Copolyimide film with low dielectric constant and low thermal expansion coefficient and preparation method thereof

Abstract

The invention discloses a copolyimide film with low dielectric constant and low thermal expansion coefficient and a preparation method thereof, and the preparation method comprises the following steps: reacting 0.019-0.021 mol of aromatic dianhydride and 0.017-0.023 mol of diamine unit in 0.45-0.48 mol of solvent, then adding 0.0004 mol of end-capping reagent dissolved in 0.13-0.15 mol of solvent, and reacting to prepare polyamide acid with a main chain containing o-hydroxyl; the diamine unit comprises 10-40 mol% of a monomer with a main chain containing o-hydroxyl and the balance of aromatic diamine; performing film coating and thermal imidization on polyamide acid to prepare a polyimide film; and heating to carry out thermal rearrangement reaction on the o-hydroxyl to obtain the copolyimide film with the main chain containing the oxazole ring. The dielectric constant of the prepared copolyimide film is 2.7-3.0, and the thermal expansion coefficient of the copolyimide film is 19.5-26.5 ppm / K.

Description

Technical Field

[0001] The invention relates to a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient and a preparation method thereof, belonging to the technical field of polyimide films. Background Art

[0002] Polyimide film is a high-performance engineering plastic and has become one of the important raw materials for microelectronic products. Due to its excellent thermal stability, high mechanical strength, high insulation, low moisture absorption, radiation resistance and other excellent properties, polyimide film shines in the fields of electronic packaging, integrated circuits, flexible display substrates, solar energy devices, etc. However, with the rapid development of the electronic information industry, people have put forward higher requirements for electronic materials with low dielectric constant, high mechanical and high thermal properties. Among them, achieving low thermal expansion coefficient and low dielectric constant in polyimide film at the same time has become a major problem.

[0003] There are usually two ways to reduce the dielectric constant of polyimide materials: one is to add fluorine atoms to the main chain to reduce the polarizability, such as introducing -CF3 groups, but this method will reduce the molecular weight and lead to a decrease in mechanical properties; the other is to add asymmetric molecular units or attach large volume groups to the molecular chain to expand the free volume fraction. However, both methods will create more space for polyimide, promote the free movement of chain segments, and may increase the thermal expansion coefficient of polyimide films. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a polyimide film with low dielectric constant and low thermal expansion coefficient and a preparation method thereof.

[0005] In order to achieve the above object, the present invention adopts a method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient, comprising the following steps:

[0006] S1, reacting 0.019-0.021 mol of aromatic dianhydride and 0.017-0.023 mol of diamine unit in 0.45-0.48 mol of solvent, and then adding 0.0004 mol of end-capping agent dissolved in 0.13-0.15 mol of solvent to react, to prepare a polyamic acid containing ortho-hydroxyl group in the main chain;

[0007] The diamine unit comprises 10% to 40% by mole of a main chain monomer containing ortho-hydroxyl groups and the remainder being an aromatic diamine;

[0008] S2, preparing a polyimide film by coating and thermal imidization of polyamic acid;

[0009] S3, heating the prepared polyimide film to allow the ortho-hydroxyl groups to undergo thermal rearrangement reaction, thereby obtaining a copolymerized polyimide film containing an oxazole ring in the main chain.

[0010] As an improvement, in step S1, the monomer containing ortho-hydroxyl groups in the main chain is 2,2-bis(4-hydroxy-3-aminophenyl)propane.

[0011] As an improvement, in step S1, the aromatic dianhydride is at least one of 4,4'-biphenyl ether dianhydride, pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and bisphenol A diether dianhydride.

[0012] As an improvement, in step S1, the aromatic diamine is at least one of 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether.

[0013] As an improvement, in step S1, the end-capping agent is cage-shaped polysilsesquioxane.

[0014] As an improvement, in step S1, the solvent is at least one of tetrahydrofuran, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0015] As an improvement, in step S2, the polyamic acid solution is evenly coated on a glass plate, placed in a vacuum drying oven at 130-150°C for 2-4 hours, and then placed in a muffle furnace for thermal imidization, and the thermal imidization procedure is: 200°C×1h, 300°C×1h, 330°C×1h.

