Interpenetrating network type polyimide material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of polyimide materials, and particularly relates to an interpenetrating network type polyimide material as well as a preparation method and application thereof. The preparation method comprises the following steps: carrying out first polycondensation on pyromellitic dianhydride and 4, 4 '-diaminodiphenyl ether to obtain first polyamide acid; performing first cross-linking on the first polyamide acid under the action of a first cross-linking agent to obtain a first cross-linked network; carrying out second polycondensation on the amino-terminated poly (dimethyl siloxane) and 4, 4 '-(hexafluoroisopropenyl) diphthalic anhydride to obtain second polyamide acid; mixing the first polyamic acid and the second polyamic acid for pre-reaction, and then adding a second cross-linking agent for second cross-linking to obtain a precursor solution; and carrying out imidization on the precursor solution to obtain the interpenetrating network type polyimide material. The interpenetrating network type polyimide material obtained by the preparation method provided by the invention realizes synergistic enhancement of strength and toughness.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyimide materials, in particular to an interpenetrating network type polyimide material and a preparation method and application thereof. BACKGROUND

[0002] Polyimide is known as "golden polymer" due to its excellent high-temperature resistance, excellent mechanical strength and stable chemical properties, and plays an irreplaceable role in the fields of aerospace, microelectronics, flexible display and other high-end fields. With the rapid development of flexible electronics, intelligent sensing and other "intelligent new era" technologies, unprecedented new requirements are put forward for polyimide materials: while maintaining its inherent high strength and high heat resistance, it must have extremely high toughness, stretchability and even dynamic adaptability to realize reliable operation of the device under complex deformation. However, the inherent rigidity and brittleness of traditional polyimide materials result in extremely low elongation at break, making it difficult to withstand repeated bending and stretching, which has become a key bottleneck restricting its wide application in the field of flexible electronics. How to break through the inherent contradiction between strength and toughness of polyimide and realize the synergistic enhancement of both is a major challenge currently faced. SUMMARY

[0003] Therefore, the present application aims to provide an interpenetrating network type polyimide material and a preparation method and application thereof. The interpenetrating network type polyimide material obtained by the preparation method provided by the present application realizes synergistic enhancement of strength and toughness.

[0004] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions: The present application provides a preparation method of an interpenetrating network type polyimide material, comprising the following steps: performing first polycondensation on pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) to obtain a first polyamic acid; performing first crosslinking on the first polyamic acid under the action of a first crosslinking agent to obtain a first crosslinking network; performing second polycondensation on amino-terminated poly(dimethylsiloxane) (PMDS-NH2, CAS No.: 106214-84-0) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) to obtain a second polyamic acid; mixing the first polyamic acid and the second polyamic acid, performing pre-reaction, and then adding a second crosslinking agent to perform second crosslinking to obtain a precursor solution; performing imidization on the precursor solution to obtain the interpenetrating network type polyimide material.

[0005] Preferably, the molar ratio of the pyromellitic dianhydride and the 4,4'-diaminodiphenyl ether is 1:1; The solvent used in the first polycondensation is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC) and N-methyl pyrrolidone (NMP).

[0006] Preferably, the first polycondensation is carried out under ice water bath and protective atmosphere, and the time of the first polycondensation is 18-30 h.

[0007] Preferably, the first crosslinking agent comprises one or more of 3,3'-diaminobenzidine (DAB), 1,3,5-tris(4-aminophenoxy)benzene (TAPOB, CAS: 102852-92-6) and tris(2-aminoethyl)amine (CAS: 4097-89-6); The molar ratio of the pyromellitic dianhydride and the first crosslinking agent is 1:0.01-0.05; The first crosslinking is carried out under ice water bath and protective atmosphere, and the time of the first crosslinking is 10-14 h.

[0008] Preferably, the molar ratio of the amino-terminated poly(dimethylsiloxane) (PMDS-NH2) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) is 1:0.95-1; The solvent used in the second polycondensation comprises tetrahydrofuran and N,N-dimethylacetamide; The second polycondensation is carried out under ice water bath and protective atmosphere, and the time of the second polycondensation is 18-30 h.

[0009] Preferably, the molar ratio of the pyromellitic dianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is 1:0.95-1; The pre-reaction is carried out at room temperature and under protective atmosphere, and the time of the pre-reaction is 18-30 h.

