A fluorinated phenylanthracene-containing polyimide and a method for preparing the same

Abstract

This invention discloses a fluorinated polyimide containing phenyl anthracene and its preparation method, belonging to the field of polymer materials technology. The fluorinated polyimide containing phenyl anthracene has the following molecular structure: by introducing asymmetric phenyl anthracene structural units with trifluoromethyl side groups, flexible ether bonds, and twisted non-coplanar structures into the polymer backbone, this polyimide possesses excellent comprehensive properties, such as superior solubility, heat resistance, optical properties, mechanical properties, crystallinity, dielectric properties, and hydrophobicity.

Description

Technical Field

[0001] This invention relates to a polyimide, particularly to a fluorinated polyimide containing a phenyl anthracene structure, and also to its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] Polyimide, as a high-performance polymer, possesses excellent properties such as high-temperature stability, solvent resistance, and high strength, making it widely used in aerospace, microelectromechanical systems, and electrical insulation fields in various forms, including films, fibers, foams, adhesives, composites, and coatings. However, due to its unique molecular structure, polyimide exhibits drawbacks such as poor solubility, poor optical transparency, high dielectric constant, and high water absorption, severely hindering its application in some emerging high-tech fields. In particular, traditional aromatic polyimides also suffer from difficulties in melting and dissolving, as well as high curing temperatures, making processing challenging. Furthermore, the excessive rigidity of traditional aromatic polyimide materials makes them hard and brittle, resulting in insufficient strength and making it difficult to achieve an effective balance between mechanical strength and thermal expansion coefficient in microelectronic applications. The charge-transfer complex (CTC) effect generated within and between polyimide molecular chains forms charge-transfer complexes, reducing the transparency of polyimide films and severely limiting their application in optoelectronics. Especially with the rapid development of flexible display technology and 5G technology, this problem needs to be addressed as soon as possible.

[0003] In response to the limitations of polyimide in terms of solubility, light transmittance and mechanical properties, various modification methods have been proposed in the existing technology. The main components include 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, Yu Y, 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.).Methods such as "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) can be used to adjust the packing density of molecular chains, 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 novel polyimides with better overall performance. However, these existing modification methods are all singular and limited, and the overall performance of polyimides is difficult to improve effectively. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the first objective of this invention is to provide a fluorinated polyimide containing a phenyl anthracene structure. The key lies in introducing a structural unit containing a large-volume trifluoromethyl side group, a flexible ether bond, and a twisted, non-coplanar, asymmetric phenyl anthracene structure into the polymer backbone. This effectively hinders the stacking of polyimide molecular chains and disrupts the formation of CTCs, increasing the inter-chain spacing and thus improving its solubility and optical transparency. Simultaneously, the introduction of the trifluoromethyl hydrophobic group effectively reduces the water absorption rate of the polyimide, significantly lowering its dielectric constant. This results in excellent overall performance in terms of solubility, heat resistance, optical properties, mechanical properties, crystallinity, dielectric properties, and hydrophobicity.

[0005] The second objective of this invention is to provide a method for preparing a fluorinated polyimide containing a phenyl anthracene structure. This polyimide monomer is readily available and can be synthesized using a mature polymerization process, which is beneficial for industrial production.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a fluorinated polyimide containing a phenyl anthracene structure, which has the molecular structure of Formula 1:

[0007]

[0008] in,

[0009] Ar for

[0010] The key to the fluorinated phenyl anthracene-containing polyimide of this invention lies in the introduction of a special fluorinated phenyl anthracene-containing structural unit. This fluorinated phenyl anthracene-containing structural unit has the following characteristics: First, it has flexible ether bonds (–O–), which can, to a certain extent, disrupt the regularity of the polymer molecular backbone, reduce the rigidity of the backbone structure, and improve the solubility and flexibility of the polymer; second, it has a twisted non-coplanar structure, which can effectively prevent the close packing of polymer molecular chains, weaken its crystallization ability, reduce the intermolecular interaction forces, and increase the free volume between molecules, thereby reducing its melting temperature and improving its solubility; third, it has a non-parallel structure. The structure of the polyimide structure can disrupt the regularity of the polymer backbone and impart polarity, thus improving its solubility. Furthermore, the introduction of numerous trifluoromethyl side groups not only effectively prevents the close packing of polymer chains and weakens their crystallinity, but also enhances their solubility, while simultaneously imparting a low dielectric constant and improving their hydrophobic properties. Finally, the large-volume side groups can reduce the regularity of the backbone, increase the spacing between polymer chains, thereby effectively reducing the degree of backbone packing, weakening inter- and intra-chain interactions, and decreasing the probability of CTC formation, thereby improving the polymer's solubility and light transmittance. In summary, the introduction of fluorinated phenyl anthracene structures can endow polyimides with excellent comprehensive properties.

