Polyimide, transparent polyimide material and method for producing the same

Abstract

The application discloses a kind of polyimide, transparent polyimide material and its preparation method, wherein polyimide is prepared by dianhydride and diamine polymerization, dianhydride is fluorine-containing dianhydride or alicyclic dianhydride, and the total mole of hydroxyl diamine in polyimide is more than 10% of diamine involved in polymerization, and hydroxyl diamine has the general formula shown in the following structural formula:Polyimide material prepared by the application increases the glass transition temperature of transparent polyimide material, while can reduce the thermal expansion coefficient of material, improve the transparency of material, so that it can better meet the application of downstream industry.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and particularly relates to a polyimide, a transparent polyimide material and its preparation method. Background Technology

[0002] Polyimide materials possess excellent characteristics such as high temperature resistance, good mechanical properties, and stable performance, and are gradually gaining attention in various fields. As display panels become more flexible and thinner, using transparent organic materials to replace traditional rigid glass is a major method for achieving device flexibility. The inorganic materials that replace organic glass need to possess characteristics such as high temperature resistance, bending resistance, and good dimensional stability; currently, only transparent polyimide meets these requirements. Similarly, in the photovoltaic power generation field, using transparent polyimide films as cover materials enables flexible solar panels. In the field of electronic circuits, certain specific devices (such as light sensors) require transparent encapsulation materials, and the good insulation and dimensional stability of transparent polyimide make it the best candidate material.

[0003] The core technology for developing transparent polyimide materials lies in the selection of synthetic monomers. Choosing the right monomers can produce polyimides with excellent performance.

[0004] Chinese patent document CN107722268A discloses a method for manufacturing a polyimide precursor, polyimide, and a transparent polyimide film. The polyimide precursor disclosed in this patent has structural units derived from 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and structural units derived from 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride. The film prepared by imidization has a transmittance of less than 5% at 308 nm and more than 70% at 400 nm, and a coefficient of thermal expansion of less than 45 ppm / K. Chinese patent document CN105694035B discloses a highly transparent polyimide film material containing a tetramethyldiphenyl sulfone diether structure and its preparation method. This type of polyimide film material exhibits excellent solubility and film-forming properties, high optical transparency, and good thermal stability. The transparent polyimide materials in the above patents generally suffer from low temperature resistance and dimensional stability. Summary of the Invention

[0005] To overcome the problems in the prior art, the present invention provides a polyimide, a transparent polyimide material and a method for preparing the same, which increases the glass transition temperature of the transparent polyimide material, reduces the coefficient of thermal expansion, and improves the transparency of the material, enabling it to better meet the needs of downstream industries.

[0006] To solve the above-mentioned technical problems, the present invention proposes the following technical solution:

[0007] The first aspect of this invention provides a polyimide with a linear structure, prepared by polymerization of a dianhydride and a diamine, wherein the dianhydride is a fluorinated dianhydride or an alicyclic dianhydride, and the polyimide contains a hydroxyl-containing diamine accounting for more than 10% of the total molar amount of the diamines participating in the polymerization, and the hydroxyl-containing diamine has the general formula shown in the following structural formula (X):

[0008]

[0009] In this invention, the structure of the hydroxyl-containing diamine is such that hydroxyl groups are located at positions 2 and 2' of the benzene ring, and other functional groups (R2 and R3) are located at positions 5 and 5'. The purpose is twofold: firstly, hydroxyl groups have less steric hindrance and weaker electron-withdrawing effect, and being adjacent to the amino group, they do not significantly reduce the reactivity of the amino group. If the reactivity is too low, it will result in low degree of polymerization and low molecular weight of the polymer, ultimately leading to poor overall performance after curing into a film; secondly, placing other functional groups at positions 5 and 5' will not affect the reactivity of the amino group, while reducing the intramolecular electron complexation effect (CTC effect) and improving the final transparency of the material.

[0010] Meanwhile, in the hydroxyl diamine structure of this invention, the amino group and R1 are in the para position, resulting in a polymer with higher linearity and more compact molecular chain packing, which is beneficial to improving the mechanical properties (strength, elongation, modulus) of the final polyimide material.

