Intelligent paper based on fluorine-containing maleimide group stimulus-responsive polymer and application thereof

Abstract

The application discloses smart paper based on fluorine-containing maleimide-based stimulus-responsive polymer and application thereof. Maleimide, perfluoroalkyl alcohol, triphenylphosphine and diisopropyl azodicarboxylate are reacted to obtain fluorine-containing maleimide monomer; the fluorine-containing maleimide monomer and a dienyl amine monomer are dissolved in an organic solvent, and an initiator is added to carry out polymerization to obtain fluorine-containing maleimide-based stimulus-responsive polymer; the fluorine-containing maleimide-based stimulus-responsive polymer is dissolved in THF, heated and stirred to carry out reaction to obtain a uniform deep red transparent solution, paper is soaked in the deep red transparent solution and ultrasonic treatment is carried out, and then drying is carried out to obtain smart paper. The smart paper prepared by the application has excellent acid stimulus response and pollution resistance, and has a good application prospect in information storage, double anti-counterfeiting and other aspects of functional paper.

Description

Technical Field

[0001] This invention relates to the field of smart paper technology, and more specifically to smart paper based on fluorinated maleimide-based stimulus-responsive polymers and their applications. Background Technology

[0002] Reversible erasable paper, by enabling the reuse of information carriers, fundamentally reduces deforestation and waste pollution, representing a key innovation for promoting green and sustainable development and reshaping how humans record information. Stimulus-responsive materials, capable of generating unique physical or chemical signals in response to single or multiple stimuli such as temperature, humidity, pH, light, and electricity, are widely used in the construction of smart devices and are crucial materials for the industrialization of reversible erasable paper. From the perspective of material molecular design and device structure design, endowing erasable paper with rapid responsiveness, high sensitivity, high stability, and high integration is currently a research hotspot in this field. Research shows that the molecular structure and aggregation state of materials are key factors affecting the sensing performance of stimulus-responsive materials and their devices. However, achieving precise and controllable regulation of the aggregation state and stimulus responsiveness of stimulus-responsive materials based on precise molecular engineering, and realizing their application in paper-based fields such as reversible erasing, information storage, and anti-counterfeiting, remains a challenging task.

[0003] Maleimide (MI) and its derivatives (NMI) possess advantages such as a stable five-membered ring structure and easily tunable substituents, making them widely used in copolymerization to prepare polymer materials with high heat resistance and radiation resistance. Recently, the unique unsaturated carbonyl group, stable five-membered ring structure, highly reactive double bonds, and tunable substituents in the MI structure have endowed these materials with broad application prospects in fields such as smart color development and sensing. For example, by copolymerizing tetraphenylvinyl dimaleimide, which exhibits fluorescence response, with methyl methacrylate, a temperature-triggered Diels-Alder (DA) / retro-DA reaction was used to achieve reversible "on / off" control of fluorescence emission in the copolymer system. Patent CN 110054731 A reports a method for preparing a reversible acid-base chromogenic maleimide copolymer, exhibiting good reversible cycle stability. This patent provides a good research approach for preparing smart materials with rapid stimulus response and stable performance. However, due to the presence of different benzene ring functional groups in the prepared maleimide, it exhibits significant steric hindrance, resulting in a small molecular weight of the polymer after polymerization, making film formation impossible and affecting subsequent industrial applications. Therefore, it is necessary to develop a high molecular weight stimulus-responsive polymer to form a stain-resistant stimulus-responsive coating on the paper surface using an impregnation technique through a porous paper structure. This would enable reusable, erasable, and writeable smart paper, serving as a high-performance, sustainable information storage medium. Various intricate patterns can be repeatedly and rapidly written / erased on the polymer-modified paper surface. Simultaneously, the resulting pattern information exhibits high resolution, good stimulus responsiveness, and stable storage, demonstrating promising application prospects in energy conservation and environmental protection. Summary of the Invention

