Diamine monomer, polyimide with low dielectric constant and preparation method and application of polyimide film

Abstract

The invention discloses a diamine monomer, polyimide with low dielectric constant and a preparation method and application of a polyimide film with low dielectric constant, and belongs to the technical field of high polymer materials. The preparation method comprises the following steps: mixing a first diamine and a diamine with a side group containing boric acid ester, dissolving by using a polar solvent, then adding diacyl chloride containing an imide structure for polymerization to prepare polyimide resin with a side group containing boric acid ester, and carrying out a film forming process and heat treatment to prepare the cross-linked polyimide film. Polyimide is prepared through reaction of diamine and diacyl chloride, amido and a boric acid ester side group are introduced into polyimide, the effect that the acting force of a fluorine-containing group and a large side group on a polymer chain is weakened can be avoided, and the prepared polyimide film has the comprehensive performance of low dielectric constant, high mechanical property and good solvent resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials. More specifically, it relates to a diamine monomer, a preparation method and application of a low dielectric constant polyimide crosslinked with boric acid and its film. Background Art

[0002] With the rapid development of communication technology, especially the rise of the fifth-generation (5G) mobile communication technology, higher requirements have been put forward for interlayer insulating materials in the microelectronics field. In order to avoid the adverse phenomena of signal delay and crosstalk interference, the development of insulating layers with low dielectric constants has become an urgent problem to be solved in the industry. Polyimide has always been an important insulating layer material in the microelectronics industry due to its excellent mechanical properties, thermal properties and chemical stability. However, traditional polyimide has a relatively high dielectric constant (~3.5), making it difficult to meet the development requirements of modern electronic communication and microelectronics technology fields.

[0003] It can be seen from the Maxwell-Garnett equation and the Clausius-Mossotti equation that there is a negative correlation between the dielectric constant, the system polarizability and the free volume of the material. Therefore, in order to reduce the dielectric constant of polyimide, introducing fluorine-containing groups, large-volume side groups in diamine or dianhydride monomers or introducing micro-nano pores into the polyimide matrix to increase the free volume of polyimide and reduce the polarizability are effective methods for developing low dielectric constant polyimide at present.

[0004] However, the introduction of fluorine-containing monomers or large-volume side groups will reduce the interaction between polymer chains, resulting in a serious reduction in the solvent resistance of polyimide. In addition, the introduction of holes or voids will damage the thermal and mechanical properties of polyimide, reducing its reliability as an insulating layer. Summary of the Invention

[0005] In order to solve the problem that the development of low dielectric constant polyimide films in the prior art cannot balance solvent resistance and high mechanical properties, the present invention provides a diamine monomer, a preparation method and application of a low dielectric constant polyimide crosslinked with boric acid and its film. Specifically, the present invention is realized by adopting the following technical solutions:

[0006] The present invention provides a diamine monomer, which is a diamine with a boric acid ester-containing side group, and its molecular structural formula is:

[0007] The present invention provides a low dielectric constant polyimide. The diamine monomer forming the polyimide includes the above-mentioned diamine monomer, and the structure of the polyimide is as follows:

[0008]

[0009] A:

[0010]

[0011] B:

[0012]

[0013] Wherein: m and n represent the degree of polymerization, and m / n = 10 / 90 - 90 / 10.

[0014] The present invention also provides a boric acid cross-linked polyimide film with a low dielectric constant, which contains the above-mentioned low dielectric constant polyimide.

[0015] A method for preparing a low dielectric constant polyimide film includes the following steps:

[0016] 1) Mix a first diamine with a diamine containing a borate group in the side chain and dissolve them in a polar organic solvent to obtain a mixed diamine solution;

[0017] 2) Add a diacid chloride containing an imide structure to the mixed diamine solution to react to obtain a reaction solution;

[0018] 3) Add the reaction solution to a precipitant for precipitation, and after washing and drying, obtain a resin;

[0019] 4) Dissolve the resin in a polar organic solvent to prepare a solution, and after forming a film by a film-forming process, form a polyimide film containing a borate side group through a programmed temperature rise treatment;

[0020] 5) Perform heat treatment on the formed film to cause the cross-linking reaction of the side group borate to form a boron-oxygen six-membered ring, and obtain a low dielectric constant polyimide film.

