Cyclohexane-containing diamine monomer, transparent polyimide film and preparation method thereof

Abstract

The present invention relates to a cyclohexane-containing diamine monomer, a transparent polyimide film, and a preparation method thereof. The preparation method comprises: mixing a first dehydrating agent, cyclohexanedicarboxylic acid, a catalyst, and a diaminobenzene ring compound in an inert gas atmosphere, then adding a second dehydrating agent, mixing, and reacting; pouring the mixture into a coolant and mixing; adjusting the pH, then filtering to obtain a crude product; and washing and purifying the crude product to obtain the cyclohexane-containing diamine monomer. Compared with the prior art, the present invention introduces a six-membered aliphatic ring structure, heteroatoms, and non-coplanar benzene rings into the diamine monomer through molecular design, thereby improving the optical properties of the polyimide film while maintaining good thermal stability.

Description

Technical Field

[0001] The invention belongs to the technical field of organic photoelectric materials and relates to a cyclohexane-containing diamine monomer, a transparent polyimide film and a preparation method thereof. Background Art

[0002] Polyimide (PI) is one of the earliest discovered high-heat-resistant polymers and remains one of the most common commercial materials. Traditional fully aromatic polyimide films, due to their excellent heat and chemical resistance, good mechanical and dielectric properties, dimensional stability, low toxicity, and self-extinguishing properties, have become a representative specialty engineering plastic with promising development prospects in the field of polymer materials. They are widely used in aerospace, fireproofing, packaging, microelectronic components, flexible display panels, specialty fibers, and medical materials.

[0003] With the rapid development of microelectronic information engineering, the requirements for high reliability, high integration and high signal transmission speed of optoelectronic devices are getting higher and higher, and the requirements for high temperature resistant optical films are also getting higher and higher. Optical polymer films are characterized by their glass transition temperature (T g ) can be divided into three types, including traditional optical films (T g <100℃)、Ordinary high temperature optical film (100℃≤T g ≤200℃) and high temperature optical films (T g >200℃). Although traditional polymer optical films (such as polyethylene terephthalate, PET, T g About 78℃; polyethylene naphthalate, PEN, T g About 123℃; Polycarbonate, PC, T g While polyimide films have excellent optical transparency (approximately 145°C), their limited glass transition temperature restricts their application in advanced optoelectronic engineering. In contrast, polyimide films offer a good combination of thermal stability and excellent dielectric and mechanical properties.

[0004] Polyimide films are dark in color, ranging from yellow to dark brown, and have poor transmittance in the visible light region. This is due to the presence of strong electron donors and acceptors in the polyimide molecular structure, which form strong charge transfer complexes (CTCs) within or between the molecular chains. This results in strong absorption of polyimide in the visible light range, severely limiting its application in optoelectronic engineering. Consequently, colorless and transparent polyimides (CPIs) with high temperature resistance have gained increasing attention in recent years. The introduction of alicyclic substituents can improve the thermal stability and optical transparency of polyimides; the introduction of highly electronegative groups can enhance the optical properties of the films; and the introduction of asymmetric or twisted rigid substituents and non-coplanar structures, including kinks, helices, and axial knots, can increase the optical transmittance of the films and reduce the water and oxygen transmission rate. However, molecular structural designs that favor optical transparency often compromise the thermal performance of the material. Furthermore, structural factors that enhance thermal performance, such as rigid aromatic structures and highly conjugated structures, can induce charge transfer complex effects, often compromising the material's optical transparency. Therefore, it is necessary to suppress the charge transfer complex effect to a certain extent through molecular design so that the various properties of polyimide can achieve a good balance.

[0005] Patent CN116162243A discloses a cardo ring structure copolymer polyimide and its preparation method. The patent uses 4,4-diaminodiphenyl ether as a diamine monomer, pyromellitic anhydride as a dianhydride monomer, and 9,9-bis(4-aminophenyl)fluorene as a third monomer to introduce the cardo ring structure through copolymerization. The resulting random copolymer polyimide has a cardo ring structure. Although the patent incorporates the cardo group, the film is reddish-brown in color.

