Crystalline polyimide, preparation method and application thereof, polyimide film and application thereof

Abstract

The invention provides crystalline polyimide, a preparation method and application thereof, a polyimide film and application thereof, and relates to the technical field of polymer film materials. The polyimide molecular structure provided by the invention contains a terphenyl group for promoting polyimide molecular crystallization and an ether bond for improving the movement ability of a polyimide molecular chain, and the terphenyl group and the ether bond synergistically regulate and optimize polyimide molecules, so that molecules in a polyimide molecule crystallization region are arranged in order; molecular chains are promoted to be arranged in order to form a crystal phase structure, and high crystallinity is achieved; the spherocrystals are mutually connected and stacked, so that a continuous heat conduction path is favorably formed, high-efficiency conduction of phonons is facilitated, heat is propagated at higher efficiency through lattice thermal vibration, and crystalline polyimide and a polyimide film formed by the crystalline polyimide have higher intrinsic heat conduction performance.

Description

Technical Field

[0001] This invention relates to the field of polymer membrane materials technology, specifically to a crystalline polyimide, its preparation method and application, and a polyimide membrane and its application. Background Technology

[0002] With the rapid development of electronic and electrical equipment and components towards miniaturization, integration, and intelligence, the heat density of electronic and electrical products is increasing dramatically, severely affecting their working efficiency and service life. Polyimide (PI) films, due to their excellent insulation, mechanical properties, high / low temperature resistance, radiation resistance, flame retardancy, and chemical stability, are often used as outer films, interlayer dielectrics, and sealing materials for flexible screens, packaging substrates, and other electronic and electrical products. However, polyimide materials are saturated systems internally, and thermal conductivity is mainly dominated by phonons. Due to molecular chain entanglement and defects, the degree of order in polymer chain segments is low, and the incoordination between molecular vibrations and lattice vibrations easily induces phonon scattering during heat transfer. Therefore, the intrinsic thermal conductivity of polyimide films is relatively low, which cannot meet the high-efficiency and rapid heat dissipation requirements of 5G and 6G era electronic products, greatly limiting the further application of polyimide films in new electronic and electrical products. Summary of the Invention

[0003] In view of this, the object of the present invention is to provide a crystalline polyimide, a method for preparing the same, and its application, as well as a polyimide film and its application. The crystalline polyimide provided by the present invention has high crystallinity, and both the crystalline polyimide and the polyimide film formed from the crystalline polyimide exhibit excellent intrinsic thermal conductivity.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a crystalline polyimide, the polyimide molecule having the structure shown in Formula I: Formula I; Where m:n = 1:0 ~ 0:1, and n is not 0; The crystalline polyimide has a spherulite morphology.

[0005] This invention provides a method for preparing the crystalline polyimide described in the above technical solution, comprising the following steps: A diamine solution was obtained by mixing 4,4'-diaminoterphenyl with a first polar aprotic solvent. A dianhydride solution is obtained by mixing 4,4'-biphenyl ether dianhydride, pyromellitic anhydride, and a second polar aprotic solvent. The diamine solution and the dianhydride solution are mixed and subjected to a polycondensation reaction to obtain a polyamic acid solution; The polyamic acid solution was desolventized and crystallized, followed by thermal imidization to obtain the crystalline polyimide; The molar ratio of 4,4'-biphenyl ether dianhydride and pyromellitic anhydride is 1:0 to 0:1, and the amount of pyromellitic anhydride used is not zero.

[0006] Preferably, the ratio of the total molar amount of 4,4'-biphenyl ether dianhydride and pyromellitic anhydride to the molar amount of 4,4'-diaminoterphenyl is 0.998~1.002:1.