[0004] In view of the above-mentioned prior art, the purpose of this invention is to provide smart paper based on fluorinated maleimide-based stimulus-responsive polymers and its applications. This invention utilizes a novel fluorinated maleimide copolymer based on a five-membered ring of maleimide, diallylamine, and fluorinated functional groups. The copolymer exhibits excellent acid-stimulation responsiveness and stain resistance, and smart paper has been prepared using this copolymer. This smart paper shows promising application prospects in information storage, dual anti-counterfeiting, and other functional paper applications.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a smart paper based on a fluorinated maleimide-based stimulus-responsive polymer, said smart paper being prepared by the following method: (1) Maleimide, perfluoroalkyl alcohol and triphenylphosphine were added to tetrahydrofuran, and then diisopropyl azodicarbonate was added at low temperature. The mixture was heated to room temperature and stirred. After the reaction was completed, the mixture was purified to obtain fluorinated maleimide monomer. (2) Dissolve fluorinated maleimide monomers and diallylamine monomers in an organic solvent to obtain a clear and transparent solution, add an initiator, stir and heat to carry out polymerization to obtain a fluorinated maleimide-based stimulus-responsive polymer. (3) Dissolve the fluorinated maleimide-based stimuli-responsive polymer in THF to obtain a polymer solution, heat and stir to react, and obtain a uniform dark red transparent solution. Soak the paper in the dark red transparent solution and sonicate it, and then dry it to obtain smart paper.

[0006] Preferably, in step (1), the perfluoroalkyl alcohol is selected from trifluoroethanol, tetrafluoropropanol, octafluoropentanol or dodecafluoroheptanol; the molar ratio of maleimide, perfluoroalkyl alcohol, triphenylphosphine and diisopropyl azodicarbonate is 5.5:5:6:6.

[0007] Preferably, in step (1), the low temperature is -5~0℃; and the stirring reaction time is 24h~30h.

[0008] Preferably, in step (1), the purification process involves concentration under vacuum, and the resulting mixture is purified by column chromatography.

[0009] Preferably, in step (2), the diallylamine monomer is selected from diallylmethylamine, diallylamine or diallyldimethylamine; the organic solvent is selected from DMF, butyl acetate, ethyl acetate, 1,4-dioxane, tetrahydrofuran or DMSO; and the initiator is selected from AIBN, BPO or TPPPI.

[0010] Preferably, in step (2), the mass ratio of the fluorinated maleimide monomer, diallylamine monomer and organic solvent is 20~40:20~40:10~60; the initiator accounts for 0.01~10% of the total mass of all monomers; the polymerization temperature is 60-90℃ and the time is 16~24h.

[0011] Preferably, in step (3), the concentration of the polymer solution is 0.5-10.0 wt%; the ultrasonic treatment is performed for 10 min before heating; the stirring reaction temperature is 40℃ and the time is 5 h.

[0012] Preferably, in step (3), the ultrasonic treatment time is 20 min; the drying is performed by drying in an 80 °C oven for 10 h and then in a 70 °C vacuum oven for 12 h.

[0013] A second aspect of the invention provides the application of smart paper in stain resistance or acid / alkali response.

[0014] Preferably, the contact angle of the smart paper is 140~150°; the acid-base response is as follows: under acidic stimulation, the smart paper changes from red to colorless; under alkaline stimulation, it returns to red.

[0015] The beneficial effects of this invention are: (1) This invention develops a low steric hindrance fluorinated maleimide-based high molecular weight stimulus-responsive polymer. Through a porous paper structure, a stain-resistant stimulus-responsive coating is formed on the paper surface using an impregnation technique, realizing a reusable erasable smart paper. As a high-performance and sustainable information storage medium, various fine pattern information can be repeatedly and quickly written / erased on the polymer-modified paper surface. At the same time, the obtained pattern information has high resolution, good stimulus responsiveness, and stable pattern information storage, and has good application prospects in terms of energy saving and green environmental protection.

[0016] (2) The fluorinated maleimide-based stimulus-responsive polymer prepared by this invention has good film-forming, processing, and industrialization properties. Structural characterization and acid-stimulation response tests showed that the copolymer has excellent acid-stimulation responsiveness and stain resistance, and has good application prospects in functional paper for information storage and dual anti-counterfeiting applications. Attached Figure Description

[0017] Figure 1 Example 1: NMR structural characterization of dodecafluoroheptylmaleimide; Figure 2 Characterization of the molecular weight of the polymer prepared in Example 1; Figure 3 Examples 1-5: Preparation of fluorinated copolymers and infrared characterization; Figure 4 The wetting properties of the fluorinated maleimide copolymer coating obtained in Example 1; Figure 5 Acid-stimulated responsiveness of the fluorinated maleimide copolymer in Example 1; Figure 6 Comparative Example 4: Smart Paper Photo. Detailed Implementation

[0018] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0019] As described in the background section, existing reversible acid-base chromogenic maleimide copolymers contain different benzene ring functional groups in the maleimide, exhibiting significant steric hindrance. This results in a small molecular weight of the polymer obtained after polymerization, making it unable to form a film and affecting subsequent industrial applications.

