shorten the imidization time through the synergistic treatment of chemical imidization and thermal imidization, can reduce the reaction temperature compared to simple thermal imidization, and can avoid the occurrence of side reactions.

[0051] After the imidization reaction, the present invention does not perform post-treatment on the obtained imidization reaction liquid, and directly uses it in the next reaction.

[0052] After obtaining the polyimide oligomer, the polyimide oligomer and terephthalaldehyde undergo a second polycondensation reaction to obtain a polyimide oligomer containing dynamic imine. As a specific embodiment of the present invention, the structural formula of the polyimide oligomer containing dynamic imine is shown in formula b:

[0053]

[0054] In the present invention, the second polycondensation reaction is preferably carried out in an organic solvent, and the organic solvent is preferably the same as the organic solvent used in the first polycondensation reaction. In the present invention, the molar ratio of the polyimide oligomer to terephthalaldehyde is preferably 1:0.4-2.6. As a specific embodiment of the present invention, the molar ratio of the polyimide oligomer to terephthalaldehyde is 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.5, 1:1.8, 1:2 or 1:2.4.

[0055] In the present invention, the temperature of the second condensation reaction is preferably 40-90°C, and the time is preferably 2-6h; as a specific embodiment of the present invention, the temperature of the second condensation reaction is 40°C, 50°C, 60°C, 70°C, 80°C or 90°C, and the time is 2h, 3h, 4h, 5h or 6h. In the present invention, the solid content of the second condensation reaction system is preferably 10-30%, specifically 10%, 15%, 20, 25% or 30%, more preferably 25%. In the present invention, the molecular weight of the dynamic imide-containing polyimide oligomer is preferably 1000-20000, more preferably 2000-10000, and more preferably 3000-8000.

[0056] After the second condensation reaction, the present invention preferably performs post-treatment on the obtained second condensation reaction liquid, and the post-treatment preferably includes the following steps:

[0057] The second condensation reaction liquid is sequentially washed, solid-liquid separated and dried to obtain a polyimide oligomer powder containing dynamic imine.

[0058] In the present invention, the washing is preferably: slowly pouring the second condensation reaction liquid into cold ethanol and washing under stirring. In the present invention, the washing speed is preferably 340-520 rpm. In the present invention, the solid-liquid separation is preferably suction filtration; in the present invention, the drying is preferably oven drying.

[0059] As a specific embodiment of the present invention, the synthetic route of the dynamic imide-containing polyimide oligomer is as follows: Figure 1 shown.

[0060] After obtaining the dynamic imine-containing polyimide oligomer, the present invention mixes the dynamic imine-containing polyimide oligomer with hexamethylene diisocyanate trimer and an organic solvent to carry out a third polycondensation reaction, and adds benzyl isothiocyanate to the obtained third polycondensation reaction system to carry out a capping reaction to obtain a thermosetting polyimide with intrinsic self-healing and low friction properties. In the present invention, the molar ratio of the dynamic imine-containing polyimide oligomer to the hexamethylene diisocyanate trimer is preferably 1:0.3 to 0.6; as a specific embodiment of the present invention, the molar ratio of the dynamic imine-containing polyimide oligomer to the hexamethylene diisocyanate trimer is 1:0.3, 1:0.4, 1:0.5 or 1:0.6.

[0061] In the present invention, the organic solvent is preferably one or more of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The present invention has no special requirements for the mixing method, and a mixing method well known in the art can be used, such as stirring mixing.

[0062] In the present invention, the third polycondensation reaction is preferably carried out under nitrogen and stirring conditions. In the present invention, the temperature of the third polycondensation reaction is preferably 60-100°C, and the time is preferably 1-4h; as a specific embodiment of the present invention, the temperature of the third polycondensation reaction is 60°C, 70°C, 80°C, 90°C or 100°C, and the time is preferably 1h, 2h, 3h or 4h.

[0063] In the present invention, the molar ratio of the dynamic imine-containing polyimide oligomer to benzyl isothiocyanate is preferably 0.5 to 1:1; as a specific embodiment of the present invention, the molar ratio of the dynamic imine-containing polyimide oligomer to benzyl isothiocyanate is 0.5:1, 0.6:1, 0.8:1 or 1:1.

