An electrochromic polymer, its preparation method, and an electrochromic polymer film

Abstract

An electrochromic polymer, its preparation method, and an electrochromic polymer film are provided. The electrochromic polymer includes the following structural formula: R1 is a straight-chain alkyl group with 6 or more carbons, R2 is a branched alkyl group with 8 or more carbons, R is a branched alkyl group with 20 or more carbons, and n represents the degree of polymerization, with n being a natural number between 8 and 100. The polymer has visible to near-infrared synergistic color-changing properties and is prepared by Stille coupling.

Description

Technical Field

[0001] This invention relates generally to the field of polymer electrochromic technology, and more specifically to an electrochromic polymer, its preparation method, and an electrochromic polymer film. Background Technology

[0002] Electrochromic materials can undergo reversible redox reactions under appropriate applied voltage, achieving reversible transitions between colored and bleached states. They hold significant promise for applications in numerous fields, such as smart windows and non-emissive displays. As a type of electrochromic material, electrochromic polymers possess advantages such as designable colors, fast response speed, high optical contrast, and high coloring efficiency. However, reports on electrochromic polymers with synergistic color changes from visible to near-infrared light are limited. Therefore, developing polymers with broad spectral absorption is of great importance to the field of electrochromism.

[0003] Designing donor-acceptor polymer structures is an effective means of achieving broad-spectrum absorption. First, a strong charge-withdrawing acceptor structure is designed by connecting an acceptor with a low LUMO energy level to a donor, thereby achieving intramolecular charge transfer with an ultra-low bandgap, which red-shifts the polymer's absorption spectrum to the near-infrared region. Second, donor units within the polymer are designed, and the π-π phase, directly related to short-wavelength absorption, is modulated. The transition effect optimizes its short-wavelength color-changing performance; finally, based on the optical compensation mechanism, absorption units with corresponding optical characteristics are introduced into the polymer backbone to target the absorption trough, achieving a synergistic color-changing effect from visible light to near-infrared.

[0004] In recent years, the thiophene[3,2-b]-thiophene (TT) structure has been widely used in the field of organic photovoltaics, and homopolymers of TT derivatives, such as poly(indadadithieno[3,2-b]thiophene) (PIDTT), have been shown to have strong and broad absorption spectra. On the one hand, the unique coplanar "trapezoidal" structure of the IDTT unit effectively increases the delocalization of π electrons, giving it high electron enrichment and thus stronger electron-donating ability and higher HOMO energy level. On the other hand, 7-(2-octyldodecyl)benzo(triazole-thiadiazole) (TNZ) is used as the acceptor unit because its conjugated ring incorporates a large number of nitrogen atoms. The electronegativity of nitrogen atoms can effectively enhance the electron-withdrawing ability of TNZ, while the planar regularity brought by the conjugated ring is also conducive to the migration of π electrons, causing a red shift in the absorption spectrum. At the same time, in addition to the conjugated structure, its long-chain alkyl side chains also give it good solubility. Meanwhile, the introduction of 2,1,3-benzothiadiazole (TZ) and 3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thieno[3,4-B][1,4]dioxane-heptene (ProDOT(CH2OEtHx)2) effectively compensates for the absorption trough region in the visible light band, thus achieving broad spectral absorption. Currently, no related polymers have been reported. Summary of the Invention

[0005] The purpose of this invention is to design and prepare an electrochromic polymer and an electrochromic film comprising the electrochromic polymer. The electrochromic polymer contains indadadithienro[3,2-b]thiophene (IDTT), 2,1,3-benzothiadiazole (TZ), 7-(2-octyldodecyl)benzo(triazole-thiadiazole) (TNZ), and 3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thienro[3,4-B][1,4]dioxane-heptene (ProDOT(CH2OEtHx)2) units. The polymer has synergistic color-changing properties covering the visible to near-infrared range. The preparation method mainly involves Stille coupling to synthesize a novel random quaternary conjugated polymer.

