Polyimide aerogel with radiation cooling characteristic as well as preparation method and application thereof

Abstract

The invention discloses a preparation method and application of polyimide aerogel with radiation refrigeration characteristics. As an infrared fingerprint area of 1500-600cm <-1 > just covers an atmospheric transparent window (8-13 microns), diamine and dianhydride structures with strong electron absorption groups in the area are selected, and polyimide with higher emissivity in the atmospheric transparent window (8-13 microns) is prepared in a random copolymerization manner. And meanwhile, due to a relatively low molecular band gap, a device with a polyimide structure has relatively high whiteness. The aerogel prepared by utilizing the characteristics has higher reflectivity in a sunlight wave band. Therefore, the polyimide aerogel prepared by the method has the radiation cooling characteristic and is expected to be applied to the aspects of building heat preservation, aerospace and aviation, electronic product heat dissipation and the like.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to a polyimide aerogel with radiation cooling characteristics and a preparation method thereof. Background Art

[0002] With the rapid growth of global industrialization and population, the massive consumption of energy has led to the massive emission of greenhouse gases and caused global warming. However, the commonly used traditional cooling methods consume a lot of electricity and energy, exacerbating the trend of global warming. Passive radiation cooling, as an environmentally friendly cooling method, can continuously dissipate heat to the cold outer space through the atmospheric transparent window (8-13μm) without the need for any other equipment or energy input. The polymer matrix has absorption and reflection in the infrared range and excellent physical properties, which makes the polymer matrix material have great application prospects in the field of radiation cooling.

[0003] Polyimides (PIs) have shown important application prospects and potential in aerospace, thermal insulation, environmental protection and other fields due to their excellent physical and chemical properties, such as excellent thermal stability, excellent electrical insulation and excellent acoustic impedance. However, due to the formation of intermolecular and intramolecular charge transfer complexes (CTCs), most polyimide devices on the market are yellow or brown, which is not conducive to the reflection of the sunlight band, thereby affecting the daytime radiation cooling performance. The present invention controls the molecular band gap through reasonable design, obtains a polyimide structure with higher whiteness, and makes the aerogel have a higher reflectivity in the sunlight band. At the same time, electronic groups with strong absorption in the atmospheric window band are introduced into the diamine and dianhydride structures, so that the copolymerized polyimide structure has a higher emissivity in the atmospheric window band, thereby obtaining an aerogel with radiation cooling characteristics, which is expected to be applied to building insulation, aerospace, electronic product heat dissipation and other aspects. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a preparation method and application of a polyimide aerogel with radiation cooling properties.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a polyimide molecule, the structural formula of which is shown in Formula I:

[0007]

[0008] In Formula I, R1 is one of Formula II-1 to Formula II-10, R2 is Formula III-1 (x=0 to 100), and R3 is one of Formula III-2 to Formula III-6:

[0009]

[0010] The present invention also provides a method for preparing the polyimide aerogel with radiation cooling characteristics described in the above technical solution, comprising the following steps:

[0011] Dissolving dianhydride and diamine monomers in an organic solvent for polymerization to obtain polyamic acid;

[0012] The water-soluble polyamic acid is added as a precursor into water, and triethylamine is added as a cosolvent to obtain a hydrogel through sol-gel conversion;

[0013] freeze-drying the hydrogel to obtain a polyamic acid aerogel;

[0014] imidizing the polyamic acid aerogel to obtain the polyimide aerogel;

[0015] The dianhydride monomer includes cyclohexanetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride, pyromellitic dianhydride, hexafluoroisopropylphthalic anhydride, biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride or 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride;

[0016] The diamine monomer is aminopropyl dicapped polydimethylsiloxane, trans-1,4-cyclohexanediamine, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminooctafluorobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane or 2,2'-bis(trifluoromethyl)diaminobiphenyl.

[0017] Preferably, the method for preparing a polyimide aerogel with radiation cooling properties as described in claim 2 is characterized in that the polymerization method is random copolymerization, the dianhydride monomer and the diamine monomer are in equimolar amounts, the range of n in the molecular formula is 10 to 10000, and the range of m is 10 to 10000.

[0018] Preferably, the organic solvent mainly includes N,N-dimethylformamide, dioxane and tert-butanol, and the amount used is 5 times the amount of the polymerization monomer.

[0019] Preferably, before the reaction starts, vacuum pumping and nitrogen blowing are required, and the process is repeated three times to ensure that oxygen and water are completely removed.

[0020] Preferably, the reaction is carried out at low temperature (ice water bath) for 12h-24h.

