Fluorinated phenyl anthracene structure-containing polyimide and preparation method thereof

Abstract

The invention discloses fluorinated phenyl anthracene structure-containing polyimide and a preparation method thereof, and belongs to the technical field of high polymer materials. The fluorinated phenyl anthracene structure-containing polyimide has the following molecular structure: # imgabs0. The polyimide is endowed with good comprehensive performance by introducing an asymmetric phenyl anthracene structural unit with a trifluoromethyl side group, a flexible ether bond and a distorted non-coplanar structure into a polymer main chain; the solubility, the heat resistance, the optical performance, the mechanical performance, the crystallization performance, the dielectric performance, the hydrophobicity and the like are excellent.

Description

Technical Field

[0001] The present invention relates to a polyimide, in particular to a fluorinated polyimide containing a phenylanthracene structure and a preparation method thereof, belonging to the technical field of polymer materials. Background Art

[0002] As a high-performance polymer, polyimide (PI) boasts excellent properties such as high-temperature stability, solvent resistance, and high strength. It can be used in a variety of forms, including films, fibers, foams, adhesives, composites, and coatings, in aerospace, microelectronics, and electrical insulation. However, due to its unique molecular structure, PI suffers from shortcomings such as poor solubility, poor optical transparency, and relatively high dielectric constant and water absorption, severely hindering its application in several emerging high-tech fields. Traditional aromatic PIs, in particular, suffer from difficulties in melting, dissolving, and curing at high temperatures, making processing difficult. Furthermore, their excessive rigidity makes them hard and brittle, and their insufficient strength makes it difficult to achieve an effective balance between mechanical strength and thermal expansion coefficient in microelectronic applications. Charge transfer complex (CTC) effects, which form within and between polyimide chains, reduce the transparency of PI films, severely limiting their application in optoelectronics. This issue needs to be addressed urgently, especially given the rapid development of flexible display and 5G technologies.

[0003] In the prior art, various modification methods have been proposed to address the limitations of polyimide in terms of solubility, light transmittance, and mechanical properties. It mainly includes the introduction of fluorinated groups into the polyimide molecular chain (Li L, Xu Y, Che J, et al. Preparation, characterization and degradation kinetics of transparent fluorinated polyimides with low dielectric constants and excellent hydrophobic properties [J]. Polymer Bulletin, 2018, 75: 5777-5793), flexible structural units, twisted non-coplanar structures (Habib T, Zubair M, Bilquees S, et al. Polyimides with noncoplanar carbazole-TPA units: synthesis and characterization [J]. Polymer-Plastics Technology and Materials, 2021, 60 (5): 536-549), and bulky side groups (She YK, Wang SX, Liao Q, et al. Transparent and highly organosoluble aromatic polyimides with twisted backbone and bulky side substituents for flexible substrate materials [J]. Journal of Polymer Science, 2024, 62(6): 1061-1073.), alicyclic structure (Lan Z, Li C, YuY, et al. Colorless semi-alicyclic copolyimides with high thermal stability and solubility[J]. Polymers, 2019, 11(8): 1319) and copolymerization modification (Li K, Zhou L, Wu S, et al.Afacile synthesis of soluble polyimides with high glass transition temperature and excellent mechanical properties due to intermolecular hydrogen bonds[J].High Performance Polymers, 2020, 32(3):316-323) and other methods are used to adjust the packing density of molecular chains and increase the free volume fraction between molecular chains, thereby weakening the aromatic conjugation effect and CTC effect between polyimide molecules, and ultimately achieving the goal of synthesizing new polyimides with better comprehensive performance. However, these modification methods in the existing technology are all single and limited, and the comprehensive performance of polyimides is difficult to effectively improve. Summary of the Invention

[0004] In response to the defects of the prior art, the first object of the present invention is to provide a fluorinated polyimide containing a phenylanthracene structure. The key lies in the introduction of a fluorinated polyimide containing a bulky trifluoromethyl side group, a flexible ether bond, and a twisted non-coplanar asymmetric phenylanthracene structural unit into the polymer main chain. This can effectively hinder the stacking of polyimide molecular chains and effectively destroy the formation of CTC, increase the distance between molecular chains, and thus improve its solubility and optical transparency. At the same time, the introduction of the trifluoromethyl hydrophobic group can effectively reduce the water absorption rate of the polyimide and significantly reduce its dielectric constant. It has excellent comprehensive properties such as solubility, heat resistance, optical properties, mechanical properties, crystallization properties, dielectric properties and hydrophobicity.