[0006] The technical solution of this invention is to first provide an electrochromic polymer, the structural formula of which is shown in the figure below:

[0007] ;

[0008] Wherein, R1 is a straight-chain alkyl group with 6 or more carbon atoms, R2 is a branched alkyl group with 8 or more carbon atoms, R is a branched alkyl group with 20 or more carbon atoms, and n represents the degree of polymerization, which is a natural number between 8 and 100. Preferably, R2 and R in the molecular structure are monobranched alkyl groups, wherein the monobranch is attached to the 2nd or 3rd carbon position of the main chain, and the number of carbon atoms in the monobranch differs from the number of carbon atoms in the main chain by less than or equal to 4. More specifically, , , .

[0009] It can be seen that the structural units provided by the present invention include indadadithienro[3,2-b]thiophene (IDTT), 2,1,3-benzothiadiazole (TZ), 7-(2-octyldodecyl)benzo(triazole-thiadiazole) (TNZ), and 3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thienro[3,4-B][1,4]dioxane-heptene (ProDOT(CH2OEtHx)2) units, which have the characteristic of synergistic color change covering the range from 400 nm in the visible light spectrum to 900 nm in the near-infrared spectrum.

[0010] The present invention also provides a method for preparing the above-mentioned electrochromic polymer, comprising the following steps:

[0011] 1) Preparation of polymer via Stille coupling: Trimethyltin-indadadithiophene[3,2-b]thiophene (M1), 4,7-dibromo-2,1,3-benzothiadiazole (M2), 4,10-dibromo-7-(2-octyldodecyl)benzo(triazole-thiadiazole) (M3), 6,8-dibromo-3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thiophene[3,4-B][1,4]dioxane-heptene (M4), xylene, tris(dibenzylacetone)dipalladium and tris(2-methylphenyl)phosphine were added to a two-necked flask with a protective atmosphere and a condenser at the top. The atmosphere was evacuated and maintained in the flask. The mixture was heated to react and then cooled to room temperature. The reaction solution was added dropwise to methanol to precipitate the mixture. The black precipitate was collected by filtration.

[0012] 2) Polymer purification by Soxhlet extraction: The dark brown precipitate was wrapped in filter paper and placed in a fat extractor. It was washed sequentially with methanol, n-hexane and chloroform. The chloroform washing solution was concentrated and added dropwise to methanol for precipitation. The precipitate was collected by filtration, which is the purified electrochromic polymer.

[0013] The synthesis route is as follows:

[0014] ;

[0015] Wherein, R1 is a straight-chain alkyl group with 6 or more carbon atoms, R2 is a branched alkyl group with 8 or more carbon atoms, R is a branched alkyl group with 20 or more carbon atoms, and n represents the degree of polymerization, which is a natural number between 8 and 100; preferably, R2 and R in the molecular structure are monobranched alkyl groups, wherein the monobranch is attached to the 2nd or 3rd carbon position of the main chain, and the number of carbon atoms in the monobranch differs from the number of carbon atoms in the main chain by less than or equal to 4; specifically, , , .

[0016] Furthermore, in step 1 above, the molar ratio of trimethyltin-indadadithiophene[3,2-b]thiophene (M1) to 4,7-dibromo-2,1,3-benzothiadiazole (M2) is (3:1)-(5:2), the molar ratio of trimethyltin-indadadithiophene[3,2-b]thiophene (M1) to 4,10-dibromo-7-(2-octyldodecyl)benzo(triazole-thiadiazole) (M3) is (3:1)-(3:2), and the molar ratio of trimethyltin-indadadithiophene[3,2-b]thiophene (M1):6,8-dibromo-3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thiene[3,4-B][1,4]dioxane-heptene (M4) is (3:1)-(11:1).

[0017] Furthermore, in step 1 above: the molar ratio of trimethyltin-indadadithiopheno[3,2-b]thiophene (M1) to tris(dibenzylideneacetone)dipalladium is 1:(0.02~0.04); the molar ratio of trimethyltin-indadadithiopheno[3,2-b]thiophene (M1) to tris(2-methylphenyl)phosphine is 1:(0.1~0.2); and the amount of xylene used is such that the total monomer concentration is 0.04 mol / L.

[0018] Furthermore, the reaction temperature in step 1 above is 100~120℃, and the reaction time is 48~96 hours.

[0019] Furthermore, the purification process in step 2 above is a Soxhlet extraction process, in which methanol, n-hexane, and chloroform are used for extraction in sequence, and the chloroform solution is precipitated.

