Biphenyl dialicyclic dianhydride monomer, polyimide compound and preparation methods of biphenyl dialicyclic dianhydride monomer and polyimide compound

Abstract

The invention relates to the technical field of organic polymer materials, and particularly discloses a biphenyl dialicyclic dianhydride monomer, a polyimide compound and a preparation method. The bistrifluoromethyl or ether bond unit is introduced into the structure of the dianhydride monomer, so that the molecular polarity can be effectively reduced, the dipole-dipole interaction is reduced, the dielectric constant and dielectric loss of the polyimide material are remarkably reduced, and the energy loss and signal attenuation in the signal transmission process are reduced; in addition, the introduction of fluorine atoms can increase the interaction between molecules and improve the rigidity of molecular chains, so that the material is more difficult to generate chain segment movement and decomposition at high temperature, the thermal decomposition temperature is increased, and the heat resistance is enhanced; the biphenyl dialicyclic structure has high rigidity, can enhance the interaction between molecular chains and improve the movement difficulty of the molecular chains, so that the material is more stable at a high temperature, the heat resistance is improved, and the application range of the polyimide material under a high-temperature working condition is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of organic polymer materials, and in particular to a biphenyl alicyclic dianhydride monomer, a polyimide compound and a preparation method thereof. Background Art

[0002] Polyimide (PI), a high-performance polymer material with excellent overall properties, holds a crucial position in numerous key sectors, including aerospace, electronics, and automotive manufacturing, thanks to its outstanding heat resistance, good mechanical properties, and exceptional chemical stability. In aerospace, polyimide is used to manufacture high-temperature-resistant, high-strength structural components; in electronics, it is often used as an insulating material and substrate for flexible circuit boards.

[0003] Traditional polyimide materials have a high dielectric constant due to the presence of numerous polar groups in their molecular structure. This high dielectric constant can cause severe signal attenuation and delay during high-frequency signal transmission, significantly limiting improvements in communication speed and quality. Furthermore, traditional polyimides also exhibit high dielectric loss, meaning a significant amount of energy is lost as heat during signal transmission. This not only reduces energy efficiency but also causes significant overheating in devices, impacting their stability and service life. Furthermore, while the conjugated structure of the aromatic and imide rings in traditional polyimide molecular chains imparts a degree of thermal stability, the molecular chains are primarily held together by weak van der Waals forces and hydrogen bonding. These relatively weak intermolecular forces allow the molecular chains to readily absorb sufficient energy for relative sliding and conformational changes at high temperatures, resulting in reduced thermal stability. Furthermore, weak links in the molecular structure, such as the junctions between the imide and aromatic rings, can easily become starting points for thermal decomposition at high temperatures, accelerating material degradation.

[0004] Therefore, there is an urgent need to develop a new technical route that can not only effectively improve the dielectric constant and dielectric loss of polyimide, but also improve the heat resistance of polyimide materials to meet the urgent demand for high-performance polyimide materials in emerging fields. Summary of the Invention

[0005] In response to the technical problems of low heat resistance, high dielectric constant and dielectric loss, and the inability to balance thermal and dielectric properties in current polyimide materials, the present invention provides a biphenyl dialicyclic dianhydride monomer, a polyimide compound, and a preparation method.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0007] In the first aspect, the present invention provides a biphenyl alicyclic dianhydride monomer, the structure of which is shown in formula (I):

[0008]

[0009] Wherein, R is bis(trifluoromethyl) or O.

[0010] Compared with the prior art, the present invention introduces a bis(trifluoromethyl) or ether bond unit into the structure of the dianhydride monomer, which can effectively reduce the molecular polarity, reduce the dipole-dipole interaction, and significantly reduce the dielectric constant and dielectric loss of the polyimide material, thereby reducing energy loss and signal attenuation during signal transmission; in addition, the introduction of fluorine atoms can increase the interaction between molecules, improve the rigidity of the molecular chain, make the material more difficult to undergo chain segment movement and decomposition at high temperatures, increase the thermal decomposition temperature, and enhance heat resistance; the biphenyl and dialicyclic structure has high rigidity, can enhance the interaction between molecular chains, increase the difficulty of molecular chain movement, make the material more stable at high temperatures, improve heat resistance, and broaden the application range of polyimide materials under high temperature conditions.

[0011] Specifically, the structure of the biphenyl alicyclic dianhydride monomer is shown in formula (A) and formula (B):

[0012]

[0013] In a second aspect, the present invention further provides a method for preparing a biphenyl alicyclic dianhydride monomer, comprising the following steps:

[0014] Under inert atmosphere and catalyst conditions, the compound represented by formula (a) and maleic anhydride undergo Diels-Alder reaction to obtain the biphenyl alicyclic dianhydride monomer represented by formula (I);

[0015]

[0016] The reaction route is as follows:

[0017]

[0018] Furthermore, the catalyst is an iodine salt; the molar ratio of the compound represented by formula (a) to the catalyst is 1:(8-12).

[0019] Furthermore, the molar ratio of the compound represented by formula (a) to maleic anhydride is 1:(2-6).

[0020] Furthermore, the solvent of the Diels-Alder reaction is N,N-dimethylformamide; the volume mass ratio of N,N-dimethylformamide to the compound represented by formula (a) is (5-10) mL:1 g.

[0021] Furthermore, the temperature of the Diels-Alder reaction is 100°C to 150°C.

[0022] The preparation method of the dianhydride monomer provided by the present invention has high atom utilization rate and simple reaction steps, which facilitates the efficient preparation and industrial application of the dianhydride monomer.

[0023] As a specific embodiment of the present invention, after the Diels-Alder reaction is completed, a purification step is further included:

[0024] Step 1: dissolving the crude biphenyl dialicyclic dianhydride monomer in an alcohol solvent, adding thionyl chloride, and performing an esterification reaction to obtain a compound represented by formula (b);

[0025]

[0026] Step 2: dissolving the compound represented by formula (b) in an organic solvent, adding an alkaline solution, and performing a hydrolysis reaction to obtain a compound represented by formula (c);

[0027]

[0028] Step 3: Under an inert atmosphere, the compound represented by formula (c) is subjected to a dehydration cyclization reaction with acetic anhydride, followed by recrystallization to obtain a purified biphenyl dialicyclic dianhydride monomer. The specific purification route is as follows:

[0029]

[0030] The synthesis of the dianhydride monomer requires a high reaction temperature, which easily generates impurities. Furthermore, the target product is unstable and easily hydrolyzed, making purification difficult and preventing the production of a relatively pure target product. The inventors have attempted various methods to optimize the reaction conditions or perform conventional extractions on the crude product, but have been unable to obtain a relatively pure target product.

