A low-migration, oxygen-resistant photoinitiator, its preparation method and application

Abstract

This invention relates to the field of photopolymerization materials technology, and more particularly to a low-migration, oxygen-resistant photoinitiator, its preparation method, and applications, applicable to environmentally friendly coatings, 3D printing resins, and biomedical adhesives. The nano-photoinitiator of this invention is prepared from a trivalent iron salt compound and an organic ligand containing a carboxylic acid group; it generates initiating free radicals under ultraviolet and / or visible light irradiation, which are used to initiate the free radical polymerization reaction of unsaturated monomers. The system of this invention can still achieve rapid and complete curing in an air environment, significantly reducing or avoiding the oxygen inhibition effect commonly found in traditional free radical photocuring, and exhibits high stability; simultaneously, it has advantages such as wide availability of raw materials, low cost, easy aqueous phase conversion, and reduced potential irritation and migration risks, thus improving the system's biocompatibility and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of photopolymer materials technology, and in particular to a low-migration, oxygen-resistant, polymerization-inhibiting nano-photoinitiator, its preparation method, and its applications, applicable to fields such as environmentally friendly coatings, 3D printing resins, and biomedical adhesives. Background Technology

[0002] Photopolymerization is a rapid curing method that utilizes photoinitiators to initiate free radical or cationic polymerization under ultraviolet or visible light irradiation. It is widely used in coatings, inks, 3D printing, and biomedical materials. Current photopolymerization systems primarily rely on organic photoinitiators, such as benzophenone, thioxanthone, and iodonium salts. However, these traditional photoinitiators suffer from the following main problems: (1) Environmental and health risks: Some organic photoinitiators have potential toxicity, may cause skin allergies, and have extremely high migration rates. They release volatile organic compounds (VOCs) during the curing process, which does not meet environmental protection requirements.

[0003] (2) Oxygen inhibition effect: Most free radical photocuring systems have oxygen inhibition problems in the air environment. Oxygen will react with free radicals, causing free radicals to be quenched or generating peroxide free radicals with lower activity (as shown in the following formula), resulting in a decrease in polymerization rate and ultimately limited curing depth.

[0004] ; (3) Limited spectral response: Some traditional photoinitiators mainly absorb ultraviolet light (UV) and have poor adaptability to visible light curing.

[0005] (4) Low initiation efficiency in aqueous phase: Traditional photoinitiators are mainly oil-soluble initiators, which are difficult to dissolve or disperse in water, and the initiation rate in aqueous phase is low.

[0006] In recent years, to address the shortcomings of traditional organic photoinitiators in terms of spectral response range and environmental friendliness, some technologies have attempted to introduce natural products as photosensitive components and synergistically construct photoinitiation systems with organic initiating salts. For example, Chinese patent application CN118126214A, "A method for UV-LED curing using a capsanthin / iodonium salt-based photoinitiating system," discloses a photoinitiating system that combines capsanthin and iodonium salts for UV-LED curing. This system broadens the absorption capacity of long-wavelength light through natural pigments and, to some extent, improves the curing effect of free radical photopolymerization systems in air. However, this type of technology still relies on the synergistic generation of free radicals by organic photosensitizers and organic initiating salts (iodonium salts) under light irradiation. Its curing mechanism is essentially still a free radical photopolymerization system, exhibiting strong dependence on multi-component formulations and specific co-initiators. The system composition is relatively complex, and the curing efficiency and stability are still affected by factors such as oxygen concentration and mixing conditions. Therefore, it is difficult to achieve a stable, efficient, and simplified photocuring process in an aerobic environment from the perspective of photochemical reaction mechanisms. Therefore, it is still necessary to explore novel photocuring mechanisms that differ from traditional organic free radical initiation pathways in order to achieve photocuring systems that are truly suitable for aerobic conditions.

[0007] To address the issue of traditional photoinitiators primarily responding to ultraviolet light and exhibiting low utilization efficiency in the visible light region, existing technologies have explored expanding the spectral response range by introducing visible light sensitizing structures. For instance, Chinese patent CN103249713B, "Compounds Applicable to Photopolymerization Initiators, Photopolymerization Initiators, and Photocurable Resin Compositions," discloses a photopolymerization initiator system that combines dimethylaminobenzoic acid-based photoinitiators with hydroxythioxanthone-based visible light sensitizing compounds. This system enables the photocurable system to possess a certain photoinitiation capability in the visible light region, thereby expanding the light response wavelength range. However, this type of technical solution still relies on organic photoinitiators and photosensitizers generating free radicals under light conditions to initiate the polymerization reaction. The curing process essentially still belongs to the traditional free radical photopolymerization mechanism, and it is still inevitably affected by oxygen inhibition in the air environment. Furthermore, the use of organic photoinitiators and sensitizers still has limitations in terms of environmental friendliness and biosafety, making it difficult to simultaneously meet the application requirements of low toxicity, low volatility, and efficient curing under aerobic conditions. Therefore, developing a novel nano-photoinitiator that can overcome the limitations of traditional organic free radical photoinitiation mechanisms and achieve efficient photocuring under aerobic conditions still has important research and application value.

[0008] In summary, there is an urgent need to develop a photoinitiator with low migration, environmental friendliness, high biocompatibility, and broad spectral response suitable for coatings, inks, 3D printing, biomedical materials, and other fields. Furthermore, it is essential to construct matching preparation methods and application systems to overcome the problems of traditional photoinitiators, thereby promoting the development of photocuring technology in the directions of environmental protection, high efficiency, and high responsiveness. Summary of the Invention

[0009] The present invention aims to provide a low-migration, oxygen-resistant photoinitiator, its preparation method and application, to solve the problems of environmental and health risks, oxygen inhibition effect, limited spectral response and low initiation efficiency in aqueous phase of traditional photoinitiators in the prior art. Compared with traditional organic photoinitiator systems, the nano-photoinitiator system of this invention can consume dissolved oxygen in situ during photoinitiation / curing, thus achieving rapid and complete curing even in an air environment. This significantly reduces or avoids the oxygen inhibition effect commonly found in traditional free radical photocuring (such as surface stickiness, insufficient curing depth, reduced conversion rate, and high migration rate). Moreover, due to the high specific surface area and abundant surface carboxyl coordination sites of the nanoparticle structure, ferric ions are preferentially distributed on the nanoparticle surface and its interface region, forming a local enrichment effect. This improves the effective utilization rate of iron ions and promotes the generation rate of free radicals. At the same time, iron ions are fixed in the nanoparticle structure through carboxyl coordination, which can reduce the migration of iron ions to a certain extent. Furthermore, this invention uses commercially available ferric salt compounds and bio-based / water-soluble carboxylic acid ligands to construct a photoinitiation complex system nano-photoinitiator, which has advantages such as wide availability of raw materials, low cost, easy aqueous phase conversion, and reduced potential irritation and migration risks. This can improve the biocompatibility and environmental friendliness of the system, which is in line with the development trend of green chemistry and sustainable materials.