[0020] Therefore, the purpose of this invention is to provide smart paper based on fluorinated maleimide-based stimulus-responsive polymers and its applications. This invention first introduces highly stable, strongly polar fluorinated groups onto a maleimide monomer, and then copolymerizes it with diallyl methylamine (diallyl dimethylamine, diallylamine) to obtain an acid-stimulated fluorinated maleimide polymer resin. The synthetic route is as follows: .

[0021] After the resin is directly coated onto the paper surface using techniques such as spin coating and dip-dyeing, it exhibits excellent stimuli responsiveness when stimulated with trifluoroacetic acid. Under trifluoroacetic acid stimulation, the carbonyl oxygen in the polymer structure combines with hydrogen protons to form an enol structure, turning the deep red color colorless. When triethylamine or ammonia vapor is added to the paper, the amino protons combine with the nitrogen element in the five-membered ring formed by the diallyl monomer, causing electron transfer of the carbonyl oxygen to form an enol structure, resulting in color recovery. Acid / base interactions cause reversible changes in the polymer's conjugated system or charge transfer state, leading to color development / fading. The principle is as follows: .

[0022] This invention utilizes the unique five-membered ring structure of maleimide, along with its strong electron-withdrawing ability and double bond structure, to introduce highly electronegative fluorine atoms into the maleimide structure. This alters the electron cloud density of the maleimide structure, making it an ideal material for constructing intelligent information storage systems. The bifunctional structure of diallylamine monomers primarily forms linear soluble polymers through cyclization reactions during polymerization, avoiding the cross-linking drawbacks of traditional diene monomers. This allows for the preparation of polymers with regular structures and controllable molecular weights. Fluoropolymers, due to the high electronegativity and small atomic radius of fluorine atoms, possess excellent acid and alkali resistance, corrosion resistance, and UV resistance. Therefore, when applied to stimulus-responsive systems, after polymer film formation, fluorine atoms migrate to the film surface. Since the CF bond energy reaches 485.6 kJ / mol, higher than UV light energy, it protects the coating and prevents the decomposition of ester groups within the coating. By copolymerizing fluorinated maleimide monomers with diallylamine monomers, the advantages of each element are integrated to obtain a stable, rapidly responsive, and reusable fluorinated maleimide-based polymer. This polymer has been successfully applied to the coating of reversible erasable paper, solving the problem of reduced strength and inability to be reused after paper becomes wet during use. This is of great significance for ensuring resource reuse and information storage applications.

[0023] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0024] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0025] Example 1 (1) Preparation of dodecafluoroheptylmaleimide monomer In a 500 mL round-bottom flask, a magnetic stir bar, maleimide (5.34 g, 55 mmol), dodecafluoroheptanol (50 mmol), and anhydrous tetrahydrofuran (200 mL) were added, and magnetic stirring was started. After stirring for 5 minutes, triphenylphosphine (PPh3, 15.74 g, 60 mmol) was added to the flask, followed by diisopropyl azodicarbonate (DIAD, 12.13 g, 60 mmol) at 0 °C. The mixture was heated to room temperature and stirred for 24 h. After the reaction was complete, the reaction mixture was concentrated under vacuum. The resulting mixture was purified by column chromatography (eluent composition: ethyl acetate / petroleum ether, v / v ratio 5-10:90-95), and the sample was collected and rotary evaporated to obtain the target compound, dodecafluoroheptylmaleimide monomer. 19 F NMR see Figure 1 .

[0026] (2) Preparation of dodecafluoroheptylmaleimide stimulus-responsive polymer Dodecylfluoroheptylmaleimide (25 wt%) and diallyl methylamine (30 wt%) were dissolved in DMF (45 wt%) and stirred to obtain a clear, transparent solution. Initiator AIBN (0.1% of the total monomer mass) was added, and polymerization was carried out at 70 °C for 24 h under magnetic stirring. After the reaction was complete, a deep red polymer solution was obtained. The reaction was stopped by quenching in ice water, and a mixture of anhydrous ethanol and water (volume ratio 1:1) was added dropwise. During the dropwise addition, a large amount of deep red precipitate was produced. The product was filtered to obtain a deep red solid product. The product was dissolved in THF, reprecipitated, and filtered again. This process was repeated three times. The product was dried in a vacuum oven at 70 °C for 12 h to obtain the dodecylfluoroheptylmaleimide stimulus-responsive polymer. The yield was calculated to be 89.3%.

