A kind of polyphenol functionalized graphene oxide and its preparation method and application

Abstract

This invention discloses a polyphenol-functionalized graphene oxide, its preparation method, and its applications, relating to the field of photocurable materials technology. The preparation method includes the following steps: dissolving a polyphenol compound and N-(hydroxymethyl)acrylamide in an organic solvent, adding an acidic catalyst, and then performing a Friedel-Crafts alkylation reaction to obtain a polyphenol-based acrylamide monomer; dissolving the polyphenol-based acrylamide monomer and a thiol-containing silane coupling agent in an organic solvent, adding a photoinitiator, and then performing a thiol-alkene click reaction under ultraviolet light irradiation to obtain a polyphenol-based silanized product; dispersing the polyphenol-based silanized product and graphene oxide in a mixed solvent, and heating the reaction to obtain the polyphenol-functionalized graphene oxide. This invention introduces fluorescent chromophores onto the surface of GO through chemical modification, solving the problem that GO cannot meet the requirements for self-warning of material damage, while also improving the dispersibility of GO in resin and its interfacial bonding with the resin.

Description

Technical Field

[0001] This invention relates to the field of photocurable materials technology, and in particular to a polyphenol-functionalized graphene oxide, its preparation method, and its application. Background Technology

[0002] Graphene oxide (GO), due to its unique two-dimensional sheet structure and excellent mechanical and barrier properties, is considered an ideal reinforcing filler for polymer composites. However, the strong π-π interactions and hydrogen bonds between GO sheets make it prone to aggregation, and its poor dispersibility and interfacial compatibility in hydrophobic polymer resin matrices severely limit its reinforcing effect. Furthermore, traditional GO fillers have limited functionality and cannot meet the demands of advanced materials for intelligent features, such as damage self-warning capabilities.

[0003] Vinyl ester resins (VER) and unsaturated polyester resins are common UV-curable resins, known for their fast curing speed and good corrosion resistance, and are widely used in anti-corrosion coatings. However, their cured network is relatively brittle, and their toughness and mechanical strength need further improvement. Reinforcement and toughening are usually achieved by adding nanofillers, but the interfacial bonding strength between the filler and the matrix, as well as the uniformity of the filler's dispersion in the matrix, are crucial to determining the modification effect.

[0004] Modifying graphene oxide (GO) could improve its dispersibility in resin materials such as vinyl esters (VERs) and its interfacial bonding with resins, while also endowing the composite material with fluorescent properties, thus enabling a damage self-warning function. This would be of great significance for structural health monitoring and safety assurance. Therefore, developing a novel graphene oxide material based on this idea is crucial. Summary of the Invention

[0005] The purpose of this invention is to provide a polyphenol-functionalized graphene oxide (GO), its preparation method, and its application, to solve the problems existing in the prior art. This invention introduces fluorescent chromophores onto the surface of GO through chemical modification, solving the technical problem that GO as a filler is difficult to meet the requirements for self-warning of material damage in the prior art. It also improves the dispersibility of GO in resin materials and its interfacial bonding with resin materials.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] One of the technical solutions of the present invention: a method for preparing polyphenol-functionalized graphene oxide, comprising the following steps:

[0008] Polyphenolic compounds and N-(hydroxymethyl)acrylamide were dissolved in an organic solvent, an acidic catalyst was added, and then Friedel-Crafts alkylation was carried out to obtain polyphenolic acrylamide monomers.

[0009] The polyphenolic acrylamide monomer and a thiol-containing silane coupling agent are dissolved in an organic solvent, a photoinitiator is added, and then a thiol-alkene click reaction is carried out under ultraviolet light irradiation to obtain the polyphenolic silanized product.

[0010] The polyphenol-based silanized product and graphene oxide are dispersed in a mixed solvent and heated to react (a siloxane hydrolysis-condensation reaction occurs during the heating reaction) to obtain the polyphenol-functionalized graphene oxide.

[0011] The polyphenol-functionalized graphene oxide of this invention utilizes the characteristics of polyphenol compounds containing benzene rings and phenolic hydroxyl groups, and N-(hydroxymethyl)acrylamide containing amide bonds, carbon-carbon double bonds, and other fluorescent chromophores. Based on polyphenol compounds, fluorescent chromophores are introduced through chemical modification, giving the final product intrinsic fluorescent properties. More importantly, an organic-inorganic hybrid interface layer is constructed on the GO surface through the above series of reactions: on the one hand, the grafted organosilane long chains and polyphenol structures effectively improve the surface polarity of GO, weaken the strong interactions between layers, and significantly improve its dispersion uniformity and long-term stability in hydrophobic resin matrices; on the other hand, the active carbon-carbon double bonds retained on the functionalized GO surface can undergo copolymerization reactions with the unsaturated bonds in the resin matrix (such as vinyl ester resin) during photocuring, forming a strong chemical bond interface, which greatly enhances the interfacial bonding force between the filler and the matrix, thereby more effectively transferring and dispersing stress and achieving simultaneous enhancement of the mechanical properties of the composite material. In summary, this invention synthesizes polyphenolic acrylamide monomers by Friedel-Crafts alkylation of polyphenolic compounds and N-(hydroxymethyl)acrylamide, and then grafts them onto GO via two key reactions: mercapto-olefin click chemistry and siloxane hydrolysis-condensation. This constructs an organic-inorganic hybrid structure on the GO surface that combines enhancement effects and fluorescence properties. This not only improves the dispersibility of GO in resin materials and its interfacial bonding with resin materials, but also endows the materials with fluorescence properties, enabling the obtained polyphenol-functionalized graphene oxide to achieve self-warning of damage in composite materials when used as a filler.