[0006] Patent CN116396262A discloses a spiro-asymmetric aromatic diamine for polyimide and its preparation method and application. A spiro-asymmetric aromatic diamine is prepared, and a novel polyimide is obtained by combining the spiro-asymmetric aromatic diamine with a tetracarboxylic dianhydride derivative. Although this patent uses a large spiro ring structure, the transmittance is poor, T 400 nm Both are less than 60%.

[0007] Patent CN115819761A discloses the preparation of a polyimide material with high light transmittance and high heat resistance. The main method is to synthesize a new fluorine-containing and ketone-containing dianhydride bis(6'-(trifluoromethyl)-[1,1':3',3"-terphenyl]-3,4-dicarboxylic anhydride) ketone, and use it to modify the properties of polyimide. Although the patent uses a trifluoromethyl structure, the maximum light transmittance is only 93%, which is not significantly improved compared with the comparative example of the patent. Summary of the Invention

[0008] The purpose of the present invention is to provide a cyclohexane-containing diamine monomer, a transparent polyimide film and a preparation method thereof in order to overcome at least one of the defects of the above-mentioned prior art, such as poor transparency, low transmittance, and the inability to balance thermal performance and optical transparency. The present invention introduces a six-membered cyclic aliphatic structure, heteroatoms, and non-coplanar benzene rings into the diamine monomer through molecular design, thereby improving the optical properties of the polyimide film while maintaining good thermal stability.

[0009] The purpose of the present invention can be achieved by the following technical solutions:

[0010] One of the technical solutions of the present invention is to provide a cyclohexane-containing diamine monomer, the structural formula of the diamine monomer is:

[0011]

[0012]

[0013] Wherein R1 and R2 are selected from one of the following structures:

[0014]

[0015] The dotted lines represent the bonds to the parent nucleus.

[0016] As a preferred technical solution, the structural formula of the diamine monomer is:

[0017]

[0018] One of the technical solutions of the present invention is to provide a method for preparing a cyclohexane-containing diamine monomer, the method comprising the following steps:

[0019] In an inert gas atmosphere, a first dehydrating agent, cyclohexanedicarboxylic acid, a catalyst and a diaminobenzene ring compound are mixed, and then a second dehydrating agent is added and mixed, and reacted; poured into a coolant and mixed; the pH is adjusted, and then filtered to obtain a crude product; the crude product is washed and purified to obtain a cyclohexane-containing diamine monomer.

[0020] As a preferred technical solution, the reaction equation of the method is:

[0021]

[0022] In the formula, X1 includes amino, hydroxyl or thiol, and X2 includes nitrogen, oxygen or sulfur.

[0023] As a preferred technical solution, the inert gas includes nitrogen or argon.

[0024] Furthermore, the first dehydrating agent is polyphosphoric acid (PPA), the cyclohexanedicarboxylic acid includes 1,4-cyclohexanedicarboxylic acid or 1,3-cyclohexanedicarboxylic acid, the catalyst is stannous chloride (SnCl2), the diaminobenzene ring compound includes diaminoaniline, diaminophenol or diaminothiophenol, and the amino substitution position in the diaminobenzene ring compound includes 2,5 substitution or 2,4 substitution;

[0025] The second dehydrating agent includes phosphorus pentoxide (P2O5) or concentrated sulfuric acid (H2SO4). The second dehydrating agent is added to maintain the concentration of the first dehydrating agent to achieve a better dehydration effect.

[0026] As a preferred technical solution, the content of the first dehydrating agent (calculated as phosphorus pentoxide) is 83.0-87.0%.

[0027] Furthermore, the molar / mass ratio of the cyclohexanedicarboxylic acid to the first dehydrating agent is 1 mol:(5000-6000 g), and the molar ratio of the cyclohexanedicarboxylic acid, the catalyst and the diaminobenzene ring compound is 1:(0.1-0.2):(2-4);

[0028] The molar ratio of the cyclohexanedicarboxylic acid to the second dehydrating agent is 1:(1-2).

