Reversible cross-linked polyimide and manufacturing method of film of reversible cross-linked polyimide

Abstract

The invention discloses reversible cross-linked polyimide and a manufacturing method of a film of the reversible cross-linked polyimide. The molecular formula of the reversible cross-linked polyimide is shown as a formula I. The polyimide can ensure that the material has thermal degradation temperature similar to that of a non-grafted material and higher toughness. Meanwhile, a cross-linked structure can be conveniently and controllably added into the obtained polyimide material, especially a film material, so that the polyimide film has lower internal stress, better dimensional stability, stronger interface bonding force and more excellent ultraviolet resistance. Meanwhile, the film coating and volatilization process can be more controllable through the reversible cross-linking reaction, and the film which is higher in size precision and more uniform can be obtained. The obtained film is more suitable for being used in complex environments such as high voltage, high stress, ultraviolet radiation and high adhesion.

Description

Technical Field

[0001] This invention belongs to the field of polyimide material preparation technology, specifically relating to a method for manufacturing a reversible crosslinked polyimide and its film. Background Technology

[0002] Polyimide is a general term for a class of high-molecular polymer materials whose main chain contains imide bonds. It boasts the best heat resistance among existing polymer materials and is widely used in fields requiring high heat resistance, such as films, plastics, aerogels, and composite materials. Aromatic polyimides, in particular, can withstand temperatures exceeding 500℃ and can operate continuously at temperatures above 300℃. Furthermore, polyimide materials possess excellent comprehensive properties, including mechanical, environmental, chemical, and photothermal stability, making them promising for widespread application in batteries, motors, high-voltage power transmission, and aerospace. However, polyimide materials still have some shortcomings. During processing, insufficient fluid strength and solvent evaporation can lead to unstable longitudinal or tangential flow in the film, resulting in structures such as pores, unevenness, and ripples, especially noticeable in thick-film coating processes. Meanwhile, crosslinking greatly improves the mechanical properties, creep resistance, and thermomechanical stability of materials. However, if crosslinking is done too early in the preparation of polyimides, it will increase internal stress in fluid flow or inhibit the ring-closing reaction, leading to a decrease in the degree of reaction; while if crosslinking is done too late, the degree of crosslinking will be reduced, failing to achieve the effect of strengthening and stabilizing. In addition, polyimides also have problems such as insufficient UV resistance and insufficient adhesion strength with other matrices. Therefore, in order to meet the complex processing and diverse application scenarios of polyimides, it is necessary to introduce reversible crosslinking as needed without sacrificing the mechanical properties of polyimides, and to develop polyimide varieties with higher quality, less residual internal stress, and excellent mechanical properties.

[0003] Lipoic acid (LA) is a small molecule compound found in nature, widely present in the aerobic metabolic systems of plants and animals. It is a widely available, inexpensive, and biofriendly organic molecule. Its core molecular structure consists of a 1,2-dithiopentane ring (a five-membered ring disulfide), with a carboxylic acid group attached to the chain end, giving it reactivity, designability, and amphiphilic properties. This unique molecular structure, which also possesses dynamic covalent bonds (disulfide bonds), makes lipoic acid an ideal molecule for designing self-healing and recyclable polymer materials, holding significant application value in life sciences and materials science. Summary of the Invention

[0004] The purpose of this invention is to provide a method for manufacturing reversible crosslinked polyimide and its film.

[0005] A reversible crosslinked polyimide, the molecular formula of which is shown in Formula I:

[0006]

[0007] In the formula, n = 1-40, m = 1-40; Ar is a dianhydride monomer; Ar' is a diamine monomer.

[0008] The dianhydride monomer is one or more of the following: pyromellitic dianhydride (PMDA), 4,4'-diphenyl ether dianhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-(hexafluoroisopropyl)bisphthalic anhydride (6FDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 1,4,5,8-naphthalenetetracarboxylic anhydride (NTDA), cyclobutane dianhydride (CBDA), and 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride (DSDA).

[0009] The diamine monomer is an aromatic diamine, which is one or more of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PPD), 4,4'-diaminodiphenylmethane (MDA), 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl (m-TB), benzidine, 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), and 2,2-bis(4-aminophenyl)hexafluoropropane (6FpDA).

[0010] A method for manufacturing a reversibly crosslinked polyimide, comprising the following steps:

[0011] (1) Under the protection of an inert gas with a stirrer, add solvent, diamine monomer, dianhydride monomer, thioctic acid and its derivatives to the reaction vessel, stir and dissolve at 20-30℃, and then stir and react at 40-60℃ for 8-12 hours to obtain a polyamic acid solution.

