Polyimide as well as synthesis method and application thereof

Abstract

The invention belongs to the field of polymer materials, and particularly relates to polyimide and a synthesis method and application thereof. A first diamine monomer containing an X1 element (any one of sulfur, selenium and tellurium elements), a second diamine monomer containing an X2 element (any one of carbon, oxygen and sulfur elements) and a dianhydride monomer containing a fluorine group or trifluoromethyl group are subjected to condensation polymerization, so that a macromolecular chain of polyimide is designed, the flexibility of the macromolecular chain is improved, and the flexibility of the polyimide is improved; meanwhile, the charge transfer effect generated in molecular chains and between the molecular chains is reduced, the polyimide material is endowed with the characteristic of solution processing, the optical quality of a film prepared based on the polyimide material is improved, and the polyimide film with high refractive index and high light transmittance can be prepared and is suitable for being used as a high-performance optical material.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and more specifically, to a polyimide and a synthesis method and application thereof. Background Art

[0002] Polyimide refers to a class of polymer materials containing imide rings on the main chain of the polymer. As a special engineering material, it has excellent environmental weather resistance, good dielectric properties and mechanical properties. It is called "golden film" and has been widely used in aviation, aerospace, microelectronics, nano, liquid crystal, separation membranes, lasers and other fields. It is considered to be one of the most promising engineering plastics in the 21st century.

[0003] Polyimide has a rigid structure and has strong interactions between molecules, which makes this type of material difficult to dissolve in solvents and has a high viscosity flow temperature. It cannot be processed by solution and needs to be melt-processed at a higher temperature, and has poor processability. On the other hand, the refractive index of polyimide is generally below 1.6, which is lower than other aromatic polymers, which limits the application of polyimide in optical materials. In addition, due to the charge transfer effect generated within and between polyimide molecular chains, the currently commercially available polyimide films are generally brown or brownish yellow, with low light transmittance, and are difficult to use as high-performance optical materials. In summary, existing polyimide materials have problems such as difficulty in solution processing and low refractive index. At the same time, due to the limitation of the color of the polyimide film itself, it cannot be applied to the field of high-performance optical materials.

[0004] Therefore, providing a solution-processable polyimide material and, on this basis, providing a polyimide film with high refractive index and high transmittance is of great significance for broadening the application scope of polyimide. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of this application is to provide a polyimide and its synthesis method and application, aiming to solve the problems that the existing polyimide materials have poor solution processing performance, low refractive index, low light transmittance of polyimide films, and cannot be used as high-performance optical materials.

[0006] To achieve the above objectives, in a first aspect, the present application provides a polyimide, the structural formula of which is as follows: , Wherein, X1 is any one of sulfur, selenium and tellurium; X2 is any one of carbon, oxygen and sulfur; R is selected from any one of the following structures: , , ; n is an integer of 1 to 20, and the sum of n and m is an integer of 2 to 30.

[0007] Preferably, in the structural formula of the polyimide, n is an integer of 1-20, and the sum of n and m is an integer of 10-30.

[0008] More preferably, in the structural formula of the polyimide, n is an integer of 4-15, and the sum of n and m is an integer of 15-30.

[0009] In a second aspect, the present application provides a method for synthesizing the above-mentioned polyimide, comprising the following steps: S1. Under the condition of anhydrous and oxygen-free and inert gas protection, diamine monomer and dianhydride monomer are mixed and dissolved in an organic solvent for polycondensation reaction to obtain a polyamic acid solution; The diamine monomers include a first diamine monomer containing the X1 element and a second diamine monomer containing the X2 element; The above-mentioned dianhydride monomer is a dianhydride monomer containing a fluorine group or a trifluoromethyl group; S2, mixing the polyamic acid solution and a chemical imidization agent to carry out a chemical imidization reaction to obtain a reaction solution, and then precipitating, washing, and drying to obtain a completely imidized polyimide; or, The polyamic acid solution is coated on a substrate and subjected to thermal imidization treatment to obtain a completely imidized polyimide.

[0010] Preferably, the first diamine monomer is one or more of 4,4'-diaminodiphenyl telluride, 4,4'-diaminodiphenyl selenide, and 4,4'-diaminodiphenyl sulfide.

[0011] Preferably, the second diamine monomer is one or more of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenyl sulfide.

