Preparation method and application of conjugated polymer film based on acid-cleavable side chain

Abstract

The invention relates to a preparation method and application of a conjugated polymer film based on an acid-cleavable side chain. The preparation method comprises the following steps: dissolving a conjugated polymer based on an acid-cleavable side chain in a solvent to prepare a polymer solution; uniformly stirring the polymer solution and the first acid solution to prepare a polymer / acid mixed solution pre-processed by the acid solution; coating a substrate with the polymer / acid mixed solution pre-processed by the acid liquid, and forming a polymer film after the solvent is volatilized; performing first thermal annealing on the polymer film; and applying a second acid solution to the surface of the polymer film after the first thermal annealing, and then carrying out second thermal annealing to obtain the conjugated polymer film without the side chain reprocessed by the acid solution. By utilizing the acid sensitivity characteristic of a side chain, an acid solution is added into a polymer solution before a polymer film is formed to pre-remove part of the side chain so as to synergistically induce ordering of the polymer, so that the film forming quality and the comprehensive performance of the polymer are improved.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and relates to a method for preparing and applying conjugated polymer films based on acid-crackable side chains. Background Technology

[0002] Conjugated polymers, with their solution processability, structural tunability, and unique electrical properties, have demonstrated significant application value in thermoelectric conversion, organic semiconductors, and flexible electronic devices. Solution processing technology for conjugated polymers has stringent requirements for solubility. Introducing solubility-regulating groups such as alkyl chains, ester groups, or alkoxy groups into the conjugated backbone can significantly improve the solubility of materials in organic solvents. However, sp... 3 Hybridized alkyl side chains possess high conformational freedom, which can easily disrupt the planarity of the main chain, leading to a decrease in the π-π stacking order between molecules, resulting in degraded performance and insufficient thermal stability. Therefore, the selection of functionalized side chains and subsequent post-processing improvements have been extensively studied. For example, introducing thermally degradable ester side chains, acid-degradable silane side chains, and hydrolyzable tert-butoxycarbonyl side chains allows the material to maintain excellent solubility during solution processing. After film formation, the side chains can be partially or completely removed through controlled chemical or thermally triggered reactions, thereby improving the overall performance of the material.

[0003] In acid-spliable side-chain design, silane or ester side chains have significant advantages due to their ease of cleavage under acidic conditions and simple processing. However, some atoms in these side chains (such as silicon atoms in silane side chains and oxygen atoms in ester side chains) often introduce significant steric hindrance, posing certain difficulties in synthesis. Simultaneously, the molecular weight of these polymers is generally low. Although solution processability is significant, the short molecular chains restrict charge transport and result in dense grain boundary defects in solid films, making it difficult to meet the requirements for fabricating high-performance devices. Moreover, excessively short molecular chains exhibit overly active Brownian motion in thermal fields, hindering ordered arrangement. This contradiction is particularly prominent in silane-substituted systems, where the steric hindrance of large-volume side chains and insufficient chain length due to low molecular weight create a double constraint, leading to poor film surface morphology, disordered molecular packing, and severely limited mobility and crystal size. Effectively suppressing the relatively active movement of short molecular chains in solution will improve the film quality and microstructure of polymer films. Therefore, for polymers based on acid-spliable side chains, there is an urgent need to find a universal method to prepare continuous and uniform films. Summary of the Invention

[0004] To address the aforementioned problems associated with conjugated polymers based on acid-crackable side chains, this invention proposes a method for preparing thin films based on conjugated polymers with acid-crackable side chains. Utilizing the acid-sensitive properties of the side chains, a portion of the side chains are pre-treated with acid before polymer film formation to synergistically induce polymer ordering. Subsequently, after preparing a continuous and uniform thin film, it is further processed with acid solution and annealed to remove all side chains, resulting in a polymer film without side chains.

[0005] In a first aspect, the method for preparing conjugated polymer films based on acid-crackable side chains of the present invention includes the following steps: Step (1) dissolves the conjugated polymer based on acid-crackable side chains in a solvent to prepare a polymer solution; Step (2) Stir the polymer solution and the first acid solution evenly to prepare a polymer / acid mixture solution for acid pretreatment; Step (3) The polymer / acid mixture pre-processed with the acid solution is coated onto the substrate, and the solvent is allowed to evaporate to form a polymer film; Step (4) The polymer film is subjected to a first thermal annealing; Step (5) Apply the second acidic solution to the surface of the polymer film after the first heat annealing, and then perform a second heat annealing to obtain a polymer film without side chains after acid reprocessing.