[0010] Preferably, the second crosslinking agent is one or more of 3,3'-diaminobenzidine (DAB), 1,3,5-tris(4-aminophenoxy)benzene (TAPOB) and tris(2-aminoethyl)amine; The molar ratio of the amino-terminated poly(dimethylsiloxane) (PMDS-NH2) and the second crosslinking agent is 1:0.03-0.05; The second crosslinking is carried out under ice water bath and protective atmosphere, and the time of the second crosslinking is 10-14 h.

[0011] Preferably, the imidization comprises sequentially carrying out a first heating, a second heating, a third heating and a fourth heating; The temperature of the first heating is 80℃, and the holding time is 5-7 h; The temperature of the second heating is 120℃, and the holding time is 3-5 h; The temperature of the third heating is 160 DEG C, and the holding time is 3-5h; The temperature of the fourth heating is 200 DEG C, and the time is 10-14h.

[0012] The application further provides the interpenetrating network type polyimide material prepared by the preparation method.

[0013] The application further provides application of the interpenetrating network type polyimide material in the fields of aerospace, microelectronics and flexible display.

[0014] The application provides a preparation method of an interpenetrating network type polyimide material.

[0015] The inventor finds that the macro mechanical properties of a polymer material fundamentally depend on the topological structure of a molecular network. Traditional linear or simple crosslinking structures are often difficult to balance strength and toughness. In nature, biological composite materials such as bones and shells realize the perfect unity of strength and toughness through ordered multi-level and multi-component compounding, and the core mechanism lies in the construction of an effective energy dissipation mechanism. Inspired by this, a biomimetic network topology is designed at the molecular level, which provides a new idea for solving the above-mentioned problems. The application innovatively proposes a preparation method of an interpenetrating network type polyimide material based on rigid-flexible chain segment cooperation. By constructing a rigid polyimide network and a flexible siloxane network respectively, and making them interpenetrate at the molecular level to form a stable topological interpenetrating structure, an efficient energy dissipation level is successfully established in the material. The rigid polyimide network acts as a solid skeleton, responsible for bearing stress and giving the material high strength; and the flexible siloxane network acts as a sacrificial phase, which preferentially dissipates energy through molecular chain slipping and network deformation under external force, thereby significantly improving the toughness of the material. This “sacrificial network” mechanism is similar to the “energy absorption box” in machinery, which can effectively absorb impact energy without damaging the main structure. Compared with single covalent crosslinking or supramolecular crosslinking, the interpenetrating network type polyimide material obtained by the application can organically integrate the stability of the covalent network and the dynamic energy dissipation capacity of the physical network, realizing a leap-forward improvement in performance. At the same time, the proportion and crosslinking density of the two networks can be accurately controlled, so that the macro mechanical properties of the interpenetrating network type polyimide material can be flexibly customized. Therefore, the interpenetrating network type polyimide material obtained by the application not only retains the high strength, heat resistance and film-forming property of traditional polyimide, but also obtains extraordinary toughness (elongation at break > 280%) and stretchability, which provides key material support for the next generation of flexible electronic devices, intelligent robots and aerospace flexible equipment, and opens up a new paradigm for the design of high-performance polymer materials.

[0016] Data from the examples show that the obtained interpenetrating network polyimide material has a tensile strength of 170~242MPa, an elongation at break of 284~291%, and a toughness of 282.66~397.92MJ / m. 3 It possesses both excellent toughness and strength. Attached Figure Description

[0017] Figure 1 The infrared spectra of the interpenetrating cross-linked network polyimide obtained in Examples 1-3 and Comparative Example 1 are shown below. Figure 2 This is a summary diagram of the stress-strain curves of the interpenetrating cross-linked network polyimide obtained in Examples 1-3 and Comparative Example 1; Figure 3 This is a schematic diagram of the thermogravimetric curve of the interpenetrating cross-linked network polyimide obtained in Example 1. Detailed Implementation

[0018] This invention provides a method for preparing an interpenetrating network polyimide material, comprising the following steps: The first polycondensation of pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether (ODA) yields the first polyamic acid. The first polyamic acid undergoes a first crosslinking process under the action of a first crosslinking agent to obtain a first crosslinked network; A second polycondensation was carried out between amino-terminated poly(dimethylsiloxane) (PMDS-NH2) and 4,4′-(hexafluoroisopropene) phthalic anhydride (6FDA) to obtain a second polyamic acid; The first polyamic acid and the second polyamic acid are mixed and pre-reacted, and then a second crosslinking agent is added to carry out a second crosslinking to obtain a precursor solution. The precursor solution is imidized to obtain the interpenetrating network polyimide material.