[0031] The present invention dissolves a crude biphenyl alicyclic dianhydride monomer in an alcohol solvent, and then adds thionyl chloride to carry out an esterification reaction. The reaction has good reaction selectivity for anhydride functional groups and can convert them into ester groups. The compound of formula (b) generated after the esterification reaction has different properties from impurities in the original crude product, which facilitates the subsequent removal of most impurities through simple extraction, distillation, etc.; then, the compound of formula (b) is dissolved in an organic solvent and an alkaline solution is added to carry out a hydrolysis reaction. The hydrolysis process changes the product structure, further widening the difference between the product and the residual impurities in terms of polarity and solubility, which is conducive to further separation of impurities by extraction and other methods, thereby improving the product purity; finally, the hydrolysis product (compound of formula (c)) is subjected to a dehydration cyclization reaction with acetic anhydride. The reaction can promote the efficient dehydration cyclization of carboxyl groups to form a target anhydride structure, with a high reaction conversion rate. The obtained biphenyl alicyclic dianhydride monomer has high purity, meeting the strict requirements of high-end applications on product purity.

[0032] Furthermore, in step 1, the ratio of the crude biphenyl dialicyclic dianhydride monomer to the alcohol solvent is 1 g: (3-5) mL.

[0033] Furthermore, in step 1, the alcohol solvent is methanol.

[0034] Furthermore, in step 1, the ratio of the crude biphenyl dialicyclic dianhydride monomer to thionyl chloride is 1 g: (0.5-1) mL.

[0035] Furthermore, in step 1, the temperature of the esterification reaction is 60°C to 70°C.

[0036] Furthermore, in step 2, the organic solvent is at least one of tetrahydrofuran, methanol, ethanol, acetonitrile or acetone.

[0037] Furthermore, in step 2, the alkaline solution is an aqueous solution of sodium hydroxide, potassium hydroxide, lithium hydroxide or sodium carbonate, with a mass concentration of 10% to 20%.

[0038] Furthermore, in step 2, the volume ratio of the organic solvent to the alkaline solution is 1:(0.8-1.2).

[0039] Furthermore, in step 2, the hydrolysis temperature is 60°C to 100°C.

[0040] Furthermore, in step 3, the ratio of the compound represented by formula (c) to acetic anhydride is 1 g: (5-20) mL.

[0041] Furthermore, in step three, the temperature of the dehydration cyclization reaction is 100°C to 140°C.

[0042] Furthermore, in step three, the recrystallization solvent is a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:(4-6), the recrystallization temperature is 50°C-60°C, and the recrystallization time is 30min-40min.

[0043] The above-mentioned purification process has coherent steps, mild and easy-to-control reaction conditions, and gradually removes impurities through multi-step reactions and separation operations, which can effectively improve the purity of the diphenyl dialicyclic dianhydride monomer and lay a good foundation for subsequent applications.

[0044] As a specific embodiment of the present invention, when R is a bistrifluoromethyl group, the preparation method of the compound represented by formula (a) comprises the following steps:

[0045] Under an inert atmosphere, 2,2-bis(3,4-dimethylphenyl)hexafluoropropane, N-bromosuccinimide, and an initiator are subjected to a substitution reaction in an organic solvent to obtain a compound represented by formula (a). The reaction scheme is as follows:

[0046]

[0047] Furthermore, the organic solvent is carbon tetrachloride, and the ratio of carbon tetrachloride to 2,2-bis(3,4-xylyl)hexafluoropropane is (5-10) mL:1 g.

[0048] Furthermore, the initiator is at least one of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN) or lauroyl peroxide (LPO); and the molar ratio of the initiator to 2,2-bis(3,4-xylyl)hexafluoropropane is (0.05-0.10):1.

[0049] Furthermore, the molar ratio of the N-bromosuccinimide to 2,2-bis(3,4-xylyl)hexafluoropropane is (4-5.5):1.

[0050] Furthermore, the temperature of the substitution reaction is 30°C to 65°C.

[0051] As a specific embodiment of the present invention, when R is O, the preparation method of the compound represented by formula (a) comprises the following steps:

[0052] S1, subjecting 4,4'-oxydiphthalic anhydride, methanol and thionyl chloride to an acylation reaction to obtain a compound represented by formula (a-1);

[0053]

[0054] S2, under an inert atmosphere, reducing the compound represented by formula (a-1) to obtain the compound represented by formula (a-2);

[0055]

[0056] S3, the compound represented by formula (a-2) is subjected to bromination reaction to obtain the compound represented by formula (a). The reaction scheme is as follows:

[0057]

[0058] Furthermore, in S1, the ratio of the 4,4'-oxydiphthalic anhydride to methanol is 1 g: (8-12) mL.

[0059] Furthermore, in S1, the ratio of the 4,4'-oxydiphthalic anhydride to thionyl chloride is 1 g: (2-3) mL.

[0060] Furthermore, in S1, the temperature of the acylation reaction is 50°C to 70°C.

[0061] Furthermore, in S2, the reducing agent for the reduction reaction is lithium aluminum hydride, and the molar ratio of the reducing agent to the compound represented by formula (a-1) is (1-5):1.

[0062] Furthermore, in S2, the solvent for the reduction reaction is tetrahydrofuran, and the ratio of tetrahydrofuran to the compound represented by formula (a-1) is (3-6) mL:1 g.

[0063] Furthermore, in S2, the temperature of the reduction reaction is 50°C to 66°C.

[0064] Furthermore, in S3, the solvent for the bromination reaction is dichloromethane, and the ratio of dichloromethane to the compound represented by formula (a-2) is (10-20) mL:1 g.

[0065] Furthermore, in S3, the bromination raw material of the bromination reaction is phosphorus tribromide, and the molar ratio of phosphorus tribromide to the compound represented by formula (a-2) is (1.5-3):1.

[0066] Furthermore, in S3, the temperature of the bromination reaction is -5°C to 5°C.

[0067] The method for synthesizing the compound represented by formula (a) provided by the present invention has a wide range of raw material sources, a simple reaction route, and is easy to implement industrial-scale production.

[0068] In a third aspect, the present invention further provides a polyimide compound, the structure of which is shown in formula (II):

[0069]

[0070] Wherein, R is bistrifluoromethyl or O;

[0071] m and n are positive integers, and m+n=10, m=1~4.

[0072] Relative to prior art, the polyimide compound structure provided by the present invention contains bis(trifluoromethyl) or ether bond groups, the molecular polarity of polyimide compound can be significantly reduced, molecular dipole moment is reduced, so as to effectively reduce the dielectric constant of polyimide, reduce signal transmission loss;Meanwhile, the presence of biphenyl and two alicyclic ring structures and nitrogen-containing heterocycles, limits molecular segment motion and dipole orientation, reduces dipole polarization loss, reduces dielectric loss, improves the stability of material under high-frequency electric field;In addition, biphenyl and two alicyclic ring structures give molecular chain higher rigidity, and groups such as nitrogen-containing heterocycles and bis(trifluoromethyl) have higher thermal stability, are conducive to enhancing the heat resistance of polyimide. By the synergistic effect of bis(trifluoromethyl) (or ether bond groups), biphenyl and two alicyclic ring structures, nitrogen-containing heterocycles, the collaborative optimization of dielectric properties and heat resistance is achieved, the comprehensive performance of polyimide is improved, there is broad application prospect in microelectronics industry.

