Passive cooling polyurethane film capable of being self-repaired at normal temperature as well as preparation method and application of passive cooling polyurethane film

Abstract

The invention provides a passive cooling polyurethane film capable of being self-repaired at normal temperature as well as a preparation method and application thereof, and belongs to the technical field of high polymer materials. The polyurethane film integrates double functions of efficient passive cooling and self-repairing, and a high-performance cooling filler is combined with an intrinsic self-repairing polymer matrix (polyurethane precursor), so that the polyurethane film not only has the capability of automatically recovering the cooling performance which is reduced due to damage, but also has excellent initial cooling performance. And meanwhile, TiO2 also endows the polyurethane film with surface hydrophobicity and self-cleaning capability, so that dust attachment can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a self-healing passive cooling polyurethane film at room temperature, its preparation method, and its application. Background Technology

[0002] Passive radiation cooling technology is a cutting-edge technology that achieves zero-energy cooling by utilizing the high solar reflectance and high atmospheric emittance of the material itself. The basic principle is that the material can efficiently reflect sunlight (mainly in the wavelength range of 0.3~2.5 μm), thereby minimizing the heat gain from solar radiation; at the same time, it can efficiently dissipate its own heat through the "atmospheric window" to the cold deep space in the form of thermal radiation (mainly in the wavelength range of 8~13 μm), thereby achieving a cooling effect below the ambient temperature.

[0003] Generally, ideal passive radiative cooling materials need to have high reflectivity in the solar spectrum (especially visible light and near-infrared light, NIR) and extremely high emissivity in the atmospheric window. Titanium dioxide (TiO2), due to its high refractive index and excellent reflectivity in the visible and near-infrared bands, is often introduced as a functional filler into various polymer matrices (such as acrylic resins, polysiloxanes, and polyurethanes) to prepare high-performance cooling coatings or films. However, in practical outdoor applications, these materials face two main challenges when exposed to complex and harsh environments for extended periods, leading to a significant degradation in their cooling performance:

[0004] (1) Surface dust accumulation: Dust, particulate matter, and other substances in the air will gradually adhere to and accumulate on the surface of the material, forming a low-reflectivity shielding layer. This layer will hinder the reflection of sunlight on the material surface, leading to an increase in the absorption rate of sunlight, which in turn causes the material to heat up and its cooling performance to drop significantly.

[0005] (2) Physical damage (scratches, cracks): Physical factors such as wind and sand erosion, mechanical abrasion, and changes in thermal stress in the outdoor environment can easily cause microcracks, scratches and other damage on the material surface. These surface defects will destroy the original smoothness and optical uniformity of the material. On the one hand, they will increase the scattering and absorption of sunlight and reduce reflectivity; on the other hand, they may also destroy the surface's reflectivity and become stress concentration points, accelerating the further aging and failure of the material.

[0006] To address these issues, researchers have explored various approaches, such as developing superhydrophobic self-cleaning surfaces to reduce dust adhesion or preparing high-hardness, wear-resistant coatings to resist physical damage. However, these strategies only solve a single problem, and their effects are not sustainable. Once the self-cleaning surface loses its hydrophobicity due to scratching, or the wear-resistant coating is compromised, performance degradation is inevitable. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a self-healing passive cooling polyurethane film at room temperature, its preparation method, and its application. The polyurethane film has high reflectivity, high cooling performance, can achieve self-healing through ultraviolet initiation at room temperature, and also possesses self-cleaning functionality.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a passively cooling polyurethane film that can self-heal at room temperature, characterized in that it is obtained by curing a mixture comprising a polyurethane precursor and a cooling filler.

[0010] The polyurethane precursor is obtained by reacting a soft segment component, a hard segment component, a crosslinking agent, and a chain extender. The chain extender is selected from 4-(aminomethyl)benzyl-4-(2-aminoethoxy)-9H-carbazole-9-carbon dithioester.

[0011] The cooling filler includes titanium dioxide.

[0012] Preferably, in this invention, the chain extender is prepared according to the following method:

[0013] (1) 4-hydroxycarbazole and 2-(Boc-amino)bromoethane react in the presence of a catalyst to give tert-butyl(2-((9H-carbazole-4-yl)oxy)ethyl)carbamate;

[0014] (2) Tert-butyl (2-((9H-carbazole-4-yl)oxy)ethyl)carbamate reacts with N-Boc-(4-(bromomethyl)phenyl)methylamine and carbon disulfide to give 4-((tert-butoxycarbonyl)amino)methylphenyl-4-(2-((tert-butoxycarbonyl)amino)ethoxy)-9H-carbazole-9-carbonyl dithioester. After de-Boc, 4-(aminomethyl)benzyl-4-(2-aminoethoxy)-9H-carbazole-9-carbon dithioester is given.