[0019] Unless otherwise specified, the raw materials used in this invention are preferably commercially available products.

[0020] The present invention involves a first polycondensation of pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether (ODA) to obtain a first polyamic acid.

[0021] In this invention, the solvent used for the first polycondensation (referred to as the first solvent) is preferably one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC) and N-methylpyrrolidone (NMP), and more preferably N,N-dimethylacetamide (DMAC).

[0022] In this invention, the molar ratio of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether is preferably 1:1.

[0023] In this invention, the preferred ratio of the amount of pyromellitic dianhydride to the first solvent is 5 mmol: 15 mL.

[0024] In this invention, the first polycondensation is preferably carried out in an ice-water bath and under a protective atmosphere, wherein the temperature of the ice-water bath is preferably 0-5°C and the protective atmosphere is preferably nitrogen; the first polycondensation is preferably carried out under stirring. In this invention, the first polycondensation time is preferably 18-30 hours, more preferably 24 hours.

[0025] In this invention, the first polycondensation of the pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether (ODA) preferably includes the following steps: 4,4′-diaminodiphenyl ether and a first solvent are dissolved in a container (denoted as the first dissolution), and then pyromellitic dianhydride is added in batches to carry out the first polycondensation. In this invention, the first dissolution is preferably carried out under the conditions of an ice-water bath, a protective atmosphere, and stirring; the temperature of the ice-water bath and the type of protective atmosphere are preferably consistent with the above-described technical solution, and will not be repeated here.

[0026] After the first polycondensation, the present invention preferably obtains the first polyamic acid without any post-processing.

[0027] After obtaining the first polyamic acid, the first polyamic acid of the present invention undergoes a first crosslinking under the action of a first crosslinking agent to obtain a first crosslinked network.

[0028] In this invention, the first crosslinking agent preferably includes one or more of 3,3'-diaminobenzidine (DAB), 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and tris(2-aminoethyl)amine, and more preferably 3,3'-diaminobenzidine (DAB).

[0029] In this invention, the molar ratio of the pyromellitic dianhydride and the first crosslinking agent is preferably 1:0.01 to 0.05, and more preferably 1:0.01, 1:0.02, 1:0.03, 1:0.04 or 1:0.05.

[0030] In this invention, the first crosslinking is preferably carried out in an ice-water bath and under a protective atmosphere. The temperature of the ice-water bath and the type of protective atmosphere are preferably the same as those described above, and will not be repeated here. The first crosslinking time is preferably 10-14 hours, and more preferably 12 hours.

[0031] After the first crosslinking is completed, the present invention preferably obtains the first crosslinked network without any post-processing.

[0032] The present invention involves a second polycondensation of amino-terminated poly(dimethylsiloxane) (PMDS-NH2) and 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA) to obtain a second polyamic acid.

[0033] In this invention, the solvent used for the second polycondensation (denoted as the second solvent) preferably includes tetrahydrofuran (THF) and N,N-dimethylacetamide (DMAc); the volume ratio of the tetrahydrofuran to N,N-dimethylacetamide is preferably 2:1.

[0034] In this invention, the molar ratio of the amino-terminated poly(dimethylsiloxane) (PMDS-NH2) and 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA) is preferably 1:0.95~1, and more preferably 1:0.95, 1:0.96, 1:0.97, 1:0.98, 1:0.99 or 1:1.

[0035] In this invention, the preferred ratio of amino-terminated poly(dimethylsiloxane) to the second solvent is 5 mmol:45 mL.

[0036] In this invention, the second polycondensation is preferably carried out in an ice-water bath and under a protective atmosphere. The temperature of the ice-water bath and the type of protective atmosphere are preferably consistent with the above-described technical solution, and will not be repeated here. In this invention, the second polycondensation time is preferably 18-30 hours, more preferably 24 hours. In this invention, the second polycondensation is preferably carried out under stirring conditions.