[0064] In the present invention, the temperature of the end-capping reaction is preferably 30-60°C, and the time is preferably 10-48h; as a specific embodiment of the present invention, the temperature of the end-capping reaction is 30°C, 40°C, 50°C or 60°C, and the time is 10h, 18h, 24h, 30h, 36h or 48h.

[0065] After the end-capping reaction, the present invention obtains a solution containing a thermosetting polyimide having intrinsic self-healing and low friction properties, and the solid content of the reaction solution containing the thermosetting polyimide having intrinsic self-healing and low friction properties is preferably 10-30%, specifically 10%, 15%, 20, 25% or 30%, more preferably 25%. The present invention preferably does not post-treat the obtained solution containing the thermosetting polyimide having intrinsic self-healing and low friction properties, but directly casts and heat-cures to obtain a thermosetting polyimide film having intrinsic self-healing and low friction properties.

[0066] As a specific embodiment of the present invention, the synthesis route of thermosetting polyimide having intrinsic self-healing and low friction properties is as follows Figure 2 shown. Figure 2 In, n=1~10.

[0067] The invention provides a thermosetting polyimide prepared by the above preparation method and having intrinsic self-repairing and low friction properties.

[0068] The invention provides a thermosetting polyimide film with intrinsic self-repairing and low friction properties, which is obtained by sequentially casting and stepwise thermal curing the thermosetting polyimide film with intrinsic self-repairing and low friction properties.

[0069] In the present invention, the object of the pouring is preferably the above-mentioned solution containing the thermosetting polyimide having intrinsic self-healing and low friction properties. Before the pouring, the present invention preferably dries the reaction solution containing the thermosetting polyimide having intrinsic self-healing and low friction properties, the drying is preferably vacuum drying, and the drying time is preferably 5 to 20 minutes.

[0070] In the present invention, the casting method is preferably casting by tape casting. In the present invention, the solution containing the thermosetting polyimide having intrinsic self-healing and low friction properties is preferably cast on a substrate, and the substrate is preferably a glass plate.

[0071] In the present invention, the temperature rise program of the step thermal curing preferably includes:

[0072] First keep warm at 40-60°C for 2-4h;

[0073] Second insulation at 70-80°C for 2-4h;

[0074] The third heat preservation is at 100-120°C for 1-2 hours;

[0075] The fourth heat preservation is at 130-150°C for 1-2 hours;

[0076] The fifth heat preservation is carried out at 200-250°C for 5-8 hours.

[0077] As a specific embodiment of the present invention, the temperature rise program of the step thermal curing is:

[0078] First insulation at 60°C for 4h;

[0079] Second insulation at 80°C for 2h;

[0080] The third heat preservation was carried out at 100°C for 1 hour;

[0081] The fourth heat preservation was carried out at 150°C for 1 hour;

[0082] The fifth heat preservation was carried out at 200°C for 5 hours.

[0083] The present invention performs thermal curing under the above conditions, which can control the volatilization rate of the solvent to make it fully volatilize, and can reduce the internal stress generated during the curing process.

[0084] In the present invention, the thickness of the thermosetting polyimide film having intrinsic self-healing and low friction properties is preferably 0.03 mm to 0.08 mm, more preferably 0.05 mm.

[0085] The thermosetting polyimide film with intrinsic self-healing and low friction properties provided by the present invention can achieve self-healing under the condition of thermal pressure stimulation; the temperature of the thermal pressure stimulation is preferably 213-230°C, the pressure is preferably 5-15kPa, and the time is preferably 2-6h.

[0086] The thermosetting polyimide with intrinsic self-healing and low friction properties and the preparation method thereof provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0087] Example 1

[0088] A method for preparing a thermosetting polyimide film having intrinsic self-healing and low friction properties, using the following steps:

[0089] (1) Preparation of dynamic imide-containing polyimide oligomer powder (DFBPO):

[0090] Dissolve 13g 6FODA in 90g NMP, add 10g BPADA in three batches slowly in an ice-water bath, react for 18h, then add 8g toluene, stir for 0.5h, place in a sealed 220℃ heating device, dehydrate for 5h, then cool the reaction solution to 60℃, add 1.8g terephthalaldehyde, react for 4h, obtain a uniform solution, slowly drop the solution into a rapidly stirred cold ethanol solution, precipitate and filter, obtain a light yellow powder, which is a polyimide oligomer powder containing dynamic imine. The molar ratio of 6FODA, BPADA and terephthalaldehyde is 2:1:0.665;