[0021] Further, the polar organic solvent is one of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

[0022] Further, the molar ratio of the first diamine to the diamine containing a borate group in the side chain is (1 - 9):(9 - 1):10. Wherein the total molar ratio of the first diamine and the diamine containing a borate group in the side chain to the diacid chloride containing an imide structure is 1:1 - 1.05, preferably 1:1.

[0023] Further, the structure of the first diamine is as follows: Wherein the structure of B' is the same as the structure of B above.

[0024] Further, the structure of the diacid chloride containing an imide structure is as follows:

[0025] The structure of A' is the same as that of A above.

[0026] Furthermore, the synthesis steps of the diacid chloride containing an imide structure are as follows:

[0027] Add the diamine containing the A' structure and trimellitic anhydride to acetic acid, reflux at 115 °C for 24 h, then add the reaction solution to a large amount of ethanol or methanol, collect the precipitate, and dry it under vacuum to obtain the diacid monomer containing an imide structure. Then react the diacid monomer containing an imide structure with thionyl chloride at 80 °C for 4 h, and rotary evaporate to remove the excess thionyl chloride to obtain the diacid chloride monomer containing an imide structure. Among them, the molar ratio of the diamine containing the A' structure to trimellitic anhydride is 1:2.

[0028] Furthermore, the structural formula of the diamine with a borate ester-containing side group is as follows:

[0029] Furthermore, the synthesis route of the diamine with a borate ester-containing side group is as shown below:

[0030]

[0031] Furthermore, the specific synthesis steps of the diamine with a borate ester-containing side group are as follows:

[0032] 1.1. Under a nitrogen atmosphere, stir 2,6-dimethylaniline and deionized water evenly, add concentrated hydrochloric acid, then add 4-formylphenylboronic acid, reflux at 100 °C for 12 h, adjust the pH to neutral after it cools to room temperature, collect the precipitate, and filter and dry it to obtain the diamine with a phenylboronic acid-containing side group; among them, the molar ratio of 2,6-dimethylaniline to 4-formylphenylboronic acid is (3 - 2):1;

[0033] 1.2. Add the diamine with a phenylboronic acid-containing side group, pinacol, and a small amount of deionized water obtained in step 1.1 to tetrahydrofuran, stir at room temperature for 0.5 h, then add anhydrous magnesium sulfate, continue to stir at room temperature for 2 h, then filter to remove magnesium sulfate, collect the filtrate, and rotary evaporate to remove tetrahydrofuran to obtain the diamine with a borate ester-containing side group. Among them, the molar ratio of the diamine with a phenylboronic acid-containing side group to pinacol is 1:(1 - 1.1).

[0034] Furthermore, in step 1), the mixed diamine is stirred and dissolved at 0 °C - 30 °C.

[0035] Furthermore, in step 2), control the reaction solid content to be 10% - 15%, maintain the reaction temperature at 0 °C - 30 °C, after reacting for 20 min - 2 h, react at 25 °C - 50 °C for 10 h - 24 h.

[0036] Further, in step 3), the precipitant is ethanol, deionized water, methanol or a mixture of any two of them, and the drying temperature is 110°C - 130°C.

[0037] Further, in step 4), the solid content of the solution is 10% - 20%, and the programmed temperature rise is specifically as follows: maintain at 80°C - 100°C for 1 - 2 h, maintain at 120°C - 130°C for 1 - 2 h, maintain at 150°C - 160°C for 1 - 2 h, and maintain at 230°C - 240°C for 1 - 2 h.

[0038] Further, in step 5), the heat treatment temperature is 260°C - 280°C, and the time is 2 - 24 h.

[0039] Further, the thickness range of the low - dielectric - constant polyimide film prepared in step 5) is 45 - 55 μm.

[0040] The synthesis process of the above - mentioned low - dielectric - constant polyimide is as follows:

[0041]

[0042] The above - mentioned low - dielectric - constant polyimide film is used as an insulating layer material in high - frequency communication electronic devices.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] 1. The present invention uses diacyl chloride and diamine containing imide structure to polymerize to prepare polyimide, which is different from the traditional method of polymerizing dianhydride and diamine to prepare polyimide. Polymerization using diacyl chloride containing imide structure can be completed under milder conditions and can avoid subsequent high - temperature imidization.

