Semi-aromatic polyimide resin, polyimide composition, and method of making and use

Abstract

The application provides a semi-alicyclic polyimide resin, a polyimide composition, a preparation method and an application, and the preparation method of the semi-alicyclic polyimide resin comprises the following steps: under the protection of inert gas, reacting an alicyclic dianhydride monomer and an aromatic diamine monomer in a polar aprotic solvent, then adding an end-capping agent to obtain a polyamic acid resin solution; adding a catalyst and a dehydrating agent into the solution, and after dehydration, performing precipitation and drying treatment to obtain the semi-alicyclic polyimide resin. The application further discloses a semi-alicyclic low-thermal expansion coefficient transparent polyimide composition comprising the semi-alicyclic polyimide resin and the polar aprotic solvent. The semi-alicyclic low-thermal expansion coefficient transparent polyimide composition effectively balances the low thermal expansion coefficient and high heat resistance while maintaining high transmittance, and has good application prospect and large-scale promotion potential in the field of flexible display cover plates.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, in particular to a semi-alicyclic polyimide resin, a polyimide composition, and a preparation method and application thereof. BACKGROUND

[0002] Flexible display technology is the core direction of future display industry, and the new forms such as foldable, curlable and wearable it brings are deeply changing the way of human-computer interaction. In this technology, the flexible display cover material plays a crucial role. At present, the mainstream cover materials mainly include transparent polyimide (CPI) and ultra-thin flexible glass (UTG). CPI has excellent flexibility, can withstand very small bending radius, and has very high bending resistance, which is very suitable for various forms such as inner folding and outer folding. UTG performs excellently in optical performance, with very high light transmittance, but its impact resistance and drop resistance are poor, and it has the risk of breaking. Therefore, CPI has become the preferred cover material for most folding screen mobile phones in the early stage and at present.

[0003] CPI mainly reduces or inhibits the charge transfer (CTC) effect existing in the intramolecular and intermolecular of polyimide (PI) through chemical modification method, thereby effectively improving the light transmittance of CPI and making the material present colorless and transparent state. At present, the main chemical modification methods include: 1) introducing fluorine atoms or trifluoromethyl groups with strong electronegativity into the PI molecular chain, such as the patent CN119081178B uses fluorine-containing dianhydride and fluorine-containing diamine to improve the light transmittance of polyimide film to 89.4% at 550 nm. The patent CN103788650B copolymerizes 4,4'-bis(4-amino-2-trifluoromethyl phenoxy) diphenyl ether with alicyclic dianhydride, and the obtained film has a transmittance of ≥90% at 450 nm and a glass transition temperature (Tg) of ≥290℃. Both of them are technical routes for improving the optical performance of polyimide by introducing fluorine-containing monomers, which cut off the conjugation of electron cloud by using the electronegativity of fluorine atom, thereby inhibiting the formation of CTC and improving the light transmittance of the film, but the application of fluorine-containing CPI is facing restrictions due to the ban of PFAS fluorinated compounds by the European Union. 2) Using monomers with bulky side groups, such as CN110467728A, which introduces fluorene groups into polyimide to effectively destroy the conjugated structure in the molecular structure of polyimide film, achieving high transmittance (T 550 ≥90%) of the film. However, introducing too many side groups into polyimide may reduce the rigidity of the molecular chain, resulting in a decrease in modulus and Tg. 3) Using alicyclic structure monomers to reduce the content of aromatic structure in the molecular structure of polyimide, destroy the conjugated structure on the PI chain segment, reduce the interaction between the molecular chains, and increase the free volume between the chains, thereby reducing the CTC effect. For example, CN118852622A discloses a polyimide prepared from an alicyclic dianhydride and a diamine containing imidazole, and the transmittance of the film can be maintained at ≥85%.