[0011] This invention also provides a method for preparing fluorinated polyimide containing a phenyl anthracene structure, which includes the following steps:

[0012] 1) The diamine monomer and the dianhydride monomer are subjected to a polycondensation reaction to obtain a polyamic acid intermediate;

[0013] 2) The polyamic acid intermediate is chemically imidized under the promotion of acetic anhydride and pyridine; or, the polyamic acid intermediate is thermally imidized to obtain fluorinated polyimide containing phenyl anthracene structure.

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

[0015]

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

[0017]

[0018] Where Ar is

[0019] As a preferred embodiment, the polycondensation reaction is carried out under the following conditions: first, the reaction is carried out at a temperature of -5℃ to 5℃ for 0.5 to 1.5 hours, and then the reaction is continued to be stirred at room temperature for 10 to 12 hours.

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

[0021] As a preferred embodiment, the amount of anhydrous NMP used is such that the solid content of the polymerization system is maintained at 15-25%.

[0022] As a preferred embodiment, the chemical imidization conditions are as follows: first, acetic anhydride and pyridine are added and stirred evenly at room temperature, then the temperature is raised to 105-115°C and stirred for 6-8 hours.

[0023] As a preferred embodiment, the thermal imidization conditions are as follows: the polyamic acid intermediate is heated at 70–90°C for 6–10 h to evaporate the solvent, followed by imidization through a gradient temperature increase; the gradient temperature increase process is as follows: 90–110°C, held for 0.5–1.5 h; 140–150°C, held for 0.5–1.5 h; 190–210°C, held for 0.5–1.5 h; 240–260°C, held for 0.5–1.5 h; 290–310°C, held for 0.2–0.5 h.

[0024] Compared with the prior art, the beneficial technical effects of this invention are as follows:

[0025] This invention introduces 9-(4-amino-2-trifluoromethylphenoxy)-10-(4-amino-2-trifluoromethylphenyl)anthracene repeating units containing trifluoromethyl, phenylanthracene structures and ether bonds into the polyimide backbone, which can significantly improve the solubility, optical properties, heat resistance, mechanical properties, dielectric properties and hydrophobic properties of aromatic polyimides.

[0026] 1) The polyimide of the present invention has a high glass transition temperature (T0). g =242.4~300.5℃), and has excellent thermal properties (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, light transmittance at 500nm is 25.6%~85.1%), and the saturated water absorption rate is less than 2%.

[0027] 2) The polyimide of this invention exhibits the best performance with a carbon residue of 50.2% at 800℃, demonstrating 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 it possesses the highest tensile strength (T). s=87.47MPa); it has the best light transmittance, with the film having a light transmittance of over 85% at 500nm; it has good insulation (dielectric constant <3) and a saturated water absorption rate of 0.83%, indicating that it has broad application prospects in high humidity environments. Attached Figure Description

[0028] Figure 1 The infrared spectra of PI-1 to PI-5 are shown.

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

[0030] Figure 3 The thermogravimetric curves (a) and DSC curves (b) for PI-1 to PI-5 are shown.

[0031] Figure 4 The stress-strain curves are for PI-1 to PI-5.

[0032] Figure 5 represents the dielectric constant of PI-1 to PI-5 thin films. Detailed Implementation

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

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

[0035] Testing and characterization methods:

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

[0037] (2) Ultraviolet-Vis absorption spectroscopy (UV-Vis) test: The sample was prepared to approximately 10 μL using a Hitachi U-3100 spectrophotometer. -5 The test solution M was subjected to ultraviolet-visible absorption spectroscopy (UV-Vis) testing, with a test range of 200-800 nm.