[0012] (2) Apply the polyamic acid solution onto the glass substrate using a scraper. Degas the coating at 20-30°C under reduced pressure and pre-dry it for 20-40 minutes. Then, place it in a hot air dryer under normal pressure nitrogen atmosphere for heat treatment.

[0013] The lipoic acid and its derivatives are one or more of lipoic dianhydride, lipoic acid, lipoamide, and methyl lipoate. Their molecular formulas are as follows:

[0014]

[0015] The solvent is one or more of N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), toluene, xylene, chloroform, and dichloromethane (DCM).

[0016] The molar ratio of the total amount of diamine monomer to the total amount of dianhydride monomer is (0.8-1.2):1.

[0017] The heat treatment is as follows: heating at 110-130℃ for 40-80 min, heating at 140-160℃ for 40-80 min, heating at 180-220℃ for 20-40 min, heating at 230-270℃ for 20-40 min, heating at 300-340℃ for 10-30 min, and heating at 380-420℃ for 8-12 min.

[0018] The polyimide of this invention is reversibly crosslinked, which can automatically open at high temperatures (above 180°C) and reconnect at low temperatures. By controlling the content of the crosslinking monomer and the temperature of polyamic acid preparation, it is possible to avoid affecting the polycondensation reaction in solution and the ring-closing reaction at high temperatures, while also increasing the stability of liquid film flow during film scraping and solvent evaporation.

[0019] The ring-opening polymerization reaction of cyclic disulfide bonds under ultraviolet light or heating is as follows:

[0020]

[0021] The molecular structure of the crosslinked polyimide copolymerized with cyclic disulfide groups is as follows:

[0022]

[0023] The beneficial effects of this invention are as follows: The polyimide containing cyclic disulfide bonds involved in this invention can ensure that the material has a thermal degradation temperature similar to that of the ungrafted material and higher toughness. Simultaneously, the obtained polyimide material, especially the film material, can be easily and controllably incorporated with cross-linking structures, resulting in polyimide films with lower internal stress, better dimensional stability, stronger interfacial adhesion, and superior UV resistance. Furthermore, the reversible cross-linking reaction allows for more controllable film coating and volatilization processes, contributing to the obtaining of films with higher dimensional accuracy and greater uniformity. The resulting film is more suitable for use in complex environments such as high voltage, high stress, UV irradiation, and high adhesion environments. Detailed Implementation

[0024] To facilitate understanding of the present invention, a more comprehensive description will be given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0025] Example 1

[0026] In a 500 mL glass reaction vessel equipped with a stirrer and under inert gas protection, 300 g of NMP and 100 g of toluene were added as solvents. 0.25 mol of PPD, 0.20 mol of BPDA, and 0.05 mol of thioctic dianhydride were then added. The mixture was stirred at room temperature until completely dissolved, and then stirred at 50 °C for 10 h to obtain a polyamic acid solution composition with a solution viscosity of 58.0 Pa·s. No flocculants or insoluble matter were formed in the reaction product.

[0027] The polyamic acid solution composition was coated onto a glass substrate using a doctor blade. The coating was degassed and pre-dried at 25°C under reduced pressure for 30 minutes. Then, it was placed in a hot air dryer under normal pressure nitrogen atmosphere for heat treatment, including 60 minutes at 120°C, 60 minutes at 150°C, 30 minutes at 200°C, 30 minutes at 250°C, 20 minutes at 320°C, and 10 minutes at 400°C. The resulting polyimide film was smooth, flat, and free of pores.

[0028] Example 2

[0029] In a 500 mL glass reaction vessel equipped with a stirrer and under inert gas protection, 300 g of NMP and 100 g of p-xylene were added as solvents. 0.25 mol of PPD, 0.20 mol of BPDA, and 0.1 mol of methyl thiocate were then added. The mixture was stirred at room temperature until completely dissolved, and then stirred at 50 °C for 10 h to obtain a polyamic acid solution composition with a solution viscosity of 58.0 Pa·s. No flocculants or insoluble matter were formed in the reaction product.

[0030] The polyamic acid solution composition was coated onto a glass substrate using a doctor blade. The coating was degassed and pre-dried at 25°C under reduced pressure for 30 minutes. Then, it was placed in a hot air dryer under normal pressure nitrogen atmosphere for heat treatment, including 60 minutes at 120°C, 60 minutes at 150°C, 30 minutes at 200°C, 30 minutes at 250°C, 20 minutes at 320°C, and 10 minutes at 400°C. The resulting polyimide film was smooth, flat, and free of pores.