[0004] Alicyclic CPIs can be classified into full-alicyclic CPIs, alicyclic diamine-type CPIs, and alicyclic dianhydride-type CPIs according to the position of the alicyclic structure in the polymer main chain. Full-alicyclic CPIs are polymerized using alicyclic dianhydride and alicyclic diamine, and can theoretically achieve the best optical performance due to the complete elimination of all aromatic rings and conjugated systems in the main chain, but the thermal performance is poor. Alicyclic diamine-type CPIs are polymerized using alicyclic diamine monomers and aromatic dianhydride monomers. However, the alicyclic diamine monomers have strong basicity, which leads to the formation of ammonium salt of polyamide acid at the beginning of polymerization, making it difficult to prepare high molecular weight PI. Alicyclic dianhydride-type CPIs are polymerized using alicyclic dianhydride monomers and aromatic diamine monomers. The aromatic diamine monomers have a relatively moderate basicity, and the alicyclic dianhydride can provide relatively high reactivity, especially at high temperatures. Therefore, semi-alicyclic CPIs based on alicyclic dianhydride and aromatic diamine monomers often have more excellent comprehensive performance.

[0005] However, due to the excessive twisting of the flexible aliphatic molecular chain, the molecular chain is loosely packed and contains a large number of methylene groups, resulting in a high coefficient of thermal expansion (CTE) and poor heat resistance of the alicyclic dianhydride-type CPI, i.e., the introduction of aliphatic dianhydride units often fails to ensure the dimensional stability of the film, and cannot simultaneously meet the requirements of high optical transparency and low expansion coefficient of display devices.

[0006] In recent years, people have focused on molecular structure design and complex synergies to reduce the CTE value of the film, and have achieved certain results. For example, CN117050305A discloses a class of polyimides prepared from alicyclic dianhydride and diamine containing fluorene structure, and the CTE of the film is reduced to 21.05 ppm / K, and the Tg is adjusted to 457.1℃. However, due to the introduction of the more rigid fluorene structure in the molecular main chain, the intramolecular or intermolecular charge transfer is enhanced, which is very unfavorable for maintaining the transmittance of the film. Moreover, the polyimide molecular structure contains fluorine or chlorine elements, which poses a risk of releasing harmful halogen-containing gases when heated or burned. CN109824894A provides a polyimide film with a molecular main chain composed of alternating alicyclic anhydride and aromatic anhydride, which can effectively control the CTE of the film below 30 ppm / K and maintain the Tg above 280℃, but the preparation process of the polyimide is complex and generates a large amount of by-products. CN111040164A indicates that the polyimide prepared from alicyclic dianhydride can further reduce the thermal expansion coefficient of the film when combined with colloidal silica, but the transmittance of the film after combination is lost, only about 82%, which is difficult to meet the application requirements of high-tech fields. SUMMARY

[0007] The present application aims at the problem of poor dimensional stability and heat resistance of traditional alicyclic dianhydride type CPI, and provides a semi-alicyclic polyimide resin, which introduces a mono-amino heterocyclic compound as an end-capping agent in the molecular chain of semi-alicyclic CPI to construct molecular chain interaction, thereby significantly improving the dimensional stability (expressed as low thermal expansion coefficient) and heat resistance (expressed as high glass transition temperature) of the polyimide film on the basis of meeting the optical performance.

[0008] It should be noted that in the present application, unless otherwise specified, the specific meaning of "including" involved in the composition limitation and description includes both the open "including", "containing" and the like and their similar meanings, and the closed "consisting of", "consisting" and the like and their similar meanings.

[0009] To achieve the above object, the technical scheme adopted by the present application is as follows: a semi-alicyclic polyimide resin, whose structural formula is shown in formula I:

[0010] ;

[0011] Formula I;

[0012] In formula I, n represents the number of repeating units, and n is a positive integer greater than 0; A is the residue of an alicyclic dianhydride monomer, i.e. the residue formed by removing two anhydride groups from the alicyclic dianhydride monomer, which can be independently selected from one of the following structural formulas:

[0013] 、 、 、 、 、 ;

[0014] In formula I, A' is the residue of an aromatic diamine monomer, i.e. the residue formed by removing two amino groups from the aromatic diamine monomer, which can be independently selected from one of the following structural formulas:

[0015] 、 、 、

[0016] 、 、 、 、 、 、 ;

[0017] In formula I, R is the residue of an end-capping agent, i.e. the residue formed by removing one amino group from the molecule of the end-capping agent, and R is independently selected from one of the following structural formulas:

[0018] 、 、 、 、 、 .

[0019] The chemical bond marked as in the structural formula of A, A' and R in formula I is the connection site with other parts in the structural formula of the semi-alicyclic polyimide resin, but the specific connection mode and connection order are not limited.

[0020] Further, the n is a positive integer of 1-300.

