Low-migration photoinitiator based on molecular fixation mechanism, uv curing composition and synthesis and application thereof

Abstract

This invention relates to a low-migration photoinitiator based on a molecular immobilization mechanism, a UV-curable composition, and their synthesis and application. The general structural formula is as follows: R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, cyano, C1-C20 alkyl, aryl, or substituted aryl; R has the following structural formula: R5, R6, R7, and R8 are independently selected from C1-C10 alkyl, hydroxylated alkyl, aryl, substituted aryl, benzyl, or substituted benzyl; n is an integer from 1 to 20; M is a hydrogen ion, an alkali metal ion, or an organic ammonium salt cation; X is a halogen. The low-migration photoinitiator of this invention maintains good photoinitiation performance while exhibiting higher gel content, lower swelling ratio, and superior thermal stability. Furthermore, the migration amount is reduced by approximately 82.6% to 87.0% compared to commercial photoinitiators, achieving synergistic optimization of photoinitiation performance and low-migration performance. It can be used in UV-curable coatings, inks or adhesive systems, optoelectronic device encapsulation, or biomedical and food contact materials.

Description

Technical Field

[0001] This invention belongs to the field of polymer compound technology, specifically relating to a low-migration photoinitiator based on a molecular fixation mechanism, its UV-curable composition, and its synthesis and application. Background Technology

[0002] Photopolymerization technology has been widely used in coatings, inks, adhesives, 3D printing, and optoelectronic device packaging due to its advantages such as fast curing speed, low energy consumption, environmental friendliness, and applicability to various substrates. In photopolymerization systems, photoinitiators are key components that generate free radicals or cations under ultraviolet or visible light irradiation, thereby initiating polymerization reactions of monomers or oligomers to form cross-linked network structures.

[0003] Currently, α-hydroxyketone photoinitiators (such as 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, trade name: Irgacure 2959) are widely used in high-end applications such as aqueous systems, biomedical materials, and flexible electronics due to their good photoinitiation efficiency, low toxicity, and good water solubility. However, these photoinitiators are inherently small molecules and remain non-covalent in the cured system, making them difficult to effectively immobilize in the polymer network, which may lead to migration during use.

[0004] Achieving effective fixation of photoinitiators in curing systems has become an important research direction in the field of photocuring. However, existing technologies generally have the following shortcomings: (1) the fixation method is mainly physical embedding or selective reaction, which makes it difficult to achieve effective fixation of inert substrates; (2) the photoinitiation function and molecular fixation function are usually separated, resulting in complex systems and low synergistic efficiency; (3) for general organic substrates lacking active functional groups, the existing fixation strategies have limited applicability; it is difficult to achieve a stable and universally applicable low migration effect while ensuring high photoinitiation efficiency. In recent years, diazacyclopropylene structures have attracted attention due to their ability to generate highly reactive carbene intermediates under light irradiation. However, existing diazacyclopropylene compounds are mainly used as independent photolabeling or crosslinking agents, lacking photoinitiation capabilities. Their application in UV curing systems remains limited, and a structural design system integrating photoinitiation and covalent fixation has not yet been formed.

[0005] Therefore, it is necessary to develop a novel photoinitiator that achieves a synergistic effect of photoinitiation and C–H insertion covalent fixation by introducing α-hydroxyketone photoinitiating units and diazacyclopropene structural units into the molecular structure. Furthermore, by combining molecular confinement design, the photoinitiator can be effectively fixed while ensuring photoinitiation performance and reducing its migration behavior. Summary of the Invention

[0006] The purpose of this invention is to provide a low-migration photoinitiator containing an α-hydroxy ketone-derived photoinitiating unit and a diazacyclopropene structural unit, a UV-curable composition, and its synthesis method and application, in order to solve the problem of easy migration of existing small molecule photoinitiators.