[0027] (3) Construction of intelligent paper coating The dodecafluoroheptylmaleimide stimuli-responsive polymer prepared in step (2) was dissolved in THF to prepare a polymer solution with a concentration of 0.5 wt%. After sonication for 10 min, the solution was heated to 40 °C and magnetically stirred for 5 h to form a homogeneous, deep red transparent solution. At room temperature, A4 paper was immersed in the deep red transparent solution and sonicated for 20 min. After immersion, the paper was removed and dried in an 80 °C oven for 10 h, followed by drying in a 70 °C vacuum oven for 12 h. The smart paper coating was then prepared and collected for later use.

[0028] Example 2 (1) Preparation of octafluoropentylmaleimide monomer In a 500 mL round-bottom flask, a magnetic stir bar, maleimide (5.34 g, 55 mmol), octafluoropentanol (50 mmol), and anhydrous tetrahydrofuran (200 mL) were added, and magnetic stirring was started. After stirring for 5 minutes, triphenylphosphine (PPh3, 15.74 g, 60 mmol) was added to the flask, followed by diisopropyl azodicarbonate (DIAD, 12.13 g, 60 mmol) at 0 °C. The mixture was heated to room temperature and stirred for 24 h. After the reaction was complete, the reaction mixture was concentrated under vacuum. The resulting mixture was purified by column chromatography (eluent composition: ethyl acetate / petroleum ether, v / v ratio 5–10: 90–95), and the sample was collected and rotary evaporated to obtain the target compound, octafluoropentylmaleimide monomer.

[0029] (2) Preparation of octafluoropentylmaleimide stimulus-responsive polymer Octafluoropentylmaleimide (25 wt%) and diallylamine (30 wt%) were dissolved in DMF (45 wt%) and stirred to obtain a clear, transparent solution. Initiator AIBN (0.1% of the total monomer mass) was added, and polymerization was carried out at 70 °C for 24 h under magnetic stirring. After the reaction was complete, a deep red polymer solution was obtained. The reaction was stopped by quenching in ice water, and the solution was then added dropwise to a mixture of anhydrous ethanol and water (volume ratio of anhydrous ethanol to water 1:1). During the dropwise addition, a large amount of deep red precipitate was formed, which was filtered to obtain a deep red solid product. The product was dissolved in THF, reprecipitated, and filtered again, repeating this process three times. The product was dried in a vacuum oven at 70 °C for 12 h to obtain the octafluoropentylmaleimide stimulus-responsive polymer. The yield was calculated to be 90.5%.

[0030] (3) Construction of intelligent paper coating The octafluoropentylmaleimide stimuli-responsive polymer prepared in step (2) was dissolved in THF to prepare a polymer solution with a concentration of 0.5 wt%. After sonication for 10 min, the solution was heated to 40 °C and magnetically stirred for 5 h to form a homogeneous, deep red, transparent solution. At room temperature, A4 paper was immersed in the deep red transparent solution and sonicated for 20 min. After immersion, the paper was removed and dried in an 80 °C oven for 10 h, followed by drying in a 70 °C vacuum oven for 12 h. The smart paper coating was then prepared and collected for later use.

[0031] Example 3 (1) Preparation of tetrafluoropropylmaleimide monomer In a 500 mL round-bottom flask, a magnetic stir bar, maleimide (5.34 g, 55 mmol), tetrafluoropropanol (50 mmol), and anhydrous tetrahydrofuran (200 mL) were added, and magnetic stirring was started. After stirring for 5 minutes, triphenylphosphine (PPh3, 15.74 g, 60 mmol) was added to the flask, followed by diisopropyl azodicarbonate (DIAD, 12.13 g, 60 mmol) at 0 °C. The mixture was heated to room temperature and stirred for 24 h. After the reaction was complete, the reaction mixture was concentrated under vacuum. The resulting mixture was purified by column chromatography (eluent composition: ethyl acetate / petroleum ether, v / v ratio 5–10: 90–95), and the sample was collected and rotary evaporated to obtain the target compound, tetrafluoropropyl maleimide monomer.