[0006] In an optional embodiment, in step (1), the conjugated backbone of the conjugated polymer based on acid-crackable side chains is selected from conjugated structures based on thiophene, thiazole, pyridine, pyrrolopyrroledione, benzothiadiazole, benzobisthiadiazole, aromatic imide, or derivatives thereof; the side chains of the conjugated polymer based on acid-crackable side chains are selected from at least one of silane side chains, alkoxy side chains, carbonyl side chains, ester side chains, and imine side chains.

[0007] Conjugated polymers based on acid-crackable side chains typically employ silane or ester side chains to improve solubility, which are then removed through post-treatment. However, this often leads to the formation of discrete aggregates of short molecular chains during film formation, making it difficult to control film morphology and molecular stacking, resulting in poor film quality. To address these issues, this invention designs a film preparation method based on acid-crackable conjugated polymers. Utilizing the acid-sensitive nature of the side chains, an acidic solution is added to the polymer solution before film formation to pre-remove some side chains, synergistically inducing polymer ordering and thus improving film quality and overall performance.

[0008] In an optional embodiment, in step (2), the acidic solute of the first acidic solution is an organic or inorganic acid with an acidity coefficient greater than or equal to -2 and less than or equal to 5, preferably at least one of trichloroacetic acid, acetic acid, trifluoroacetic acid, citric acid, oxalic acid, benzoic acid, phosphoric acid, oxalic acid, and ethylenediaminetetraacetic acid.

[0009] In an optional embodiment, in step (2), the molar ratio of the acidic solute in the first acidic solution to the conjugated polymer repeating unit in the polymer / acid mixed solution is 0.1:1 to 50:1. The molar amount of the polymer is defined as the polymer mass / the molar mass of the repeating unit.

[0010] In an optional embodiment, in step (3), the coating method of the pre-processed polymer / acid mixture is selected from spin coating, drop coating, spray coating, and heat-assisted rapid film formation method; preferably, the heat-assisted rapid film formation method includes the following steps: preheating the heating table, placing the substrate on the heating table, applying the pre-processed polymer / acid mixture and spreading it on the surface of the substrate, and obtaining a polymer film after the solvent evaporates.

[0011] In an optional embodiment, in step (4), the atmosphere of the first heat annealing is anhydrous and oxygen-free, the temperature of the first heat annealing is 120~300℃, and the time of the first heat annealing is 0.1~24h.

[0012] In an optional embodiment, in step (5), the acidic solute of the second acidic solution is selected from at least one of hydrochloric acid, sulfuric acid, acetic acid, trichloroacetic acid, p-toluenesulfonic acid, hydrobromic acid, hydrofluoric acid, and trifluoromethanesulfonic acid.

[0013] In an optional implementation, in step (5), the temperature of the second heat annealing is 100~170℃ and the time of the second heat annealing is 0.1~0.5h.

[0014] In an optional embodiment, the solvents of the first acidic solution and the second acidic solution are selected from at least one of methanol, acetonitrile, acetone, chloroform, dichloromethane, ethyl acetate, n-hexane, benzene, chlorobenzene, o-dichlorobenzene, and tetrahydrofuran.

[0015] Secondly, the thin film based on the acid-crackable side chain of the conjugated polymer obtained by the thin film preparation method of the present invention is used in thermoelectric devices, thermal conductive devices, and heat dissipation devices.

[0016] Compared with the prior art, the present invention has the following beneficial effects: For polymers based on acid-crackable side chains, this invention, during solution processing, triggers partial cleavage of the side chains by adding an acidic solution and heating and stirring. This inhibits the thermal motion of the molecular chains and promotes the self-assembly of the main chain. Simultaneously, the released steric hindrance allows for planar reconstruction of the main chain, improving the molecular packing morphology of the polymer and resulting in a continuous and uniform polymer film. This invention successfully solves the problem of poor film quality in low molecular weight polymers, providing a universal solution for performance reconstruction. The preparation process of this invention is simple, and the resulting polymer film based on acid-crackable side chains has a continuous and uniform surface with excellent electrical and thermal conductivity, making it promising for applications in thermoelectric and heat transfer devices. Attached Figure Description

[0017] Figure 1 Digital photographs of films prepared from thiophene polymers (SiDT-DT) containing silane side chains in Example 1 and Comparative Example 1 without trichloroacetic acid (0 eq) and with different proportions of trichloroacetic acid (5 eq, 10 eq, 15 eq).