[0037] In this invention, the second polycondensation of the amino-terminated poly(dimethylsiloxane) (PMDS-NH2) and 4,4′-(hexafluoroisopropene) phthalic anhydride (6FDA) preferably includes the following steps: The amino-terminated poly(dimethylsiloxane) and a second solvent are dissolved in a container (denoted as the second dissolution), and then 4,4′-(hexafluoroisopropene)phthalic anhydride is added in batches to carry out the second polycondensation. In this invention, the second dissolution is preferably carried out under the conditions of an ice-water bath, a protective atmosphere, and stirring. The temperature of the ice-water bath and the type of protective atmosphere are preferably consistent with the above-described technical solution, and will not be repeated here.

[0038] After the second polycondensation is completed, the present invention preferably obtains the second polyamic acid directly without any post-processing.

[0039] After obtaining the first polyamic acid and the second polyamic acid, the present invention mixes the first polyamic acid and the second polyamic acid for pre-reaction, and then adds a second crosslinking agent for second crosslinking to obtain a precursor solution.

[0040] In this invention, the molar ratio of pyromellitic dianhydride and 4,4′-(hexafluoroisopropene)phthalic anhydride is preferably 1:0.95~1, specifically preferably 1:0.95, 1:0.96, 1:0.97, 1:0.98, 1:0.99 or 1:1; the molar ratio of the repeating units of the first polyamic acid and the second polyamic acid is preferably 1:0.95~1.

[0041] In this invention, the pre-reaction is preferably carried out at room temperature and under a protective atmosphere, preferably nitrogen; the pre-reaction time is 18-30 hours, more preferably 24 hours. In this invention, the pre-reaction is preferably carried out under stirring. In this invention, the pre-reaction enables the networks of the first and second polyamic acids to initially interpenetrate.

[0042] In this invention, the second crosslinking agent is preferably one or more of 3,3'-diaminobenzidine (DAB), 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and tris(2-aminoethyl)amine, and more preferably 3,3'-diaminobenzidine (DAB).

[0043] In this invention, the molar ratio of the amino-terminated poly(dimethylsiloxane) (PMDS-NH2) and the second crosslinking agent is preferably 1:0.03~0.05, and more preferably 1:0.03, 1:0.04 or 1:0.05.

[0044] In this invention, the second crosslinking is carried out in an ice-water bath and under a protective atmosphere. The temperature of the ice-water bath and the type of protective atmosphere are preferably consistent with the above-described technical solution, and will not be repeated here. In this invention, the second crosslinking time is preferably 10-14 hours, more preferably 12 hours. In this invention, the second crosslinking causes the molecular chains of the second polyamic acid to crosslink, ultimately forming a precursor solution with an interpenetrating crosslinked network structure.

[0045] After obtaining the precursor solution, the present invention imidizes the precursor solution to obtain the interpenetrating network polyimide material.

[0046] In this invention, the imidization preferably includes sequentially performing a first heating, a second heating, a third heating, and a fourth heating.

[0047] In this invention, the temperature of the first heating is preferably 80°C, and the heat preservation time is preferably 5-7 hours, more preferably 6 hours.

[0048] In this invention, the temperature of the second heating is preferably 120°C, and the heat preservation time is preferably 3 to 5 hours, specifically 3 hours, 4 hours or 5 hours.

[0049] In this invention, the temperature of the third heating is preferably 160°C, and the heat preservation time is preferably 3 to 5 hours, specifically 3 hours, 4 hours or 5 hours.

[0050] In this invention, the temperature of the fourth heating is preferably 200°C, and the time is preferably 10-14 hours, more preferably 12 hours.

[0051] The present invention also provides an interpenetrating network polyimide material prepared by the preparation method described in the above technical solution.

[0052] In this invention, the interpenetrating network polyimide material possesses both excellent strength and toughness.

[0053] This invention also provides the application of the interpenetrating network polyimide material described above in the fields of aerospace, microelectronics and flexible displays.

[0054] This invention does not impose specific limitations on the application of the interpenetrating network polyimide material; those skilled in the art can make settings according to actual needs.