[0029] Furthermore, the first dehydrating agent, cyclohexanedicarboxylic acid, catalyst and diaminobenzene ring compound are mixed at a temperature of 60-70° C. for 2-3 hours;

[0030] The mixing time of the second dehydrating agent is 0.5-0.7h;

[0031] The reaction temperature is 180-200°C and the reaction time is 10-12h;

[0032] The pH is adjusted to 8-10.

[0033] As a preferred technical solution, the coolant is ice water, and the mixing time in the coolant is 10-14 hours.

[0034] As a preferred technical solution, the pH adjusting agent includes sodium hydroxide, sodium carbonate or sodium bicarbonate.

[0035] As a preferred technical solution, the purification adopts recrystallization, and the recrystallization reagent includes N,N-dimethylformamide (DMF) or N-methylpyrrolidone (NMP).

[0036] One of the technical solutions of the present invention is to provide a transparent polyimide film, which is polymerized using the cyclohexane-containing diamine monomer. The structural formula of the film is:

[0037]

[0038] In the formula Select one of the following structures:

[0039]

[0040] Y is selected from one of the following structures:

[0041]

[0042] m and n independently represent the average number of repeating structural units.

[0043] One of the technical solutions of the present invention is to provide a method for preparing a transparent polyimide film, the method comprising the following steps:

[0044] In an inert gas atmosphere, a cyclohexane-containing diamine monomer, a second diamine monomer and a polar aprotic solvent are mixed, and then a dianhydride monomer is added for reaction; the mixture is spin-coated on a plate, allowed to stand, heated to dry, and cooled to obtain a transparent polyimide film.

[0045] As a preferred technical solution, the inert gas includes nitrogen or argon.

[0046] Further, the second diamine monomer includes 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 1,4-cyclohexanediamine or 4,4'-diaminobenzanilide, and the polar aprotic solvent includes N,N-dimethylformamide (DMF) or N-methylpyrrolidone (NMP);

[0047] The dianhydride monomer includes 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) or 4,4'-diphenyl ether dianhydride (ODPA).

[0048] Further, the molar ratio of the cyclohexane-containing diamine monomer to the second diamine monomer is (0.25-4):1, and the molar / volume ratio of the sum of the cyclohexane-containing diamine monomer and the second diamine monomer to the polar aprotic solvent is 1 mol:(1-5 L);

[0049] The molar ratio of the sum of the cyclohexane-containing diamine monomer and the second diamine monomer to the dianhydride monomer is 1:(1-2).

[0050] Furthermore, the mixing temperature is room temperature (20-30° C.) and the mixing time is 0.5-1.5 h;

[0051] The reaction temperature is room temperature (20-30° C.) and the reaction time is 12-18 hours.

[0052] As a preferred technical solution, a polar aprotic solvent is added after the reaction to control the solid content, and the solid content is 10-30 wt%.

[0053] As a preferred technical solution, the plate is a silica glass plate.

[0054] As a preferred technical solution, the static pressure is vacuum, the temperature is room temperature (20-30° C.), and the time is 0.5-1.5 h.

[0055] As a preferred technical solution, the drying temperature is 50-400° C. and the drying time is 3-4 hours.

[0056] As a preferred technical solution, the cooling temperature is room temperature (20-30° C.) and the cooling time is 1-2 hours.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The cyclohexane-containing diamine monomer of the present invention also contains heteroatoms (nitrogen, oxygen or sulfur), a six-membered aliphatic ring structure, and a non-coplanar benzene ring, and has a symmetrical molecular configuration. The transparent polyimide film prepared using it as a raw material has better optical properties. On the one hand, the six-membered aliphatic ring in the molecular structure of the diamine monomer is conducive to interrupting electronic conjugation and reducing the formation of charge transfer complexes, thereby improving the optical properties of the polyimide film. On the other hand, the introduction of symmetrically distributed heteroatoms increases the steric hindrance of the monomer, and the addition of non-coplanar benzene rings increases the degree of distortion of the molecular chain, thereby solving the problems of poor optical properties and low thermal stability of polyimide films synthesized using traditional diamine monomers.