[0032] (2) Preparation of tetrafluoropropylmaleimide stimulus-responsive polymer Tetrafluoropropylmaleimide (25 wt%) and diallyl dimethylamine (30 wt%) were dissolved in DMF (45 wt%) and stirred to obtain a clear, transparent solution. Then, initiator AIBN (0.1% of the total monomer mass) was added, and polymerization was carried out at 70 °C for 24 h under magnetic stirring. After the reaction was complete, a deep red polymer solution was obtained. The reaction was stopped by quenching in ice water, and the solution was then added dropwise to a mixture of anhydrous ethanol and water (volume ratio of anhydrous ethanol to water 1:1). A large amount of deep red precipitate was immediately formed during the dropwise addition. The product was filtered to obtain a deep red solid product. The product was dissolved in THF, reprecipitated, and filtered again. This process was repeated three times. The product was dried in a vacuum oven at 70 °C for 12 h to obtain the tetrafluoropropylmaleimide stimuli-responsive polymer. The yield was calculated to be 92.2%.

[0033] (3) Construction of intelligent paper coating A 0.5 wt% polymer solution was prepared by dissolving tetrafluoropropylmaleimide stimuli-responsive polymer in THF. After sonication for 10 min, the solution was heated to 40 °C and magnetically stirred for 5 h to form a homogeneous, deep red, transparent solution. A4 paper was then immersed in the solution at room temperature and sonicated for 20 min. After immersion, the paper was removed and dried in an 80 °C oven for 10 h, followed by drying in a 70 °C vacuum oven for 12 h. The smart paper coating was then prepared and collected for later use.

[0034] Example 4 (1) Preparation of trifluoroethyl maleimide monomer In a 500 mL round-bottom flask, a magnetic stir bar, maleimide (5.34 g, 55 mmol), trifluoroethanol (50 mmol), and anhydrous tetrahydrofuran (200 mL) were added, and magnetic stirring was started. After stirring for 5 minutes, triphenylphosphine (PPh3, 15.74 g, 60 mmol) was added to the flask, followed by diisopropyl azodicarbonate (DIAD, 12.13 g, 60 mmol) at 0 °C. The mixture was heated to room temperature and stirred for 24 h. After the reaction was complete, the reaction mixture was concentrated under vacuum. The resulting mixture was purified by column chromatography (eluent composition: ethyl acetate / petroleum ether, v / v ratio 5–10: 90–95), and the sample was collected and rotary evaporated to obtain the target compound, trifluoroethyl maleimide monomer.

[0035] (2) Preparation of trifluoroethyl maleimide stimuli-responsive polymers Trifluoroethyl maleimide (25 wt%) and diallyl methylamine (30 wt%) were dissolved in DMF (45 wt%). The solution was stirred to obtain a clear, transparent solution. Initiator AIBN (0.1% of the total monomer mass) was added, and polymerization was carried out at 70 °C for 24 h under magnetic stirring. After the reaction was complete, a deep red polymer solution was obtained. The reaction was stopped by quenching in ice water, and the solution was then added dropwise to a mixture of anhydrous ethanol and water (volume ratio of anhydrous ethanol to water 1:1). A large amount of deep red precipitate was immediately formed during the dropwise addition. The product was filtered to obtain a deep red solid product. The product was dissolved in THF, reprecipitated, and filtered again. This process was repeated three times. The product was dried in a vacuum oven at 70 °C for 12 h to obtain the trifluoroethyl maleimide stimulus-responsive polymer. The yield was calculated to be 93.1%.

[0036] (3) Construction of intelligent paper coating A 0.5 wt% polymer solution was prepared by dissolving trifluoroethyl maleimide stimuli-responsive polymer in THF. After sonication for 10 min, the solution was heated to 40 °C and magnetically stirred for 5 h to form a homogeneous, deep red, transparent solution. A4 paper was then immersed in the solution at room temperature and sonicated for 20 min. After immersion, the paper was removed and dried in an 80 °C oven for 10 h, followed by drying in a 70 °C vacuum oven for 12 h. The smart paper coating was then prepared and collected for later use.