[0073] In a fourth aspect, the present invention further provides a method for preparing the above-mentioned polyimide compound, comprising the following steps:

[0074] Under an inert atmosphere, a dianhydride monomer is subjected to a condensation reaction with 2,2'-bis(trifluoromethyl)diaminobiphenyl, followed by a dehydration cyclization reaction to obtain a polyimide compound represented by formula (II);

[0075] Wherein, the dianhydride monomer is a biphenyl alicyclic dianhydride monomer represented by formula (I) or a mixed monomer of a biphenyl alicyclic dianhydride monomer represented by formula (I) and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride;

[0076]

[0077] Wherein, R is bis(trifluoromethyl) or O.

[0078] Furthermore, the preparation method of the polyimide compound specifically comprises the following steps:

[0079] S1, under an inert atmosphere, dissolving a dianhydride monomer and 2,2'-bis(trifluoromethyl)diaminobiphenyl in a polar aprotic solvent, and reacting at -5°C to 25°C for 4 hours to 12 hours to obtain a polyamic acid reaction solution;

[0080] S2, adding a catalyst to the polyamic acid reaction solution, reacting at -5°C to 25°C for 12 hours to 24 hours, washing, and drying to obtain a polyimide compound represented by formula (II). The specific synthesis route is as follows:

[0081]

[0082] In the formula, m and n are the ratios of the biphenyl dialicyclic dianhydride monomer represented by formula (I) to 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride.

[0083] Furthermore, the polar aprotic solvent includes at least one of N,N-dimethylacetamide, N-methylpyrrolidone or m-cresol.

[0084] Furthermore, the molar ratio of the biphenyl dialicyclic dianhydride monomer represented by formula (I) to 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride is (0.1-0.4):(0.9-0.6).

[0085] Furthermore, the molar ratio of the total amount of the dianhydride monomer to the diamine monomer is 1:(1-1.2).

[0086] Furthermore, the mass volume ratio of the sum of the mass of 2,2'-bis(trifluoromethyl)diaminobiphenyl and the dianhydride monomer to the polar aprotic solvent is 1 g:(2-5) mL.

[0087] Furthermore, the molar ratio of the catalyst to 2,2'-bis(trifluoromethyl)diaminobiphenyl is (1.5-3):1.

[0088] Furthermore, the catalyst is at least one of isoquinoline, quinoline, pyridine or collidine.

[0089] It should be noted that the inert atmosphere in the present invention can be provided by conventional inert gases in the art, such as nitrogen, argon, etc.

[0090] It should be noted that after the reaction in step S2 is completed, a post-processing process is also included: adding a poor solvent to the reaction solution for precipitation, solid-liquid separation, and drying to obtain a polyimide compound.

[0091] Furthermore, the poor solvent is methanol, anhydrous ethanol or deionized water.

[0092] The preparation method of the polyimide compound provided by the present invention has low production cost, short synthesis steps, simple operation, mild reaction conditions, high purity of the prepared product, good industrial utilization value, and high promotion and application value.

[0093] In a fifth aspect, the present invention further provides a low-dielectric and high-heat-resistant polyimide film, comprising the above-mentioned polyimide compound or a polyimide compound prepared by any of the above-mentioned preparation methods.

[0094] In a sixth aspect, the present invention further provides a method for preparing the above-mentioned low-dielectric and high-heat-resistant polyimide film, comprising the following steps:

[0095] The polyimide compound is dissolved in an organic solvent, casted into a film, the solvent is evaporated, and the film is peeled off to obtain a low-dielectric and high-heat-resistant polyimide film.

[0096] Furthermore, the organic solvent is dimethylacetamide, and the solid content is controlled to be 8% to 10%.

[0097] Furthermore, the temperature for film laying is 60° C. to 80° C., and the time for evaporating the solvent after film laying is 6 h to 8 h.

[0098] The polyimide film provided by the present invention has excellent dielectric properties and heat resistance. It can effectively reduce signal loss under high-frequency electric fields and ensure stable signal transmission. At the same time, it can maintain good mechanical and dimensional stability in high-temperature environments and is not easy to deform or decompose. It can be used to manufacture high-frequency circuit boards, flexible electronic devices, etc., meeting the development needs of miniaturization, high frequency and high speed of electronic equipment, and has high promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0099] Figure 1 This is the H NMR spectrum of the FBG-1 compound prepared in Example 1 of the present invention;

[0100] Figure 2 This is the NMR carbon spectrum of the FBG-1 compound prepared in Example 1 of the present invention;

[0101] Figure 3 This is the single crystal diffraction pattern of the FBG-2 compound prepared in Example 1 of the present invention;

[0102] Figure 4 This is the H NMR spectrum of the FBG compound prepared in Example 1 of the present invention;

[0103] Figure 5 This is the NMR carbon spectrum of the FBG compound prepared in Example 1 of the present invention;

[0104] Figure 6 This is the H NMR spectrum of the OBG-3 compound prepared in Example 2 of the present invention;

[0105] Figure 7 This is the NMR carbon spectrum of the OBG-3 compound prepared in Example 2 of the present invention;

[0106] Figure 8 This is the single crystal diffraction pattern of the OBG-4 compound prepared in Example 2 of the present invention;

[0107] Figure 9 This is the H NMR spectrum of the OBG compound prepared in Example 2 of the present invention;

[0108] Figure 10 This is the C NMR spectrum of the OBG compound prepared in Example 2 of the present invention;

[0109] Figure 11 These are pictures of polyimide films prepared in Examples 3 to 6;

[0110] Figure 12 These are pictures of the polyimide films prepared in Examples 7 to 10;

[0111] Figure 13 This is the infrared spectra of the polyimide films prepared in Examples 3 to 10. DETAILED DESCRIPTION

[0112] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0113] In order to better illustrate the present invention, further examples are given below.

[0114] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; unless otherwise specified, the reagents used are all commercially available products or prepared by conventional methods in the art.

[0115] Example 1

[0116] This embodiment provides a method for preparing a biphenyl alicyclic dianhydride monomer (R is difluorotrimethyl):

[0117] 1. Synthesis of 4,4'-(perfluoropropane-2,2-diyl)bis(1,2-bis(bromomethyl)benzene) (FBG-1)

[0118] To a 100 mL three-necked flask equipped with a magnetic rod, 5 g (13.9 mmol) of 2,2-bis(3,4-xylyl)hexafluoropropane, 12.36 g (69.4 mmol) of N-bromosuccinimide, 0.20 g (1.188 mmol) of azobisisobutyronitrile, and 36.5 mL of carbon tetrachloride were added as a solvent. Nitrogen was introduced to replace the air for protection. Stirring was started and the oil bath was heated to 60°C. The reaction progress was monitored by TLC. The reaction was stopped after 6 hours. The reaction solution was cooled to room temperature and filtered. The filter cake was the byproduct succinimide produced in the reaction. The filtrate was concentrated by rotary evaporation, slurried with 25 mL of ethanol, and then filtered. Slurried with petroleum ether three times, and dried under vacuum at 55°C for 8 hours to obtain 3 g of a white solid with a yield of 33%. It was named FBG-1. The reaction route is as follows:

[0119]

[0120] 1 H NMR (500MHz, DMSO-d6) δ7.65(d,J=8.3Hz,2H),7.50(s,2H),7.35–7.27(m,2H),4.88(d,J=6.9Hz,8H).

