Composite moisture-sensing material prepared by sol-gel method and preparation method thereof

Abstract

The present application relates to the field of composite hygroscopic material, and particularly to a composite hygroscopic material prepared by sol-gel method and a preparation method thereof, which is used to solve the technical problems of low sensitivity, slow response, large humidity hysteresis, poor mechanical strength and insufficient cycle stability of traditional hygroscopic materials; polyvinyl alcohol-based hygroscopic functional polymer, anhydrous ethanol and deionized water are added into a beaker and stirred, SiO2-TiO2 sol is added and stirred, lithium chloride is added and continuously stirred to obtain a composite sol, the composite sol is sealed and aged at room temperature, then centrifuged, the upper sol is taken, dried, and cooled to obtain the composite hygroscopic material; the composite hygroscopic material has high hygroscopic sensitivity, fast hygroscopic response speed, small humidity hysteresis error and good cycle stability.

Description

Technical Field

[0001] This invention relates to the field of composite moisture-sensitive materials, specifically to a composite moisture-sensitive material prepared by the sol-gel method and its preparation method. Background Technology

[0002] Humidity sensors are widely used in meteorological monitoring, industrial production, smart homes and precision warehousing, among which polymer-based humidity-sensitive materials have become a research hotspot due to their advantages such as good film-forming properties, mild preparation process and easy functionalization.

[0003] While traditional polyvinyl alcohol-based hydrophilic polymers possess certain hygroscopic properties, they suffer from problems such as high moisture hysteresis, slow response speed, insufficient mechanical strength, and easy swelling and deformation after long-term use. Pure inorganic metal oxides, although structurally stable and with fast mass transfer, exhibit drawbacks such as poor film-forming properties, high brittleness, and poor compatibility with devices. Currently, conventional organic / inorganic composite moisture-sensing materials are mostly physical blends, exhibiting problems such as weak interfacial bonding, uneven component distribution, and a single humidity response signal. Furthermore, most materials rely solely on hydrophilic groups to achieve resistive humidity sensing, lacking an integrated functional system that combines high sensitivity, fast response, low moisture hysteresis, and excellent cycling stability. In addition, traditional moisture-sensing materials struggle to achieve efficient humidity response while simultaneously maintaining structural stability and optical / electrical dual-modal output, limiting their application in high-precision, interference-resistant humidity detection scenarios.

[0004] Therefore, developing a novel composite humidity-sensing material that is structurally stable, has a rapid response, low moisture hysteresis, and can synergize the advantages of organic and inorganic materials is of great significance for promoting the development of high-performance humidity sensors. Summary of the Invention

[0005] In order to overcome the above-mentioned technical problems, the purpose of this invention is to provide a composite moisture-sensitive material prepared by sol-gel method and its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] In a first aspect, this application provides a composite moisture-sensitive material prepared by a sol-gel method, comprising the following components in parts by weight:

[0008] The mixture consists of 2-4 parts polyvinyl alcohol-based moisture-sensitive polymer, 50-100 parts anhydrous ethanol, 20-40 parts deionized water, 2-4 parts SiO2-TiO2 sol, and 0.2-0.4 parts lithium chloride.

[0009] The SiO2-TiO2 sol is prepared by the following steps:

[0010] Tetraethyl orthosilicate and anhydrous ethanol were added to a three-necked flask, and a magnetic stirrer was turned on. The mixture was stirred for 10-12 minutes at a stirring rate of 280-300 r / min. Deionized water and concentrated hydrochloric acid were added dropwise, and stirring was continued for 30-32 minutes. Tetrabutyl titanate-anhydrous ethanol solution was added dropwise at a rate of 1 drop / s. After the addition was complete, the temperature was raised to 40℃, and the mixture was stirred at a constant temperature for 3-4 hours. The mixture was then aged at room temperature for 10-12 hours to obtain SiO2-TiO2 sol.

[0011] In a preferred embodiment of the present invention, the ratio of the amount of tetraethyl orthosilicate, anhydrous ethanol, deionized water, concentrated hydrochloric acid, and tetrabutyl titanate-anhydrous ethanol solution is 10-12 mL: 40-48 mL: 10-12 mL: 0.5-0.6 mL: 10-12 mL.

[0012] In a preferred embodiment of the present invention, the tetrabutyl titanate-anhydrous ethanol solution is a solution prepared by mixing tetrabutyl titanate and anhydrous ethanol in a volume ratio of 1 mL: 5 mL.

[0013] In a preferred embodiment of the present invention, the concentrated hydrochloric acid has a mass fraction of 37%.

[0014] The polyvinyl alcohol-based moisture-sensitive polymer is prepared by the following steps:

[0015] Step a1: 3-Nitrophthalic anhydride, N,N-dibutyl-m-aminophenol, anhydrous zinc chloride, and toluene were added to a three-necked flask equipped with a stirrer, thermometer, water separator, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 105-110℃ and a stirring rate of 300-400 r / min for 5-5.2 h. After the reaction was completed, the mixture was cooled to room temperature, distilled under reduced pressure, and then dissolved in anhydrous dichloromethane. The solution was washed twice each with dilute hydrochloric acid, deionized water, and saturated brine, and then dried with anhydrous sodium sulfate for 2 h. After filtration, the solution was concentrated by rotary evaporation and then purified by column chromatography with eluent A. The solution was then placed in a vacuum drying oven and dried at 35-40℃ for 6-8 h to obtain the first intermediate.

[0016]

[0017] Step a2: Add 4-methoxy-2-methyldiphenylamine and the first intermediate to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection and add concentrated sulfuric acid dropwise under 0°C ice-water bath conditions. After the addition is complete, raise the temperature to room temperature and stir the reaction at a stirring rate of 300-400 r / min for 24-25 h. After the reaction is complete, pour the reaction solution into the stirred ice water and let it stand for 30-32 min. Filter the solution and wash the filter cake 2-3 times with deionized water. Then disperse the filter cake in deionized water and adjust the pH to neutral with sodium hydroxide aqueous solution while stirring. Extract the solution 3 times with anhydrous dichloromethane. Dry the organic phase with anhydrous sodium sulfate for 2 h and filter. Vacuum rotary evaporate the organic phase and then purify it by column chromatography with eluent B. Then place it in a vacuum drying oven and dry it at 40-45°C for 8-9 h to obtain the second intermediate.

[0018]

[0019] Step a3: Add the second intermediate, palladium on carbon catalyst, and ethyl acetate-water mixed solution to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection and start stirring at a rate of 300-400 r / min. Add hypophosphorous acid, sodium hypophosphorous acid monohydrate, and deionized water to a beaker and stir for 15-17 min to obtain an aqueous solution. Pour the aqueous solution into the three-necked flask and heat to 75°C. React for 7 h. After the reaction is complete, cool to room temperature and filter with a diatomaceous earth filter cake under nitrogen protection to remove the palladium on carbon catalyst. Allow the filtrate to stand and separate into layers. Collect the organic phase. Extract the aqueous phase twice with ethyl acetate. Combine the organic phases and dry them with anhydrous sodium sulfate for 2 h. After filtration, vacuum rotary evaporation is performed. Purify by column chromatography with eluent C. Then place in a vacuum drying oven and dry at 40-45°C for 8-9 h to obtain the third intermediate.

[0020]

[0021] Step a4: Add the third intermediate, anhydrous dichloromethane, and triethylamine to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection. Add a mixed solution of acryloyl chloride and anhydrous dichloromethane dropwise at 0°C and a stirring rate of 300-400 r / min, with the dropping rate controlled at 1-2 drops / s. After the addition is complete, allow the temperature to rise naturally to room temperature and continue stirring for 2-3 hours. Wash with saturated sodium bicarbonate solution until pH=8-9, then wash with deionized water until neutral. Dry with anhydrous sodium sulfate for 2 hours, filter, and vacuum rotary evaporate. Purify by column chromatography with eluent D. Then place in a vacuum drying oven and dry at 35-40°C for 6-8 hours to obtain acrylamide-functionalized polymerizable moisture-sensitive dye monomer.