[0018] Figure 2 Atomic force microscopy height maps of films prepared from thiophene polymers (SiDT-DT) with silane side chains in Example 1 and Comparative Example 1 without trichloroacetic acid (0 eq) and with trichloroacetic acid (10 eq). a) refers to 0 eq, b) refers to 10 eq.

[0019] Figure 3 Grazing incidence wide-angle X-ray scattering (GRS) spectra of films prepared from thiophene polymers (SiDT-DT) containing silane side chains in Example 1 and Comparative Example 1 with and without trichloroacetic acid (0 eq) and with trichloroacetic acid (10 eq). a) refers to 0 eq, b) refers to 10 eq.

[0020] Figure 4 Digital photographs of films prepared from thiophene polymers (SiDT-TT) with silane side chains in Example 2 and Comparative Example 2 with and without trichloroacetic acid (0 eq) and with trichloroacetic acid (10 eq).

[0021] Figure 5 Infrared spectra of the intrinsic SiDT-TT film (0eq) obtained in Comparative Example 2, the SiDT-TT polymer film (10eq) obtained in Example 2, and the DT-TT polymer film obtained in Example 2.

[0022] Figure 6 Digital photographs of the films prepared by adding trichloroacetic acid in Example 3 and the films prepared by adding trifluoromethanesulfonic acid in Comparative Example 4. a) refers to the addition of trichloroacetic acid, and b) refers to the addition of trifluoromethanesulfonic acid. Detailed Implementation

[0023] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0024] Traditional polymers typically incorporate solubility-regulating groups such as alkyl, ester, or alkoxy side chains into their conjugated backbones to improve solubility in organic solvents. However, the low dielectric properties of these side chains exacerbate carrier localization, severely limiting charge transport efficiency. Therefore, introducing acid-cleavable side chains is an effective improvement strategy. Silane and ester side chains are commonly chosen and removed through post-processing to obtain a polymer backbone structure that combines solution processability and high mobility. However, these polymers generally have low molecular weights, leading to the formation of discrete aggregates during film formation. This makes it difficult to control film morphology and molecular stacking, resulting in poor film quality. Therefore, there is an urgent need in the field for a film preparation method based on conjugated polymers with acid-cleavable side chains to improve the film quality and microstructure of such polymers.

[0025] The characteristic of conjugated polymers based on acid-splitable side chains is that the conjugated backbone is used to construct charge transport channels, while the side chains are used to improve solubility and are easily cleaved in acidic environments. This invention utilizes the acid-sensitive properties of the side chains by adding an acidic solution dropwise to the polymer solution, inducing partial cleavage of the side chains. During polymer drop-coating, this inhibits the thermal motion of the molecular chains and promotes the self-assembly of the backbone. Simultaneously, the released steric hindrance allows for planar reconstruction of the backbone, significantly improving the molecular packing morphology of the polymer, thereby obtaining a continuous and uniform polymer film. This lays a solid foundation for subsequent performance optimization in processing methods.

[0026] To achieve the above objectives, the present invention provides a simple and effective method for preparing conjugated polymer films based on acid-crackable side chains. The following exemplarily illustrates the method for preparing films based on acid-crackable side chains of conjugated polymers.

[0027] Polymer solution preparation. A conjugated polymer with acid-crackable side chains is dissolved in a solvent and stirred until homogeneous to obtain a polymer solution.

[0028] The conjugated polymer based on acid-crackable side chains consists of a conjugated backbone and acid-crackable side chains. The conjugated polymer is soluble in common organic solvents, and the side chains can be partially or completely cleaved under acidic conditions.

[0029] The conjugated backbone of the conjugated polymer includes, but is not limited to, conjugated structures based on thiophene, thiazole, pyridine, pyrrolopyrroledione, benzothiadiazole, benzobisthiadiazole, aromatic imides, or their derivatives.

[0030] The side chains of the conjugated polymer are acid-crackable side chains, selected from at least one of silane side chains, alkoxy side chains, carbonyl side chains, ester side chains, and imine side chains.

[0031] The solvent is preferably an organic solvent. The organic solvent includes, but is not limited to, at least one selected from benzene, chlorobenzene, chloroform, o-dichlorobenzene, and tetrahydrofuran. In an optional embodiment, the concentration of the polymer solution is 0.1–50 mg / mL. The dissolution of the polymer in the solvent can be promoted by heating and stirring. As an example, but not limited to, the heating and stirring temperature is 20–120°C, and the heating and stirring time is 0.5–5 h.

[0032] Preparation of polymer / acid mixed solution. Add an appropriate amount of the first acid solution to the polymer solution, heat and stir until homogeneous to prepare the polymer / acid mixed solution.