[0012] Preferably, the dianhydride monomer is one or more of hexafluorodianhydride, 1,4-difluoro-2,3,5,6-pyromellitic dianhydride, and 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthenetetracarboxylic dianhydride.

[0013] Preferably, the organic solvent is super dry dimethyl sulfoxide, super dry tetrahydrofuran, super dry N,N -Dimethylformamide, super dry N,N -Dimethylacetamide, super dry N - one or more of methyl pyrrolidone.

[0014] Preferably, in step S1, the molar ratio of the first diamine monomer to the diamine monomer is (0.1-0.8):1.

[0015] Preferably, in step S1, the molar ratio of the diamine monomer to the dianhydride monomer is 1:(0.8-1.2).

[0016] Preferably, in step S1, the temperature of the polycondensation reaction is 15°C to 45°C, and the time of the polycondensation reaction is 8 h to 15 h.

[0017] Preferably, in step S2, the chemical imidization reagent is a mixture of acetic anhydride and pyridine.

[0018] Preferably, the temperature of the chemical imidization reaction is 25° C. to 45° C., and the time of the chemical imidization reaction is 10 to 16 h.

[0019] Preferably, in step S2, the drying temperature is 30°C to 80°C, and the drying time is 5 to 15 hours.

[0020] Preferably, in step S2, the temperature of the thermal imidization is 80°C to 200°C, and the time of the thermal imidization is 2 to 10 hours.

[0021] In a third aspect, the present application provides the use of the above-mentioned polyimide in the preparation of optical products with high refractive index and high light transmittance.

[0022] In a fourth aspect, the present application provides a polyimide film, which is prepared by dissolving the above-mentioned polyimide and a leveling agent in an additive to obtain a polyimide solution, and then coating the above-mentioned polyimide solution on a substrate and drying it.

[0023] Preferably, the leveling agent is one or more of the leveling agent 310 , the leveling agent 313 , the leveling agent 333 , the leveling agent 354 , and the leveling agent 381 .

[0024] Preferably, the added amount of the leveling agent is 0.01 wt% to 2 wt% of the polyimide.

[0025] Preferably, the above-mentioned additive is dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N - one or more of methyl pyrrolidone.

[0026] Preferably, the thickness of the polyimide film is 1-10 μm.

[0027] In general, the above technical solutions conceived by this application have the following technical advantages compared with the prior art: (1) The present application designs the polymer chain of polyimide by subjecting a first diamine monomer containing an X1 element (any one of sulfur, selenium, and tellurium), a second diamine monomer containing an X2 element (any one of carbon, oxygen, and sulfur), and a dianhydride monomer to a condensation reaction, thereby increasing the flexibility of the polymer chain and reducing the charge transfer effect within and between the molecular chains, thereby giving the polyimide material the property of being solution processable, and improving the optical quality of a film prepared based on the polyimide material, thereby being able to prepare a polyimide film with a high refractive index and high transmittance, which is suitable for use as a high-performance optical material.

[0028] (2) The polyimide provided in this application is soluble in tetrahydrofuran, dimethyl sulfoxide, N , N -dimethylformamide, N,N -Dimethylacetamide, N -Common organic solvents such as methyl pyrrolidone have excellent solution processing characteristics.

[0029] (3) The polyimide film provided in this application has excellent optical quality, with a refractive index greater than 1.62 at a wavelength of 589 nm and a transmittance T of less than 1.00 at a wavelength of 500 nm. 500 The transmittance T at a wavelength of 400 nm is 100%. 400 Greater than 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is the reaction equation for synthesizing polyimide in the embodiment of the present application; Figure 2 is the NMR spectrum of the polyimide provided in Example 1 of the present application; Figure 3 is a refractive index curve diagram of the polyimide film provided in the embodiment of the present application; Figure 4 is a light transmittance curve of the polyimide film provided in Example 1 of the present application; Figure 5 is a light transmittance curve of the polyimide film provided in Example 2 of the present application; Figure 6 This is the NMR spectrum of the polyimide provided in Example 4 of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] In the description of this application, it should be understood that the term "and / or" is a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In this application, the symbol " / " indicates that the associated objects are in an or relationship, for example, A / B means A or B.

[0033] In the specification and claims of the present application, the terms "first" and "second" etc. are used to distinguish different objects rather than to describe the specific order of the objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0034] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a concrete manner.

[0035] In the description of the present application, unless otherwise specified, “plurality” means two or more.