[0005] The second object of the present invention is to provide a method for preparing a fluorinated polyimide containing a phenylanthracene structure. The polyimide monomer is easy to obtain and can be synthesized using a mature polymerization process, which is conducive to industrial production.

[0006] In order to achieve the above technical objectives, the present invention provides a fluorinated polyimide containing a phenylanthracene structure, which has a molecular structure of Formula 1:

[0007]

[0008] in,

[0009] Ar is

[0010] The key to the fluorinated phenylanthracene-containing polyimide of the present invention lies in the introduction of a special fluorinated phenylanthracene-containing structural unit. The fluorinated phenylanthracene-containing structural unit has the following characteristics: on the one hand, it has a flexible ether bond (-O-) which can destroy the regularity of the polymer molecular main chain to a certain extent, reduce the rigidity of the main chain structure, and improve the solubility and flexibility of the polymer; on the other hand, it has a twisted non-coplanar structure, which can effectively prevent the close stacking of polymer molecular chains, weaken its crystallization ability, reduce the interaction force between molecules, increase the free volume between molecules, thereby reducing its melting temperature and improving solubility; on the other hand, it has a non-coplanar structure. On the one hand, the structure is called trifluoromethyl, which can destroy the regularity of the polymer main chain, give it polarity, and improve its solubility. On the other hand, it introduces a large number of trifluoromethyl side groups, which can not only effectively prevent the close stacking of polymer molecular chains and weaken its crystallization ability, but also improve its solubility, while giving it a low dielectric constant and improving its hydrophobicity. On the other hand, it has a large side group, which can reduce the regularity of the main chain and increase the spacing between polymer chains, thereby effectively reducing the stacking degree of the main chain, weakening the interaction between molecular chains and within the chain, and reducing the probability of CTC formation, thereby improving the solubility and light transmittance of the polymer. In summary, the introduction of fluorinated phenyl-containing anthracene structure can give polyimide good comprehensive properties.

[0011] The present invention also provides a method for preparing a fluorinated polyimide containing a phenylanthracene structure, which comprises the following steps:

[0012] 1) subjecting a diamine monomer and a dianhydride monomer to a condensation polymerization reaction to obtain a polyamic acid intermediate;

[0013] 2) chemical imidization of the polyamic acid intermediate under the promotion of acetic anhydride and pyridine; or thermal imidization of the polyamic acid intermediate to obtain a fluorinated polyimide containing a phenylanthracene structure;

[0014] The diamine monomer has a structure of Formula 2:

[0015]

[0016] The dianhydride monomer has a structure of Formula 3:

[0017]

[0018] Among them, Ar is

[0019] As a preferred solution, the conditions for the polycondensation reaction are: first react at a temperature of -5°C to 5°C for 0.5 to 1.5 hours, and then continue to react at room temperature with stirring for 10 to 12 hours.

[0020] As a preferred solution, the polycondensation reaction is carried out in anhydrous NMP.

[0021] As a preferred solution, the amount of anhydrous NMP used is to maintain the solid content of the polymerization system at 15-25%.

[0022] As a preferred solution, the chemical imidization conditions are: first add acetic anhydride and pyridine and stir evenly at room temperature, then heat to 105-115° C. and stir to react for 6-8 hours.

[0023] As a preferred solution, the conditions for the thermal imidization are: the polyamic acid intermediate is heated at 70-90°C for 6-10 hours to volatilize the solvent, and then imidization is carried out by gradient temperature increase; the gradient temperature increase process is: 90-110°C, heat preservation for 0.5-1.5 hours; 140-150°C, heat preservation for 0.5-1.5 hours; 190-210°C, heat preservation for 0.5-1.5 hours; 240-260°C, heat preservation for 0.5-1.5 hours; 290-310°C, heat preservation for 0.2-0.5 hours.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] The present invention introduces 9-(4-amino-2-trifluoromethylphenoxy)-10-(4-amino-2-trifluoromethylphenyl)anthracene repeating units containing a trifluoromethyl group, a phenylanthracene structure and an ether bond into the polyimide main chain, which can significantly improve the solubility, optical properties, heat resistance, mechanical properties, dielectric properties and hydrophobic properties of the aromatic polyimide.