[0011] The polyimide prepared using the above-mentioned diamine and dianhydride has the general formula shown in the following structural formula (Y):

[0012]

[0013] In this invention, the hydrogen bonding of hydroxyl groups in polyimide, the cleavage of conjugated electrons by the R1 group in the main chain and the R2 and R3 groups in the side chains work synergistically to find a balance point for comprehensive performance under the combined action of multiple groups, thereby increasing the glass transition temperature of transparent polyimide materials and reducing the coefficient of thermal expansion of the materials, thus improving the transparency of the materials.

[0014] As an optional implementation, in the polyimide provided by the present invention, R1 is selected from one of the following structural formulas (1)-(14):

[0015] In this invention, R1 is a structure on the main chain, responsible for the rotation and flexibility of the main chain, which ultimately affects the mechanical and thermal properties of the material. The following groups have a certain degree of flexibility and moderate rigidity, which ensures good material formability on the one hand, and does not significantly reduce the heat resistance of the material on the other hand.

[0016]

[0017] As an optional implementation, in the polyimide provided by the present invention, R2 and R3 are selected from the same or different groups that have an electron-withdrawing effect.

[0018] As an optional implementation, in the polyimide provided by the present invention, R2 and R3 are independently selected from one of the following structural formulas (16)-(66):

[0019] In this invention, the R2 and R3 groups can disrupt the molecular chain and the CTC effect between molecules to varying degrees, thereby improving the transparency of the material.

[0020]

[0021] As an optional implementation, in the polyimide provided by the present invention, the fluorinated dianhydride is selected from one or more of 6FDA, 3FDA, 8FDA, and 3FCDA.

[0022] The chemical structural formulas of 6FDA, 3FDA, 8FDA, and 3FCDA in this invention are shown below:

[0023]

[0024] As an optional embodiment, in the polyimide provided by the present invention, the alicyclic dianhydride is selected from one or more of 1,2,4,5-cyclohexanetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, octahydrobiphenylene-4a,8b:4b,8a-tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, and Meso-butane-1,2,3,4-tetracarboxylic anhydride.

[0025] The chemical structural formula of the above-mentioned substance in this invention is shown below:

[0026]

[0027] As an optional implementation, in the polyimide provided by the present invention, the molar ratio of the dianhydride to the diamine is 0.9 to 1.1.

[0028] In this invention, by controlling the molar ratio of dianhydride to diamine within the range of 0.9 to 1.1, a polymer with a high degree of polymerization can be obtained. Beyond this range, the molecular weight of the polymer is too low and has no practical value.

[0029] As an optional implementation, in the polyimide provided by the present invention, after the polymerization of dianhydride and diamine is completed, an end-capping agent is added for end-capping.

[0030] When the molar ratio of dianhydride to diamine is 0.9 to 1, including the case where the molar ratio of dianhydride to diamine is 1, the end-capping agent is selected from one or more of phthalic anhydride, 2,3-dichloromaleic anhydride, tetrafluorophthalic anhydride, biphenyl anhydride, succinic anhydride, glutaric anhydride, adipic anhydride, chlorobridged anhydride, 3-fluorophthalic anhydride, 3-chlorophthalic anhydride, nadic anhydride, tetrabromophthalic anhydride, and citralic anhydride;

[0031] When the molar ratio of dianhydride to diamine is 1 to 1.1 (excluding the case where the molar ratio of dianhydride to diamine is 1), the end-capping agent is selected from one or more of aminofluorene, pyrazinamide, aniline, chamomile-2-amine, benzylamine, amantadine, and sulfapyridine.

[0032] As an optional implementation, in the polyimide provided by the present invention, the solvent is selected from one or more of N,N'-dimethylformamide, N,N'-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone, and dimethyl sulfoxide.

