Transparent shape memory polyimide film and preparation method thereof
Transparent shape memory polyimide films were prepared by reacting specific monomers, which solved the problems of high temperature dependence and poor transparency. This resulted in transparent polyimide films with shape memory function at low temperatures, which are suitable for optical devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2026-04-01
- Publication Date
- 2026-05-12
AI Technical Summary
Existing transparent shape memory polyimide films can only achieve shape memory function at high temperatures, and low-temperature transparent materials have poor light transmittance, making them difficult to apply to optical devices.
Transparent shape memory polyimide films were prepared by reacting 1,12-diaminododecane and 1,3-bis(3-aminophenoxy)benzene as diamine monomers with bisphenol A type diether dianhydride and controlling the molar ratio and reaction conditions. This process reduced the glass transition temperature and improved the transparency and shape memory properties.
The prepared polyimide film exhibits good transparency and shape memory properties below 100°C, making it suitable for optical devices.
Smart Images
Figure CN122011457A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical thin film technology, and more specifically, to a transparent shape memory polyimide thin film and its preparation method. Background Technology
[0002] Shape memory polymers (SMPs) have shown broad application prospects in aerospace, biomedicine, and flexible electronics due to their programmable properties and ability to recover from temporary to permanent shapes under various external stimuli such as heat, light, electricity, and pH. Among them, shape memory polyimides (SMPIs) have become a research hotspot in high-temperature shape memory materials because they combine the excellent thermal stability, mechanical properties, and radiation resistance inherent in polyimides.
[0003] In recent years, with the rapid development of flexible optoelectronic devices such as flexible perovskite solar cells, flexible displays, and space-based self-deploying structures, there has been an urgent need for polymer materials that combine optical transparency and shape memory functions. Currently, reported research on transparent shape memory polyimides mainly focuses on high-temperature triggered materials, whose glass transition temperatures (Tg) are generally above 150°C. In practical applications, heating equipment is required to provide a high-temperature environment to achieve the shape memory function, which is not only energy-intensive but also unsuitable for heat-sensitive optoelectronic devices. On the other hand, while existing low-temperature shape memory polymers are easily deformable, they are mostly opaque materials with poor light transmittance, making them difficult to apply to optical devices. Therefore, how to obtain polyimide films that combine good transparency, good shape memory performance, and a low glass transition temperature has become a pressing problem to be solved. Summary of the Invention
[0004] The problem solved by this invention is: how to obtain a polyimide film that has good transparency, good shape memory properties, and a low glass transition temperature.
[0005] To address the above problems, this invention provides a method for preparing a transparent shape memory polyimide film, comprising: Step S1: Under a protective gas atmosphere, the mixed diamine monomer, dianhydride monomer and the first high-boiling-point polar aprotic solvent are mixed evenly and a first stirring reaction is carried out to obtain a polyamic acid solution; wherein, the mixed diamine monomer includes 1,12-diaminododecane and 1,3-bis(3-aminophenoxy)benzene, and the dianhydride monomer includes bisphenol A type diether dianhydride. Step S2: Use the polyamic acid solution to form a film to obtain a polyimide film.
[0006] Optionally, in step S1, the molar ratio of 1,12-diaminododecane to 1,3-bis(3-aminophenoxy)benzene in the mixed diamine monomer is (1 to 9):(1 to 9).
[0007] Optionally, in step S1, the molar ratio of the diamine monomer to the dianhydride monomer in the mixed diamine monomer is (0.98 to 1.02):1.
[0008] Optionally, in step S1, the first stirring reaction takes 23 to 25 hours.
[0009] Optionally, in step S1, the first high-boiling-point polar aprotic solvent includes at least one of N,N-dimethylformamide and N,N-dimethylacetamide.
[0010] Optionally, in step S2, the process of forming a film using the polyamic acid solution includes: Acetic anhydride and pyridine were added to the polyamic acid solution, and a second stirring reaction was carried out to obtain a polyimide mixed solution. The polyimide mixture was added to ethanol to precipitate the polyimide, and the precipitate was collected to obtain polyimide fibers. The polyimide fiber is dissolved in a second high-boiling-point polar aprotic solvent to obtain a polyimide solution; The polyimide solution is coated onto a substrate and dried to obtain a polyimide film.