[0033] For example, a first acidic substance is dissolved in an (organic) solvent to prepare a first acidic solution, and then an appropriate amount of the first acidic solution is added to the polymer solution, heated and stirred until homogeneous to obtain a polymer / acid mixed solution.

[0034] The solute in the first acidic solution is an organic or inorganic acid with an acidity coefficient greater than or equal to -2 and less than or equal to 5 (-2≤pKa≤5), preferably at least one of trichloroacetic acid, acetic acid, trifluoroacetic acid, citric acid, oxalic acid, benzoic acid, phosphoric acid, oxalic acid, and ethylenediaminetetraacetic acid.

[0035] The solvent for the first acidic solution can be at least one selected from methanol, acetonitrile, acetone, chloroform, dichloromethane, ethyl acetate, n-hexane, benzene, chlorobenzene, o-dichlorobenzene, and tetrahydrofuran. The solvent can be adjusted according to the properties of the acidic solute.

[0036] The concentration of the first acidic solution can be 10~200 mg / mL.

[0037] In the polymer / acid mixed solution, the molar ratio of the first acidic solute (the solute in the first acidic solution) to the conjugated polymer repeating unit can be 0.1:1 to 50:1. The amount of the first acidic solute can be adjusted according to the polymer system.

[0038] In an optional embodiment, the heating and stirring temperature is 50~150℃, and the heating and stirring time is 0.5~5h.

[0039] Polymer film preparation. The above polymer / acid mixed solution is coated on a substrate, and after the solvent evaporates, the polymer film is formed.

[0040] In an optional embodiment, the substrate coated with the polymer / acid mixture solution may be glass, silicon wafer, or flexible substrate.

[0041] It should be understood that any method capable of preparing a thin film is applicable to this invention. Coating methods include, but are not limited to, spin coating, drop coating, and heat-assisted rapid film formation methods.

[0042] In an optional embodiment, the heat-assisted rapid film formation method may employ the following steps: after preheating the heating stage to a certain temperature, the substrate is placed on the heating stage, and the aforementioned polymer / acid mixed solution is rapidly added and spread across the substrate surface. After the solvent evaporates rapidly, a polymer film is obtained. Preferably, the temperature of the heating stage is 80~150℃. The temperature of the heating stage can be adjusted appropriately according to the boiling point of the solvent.

[0043] Thin film annealing. The polymer film prepared above is subjected to a first thermal annealing in an anhydrous and oxygen-free atmosphere to obtain a continuous and uniform polymer film.

[0044] In an optional embodiment, the first heat annealing temperature can be controlled to be 120~300℃, and the heat annealing time can be controlled to be 0.1~24h, preferably 0.5~24h, and more preferably 0.5~3h.

[0045] Acid reprocessing. A second acidic solution is applied to the surface of the polymer film after the first thermal annealing, and a second thermal annealing is performed to obtain a side-chain-free polymer film after acid reprocessing.

[0046] The acidic solute in the second acidic solution is selected from at least one of hydrochloric acid, sulfuric acid, acetic acid, trichloroacetic acid, p-toluenesulfonic acid, hydrobromic acid, hydrofluoric acid, and trifluoromethanesulfonic acid.

[0047] The concentration of the second acidic solution can be 0.01~10 mol / L.

[0048] The amount of the second acidic solution is not limited, as long as the side chains are completely removed. As an example, the volume ratio of the second acidic solution to the polymer / acid mixture used for coating is 1~10:1~10, for example, 1~5:1~5. For example, the amount of the second acidic solution used is 100~500 μL.

[0049] As an example, the temperature of the second heat annealing is 100~170℃, and the time of the second heat annealing is 0.1~0.5h.

[0050] The solvent of the second acidic solution is selected, for example, from at least one of methanol, acetonitrile, acetone, chloroform, dichloromethane, ethyl acetate, n-hexane, benzene, chlorobenzene, o-dichlorobenzene, and tetrahydrofuran.

[0051] The second acidic solution can be applied by methods including, but not limited to, drop application.

[0052] The polymer films prepared by the method provided in this invention can have their properties optimized through subsequent processing, and can be applied to organic thermoelectric conversion devices, thermal conductive devices, etc.