[0031] Example 3

[0032] In a 500 mL glass reaction vessel equipped with a stirrer and under inert gas protection, 300 g of NMP and 100 g of toluene were added as solvents. 0.25 mol of PPD, 0.20 mol of BPDA, and 0.05 mol of thioctic dianhydride were then added. The mixture was stirred at room temperature until completely dissolved, and then stirred at 50 °C for 10 h to obtain a polyamic acid solution composition with a solution viscosity of 58.0 Pa·s. No flocculants or insoluble matter were formed in the reaction product.

[0033] The polyamic acid solution composition was coated onto a glass substrate using a doctor blade and then crosslinked and cured by ultraviolet light. The resulting polyimide film was smooth, flat, and free of pores.

[0034] Example 4

[0035] In a 500 mL glass reaction vessel equipped with a stirrer and under inert gas protection, 300 g of DMF and 100 g of chloroform were added as solvents. Then, 0.25 mol of ODA, 0.20 mol of PMDA, and 0.1 mol of thioctic acid were added. The mixture was stirred at room temperature until completely dissolved, and then stirred at 50 °C for 10 h to obtain a polyamic acid solution composition with a solution viscosity of 58.0 Pa·s. No flocculants or insolubles were formed in the reaction product.

[0036] The polyamic acid solution composition was coated onto a glass substrate using a doctor blade. The coating was degassed and pre-dried at 25°C under reduced pressure for 30 minutes. Then, it was placed in a hot air dryer under normal pressure nitrogen atmosphere for heat treatment, including 60 minutes at 120°C, 60 minutes at 150°C, 30 minutes at 200°C, 30 minutes at 250°C, 20 minutes at 320°C, and 10 minutes at 400°C. The resulting polyimide film was smooth, flat, and free of pores.

[0037] Example 5

[0038] In a 500 mL glass reaction vessel equipped with a stirrer and under inert gas protection, 300 g of DMAc and 100 g of chloroform were added as solvents. Then, 0.25 mol of ODA, 0.20 mol of PMDA, and 0.05 mol of thioctic dianhydride were added. The mixture was stirred at room temperature until completely dissolved, and then stirred at 50 °C for 10 h to obtain a polyamic acid solution composition with a solution viscosity of 58.0 Pa·s. No flocculants or insolubles were formed in the reaction product.

[0039] The polyamic acid solution composition was coated onto a glass substrate using a doctor blade. The coating was degassed and pre-dried at 25°C under reduced pressure for 30 minutes. Then, it was placed in a hot air dryer under normal pressure nitrogen atmosphere for heat treatment, including 60 minutes at 120°C, 60 minutes at 150°C, 30 minutes at 200°C, 30 minutes at 250°C, 20 minutes at 320°C, and 10 minutes at 400°C. The resulting polyimide film was smooth, flat, and free of pores.

[0040] Comparative Example 1

[0041] In a 500 mL glass reaction vessel equipped with a stirrer and under inert gas protection, 300 g of NMP and 100 g of toluene were added as solvents. 0.25 mol of PPD and 0.25 mol of BPDA were then added. The mixture was stirred at room temperature until completely dissolved. The reaction was carried out at 50 °C for 10 h to obtain a polyamic acid solution composition with a solution viscosity of 58.0 Pa·s. No flocculants or insolubles were formed in the reaction product.

[0042] The polyamic acid solution composition was coated onto a glass substrate using a doctor blade. The coating was degassed and pre-dried at 25°C under reduced pressure for 30 minutes. Then, it was placed in a hot air dryer under normal pressure nitrogen atmosphere for heat treatment, including 60 minutes at 120°C, 60 minutes at 150°C, 30 minutes at 200°C, 30 minutes at 250°C, 20 minutes at 320°C, and 10 minutes at 400°C. The resulting polyimide film was smooth, flat, and free of pores.

[0043] Comparative Example 2

[0044] In a 500 mL glass reaction vessel equipped with a stirrer and under inert gas protection, 300 g of NMP and 100 g of toluene were added as solvents. 0.25 mol of PPD and 0.25 mol of thioctic dianhydride were then added. The mixture was stirred at room temperature until completely dissolved, and then stirred at 50 °C for 10 h to obtain a polyamic acid solution composition with a solution viscosity of 58.0 Pa·s. No flocculants or insolubles were formed in the reaction product.

[0045] The polyamic acid solution composition was coated onto a glass substrate using a doctor blade. The coating was degassed and pre-dried at 25°C under reduced pressure for 30 minutes. Then, it was placed in a hot air dryer under normal pressure nitrogen atmosphere for heat treatment, including 60 minutes at 120°C, 60 minutes at 150°C, 30 minutes at 200°C, 30 minutes at 250°C, 20 minutes at 320°C, and 10 minutes at 400°C. The resulting polyimide film was smooth, flat, and free of pores.