[0020] This invention also provides an electrochromic polymer film, which is obtained by spraying or blade coating of the electrochromic polymer provided by this invention. The film thickness is 200-800 nm. The electrochromic polymer, which absorbs visible and near-infrared light, can be formed on the surface of a conductive substrate by solution blade coating or spraying. Its color transitions between black and transparent states, and it features low driving voltage, high optical contrast, and high stability, making it suitable for the assembly and application of electrochromic devices.

[0021] The advantage of this invention over the prior art lies in:

[0022] 1) The electrochromic polymer provided by the present invention contains indadadithiopheno[3,2-b]thiophene (IDTT), 2,1,3-benzothiadiazole (TZ), 7-(2-octyldodecyl)benzo(triazole-thiadiazole) (TNZ), and 3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thieno[3,4-B][1,4]dioxane-heptene (ProDOT(CH2OEtHx)2) units, which makes the electrochromic polymer of the present invention and the electrochromic polymer film containing it exhibit a wide range of spectral absorption behavior, have synergistic color-changing characteristics covering visible light to near-infrared light, can display the transformation from black to transparent color, and have high contrast, fast response rate and high stability, and can be applied to electrochromic devices.

[0023] 2) All thiophene derivatives used in this invention have alkyl or alkoxy side chains. On the one hand, alkyl or alkoxy side chain substitution is often used to increase the solubility of polymers in organic solvents (such as chloroform), which enables the polymer to be solution-processed. On the other hand, due to the low solubility caused by the rigid main chain of the polymer, sufficiently long alkyl or alkoxy groups are required to produce the desired effect. In this invention, the substituents of each monomer can meet the requirements for solution processing of the polymer.

[0024] 3) This invention designs a method for synthesizing two novel random quaternary conjugated polymers. Utilizing the principle of polymer spectral absorption, it realizes the preparation of electrochromic polymers that cover the visible to near-infrared synergistic color change. Moreover, the preparation process is simple and can be used for the large-scale synthesis of electrochromic polymers.

[0025] 4) The copolymerization method of the present invention is random copolymerization. There are three donor-acceptor structures in the conjugated backbone of the copolymer. Due to the characteristic absorption brought about by these structures, the absorption curve of the polymer can be adjusted by adjusting the proportion of each monomer to obtain a flat high absorption curve. Attached Figure Description

[0026] These and / or other aspects and advantages of the present invention will become clearer and more readily understood from the following detailed description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 The 1H NMR spectrum of the target polymer IDTT-ProDOT-TZ-TNZ-3-1-1-1 obtained in the embodiments of the present invention;

[0028] Figure 2 The 1H NMR spectrum of the target polymer IDTT-ProDOT-TZ-TNZ-2.75-0.25-1-1.5 obtained in the embodiments of the present invention;

[0029] Figure 3 The above are the spectral absorption curves of the polymer obtained in the embodiments of the present invention dissolved in chloroform;

[0030] Figure 4 The images show the UV-Vis absorption spectra and color transformations of the copolymer films obtained in the embodiments of the present invention at different potentials, wherein (a) is the UV-Vis absorption spectrum of the target polymer IDTT-ProDOT-TZ-TNZ-3-1-1-1; (b) is the color transformation image of the target polymer IDTT-ProDOT-TZ-TNZ-3-1-1-1; (c) is the UV-Vis absorption spectrum of the target polymer IDTT-ProDOT-TZ-TNZ-2.75-0.25-1-1.5; and (d) is the color transformation image of the target polymer IDTT-ProDOT-TZ-TNZ-2.75-0.25-1-1.5.

[0031] Figure 5 The electrochemical cyclic voltammetry curves of the copolymer thin film obtained in the embodiments of the present invention are shown below.