[0026] 1) The polyimide of the present invention has a high glass transition temperature (T g =242.4~300.5℃), and has excellent thermal performance (T 5％ =369.6~490.6℃, at 800℃, the residual carbon rate is 50.2~54.4%), mechanical properties (tensile strength is 69.82~87.47MPa, elastic modulus is 1.25~1.88GPa, elongation at break is 5.29~10.0%) and light transmittance (λ0 is 410.5~421.5nm, transmittance at 500nm is 25.6%~85.1%), and the saturated water absorption rate is less than 2%.

[0027] 2) The polyimide with the best performance in the present invention has a residual carbon rate of 50.2% at 800°C and good heat resistance; it is soluble in high-boiling-point aprotic solvents such as N,N-dimethylacetamide (DMAc) and low-boiling-point tetrahydrofuran (THF) at room temperature; and has the highest tensile strength (T s=87.47MPa); the light transmittance of the film is the best, with the transmittance of the film exceeding 85% at 500nm; it has good insulation properties (dielectric constant <3), and the saturated water absorption rate is 0.83%, indicating that it has broad application prospects in high humidity environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Infrared spectra of PI-1 to PI-5.

[0029] Figure 2 UV-Vis curves of PI-1 to PI-5 and photos of film appearance.

[0030] Figure 3 Thermogravimetric curves (a) and DSC curves (b) of PI-1 to PI-5.

[0031] Figure 4 These are the stress-strain curves of PI-1 to PI-5.

[0032] Figure 5 is the dielectric constant of PI-1 to PI-5 films. DETAILED DESCRIPTION

[0033] The following specific examples are intended to further illustrate the present invention in detail, rather than to limit the scope of protection of the claims.

[0034] The raw materials and reagents involved in the following examples are all conventional commercially available products.

[0035] Test and characterization methods:

[0036] (1) Nuclear magnetic resonance hydrogen spectrum and carbon spectrum test ( 1 H NMR, 13 C NMR: The chemical structures of the samples were characterized on a Bruker-Avance 400 MHz and 600 MHz superconducting NMR spectrometer using deuterated dimethyl sulfoxide (DMSO-d6) or deuterated chloroform (CDCl3) as solvent and tetramethylsilane (TMS) as the internal standard.

[0037] (2) UV-Vis absorption spectrum test: The sample was prepared into about 10 -5 The test solution of M was subjected to ultraviolet-visible absorption spectroscopy (UV-Vis) test in the test range of 200-800nm.

[0038] (3) Thermogravimetric analysis (TGA): Thermogravimetric analysis was performed using a Diamond TG / DTAEXSTAR 600 instrument (Perkin-Elmer, USA) with a nitrogen flow rate of 200 mL / min. A 1-5 mg sample was placed in an alumina crucible and the temperature was increased from 30°C to 800°C in a nitrogen atmosphere at a rate of 10°C / min.

[0039] (4) Fluorescence quantum efficiency test (Φ f ): Fluorescence quantum efficiency test (Φ f ): The maximum excitation wavelength, maximum emission wavelength, fluorescence lifetime, and fluorescence quantum efficiency of the polyamide film were measured using a Hamamatsu steady-state transient fluorescence spectrometer (Edinburgh Instruments, FLS980) using the integrating sphere method.

[0040] (5) Solubility test: Weigh 10 mg of sample into 1 mL of organic solvent and observe its dissolution at room temperature. If it is not completely dissolved, increase the temperature and continue to observe its dissolution to obtain the solubility of each polymer.

[0041] (6) Relative molecular weight test (GPC): DMF was used as the mobile phase and the measurement was performed using a DAWNHELEOS II multi-angle laser light scattering instrument from Wyatt Technology Company, USA. The flow rate was 0.1 mL / min. The sample was prepared into a 3 mg / mL solution. The sample solution was filtered through a filter with a pore size of 0.24 μm and tested at 40°C to obtain the weight average molecular weight (M) of the polymer. w ), number average molecular weight (M n ) and polydispersity index (PDI).

[0042] (7) Differential Scanning Calorimetry (DSC): The test was performed using a DSC800 differential scanning calorimeter from Perkin-Elmer, USA. Approximately 5 mg of solid sample was weighed and pressed into an aluminum crucible. The test was performed under a nitrogen atmosphere with a nitrogen flow rate of 20 mL / min. The temperature was raised from 30°C to 400°C at a heating rate of 20°C / min.

