Intrinsic photothermal polyimide and preparation method and application thereof

Abstract

The present invention belongs to the field of polymer materials, and specifically relates to an intrinsic photothermal polyimide and a preparation method and application thereof. The present invention provides an intrinsic photothermal polyimide, the structural formula of which is shown in Formula I. Long conjugated and electron-donating groups with photothermal effects in the ultraviolet or near-infrared region are introduced into the polyimide structure of the present invention, and the molecular band gap is regulated so that the polyimide has a good solar photothermal effect, while also retaining its stable thermodynamic properties, and is expected to be used in the fields of solar desalination, crude oil collection, etc.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to an intrinsic photothermal polyimide and a preparation method and application thereof. Background Art

[0002] In recent years, due to the rapid growth of the world's population and the acceleration of modernization, energy consumption has increased dramatically. In order to obtain cleaner energy, solar energy, an inexhaustible energy source, has attracted widespread attention from researchers. Thermal energy is essential for human production and life. There are many ways to obtain thermal energy, among which photothermal conversion is the most convenient and efficient, and has been successfully applied in biomedicine, catalysis, motors and actuators.

[0003] Materials with efficient solar thermal effect can achieve significant temperature rise by sunlight exposure without external energy consumption, and are widely used in many fields such as seawater desalination and photothermal energy storage. However, researchers' research on photothermal materials mostly focuses on carbon-based materials, metal nanomaterials and semiconductor materials, which are very unfavorable for sustainable development due to their high prices. In recent years, organic polymers have a small band gap due to their long conjugated structure, so they have a wide absorption range from visible to near-infrared light.

[0004] Polyimide is a polymer material with good mechanical properties and excellent thermal stability. Researchers have obtained a composite with photothermal effect by compounding carbon black, carbon nanotubes and other substances with high molar extinction coefficients with polyimide. However, the use of these materials in combination with polyimide will destroy the properties of the polyimide itself, and the thermodynamic properties of the prepared composite will be reduced. Summary of the invention

[0005] In view of this, the object of the present invention is to provide an intrinsic photothermal polyimide and a preparation method and application thereof. The polyimide of the present invention has good solar photothermal effect while maintaining excellent thermodynamic properties of the polyimide.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides an intrinsic photothermal polyimide, the structural formula of which is shown in Formula I:

[0008]

[0009] In Formula I, R1 is one of Formula II-1 to Formula II-10, and R2 is one of Formula III-1 to Formula III-6:

[0010]

[0011] The present invention also provides a method for preparing the intrinsic photothermal polyimide described in the above technical solution, comprising the following steps:

[0012] The dianhydride monomer, the diamine monomer and the organic solvent are mixed to carry out polymerization reaction to obtain polyamic acid;

[0013] imidizing the polyamic acid to obtain the intrinsic photothermal polyimide;

[0014] The dianhydride monomer includes pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, hexafluoroisopropylphthalic anhydride, cyclobutanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride or 3,3,4,4-diphenyl sulfonetetracarboxylic dianhydride;

[0015] The diamine monomer is a square acid derivative, and the square acid derivative includes 2,4-bis(5-(aminomethyl)thiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-(aminomethyl)thiophene-2-yl)-3-oxocyclobutane, 2,4-bis(5-aminothiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-aminothiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-aminothiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-aminophenyl)-3-oxocyclobutane or 2,4-bis(3-aminophenyl)-3-oxocyclobutane.

[0016] Preferably, the molar ratio of the dianhydride monomer to the diamine monomer is 0.9-1.1:1.

[0017] Preferably, the organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, N-ethyl-2-pyrrolidone and tetrahydrofuran.

[0018] Preferably, the usage ratio of the dianhydride monomer to the organic solvent is 0.01 mol: 20-30 mL.

[0019] Preferably, the polymerization reaction further includes dehydrating and deoxygenating the mixed system, and the dehydrating and deoxygenating method is vacuuming and nitrogen blowing.

[0020] Preferably, the polymerization reaction is carried out in an ice water bath for 12 hours to 24 hours.

[0021] Preferably, after the polymerization reaction, the process further comprises: subjecting the obtained reaction liquid to sedimentation treatment, and then subjecting the solid-liquid separation and drying.

[0022] Preferably, the imidization is thermal imidization, and the process of the thermal imidization includes: heating to 60-80°C and maintaining for 1 hour, continuing to heat to 120-150°C and maintaining for 1-2 hours, then heating to 180-200°C and maintaining for 1-2 hours, then heating to 220-250°C and maintaining for 1-2 hours, and finally heating to 280-300°C and maintaining for 1-2 hours.