[0055] The following detailed description, in conjunction with embodiments, illustrates the interpenetrating network polyimide material, its preparation method, and its applications provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1 (1) Weigh 5 mmol (1.0012 g) of 4,4′-diaminodiphenyl ether (ODA) into a three-necked flask, and measure 15 mL of N,N-dimethylacetamide (DMAc) as a solvent. Stir the solution in an ice-water bath (0~5℃) under N2 atmosphere until fully dissolved. Then, under continuous stirring and N2 protection, slowly add 5 mmol (1.0906 g) of pyromellitic dianhydride (PMDA) in batches, controlling the temperature of the reaction system to not exceed 5℃. After the addition is complete, continue stirring in an ice-water bath under N2 atmosphere for 24 h to obtain a polyamic acid (PAA) solution. Keeping the ice-water bath conditions, add 0.05 mmol (0.0107 g) of crosslinking agent 3,3′-diaminobenzidine (DAB) to this solution (corresponding to a feed ratio of PMDA:ODA:DAB=1:1:0.01), and continue the reaction in an N2 atmosphere for 12 h. The resulting product is named crosslinked PAA-1.

[0057] (2) Weigh 5 mmol (10.0000 g) of amino-terminated poly(dimethylsiloxane) (PDMS-NH2) into another three-necked flask, measure 30 mL of a mixed solvent of tetrahydrofuran (THF) and 15 mL of N,N-dimethylacetamide (DMAc), and stir under ice-water bath conditions (0~5℃) and N2 atmosphere to ensure complete dissolution. Then, under continuous stirring and N2 protection, slowly add 5 mmol (2.2212 g) of 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA) in batches, controlling the reaction system temperature to not exceed 5℃. After the addition is complete, continue stirring and reacting under ice-water bath and N2 atmosphere for 24 h to obtain a polyamic acid (PAA) solution, named PAA-2 (corresponding to a feed ratio of PDMS-NH2:6FDA=1:0.97).

[0058] (3) All the crosslinked PAA-1 solution and PAA-2 solution prepared above were transferred together into a clean three-necked flask (based on the molar ratio of PMDA and 6FDA being 5 mmol each, i.e., the molar ratio of PAA-1 to PAA-2 chain segments being 1:1). The mixture was stirred thoroughly for 24 h at room temperature and under a N2 atmosphere to allow the two networks to initially interpenetrate. Then, 0.15 mmol (0.0321 g) of the crosslinking agent 3,3'-diaminobenzidine (DAB) (molar ratio with PMDS-NH2 being 0.03:1) was added to this mixed solution, and the reaction was continued for 12 h in an ice-water bath under a N2 atmosphere to allow the PAA-2 molecular chains to crosslink, thereby finally forming a precursor solution with an interpenetrating crosslinked network structure.

[0059] (4) The synthesized polyamic acid solution was coated onto a clean glass plate using a glass rod and placed in a programmable temperature-controlled oven for stepwise imidization treatment: first, it was kept at 80°C for 6 hours, then successively increased to 120°C and 160°C and kept at each temperature for 3 hours, and finally increased to 200°C and kept at each temperature for 12 hours. After natural cooling, it was peeled off from the glass plate to obtain an interpenetrating network polyimide film. The sample in Example 1 was named IPN-SiPI. 3% .

[0060] Example 2 (1) It is consistent with step 1 of Example 1.

[0061] (2) Weigh 5 mmol (10.0000 g) of amino-terminated poly(dimethylsiloxane) (PDMS-NH2) into another three-necked flask, and measure 30 mL of a mixed solvent of tetrahydrofuran (THF) and 15 mL of N,N-dimethylacetamide (DMAc). Stir the mixture under an ice-water bath (0~5℃) and an N2 atmosphere until fully dissolved. Then, under continuous stirring and N2 protection, slowly add 4.8 mmol (2.1324 g) of 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA) in batches, controlling the temperature of the reaction system to not exceed 5℃. After the addition is complete, continue stirring and reacting under an ice-water bath and an N2 atmosphere for 24 h to obtain a polyamic acid (PAA) solution, named PAA-2 (corresponding to a feed ratio of PDMS-NH2:6FDA=1:0.96).