[0043] (8) Optical performance test (UV-Vis): The light transmittance of the film was tested using a Hitachi U-3310 ultraviolet-visible spectrometer (UV-Vis). The film with a thickness of 30 to 40 μm was cut into a size of 1 cm × 4 cm, the slit was 1 nm, and the test wavelength range was 200 to 800 nm.

[0044] (9) Mechanical property test: The film was tensile tested using a Shimadzu AG22000 universal electronic testing machine. The film with a thickness of 30 to 40 μm was cut into a size of 3 cm × 6 cm and tested at room temperature with a tensile rate of 10 mm / min. The average value of the three test results was taken.

[0045] (10) Water absorption test (WU): Before the test, a film with a thickness of 30-40 μm was cut into a size of 2 cm × 2 cm and dried in a vacuum oven at 120 °C for 24 h. The mass (m dry Then, the film was placed in deionized water for 24 h, and the water on the surface of the film was quickly wiped off with a paper towel. The mass of the film after water absorption (m wet ), calculate the water absorption rate of the film, test each sample 3 times, and take the average value of the results.

[0046] Water absorption calculation formula:

[0047] where m dry is the mass of the film after drying, m wet is the mass of the film after water absorption.

[0048] (11) Water contact angle test (CA): The test was performed using the OCA15EC contact angle measuring instrument from Dataphysics, Germany. The test liquid was distilled water and the test temperature was room temperature. Each sample was tested 3 to 5 times, and the results were averaged.

[0049] (12) Dielectric performance test (DC): At room temperature, the test was performed using a KEYSIGHT E4980A precision impedance analyzer. The film with a thickness of 30 to 40 μm was cut into a size of 2 cm × 2 cm, and the contact area with the conductive adhesive was 0.8 cm × 0.8 cm. The test frequency was 10 2 ~10 5 Hz, each sample was tested 3 to 5 times and the results were averaged.

[0050] (13) Fourier transform infrared spectroscopy (FT-IR): The test was performed using a PerkinElmer FT-IR Spectrum Two infrared spectrometer. The solid sample was mixed with spectrally pure potassium bromide (KBr) and pressed into a thin sheet with potassium bromide as the background. The wave number range of the test was 4000–500 cm -1 .

[0051] Example 1

[0052] (1) Synthesis of 9-(2-trifluoromethyl-4-nitrophenoxy)-10-(2-trifluoromethyl-4-nitrophenyl)anthracene (NTPNTPA)

[0053]

[0054] In a 500mL dry three-necked flask with a nitrogen inlet, anthrone (19.42g, 0.1mol), 2-fluoro-5-nitrobenzotrifluoride (46.0g, 0.22mol), potassium tert-butoxide (28.0g, 0.25mol) and DMF (300mL) were added and reacted at about 140°C under a N2 atmosphere for 12h. After the reaction, the reaction solution was cooled to room temperature, and then the reaction solution was slowly added dropwise to a stirred sodium chloride / ammonium chloride saturated aqueous solution to precipitate a yellow-brown viscous solid. 100mL of hydrochloric acid solution was added, stirred until no longer viscous, filtered, and washed with water until neutral to obtain a yellow crude product. The product was vacuum dried in a vacuum drying oven at 100°C for 24h. The DMF was then recrystallized, filtered, and the solid product obtained after drying was precipitated with a mixture of dichloromethane and petroleum ether (V DCM :V PE =1:5) as the eluent, 45.8 g of a yellow solid was isolated and obtained with a yield of about 80%. The melting point was 272.3-275.6°C.

[0055] 1 H NMR (400MHz, CDCl3): δ = 8.88 (s, 1H), 8.76 (s, 1H), 8.65 (d, J = 12.1Hz, 1H), 8.15 (dd, J = 16.6, 9.2Hz, 1H), 8.01 (d, J = 8.5Hz, 2H), 7.70(dd,J=23.0,8.2Hz,1H),7.51(t,J=7.6Hz,2H),7.45(t,J=6.9Hz,2H),7.32(d,J=8.6Hz,2H),6.35(dd,J=28.2,9.2Hz,1H).