[0021] Preferably, the post-polymerization treatment comprises: settling, filtering and drying the product of the polymerization reaction.

[0022] Preferably, the solid content of the polyamic acid during the sol-gel conversion process is 2 wt % to 10 wt %.

[0023] Preferably, the freeze-drying conditions are: 2-10 Pa, -60 to -50°C, and freeze-drying for 24 to 30 hours.

[0024] Preferably, the imidization method is thermal imidization, and the process adopts a programmed temperature rising method: the polyimide aerogel is placed on a hot table, first at 80°C, 100°C, and 150°C for 1 hour respectively, and then at 200°C and 250°C for 0.5 hour respectively.

[0025] The present invention also provides the application of the polyimide aerogel with radiation cooling properties prepared above or the polyimide aerogel with radiation cooling properties obtained by the preparation method in building thermal insulation or heat dissipation of electronic products.

[0026] Compared with other technologies, the present invention has the following technical effects:

[0027] The present invention introduces a novel infrared fingerprint region (1500-600cm -1 ) has a strong absorption electronic group. Since the infrared fingerprint area of ​​this region just covers the atmospheric transparent window (8-13μm), polyimide has a high emissivity in the atmospheric transparent window (8-13μm). By controlling the molecular band gap, the yellow index of the device is reduced, making it have a high reflectivity, thereby obtaining excellent radiation cooling characteristics. At the same time, the high thermal stability of polyimide is retained, and it is expected to be used in building insulation, aerospace, and heat dissipation of electronic products. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a physical picture of the polyimide aerogel with radiation cooling properties in Example 1;

[0029] Figure 2 This is an infrared image of the polyimide aerogel with radiation cooling properties in Example 1;

[0030] Figure 3 This is the total emission reflection spectrum of the polyimide aerogel with radiation cooling characteristics in Example 1;

[0031] Figure 4 This is a temperature test diagram of the outdoor experiment of the polyimide aerogel with radiation cooling characteristics in Example 1;

[0032] Figure 5 This is a temperature test diagram of the outdoor experiment of the polyimide aerogel with radiation cooling characteristics in Example 2;

[0033] Figure 6This is a temperature test diagram of the outdoor experiment of the polyimide aerogel with radiation cooling characteristics in Example 3. DETAILED DESCRIPTION

[0034] The present invention provides a method for preparing a polyimide aerogel with radiation cooling properties, the structural formula of which is shown in Formula I:

[0035]

[0036] In Formula I, R1 is one of Formula II-1 to Formula II-10, R2 is Formula III-1 (x=0 to 100), and R3 is one of Formula III-2 to Formula III-6:

[0037]

[0038] 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.

[0039] The present invention also provides a method for preparing the polyimide aerogel with radiation cooling characteristics described in the above technical solution, comprising the following steps:

[0040] Dissolving dianhydride and diamine monomers in an organic solvent for polymerization to obtain polyamic acid;

[0041] The water-soluble polyamic acid is added as a precursor into water, and triethylamine is added as a cosolvent to obtain a hydrogel through sol-gel conversion;

[0042] freeze-drying the hydrogel to obtain a polyamic acid aerogel;

[0043] imidizing the polyamic acid aerogel to obtain the polyimide aerogel;

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

[0045] The diamine monomer is aminopropyl dicapped polydimethylsiloxane, trans-1,4-cyclohexanediamine, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminooctafluorobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane or 2,2'-bis(trifluoromethyl)diaminobiphenyl.

[0046] In the present invention, equimolar amounts of dianhydride and diamine monomers are dissolved in an organic solvent for polymerization reaction to obtain polyamic acid.

[0047] In the present invention, the polymerization method is random copolymerization, the dianhydride monomer and the diamine monomer are in equimolar amounts, and the range of n in the molecular formula is 10 to 10000, and the range of m is 10 to 10000.

[0048] In the present invention, the organic solvent mainly includes N,N-dimethylformamide, dioxane and tert-butanol, and the amount used is 5 times the amount of the polymerization monomer.

[0049] In the present invention, before the reaction starts, it is necessary to evacuate and pump nitrogen three times to ensure that oxygen and water are completely removed.

[0050] In the present invention, the reaction is carried out at low temperature (ice water bath) for 12h-24h.

[0051] In the present invention, the post-reaction treatment further comprises: settling, filtering and drying the product of the polymerization reaction.

[0052] In the present invention, the solid content of the polyamic acid during the sol-gel conversion process is 2 wt % to 10 wt %.