[0091] (2) Preparation of thermosetting polyimide (DFBSPI) solution with intrinsic self-healing and low friction properties:

[0092] 4 g of DFBPO was weighed and dissolved in 90 g of NMP, and then 0.2 g of hexamethylene diisocyanate trimer was added to the DFBPO solution, and the reaction was carried out at 80 ° C for 3 hours. Then, the system was slowly cooled to 60 ° C, 0.15 g of benzyl isothiocyanate was added, and the reaction was carried out for 24 hours to obtain a yellow transparent solution, which is a thermosetting polyimide solution with intrinsic self-healing and low friction properties, wherein the molar ratio of dynamic imide polyimide oligomer, hexamethylene diisocyanate trimer and benzyl isothiocyanate is 1:0.34:1.

[0093] (3) Preparation of thermosetting polyimide films with intrinsic self-healing and low friction properties:

[0094] The yellow transparent solution was placed in a vacuum oven for 10 min, and then cast on a glass plate by a casting method for thermal curing treatment: 60°C for 4 h, 80°C for 2 h, 100°C for 1 h, 150°C for 1 h, and 200°C for 5 h. All procedures were carried out in a vacuum oven.

[0095] The infrared spectra of conventional polyimide oligomer powder (FBPO), dynamic imide-containing polyimide oligomer powder (DFBPO) and thermosetting polyimide with intrinsic self-healing and low friction properties (DFBSPI) are shown in Figure 2. Figure 3 As shown, it can be seen that compared with FBPO, DFBPO has a -1 The vibration peak of C=N double bond appeared, which proved the successful synthesis of DFBPO powder. Compared with DFBPO powder, the disappearance of -NH2 at 3313cm -1 The appearance of -NH- and 1560cm -1 The vibration peak of the -C=S bond at , proves the successful synthesis of thermosetting polyimide with intrinsic self-healing and low friction properties.

[0096] Dynamic thermomechanical analysis test results of thermosetting polyimide films with intrinsic self-healing and low friction properties are shown in Figure 2. Figure 4 As shown, it can be seen that the polyimide film still maintains a high glass transition temperature of 213°C and a storage modulus of approximately 2000 MPa. The high storage modulus is conducive to providing sufficient power for subsequent self-repair.

[0097] The reciprocating friction test results of thermosetting polyimide films with intrinsic self-healing and low friction properties are shown in Figure 5As shown, the test conditions are 3N load and 1000 cycles. It can be seen that the average friction coefficient is maintained at about 0.2, which is lower than that of traditional polyimide, proving that the polyimide film provided by the present invention has a low friction coefficient without adding fillers.

[0098] The scratch self-healing results of thermosetting polyimide films with intrinsic self-healing and low friction properties are shown in Figure 2. Figure 6 As shown, Figure 6 A heat pressure stimulus of 225°C and 10 kPa was applied. Figure 6 It can be seen that the polyimide provided by the present invention still has self-repairing ability while maintaining a rigid structure.

[0099] Example 2

[0100] (1) Preparation of dynamic imide-containing polyimide oligomer powder (DFBPO):

[0101] 13g 6FODA was dissolved in 90g NMP. 10g BPADA was slowly added thereto in batches under ice-water bath conditions. The reaction was carried out for 18h. Then 8g toluene was added and stirred for 0.5h. The mixture was placed in a closed heating device at 220°C and dehydrated for 5h. The reaction was then cooled to 60°C. 2g terephthalaldehyde was added and reacted for 4h to obtain a uniform solution. The solution was slowly added dropwise to a rapidly stirred cold ethanol solution. The solution was precipitated and filtered to obtain a light yellow powder, which was a polyimide oligomer powder containing dynamic imine, wherein the molar ratio of 6FODA, BPADA and terephthalaldehyde was 2:1:0.75.

[0102] (2) Preparation of thermosetting polyimide (DFBSPI) solution with intrinsic self-healing and low friction properties:

[0103] 7 g of DFBPO was weighed and dissolved in 90 g of NMP, and then 0.2 g of hexamethylene diisocyanate trimer was added to the DFBPO solution, and the reaction was carried out at 80 ° C for 3 hours. Then, the system was slowly cooled to 60 ° C, 0.15 g of benzyl isothiocyanate was added, and the reaction was carried out for 24 hours to obtain a yellow transparent solution, which is a thermosetting polyimide solution with intrinsic self-healing and low friction properties, wherein the molar ratio of dynamic imide polyimide oligomer, hexamethylene diisocyanate trimer and benzyl isothiocyanate is 1:0.34:1.