[0015] Preferably, the mass ratio of the polyurethane precursor to the cooling filler is 1:(0.05~0.3).

[0016] Preferably, the soft segment component is selected from different diols, specifically from any one or more of PTMEG (polytetramethylene ether glycol), PCL (polycaprolactone), or PEG (polyethylene glycol).

[0017] Preferably, the hard segment component is selected from different diisocyanates, specifically from any one or more of HMDI (dicyclohexylmethane diisocyanate), MDI (diphenylmethane diisocyanate), TDI (toluene diisocyanate) or HDI (hexamethylene diisocyanate).

[0018] Preferably, the crosslinking agent is selected from substances containing three active groups, specifically from any one or more of TAEA (tris(2-aminoethyl)amine), DETA (diethylenetriamine), or TETA (triethylenetetramine).

[0019] Preferably, the surface of the polyurethane film is a flat surface; or it has a raised structure and / or a recessed structure. More preferably, the surface of the polyurethane film has a raised structure.

[0020] Preferably, the cross-sectional shape of the protruding or recessed structure includes a rectangle and / or a square.

[0021] Preferably, the depth of the protruding or recessed structure is 0.5~2 mm, and the cross-sectional dimensions of the protruding or recessed structure are 0.5~2 mm × 0.5~2 mm.

[0022] Preferably, the polyurethane film has a reflectivity of 75% or higher.

[0023] Preferably, the water contact angle of the polyurethane film is greater than 110°.

[0024] Secondly, the present invention provides a method for preparing the above-mentioned self-healing passive cooling polyurethane film at room temperature, comprising the following steps:

[0025] S1: In an inert atmosphere, the soft segment component, hard segment component, crosslinking agent and chain extender react to obtain a polyurethane precursor;

[0026] S2: After mixing the polyurethane precursor and the cooling filler, the mixture is cured to obtain a polyurethane film.

[0027] Preferably, the bottom of the mold used for curing is flat, or has a raised structure and / or a recessed structure.

[0028] It should be noted that in this application, the ratio of soft segment component, hard segment component, crosslinking agent and chain extender should satisfy the molar ratio of -NCO to (-OH and -NH2) being 1:1.

[0029] Thirdly, the present invention provides an application of the above-mentioned self-healing passive cooling polyurethane film at room temperature in outdoor building cooling, human body thermal management, electronic device cooling, or automobile cooling.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) This invention provides a self-healing cooling smart material with simpler triggering conditions and more suitable for outdoor applications, namely a passive cooling polyurethane film that can self-heal at room temperature. The polyurethane film does not require external heating and can trigger self-healing using only the ultraviolet light of the sun in the natural environment. This can overcome the disadvantages of high energy consumption and harsh conditions of thermal triggering mechanisms, and achieve more convenient and low-cost damage repair.

[0032] (2) The polyurethane film provided by the present invention integrates the dual functions of efficient passive cooling and self-repair. It combines high-performance cooling filler (titanium dioxide, TiO2) with intrinsic self-repairing polymer matrix (polyurethane precursor, which can be simply referred to as PCDU-SS), so that the polyurethane film not only has the ability to recover the cooling performance that has decreased due to damage, but also has excellent initial cooling performance, thus achieving the unity of "active protection" and "passive defense".

[0033] (3) This invention introduces the chain extender 4-(aminomethyl)benzyl-4-(2-aminoethoxy)-9H-carbazole-9-carbon dithioester into the polyurethane precursor, thereby introducing dynamic dithiocarbamate and carbazole groups into the polyurethane system. The dynamic dithiocarbamate can absorb ultraviolet light, which is typically harmful to materials, and trigger self-healing without additional heating, thus solving the problems of difficult outdoor repair and challenging repair conditions. It also improves resistance to photoaging. The fluorescence effect of the carbazole group can dissipate the absorbed ultraviolet light, and the two work together to enhance the photoaging resistance of the polyurethane film. Furthermore, titanium dioxide has high reflectivity in the visible and near-infrared ranges but low reflectivity in the ultraviolet range. This unreflected ultraviolet energy can be used for self-healing, and the fluorescence absorption and dissipation effect of the carbazole group in the ultraviolet range complements the high reflectivity of titanium dioxide, achieving superior performance and further reducing ultraviolet aging. Therefore, the polyurethane film provided by this invention can utilize ultraviolet light to transform it into a beneficial energy source that drives the self-repair of materials, thereby achieving functional self-sustaining by utilizing environmental energy, which is an intelligent design that "turns harm into benefit".