[0036] The term "ultra-dry solvent" refers to a solvent with extremely low water content, which can provide a purer reaction environment, reduce the interference of water on chemical reactions, and improve reaction efficiency and product quality.

[0037] The present application provides a polyimide, the structural formula of which is as follows: , Wherein, X1 is any one of sulfur, selenium and tellurium; X2 is any one of carbon, oxygen and sulfur; R is selected from any one of the following structures: , , ; n is an integer of 1 to 20, and the sum of n and m is an integer of 2 to 30.

[0038] In some embodiments, in the structural formula of the polyimide, n is an integer of 1-20, and the sum of n and m is an integer of 10-30.

[0039] In a preferred embodiment, in the structural formula of the polyimide, n is an integer of 4-15, and the sum of n and m is an integer of 15-30.

[0040] On the other hand, the present application also provides a method for synthesizing the polyimide. The reaction equation for synthesizing the polyimide is as follows: Figure 1 As shown, the synthesis method comprises the following steps: S1. Under the condition of anhydrous and oxygen-free and inert gas protection, diamine monomer and dianhydride monomer are mixed and dissolved in an organic solvent for polycondensation reaction to obtain a polyamic acid solution; The diamine monomers include a first diamine monomer containing the X1 element and a second diamine monomer containing the X2 element; The above-mentioned dianhydride monomer is a dianhydride monomer containing a fluorine group or a trifluoromethyl group; S2, mixing the polyamic acid solution and the chemical imidization agent to carry out a chemical imidization reaction to obtain a reaction solution, and then precipitating, washing and drying to obtain a completely imidized polyimide.

[0041] In some embodiments, in step S1, the first diamine monomer is one or more of 4,4'-diaminodiphenyl telluride, 4,4'-diaminodiphenyl selenide, and 4,4'-diaminodiphenyl sulfide.

[0042] In some embodiments, in step S1, the second diamine monomer is one or more of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenyl sulfide.

[0043] In some embodiments, in step S1, the dianhydride monomer is one or more of hexafluorodianhydride, 1,4-difluoro-2,3,5,6-benzenetetracarboxylic dianhydride, and 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthenetetracarboxylic dianhydride (CAS No. 139162-14-4).

[0044] In some embodiments, when the dianhydride monomer is hexafluorodianhydride, the structural formula of the polyimide is as follows: , Wherein, X1 is any one of sulfur, selenium and tellurium; X2 is any one of carbon, oxygen and sulfur; n is an integer of 1 to 20, and the sum of n and m is an integer of 2 to 30.

[0045] In some embodiments, when the dianhydride monomer is hexafluorodianhydride, in the structural formula of the polyimide, n is an integer of 1-20, and the sum of n and m is an integer of 10-30.

[0046] In a preferred embodiment, when the dianhydride monomer is hexafluorodianhydride, in the structural formula of the polyimide, n is an integer of 4-15, and the sum of n and m is an integer of 15-30.

[0047] In some embodiments, in step S1, the organic solvent is super dry dimethyl sulfoxide, super dry tetrahydrofuran, super dry N,N -Dimethylformamide, super dry N,N -Dimethylacetamide, super dry N - one or more of methyl pyrrolidone. The present application does not limit the source of the above-mentioned ultra-dry solvent, which can be purchased from commercial products.

[0048] In some embodiments, the molar ratio of the first diamine monomer to the diamine monomer is (0.1-0.8):1.

[0049] In some embodiments, the molar ratio of the diamine monomer to the dianhydride monomer is 1:(0.8-1.2).

[0050] In some embodiments, in step S1, the temperature of the polycondensation reaction is 15°C to 45°C, and the time of the polycondensation reaction is 8 to 15 hours.

[0051] In a preferred embodiment, in step S1, the temperature of the polycondensation reaction is 30°C to 35°C, and the time of the polycondensation reaction is 10 to 12 hours.

[0052] In some embodiments, in step S2, during the chemical imidization treatment, the chemical imidization agent is a mixture of acetic anhydride and pyridine. It is understood that the present application does not limit the volume fraction of acetic anhydride in the above-mentioned mixture, and the ratio of the chemical imidization agent to the polyamic acid solution. As long as a fully imidized polyimide can be prepared, it is within the scope of protection of the present application. In some embodiments, the volume fraction of acetic anhydride in the above-mentioned mixture can be 30% to 80%.