[0011] Optionally, the molar ratio of the acetic anhydride, the pyridine, and the dianhydride monomer is (4 to 10):(4 to 10):1.
[0012] Optionally, the mass of the polyimide mixture is m grams, the volume of the ethanol is v milliliters, and the ratio of m to v is 1:(9 to 11).
[0013] Optionally, in step S2, the process of forming a film using the polyamic acid solution includes: The polyamic acid solution is coated onto a substrate, first heated to 60°C to 90°C and held for 1 to 3 hours, then heated to 100°C to 150°C and held for 1 to 3 hours, then heated to 160°C to 180°C and held for 1 to 3 hours, and finally heated to 190°C to 210°C and held for 1 to 3 hours to obtain a polyimide film.
[0014] The present invention also provides a transparent shape memory polyimide film, which is made by the preparation method of transparent shape memory polyimide film as described above.
[0015] Compared with related technologies, this invention selects 1,12-diaminododecane and 1,3-bis(3-aminophenoxy)benzene as diamine monomers to react with bisphenol A type diether dianhydride to prepare polyimide films. 1,12-diaminododecane acts as a reversible phase to provide deformation capability, while the rigid aromatic rings and hydrogen bonds in the aromatic diamine 1,3-bis(3-aminophenoxy)benzene and bisphenol A type diether dianhydride act as stationary phases to provide shape memory resilience, resulting in polyimide films with superior shape memory properties. Furthermore, 1,12-diaminododecane has a long-chain structure with multiple methylene groups, which effectively lowers the glass transition temperature of the polyimide film. Additionally, the bisphenol A type diether dianhydride contains numerous ether bonds and bisphenol A structures, effectively increasing the interchain spacing and suppressing intramolecular and intermolecular charge transfer complexation effects. Simultaneously, the introduction of the long-chain structure of 1,12-diaminododecane further reduces the conjugation degree of the molecular chains, resulting in polyimide films with superior transparency. In summary, the polyimide film prepared by the method of the present invention has better transparency, better shape memory properties, and a lower glass transition temperature (below approximately 100°C). Attached Figure Description
[0016] Figure 1 This is a schematic diagram of the preparation method of transparent shape memory polyimide film in an embodiment of the present invention; Figure 2 The infrared spectrum of the polyimide film prepared in Example 1 of this invention; Figure 3 The image shows the ultraviolet-visible spectrum of the polyimide film prepared in Example 1 of this invention. Figure 4 The infrared spectrum of the polyimide film prepared in Example 3 of this invention; Figure 5 The image shows the ultraviolet-visible spectrum of the polyimide film prepared in Example 3 of this invention. Figure 6 This is a dynamic thermomechanical property diagram of the polyimide film prepared in Example 3 of the present invention; Figure 7 This is a diagram showing the shape change process of the polyimide film prepared in Example 3 of the present invention after being folded and placed on a heating stage at 100°C. Figure 8 This is a diagram illustrating the shape change process of the polyimide film prepared in Example 4 of the present invention after being folded and placed in water at 84°C. Figure 9 This is a diagram showing the shape change process of the polyimide film prepared in Comparative Example 1 after folding and placing it in water at 100°C. Figure 10This is a diagram showing the shape change process of the polyimide film prepared in Comparative Example 1 after folding and placing it on a heating stage at 170°C. Detailed Implementation
[0017] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.
[0018] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0019] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the following description. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.
[0020] like Figure 1 As shown, this embodiment of the invention provides a method for preparing a transparent shape memory polyimide film, comprising: Step S1: Under a protective gas atmosphere, the mixed diamine monomer, dianhydride monomer and the first high-boiling-point polar aprotic solvent are mixed evenly and a first stirring reaction is carried out to obtain a polyamic acid solution; wherein, the mixed diamine monomer includes 1,12-diaminododecane and 1,3-bis(3-aminophenoxy)benzene, and the dianhydride monomer includes bisphenol A type diether dianhydride. Step S2: Use the polyamic acid solution to form a film to obtain a polyimide film.
