A heat-resistant fluorine-free semi-cycloaliphatic polyimide, a preparation method and application thereof

Abstract

The application belongs to the technical field of high polymer materials, and particularly relates to a heat-resistant fluorine-free semi-alicyclic polyimide and a preparation method and application thereof. The heat-resistant fluorine-free semi-alicyclic polyimide is characterized in that the semi-alicyclic polyimide composition is prepared by polymerization reaction of diamines and dianhydrides; the molar ratio of the total amount of the diamines to the total amount of the dianhydrides is 0.9-1.1:1; the diamines comprise first diamines and second diamines; and the dianhydrides are fluorine-free dianhydrides. The specific dianhydrides and diamines are selected for reaction, and a segmented temperature rising method is adopted to optimize the preparation process, so that the prepared heat-resistant fluorine-free semi-alicyclic polyimide has better thermal stability and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a heat-resistant, fluorine-free, semi-alicyclic polyimide, its preparation method, and its application. Background Technology

[0002] Polyimide (PI) is a class of aromatic heterocyclic polymers containing imine rings in its main chain. It is also a high-performance functional material with excellent thermal stability, chemical resistance, moisture resistance, radiation resistance, mechanical properties, and dielectric properties. It has wide applications in aerospace, electrical appliances, microelectronics, low-temperature superconductivity, gas separation, and photolithography, and has been a hot topic of interest for over a decade. Currently, with technological advancements and the development of emerging industries, the demand for PI is increasing daily. Due to its highly stable chemical structure and excellent physical properties, PI has a wide range of applications, including thin films, fibers, resins, adhesives, photoresists, engineering plastics, gas separation membranes, liquid crystal alignment agents, and foam plastics. Among these, the PI thin film industry has the largest demand, the widest application, and was the first to enter commercial circulation. Besides its widespread use in flexible printed circuit boards, photoresists, and chip packaging in microelectronics, PI thin films are also gaining increasing attention in flexible displays, organic photovoltaic solar panels, and liquid crystal displays.

[0003] Traditional polyimide materials often exhibit a yellow or brownish-yellow appearance due to the charge-transfer complex (CTC) effect between molecular chains. This color limitation restricts the further development of polyimides in applications requiring high transparency. To address this issue, researchers have employed innovative chemical structural designs. By introducing fluorine groups, flexible ether bonds, and aromatic rigid non-planar conjugated structures, they have effectively increased the distance between molecular chains and reduced the polymer's packing density. The aim is to weaken the conjugation effect between polyimide molecular chains, reduce chain stacking, and thus decrease the absorption of visible light, achieving a transparent effect. Simultaneously, molecular design plays a crucial role in regulating the thermal stability, dimensional stability, optical properties, and solubility of polyimides.

[0004] With the rapid development of the electronics and information industry, the requirements for thin films are becoming increasingly stringent. While meeting the requirements of thinness, flexibility, and light transmittance, higher demands are being placed on basic thermal and mechanical properties such as heat resistance and dimensional stability. Colorless and transparent polyimide (CPI) films have attracted much attention due to their combination of the performance advantages of conventional PI films and the optical properties of optical films, making them promising candidates for flexible electronics. Currently, CPI films mainly include fluorinated and semi-alicyclic types; among them, fluorinated CPI films have been studied more extensively.