[0045] 2. The diacyl chloride containing imide structure used in the present invention has high reactivity and can polymerize with sterically hindered diamine at room temperature, avoiding the problem that the reactivity of diamine is low due to steric hindrance and polymerization cannot be completed.

[0046] 3. The present invention uses diacyl chloride and diamine containing imide structure to polymerize to prepare polyimide. The main chain of the polymerized polyimide contains amide groups, and the intermolecular interaction of the polymer chains can be strengthened through hydrogen bonds, which can alleviate the problem of the decrease in the mechanical properties of the film caused by the weakening of the intermolecular force between polymer chains due to the introduction of large side groups.

[0047] 4. The diamine with borate ester in the side group used in the present invention has a relatively large - volume side group, which can increase the free volume of the polymer and is beneficial to the reduction of the dielectric constant. At the same time, the diamine with borate ester in the side group can cross - link to form a boron - oxygen six - membered ring at high temperature, improving the solvent resistance between polyimide films.

[0048] 5. The polyimide prepared by the present invention has an amide group in the main chain, and cooperates with the boron-oxygen six-membered ring formed by high-temperature crosslinking to synergistically improve the mechanical properties of the polyimide.

[0049] 6. The polyimide of the present invention has both a low dielectric constant, good solvent resistance, and high mechanical properties, and is suitable for use as an insulating layer in semiconductor devices.

[0050] Other features and beneficial effects of the present invention will be described in the following specification, and in part, will be apparent from the specification, or will be understood by practicing the present invention. Description of the Drawings

[0051] Figure 1 1H NMR spectrum of the diamine with borate ester side groups prepared in Example 1;

[0052] Figure 2 1H NMR spectrum of the diacid 1 with imide structure prepared in Example 2;

[0053] Figure 3 Infrared spectrum of the low dielectric constant polyimide film 1 prepared in Example 2;

[0054] Figure 4 Tensile curve of the low dielectric constant polyimide film 2 prepared in Example 3;

[0055] Figure 5 Dielectric constant curve of the low dielectric constant polyimide film 4 prepared in Example 5;

[0056] Figure 6 Comparison chart of the solvent resistance test results of the polyimide films of Example 4 and Comparative Example 1. Detailed Description of the Invention

[0057] The following examples are further descriptions of the content of the present invention to illustrate the technical content of the present invention. However, the substantial content of the present invention is not limited to the following examples. Those of ordinary skill in the art can and should know that any simple changes or substitutions based on the substantial spirit of the present invention should fall within the protection scope required by the present invention. The dielectric constant in the present invention is detected by a conventional method. The capacitance between the films is measured by an impedance analyzer, and then the dielectric constant is calculated according to the formula where ε is the dielectric constant, representing the electrical properties of the medium, C is the capacitance, referring to the capacitance value measured by the impedance analyzer, d is the thickness of the dielectric layer, A is the area between the electrodes, and ε 0 is the dielectric constant in a vacuum, which is a physical constant. The mechanical properties of the material are tested using a universal material tensile testing machine. The stress-strain curve of the film is tested under the conditions of room temperature 25°C, humidity: 53% RH, and tensile rate 10 mm / min.

[0058] Example 1:

[0059] Under a nitrogen atmosphere, 60 mmol of 2,6-dimethylaniline was mixed with 60 mL of deionized water and stirred for 30 min. Subsequently, 7.5 mL of concentrated hydrochloric acid was added. After 10 min, 30 mmol of 4-formylphenylboronic acid was added, and the mixture was refluxed at 100 °C for 12 h. After the reaction solution was cooled to room temperature, it was poured into a large amount of deionized water, and anhydrous potassium carbonate was added in small portions multiple times to adjust the pH to neutral, producing a large amount of blue powder. Then, it was washed with water twice, filtered by suction, and dried thoroughly at 100 °C to obtain a diamine with a phenylboronic acid-containing side group.