[0059] (2) The preparation method of the cyclohexane-containing diamine monomer of the present invention is to synthesize the diamine monomer by condensing a six-membered alicyclic carboxylic acid with a phenol having a heteroatom and a benzene ring. The method is environmentally friendly and simple, does not require the use of a highly corrosive chlorination reagent, and reduces the number of synthesis steps. The target diamine monomer can be directly synthesized in one step.

[0060] (3) The transparent polyimide film of the present invention is obtained by polymerizing the cyclohexane-containing diamine monomer of the present invention with a second diamine monomer and a dianhydride monomer. With the addition of the second diamine monomer, the optical properties of the polyimide film are enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 Graph showing optical performance test results of the polyimide films in Comparative Example 1 and Examples 3 to 6 of the present invention;

[0062] Figure 2 Graphs showing optical performance test results of the polyimide films of Comparative Example 2 and Examples 7 to 10 of the present invention;

[0063] Figure 3 Graph showing thermal performance test results of polyimide films in Comparative Example 1 and Examples 3 to 6 of the present invention;

[0064] Figure 4 Graph showing the thermal performance test results of the polyimide films in Comparative Example 2 and Examples 7 to 10 of the present invention. DETAILED DESCRIPTION

[0065] The present invention is described in detail below with reference to specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0066] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; the reagents used are all commercially available products or prepared by conventional methods in the art unless otherwise specified. Anything not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0067] Example 1:

[0068] A 1,4-cyclohexanebenzoxazole diamine and a preparation method thereof, the reaction equation is as follows:

[0069]

[0070] The specific steps are as follows:

[0071] Under nitrogen protection, polyphosphoric acid (PPA, 100 g, with a content of 85.0% based on phosphorus pentoxide (P2O5)), 1,4-cyclohexanedicarboxylic acid (3.444 g, 0.02 mol), anhydrous stannous chloride (SnCl2, 0.451 g, 0.002 mol) and 2,5-diaminophenol dihydrochloride (7.88 g, 0.04 mol) were added to a 500 mL flask, and the mixture was stirred at 60°C for 2.5 h. Then, P2O5 (2.84 g, 0.02 mol) was added and stirring was continued for 0.5 h. The mixture was reacted at 200°C for 11 h. The mixture was slowly poured into ice water and stirred for 12 h. The pH of the solution was adjusted to 9 with sodium carbonate, and then filtered to obtain a crude product. The crude product was washed and purified by recrystallization with N-methylpyrrolidone (NMP) to obtain a light yellow solid with a yield of 6.47 g and a yield of 93%.

[0072] 1H NMR (400MHz, DMSO-d6) δ8.38(s,2H),8.05(s,2H),7.67(s,2H),5.74(s,2H),3.02(s,2H),2.25(s,4H),1.81(s,2H).

[0073] Example 2:

[0074] A 1,3-cyclohexanebenzoxazole diamine and a preparation method thereof, the reaction equation is as follows:

[0075]

[0076] The specific steps are as follows:

[0077] Under nitrogen protection, PPA (100 g, 85.0% content based on P2O5), 1,3-cyclohexanedicarboxylic acid (3.444 g, 0.02 mol), anhydrous SnCl2 (0.451 g, 0.002 mol) and 2,5-diaminophenol dihydrochloride (7.88 g, 0.04 mol) were added to a 500 mL flask, and the mixture was stirred at 60°C for 2.5 h. Then, P2O5 (2.84 g, 0.02 mol) was added and stirring was continued for 0.5 h. The mixture was reacted at 200°C for 11 h. The mixture was slowly poured into ice water and stirred for 12 h. The pH of the solution was adjusted to 9 with sodium carbonate, and then filtered to obtain a crude product. The crude product was washed and purified by recrystallization with NMP to obtain a light yellow solid with a yield of 6.60 g and a yield of 95%.

[0078] 1H NMR (400MHz, DMSO-d6) δ7.26(s,2H),6.76(s,2H),6.58(s,2H),4.99(s,4H),3.11(s,2H),2.17(s,2H),1.85(s,1H),1.55(s,1H).