[0005] For example, Huang Tao et al., in their paper "Preparation and Performance Study of High Heat-Resistant Colorless and Transparent Polyimide Films" (Chemical New Materials, 2025.12.029), used 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA) and 4,4'-diaminodiphenyl ether (ODA) as diamine monomers and hexafluorodianhydride (6FDA) as an anhydride monomer. They constructed a non-planar conjugated aromatic structure by introducing fluorine groups and flexible ether bonds into the monomers, and simultaneously controlled the molar ratio of monomers in the polycondensation reaction to reduce the charge-transfer complex (CTC) effect, thus preparing a series of fluorinated colorless and transparent polyimide films. The results showed that the films exhibited excellent optical transparency and thermal stability, with a transmittance exceeding 80%; the thermal weight loss temperature was 500℃ when the weight loss was 5%; and the carbon residue of the films was above 50% when the temperature reached 800℃. These films not only exhibited high-temperature resistance but also achieved colorless and transparent properties. However, it faces drawbacks such as high cost of fluorinated monomers, increased water absorption, large equipment investment, and extremely high engineering difficulty. Furthermore, in recent years, fluorinated monomers have been restricted by international PFAS (Persistent Organic Compounds) regulations. PFAS are known as "persistent organic compounds (POPs)" because their degradation time in soil and water can reach hundreds of years. PFAS also easily migrates in the environment. When humans and animals ingest PFAS, they accumulate in the body and produce toxicity, affecting the immune and reproductive systems, interfering with the endocrine system, impacting infant growth and development, causing liver damage, and even increasing the risk of thyroid disease, kidney cancer, hypertension, testicular cancer, and other diseases.

[0006] Currently, most semi-alicyclic polyimides suffer from insufficient heat resistance. For example, Chinese patent CN118852622A provides a fluorine-free semi-alicyclic low-CTE transparent polyimide, its preparation method, and a polyimide film, relating to the field of polyimide and its preparation technology. The fluorine-free semi-alicyclic low-CTE transparent polyimide is prepared by a polycondensation reaction between a dianhydride containing an alicyclic group and a diamine. This invention also provides a polyimide film prepared from the aforementioned semi-alicyclic low-CTE transparent polyimide. By selecting specific diamines and dianhydrides and optimizing the preparation process, this invention yields a product with excellent optical and mechanical properties, as well as heat resistance, overcoming the shortcomings of existing technologies. It can be used as a substrate for flexible electronics such as flexible displays, solar energy, and wearable devices. However, its heat resistance still needs improvement.

[0007] With the rapid development of modern technology, especially in high-tech fields such as optoelectronics, microelectronics, and solar energy, the performance requirements for materials are becoming increasingly stringent, particularly regarding heat resistance. Therefore, developing a fluorine-free semi-alicyclic polyimide that possesses both excellent optical and mechanical properties while also exhibiting good heat resistance is imperative. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the present invention aims to provide a heat-resistant, fluorine-free, semi-alicyclic polyimide, its preparation method and application.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] On the one hand, the present invention provides a heat-resistant, fluorine-free, half-cycloaliphatic polyimide, wherein the half-cycloaliphatic polyimide composition is prepared by polymerization of diamine and dianhydride;

[0011] The molar ratio of the total diamine to the total dianhydride is 0.9-1.1:1;

[0012] The diamine comprises a first diamine and a second diamine;

[0013] The first diamine is 4,4'-methylenebis(2,6-diethylaniline) (M-DEA) and / or 4,4'-methylenebis(2-ethyl)aniline (O-DEA); the second diamine is 4,4'-diaminodiphenyl ether (ODA) and / or 4,4'-diaminobenzoyl aniline (DABA).

[0014] More preferably, the first diamine is M-DEA and the second diamine is ODA.

[0015] Preferably, the molar ratio of the first diamine to the second diamine is 3-5:5-8, more preferably 4:7.

[0016] Preferably, the dianhydride is a fluorine-free dianhydride.

[0017] More preferably, the dianhydride is a dianhydride containing a bulky side group, wherein the bulky side group is selected from one of fluorene, phthalic acid, o-phenylimine, and cyclododecyl.

[0018] More preferably, the dianhydride is selected from one of 2,2'-dichloro-4,4',5,5'-biphenyltetracarboxylic dianhydride (DCBPDA), dicyclohexyl-2,3',3,4'-tetracarboxylic dianhydride (3,4'-HBPDA), and dicyclohexyl-2,2',3,3'-tetracarboxylic dianhydride (3,3'-HBPDA).