[0053] Traditional polymer films are typically prepared using drop-coating. This invention addresses the poor film quality issues caused by conventional drop-coating methods for conjugated polymers with acid-crackable side chains. Utilizing the acid-sensitive nature of the side chains, an acidic solution is added during polymer solution processing to pre-remove some side chains, inducing ordered stacking during film formation. This significantly improves the macroscopic morphology and microstructure of the polymer film, resulting in a continuous and uniform film. This overcomes the film formation defects caused by insufficient chain length and steric hindrance of side chains in low molecular weight polymers. In other words, for conjugated polymers with acid-crackable side chains, this invention, during solution processing, triggers partial cleavage of the side chains to induce polymer ordering, successfully solving the problem of poor film quality in low molecular weight polymers and providing a universal solution for performance reconstruction. The preparation process of this invention is simple, and the resulting polymer film with acid-crackable side chains has a continuous and uniform surface. Post-processing steps can significantly improve the overall performance of the polymer, making it promising for widespread application.

[0054] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention fall within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0055] Example 1

[0056] A thiophene polymer SiDT-DT (n=12~13) with a number-average molecular weight of 10.0 kDa containing silane side chains was selected, and its structure is as follows:

[0057] The specific implementation steps of the polymer film preparation method described in this invention are as follows: (1) Weigh the above polymer, dissolve it in chloroform to prepare a polymer solution of 5 mg / mL, heat and stir at 50°C for 2 hours to fully dissolve the polymer and obtain a polymer solution.

[0058] (2) Weigh out trichloroacetic acid solid and dissolve it in chloroform to prepare a 50 mg / mL trichloroacetic acid solution. According to the molar ratio of trichloroacetic acid to polymer repeating unit of 5:1 (5eq), 10:1 (10eq), and 15:1 (15eq), add the corresponding proportion of trichloroacetic acid solution to the polymer solution respectively, heat and stir at 50°C for 2h to obtain polymer / trichloroacetic acid mixed solution.

[0059] (3) Thin film was prepared using a heat-assisted rapid film formation method. The heating stage was preheated to 120°C, and a quantitative volume (150 μL) of polymer / trichloroacetic acid mixed solution was dropped onto the glass substrate using a pipette. Under the heat assistance, the solvent evaporated rapidly, and the polymer formed a film.

[0060] (4) The film was placed on a hot table in a glove box and annealed in an anhydrous and oxygen-free atmosphere. The annealing temperature was 200℃ and the annealing time was 3h. They were labeled as polymer films SiDT-DT (5eq), SiDT-DT (10eq), and SiDT-DT (15eq).

[0061] (5) Disperse trifluoromethanesulfonic acid in methanol to prepare a trifluoromethanesulfonic acid solution with a concentration of 3 mol / L. Use 100 μL of trifluoromethanesulfonic acid solution to drop coat the film surface. Anneal the film at 150 °C for 20 minutes. Remove the film and cool it to room temperature to obtain a polymer film without silane side chains.

[0062] Example 2

[0063] A thiophene polymer SiDT-TT (n=14~15) with a number-average molecular weight of 11.1 kDa containing silane side chains was selected, and its structure is as follows:

[0064] The specific implementation steps of the polymer film preparation method described in this invention are as follows: (1) Weigh the above polymer, dissolve it in chloroform to prepare a polymer solution of 5 mg / mL, heat and stir at 50°C for 2 hours to fully dissolve the polymer and obtain a polymer solution.

[0065] (2) Weigh out trichloroacetic acid solid and dissolve it in chloroform to prepare a 50 mg / mL trichloroacetic acid solution. According to the molar ratio of trichloroacetic acid molecules to polymer repeating units of 10:1 (10 eq), add trichloroacetic acid solution to polymer solution, heat and stir at 50°C for 2 h to obtain polymer / trichloroacetic acid mixed solution.

[0066] (3) Thin film was prepared using a heat-assisted rapid film formation method. The heating stage was preheated to 120°C, and a quantitative volume (150 μL) of polymer / trichloroacetic acid mixed solution was dropped onto the glass substrate using a pipette. Under the heat assistance, the solvent evaporated rapidly, and the polymer formed a film.

[0067] (4) The film was placed on a hot table in a glove box and annealed in an anhydrous and oxygen-free atmosphere. The annealing temperature was 200℃ and the annealing time was 3h. It was labeled as SiDT-TT polymer film (10eq).

[0068] (5) Prepare a 3 mol / L trifluoromethanesulfonic acid solution by dispersing trifluoromethanesulfonic acid in methanol. Drop 100 μL of the trifluoromethanesulfonic acid solution onto the surface of the film. Anneal the film at 150 °C for 20 minutes. Remove the film and cool it to room temperature to obtain a polymer film without silane side chains. Label it as a side-chain-free polymer film (DT-TT).