[0023] The present invention also provides the use of the intrinsic photothermal polyimide described in the above technical solution or the intrinsic photothermal polyimide obtained by the above preparation method in solar seawater desalination or crude oil collection.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides an intrinsic photothermal polyimide, the structural formula of which is shown in Formula I. Long conjugated and electron-donating groups with photothermal effects in the ultraviolet region or near-infrared region are introduced into the polyimide structure of the present invention, and the molecular band gap is regulated so that the polyimide has both efficient solar photothermal effects and strong thermodynamic properties.

[0026] The data of the examples show that the polyimide powder prepared in the examples has good photothermal properties in the ultraviolet to visible near infrared light region.

[0027] The present invention also provides a method for preparing an intrinsic photothermal polyimide, by introducing a diamine monomer having a photothermal effect in the ultraviolet region or near-infrared region into the polyimide, and by simple polycondensation, a polyimide having good photothermal effect and strong thermodynamic properties can be obtained; the polyimide is expected to be utilized in the fields of solar energy desalination, crude oil collection, etc., greatly improving the utilization rate of energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 This is a physical picture of the intrinsic photothermal polyimide in Example 1;

[0030] Figure 2 This is the infrared image of the intrinsic photothermal polyimide in Example 1;

[0031] Figure 3 This is the UV-visible absorption diagram of the intrinsic photothermal polyimide in Example 1;

[0032] Figure 4 This is the thermogravimetric analysis diagram of the intrinsic photothermal polyimide in Example 1;

[0033] Figure 5 This is the solar light temperature rise diagram of the intrinsic photothermal polyimide in Example 1;

[0034] Figure 6 This is the solar light temperature rise diagram of the intrinsic photothermal polyimide in Example 2;

[0035] Figure 7 This is the solar light heating diagram of the intrinsic photothermal polyimide in Example 3. DETAILED DESCRIPTION

[0036] The present invention provides an intrinsic photothermal polyimide, the structural formula of which is shown in Formula I:

[0037]

[0038] In Formula I, R1 is one of Formula II-1 to Formula II-10, and R2 is one of Formula III-1 to Formula III-6:

[0039]

[0040] In the present invention, the structures of formula II-1 to II-10 and formula III-1 to III-6 are Both represent connection ends.

[0041] The present invention also provides a method for preparing the intrinsic photothermal polyimide described in the above technical solution, comprising the following steps:

[0042] The dianhydride monomer, the diamine monomer and the organic solvent are mixed to carry out polymerization reaction to obtain polyamic acid;

[0043] imidizing the polyamic acid to obtain the intrinsic photothermal polyimide;

[0044] The dianhydride monomer includes pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, hexafluoroisopropylphthalic anhydride, cyclobutanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride or 3,3,4,4-diphenyl sulfonetetracarboxylic dianhydride;

[0045] The diamine monomer is a square acid derivative, and the square acid derivative includes 2,4-bis(5-(aminomethyl)thiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-(aminomethyl)thiophene-2-yl)-3-oxocyclobutane, 2,4-bis(5-aminothiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-aminothiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-aminothiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-aminophenyl)-3-oxocyclobutane or 2,4-bis(3-aminophenyl)-3-oxocyclobutane.

[0046] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0047] The invention mixes dianhydride monomer, diamine monomer and organic solvent to carry out polymerization reaction to obtain polyamic acid.

[0048] In the present invention, the molar ratio of the dianhydride monomer to the diamine monomer is preferably 0.9 to 1.1:1, more preferably 1:1.

[0049] In the present invention, the organic solvent is preferably an aprotic strong polar solvent, and the organic solvent preferably includes one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP) and tetrahydrofuran (THF).

[0050] In the present invention, the usage ratio of the dianhydride monomer to the organic solvent is preferably 0.01 mol: 20-30 mL, more preferably 0.01 mol: 25 mL.

[0051] In the present invention, the method of mixing the dianhydride monomer, the diamine monomer and the organic solvent is preferably ultrasound, and a homogeneous solution is formed by the ultrasound.

[0052] In the present invention, the process of dehydrating and deoxygenating the mixed system before the polymerization reaction is also included. The dehydration and deoxygenation method is preferably vacuum pumping and nitrogen blowing. The vacuum pumping and nitrogen blowing are preferably performed 3 times.

[0053] In the present invention, the polymerization reaction is preferably carried out in a nitrogen atmosphere, the polymerization reaction is preferably carried out in an ice water bath, and the time is preferably 12h to 24h; after the polymerization reaction, a viscous liquid containing polyamic acid (PAA) is obtained, and the structural formula of the polyamic acid is preferably as shown in Formula IV:

[0054] R1 and R2 in formula IV are the same as R1 and R2 in formula I.