[0019] More preferably, the dianhydride is 2,2'-dichloro-4,4',5,5'-biphenyltetracarboxylic dianhydride.

[0020] On the other hand, the present invention also provides a method for preparing the above-mentioned heat-resistant, fluorine-free, semi-alicyclic polyimide composition, comprising the following steps:

[0021] (1) Mix diamine, dianhydride and solvent at 0-25℃ to obtain polyimide resin;

[0022] (2) The polyimide resin obtained in step (1) is mixed with the additive and heated to dehydrate under inert gas protection to obtain polyimide.

[0023] Preferably, the solvent in step (1) is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, γ-valerolactone, methyltetrahydrofuran, and dimethylacetamide, and more preferably N-methylpyrrolidone.

[0024] Preferably, the amount of solvent added in step (1) is 4-8 times the total molar amount of diamine and dianhydride, more preferably 5 times the total molar amount of diamine and dianhydride.

[0025] Preferably, the additive in step (2) is a mixture of 3-acetylene aniline and N-acetylene aniline, with a molar ratio of 0.5-1:1-1.5, more preferably 1:1.

[0026] Preferably, the amount of additive added in step (2) is 0.3-0.6% of the total molar amount of diamine and dianhydride, more preferably 0.5%.

[0027] Preferably, the inert gas in step (2) is selected from argon, nitrogen, and helium, and more preferably argon.

[0028] Preferably, the heating in step (2) is a segmented heating.

[0029] More preferably, the segmented heating specifically refers to:

[0030] First stage: 25-100℃, heating rate 1-3℃ / min; hold at 100℃ for 30-50min;

[0031] Second stage: 100-200℃, heating rate 2-4℃ / min; hold at 200℃ for 20-30min;

[0032] Third stage: 200-300℃, heating rate 1-2℃ / min; hold at 300℃ for 30-60min.

[0033] More preferably, the segmented heating specifically refers to:

[0034] First stage: 25-100℃, heating rate 2℃ / min; hold at 100℃ for 40min;

[0035] Second stage: 100-200℃, heating rate 3℃ / min; hold at 200℃ for 25min;

[0036] Third stage: 200-300℃, heating rate 1℃ / min; hold at 300℃ for 50min.

[0037] Finally, the present invention also provides the application of the above-mentioned heat-resistant, fluorine-free, semi-alicyclic polyimide in the preparation of polyimide films.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The present invention selects dianhydride and diamine reaction at a specific ratio and adds additives to optimize the preparation process by combining segmented heating method, so that the prepared fluorine-free semi-alicyclic polyimide has better heat resistance and mechanical properties, and significantly improves the glass transition temperature of polyimide without reducing light transmittance.

[0040] (2) Through the design of a semi-alicyclic structure, the yellowing defect of high aromatic rings is avoided while reducing the degree of conjugation of molecular chains. Currently, it is completely free of fluorine, solving the environmental risks and performance imbalance problems of fluorine-containing components, and further improving heat resistance. The achievable effects are: 1. High transparency: The semi-alicyclic structure effectively inhibits intramolecular / intermolecular electronic transitions, with visible light transmittance of over 90% and yellowing index (YI) of less than 2; 2. Excellent thermal stability: Glass transition temperature (Tg) > 410℃, with better heat resistance; 3. Good mechanical properties: Tensile strength ≥ 140MPa, elongation at break ≥ 20%, meeting the mechanical requirements of flexible devices; 4. Environmentally friendly: No fluorine monomers added, making it green and environmentally friendly. Detailed Implementation

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0043] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0044] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0045] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0046] Unless otherwise specified, all raw materials used in the following examples are commercially available or prepared by conventional methods in the art.

[0047] Examples 1-4: A heat-resistant, fluorine-free, semi-acid-free cyclic polyimide

[0048] It is prepared by the polymerization reaction of diamine and dianhydride, and its composition is shown in Table 1 below.