[0021] In this embodiment of the invention, 1,12-diaminododecane and 1,3-bis(3-aminophenoxy)benzene are selected as diamine monomers and reacted with bisphenol A type diether dianhydride to prepare polyimide films. 1,12-diaminododecane serves as a reversible phase, providing deformation capability, while the rigid aromatic rings and hydrogen bonds in the aromatic diamine 1,3-bis(3-aminophenoxy)benzene and bisphenol A type diether dianhydride serve as stationary phases, providing shape memory resilience. This results in polyimide films with excellent shape memory properties. Furthermore, 1,12-diaminododecane has a long-chain structure with multiple methylene groups, which effectively lowers the glass transition temperature of the polyimide film. Additionally, the bisphenol A type diether dianhydride contains numerous ether bonds and bisphenol A structures, effectively increasing the interchain spacing and suppressing intramolecular and intermolecular charge transfer complexation effects. Simultaneously, the introduction of the long-chain structure of 1,12-diaminododecane further reduces the conjugation degree of the molecular chains, resulting in polyimide films with better transparency. In summary, the polyimide film prepared by the method of the present invention has better transparency, better shape memory properties, and a lower glass transition temperature (below approximately 100°C).
[0022] In some embodiments of the present invention, in step S1, the molar ratio of 1,12-diaminododecane to 1,3-bis(3-aminophenoxy)benzene in the mixed diamine monomers is (1 to 9):(1 to 9). In this embodiment, by controlling the molar ratio of 1,12-diaminododecane (flexible aliphatic segment) to 1,3-bis(3-aminophenoxy)benzene, the rigid-flexible structural balance of the polyimide backbone can be precisely controlled, thereby achieving low Tg and high shape memory properties of the polyimide film.
[0023] In some embodiments of the present invention, the molar ratio of the diamine monomer to the dianhydride monomer in the mixed diamine monomer is (0.98 to 1.02):1. In this embodiment, by controlling the molar ratio of the diamine monomer to the dianhydride monomer to (0.98 to 1.02):1, a near-stoichiometric match of functional groups in the polycondensation reaction is ensured, avoiding chain end blocking or broadening of molecular weight distribution caused by excess of any monomer. This significantly improves the polymerization completeness and molecular weight uniformity of the polyamic acid precursor, reduces unreacted group residues, and lowers the internal stress and micro-defect density of the film, thereby significantly improving the consistency of the optical transparency and mechanical properties of the polyimide film.
[0024] In some embodiments of the present invention, in step S1, the time for the first stirring reaction is 23h to 25h.
[0025] Optionally, in step S1, the first high-boiling-point polar aprotic solvent includes at least one of N,N-dimethylformamide and N,N-dimethylacetamide. In this embodiment, N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAc) is used as the high-boiling-point polar aprotic solvent. Due to its strong polarity and excellent solubility, it can efficiently dissolve diamine and dianhydride monomers and intermediate polyamic acid to form a uniform and transparent casting solution. Its molecular structure inhibits the aggregation of polymer chain segments and the formation of light scattering centers, which is beneficial to improving the transparency of the film. At the same time, its high boiling point and thermal stability ensure that the reaction process is controllable, reduce solvent residue, and avoid film cracking due to bubbles or stress.