[0053] In some embodiments, in step S2, the temperature of the chemical imidization reaction is 25°C to 45°C, and the time of the chemical imidization reaction is 10 to 16 hours, so that a fully imidized polyimide can be prepared.

[0054] In a preferred embodiment, in step S2, the temperature of the chemical imidization reaction is 33° C. to 37° C., and the time of the chemical imidization reaction is 12 to 14 h.

[0055] In some embodiments, in step S2, the specific process of the precipitation is: mixing the polyimide solution and a polar solvent to perform precipitation treatment.

[0056] In some embodiments, the polar solvent is one or more of anhydrous methanol, ethanol, and acetone.

[0057] In some embodiments, the drying temperature is 30° C. to 80° C., and the drying time is 5 to 15 hours.

[0058] In some embodiments, in step S2, during the thermal imidization treatment, the present application does not limit the coating method, which may be but is not limited to spin coating, brush coating, or scraper coating. In some embodiments, the substrate may be but is not limited to a glass plate.

[0059] In some embodiments, the thermal imidization temperature is 80° C. to 200° C., and the thermal imidization time is 2 to 10 h, so that a fully imidized polyimide can be prepared.

[0060] On the other hand, the present application also provides the use of the above polyimide in preparing optical products with high refractive index and high light transmittance.

[0061] The present application also provides a polyimide film, which is prepared by dissolving the above-mentioned polyimide and a leveling agent in an additive to obtain a polyimide solution, and then coating the above-mentioned polyimide solution on a substrate and drying it.

[0062] In some embodiments, the leveling agent is one or more of the leveling agent 310 , the leveling agent 313 , the leveling agent 333 , the leveling agent 354 , and the leveling agent 381 .

[0063] In some embodiments, the added amount of the leveling agent is 0.01 wt% to 2 wt% of the polyimide, which can solve the problem of film shrinkage after polyimide film formation.

[0064] In some embodiments, the additive is tetrahydrofuran, dichloromethane, dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N - one or more of methyl pyrrolidone.

[0065] In some embodiments, the drying temperature is 35-80° C., and the drying time is 10-120 min.

[0066] In some embodiments, the thickness of the polyimide film is 1-10 μm.

[0067] The present application designs the polymer main chain of the polyimide by conducting a condensation reaction between a first diamine monomer containing an X1 element (any one of sulfur, selenium, and tellurium), a second diamine monomer containing an X2 element (any one of carbon, oxygen, and sulfur), and a dianhydride monomer containing a fluorine group or a trifluoromethyl group, thereby increasing the flexibility of the polymer chain and reducing the charge transfer effect within and between the molecular chains, giving the polyimide material the property of being solution-processable, and improving the optical quality of a film prepared based on the polyimide material, so as to prepare a polyimide film with a high refractive index and high transmittance, which is suitable for use as a high-performance optical material.

[0068] It should be understood that materials of the same or similar type, model, quality, nature or function as the reagents and instruments used in the following examples can be used to implement the present application. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

[0069] The following are examples and comparative examples: Example 1 The structural formula of the polyimide provided in this embodiment is as follows: Then, the polyimide was subjected to nuclear magnetic resonance structural characterization test using deuterated chloroform as solvent. The nuclear magnetic resonance hydrogen spectrum is shown in Figure 2 shown.

[0070] The synthesis method of the polyimide comprises the following steps: S1. Preparation of polyamic acid: Under argon atmosphere, 26.32 g of 4,4'-diaminodiphenyl selenide (first diamine monomer), 19.82 g of 4,4'-diaminodiphenylmethane (second diamine monomer), and 89.73 g of hexafluorodianhydride (dianhydride monomer) were placed in a reaction vessel, and 600 mL of ultra-dry N,N -dimethylformamide (DMF), stir until completely dissolved, maintain the reaction temperature at 35 °C, stir and react for 10 h to obtain a polyamic acid solution.

[0071] S2. Preparation of polyimide: Add a mixed solution containing 100 mL of acetic anhydride and 34 mL of pyridine to the polyamic acid solution prepared in step (1), maintain the reaction temperature at 35°C, and stir the reaction for 14 hours to obtain a reaction solution. Then, drop the reaction solution into anhydrous methanol for precipitation, collect the precipitate by filtration, and place it in a vacuum oven at 45°C for 12 hours to obtain a polyimide, which is recorded as PI-1.