[0038] (3) Thermogravimetric analysis (TGA): Thermogravimetric analysis was performed using a PerkinElmer Diamond TG / DTAEXSTAR600 instrument with a nitrogen flow rate of 200 mL / min. 1-5 mg of sample was placed in an alumina crucible and tested in a nitrogen atmosphere, starting at 30 °C and increasing to 800 °C 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 polyamide thin films were measured using an integrating sphere method with a Hamamatsu steady-state transient fluorescence spectrometer (Edinburgh Instruments, FLS980).

[0040] (5) Solubility test: Weigh 10mg of sample into 1mL of organic solvent and observe its solubility at room temperature. If it fails to dissolve completely, raise the temperature and continue to observe its solubility to obtain the solubility of each polymer.

[0041] (6) Relative molecular weight determination (GPC): Using DMF as the mobile phase, the GPC was determined using a DAWNHELEOS II multi-angle laser light scattering instrument from Wyatt Technologies, Inc., USA, at a flow rate of 0.1 mL / min. The sample was prepared into a 3 mg / mL solution, filtered through a 0.24 μm pore size filter, and tested at 40 °C to obtain the weight-average molecular weight (M). w Number-average molecular weight (M) n ) and the Polydispersity Index (PDI).

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

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

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

[0045] (10) Water Absorption Test (WU): Before the test, the film with a thickness of 30-40 μm was cut into 2 cm × 2 cm pieces and dried in a vacuum oven at 120 °C for 24 h. The mass (m) was then measured. dry The membrane was then placed in deionized water for 24 hours, and the surface moisture was quickly wiped off with a paper towel. The mass of the membrane after absorbing water was then measured (m). wet The water absorption rate of the film was calculated. Each sample was tested three times, and the average value of the results was taken.

[0046] Water absorption rate calculation formula:

[0047] Where m dry For the mass of the film after drying, m wet This refers to the mass of the film after it absorbs water.

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

[0049] (12) Dielectric property testing (DC): At room temperature, the test was conducted using a Keysight E4980A precision impedance analyzer. A 30–40 μm thick film was cut into 2 cm × 2 cm pieces, with a contact area of ​​0.8 cm × 0.8 cm with the conductive adhesive. The test frequency was 10 Hz. 2 ~10 5 Hz, each sample was tested 3 to 5 times, and the average value of the results was taken.

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

[0051] Example 1

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

[0053]

[0054] In a 500 mL dry three-necked flask with a nitrogen inlet, anthrone (19.42 g, 0.1 mol), 2-fluoro-5-nitrotrifluorotoluene (46.0 g, 0.22 mol), potassium tert-butoxide (28.0 g, 0.25 mol), and DMF (300 mL) were added. The mixture was reacted at approximately 140 °C for 12 h under a nitrogen atmosphere. After the reaction was complete, the reaction solution was cooled to room temperature, and then slowly added dropwise to a stirred, saturated aqueous solution of sodium chloride / ammonium chloride to precipitate a yellow-brown viscous solid. 100 mL of hydrochloric acid solution was added, and the mixture was stirred until it was no longer viscous. The solid was filtered, washed with water until neutral, and a yellow crude product was obtained. This crude product was dried under vacuum at 100 °C for 24 h. The DMF was then recrystallized, filtered, and dried. The resulting solid product was then reacted with a mixture of dichloromethane and petroleum ether (V... DCM :V PE Using a 1:5 eluent, column chromatography was performed to separate 45.8 g of a yellow solid, with a yield of approximately 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] Add 5.72 g (10 mmol) of 9-(2-trifluoromethyl-4-nitrophenoxy)-10-(2-trifluoromethyl-4-nitrophenyl)anthracene, 0.5 g of Pd / C, and 30 mL of ethanol to a 250 mL dry three-necked flask. Incubate under a nitrogen atmosphere. ，The oil bath temperature was raised to 60°C. Then, a mixture of hydrazine hydrate and anhydrous ethanol (1:1, 20 mL) was slowly added dropwise to the reaction solution, and the temperature was raised to 80°C. The mixture was stirred for 10 hours. After the reaction was complete, the hot reaction solution was filtered through a vacuum funnel lined with filter paper to remove palladium on carbon. The filter cake was dissolved in dichloromethane, and the filtrate was concentrated by rotary evaporation. The concentrated crude solid product was purified by column chromatography (PE / DCM as eluent, V...). PE / V DCM The ratio of 5:1 yielded 3.69 g of a pale yellow solid, with a yield of approximately 72%. The melting point was 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] The synthesized diamine monomer (ATPAYTA) was condensed with five commercially available dianhydrides: pyromellitic dianhydride (PMDA), 4,4'-(hexafluoroisopropane)carboxylic acid dianhydride (6FDA), 3,3',4,4'-biphenyl ether dianhydride (BPDA), 3,3',4,4'-benzophenone dianhydride (BTDA), and 4,4'-biphenyl ether dianhydride (ODPA). A series of homopolymer polyimides were synthesized using a two-step method. Specifically, the diamine was dissolved in NMP at low temperature and then reacted with dianhydrides in a stepwise polycondensation reaction at low temperature to obtain polyamic acid (PEAAs). These PEAAs were then subjected to chemical imidization or thermal imidization to obtain polyimides (PIs). 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. 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. The mixture was stirred in an ice-water bath until the ATPAYTA solid was completely dissolved. Then, PMDA (0.4362 g, 2 mmol) was 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 under ice bath conditions for 1 h, and then stirred at room temperature for 11 h to obtain a viscous polyamic acid solution. The viscous liquid was then appropriately diluted with NMP and injected with a mixture of 2 mL acetic anhydride and 2 mL pyridine. The mixture was stirred at room temperature for 1 hour, and after thorough mixing, the temperature was raised to 110°C and stirred for 7 hours. After cooling to room temperature, the viscous liquid was slowly added dropwise to 100 mL of methanol solution under stirring using a pipette. The mixture was stirred for 3 hours, filtered, and a gray-brown fibrous product was obtained. The gray-brown fibrous product was wrapped in 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 a similar method.