[0007] Preferably, the mass ratio of the 4,4'-diaminoterphenyl to the first polar aprotic solvent is 0.05~0.15:1; The first polar aprotic solvent includes one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0008] Preferably, the ratio of the total mass of the 4,4'-biphenyl ether dianhydride and pyromellitic anhydride to the mass of the second polar aprotic solvent is 0.05~0.15:1; The second polar aprotic solvent independently includes one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0009] Preferably, the polycondensation reaction is carried out at a temperature of -5 to 5°C for 4 to 6 hours. The polycondensation reaction is carried out under a protective atmosphere.

[0010] Preferably, the temperature for desolvation and crystallization is 60~80℃, and the time is 1~2h.

[0011] Preferably, the thermal imidization is a gradient thermal imidization, wherein the initial holding temperature of the gradient thermal imidization is 110~130℃, the final holding temperature is 280~320℃, and the total holding time is 4.1~10h.

[0012] The present invention also provides a polyimide film, wherein the polyimide film is made of the crystalline polyimide described in the above technical solution or the crystalline polyimide prepared by the preparation method described in the above technical solution.

[0013] This invention provides the application of the crystalline polyimide or the polyimide film described in the above-mentioned technical solutions in electronic and electrical products.

[0014] The polyimide molecular structure provided by this invention contains terphenyl groups that promote polyimide crystallization and ether bonds that increase the mobility of polyimide molecular chains. The terphenyl groups consist of three benzene rings directly linked by single bonds, forming a highly symmetrical linear rigid structure with strong intermolecular forces and a strong π-π stacking effect. The flexibility of the ether bonds can regulate the local mobility of the molecular chains. The terphenyl groups and ether bonds synergistically regulate and optimize the polyimide molecule, resulting in an ordered molecular arrangement within the crystalline regions of the polyimide molecule. This promotes the orderly arrangement of molecular chains to form a crystalline structure with high crystallinity. Furthermore, the interconnection and stacking of spherulites facilitates the formation of continuous heat conduction pathways, promoting efficient phonon conduction. Lattice thermal vibrations enable heat to spread more efficiently, giving the crystalline polyimide and the polyimide film formed from it higher intrinsic thermal conductivity.

[0015] The method for preparing crystalline polyimide provided in this application involves a polycondensation reaction of a diamine (4,4'-diaminoterphenyl) and a dianhydride (pyromellitic anhydride, or 4,4'-diphenyl ether dianhydride and pyromellitic anhydride), followed by crystallization through solvent removal and thermal imidization. During the solvent removal crystallization process, the terphenyl groups and ether bonds readily adjust their conformation in solution, facilitating orderly arrangement and crystal nucleation during solvent evaporation. Uncrystallized polyamic acid and unprecipitated but already crystalline polyamic acid gradually precipitate as spherulites, which further crystallize during thermal imidization. The resulting crystalline polyimide exhibits a spherulite morphology with large size, abundant quantity, uniform distribution, and high crystallinity. The crystalline polyimide and the polyimide film formed from it possess excellent intrinsic thermal conductivity. Furthermore, the preparation method provided by this invention is simple to operate and suitable for industrial production. Attached Figure Description

[0016] Figure 1 A polarizing microscope image of the process of thermal imidization of polyamic acid to form polyimide obtained in Example 1; Figure 2 This is a polarizing microscope image of the process of thermal imidization of polyamic acid to form polyimide obtained in Example 2. Figure 3 A polarizing microscope image of the process of thermal imidization of polyamic acid to form polyimide prepared in Example 3; Figure 4 This is a polarizing microscope image of the polyamic acid thermal imidization process to produce polyimide in Comparative Example 1. Detailed Implementation

[0017] This invention provides a crystalline polyimide, the polyimide molecule having the structure shown in Formula I: Formula I; Wherein, m:n = 1:0 ~ 0:1, and n is not 0; the crystalline morphology of the crystalline polyimide is spherulite.

[0018] In this invention, the ratio of m to n in the polyimide molecule is m:n = 1:0 to 0:1, specifically 9.5:0.5, 9:1, 7:3, 5:5, 3:7, 1:9 or 0:10; n is not 0; the number average molecular weight of the polyimide molecule can be 20,000 to 30,000, specifically 20,000, 22,000, 24,000, 26,000, 28,000 or 30,000.