[0034] (4) To further explain, the present invention imparts hydrophobicity and self-cleaning ability to the surface of the polyurethane film by adding TiO2, which enables it to reduce dust adhesion and keep the surface clean through rainwater rinsing. In terms of both "reducing dust accumulation" and "repairing damage", the polyurethane film maintains a long-term stable high reflectivity, i.e., cooling efficiency. Therefore, the polyurethane film provided by the present invention has self-cleaning properties and can comprehensively improve outdoor durability. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the synthetic route of CDC-amine and PCDU-SS in Example 1;

[0036] Figure 2 Macroscopic views of the polyurethane films obtained in Examples 5 and 11;

[0037] Wherein, a corresponds to Example 5 and b corresponds to Example 11. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Given that in the prior art, when titanium dioxide (TiO2) is introduced as a functional filler into various polymer matrices (such as acrylic resin, polysiloxane, and polyurethane), the resulting cooling coating has problems such as physical damage that is difficult to repair and insufficient resistance to dust accumulation, the present invention provides a passive cooling polyurethane film that can self-heal at room temperature, which is obtained by curing a mixture including a polyurethane precursor and a cooling filler.

[0040] In this invention, the polyurethane precursor is obtained by reacting a soft segment component, a hard segment component, a crosslinking agent, and a chain extender. The chain extender is a key component, while the soft segment component, hard segment component, and crosslinking agent can be components well-known to those skilled in the art. In this invention, the chain extender covalently integrates a carbazole group capable of absorbing ultraviolet light with a dynamic dithiocarbamate bond, specifically selected from 4-(aminomethyl)benzyl-4-(2-aminoethoxy)-9H-carbazole-9-carbon dithioester, abbreviated as (CDC-amine). The introduction of this specific chain extender in this invention achieves integrated "energy capture-bond exchange," enabling the polyurethane film to self-heal scratches using only the ultraviolet band of sunlight at room temperature and without an external heat source.

[0041] In some embodiments of the present invention, the soft segment component is selected from any one or more of PTMEG, PCL, or PEG; the hard segment component is selected from any one or more of HMDI, MDI, TDI, or HDI; and the crosslinking agent is selected from any one or more of TAEA, DETA, or TETA.

[0042] In this invention, the cooling filler comprises titanium dioxide, which is introduced through physical mixing. The synergistic design of "physically mixed TiO2 + chemically bonded dithiocarbamate bonds" allows carbazole to absorb TiO2 in the low-reflectivity region of the ultraviolet spectrum, converting it into the energy required for the breaking and recombination of dithiocarbamate bonds. This transforms a defect into a function, effectively overcoming the side effect of "matrix degradation" in existing photocatalytic systems.

[0043] In some embodiments of the present invention, the mass ratio of the polyurethane precursor to the cooling filler is 1:(0.05~0.3), such as 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25 or 1:0.3, etc.

[0044] Because the yellow color from the carbazole group absorbs light in a specific wavelength range, it reduces reflectivity. Therefore, this invention designs raised and / or recessed structures on the surface of the polyurethane film to compensate for this problem. In some preferred embodiments of this invention, the polyurethane film surface also has raised and / or recessed structures. The presence of these raised and / or recessed structures can compensate for the influence of color and increase the reflectivity of the material by 2-10%.

[0045] In some specific embodiments of the present invention, the surface of the polyurethane film preferably has a raised structure, and preferably is presented as a cube.

[0046] In this invention, the cross-sectional shape of the protruding or recessed structure includes a rectangle and / or a square. The depth of the protruding or recessed structure is 0.5~2 mm, and the cross-sectional dimensions of the protruding or recessed structure are 0.5~2 mm × 0.5~2 mm. The 0.5~2 mm can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, or 2 mm.

[0047] In this invention, the vertical and horizontal spacing of each protruding structure is 0.5 to 2 mm; similarly, the vertical and horizontal spacing of each recessed structure is 0.5 to 2 mm. The 0.5 to 2 mm can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, or 2 mm.