[0032] Figure 6 The time transmittance response of the copolymer film obtained in the embodiments of the present invention;

[0033] Figure 7 The stability curve of the copolymer film obtained in the embodiments of the present invention;

[0034] Figure 8 The image shows the thermal stability curve of the copolymer obtained in the embodiments of the present invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Example 1:

[0037] A method for preparing an electrochromic polymer that exhibits synergistic color change from visible light to near-infrared light includes the following steps:

[0038] (1) Synthesis of 4,10-dibromo-7-(2-octyldodecyl)benzo(triazole-thiadiazole) (TNZ-Br), the synthetic route is shown in the figure below:

[0039] ;

[0040] Synthesis of the compound described in Formula 1: Fuming nitric acid (6 g, 0.095 mol) was added dropwise to a two-necked flask containing trifluoromethanesulfonic acid (50 g, 0.333 mol), rapidly forming a solid 2CF3SO3H / HNO3 at 0 °C. 4,7-Dibromobenzo-2,1,3-thiadiazole (6 g, 0.020 mol) was added directly, and the reaction was carried out at 55 °C with stirring for 48 h. The mixture was poured into 500 mL of an ice-water mixture and filtered. The precipitate was washed with pure water. The mixture was dried under vacuum at 80 °C for at least 8 h to obtain a pale yellow solid, which is the compound described in Formula 1, with a yield of 86%.

[0041] Synthesis of the compound described in Formula 2: The compound described in Formula 1 (3 g, 7.8 mmol) and iron powder (3 g, 54 mmol) were placed in acetic acid (110 mL) and heated and stirred at 80 °C for 6 h. After cooling to room temperature, the mixture was poured into 500 mL of ice-water mixture, the precipitate was filtered and washed, and dried under vacuum at 80 °C for more than 8 h to obtain a yellow-green solid, namely the compound described in Formula 2, with a yield of 65%.

[0042] Synthesis of the compound described in Formula 3: The compound described in Formula 2 (700 mg, 2.20 mmol) was added to a dry 25 mL round-bottom flask, followed by glacial acetic acid (4 mL). Sodium nitrite (167 mg, 2.42 mmol) was dissolved in deionized water (8 mL), and the sodium nitrite solution was added dropwise to the reaction mixture using a constant-pressure dropping funnel. The mixture was stirred at room temperature for 30 minutes. After the reaction was complete, the mixture was filtered through a 0.45 μm nylon membrane, and the solid was collected and dried to obtain a brownish-yellow precipitate, which is the compound described in Formula 3, with a yield of 77%. Further purification was not required for the next step.

[0043] Synthesis of the compound described in Formula 4: Triethylamine (0.25 mL) was added dropwise to a solution containing anhydrous DMF (10 mL) and compound 3 of Formula 3 (500 mg, 1.49 mmol). The reaction was stirred at room temperature for 20 minutes, and the solution color changed from turmeric to deep red, indicating the formation of anion. Next, 9-(bromomethyl)nonadecane (646 mg, 1.79 mmol) was added dropwise to the reaction vessel. The reaction was stirred overnight at room temperature under argon. The completion of the reaction was monitored by thin-layer chromatography (TLC) (dichloromethane:ethyl acetate = 4:1). Extraction was performed using a separatory funnel to extract the crude product in ethyl acetate and deionized water. The organic fraction was collected, washed first with deionized water, then with brine, dried over MgSO4, and filtered. The filtrate was collected, and the solvent was removed by rotary evaporation. The crude product was separated by column chromatography (silica gel, dichloromethane:ethyl acetate = 4:1) and finally dried under vacuum to give a dark red viscous liquid, namely compound 4, with a yield of 24%. 1H NMR (400 MHz, CDCl3) δ: 5.30 (s, 1H), 4.83 (d, J = 7.2 Hz, 1H), 2.17 (s, 2H), 1.56 (s, 6H), 1.40 – 1.13 (m, 28H), 0.86 (dd, J = 12.2, 5.9 Hz, 6H).

[0044] (2) Synthesis of electrochromic polymers covering visible to near-infrared synergistic color change