[0012] Furthermore, the polyphenolic compound includes at least one of pyrogallol, catechol, and hydroquinone.

[0013] Furthermore, the acidic catalyst includes at least one of concentrated sulfuric acid, phosphotungstic heteropoly acid, and aluminum trichloride.

[0014] Furthermore, the mercapto-containing silane coupling agent includes at least one of (3-mercaptopropyl)trimethoxysilane and (3-mercaptopropyl)triethoxysilane.

[0015] Further, the photoinitiator includes at least one of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone (1173), 2-hydroxy-2-methyl-1-phenyl-1-propanone (2959), 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone (369), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (819).

[0016] Furthermore, the organic solvent used to dissolve the polyphenolic compound and N-(hydroxymethyl)acrylamide includes at least one of anhydrous ethanol, isopropanol and n-butanol, preferably anhydrous ethanol.

[0017] Furthermore, the organic solvent used to dissolve the polyphenolic acrylamide monomer and the mercapto-containing silane coupling agent includes at least one of anhydrous ethanol, isopropanol, and n-butanol, preferably anhydrous ethanol.

[0018] Furthermore, the mixed solvent is a mixture of anhydrous ethanol and water.

[0019] Preferably, the mixed solvent is obtained by mixing anhydrous ethanol and water in a volume ratio of 8:2.

[0020] Furthermore, the molar ratio of the polyphenol compound to the N-(hydroxymethyl)acrylamide is 1:2.3~2.5, preferably 1:2.4.

[0021] Furthermore, the molar ratio of the polyphenolic acrylamide monomer to the mercapto-containing silane coupling agent is 1:1 to 1.2.

[0022] Furthermore, the mass ratio of the polyphenol-silanized product to the graphene oxide is 2-4:1.

[0023] Furthermore, the molar ratio of the polyphenol compound to the acidic catalyst is 1:0.5~2.5, preferably 1:1.5~2.0.

[0024] Furthermore, the mass of the photoinitiator is 0.5 to 5% of the total mass of the polyphenolic acrylamide monomer and the mercapto-containing silane coupling agent.

[0025] Furthermore, the Friedel-Crafts alkylation reaction is carried out at a temperature of 30-40°C for a time of 48-96 hours.

[0026] Furthermore, the click reaction time of the mercapto-alkene is 4-8 hours.

[0027] Furthermore, the heating reaction is carried out at a temperature of 60-80°C for a duration of 10-14 hours.

[0028] Furthermore, the mercapto-alkene click reaction is carried out at room temperature under an inert atmosphere.

[0029] Furthermore, the heating reaction is carried out under an inert atmosphere.

[0030] Preferably, the inert atmosphere is a nitrogen atmosphere.

[0031] Furthermore, the ultraviolet light irradiation specifically refers to irradiation using an ultraviolet lamp with a wavelength of 365nm and a power of 300W.

[0032] Furthermore, after the Friedel-Crafts alkylation reaction is completed, the process also includes steps of filtration, washing, and recrystallization.

[0033] Furthermore, after the mercapto-alkene click reaction is completed, the step of removing the organic solvent by rotary evaporation is also included.

[0034] Furthermore, after the heating reaction is completed, the process also includes washing and freeze-drying steps.

[0035] The second technical solution of the present invention: a polyphenol-functionalized graphene oxide prepared by the above-described method.

[0036] The third technical solution of the present invention: the application of the above-mentioned polyphenol functionalized graphene oxide in the preparation of photocurable composite materials.

[0037] The fourth technical solution of the present invention: a photocurable composite material, characterized in that the raw materials include a photocurable resin, the above-mentioned polyphenol-functionalized graphene oxide and a photoinitiator;

[0038] The mass of the polyphenol-functionalized graphene oxide is 0.025~0.5% of the mass of the photocurable resin;

[0039] The mass of the photoinitiator is 0.5 to 5% of the total mass of the photocurable resin and the polyphenol-functionalized graphene oxide.

[0040] Furthermore, the photocurable resin includes vinyl ester resin, unsaturated polyester resin, polyurethane, or acrylate.

[0041] Further, the photoinitiator includes at least one of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone (1173), 2-hydroxy-2-methyl-1-phenyl-1-propanone (2959), 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone (369), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (819), preferably 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone.

[0042] Fifth technical solution of the present invention: A method for preparing the above-mentioned photocurable composite material, comprising the following steps:

[0043] The photocurable composite material is obtained by mixing a photocurable resin, polyphenol-functionalized graphene oxide, and a photoinitiator.

[0044] The sixth technical solution of the present invention: the application of the above-mentioned polyphenol functionalized graphene oxide or the above-mentioned photocurable composite material in the preparation of materials with damage self-warning function.

[0045] Preferably, the material with damage self-warning function includes a coating with damage self-warning function.

[0046] Preferably, when the photocurable composite material is used to prepare a material with a damage self-warning function, the preparation steps of the material with the damage self-warning function include: coating the photocurable composite material on the surface of a substrate or pouring it into a mold, and then placing it under ultraviolet light for curing to obtain a material with a self-warning function.