[0026] In some embodiments of the present invention, in step S2, the polyamic acid solution is used to form a film, which can be prepared by either chemical imidization or thermal imidization; wherein, the film formation using the polyamic acid solution via the chemical imidization method includes: Acetic anhydride and pyridine are added to the polyamic acid solution, and a second stirring reaction is carried out to obtain a polyimide mixed solution; wherein, the molar ratio of the acetic anhydride, the pyridine and the dianhydride monomer is (4 to 10):(4 to 10):1; the time of the second stirring reaction is 23 h to 25 h; The polyimide mixture is added to ethanol to precipitate the polyimide, and the precipitate is collected to obtain polyimide fibers. The mass of the polyimide mixture is m grams, the volume of the ethanol is v milliliters, and the ratio of m to v is 1:(9 to 11). The polyimide fiber is dissolved in a second high-boiling-point polar aprotic solvent to obtain a polyimide solution; the second high-boiling-point polar aprotic solvent includes at least one of N,N-dimethylformamide and N,N-dimethylacetamide. The polyimide solution is coated onto a substrate and dried to obtain a polyimide film.
[0027] In some embodiments of the present invention, step S2, which involves forming a film using the polyamic acid solution via thermal imidization, includes: The polyamic acid solution is coated onto a substrate, first heated to 60°C to 90°C and held for 1 to 3 hours, then heated to 100°C to 150°C and held for 1 to 3 hours, then heated to 160°C to 180°C and held for 1 to 3 hours, and finally heated to 190°C to 210°C and held for 1 to 3 hours to obtain a polyimide film.
[0028] This invention also provides a transparent shape memory polyimide film, which is prepared using the method described above.
[0029] The present invention will be further described below with reference to specific embodiments.
[0030] Example 1 A1. Under a nitrogen atmosphere, a mixture of diamine monomers, dianhydride monomers, and N,N-dimethylacetamide is thoroughly mixed and subjected to a first stirring reaction to obtain a polyamic acid solution. The mixed diamine monomers include 1,12-diaminododecane and 1,3-bis(3-aminophenoxy)benzene, with a molar ratio of 1,12-diaminododecane to 1,3-bis(3-aminophenoxy)benzene of 9:1. The dianhydride monomers include bisphenol A diether dianhydride. The molar ratio of the diamine monomers to the dianhydride monomers in the mixed diamine monomers is 1:1. The first stirring reaction is carried out for 24 hours at a temperature of 75°C, and the solid content of the polyamic acid solution is 25%.
[0031] A2. Acetic anhydride and pyridine are added to the polyamic acid solution, and a second stirring reaction is carried out to obtain a polyimide mixed solution; wherein, the molar ratio of acetic anhydride, pyridine and dianhydride monomer is 8:8:1; the time of the second stirring reaction is 24h.
[0032] A3. The polyimide mixed solution is added to ethanol to precipitate, and the precipitate is collected to obtain polyimide fibers; the mass of the polyimide mixed solution is m grams, the volume of the ethanol is v milliliters, and the ratio of m to v is 1:10.
[0033] A4. Dissolve the polyimide fiber in N,N-dimethylacetamide to obtain a polyimide solution; the solid content of the polyimide solution is 16%.
[0034] A5. The polyimide solution is coated onto the substrate and dried to obtain a polyimide film.
[0035] Example 2 The difference from Example 1 is that, in step A1, the molar ratio of 1,12-diaminododecane to 1,3-bis(3-aminophenoxy)benzene in the mixed diamine monomer is 7:3.
[0036] Example 3 The difference from Example 1 is that, in step A1, the molar ratio of 1,12-diaminododecane to 1,3-bis(3-aminophenoxy)benzene in the mixed diamine monomer is 1:1.
[0037] Example 4 B1. Under a nitrogen atmosphere, a mixture of diamine monomers, dianhydride monomers, and N,N-dimethylacetamide is thoroughly mixed and subjected to a first stirring reaction to obtain a polyamic acid solution. The mixed diamine monomers include 1,12-diaminododecane and 1,3-bis(3-aminophenoxy)benzene, with a molar ratio of 1,12-diaminododecane to 1,3-bis(3-aminophenoxy)benzene of 1:1. The dianhydride monomers include bisphenol A diether dianhydride. The molar ratio of the diamine monomers to the dianhydride monomers in the mixed diamine monomers is 1:1. The first stirring reaction is carried out for 24 hours at a temperature of 75°C, and the solid content of the polyamic acid solution is 25%.