[0053] In the present invention, the freeze-drying conditions are: 2-10Pa, -60 to -50°C, freeze-drying for 24h to 30h.

[0054] After the polyamic acid aerogel is obtained, it is subjected to a thermal imidization method to obtain the final polyimide aerogel.

[0055] In the present invention, the imidization method is thermal imidization, and the process adopts a programmed temperature rising method: the polyimide aerogel is placed on a hot table, first at 80°C, 100°C, and 150°C for 1 hour respectively, and then at 200°C and 250°C for 0.5 hour respectively.

[0056] The preparation method of the present invention first screens out suitable dianhydride and diamine monomers through molecular design, then randomly copolymerizes the dianhydride and diamine monomers, then precipitates in deionized water, filters, and freeze-dries to obtain polyamic acid. Then the water-soluble polyamic acid is added to water as a precursor, and triethylamine is added as a cosolvent to obtain a hydrogel through sol-gel conversion, and then the hydrogel is freeze-dried to obtain a polyamic acid aerogel, and then it is thermally imidized using programmed temperature to prepare a polyimide aerogel with radiation cooling characteristics. The polyimide aerogel has a high reflectivity in the sunlight band and a high emissivity in the mid-infrared region, so it has a radiation cooling characteristic.

[0057] The present invention also provides the application of the polyimide aerogel with radiation cooling characteristics described in the above technical solution in the fields of building thermal insulation, aerospace, and heat dissipation of electronic products.

[0058] It will be described in more detail below through specific examples and drawings, but they are not limited thereto.

[0059] Example 1

[0060] A polyimide aerogel PI-1 with radiation cooling properties, the structure of which is shown in Formula V:

[0061]

[0062] The raw materials include: hexafluoroisopropylphthalic anhydride (6FDA), 2,2-bis(4-aminophenyl)hexafluoropropane (6TFMB), aminopropyl di-terminated polydimethylsiloxane (BATMS), deionized water, N,N-dimethylformamide (DMF), and triethylamine.

[0063] The preparation method is as follows:

[0064] (1) Preparation of polyamic acid

[0065] 6FDA4.42g (0.01mol), 15mL refined DMF, added to a 100mL Shrek tube with a magnet, after 20min of ultrasonic assisted dissolution, after complete dissolution, 6TFMB 2.24g (0.0067mol), 10mL refined DMF were added, and ultrasonication was continued for 10min, and then the vacuum and nitrogen blowing operation was repeated three times. Under nitrogen protection, the Shrek tube was placed in an ice water bath (0℃), and the stirring became stable. Then BATMS (0.082g, 0.0033mmol) was injected into the transparent solution through a syringe, and stirred for about 24h to obtain a white viscous PAA-1 solution. Pour it into deionized water for sedimentation to obtain a white PAA-1 solid. The obtained product was then filtered and washed. The washed solid was placed in a freeze dryer (2-10Pa, -60~-50℃) and frozen for 24h to obtain a white solid powder polyamic acid PAA-1.

[0066] (2) Preparation of polyamic acid aerogel

[0067] Weigh 0.263 g of soluble polyamic acid PAA-1, put it into a small beaker with a diameter of 3.5 cm, then add 4.65 g of deionized water and 0.35 g of TEA, then mix evenly by ultrasound and stirring, and then put it into liquid nitrogen (77K) for freezing. After completion, freeze-dry it for 24 hours (2-10Pa, -60~-50℃) to obtain an aerogel of polyamic acid PAA-1.

[0068] (3) Preparation of polyimide aerogel

[0069] The imidization method is thermal imidization, and the process adopts a programmed temperature rise method: the polyimide aerogel PAA-1 is placed on a hot stage, first at 80°C, 100°C, 150°C for 1 hour respectively, and then at 200°C, 250°C for 0.5 hour respectively, to obtain the final polyimide aerogel PI-1.

[0070] Figure 1 This is a physical picture of the polyimide aerogel with radiation cooling properties in Example 1;

[0071] Figure 2 This is an infrared image of the polyimide aerogel with radiation cooling properties in Example 1;

[0072] Figure 3 This is the total emission reflection spectrum of the polyimide aerogel with radiation cooling characteristics in Example 1;

[0073] Figure 4 This is a temperature test diagram of the outdoor experiment of the polyimide aerogel with radiation cooling characteristics in Example 1;

[0074] Figure 1 This is a physical picture of polyimide aerogel PI-1. Figure 1 It can be observed that polyimide has a white appearance, which is conducive to the reflection of sunlight band.