[0047] Photocurable composite materials utilize the fluorescence properties of polyphenol-functionalized graphene oxide. When the material with self-warning function is subjected to mechanical damage (such as scratches or cracks), the local fluorescence is quenched or enhanced due to stress or exposure of fresh fracture surfaces. Under ultraviolet light, it shows a signal that can be distinguished from the surrounding intact area, thereby realizing the self-warning function of material damage.

[0048] The present invention discloses the following technical effects:

[0049] (1) The preparation method of the present invention is simple. Through two key reactions, namely mercapto-alkene click chemistry and siloxane hydrolysis condensation, the designed and synthesized polyphenolic acrylamide monomer is covalently grafted onto the surface of GO. By selecting the reaction sequence and the amount of raw materials, the amount of mercapto grafted onto GO is determined, and its reaction with polyphenolic acrylamide monomer is controlled, so that the polyphenol functionalized graphene oxide retains carbon-carbon double bonds as much as possible. The carbon-carbon double bonds retained on its surface can copolymerize with resins such as VER to form strong chemical bonds, which greatly enhances the interfacial bonding force.

[0050] (2) The polyphenol-functionalized graphene oxide prepared by the present invention is uniformly dispersed and has good stability in the VER matrix. An appropriate amount of polyphenol-functionalized GO can significantly increase the tensile strength of the composite material from 47.6 MPa of pure VER to 68.8 MPa and the elongation at break from 8.11% to 12.84%, thus achieving simultaneous optimization of strength and toughness.

[0051] (3) The polyphenol-functionalized graphene oxide of the present invention is used as a filler and, when introduced into the VER, serves as an additional crosslinking point, thereby increasing the crosslinking density of the composite material (from 790.98 mol / m³). 3 Increased to 856.94 mol / m 3 Meanwhile, the organic-inorganic hybrid layer formed on the GO surface by the polyphenol silanization products and the Si-OC crosslinking network that may form at high temperatures effectively improve the thermal stability of the composite material.

[0052] (4) This invention successfully introduces the fluorescence properties of polyphenolic acrylamide monomer molecules into the composite material system. When the cured composite material is damaged by microcracks or other damage, under ultraviolet light irradiation, the damaged area will show fluorescence different from the bulk due to stress-induced fluorescence changes or exposure of fresh fracture surfaces, thereby realizing the visualization and in-situ early warning of material damage, which greatly expands the application potential of composite materials in the field of critical structural health monitoring.

[0053] (5) The present invention uses biomass-related polyphenol compounds as one of the raw materials, which partially replaces petrochemical resources and is in line with the development direction of green chemistry. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 This is a synthetic route diagram for polyphenol-functionalized graphene oxide in Example 1.

[0056] Figure 2 The infrared spectra of the polyphenolic acrylamide monomer (PHAM), polyphenolic silanized product (PMSi), polyphenol-functionalized graphene oxide (PMGO), and raw material graphene oxide (GO) prepared in Example 1 are shown.

[0057] Figure 3 The X-ray photoelectron spectra of the polyphenol-functionalized graphene oxide prepared in Example 1 and the raw graphene oxide are shown.

[0058] Figure 4 This is a photograph showing the dispersion of the polyphenol-functionalized graphene oxide prepared in Example 1 and the raw graphene oxide in VER resin.

[0059] Figure 5 This is a schematic diagram (i.e., a fluorescence photograph) of the polyphenol-based acrylamide monomer, polyphenol-functionalized graphene oxide, and raw material graphene oxide prepared in Example 1 in DMF.

[0060] Figure 6 Schematic diagram of fluorescence phenomena of photocurable films prepared from photocurable composite materials obtained in Examples 2-5 and photocurable materials obtained in Comparative Example 1.

[0061] Figure 7 This is a schematic diagram of the scratch fluorescence phenomenon of the photocurable film prepared from the photocurable composite material obtained in Example 2. Detailed Implementation

[0062] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0063] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0064] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0065] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0066] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0067] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0068] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the implementation of the present invention is not limited thereto.

[0069] The synthetic route of polyphenol-functionalized graphene oxide in this invention is as follows: Figure 1 As shown, pyrogallol first undergoes a Friedel-Crafts alkylation reaction with N-(hydroxymethyl)acrylamide at 35°C under an acidic catalyst to synthesize a polyphenolic acrylamide monomer (PHAM) containing an acrylamide structure and a pyrogallol structure. Then, the polyphenolic acrylamide monomer undergoes a mercapto-alkene click reaction with a mercapto-containing silane coupling agent to graft the siloxane onto PHAM, yielding a polyphenolic silanized product (PMSi). Finally, the siloxane from the polyphenolic silanized product undergoes a hydrolytic condensation reaction with the hydroxyl and carboxyl groups at the edge sites (defect sites) of graphene oxide (GO), successfully grafting the polyphenolic silanized product onto the GO surface. Functional groups within graphene oxide generally do not participate in the reaction.

[0070] Pyrogallol is one embodiment of this invention; polyphenolic compounds such as catechol and hydroquinone can also be used. In addition to thiol-containing silane coupling agents... Figure 1 The (3-mercaptopropyl)triethoxysilane (MPTES) shown can also be replaced by (3-mercaptopropyl)trimethoxysilane.