[0021] Further, the n is preferably a positive integer of 80-300.

[0022] Further, the alicyclic dianhydride monomer is selected from one or more of 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, hydrogenated biphenyl tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride.

[0023] Further, the aromatic diamine monomer is selected from one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-oxydianiline, 3,4'-oxydianiline, 1,3-bis(aminomethyl)benzene, 4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl methane, 1,4-bis(4'-aminophenoxy)benzene, 4,4'-diaminodiphenyl sulfone and 4,4'-diaminobenzophenone.

[0024] Further, the end-capping agent is one or more of a monoamino heterocyclic compound containing imino and thione structures, a monoamino heterocyclic compound containing a sulfenyl group and a nitrogen atom.

[0025] Further, the end-capping agent is selected from one or more of 6-thioguanine, 2-amino-3-sulfenylpyridine, 2-amino-4-sulfenylpyridine, 5-amino-2-sulfenylthiazole, 2-amino-5-sulfenyl-1,3,4-thiadiazole and 6-amino-2-sulfenylbenzothiazole.

[0026] Further, the molecular weight of the semi-alicyclic polyimide resin is 30,000-100,000 g / mol.

[0027] Another object of the present application also discloses a preparation method of the semi-alicyclic polyimide resin, comprising the following steps:

[0028] Step 1: under the protection of inert atmosphere, alicyclic dianhydride monomer and aromatic diamine monomer are added into polar aprotic solvent, after reacting for a certain time, end-capping agent is added to obtain polyamic acid resin solution;

[0029] Step 2: catalyst and dehydrating agent are added into the polyamic acid resin solution to carry out dehydration reaction to obtain polyimide resin solution, then through precipitation and drying treatment, semi-alicyclic polyimide resin is obtained.

[0030] Further, the solid content of the polyamic acid resin solution in step 1 is 10-30wt%.

[0031] Further, in step 1, the alicyclic dianhydride monomer and aromatic diamine are added into polar aprotic solvent, the reaction temperature is 20-50℃, and the reaction time is 8-24h.

[0032] Further, in step 1, the end-capping agent is added to continue the reaction for 2-8h.

[0033] Further, in step 2, the dehydration reaction time is 6-12h.

[0034] Further, the inert atmosphere in step 1 is nitrogen and / or argon.

[0035] Further, in step 1, any alicyclic dianhydride monomer can be used as raw material for preparing semi-alicyclic polyimide resin, and the more suitable alicyclic dianhydride monomer is selected from one or more of 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, hydrogenated biphenyl tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride.

[0036] Further, the alicyclic dianhydride monomer in step 1 is preferably one or more of 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride.

[0037] Further, in step 1, any aromatic diamine monomer can be used as raw material for preparing semi-alicyclic polyimide resin, and the more suitable aromatic diamine monomer is selected from one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-oxydianiline, 3,4'-oxydianiline, 1,3-bis(aminomethyl)benzene, 4,4'-diaminobiphenyl, 4,4'-diaminodiphenylmethane, 1,4-bis(4'-aminophenoxy)benzene, 4,4'-diaminodiphenyl sulfone and 4,4'-diaminobenzophenone.

[0038] Further, the aromatic diamine monomer of step 1 is preferably one or more of p- phenylenediamine, 4,4'-oxydianiline, 4,4'-diaminobiphenyl, and 4,4'- diaminodiphenylmethane.

[0039] Further, the end-capping agent of step 1 is one or more of a monoamino heterocyclic compound containing an imino group and a thione structure, and a monoamino heterocyclic compound containing a sulfur group and a nitrogen atom.

[0040] Further, the end-capping agent of step 1 is selected from one or more of 6- thioguanine, 2-amino-3-thiopyridine, 2-amino-4-thiopyridine, 5-amino-2- thiopyridine, 2-amino-5-thio-l,3,4-thiadiazole, and 6-amino-2-thiobenzothiazole.

[0041] Further, the end-capping agent of step 1 is preferably one or more of 6- thioguanine, 2-amino-4-thiopyridine, 2-amino-5-thio-l,3,4-thiadiazole, and 6-amino- 2-thiobenzothiazole.

[0042] Further, the molar ratio of the aromatic diamine monomer to the alicyclic dianhydride monomer of step 1 is 0.80 to 0.99: 1.