[0072] The method for preparing the polyimide film provided in this embodiment comprises the following steps: 0.1 g of polyimide (PI-1), 0.0008 mL of leveling agent 310, and 1 mL of tetrahydrofuran were mixed to obtain a polyimide solution. The polyimide solution was then dropped onto inorganic glass and coated with a doctor blade. The film was dried at 45 °C for 0.5 h to obtain a polyimide film with a thickness of 6 μm.

[0073] The properties of the above-mentioned polyimide and polyimide film were tested, and the test method is as follows: (1) Solution processing characteristics of polyimide: 100 mg of polyimide was placed in a sample bottle with a small magnet, and then 1 mL of dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N -methyl pyrrolidone and stirred at room temperature for 1 h to test the solubility of polyimide in common organic solvents and then determine the solution processing properties.

[0074] (2) Refractive index of polyimide and polyimide film: tested using an ellipsometer.

[0075] (3) Light transmittance of polyimide film: The light transmittance of polyimide film was characterized by ultraviolet-visible spectroscopy (UV-Vis) and tested using a UV-visible spectrophotometer.

[0076] It can be seen from Table 1 that the polyimide prepared in this embodiment is soluble in dichloromethane (DCM), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N,N -Dimethylformamide (DMF), N,N -Dimethylacetamide (DMAc), N -methyl pyrrolidone (NMP) and other organic solvents, indicating that the polyimide prepared in this embodiment has excellent solution processability. The refractive index of the polyimide film prepared in this embodiment at a wavelength of 589 nm is 1.6261 (e.g. Figure 3 The transmittance T at a wavelength of 500 nm is 500 The transmittance T at a wavelength of 400 nm is 100%. 400 is 80.03% (e.g. Figure 4 as shown).

[0077] Example 2 The structural formula of the polyimide provided in this embodiment is as follows: .

[0078] The synthesis method of the polyimide comprises the following steps: S1. Preparation of polyamic acid: Under argon atmosphere, 11.92 g of 4,4'-diaminodiphenyl sulfide (first diamine monomer), 33.40 g of 4,4'-diaminodiphenyl ether (second diamine monomer), and 89.73 g of hexafluorodianhydride (dianhydride monomer) were placed in a reaction vessel, and 600 mL of ultra-dry N , N -dimethylformamide (DMF), stir until completely dissolved, maintain the reaction temperature at 35 °C, stir and react for 10 h to obtain a polyamic acid solution.

[0079] S2. Preparation of polyimide: Add a mixed solution containing 100 mL of acetic anhydride and 34 mL of pyridine to the polyamic acid solution prepared in step (1), maintain the reaction temperature at 35°C, and stir the reaction for 14 hours to obtain a reaction solution. Then, drop the reaction solution into anhydrous methanol for precipitation, collect the precipitate by filtration, and place it in a vacuum oven at 30°C for 15 hours to obtain a polyimide, which is recorded as PI-2.

[0080] The method for preparing the polyimide film provided in this embodiment comprises the following steps: 0.1 g polyimide (PI-2), 0.0006 mL leveling agent 310, 1 mL N,N -dimethylformamide to obtain a polyimide solution, which is then dropped onto inorganic glass and coated with a doctor blade to form a film, which is then dried at 60 °C for 1 h to obtain a polyimide film with a thickness of 6 μm.

[0081] According to the method provided in Example 1, the properties of the polyimide and polyimide film prepared in this example were tested.

[0082] It can be seen from Table 1 that the polyimide prepared in this example is soluble in dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N -methylpyrrolidone; when dichloromethane and tetrahydrofuran are heated to 50°C, the above polyimide can be completely dissolved, indicating that the polyimide prepared in this embodiment has good solution processability. The refractive index of the polyimide film prepared in this embodiment at a wavelength of 589 nm is 1.6261 (such as Figure 3 The transmittance T at a wavelength of 500 nm 500 The transmittance T at a wavelength of 400 nm is 100%. 400 is 83.41% (e.g. Figure 5 as shown).

[0083] Example 3 The structural formula of the polyimide provided in this embodiment is as follows: .

[0084] The synthesis method of the polyimide comprises the following steps: S1. Preparation of polyamic acid: Under argon atmosphere, 18.48 g of 4,4'-diaminodiphenyl selenide (first diamine monomer), 21.02 g of 4,4'-diaminodiphenyl ether (second diamine monomer), and 89.73 g of hexafluorodianhydride (dianhydride monomer) were placed in a reaction container, and 600 mL of ultra-dry N,N-dimethylformamide (DMF), stir until completely dissolved, maintain the reaction temperature at 35 °C, stir and react for 10 h to obtain a polyamic acid solution.