[0121] 13 C NMR (126MHz, DMSO-d6) δ138.64,137.77,132.95,132.68,132.17,130.78,125.29,123.00,64.12,30.68,30.04.

[0122] 2. Synthesis of Tetramethyl 6,6'-(perfluoropropane-2,2-diyl)bis(1,2,3,4-tetrahydronaphthalene-2,3-dicarboxylate) (FBG-2)

[0123] In a 250mL three-necked round-bottom flask equipped with a magnetic rod, 10g (14.87mmol) of the above-prepared FBG-1, 8.25g (84.18mmol) of maleic anhydride, 24.71g (148.85mmol) of potassium iodide, and 80mL of N,N-dimethylformamide were added. The air was replaced with nitrogen for protection. Stirring was started and the oil bath was heated to 150°C for reflux reaction for 12h. TLC monitored the reaction completion. The reaction solution was poured into water to precipitate a brown solid and then filtered. The filter cake was washed with water to remove the remaining potassium iodide and maleic anhydride. After filtration, it was dissolved in ethyl acetate and neutral activated carbon was added for decolorization several times until the color of the filtrate no longer changed. Finally, it was dried with anhydrous sodium sulfate for 12h, filtered, spin-dried, and dried in vacuo at 45°C for 8h to obtain a yellow solid, which was recorded as crude FBG. The reaction route is as follows:

[0124]

[0125] 3. Synthesis of FBG-2:

[0126] 20g of the crude product FBG prepared above was added to a 250mL single-necked round-bottom flask equipped with a magnetic rod, 80mL of methanol was added and stirred to dissolve it completely, 13mL (178.98mmol) of thionyl chloride was added dropwise under an ice bath, and the addition was completed within 30min. The oil bath was heated to 65°C, and a 10% aqueous sodium hydroxide solution was used for tail gas absorption. The reaction progress was monitored by TLC. The reaction was complete after 12h. After the reaction solution cooled to room temperature, the remaining thionyl chloride and methanol were removed by atmospheric distillation. The product was added dropwise to a 5% aqueous potassium carbonate solution, and the product was extracted with ethyl acetate. The organic phase was washed twice with water, dried over anhydrous magnesium sulfate for 8h, filtered, and spin-dried. Finally, it was recrystallized from methanol to obtain a white solid. After drying at 55°C in vacuum for 8h, 2.3g of a white solid was obtained with a yield of 15%, which was named FBG-3. The reaction route is as follows:

[0127]

[0128] 1 H NMR (500MHz, Chloroform-d) δ7.15 (s, 2H), 7.08 (s, 4H), 3.70 (d, J = 6.7Hz, 12H), 3.33–3.25 (m, 4H), 3.25–3.21 (m, 4H), 3.14–3.03 (m, 4H).

[0129] 13C NMR(126MHz,Chloroform-d)δ173.22,173.17,134.86,134.84,133.81,133.79,131.24,130.64,128.76,128 .04,127.70,125.41,123.12,64.31,64.11,63.91,52.10,52.06,40.32,40.25,29.67,29.62,29.20,29.17.

[0130] FBG-2 was grown as a single crystal. Methanol was selected as the solvent to completely dissolve it. The filtrate was filtered through a 0.22μm filter membrane and the single crystal was grown by slow evaporation of the solvent. After standing for two weeks, a single crystal of sufficient size was formed for X-ray diffraction to determine its structure. It can be clearly seen from the single crystal diffraction pattern that FBG-2 exists in a relatively stable chair conformation. The single crystal diffraction pattern is as follows Figure 3 shown.

[0131] 3. Synthesis of 6,6'-(perfluoropropane-2,2-diyl)bis(1,2,3,4-tetrahydronaphthalene-2,3-dicarboxylic acid) (FBG-3):

[0132] In a 100mL single-necked flask equipped with a magnetic rod, 4.3g (6.68mmol) of the above-prepared FBG-2 was added, and a mixed solution of 15mL of 10% potassium hydroxide aqueous solution and 15mL of methanol was added. Stirring was started, and the oil bath was heated to 90°C. The reaction was monitored by TLC. The reaction was complete in 12h. After the reaction solution cooled to room temperature, the methanol was spin-dried, diluted with 20mL of water, and adjusted to pH = 2 with 10% dilute hydrochloric acid to precipitate a white solid. Ethyl acetate was then added for extraction, and the organic phase was washed with water. After separation, activated carbon was used for decolorization, filtered, and dried with anhydrous magnesium sulfate for 8h. Filtered, spin-dried, and vacuum pumped for 4.5h to remove the residual solvent. Then, it was placed in a vacuum oven at 55°C and dried for 8h to obtain 2.9g of a white solid with a yield of 74%, which was named FBG-4. The reaction route is as follows:

[0133]

[0134] 1 H NMR(500MHz,DMSO-d6)δ12.36(s,1H),7.21(d,J=8.2Hz,2H),7.10(d,J=14.8Hz,2H),6.99(dd, J=19.8,8.1Hz,2H),3.19–3.08(m,6H),3.03(ddd,J=21.8,14.7,5.6Hz,5H),2.89–2.85(m,1H).

[0135] 13 C NMR (126MHz, DMSO-d6) δ175.85,175.76,174.72,174.64,136.64,136.41,135.27,135.16,130.53,130.22,130.12,129 .81,129.61,129.27,128.01,127.85,127.56,125.73,123.44,64.06,63.86,41.76,41.65,39.75,39.70,31.58,31.00.

[0136] HRMS[MH] + (C 27 H 22 F6O8): Theoretical calculation value M = 587.1219, measured value M = 587.1136.

[0137] HRMS[M-2H] 2+ (C 27 H 22 F6O8): Theoretical calculation value M = 293.0609, measured value M = 293.0533.

[0138] 4. Synthesis of dianhydride monomer 6,6'-(perfluoropropane-2,2-diyl)bis(3a,4,9,9a-tetrahydronaphtho[2,3-c]furan-1,3-dione) (FBG):

[0139] In a 50mL single-necked flask equipped with a magnetic rod, 2.9g (4.93mmol) of the above-prepared FBG-3 was added, 20mL of acetic anhydride was added, stirring was started, and the oil bath was heated to 130°C and refluxed. The reaction was monitored by TLC. The reaction was complete after 12h. After the reaction solution was cooled, the excess acetic anhydride was distilled off and dissolved in 5mL of dichloromethane at 50°C. Then 25mL of petroleum ether was gradually added dropwise to precipitate an off-white solid. It was vacuum-dried at 100°C for 12h, filtered, and vacuum-dried at 100°C for 12h to obtain 2.17g of a light yellow solid with a yield of 80%. It was named FBG. After verification by H-NMR and C-NMR spectra, it was shown that FBG-4 was successfully cyclized to obtain the dianhydride monomer FBG. Its melting point was measured to be 205-210°C. The reaction route is as follows:

[0140]

[0141] 1H NMR (500MHz, DMSO-d6) δ7.33(t,J=8.9Hz,2H),7.17(s,2H),7.10–7.03(m,2H),3.71(q,J=5.0Hz,4H),3.03(t,J=4.6Hz,4H),3.01–2.95(m,4H).