[0022]

[0023] Step a5: In an anhydrous and oxygen-free glove box, acrylamide-functionalized polymerizable moisture-sensitive dye monomer, vinyl acetate, anhydrous tetrahydrofuran, and azobisisobutyronitrile are added sequentially to a dry, thick-walled pressure-resistant tube. The pressure-resistant tube is then sealed and placed in an oil bath at 63°C for 48 hours. After the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is poured into anhydrous petroleum ether under stirring to precipitate. The solid is collected by filtration, dissolved in anhydrous tetrahydrofuran, and the precipitation is repeated three times. The mixture is then distilled under reduced pressure and placed in a vacuum drying oven at 40-45°C for 10-12 hours to obtain a moisture-sensitive random copolymer of polyvinyl alcohol precursor.

[0024] Step a6: Add the polyvinyl alcohol precursor moisture-sensitive random copolymer and anhydrous tetrahydrofuran to a round-bottom flask and stir for 10-12 min. Add anhydrous methanol and sodium hydroxide-anhydrous methanol solution and stir the reaction at 40-45℃ and 300-400 r / min for 5-5.2 h. After the reaction is complete, distill under reduced pressure and then pour the precipitate into deionized water. Centrifuge to collect the solid and wash it 1-2 times with anhydrous ethanol. Then place it in a vacuum drying oven and dry it at 40-45℃ for 11-12 h to obtain the polyvinyl alcohol-based moisture-sensitive polymer.

[0025] In a preferred embodiment of the present invention, the ratio of 3-nitrophthalic anhydride, N,N-dibutyl-m-aminophenol, anhydrous zinc chloride and toluene in step a1 is 20-30 mmol: 20-30 mmol: 2-3 mmol: 60-90 mL.

[0026] In a preferred embodiment of the present invention, the eluent A in step a1 is a solution of anhydrous methanol and anhydrous dichloromethane mixed in a volume ratio of 1:10; the mass fraction of the dilute hydrochloric acid is 5%.

[0027] In a preferred embodiment of the present invention, the ratio of 4-methoxy-2-methyldiphenylamine, the first intermediate, and concentrated sulfuric acid in step a2 is 3-6 mmol: 3-6 mmol: 0.5-1.0 mL.

[0028] In a preferred embodiment of the present invention, the sodium hydroxide aqueous solution in step a2 has a mass fraction of 5%; and the concentrated sulfuric acid has a mass fraction of 98%.

[0029] In a preferred embodiment of the present invention, the eluent B in step a2 is a solution of ethyl acetate, petroleum ether and triethylamine mixed in a volume ratio of 3:10:0.5.

[0030] In a preferred embodiment of the present invention, the ratio of the second intermediate, palladium on carbon catalyst, ethyl acetate-water mixed solution, hypophosphorous acid, sodium hypophosphorous acid monohydrate and deionized water in step a3 is 1-2 mmol: 50-100 mg: 4-8 mL: 1.5-3.0 mmol: 4.5-9.0 mmol: 3-6 mL.

[0031] In a preferred embodiment of the present invention, the ethyl acetate-water mixed solution in step a3 is a solution composed of ethyl acetate and deionized water in a volume ratio of 1.5:1.

[0032] In a preferred embodiment of the present invention, the eluent C in step a3 is a solution of anhydrous dichloromethane and triethylamine mixed in a volume ratio of 20:1.

[0033] In a preferred embodiment of the present invention, the palladium-carbon catalyst in step a3 is a wet product containing water with a water content of 55%, and the loading of palladium metal in the dry product after removing the water is 10 wt%.

[0034] In a preferred embodiment of the present invention, the ratio of the third intermediate, anhydrous dichloromethane, triethylamine, and the acryloyl chloride-anhydrous dichloromethane mixed solution in step a4 is 9-11 mmol: 40-48 mL: 23-28 mmol: 6-7 mL.

[0035] In a preferred embodiment of the present invention, the acryloyl chloride-anhydrous dichloromethane mixed solution in step a4 is a solution formed by mixing acryloyl chloride and anhydrous dichloromethane in a volume ratio of 1:5.

[0036] In a preferred embodiment of the present invention, the eluent D in step a4 is a solution of petroleum ether and ethyl acetate mixed in a volume ratio of 4:1.

[0037] In a preferred embodiment of the present invention, the ratio of acrylamide-functionalized polymerizable moisture-sensitive dye monomer, vinyl acetate, anhydrous tetrahydrofuran, and azobisisobutyronitrile in step a5 is 0.5-0.7 mmol: 5-7 mmol: 5-7 mL: 0.03-0.06 mmol.

[0038] In a preferred embodiment of the present invention, the ratio of the polyvinyl alcohol precursor moisture-sensitive random copolymer, anhydrous tetrahydrofuran, anhydrous methanol, and sodium hydroxide-anhydrous methanol solution in step a6 is 1-2g: 20-40mL: 10-20mL: 5-10mL.

[0039] In a preferred embodiment of the present invention, the molar concentration of the sodium hydroxide-anhydrous methanol solution in step a6 is 2 mol / L.

[0040] Secondly, this application provides a method for preparing a composite moisture-sensitive material using a sol-gel method, comprising the following steps:

[0041] Step 1: Weigh out 2-4 parts by weight of polyvinyl alcohol-based moisture-sensitive polymer, 50-100 parts by weight of anhydrous ethanol, 20-40 parts by weight of deionized water, 2-4 parts by weight of SiO2-TiO2 sol, and 0.2-0.4 parts by weight of lithium chloride, and set aside.

[0042] Step 2: Add polyvinyl alcohol-based moisture-sensitive polymer, anhydrous ethanol and deionized water to a beaker, stir for 10-12 min at a stirring rate of 280-300 r / min, add SiO2-TiO2 sol, continue stirring for 30-32 min, add lithium chloride, and continue stirring for 20-22 min to obtain composite sol.

[0043] Step 3: After sealing the composite sol, age it at room temperature for 10-12 hours. Then transfer it to a centrifuge tube, put it in a centrifuge, adjust the speed to 3000 r / min, centrifuge for 10-12 minutes, take the upper layer of sol, transfer it to a petri dish, put it in a vacuum oven, dry it at a temperature of 40-45℃ for 8-9 hours, and cool it to room temperature to obtain the composite moisture-sensitive material.

[0044] The beneficial effects of this invention are:

[0045] This invention discloses a composite moisture-sensitive material prepared by a sol-gel method and its preparation method. The method involves adding polyvinyl alcohol-based moisture-sensitive polymers, anhydrous ethanol, and deionized water to a beaker and stirring. SiO2-TiO2 sol is then added and stirred. Lithium chloride is added, and stirring continues to yield a composite sol. The composite sol is sealed and aged at room temperature, then centrifuged. The upper sol layer is collected, dried, and cooled to obtain the composite moisture-sensitive material. The polyvinyl alcohol-based moisture-sensitive polymer provides a large number of hydrophilic hydroxyl groups to the composite system, enabling rapid and sensitive moisture absorption. Simultaneously, the covalently linked conjugated dye units impart optical humidity response capabilities to the material, while also ensuring good film-forming properties and structural stability. The SiO2-TiO2 sol can construct a porous inorganic network, improving the mechanical strength, thermal stability, and structural uniformity of the composite moisture-sensitive material. It also accelerates the water molecule transport rate, synergistically enhancing the humidity response speed and long-term stability. This composite moisture-sensitive material exhibits excellent comprehensive moisture-sensing performance, including high moisture sensitivity, fast moisture absorption response, small hysteresis error, and good cyclic stability.