[0045] Electrochromic polymer 1: Trimethyltin-substituted monomer IDTT-SnMe3 (0.1 mmol) and bromine monomers ProDOT(CH2OEtHx)2-Br, TZ-Br, and TNZ-Br (i.e., compounds shown in Formula 4), each 0.033 mmol, were added to a 50 mL double-necked flask. Then, tris(dibenzylacetone)dipalladium (Pd2(dba)3) (0.002 mmol) and tri-o-tolylphosphine (P(tol)3) (0.004 mmol) were added to the flask. The mixture was degassed by three freeze / pump / thaw cycles to fill with argon. Then, 5 mL of xylene was injected into the flask to degassed the mixture and refill with argon. The mixture was heated at 118°C for 48 h. After cooling to room temperature, the mixture was added dropwise to cold methanol and cooled in a refrigerator for 30 min. The mixture was filtered, and the precipitate was collected. It was then washed sequentially with methanol and n-hexane using Soxhlet extraction, and finally with chloroform. The chloroform fraction was collected, concentrated using a rotary evaporator, and reprecipitated in cold methanol. Finally, the target polymer was collected by filtration and dried under vacuum. The target polymer was IDTT-ProDOT-TZ-TNZ-3-1-1-1 (where 3-1-1-1 in the target polymer formula indicates a molar ratio of IDTT:ProDOT(CH2OEtHx)2-Br:TZ-Br:TNZ-Br in the feedstock of 3:1:1:1), with a yield of 64%. 1 H NMR (400 MHz, CDCl3) δ: 8.57 (s, 1H), 7.54 (s, 2H), 7.25 (d, J =44.9 Hz, 16H), 7.12 (s, 5H), 5.30 (s, 2H), 2.59 (d, J = 18.4 Hz, 10H), 1.55 (s, 28H), 1.24 (t, J = 17.3 Hz, 41H), 0.85 (dd, J = 17.3, 12.8 Hz, 18H).

[0046] Electrochromic polymer 2: A 50 mL double-necked flask was formed by adding 0.1 mmol of trimethyltin-substituted monomer IDTT-SnMe3 and 0.009 mmol of brominated monomers ProDOT(CH2OEtHx)2-Br, 0.036 mmol of TZ-Br, and 0.055 mmol of TNZ-Br (i.e., the compound shown in Formula 4). Then, tris(dibenzylacetone)dipalladium (Pd2(dba)3) (0.002 mmol) and tri-o-tolylphosphine (P(tol)3) (0.004 mmol) were added to the flask. The mixture was degassed by three freeze / pump / thaw cycles to fill with argon. Then, 5 mL of xylene was injected into the flask to degassed the mixture and refill with argon. The mixture was heated at 118°C for 48 h. After cooling to room temperature, the mixture was added dropwise to cold methanol and cooled in a refrigerator for 30 min. The mixture was filtered, and the precipitate was collected. It was then washed sequentially with methanol and n-hexane using Soxhlet extraction, and finally with chloroform. The chloroform fraction was collected, concentrated using a rotary evaporator, and reprecipitated again in cold methanol. Finally, the target polymer was collected by filtration and dried under vacuum. The target polymer was IDTT-ProDOT-TZ-TNZ-2.75-0.25-1-1.5 (where 2.75-0.25-1-1.5 in the target polymer formula indicates that the molar ratio of IDTT:ProDOT(CH2OEtHx)2-Br:TZ-Br:TNZ-Br in the feedstock was 2.75:0.25:1:1.5), with a yield of 60%. 1 H NMR (400MHz, CDCl3) δ 8.57 (s, 1H), 7.55 (s, 2H), 7.25 (d, J = 51.0 Hz, 16H), 7.13 (s, 9H), 2.57 (s, 10H), 1.57 (s, 20H), 1.43 (s, 3H), 1.39–1.13 (m, 50H), 1.03 (s, 2H), 0.93–0.75 (m, 22H).

[0047] The proton NMR spectra of the obtained electrochromic polymer 1 and electrochromic polymer 2 are shown below. Figure 1 and Figure 2 .

[0048] Example 2:

[0049] The polymer prepared in Example 1 was subjected to solution spectroscopy and electrochemical performance tests. The polymer was dissolved in chloroform to prepare a solution with a concentration of 2*10. -4 The absorption curve of the solution is shown in the figure. Figure 3As shown, both polymer solutions are black. Measurements using a UV-Vis spectrophotometer revealed that both polymer solutions exhibited a wide absorption range and several high absorption peaks, a result of the combined effects of π-electron transitions and intramolecular charge transfer. Figure 3 (a) shows the absorption peaks of the target polymer IDTT-ProDOT-TZ-TNZ-3-1-1-1 at 474 nm, 613 nm and 840 nm, respectively. Figure 3 (b) shows that the absorption peaks of the target polymer IDTT-ProDOT-TZ-TNZ-2.75-0.25-1-1.5 are at 468 nm, 610 nm and 849 nm, respectively.