[0010] The technical solution of the present invention is as follows: A low-migration, oxygen-resistant photoinitiator is prepared from a trivalent iron salt compound and an organic ligand containing a carboxylic acid group. The nano-photoinitiator generates initiating free radicals under ultraviolet and / or visible light irradiation.

[0011] Preferably, the low-migration, antioxidant-resistant photoinitiator comprises a ferric salt compound and an organic ligand containing a carboxylic acid group; The trivalent iron salt compound and the organic ligand containing a carboxylic acid group are combined in a predetermined ratio to form a nano-photoinitiator; The nano-photoinitiator can generate initiating free radicals under ultraviolet and / or visible light irradiation, which are used to initiate the free radical polymerization reaction of unsaturated monomers.

[0012] The "nanophotoinitiator" mentioned in this invention refers to a photocurable system that can still undergo effective photoinitiation polymerization reaction in a normal air environment without deoxygenation treatment. Its nanostructure not only helps to improve initiation efficiency, but also reduces the migration rate of metal ions.

[0013] Unlike traditional photocuring systems where oxygen quenches free radicals, the active intermediate formed in the nano-photoinitiator of this invention can react with oxygen under light irradiation to generate superoxide radicals, hydroxyl radicals, or other reactive oxygen species with initiation capabilities, thereby avoiding or weakening the oxygen inhibition effect.

[0014] Preferably, the nano-photoinitiator comprises one or more ferric salt compounds that are complexed with an organic ligand containing a carboxylic acid group to form a stable photoinitiating complex, thereby replacing traditional organic photoinitiators.

[0015] The organic ligand compound containing a carboxylic acid group has the following effects: (1) Organic ligands containing carboxylic acid groups and Fe³ + Complexation forms stable photoinitiating complexes, which can improve the effective absorption of the system in the ultraviolet / visible region; (2) It can promote Fe³ + Under light conditions, photochemical transformation occurs and the reaction cycle is participated in, thereby improving the efficiency of free radical generation during the initiation process; (3) Reduce insufficient surface curing caused by oxygen inhibition by coupling in-situ oxygen consumption with free radical chain reaction; (4) Improve the stability and operability of the formulation in aqueous phase or water-containing system.

[0016] In this invention, Fe³ + It can form photoresponsive complexes with organic ligands containing carboxylic acid groups. When excited by light, it promotes the Fe(III) / Fe(II) cycle and the generation of active species, thereby initiating the free radical polymerization reaction of polymerizable monomers / oligomers such as (meth)acrylates. It achieves efficient curing under air conditions through the combined effect of oxygen consumption and chain growth, which significantly weakens or avoids the oxygen inhibition effect (such as surface stickiness, insufficient curing depth, reduced conversion rate, and high migration rate) that is common in traditional free radical photocuring.

[0017] Furthermore, the mass ratio of the trivalent iron salt compound to the organic ligand containing a carboxylic acid group is 1:(0.5-5); the organic ligand containing a carboxylic acid group is a nanomaterial containing a carboxylic acid group.

[0018] Furthermore, the mass ratio of the trivalent iron salt compound to the organic ligand containing a carboxylic acid group is 1:(1-4).

[0019] Within the above range, complexation stability, photoresponsiveness, and curing efficiency can be balanced.

[0020] Furthermore, the organic ligand containing a carboxylic acid group includes modified carboxylic acid ligand nanomaterials or alginate nanoparticles SA-NPs.

[0021] Furthermore, the preparation method of the modified carboxylic acid ligand nanomaterial is as follows: First, 15-25 mL of natural polymer nanomaterials with a mass fraction of 0.1 wt%-1.5 wt% and 0.8-1.0 mL of sodium citrate aqueous solution with a concentration of about 0.9-1.2 mol / L are mixed and stirred at 30-40℃ while an inert gas is introduced to remove oxygen from the system. Then, 0.01-0.07 g of cerium ammonium nitrate and 0.1-1.5 g of acrylic acid are added sequentially, and the mixture is reacted under magnetic stirring for 1.5-2.5 h to obtain modified carboxylic acid ligand nanomaterials.

[0022] Furthermore, the natural polymer nanomaterials are cellulose nanocrystals (CNC), cellulose nanofibers (CNF), and starch nanocrystals (SNC).

[0023] Furthermore, the grafting rate of the prepared modified carboxylic acid ligand nanomaterial is 20-250%.

[0024] In the preparation method of the modified carboxylic acid ligand nanomaterial of the present invention, the grafting rate of the material will vary when different amounts of monomer acrylic acid (AA) are added. For example, when the mass ratio of natural polymer nanomaterial to monomer acrylic acid is 1:1, the grafting rate is 23.3%; when the mass ratio is 1:3, the grafting rate is 56.5%; when the mass ratio is 1:5, the grafting rate is 185.5%; and when the mass ratio is 1:6, the grafting rate is 222.5%.

[0025] Furthermore, the trivalent iron salt compounds include, but are not limited to, FeCl3, Fe(NO3)3, Fe2(SO4)3, and NH4Fe(SO4)2.

[0026] Organic ligands containing carboxylic acid groups mainly act as ligands for iron ions in the nano-photoinitiator of this invention. By forming a coordination complex system with iron ions, they promote the transfer of photogenerated electrons and the generation of free radicals, and cause iron ions to accumulate at a high concentration around the nanomaterial, thereby accelerating the photoinitiation reaction and reducing the migration rate of iron ions.

[0027] Generally, compounds containing at least one carboxyl group and capable of forming effective coordination with iron ions can improve the photoinitiation reaction rate to some extent. However, different carboxylic acid ligands (α-aliphatic carboxylic acid ligands, strongly electron-withdrawing carboxylic acids, weaker common aliphatic carboxylic acids, and sterically hindered aromatic carboxylic acids) may have different degrees of promotion on the photoinitiation reaction rate and curing efficiency due to differences in their molecular structure, acidity, number of carboxyl groups, and coordination ability with iron ions.

[0028] Generally speaking, ligands with more open molecular structures, less steric hindrance, or containing multiple carboxyl groups are more likely to form stable coordination complexes with iron ions and have visible light responsiveness, thus exhibiting higher initiation efficiency under light conditions; while carboxylic acid ligands with stronger structural rigidity or greater steric hindrance may have a relatively weaker promoting effect, but can still endow the system with a certain photoinitiation activity.

[0029] This invention does not limit the specific structural type of carboxylic acid ligands. The above differences only reflect the performance of different ligands under specific implementation conditions, and do not affect their applicability as a component of an aerobic photocuring photoinitiator system.