[0085] S2. Preparation of polyimide: Add a mixed solution containing 100 mL of acetic anhydride and 34 mL of pyridine to the polyamic acid solution prepared in step (1), maintain the reaction temperature at 35°C, and stir the reaction for 14 hours to obtain a reaction solution. Then, drop the reaction solution into anhydrous methanol for precipitation, collect the precipitate by filtration, and place it in a vacuum oven at 80°C for drying for 5 hours to obtain a polyimide, which is recorded as PI-3.

[0086] The method for preparing the polyimide film provided in this embodiment comprises the following steps: 0.1 g of polyimide (PI-3), 0.001 mL of leveling agent 310, and 1 mL of tetrahydrofuran were mixed to obtain a polyimide solution. The polyimide solution was then dropped onto inorganic glass and coated with a doctor blade. The film was dried at 45 °C for 1 h to obtain a polyimide film with a thickness of 6 μm.

[0087] According to the method provided in Example 1, the properties of the polyimide and polyimide film prepared in this example were tested.

[0088] It can be seen from Table 1 that the polyimide prepared in this embodiment is soluble in dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N -methyl pyrrolidone and other organic solvents, indicating that the polyimide prepared in this embodiment has excellent solution processability. The refractive index of the polyimide film prepared in this embodiment at a wavelength of 589nm is 1.6235 (such as Figure 3 The transmittance T at a wavelength of 500 nm 500 The transmittance T at a wavelength of 400 nm is 100%. 400 It is 85.17%.

[0089] Example 4 The structural formula of the polyimide provided in this embodiment is as follows: Then, the polyimide was subjected to nuclear magnetic resonance structural characterization test using deuterated chloroform as solvent. The nuclear magnetic resonance hydrogen spectrum is shown in Figure 6 shown.

[0090] In the above-mentioned method for synthesizing polyimide, the first diamine monomer and the second diamine monomer are both 4,4'-diaminodiphenyl sulfide, the amount of the diamine monomer is 43.26 g, and the remaining steps are the same as those in Example 1 to obtain a polyimide, which is recorded as PI-4.

[0091] The preparation process of the polyimide film provided in this embodiment includes the following steps: 0.1 g polyimide (PI-4), 0.001 mL leveling agent 310, 1 mL N,N -dimethylformamide to obtain a polyimide solution, which is then dropped onto inorganic glass and coated with a doctor blade to form a film, which is then dried at 60 °C for 0.5 h to obtain a polyimide film with a thickness of 6 μm.

[0092] According to the method provided in Example 1, the properties of the polyimide and polyimide film prepared in this example were tested.

[0093] It can be seen from Table 1 that the polyimide prepared in this example is soluble in dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N -methylpyrrolidone; when tetrahydrofuran is heated to 50 °C, the above polyimide can be completely dissolved, but is insoluble in dichloromethane; this shows that the polyimide prepared in this embodiment has good solution processability. The refractive index of the polyimide film prepared in this embodiment at a wavelength of 589 nm is 1.6201; the transmittance T at a wavelength of 500 nm is 500 The transmittance T at a wavelength of 400 nm is 100%. 400 It is 88.76%.

[0094] Example 5 The structural formula of the polyimide provided in this embodiment is as follows: .

[0095] The above-mentioned method for synthesizing polyimide comprises the following steps: S1. Preparation of polyamic acid: Under argon atmosphere, 24.95 g of 4,4'-diaminodiphenyl telluride (first diamine monomer), 31.72 g of 4,4'-diaminodiphenylmethane (second diamine monomer), and 89.73 g of hexafluorodianhydride (dianhydride monomer) were placed in a reaction vessel, and 600 mL of ultra-dry N,N -dimethylformamide (DMF), stir until completely dissolved, maintain the reaction temperature at 35 °C, stir and react for 10 h to obtain a polyamic acid solution.