[0050] Polymer film preparation: The polymer was dissolved in chloroform to prepare a 5 mg / ml solution. Insoluble matter was filtered out through a filter, and the solution was then placed in a spray gun and sprayed onto conductive glass under a controlled pressure of 2 MPa. The absorbance of the film was approximately 1.0. After spraying, the film was dried in a vacuum drying oven at 40°C until ready for use. A three-electrode system was used, with the polymer film as the working electrode, a platinum wire as the counter electrode, and a calibrated silver wire as the reference electrode. The supporting electrolyte was a 0.1 mol / L lithium perchlorate propylene carbonate solution.

[0051] The spectroelectrochemical performance of the copolymer film under different voltages was tested. A three-electrode system was used, with an ITO glass slide (1 cm × 5 cm) loaded with the electrochromic polymer film as the working electrode and a silver wire as the quasi-reference electrode (based on Fc / Fc). + (Calibration) and a platinum wire was used as the counter electrode. The electrolyte solution was a 0.1 M lithium perchlorate / propylene carbonate (LiClO4 / PC) solution. The spectroelectrochemical spectra and discoloration photographs of the two copolymer films under different applied voltages are shown below. Figure 4 It is easy to see that both electrochromic films underwent significant electrochromic transitions. Furthermore, due to the accumulation of π-π* bonds, the polymer film exhibits a red shift in its spectrum relative to the solution. With increasing voltage, both polymer films transition from a high-absorption state covering approximately 400–900 nm to a transparent state.

[0052] The electrochemical properties of the copolymer were tested using cyclic voltammetry, such as... Figure 5As shown, both polymers exhibit relatively high oxidation potentials. IDTT-ProDOT-TZ-TNZ-3-1-1-1 shows an oxidation peak at 1.01 V and double reduction peaks at 0.94 V and 0.60 V, while IDTT-ProDOT-TZ-TNZ-2.75-0.25-1-1.5 shows an oxidation peak at 1.02 V and double reduction peaks at 0.72 V and 0.47 V. Both polymers demonstrate reversible redox activity, accompanied by reversible color changes.

[0053] Response time refers to the time required for a material to reach 95% of its maximum transmittance. The response time and cycle stability of the polymer were tested using a UV-Vis spectrophotometer coupled with an electrochemical workstation. A three-electrode system was connected to the electrochemical workstation, and a quartz cuvette was placed in the UV-Vis spectrophotometer. While applying a voltage to the polymer film, the transmittance change at the wavelength of maximum transmittance was measured simultaneously. The test results are as follows: Figure 6 and Figure 7 As shown, the dual potential steps set for IDTT-ProDOT-TZ-TNZ-3-1-1-1 in a square wave cycle at 470 nm are 1.2 V and 0 V, with durations of 80 s and 20 s, respectively. The initial optical contrast of IDTT-ProDOT-TZ-TNZ-3-1-1-1 is 46.6%, which decreases to 43.6% after 120 square wave cycles. The dual potential steps set for IDTT-ProDOT-TZ-TNZ-2.75-0.25-1-1.5 in a square wave cycle at 466 nm are 1.0 V and 0 V, with durations of 60 s and 40 s, respectively. The initial optical contrast of IDTT-ProDOT-TZ-TNZ-2.75-0.25-1-1.5 is 42.8%, which decreases to 32.5% after 560 square wave cycles. Furthermore, during the switching response process, the coloring time (t) of IDTT-ProDOT-TZ-TNZ-3-1-1-1 is... c The fading time is 9.5s, and the fading time (t) is 9.5s. b The shading time (t) of IDTT-ProDOT-TZ-TNZ-2.75-0.25-1-1.5 is 44.5 s; c The fading time is 6.3s, and the fading time (t) is 6.3s. b The value is 27.0 s.

[0054] The results of testing the thermal stability of the electrochromic polymer film are as follows: Figure 8 As shown, the thermal decomposition temperature of the polymers is greater than 300℃, indicating that they can be used in high-temperature working environments.