[0104] (3) Preparation of thermosetting polyimide films with intrinsic self-healing and low friction properties:

[0105] The yellow transparent solution was placed in a vacuum oven for 10 min, and then cast on a glass plate by a casting method for thermal curing treatment: 60°C for 4 h, 80°C for 2 h, 100°C for 1 h, 150°C for 1 h, and 200°C for 5 h. All procedures were carried out in a vacuum oven.

[0106] Example 3

[0107] (1) Preparation of dynamic imide-containing polyimide oligomer powder (DFBPO):

[0108] 13g 6FODA was dissolved in 90g NMP. 10g BPADA was slowly added thereto in batches under ice-water bath conditions. The reaction was carried out for 18h. Then 8g toluene was added and stirred for 0.5h. The mixture was placed in a closed heating device at 220°C and dehydrated for 5h. The reaction was then cooled to 60°C. 2.5g terephthalaldehyde was added and reacted for 4h to obtain a uniform solution. The solution was slowly added dropwise to a rapidly stirred cold ethanol solution. The solution was precipitated and filtered to obtain a light yellow powder, which was a polyimide oligomer powder containing dynamic imine, wherein the molar ratio of 6FODA, BPADA and terephthalaldehyde was 2:1:0.935.

[0109] (2) Preparation of thermosetting polyimide (DFBSPI) solution with intrinsic self-healing and low friction properties:

[0110] 15 g of DFBPO was weighed and dissolved in 90 g of NMP, and then 0.2 g of hexamethylene diisocyanate trimer was added to the DFBPO solution, and the reaction was carried out at 80 ° C for 3 hours. Then, the system was slowly cooled to 60 ° C, 0.15 g of benzyl isothiocyanate was added, and the reaction was carried out for 24 hours to obtain a yellow transparent solution, which is a thermosetting polyimide solution with intrinsic self-healing and low friction properties, wherein the molar ratio of dynamic imide polyimide oligomer, hexamethylene diisocyanate trimer and benzyl isothiocyanate is 1:0.34:1.

[0111] (3) Preparation of thermosetting polyimide films with intrinsic self-healing and low friction properties:

[0112] The yellow transparent solution was placed in a vacuum oven for 10 min, and then cast on a glass plate by a casting method for thermal curing treatment: 60°C for 4 h, 80°C for 2 h, 100°C for 1 h, 150°C for 1 h, and 200°C for 5 h. All procedures were carried out in a vacuum oven.

[0113] Example 4

[0114] (1) Preparation of dynamic imide-containing polyimide oligomer powder (DFBPO):

[0115] 13g 6FODA was dissolved in 90g NMP. 10g BPADA was slowly added thereto in batches under ice-water bath conditions. The mixture was reacted for 18h. Then 8g toluene was added and stirred for 0.5h. The mixture was placed in a closed heating device at 220°C and dehydrated for 5h. The reaction mixture was then cooled to 60°C. 1.3g terephthalaldehyde was added and reacted for 4h to obtain a uniform solution. The solution was slowly added dropwise to a rapidly stirred cold ethanol solution. The solution was precipitated and filtered to obtain a light yellow powder, which was a polyimide oligomer powder containing dynamic imine, wherein the molar ratio of 6FODA, BPADA and terephthalaldehyde was 2:1:0.485.

[0116] (2) Preparation of thermosetting polyimide (DFBSPI) solution with intrinsic self-healing and low friction properties:

[0117] 2 g of DFBPO was weighed and dissolved in 90 g of NMP, and then 0.2 g of hexamethylene diisocyanate trimer was added to the DFBPO solution, and the reaction was carried out at 80 ° C for 3 hours. Then, the system was slowly cooled to 60 ° C, 0.15 g of benzyl isothiocyanate was added, and the reaction was carried out for 24 hours to obtain a yellow transparent solution, which is a thermosetting polyimide solution with intrinsic self-healing and low friction properties, wherein the molar ratio of dynamic imide polyimide oligomer, hexamethylene diisocyanate trimer and benzyl isothiocyanate is 1:0.34:1.