[0048] It should be noted that the above-mentioned protruding or recessed structures can increase the number of scattering events of the material to improve reflectivity. Different structure sizes are suitable for different wavebands. If the structure is too large or too small, the improvement in reflectivity will not be significant. Therefore, the present invention preferably places the depth and cross-sectional dimensions of the above-mentioned protruding or recessed structures within the above-mentioned range.

[0049] This invention also provides a method for preparing the above-mentioned self-healing passive cooling polyurethane film at room temperature, comprising the following steps:

[0050] S1: In an inert atmosphere, the soft segment component, hard segment component, crosslinking agent and chain extender react to obtain a polyurethane precursor;

[0051] S2: After mixing the polyurethane precursor and the cooling filler, the mixture is cured to obtain a polyurethane film.

[0052] According to the present invention, the soft segment component, the hard segment component, the crosslinking agent and the chain extender are first reacted in an inert atmosphere to obtain a polyurethane precursor.

[0053] In this invention, the chain extender is prepared according to the following method:

[0054] (1) 4-hydroxycarbazole and 2-(Boc-amino)bromoethane react in the presence of a catalyst to give tert-butyl(2-((9H-carbazole-4-yl)oxy)ethyl)carbamate;

[0055] (2) Tert-butyl (2-((9H-carbazole-4-yl)oxy)ethyl)carbamate reacts with N-Boc-(4-(bromomethyl)phenyl)methylamine and carbon disulfide to give 4-((tert-butoxycarbonyl)amino)methylphenyl-4-(2-((tert-butoxycarbonyl)amino)ethoxy)-9H-carbazole-9-carbonyl dithioester. After de-Boc, 4-(aminomethyl)benzyl-4-(2-aminoethoxy)-9H-carbazole-9-carbon dithioester is given.

[0056] In some embodiments of the present invention, the chain extender is prepared by the following method:

[0057] (1) CZOLA-Boc was synthesized from 4-hydroxycarbazole (CZOL) and 2-(Boc-amino)bromoethane (TBBEC) under the catalysis of potassium carbonate (K2CO3). The specific steps are as follows:

[0058] First, K₂CO₃, CZOL, and dimethylformamide (DMF) were added to a three-necked flask, and the mixture was stirred at room temperature under a nitrogen atmosphere for 2–4 h. Next, tert-butyl 2-bromo-2-methylpropionate (TBBEC) was added, and the reaction was continued for 8–12 h. Finally, the reaction mixture was poured into a large volume of water and extracted with ethyl acetate (EtOAc) (100 mL × 3 times). The organic phase was collected and dried over anhydrous Na₂SO₄. After removing the solvent and washing with petroleum ether, the product CZOLA-Boc was obtained.

[0059] (2) CDC-amine-Boc was synthesized from tert-butyl (2-((9H-carbazole-4-yl)oxy)ethyl)carbamate (CZOLA-Boc), N-Boc-(4-(bromomethyl)phenyl)methylamine (TBBBC), and carbon disulfide (CS2). Specific synthetic steps: CZOLA-Boc, finely ground KOH powder, and dimethyl sulfoxide (DMSO) were added to a dry three-necked flask, and the mixture was stirred for 1–2 h at room temperature under a N2 atmosphere. After cooling to 20 °C, CS2 was slowly added dropwise to the reaction mixture, and the reaction continued for 4–6 h. Then, TBBBC (50 mmol, 15.47 g) was added, and the mixture was stirred for another 24 h. After precipitation in water, vacuum filtration, and washing with a large amount of petroleum ether, CDC-amine-Boc was obtained accordingly.

[0060] (3) CDC-amine was prepared from 4-((tert-butoxycarbonyl)amino)methylphenyl-4-(2-((tert-butoxycarbonyl)amino)ethoxy)-9H-carbazole-9-carbonyl dithioester (CDC-amine-Boc) by deprotection. The specific synthetic steps are as follows: CDC-amine-Boc was deprotected in CF3COOH / CH2Cl2 (1:2 molar ratio) at room temperature for 2-6 h (the completion of the reaction was monitored by thin-layer chromatography). After neutralization with saturated NaHCO3 aqueous solution, a solid crude product was precipitated, filtered, and dried under vacuum. After washing with a large amount of petroleum ether, pure CDC-amine was obtained.