[0019] This invention provides a method for preparing the crystalline polyimide described above, comprising the following steps: mixing 4,4'-diaminoterphenyl and a first polar aprotic solvent to obtain a diamine solution; mixing 4,4'-biphenyl ether dianhydride, pyromellitic tetracarboxylic anhydride, and a second polar aprotic solvent to obtain a dianhydride solution; mixing the diamine solution and the dianhydride solution to perform a polycondensation reaction to obtain a polyamic acid solution; and thermally imidizing the polyamic acid solution after solvent removal and crystallization to obtain the crystalline polyimide; wherein the molar ratio of the 4,4'-biphenyl ether dianhydride and pyromellitic tetracarboxylic anhydride is 1:0 to 0:1, and the amount of pyromellitic tetracarboxylic anhydride is not zero.

[0020] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0021] In this invention, the preparation route of the polyimide molecule is shown in Route 1: Route 1.

[0022] In this invention, 4,4'-diaminoterphenyl and a first polar aprotic solvent are mixed (denoted as the first mixture) to obtain a diamine solution.

[0023] In this invention, the first polar aprotic solvent may include one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone; the mass ratio of the 4,4'-diaminoterphenyl to the first polar aprotic solvent may be 0.05~0.15:1, specifically 0.05:1, 0.06:1, 0.08:1, 0.1:1, 0.12:1, 0.14:1, or 0.15:1.

[0024] In this invention, the temperature of the first mixing can be -5 to 5°C, specifically -5°C, -3°C, -2°C, 0°C, 2°C, or 5°C; the time of the first mixing can be 0.5 to 1 hour, specifically 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, or 1 hour; the first mixing can be carried out under a protective atmosphere; the protective atmosphere can be one or more of nitrogen, helium, and argon. This invention does not specifically limit the method of the first mixing, as long as it ensures complete mixing of 4,4'-diaminoterphenyl and the first polar aprotic solvent, such as through mechanical stirring. The first mixing under a protective atmosphere in this invention can prevent the oxidation of 4,4'-diaminoterphenyl.

[0025] In this invention, 4,4'-biphenyl ether dianhydride, pyromellitic anhydride, and a second polar aprotic solvent are mixed (denoted as the second mixture) to obtain a dianhydride solution.

[0026] In this invention, the molar ratio of 4,4'-biphenyl ether dianhydride and pyromellitic anhydride is 1:0 to 0:1, specifically 9.5:0.5, 9:1, 7:3, 5:5, 3:7, 1:9 or 0:10; the amount of pyromellitic anhydride used is not 0.

[0027] In this invention, the second polar aprotic solvent may include one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone; the mass ratio of the total mass of the 4,4'-biphenyl ether dianhydride and pyromellitic anhydride to the mass of the second polar aprotic solvent may be 0.05 to 0.15:1, specifically 0.05:1, 0.06:1, 0.08:1, 0.1:1, 0.12:1, 0.14:1, or 0.15:1.

[0028] In this invention, the temperature of the second mixing can be -5 to 5°C, specifically -5°C, -3°C, -2°C, 0°C, 2°C, or 5°C; the time of the second mixing can be 0.5 to 1 hour, specifically 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, or 1 hour; the second mixing can be carried out under a protective atmosphere, which can be a nitrogen atmosphere and / or an argon atmosphere. This invention does not specifically limit the method of the second mixing, as long as it ensures complete mixing of 4,4'-biphenyl ether dianhydride, pyromellitic anhydride, and the second polar aprotic solvent, such as ultrasonic mixing. The second mixing under a protective atmosphere in this invention prevents the 4,4'-biphenyl ether dianhydride and pyromellitic anhydride from reacting with water in the air and undergoing hydrolysis.

[0029] After obtaining the diamine solution and the dianhydride solution, the present invention mixes the diamine solution and the dianhydride solution (referred to as the third mixture) and carries out a polycondensation reaction to obtain a polyamic acid solution.