[0046] In the preparation of the composite moisture-sensitive material, a polyvinyl alcohol-based moisture-sensitive polymer was first prepared. Initially, under Lewis acid catalysis with anhydrous zinc chloride, 3-nitrophthalic anhydride underwent anhydride ring-opening and reacted with the electron-rich substrate N,N-dibutyl-m-aminophenol in a nucleophilic addition-dehydration reaction, generating a first intermediate containing an o-benzoylbenzoic acid structure, a nitro group, a carboxyl group, and a dibutylamino electron-donating side chain. Toluene was used as the aqueous solvent, and trace amounts of water generated in the reaction were continuously separated by high-temperature reflux, driving the reaction to complete in the forward direction. Subsequently, a Friedel-Crafts acylation-intramolecular cyclization was performed under strong acid catalysis. In the tandem reaction, the carboxyl group of the first intermediate is dehydrated and activated under concentrated sulfuric acid, undergoing intramolecular electrophilic substitution and dehydration cyclization with the electron-rich aromatic ring of 4-methoxy-2-methyldiphenylamine to form the conjugated core of xanthane (xanthonesin). This is followed by a catalytic hydrogen transfer reduction reaction using a hypophosphite / sodium hypophosphite system. With Pd / C as the catalyst and hypophosphite and sodium hypophosphite as the hydrogen source, the aromatic ring nitro group is selectively reduced to an active primary amino group. This reaction is mild and does not damage the sensitive structures such as xanthonesin, diphenylamine, or the conjugated core. The core objective is to introduce a modifiable active amino group. The site prepares for the subsequent acrylation reaction of the polymerizable double bond, followed by an N-acylation nucleophilic substitution reaction. Using the active primary amino group of the reduction product as the nucleophilic site, it undergoes an amidation reaction with acrylamide chloride. Triethylamine acts as an acid-binding agent to neutralize the hydrogen chloride generated in the reaction, inhibiting side reactions such as amino protonation and raw material hydrolysis. Low-temperature dropwise addition avoids the self-polymerization of acrylamide chloride, yielding an acrylamide-functionalized polymerizable moisture-sensitive dye monomer with acrylamide polymerizable double bonds. Subsequently, a free radical random copolymerization reaction initiated by azobisisobutyronitrile (AIBN) is conducted, where the acrylamide double bonds of the functional dye monomer react with vinyl acetate. The vinyl double bond of the ester undergoes free radical addition polymerization to form a polyvinyl alcohol precursor moisture-sensitive random copolymer with covalently suspended functional dye side groups on the polymer backbone, possessing both dye optical response properties and polymer film-forming properties. Subsequently, through alkaline transesterification alcoholysis, the vinyl acetate structural units in the copolymer undergo directional deacetylation in anhydrous methanol and sodium hydroxide-anhydrous methanol systems, converting the hydrophobic acetate groups into hydrophilic hydroxyl groups. The carbon-carbon backbone structure of the polymer remains unchanged, while the side groups are converted into a large number of highly active hydrophilic hydroxyl groups, ultimately yielding a polyvinyl alcohol-based moisture-sensitive polymer.In terms of molecular structure, the polyvinyl alcohol backbone contains a large number of highly active hydrophilic hydroxyl groups, enabling rapid and reversible adsorption and desorption of water molecules. This endows the material with high humidity sensitivity and a fast response / recovery rate, while also providing excellent film-forming properties, flexibility, and matrix compatibility. The covalently grafted diphenylamine-substituted xanthonolide conjugated dye side chain exhibits strong UV-Vis absorption characteristics and environmentally responsive fluorescence / colorimetric color-changing properties, converting humidity changes into a visible optical signal. This enables optical humidity sensing without electrical components, unlike traditional resistive / capacitive humidity-sensitive materials. It has strong anti-electromagnetic interference capabilities, requires no complex testing equipment, and has a wider range of applications. The rigid fused ring structure of xanthonol improves the material's heat resistance, light aging resistance, chemical stability, and oxidation resistance, preventing dye degradation and performance degradation during long-term use. The dibutylaminoalkyl side chain can precisely regulate the hydrophilic-hydrophobic balance of the polymer, alleviating excessive water swelling and structural softening of the material under high humidity conditions. This polymer enhances the water resistance and mechanical strength of the material. It possesses both hydrophilic hygroscopic and optical responsive properties. Humidity changes alter the polymer chain aggregation state through hydroxyl group swelling, thereby regulating the polarity of the dye conjugated microregions and the intensity of intramolecular charge transfer / environmental responsiveness. Ultimately, it outputs a stable and quantifiable optical signal with stronger anti-interference capabilities. When combined with SiO2-TiO2 sol, it further improves the mechanical strength, thermal stability, and film uniformity of the hygroscopic film. The porous network structure of the inorganic sol accelerates the adsorption-desorption transport rate of water molecules, broadening the humidity response range. Combined with the strong hygroscopic and sensitizing effect of lithium chloride, a synergistic effect is achieved between the polyvinyl alcohol-based hygroscopic polymer, the porous inorganic phase of SiO2-TiO2 sol, and the lithium chloride hygroscopic sensitizer. This results in a composite hygroscopic material exhibiting superior linearity, more uniform and stable response, high sensitivity, and excellent long-term cycling stability across the entire humidity range.

[0047] In the preparation of the composite moisture-sensitive material, a SiO2-TiO2 sol was first prepared. The SiO2-TiO2 sol was prepared using an acid-catalyzed sol-gel method. Tetrabutyl orthosilicate and tetrabutyl titanate under acidic conditions underwent sequential hydrolysis to generate corresponding silanols and titanium alcohols. Subsequently, through dehydration condensation, Si-O-Si, Ti-O-Ti, and Si-O-Ti crosslinked network structures were gradually formed. The silicon source was pre-hydrolyzed to inhibit rapid aggregation of the titanium source. Then, low-temperature curing and room-temperature aging were performed to homogenize the sol, ultimately obtaining a stable SiO2-TiO2 sol. This method is characterized by mild reaction conditions and precise component ratios. The controllable addition sequence of silicon followed by titanium effectively avoids the formation of white precipitates from the rapid polymerization of tetrabutyl titanate. The resulting sol has uniform particle size and good dispersibility. The acidic system can significantly improve the stability of the system. The aging process can further optimize the microstructure. Moreover, this inorganic sol has excellent compatibility with polyvinyl alcohol-based moisture-sensitive polymers. After composite, it can provide a porous structure for the moisture-sensitive material to accelerate water molecule diffusion and improve the response speed. It can also significantly enhance the mechanical strength, thermal stability and structural density of the material. At the same time, the hydrophilic properties of SiO2-TiO2 can also synergistically improve the humidity response performance of the material, so that the overall humidity sensitivity and service life are significantly improved. Detailed Implementation

[0048] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0049] Example 1:

[0050] This embodiment describes a method for preparing a composite moisture-sensitive material using the sol-gel method, comprising the following steps:

[0051] Step S1: 20 mmol of 3-nitrophthalic anhydride, 20 mmol of N,N-dibutyl-m-aminophenol, 2 mmol of anhydrous zinc chloride, and 60 mL of toluene were added to a three-necked flask equipped with a stirrer, thermometer, water separator, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 105 °C and a stirring rate of 300 r / min for 5 h. After the reaction was completed, the mixture was cooled to room temperature, distilled under reduced pressure, and then dissolved in anhydrous dichloromethane. The solution was washed twice each with 5% hydrochloric acid, deionized water, and saturated brine. After drying with anhydrous sodium sulfate for 2 h, the solution was filtered and concentrated by rotary evaporation. Then, it was purified by column chromatography using eluent A (eluent A is a solution of anhydrous methanol and anhydrous dichloromethane mixed in a volume ratio of 1:10). The solution was then placed in a vacuum drying oven and dried at 35 °C for 6 h to obtain the first intermediate.

[0052] Step S2: Add 3 mmol of 4-methoxy-2-methyldiphenylamine and 3 mmol of the first intermediate to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection. Add 0.5 mL of 98% concentrated sulfuric acid dropwise under 0°C ice-water bath conditions. After the addition is complete, raise the temperature to room temperature and stir at 300 rpm for 24 h. After the reaction is complete, pour the reaction solution into the stirred ice water, let it stand for 30 min, filter, and wash the filter cake twice with deionized water. Then, filter... The cake was dispersed in deionized water and adjusted to neutral pH with 5% sodium hydroxide aqueous solution under stirring. It was extracted three times with anhydrous dichloromethane. The organic phase was dried with anhydrous sodium sulfate for 2 hours, filtered, and then vacuum rotary evaporated. The organic phase was then purified by column chromatography with eluent B (eluent B is a solution of ethyl acetate, petroleum ether and triethylamine in a volume ratio of 3:10:0.5). The solution was then placed in a vacuum drying oven and dried at 40°C for 8 hours to obtain the second intermediate.