[0030] Moreover, compounds containing at least one carboxyl group that can form effective coordination with ferric ions can generally improve the photoinitiation reaction rate to some extent. This is because the carboxyl group forms a coordination complex system with the ferric ion, which is conducive to the generation of free radicals under light conditions. However, the inventors found during their research that in complex systems constructed using only small molecule carboxylic acids or common carboxyl-containing polymers, ferric ions still tend to migrate out of the system, especially in aqueous or humid environments, thus affecting the stability and long-term performance of the photoinitiation system.

[0031] Further research by the inventors revealed that simply increasing the carboxyl group content or changing the type of carboxylic acid, while enhancing the coordination of iron ions, still failed to effectively reduce the migration rate of iron ions. The key lies in providing a high density of carboxyl group coordination sites while introducing a nanoscale spatial confinement structure, enabling iron ions to be stably anchored at the nanostructure interface through multi-point coordination.

[0032] Based on this, the inventors discovered that when carboxyl-containing materials exist at the nanoscale, whether by modifying natural polymer nanomaterials with acrylic acid grafting to increase the carboxyl density, or by using materials that are rich in carboxyl groups and can be prepared in a nanoscale state (such as alginate nanoparticles), high-density coordination sites can be formed at the nanoscale interface, causing ferric ions to be locally enriched at the interface on the surface of the nanoparticles and forming a multi-point coordination and fixation structure, thereby significantly reducing the migration rate of iron ions while maintaining or improving the photoinitiation efficiency.

[0033] Therefore, the core of this invention is not limited to a specific modification method, but rather to construct a multi-point coordination structure system rich in carboxyl groups and with nano-fixation, so as to achieve a synergistic effect of low migration and efficient photoinitiation.

[0034] Compared with commercially available photoinitiators, the nano-photoinitiator of the present invention still shows significant advantages in terms of initiation speed and antioxidant inhibition ability, while its preparation method is simple and suitable for practical applications.

[0035] Secondly, the present invention also provides a method for preparing the low-migration, antioxidant-resistant photoinitiator as described above. The low-migration, antioxidant-resistant photoinitiator is prepared by mixing a trivalent iron salt compound with an organic ligand containing a carboxylic acid group in a solvent in a predetermined ratio to form a photoinitiator.

[0036] Furthermore, the present invention also provides the application of the low-migration, oxygen-resistant, polymerization-inhibiting nano-photoinitiator as described above, which is used to initiate free radical polymerization or photocuring reactions of monomers or polymerizable components containing unsaturated bonds.

[0037] Furthermore, the present invention also provides a photocuring or free radical polymerization method, comprising the following steps: (1) The above-mentioned low-migration, antioxidant photoinitiator is added to a monomer or polymerizable component containing unsaturated bonds to form a reaction system; (2) Irradiate the reaction system obtained in step (1) with ultraviolet light and / or visible light to generate initiating free radicals in the low migration and antioxidant photoinitiator, thereby initiating free radical polymerization or curing of the monomer or polymerizable component.

[0038] Preferably, the present invention also provides a method for preparing the above-mentioned low-migration, antioxidant-resistant nanophotoinitiator, comprising the following steps: Step 1: Preparation of aqueous solution of ferric salt compound The ferric salt compound was dissolved in deionized water to obtain an aqueous solution of the ferric salt compound with a mass fraction of 1 wt%-30 wt%.

[0039] The dissolution process can be carried out using magnetic or mechanical stirring. If necessary, it can be carried out under light-protected conditions to reduce side reactions caused by ambient light and improve solution stability.

[0040] Step 2: Complexation with carboxylic acid ligands to obtain nano-photoinitiators. In the aqueous solution of the ferric salt compound obtained in step 1, an organic ligand containing a carboxylic acid group is added at a mass ratio of 1:(0.5-5) of the ferric salt compound to the organic ligand containing a carboxylic acid group; the mixture is stirred continuously to allow it to fully complex, thereby obtaining a nano-photoinitiator.

[0041] More preferably, the stirring time is 5-60 min, more preferably 10-30 min; the stirring temperature is 15-35 ℃.

[0042] For organic ligands containing carboxylic acid groups, it is preferable to first dissolve or disperse them in a small amount of water, and then slowly add them to the iron salt solution to obtain a more uniform and stable complexation system. If necessary, the appearance and stability can be improved by increasing the shear rate, extending the stirring time, or filtering to remove insoluble matter.

[0043] This invention is based on a nano-photoinitiator—a coordination complex system (iron-carboxylic acid complex) formed by trivalent iron ions and carboxylic acid ligands. Under ultraviolet and / or visible light irradiation, the iron-carboxylic acid complex undergoes photochemical processes such as charge transfer from the ligand to the metal, generating free radical active species in situ. In an air environment, these free radical active species react synergistically with dissolved oxygen in the system during initiation and chain growth, continuously consuming dissolved oxygen and maintaining a stable free radical flux, thereby effectively weakening or avoiding the polymerization inhibition effect caused by oxygen in traditional free radical photocuring processes. Moreover, this nano-photoinitiator not only has visible light responsiveness but also good water dispersion stability, facilitating practical applications.

[0044] Therefore, the present invention can achieve rapid and efficient light curing under air conditions, significantly improving problems such as surface stickiness, insufficient curing depth and reduced conversion rate.

[0045] Compared with traditional photocuring systems, the present invention has the following advantages: (1) Overcoming oxygen inhibition effect: The nano-photoinitiator can achieve efficient photocuring in air without the need for inert gas protection. Its mechanism is illustrated below: ; After carboxylic acids form complexes with ferric ions, a charge transfer reaction occurs from ligand to metal under light irradiation. This causes the carboxylate ion to lose electrons while the ferric ion gains electrons, generating carboxyl radicals. These carboxyl radicals attack oxygen in the system, forming superoxide radicals. Subsequently, the superoxide radicals generate hydroxyl radicals under proton action. These radicals can effectively initiate the free radical polymerization of unsaturated monomers. Furthermore, due to the high specific surface area and abundant surface carboxyl coordination sites of nanoparticles, ferric ions can be anchored to the nanoparticle surface through coordination, forming localized interfacial enrichment. This increases the effective concentration of iron ions and the efficiency of free radical generation during photoinitiation. Simultaneously, the iron ions are fixed by the nanoparticle structure, reducing their migration during use. Ultimately, this allows the nano-photoinitiator to generate a higher free radical concentration in a shorter time, maintaining a high free radical flux under air conditions. This enables rapid, heterogeneous photocuring, significantly reducing or avoiding the oxygen inhibition effect of traditional free radical photocuring.