[0049] The preparation method of Example 1 is as follows:

[0050] (1) Mix diamine, dianhydride and N-methylpyrrolidone (addition amount is 5 times the total molar amount of diamine and dianhydride) at 10°C to obtain polyimide resin;

[0051] (2) The polyimide resin obtained in step (1) is mixed with additives (3-acetyleneaniline and N-acetyleneaniline, molar ratio 1:1). The amount of additives added is 0.5% of the total molar amount of diamine and dianhydride. The mixture is heated and dehydrated under argon protection according to the following heating process to obtain polyimide.

[0052] First stage: 25-100℃, heating rate 2℃ / min; hold at 100℃ for 40min;

[0053] Second stage: 100-200℃, heating rate 3℃ / min; hold at 200℃ for 25min;

[0054] Third stage: 200-300℃, heating rate 1℃ / min; hold at 300℃ for 50min.

[0055] The preparation method of Example 2 is as follows:

[0056] (1) Mix diamine, dianhydride and N-methylpyrrolidone (addition amount is 5 times the total molar amount of diamine and dianhydride) at 10°C to obtain polyimide resin;

[0057] (2) The polyimide resin obtained in step (1) is mixed with additives (3-acetyleneaniline and N-acetyleneaniline, with a molar ratio of 0.5:1). The amount of additives added is 0.5% of the total molar amount of diamine and dianhydride. The mixture is heated and dehydrated under argon protection according to the following heating process to obtain polyimide.

[0058] First stage: 25-100℃, heating rate 1℃ / min; hold for 50min;

[0059] Second stage: 100-200℃, heating rate 2℃ / min; hold for 20min;

[0060] Third stage: 200-300℃, heating rate 1℃ / min; hold for 60min.

[0061] The preparation method of Example 3 is as follows:

[0062] (1) Mix diamine, dianhydride and N-methylpyrrolidone (addition amount is 5 times the total molar amount of diamine and dianhydride) at 10°C to obtain polyimide resin;

[0063] (2) The polyimide resin obtained in step (1) is mixed with additives (3-acetyleneaniline and N-acetyleneaniline, with a molar ratio of 1:1.5). The amount of additives added is 0.5% of the total molar amount of diamine and dianhydride. The mixture is heated and dehydrated under argon protection according to the following heating process to obtain polyimide.

[0064] First stage: 25-100℃, heating rate 3℃ / min; hold at 100℃ for 30min;

[0065] Second stage: 100-200℃, heating rate 4℃ / min; hold at 200℃ for 30min;

[0066] Third stage: 200-300℃, heating rate 2℃ / min; 300℃ for 30min.

[0067] Example 4

[0068] The preparation method is the same as in Example 1.

[0069] Table 1

[0070]

[0071] Comparative Example 1

[0072] The difference from Example 1 lies in the heating process, as detailed below:

[0073] First stage: 25-100℃, heating rate 4℃ / min; hold at 100℃ for 20min;

[0074] Second stage: 100-200℃, heating rate 1℃ / min; hold at 200℃ for 40min;

[0075] Third stage: 200-300℃, heating rate 3℃ / min; hold at 300℃ for 20min.

[0076] Comparative Example 2

[0077] The difference from Example 1 lies in the heating process, as detailed below:

[0078] First stage: 25-150℃, heating rate 2℃ / min; hold at 150℃ for 40min;

[0079] Second stage: 150-300℃, heating rate 3℃ / min; hold at 300℃ for 25min.

[0080] Comparative Example 3

[0081] The difference from Example 1 is that the first diamine is replaced with 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA).

[0082] Comparative Example 4

[0083] The difference from Example 1 is that the molar ratio of 3-acetylene aniline and N-acetylene aniline in the additive described in step (2) is 1:0.

[0084] Comparative Example 5

[0085] The difference from Example 1 is that the molar ratio of 3-acetylene aniline and N-acetylene aniline in the additive described in step (2) is 2:1.