[0053] Step S3: Add 1 mmol of the second intermediate, 50 mg of palladium-on-carbon catalyst (the palladium-on-carbon catalyst is a wet product containing 55% water; in the dried product after removing the water, the palladium metal loading is 10 wt%), and 4 mL of ethyl acetate-water mixture (the ethyl acetate-water mixture is a solution of ethyl acetate and deionized water mixed in a volume ratio of 1.5:1) to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection, start stirring at a rate of 300 rpm, and add 1.5 mmol of hypophosphite, 4.5 mmol of sodium hypophosphite monohydrate, and 3 mL of deionized water to... In a beaker, the mixture was stirred for 15 minutes to obtain an aqueous solution. The aqueous solution was then poured into a three-necked flask, and the temperature was raised to 75°C. The reaction was carried out for 7 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered with a diatomaceous earth filter cake under nitrogen protection to remove the palladium catalyst on carbon. The filtrate was allowed to stand and separate into layers. The organic phase was collected, and the aqueous phase was extracted twice with ethyl acetate. The organic phases were combined and dried with anhydrous sodium sulfate for 2 hours. After filtration, the mixture was vacuum rotary evaporated and purified by column chromatography with eluent C (eluent C is a solution of anhydrous dichloromethane and triethylamine mixed in a volume ratio of 20:1). The solution was then placed in a vacuum drying oven and dried at 40°C for 8 hours to obtain the third intermediate.

[0054] Step S4: Add 9 mmol of the third intermediate, 40 mL of anhydrous dichloromethane, and 23 mmol of triethylamine to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection. At 0°C and a stirring rate of 300 rpm, add 6 mL of a acryloyl chloride-anhydrous dichloromethane mixture (a solution of acryloyl chloride and anhydrous dichloromethane mixed in a volume ratio of 1:5). The dropping rate should be controlled at [missing information]. 1 drop / s was added, and after the addition was complete, the temperature was naturally raised to room temperature. The reaction was stirred for 2 hours. The mixture was washed with saturated sodium bicarbonate solution until pH=8, then washed with deionized water until neutral. After that, it was dried with anhydrous sodium sulfate for 2 hours, filtered, and then vacuum rotary evaporated. The mixture was purified by column chromatography with eluent D (eluent D is a solution of petroleum ether and ethyl acetate mixed in a volume ratio of 4:1). After that, it was placed in a vacuum drying oven and dried at 35°C for 6 hours to obtain acrylamide functionalized polymerizable moisture-sensitive dye monomer.

[0055] Step S5: In an anhydrous and oxygen-free glove box, 0.5 mmol of acrylamide-functionalized polymerizable moisture-sensitive dye monomer, 5 mmol of vinyl acetate, 5 mL of anhydrous tetrahydrofuran, and 0.03 mmol of azobisisobutyronitrile were added sequentially to a dry, thick-walled pressure-resistant tube. The pressure-resistant tube was then sealed and placed in an oil bath at 63°C for 48 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into anhydrous petroleum ether under stirring to precipitate. The solid was collected by filtration, dissolved in anhydrous tetrahydrofuran, and the precipitation was repeated 3 times. The mixture was then distilled under reduced pressure and placed in a vacuum drying oven at 40°C for 10 h to obtain a moisture-sensitive functional random copolymer of polyvinyl alcohol precursor.

[0056] Step S6: Add 1g of polyvinyl alcohol precursor moisture-sensitive random copolymer and 20mL of anhydrous tetrahydrofuran to a round-bottom flask, stir for 10min, add 10mL of anhydrous methanol and 5mL of sodium hydroxide-anhydrous methanol solution (the molar concentration of sodium hydroxide-anhydrous methanol solution is 2mol / L), and stir the reaction at 40℃ and 300r / min for 5h. After the reaction is completed, distill under reduced pressure, then pour it into deionized water to precipitate, centrifuge to collect the solid, wash it once with anhydrous ethanol, and then place it in a vacuum drying oven and dry it at 40℃ for 11h to obtain polyvinyl alcohol-based moisture-sensitive polymer.

[0057] Step S7: Add 10 mL of tetraethyl orthosilicate and 40 mL of anhydrous ethanol to a three-necked flask, turn on the magnetic stirrer, and stir for 10 min at a stirring rate of 280 r / min. Add 10 mL of deionized water and 0.5 mL of concentrated hydrochloric acid (mass fraction of concentrated hydrochloric acid is 37%) dropwise, continue stirring for 30 min, and add 10 mL of tetrabutyl titanate-anhydrous ethanol solution (tetrabutyl titanate-anhydrous ethanol solution is a solution of tetrabutyl titanate and anhydrous ethanol mixed in a volume ratio of 1 mL: 5 mL) at a dropping rate of 1 drop / s. After the addition is complete, raise the temperature to 40 °C, stir at a constant temperature for 3 h, and age at room temperature for 10 h to obtain SiO2-TiO2 sol.

[0058] Step S8: Weigh out 2 parts by weight of polyvinyl alcohol-based moisture-sensitive polymer, 50 parts by weight of anhydrous ethanol, 20 parts by weight of deionized water, 2 parts by weight of SiO2-TiO2 sol and 0.2 parts by weight of lithium chloride, and set aside.

[0059] Step S9: Add polyvinyl alcohol-based moisture-sensitive polymer, anhydrous ethanol and deionized water to a beaker, stir for 10 min at a stirring rate of 280 r / min, add SiO2-TiO2 sol, continue stirring for 30 min, add lithium chloride, and continue stirring for 20 min to obtain composite sol.

[0060] Step S10: After sealing the composite sol, age it at room temperature for 10 hours, then transfer it to a centrifuge tube, put it in a centrifuge, adjust the speed to 3000 r / min, centrifuge for 10 minutes, take the upper layer of sol, transfer it to a petri dish, put it in a vacuum oven, dry it at 40℃ for 8 hours, and cool it to room temperature to obtain the composite moisture-sensitive material.

[0061] Example 2:

[0062] This embodiment describes a method for preparing a composite moisture-sensitive material using the sol-gel method, comprising the following steps:

[0063] Step S1: 25 mmol of 3-nitrophthalic anhydride, 25 mmol of N,N-dibutyl-m-aminophenol, 2.5 mmol of anhydrous zinc chloride, and 75 mL of toluene were added to a three-necked flask equipped with a stirrer, thermometer, water separator, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 107 °C and a stirring rate of 350 r / min for 5.1 h. After the reaction was completed, the mixture was cooled to room temperature, distilled under reduced pressure, and then dissolved in anhydrous dichloromethane. The solution was washed twice each with 5% hydrochloric acid, deionized water, and saturated brine. After drying with anhydrous sodium sulfate for 2 h, the solution was filtered, concentrated by rotary evaporation, and then purified by column chromatography using eluent A (a solution of anhydrous methanol and anhydrous dichloromethane in a volume ratio of 1:10). The solution was then placed in a vacuum drying oven and dried at 37 °C for 7 h to obtain the first intermediate.

[0064] Step S2: Add 4.5 mmol of 4-methoxy-2-methyldiphenylamine and 4.5 mmol of the first intermediate to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection. Add 0.7 mL of 98% concentrated sulfuric acid dropwise under an ice-water bath at 0°C. After the addition is complete, raise the temperature to room temperature and stir at 350 rpm for 24 hours. After the reaction is complete, pour the reaction mixture into the stirred ice water bath, let it stand for 31 minutes, filter, and wash the filter cake twice with deionized water. The filter cake was then dispersed in deionized water and adjusted to neutral pH with a 5% sodium hydroxide aqueous solution while stirring. It was then extracted three times with anhydrous dichloromethane. The organic phase was dried with anhydrous sodium sulfate for 2 hours, filtered, and then vacuum rotary evaporated. The organic phase was then purified by column chromatography using eluent B (eluent B is a solution of anhydrous methanol and anhydrous dichloromethane mixed in a volume ratio of 1:10). The solution was then placed in a vacuum drying oven and dried at 43°C for 8.5 hours to obtain the second intermediate.