[0046] (2) Green and environmentally friendly: The nano photoinitiator of the present invention does not contain traditional organic photoinitiators such as benzene or iodonium salts, thus avoiding the release of volatile organic compounds (VOCs), reducing the risk of environmental pollution, and the raw materials are widely available, low in cost, and easy to disperse in aqueous phase, thus improving environmental friendliness.

[0047] (3) Biocompatibility: The metal iron ions used in the nano photoinitiator of this invention have low toxicity, good stability of the ligand and nano photoinitiator system, and low migration rate of metal ions. Therefore, it can be used in biomedical materials, such as dental repair resins, wound dressings and other biomedical adhesives, and has good safety and biocompatibility.

[0048] (4) Broad spectrum response: The nano photoinitiator of the present invention—metal ion-carboxylic acid complex has strong light absorption capacity and can be effectively cured under ultraviolet and visible light (especially blue light) conditions, which expands the wavelength range of photoinitiation and enhances the applicability and flexibility of the photocuring system.

[0049] (5) Simple operation and wide application: The preparation method of the present invention is simple and easy to use in aqueous system, which can reduce potential irritation and migration risk. It is suitable for environmentally friendly coatings, 3D printing resins, light-curing adhesives and other industrial and biomedical photopolymer materials, and is easy to scale up. Attached Figure Description

[0050] Figure 1 Fe³ nanophotoinitiator of Example 3 + @SNC-PAA triggering hydroxyethyl methacrylate under blue light; Figure 2 For comparative examples 2, 5-8, the photoinitiator is α-ketoglutaric acid, Fe³⁺ + Fe³ + @Oxalic acid, Fe³ + @Polyacrylic acid and Fe³ + @Conversion rate of benzoic acid initiating the polymerization of hydroxyethyl methacrylate under the same light conditions; Figure 3 Fe³ nanophotoinitiators from Examples 1-4 + @SNC-PAA、Fe³ + @SA-NPs、Fe³ + @CNF-PAA、Fe³ + Conversion rate of hydroxyethyl methacrylate polymerization initiated by @CNC-PAA under the same light conditions; Figure 4 The conversion rate of hydroxyethyl methacrylate polymerization initiated by nano-photoinitiators with different grafting ratios in Examples 5-8 under the same light irradiation conditions is shown in the graph. Figure 5 Nanophotoinitiators Fe³ in Examples 1-4 + @SNC-PAA、Fe³ + @SA-NPs、Fe³ + @CNF-PAA、Fe³ + UV-Vis absorption spectrum of @CNC-PAA; Figure 6 Fe³ nanophotoinitiator of Example 1 + Electron paramagnetic resonance (EPR) spectrum of @CNC-PAA under blue light irradiation; Figure 7 Comparative Example 3: Before and after the removal of dissolved oxygen in the system, the appearance of the nano-photoinitiator after reaction under the same light conditions is compared. Figure 8 These are comparative photos of the appearance of the nano-photoinitiators of Examples 1 and 2 before and after being dispersed in water and left to stand at room temperature for 30 days. Before taking the photos, the nano-photoinitiator of Example 1 was placed on the left and the nano-photoinitiator of Example 2 was placed on the right. Figure 9 Fe³ nanophotoinitiator of Example 1 + Mobility plots of Irgacure-2959, α-ketoglutarate, and LAP in @CNC-PAA and comparative examples 1, 2, and 4; Figure 10 The image shows a physical sample of the nano-photoinitiator with a grafting rate of 300% obtained in Comparative Example 9. Detailed Implementation

[0051] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0052] Unless otherwise specified, all reagents and equipment used in the following examples were purchased commercially. Purchase information for some of the raw materials is as follows: Alginate nanoparticles: The preparation method refers to the research progress of "Alginate nanocarrier delivery of lipophilic active substances and its application" published by Chen Shan in "Food Science" in 2024.

[0053] Cellulose nanocrystals: Purchased from Taobao store "Keming Naxian"; Product name: Carboxylated cellulose nanocrystals; Length: 150-350nm, Diameter: 3-20nm; Crystallinity: >90%; Surface carboxyl content: 0.5mmol / g.

[0054] Cellulose nanofibers: Purchased from Taobao store "Keming Nanofibers"; Product name: Carboxylated cellulose nanofibers; Length > 1 μm, diameter 3-10 nm; Aspect ratio > 500; Surface carboxyl content: 1.2 mmol / g.

[0055] Starch nanocrystals: The preparation method refers to "Rapid preparation of starch nanocrystals by the mixed acid of sulfuric acid and hydrochloric acid" published by Yun Chen in the "International Journal of Biological Macromolecules" in 2023.

[0056] 2-Hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone (also known as: photoinitiator 2959, Irgacure-2959): purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0057] α-Ketoglutarate: Purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0058] Lithium phenyl (2,4,6-trimethylbenzoyl) phosphate (LAP): purchased from DeepContent Biotechnology Co., Ltd.

[0059] This invention provides a method for preparing a low-migration, antioxidant-resistant nano-photoinitiator, and a method for initiating the preparation of monomers / polymerizable components using the nano-photoinitiator as an initiator, comprising the following steps: Step (1) Raw material preparation Organic ligands containing carboxylic acid groups: The organic ligand containing carboxylic acid groups is a nanomaterial containing carboxylic acid groups, including natural polymer nanomaterials modified by acrylic acid grafting, and materials that are rich in carboxyl groups and can be prepared in a nanoscale state (such as alginate nanoparticles).

[0060] The natural polymer nanomaterials are cellulose nanocrystals, cellulose nanofibers, and starch nanocrystals.

[0061] Organic ligands containing carboxylic acid groups act as cooperating ligands for interaction with Fe³⁺. + Complexation modulates photoresponse and redox cycle efficiency, reduces iron ion migration rate, and increases curing reaction rate.

[0062] Ferrous salt compounds: The trivalent iron salt compounds include, but are not limited to: FeCl3, Fe(NO3)3, Fe2(SO4)3, and NH4Fe(SO4)2.

[0063] The mass ratio of the trivalent iron salt compound to the nanomaterial containing carboxylic acid groups is 1:(0.5-5) to ensure sufficient complexation and obtain a stable photoactive complex.

[0064] Step (2) Preparation of nano-photoinitiators First, 15-25 mL of 0.1 wt%-1.5 wt% natural polymer nanomaterials and 0.8-1.0 mL of 0.9-1.2 mol / L sodium citrate aqueous solution were added to a 100 mL three-necked flask. The mixture was stirred at 30-40 °C and nitrogen gas was purged for 15 min to remove oxygen from the system. Subsequently, 0.01-0.07 g of cerium ammonium nitrate (CAN) and 0.1-1.5 g of acrylic acid (AA) were added sequentially, and the mixture was reacted under magnetic stirring for 1.5-2.5 h to obtain a yellow precipitate of modified natural polymer nanomaterial particles grafted with PAA.