[0060] 10 mmol of the diamine with a phenylboronic acid-containing side group synthesized in the previous step, 10.059 mmol of pinacol, and 10 μL of deionized water were added to a 50 mL single-necked flask. Then, 25 mL of tetrahydrofuran was added as a solvent, and the mixture was stirred at room temperature for 0.5 h. Then, 0.5 g of anhydrous magnesium sulfate was added, and stirring was continued at room temperature for 2 h. Subsequently, magnesium sulfate was removed by filtration through a sintered glass funnel, tetrahydrofuran was removed by rotary evaporation, the product was scraped out, dried under vacuum at 80 °C overnight, and then the product was dissolved in dichloromethane and rotary evaporated again, and dried at 60 °C to obtain a diamine monomer with a borate ester-containing side group.

[0061] Reference Figure 1 The 1H NMR spectrum of the diamine with a borate ester-containing side group shows that the NMR peaks correspond one by one without impurity peaks, indicating the high purity of the diamine with a borate ester-containing side group. This diamine monomer with a borate ester-containing side group can be used for the synthesis of polyimide.

[0062] Example 2:

[0063] Synthesis of a diacid chloride containing an imide structure:

[0064] 10 mmol of 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl and 20 mmol of trimellitic anhydride were added to 60 mL of glacial acetic acid and refluxed at 115 °C for 24 h. After the system temperature was cooled to room temperature, it was poured into ethanol, the precipitate was collected, filtered by suction, and repeatedly washed with ethanol 3 times. Finally, it was dried in a vacuum oven at 150 °C for 24 h to obtain a diacid 1 containing an imide structure. Reference Figure 2 The 1H NMR spectrum of the diacid 1 containing an imide structure shows that the NMR peaks correspond one by one without impurity peaks, indicating the high purity of the diacid 1 containing an imide structure.

[0065] The diacid 1 containing an imide structure (8 g) prepared in the previous step was dispersed in 40 mL of thionyl chloride and reacted at 80 °C until the solution became transparent. Thionyl chloride was removed by rotary evaporation to obtain a diacid chloride 1 containing an imide structure.

[0066] Preparation of polyimide film:

[0067] Under a nitrogen atmosphere, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (1.6 mmol) and the diamine with a borate ester-containing side group of Example 1 (0.4 mmol) were dissolved in 20 mL of anhydrous DMAc. After stirring at 0 °C for 20 min, the diacid chloride 1 with an imide structure (2 mmol) was slowly added in batches. After stirring and reacting at room temperature for 10 h, the reaction solution was slowly poured into a mixed solvent of ethanol and deionized water at a ratio of 1:1 to obtain a fibrous white resin. Then, it was washed twice with the same solvent, filtered by suction, and the resin was collected and dried in vacuo at 120 °C. The dried resin was dissolved in anhydrous DMAc to prepare a solution with a solid content of 10%. The solution was coated on a glass substrate and dried at 80 °C for 2 h, 120 °C for 1 h, 150 °C for 1 h, and 230 °C for 1 h to remove the solvent. After peeling, a polyimide film with a borate ester side group was obtained. The above film was heat-treated in a muffle furnace at 270 °C for 10 h to cause the cross-linking reaction of the side-group borate ester to form a boron-containing six-membered ring, and a boron-crosslinked low-dielectric-constant polyimide film 1 with a thickness of about 50 μm was prepared. Figure 3 is the infrared spectrum of the prepared polyimide film 1. As can be seen from the figure, the characteristic absorption peak of the C-B bond is located at 1088 cm -1 .

[0068] Example 3:

[0069] Synthesis of diacid chloride with an imide structure:

[0070] During the implementation process, except that 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl was replaced with 2,2-bis(4-aminophenyl)hexafluoropropane, the rest were the same as in Example 2. Finally, diacid chloride 2 with an imide structure was prepared.

[0071] Preparation of polyimide film:

[0072] Under a nitrogen atmosphere, 2,2-bis(4-aminophenyl)hexafluoropropane (1.6 mmol) and the diamine with borate ester side groups in Example 1 (0.4 mmol) were dissolved in 20 mL of anhydrous DMAc. After stirring at 0 °C for 20 min, the diacid chloride 2 with imide structure (2 mmol) was added slowly in batches. After stirring at room temperature for 10 h, the reaction solution was slowly poured into a mixed solvent of ethanol and deionized water at a ratio of 1:1 to obtain a fibrous white resin. The resin was washed twice with the same solvent, filtered by suction, and then collected and dried in vacuo at 120 °C. The dried resin was dissolved in anhydrous DMAc to prepare a solution with a solid content of 15%. The solution was coated on a glass substrate and dried at 80 °C for 2 h, 120 °C for 1 h, 150 °C for 1 h, and 230 °C for 1 h to remove the solvent. After peeling, a polyimide film with borate ester side groups was obtained. The above film was heat-treated in a muffle furnace at 270 °C for 24 h to cause the cross-linking reaction of the side-group borate ester to form a boroxine ring, and a borate-crosslinked low dielectric constant polyimide film 2 with a thickness of about 50 μm was prepared.

[0073] Example 4:

[0074] Synthesis of diacid chloride with imide structure:

[0075] During the implementation process, except that 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl was replaced by 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, the rest was the same as in Example 2. Finally, diacid chloride 3 with imide structure was obtained.

[0076] Preparation of polyimide film:

[0077] Under a nitrogen atmosphere, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (1.2 mmol) and the diamine with borate ester side groups in Example 1 (0.8 mmol) were dissolved in 20 mL of anhydrous DMAc. After stirring at 0 °C for 20 min, the diacid chloride 3 with imide structure (2 mmol) was added slowly in batches. After stirring at room temperature for 10 h, the reaction solution was slowly poured into a mixed solvent of ethanol and deionized water at a ratio of 1:1 to obtain a fibrous white resin. The resin was washed twice with the same solvent, filtered by suction, and then collected and dried in vacuo at 120 °C. The dried resin was dissolved in anhydrous DMAc to prepare a solution with a solid content of 15%. The solution was coated on a glass substrate and dried at 80 °C for 2 h, 120 °C for 1 h, 150 °C for 1 h, and 230 °C for 1 h to remove the solvent. After peeling, a polyimide film with borate ester side groups was obtained. The above film was heat-treated in a muffle furnace at 270 °C for 18 h to cause the cross-linking reaction of the side-group borate ester to form a boroxine ring, and a borate-crosslinked low dielectric constant polyimide film 3 with a thickness of about 50 μm was prepared.

[0078] Example 5:

[0079] Synthesis of Diacyl Chloride with Imide Structure:

[0080] During the implementation process, except that 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl was replaced with 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, the rest were the same as in Example 2. Finally, diacyl chloride 4 with an imide structure was obtained.

[0081] Preparation of Polyimide Film:

[0082] Under a nitrogen atmosphere, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (1.2 mmol) and the diamine with borate ester side groups in Example 1 (0.8 mmol) were dissolved in 20 mL of anhydrous DMAc. After stirring at 0 °C for 20 min, diacyl chloride 4 with an imide structure (2 mmol) was added slowly in batches. After stirring and reacting at room temperature for 10 h, the reaction solution was slowly poured into a mixed solvent of ethanol and deionized water at a ratio of 1:1 to obtain a fibrous white resin. Then it was washed twice with the same solvent, filtered by suction, and the resin was collected and dried in vacuo at 120 °C. The dried resin was dissolved in anhydrous DMAc to prepare a solution with a solid content of 15%. The solution was coated on a glass substrate and dried at 80 °C for 2 h, 120 °C for 1 h, 150 °C for 1 h, and 230 °C for 1 h to remove the solvent. After peeling, a polyimide film with borate ester side groups was obtained. The above film was heat-treated in a muffle furnace at 270 °C for 24 h to cause the cross-linking reaction of the side-group borate ester to form a boron-oxygen six-membered ring, and a boron-crosslinked low-dielectric-constant polyimide film 4 with a thickness of about 50 μm was prepared.

[0083] Example 6:

[0084] Synthesis of Diacyl Chloride with Imide Structure:

[0085] During the implementation process, except that 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl was replaced with 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, the rest were the same as in Example 2. Finally, diacyl chloride 5 with an imide structure was obtained.