[0065] Step S3: Add 1.5 mmol of the second intermediate, 75 mg of palladium-on-carbon catalyst (the palladium-on-carbon catalyst is a wet product containing 55% water; in the dried product after removing the water, the palladium metal loading is 10 wt%), and 6 mL of ethyl acetate-water mixture (the ethyl acetate-water mixture is a solution of ethyl acetate and deionized water mixed in a volume ratio of 1.5:1) to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection, start stirring at a speed of 350 r / min, and add 2.25 mmol of hypophosphite, 6.75 mmol of sodium hypophosphite monohydrate, and 4.5 mL of deionized water. The solution was stirred in a beaker for 16 minutes to obtain an aqueous solution. The aqueous solution was then poured into a three-necked flask, and the temperature was raised to 75°C. The reaction was carried out for 7 hours. After the reaction was completed, the solution was cooled to room temperature and filtered with a diatomaceous earth filter cake under nitrogen protection to remove the palladium catalyst on carbon. The filtrate was allowed to stand and separate into layers. The organic phase was collected, and the aqueous phase was extracted twice with ethyl acetate. The organic phases were combined and dried with anhydrous sodium sulfate for 2 hours. After filtration, the solution was vacuum rotary evaporated and then purified by column chromatography with eluent C (eluent C is a solution of anhydrous methanol and anhydrous dichloromethane mixed in a volume ratio of 1:10). The solution was then placed in a vacuum drying oven and dried at 43°C for 8.5 hours to obtain the third intermediate.

[0066] Step S4: Add 10 mmol of the third intermediate, 44 mL of anhydrous dichloromethane, and 25.5 mmol of triethylamine to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection. Under conditions of 0°C and a stirring rate of 350 r / min, add 6.5 mL of a acryloyl chloride-anhydrous dichloromethane mixed solution (a solution of acryloyl chloride and anhydrous dichloromethane mixed in a volume ratio of 1:5). The dropping rate is controlled. The reaction was carried out at a rate of 1 drop / s. After the addition was complete, the mixture was allowed to naturally warm to room temperature and stirred for 2.5 hours. The mixture was then washed with saturated sodium bicarbonate solution until pH=8, followed by washing with deionized water until neutral. After drying with anhydrous sodium sulfate for 2 hours, the mixture was filtered and then vacuum rotary evaporated. The mixture was purified by column chromatography using eluent D (eluent D is a solution of petroleum ether and ethyl acetate mixed in a volume ratio of 4:1). The mixture was then placed in a vacuum drying oven and dried at 37°C for 7 hours to obtain acrylamide-functionalized polymerizable moisture-sensitive dye monomer.

[0067] Step S5: In an anhydrous and oxygen-free glove box, 0.6 mmol of acrylamide-functionalized polymerizable moisture-sensitive dye monomer, 6 mmol of vinyl acetate, 6 mL of anhydrous tetrahydrofuran, and 0.04 mmol of azobisisobutyronitrile were added sequentially to a dry, thick-walled pressure-resistant tube. The pressure-resistant tube was then sealed and placed in an oil bath at 63°C for 48 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into anhydrous petroleum ether under stirring to precipitate. The solid was collected by filtration, dissolved in anhydrous tetrahydrofuran, and the precipitation was repeated 3 times. The mixture was then distilled under reduced pressure and placed in a vacuum drying oven at 43°C for 11 h to obtain a moisture-sensitive functional random copolymer of polyvinyl alcohol precursor.

[0068] Step S6: Add 1.5g of polyvinyl alcohol precursor moisture-sensitive random copolymer and 30mL of anhydrous tetrahydrofuran to a round-bottom flask, stir for 11min, add 15mL of anhydrous methanol and 7.5mL of sodium hydroxide-anhydrous methanol solution (the molar concentration of sodium hydroxide-anhydrous methanol solution is 2mol / L), and stir the reaction at 43℃ and a stirring rate of 350r / min for 5.1h. After the reaction is completed, distill under reduced pressure, then pour it into deionized water to precipitate, centrifuge to collect the solid, wash it once with anhydrous ethanol, and then place it in a vacuum drying oven and dry it at 43℃ for 11.5h to obtain polyvinyl alcohol-based moisture-sensitive polymer.

[0069] Step S7: Add 11 mL of tetraethyl orthosilicate and 44 mL of anhydrous ethanol to a three-necked flask, turn on the magnetic stirrer, and stir for 11 min at a stirring rate of 290 r / min. Add 11 mL of deionized water and 0.55 mL of concentrated hydrochloric acid (mass fraction of concentrated hydrochloric acid is 37%) dropwise, and continue stirring for 31 min. Add 11 mL of tetrabutyl titanate-anhydrous ethanol solution (tetrabutyl titanate-anhydrous ethanol solution is a solution of tetrabutyl titanate and anhydrous ethanol mixed in a volume ratio of 1 mL: 5 mL) at a dropping rate of 1 drop / s. After the addition is complete, raise the temperature to 40 °C, stir at a constant temperature for 3.5 h, and age at room temperature for 11 h to obtain SiO2-TiO2 sol.

[0070] Step S8: Weigh out 3 parts by weight of polyvinyl alcohol-based moisture-sensitive polymer, 75 parts by weight of anhydrous ethanol, 30 parts by weight of deionized water, 3 parts by weight of SiO2-TiO2 sol and 0.3 parts by weight of lithium chloride, and set aside.

[0071] Step S9: Add polyvinyl alcohol-based moisture-sensitive polymer, anhydrous ethanol and deionized water to a beaker, stir for 11 min at a stirring rate of 290 r / min, add SiO2-TiO2 sol, continue stirring for 31 min, add lithium chloride, and continue stirring for 21 min to obtain composite sol.

[0072] Step S10: After sealing the composite sol, age it at room temperature for 11 hours, then transfer it to a centrifuge tube, put it in a centrifuge, adjust the speed to 3000 r / min, centrifuge for 11 minutes, take the upper layer of sol, transfer it to a petri dish, put it in a vacuum oven, dry it at 43℃ for 8.5 hours, and cool it to room temperature to obtain the composite moisture-sensitive material.

[0073] Example 3:

[0074] This embodiment describes a method for preparing a composite moisture-sensitive material using the sol-gel method, comprising the following steps:

[0075] Step S1: 30 mmol of 3-nitrophthalic anhydride, 30 mmol of N,N-dibutyl-m-aminophenol, 3 mmol of anhydrous zinc chloride, and 90 mL of toluene were added to a three-necked flask equipped with a stirrer, thermometer, water separator, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 110 °C and a stirring rate of 400 r / min for 5.2 h. After the reaction was completed, the mixture was cooled to room temperature, distilled under reduced pressure, and then dissolved in anhydrous dichloromethane. The solution was washed twice each with 5% hydrochloric acid, deionized water, and saturated brine. After drying with anhydrous sodium sulfate for 2 h, the solution was filtered and concentrated by rotary evaporation. Then, it was purified by column chromatography using eluent A (eluent is a solution of anhydrous methanol and anhydrous dichloromethane mixed in a volume ratio of 1:10). The solution was then placed in a vacuum drying oven and dried at 40 °C for 8 h to obtain the first intermediate.

[0076] Step S2: Add 6 mmol of 4-methoxy-2-methyldiphenylamine and 6 mmol of the first intermediate to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection. Add 1.0 mL of 98% concentrated sulfuric acid dropwise under 0°C ice-water bath conditions. After the addition is complete, raise the temperature to room temperature and stir at 400 rpm for 25 h. After the reaction is complete, pour the reaction mixture into the stirred ice water, let it stand for 32 min, filter, and wash the filter cake three times with deionized water. The filter cake was then dispersed in deionized water and adjusted to neutral pH with a 5% sodium hydroxide aqueous solution while stirring. It was then extracted three times with anhydrous dichloromethane. The organic phase was dried with anhydrous sodium sulfate for 2 hours, filtered, and then vacuum rotary evaporated. The organic phase was then purified by column chromatography using eluent B (eluent B is a solution of anhydrous methanol and anhydrous dichloromethane mixed in a volume ratio of 1:10). The solution was then placed in a vacuum drying oven and dried at 45°C for 9 hours to obtain the second intermediate.

[0077] Step S3: Add 2 mmol of the second intermediate, 100 mg of palladium catalyst on carbon (the palladium catalyst on carbon is a wet product containing 55% water; in the dried product after removing the water, the palladium metal loading is 10 wt%), and 8 mL of ethyl acetate-water mixture (the ethyl acetate-water mixture is a solution of ethyl acetate and deionized water in a volume ratio of 1.5:1) to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection, start stirring at a rate of 400 rpm, and add 3.0 mmol of hypophosphite, 9.0 mmol of sodium hypophosphite monohydrate, and 6 mL of deionized water to the flask. Stirring in a beaker for 17 minutes yields an aqueous solution. Pour the aqueous solution into a three-necked flask, then heat to 75°C and react for 7 hours. After the reaction is complete, cool to room temperature and filter with a diatomaceous earth filter cake under nitrogen protection to remove the palladium catalyst on carbon. Allow the filtrate to stand and separate into layers, collect the organic phase, extract the aqueous phase twice with ethyl acetate, combine the organic phases, dry the organic phase with anhydrous sodium sulfate for 2 hours, filter, and then vacuum rotary evaporate. Then, purify by column chromatography with eluent C (eluent C is a solution of anhydrous methanol and anhydrous dichloromethane mixed in a volume ratio of 1:10). Then place in a vacuum drying oven and dry at 45°C for 9 hours to obtain the third intermediate.