[0065] The nanomaterial containing carboxylic acid groups and the ferric salt compound were sequentially added to a reaction vessel or beaker equipped with a stirrer, and stirred at room temperature for 5-10 minutes to allow the Fe³⁺ to form a ferric salt compound. + By fully coordinating and complexing with nanomaterials containing carboxylic acid groups, nanophotoinitiators are obtained.

[0066] It is preferable to operate under conditions of light protection or low light to improve storage stability and repeatability.

[0067] Step (3) Mixing and homogenizing The nano-photoinitiator obtained in step (2) is added to the monomer / polymerizable component (e.g., hydroxyethyl methacrylate, acrylic acid, methacrylic acid, acrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, polyethylene glycol acrylate, N-hydroxymethylacrylamide, methyl acrylate, butyl acrylate, styrene, methylstyrene, p-methylstyrene, p-chlorostyrene, diethylbenzene), and after stirring and premixing, it is ultrasonically dispersed for 10-20 min (preferably about 20 min) to uniformly disperse the nano-photoinitiator in the monomer, thereby obtaining the oxygen-based photocuring reaction system to be cured.

[0068] The monomers listed in this invention are only used to illustrate the initiation ability of the nano-photoinitiator and are not intended to limit the monomers / polymerizable components that are initiated. The nano-photoinitiator can effectively initiate the free radical polymerization reaction of most unsaturated monomers and polymerizable components, showing good universality and wide applicability.

[0069] Step (4) UV / Vis light-induced curing The ultraviolet light source is placed above the reaction system for irradiation and curing. Wavelength: 254-405 nm, preferably 365 nm (405 nm can also be selected depending on the ligand type and light source conditions). Power: 50-200 W, preferably 100-150 W; Distance: 5-10 cm between the light source and the surface of the reaction system; Irradiation time: 10-30 min.

[0070] Under the above conditions, the nano-photoinitiator—Fe³ + - Carboxylic acid complexes generate free radicals when excited by light, and the curing process continuously consumes oxygen, thus enabling rapid curing even in an air environment and significantly reducing adhesion and incomplete curing problems caused by surface oxygen inhibition, resulting in a cured product.

[0071] Example 1 Step (1): Preparation of aqueous solution of ferric salt compound Under light-protected conditions, 1.6 g of the ferric salt compound FeCl3 was added to deionized water and stirred for 10 min at a stirring temperature of 25 °C to obtain an aqueous solution of the ferric salt compound with a mass fraction of 5 wt%.

[0072] Step (2): Complexation with carboxylic acid ligands to obtain nano-photoinitiators. Preparation of modified carboxylic acid ligand nanomaterials: First, 20 mL of 1.5 wt% natural polymer nanomaterial cellulose nanocrystals (CNC) and 0.8 mL of 0.9 mol / L sodium citrate aqueous solution were added to a 100 mL three-necked flask. The mixture was stirred at 30 °C and nitrogen gas was purged for 15 min to remove oxygen from the system. Then, 0.01 g of cerium ammonium nitrate (CAN) and 0.6 g of acrylic acid (AA) were added sequentially, and the mixture was reacted for 1.5 h under magnetic stirring to obtain a yellow precipitate of modified natural polymer nanomaterial particles grafted with PAA, namely modified carboxylic acid ligand nanomaterials Fe³. + @CNC-PAA. The mass ratio of the natural polymer nanomaterial to acrylic acid is 1:6.

[0073] In the aqueous solution of the ferric salt compound obtained in step (1), modified carboxylic acid ligand nanomaterials are added at a mass ratio of 1:1 between the ferric salt compound and the organic ligand containing carboxylic acid groups; the mixture is stirred continuously to allow it to fully complex, thereby obtaining a nano-photoinitiator.

[0074] Step (3) Mixing and homogenizing The nano-photoinitiator obtained in step (2) is added to the monomer / polymerizable component hydroxyethyl methacrylate, stirred and premixed, and then ultrasonically dispersed for 10 min to uniformly disperse the nano-photoinitiator in the monomer, thus obtaining the oxygen photocuring reaction system to be cured.

[0075] Step (4) UV / Vis light-induced curing The ultraviolet light source is placed above the reaction system for irradiation and curing. Wavelength: 365 nm; Power: 100 W; Distance: 10 cm between the light source and the surface of the reaction system; Irradiation time: 10 min.

[0076] Under the above conditions, the nano-photoinitiator—Fe³ + - Carboxylic acid complexes generate free radicals when excited by light, and the curing process continuously consumes oxygen, thereby achieving rapid curing in an air environment and significantly reducing the adhesion and incomplete curing problems caused by surface oxygen inhibition, resulting in a cured product.

[0077] Example 2 Step (1): Preparation of aqueous solution of ferric salt compound Under light-protected conditions, 2.4 g of ferric salt compound Fe(NO3)3 was added to deionized water and stirred for 10 min at a temperature of 35 °C to obtain an aqueous solution of ferric salt compound with a mass fraction of 15 wt%.

[0078] Step (2): Complexation with carboxylic acid ligands to obtain nano-photoinitiators. Preparation of modified carboxylic acid ligand nanomaterials: First, 25 mL of 1.0 wt% natural polymer nanomaterial cellulose nanofibers (CNF) and 1.0 mL of 1.2 mol / L sodium citrate aqueous solution were added to a 100 mL three-necked flask. The mixture was stirred at 40 °C and nitrogen gas was purged for 15 min to remove oxygen from the system. Then, 0.07 g of cerium ammonium nitrate (CAN) and 1.5 g of acrylic acid (AA) were added sequentially, and the mixture was reacted under magnetic stirring for 2.5 h to obtain a yellow precipitate of modified natural polymer nanomaterial particles grafted with PAA, namely modified carboxylic acid ligand nanomaterials Fe³. + @CNF-PAA. The mass ratio of the natural polymer nanomaterial to acrylic acid is 1:6.

[0079] In the aqueous solution of the ferric salt compound obtained in step (1), the modified carboxylic acid ligand nanomaterial is added at a mass ratio of 1:2 between the ferric salt compound and the organic ligand containing the carboxylic acid group; the mixture is stirred continuously to allow it to fully complex, thereby obtaining a nano-photoinitiator.

[0080] Step (3) Mixing and homogenizing The nano-photoinitiator obtained in step (2) is added to the monomer / polymerizable component hydroxyethyl methacrylate, stirred and premixed, and then ultrasonically dispersed for 20 min to uniformly disperse the nano-photoinitiator in the monomer, thus obtaining the oxygen photocuring reaction system to be cured.