[0055] In the present invention, after the polymerization reaction, the step further includes: subjecting the obtained reaction liquid to sedimentation treatment, and then subjecting the reaction liquid to solid-liquid separation and drying to obtain polyamic acid. The sedimentation treatment preferably uses an organic solvent, and the organic solvent preferably includes tetrahydrofuran, acetone or dichloromethane. The solid-liquid separation method is preferably filtration.

[0056] After obtaining the polyamic acid, the present invention performs imidization on the polyamic acid to obtain the intrinsic photothermal polyimide.

[0057] In the present invention, the imidization is preferably thermal imidization, and the thermal imidization is preferably carried out in air. The process of the thermal imidization preferably includes: heating to 60-80°C and maintaining for 1 hour, continuing to heat to 120-150°C and maintaining for 1-2 hours, then heating to 180-200°C and maintaining for 1-2 hours, then heating to 220-250°C and maintaining for 1-2 hours, and finally heating to 280-300°C and maintaining for 1-2 hours.

[0058] The preparation method of the present invention polycondenses dianhydride and diamine through reasonable molecular design, obtains polyamic acid after sedimentation and drying, and then thermal imidizes the polyamic acid by programmed temperature to prepare polyimide with intrinsic high-efficiency solar light thermal effect. The polyimide obtained by the preparation method of the present invention has good solar light thermal effect while maintaining its excellent thermodynamic properties.

[0059] The present invention also provides the use of the intrinsic photothermal polyimide described in the above technical solution or the intrinsic photothermal polyimide obtained by the above preparation method in solar seawater desalination or crude oil collection.

[0060] In the present invention, the application is preferably to prepare the intrinsic photothermal polyimide into a film for use.

[0061] In order to further illustrate the present invention, the intrinsic photothermal polyimide provided by the present invention and its preparation method and application are described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0062] Example 1

[0063] An intrinsic high-efficiency solar photothermal effect polyimide PI-1, whose structure is shown in Formula V:

[0064]

[0065] The raw materials include: 2-methylaminothiophene, squaric acid, pyromellitic anhydride (PMDA), toluene, n-butanol, N,N-dimethylformamide (DMF), tetrahydrofuran (THF), and homemade 2,4-bis(5-(aminomethyl)thiophen-2-yl)-3-oxocyclobutane (SQU-1, with a structural formula such as formula V-1).

[0066]

[0067] The preparation method is as follows:

[0068] (1) Preparation of SQU-1

[0069] In a clean round-bottom flask, add 1.04 g (9.2 mmol) of 2-methylaminothiophene and 0.53 g (4.6 mmol) of squaric acid, and then add 100 mL of a mixed solution of toluene and n-butanol (volume ratio of 1:1). Under nitrogen protection, react at 100-120°C for 3-5 h, filter, and dry in an oven at 80-100°C for 2-4 h to obtain 2,4-bis(5-(aminomethyl)thiophene-2-yl)-3-oxocyclobutane (SQU-1, structural formula is as shown in Formula V-1).

[0070] (2) Preparation of polyamic acid

[0071] First, the Shrek polymerization tube was cleaned, 2.18 g (0.01 mol) of PMDA was added, and then 25 mL of refined DMF was added and ultrasonically dissolved. Subsequently, 3.06 g (0.01 mol) of the square acid derivative SQU-1 was added. After three vacuum evacuation and nitrogen bubbling processes, water and oxygen were fully removed. The mixture was reacted in an ice-water bath in a nitrogen atmosphere for 24 h to produce a light black viscous liquid. Then, THF was poured into the mixture for sedimentation. The obtained product was filtered and dried in an oven at 60-80°C for 2-4 h to obtain a soluble polyamic acid PAA-1.

[0072] (3) Preparation of photothermal polyimide

[0073] The obtained PAA-1 powder was placed on a hot plate and thermally imidized in air, and the temperature was raised according to the following procedure: heated to 80°C and maintained for 1 hour, then continued to heat to 100°C and maintained for 1 hour, 150°C and maintained for 1 hour, 200°C and maintained for 1 hour, 250°C and maintained for 1 hour, and 300°C and maintained for 1 hour to obtain intrinsic photothermal polyimide PI-1.

[0074] Figure 1 This is a physical picture of polyimide PI-1, composed of Figure 1 It can be observed that the surface of polyimide is brownish yellow, which is very conducive to the full spectrum absorption of sunlight.