[0078] Step S4: Add 11 mmol of the third intermediate, 48 mL of anhydrous dichloromethane, and 28 mmol of triethylamine to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection. At 0°C and a stirring rate of 400 rpm, add 7 mL of a acryloyl chloride-anhydrous dichloromethane mixed solution (a solution of acryloyl chloride and anhydrous dichloromethane mixed in a volume ratio of 1:5). The dropping rate is controlled at 2... The mixture was added dropwise per second. After the addition was complete, the temperature was naturally raised to room temperature, and the reaction was stirred for 3 hours. The mixture was washed with saturated sodium bicarbonate solution until pH=9, then washed with deionized water until neutral. After that, it was dried with anhydrous sodium sulfate for 2 hours, filtered, and then vacuum rotary evaporated. The mixture was purified by column chromatography using eluent D (eluent D is a solution of petroleum ether and ethyl acetate mixed in a volume ratio of 4:1). After that, it was placed in a vacuum drying oven and dried at a temperature of 35-40℃ for 8 hours to obtain acrylamide-functionalized polymerizable moisture-sensitive dye monomer.

[0079] Step S5: In an anhydrous and oxygen-free glove box, 0.7 mmol of acrylamide-functionalized polymerizable moisture-sensitive dye monomer, 7 mmol of vinyl acetate, 7 mL of anhydrous tetrahydrofuran, and 0.06 mmol of azobisisobutyronitrile were added sequentially to a dry, thick-walled pressure-resistant tube. The pressure-resistant tube was then sealed and placed in an oil bath at 63°C for 48 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into anhydrous petroleum ether under stirring to precipitate. The solid was collected by filtration, dissolved in anhydrous tetrahydrofuran, and the precipitation was repeated 3 times. The mixture was then distilled under reduced pressure and placed in a vacuum drying oven at 45°C for 12 h to obtain a moisture-sensitive random copolymer of polyvinyl alcohol precursor.

[0080] Step S6: Add 2g of polyvinyl alcohol precursor moisture-sensitive random copolymer and 40mL of anhydrous tetrahydrofuran to a round-bottom flask, stir for 12min, add 20mL of anhydrous methanol and 10mL of sodium hydroxide-anhydrous methanol solution (the molar concentration of sodium hydroxide-anhydrous methanol solution is 2mol / L), and stir the reaction at 45℃ and 400r / min for 5.2h. After the reaction is completed, distill under reduced pressure, then pour it into deionized water to precipitate, centrifuge to collect the solid, wash it twice with anhydrous ethanol, and then place it in a vacuum drying oven and dry it at 45℃ for 12h to obtain polyvinyl alcohol-based moisture-sensitive polymer.

[0081] Step S7: Add 12 mL of tetraethyl orthosilicate and 48 mL of anhydrous ethanol to a three-necked flask, turn on the magnetic stirrer, and stir for 12 min at a stirring rate of 300 r / min. Add 12 mL of deionized water and 0.6 mL of concentrated hydrochloric acid (mass fraction of concentrated hydrochloric acid is 37%) dropwise, continue stirring for 32 min, and add 12 mL of tetrabutyl titanate-anhydrous ethanol solution (tetrabutyl titanate-anhydrous ethanol solution is a solution made by mixing tetrabutyl titanate and anhydrous ethanol at a volume ratio of 1 mL: 5 mL) dropwise at a rate of 1 drop / s. After the addition is complete, raise the temperature to 40 °C, stir at a constant temperature for 4 h, and age at room temperature for 12 h to obtain SiO2-TiO2 sol.

[0082] Step S8: Weigh out 4 parts by weight of polyvinyl alcohol-based moisture-sensitive polymer, 100 parts by weight of anhydrous ethanol, 40 parts by weight of deionized water, 4 parts by weight of SiO2-TiO2 sol and 0.4 parts by weight of lithium chloride, and set aside.

[0083] Step S9: Add polyvinyl alcohol-based moisture-sensitive polymer, anhydrous ethanol and deionized water to a beaker, stir for 12 min at a stirring rate of 300 r / min, add SiO2-TiO2 sol, continue stirring for 32 min, add lithium chloride, and continue stirring for 22 min to obtain composite sol.

[0084] Step S10: After sealing the composite sol, age it at room temperature for 12 hours, then transfer it to a centrifuge tube, put it in a centrifuge, adjust the speed to 3000 r / min, centrifuge for 12 minutes, take the upper layer of sol, transfer it to a petri dish, put it in a vacuum oven, dry it at 45℃ for 9 hours, and cool it to room temperature to obtain the composite moisture-sensitive material.

[0085] Comparative Example 1:

[0086] This comparative example illustrates a method for preparing a composite moisture-sensitive material using a sol-gel method, comprising the following steps:

[0087] Step S1: 20 mmol of 3-nitrophthalic anhydride, 20 mmol of N,N-dibutyl-m-aminophenol, 2 mmol of anhydrous zinc chloride, and 60 mL of toluene were added to a three-necked flask equipped with a stirrer, thermometer, water separator, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 105 °C and a stirring rate of 300 r / min for 5 h. After the reaction was completed, the mixture was cooled to room temperature, distilled under reduced pressure, and then dissolved in anhydrous dichloromethane. The solution was washed twice each with 5% hydrochloric acid, deionized water, and saturated brine. After drying with anhydrous sodium sulfate for 2 h, the solution was filtered and concentrated by rotary evaporation. Then, it was purified by column chromatography using eluent A (eluent is a solution of anhydrous methanol and anhydrous dichloromethane mixed in a volume ratio of 1:10). The solution was then placed in a vacuum drying oven and dried at 35 °C for 6 h to obtain the first intermediate.

[0088] Step S2: Add 3 mmol of 4-methoxy-2-methyldiphenylamine and 3 mmol of the first intermediate to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection. Add 0.5 mL of 98% concentrated sulfuric acid dropwise under 0°C ice-water bath conditions. After the addition is complete, raise the temperature to room temperature and stir at 300 rpm for 24 h. After the reaction is complete, pour the reaction solution into the stirred ice water, let it stand for 30 min, filter, and wash the filter cake twice with deionized water. Then, filter... The cake was dispersed in deionized water and adjusted to neutral pH with 5% sodium hydroxide aqueous solution under stirring. It was extracted three times with anhydrous dichloromethane. The organic phase was dried with anhydrous sodium sulfate for 2 hours, filtered, and then vacuum rotary evaporated. The organic phase was then purified by column chromatography with eluent B (eluent B is a solution of ethyl acetate, petroleum ether and triethylamine in a volume ratio of 3:10:0.5). The solution was then placed in a vacuum drying oven and dried at 40°C for 8 hours to obtain the second intermediate.

[0089] Step S3: Add 1 mmol of the second intermediate, 50 mg of palladium-on-carbon catalyst (the palladium-on-carbon catalyst is a wet product containing 55% water; in the dried product after removing the water, the palladium metal loading is 10 wt%), and 4 mL of ethyl acetate-water mixed solution (the ethyl acetate-water mixed solution is a solution of ethyl acetate and deionized water mixed in a volume ratio of 1.5:1) to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection, start stirring at a speed of 300 r / min, and add 1.5 mmol of hypophosphite, 4.5 mmol of sodium hypophosphite monohydrate, and 3 mL of deionized water to the flask. Stir in a beaker for 15 minutes to obtain an aqueous solution. Pour the aqueous solution into a three-necked flask, then heat to 75°C and react for 7 hours. After the reaction is complete, cool to room temperature and filter with a diatomaceous earth filter cake under nitrogen protection to remove the palladium catalyst on carbon. Allow the filtrate to stand and separate into layers, collect the organic phase, extract the aqueous phase twice with ethyl acetate, combine the organic phases, dry the organic phase with anhydrous sodium sulfate for 2 hours, filter, and then vacuum rotary evaporate. Then, purify by column chromatography with eluent C (eluent C is a solution of anhydrous methanol and anhydrous dichloromethane mixed in a volume ratio of 1:10). Then place in a vacuum drying oven and dry at 40°C for 8 hours to obtain the third intermediate.