[0118] (3) Preparation of thermosetting polyimide films with intrinsic self-healing and low friction properties:

[0119] The yellow transparent solution was placed in a vacuum oven for 10 min, and then cast on a glass plate by a casting method for thermal curing treatment: 60°C for 4 h, 80°C for 2 h, 100°C for 1 h, 150°C for 1 h, and 200°C for 5 h. All procedures were carried out in a vacuum oven.

[0120] The reciprocating friction test results and scratch self-repair results of the thermosetting polyimide films with intrinsic self-repairing and low friction properties obtained in Examples 2 to 4 are similar to those in Example 1.

[0121] It can be seen from the above examples that the thermosetting polyimide with intrinsic self-repairing and low friction properties prepared by the present invention has a low friction coefficient and self-repairing ability, which is attributed to the synergistic effect of the double decomposition reaction of the dynamic imide bond and the strong and weak hydrogen bonds generated by the thiourea and urea groups. The present invention realizes the unification of the intrinsic self-repairing performance and friction performance of thermosetting polyimide for the first time, provides a way to achieve the low friction of intrinsic self-repairing polyimide, and expands the application of self-repairing materials in engineering.

[0122] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a thermosetting polyimide having intrinsic self-healing and low friction properties, characterized in that: The following steps are involved: Mixing BPADA, 6FODA and an organic solvent to carry out a first polycondensation reaction to obtain a polyimide precursor solution; Adding toluene to the polyimide precursor solution, and performing chemical imidization and thermal imidization synergistic treatment under heating conditions to obtain a polyimide oligomer; The polyimide oligomer and terephthalaldehyde undergo a second polycondensation reaction to obtain a polyimide oligomer containing dynamic imine; The dynamic imine-containing polyimide oligomer is mixed with hexamethylene diisocyanate trimer and an organic solvent to carry out a third polycondensation reaction, and benzyl isothiocyanate is added to the obtained third polycondensation reaction system to carry out a capping reaction to obtain a thermosetting polyimide with intrinsic self-healing and low friction properties.

2. The preparation method according to claim 1, characterized in that: The molar ratio of 6FODA to BPADA is 1.5 to 2.5:1; The first condensation reaction is carried out in an ice-water bath, and the time of the first condensation reaction is 10 to 20 hours.

3. The preparation method according to claim 1, characterized in that: The mass of the toluene is 1 / 10 to 1 / 5 of the mass of the organic solvent in the first polycondensation reaction liquid; The temperature of the chemical imidization and thermal imidization synergistic treatment is 200-240° C. and the time is 3-7 hours.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the polyimide oligomer to terephthalaldehyde is 1:0.4-2.6; The temperature of the second polycondensation reaction is 40 to 90° C., and the time is 2 to 6 hours.

5. The preparation method according to claim 1 or 4, characterized in that: The molecular weight of the dynamic imide-containing polyimide oligomer is 1,000 to 20,000.

6. The preparation method according to claim 1, characterized in that: The molar ratio of the dynamic imine-containing polyimide oligomer to the hexamethylene diisocyanate trimer is 1:0.3-0.6; The temperature of the third polycondensation reaction is 60-100° C., and the time is 1-4 hours.

7. The preparation method according to claim 1, characterized in that: The molar ratio of the dynamic imine-containing polyimide oligomer to benzyl isothiocyanate is 0.5 to 1:1; The temperature of the end-capping reaction is 30-60° C. and the time is 10-48 hours.

8. Thermosetting polyimide with intrinsic self-healing and low friction properties prepared by the preparation method according to any one of claims 1 to 7.

9. A thermosetting polyimide film having intrinsic self-healing and low friction properties, characterized in that: The thermosetting polyimide with intrinsic self-healing and low friction properties as described in claim 8 is obtained by sequentially casting and step-by-step thermal curing.

10. The thermosetting polyimide film with intrinsic self-healing and low friction properties according to claim 9, characterized in that: The temperature rise program of the step thermal curing includes: First keep warm at 40-60°C for 2-4h; Second insulation at 70-80°C for 2-4h; The third heat preservation is at 100-120°C for 1-2 hours; The fourth heat preservation is at 130-150°C for 1-2 hours; The fifth heat preservation is carried out at 200-250°C for 5-8 hours.

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