[0071] It should be noted that if the reaction sequence is adjusted, adopting a synthetic pathway where graphene oxide first undergoes a hydrolysis-condensation reaction with a thiol-containing silane coupling agent, and the product then undergoes a thiol-ene click reaction with PHAM, the uneven distribution and varying reactivity of active sites such as hydroxyl and carboxyl groups on the GO surface make it difficult to precisely control the grafting amount, grafting density, and distribution pattern of the silane coupling agent. Furthermore, since the exact content of thiol groups cannot be determined, the feed ratio loses its scientific basis when performing the thiol-ene click reaction with PHAM. In addition, one of the key aspects of this invention is ensuring that the final product PMGO retains carbon-carbon double bonds suitable for photocuring, but in the pathway of silanization followed by click, due to the aforementioned uncontrollability, it is impossible to guarantee whether double bonds are retained in the final product. In summary, the inability to determine the amount of thiol groups grafted onto GO makes it impossible to control its reaction with the polyphenolic acrylamide monomer, resulting in an inability to determine whether double bonds are retained in the product. This will be detrimental to the chemical bonding between modified graphene oxide and VER.

[0072] In the following embodiments, comparative examples and test examples of the present invention, if room temperature is involved, it specifically refers to 20-30 ℃.

[0073] All raw materials used in the following examples, comparative examples and test examples of this invention are common commercial products, wherein the concentration of concentrated sulfuric acid is 18.4 mol / L.

[0074] Example 1

[0075] A method for preparing polyphenol-functionalized graphene oxide (synthetic route as follows) Figure 1 (As shown), the steps are as follows:

[0076] (1) Dissolve 0.2 mol of pyrogallic acid (PG) and 0.48 mol of N-(hydroxymethyl)acrylamide (HMAA) in 200 mL of anhydrous ethanol and stir until homogeneous. Then slowly add 20 mL of concentrated sulfuric acid (containing 0.37 mol of H2SO4) to the reaction system. After the addition is complete, stir the reaction at 35 °C for 72 h. After the reaction is complete, filter the solution and wash the filter cake with water until the pH of the filtrate is neutral to obtain the crude product. The crude product is recrystallized three times using anhydrous ethanol as the solvent. The specific operation is as follows: transfer the crude product to a round-bottom flask, add sufficient anhydrous ethanol, heat to 750 °C and stir to completely dissolve it to form a nearly saturated clear solution. Then, allow the solution to cool naturally to room temperature and stand for aging to allow the crystals to fully separate. Collect the crystals by filtration and wash with a small amount of anhydrous ethanol. Repeat the above steps three times to finally obtain a white pure substance, which is the polyphenolic acrylamide monomer (denoted as PHAM).

[0077] (2) Weigh 0.1 mol (23.8 g) of (3-mercaptopropyl)triethoxysilane (MPTES) and 0.1 mol (29.2 g) of PHAM prepared in step (1) and place them in a 250 mL flask. Dissolve them in 30 mL of anhydrous ethanol, and then add 0.5 g of photoinitiator 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone. Stir the reaction magnetically for 6 h at room temperature, under nitrogen protection and irradiation with 365 nm ultraviolet light (specifically, use an ultraviolet lamp with a wavelength of 365 nm and a power of 300 W). After the reaction is completed, remove the anhydrous ethanol by rotary evaporation to obtain a pale yellow solid, which is the polyphenol silanized product (denoted as PMSi).

[0078] (3) Using a flask as a container, 0.3 g of PMSi and 0.1 g of GO prepared in step (2) were uniformly dispersed in 100 mL of anhydrous ethanol / water (volume ratio of anhydrous ethanol to water is 8:2), and sonicated for 30 min to form a stable suspension. The flask was then transferred to an oil bath, heated to 70 °C, and magnetically stirred for 12 h under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature, and the product was washed three times with anhydrous ethanol and then freeze-dried to obtain polyphenol-functionalized graphene oxide (denoted as PMGO).

[0079] The graphene oxide (GO), polyphenolic acrylamide monomer (PHAM), polyphenolic silanized product (PMSi), and polyphenol-functionalized graphene oxide (PMGO) in Example 1 were characterized using a Thermo Fisher Nicolet iS10 Fourier transform infrared spectrometer (using a 25 mm × 4 mm potassium bromide window, scanning range 4000-400 cm⁻¹). -1(32 scans were performed), results are shown below. Figure 2 .

[0080] from Figure 2 It can be seen that for PHAM, at 3395cm -1 The stretching vibration signal of the hydroxyl group was observed at 3299 cm⁻¹; the stretching vibration peak of the NH group of the amide group was located at 3299 cm⁻¹. -1 3104cm -1 The absorption peak at 1655 cm⁻¹ is attributed to the bending vibration of C=CH; the characteristic stretching vibration peak of the carbonyl group appears at 1655 cm⁻¹. -1 1600cm -1 The peak at 1548 cm⁻¹ indicates the presence of C=C stretching vibrations at the ends of the acrylamide chain segments, and both together confirm the existence of the amide structure. -1 The absorption peak at [location] indicates the presence of a benzene ring structure. These results show that the synthesized PHAM molecule contains a benzene ring, a phenolic hydroxyl group, an amide bond, and a terminal carbon-carbon double bond, indicating that PHAM was successfully synthesized.