[0043] Further, the molar ratio of the aromatic diamine monomer to the alicyclic dianhydride monomer of step 1 is preferably 0.90 to 0.99: 1.

[0044] Further, the molar ratio of the end-capping agent to the alicyclic dianhydride monomer of step 1 is 0.02 to 0.40: 1.

[0045] Further, the molar ratio of the end-capping agent to the alicyclic dianhydride monomer of step 1 is preferably 0.02 to 0.20: 1.

[0046] Further, the polar aprotic solvent of step 1 is selected from an amide-based solvent and / or a sulfone-based solvent.

[0047] Further, the polar aprotic solvent of step 1 is preferably one or more of N- methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0048] Further, the catalyst of step 2 is one or more of quinoline, isoquinoline, triethylamine, and pyridine.

[0049] Further, the dehydrating agent of step 2 is one or more of acetic anhydride, propionic anhydride, and butyric anhydride.

[0050] Further, the molar ratio of the dehydrating agent to the alicyclic dianhydride monomer of step 2 is 0.8 to 1.5: 1.

[0051] Further, the molar ratio of the dehydrating agent to the alicyclic dianhydride monomer in step 2 is preferably 0.9-1.1:1.

[0052] Further, the molar ratio of the catalyst to the dehydrating agent in step 2 is 0.7-1.2:1.

[0053] Further, the molar ratio of the catalyst to the dehydrating agent in step 2 is preferably 0.8-1.1:1.

[0054] Further, the precipitation process in step 2 is: adding the same mass of polar aprotic solvent to the polyimide resin solution, stirring uniformly, then dropping the reaction solution into the precipitant for precipitation, and washing the obtained precipitate with deionized water to remove by-products, with the washing frequency being three times or more.

[0055] Further, the precipitant used in step 2 is water or a mixture of water and alcohol.

[0056] Further, the alcohol is one or more of methanol, ethanol, propanol, butanol or isopropanol.

[0057] Further, the drying process in step 2 is: heating the washed polyimide resin in a vacuum drying oven at 30-50℃ for 12-24h.

[0058] Further, the aprotic solvent in step 2 is selected from amide solvents and / or sulfone solvents.

[0059] Further, the polar aprotic solvent in step 2 is preferably one or more of N-methyl pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

[0060] Another object of the present application also discloses an application of the semi-alicyclic polyimide resin in the field of flexible display cover plates.

[0061] Another object of the present application also discloses a semi-alicyclic low-thermal expansion coefficient transparent polyimide composition, comprising a semi-alicyclic polyimide resin and a polar aprotic solvent in a mass ratio of 10-30:70-90.

[0062] Further, the polar aprotic solvent is selected from amide solvents and / or sulfone solvents.

[0063] Further, the polar aprotic solvent is preferably one or more of N-methyl pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

[0064] Another object of the present application also discloses a method for preparing the semi-alicyclic low-thermal expansion coefficient transparent polyimide composition, comprising the following steps: dissolving the semi-alicyclic polyimide resin in a polar aprotic solvent to obtain the semi-alicyclic low-thermal expansion coefficient transparent polyimide composition.

[0065] Another object of the present application also discloses an application of the semi-alicyclic low-thermal expansion coefficient transparent polyimide composition in the field of flexible display cover plate.

[0066] Another object of the present application also discloses a semi-alicyclic low-thermal expansion coefficient transparent polyimide film, which is prepared by performing thermal imidization treatment on the semi-alicyclic low-thermal expansion coefficient transparent polyimide composition under the protection of inert atmosphere.

[0067] Further, the process of thermal imidization is as follows: first, vacuum drying at 80-120℃ for 5-10 min, and then performing stepwise temperature rising in a drying box with nitrogen protection according to the following procedure: 120-150℃ for 0.5-1h, 200-250℃ for 0.5-1h, and 300-350℃ for 1-1.5h, wherein the rising rate of all the temperature rising processes is 4-6℃ / min.