[0030] In this invention, the ratio of the total molar amount of 4,4'-biphenyl ether dianhydride and pyromellitic anhydride to the molar amount of 4,4'-diaminoterphenyl can be 0.998 to 1.002:1, specifically 0.998:1, 0.999:1, 1:1, 1.001:1, or 1.002:1.

[0031] In this invention, the temperature of the polycondensation reaction can be -5 to 5°C, specifically -5°C, -2°C, 0°C, 3°C, or 5°C; the time of the polycondensation reaction can be 4 to 6 hours, specifically 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours; the polycondensation reaction can be carried out under mechanical stirring and a protective atmosphere; the speed of the mechanical stirring can be 100 to 180 rpm, specifically 100 rpm, 120 rpm, 140 rpm, 160 rpm, or 180 rpm; the protective atmosphere can be a nitrogen atmosphere and / or an argon atmosphere.

[0032] In this invention, the third mixing may include adding the diamine solution to the dianhydride solution in batches for mixing; the third mixing may be carried out under a protective atmosphere; the protective atmosphere may be a nitrogen atmosphere and / or an argon atmosphere.

[0033] After obtaining the polyamic acid solution, the present invention desolventizes and crystallizes the polyamic acid solution, followed by thermal imidization to obtain crystalline polyimide.

[0034] In this invention, the temperature for desolvation and crystallization can be 60~80℃, specifically 60℃, 65℃, 70℃, 75℃ or 80℃; the time for desolvation and crystallization is 1~2h, specifically 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2h.

[0035] In this invention, the thermal imidization can be a gradient thermal imidization, which may include sequentially performing a first heating, a first holding (initial holding), a second heating, a second holding, a third heating, a third holding, a fourth heating, a fourth holding, a fifth heating, and a fifth holding (final holding). In this invention, the total holding time for the gradient thermal imidization can be 4.1~10h, specifically 4.1h, 5h, 6h, 8h, 9h, 9.5h, or 10h. In this invention, the temperature of the first holding can be 110~130℃, specifically 110℃, 115℃, 120℃, 125℃, or 130℃; the duration of the first holding can be 0.5~1.5h, specifically 0.5h, 1h, or 1.5h. In this invention, the second heat preservation temperature can be 150~170℃, specifically 150℃, 155℃, 160℃, 165℃, or 170℃; the second heat preservation time can be 0.5~1.5h, specifically 0.5h, 1h, or 1.5h. In this invention, the third heat preservation temperature can be 190~210℃, specifically 190℃, 195℃, 200℃, 205℃, or 210℃; the third heat preservation time can be 0.8~2h, specifically 0.8h, 1h, 1.5h, or 2h. In this invention, the fourth heat preservation temperature can be 240~260℃, specifically 240℃, 245℃, 250℃, 255℃, or 260℃; the fourth heat preservation time can be 0.8~2h, specifically 0.8h, 1h, 1.5h, or 2h. In this invention, the temperature of the fifth heat preservation can be 280~320℃, specifically 280℃, 285℃, 290℃, 295℃, 300℃, 305℃, 310℃, 315℃, or 320℃; the time of the fifth heat preservation can be 1.5~3h, specifically 1.5h, 2h, 2.5h, or 3h. In this invention, the heating rates of the first, second, third, fourth, and fifth heating processes can independently be 1~3℃ / min, specifically 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, or 3℃ / min. In this invention, the gradient thermal imidization can specifically be achieved by sequentially heating to 120°C and holding for 1 hour, heating to 160°C and holding for 1 hour, heating to 200°C and holding for 1 hour, heating to 250°C and holding for 1 hour, and heating to 300°C and holding for 2 hours.This invention employs gradient thermal imidization, which optimizes the condensed-state structure of the polyimide film, thereby avoiding the structural defects caused by non-gradient thermal imidization. The gradient heating and holding method allows the solvent sufficient time to slowly and orderly escape from the system, giving the molecular chains ample time and mobility to rearrange and regularize, thus forming a more perfect and stable crystal structure. It also avoids the formation of bubbles and pores on the surface and inside of the crystalline polyimide due to rapid solvent evaporation, thereby improving the crystallinity of the crystalline polyimide and the compactness of the polyimide film formed by the crystalline polyimide. In addition, the gradient thermal imidization of this invention can also prevent stress-induced crystallization, avoid the molecular chains being forced to form an imperfect crystal structure under stress, reduce internal stress concentration, and improve the dimensional stability and mechanical properties of the crystalline polyimide.