[0142] 13 C NMR(151MHz,DMSO-d6)δ175.22,175.03,175.01,137.62,136.48,136.45,131.53,131.50,129.27,128.97,128 .78,128.39,127.26,125.36,123.46,121.55,64.21,41.03,40.97,40.87,40.83,29.40,29.36,28.96,28.92.

[0143] Example 2

[0144] This embodiment provides a method for preparing a biphenyl alicyclic dianhydride monomer (R is O):

[0145] 1. Synthesis of 4,4'-oxyphthalic acid tetramethyl ester (OBG-1):

[0146] 30g (96.77mmol) of 4,4'-oxydiphthalic anhydride (ODPA) was added to a 250mL single-necked round-bottom flask equipped with a magnetic electron. After adding 300mL of methanol, stirring was started to completely dissolve it. 70mL (178.98mmol) of thionyl chloride was added dropwise under an ice bath. The addition was completed over 30min. Then, the temperature was raised to 65°C using an oil bath. 10% aqueous sodium hydroxide solution was used for tail gas absorption. The reaction progress was monitored by TLC. The reaction was completed in 4h. After the reaction solution was cooled, the remaining methanol and thionyl chloride were removed by atmospheric distillation. The product was added dropwise to a 5% aqueous potassium carbonate solution. The product was extracted with ethyl acetate and the organic phase was washed twice with water. It was dried over anhydrous magnesium sulfate for 8h and then filtered. The solvent was removed by vacuum concentration and dried at 45°C for 12h to obtain 37.7g of a white solid with a yield of 97%. It was named OBG-1. The reaction scheme is as follows:

[0147]

[0148] 2. Synthesis of (oxybis(benzene-4,1,2-triacyl))tetraethanol (OBG-2):

[0149] A 250 mL three-necked flask equipped with a magnetic rod was charged with 13 g (342.5 mmol) of lithium aluminum hydride. 70 mL of anhydrous tetrahydrofuran was added and nitrogen was introduced to replace the air for protection. Stirring was started. 35 g (87.06 mmol) of the above-prepared OBG-1 was dissolved in 50 mL of tetrahydrofuran and gradually added dropwise to the reaction solution. The addition was completed over 20 min. The temperature was raised to 66 ° C and refluxed. The reaction was monitored by TLC. The reaction was complete after 12 h. The reaction solution was cooled to room temperature. 32% dilute sulfuric acid was added dropwise to the reaction solution in an ice-water bath to adjust the pH to 2. The product was extracted three times with ethyl acetate. The organic phases were combined and washed twice with water to remove residual sulfuric acid. After extraction and separation, the liquid was dried over anhydrous sodium sulfate for 12 h, filtered, and then concentrated in vacuo to remove the solvent. The solvent was dried in vacuo at 55 ° C for 8 h to obtain 21.9 g of a white solid with a yield of 87%, which was named OBG-2. The reaction scheme is as follows:

[0150]

[0151] 1 H NMR (500MHz, DMSO-d6) δ7.37(d,J=8.3Hz,2H),7.08(d,J=2.6Hz,2H),6.87(dd,J=8.2,2.6Hz,2 H), 5.16 (t, J = 5.5Hz, 2H), 5.07 (t, J = 5.4Hz, 2H), 4.56 (d, J = 5.5Hz, 4H), 4.50 (d, J = 5.4Hz, 4H).

[0152] 13 C NMR (126MHz, DMSO-d6) δ156.44,142.44,134.39,129.16,117.00,116.78,60.56,60.35.

[0153] 3. Synthesis of 4,4'-oxybis(1,2-bis(bromomethyl)benzene)(OBG-3):

[0154] To a 500mL three-necked flask equipped with a magnetic electron, 16g (55.17mmol) of the above-prepared OBG-2 was added, and stirring was started after adding 160mL of dichloromethane solution. After 1.5h, it was completely dissolved. 36.9g (137.83mmol) of phosphorus tribromide was diluted with 100mL of dichloromethane solution. The dichloromethane solution of phosphorus tribromide was added dropwise to the reaction solution under ice bath conditions. The addition was completed in 40min. The reaction was monitored by TLC. After 6h, the reaction solution was added dropwise to 15% sodium carbonate aqueous solution. After adjusting the pH to 7, the dichloromethane solution was used to extract three times. The organic phases were combined and washed twice with water. After the extraction and separation, the organic phase was dried over anhydrous magnesium sulfate for 6h, filtered and dried under vacuum at 55°C for 8h to obtain 30.93g of a white solid with a yield of 95.9%, which was named OBG-3. The reaction scheme is as follows:

[0155]

[0156] 1 H NMR (500MHz, DMSO-d6) δ7.55(d,J=8.4Hz,2H),7.23(d,J=2.7Hz,2H),7.02(dd,J=8.4,2.6Hz,2H),4.84(d,J=18.0Hz,8H).

[0157] 13 C NMR (126MHz, DMSO-d6) δ156.77,139.42,133.81,132.47,121.53,119.72,31.15,30.72.

[0158] 4. Synthesis of tetramethyl 6,6'-oxybis(1,2,3,4-tetrahydronaphthalene-2,3-dicarboxylate) (OBG-4):

[0159] In a 250mL three-necked round-bottom flask equipped with a magnetic rod, 10g (18.60mmol) of the above-prepared OBG-3, 9.11g (92.96mmol) of maleic anhydride, 30.9g (186mmol) of potassium iodide, and 80mL of N,N-dimethylformamide were added. The air was replaced with nitrogen for protection. Stirring was started and the oil bath was heated to 150°C for reflux reaction. The reaction progress was monitored by TLC. The reaction was complete after 12h. The reaction solution was poured into water to precipitate a brown solid and then filtered. The solid was washed twice with water to remove residual potassium iodide and maleic anhydride. After filtration, it was dissolved in ethyl acetate and decolorized with neutral activated carbon three times until the color of the filtrate no longer changed. The filtrate was dried with anhydrous sodium sulfate for 12h, filtered, spin-dried, and vacuum-dried at 55°C for 8h to obtain crude OBG. The reaction scheme is as follows:

[0160]

[0161] 5. Synthesis of OBG-4:

[0162] 20g of the crude product OBG prepared above was added to a single-necked round-bottom flask equipped with a 250mL magnetic son. After adding 80mL of methanol, stirring was started to dissolve it completely. 13mL (178.98mmol) of thionyl chloride was added dropwise under an ice bath. The addition was completed within 30min. An oil bath was used to raise the temperature to 65°C. A 10% aqueous sodium hydroxide solution was used for tail gas absorption. The reaction process was monitored by TLC. The reaction was complete after 12h. After the reaction solution was cooled to room temperature, the remaining thionyl chloride and methanol were removed by atmospheric distillation and the product was added dropwise to a 5% aqueous potassium carbonate solution. The product was extracted with ethyl acetate and washed twice with water. After the extraction and separation, it was dried with anhydrous magnesium sulfate for 8h, then filtered, concentrated in vacuo to remove the solvent, and finally recrystallized from methanol to obtain a white solid. After drying at 55°C in vacuo for 8h, 3.65g of a white solid was obtained with a yield of 15%, which was named OBG-4. The reaction route is as follows:

[0163]

[0164] 1 H NMR (500MHz, Chloroform-d) δ7.09(d,J=8.3Hz,2H),6.83–6.76(m,4H),3.73(d,J=3.4Hz,12H),3.26(q,J=7.3,6.6Hz,8H),3.08(p,J=9.0Hz,4H).