[0068] The semi-alicyclic polyimide resin, polyimide composition, and the method for preparing and the application thereof of the present application have the following advantages compared with the prior art:

[0069] 1) The semi-alicyclic polyimide resin of the present application introduces a mono-amino heterocyclic compound containing imino and thione structure, or a mono-amino heterocyclic compound containing sulfide and nitrogen atom as a capping agent, which can form hydrogen bonds at both ends of the molecular chain, rather than in the main chain structure, thereby effectively reducing or avoiding the CTC effect of the film, and introducing aliphatic structure into the alicyclic dianhydride monomer can effectively reduce the charge transfer effect within and between polyimide molecules, thereby greatly improving the light transmittance of the polyimide film.

[0070] 2) The polarity of the capping agent and the formed hydrogen bonds make the combination between the molecular chains more compact, and the mono-amino heterocyclic compound makes the molecular chains have stronger rigidity, which together restricts the relative sliding and thermal motion of the molecular chains, thereby making the polyimide film have better dimensional stability and heat resistance, which is manifested as low CTE and high Tg.

[0071] In summary, the semi-alicyclic low-thermal expansion coefficient transparent polyimide of the present application effectively balances low thermal expansion coefficient and high heat resistance while maintaining high transmittance, and has good application prospect and large-scale promotion potential in the field of flexible display cover plate. BRIEF DESCRIPTION OF DRAWINGS

[0072] Figure 1Fourier transform infrared spectrum of the semi-alicyclic polyimide film prepared in Example 13. DETAILED DESCRIPTION

[0073] Hereinafter, the present application will be further described with reference to Examples. The description of the technical features described below is based on representative embodiments, specific examples of the present application, but the present application is not limited to these embodiments, specific examples. Note that:

[0074] Unless otherwise specified, the units used in the present specification are international standard units, and the numerical values, numerical value ranges appearing in the present application should be understood to include systematic errors that are inevitable in industrial production.

[0075] In the present specification, the numerical value range expressed using "numerical value A ~ numerical value B" means a range including the end point numerical values A, B.

[0076] In the present specification, the numerical value range expressed using "above" or "below" means a numerical value range including the present number.

[0077] In the present specification, the meaning expressed using "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0078] In the present specification, the use of "optional" or "optionally" means the use or non-use of certain substances, components, execution steps, applied conditions, and the like.

[0079] In the present specification, when "room temperature" or "normal temperature" is used, the temperature thereof can be 15 to 25°C.

[0080] In the present specification, when the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained by purchase on the market.

[0081] Examples 1-12

[0082] Examples 1-12 of the present application disclose various semi-alicyclic low thermal expansion coefficient transparent polyimide resins, and the preparation method thereof is as follows:

[0083] Step 1: under the protection of nitrogen atmosphere, alicyclic dianhydride monomers and aromatic diamine monomers are added to polar aprotic solvent 1, after reacting at 30°C for 12 h, a capping agent is added and the reaction is continued for 6 h to obtain a polyamic acid resin solution;

[0084] Step 2: After adjusting the reaction temperature to room temperature, a catalyst and a dehydrating agent are added to the polyamic acid resin solution, and a dehydration reaction is carried out for 6 hours. After precipitation and drying treatment, a semi-cycloaliphatic polyimide resin with a capped structure is obtained. The precipitation process is as follows: a polar aprotic solvent 2 is added to the polyimide resin solution, and after stirring uniformly, the reaction solution is added dropwise into water for precipitation. The obtained precipitate is washed with deionized water three times to remove by-products (such as unreacted catalyst, dehydrating agent, and polar aprotic solvents used in steps 1 and 2, etc.). The drying treatment process is as follows: the washed semi-cycloaliphatic polyimide resin is heated in a vacuum drying oven at 50°C for 24 hours.

[0085] The raw materials and proportions of the plurality of semi-cycloaliphatic polyimide resins are shown in Table 1:

[0086] Table 1 Raw materials and proportions of polyimide resins in Examples 1-12

[0087]

[0088] Comparative Examples 1-4

[0089] Comparative Examples 1-4 disclose a plurality of polyimide resins, which are prepared by the same method as Example 1, and the raw materials and proportions are shown in Table 2:

[0090] Table 2 Raw materials and proportions of polyimide resins in Comparative Examples 1-4

[0091]

[0092] Examples 13-24

[0093] Examples 13-24 disclose a plurality of semi-cycloaliphatic low-CTE transparent polyimide compositions, which are prepared as follows:

[0094] The semi-cycloaliphatic polyimide resin is dissolved in a polar aprotic solvent to obtain a semi-cycloaliphatic low-CTE transparent polyimide composition. The raw materials and proportions of the polyimide compositions in Examples 13-24 are shown in Table 3.