[0036] The present invention also provides a polyimide film, wherein the polyimide film is made of the crystalline polyimide described in the above technical solution or the crystalline polyimide prepared by the preparation method described in the above technical solution.

[0037] In this invention, the thickness of the polyimide film can be 60~120µm, and in specific embodiments it can be 60µm, 70µm, 80µm, 90µm, 100µm, 110µm or 120µm.

[0038] In this invention, the preparation method of the polyimide film may include the following steps: mixing 4,4'-diaminoterphenyl and a first polar aprotic solvent to obtain a diamine solution; mixing 4,4'-biphenyl ether dianhydride, pyromellitic anhydride, and a second polar aprotic solvent to obtain a dianhydride solution; mixing the diamine solution and the dianhydride solution to perform a polycondensation reaction to obtain a polyamic acid solution; and sequentially subjecting the polyamic acid solution to film formation, solvent removal crystallization, and thermal imidization to obtain a polyimide film; wherein the molar ratio of 4,4'-biphenyl ether dianhydride and pyromellitic anhydride is 1:0 to 0:1, wherein the pyromellitic anhydride is not 0.

[0039] In this invention, the intrinsic viscosity of the polyamic acid solution can be 1.2~2 dL / g, specifically 1.2 dL / g, 1.34 dL / g, 1.5 dL / g, 1.82 dL / g, 1.93 dL / g, 1.94 dL / g, or 2 dL / g. When the intrinsic viscosity is <1.2 dL / g, the polyamic acid is difficult to coat into a film or is coated into fragments, resulting in an incomplete polyimide film. When the intrinsic viscosity is >2 dL / g, the polyamic acid is too viscous, making film coating difficult. This invention limits the intrinsic viscosity of the polyamic acid solution to between 1.2 and 2 dL / g, making it easier to coat the polyamic acid into a smooth and complete film, thereby ensuring a smooth and complete polyimide film.

[0040] In this invention, the film formation may include a blade coating process, specifically: pouring the polyamic acid solution onto a substrate and then coating it with a blade to obtain a polyamic acid film. In this invention, the substrate may be a glass substrate, specifically a dry and clean glass substrate.

[0041] In this invention, the other preparation methods of the polyimide film are the same as those of the crystalline polyimide, and will not be described in detail here.

[0042] This invention provides the application of the crystalline polyimide or polyimide film described in the above-mentioned technical solutions in electronic and electrical products. The crystalline polyimide and polyimide film provided by this invention have high crystallinity and excellent intrinsic thermal conductivity, showing promising application prospects in the outer film, interlayer dielectric, and sealing materials of electronic and electrical products such as flexible screens and packaging substrates.

[0043] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a crystalline polyimide, its preparation method and application, and a polyimide film and its application, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1 Under a nitrogen atmosphere, 4,4'-diaminoterphenyl and N,N-dimethylacetamide were mixed and mechanically stirred in an ice-water bath to completely dissolve the 4,4'-diaminoterphenyl, resulting in a diamine solution with a concentration of 0.7 mol / L.

[0045] 4,4'-biphenyl ether dianhydride, pyromellitic anhydride, and N,N-dimethylacetamide were ultrasonically mixed for 10 min to obtain a dianhydride solution with a total concentration of 0.7 mol / L.