[0165] 13 C NMR (126MHz, Chloroform-d) δ173.37,173.30,155.48,135.42,130.21,128.54,118.74,117.06,52.05,40.59,40.34,29.65,28.96.

[0166] After completely dissolving OBG-4 in a mixed solvent of methanol and acetone, the filtrate was filtered using a 0.22 μm filter membrane and single crystal cultivation was performed by slow solvent evaporation. After standing for a week, single crystals of sufficient size were formed for X-ray diffraction to determine its structure. It can be clearly seen from the single crystal diffraction pattern that OBG-4 exists in a relatively stable chair conformation. The single crystal diffraction structure diagram is shown in FIG. Figure 8 shown.

[0167] 6. Synthesis of 6,6'-oxybis(1,2,3,4-tetrahydronaphthalene-2,3-dicarboxylic acid) (OBG-5):

[0168] In a 100mL single-necked flask equipped with a magnetic rod, 4.3g (8.43mmol) of the above-prepared OBG-4, 15mL of a 10% potassium hydroxide aqueous solution, and 15mL of a methanol mixed solution were added. Stirring was started, and the oil bath was heated to 90°C. The reaction was monitored by TLC. The reaction was complete in 6h. After the reaction solution was cooled, the residual methanol was spin-dried, 20mL of water was added to dilute the reaction solution, and 10% dilute hydrochloric acid was slowly added dropwise to adjust the pH to 2. After the white solid precipitated, it was extracted with ethyl acetate. The organic phases were combined, washed with water, dried over anhydrous magnesium sulfate for 8h, filtered, and concentrated in vacuo to remove the solvent. Then, a vacuum oil pump was used to remove the residual solvent for 4.5h. Finally, 2.87g of a white solid was obtained after vacuum drying at 55°C with a yield of 75%, which was named OBG-5. The reaction scheme is as follows:

[0169]

[0170] 1 H NMR(500MHz,DMSO-d6)δ12.36(s,3H),7.11(d,J=8.7Hz,2H),6.82–6.69(m,4H),3 .13(d,J=4.5Hz,4H),3.07(d,J=6.7Hz,2H),3.05–2.94(m,4H),2.87–2.76(m,2H).

[0171] 13 C NMR(126MHz,DMSO-d6)δ176.04,176.00,174.83,174.77,155.37,155.22,136.78,136.53,130.69,130.35,129.83,129 .62,118.85,118.78,118.68,118.59,117.06,116.75,116.71,42.12,41.84,40.04,39.76,31.59,30.95,30.01,29.30.

[0172] HRMS[MH] + (C 24 H 22 O9): Theoretical calculated value M = 453.1264, measured value M = 453.1203.

[0173] HRMS[M-2H] 2+ (C 24 H 22 O9): Theoretical calculated value M = 226.0602, measured value M = 226.0560.

[0174] 7. Synthesis of dianhydride monomer 6,6'-oxybis(3a,4,9,9a-tetrahydronaphtho[2,3-c]furan-1,3-dione) (OBG):

[0175] 4 g (8.81 mmol) of the above-prepared OBG-5 was added to a 50 mL single-necked flask equipped with a magnetic rod, 25 mL of acetic anhydride was added to dissolve it, stirring was turned on, the oil bath was heated to 130 ° C and refluxed, and the reaction was monitored by TLC. The reaction was complete in 12 hours. After the reaction solution was cooled, the excess acetic anhydride was removed by vacuum distillation, and 5 mL of dichloromethane was used to dissolve it. Then 25 mL of petroleum ether was gradually added dropwise to precipitate an off-white solid. After filtration, it was vacuum-dried at 100 ° C for 12 hours to obtain 2.94 g of off-white solid with a yield of 80%. It was named OBG. After verification by nuclear magnetic hydrogen spectrum and carbon spectrum, according to the analysis of integral value and chemical shift value, it was shown that OBG-5 was successfully cyclized to obtain dianhydride monomer OBG. Its melting point was measured to be 198-200 ° C. The reaction route is as follows:

[0176]

[0177] 1 H NMR(500MHz,DMSO-d6)δ7.22(ddd,J=11.1,8.3,3.7Hz,2H),6.93–6.87(m,2H), 6.86–6.77(m,2H),3.72(q,J=2.7Hz,3H),3.55–3.52(m,1H),3.16–2.90(m,8H).

[0178] 13 C NMR(126MHz,DMSO-d6)δ175.46,175.44,175.36,175.34,175.32,171.97,171.90,156.45,156 .15,155.21,137.87,137.81,136.76,136.73,131.83,131.79,130.84,130.59,129.99,129.7 5,129.61,129.58,120.40,119.99,118.61,118.57,118.17,117.74,117.47,117.45,117.39,117.17,117.14,42.76,42.47,41.29,41.27,40.98,40.95,29.47,29.44,28.75,28.59,27.98.

[0179] Examples 3-6

[0180] A method for preparing a low-dielectric and high-heat-resistant polyimide film:

[0181] A 50 mL three-necked flask was installed on a stirring device with mechanical stirring, and an argon flow was used to replace the air in the bottle and maintain the argon environment. The flask was thoroughly dried using a 300 ° C hot air gun. 0.8000 g (2.499 mmol) of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB) was accurately weighed and put into the three-necked flask under ice bath conditions. 2 mL of dimethylacetamide was added and the speed was set to 200 r / min. Stirring was continued until dissolved. 0.6658 g (1.499 mmol) of 2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride (6FDA) was weighed and put into the three-necked flask. 1.5 mL of dimethylacetamide was added. After the solid was completely dissolved, the dianhydride monomer FBG prepared in Example 1 was weighed. 0.5520 g (0.1000 mmol) of methyl benzoate was added to a three-necked flask, and 1.5 mL of dimethylacetamide was added to dissolve it. After 2 h, the ice-water bath was removed and stirred at room temperature for 8 h. Then, 0.15 g (4.050 mmol) of isoquinoline was added as a catalyst. 5 mL of toluene was added and water was separated using a water separator. The temperature was raised to 160 ° C. and stirring was continued for 12 h. After termination of the reaction, the reaction solution was poured into 150 mL of methanol to precipitate a fibrous precipitate. The product was washed twice with water and once with methanol, filtered and dried in a vacuum at 80 ° C to obtain 1.95 g of a light yellow solid with a yield of 97%. The product was recorded as 40% FBG / 60% 6FDA / TFMB.