[0061] In some embodiments of the present invention, step S1 preferably includes the following steps:

[0062] In an inert atmosphere, the soft segment component and the hard segment component are reacted at 60-90°C, preferably 80°C, for 4-6 h in the presence of a catalyst (including but not limited to dibutyltin dilaurate). The reaction mixture is then cooled to 40-50°C, preferably 45°C, and a solvent (such as DMF) and a chain extender are added, and the reaction continues for 4-8 h, preferably 6 h, to obtain the prepolymer. Subsequently, the prepolymer is mixed with a crosslinking agent and reacted for 4-8 h, preferably 6 h, to obtain the polyurethane precursor. The selection of the soft segment component, hard segment component, crosslinking agent, and chain extender is as described above and will not be repeated here.

[0063] In some embodiments of the present invention, it is preferred to use HDMI as the hard segment, PTMEG2000 as the soft segment, and CDC-amine as the chain extender to synthesize a prepolymer, and then add TAEA to prepare a crosslinked polyurethane, abbreviated as PCDU-SS.

[0064] In some specific embodiments of the present invention, the specific synthesis method of PCDU-SS is as follows:

[0065] HMDI and three drops of dibutyltin dilaurate (DBTDL) were added to a three-necked flask containing dehydrated PTMEG, and argon gas was introduced. After stirring at 80°C for 4–6 h, the reaction mixture was cooled to 40–50°C. Then, DMF and CDC-amine were added, and the reaction was continued for 6 h. Subsequently, the prepolymer was crosslinked with TAEA for an additional 6 h. Finally, the reaction mixture was poured into a polytetrafluoroethylene mold and cured at 60°C to prepare PCDU-SS.

[0066] After obtaining the polyurethane precursor, according to the present invention, the polyurethane precursor and the cooling filler (such as TiO2) are mixed and cured to obtain a polyurethane film.

[0067] In some embodiments of the present invention, it is preferable to mix the polyurethane precursor and the cooling filler (such as TiO2) at a certain mass ratio, pour the resulting mixture into a mold, and cure it. The mold can be a polytetrafluoroethylene mold well known to those skilled in the art.

[0068] It should be noted that in some embodiments of the present invention, the bottom of the polytetrafluoroethylene mold can be a smooth and flat plane, and the resulting polyurethane film surface is smooth and flat.

[0069] In other embodiments of the present invention, the bottom of the polytetrafluoroethylene mold has a regular grid structure, which can be a raised structure or a recessed structure. Specifically, when the bottom of the polytetrafluoroethylene mold has a raised structure, the surface of the resulting polyurethane film has a recessed structure; when the bottom of the polytetrafluoroethylene mold has a recessed structure, the surface of the resulting polyurethane film has a raised structure.

[0070] The preparation method provided by the present invention is simple, convenient, and easy to implement, which is conducive to large-scale or industrialized production.

[0071] In summary, the polyurethane film provided by this invention has the following characteristics:

[0072] (1) Unique UV energy processing method: In the chain extender CDC-amine, the "carbazole UV absorption unit" and the "dynamic dithiocarbamate bond" are covalently connected in series, so that the part of TiO2 with insufficient reflection in the UV region (300~400 nm reflectivity <30%) is captured by carbazole and directly converted into the energy required for the breaking and recombination of dithiocarbamate bonds (bond energy ≈240kJ mol). -1 ).

[0073] (2) Self-healing mechanism that can be constructed on-site at room temperature without heat source: The ultraviolet energy in sunlight promotes the self-healing of polyurethane at room temperature, avoiding the side effects of scratches on the material.

[0074] (3) Grid structure: The reflectivity of the material is further improved by preparing a regular grid structure on the surface of the film. The essence of the grid structure to improve the reflectivity is to use a regular geometric array at the micron / submicron scale to reflect, scatter and diffract sunlight (0.3~2.5µm band) multiple times and reorient it, so that the photons that would have entered the polyurethane film and been absorbed are "returned" to the atmosphere, thereby effectively increasing the effective reflectivity of the material.

[0075] (4) The three functions of "hydrophobicity + high reflectivity + self-healing" work together to improve the adaptability of polyurethane film when used outdoors, increase the service life of polyurethane film, and expand the application range of polyurethane film.

[0076] Tests have shown that the polyurethane film provided by this invention has a reflectivity of over 75%, exhibiting high reflectivity; the water contact angle of the polyurethane film is over 110°, exhibiting hydrophobicity; and it can achieve self-repair of surface damage after 6 hours of sunlight exposure.