[0046] The diamine solution was added to the obtained dianhydride solution in batches and mixed. After mixing, the mixture was mechanically stirred in an ice-water bath for 5 hours at a stirring rate of 150 r / min to prepare a polyamic acid solution with an intrinsic viscosity of 1.83 dL / g. The molar ratio of 4,4'-diaminoterphenyl, 4,4'-diphenyl ether dianhydride, and pyromellitic anhydride was 1:0.3:0.7.

[0047] The prepared polyamic acid solution was poured onto a clean glass substrate and coated with a doctor blade to obtain a polyamic acid film of uniform thickness. The film was then dried in a forced-air oven at 80°C for 1 hour to remove N,N-dimethylacetamide and induce crystallization. After solvent removal and crystallization, gradient thermal imidization was performed to obtain a polyimide film. The temperature program for gradient thermal imidization was 120°C for 1 hour, 160°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 300°C for 2 hours, with a heating rate of 3°C / min to reach the target holding temperature.

[0048] The crystal morphology of the prepared polyimide film was characterized using polarized light microscopy. Figure 1 These are polarized light microscope images of the polyamic acid thermal imidization process to produce polyimide obtained in Example 1, where the temperatures corresponding to (a) to (h) are 20℃, 40℃, 60℃, 80℃, 120℃, 160℃, 200℃, and 300℃, respectively. Figure 1 It can be seen that the polyimide film prepared in this embodiment has a crystallinity of 19.32%, which is relatively high. The spherulites are small in size, numerous, and uniformly distributed. The thermal conductivity of the polyimide film was tested using a Hot Disk thermal constant analyzer. The in-plane thermal conductivity was 2.16 W / mK, and the inter-plane thermal conductivity was 0.15 W / mK. The polyimide film prepared has excellent intrinsic thermal conductivity.

[0049] Example 2 Under a nitrogen atmosphere, 4,4'-diaminoterphenyl and N,N-dimethylacetamide were mixed and mechanically stirred in an ice-water bath to completely dissolve the 4,4'-diaminoterphenyl, resulting in a diamine solution with a concentration of 0.74 mol / L.

[0050] Add pyromellitic anhydride to N,N-dimethylacetamide and sonicate for 10 min to obtain a dianhydride solution with a concentration of 0.74 mol / L.

[0051] A diamine solution was added to the obtained dianhydride solution in batches and mixed. After mixing, the mixture was mechanically stirred in an ice-water bath for 5 hours at a stirring rate of 150 r / min to prepare a polyamic acid solution with an intrinsic viscosity of 1.94 dL / g. The molar ratio of 4,4'-diaminoterphenyl and pyromellitic anhydride was 1:1.

[0052] The prepared polyamic acid solution was poured onto a clean glass substrate and coated with a doctor blade to obtain a polyamic acid film of uniform thickness. The film was then dried in a forced-air oven at 80°C for 1 hour to remove N,N-dimethylacetamide and induce crystallization. After solvent removal and crystallization, gradient thermal imidization was performed to obtain a polyimide film. The temperature program for gradient thermal imidization was 120°C for 1 hour, 160°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 300°C for 2 hours, with a heating rate of 3°C / min to reach the target holding temperature.

[0053] The crystallization effect is influenced by the ratio of acid anhydrides. The rigid structure of pyromellitic anhydride promotes orderly molecular arrangement and crystallization, but it restricts the mobility of molecular chains. While 4,4'-biphenyl ether dianhydride, containing ether bonds, enhances chain mobility and facilitates the adjustment of the crystallization process, it also disrupts the close packing of molecules, negatively impacting the crystal structure. In Example 2, using only pyromellitic anhydride, it is easier to form a larger number of smaller crystals. In Example 1, the introduction of more ether bonds increases molecular mobility but weakens the stacking order, resulting in a smaller number of crystals.