[0016] As an improvement, in step S3, the prepared polyimide film is placed in a tubular furnace filled with argon gas for thermal rearrangement reaction, heated to 300-500° C. and kept warm for 1-2 hours, so that the hydroxyl group and the five-membered ring undergo thermal rearrangement reaction to transform into an oxazole ring.

[0017] The second aspect of the present invention also provides a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient, which is prepared by the preparation method.

[0018] As an improvement, the dielectric constant of the copolymerized polyimide film is 2.7-3.0, and the thermal expansion coefficient is 19.5-26.5 ppm / K.

[0019] Compared with the prior art, the present invention enhances the structural stability and thermal stability of the copolymer polyimide by introducing an ortho-hydroxyl group into the main chain and converting the ortho-hydroxyl group into an oxazole ring through a thermal rearrangement reaction; at the same time, cage-shaped polysilsesquioxane is used as a main chain end-capping agent for end-capping, and the introduced end-capping group is equivalent to the introduction of a porous material (the introduction of air), which can reduce the dielectric constant. The dielectric constant of the copolymer polyimide film prepared by the present invention is 2.7-3.0, and the thermal expansion coefficient is 19.5-26.5ppm / K. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a preparation flow chart of the present invention, wherein FIG. 1( b ) is a reaction process following FIG. 1( a );

[0021] Figure 2 is the structural formula of the copolymerized polyimide of the present invention;

[0022] Figure 3 Infrared test images of the copolymerized polyimide film obtained in the embodiment of the present invention and the polyimide film obtained in the control example;

[0023] Figure 4 The dielectric constant diagram of the copolymerized polyimide film obtained in the embodiment of the present invention and the polyimide film obtained in the comparative example;

[0024] Figure 5 The thermomechanical analysis test diagrams of the copolymerized polyimide film prepared in the embodiment of the present invention and the polyimide film prepared in the control example are shown. DETAILED DESCRIPTION

[0025] The following embodiments are further descriptions of the content of the present invention as an explanation of the technical content of the present invention, but the essential content of the present invention is not limited to the following embodiments. Ordinary technicians in this field can and should know that any simple changes or replacements based on the essential spirit of the present invention should fall within the scope of protection required by the present invention.

[0026] As shown in FIG1 , a method for preparing a copolymerized polyimide film with a low dielectric constant and a low thermal expansion coefficient comprises the following steps:

[0027] S1, reacting 0.019-0.021 mol of aromatic dianhydride and 0.017-0.023 mol of diamine unit in 0.45-0.48 mol of solvent, and then adding 0.0004 mol of end-capping agent dissolved in 0.13-0.15 mol of solvent to react, to prepare a polyamic acid containing ortho-hydroxyl group in the main chain;

[0028] The diamine unit comprises 10% to 40% by mole of a main chain monomer containing ortho-hydroxyl groups and the remainder being an aromatic diamine;

[0029] S2, the polyamic acid solution is evenly coated on a glass plate, placed in a vacuum drying oven at 130-150°C for 2-4 hours, and then placed in a muffle furnace for thermal imidization, the thermal imidization procedure is: 200°C × 1 hour, 300°C × 1 hour, 330°C × 1 hour;

[0030] S3, placing the prepared polyimide film in a tubular furnace filled with argon gas for thermal rearrangement reaction, heating to 300-500°C and keeping the temperature for 1-2 hours, so that the hydroxyl group and the five-membered ring undergo thermal rearrangement reaction to transform into an oxazole ring, and obtain a copolymer polyimide film containing an oxazole ring in the main chain. The present invention enhances the structural stability and thermal stability of the copolymer polyimide by introducing an ortho-hydroxyl rigid group oxazole ring in the main chain; in addition, the structure of the obtained copolymer polyimide is as follows Figure 2 shown.