[0081] Step (4) UV / Vis light-induced curing The ultraviolet light source is placed above the reaction system for irradiation and curing. Wavelength: 365 nm; Power: 150 W; Distance: 10 cm between the light source and the surface of the reaction system; Irradiation time: 30 min.

[0082] Under the above conditions, the nano-photoinitiator—Fe³ + - Carboxylic acid complexes generate free radicals when excited by light, and the curing process continuously consumes oxygen, thereby achieving rapid curing in an air environment and significantly reducing the adhesion and incomplete curing problems caused by surface oxygen inhibition, resulting in a cured product.

[0083] Example 3 Step (1): Preparation of aqueous solution of ferric salt compound Under light-protected conditions, 2 g of ferric salt compound Fe2(SO4)3 was added to deionized water and stirred for 30 min. The stirring temperature was 35℃, resulting in an aqueous solution of ferric salt compound with a mass fraction of 20 wt%.

[0084] Step (2): Complexation with carboxylic acid ligands to obtain nano-photoinitiators. Preparation of modified carboxylic acid ligand nanomaterials: First, 20 mL of 1.0 wt% natural polymeric nanomaterial starch nanocrystals (SNC) and 1.0 mL of 1.0 mol / L sodium citrate aqueous solution were added to a 100 mL three-necked flask. The mixture was stirred at 35 °C and nitrogen gas was purged for 15 min to remove oxygen from the system. Subsequently, 0.04 g of cerium ammonium nitrate (CAN) and 1.2 g of acrylic acid (AA) were added sequentially, and the mixture was reacted under magnetic stirring for 2 h to obtain a yellow precipitate of modified natural polymeric nanomaterial particles grafted with PAA, namely modified carboxylic acid ligand nanomaterials Fe³. + @SNC-PAA. The mass ratio of the natural polymer nanomaterial to acrylic acid is 1:6.

[0085] In the aqueous solution of the ferric salt compound obtained in step (1), the modified carboxylic acid ligand nanomaterial is added at a mass ratio of 1:3 between the ferric salt compound and the organic ligand containing the carboxylic acid group; the mixture is stirred continuously to allow it to fully complex, thereby obtaining a nano-photoinitiator.

[0086] Step (3) Mixing and homogenizing The nano-photoinitiator obtained in step (2) is added to the monomer / polymerizable component hydroxyethyl methacrylate, stirred and premixed, and then ultrasonically dispersed for 20 min to uniformly disperse the nano-photoinitiator in the monomer, thus obtaining the oxygen photocuring reaction system to be cured.

[0087] Step (4) UV / Vis light-induced curing The ultraviolet light source is placed above the reaction system for irradiation and curing. Wavelength: 405 nm; Power: 100 W; Distance: 10 cm between the light source and the surface of the reaction system; Irradiation time: 30 min.

[0088] Under the above conditions, the nano-photoinitiator—Fe³ + - Carboxylic acid complexes generate free radicals when excited by light, and the curing process continuously consumes oxygen, thereby achieving rapid curing in an air environment and significantly reducing the adhesion and incomplete curing problems caused by surface oxygen inhibition, resulting in a cured product.

[0089] like Figure 1 The nano-photoinitiator Fe³ shown in Example 3 + A photograph of @SNC-PAA initiating hydroxyethyl methacrylate under blue light shows that the prepared nano-photoinitiator has a good initiation effect on hydroxyethyl methacrylate.

[0090] Example 4 Step (1): Preparation of aqueous solution of ferric salt compound Under light-protected conditions, 2.66 g of NH4Fe(SO4)2, a ferric salt compound, was added to deionized water and stirred for 10 min at a stirring temperature of 25 °C to obtain an aqueous solution of the ferric salt compound with a mass fraction of 10 wt%.

[0091] Step (2): Complexation with carboxylic acid ligands to obtain nano-photoinitiators. In the aqueous solution of the ferric salt compound obtained in step (1), sodium alginate nanoparticles SA-NPs were added at a mass ratio of 1:5 between the ferric salt compound and the organic ligand containing a carboxylic acid group; the mixture was stirred continuously to allow it to fully complex, thus obtaining the nano-photoinitiator Fe³. + @SA-NPs.

[0092] Step (3) Mixing and homogenizing The nano-photoinitiator obtained in step (2) is added to the monomer / polymerizable component hydroxyethyl methacrylate, stirred and premixed, and then ultrasonically dispersed for 20 min to uniformly disperse the nano-photoinitiator in the monomer, thus obtaining the oxygen photocuring reaction system to be cured.

[0093] Step (4) UV / Vis light-induced curing The ultraviolet light source is placed above the reaction system for irradiation and curing. Wavelength: 405 nm; Power: 150 W; Distance: The distance between the light source and the surface of the reaction system - 10 cm; Irradiation time: 20 min.

[0094] Under the above conditions, the nano-photoinitiator—Fe³ + - Carboxylic acid complexes generate free radicals when excited by light, and the curing process continuously consumes oxygen, thereby achieving rapid curing in an air environment and significantly reducing the adhesion and incomplete curing problems caused by surface oxygen inhibition, resulting in a cured product.

[0095] Example 5 The difference between Example 5 and Example 1 is that in the preparation method of the modified carboxylic acid ligand nanomaterial, the mass ratio of the cellulose nanocrystals (CNC) to the monomer acrylate is 1:1, and the other preparation steps are similar to those in Example 1. The grafting rate of the obtained modified carboxylic acid ligand nanomaterial is 23.3%.

[0096] Example 6 The difference between Example 6 and Example 1 is that in the preparation method of the modified carboxylic acid ligand nanomaterial, the mass ratio of the cellulose nanocrystals (CNC) to the monomer acrylate is 1:3, and the other preparation steps are similar to those in Example 1. The grafting rate of the obtained modified carboxylic acid ligand nanomaterial is 56.5%.

[0097] Example 7 The difference between Example 7 and Example 1 is that in the preparation method of the modified carboxylic acid ligand nanomaterial, the mass ratio of the cellulose nanocrystals (CNC) to the monomer acrylate is 1:5, and the other preparation steps are similar to those in Example 1. The grafting rate of the obtained modified carboxylic acid ligand nanomaterial is 185.5%.

[0098] Example 8 The difference between Example 8 and Example 1 is that in the preparation method of the modified carboxylic acid ligand nanomaterial, the mass ratio of the cellulose nanocrystals (CNC) to the monomeric acrylate is 1:6, and the other preparation steps are similar to those in Example 1. The grafting rate of the obtained modified carboxylic acid ligand nanomaterial is 222.5%.

[0099] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Irgacure-2959 was used as the initiator, while the other preparation steps were similar to those in Example 1.

[0100] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that α-ketoglutaric acid is used as the initiator, while the other preparation steps are similar to those in Example 1.