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

[0065] Taking the preparation of polymer PI-3 as an example, polyimide was prepared by thermal imidization. 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 flask was cooled in an ice-water bath. 5 mL of redistilled NMP was added and stirred until the solid was completely dissolved. Then, BPDA (2 mmol, 0.5884 g) was added in batches, and an appropriate amount of NMP was added to adjust the solid content to about 18%. The reaction was carried out under ice bath conditions for 1 h, followed by a reaction at room temperature for 12 h to obtain a viscous polyamic acid solution. The viscous solution was diluted to an appropriate concentration with NMP to completely dissolve it into a homogeneous and transparent solution. After filtration through a nylon filter, the solution was placed in a refrigerator to remove air bubbles. The solution was then coated onto a clean 5 cm × 5 cm glass plate using a flow coating method on a constant-temperature heating stage and heated at 80 °C for 8 h to prepare a polyamic acid film. The film was then placed in a high-temperature vacuum oven and imidized using a gradient heating method at temperatures of 100℃, 145℃, 200℃, 250℃ and 300℃ to finally obtain a polyimide film (PI-3).

[0066]

[0067] Example 3

[0068] Preparation of fluorinated polyimide films containing phenyl anthracene structure

[0069] Taking the preparation of polyimide PI-1 film as an example, a PI-1 sample (0.1g) was dissolved in an appropriate amount of NMP to obtain a homogeneous, transparent, and highly fluid viscous liquid. The viscous liquid was then filtered through a nylon filter and placed in a refrigerator to remove air bubbles. A cleaned 5cm × 5cm square glass plate was placed on an 80℃ constant-temperature heating stage. Once the temperature stabilized, the polyimide viscous liquid was spread evenly on the glass plate from the center using a flow-casting method. It was then dried under infrared light for 8 hours to slowly evaporate most of the solvent. The plate was then transferred to a 120℃ constant-temperature vacuum drying oven and dried for another 24 hours. After cooling to room temperature, the film detached from the glass plate, yielding a uniformly thick polyimide film PI-1. Other polyimide films were prepared using a similar method.