[0007] This invention provides a low-migration photoinitiator based on a molecular immobilization mechanism, namely a low-migration photoinitiator containing α-hydroxy ketone and diazacyclic propylene structural units, with the following general structural formula:

[0008] The low-migration photoinitiator molecule based on the molecular immobilization mechanism of the present invention comprises the following functional structures: (1) Two α-hydroxyketone-derived photoinitiating units, wherein the α-hydroxyketone-derived photoinitiating units are 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959)-derived structures, which are used to undergo photolysis under light conditions to generate free radicals to initiate the polymerization reaction of unsaturated monomers or oligomers; (2) Two diazacyclic propylene structural units, wherein the diazacyclic propylene structure is preferably an aryl-substituted diazacyclic propylene structure, i.e., the following segment in the general formula:

[0009] R1, R 2、 R3 and R4 are independently selected from hydrogen, fluorine, cyano, C1–C20 alkyl, aryl or substituted aryl, preferably all of them are H; Under light irradiation, a carbene intermediate can be generated and undergo an insertion reaction with the C–H bonds in the surrounding molecules, thereby achieving non-selective covalent fixation of the polymer network or matrix molecules; the preferred structure is a phenyl-substituted diazacyclopropene structure. (3) Ionic structural units, preferably structures containing quaternary ammonium salt cationic groups and sulfonate or carboxylate anionic groups, i.e., the following segments in the general structural formula:

[0010] Among them, R5, R 6、 R7 and R8 are independently selected from C1-C10 alkyl, hydroxylated alkyl, aryl, substituted aryl, benzyl, substituted benzyl, etc.; n is an integer from 1 to 20; M is a hydrogen ion, an alkali metal ion, or an organic ammonium salt cation, preferably Na. + X is a halogen, preferably Cl. - The ionic structural unit includes a quaternary ammonium cation group, a sulfonate or carboxylate anion group, and the corresponding external ion.

[0011] It can enhance the interaction between the photoinitiator and the curing system, thereby reducing its migration behavior in the curing system.

[0012] The low-migration photoinitiator molecule of the present invention is based on a multifunctional central skeleton, and α-hydroxy ketone-derived photoinitiating units, diazacyclopropene structural units and ionic structural units are synergistically introduced into the same molecule.

[0013] Specifically, representative compounds are: .

[0014] The low-migration photoinitiator of this invention, based on a molecular fixation mechanism, is grounded in a multifunctional central framework, synergistically incorporating α-hydroxyketone-derived photoinitiating units, diazacyclopropene structural units, and ionic structural units within the same molecule. The α-hydroxyketone-derived photoinitiating units generate free radicals under UV irradiation, initiating polymerization reactions in unsaturated systems. The diazacyclopropene structural units generate highly reactive intermediates under light irradiation and react with C–H bonds in the organic matrix, thereby enabling the photoinitiator to form a stable bond with the polymer network during curing. The ionic structural units enhance intermolecular interactions, improving the compatibility and retention capacity of the photoinitiator in the curing system, thus further reducing migration behavior.

[0015] The structural uniqueness of the low-migration photoinitiator based on the molecular immobilization mechanism of this invention is mainly reflected in the following aspects: (1) Integration of multifunctional structural units. This invention integrates an α-hydroxyketone-derived photoinitiator, a diazacyclopropene structural unit, and an ionic structural unit into the same molecular structure, achieving a unity of photoinitiation and low-migration functions. Specifically, the α-hydroxyketone-derived photoinitiator provides photoinitiation capability; the diazacyclopropene structural unit generates an active intermediate under illumination, achieving reactive fixation of the organic matrix; and the ionic structural unit enhances intermolecular interactions, thereby reducing migration behavior. (2) Molecular fixation mechanism based on C–H insertion reaction. Unlike existing low-migration strategies that rely on polymerizable groups or physical confinement, this invention introduces a diazacyclic propylene structural unit, enabling the photoinitiator to react with the C–H bonds in the organic matrix under light irradiation, thereby achieving molecular-level fixation of the photoinitiator. This fixation method does not depend on the presence of specific reactive groups in the matrix, is applicable to a variety of inert organic systems, and has wider applicability.

[0016] (3) Further regulation of migration behavior by ionic structure. This invention introduces ionic structural units into the molecule and utilizes their ionic interaction properties to improve the compatibility and retention capacity of the photoinitiator in the curing system, thereby further reducing migration behavior.

[0017] (4) Synergistic optimization of structure and performance. While maintaining the good photoinitiation performance of α-hydroxy ketone photoinitiators, the present invention achieves a synergistic improvement in photoinitiation performance and low migration performance.