[0090] Step S4: Add 9 mmol of the third intermediate, 40 mL of anhydrous dichloromethane, and 23 mmol of triethylamine to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection. Under conditions of 0°C and a stirring rate of 300 rpm, add 6 mL of a acryloyl chloride-anhydrous dichloromethane mixed solution (a solution of acryloyl chloride and anhydrous dichloromethane mixed in a volume ratio of 1:5). The dropping rate should be controlled at 1... The mixture was added dropwise per second. After the addition was complete, the temperature was naturally raised to room temperature, and the reaction was stirred for 2 hours. The mixture was washed with saturated sodium bicarbonate solution until the pH reached 8-9, then washed with deionized water until neutral. After that, it was dried with anhydrous sodium sulfate for 2 hours, filtered, and then vacuum evaporated. The mixture was purified by column chromatography using eluent D (eluent D is a solution of petroleum ether and ethyl acetate mixed in a volume ratio of 4:1). After that, it was placed in a vacuum drying oven and dried at 35°C for 6 hours to obtain acrylamide-functionalized polymerizable moisture-sensitive dye monomer.

[0091] Step S5: In an anhydrous and oxygen-free glove box, 0.5 mmol of acrylamide-functionalized polymerizable moisture-sensitive dye monomer, 5 mmol of vinyl acetate, 5 mL of anhydrous tetrahydrofuran, and 0.03 mmol of azobisisobutyronitrile were added sequentially to a dry, thick-walled pressure-resistant tube. The pressure-resistant tube was then sealed and placed in an oil bath at 63°C for 48 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into anhydrous petroleum ether under stirring to precipitate. The solid was collected by filtration, dissolved in anhydrous tetrahydrofuran, and the precipitation was repeated 3 times. The mixture was then distilled under reduced pressure and placed in a vacuum drying oven at 40°C for 10 h to obtain a moisture-sensitive functional random copolymer of polyvinyl alcohol precursor.

[0092] Step S6: Add 1g of polyvinyl alcohol precursor moisture-sensitive random copolymer and 20mL of anhydrous tetrahydrofuran to a round-bottom flask, stir for 10min, add 10mL of anhydrous methanol and 5mL of sodium hydroxide-anhydrous methanol solution (the molar concentration of sodium hydroxide-anhydrous methanol solution is 2mol / L), and stir the reaction at 40℃ and 300r / min for 5h. After the reaction is completed, distill under reduced pressure, then pour it into deionized water to precipitate, centrifuge to collect the solid, wash it once with anhydrous ethanol, and then place it in a vacuum drying oven and dry it at 40℃ for 11h to obtain polyvinyl alcohol-based moisture-sensitive polymer.

[0093] Step S7: Weigh out 2 parts by weight of polyvinyl alcohol-based moisture-sensitive polymer, 50 parts by weight of anhydrous ethanol, 20 parts by weight of deionized water and 0.2 parts by weight, and set aside.

[0094] Step S8: Add polyvinyl alcohol-based moisture-sensitive polymer, anhydrous ethanol and deionized water to a beaker, stir for 10 min at a stirring rate of 280 r / min, add lithium chloride, and continue stirring for 20 min to obtain a composite sol.

[0095] Step S9: After sealing the composite sol, age it at room temperature for 10 hours, then transfer it to a centrifuge tube, put it in a centrifuge, adjust the speed to 3000 r / min, centrifuge for 10 minutes, take the upper layer of sol, transfer it to a petri dish, put it in a vacuum oven, dry it at 40℃ for 8 hours, and cool it to room temperature to obtain the composite moisture-sensitive material.

[0096] Comparative Example 2:

[0097] This comparative example illustrates a method for preparing a composite moisture-sensitive material using a sol-gel method, comprising the following steps:

[0098] Step S1: Add 10 mL of tetraethyl orthosilicate and 40 mL of anhydrous ethanol to a three-necked flask, turn on the magnetic stirrer, and stir for 10 min at a stirring rate of 280 r / min. Add 10 mL of deionized water and 0.5 mL of concentrated hydrochloric acid (mass fraction of concentrated hydrochloric acid is 37%) dropwise, continue stirring for 30 min, and add 10 mL of tetrabutyl titanate-anhydrous ethanol solution (tetrabutyl titanate-anhydrous ethanol solution is a solution made by mixing tetrabutyl titanate and anhydrous ethanol at a volume ratio of 1 mL: 5 mL) at a dropping rate of 1 drop / s. After the addition is complete, raise the temperature to 40℃, stir at a constant temperature for 3 h, and age at room temperature for 10 h to obtain SiO2-TiO2 sol.

[0099] Step S2: Weigh out 2 parts by weight of ordinary polyvinyl alcohol (model 1788), 50 parts of anhydrous ethanol, 20 parts of deionized water, 2 parts of SiO2-TiO2 sol and 0.2 parts of lithium chloride, and set aside.

[0100] Step S3: Add polyvinyl alcohol, anhydrous ethanol and deionized water to a beaker and stir for 10 min at a stirring rate of 280 r / min. Add SiO2-TiO2 sol and continue stirring for 30 min. Add lithium chloride and continue stirring for 20 min to obtain a composite sol.

[0101] Step S4: After sealing the composite sol, age it at room temperature for 10 hours, then transfer it to a centrifuge tube, put it in a centrifuge, adjust the speed to 3000 r / min, centrifuge for 10 minutes, take the upper layer of sol, transfer it to a petri dish, put it in a vacuum oven, dry it at 40℃ for 8 hours, and cool it to room temperature to obtain the composite moisture-sensitive material.

[0102] Comparative Example 3:

[0103] This comparative example illustrates a method for preparing a composite moisture-sensitive material using a sol-gel method, comprising the following steps:

[0104] Step S1: Weigh out 2 parts by weight of ordinary polyvinyl alcohol (model 1788), 50 parts of anhydrous ethanol, 20 parts of deionized water and 0.2 parts of lithium chloride, and set aside.

[0105] Step S2: Add polyvinyl alcohol, anhydrous ethanol and deionized water to a beaker, stir for 10 min at a stirring rate of 280 r / min, add lithium chloride, and continue stirring for 20 min to obtain a composite sol.

[0106] Step S3: After sealing the composite sol, age it at room temperature for 10 hours, then transfer it to a centrifuge tube, put it in a centrifuge, adjust the speed to 3000 r / min, centrifuge for 10 minutes, take the upper layer of sol, transfer it to a petri dish, put it in a vacuum oven, dry it at 40℃ for 8 hours, and cool it to room temperature to obtain the composite moisture-sensitive material.

[0107] Performance testing

[0108] The composite moisture-sensitive materials of Examples 1-3 and Comparative Examples 1-3 were tested according to the following methods;

[0109] Humidity sensitivity test: At a temperature of 25℃ and a humidity range of 11%RH-97%RH, the composite humidity-sensitive material was prepared into a uniform humidity-sensitive film by using a saturated salt solution method to prepare different humidity points (LiCl, MgCl2, Mg(NO3)2, NaCl, KNO3). The film was placed in different humidity environments until the impedance stabilized, and the film impedance R was measured using a high-resistivity meter. The relative rate of change of impedance ΔR / R0 was linearly fitted to the humidity change ΔRH, and the humidity sensitivity S was the slope of the fitted curve: S=(ΔR / R0) / ΔRH.

[0110] Moisture absorption response time test: The moisture sensing element is quickly switched from a low humidity environment (11%RH) to a high humidity environment (97%RH), and the time required for the impedance to reach 90% of the stable value is recorded, which is the moisture absorption response time.

[0111] Moisture hysteresis error test: The impedance-humidity curves of the moisture absorption process and the dehumidification process are measured separately. Under the same humidity, the maximum humidity difference between the two curves is the moisture hysteresis error.