[0086] Preparation of Polyimide Film:

[0087] Under a nitrogen atmosphere, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (1 mmol) and the diamine with borate ester-containing side groups in Example 1 (1 mmol) were dissolved in 20 mL of anhydrous DMAc. After stirring at 0 °C for 20 min, the diacid chloride 5 with imide structure (2 mmol) was slowly added in batches. After stirring and reacting at room temperature for 10 h, the reaction solution was slowly poured into a mixed solvent of ethanol and deionized water at a ratio of 1:1 to obtain a fibrous white resin. The resin was washed twice with the same solvent, filtered by suction, and then collected and dried in vacuo at 120 °C. The dried resin was dissolved in anhydrous DMAc to prepare a solution with a solid content of 15%. The solution was coated on a glass substrate and dried at 80 °C for 2 h, 120 °C for 1 h, 150 °C for 1 h, and 230 °C for 1 h to remove the solvent. After peeling, a polyimide film with borate ester side groups was obtained. The above film was heat-treated in a muffle furnace at 270 °C for 24 h to cause the cross-linking reaction of the side-group borate ester to form a boron-oxygen six-membered ring, and a boron-crosslinked low-dielectric-constant polyimide film 5 with a thickness of about 50 μm was prepared.

[0088] Example 7:

[0089] Under a nitrogen atmosphere, 4-aminophenyl 4-aminobenzoate (1.2 mmol) and the diamine with borate ester-containing side groups in Example 1 (0.8 mmol) were dissolved in 20 mL of anhydrous DMAc. After stirring at 0 °C for 20 min, the diacid chloride 1 with imide structure prepared in Example 2 (2 mmol) was slowly added in batches. After stirring and reacting at room temperature for 10 h, the reaction solution was slowly poured into a mixed solvent of ethanol and deionized water at a ratio of 1:1 to obtain a fibrous white resin. The resin was washed twice with the same solvent, filtered by suction, and then collected and dried in vacuo at 120 °C. The dried resin was dissolved in anhydrous DMAc to prepare a solution with a solid content of 15%. The solution was coated on a glass substrate and dried at 80 °C for 2 h, 120 °C for 1 h, 150 °C for 1 h, and 230 °C for 1 h to remove the solvent. After peeling, a polyimide film with borate ester side groups was obtained. The above film was heat-treated in a muffle furnace at 270 °C for 24 h to cause the cross-linking reaction of the side-group borate ester to form a boron-oxygen six-membered ring, and a boron-crosslinked low-dielectric-constant polyimide film 6 with a thickness of about 50 μm was prepared.

[0090] Comparative Example 1

[0091] Under a nitrogen atmosphere, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (1.2 mmol) and the diamine with borate ester-containing side groups in Example 1 (0.8 mmol) were dissolved in 20 mL of anhydrous DMAc. After stirring at 0 °C for 20 min, 3 (2 mmol) of the diacyl chloride with imide structure in Example 4 was added slowly in batches. After stirring and reacting at room temperature for 10 h, the reaction solution was slowly poured into a mixed solvent of ethanol and deionized water at a ratio of 1:1 to obtain a fibrous white resin. The resin was washed twice with the same solvent, filtered by suction, and then collected and dried in vacuo at 120 °C. The dried resin was dissolved in anhydrous DMAc to prepare a solution with a solid content of 15%. The solution was coated on a glass substrate and dried at 80 °C for 2 h, 120 °C for 1 h, 150 °C for 1 h, and 230 °C for 1 h to remove the solvent, and then peeled off to obtain a polyimide film with borate ester side groups. The above film was not subjected to heat treatment.

[0092] The polyimide films prepared in the above examples were subjected to mechanical tests and dielectric constant tests; among them, the tensile curve of the polyimide film 2 in Example 3 is as Figure 4 shown; the dielectric constant curve of the polyimide film 4 in Example 5 is as Figure 5 shown, and the test frequency range is from 10 2 Hz to 10 6 Hz; the rest adopted a similar test scheme, and the results are shown in Table 1.