[0095] Table 3 Raw materials and proportions of polyimide compositions in Examples 13-24

[0096]

[0097] Comparative Examples 5-8

[0098] Comparative Examples 5-8 disclose a plurality of polyimide compositions, which are prepared by the same method as Example 13. The raw materials and proportions of the polyimide compositions in Comparative Examples 5-8 are shown in Table 4.

[0099] Table 4 Raw materials and proportions of polyimide compositions in Comparative Examples 5-8

[0100]

[0101] The semi-cycloaliphatic low-CTE transparent polyimide compositions of Examples 13-24 and the polyimide compositions of Comparative Examples 5-8 were tested for transmittance, CTE, and thermal stability, respectively, using the following test methods and results:

[0102] The semi-cycloaliphatic low-CTE transparent polyimide compositions of Examples 13-24 and the polyimide compositions of Comparative Examples 5-8 were each prepared into a polyimide film using the following method: The polyimide composition was coated onto a clean, smooth glass plate and a polyimide film was prepared using a thermal imidization method in a nitrogen atmosphere. The thermal imidization process was as follows: vacuum drying at 80°C for 10 min, then heating in a nitrogen-protected drying oven according to the following program: 120°C for 30 min, 220°C for 30 min, 350°C for 1 h, with a heating rate of 6°C / min for all heating processes.

[0103] Property 1: Transmittance

[0104] The transmittance of the polyimide film was measured using a UV spectrophotometer.

[0105] The film (with substrate) was cut into a 5 cm x 5 cm sample, and the sample was tested for transmittance at 380 nm to 780 nm under D65 light source, transmission mode, and the average transmittance was recorded for the wavelength range of 450 nm to 550 nm.

[0106] Property 2: Coefficient of Thermal Expansion (CTE)

[0107] The coefficient of thermal expansion of the polyimide was measured using a static thermal mechanical analyzer (TMA).

[0108] The film was cut into a 3 mm x 24 mm sample, and after clamping the sample, the initial length of the sample was measured in the instrument. Then, under a 100 ml / min nitrogen atmosphere, a 50 mN pulling force was applied, and the sample was heated at a rate of 5°C / min from room temperature to 500°C, and the dimensional change curve was recorded for the temperature range of 30°C to 500°C, and the coefficient of thermal expansion (CTE) of the film was calculated for the temperature range of 50°C to 450°C.

[0109] Property 3: Glass Transition Temperature (Tg)

[0110] The glass transition temperature of the polyimide film was measured using a TMA.

[0111] The film was made into 3mm x 24mm sample, after clamping with a clamp, the sample was put into the instrument to measure the initial length. Then, under the atmosphere of 100ml / min nitrogen, 50mN tension was applied, heated from room temperature to 500℃ at 5℃ / min, the size change curve in the range of 30℃-500℃ was recorded, the intersection temperature of the two curve segments with obvious change of thermal expansion coefficient was recorded as the glass transition temperature (Tg).

[0112] The test results are shown in Table 5:

[0113] Table 5 Test results

[0114]

[0115] Based on the above table, it can be seen that the polyimide films prepared in Examples 13-24 exhibit good dimensional stability and thermal stability, with CTE less than 34ppm / K, Tg above 381℃, and still maintain a high transmittance (≥85%).

[0116] Comparative Example 5, due to the lack of end-capping agent, the prepared polyimide film exhibits lower dimensional stability and heat resistance. Comparative Example 6 uses 2-aminoimidazole as an end-capping agent to enhance the dimensional stability and heat resistance of the polyimide through hydrogen bonding, but the end-capping agent mentioned in the present application has a stronger rigid cyclic structure, contains more strongly electronegative atoms or groups, and thus the dimensional stability and heat resistance of the film are greatly improved. Comparative Example 7 uses pyromellitic dianhydride as a dianhydride monomer, since the monomer does not contain a fatty structure, the polyimide formed with the aromatic diamine monomer has a strong CTC effect within and between molecules, the transmittance of the film is poor, and the more aromatic ring structures in the main chain result in a more rigid molecule, thereby the polyimide film exhibits a lower CTE and a higher Tg. In Comparative Example 8, the 4,6-diamino-2-sulfur pyrimidine structure contains multiple amino groups, without end-capping effect, the introduction of the structure into the molecular main chain, the imino group in the structure can form hydrogen bonds between the molecular chains, the intermolecular interaction force is enhanced, the dimensional stability and heat resistance of the polyimide are improved, but the structure enhances the CTC effect within and between molecules, resulting in a decrease in the transmittance of the film.