[0101] Comparative Example 3 Comparative Example 3 used the same raw material composition and reaction conditions as Example 3. The only difference was that an inert gas was introduced before the reaction was initiated to remove dissolved oxygen from the system. Other preparation steps were similar to those in Example 1.

[0102] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that phenyl-2,4,6-trimethylbenzoyl lithium phosphine sulfate (LAP) was used as the initiator, while the other preparation steps were similar to those in Example 1.

[0103] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the organic ligand containing the carboxylic acid group is oxalic acid, while the other preparation steps are similar to those in Example 1.

[0104] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that FeCl3, a trivalent iron salt compound, is used as the photoinitiator, while the other preparation steps are similar to those in Example 1.

[0105] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the organic ligand containing the carboxylic acid group is polyacrylic acid, while the other preparation steps are similar to those in Example 1.

[0106] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that the organic ligand containing the carboxylic acid group is benzoic acid, while the other preparation steps are similar to those in Example 1.

[0107] Comparative Example 9 The difference between Comparative Example 9 and Example 1 is that only step (1) preparation of the aqueous solution of the trivalent iron salt compound and step (2) preparation of the nano-photoinitiator were carried out. After adding iron ions in step (2), gel appeared. Therefore, no subsequent curing operation experiment was carried out.

[0108] In the preparation method of the modified carboxylic acid ligand nanomaterial, the mass ratio of the cellulose nanocrystals (CNC) to the monomeric acrylate is 1:10, and the preparation steps are similar to those in Example 1, wherein the grafting rate of the obtained modified carboxylic acid ligand nanomaterial is 300%.

[0109] Test case I. Real-time photocuring kinetics test (a) Comparison of different initiators 1. Test subjects: Examples 1-4 and Comparative Examples 2, 5-8 2. Experimental Methods: The initiation performance of different photoinitiation systems was characterized using a real-time photocuring kinetics test method (real-time infrared measurement of double bond conversion rate). Under the same light source conditions, the change in conversion rate of the monomer system over time during illumination was recorded to evaluate the initiation rate and curing efficiency of different photoinitiator systems.

[0110] 3. Test Results: like Figure 2 As shown, under the same light source conditions, the photoinitiators α-ketoglutaric acid and Fe³⁺ formed in Comparative Examples 2, 5, 7, and 8... + @Oxalic acid, Fe³ + @Polyacrylic acid and Fe³ + Benzoic acid showed a significantly higher initiation rate than the individual ferric salts in the six comparative groups. And as... Figure 3 As shown, the curing rate of the nano-photoinitiator system obtained in Examples 1-4 of the present invention is significantly higher than that of the comparative examples, which indicates that the nano-photoinitiator system has excellent photoinitiation efficiency.

[0111] Secondly, the experimental results show that the nano-photoinitiator formed by ferric salts with oxalic acid, polyacrylic acid, and benzoic acid can effectively initiate the polymerization reaction of unsaturated monomers under light irradiation. Its conversion rate gradually increases with irradiation time, and its overall initiation efficiency is significantly better than the comparative system using ferric salts alone. However, compared to other nano-carboxylic acid ligand systems used in the examples, its initiation rate and final conversion rate are significantly lower. Among these, benzoic acid, as an aromatic carboxylic acid ligand, although it can form a coordination complex system with ferric ions and endow the system with a certain visible light response capability, has a relatively weak promoting effect on the photochemical conversion of iron ions and the generation of free radicals due to the steric hindrance effect and electronic structure characteristics introduced by its aromatic ring structure. This results in an overall initiation efficiency lower than that of the nano-photoinitiators formed by ferric salts with oxalic acid and polyacrylic acid in the other comparative groups.

[0112] The above experimental results further verify the findings of this invention: compounds containing at least one carboxyl group and capable of forming effective coordination with iron ions can all improve the photoinitiation reaction rate to a certain extent; however, due to differences in structure and coordination ability, different carboxylic acid ligands exhibit varying degrees of promoting effect. This difference does not affect its feasibility as an aerobic photocuring photoinitiation system, but mainly manifests in differences in initiation efficiency and reaction rate. Moreover, when carboxyl-containing materials exist at the nanoscale, both methods—such as modifying natural polymer nanomaterials with acrylic acid grafting to increase carboxyl density, and using carboxylic acid ligand material systems that are rich in carboxyl groups and can be prepared in a nanoscale state—can significantly improve the initiation rate of the photoinitiator.

[0113] It should be noted that the above tests are only used to reflect the performance differences of different carboxylic acid ligands under specific implementation conditions, and are not intended to limit the types of carboxylic acid ligands used in this invention; nor are they limited to specific modification methods, but rather aim to construct a multi-point coordination structure system rich in carboxyl groups and with nano-fixation, achieving a synergistic effect of low migration and efficient photoinitiation. The technical solution of this invention does not depend on the specific structural type of carboxylic acid ligands. Any nano-carboxylic acid compound that can form a coordination complex with ferric ions and participate in the photochemical conversion process can be used as a component of the nano-photoinitiator of this invention.

[0114] (II) Comparison of different proportions 1. Test subjects: Examples 5-8, Comparative Example 9 2. Test method: The test method is the same as that used for the comparison with the different initiators mentioned above.

[0115] 3. Test Results: like Figure 4 and Figure 10 As shown, under the same conditions, the grafting rate of the modified carboxylic acid ligand nanomaterials has a significant impact on the curing behavior of the system. When the grafting rate is gradually increased from a low level to a certain range, the iron-carboxylic acid coordination is enhanced with the increase of carboxyl content, and the initiation rate of the system is significantly improved, exhibiting excellent photocuring kinetics. However, when the grafting rate is further increased to 300% (Comparative Example 9), the system rapidly gels after the addition of iron ions, and subsequent photocuring is impossible. This indicates that excessively high carboxyl content leads to over-coordination and cross-linking, inhibiting the initiation reaction and preventing subsequent photo-initiated polymerization. These results show that a higher carboxyl content is not necessarily more beneficial, but rather there is a reasonable controllable range. This invention limits the grafting rate of the modified carboxylic acid ligand nanomaterials to the range of 20-250%, ensuring effective coordination and local enrichment of iron ions while avoiding gelation problems caused by excessive cross-linking, thereby achieving synergistic optimization of low migration and high-efficiency photoinitiation performance.

[0116] II. Visible Light Absorption Test The trivalent iron salts of Examples 1-4 and their complex systems with organic ligands containing different carboxylic acid groups were characterized by ultraviolet-visible spectrophotometry.

[0117] like Figure 5 As shown, trivalent iron salts (Fe 3+ After coordinating with the carboxyl groups in cellulose nanocrystals (CNC), cellulose nanofibers (CNF), starch nanocrystals (SNC), and sodium alginate nanoparticles (SA-NPs), respectively, the iron-carboxylic acid complex system exhibits visible light response capability, providing spectroscopic evidence for its use as a photoinitiator under visible light conditions.