[0077] Finally, the present invention also provides an application of the above-mentioned self-healing passive cooling polyurethane film at room temperature in outdoor building cooling, human body thermal management, electronic device cooling, or automobile cooling.

[0078] To further illustrate the present invention, the following embodiments provide a detailed description. The experimental materials used in the following embodiments of the present invention are all commercially available products.

[0079] CZOL's Chinese name is 4-hydroxycarbazole;

[0080] The English name of CZOLA-Boc is tert-butyl (2-((9H-carbazol-4-yl)oxy)ethyl)carbamate, and the Chinese name is tert-butyl (2-((9H-carbazol-4-yl)oxy)ethyl)carbamate.

[0081] The English name of CDC-amine-Boc is 4-(((tert-butoxycarbonyl)amino)methyl)benzyl-4-(2-((tert-butoxycarbonyl)amino)ethoxy)-9H-carbazole-9-carbodithioate, and the Chinese name is 4-((tert-butoxycarbonyl)amino)methylphenyl-4-(2-((tert-butoxycarbonyl)amino)ethoxy)-9H-carbazole-9-carbonyl dithioate.

[0082] The English name of CDC-amine is 4-(aminomethyl)benzyl-4-(2-aminoethoxy)-9H-carbazole-9-carbodithioate, and the Chinese name is 4-(aminomethyl)benzyl-4-(2-aminoethoxy)-9H-carbazole-9-carbodithioate.

[0083] The Chinese name for TBBBC is N-Boc-(4-(bromomethyl)phenyl)methylamine;

[0084] The Chinese name for HMDI is hexamethylene diisocyanate.

[0085] The Chinese name for PTMEG is polytetramethylene ether glycol.

[0086] The Chinese name for TAEA is tri(2-aminoethyl)amine.

[0087] Example 1

[0088] First, K₂CO₃ (90 mmol, 12.56 g), CZOL (60 mmol, 11.58 g), and 300 mL of dimethylformamide (DMF) were added to a three-necked flask, and the mixture was stirred at room temperature for 2 h under a nitrogen atmosphere. Next, tert-butyl 2-bromo-2-methylpropionate (TBBEC, 90 mmol, 20.80 g) was added, and the reaction was continued for another 8 h. Finally, the reaction mixture was poured into a large volume of water and extracted with ethyl acetate (EtOAc) (100 mL × 3 times). The organic phase was collected and dried over anhydrous Na₂SO₄. After removing the solvent and washing with petroleum ether, the product CZOLA-Boc was obtained.

[0089] CZOLA-Boc (50 mmol, 16.31 g), finely ground KOH powder (75 mmol, 4.21 g), and 200 mL of dimethyl sulfoxide (DMSO) were added to a dry three-necked flask and stirred for 1 h at room temperature under a nitrogen atmosphere. After cooling to 20 °C, CS2 (75 mmol, 5.82 g) was slowly added dropwise to the reaction mixture, and the reaction was continued for 4 h. Then, TBBBC (50 mmol, 15.47 g) was added, and the mixture was stirred for another 24 h. After precipitation in water, vacuum filtration, and washing with a large amount of petroleum ether, CDC-amine-Boc was obtained accordingly.

[0090] CDC-amine-Boc was prepared in CF3COOH / CH2Cl2 (70 mL, 1.9 mol·L⁻¹). -1 The deprotection reaction was carried out at room temperature over 2 hours (Note: the completion of the reaction was monitored by thin-layer chromatography). After neutralization with saturated NaHCO3 aqueous solution, a crude solid product was precipitated, filtered, and dried under vacuum. After washing with a large amount of petroleum ether, pure CDC-amine was obtained. The synthetic route is shown in the figure. Figure 1 As shown.

[0091] HMDI (3 mmol, 0.80 g) and three drops of dibutyltin dilaurate (DBTDL) were added to a three-necked flask containing dehydrated PTMEG (1.63 mmol, 3.25 g), and argon gas was introduced. After stirring at 80 °C for 4 h, the reaction mixture was cooled to 45 °C. Then, 70 mL of DMF and CDC-amine (1 mmol, 0.42 g) were added, and the reaction was continued for 6 h. Subsequently, the prepolymer was crosslinked with TAEA (0.25 mmol, 0.04 g) for an additional 6 h. Finally, the reaction mixture was poured into a planar polytetrafluoroethylene mold and cured at 60 °C for 48 h to prepare PCDU-SS. The synthetic route is shown in the figure. Figure 1 As shown.