[0038] B2. The polyamic acid solution is coated onto the substrate, heated to 75°C and held for 2 hours, then heated to 125°C and held for 2 hours, then heated to 170°C and held for 2 hours, and finally heated to 200°C and held for 2 hours to obtain a polyimide film.
[0039] Example 5 The difference from Example 4 is that, in step B1, the molar ratio of 1,12-diaminododecane to 1,3-bis(3-aminophenoxy)benzene in the mixed diamine monomer is 3:7.
[0040] Example 6 The difference from Example 4 is that, in step B1, the molar ratio of 1,12-diaminododecane to 1,3-bis(3-aminophenoxy)benzene in the mixed diamine monomer is 1:9.
[0041] Comparative Example 1 (without 1,12-diaminododecane) The difference from Example 4 is that step B1 is as follows: under a nitrogen atmosphere, the diamine monomer, the dianhydride monomer, and N,N-dimethylacetamide are mixed evenly and subjected to a first stirring reaction to obtain a polyamic acid solution; wherein, the diamine monomer includes 1,3-bis(3-aminophenoxy)benzene, and the dianhydride monomer includes bisphenol A type diether dianhydride; the molar ratio of the diamine monomer to the dianhydride monomer is 1:1; the first stirring reaction takes 24 hours at a temperature of 75°C, and the solid content of the polyamic acid solution is 25%.
[0042] Effect Example The polyimide film prepared in Example 1 was characterized by infrared spectroscopy and ultraviolet-visible spectroscopy. The results are shown in the figure. Figure 2 and Figure 3 ,from Figure 2 As can be seen from the characteristic absorption peaks, the polyimide film prepared in Example 1 has been completely imidized. Figure 3As can be seen, the polyimide film prepared in Example 1 has a transmittance of up to 88.7% at 500 nm.
[0043] The polyimide film prepared in Example 3 was characterized by infrared spectroscopy and ultraviolet-visible spectroscopy. The results are shown in the figure. Figure 4 and Figure 5 ,from Figure 4 As can be seen from the characteristic absorption peaks, the polyimide film prepared in Example 3 has been completely imidized. Figure 5 It can be seen that the polyimide film prepared in Example 3 has a transmittance of up to 87.8% at 500 nm. Dynamic thermomechanical properties of the polyimide film prepared in Example 3 were tested, and the results are shown below. Figure 6 ,from Figure 6 It can be seen that the glass transition temperature of the polyimide film prepared in Example 3 is 98°C. It should be noted that... Figure 6 In the middle (a), the loss factor changes with temperature. Figure 6 (b) shows the change in storage modulus with temperature. The polyimide film prepared in Example 3 was folded and placed on a heating stage at 100°C. Its shape change process was observed, and the results are shown in [Figure 1]. Figure 7 ,from Figure 7 It can be seen that the polyimide film prepared in Example 3 gradually recovers from the folded state to the unfolded state, indicating that it has good shape memory properties. Figure 7 Image (a) shows the polyimide film prepared in Example 3 after folding. Figure 7 Images (b) to (d) show the polyimide film prepared in Example 3 after folding and heating on a 100°C heating table for 17s, 24s, and 36s, respectively.
[0044] The polyimide film prepared in Example 4 was folded and placed in water at 84°C. Its shape change process was observed, and the results are shown below. Figure 8 ,from Figure 8 It can be seen that the polyimide film prepared in Example 4 gradually recovers from its folded state to its unfolded state in water at 84°C, indicating that it has good shape memory properties and a low glass transition temperature. It should be noted that... Figure 8 Image (a) shows the polyimide film prepared in Example 4 after folding. Figure 8 Images (b) to (e) show the polyimide film prepared in Example 4 after being folded and placed in water at 84°C for 3s, 4s, 5s, and 20s, respectively.