[0031] Among them, in step S1, the monomer containing ortho-hydroxyl groups in the main chain is 2,2-bis(4-hydroxy-3-aminophenyl)propane; the aromatic dianhydride is at least one of 4,4'-biphenyl ether dianhydride, pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and bisphenol A type diether dianhydride; the aromatic diamine is at least one of 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether; the end-capping agent is cage-shaped polysilsesquioxane; and the solvent is at least one of tetrahydrofuran, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0032] The present invention adopts a thermomechanical analysis method, referred to as TMA method, to characterize the thermal expansion coefficient of copolymerized polyimide film. The method uses a thermomechanical analyzer to measure the change of film length with temperature in a tensile mode, and calculates the CTE / / values ​​of different temperature intervals according to the slope of the size-temperature curve. The method has high test accuracy, convenient sample processing and fast test speed, and is currently the most common method for testing the CTE / / of film materials.

[0033] Secondly, cage-shaped polysilsesquioxane (POSS) was introduced as a capping agent to effectively reduce the dielectric constant of PI by utilizing its low dielectric properties and steric hindrance effect.

[0034] According to the Debye formula:

[0035]

[0036] Where k is the dielectric constant, - is the dipole number density, α e is the electric polarization, α d is the distortion polarization, μ is the orientation polarization related to the dipole moment, k b is the Boltzmann constant, and T is the temperature. In polyimide, polarization includes α e , α d First, the introduction of cage-shaped polysilsesquioxane (POSS) can directly reduce the polarizability of polyimide. At the same time, the introduction of ortho-hydroxyl groups can directly increase the free volume of polyimide, thereby reducing its dielectric constant.

[0037] The dielectric constant in the present invention is detected by a conventional method, using an impedance analyzer to measure the inter-film capacitance, and then calculating the dielectric constant according to formula (2).

[0038]

[0039] Among them, K is the dielectric constant, which represents the electrical properties of the medium; c is the capacitance, which refers to the capacitance value measured by the impedance analyzer; d is the thickness of the dielectric layer; A is the area between the electrodes; k0 is the dielectric constant in a vacuum, which is a physical constant.

[0040] Example 1

[0041] A method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient comprises the following steps:

[0042] (1) N2 was passed into a three-necked flask, and 0.014 mol of 4,4'-diaminodiphenyl ether (ODA), 0.006 mol of 2,2-bis(4-hydroxy-3-aminophenyl)propane (BAP), and 0.47 mol of N,N-dimethylacetamide (DMAC) solvent were weighed and added into the three-necked flask (0.3 mol of DMAC was added first, and 0.17 mol of DMAC was left). DMAC in beaker, is convenient to flush the reagent remaining on flask), stirring and mixing, after monomer is thoroughly dissolved, weigh 0.02mol pyromellitic anhydride (PMDA), add twice, interval 15min, each time with DMAC, the PMDA residual in bottle mouth is washed down, weigh 0.0004mol aminopropyl heptyl-cage polysilsesquioxane (POSS-NH2) and 0.143mol tetrahydrofuran (THF), POSS end-capping agent is fully incorporated in THF, after adding PMDA for the second time, start timing, add POSS end-capping agent after 1h, at room temperature react 4 hours, obtain polyamic acid solution;

[0043] (2) The polyamic acid solution is coated on a glass slide, placed in a vacuum drying oven and heated to 140°C for 4 h, and then placed in a muffle furnace for thermal imidization. The thermal imidization procedure is: 200°C × 1 h, 300°C × 1 h, 330°C × 1 h. Ensure that the solvent is completely volatilized. The film is placed in a tubular furnace with argon gas for thermal rearrangement reaction, heated to 400°C and kept warm for 1 h, so that the hydroxyl group and the five-membered ring undergo thermal rearrangement reaction to transform into an oxazole ring, thereby obtaining a copolymer polyimide film.

[0044] The thermal expansion coefficient of the copolymerized polyimide film obtained in Example 1 is 25.48 ppm / K, and the dielectric constant is 2.95.