[0092] Example 2

[0093] Unlike Example 1, after adding TAEA for 6 hours for crosslinking, 5 wt% titanium dioxide was added and stirred for 1 hour. The reaction mixture was then poured into a planar polytetrafluoroethylene mold and cured at 60°C for 48 hours to prepare 5%-TiO2@PCDU-SS.

[0094] Example 3

[0095] Unlike Example 2, the added TiO2 had a mass fraction of 10 wt%, while the remaining parameters and steps were the same as in Example 1, to obtain 10%-TiO2@PCDU-SS.

[0096] Example 4

[0097] Unlike Example 2, the added TiO2 had a mass fraction of 15 wt%, while the remaining parameters and steps were the same as in Example 1, resulting in 15%-TiO2@PCDU-SS.

[0098] Example 5

[0099] Unlike Example 2, the added TiO2 had a mass fraction of 20 wt%, while the remaining parameters and steps were the same as in Example 1, resulting in 20%-TiO2@PCDU-SS.

[0100] Example 6

[0101] Unlike Example 2, the added TiO2 had a mass fraction of 30 wt%, while the remaining parameters and steps were the same as in Example 1, resulting in 30%-TiO2@PCDU-SS.

[0102] Example 7

[0103] Unlike Example 1, the reaction mixture was poured into a polytetrafluoroethylene mold with a regular grid structure (specifically: a recessed structure, 1 mm × 1 mm × 1 mm, with each recess spaced 1 mm to the right and up and down), and cured at 60°C for 48 h to prepare PCDU-SS with a raised structure (1 mm × 1 mm × 1 mm, with each raised structure spaced 1 mm to the left and right and up and down).

[0104] Example 8

[0105] Unlike Example 2, the reaction mixture was poured into a polytetrafluoroethylene mold with a regular grid structure (same as Example 7) and cured at 60°C for 48 h to prepare PCDU-SS with a raised structure.

[0106] Example 9

[0107] Unlike Example 3, the reaction mixture was poured into a polytetrafluoroethylene mold with a regular grid structure (same as Example 7) and cured at 60°C for 48 h to prepare PCDU-SS with a raised structure.

[0108] Example 10

[0109] Unlike Example 4, the reaction mixture was poured into a polytetrafluoroethylene mold with a regular grid structure (same as Example 7) and cured at 60°C for 48 h to prepare PCDU-SS with a raised structure.

[0110] Example 11

[0111] Unlike Example 5, the reaction mixture was poured into a polytetrafluoroethylene mold with a regular grid structure (same as Example 7) and cured at 60°C for 48 h to prepare PCDU-SS with a raised structure.

[0112] Example 12

[0113] Unlike Example 6, the reaction mixture was poured into a polytetrafluoroethylene mold with a regular grid structure (same as Example 7) and cured at 60°C for 48 h to prepare PCDU-SS with a raised structure.

[0114] Macroscopic images of the polyurethane films obtained in Examples 5 and 11 above are shown below. Figure 2 As shown, it can be seen that a corresponds to Example 5 and b corresponds to Example 11. It can be seen that the polyurethane film obtained in Example 11 has a regular protruding structure.

[0115] Performance Characterization

[0116] The reflectance of the products obtained in Examples 1-12 was tested. Reflectance characterization: The reflectance of the prepared thin film was tested at 5 nm intervals in the 200 nm to 2500 nm band using an ultraviolet-visible-near-infrared spectrometer with an integrating sphere (LAMBDA1050, PerkinElmer). The standard white plate for reflectance testing was barium sulfate.

[0117] The formula for calculating the average reflectivity of a material is shown below:

[0118]

[0119] In the formula:

[0120] —The average solar reflectance of the sample;

[0121] —The solar reflectance of a standard whiteboard;

[0122] —The solar reflectance of the sample;

[0123] —Relative spectral distribution of solar radiation;

[0124] — Wavelength interval, in nanometers (nm).