[0081] For PMSi, at 1636cm -1 and 1548cm -1 The characteristic peaks of the amide carbonyl group at the 1600 cm⁻¹ are clearly preserved, and the carbon-carbon double bond peaks at 1600 cm⁻¹ are also clearly preserved. -1 The absorption peak at 2560 cm⁻¹ decreased significantly but did not disappear, which is consistent with a 1:1 molar ratio of feed. -1 The complete disappearance of the characteristic thiol peak at 1079 cm⁻¹ directly confirms that the thiol group participated in the reaction; -1 The newly emerging strong absorption peak is attributed to the stretching vibration of the silicon-oxygen-silicon bond Si-O-Si, and at 2927 cm⁻¹ -1 and 2835cm -1 The enhanced methylene stretching vibration peak at the saturation point confirms the successful integration of the silane structure into PHAM, indicating the successful synthesis of PMSi.

[0082] For the product PMGO, compared with the original GO, at 1725cm -1 The intensity of the characteristic peak of the carboxyl group C=O at 2927 cm⁻¹ decreases, while the intensity of the characteristic peak at 2927 cm⁻¹ decreases. -1 A new peak belonging to the methylene stretching vibration appeared at 1099 cm⁻¹. -1 The newly observed peak corresponds to silicon-oxygen-carbon bonds, confirming that PMSi formed a Si-OC interface layer on the GO surface through hydrolysis and condensation. Furthermore, at 1636 cm⁻¹... -1 With 1548cm -1 The bimodal peaks at 3080 cm⁻¹ are attributed to the stretching vibration of the amide carbonyl group and the bending vibration of the NH group, respectively. -1 The characteristic peaks at the specified locations originate from the =CH bonds of acrylamide. The combined appearance of these characteristic peaks confirms the successful preparation of PMGO.

[0083] The polyphenol-functionalized graphene oxide (PMGO) and GO prepared in Example 1 were characterized by XPS using a Thermo Fisher Scientific K-Alpha+ X-ray photoelectron spectroscopy system (Al Kα radiation source, spot size 500 μm, energy step size 0.100 eV). The results are shown in [Figure number missing]. Figure 3 .from Figure 3 It can be seen that GO only has two characteristic peaks, C 1s and O 1s. However, PMGO obtained by PMSi modification shows additional new characteristic peaks of N 1s, Si 2s, Si 2p, S 2s, and S 2p, indicating that PMSi was successfully grafted with GO.

[0084] Example 2

[0085] A method for preparing a photocurable composite material, comprising the following steps:

[0086] Weigh 0.1 wt% (0.01 g) of PMGO (total mass of VER) and add it to 10 g of VER. Sonicate for 20 min to initially disperse the PMGO. Then add 0.1 g of photoinitiator 1173 and mechanically stir for 30 min to fully mix the PMGO to obtain the photocurable composite material.

[0087] Example 3

[0088] A method for preparing a photocurable composite material, comprising the following steps:

[0089] Weigh 0.025 wt% PMGO (total mass of VER) and add it to 10 g of VER. Sonicate for 20 min to initially disperse the VER. Then add 0.1 g of photoinitiator 1173 and mechanically stir for 30 min to fully mix the VER to obtain the photocurable composite material.

[0090] Example 4

[0091] A method for preparing a photocurable composite material, comprising the following steps:

[0092] Weigh 0.25 wt% PMGO (total mass of VER) and add it to 10 g of VER. Sonicate for 20 min to initially disperse the VER. Then add 0.1 g of photoinitiator 1173 and mechanically stir for 30 min to fully mix the VER to obtain the photocurable composite material.

[0093] Example 5

[0094] A method for preparing a photocurable composite material, comprising the following steps:

[0095] Weigh PMGO at 0.5 wt% of the total mass of VER and add it to 10 g of VER. Sonicate for 20 min to disperse it initially. Then add 0.1 g of photoinitiator 1173 and mechanically stir for 30 min to mix it thoroughly, thus obtaining the photocurable composite material.

[0096] Comparative Example 1

[0097] A method for preparing a photocurable material, comprising the following steps:

[0098] Add 0.1g of photoinitiator 1173 to 10g VER and mechanically stir for 30min to mix thoroughly to obtain the photocurable material.

[0099] Test Example 1

[0100] The dispersion stability of PMGO prepared in Example 1 in resin was tested. 0.1 g of GO and 0.1 g of PMGO were dispersed in 5 g of VER resin respectively, and observed after soaking for 24 h. Pure VER resin was used as a blank control group. The results are as follows: Figure 4 As shown.

[0101] from Figure 4 As can be seen, after 24 hours of soaking, GO had completely settled to the bottom, while PMGO remained uniformly dispersed in the resin, indicating that PMGO possesses excellent dispersion stability. This is because GO and VER resin have different polarities, exhibiting extremely poor compatibility. PMGO, through its surface-grafted polyphenolic silanized layer, effectively covers the hydrophilic surface of GO, and the introduced long organic chains enhance its affinity with the resin. Simultaneously, the siloxane structure can form physical entanglements or weak interactions with the resin, thereby significantly improving its dispersion uniformity and stability within the resin. These results demonstrate that PMGO, obtained by modifying GO, exhibits significantly improved dispersibility in VER resin.

[0102] Test Example 2

[0103] The photocurable composite materials obtained in Examples 2-5 and the photocurable material obtained in Comparative Example 1 were used to prepare photocurable films, and the mechanical and thermodynamic properties of the obtained photocurable films were tested.