[0069] The conductivity and Seebeck coefficient of the thiophene polymer film (DT-TT) without side chains described in Example 2 were tested using the four-probe method, revealing its excellent thermoelectric properties. The conductivity was measured to be 357.3 S / cm at room temperature. -1 The Zebeck coefficient is 35.4 µVK. -1 A power factor of 44.8 µW K was obtained. -2 m -1 .

[0070] Example 3

[0071] The polymer SiBT-TT (n=39~40), with a number-average molecular weight of 35.3 kDa and containing silane side chains and benzothiadiazole units, has the following structure:

[0072] The specific implementation steps of the polymer film preparation method are as follows: (1) Weigh the above polymer, dissolve it in chlorobenzene to prepare a polymer solution of 5 mg / mL, heat and stir at 50°C for 4 hours to fully dissolve the polymer and obtain a polymer solution.

[0073] (2) Weigh out trichloroacetic acid and dissolve it in chlorobenzene to prepare a 100 mg / mL trichloroacetic acid solution. According to the molar ratio of trichloroacetic acid to polymer repeating unit of 4:1, add trichloroacetic acid solution to polymer solution, heat and stir at 50°C for 2 hours to obtain polymer / trichloroacetic acid mixed solution.

[0074] (3) Use a pipette to drop a quantitative volume (100 μL) of polymer / trichloroacetic acid mixed solution onto a glass substrate and allow the solvent to evaporate naturally to form a polymer film.

[0075] (4) The film was placed on a hot table in a glove box and annealed in an anhydrous and oxygen-free atmosphere to obtain a polymer film with a continuous and uniform surface. The annealing temperature was 200℃ and the annealing time was 2h.

[0076] (5) Disperse trifluoromethanesulfonic acid in methanol to prepare a trifluoromethanesulfonic acid solution with a concentration of 3 mol / L. Use 150 μL of trifluoromethanesulfonic acid solution to drop coat the film surface. Anneal the film at 150 °C for 20 minutes. Remove the film and cool it to room temperature to obtain a polymer film without silane side chains.

[0077] Example 4

[0078] The polymer SiBBT-T (n=13), containing silane side chains and benzobisthiadiazole units with a number-average molecular weight of 12.7 kDa, has the following structure:

[0079] The specific implementation steps of the polymer film preparation method are as follows: (1) Weigh the above polymer and dissolve it in o-dichlorobenzene to prepare a polymer solution of 5 mg / mL. Heat and stir at 80°C for 4 hours to fully dissolve the polymer.

[0080] (2) Weigh out trichloroacetic acid and dissolve it in o-dichlorobenzene to prepare a 100 mg / mL trichloroacetic acid solution. According to the molar ratio of trichloroacetic acid to polymer repeating unit of 2:1, add trichloroacetic acid solution to polymer solution, heat and stir at 80℃ for 3h to obtain polymer / trichloroacetic acid mixed solution.

[0081] (3) Use a pipette to drop a quantitative volume (100 μL) of polymer / trichloroacetic acid mixed solution onto the glass substrate in the glove box, and wait for the solvent to evaporate naturally and the polymer to form a film.

[0082] (4) The film was placed on a hot table in a glove box and annealed under anhydrous and oxygen-free conditions to obtain a polymer film with a continuous and uniform surface. The annealing temperature was 200℃ and the annealing time was 2h.

[0083] (5) Disperse trifluoromethanesulfonic acid in methanol to prepare a trifluoromethanesulfonic acid solution with a concentration of 3 mol / L. Use 200 μL to drop coat the film surface. Anneal the film at 150 °C for 20 minutes. Remove the film and cool it to room temperature to obtain a polymer film without silane side chains.

[0084] Comparative Example 1 Referring to Example 1, a thiophene polymer SiDT-DT (n=12~13) containing silane side chains was dissolved in chloroform to prepare a concentration of 5 mg / mL. The solution was heated and stirred at 50°C for 2 hours to ensure complete dissolution, yielding a SiDT-DT polymer solution. The SiDT-DT polymer solution was then directly drop-coated onto a glass substrate. After the chloroform solvent evaporated, a polymer film (Oeq) was obtained. This film was labeled as SiDT-DT (Oeq).