[0037] Example 5: (1) Preparation of octafluoropentylmaleimide monomer In a 1000 mL round-bottom flask, a magnetic stir bar, maleimide (10.68 g, 110 mmol), octafluoropentanol (100 mmol), and anhydrous tetrahydrofuran (400 mL) were added, and magnetic stirring was started. After stirring for 5 minutes, triphenylphosphine (PPh3, 31.48 g, 120 mmol) was added to the flask, followed by diisopropyl azodicarbonate (DIAD, 24.26 g, 120 mmol) at 0 °C. The mixture was heated to room temperature and stirred for 24 h. After the reaction was complete, the reaction mixture was concentrated under vacuum. The resulting mixture was purified by column chromatography (eluent composition: ethyl acetate / petroleum ether, v / v ratio 5–10:90–95), and the sample was collected and rotary evaporated to obtain the target compound, octafluoropentylmaleimide monomer.

[0038] (2) Preparation of octafluoropentylmaleimide stimulus-responsive polymer Octafluoropentylmaleimide (35 wt%) and diallylamine (35 wt%) were dissolved in DMF (30 wt%) and stirred to obtain a clear, transparent solution. Then, initiator AIBN (0.1% of the total monomer mass) was added, and polymerization was carried out at 70 °C for 24 h under magnetic stirring. After the reaction was complete, a deep red polymer solution was obtained. The reaction was stopped by quenching in ice water, and the solution was then added dropwise to a mixture of anhydrous ethanol and water (volume ratio of anhydrous ethanol to water 1:1). A large amount of deep red precipitate was immediately formed during the dropwise addition. The product was filtered to obtain a deep red solid product. The product was dissolved in THF, reprecipitated, and filtered again. This process was repeated three times. The product was dried in a vacuum oven at 70 °C for 12 h to obtain the octafluoropentylmaleimide stimulus-responsive polymer. The yield was calculated to be 90.9%.

[0039] (3) Construction of intelligent paper coating Octafluoropentylmaleimide stimuli-responsive polymer was dissolved in THF to prepare a 1 wt% polymer solution. After sonication for 10 min, the solution was heated to 40 °C and magnetically stirred for 5 h to form a homogeneous, deep red, transparent solution. A4 paper was immersed in the deep red transparent solution at room temperature and sonicated for 20 min. After immersion, the paper was removed and dried in an 80 °C oven for 10 h, followed by drying in a 70 °C vacuum oven for 12 h. The smart paper coating was then prepared and collected for later use.

[0040] Comparative Example 1 Dodecylfluoroheptylmaleimide (55 wt%) was dissolved in DMF (45 wt%) and stirred to obtain a clear, transparent solution. Then, initiator AIBN (0.1% of the total monomer mass) was added, and polymerization was carried out at 70 °C for 24 h under magnetic stirring. After the reaction was complete, a polymer solution was obtained. The reaction was stopped by quenching in ice water, and the solution was then added dropwise to a mixture of anhydrous ethanol and water (volume ratio of anhydrous ethanol to water 1:1). A small amount of white precipitate was immediately formed during the dropwise addition. The precipitate was filtered to obtain a white solid product. The product was dissolved in THF, reprecipitated, and filtered again. This process was repeated three times. The product was dried in a vacuum oven at 70 °C for 12 h, weighed, and the yield was calculated to be 65%.

[0041] The solution showed no color change after the polymer was subjected to acid stimulation, indicating that the maleimide homopolymer has no irritant response.

[0042] Comparative Example 2 Diallyl methylamine (55 wt%) was dissolved in DMF (45 wt%) and stirred to obtain a clear, transparent solution. Then, initiator AIBN (0.1% of the total monomer mass) was added, and polymerization was carried out at 70 °C for 24 h under magnetic stirring. After the reaction was complete, a polymer solution was obtained. The reaction was stopped by quenching in ice water, and the solution was then added dropwise to a mixture of anhydrous ethanol and water (volume ratio of anhydrous ethanol to water 1:1). A small amount of white precipitate was immediately formed during the dropwise addition. The precipitate was filtered to obtain a white solid product. The product was dissolved in THF, reprecipitated, and filtered again. This process was repeated three times. The product was dried in a vacuum oven at 70 °C for 12 h, weighed, and the yield was calculated to be 86%.