[0033] As an optional embodiment, in the polyimide provided by the present invention, the dianhydride is 6 FDA, the hydroxyl-containing diamine accounts for 10% of the total molar amount of the diamines participating in the polymerization, the molar ratio of the dianhydride to the diamine is 0.9, and the structural formula of the diamine is shown in formulas A and B below:

[0034]

[0035] In this invention, the polyimide prepared by combining the above-mentioned dianhydride and diamine exhibits the best overall performance.

[0036] Based on the same technical concept, the present invention also provides a transparent polyimide material, wherein the transparent polyimide material is formed by imidizing the above-mentioned polyimide.

[0037] Based on the same technical concept, the present invention also provides a method for preparing the above-mentioned transparent polyimide material, comprising the following steps:

[0038] The above-mentioned polyimide solution is coated on the surface of the support substrate, and then the polyimide coating is heated to imidize it, forming an imide layer on the surface of the support substrate. The polyimide layer is then peeled off from the surface of the support substrate to obtain a transparent polyimide material.

[0039] As an optional implementation, in the preparation method provided by the present invention, the supporting substrate is glass, and the polyimide layer is peeled off from the glass supporting substrate by laser irradiation.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] (1) The present invention uses a diamine containing hydroxyl groups to prepare a polyimide with hydroxyl groups in its molecular chain, which can form intermolecular hydrogen bonds, increasing the heat resistance and dimensional stability of the transparent polyimide, so as to better meet the application requirements of flexible display, photovoltaic power generation and electronic circuit fields.

[0042] (2) The hydroxyl-containing diamine used in this invention has hydroxyl groups located at the 2' and 2' positions of the benzene ring, and R2 and R3 groups located at the 5' and 5' positions of the benzene ring. Compared with the hydroxyl-containing diamines in the prior art that do not contain R2 and R3 groups, it can reduce the intramolecular electron complexation effect (CTC effect) and improve the transparency of the material. Detailed Implementation

[0043] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below in conjunction with the specification and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0044] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0045] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0046] Example 1

[0047] The reaction is carried out using 6FDA (4,4'-(hexafluoroisopropene)phthalic anhydride) and a diamine having the following structure:

[0048]

[0049] A polyamic acid slurry solution was prepared by using 4,4'-(hexafluoroisopropene) phthalic anhydride and diamine in a molar ratio of 90 / 100, phthalic anhydride as the end-capping agent, and N,N-dimethylformamide as the solvent. The specific process was as follows: the diamine was first dissolved in the solvent, then the dianhydride was added in three equal portions. After the reaction was complete, the end-capping agent was added, and the mixture was stirred until homogeneous, yielding the polyamic acid slurry solution. The solution was then coated onto a glass substrate and placed in an oven with a programmed temperature increase: 100℃ for 30 min, 150℃ for 20 min, 200℃ for 10 min, 250℃ for 10 min, and 320℃ for 5 min, resulting in imidization and the acquisition of a transparent polyimide material.

[0050] Example 2

[0051] The reaction is carried out using 6FDA and diamines A and B, which have the following structures:

[0052]

[0053] The molar ratio of diamine A to diamine B is 10 / 90, and the molar ratio of 4,4'-(hexafluoroisopropene)phthalic anhydride to (diamine A + diamine B) is 90 / 100. Phthalic anhydride is used as the end-capping agent, and N,N-dimethylformamide is used as the solvent to prepare a polyamic acid slurry solution. The solution is coated onto a glass substrate and placed in an oven with programmed temperature rise to imidize and obtain a transparent polyimide material. The specific preparation process and the temperature rise program in the oven are the same as in Example 1.

[0054] Example 3

[0055] The reaction is carried out using 3FDA and diamines A and B, which have the following structures:

[0056]

[0057] The molar ratio of diamine A to diamine B is 50 / 50, and the molar ratio of 3FDA to (diamine A + diamine B) is 95 / 100. Phthalic anhydride is used as the end-capping agent, and N-methylpyrrolidone is used as the solvent to prepare a polyamic acid slurry solution. The solution is coated onto a glass substrate and placed in an oven with programmed temperature rise to imidize and obtain a transparent polyimide material. The specific preparation process and the temperature rise program in the oven are the same as in Example 1.