[0062] (3) All the crosslinked PAA-1 solution and PAA-2 solution prepared above were transferred together into a clean three-necked flask (based on the addition of 5 mmol of PMDA and 4.8 mmol of 6FDA, i.e., the molar ratio of PAA-1 to PAA-2 chain segments was 1:0.96). The mixture was stirred thoroughly at room temperature and under N2 atmosphere for 24 h to allow the two networks to initially interpenetrate. Then, 0.2 mmol (0.0429 g) of the crosslinking agent 3,3'-diaminobenzidine (DAB) (molar ratio of 0.04:1 with PDMS-NH2) was added to this mixed solution, and the reaction was continued for 12 h under ice-water bath and N2 atmosphere to allow the molecular chains of PAA-2 to crosslink, thereby finally forming a precursor solution with an interpenetrating crosslinked network structure.

[0063] (4) The synthesized polyamic acid solution was coated onto a clean glass plate using a glass rod and placed in a programmable temperature-controlled oven for stepwise imidization treatment: first, it was kept at 80°C for 6 hours, then successively increased to 120°C and 160°C and kept at each temperature for 3 hours, and finally increased to 200°C and kept at each temperature for 12 hours. After natural cooling, it was peeled off from the glass plate to obtain an interpenetrating network polyimide film. The sample in Example 2 was named IPN-SiPI. 4% .

[0064] Example 3 (1) It is consistent with step 1 of Example 1.

[0065] (2) Weigh 5 mmol (10.0000 g) of amino-terminated poly(dimethylsiloxane) (PDMS-NH2) into another three-necked flask, and measure 30 mL of a mixed solvent of tetrahydrofuran (THF) and 15 mL of N,N-dimethylacetamide (DMAc). Stir the mixture under an ice-water bath (0~5℃) and an N2 atmosphere until fully dissolved. Then, under continuous stirring and N2 protection, slowly add 4.75 mmol (2.1101 g) of 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA) in batches, controlling the temperature of the reaction system to not exceed 5℃. After the addition is complete, continue stirring under an ice-water bath and an N2 atmosphere for 24 h to obtain a polyamic acid (PAA) solution, named PAA-2.

[0066] (3) All the crosslinked PAA-1 solution and PAA-2 solution prepared above were transferred together into a clean three-necked flask (based on the addition of 5 mmol of PMDA and 4.75 mmol of 6FDA, i.e., the molar ratio of PAA-1 to PAA-2 chain segments was 1:0.95). The mixture was stirred thoroughly at room temperature and under N2 atmosphere for 24 h to allow the two networks to initially interpenetrate. Then, 0.25 mmol (0.0536 g) of the crosslinking agent 3,3'-diaminobenzidine (DAB) (molar ratio of 0.05:1 with PDMS-NH2) was added to this mixed solution, and the reaction was continued for 12 h under ice-water bath and N2 atmosphere to allow the molecular chains of PAA-2 to crosslink, thereby finally forming a precursor solution with an interpenetrating crosslinked network structure.

[0067] (4) The synthesized polyamic acid solution was coated onto a clean glass plate using a glass rod and placed in a programmable temperature-controlled oven for stepwise imidization treatment: first, it was kept at 80°C for 6 hours, then successively increased to 120°C and 160°C and kept at each temperature for 3 hours, and finally increased to 200°C and kept at each temperature for 12 hours. After natural cooling, it was peeled off from the glass plate to obtain an interpenetrating network polyimide film. The sample in Example 3 was named IPN-SiPI. 5% .

[0068] Comparative Example 1 (1) The steps are consistent with those in Example 1.

[0069] (2) Weigh 5 mmol (10.0000 g) of amino-terminated poly(dimethylsiloxane) (PDMS-NH2) into another three-necked flask, and measure 30 mL of a mixed solvent of tetrahydrofuran (THF) and 15 mL of N,N-dimethylacetamide (DMAc). Stir the solution in an ice-water bath (0~5℃) under N2 atmosphere until fully dissolved. Then, under continuous stirring and N2 protection, slowly add 5 mmol (2.2212 g) of 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA) in batches, controlling the temperature of the reaction system to not exceed 5℃. After the addition is complete, continue stirring in an ice-water bath under N2 atmosphere for 24 h to obtain a polyamic acid (PAA) solution, named PAA-2.

[0070] (3) Transfer all the crosslinked PAA-1 solution and PAA-2 solution prepared above into a clean three-necked flask (based on the molar ratio of PMDA and 6FDA being 5 mmol each, i.e., the molar ratio of PAA-1 to PAA-2 chain segments is 1:1). Stir and mix thoroughly at room temperature and under N2 atmosphere for 24 h to allow the two polymer networks to initially interpenetrate, thereby forming a precursor solution with a semi-interpenetrating network structure.