[0085] Digital photographs of polymer films with different trichloroacetic acid contents (5 eq, 10 eq, 15 eq) obtained in step (4) of Example 1 (e.g.) Figure 1 As shown in the figure, when the amount of trichloroacetic acid added is 10 eq, the resulting film surface is smooth and exhibits a mirror-like gloss. Atomic force microscopy (AFM) was used to test the surface roughness of the intrinsic polymer film (0 eq) and the film prepared with added trichloroacetic acid (10 eq). The addition of trichloroacetic acid effectively reduces film roughness and promotes the formation of a smoother polymer film (e.g., ...). Figure 2 As shown); Grazing incidence wide-angle X-ray scattering (GIWAXS) tests showed that the intrinsic SiDT-DT film (0eq) prepared without trichloroacetic acid exhibited diffuse (100) and (003) Debye rings, with molecules exhibiting disordered stacking characteristics. In contrast, the (100) diffraction rings completely disappeared in the film (10eq) prepared with added trichloroacetic acid, and the (003) rings were significantly sharpened in the out-of-plane direction (as shown). Figure 3 As shown in the figure, the significant improvement in molecular orientation order is confirmed. The above experimental results demonstrate that the thin film preparation method described in this invention can significantly improve polymer molecular packing and prepare high-quality polymer thin films.

[0086] Comparative Example 2 Referring to Example 2, a thiophene polymer SiDT-TT (n=14~15) with a number-average molecular weight of 11.1 kDa containing silane side chains was dissolved in chloroform to prepare a concentration of 5 mg / mL. The solution was heated and stirred at 50°C for 2 hours to ensure complete dissolution, yielding a SiDT-TT polymer solution. The SiDT-TT polymer solution was then directly drop-coated onto a glass substrate. After the chloroform solvent evaporated, a polymer film (Oeq) was obtained. This film was labeled as polymer film SiDT-TT (Oeq).

[0087] The SiDT-TT film prepared by adding trichloroacetic acid (10 eq) has a smoother and more even surface compared to the SiDT-TT film prepared by direct drop casting (0 eq). Figure 4 As shown). The intrinsic SiDT-TT film (0eq) obtained in this comparative example, the SiDT-TT polymer film (10eq) obtained in step (4) of Example 2, and the DT-TT polymer film obtained in step (5) were subjected to infrared spectroscopy tests respectively (e.g. Figure 5 As shown in the figure, it can be seen that the distance is between 2850 and 2960 cm. -1 (Aliphatic CH bond stretching vibration) and 700~850 cm -1 The peak intensity at the (Si-C bond characteristic vibration) shows a decreasing trend, confirming that trichloroacetic acid has the ability to cleave part of the side chain. In DT-TT, the aforementioned characteristic vibration peak significantly weakens to the baseline level, confirming that the silane side chain can be completely cleaved. These results indicate that the addition of a small amount of acidic solution can induce partial cleavage of the silane side chain, achieving an ordered arrangement of the molecular chain and significantly improving the film-forming quality of the polymer.

[0088] Comparative Example 3 Referring to Example 2, a thiophene polymer SiDT-TT (n=14~15) with a number-average molecular weight of 11.1 kDa containing silane side chains was dissolved in chloroform to prepare a polymer solution of 5 mg / mL. The solution was heated and stirred at 50°C for 2 hours to ensure complete dissolution. The polymer solution was then directly drop-coated onto a glass substrate, and the solvent was rapidly evaporated under heat assistance to form a polymer film. A 3 mol / L trifluoromethanesulfonic acid solution was prepared by dispersing trifluoromethanesulfonic acid in methanol. 100 μL of the trifluoromethanesulfonic acid solution was drop-coated onto the film surface. The film was annealed at 150°C for 20 minutes. After removing the film and cooling it to room temperature, a polymer film without silane side chains was obtained. This film was labeled as a side-chain-free polymer film (DT-TT-control).

[0089] The conductivity and Seebeck coefficient of the thin film were tested using the four-probe method. The conductivity of the DT-TT-control polymer film prepared without the addition of trichloroacetic acid in this comparative example was found to be 7.8 S / cm. -1 The Zebeck coefficient is 53.1 µV K. -1 A power factor of 2.2 µW K was obtained. -2 m -1 The test data compared with those in Example 2 show that the thin film preparation method described in this invention not only significantly improves the macroscopic morphology and microscopic order of the thin film, but also lays a good foundation for the subsequent complete removal of side chains and acid doping. This method provides a universal solution for performance reconstruction by optimizing the microstructure of the main chain and the carrier transport channels.

[0090] Comparative Example 4 Refer to Example 3. The only difference is that in step (2), a 1 mol / mL trifluoromethanesulfonic acid / chlorobenzene solution is prepared, and the trifluoromethanesulfonic acid solution is added to the polymer solution according to the molar ratio of trifluoromethanesulfonic acid to polymer repeating units of 4:1 to obtain a polymer / trifluoromethanesulfonic acid mixed solution.