[0045] Comparative Example 1

[0046] A method for preparing a polyimide film comprises the following steps:

[0047] (1) N2 was passed into a three-necked flask, and 0.014 mol of 4,4'-diaminodiphenyl ether (ODA), 0.006 mol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 0.61 mol of N,N-dimethylacetamide (DMAC) solvent were weighed and added into the three-necked flask (0.5 mol of DMAC was added first, and 0.11 mol of DMAC was left in the beaker to facilitate washing away the reagents remaining on the flask), and the mixture was stirred and mixed evenly. After the monomers were completely dissolved, 0.02 mol of pyromellitic dianhydride (PMDA) was weighed and added twice with an interval of 15 minutes, and the PMDA remaining at the mouth of the flask was washed down with DMAC each time, and the mixture was reacted at room temperature for 4 hours to obtain a polyamic acid solution;

[0048] (2) The polyamic acid solution was coated on a glass slide, placed in a vacuum drying oven and heated to 140°C for 4 h, and then placed in a muffle furnace for thermal imidization. The thermal imidization procedure was: 200°C × 1 h, 300°C × 1 h, 330°C × 1 h. Ensure that the solvent is completely evaporated. The film was placed in a tubular furnace with argon gas, heated to 400°C and kept warm for 1 h to obtain a polyimide film.

[0049] The thermal expansion coefficient of the polyimide film obtained in Control Example 1 is 43.07 ppm / K and the dielectric constant is 3.32.

[0050] Example 2

[0051] A method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient comprises the following steps:

[0052] (1) N2 was passed into a three-necked flask, and 0.012 mol of 4,4'-diaminodiphenyl ether (ODA), 0.008 mol of 2,2-bis(4-hydroxy-3-aminophenyl)propane (BAP), and 0.476 mol of N,N-dimethylacetamide (DMAC) solvent were weighed and added into the three-necked flask (0.35 mol of DMAC was added first, and 0.126 mol of DMAC was left). DMAC in beaker, is convenient to flush the reagent remaining on flask), stirring and mixing, after monomer is thoroughly dissolved, weigh 0.02mol pyromellitic anhydride (PMDA), add twice, interval 15min, each time with DMAC, the PMDA residual in bottle mouth is washed down, weigh 0.0004mol aminopropyl heptyl-cage polysilsesquioxane (POSS-NH2) and 0.143mol tetrahydrofuran (THF), POSS end-capping agent is fully incorporated in THF, after adding PMDA for the second time, start timing, add POSS end-capping agent after 1h, at room temperature react 4 hours, obtain polyamic acid solution;

[0053] (2) Place the film in a vacuum drying oven and heat at 130°C for 4 h, then place it in a muffle furnace for thermal imidization. The thermal imidization procedure is: 200°C × 1 h, 300°C × 1 h, 330°C × 1 h. Ensure that the solvent is completely evaporated. Place the film in a tubular furnace with argon gas for thermal rearrangement reaction. Heat to 400°C and keep warm for 1 h to allow the hydroxyl group and the five-membered ring to undergo thermal rearrangement reaction to transform into an oxazole ring, thereby obtaining a copolymer polyimide film.

[0054] The thermal expansion coefficient of the copolymerized polyimide film obtained in Example 2 is 26.36 ppm / K and the dielectric constant is 2.85.

[0055] Comparative Example 2

[0056] A method for preparing a polyimide film comprises the following steps:

[0057] (1) N2 was passed into a three-necked flask, and 0.012 mol of 4,4'-diaminodiphenyl ether (ODA), 0.008 mol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 0.63 mol of N,N-dimethylacetamide (DMAC) solvent were weighed and added into the three-necked flask (0.4 mol of DMAC was added first, and 0.23 mol of DMAC was left in the beaker to facilitate washing away the reagents remaining on the flask), and the mixture was stirred and mixed evenly. After the monomers were completely dissolved, 0.02 mol of pyromellitic dianhydride (PMDA) was weighed and added twice with an interval of 15 min, and the PMDA remaining at the mouth of the flask was washed down with DMAC each time, and the mixture was reacted at room temperature for 4 hours to obtain a polyamic acid solution;