[0056] (2) Synthesis of 9-(4-amino-2-trifluoromethylphenoxy)-10-(4-amino-2-trifluoromethylphenyl)anthracene (ATPAYTA)

[0057]

[0058] 9-(2-trifluoromethyl-4-nitrophenoxy)-10-(2-trifluoromethyl-4-nitrophenyl)anthracene (5.72 g, 10 mmol), Pd / C (0.5 g), and ethanol (30 mL) were added to a 250 mL dry three-necked flask. Under a N2 atmosphere, the oil bath temperature was raised to 60°C. A mixed solution of hydrazine hydrate / anhydrous ethanol (1:1, 20 mL) was then slowly added dropwise to the reaction solution, and the temperature was raised to 80°C and stirred for 10 hours. After the reaction was completed, the reaction solution was filtered while hot through a suction funnel equipped with filter paper to remove palladium carbon. The filter cake was dissolved with dichloromethane, and the filtrate was concentrated by rotary evaporation. The crude solid product obtained by concentration was purified by column chromatography (PE / DCM as eluent, V PE / V DCM =5:1) to obtain 3.69 g of a light yellow solid with a yield of about 72% and a melting point of 278.2-282.5°C.

[0059] 1 H NMR (600MHz, CDCl3): δ = 8.09 (d, J = 8.7Hz, 2H), 7.51 (d, J = 8.7Hz, 2H), 7.39 (t, J = 7.1Hz, 2H), 7.34 (t, J = 7.0Hz, 2H), 7.23 (d, J = 2.3Hz, 1H), 7.15 (d d,J=34.3,8.1Hz,1H),7.09(s,1H),7.01(d,J=7.9Hz,1H),6.49(dd,J=15.4,9.0Hz,1H),6.03(dd,J=26.3,8.8Hz,1H),4.04(s,2H),3.56(s,2H).

[0060] Example 2

[0061] A series of homopolymeric polyimides (PIs) were synthesized by condensing the synthesized diamine monomer (ATPAYTA) with five commercial dianhydrides: pyromellitic dianhydride (PMDA), 4,4'-(hexafluoroisopropane)carboxylic dianhydride (6FDA), 3,3',4,4'-biphenylene ether tetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), and 4,4'-biphenylene ether dianhydride (ODPA). This was achieved by a two-step synthesis method. The diamine was dissolved in NMP at low temperature and then reacted with the dianhydride in a stepwise condensation reaction at low temperature to form polyamic acids (PEAAs). These polyimides (PIs) were then obtained through chemical or thermal imidization. PI-1, PI-2, PI-4, and PI-5 were chemically imidized, while PI-3 was thermally imidized.

[0062] (1) Preparation of polyimide by chemical imidization

[0063] Taking the preparation of polymer PI-1 as an example, polyimide was prepared by chemical imidization method. The specific steps are as follows: ATPAYTA (2 mmol, 1.0249 g) and redistilled NMP (5 mL) were added to a 25 mL three-necked round-bottom flask with N2, and stirred in an ice-water bath until the ATPAYTA solid was completely dissolved. PMDA (0.4362 g, 2 mmol) was then added in batches, and an appropriate amount of NMP was added to adjust the solid content of the solution to about 18%. The reaction was carried out in an ice bath for 1 h and stirred at room temperature for 11 h to obtain a viscous polyamic acid solution. The viscous solution was then diluted appropriately with NMP and a mixture of 2 mL of acetic anhydride and 2 mL of pyridine was added by injection. The mixture was stirred at room temperature for 1 hour. After mixing thoroughly, the temperature was raised to 110°C and stirred for 7 hours. After cooling to room temperature, the viscous solution was slowly added dropwise to a stirring 100 mL methanol solution using a pipette. The mixture was stirred for 3 hours and filtered to obtain a gray-brown fibrous product. The gray-brown fibrous product was wrapped with filter paper and extracted with hot methanol in a Soxhlet extractor for 24 hours. After extraction, the product was vacuum-dried at 120°C for 24 hours to obtain polyimide PI-1. Polyimides PI-2, PI-4, and PI-5 were prepared using similar methods.

[0064] (2) Preparation of polyimide by thermal imidization

[0065] Taking the preparation of polymer PI-3 as an example, a thermal imidization method was used to prepare polyimide. The specific steps are as follows: ATPAYTA (2 mmol, 1.0249 g) was added to a 25 mL three-necked round-bottom flask purged with nitrogen. The mixture was cooled in an ice-water bath. 5 mL of redistilled NMP was added and stirred until the solid was completely dissolved. BPDA (2 mmol, 0.5884 g) was then added in batches. An appropriate amount of NMP was added to adjust the solid content to approximately 18%. The reaction was continued in an ice bath for 1 hour and then at room temperature for 12 hours to obtain a viscous polyamic acid solution. The reaction solution was diluted to an appropriate concentration with the solvent NMP and completely dissolved into a homogeneous, transparent solution. The solution was then filtered through a nylon filter and placed in a refrigerator to remove bubbles. The solution was then applied to a clean 5 cm × 5 cm glass plate using a cast method on a constant temperature heating table and heated at 80°C for 8 hours to prepare a polyamic acid film. The film was then placed in a high-temperature vacuum oven and imidized using a gradient temperature increase method, namely, at temperatures of 100° C., 145° C., 200° C., 250° C., and 300° C., to finally obtain a polyimide film (PI-3).