[0075] Figure 2 This is the infrared image of polyimide aerogel PI-1, 1780cm -1 and 1730cm -1 The asymmetric stretching vibration and symmetric stretching vibration of C=O indicate that the polyimide aerogel has been successfully prepared.

[0076] Figure 3 This is the total emission reflection spectrum of polyimide aerogel PI-1. It can be seen that the polyimide aerogel has good reflection in the solar light band and good emission in the mid-infrared region.

[0077] Figure 4 This is the outdoor experimental temperature test diagram of polyimide aerogel PI-1, which proves that it has good radiation cooling properties.

[0078] Example 2

[0079] A polyimide aerogel PI-2 with radiation cooling properties, the structure of which is shown in Formula VI:

[0080]

[0081] Raw materials: hexafluoroisopropylphthalic anhydride (6FDA), 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), aminopropyl di-terminated polydimethylsiloxane (BATMS), deionized water, N,N-dimethylformamide (DMF), triethylamine.

[0082] The preparation method is as follows:

[0083] (1) Preparation of polyamic acid

[0084] First, accurately weigh 4.42g (0.01mol) of 6FDA and 15mL of refined DMF, add them to a 100mL Shrek tube with a magnet, dissolve them with ultrasound assistance for 20 minutes, and then add 2.98g (0.0067mol) of TFMB and 10mL of refined DMF after complete dissolution, and then ultrasonicate for 10 minutes. Then repeat the vacuum and nitrogen gas operation three times. Under nitrogen protection, place the Shrek tube in an ice water bath (0°C), wait until the stirring becomes stable, and then inject BATMS (0.082g, 0.0033mmol) into the transparent solution through a syringe. Stir for about 24 hours to obtain a white viscous PAA-2 solution. Pour it into deionized water for sedimentation to obtain a white PAA-2 solid. Then filter and wash the obtained product. Put the washed solid into a freeze dryer (2-10Pa,

[0085] -60~-50℃) and frozen for 24h to obtain white solid powder polyamic acid PAA-2.

[0086] (2) Preparation of polyamic acid aerogel

[0087] Weigh 0.263 g of soluble polyamic acid PAA-2, put it into a small beaker with a diameter of 3.5 cm, then add 4.65 g of deionized water and 0.35 g of TEA, then mix evenly by ultrasound and stirring, and then put it into liquid nitrogen (77K) for freezing. After completion, freeze-dry it for 24 hours (2-10Pa, -60~-50℃) to obtain polyamic acid PAA-2 aerogel.

[0088] (3) Preparation of polyimide aerogel

[0089] The imidization method is thermal imidization, and the process adopts a programmed temperature rise method: the polyimide aerogel PAA-2 is placed on a hot stage, first at 80°C, 100°C, 150°C for 1 hour respectively, and then at 200°C, 250°C for 0.5 hour respectively, to obtain the final polyimide aerogel PI-2.

[0090] Figure 5 This is the outdoor experimental temperature test diagram of polyimide aerogel PI-2, which proves that it has good radiation cooling properties.

[0091] Example 3

[0092] A polyimide aerogel PI-3 with radiation cooling properties, the structure of which is shown in Formula VII:

[0093]

[0094] Raw materials: hexafluoroisopropylphthalic anhydride (6FDA), 4,4'-diaminooctafluorobiphenyl (DFP), aminopropyl di-terminated polydimethylsiloxane (BATMS), deionized water, N,N-dimethylformamide (DMF), triethylamine.

[0095] The preparation method is as follows:

[0096] (1) Preparation of polyamic acid

[0097] First, accurately weigh 6FDA4.42g (0.01mol), 15mL refined DMF, add to a 100mL Shrek tube with a magnet, dissolve after 20min of ultrasonic assisted dissolution, add DFP 2.20g (0.0067mol), 10mL refined DMF after complete dissolution, ultrasonicate for 10min, then repeat the vacuum and nitrogen gas operation three times, under nitrogen protection, place the Shrek tube in an ice water bath (0℃), wait for the stirring to stabilize, then inject BATMS (0.082g, 0.0033mmol) into the transparent solution through a syringe, stir for about 24h, and obtain a white viscous PAA-2 solution. Pour it into deionized water for sedimentation to obtain a white PAA-3 solid. Then filter and wash the obtained product. Put the washed solid into a freeze dryer (2-10Pa, -60~-50℃), freeze for 24h, and obtain a white solid powder polyamic acid PAA-3.