[0104] The method for preparing the photocurable film is as follows: the mixture obtained in Examples 2-5 and Comparative Example 1 is ultrasonically treated for 10 minutes to remove air bubbles, then poured into a silicone mold, and irradiated under a UV lamp with a wavelength of 365nm and a power of 300W for 5 minutes to cure. After curing, the film is demolded to obtain the final product.

[0105] (1) Mechanical property testing

[0106] The mechanical properties of the photocurable film were tested using a UTM 4204 electronic universal testing machine. The crosshead speed was 10 mm / min, and the sample size was 20 mm × 10 mm × 0.5 mm. To ensure testing accuracy, all cured films were tested at least five times under the same conditions, and the average values ​​of tensile strength and elongation at break were calculated.

[0107] (2) Thermodynamic performance testing

[0108] The photocurable film was analyzed using a Netzsch DMA242C dynamic thermomechanical analyzer from Germany. The double cantilever mode was selected, the frequency was 1Hz, the sample size was 64.0mm×10.0mm×3.5mm, the temperature range was -80℃ to 200℃, and the heating rate was 3℃ / min.

[0109] The test results of the mechanical and thermodynamic properties of each photocurable film are shown in Table 1.

[0110] Table 1. Test results of mechanical and thermodynamic properties of the photocurable film.

[0111]

[0112] Regarding the mechanical properties of the photocurable film, Table 1 shows that the amount of PMGO added significantly affects the tensile strength of the photocurable film. The tensile strength of the pure VER system in Comparative Example 1 is 47.6 MPa, and the elongation at break is 8.11%. When 0.025 wt% PMGO is introduced, the tensile strength significantly increases to 58.78 MPa, and the elongation at break increases to 10.18%. As the amount of PMGO added increases to 0.1 wt%, the performance reaches its peak, with the tensile strength increasing to 68.8 MPa and the elongation at break increasing to 12.84%. This indicates that an appropriate amount of PMGO, through uniform dispersion and the effective chemical bonding formed between the PHAM double bonds retained on its surface and the VER matrix, synergistically strengthens the interfacial bonding, greatly improving the load-bearing capacity and toughness of the resin matrix, thereby more efficiently transferring and dispersing stress. However, when the PMGO content was further increased to 0.25 wt% and 0.5 wt%, the performance showed a downward trend, with tensile strength decreasing to 63.29 MPa and 61.3 MPa, respectively, and elongation at break falling to 11.65% and 11.39%. This degradation was mainly attributed to the nanoparticle aggregation induced by excessive PMGO. Although the PHAM double bonds on the surface of the aggregated particles could still react with VER, the excessive aggregates formed significant stress concentration points and structural defects in the matrix, disrupting the material's homogeneity, hindering effective stress transfer, and ultimately weakening the reinforcing effect of PMGO, even leading to performance lower than at lower addition levels.

[0113] Regarding the thermodynamic properties of the photocurable films, Table 1 shows that the storage modulus (E′) of the composites increased with the addition of PMGO. In particular, the photocurable film with 0.1 wt% PMGO achieved an E′ of 2374 MPa at room temperature, significantly higher than that of pure VER (Comparative Example 1). This improvement is attributed to the fact that the presence of fillers typically restricts chain migration and transfers stress, leading to enhanced modulus. Increased filler loading further restricts migration, resulting in a higher E′ at room temperature. The addition of PMGO slightly increases the glass transition temperature (Tg) of the composites. g However, overall there was no significant difference. This may be due to the phase separation between PMGO and VER, which disrupts the spatial structure of the material and leads to T g Deterioration occurs; however, PMGO forms a covalent cross-linked network with VER, making the bond between the filler and the resin tighter, which in turn causes T g The increase in T. The two factors cancel each other out, resulting in a rise in material T. g The occurrence of subtle phenomena increases. And in T... g In the above, all cured films exhibit a rubber plateau. Based on this, the crosslinking density (ν) of the composite material can be obtained according to the rubber elastic dynamics theory (Equation (1)). e mol / m 3 ).

[0114] Formula (1);

[0115] In formula (1), T(K) represents the sample in the rubbery state (T g The absolute temperature at +30℃, E′ (MPa) corresponds to the storage modulus at T, and R is the gas molar constant (8.314 J / (mol·K)). The ν calculated from this is... e As shown in Table 1, with the increase of PMGO addition, ν e It shows a trend of first increasing and then decreasing, which is similar to the changing pattern of E′. Especially the cured film with 0.1wt% PMGO added, its ν e Reaching 856.94 mol / m 3 It is higher than the 790.98 mol / m of the pure VER membrane (Comparative Example 1). 3 This performance improvement is due to the chemical cross-linking of the double bonds on PMGO and in VER under the action of a photoinitiator. This results in a better chemical bond between PMGO and the resin substrate, fully utilizing the excellent mechanical properties and stress transfer behavior of the graphene filler. Therefore, the composite material's ν eCompared to pure VER, it shows some improvement. However, when the amount of PMGO added is too high, the nanosheets are prone to agglomeration due to van der Waals forces, resulting in a reduction of crosslinking points and the formation of stress defect points, which in turn leads to ν e The decline.

[0116] Test Example 3

[0117] The fluorescence properties of PHAM and PMGO prepared in Example 1 were tested. 0.1 g GO, 0.1 g PHAM, and 0.1 g PMGO were dissolved in 5 mL of DMF, respectively. Fluorescence characteristics were tested under 365 nm, 80 W UV light, with pure DMF as a blank control group. The results are as follows: Figure 5 As shown.