[0058] (2) The polyamic acid solution was coated on a glass slide, placed in a vacuum drying oven and heated to 130°C for 4 h, and then placed in a muffle furnace for thermal imidization. The thermal imidization procedure was: 200°C × 1 h, 300°C × 1 h, 330°C × 1 h. Ensure that the solvent is completely evaporated. The film was placed in a tubular furnace with argon gas, heated to 400°C and kept warm for 1 h to obtain a polyimide film.

[0059] The thermal expansion coefficient of the polyimide film obtained in Control Example 2 is 41.16 ppm / K and the dielectric constant is 3.3.

[0060] Example 3

[0061] A method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient comprises the following steps:

[0062] (1) N2 was passed into a three-necked flask, and 0.016 mol of 4,4'-diaminodiphenyl ether (ODA), 0.004 mol of 2,2-bis(4-hydroxy-3-aminophenyl)propane (BAP), and 0.463 mol of N,N-dimethylacetamide (DMAC) solvent were weighed and added into the three-necked flask (0.3 mol of DMAC was added first, and 0.163 mol of DMAC was left). DMAC in beaker, is convenient to flush the reagent remaining on flask), stirring and mixing, after monomer is thoroughly dissolved, weigh 0.02mol pyromellitic anhydride (PMDA), add twice, interval 15min, each time with DMAC, the PMDA residual in bottle mouth is washed down, weigh 0.0004mol aminopropyl heptyl-cage polysilsesquioxane (POSS-NH2) and 0.140mol tetrahydrofuran (THF), POSS end-capping agent is fully incorporated in THF, after adding PMDA for the second time, start timing, add POSS end-capping agent after 1h, at room temperature react 4 hours, obtain polyamic acid solution;

[0063] (2) The polyamic acid solution is coated on a glass slide, placed in a vacuum drying oven and heated to 140°C for 4 h, and then placed in a muffle furnace for thermal imidization. The thermal imidization procedure is: 200°C × 1 h, 300°C × 1 h, 330°C × 1 h. Ensure that the solvent is completely volatilized. The film is placed in a tubular furnace with argon gas for thermal rearrangement reaction, heated to 400°C and kept warm for 1 h, so that the hydroxyl group and the five-membered ring undergo thermal rearrangement reaction to transform into an oxazole ring, thereby obtaining a copolymer polyimide film.

[0064] The thermal expansion coefficient of the copolymerized polyimide film obtained in Example 3 is 22.74 ppm / K, and the dielectric constant is 2.85.

[0065] Comparative Example 3

[0066] A method for preparing a polyimide film comprises the following steps:

[0067] (1) N2 was passed into a three-necked flask, and 0.016 mol of 4,4'-diaminodiphenyl ether (ODA), 0.004 mol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 0.59 mol of N,N-dimethylacetamide (DMAC) solvent were weighed and added into the three-necked flask (0.4 mol of DMAC was added first, and 0.19 mol of DMAC was left in the beaker to facilitate washing away the reagents remaining on the flask), and the mixture was stirred and mixed evenly. After the monomers were completely dissolved, 0.02 mol of pyromellitic dianhydride (PMDA) was weighed and added twice with an interval of 15 minutes, and the PMDA remaining at the mouth of the flask was washed down with DMAC each time, and the mixture was reacted at room temperature for 4 hours to obtain a polyamic acid solution;

[0068] (2) The polyamic acid solution was coated on a glass slide, placed in a vacuum drying oven and heated to 140°C for 4 h, and then placed in a muffle furnace for thermal imidization. The thermal imidization procedure was: 200°C × 1 h, 300°C × 1 h, 330°C × 1 h. Ensure that the solvent is completely evaporated. The film was placed in a tubular furnace with argon gas, heated to 400°C and kept warm for 1 h to obtain a polyimide film.