[0079] Example 3:

[0080] A 1,4-cyclohexanebenzoxazole polyimide film and a preparation method thereof, the specific steps are as follows:

[0081] Under nitrogen protection, 1,4-cyclohexanebenzoxazole diamine (0.8352 g, 0.0024 mol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB, 0.192 g, 0.0006 mol) and NMP (9 mL) were added to a 25 mL test tube. The mixture was stirred at room temperature for 1 h until completely dissolved. Then, 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA, 1.332 g, 0.003 mol) was slowly added. The mixture was continued to react at room temperature for 12 h to obtain a light yellow viscous polyurethane solution. , NMP was added to control the solid content to 20wt%; the polyamine solution was spin-coated on a dry and clean 10×10cm silica glass plate, allowed to stand at room temperature for 0.5h under vacuum conditions, heated to 100°C and dried for 1h to dry the solvent, then heated to 120°C and dried for 0.5h, then heated to 180°C and dried for 0.5h, then heated to 240°C and dried for 0.5h, then heated to 300°C and dried for 0.5h, and finally heated to 350°C and dried for 0.5h, and cooled to room temperature for 2h to obtain a transparent polyimide film with the following structural formula:

[0082]

[0083] The ratio of m to n in the formula is the molar ratio of the diamine monomers.

[0084] Comparative Example 1 and Examples 4 to 6:

[0085] A 1,4-cyclohexanebenzoxazole polyimide film and a preparation method thereof are basically the same as those in Example 3, except that the types and proportions of the diamine monomers used are different, as shown in Table 1.

[0086] Table 1 Types and ratios of monomers in Comparative Example 1 and Examples 3 to 6

[0087]

[0088] Example 7:

[0089] A 1,3-cyclohexanebenzoxazole polyimide film and a preparation method thereof, the specific steps are as follows:

[0090] Under nitrogen protection, 1,3-cyclohexanebenzoxazole diamine (0.8352 g, 0.0024 mol), TFMB (0.192 g, 0.0006 mol) and NMP (9 mL) were added to a 25 mL test tube. The mixture was stirred at room temperature for 1 h until it was completely dissolved. Then, 6FDA (1.332 g, 0.003 mol) was slowly added. The mixture was continued to react at room temperature for 12 h to obtain a light yellow viscous polyurethane solution. NMP was added to control the solid content to 20 wt%. The polyurethane was added to the mixture. The acid solution was spin-coated on a dry and clean 10×10 cm silica glass plate, allowed to stand at room temperature for 0.5 h under vacuum conditions, heated to 100°C and dried for 1 h to dry the solvent, then heated to 120°C and dried for 0.5 h, then heated to 180°C and dried for 0.5 h, then heated to 240°C and dried for 0.5 h, then heated to 300°C and dried for 0.5 h, and finally heated to 350°C and dried for 0.5 h, and cooled to room temperature for 2 h to obtain a transparent polyimide film with the following structural formula:

[0091]

[0092] The ratio of m to n in the formula is the molar ratio of the diamine monomers.

[0093] Comparative Example 2 and Examples 8 to 10:

[0094] A 1,3-cyclohexanebenzoxazole polyimide film and a preparation method thereof are basically the same as those in Example 7, except that the types and proportions of the diamine monomers used are different, as shown in Table 2.

[0095] Table 2 Types and ratios of monomers in Comparative Example 2 and Examples 7 to 10

[0096]

[0097] The optical properties of the polyimide film were tested by measuring the absorbance in the range of 250-800 nm using a PerkinElmer Lambda 950 UV-visible spectrophotometer (USA).

[0098] The optical performance test results of the 1,4-cyclohexanebenzoxazole polyimide films in Comparative Example 1 and Examples 3 to 6 are as follows: Figure 1 As shown in Table 3, 1,4-cyclohexanebenzoxazole diamine is referred to as 14EZ. With the addition of the second diamine monomer, the optical properties of the film gradually improved. 500 % increased from 71.04% to 91.80%, T 800 % increased from 90.36% to 99.98%, and the optical properties of the film remained basically unchanged when the molar ratio of diamine monomer exceeded 4:6.