[0182] Keeping the total molar amount of the dianhydride monomer unchanged, the ratio of the dianhydride monomer FBG and 6FDA was changed, and 10% FBG / 90% 6FDA / TFMB, 20% FBG / 80% 6FDA / TFMB, and 30% FBG / 70% 6FDA / TFMB were prepared according to the same method as above. The reaction scheme is as follows:

[0183]

[0184] In the above formula, the ratio of m to n is the ratio of the dianhydride monomers FBG and 6FDA.

[0185] Weigh 0.4 g of each of the four polyimides prepared above and put them into a 15 mL centrifuge tube. Dissolve them completely with 4.0 mL of anhydrous dimethylacetamide, control the solid content to 10%, and centrifuge at 4000 r / min for 3 minutes. After the centrifugation is completed, aspirate the supernatant and spread it evenly on a glass plate using a casting method. Place the glass plate on a constant temperature heating table, set the temperature to 80°C, and continue heating for 6 hours. After the temperature drops to room temperature, carefully peel off the film. The five films obtained were named PIG-1 (10% FBG / 90% 6FDA / 100% TFMB), PIG-2 (20% FBG / 80% 6FDA / 100% TFMB), PIG-3 (30% FBG / 40% 6FDA / 100% TFMB), and PIG-4 (40% FBG / 60% 6FDA / 100% TFMB). The film pictures are as follows. Figure 11 shown.

[0186] Example 7 to Example 10

[0187] A method for preparing a low-dielectric and high-heat-resistant polyimide film:

[0188] A 50 mL three-necked flask was installed on a stirring device with mechanical stirring, an argon flow was used to replace the air in the bottle, and an argon environment was maintained. The flask was thoroughly dried using a 300 ° C hot air gun. 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB) 0.8000 g (2.499 mmol) was accurately weighed under ice bath conditions and put into the three-necked flask. 2 mL of dimethylacetamide was added, the speed was set to 200 r / min, and stirring was continued until dissolved. 0.418 g (1.499 mmol) of 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride (6FDA) was weighed and put into the three-necked flask. 1 mL of dimethylacetamide was added. After the solid was completely dissolved, the dianhydride monomer OBG prepared in Example 2 was weighed. 0.5520 g (0.1000 mmol) of methyl benzoate was added to a three-necked flask, and 1.5 mL of dimethylacetamide was added to dissolve it. After 2 h, the ice-water bath was removed and stirred at room temperature for 8 h. Then, 0.15 g (4.050 mmol) of isoquinoline was added as a catalyst. 5 mL of toluene was added and water was separated using a water separator. The temperature was raised to 160 ° C. and stirring was continued for 12 h. After termination of the reaction, the reaction solution was poured into 150 mL of methanol to precipitate a fibrous precipitate. The product was washed twice with water and once with methanol, filtered and dried in a vacuum at 80 ° C to obtain 1.73 g of a white solid with a yield of 98%. The product was recorded as 40% OBG / 60% 6FDA / TFMB.

[0189] Keeping the total molar amount of the dianhydride monomer unchanged, changing the ratio of the dianhydride monomer OBG and 6FDA, 10% OBG / 90% 6FDA / TFMB, 20% OBG / 80% 6FDA / TFMB, and 30% OBG / 70% 6FDA / TFMB were prepared according to the same method as above. The reaction scheme is as follows:

[0190]

[0191] Weigh 0.4 g of each of the four polyimide compounds prepared above and put them into a 15 mL centrifuge tube. Dissolve them completely with 4.0 mL of anhydrous dimethylacetamide, control the solid content to 10%, and centrifuge at 4000 r / min for 3 minutes. After the centrifugation is completed, aspirate the supernatant and spread it evenly on a glass plate using a casting method. Place the glass plate on a constant temperature heating table, set the temperature to 80°C, and continue heating for 6 hours. After the temperature drops to room temperature, carefully peel off the film. The five films obtained were named PIG-5 (10% OBG / 90% 6FDA / 100% TFMB), PIG-6 (20% OBG / 80% 6FDA / 100% TFMB), PIG-7 (30% OBG / 40% 6FDA / 100% TFMB), and PIG-8 (40% OBG / 60% 6FDA / 100% TFMB). The film pictures are as follows. Figure 12 shown.

[0192] Comparative Examples 1 to 10

[0193] Polyimide was prepared using the diamine monomer and dianhydride monomer in Table 1 in the same manner as in Example 3. The structure of the prepared polyimide is shown in Table 2.

[0194] Table 1 Types and molar ratios of monomers in Examples and Comparative Examples

[0195]

[0196]

[0197] Table 2 Structure and film forming state of polyimide films prepared in Examples and Comparative Examples

[0198]

[0199]

[0200]

[0201] The preparation method of the diamine monomer in the above comparative examples 4 to 5 comprises the following steps:

[0202] (1) Synthesis of 2-(4-aminophenyl)-1,1,3,3-hexafluoropropan-2-ol (FBA-1):

[0203] A 250 mL single-necked flask equipped with a magnetic element was charged with 20 g (215 mmol) of aniline and 70 mL of xylene as a solvent. The flask was fixed on a heat-collecting stirrer and stirred. 36 mL (288 mmol) of hexafluoroacetone trihydrate was gradually added dropwise to the reaction solution over 20 min. 1.6 g (9.3 mmol) of p-toluenesulfonic acid was added as a catalyst. The flask was heated to 130°C in an oil bath and refluxed. The reaction was monitored by TLC. The reaction was complete after 16 h. After the reaction solution cooled to room temperature, it was placed in a -5°C ice bath and crystallized for 1 h. The product was completely precipitated and filtered. The filter cake was beaten with 500 mL of 5% potassium carbonate solution to remove residual p-toluenesulfonic acid. After filtration, it was washed twice with 500 mL of water, filtered again, and dried under vacuum at 55°C for 8 h to obtain 17 g of a white solid with a yield of 31%. The synthetic route is as follows:

[0204]

[0205] 1 H NMR (500MHz, DMSO-d6) δ8.19 (s, 1H), 7.30 (d, J = 8.4Hz, 2H), 6.65–6.60 (m, 2H), 5.45 (s, 2H).

[0206] 13 C NMR (126MHz, DMSO-d6) δ150.57,128.01,127.17,124.88,122.58,120.29,117.17,113.69,77.41,77.18,76.95.