[0069] The thermal expansion coefficient of the polyimide film obtained in Control Example 3 is 41.538 ppm / K and the dielectric constant is 3.19.

[0070] Example 4

[0071] A method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient comprises the following steps:

[0072] (1) N2 was passed into a three-necked flask, and 0.01532 mol of 4,4'-diaminodiphenyl ether (ODA), 0.002 mol of 2,2-bis(4-hydroxy-3-aminophenyl)propane (BAP), and 0.4576 mol of N,N-dimethylacetamide (DMAC) solvent were weighed and added into the three-necked flask (0.3076 mol of DMAC was added first, and 0.15 mol of DMAC was left). DMAC in beaker, is convenient to flush the reagent remaining on flask), stirring and mixing, after monomer is thoroughly dissolved, weigh 0.02mol pyromellitic anhydride (PMDA), add twice, interval 15min, each time with DMAC, the PMDA residual in bottle mouth is washed down, weigh 0.0004mol aminopropyl heptyl-cage polysilsesquioxane (POSS-NH2) and 0.1386mol tetrahydrofuran (THF), POSS end-capping agent is fully incorporated in THF, after adding PMDA for the second time, start timing, add POSS end-capping agent after 1h, at room temperature react 4 hours, obtain polyamic acid solution;

[0073] (2) The polyamic acid solution is coated on a glass slide, placed in a vacuum drying oven and heated to 140°C for 4 h, and then placed in a muffle furnace for thermal imidization. The thermal imidization procedure is: 200°C × 1 h, 300°C × 1 h, 330°C × 1 h. Ensure that the solvent is completely volatilized. The film is placed in a tubular furnace with argon gas for thermal rearrangement reaction, heated to 400°C and kept warm for 1 h, so that the hydroxyl group and the five-membered ring undergo thermal rearrangement reaction to transform into an oxazole ring, thereby obtaining a copolymer polyimide film.

[0074] The thermal expansion coefficient of the copolymerized polyimide film obtained in Example 4 is 19.65 ppm / K, and the dielectric constant is 2.79.

[0075] Comparative Example 4

[0076] A method for preparing a polyimide film comprises the following steps:

[0077] (1) N2 was passed into a three-necked flask, 0.018 mol of 4,4'-diaminodiphenyl ether (ODA), 0.002 mol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 0.567 mol of N,N-dimethylacetamide (DMAC) solvent were weighed and added into the three-necked flask (0.45 mol of DMAC was added first, and 0.117 mol of DMAC was left in the beaker), and the mixture was stirred and mixed evenly. After the monomers were completely dissolved, 0.02 mol of pyromellitic anhydride (PMDA) was weighed and added twice, with an interval of 15 minutes. The PMDA remaining at the mouth of the flask was washed down with DMAC each time, and the mixture was reacted at room temperature for 4 hours to obtain a polyamic acid solution;

[0078] (2) The polyamic acid solution was coated on a glass slide, placed in a vacuum drying oven and heated to 140°C for 4 h, and then placed in a muffle furnace for thermal imidization. The thermal imidization procedure was: 200°C × 1 h, 300°C × 1 h, 330°C × 1 h. Ensure that the solvent is completely evaporated. The film was placed in a tubular furnace with argon gas, heated to 400°C and kept warm for 1 h to obtain a polyimide film.

[0079] The thermal expansion coefficient of the polyimide film obtained in Control Example 4 is 40.0224 ppm / K and the dielectric constant is 3.22.