[0099] Table 3 Optical properties test results of the films in Comparative Example 1 and Examples 3 to 6

[0100] Case Diamine monomer molar ratio <![CDATA[T 500 %]]> <![CDATA[T 800 %]]> Comparative Example 1 10:0 71.04％ 90.36％ Example 3 8:2 82.70％ 98.96％ Example 4 6:4 88.80％ 99.40％ Example 5 4:6 91.57％ 99.76％ Example 6 2:8 91.80％ 99.98％

[0101] The optical performance test results of the 1,3-cyclohexanebenzoxazole polyimide films in Comparative Example 2 and Examples 7 to 10 are as follows: Figure 2 As shown in Table 4, 1,3-cyclohexanebenzoxazole diamine is referred to as 13EZ. With the addition of the second diamine monomer, the optical properties of the film gradually improved. 500 % increased from 80.86% to 91.92%, T 800 % increased from 95.10% to 99.93%, and the best performance was achieved when the molar ratio of diamine monomer was 4:6. When the molar ratio increased to 2:8, T 800 % has increased but T 500 % has decreased.

[0102] Table 4 Optical properties test results of the films in Comparative Example 2 and Examples 7 to 10

[0103] Case Diamine monomer molar ratio <![CDATA[T 500 %]]> <![CDATA[T 800 %]]> Comparative Example 2 10:0 80.86％ 95.10％ Example 7 8:2 88.53％ 99.79％ Example 8 6:4 87.17％ 99.35％ Example 9 4:6 91.92％ 99.76％ Example 10 2:8 86.01％ 99.93％

[0104] The thermal properties of the polyimide film were tested by measuring the thermal weight loss temperature using a German Netzsch thermogravimetric analyzer TG 209F3 Tarsus with a measuring range of 30-750°C and a heating rate of 10°C / min.

[0105] The thermal performance test results of the 1,4-cyclohexanebenzoxazole polyimide films in Comparative Example 1 and Examples 3 to 6 are as follows: Figure 3 As shown in Table 5, with the increase of the proportion of the second diamine monomer added, the thermal weight loss temperature T 5％ and T 10％ It first decreases and then increases. It is speculated that the addition of the second diamine monomer introduces a fluorinated group, which increases steric hindrance and hinders the formation of intermolecular hydrogen bonds, thereby lowering the thermal gravimetric temperature. As the proportion of the second diamine monomer increases, the reaction activity increases, the average molecular weight of the film increases, and the thermal gravimetric temperature rises.

[0106] Table 5 Thermal performance test results of the films in Comparative Example 1 and Examples 3 to 6

[0107] Case Diamine monomer molar ratio <![CDATA[T 5％ (℃)]]> <![CDATA[T 10％ (℃)]]> Comparative Example 1 10:0 473.09 495.34 Example 3 8:2 460.30 484.85 Example 4 6:4 479.33 505.10 Example 5 4:6 493.61 525.09 Example 6 2:8 508.93 535.19

[0108] The thermal performance test results of the 1,3-cyclohexanebenzoxazole polyimide films in Comparative Example 2 and Examples 7 to 10 are as follows: Figure 4 As shown in Table 6, with the increase of the proportion of the second diamine monomer added, the thermal weight loss temperature T 5％ and T 10％It first changes slightly and then rises. It is speculated that the addition of the second diamine monomer introduces a fluorinated group, which increases steric hindrance and hinders the formation of intermolecular hydrogen bonds, thus lowering the thermal gravimetric temperature. As the proportion of the second diamine monomer increases, the reaction activity increases, the average molecular weight of the film increases, and the thermal gravimetric temperature rises.