[0066]

[0067] Example 3

[0068] Preparation of Fluorinated Polyimide Films Containing Phenylanthracene Structure

[0069] For example, the preparation of polyimide PI-1 thin films involves dissolving a 0.1g sample of PI-1 in an appropriate amount of NMP to obtain a uniform, transparent, and fluid viscous liquid. The viscous liquid is then filtered through a nylon filter and placed in a refrigerator to remove any bubbles. A clean 5cm x 5cm square glass plate is then placed on a constant-temperature heating plate at 80°C. Once the temperature stabilizes, the polyimide viscous liquid is evenly spread across the glass plate using a cast-on method, starting from the center. The polyimide viscous liquid is then dried under infrared light for 8 hours to slowly evaporate most of the solvent. The film is then transferred to a constant-temperature vacuum drying oven at 120°C and dried for another 24 hours. After cooling to room temperature, the film is removed from the glass plate, resulting in a polyimide film of uniform thickness, PI-1. Other polyimide films were prepared using similar methods.

[0070] Performance testing:

[0071] (1) Structural characterization of fluorinated polyimide containing phenylanthracene structure

[0072] The Fourier transform infrared absorption spectra of the five polyimides PI-1 to PI-5 in this series are as follows Figure 1 As shown, 1783cm –1 and 1726cm –1 The absorption peaks at 743 cm are the symmetric and asymmetric stretching vibration peaks of C=O on the imide ring; –1 The peak at 1378 cm is the bending vibration absorption peak of C=O on the imide ring; –1 The peak at 1320 cm is the stretching vibration absorption peak of CN on the imide ring; –1 The peak at 1240 cm is the characteristic absorption peak of trifluoromethyl (-CF3); –1 The peak at is the characteristic absorption peak of ether bond (COC); and at a wave number of 3200 cm –1 and 1520cm –1 The characteristic absorption peaks of the amidic acid structure disappeared. The above results show that the imidization has been successful, and the chemical structure of this series of polyimides has been confirmed by FT-IR spectrum.

[0073] (2) Molecular weight

[0074] The polymer samples were dissolved in DMF, and the molecular weights of the polyimides in this series were measured using gel chromatography and multi-angle laser light scattering (undissolved samples were not tested). The test data are shown in Table 1. As can be seen from Table 1, the molecular weights of the polyimides in this series are all above 100,000, which is conducive to polymer film formation.

[0075] Table 1. Molecular weight of PI-1 to PI-5

[0076]

[0077] a M W : weight average molecular weight; Mn: number average molecular weight; PDI: dispersion index (M W / Mn).

[0078] (3) Solubility

[0079] Table 2. Solubility of PI-1 to PI-5

[0080]

[0081]

[0082] a Solubility: +++Soluble at room temperature; +––Partially soluble when heated; ++–Completely soluble after heating; –––Insoluble when heated.

[0083] Table 2 details the solubility test results for the polyimides PI-1 to PI-5 in some common organic solvents. As can be seen from Table 2, this series of polyimides exhibits excellent solubility, with the best solubility in DMAc, NMP, THF, and pyridine. This is primarily due to the presence of trifluoromethyl groups and ether bonds in the backbone, which increase the free volume, disrupt the tight stacking of the molecular chains, and reduce the intermolecular interactions of the polyimide, thereby improving the solubility of the polymer. The table also shows that PI-2 in this series exhibits good solubility due to the presence of more trifluoromethyl side groups in its backbone, which further inhibits the stacking of the molecular chains and thus improves solubility. PI-3 exhibits the worst solubility, being insoluble in CHCl₃, acetone, and toluene at room temperature or upon heating. It requires heating to completely dissolve in DMF, DMSO, and m-cresol, due to the rigid biphenyl structure in its backbone.