[0043] When the polymer was stimulated with acid, the solution did not change color, indicating that the diallyl methylamine homopolymer had no stimuli response, and the color of the polymer was that of the copolymer of the two.

[0044] Comparative Example 3 (1) Preparation of heptaylmaleimide monomer In a 500 mL round-bottom flask, a magnetic stir bar, maleimide (55 mmol), heptanol (50 mmol), and anhydrous tetrahydrofuran (200 mL) were added, and magnetic stirring was started. After stirring for 5 minutes, triphenylphosphine (PPh3, 15.74 g, 60 mmol) was added to the flask, followed by diisopropyl azodicarbonate (DIAD, 12.13 g, 60 mmol) at 0 °C. The mixture was heated to room temperature and stirred for 24 h. After the reaction was complete, the reaction mixture was concentrated under vacuum. The resulting mixture was purified by column chromatography (eluent composition: ethyl acetate / petroleum ether, v / v ratio 5–10: 90–95), and the sample was collected and rotary evaporated to obtain the target compound, heptapropyl maleimide monomer.

[0045] (2) Preparation of heptaylmaleimide polymer Heptylmaleimide (25 wt%) and diallyl methylamine (30 wt%) were dissolved in DMF (45 wt%) and stirred to obtain a clear, transparent solution. Initiator AIBN (0.1% of the total monomer mass) was added, and polymerization was carried out at 70 °C for 24 h under magnetic stirring. After the reaction was complete, a transparent polymer solution was obtained. The reaction was stopped by quenching in ice water, and a mixture of anhydrous ethanol and water (volume ratio 1:1) was added dropwise. During the dropwise addition, a large amount of white precipitate was formed, which was filtered to obtain a white solid product. The product was dissolved in THF, reprecipitated, and filtered again, repeating this process three times. The product was dried in a vacuum oven at 70 °C for 12 h to obtain the heptylmaleimide polymer. The yield was calculated (yield 85%).

[0046] The polymer showed no color change after being acid-stimulated, indicating that the heptylmaleimide polymer is non-responsive to stimuli. This may be because the alkyl group is an electron-donating group, which disrupts the electron-withdrawing structure of the polymer.

[0047] Comparative Example 4: A reversible acid-base chromogenic maleimide copolymer was prepared according to the preparation method of a reversible acid-base chromogenic maleimide copolymer as described in application number CN 110054731A. Step 1: Take cyclohexylmaleimide, diallyl dimethylamine and azobisisobutyronitrile in a molar ratio of 1:1:0.02 and place them in a reaction vessel. Then add 1% DMF solution of the total mass of the above three monomers, stir and mix evenly, evacuate the vacuum, and then react at 65°C for 20 h under nitrogen protection. Step 2: After the reaction is complete, the reaction product from Step 1 is transferred to a dialysis bag for dialysis. The parameters of the dialysis bag are: 2000 g / mol, dialysis time 10 h. Then, the mixture is centrifuged at 10000 r / min for 8 min and dried under vacuum at 60℃ for 10 h to obtain polymers containing maleimides with different functional groups.

[0048] Step 3: The difference from step (3) of Example 1 is that the polymer containing maleimide with different functional groups obtained in step 2 is used to replace the dodecafluoroheptylmaleimide stimulus-responsive polymer to obtain an oligomer solution. At room temperature, A4 paper is immersed in the oligomer solution and sonicated for 20 min. After immersion, the paper is removed and dried in an 80 °C oven for 10 h, followed by drying in a 70 °C vacuum oven for 12 h.

[0049] The resulting smart paper, such as Figure 6 As shown, oligomers cannot form a film that adheres to the paper surface.

[0050] Comparative Example 5 The difference from Example 1 is that diallyl methylamine is not added in step (2), and a dodecylfluoroheptylmaleimide homopolymer is prepared. Replacing the dodecylfluoroheptylmaleimide stimuli-responsive polymer in step (3) with the dodecylfluoroheptylmaleimide homopolymer, paper is prepared. The paper does not change color under acid and alkali stimulation, indicating that the dodecylfluoroheptylmaleimide homopolymer has no stimuli-responsiveness.

[0051] Example 6: Characterization The polymer obtained in Example 1 was characterized by GPC, such as... Figure 2 As shown in the figure, the polymer shows a single peak, indicating that the polymer is free of impurities. The integrated polymer molecular weight is 34892 g / mol, which is relatively large and indicates good film-forming properties.