[0055] As can be seen from the above embodiments, the color and absorption spectrum of the copolymer film prepared by the present invention can be controlled by the type of comonomer. The copolymer film can achieve synergistic color change from visible light to near infrared light, and has the characteristics of high optical contrast, high coloring efficiency and good stability. The prepared copolymer film can be applied in the fields of electrochromic display, adaptive camouflage and so on.

[0056] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An electrochromic polymer, characterized in that, Its molecular structure includes the following structures: ； Wherein, R1 is a straight-chain alkyl group with 6 or more carbons, R2 is a branched alkyl group with 8 or more carbons, R is a branched alkyl group with 20 or more carbons, and n represents the degree of polymerization, which is a natural number between 8 and 100.

2. The electrochromic polymer as described in claim 1, characterized in that, In the molecular structure, R2 and R are single-branched alkyl groups, and the single branch is attached to the 2nd or 3rd carbon position of the main chain. The number of carbon atoms in the single branch differs from the number of carbon atoms in the main chain by less than or equal to 4.

3. The electrochromic polymer as described in claim 1, characterized in that, The molecular structure , , .

4. The electrochromic polymer as described in claim 1, characterized in that, The electrochromic polymer has a synergistic color-changing property covering the range from 400 nm in the visible light spectrum to 900 nm in the near-infrared spectrum.

5. The method for preparing the electrochromic polymer according to any one of claims 1-4, characterized in that, Includes the following steps: 1) Preparation of polymers via Stille coupling: Trimethyltin-indadadithieneno[3,2-b]thiophene (M1), 4,7-dibromo-2,1,3-benzothiadiazole (M2), 4,10-dibromo-7-(2-octyldodecyl)benzo(triazole-thiadiazole) (M3), 6,8-dibromo-3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thieneno[3,4-B][1,4]dioxane-heptene (M4), xylene, tris(dibenzylacetone)dipalladium, and tris(2-methylphenyl)phosphine were added to a two-necked flask equipped with a protective atmosphere and a condenser. The atmosphere inside the flask was evacuated to maintain the protective atmosphere, and the mixture was heated to react. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was added dropwise to methanol to precipitate the product. The black precipitate was collected by filtration. 2) Polymer purification by Soxhlet extraction: The black precipitate was wrapped in filter paper and placed in a fat extractor. It was washed with methanol, n-hexane and chloroform in sequence. The chloroform washing solution was concentrated and added dropwise to methanol to precipitate. The precipitate was collected by filtration, which is the purified electrochromic polymer.

6. The method for preparing the electrochromic polymer as described in claim 5, characterized in that, In step 1, the molar ratio of trimethyltin-indadadithieno[3,2-b]thiophene (M1) to 4,7-dibromo-2,1,3-benzothiadiazole (M2) is (3:1)-(5:2), the molar ratio of trimethyltin-indadadithieno[3,2-b]thiophene (M1) to 4,10-dibromo-7-(2-octyldodecyl)benzo(triazole-thiadiazole) (M3) is (3:1)-(3:2), and the molar ratio of trimethyltin-indadadithieno[3,2-b]thiophene (M1):6,8-dibromo-3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thieno[3,4-B][1,4]dioxane-heptene (M4) is (3:1)-(11:1).

7. The method for preparing the electrochromic polymer as described in claim 5, characterized in that, In step 1: the molar ratio of trimethyltin-indadadithiopheno[3,2-b]thiophene (M1) to tris(dibenzylideneacetone)dipalladium is 1:(0.02~0.04); the molar ratio of trimethyltin-indadadithiopheno[3,2-b]thiophene (M1) to tris(2-methylphenyl)phosphine is 1:(0.1~0.2); and the amount of xylene used is such that the total monomer concentration is 0.04 mol / L.

8. The method for preparing the electrochromic polymer as described in claim 5, characterized in that, In step 1, the mixture is heated to a temperature of 100-120°C for a reaction time of 48-96 hours.

9. The method for preparing the electrochromic polymer as described in claim 5, characterized in that, The purification process in step 2 is a Soxhlet extraction process, in which methanol, n-hexane, and chloroform are extracted sequentially, and the chloroform solution is precipitated.

10. An electrochromic polymer film, characterized in that, The polymer film is obtained by spraying or scraping the electrochromic polymer as described in any one of claims 1-4, and the thickness of the polymer film is 200~800nm.

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