[0084] (4) Light transmission performance

[0085] The light transmittance of a sample film with a thickness of about 30 to 40 μm was analyzed by UV-visible spectrometer, and the obtained data was plotted as a UV-visible spectrum (UV-vis) curve with the morphology attached, such as Figure 2 The corresponding data are shown in Table 3.

[0086] From Table 3, Figure 2It can be seen that the cutoff wavelength (λ0) of this series of polyimide films is within the range of 410.5 to 421.5 nm, the transmittance is above 75% at a wavelength of 800 nm, and the transmittance is 25.6% to 85.1% at a wavelength of 500 nm. Among them, PI-2 has the best transmittance, with the smallest cutoff wavelength (410.5 nm). Its transmittance reaches 85.1%, 88.7%, 89.6% and 90.0% at 500 nm, 600 nm, 700 nm and 800 nm, respectively. Obviously, this is because both the diamine and 6FDA monomers contain trifluoromethyl (-CF3), which greatly improves the optical transparency of the polymer. Among them, PI-3 has the worst light transmittance, showing the lowest transmittance (75.4%) and the largest cutoff wavelength (421.5nm) at 800nm. This is because it contains a large amount of biphenyl rigid structure, which enhances the intermolecular interaction and increases the charge complexation transfer effect, thereby reducing its light transmittance.

[0087] Table 3. Optical properties of PI-1 to PI-5

[0088]

[0089] a Transmittance at 500nm, 600nm, 700nm, 800nm; b Cut-off wavelength.

[0090] (5) Thermal performance

[0091] Table 4. Thermal properties of PI-1 to PI-5

[0092]

[0093] a Glass transition temperature; b Residual carbon rate at 800℃; cT max : Maximum thermal weight loss temperature; T 5％ :5% thermal weight loss temperature; T 10％ :10% thermal weight loss temperature.

[0094] The thermal properties of this series of polyimides are analyzed by thermogravimetric analysis and DSC. The thermogravimetric and DSC curves of polyimides PI-1 to PI-5 are shown in Figure 2. Figure 3 (a) Figure 3 (b) is shown, and the specific values are listed in Table 4. It can be seen that this series of polyimides exhibits a higher glass transition temperature (T g), the temperature range is 242.4~300.5℃, and the maximum thermal weight loss temperatures in a nitrogen environment are relatively high, all above 560℃; the thermal weight loss temperatures at 5% are 369.6~490.6℃, the thermal weight loss temperatures at 10% are 508.5~535.4℃, and the residual carbon rate at 800℃ is 50.2~54.4%, indicating that this series of polymers has excellent heat resistance. This may be because the main chain of the polymer contains a relatively rigid anthracene structure, which hinders the intramolecular rotation and restricts the movement of the molecular chain, thereby making PI-1 to PI-5 exhibit good heat resistance.

[0095] Among them, PI-3 has the highest glass transition temperature (T g =242.4℃) and has the best heat resistance, the highest maximum thermal weight loss temperature (577.5℃) and residual carbon rate (54.4%). This is because its main chain contains a relatively rigid twisted non-coplanar biphenyl structure, which restricts the movement of the molecular chain, makes the polymer molecular chains densely packed, and has a strong intermolecular interaction force, making the glass transition temperature higher and not easy to decompose at high temperature. In contrast, PI-2 has the lowest glass transition temperature (T g =300.5℃) and has the worst heat resistance, with the lowest maximum thermal weight loss temperature (568.0℃) and residual carbon rate (50.2%). This is because its main chain contains a large number of flexible trifluoromethyl groups, which increases the free volume between molecules and makes the molecular chain easy to move, resulting in a lower temperature required for glass transition and poor heat resistance.

[0096] (6) Mechanical properties

[0097] The stress-strain curves of polyimide PI-1 to PI-5 films are shown in Figure 2. Figure 4 The tensile strength, elastic modulus, and elongation at break are shown in Table 5. The tensile strength of this type of polyimide film ranges from 77.83 to 87.47 MPa, the elastic modulus ranges from 1.25 to 1.88 GPa, and the elongation at break ranges from 6.45 to 10.0%, demonstrating excellent mechanical properties. PI-2 has more trifluoromethyl flexible groups, which improves its deformability, resulting in the highest tensile strength (87.47 MPa) and the lowest elastic modulus (1.30 GPa). The presence of a very rigid biphenyl structure in PI-3 results in the highest elastic modulus (1.88 GPa) and the lowest elongation at break (6.45%). PI-4, due to the addition of the flexible carbonyl group, has the highest elongation at break (10.0%).