[0091] A comparison of the film morphology of the polymer film prepared by adding trichloroacetic acid in Example 3 and the polymer film prepared by adding trifluoromethanesulfonic acid in this comparative example (e.g.) Figure 6 As shown in the figure, the film prepared by adding trichloroacetic acid is smooth and uniform, while the film prepared by adding trifluoromethanesulfonic acid cannot form a film on its surface and is discontinuous. Therefore, a suitable first acidic solute can trigger a small portion of the side chain cleavage, inhibit excessively active polymer chain movement, and improve the film morphology.

[0092] The above description of the embodiments is intended to facilitate understanding and use of the present invention by those skilled in the art. However, the present invention is not limited to the described implementation schemes and embodiments. Modifications and substitutions made by those skilled in the art based on the teachings of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing conjugated polymer films based on acid-crackable side chains, characterized in that, Includes the following steps: Step (1) dissolves the conjugated polymer based on acid-crackable side chains in a solvent to prepare a polymer solution; Step (2) Stir the polymer solution and the first acidic solution evenly to prepare a polymer / acid mixed solution for acid pretreatment; Step (3) The polymer / acid mixture pre-processed with acid solution is coated onto the substrate, and the solvent evaporates to form a polymer film; Step (4) The polymer film is subjected to a first thermal annealing; Step (5) Apply the second acidic solution to the surface of the polymer film after the first heat annealing, and then perform a second heat annealing to obtain a conjugated polymer film without side chains after acid reprocessing.

2. The thin film preparation method according to claim 1, characterized in that, In step (1), the conjugated backbone of the conjugated polymer based on acid-crackable side chains is selected from conjugated structures based on thiophene, thiazole, pyridine, pyrrolopyrroledione, benzothiadiazole, benzobisthiadiazole, aromatic imide, or derivatives thereof; the side chains of the conjugated polymer based on acid-crackable side chains are selected from at least one of silane side chains, alkoxy side chains, carbonyl side chains, ester side chains, and imine side chains.

3. The thin film preparation method according to claim 1 or 2, characterized in that, In step (2), the acidic solute of the first acidic solution is an organic or inorganic acid with an acidity coefficient greater than or equal to -2 and less than or equal to 5, preferably at least one of trichloroacetic acid, acetic acid, trifluoroacetic acid, citric acid, oxalic acid, benzoic acid, phosphoric acid, oxalic acid, and ethylenediaminetetraacetic acid.

4. The thin film preparation method according to any one of claims 1 to 3, characterized in that, In step (2), the molar ratio of the acidic solute in the first acidic solution to the repeating unit of the conjugated polymer in the polymer / acid mixed solution is 0.1:1 to 50:

1.

5. The thin film preparation method according to any one of claims 1 to 4, characterized in that, In step (3), the coating method of the pre-processed polymer / acid mixture is selected from spin coating, drop coating, spray coating, and heat-assisted rapid film formation method; preferably, the heat-assisted rapid film formation method includes the following steps: preheating the heating table, placing the substrate on the heating table, applying the pre-processed polymer / acid mixture and spreading it on the surface of the substrate, and obtaining a polymer film after the solvent evaporates.

6. The thin film preparation method according to any one of claims 1 to 5, characterized in that, In step (4), the atmosphere of the first heat annealing is anhydrous and oxygen-free, the temperature of the first heat annealing is 120~300℃, and the time of the first heat annealing is 0.1~24h.

7. The thin film preparation method according to any one of claims 1 to 6, characterized in that, In step (5), the acidic solute of the second acidic solution is selected from at least one of hydrochloric acid, sulfuric acid, acetic acid, trichloroacetic acid, p-toluenesulfonic acid, hydrobromic acid, hydrofluoric acid, and trifluoromethanesulfonic acid.

8. The thin film preparation method according to any one of claims 1 to 7, characterized in that, In step (5), the temperature of the second heat annealing is 100~170℃ and the time of the second heat annealing is 0.1~0.5h.

9. The thin film preparation method according to any one of claims 1 to 8, characterized in that, The solvents of the first acidic solution and the second acidic solution are independently selected from at least one of methanol, acetonitrile, acetone, chloroform, dichloromethane, ethyl acetate, n-hexane, benzene, chlorobenzene, o-dichlorobenzene, and tetrahydrofuran.

10. The application of thin films based on acid-crackable side chains of conjugated polymers obtained by the thin film preparation method according to any one of claims 1 to 9 in thermoelectric devices, thermal conductive devices, and heat dissipation devices.

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