[0070] Performance testing:

[0071] (1) Structural characterization of fluorinated polyimide containing phenyl anthracene 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 peak at 743 cm⁻¹ represents the symmetric and asymmetric stretching vibrations of the C=O ring on the imide ring; –1 The peak at 1378 cm⁻¹ is the absorption peak of the bending vibration of C=O on the imide ring; –1 The peak at 1320 cm⁻¹ is the absorption peak of the stretching vibration of CN on the imide ring; –1 The peak at 1240 cm⁻¹ is the characteristic absorption peak of trifluoromethyl (-CF₃); –1 The peak at 3200 cm⁻¹ is a characteristic absorption peak of the ether bond (COC); and at a wavenumber of 3200 cm⁻¹... –1 and 1520cm –1 All characteristic absorption peaks in the amyl acid structure disappeared. These results indicate successful imidization, and the chemical structures of this series of polyimides were confirmed using FT-IR spectroscopy.

[0073] (2) Molecular weight

[0074] The polymer samples were dissolved in DMF, and the molecular weight of this series of polyimides was determined by gel permeation chromatography and multi-angle laser light scattering (undissolved samples were not tested). The test data are shown in Table 1. Table 1 shows that the molecular weights of this series are all above 100,000, which is beneficial for polymer film formation.

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

[0076]

[0077] a M W Weight-average molecular weight; Mn: Number-average molecular weight; PDI: Dispersion index (Mn) 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 upon heating; ++– Completely soluble upon heating; ––– Insoluble upon heating.

[0083] Table 2 details the solubility test results of the polyimide series PI-1 to PI-5 in some common organic solvents. As can be seen from Table 2, this series of polyimides exhibits good solubility, with the best solubility in DMAc, NMP, THF, and pyridine. This is mainly due to the presence of trifluoromethyl and ether bonds in the main chain, which increases the free volume, disrupts the tight packing of the molecular chains, and reduces the intermolecular forces of the polyimide, thereby improving the polymer's solubility. The table also shows that PI-2 in this series has good solubility because its main chain contains more trifluoromethyl side groups, further inhibiting the packing of the molecular chains and thus improving solubility. PI-3 has the worst solubility, being insoluble in CHCl3, acetone, and toluene at both room temperature and upon heating. Furthermore, it requires heating to completely dissolve in DMF, DMSO, and m-cresol because the main chain of PI-3 contains a rigid biphenyl structure.

[0084] (4) Light transmittance

[0085] The transmittance of sample films with a thickness of approximately 30–40 μm was analyzed using ultraviolet-visible spectroscopy. The obtained data were plotted as ultraviolet-vis (UV-vis) curves, and the morphology was also included. Figure 2 As shown, the corresponding data is listed in Table 3.

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

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

[0088]

[0089] a Transmittance at 500nm, 600nm, 700nm, and 800nm; b Cutoff wavelength.

[0090] (5) Thermal properties

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

[0092]

[0093] a Glass transition temperature; b Carbon residue at 800℃; cT max Maximum thermogravimetric temperature; T 5％ 5% thermal weight loss temperature; T 10％ 10% thermal weight loss temperature.

[0094] The thermal properties of this series of polyimides were analyzed using thermogravimetric analysis (TGA) and digital subtraction angiography (DSC). The TGA and DSC curves for polyimides PI-1 to PI-5 are shown below. Figure 3 (a) Figure 3 As shown in (b), the specific values ​​are listed in Table 4. It can be seen that this series of polyimides exhibits a high glass transition temperature (T0). gThe temperature range is 242.4–300.5℃, and the maximum thermal weight loss temperature in a nitrogen environment is relatively high, all above 560℃. The thermal weight loss temperature at 5% is 369.6–490.6℃, and the thermal weight loss temperature at 10% is 508.5–535.4℃. The carbon residue at 800℃ is 50.2–54.4%, indicating that this series of polymers has excellent heat resistance. This may be due to the presence of a relatively rigid anthracene group structure in the polymer backbone, which hinders intramolecular rotation and restricts the movement of the molecular chain, thus enabling PI-1 to PI-5 to 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, with the highest maximum thermogravimetric temperature (577.5℃) and residual carbon content (54.4%). This is because its main chain contains a rigid, twisted, non-coplanar biphenyl structure, which restricts the movement of molecular chains, resulting in a close packing of polymer molecular chains and strong intermolecular forces. This leads to a higher glass transition temperature and makes it less prone to decomposition at high temperatures. In contrast, PI-2 has the lowest glass transition temperature (T = 242.4℃). 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, making the molecular chain move easily, resulting in a lower temperature required for glass transition and poorer heat resistance.