[0118] III. Test for the generation of free radicals from active substances Electron paramagnetic resonance (EPR) technology was used to study the nano-photoinitiator Fe³⁺ from Example 1. + The active species generated by the @CNC-PAA photoinitiation system under blue light irradiation were detected. During the test, the photoinitiation system was placed under blue light irradiation, and its EPR signal was acquired in real time.

[0119] like Figure 6 As shown, under blue light irradiation, Fe 3+ The @CNC-PAA system exhibits a significant EPR absorption signal in a magnetic field range of approximately 3350-3425 G, indicating the formation of hydroxyl radicals—a free radical reactive species with unpaired electrons—within the system. This result demonstrates the effectiveness of the Fe³ nanophotoinitiator in Example 1. + The @CNC-PAA system can effectively generate active free radicals under visible light irradiation, thus providing experimental evidence for its initiation of free radical polymerization reaction.

[0120] IV. Deoxidation and Curing Test In Example 3 of this invention, after mixing the nano-photoinitiator with hydroxyethyl methacrylate monomer, the system was not deoxygenated and the initiation reaction was carried out directly under air conditions.

[0121] As a comparative experiment, Comparative Example 3 used the same raw material composition and reaction conditions as Example 3, the only difference being that dissolved oxygen in the system was removed by introducing an inert gas before the reaction was initiated. Subsequently, Comparative Example 3 underwent the initiation reaction under the same light conditions, and the appearance of the systems before and after the reaction in Example 3 and Comparative Example 3 was recorded and compared.

[0122] like Figure 1 As shown, the test results of Example 3 indicate that, even without any deoxidation treatment and under direct exposure to air, the nano-photoinitiator can still achieve effective curing, and the system can undergo a significant polymerization reaction; while... Figure 7As shown, in the experiment of Comparative Example 3, the difference was only due to the deoxygenation treatment, without introducing other structural or component changes. No obvious changes were observed in the appearance of its initiation system before and after light exposure, and no visible increase in viscosity or gelation was observed. This proves that the presence of dissolved oxygen is beneficial for the nano-photoinitiator of the present invention to generate initiation activity under light exposure, thereby promoting the polymerization reaction of monomers.

[0123] V. Stability Testing The nano-photoinitiators of Examples 1 and 2 were sealed and stored at room temperature for 30 days. The appearance of the system was photographed before and after storage to evaluate the storage stability of the nano-photoinitiators in the aqueous dispersion system.

[0124] like Figure 8 As shown, after standing for 30 days, the appearance of the nano-photoinitiators in Examples 1 and 2 did not show significant changes compared to their initial state, and no obvious sedimentation, stratification, or aggregation was observed. These results indicate that the nano-photoinitiator has good storage stability, making it easy to store and use.

[0125] VI. Migration Rate Test 1. Test subjects: Example 1 and Comparative Examples 1, 2, and 4 2. Experimental method: Refer to the migration rate test method in "Type I Photoinitiator Based on Sustainable Carbon Dots" published by Ruiping Li in "Angewandte Chemie" in 2024.

[0126] 3. Test Results: In this invention, Fe³ + The CNC-PAA photoinitiator nano-photoinitiator was mixed and cured with hydroxyethyl methacrylate monomer, then stored in water at room temperature for 3 days. The migration rate of the photoinitiator was tested at different times. The results show that the migration rate of this initiation system is extremely low compared to other commercially available photoinitiators.

[0127] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A low-migration, oxygen-resistant photoinitiator, characterized in that, It is prepared from trivalent iron salt compounds and organic ligands containing carboxylic acid groups; The nano-photoinitiator generates initiating free radicals under ultraviolet and / or visible light irradiation.

2. The low-migration, oxygen-resistant photoinitiator as described in claim 1, characterized in that, The mass ratio of the trivalent iron salt compound to the organic ligand containing a carboxylic acid group is 1:(0.5-5); the organic ligand containing a carboxylic acid group is a nanomaterial containing a carboxylic acid group.

3. The low-migration, oxygen-resistant photoinitiator as described in claim 1, characterized in that, The organic ligands containing carboxylic acid groups include modified carboxylic acid ligand nanomaterials or alginate nanoparticles.

4. The low-migration, oxygen-resistant photoinitiator as described in claim 3, characterized in that, The preparation method of the modified carboxylic acid ligand nanomaterial is as follows: First, 15-25 mL of natural polymer nanomaterials with a mass fraction of 0.1 wt%-1.5 wt% and 0.8-1.0 mL of sodium citrate aqueous solution with a concentration of 0.9-1.2 mol / L are mixed and stirred at 30-40℃ while an inert gas is introduced to remove oxygen from the system. Then, 0.01-0.07 g of cerium ammonium nitrate and 0.1-1.5 g of acrylic acid are added sequentially, and the mixture is reacted under magnetic stirring for 1.5-2.5 h to obtain modified carboxylic acid ligand nanomaterials.

5. The low-migration, oxygen-resistant photoinitiator as described in claim 1, characterized in that, The natural polymer nanomaterials are cellulose nanocrystals, cellulose nanofibers, and starch nanocrystals.

6. The low-migration, oxygen-resistant photoinitiator as described in claim 4, characterized in that, The grafting rate of the modified carboxylic acid ligand nanomaterials obtained is 20-250%.

7. The low-migration, oxygen-resistant photoinitiator as described in claim 1, characterized in that, The trivalent iron salt compounds include, but are not limited to, FeCl3, Fe(NO3)3, Fe2(SO4)3, and NH4Fe(SO4)2.

8. The method for preparing the low-migration, antioxidant-resistant nanophotoinitiator according to any one of claims 1-7, characterized in that, The low-migration, antioxidant, and polymerization-inhibiting nano-photoinitiator is prepared by mixing a trivalent iron salt compound with an organic ligand containing a carboxylic acid group in a solvent in a predetermined ratio to form a nano-photoinitiator.

9. The application of the low-migration, oxygen-resistant photoinitiator as described in any one of claims 1-7, characterized in that, The low-migration, antioxidant-resistant nano-photoinitiator is used to initiate free radical polymerization or photocuring reactions of monomers or polymerizable components containing unsaturated bonds.

10. A photocuring or free radical polymerization method, characterized in that, Includes the following steps: (1) The low-migration, antioxidant-resistant nano-photoinitiator according to any one of claims 1-7 is added to a monomer or polymerizable component containing unsaturated bonds to form a reaction system; (2) Irradiate the reaction system obtained in step (1) with ultraviolet light and / or visible light to generate initiating free radicals in the low migration and antioxidant photoinitiator, thereby initiating free radical polymerization or curing of the monomer or polymerizable component.

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