[0075] Figure 2 This is the infrared image of polyimide PI-1, 1776cm -1 and 1693cm -1 Asymmetric stretching vibration and symmetric stretching vibration of C=O, 1346cm -1 The emergence of stretching vibration of the CNC absorption band indicates that the intrinsic photothermal polyimide has been successfully synthesized.

[0076] Figure 3 This is the absorption diagram of polyimide PI-1 in the ultraviolet to visible light region. It can be seen that polyimide has extensive absorption in this region, which also shows that it has excellent photothermal effect.

[0077] Figure 4 This is the thermogravimetric analysis diagram of polyimide PI-1. The thermal decomposition temperature (Td) of PI-1 powder can reach above 300°C.

[0078] Figure 5 This is the photothermal effect diagram of polyimide PI-1 carbon. Under a simulated solar radiation condition, the temperature can rise to 42°C.

[0079] Example 2

[0080] An intrinsic high-efficiency solar photothermal effect polyimide PI-2, whose structure is shown in Formula VI:

[0081]

[0082] Raw materials: 2-aminothiophene, squaric acid, pyromellitic dianhydride (PMDA), toluene, n-butanol, N,N-dimethylformamide (DMF), tetrahydrofuran (THF), 2,4-bis(5-aminothiophen-2-yl)-3-oxocyclobutane (SQU-2, structural formula as formula VI-1).

[0083]

[0084] The preparation method is as follows:

[0085] (1) Preparation of 2,4-bis(5-aminothiophene-2-yl)-3-oxocyclobutane

[0086] In a clean round-bottom flask, add 0.91 g (9.2 mmol) of 2-aminothiophene and 0.53 g (4.6 mmol) of squaric acid in sequence, and then add 100 mL of a mixed solution of toluene and n-butanol (volume ratio of 1:1). Under nitrogen protection, react at 100-120°C for 3-5 h, filter, and dry in an oven at 80-100°C to obtain 2,4-bis(5-aminothiophene-2-yl)-3-oxocyclobutane (SQU-2, with the structural formula as Formula VI-1).

[0087] (2) Preparation of polyamic acid

[0088] First, the Shrek polymerization tube was cleaned, 2.18 g (0.01 mol) of PMDA was added, and then 25 mL of refined DMF was added for ultrasonic dissolution. Subsequently, 2.78 g (0.01 mol) of SQU-2 was added. After three vacuum evacuation and nitrogen bubbling processes, water and oxygen were fully removed. The mixture was reacted in an ice-water bath in a nitrogen atmosphere for 24 h to produce a dark viscous liquid. Then, THF was poured into the reaction mixture for precipitation. The obtained product was filtered and dried in an oven at 60-80°C for 2-4 h to obtain soluble PAA-2.

[0089] (3) Preparation of photothermal polyimide

[0090] The obtained PAA-2 was placed on a hot plate and thermally imidized in air, and the temperature was raised according to the following program: heated to 80°C and maintained for 1 hour, then continued to heat to 100°C and maintained for 1 hour, 150°C and maintained for 1 hour, 200°C and maintained for 1 hour, 250°C and maintained for 1 hour, and 300°C and maintained for 1 hour to obtain intrinsic photothermal polyimide PI-2.

[0091] Figure 6 This is the photothermal effect diagram of polyimide PI-2 carbon. Under a simulated solar radiation condition, the temperature can rise to 41.6℃.

[0092] Example 3

[0093] An intrinsic high-efficiency solar photothermal effect polyimide PI-3, whose structure is shown in Formula VII:

[0094]

[0095] Raw materials: 2-methylaminothiophene, squaric acid, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), toluene, n-butanol, N,N-dimethylformamide (DMF), 2,4-bis(5-(aminomethyl)thiophen-2-yl)-3-oxocyclobutane (SQU-1, structural formula as formula V-1), tetrahydrofuran (THF).

[0096] The preparation method is as follows:

[0097] (1) Preparation of 2,4-bis(5-(aminomethyl)thiophen-2-yl)-3-oxocyclobutane

[0098] In a clean round-bottom flask, add 1.04 g (9.2 mmol) of 2-methylaminothiophene and 0.53 g (4.6 mmol) of squaric acid, and then add 100 mL of a mixed solution of toluene and n-butanol (volume ratio of 1:1). Under nitrogen protection, react at 100-120°C for 3-5 h, filter, and dry in an oven at 80-100°C to obtain 2,4-bis(5-(aminomethyl)thiophene-2-yl)-3-oxocyclobutane (SQU-1, structural formula is as shown in Formula V-1).