[0058] Example 4

[0059] The reaction is carried out using 8FDA and diamines A and B, which have the following structures:

[0060]

[0061] The molar ratio of diamine A to diamine B is 90 / 100, and the molar ratio of 8FDA to (diamine A + diamine B) is 105 / 100. Aminofluorene is used as the end-capping agent, and γ-butyrolactone is used as the solvent to prepare a polyamic acid slurry solution. The solution is coated onto a glass substrate and placed in an oven with programmed temperature rise to imidize and obtain a transparent polyimide material. The specific preparation process and oven temperature rise program are the same as in Example 1.

[0062] Example 5

[0063] The reaction is carried out using cyclobutanetetracarboxylic dianhydride and diamines A and B having the following structures:

[0064]

[0065] The molar ratio of diamine A to diamine B is 90 / 100, the molar ratio of cyclobutanetetracarboxylic dianhydride to (diamine A + diamine B) is 105 / 100, pyrazinamide is used as the end-capping agent, and γ-butyrolactone is used as the solvent to prepare a polyamic acid slurry solution. The solution is coated onto a glass substrate and placed in an oven with programmed temperature rise to imidize and obtain a transparent polyimide material. The specific preparation process and oven temperature rise program are the same as in Example 1.

[0066] Example 6

[0067] 3FCDA is selected to react with diamine A and diamine B having the following structures:

[0068]

[0069] The molar ratio of diamine A to diamine B is 90 / 100, and the molar ratio of 3FCDA to (diamine A + diamine B) is 105 / 100. Aniline is used as the end-capping agent, and γ-butyrolactone is used as the solvent to prepare a polyamic acid slurry solution. The solution is coated onto a glass substrate and placed in an oven with a programmed temperature rise to imidize and obtain a transparent polyimide material. The specific preparation process and the oven temperature rise program are the same as in Example 1.

[0070] Comparative Example 1

[0071] The reaction is carried out using 6FDA and diamines A and B, which have the following structures:

[0072]

[0073] The molar ratio of diamine A to diamine B is 10 / 90, and the molar ratio of 6FDA to (diamine A + diamine B) is 90 / 100. Phthalic anhydride is used as the end-capping agent, and N,N-dimethylformamide is used as the solvent to prepare a polyamic acid slurry solution. The solution is coated onto a glass substrate and placed in an oven with programmed temperature rise to imidize and obtain a transparent polyimide material. The specific preparation process and the temperature rise program in the oven are the same as in Example 1.

[0074] Comparative Example 2

[0075] The reaction is carried out using 6FDA and diamines A and B, which have the following structures:

[0076]

[0077] The molar ratio of diamine A to diamine B is 10 / 90, and the molar ratio of 6FDA to (diamine A + diamine B) is 90 / 100. Phthalic anhydride is used as the end-capping agent, and N,N-dimethylformamide is used as the solvent to prepare a polyamic acid slurry solution. The solution is coated onto a glass substrate and placed in an oven with programmed temperature rise to imidize and obtain a transparent polyimide material. The specific preparation process and the temperature rise program in the oven are the same as in Example 1.

[0078] Comparative Example 3

[0079] The reaction is carried out using 6FDA and diamines A and B, which have the following structures:

[0080]

[0081] The molar ratio of diamine A to diamine B is 10 / 90, and the molar ratio of 6FDA to (diamine A + diamine B) is 90 / 100. Phthalic anhydride is used as the end-capping agent, and N,N-dimethylformamide is used as the solvent to prepare a polyamic acid slurry solution. The solution is coated onto a glass substrate and placed in an oven with programmed temperature rise to imidize and obtain a transparent polyimide material. The specific preparation process and the temperature rise program in the oven are the same as in Example 1.

[0082] Performance testing

[0083] The comprehensive properties of the transparent polyimide materials prepared in Examples 1-6 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1 below.