[0117] The polyimide film prepared from the polyimide composition of Example 13 was characterized by Fourier infrared spectroscopy, from which Figure 1 It can be seen that the vibration absorption peaks of C=O in the imide ring are at 1775cm -1 and 1698cm -1 ; the stretching vibration peaks of C-N in the imide ring are at 1352cm -1 ; the stretching vibration peaks of C-N in the imide ring are at 1163cm -1corresponding to the stretching vibration absorption peak of C=S in 6-thioguanine; and no 3300 cm -1 -3500 cm -1 range of doublet, it can be seen that there is no free -NH2 group, that is, the amino group in the end-capping agent has reacted with the dianhydride monomer in the molecular chain, achieving effective end-capping.

[0118] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A semi- alic polyimide resin, characterized by, The structural formula is shown as formula I: ； Formula I; In formula I, n represents the number of repeating units, n is a positive integer greater than 1 and less than or equal to 300, A is the residue of an alicyclic dianhydride monomer; A' is the residue of an aromatic diamine monomer, and R is the residue of a capping agent, which is one or more of a monoamino heterocyclic compound containing imino and thione structures, a monoamino heterocyclic compound containing a mercapto group and a nitrogen atom; R is independently selected from one of the following structural formulas: 、 、 、 、 、 。 2. The semi-aipic polyimide resin according to claim 1, wherein The alicyclic dianhydride monomer is selected from one or more of 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, hydrogenated biphenyl tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride; And / or, the aromatic diamine monomer is selected from one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-oxydianiline, 3,4'-oxydianiline, 1,3-bis(aminomethyl)benzene, 4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl methane, 1,4-bis(4'-aminophenoxy)benzene, 4,4'-diaminodiphenyl sulfone, and 4,4'-diaminobenzophenone.

3. A process for producing the semi- alic-type polyimide resin according to claim 1 or 2, characterized by, The method comprises the following steps: Step 1: under the protection of an inert atmosphere, an alicyclic dianhydride monomer and an aromatic diamine monomer are added to a polar aprotic solvent, a capping agent is added after reacting for a certain period of time, and a polyamic acid resin solution is obtained; Step 2: a catalyst and a dehydrating agent are added to the polyamic acid resin solution to perform a dehydration reaction, and a semi-alicyclic polyimide resin is obtained through precipitation and drying treatment.

4. The method for preparing the semi-cycloaliphatic polyimide resin according to claim 3, characterized in that, The molar ratio of the aromatic diamine monomer to the alicyclic dianhydride monomer in step 1 is 0.80-0.99:1; And / or, the molar ratio of the capping agent to the alicyclic dianhydride monomer is 0.02-0.40:

1.

5. The method of producing a semi- alic-type polyimide resin according to claim 3 or 4, characterized by, In step 2, the catalyst is one or more of quinoline, isoquinoline, triethylamine, and pyridine; And / or, the dehydrating agent is one or more of acetic anhydride, propionic anhydride, and butyric anhydride; And / or, the molar ratio of the dehydrating agent to the alicyclic dianhydride monomer is 0.8-1.5:1; And / or, the molar ratio of the catalyst to the dehydrating agent in step 2 is 0.7-1.2:

1.

6. Use of the semi-alicyclic polyimide resin of claim 1 or 2 in the field of flexible display covers.

7. A semi- alic, low thermal expansion coefficient, transparent polyimide composition, characterized by comprising: The method comprises the following steps:

8. Use of the semi-alicyclic low-thermal expansion coefficient transparent polyimide composition of claim 7 in the field of flexible display covers.

9. A semi- cycloaliphatic transparent polyimide film, characterized by, Under the protection of an inert gas, the semi-alicyclic low-thermal expansion coefficient transparent polyimide composition of claim 7 is subjected to thermal imidization treatment to obtain a semi-alicyclic transparent polyimide film.

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