[0071] (4) The synthesized polyamic acid solution was coated onto a clean glass plate using a glass rod and placed in a programmable temperature-controlled oven for stepwise imidization treatment: first, it was kept at 80°C for 6 hours, then successively increased to 120°C and 160°C and kept at each temperature for 3 hours, and finally increased to 200°C and kept at each temperature for 12 hours. After natural cooling, it was peeled off from the glass plate to obtain an interpenetrating network polyimide film. It was named Semi-IPNPI.

[0072] The Fourier transform infrared (FTIR) spectra of the interpenetrating network polyimide films obtained in Examples 1-3 and Comparative Example 1 are as follows: Figure 1 As shown, by Figure 1 It can be seen that at 1772cm -1 (Symmetrical stretching of the imine carbonyl group), 1705cm -1 (Asymmetric stretching of the imine carbonyl group) and 1352cm -1 A characteristic absorption band of the imine ring was observed at the (CN stretching) region, 10¹⁶ cm⁻¹. -1 513cm -1 Characteristic absorption bands of Si-O bonds were observed. Furthermore, no characteristic vibrational peaks of polyamic acid were observed, indicating the successful preparation of the polyimide material.

[0073] To effectively evaluate the mechanical properties of the prepared interpenetrating network polyimide films, stress-strain curve tests were performed on the interpenetrating network polyimide films obtained in Examples 1-3 and Comparative Example 1. The test standard was GB / T 1040-2006, the test speed was 5 mm / min, and the test environment was 25℃. The results are shown in [Figure number missing]. Figure 2 As shown, the results are summarized in Table 1.

[0074] Table 1. Mechanical properties of the interpenetrating network polyimide films obtained in Examples 1-3 and Comparative Example 1

[0075] Depend on Figure 2 As shown in Table 1, the interpenetrating network polyimide film prepared in this invention exhibits excellent comprehensive mechanical properties. Among them, Example 1 demonstrates the most outstanding performance balance, with a tensile strength as high as 242 MPa, an elongation at break of 286%, and a thermal conductivity of 397.92 MJ / m². 3 It exhibits extremely high toughness values. Example 3 also demonstrates high tensile strength and high toughness (217 MPa, 332.62 MJ / m). 3 Example 2, while maintaining extremely high ductility (elongation at break of 284%), also exhibits excellent toughness (282.66 MJ / m). 3 Comparative Example 1 (tensile strength 117 MPa, elongation at break 243%, toughness 136.63 MJ / m) to an example without a complete interpenetrating network structure. 3 Compared to the previous embodiment, the mechanical properties of all embodiments were significantly improved. This indicates that by rationally designing the molecular structure and constructing an interpenetrating cross-linked network combining rigid and flexible segments, it is possible to successfully achieve a balance between high strength, high stretchability, and high toughness in polyimide materials. By controlling the network cross-linking density and the ratio of rigid to flexible segments, the macroscopic mechanical properties of the material can be effectively adjusted. The implementation of this invention provides an effective method for preparing high-performance polyimide materials.

[0076] This invention successfully constructed a high-performance polyimide material with an interpenetrating cross-linked network structure. This unique network configuration provides a key mechanism for achieving a synergistic improvement in the material's strength and toughness. Specifically, Examples 1-3 all exhibit superior mechanical properties far exceeding those of traditional polyimides, which is mainly attributed to the effective synergy between rigid and flexible segments in the interpenetrating network.

[0077] The core mechanism of interpenetrating cross-linked networks lies in their construction of an efficient energy dissipation system. In this system, the rigid network acts as a robust framework, primarily providing strength support; while the flexible network acts as a "sacrificial phase," whose molecular chains can slip, extend, or deform under external forces. This type of plastic deformation, which occurs before the failure of the main rigid network, can effectively dissipate a large amount of energy, thus playing the role of a "sacrificial network." The "sacrificial network" can not only eliminate stress concentration and prevent crack propagation through its own dynamic response, but also promote the reorientation of molecular chains, thereby simultaneously and significantly improving the material's elongation at break (toughness) and tensile strength.