[0046] Comparative Example 3

[0047] In a 500 mL glass reaction vessel equipped with a stirrer and under inert gas protection, 300 g of DMF and 100 g of chloroform were added as solvents. 0.25 mol of ODA and 0.3 mol of PMDA were then added. The mixture was stirred at room temperature until completely dissolved. The reaction was carried out at 50 °C for 10 h to obtain a polyamic acid solution composition with a solution viscosity of 58.0 Pa·s. No flocculants or insolubles were formed in the reaction product.

[0048] The polyamic acid solution composition was coated onto a glass substrate using a doctor blade. The coating was degassed and pre-dried at 25°C under reduced pressure for 30 minutes. Then, it was placed in a hot air dryer under normal pressure nitrogen atmosphere for heat treatment, including 60 minutes at 120°C, 60 minutes at 150°C, 30 minutes at 200°C, 30 minutes at 250°C, 20 minutes at 320°C, and 10 minutes at 400°C. The resulting polyimide film was smooth, flat, and free of pores.

[0049] Comparative Example 4

[0050] In a 500 mL glass reaction vessel equipped with a stirrer and under inert gas protection, 300 g of DMF and 100 g of chloroform were added as solvents. 0.25 mol of ODA and 0.3 mol of thioctic acid were then added. The mixture was stirred at room temperature until completely dissolved, and then stirred at 50 °C for 10 h to obtain a polyamic acid solution composition with a solution viscosity of 58.0 Pa·s. No flocculants or insolubles were formed in the reaction product.

[0051] The polyamic acid solution composition was coated onto a glass substrate using a doctor blade. The coating was degassed and pre-dried at 25°C under reduced pressure for 30 minutes. Then, it was placed in a hot air dryer under normal pressure nitrogen atmosphere for heat treatment, including 60 minutes at 120°C, 60 minutes at 150°C, 30 minutes at 200°C, 30 minutes at 250°C, 20 minutes at 320°C, and 10 minutes at 400°C. The resulting polyimide film was smooth, flat, and free of pores.

[0052] The properties of the prepared polyimide film were determined, including thermal decomposition temperature (°C), tensile strength (MPa), and elongation at break (%). The results are shown in Tables 1 and 2.

[0053] Table 1

[0054]

[0055] Note: * indicates that compared with Example 1 group, P<0.05.

[0056] Table 2

[0057]

[0058] Note: * indicates that compared with Example 4, P<0.05.

[0059] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A reversibly crosslinked polyimide, characterized by, The molecular formula is shown as formula I: In the formula, n = 1-40, m = 1-40; Ar is a dianhydride monomer; Ar' is a diamine monomer.

2. The reversibly crosslinked polyimide according to claim 1, wherein The dianhydride monomer is one or more of pyromellitic dianhydride, 4,4'-biphenyl ether dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'- (hexafluoroisopropyl) bisphthalic anhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic anhydride, cyclobutane dianhydride, 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride.

3. The reversibly crosslinked polyimide of claim 1, wherein The diamine monomer is an aromatic diamine, which is one or more of 4,4'-oxydianiline, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, benzidine, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(4-aminophenyl)hexafluoropropane.

4. A method for producing a reversibly crosslinked polyimide, characterized by, The following steps are performed: (1) under the protection of an inert gas, a solvent, a diamine monomer, a dianhydride monomer, lipoic acid and its derivatives are added to a reaction container with a stirrer, and stirred and dissolved at 20-30°C, and then heated to 40-60°C and stirred for 8-12h to obtain a polyamic acid solution; (2) the polyamic acid solution is coated on a glass substrate using a doctor blade, the coating film is degassed and pre-dried at 20-30°C under reduced pressure for 20-40min, and then heated in a hot air dryer under normal pressure nitrogen environment.

5. The method for producing the reversibly crosslinked polyimide according to claim 4, characterized by, The lipoic acid and its derivatives are one or more of lipoic acid dianhydride, lipoic acid, lipoamide, lipoic acid methyl ester.

6. The method for producing the reversibly crosslinked polyimide according to claim 4, wherein The solvent is one or more of N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, dimethylacetamide, dimethyl sulfoxide, toluene, xylene, chloroform, dichloromethane.

7. The method for producing the reversibly crosslinked polyimide according to claim 4, wherein The molar ratio of the total amount of the diamine monomer to the total amount of the dianhydride monomer is (0.8-1.2):

1.

8. The method for producing the reversibly crosslinked polyimide according to claim 4, wherein The heating treatment is: heating at 110-130°C for 40-80min, heating at 140-160°C for 40-80min, heating at 180-220°C for 20-40min, heating at 230-270°C for 20-40min, heating at 300-340°C for 10-30min, heating at 380-420 for 8-12min.

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