[0098] (2) Preparation of polyamic acid aerogel

[0099] Weigh 0.263 g of soluble polyamic acid PAA-3, put it into a small beaker with a diameter of 3.5 cm, then add 4.65 g of deionized water and 0.35 g of TEA, then mix evenly by ultrasound and stirring, and then put it into liquid nitrogen (77K) for freezing. After completion, freeze-dry it for 24 hours (2-10Pa, -60~-50℃) to obtain polyamic acid PAA-3 aerogel.

[0100] (3) Preparation of polyimide aerogel

[0101] The imidization method is thermal imidization, and the process adopts a programmed temperature rise method: the polyimide aerogel PAA-3 is placed on a hot stage, first at 80°C, 100°C, 150°C for 1 hour respectively, and then at 200°C, 250°C for 0.5 hour respectively, to obtain the final polyimide aerogel PI-3.

[0102] Figure 6 This is the outdoor experimental temperature recording curve of polyimide aerogel PI-3, proving that it has good radiation cooling properties.

[0103] It can be seen from the outdoor experimental temperature test that the polyimide aerogel prepared in the present invention has radiation cooling characteristics.

Claims

1. A method for preparing a polyimide aerogel having radiation cooling properties. The method comprises: First, through reasonable molecular design, the prepared polyimide molecular structure is shown in Formula I: In Formula I, R1 is one of Formula II-1 to Formula II-10, R2 is Formula III-1 (x=0 to 100), and R3 is one of Formula III-2 to Formula III-6: The method for preparing a polyimide aerogel having radiation cooling properties according to claim 1, characterized in that it comprises the following steps: Dissolving dianhydride and diamine monomers in an organic solvent for polymerization to obtain polyamic acid; The water-soluble polyamic acid is added as a precursor into water, and triethylamine is added as a cosolvent to obtain a hydrogel through sol-gel conversion; freeze-drying the hydrogel to obtain a polyamic acid aerogel; imidizing the polyamic acid aerogel to obtain the polyimide aerogel; The diamine monomers are aminopropyl dimethylsiloxane, aminopropyl dimethylsiloxane, trans-1,4-cyclohexanediamine, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminooctafluorobiphenyl, and 2,2-bis(4-aminophenyl)hexafluoropropane. The diamine monomer is aminopropyl dicapped polydimethylsiloxane, trans-1,4-cyclohexanediamine, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminooctafluorobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane or 2,2'-bis(trifluoromethyl)diaminobiphenyl.

2. The method for preparing a polyimide aerogel having radiation cooling properties according to claim 2, characterized in that: The polymerization method is random copolymerization, the dianhydride monomer and the diamine monomer are in equimolar amounts, the range of n in the molecular formula is 10 to 10000, and the range of m is 10 to 10000.

3. The method for preparing a polyimide aerogel having radiation cooling properties according to claim 2, characterized in that: The organic solvent mainly includes N,N-dimethylformamide, dioxane and tert-butyl alcohol, and the amount used is 5 times the amount of the polymerization monomer.

4. The method for preparing a polyimide aerogel having radiation cooling properties according to claim 2, characterized in that: Before the reaction begins, it is necessary to evacuate and blow nitrogen three times to ensure that oxygen and water are completely removed.

5. The method for preparing a polyimide aerogel having radiation cooling properties according to claim 2, characterized in that: The reaction is carried out at low temperature (ice water bath) for 12h-24h.

6. The method for preparing a polyimide aerogel having radiation cooling properties according to claim 2, characterized in that: The polymerization post-treatment comprises: settling, filtering and drying the polymerization product.

7. The method for preparing the polyimide aerogel having radiative cooling properties according to claim 2, It is characterized in that The solid content of the polyamic acid in the sol-gel conversion process is 2 wt % to 10 wt %.

8. The method for preparing a polyimide aerogel having radiation cooling properties according to claim 2, characterized in that: The freeze drying conditions are: 2-10 Pa, -60 to -50°C for 24 to 30 hours.

9. The method for preparing a polyimide aerogel having radiation cooling properties according to claim 2, characterized in that: The imidization method is thermal imidization, and the process adopts a programmed temperature rising method: the polyimide aerogel is placed on a hot table, first at 80°C, 100°C, 150°C for 1 hour respectively, and then at 200°C, 250°C for 0.5 hour respectively.

10. The method for preparing a polyimide aerogel having radiation cooling properties according to claim 2, characterized in that: The polyimide aerogel has high reflectivity in the solar light band and simultaneously obtains high emissivity in the mid-infrared region and has radiation cooling characteristics.

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