[0054] The crystal morphology of the prepared polyimide film was characterized using polarized light microscopy. Figure 2 These are polarized light microscope images of the polyamic acid thermal imidization process to produce polyimide obtained in Example 2, where the temperatures corresponding to (a) to (h) are 20℃, 40℃, 60℃, 80℃, 120℃, 160℃, 200℃, and 300℃, respectively. Figure 2 It can be seen that the polyimide film prepared in this embodiment has a crystallinity of 27.48%, which is relatively high. The spherulites are small in size, numerous, and densely distributed. The thermal conductivity of the polyimide film was tested using a Hot Disk thermal constant analyzer. The in-plane thermal conductivity was 2.34 W / mK, and the inter-plane thermal conductivity was 0.17 W / mK. The polyimide film prepared has excellent intrinsic thermal conductivity.

[0055] Example 3 Under a nitrogen atmosphere, 4,4'-diaminoterphenyl and N,N-dimethylacetamide were mixed and mechanically stirred in an ice-water bath to completely dissolve the 4,4'-diaminoterphenyl, resulting in a diamine solution with a concentration of 0.72 mol / L.

[0056] 4,4'-biphenyl ether dianhydride and pyromellitic anhydride were added to N,N-dimethylacetamide and ultrasonically mixed for 10 min to obtain a dianhydride solution with a total concentration of 0.72 mol / L.

[0057] A diamine solution was added to the obtained dianhydride solution in batches and mixed. After mixing, the mixture was mechanically stirred in an ice-water bath for 5 hours at a stirring rate of 150 r / min to prepare a polyamic acid solution with an intrinsic viscosity of 1.93 dL / g. The molar ratio of 4,4'-diaminoterphenyl, 4,4'-diphenyl ether dianhydride, and pyromellitic anhydride was 1:0.1:0.9.

[0058] The prepared polyamic acid solution was poured onto a clean glass substrate and coated with a doctor blade to obtain a polyamic acid film of uniform thickness. The film was then dried in a forced-air oven at 80°C for 1 hour to remove N,N-dimethylacetamide and induce crystallization. After solvent removal and crystallization, gradient thermal imidization was performed to obtain a polyimide film. The temperature program for gradient thermal imidization was 120°C for 1 hour, 160°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 300°C for 2 hours, with a heating rate of 3°C / min to reach the target holding temperature.

[0059] The crystal morphology of the prepared polyimide film was characterized using polarized light microscopy. Figure 3 These are polarized light microscope images of the polyamic acid thermal imidization process to produce polyimide obtained in Example 3, where the temperatures corresponding to (a) to (h) are 20℃, 40℃, 60℃, 80℃, 120℃, 160℃, 200℃, and 300℃, respectively. Figure 3 It can be seen that the polyimide film prepared in this embodiment has a crystallinity of 35.81%, which is relatively high. The spherulites are large in size, numerous, and uniformly distributed. The thermal conductivity of the polyimide film was tested using a Hot Disk thermal constant analyzer. The in-plane thermal conductivity was 2.58 W / mK, and the inter-plane thermal conductivity was 0.18 W / mK. The polyimide film prepared has excellent intrinsic thermal conductivity.

[0060] Comparative Example 1 Under a nitrogen atmosphere, 4,4'-diaminoterphenyl and N,N-dimethylacetamide were mixed and mechanically stirred in an ice-water bath to completely dissolve the 4,4'-diaminoterphenyl, resulting in a diamine solution with a concentration of 0.62 mol / L.

[0061] Add 5 mmol of 4,4'-biphenyl ether dianhydride to N,N-dimethylacetamide and sonicate for 10 min to obtain a dianhydride solution with a concentration of 0.62 mol / L.

[0062] A diamine solution was added to the obtained dianhydride solution in batches and mixed. After mixing, the mixture was mechanically stirred in an ice-water bath for 5 hours at a stirring rate of 150 r / min to prepare a polyamic acid solution with an intrinsic viscosity of 1.34 dL / g. The molar ratio of 4,4'-diaminoterphenyl and 4,4'-diphenyl ether dianhydride was 1:1.