[0078] In summary, this invention designs and constructs a stable system that interpenetrates a rigid covalent network and a flexible physical network. Compared with Comparative Example 1 (which did not form a complete interpenetrating network), the material of this invention combines the high strength of the covalently cross-linked network with the high toughness and energy dissipation advantages of the physically interpenetrating network. The results show that the interpenetrating cross-linked network can effectively integrate static stability and dynamic energy dissipation capability, successfully breaking the long-standing "strength-toughness" trade-off dilemma faced by polyimide materials, and providing a novel and promising molecular design strategy for developing next-generation high-performance polyimide materials.

[0079] In addition, the thermal stability of the interpenetrating network polyimide film obtained in Example 1 was tested. The test atmosphere was nitrogen, and the test temperature range was from room temperature to 800°C. The results are as follows: Figure 3 As shown, by Figure 3 As can be seen, taking Example 1 as an example, all samples exhibited excellent heat resistance. The thermogravimetric temperature (Td, the temperature corresponding to 5% weight loss of the sample) of 3% IPN-SiPI was approximately 496℃, which is superior to most polyurethane elastomers, demonstrating good stability. Therefore, the results of the thermogravimetric analysis fully demonstrate that the interpenetrating crosslinked network polyimide prepared in this invention not only exhibits high strength, high toughness, and high stretchability, but also excellent heat resistance, and is expected to be used in extreme conditions or complex environments.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an interpenetrating network polyimide material, characterized in that, Includes the following steps: The first polycondensation of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether yields the first polyamic acid. The first polyamic acid undergoes a first crosslinking process under the action of a first crosslinking agent to obtain a first crosslinked network; A second polycondensation was performed between amino-terminated poly(dimethylsiloxane) and 4,4′-(hexafluoroisopropene) phthalic anhydride to obtain a second polyamic acid; The first polyamic acid and the second polyamic acid are mixed and pre-reacted, and then a second crosslinking agent is added to carry out a second crosslinking to obtain a precursor solution. The precursor solution is imidized to obtain the interpenetrating network polyimide material.

2. The preparation method according to claim 1, characterized in that, The molar ratio of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether is 1:1; The solvent used in the first polycondensation is one or more of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

3. The preparation method according to claim 1 or 2, characterized in that, The first polycondensation was carried out in an ice-water bath and under a protective atmosphere for 18-30 hours.

4. The preparation method according to claim 1 or 2, characterized in that, The first crosslinking agent includes one or more of 3,3'-diaminobenzidine, 1,3,5-tris(4-aminophenoxy)benzene and tris(2-aminoethyl)amine; The molar ratio of the pyromellitic dianhydride to the first crosslinking agent is 1:0.01~0.05; The first crosslinking was carried out in an ice-water bath and under a protective atmosphere for 10-14 hours.

5. The preparation method according to claim 1, characterized in that, The molar ratio of the amino-terminated poly(dimethylsiloxane) and 4,4′-(hexafluoroisopropene) phthalic anhydride is 1:0.95~1; The solvents used in the second polycondensation include tetrahydrofuran and N,N-dimethylacetamide; The second polycondensation was carried out in an ice-water bath and under a protective atmosphere for 18-30 hours.

6. The preparation method according to claim 1, characterized in that, The molar ratio of pyromellitic dianhydride and 4,4′-(hexafluoroisopropene) diaphthalic anhydride is 1:0.95~1; The pre-reaction was carried out at room temperature and under a protective atmosphere for 18-30 hours.

7. The preparation method according to claim 1, characterized in that, The second crosslinking agent is one or more of 3,3'-diaminobenzidine, 1,3,5-tris(4-aminophenoxy)benzene and tris(2-aminoethyl)amine; The molar ratio of the amino-terminated poly(dimethylsiloxane) and the second crosslinking agent is 1:0.03~0.05; The second crosslinking was carried out in an ice-water bath and under a protective atmosphere for 10-14 hours.

8. The preparation method according to claim 1, characterized in that, The imidization includes sequentially performing a first heating, a second heating, a third heating, and a fourth heating; The first heating temperature is 80℃, and the holding time is 5~7h; The second heating temperature is 120℃, and the holding time is 3~5 hours; The third heating temperature is 160℃, and the holding time is 3~5h; The fourth heating temperature is 200℃, and the time is 10~14h.

9. The interpenetrating network polyimide material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the interpenetrating network polyimide material of claim 9 in the fields of aerospace, microelectronics and flexible displays.

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