[0118] from Figure 5As can be seen, PHAM solid powder dissolved in DMF emits strong blue fluorescence under ultraviolet light excitation. This is due to the rigid planar conjugated structure of its molecular core, the synergistic effect of electron-donating groups such as phenolic hydroxyl and amide groups, and the extended π-electron conjugation system. These structural features effectively promote radiative transitions to excited states. Specifically, PHAM is a trisubstituted benzene ring structure, not a simple monobenzene ring. Its substitution mode forces the molecule to form a highly rigid and nearly planar conformation, which greatly restricts the rotational and vibrational degrees of freedom of molecular chemical bonds. In addition, the phenolic hydroxyl group is a strong electron-donating group. Through the p-π conjugation effect, it injects its lone pair electrons into the π-electron cloud of the benzene ring, significantly increasing the electron cloud density of the entire conjugated system. The amide group is a unique donor-acceptor hybrid group. Both its nitrogen and oxygen atoms have electron-donating capabilities, while the carbonyl group is a weak electron-withdrawing group. In the PHAM structure, it works synergistically with multiple phenolic hydroxyl groups, with its electron-donating effect being dominant, forming a strong aggregate of electron-donating groups together with the phenolic hydroxyl groups. When these strong electron-donating groups are attached to the same rigid benzene ring, they work synergistically to significantly reduce the energy gap between the highest occupied orbital and the lowest unoccupied orbital. This reduced energy gap means that when excited electrons return from the S1 state to the S0 state, the released photons have lower energy, longer wavelengths, and are more readily available in the visible light range (blue fluorescence). Simultaneously, more excited electrons can return to the ground state via radiative transitions, thus significantly improving the quantum yield of fluorescence (i.e., fluorescence intensity). In summary, the strong electron-donating effect promotes electron excitation, while the rigid planar structure locks in the energy of the excited state, effectively preventing energy loss as heat through molecular vibration and rotation. Without a rigid structure, even if the molecule can be excited, the energy will dissipate quickly without emitting light. The electron-donating effect provides the driving force for luminescence, while the rigid structure ensures that the driving force is used for luminescence rather than heat generation; this close combination is key to achieving efficient fluorescence. Moreover, molecules are formed by multiple atoms connected by alternating single and double bonds, and each atom has parallel overlapping p orbitals that do not participate in hybridization. This causes the p electrons to no longer be localized between two atoms, but to be delocalized throughout the entire system, forming an extended π-electron conjugated system.

[0119] The original GO exhibits weak fluorescence due to its defect states, typically displaying a faint blue-green or yellow-green fluorescence, and under the experimental conditions of this invention, almost no obvious fluorescence is observed. However, PMGO obtained by covalent grafting with PHAM exhibits a weaker blue fluorescence than PHAM under ultraviolet light. This is due to the fluorescence resonance energy transfer quenching of the PHAM chromophores by the GO sheets, supplemented by possible conformational changes and π-π stacking effects. This phenomenon is not a defect in the material, but rather demonstrates a successful and tight chemical bond between PHAM and GO. Although the fluorescence is weakened, it still possesses a clear fluorescence signal that is distinctly different from that of GO, confirming the successful grafting of PHAM and the effective at attribution of its fluorescence properties to GO.

[0120] Test Example 4

[0121] The fluorescence properties of the photocurable composite materials prepared from Examples 2-5 and the photocurable film prepared from Comparative Example 1 were tested (test conditions were the same as in Test Example 3). The test results are as follows: Figure 6 As shown. Furthermore, to visually verify the damage self-warning function of the photocurable composite material provided by this invention, a scratch damage test was performed on the photocurable film prepared from the photocurable composite material obtained in Example 2 (the fluorescence response was observed again after scratching the photocurable film). The test results are as follows. Figure 7 As shown.

[0122] from Figure 6As can be seen, the photocurable films prepared by combining PMGO with VER resin (Examples 2-5) also exhibit clear fluorescence properties. Unlike the fluorescence phenomenon exhibited by PMGO in DMF, uniformly dispersing and fixing PMGO in a rigid polymer network can effectively avoid or weaken the quenching effect, thus exhibiting a clear fluorescence phenomenon. Under UV irradiation, all photocurable films containing PMGO emit uniform blue fluorescence. This is because PMGO has good dispersibility in VER, providing sufficient fluorescence sites while avoiding various fluorescence quenching effects caused by excessive aggregation. Moreover, the fluorescence intensity is positively correlated with the amount of PMGO added, with the photocurable films containing 0.1wt% and 0.25wt% PMGO showing the most significant fluorescence. The photocurable film with low PMGO content (0.025wt%) has weak luminescence intensity due to the small amount added; the photocurable film with high PMGO content (0.5wt%) inevitably has closer layers due to the large amount of PMGO added, and even aggregation occurs. This makes the fluorescence resonance energy transfer process extremely efficient and widespread. Energy travels between dense fluorophores, eventually being transferred to energy traps within the system and dissipated as heat rather than being emitted as photons, resulting in a significant decrease in apparent fluorescence intensity. Furthermore, many fluorescent molecules exhibit strong fluorescence in a highly dispersed state, but when they aggregate to form dimers or higher-order aggregates, their excited-state properties change, often leading to weakened or even completely absent fluorescence, a phenomenon known as fluorescence quenching due to aggregation. In contrast, photocurable films with moderate PMGO content (0.1 wt% and 0.25 wt%) exhibit strong fluorescence properties, demonstrating the best filler dispersibility. This provides sufficient fluorescent sites while avoiding various fluorescence quenching effects caused by excessive aggregation. The photocurable film obtained in Comparative Example 1, without added PMGO, shows no fluorescence at all.