[0063] The prepared polyamic acid solution was poured onto a clean glass substrate and coated with a doctor blade to obtain a polyamic acid film of uniform thickness. The film was then dried in a forced-air oven at 80°C for 1 hour to remove N,N-dimethylacetamide and induce crystallization. After solvent removal and crystallization, gradient thermal imidization was performed to obtain a polyimide film. The temperature program for gradient thermal imidization was 120°C for 1 hour, 160°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 300°C for 2 hours, with a heating rate of 3°C / min to reach the target holding temperature.

[0064] The crystal morphology of the prepared polyimide film was characterized using polarized light microscopy. Figure 4 These are polarized light microscope images of the polyamic acid thermal imidization process to produce polyimide in Comparative Example 1. The temperatures corresponding to (a) to (h) are 20℃, 40℃, 60℃, 80℃, 120℃, 160℃, 200℃, and 300℃, respectively. Figure 4 It can be seen that the crystallinity of the polyimide film prepared in this embodiment is 5.3%, which is low crystallinity, with extremely small spherulites, very few in number, and sparsely distributed. The thermal conductivity of the polyimide film was tested using a Hot Disk thermal constant analyzer. The in-plane thermal conductivity was 1.65 W / mK, and the inter-plane thermal conductivity was 0.09 W / mK. The intrinsic thermal conductivity of the prepared polyimide film is poor.

[0065] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A crystalline polyimide, characterized by, The polyimide molecule has a structure shown in Formula I: Formula I; wherein m:n = 1:0-0:1, and n is not 0. The crystal morphology of the crystalline polyimide is spherulite.

2. The method of producing the crystalline polyimide according to claim 1, characterized by, The method comprises the following steps: mixing 4,4'-diaminotriphenyl and a first polar aprotic solvent to obtain a diamine solution; mixing 4,4'-diphenyl ether dianhydride and pyromellitic dianhydride with a second polar aprotic solvent to obtain a dianhydride solution; mixing the diamine solution and the dianhydride solution to perform a polycondensation reaction to obtain a polyamic acid solution; performing thermal imidization on the polyamic acid solution after desolvation crystallization to obtain the crystalline polyimide; the molar ratio of the 4,4'-diphenyl ether dianhydride and the pyromellitic dianhydride is 1:0-0:1, and the amount of the pyromellitic dianhydride is not 0.

3. The method of claim 2, wherein, the ratio of the total molar amount of the 4,4'-diphenyl ether dianhydride and the pyromellitic dianhydride to the molar amount of the 4,4'-diaminotriphenyl is 0.998-1.002:

1.

4. The production method according to claim 2 or 3, characterized by, the mass ratio of the 4,4'-diaminotriphenyl to the first polar aprotic solvent is 0.05-0.15:1; the first polar aprotic solvent comprises one or more of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone.

5. The preparation method according to claim 2, characterized in that, the ratio of the total mass of the 4,4'-diphenyl ether dianhydride and the pyromellitic dianhydride to the mass of the second polar aprotic solvent is 0.05-0.15:1; the second polar aprotic solvent independently comprises one or more of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone.

6. The method of making according to any one of claims 2, 3 or 5, wherein, the temperature of the polycondensation reaction is -5-5°C, and the time is 4-6h; the polycondensation reaction is performed in a protective atmosphere.

7. The preparation method according to claim 2, characterized in that, the temperature of the desolvation crystallization is 60-80°C, and the time is 1-2h.

8. The production method according to claim 2 or 7, characterized by, the thermal imidization is gradient thermal imidization, the initial holding temperature of the gradient thermal imidization is 110-130°C, the final holding temperature is 280-320°C, and the total holding time is 4.1-10h.

9. A polyimide film characterized by, the material of the polyimide film is the crystalline polyimide of claim 1 or the crystalline polyimide prepared by the method of any one of claims 2-8.

10. Application of the crystalline polyimide of claim 1 or the polyimide film of claim 9 in electronic and electrical products.

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