[0052] Figure 3The infrared spectra of the fluorinated copolymer resins obtained in Examples 1-5 are shown in the figures. It can be seen from the figures that the 2900-3000 cm⁻¹ range... -1 These are the stretching vibration absorption peaks of the methyl and methylene groups in the copolymer structure, while the carbonyl absorption peak in the polymer structure mainly appears at 1741 cm⁻¹. -1 At this point, the absorption peak of the CF bond appears at 1109-1161 cm⁻¹. -1 .

[0053] A small amount of the smart paper from Example 1 was cut and tested for wetting performance. Figure 4 As shown, the contact angle of the coating is 144°, which is close to superhydrophobic, indicating that the smart paper has good stain resistance.

[0054] The smart paper prepared in Example 1 was subjected to acid and alkali stimulation, such as... Figure 5 As shown, under the stimulation of trifluoroacetic acid, the carbonyl group of maleimide in the polymer rearranges to form an enol structure, and the polymer color changes from red to colorless. When the basic component triethylamine continues to stimulate, the enol structure changes to an enol compound structure, completing the deprotonation reaction and restoring the original red color. Encouragingly, after 50 cycles of stimulation, the smart paper still exhibits good cycling stability.

[0055] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A smart paper based on a fluorinated maleimide-based stimulus-responsive polymer, characterized in that, The smart paper is prepared by the following method: (1) Maleimide, perfluoroalkyl alcohol and triphenylphosphine were added to tetrahydrofuran, and then diisopropyl azodicarbonate was added at low temperature. The mixture was heated to room temperature and stirred. After the reaction was completed, the mixture was purified to obtain fluorinated maleimide monomer. (2) Dissolve fluorinated maleimide monomers and diallylamine monomers in an organic solvent to obtain a clear and transparent solution, add an initiator, stir and heat to carry out polymerization to obtain a fluorinated maleimide-based stimulus-responsive polymer. (3) Dissolve the fluorinated maleimide-based stimuli-responsive polymer in THF to obtain a polymer solution, heat and stir to react, and obtain a uniform dark red transparent solution. Soak the paper in the dark red transparent solution and sonicate it, and then dry it to obtain smart paper.

2. The smart paper according to claim 1, characterized in that, In step (1), the perfluoroalkyl alcohol is selected from trifluoroethanol, tetrafluoropropanol, octafluoropentanol or dodecafluoroheptanol; the molar ratio of maleimide, perfluoroalkyl alcohol, triphenylphosphine and diisopropyl azodicarbonate is 5.5:5:6:

6.

3. The smart paper according to claim 1, characterized in that, In step (1), the low temperature is -5~0℃; the stirring reaction time is 24~30h.

4. The smart paper according to claim 1, characterized in that, In step (1), the purification process involves concentration under vacuum, and the resulting mixture is purified by column chromatography.

5. The smart paper according to claim 1, characterized in that, In step (2), the diallylamine monomer is selected from diallylmethylamine, diallylamine or diallyldimethylamine; the organic solvent is selected from DMF, butyl acetate, ethyl acetate, 1,4-dioxane, tetrahydrofuran or DMSO; and the initiator is selected from AIBN, BPO or TPPPI.

6. The smart paper according to claim 1, characterized in that, In step (2), the mass ratio of the fluorinated maleimide monomer, diallylamine monomer and organic solvent is 20~40:20~40:10~60; the initiator accounts for 0.01~10% of the total mass of all monomers; the polymerization temperature is 60-90℃ and the time is 16~24h.

7. The smart paper according to claim 1, characterized in that, In step (3), the concentration of the polymer solution is 0.5-10.0 wt%; the ultrasonic treatment is performed for 10 min before heating; the stirring reaction temperature is 40℃ and the time is 5 h.

8. The smart paper according to claim 1, characterized in that, In step (3), the ultrasonic treatment time is 20 min; the drying is carried out in an 80 °C oven for 10 h and then in a 70 °C vacuum oven for 12 h.

9. The application of the smart paper according to any one of claims 1 to 8 in stain resistance or acid / alkali response.

10. The application according to claim 9, characterized in that, The contact angle of the smart paper is 140~150°; the acid-base response is as follows: under acidic stimulation, the smart paper changes from red to colorless; under alkaline stimulation, it returns to red.

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