[0045] The polyimide film prepared in Comparative Example 1 was folded and placed in water at 100°C. Its shape change process was observed, and the results are shown below. Figure 9 ,from Figure 9It can be seen that the polyimide film prepared in Comparative Example 1 cannot recover from its folded state to its unfolded state in water at 100℃. The polyimide film prepared in Comparative Example 1 was folded and placed on a heating stage at 170℃, and its shape change process was observed. The results are shown in [Figure 1]. Figure 10 ,from Figure 10 It can be seen that its shape gradually returns from a folded state to an unfolded state, indicating that the polyimide film prepared in Comparative Example 1 has a higher glass transition temperature. Figure 9 Image (a) shows the polyimide film prepared in Comparative Example 1 after folding. Figure 9 Image (b) shows the polyimide film prepared in Comparative Example 1 after being folded and placed in water at 100°C for 24 hours. Figure 10 Image (a) shows the polyimide film prepared in Comparative Example 1 after folding. Figure 10 (b) Figure 10 Images in (c) show the polyimide film prepared in Comparative Example 1 after being folded and placed on a heating table at 170°C for 5 seconds and 30 seconds, respectively.
[0046] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.
Claims
1. A method for preparing a transparent shape memory polyimide film, characterized in that, include: Step S1: Under a protective gas atmosphere, the mixed diamine monomer, dianhydride monomer and the first high-boiling-point polar aprotic solvent are mixed evenly and a first stirring reaction is carried out to obtain a polyamic acid solution; wherein, the mixed diamine monomer includes 1,12-diaminododecane and 1,3-bis(3-aminophenoxy)benzene, and the dianhydride monomer includes bisphenol A type diether dianhydride. Step S2: Use the polyamic acid solution to form a film to obtain a polyimide film.
2. The method for preparing a transparent shape memory polyimide film according to claim 1, characterized in that, In step S1, the molar ratio of 1,12-diaminododecane to 1,3-bis(3-aminophenoxy)benzene in the mixed diamine monomer is (1 to 9): (1 to 9).
3. The method for preparing a transparent shape memory polyimide film according to claim 1, characterized in that, In step S1, the molar ratio of the diamine monomer to the dianhydride monomer in the mixed diamine monomer is (0.98 to 1.02):
1.
4. The method for preparing a transparent shape memory polyimide film according to claim 1, characterized in that, In step S1, the first stirring reaction takes 23 to 25 hours.
5. The method for preparing a transparent shape memory polyimide film according to claim 1, characterized in that, In step S1, the first high-boiling-point polar aprotic solvent includes at least one of N,N-dimethylformamide and N,N-dimethylacetamide.
6. The method for preparing a transparent shape memory polyimide film according to claim 1, characterized in that, In step S2, the film-forming process using the polyamic acid solution includes: Acetic anhydride and pyridine were added to the polyamic acid solution, and a second stirring reaction was carried out to obtain a polyimide mixed solution. The polyimide mixture was added to ethanol to precipitate the polyimide, and the precipitate was collected to obtain polyimide fibers. The polyimide fiber is dissolved in a second high-boiling-point polar aprotic solvent to obtain a polyimide solution; The polyimide solution is coated onto a substrate and dried to obtain a polyimide film.
7. The method for preparing a transparent shape memory polyimide film according to claim 6, characterized in that, The molar ratio of the acetic anhydride, the pyridine, and the dianhydride monomer is (4 to 10): (4 to 10):
1.
8. The method for preparing a transparent shape memory polyimide film according to claim 6, characterized in that, The mass of the polyimide mixture is m grams, the volume of the ethanol is v milliliters, and the ratio of m to v is 1:(9 to 11).
9. The method for preparing a transparent shape memory polyimide film according to claim 1, characterized in that, In step S2, the film-forming process using the polyamic acid solution includes: The polyamic acid solution is coated onto a substrate, first heated to 60°C to 90°C and held for 1 to 3 hours, then heated to 100°C to 150°C and held for 1 to 3 hours, then heated to 160°C to 180°C and held for 1 to 3 hours, and finally heated to 190°C to 210°C and held for 1 to 3 hours to obtain a polyimide film.
10. A transparent shape memory polyimide film, characterized in that, It is prepared using the method for preparing transparent shape memory polyimide film as described in any one of claims 1 to 9.