[0093] Table 1 Dielectric and mechanical properties of the polyimide films prepared in Examples 2-7

[0094] Sample Tensile strength Tensile modulus Elongation at break Dielectric constant (10KHz) Polyimide film 1 169 MPa 3.63 GPa 15.7％ 2.82 Polyimide film 2 177 MPa 3.72 GPa 17.5％ 2.75 Polyimide film 3 153 MPa 2.61 GPa 15.3％ 2.91 Polyimide film 4 162 MPa 2.72 GPa 16.3％ 2.33 Polyimide film 5 176 MPa 3.17 GPa 16.9％ 2.51 Polyimide film 6 181 MPa 3.83 GPa 15.7％ 2.46

[0095] As can be seen from Table 1, the polyimide films obtained in the above examples have a tensile strength > 150 MPa, an elongation at break > 15%, and a tensile modulus > 2.61 GPa, showing good mechanical properties; the dielectric constant of the polyimide films obtained in the above examples at a frequency of 10 KHz < 2.92, Figure 5 and the dielectric constant of the polyimide film 4 shown is 2.33 at a frequency of 1 MHz, enabling low dielectric loss.

[0096] After the polyimide films obtained in Example 4 and Comparative Example 1 were placed in N,N-dimethylacetamide for 24 h, it was found that the film prepared in Comparative Example 1 was completely dissolved, while the film prepared in Example 4 only swelled. The heat-treated polyimide film in Example 4 has good solvent resistance.

[0097] As can be seen from Table 1, the boric acid-crosslinked low-dielectric-constant polyimide film prepared in the present invention has good mechanical properties and a low dielectric constant, and is suitable as an insulating layer material in high-frequency communication electronic devices.

[0098] As mentioned above, it is only the preferred embodiment of the present invention, so the scope of implementation of the present invention cannot be limited thereby. That is, equivalent changes and modifications made according to the scope of the present invention patent and the content of the specification should still fall within the scope covered by the present invention.

Claims

1. A diamine monomer, characterized in that: The diamine monomer is a diamine with a side group containing a borate ester, and has the following structure:

2. A low dielectric constant polyimide, characterized in that: The diamine monomer forming the polyimide includes the diamine monomer according to claim 1, and the polyimide has the structure shown below: A is B is Wherein: m and n represent the degree of polymerization, m / n=10 / 90-90 / 10.

3. A low dielectric constant polyimide film, characterized in that: The invention comprises the low dielectric constant polyimide as claimed in claim 2.

4. A method for preparing a low dielectric constant polyimide film according to claim 3, characterized in that: The following steps are involved: 1) mixing a first diamine with a diamine having a side group containing a borate ester and dissolving them in a polar organic solvent to obtain a mixed diamine solution; 2) adding diacyl chloride containing an imide structure to the mixed diamine solution to react; 3) adding a precipitant to the reaction solution for precipitation, washing and drying to obtain a resin; 4) dissolving the resin in a polar organic solvent to prepare a solution, forming a film by a film forming process, and then performing a programmed temperature rise treatment to form a polyimide film containing borate side groups; 5) The formed film is subjected to heat treatment to cause the side-group boric acid ester to undergo a cross-linking reaction to form a boron-oxygen six-membered ring, thereby obtaining a low dielectric constant polyimide film.

5. The method for preparing a low dielectric constant polyimide film according to claim 4, characterized in that: The structure of the first diamine is The structure of B' is the same as that of B; and the molar ratio of the first diamine to the diamine containing a side borate ester is (1-9):(9-1).

6. The method for preparing a low dielectric constant polyimide film according to claim 4, characterized in that: The structure of the diacyl chloride containing an imide structure is The structure of A' is the same as that of A; the molar ratio of the sum of the first diamine and the diamine containing a side borate ester to the diacyl chloride containing an imide structure is 1:1-1.

05.

7. The method for preparing a low dielectric constant polyimide film according to claim 4, characterized in that: In step 2), the solid content of the reaction solution is controlled to be 10%-15%, the reaction temperature is maintained at 0°C-30°C, the reaction is carried out for 20min-2h, and then the reaction is carried out at 25°C-50°C for 10h-24h.

8. The method for preparing a low dielectric constant polyimide film according to claim 4, characterized in that: In step 4), the solid content of the solution is 10%-20%; the heating temperature curve is 80℃-100℃ for 1-2h, 120℃-130℃ for 1-2h, 150℃-160℃ for 1-2h, and 230℃-240℃ for 1-2h.

9. The method for preparing a low dielectric constant polyimide film according to claim 4, characterized in that: In step 5), the heat treatment is performed at 260° C.-280° C. for 2-24 hours.

10. The low dielectric constant polyimide film according to claim 3 is used as an insulating layer material in high-frequency communication electronic equipment.

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