[0207] (2) Synthesis of diamine monomer:

[0208] Under ice bath conditions, 8.00 g (30.9 mmol) of the above-prepared FBA-1 and 40 mL of tetrahydrofuran were added to a 250 mL single-necked flask equipped with a magnetic rod. The mixture was fixed on a normal temperature stirrer and stirred until it was completely dissolved. 9.36 g (92.5 mmol) of triethylamine was added as an acid binding agent, 1.50 g (12.3 mmol) of 4-dimethylaminopyridine was added as a catalyst, 14.30 g (77.3 mmol) of p-nitrobenzoyl chloride was dissolved in 20 mL of tetrahydrofuran and slowly added dropwise to the reaction solution. The addition was completed in 20 min, the ice water bath was removed, and the reaction was continued at room temperature. The reaction was monitored by TLC and the reaction was complete in 40 min. The reaction solution was filtered, and the filter cake was a salt by-product. The filtrate was dropped into water to precipitate a light yellow solid. After filtration, 500 mL of water was used for slurry purification, 250 mL of 10% potassium carbonate aqueous solution was used for slurry purification, 250 mL of 10% dilute hydrochloric acid solution was used for slurry purification, 500 mL of water was used for slurry purification again, and finally 60 mL of methanol was used for slurry purification. After filtration, an off-white solid was obtained, which was vacuum-dried at 55°C to obtain 14.62 g of a dinitro compound with a yield of 85%. The synthetic route is as follows:

[0209]

[0210] 1 H NMR(500MHz,DMSO-d6)δ10.86(s,1H),8.51–8.44(m,2H),8.45–8.37(m,2H),8 .37–8.30(m,2H),8.24–8.17(m,2H),8.02–7.95(m,2H),7.61(d,J=8.5Hz,2H).

[0211] 13 C NMR(126MHz,DMSO-d6)δ164.86,160.66,151.72,149.82,141.43,140.69,132.96,132.10,130 .95,130.76,129.85,127.80,124.92,124.09,123.86,123.19,120.99,120.91,120.70,83.89.

[0212] Dielectric properties test

[0213] The dielectric properties of the polyimide film were tested using an Agilent E4990A impedance analyzer with a 16451B test fixture. The film samples were vacuum-dried and then cut into 25×25 mm strips. The film thickness was accurately measured using a digital outside micrometer, maintaining a range of 280–300 μm. The test frequency was 20–1×10⁶ Hz. The data was processed and analyzed using the Keysight Materials Measurement Suite software. Since the dielectric constant is most stable and accurate at 1 MHz, the dielectric constant and dielectric loss values ​​at 1 MHz are generally used as a reference unless otherwise specified. The results are shown in Table 3.

[0214] Thermal properties

[0215] The thermal properties of the polyimide film were tested using a TMA450 thermomechanical analyzer manufactured by Waters, USA, to measure the film's coefficient of thermal expansion (CTE). Film samples were vacuum-dried and then cut into 4×25 mm strips. The film's thickness and length were accurately measured. The test conditions were set at a nitrogen flow of 50 mL / min, a heating rate of 10°C / min, a temperature range of 40–350°C, and a preload of 0.05 N. After the test, the film's coefficient of thermal expansion was simulated and analyzed using TIOR software within a temperature range of 50–120°C. The film's glass transition temperature (Tg) was also tested using a TMA450 thermomechanical analyzer manufactured by Waters, USA. Film samples were vacuum-dried and then cut into 4×25 mm strips. The film's thickness and length were accurately measured. The test conditions were set at a nitrogen flow of 50 mL / min, a heating rate of 10°C / min, a temperature range of 40–350°C, and a preload of 0.05 N. After the test, the temperature-size curve of the film was simulated and analyzed using TIOR software to obtain the glass transition temperature of the film. The results are shown in Table 3.

[0216] Table 3 Dielectric properties and thermal properties of polyimide films prepared in Examples 3 to 10 and Comparative Examples 1 to 5

[0217]

[0218] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A biphenyl alicyclic dianhydride monomer, characterized in that: Its structure is shown in formula (I): Wherein, R is bis(trifluoromethyl) or O.

2. The method for preparing the biphenyl alicyclic dianhydride monomer according to claim 1, wherein: The steps include: Under inert atmosphere and catalyst conditions, the compound represented by formula (a) and maleic anhydride undergo Diels-Alder reaction to obtain the biphenyl alicyclic dianhydride monomer represented by formula (I); 3. The method for preparing the biphenyl alicyclic dianhydride monomer according to claim 2, wherein: When R is a bistrifluoromethyl group, the preparation method of the compound represented by formula (a) comprises the following steps: Under an inert atmosphere, 2,2-bis(3,4-xylyl)hexafluoropropane, N-bromosuccinimide and an initiator are subjected to a free radical reaction in an organic solvent to obtain a compound represented by formula (a).

4. The method for preparing the biphenyl alicyclic dianhydride monomer according to claim 2, wherein: When R is O, the preparation method of the compound represented by formula (a) comprises the following steps: S1, subjecting 4,4'-oxydiphthalic anhydride, methanol and thionyl chloride to an acylation reaction to obtain a compound represented by formula (a-1); S2, under an inert atmosphere, reducing the compound represented by formula (a-1) to obtain the compound represented by formula (a-2); S3. The compound represented by formula (a-2) is subjected to bromination reaction to obtain the compound represented by formula (a).

5. The method for preparing a biphenyl alicyclic dianhydride monomer according to any one of claims 2 to 4, wherein: After the Diels-Alder reaction, a purification step is also required: Step 1: dissolving the crude biphenyl dialicyclic dianhydride monomer in an alcohol solvent, adding thionyl chloride, and performing an esterification reaction to obtain a compound represented by formula (b); Step 2: dissolving the compound represented by formula (b) in an organic solvent, adding an alkaline solution, and performing a hydrolysis reaction to obtain a compound represented by formula (c); Step 3: Under an inert atmosphere, the compound represented by formula (c) and acetic anhydride undergo a dehydration cyclization reaction, followed by recrystallization to obtain a purified biphenyl alicyclic dianhydride monomer.

6. A polyimide compound, characterized in that Its structure is shown in formula (II): Wherein, R is bistrifluoromethyl or O; m and n are positive integers, and m+n=10, m=1~4.

7. The method for preparing the polyimide compound according to claim 6, wherein The steps include: Under an inert atmosphere, a dianhydride monomer is subjected to a condensation reaction with 2,2'-bis(trifluoromethyl)diaminobiphenyl, followed by a dehydration cyclization reaction to obtain a polyimide compound represented by formula (II); Wherein, the dianhydride monomer is a biphenyl alicyclic dianhydride monomer represented by formula (I) or a mixed monomer of a biphenyl alicyclic dianhydride monomer represented by formula (I) and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride; Wherein, R is bis(trifluoromethyl) or O.

8. The method for preparing a polyimide compound according to claim 6, wherein: The specific steps include: S1, under an inert atmosphere, dissolving a dianhydride monomer and 2,2'-bis(trifluoromethyl)diaminobiphenyl in a polar aprotic solvent, and reacting at -5°C to 25°C for 4 hours to 12 hours to obtain a polyamic acid reaction solution; S2, adding a catalyst to the polyamic acid reaction solution, reacting at -5°C to 25°C for 12 hours to 24 hours, washing, and drying to obtain a polyimide compound represented by formula (II).

9. A low dielectric and high heat-resistant polyimide film, characterized in that: The invention comprises the polyimide compound according to claim 6 or the polyimide compound prepared by the preparation method according to any one of claims 7 to 8.

10. The method for preparing the low-dielectric and high-heat-resistant polyimide film according to claim 9, characterized in that: The following steps are involved: The polyimide compound is dissolved in an organic solvent, casted, the solvent is evaporated, and the film is peeled off to obtain a low-dielectric and high-heat-resistant polyimide film.

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