[0125] The test results are shown in Table 1 below:

[0126] Table 1

[0127]

[0128] Table 1 shows that the reflectivity of the material increases significantly with the increase of titanium dioxide content. However, the reflectivity of 20% and 30% titanium dioxide content is not significantly different, indicating that further increasing the titanium dioxide content after reaching a certain proportion does not improve performance much. Based on this, the optimal titanium dioxide content (around 20%) can be selected. Furthermore, since the self-healing polyurethane matrix is ​​yellow, it will result in a lower reflectivity of the material. Therefore, a film with a regular grid structure on the surface is prepared to further improve the reflectivity of the material. As shown in Examples 7-12, adding a regular grid structure to the surface can further improve the reflectivity of the material by approximately 5%. Among them, the 30%-TiO2@PCDU-SS with the grid structure achieves a reflectivity of 91.29%, exhibiting strong passive cooling capability.

[0129] Furthermore, through experiments on the surface of defective thin films (Examples 2-6, Examples 8-12) exposed to sunlight, the present invention found that the damage on the surface of the thin film can be self-repaired after 6 hours of sunlight exposure.

[0130] Furthermore, due to the addition of titanium dioxide, the water contact angle of the film increased from 80° to about 115°, indicating that it has a certain self-cleaning ability and can reduce the side effects of dust during outdoor use.

[0131] In summary, the TiO2@PCDU-SS provided by this invention possesses self-healing, self-cleaning, and radiative cooling capabilities, providing a feasible solution for the large-scale outdoor application of radiative cooling materials.

[0132] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A normal-temperature self-repairable passive cooling polyurethane film, characterized in that, obtained after curing of a mixture comprising a polyurethane precursor and a cooling filler; the polyurethane precursor is obtained after reaction of a soft segment component, a hard segment component, a crosslinking agent and a chain extender selected from 4-(aminomethyl)benzyl-4-(2-aminoethoxy)-9H-carbazole-9-carbodithioate; the cooling filler comprises titanium dioxide. 2.The ambient self-healing and passive cooling polyurethane film according to claim 1, characterized in that, the chain extender is prepared according to the following method: (1) 4-hydroxycarbazole and 2-(Boc-amino) bromoethane react in the presence of a catalyst to obtain tert-butyl (2-((9H-carbazol-4-yl)oxy)ethyl) carbamate; (2) tert-butyl (2-((9H-carbazol-4-yl)oxy)ethyl) carbamate reacts with N-Boc-(4- (bromomethyl)phenyl)methanamine and carbon disulfide to obtain 4-((tert- butyloxycarbonyl)amino)methylphenyl-4-(2-((tert-butyloxycarbonyl)amino)ethoxy)- 9H-carbazole-9-carbonyl dithioate, and Boc is removed to obtain 4-(aminomethyl) benzyl-4-(2-aminoethoxy)-9H-carbazole-9-carbodithioate. 3.The ambient self-healing and passive cooling polyurethane film according to claim 1 or 2, characterized in that, the mass ratio of the polyurethane precursor to the cooling filler is 1:(0.05-0.3). 4.The ambient self-healing and passive cooling polyurethane film according to claim 1, characterized in that, the soft segment component is selected from any one or more of PTMEG, PCL or PEG; the hard segment component is selected from any one or more of HMDI, MDI, TDI or HDI; the crosslinking agent is selected from any one or more of TAEA, DETA or TETA.

5. The room-temperature self-repairable passive cooling polyurethane film according to claim 1, wherein the surface of the polyurethane film is a flat surface; or has a convex structure and / or a concave structure. 6.The ambient self-healing and passive cooling polyurethane film according to claim 5, characterized in that, the shape of the cross section of the convex structure or the concave structure comprises a rectangle and / or a square; the depth of the convex structure or the concave structure is 0.5-2 mm, and the size of the cross section of the convex structure or the concave structure is 0.5-2 mm x 0.5-2 mm. 7.The ambient self-healing and passive cooling polyurethane film according to claim 1, wherein, the reflectivity of the polyurethane film is above 75%; the water contact angle of the polyurethane film is above 110°.

8. A method for preparing the room-temperature self-repairable passive cooling polyurethane film according to any one of claims 1 to 7, characterized in that, comprising the following steps: S1: reacting a soft segment component, a hard segment component, a crosslinking agent and a chain extender in an inert atmosphere to obtain a polyurethane precursor; S2: mixing the polyurethane precursor and a cooling filler, and curing to obtain a polyurethane film.

9. The production method according to claim 8, characterized by, the bottom of the mold used for curing is a flat surface, or has a convex structure and / or a concave structure.

10. Use of the room-temperature self-repairable passive cooling polyurethane film according to any one of claims 1-7 or prepared according to the preparation method of claim 8 or 9 in outdoor building cooling, human thermal management, electronic device cooling or automobile cooling.

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