[0096] (6) Mechanical properties

[0097] The stress-strain curves of polyimide PI-1 to PI-5 films are as follows: Figure 4 As shown in Table 5, the tensile strength, elastic modulus, and elongation at break of this type of polyimide film are as follows. It can be seen that the tensile strength of this type of polyimide film is 77.83–87.47 MPa, the elastic modulus is 1.25–1.88 GPa, and the elongation at break is 6.45–10.0%, exhibiting good mechanical properties. PI-2 has more trifluoromethyl flexible groups, which improves its deformation ability, resulting in the highest tensile strength (87.47 MPa) and a relatively low elastic modulus (1.30 GPa). The presence of a highly rigid biphenyl structure in the PI-3 structure leads to the highest elastic modulus (1.88 GPa) and the lowest elongation at break (6.45%). PI-4 has the highest elongation at break (10.0%) due to the addition of the flexible carbonyl group.

[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 rate and water contact angle

[0102] Table 6 shows that the water contact angles of the polyimide films PI-1 to PI-5 in this series ranged from 72.5° to 86.6° at room temperature, and the water absorption rates ranged from 0.83% to 1.65%, exhibiting relatively low water absorption. PI-2 showed the lowest water absorption rate (0.83%) and the highest water contact angle, likely due to the introduction of numerous trifluoromethyl hydrophobic groups into the PI-2 molecular chain, which reduced water absorption. PI-5 showed the highest water absorption rate (1.65%) and the smallest water contact angle, possibly because the numerous ether bonds introduced into the PI-5 main chain readily form intermolecular forces (hydrogen bonds) with water molecules, resulting in the highest water absorption rate.

[0103] Table 6. Water absorption rate 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. As can be seen from the table, the dielectric constants of this series of polyimides are 2.15–3.60 at 0.1 kHz, 1.80–3.34 at 1.0 kHz, and 1.70–3.14 at 10 kHz. This indicates that this series of polyimides has relatively low dielectric constants, mainly because the introduction of more trifluoromethyl side groups and large-volume non-planar phenyl anthracene structures into the main chain increases the free volume of the polyimide, increases the intermolecular distance, and reduces the polarizability of the polyimide, resulting in good dielectric properties. Among them, PI-2 has the lowest dielectric constant due to the presence of more trifluoromethyl groups. PI-5 has a higher dielectric constant due to its greater water absorption rate.

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

[0108]

Claims

1. A fluorinated polyimide containing a phenyl anthracene structure, characterized in that: It has the molecular structure of Formula 1: in, Ar for 2. The method for preparing a fluorinated polyimide containing a phenyl anthracene structure according to claim 1, characterized in that: Includes the following steps: 1) The diamine monomer and the dianhydride monomer are subjected to a polycondensation reaction to obtain a polyamic acid intermediate; 2) The polyamic acid intermediate is chemically imidized under the promotion of acetic anhydride and pyridine; or, the polyamic acid intermediate is thermally imidized to obtain fluorinated polyimide containing phenyl anthracene structure. The diamine monomer has the structure of Formula 2: The dianhydride monomer has the structure of Formula 3: Where Ar is 3. The method for preparing a fluorinated polyimide containing a phenyl anthracene structure according to claim 2, characterized in that: The conditions for the polycondensation reaction are as follows: first react at a temperature of -5℃ to 5℃ for 0.5 to 1.5 h, and then continue to react with stirring at room temperature for 10 to 12 h.

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

6. The method for preparing a fluorinated polyimide containing a phenyl anthracene structure according to claim 2, characterized in that: The conditions for the chemical imidization are as follows: first, add acetic anhydride and pyridine and stir evenly at room temperature, then raise the temperature to 105-115℃ and stir for 6-8 hours.

7. The method for preparing a fluorinated polyimide containing a phenyl anthracene structure according to claim 2, characterized in that: The conditions for thermal imidization are as follows: the polyamic acid intermediate is heated at 70–90°C for 6–10 h to evaporate the solvent, and then imidized by gradient heating; the gradient heating process is as follows: 90–110°C, holding for 0.5–1.5 h; 140–150°C, holding for 0.5–1.5 h; 190–210°C, holding for 0.5–1.5 h; 240–260°C, holding for 0.5–1.5 h; 290–310°C, holding for 0.2–0.5 h.

Images