[0086] Effect Experiment

[0087] The thin film performance testing methods are as follows:

[0088] (1) The transmittance (Tr 550nm), yellowness index, haze, etc. of the polyimide film were tested using an X-rite Ci7800 spectrophotometer;

[0089] (2) The tensile strength, elongation at break and elastic modulus of polyimide film were tested using Shimadzu AG-X plus, 1KN, at a test speed of 5mm / min, with a sample size of 10mm wide * 15mm long, a test gauge length of 50mm and an extensometer gauge length of 20mm.

[0090] (3) Glass transition temperature (Tg) was measured using a dynamic mechanical analyzer (DMA850) under the following test conditions:

[0091] The temperature was measured under a nitrogen atmosphere at a load of 0.05 N and a heating rate of 3 °C / min, within a temperature range of 200-400 °C. The inflection point of the curve with the maximum value was recorded as the glass transition temperature.

[0092] (4) Heat shrinkage rate (dimensional stability) was tested in accordance with GB / T 13542.2-2009 "Films for electrical insulation - Part 2: Test methods" (150℃), and the testing instrument was E04501 type 2.5-dimensional (CNC image tester).

[0093] The results are shown in Table 2.

[0094] Table 2

[0095]

[0096] As can be seen from the data in Table 2, the heat-resistant, fluorine-free semi-alicyclic polyimide prepared by the embodiments of the present invention not only has good mechanical properties but also better heat resistance, and its glass transition temperature is higher.

[0097] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A heat-resistant, fluorine-free, semi-alicyclic polyimide, characterized in that, The semi-alicyclic polyimide is prepared by polymerization of diamines and dianhydrides; The molar ratio of the total amount of diamines to the total amount of dianhydrides is 0.9-1.1:1; The diamines comprise a first diamine and a second diamine; The first diamine is 4,4'-methylenebis(2,6-diethylaniline) and / or 4,4'-methylenebis(2-ethyl)aniline; and the second diamine is 4,4'-oxydianiline and / or 4,4'-diaminobenzanilide; The dianhydride is a fluorine-free dianhydride selected from one of dicyclohexyl-2,3',3,4'-tetracarboxylic dianhydride and dicyclohexyl-2,2',3,3'-tetracarboxylic dianhydride.

2. The half-ester cyclopolymide according to claim 1, wherein, The first diamine is 4,4'-methylenebis(2,6-diethylaniline), and the second diamine is 4,4'-oxydianiline.

3. The half-ester cyclopolymide of claim 1, wherein, The molar ratio of the first diamine to the second diamine is 3-5:5-8.

4. The process for the preparation of a semi- cycloaliphatic polyimide according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: (1) mixing diamines, dianhydrides and a solvent at 0-25°C to obtain a polyimide resin; (2) mixing the polyimide resin obtained in step (1) with an additive, and dehydrating under the protection of inert gas to obtain a polyimide.

5. The preparation method according to claim 4, characterized in that, The additive in step (2) is a mixture of 3-ethynylaniline and N-ethynylaniline, and the molar ratio of the two is 0.5-1:1-1.

5.

6. The preparation method according to claim 4, characterized in that, The solvent in step (1) is at least one selected from N-methylpyrrolidone, N,N-dimethylformamide, γ-valerolactone, methyltetrahydrofuran, and dimethylacetamide.

7. The preparation method according to claim 4, characterized in that, The temperature rising in step (2) is a staged temperature rising, and the staged temperature rising is specifically as follows: First stage: 25-100°C, temperature rising rate 1-3°C / min; 100°C for 30-50 min; Second stage: 100-200°C, temperature rising rate 2-4°C / min; 200°C for 20-30 min; Third stage: 200-300°C, temperature rising rate 1-2°C / min; 300°C for 30-60 min.

8. Use of the semi-alicyclic polyimide of any one of claims 1-3 or the semi-alicyclic polyimide prepared by the preparation method of any one of claims 4-7 in the preparation of a polyimide film.

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