[0080] The infrared tests of the above embodiments and comparative examples are as follows: Figure 3 As shown, analysis shows that 1775cm -1 and 1703cm -1 It is the absorption peak of the symmetrical and asymmetrical stretching vibration of the carbonyl C=O on the imine ring; 1366cm -1 is the absorption peak of CN stretching vibration on the imide group. These characteristic absorption peaks indicate that the polyimide structure was successfully synthesized. 1455cm -1 The characteristic peak of the oxazole ring is 964 cm -1 It is a weak absorption peak of Si-O stretching vibration, indicating the successful polymerization of the modified copolymer polyimide;

[0081] The dielectric constant is Figure 4 As shown in the figure, the dielectric constant of the copolymerized polyimide film after adding the POSS end-capping agent is reduced. The reason is that after the introduction of the POSS group, it is equivalent to the introduction of porous materials and air, which causes the dielectric constant to decrease. As the BAP feed ratio increases, the dielectric constant increases. Because the dielectric constant and thermal expansion coefficient are mutually exclusive, the rigidity of the molecule increases after the oxazole ring is introduced into the molecular chain, and the free volume of the molecular activity decreases, so the dielectric constant will increase with the increase of BAP;

[0082] Thermomechanical analysis test Figure 5As shown in the figure (where the control examples 1 and 2 are overlapped), it can be seen from the analysis that after the addition of the POSS end-capping agent, the thermal expansion coefficient has a significant decrease. The reason for the decrease in the thermal expansion coefficient is that the thermal rearrangement reaction causes the hydroxyl group and the five-membered ring to undergo a thermal rearrangement reaction to transform into an oxazole ring. Due to the introduction of the ortho-hydroxyl rigid group oxazole ring in the main chain, the structural stability and thermal stability of the copolymerized polyimide are enhanced.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient, characterized in that: The following steps are involved: S1, reacting 0.019-0.021 mol of aromatic dianhydride and 0.017-0.023 mol of diamine unit in 0.45-0.48 mol of solvent, and then adding 0.0004 mol of end-capping agent dissolved in 0.13-0.15 mol of solvent to react, to prepare a polyamic acid containing ortho-hydroxyl group in the main chain; The diamine unit comprises 10% to 40% by mole of a main chain monomer containing ortho-hydroxyl groups and the remainder being an aromatic diamine; S2, preparing a polyimide film by coating and thermal imidization of polyamic acid; S3, heating the prepared polyimide film to allow the ortho-hydroxyl groups to undergo thermal rearrangement reaction, thereby obtaining a copolymerized polyimide film containing an oxazole ring in the main chain.

2. The method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient according to claim 1, characterized in that: In the step S1, the monomer containing ortho-hydroxyl groups in the main chain is 2,2-bis(4-hydroxy-3-aminophenyl)propane.

3. The method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient according to claim 1, characterized in that: In the step S1, the aromatic dianhydride is at least one of 4,4'-biphenyl ether dianhydride, pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and bisphenol A diether dianhydride.

4. The method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient according to claim 1, characterized in that: In the step S1, the aromatic diamine is at least one of 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether.

5. The method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient according to claim 1, characterized in that: In the step S1, the end-capping agent is cage-shaped polysilsesquioxane.

6. The method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient according to claim 1, characterized in that: In the step S1, the solvent is at least one of tetrahydrofuran, N,N-dimethylacetamide and N,N-dimethylformamide.

7. The method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient according to claim 1, characterized in that: In step S2, the polyamic acid solution is evenly coated on a glass plate, placed in a vacuum drying oven at 130-150°C for 2-4 hours, and then placed in a muffle furnace for thermal imidization. The thermal imidization procedure is: 200°C×1 hour, 300°C×1 hour, and 330°C×1 hour.

8. The method for preparing a copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient according to claim 1, characterized in that: In the step S3, the prepared polyimide film is placed in a tubular furnace filled with argon gas for thermal rearrangement reaction, and heated to 300-500° C. for 1-2 hours, so that the hydroxyl group and the five-membered ring undergo thermal rearrangement reaction to transform into an oxazole ring.

9. A copolymer polyimide film with low dielectric constant and low thermal expansion coefficient, characterized in that: The method is prepared by the method according to any one of claims 1 to 8.

10. A copolymerized polyimide film with low dielectric constant and low thermal expansion coefficient according to claim 9, characterized in that: The dielectric constant of the copolymerized polyimide film is 2.7-3.0, and the thermal expansion coefficient is 19.5-26.5 ppm / K.

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