[0123] from Figure 7 It can be seen that under ultraviolet light excitation, the photocured film perfectly exhibits uniform blue fluorescence (compared to...). Figure 6 (The results were consistent). A clear fluorescence enhancement phenomenon was observed in the scratch-damaged area; that is, the scratch trail showed a brighter blue fluorescence signal under UV light than the surrounding intact area, creating a striking contrast. This may be because, on the one hand, the fresh fracture surface produced by the scratch may have different surface morphology and refractive index, affecting the scattering and collection efficiency of the excitation light, thus manifesting as local signal enhancement in the observation; on the other hand, in the scratch-deformed area, the local concentration or orientation of the PMGO filler may change, thereby affecting the overall fluorescence intensity of that area.

[0124] The above test results fully demonstrate that the PMGO-enhanced photocurable composite material of this invention, when subjected to mechanical damage (scratches), exhibits a fluorescence signal change in the damaged area that is distinguishable from the intact area (in this experiment, this is manifested as fluorescence enhancement). This characteristic enables the material to possess a damage self-warning function, that is, through simple ultraviolet light detection, visualization and in-situ identification of micro-damage on the material surface can be achieved, which has clear application value in fields such as structural health monitoring and smart coatings.

[0125] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a polyphenol functionalized graphene oxide, characterized by, Includes the following steps: Polyphenolic compounds and N-(hydroxymethyl)acrylamide were dissolved in an organic solvent, an acidic catalyst was added, and then Friedel-Crafts alkylation was carried out to obtain polyphenolic acrylamide monomers. The polyphenolic acrylamide monomer and a thiol-containing silane coupling agent are dissolved in an organic solvent, a photoinitiator is added, and then a thiol-alkene click reaction is carried out under ultraviolet light irradiation to obtain the polyphenolic silanized product. The polyphenol-based silanized product and graphene oxide were dispersed in a mixed solvent and heated to react, thereby obtaining the polyphenol-functionalized graphene oxide. The polyphenolic compound includes at least one of pyrogallol, catechol and hydroquinone; The mercapto-containing silane coupling agent includes at least one of (3-mercaptopropyl)trimethoxysilane and (3-mercaptopropyl)triethoxysilane; The molar ratio of the polyphenol compound to the N-(hydroxymethyl)acrylamide is 1:2.3~2.5; The molar ratio of the polyphenolic acrylamide monomer to the mercapto-containing silane coupling agent is 1:1 to 1.2; The mass ratio of the polyphenol-silanized product to the graphene oxide is 2-4:

1.

2. The method for preparing polyphenol-functionalized graphene oxide as described in claim 1, characterized in that, The acidic catalyst includes at least one of concentrated sulfuric acid, phosphotungstic heteropoly acid, and aluminum trichloride; And / or, the photoinitiator comprises at least one of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; And / or, the organic solvents used to dissolve polyphenolic compounds with N-(hydroxymethyl)acrylamide include at least one of anhydrous ethanol, isopropanol and n-butanol; And / or, the organic solvents used to dissolve polyphenolic acrylamide monomers with mercapto-containing silane coupling agents include at least one of anhydrous ethanol, isopropanol, and n-butanol; And / or, the mixed solvent is a mixture of anhydrous ethanol and water.

3. The method for preparing polyphenol-functionalized graphene oxide as described in claim 1, characterized in that, The molar ratio of the polyphenol compound to the acidic catalyst is 1:0.5~2.5; And / or, the mass of the photoinitiator is 0.5 to 5% of the total mass of the polyphenolic acrylamide monomer and the mercapto-containing silane coupling agent.

4. The method for preparing polyphenol-functionalized graphene oxide as described in claim 1, characterized in that, The Friedel-Crafts alkylation reaction was carried out at a temperature of 30-40°C for a time of 48-96 hours. And / or, the time for the click reaction of the mercapto-alkene is 4-8 hours; And / or, the heating reaction is carried out at a temperature of 60-80°C for a time of 10-14 hours.

5. Polyphenol-functionalized graphene oxide prepared by a method according to any one of claims 1 to 4.

6. The application of the polyphenol-functionalized graphene oxide as described in claim 5 in the preparation of photocurable composite materials.

7. A photocured composite material, characterized by, The raw materials include a photocurable resin, the polyphenol-functionalized graphene oxide as described in claim 5, and a photoinitiator; The mass of the polyphenol-functionalized graphene oxide is 0.025~0.5% of the mass of the photocurable resin; The mass of the photoinitiator is 0.5 to 5% of the total mass of the photocurable resin and the polyphenol-functionalized graphene oxide.

8. A method of making a photocured composite material as claimed in claim 7, characterized in that, Includes the following steps: The photocurable composite material is obtained by mixing a photocurable resin, polyphenol-functionalized graphene oxide, and a photoinitiator.

9. The application of the polyphenol-functionalized graphene oxide as described in claim 5 or the photocurable composite material as described in claim 7 in the preparation of materials with damage self-warning function.

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