[0109] Table 6 Thermal performance test results of the films in Comparative Example 2 and Examples 7 to 10

[0110] Case Diamine monomer molar ratio <![CDATA[T 5％ (℃)]]> <![CDATA[T 10％ (℃)]]> Comparative Example 2 10:0 473.35 495.83 Example 7 8:2 474.00 491.71 Example 8 6:4 482.37 503.55 Example 9 4:6 485.72 518.76 Example 10 2:8 489.92 521.40

[0111] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A cyclohexane-containing diamine monomer, characterized in that: The structural formula of the diamine monomer is selected from one of the following structures:

2. A method for preparing a cyclohexane-containing diamine monomer according to claim 1, characterized in that: The method comprises the following steps: In an inert gas atmosphere, a first dehydrating agent, cyclohexanedicarboxylic acid, a catalyst and a diaminobenzene ring compound are mixed, and then a second dehydrating agent is added and mixed, and reacted; poured into a coolant and mixed; the pH is adjusted, and then filtered to obtain a crude product; the crude product is washed and purified to obtain a cyclohexane-containing diamine monomer.

3. The method for preparing a cyclohexane-containing diamine monomer according to claim 2, wherein: The first dehydrating agent is polyphosphoric acid, the cyclohexanedicarboxylic acid includes 1,4-cyclohexanedicarboxylic acid or 1,3-cyclohexanedicarboxylic acid, the catalyst is stannous chloride, the diaminobenzene ring compound includes diaminoaniline, diaminophenol or diaminothiophenol, and the amino substitution position in the diaminobenzene ring compound includes 2,5 substitution or 2,4 substitution; The second dehydrating agent includes phosphorus pentoxide or concentrated sulfuric acid.

4. The method for preparing a cyclohexane-containing diamine monomer according to claim 2, wherein: The molar / mass ratio of the cyclohexanedicarboxylic acid to the first dehydrating agent is 1 mol:(5000-6000 g), and the molar ratio of the cyclohexanedicarboxylic acid, the catalyst, and the diaminobenzene ring compound is 1:(0.1-0.2):(2-4); The molar ratio of the cyclohexanedicarboxylic acid to the second dehydrating agent is 1:(1-2).

5. The method for preparing a cyclohexane-containing diamine monomer according to claim 2, wherein: The first dehydrating agent, cyclohexanedicarboxylic acid, catalyst and diaminobenzene ring compound are mixed at a temperature of 60-70° C. for 2-3 hours; The mixing time of the second dehydrating agent is 0.5-0.7h; The reaction temperature is 180-200°C and the reaction time is 10-12h; The pH is adjusted to 8-10.

6. A transparent polyimide film, characterized in that: The film is polymerized using the cyclohexane-containing diamine monomer according to claim 1, and the structural formula of the film is selected from one of the following structures: In the formula Select one of the following structures: Y is selected from one of the following structures: m and n independently represent the average number of repeating structural units.

7. A method for preparing a transparent polyimide film according to claim 6, characterized in that: The method comprises the following steps: In an inert gas atmosphere, a cyclohexane-containing diamine monomer, a second diamine monomer and a polar aprotic solvent are mixed, and then a dianhydride monomer is added for reaction; the mixture is spin-coated on a plate, allowed to stand, heated to dry, and cooled to obtain a transparent polyimide film.

8. The method for preparing a transparent polyimide film according to claim 7, wherein: The second diamine monomer includes 2,2'-bis(trifluoromethyl)diaminobiphenyl, 1,4-cyclohexanediamine or 4,4'-diaminobenzanilide, and the polar aprotic solvent includes N,N-dimethylformamide or N-methylpyrrolidone; The dianhydride monomer includes 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride or 4,4'-biphenyl ether dianhydride.

9. The method for preparing a transparent polyimide film according to claim 7, wherein: The molar ratio of the cyclohexane-containing diamine monomer to the second diamine monomer is (0.25-4):1, and the molar / volume ratio of the sum of the cyclohexane-containing diamine monomer and the second diamine monomer to the polar aprotic solvent is 1 mol:(1-5 L); The molar ratio of the sum of the cyclohexane-containing diamine monomer and the second diamine monomer to the dianhydride monomer is 1:(1-2).

10. The method for preparing a transparent polyimide film according to claim 7, wherein: The mixing temperature is room temperature and the mixing time is 0.5-1.5h; The reaction temperature is room temperature and the reaction time is 12-18 hours.

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