[0096] S2. Preparation of polyimide: Add a mixed solution containing 100 mL of acetic anhydride and 34 mL of pyridine to the polyamic acid solution prepared in step (1), maintain the reaction temperature at 35°C, and stir the reaction for 14 hours to obtain a reaction solution. Then, drop the reaction solution into anhydrous methanol for precipitation, collect the precipitate by filtration, and place it in a vacuum oven at 60°C for 5 hours to dry it to obtain a polyimide, which is recorded as PI-5.

[0097] The method for preparing the polyimide film provided in this embodiment comprises the following steps: 0.1 g of polyimide (PI-5), 0.001 mL of leveling agent 310, and 1 mL of tetrahydrofuran were mixed to obtain a polyimide solution. The polyimide solution was then dropped onto inorganic glass and coated with a doctor blade. The film was dried at 45 °C for 0.5 h to obtain a polyimide film with a thickness of 6 μm.

[0098] The method for preparing the polyimide film provided in this embodiment is the same as that in embodiment 1.

[0099] According to the method provided in Example 1, the properties of the polyimide and polyimide film prepared in this example were tested.

[0100] The test results show that the polyimide prepared in this embodiment is soluble in dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N -methyl pyrrolidone and other organic solvents, indicating that the polyimide prepared in this embodiment has excellent solution processability. The refractive index of the polyimide film prepared in this embodiment at a wavelength of 589 nm is 1.638; the transmittance T at a wavelength of 500 nm is 500 The transmittance T at a wavelength of 400 nm is 100%. 400 It is 85.5%.

[0101] Comparative Example 1 The structural formula of the polyimide provided in this comparative example is as follows: .

[0102] The synthesis method of the polyimide comprises the following steps: S1. Preparation of polyamic acid: Under argon atmosphere, 26.41 g of 4,4'-diaminodiphenyl selenide and 44.40 g of hexafluorodianhydride (dianhydride monomer) were placed in a reaction vessel, and 300 mL of ultra-dry N,N -dimethylformamide (DMF), stir until completely dissolved, maintain the reaction temperature at 35 °C, stir and react for 10 h to obtain a polyamic acid solution.

[0103] S2. Preparation of polyimide: Add a mixed solution containing 100 mL of acetic anhydride and 34 mL of pyridine to the polyamic acid solution prepared in step (1), maintain the reaction temperature at 35°C, and stir the reaction for 14 hours to obtain a reaction solution. Then, drop the reaction solution into anhydrous methanol for precipitation, collect the precipitate by filtration, and place it in a vacuum oven at 60°C for 5 hours to dry it to obtain a polyimide, which is recorded as PI-6.

[0104] The method for preparing the polyimide film provided in this comparative example comprises the following steps: 0.1 g of polyimide (PI-6), 0.001 mL of leveling agent 310, and 1 mL of tetrahydrofuran were mixed at 50 °C to obtain a polyimide solution. The polyimide solution was then dropped onto inorganic glass and coated with a doctor blade. The film was dried at 45 °C for 0.5 h to obtain a polyimide film with a thickness of 6 μm.

[0105] The preparation method of the polyimide film provided in this comparative example is the same as that in Example 1.

[0106] According to the method provided in Example 1, the properties of the polyimide and polyimide film prepared in this comparative example were tested.

[0107] The test results show that the polyimide prepared in this comparative example can be dissolved in dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N -Methylpyrrolidone. The refractive index of the polyimide film prepared in this comparative example at a wavelength of 589 nm is 1.641; the transmittance T at a wavelength of 400 nm is 400 The transmittance is only 21.2%, which does not meet the requirements and cannot be used as a high-performance optical material.

[0108] Comparative Example 2 The structural formula of the polyimide provided in this comparative example is as follows: .

[0109] The synthesis method of the polyimide comprises the following steps: S1. Preparation of polyamic acid: Under argon atmosphere, 19.81 g of 4,4'-diaminodiphenylmethane and 21.82 g of pyromellitic dianhydride (dianhydride monomer) were placed in a reaction vessel, and 300 mL of ultra-dry N,N -dimethylformamide (DMF), stir until completely dissolved, maintain the reaction temperature at 35 °C, stir and react for 10 h to obtain a polyamic acid solution.

[0110] S2. Preparation of polyimide: Apply a polyamic acid solution on a glass substrate, heat it in a muffle furnace at 180° C. for 5 h, and obtain polyimide by thermal imidization, which is recorded as PI-7.

[0111] According to the method provided in Example 1, the properties of the polyimide prepared in this comparative example were tested.