[0098] Table 5. Mechanical properties of PI-1 to PI-5

[0099]

[0100] a T s : tensile strength; T m : elastic modulus; E b : Elongation at break.

[0101] (7) Water absorption and water contact angle

[0102] As shown in Table 6, the water contact angles of the polyimide films PI-1 to PI-5 measured at room temperature ranged from 72.5 to 86.6°, and the water absorption rates ranged from 0.83 to 1.65%, indicating relatively low water absorption. PI-2 had the lowest water absorption (0.83%) and the highest water contact angle, likely due to the introduction of a large number of trifluoromethyl hydrophobic groups into the PI-2 molecular chain, which reduces water absorption. PI-5 had the highest water absorption (1.65%) and the lowest water contact angle, likely due to the numerous ether bonds in the PI-5 backbone, which facilitate intermolecular interactions (hydrogen bonding) with water molecules, resulting in the highest water absorption.

[0103] Table 6. Water absorption and contact angle of PI-1 to PI-5

[0104]

[0105] (8) Dielectric properties

[0106] Table 7 shows the dielectric constants of polyimide films PI-1 to PI-5 measured at three different frequencies (0.1 kHz, 1.0 kHz, and 10 kHz) at room temperature. The table shows that the dielectric constants of these polyimides range from 2.15 to 3.60 at 0.1 kHz, 1.80 to 3.34 at 1.0 kHz, and 1.70 to 3.14 at 10 kHz. This series of polyimides exhibits relatively low dielectric constants, primarily due to the introduction of numerous trifluoromethyl side groups and bulky, non-planar phenylanthracene structures into the polyimide backbone. This increases the free volume of the polyimide, widens the molecular spacing, and reduces its polarizability, resulting in excellent dielectric properties. PI-2, due to its higher content of trifluoromethyl groups, has the lowest dielectric constant. PI-5 exhibits a higher dielectric constant due to its greater water absorption.

[0107] Table 7. Dielectric properties of PI-1 to PI-5

[0108]

Claims

1. A fluorinated polyimide containing a phenylanthracene structure, characterized in that: It has a molecular structure of formula 1: in, Ar is 2. The method for preparing a fluorinated polyimide containing a phenylanthracene structure according to claim 1, characterized in that: The following steps are involved: 1) subjecting a diamine monomer and a dianhydride monomer to a condensation polymerization reaction to obtain a polyamic acid intermediate; 2) chemical imidization of the polyamic acid intermediate under the promotion of acetic anhydride and pyridine; or thermal imidization of the polyamic acid intermediate to obtain a fluorinated polyimide containing a phenylanthracene structure; The diamine monomer has a structure of Formula 2: The dianhydride monomer has a structure of Formula 3: Among them, Ar is 3. The method for preparing a fluorinated polyimide containing a phenylanthracene structure according to claim 2, wherein: The conditions of the polycondensation reaction are: first react at a temperature of -5°C to 5°C for 0.5 to 1.5 hours, and then continue to stir and react at room temperature for 10 to 12 hours.

4. The method for preparing a fluorinated polyimide containing a phenylanthracene structure according to claim 2 or 3, characterized in that: The polycondensation reaction is carried out in anhydrous N-methylpyrrolidone.

5. The method for preparing a fluorinated polyimide containing a phenylanthracene structure according to claim 4, characterized in that: The amount of anhydrous NMP used is to maintain the solid content of the polymerization system at 15-25%.

6. The method for preparing a fluorinated polyimide containing a phenylanthracene structure according to claim 2, wherein: The chemical imidization conditions are as follows: first, add acetic anhydride and pyridine and stir evenly at room temperature, then heat to 105-115° C. and stir to react for 6-8 hours.

7. The method for preparing a fluorinated polyimide containing a phenylanthracene structure according to claim 2, wherein: The conditions for the thermal imidization are as follows: the polyamic acid intermediate is heated at 70-90° C. for 6-10 hours to volatilize the solvent, and then imidization is carried out by gradient heating; the gradient heating process is: 90-110° C., heat preservation for 0.5-1.5 hours; 140-150° C., heat preservation for 0.5-1.5 hours; 190-210° C., heat preservation for 0.5-1.5 hours; 240-260° C., heat preservation for 0.5-1.5 hours; 290-310° C., heat preservation for 0.2-0.5 hours.

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