[0112] Cyclic stability test: 50 consecutive moisture absorption-dehumidification cycles were performed between 11%RH and 97%RH. The ratio of the sensitivity at the 50th cycle to the sensitivity at the 1st cycle was used as the cyclic stability: Cyclic stability = S 50 / S1×100%.

[0113] The test results are shown in Table 1:

[0114] Table 1: Test Results Summary Table

[0115]

[0116] Referring to the table above, based on the comparison between Examples 1-3 and Comparative Examples 1-3, it can be seen that the polyvinyl alcohol-based moisture-sensing polymer provides highly active moisture absorption sites and optical response characteristics, and SiO2-TiO2 constructs porous and fast mass transfer channels. This composite moisture-sensing material has excellent comprehensive moisture-sensing performance, including high moisture sensitivity, fast moisture absorption response speed, small moisture hysteresis error, and good stability in cyclic use.

[0117] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0118] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. A composite moisture-sensitive material prepared by the sol-gel method, characterized in that, Includes the following components by weight: The mixture consists of 2-4 parts polyvinyl alcohol-based moisture-sensitive polymer, 50-100 parts anhydrous ethanol, 20-40 parts deionized water, 2-4 parts SiO2-TiO2 sol, and 0.2-0.4 parts lithium chloride. The SiO2-TiO2 sol is prepared by the following steps: Tetrabutyl titanate and anhydrous ethanol were added to a three-necked flask and stirred. Deionized water and concentrated hydrochloric acid were added dropwise, and stirring was continued. Tetrabutyl titanate-anhydrous ethanol solution was added dropwise, and the mixture was heated and stirred. The mixture was then aged at room temperature to obtain SiO2-TiO2 sol.

2. The composite moisture-sensitive material prepared by the sol-gel method according to claim 1, characterized in that, The volume ratio of tetrabutyl titanate, anhydrous ethanol, deionized water, concentrated hydrochloric acid, and tetrabutyl titanate-anhydrous ethanol solution is 10-12 mL: 40-48 mL: 10-12 mL: 0.5-0.6 mL: 10-12 mL; the tetrabutyl titanate-anhydrous ethanol solution is a solution prepared by mixing tetrabutyl titanate and anhydrous ethanol at a volume ratio of 1 mL: 5 mL; the mass fraction of concentrated hydrochloric acid is 37%.

3. The composite moisture-sensitive material prepared by the sol-gel method according to claim 1, characterized in that, The polyvinyl alcohol-based moisture-sensitive polymer is prepared by the following steps: Step a1: Mix 3-nitrophthalic anhydride, N,N-dibutyl-m-aminophenol, anhydrous zinc chloride and toluene, stir to react, cool, distill under reduced pressure, then dissolve in anhydrous dichloromethane, wash, dry, filter and rotary evaporate, perform column chromatography, dry, to obtain the first intermediate; Step a2: Mix 4-methoxy-2-methyldiphenylamine and the first intermediate, add concentrated sulfuric acid dropwise, stir the reaction, pour the reaction solution into the stirred ice water, let stand, filter, wash, adjust pH, extract, dry, filter, vacuum rotary evaporate, then perform column chromatography purification, dry, and obtain the second intermediate; Step a3: Add the second intermediate, palladium on carbon catalyst and ethyl acetate-water mixed solution to a three-necked flask, start stirring, mix hypophosphite, sodium hypophosphite monohydrate and deionized water, stir to obtain an aqueous solution, pour the aqueous solution into the three-necked flask, react, cool, extract, dry, filter and vacuum rotary evaporate, purify by column chromatography, dry to obtain the third intermediate; Step a4: Mix the third intermediate, anhydrous dichloromethane and triethylamine, add dropwise a mixed solution of acryloyl chloride and anhydrous dichloromethane, continue stirring the reaction, wash, extract, dry, filter, vacuum rotary evaporate, column chromatography for purification, dry, and obtain acrylamide functionalized polymerizable moisture-sensitive dye monomer. Step a5: Acrylamide-functionalized polymerizable moisture-sensitive dye monomer, vinyl acetate, anhydrous tetrahydrofuran, and azobisisobutyronitrile are added sequentially to a thick-walled pressure-resistant tube. The pressure-resistant tube is sealed, the reaction is carried out, the tube is distilled under reduced pressure, and the tube is dried to obtain a moisture-sensitive random copolymer of polyvinyl alcohol precursor. Step a6: Mix and stir the polyvinyl alcohol precursor moisture-sensitive random copolymer and anhydrous tetrahydrofuran, add anhydrous methanol and sodium hydroxide-anhydrous methanol solution, stir to react, cool, centrifuge, wash and dry to obtain polyvinyl alcohol-based moisture-sensitive polymer.

4. The composite moisture-sensitive material prepared by the sol-gel method according to claim 3, characterized in that, The ratio of 3-nitrophthalic anhydride, N,N-dibutyl-m-aminophenol, anhydrous zinc chloride, and toluene in step a1 is 20-30 mmol: 20-30 mmol: 2-3 mmol: 60-90 mL.

5. The composite moisture-sensitive material prepared by the sol-gel method according to claim 3, characterized in that, In step a2, the ratio of 4-methoxy-2-methyldiphenylamine, the first intermediate, and concentrated sulfuric acid is 3-6 mmol: 3-6 mmol: 0.5-1.0 mL; the concentrated sulfuric acid has a mass fraction of 98%.

6. The composite moisture-sensitive material prepared by the sol-gel method according to claim 3, characterized in that, In step a3, the ratio of the second intermediate, palladium catalyst on carbon, ethyl acetate-water mixed solution, hypophosphorous acid, sodium hypophosphorous acid monohydrate, and deionized water is 1-2 mmol: 50-100 mg: 4-8 mL: 1.5-3.0 mmol: 4.5-9.0 mmol: 3-6 mL; the ethyl acetate-water mixed solution is a solution of ethyl acetate and deionized water mixed in a volume ratio of 1.5:1; the palladium catalyst on carbon is a wet product containing water with a water content of 55%, and the palladium metal loading in the dried product after removing the water is 10 wt%.

7. The composite moisture-sensitive material prepared by the sol-gel method according to claim 3, characterized in that, In step a4, the ratio of the third intermediate, anhydrous dichloromethane, triethylamine, and the acryloyl chloride-anhydrous dichloromethane mixed solution is 9-11 mmol: 40-48 mL: 23-28 mmol: 6-7 mL; the acryloyl chloride-anhydrous dichloromethane mixed solution is a solution formed by mixing acryloyl chloride and anhydrous dichloromethane at a volume ratio of 1:

5.

8. The composite moisture-sensitive material prepared by the sol-gel method according to claim 3, characterized in that, In step a5, the ratio of acrylamide-functionalized polymerizable moisture-sensitive dye monomer, vinyl acetate, anhydrous tetrahydrofuran, and azobisisobutyronitrile is 0.5-0.7 mmol: 5-7 mmol: 5-7 mL: 0.03-0.06 mmol.

9. A composite moisture-sensitive material prepared by the sol-gel method according to claim 3, characterized in that, In step a6, the ratio of the polyvinyl alcohol precursor moisture-sensitive random copolymer, anhydrous tetrahydrofuran, anhydrous methanol, and sodium hydroxide-anhydrous methanol solution is 1-2 g: 20-40 mL: 10-20 mL: 5-10 mL; the molar concentration of the sodium hydroxide-anhydrous methanol solution is 2 mol / L.

10. A method for preparing a composite moisture-sensitive material using a sol-gel method, characterized in that, The preparation of the composite moisture-sensitive material as described in any one of claims 1-9 includes the following steps: Step 1: Weigh out 2-4 parts by weight of polyvinyl alcohol-based moisture-sensitive polymer, 50-100 parts by weight of anhydrous ethanol, 20-40 parts by weight of deionized water, 2-4 parts by weight of SiO2-TiO2 sol, and 0.2-0.4 parts by weight of lithium chloride, and set aside. Step 2: Add polyvinyl alcohol-based moisture-sensitive polymer, anhydrous ethanol and deionized water to a beaker, stir, add SiO2-TiO2 sol, continue stirring, add lithium chloride, continue stirring to obtain composite sol; Step 3: After sealing the composite sol, age it at room temperature, then transfer it to a centrifuge tube, centrifuge, take the upper layer of sol, transfer it to a petri dish, dry it, and cool it to obtain the composite moisture-sensitive material.

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