[0112] The test results show that the polyimide prepared in this comparative example is insoluble in dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N -Organic solvents such as methyl pyrrolidone do not have solution processing properties, that is, the polyimide prepared in this comparative example cannot be prepared into a film by solution processing.

[0113] Table 1 Properties of polyimide and polyimide films prepared in Examples 1 to 5

[0114] The test results show that the polyimide prepared in this application has the characteristics of solution processing. The polyimide film prepared on this basis has excellent optical quality, high refractive index and high transmittance. The refractive index at a wavelength of 589 nm is greater than 1.62, and the transmittance T at a wavelength of 500 nm is greater than 1.62. 500 The transmittance T at a wavelength of 400 nm is 100%. 400 Both are greater than 80%, suitable for use as high-performance optical materials.

[0115] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A polyimide, characterized in that: Its structural formula is as follows: ， Wherein, X1 is any one of sulfur, selenium and tellurium; X2 is any one of carbon, oxygen and sulfur; R is selected from any one of the following structures: 、 、 ； n is an integer of 1 to 20, and the sum of n and m is an integer of 2 to 30.

2. A method for synthesizing a polyimide as claimed in claim 1, characterized in that: The steps include: S1. Under the condition of anhydrous and oxygen-free and inert gas protection, diamine monomer and dianhydride monomer are mixed and dissolved in an organic solvent for polycondensation reaction to obtain a polyamic acid solution; The diamine monomer includes a first diamine monomer containing the X1 element and a second diamine monomer containing the X2 element; The dianhydride monomer is a dianhydride monomer containing a fluorine group or a trifluoromethyl group; S2, mixing the polyamic acid solution and a chemical imidization agent to carry out a chemical imidization reaction to obtain a reaction solution, and then precipitating, washing, and drying to obtain a completely imidized polyimide; or, The polyamic acid solution is coated on a substrate and subjected to thermal imidization treatment to obtain a completely imidized polyimide.

3. The synthesis method according to claim 2, characterized in that The first diamine monomer is one or more of 4,4'-diaminodiphenyl telluride, 4,4'-diaminodiphenyl selenide, and 4,4'-diaminodiphenyl sulfide; and / or, The second diamine monomer is one or more of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenyl sulfide; and / or, The dianhydride monomer is one or more of hexafluorodianhydride, 1,4-difluoro-2,3,5,6-pyromellitic dianhydride, and 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthene tetracarboxylic dianhydride; and / or, The organic solvent is super dry dimethyl sulfoxide, super dry tetrahydrofuran, super dry N,N -Dimethylformamide, super dry N,N -Dimethylacetamide, super dry N - one or more of methyl pyrrolidone.

4. The synthesis method according to claim 3, characterized in that The molar ratio of the first diamine monomer to the diamine monomer is (0.1-0.8):1; The molar ratio of the diamine monomer to the dianhydride monomer is 1:(0.8-1.2).

5. The synthesis method according to claim 2, characterized in that In step S1, the temperature of the polycondensation reaction is 15°C to 45°C, and the time of the polycondensation reaction is 8 h to 15 h.

6. The synthesis method according to claim 2, characterized in that In step S2, the chemical imidization reagent is a mixture of acetic anhydride and pyridine; The temperature of the chemical imidization reaction is 25°C to 45°C, and the time of the chemical imidization reaction is 10 to 16 hours; The drying temperature is 30°C to 80°C, and the drying time is 5 to 15 hours.

7. The synthesis method according to claim 2, characterized in that In step S2, the temperature of the thermal imidization is 80°C to 200°C, and the time of the thermal imidization is 2 to 10 hours.

8. Use of the polyimide according to claim 1 in preparing optical products with high refractive index and high light transmittance.

9. A polyimide film, characterized in that: The method is prepared by dissolving the polyimide as claimed in claim 1 and a leveling agent in an additive to obtain a polyimide solution, and then coating the polyimide solution on a substrate and drying the substrate.

10. The polyimide film according to claim 9, characterized in that: The leveling agent is one or more of the leveling agent 310, the leveling agent 313, the leveling agent 333, the leveling agent 354, and the leveling agent 381; and / or, The amount of the leveling agent added is 0.01 wt% to 2 wt% of the polyimide; and / or, The additives are dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N,N -dimethylformamide, N,N -Dimethylacetamide, N - one or more of methyl pyrrolidone; and / or, The thickness of the polyimide film is 1-10 μm.

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