[0084] Table 1: Performance test results of polyimide films in the examples and comparative examples

[0085] Example 1 81％ 89％ 22 347 Example 2 80.5％ 88.7％ 19 364 Example 3 82％ 90％ 27 339 Example 4 81.5％ 90％ 25 351 Example 5 83％ 91％ 29 336 Example 6 82％ 92％ 26 331 Comparative Example 1 81％ 89％ 55 308 Comparative Example 2 81％ 89％ 22 352 Comparative Example 3 78％ 85％ 18 366

[0086] Table 1 shows that introducing hydroxyl-containing diamines enhances the thermal properties of polyimide materials, primarily by reducing the coefficient of linear expansion and increasing the glass transition temperature. Polyimide materials with hydroxyl-containing diamines at the 2,2' position of the benzene ring exhibit the best performance. Furthermore, the presence of a certain proportion of groups in the hydroxyl-containing diamine that can reduce the intramolecular CTC effect improves the optical properties of the material. By adjusting the proportion of hydroxyl-containing diamines and the structure of R1, R2, and R3, high-performance polyimide products can be obtained.

[0087] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A polyimide, characterized in that, The polyimide has a linear structure and is prepared by polymerization of dianhydride and diamine. The dianhydride is a fluorinated dianhydride or an alicyclic dianhydride. The polyimide contains a hydroxyl-containing diamine accounting for more than 10% of the total molar amount of the diamines participating in the polymerization. The hydroxyl-containing diamine has the general formula shown in the following structural formula (X): （X） Wherein, R1 is selected from one of the following structural formulas (1)-(14): R2 and R3 are CF3 respectively.

2. The polyimide according to claim 1, characterized in that, The fluorinated dianhydride is selected from one or more of 6FDA, 3FDA, 8FDA, and 3FCDA.

3. The polyimide according to claim 1, characterized in that, The alicyclic dianhydride is selected from one or more of the following: 1,2,4,5-cyclohexanetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, octahydrobiphenylene-4a,8b:4b,8a-tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, and Meso-butane-1,2,3,4-tetracarboxylic anhydride.

4. The polyimide according to claim 1, characterized in that, The molar ratio of the dianhydride to the diamine is 0.9 to 1.

1.

5. The polyimide according to claim 1, characterized in that, After the polymerization of dianhydride and diamine is completed, an end-capping agent is added for end-capping. When the molar ratio of dianhydride to diamine is 0.9~1, the end-capping agent is selected from one or more of phthalic anhydride, 2,3-dichloromaleic anhydride, tetrafluorophthalic anhydride, biphenyl anhydride, succinic anhydride, glutaric anhydride, adipic anhydride, chlorobridged anhydride, 3-fluorophthalic anhydride, 3-chlorophthalic anhydride, nadic anhydride, tetrabromophthalic anhydride, and citralic anhydride. When the molar ratio of dianhydride to diamine is 1 to 1.1, the end-capping agent is selected from one or more of aminofluorene, pyrazinamide, aniline, chamomile-2-amine, benzylamine, adamantane, and sulfapyridine.

6. The polyimide according to claim 1, characterized in that, The dianhydride is 6 FDA, the hydroxyl-containing diamine accounts for 10% of the total molar amount of the diamines participating in the polymerization, the molar ratio of the dianhydride to the diamine is 0.9, and the diamines participating in the polymerization include a combination of the following structural formulas (A) and (B): 。 7. A transparent polyimide film material, characterized in that, The transparent polyimide material is formed by imidizing the polyimide according to any one of claims 1-6.

8. The method for preparing the polyimide film material according to claim 7, characterized in that, Includes the following steps: A solution containing any of the polyimides described in claims 1-6 is coated onto the surface of a support substrate. The polyimide coating is then heated to imidize it, forming an imide layer on the surface of the support substrate. The polyimide layer is then peeled off from the surface of the support substrate to obtain a transparent polyimide film material.

9. The method for preparing the polyimide film material according to claim 8, characterized in that, The supporting substrate is glass, and the polyimide layer is peeled off from the glass supporting substrate by laser irradiation.

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