[0099] (2) Preparation of polyamic acid

[0100] First, the Shrek polymerization tube was cleaned, 3.22 g (0.01 mol) of BTDA was added, and then 25 mL of refined DMF was added for ultrasonic dissolution, followed by the addition of 3.06 g (0.01 mol) of SQU-1. After three vacuum evacuation and nitrogen bubbling processes, sufficient water and oxygen removal was ensured. The mixture was reacted in an ice-water bath in a nitrogen atmosphere for 24 h to produce a dark viscous liquid, which was then poured into THF for sedimentation. The obtained product was filtered and dried in an oven at 60-80°C for 2-4 h to obtain soluble PAA-3.

[0101] (3) Preparation of photothermal polyimide

[0102] The obtained PAA-3 was placed on a hot plate and thermally imidized in air, and the temperature was raised according to the following program: heated to 80°C and maintained for 1 hour, then continued to heat to 100°C and maintained for 1 hour, 150°C and maintained for 1 hour, 200°C and maintained for 1 hour, 250°C and maintained for 1 hour, and 300°C and maintained for 1 hour to obtain intrinsic photothermal polyimide PI-3.

[0103] Figure 7 This is the photothermal effect diagram of polyimide PI-3 carbon. Under a simulated solar radiation condition, the temperature can rise to 35.4℃.

[0104] It can be seen from the photothermal performance test that the polyimide prepared in the embodiment of the present invention has photothermal performance, has good photothermal performance in the ultraviolet to visible near-infrared light region, and has stable thermodynamic properties.

[0105] Although the above-mentioned embodiments have made a detailed description of the present invention, they are only some embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on the embodiments of the present invention without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. An intrinsic photothermal polyimide, characterized in that: The structural formula is shown in Formula I: In Formula I, R1 is one of Formula II-1 to Formula II-10, and R2 is one of Formula III-1 to Formula III-6: In the structures of formula II-1 to II-10, formula III-1 to formula III-6 Both represent connection ends.

2. The method for preparing the intrinsic photothermal polyimide according to claim 1, characterized in that: The following steps are involved: The dianhydride monomer, the diamine monomer and the organic solvent are mixed to carry out polymerization reaction to obtain polyamic acid; imidizing the polyamic acid to obtain the intrinsic photothermal polyimide; The dianhydride monomer includes pyromellitic dianhydride, bisphenol A diether dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, hexafluoroisopropyl phthalic anhydride, cyclobutane tetracarboxylic dianhydride, cyclohexane tetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride or 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride; The diamine monomer is a square acid derivative, and the square acid derivative includes 2,4-bis(5-(aminomethyl)thiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-(aminomethyl)thiophene-2-yl)-3-oxocyclobutane, 2,4-bis(5-aminothiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-aminothiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-aminothiophene-2-yl)-3-oxocyclobutane, 2,4-bis(4-aminophenyl)-3-oxocyclobutane or 2,4-bis(3-aminophenyl)-3-oxocyclobutane.

3. The preparation method according to claim 2, characterized in that: The molar ratio of the dianhydride monomer to the diamine monomer is 0.9-1.1:

1.

4. The preparation method according to claim 2, characterized in that: The organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, N-ethyl-2-pyrrolidone and tetrahydrofuran.

5. The preparation method according to claim 2 or 4, characterized in that: The usage ratio of the dianhydride monomer and the organic solvent is 0.01 mol: 20-30 mL.

6. The preparation method according to claim 2, characterized in that: Before the polymerization reaction, the mixed system is dehydrated and deoxygenated by vacuuming and nitrogen blowing.

7. The preparation method according to claim 2 or 6, characterized in that: The polymerization reaction is carried out in an ice water bath for 12 hours to 24 hours.

8. The preparation method according to claim 2, characterized in that: After the polymerization reaction, the method further comprises: subjecting the obtained reaction liquid to sedimentation treatment, and then subjecting the solid-liquid separation and drying.

9. The preparation method according to claim 2, characterized in that: The imidization is thermal imidization, and the process of the thermal imidization includes: heating to 60-80°C and maintaining for 1 hour, continuing to heat to 120-150°C and maintaining for 1-2 hours, then heating to 180-200°C and maintaining for 1-2 hours, then heating to 220-250°C and maintaining for 1-2 hours, and finally heating to 280-300°C and maintaining for 1-2 hours.

10. Use of the intrinsic photothermal polyimide according to claim 1 or the intrinsic photothermal polyimide obtained by the preparation method according to any one of claims 2 to 9 in solar seawater desalination or crude oil collection.

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