[0018] The method for preparing the low-migration photoinitiator based on the molecular immobilization mechanism of the present invention includes the following steps: (1) Preparation of 2-[4-(2-hydroxy-2-methylpropionyl)phenoxy]ethyl p-toluenesulfonate (2959 p-toluenesulfonate intermediate, compound 2) 2-Hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone (compound 1, Irgacure 2959) was added to a dry reaction flask, dissolved in anhydrous organic solvent, and cooled to 0 °C under nitrogen protection. An organic base was then added, followed by the slow addition of p-toluenesulfonyl chloride under stirring to induce sulfonation of the terminal hydroxyl groups in the Irgacure 2959 molecule. After the reaction was complete, water was added to quench the reaction, and the mixture was extracted with an organic solvent. The combined organic phases were washed, dried, and the solvent removed. The crude product was purified by column chromatography or recrystallization to obtain the 2959 p-toluenesulfonate intermediate (compound 2).

[0019] (2) Preparation of intermediates with a central framework containing a diazoxide-containing propylene structure 2,2-bis(bromomethyl)propane-1,3-diol (compound 4) and 4-[3-(trifluoromethyl)-3H-diazacyclopropene-3-yl]phenol (compound 3) were added to the reaction system and subjected to a nucleophilic substitution reaction under alkaline conditions. The phenolic hydroxyl group in 4-[3-(trifluoromethyl)-3H-diazacyclopropene-3-yl]phenol (compound 3) reacted with the bromomethyl group in 2,2-bis(bromomethyl)propane-1,3-diol (compound 4), thereby introducing the diazacyclopropene structural unit into the central skeleton to obtain a central skeleton intermediate containing the diazacyclopropene structure (compound 5).

[0020]

[0021] (3) Grafting of α-hydroxyketone photoinitiating units The above-mentioned central skeleton intermediate containing diazacyclopropene structure (compound 5) and the 2959 p-toluenesulfonate intermediate obtained in step (1) (compound 2) were added to the reaction system and a nucleophilic substitution reaction was carried out under alkaline conditions, so that the hydroxyl group in the central skeleton intermediate reacted with the 2959 p-toluenesulfonate intermediate, thereby grafting the α-hydroxy ketone photoinitiator unit onto the central skeleton, to obtain an intermediate (compound 6) containing both diazacyclopropene structural unit and α-hydroxy ketone structural unit.

[0022] (4) Introduction of active chloroacetyl sites The intermediate (compound 6) containing both diazacyclopropene and α-hydroxyketone structural units was dissolved in an organic solvent, and chloroacetyl chloride was added at low temperature to induce acylation of the α-hydroxy group in the α-hydroxyketone structural unit, thereby introducing an intermediate compound (compound 7) with a chloroacetyl active site, providing a reaction site for the subsequent construction of ionic structural units.

[0023] (5) Construction of ionic structural units The intermediate containing the above-mentioned chloroacetyl active site is reacted with a compound containing a tertiary amine group and an anionic group. Through a nucleophilic substitution reaction, the tertiary amine group undergoes a quaternization reaction with the chloroacetyl group, while retaining its anionic group. This process constructs an ionic structural unit in the molecule, yielding the target low-migration photoinitiator (compound R) based on a molecular fixation mechanism.

[0024] Preferably, the reaction in step (2) is carried out in an organic solvent, and the formation of phenoxy anions from phenolic hydroxyl groups is promoted under alkaline conditions to improve the substitution reaction efficiency between phenolic hydroxyl groups and bromomethyl groups. Through this step, two diazacyclic propylene structural units can be introduced into the central skeleton while retaining the hydroxyl reaction sites in the central skeleton.

[0025] Preferably, the compound containing tertiary amine groups and anionic groups in step (5) includes sulfonates, carboxylates or derivatives thereof containing tertiary amine groups.

[0026] Preferably, the compound containing tertiary amine groups and anionic groups in step (5) includes sodium 3-[benzyl(methyl)amino]propane-1-sulfonate, sodium 3-(dimethylamino)propane-1-sulfonate, sodium 4-[benzyl(methyl)amino]butyrate, and sodium 4-(dimethylamino)butyrate.

[0027] By using the above method, the α-hydroxy ketone photoinitiating unit, the diazacyclopropene C–H insertion unit, and the ionic confinement unit are integrated into the same molecular structure to obtain a low-migration photoinitiator based on a molecular fixation mechanism.

[0028] A UV-curable composition comprising the aforementioned low-migration photoinitiator based on a molecular immobilization mechanism. Preferably, the UV-curable composition comprises a polymerizable monomer or oligomer, a reactive diluent, and the aforementioned low-migration photoinitiator based on a molecular immobilization mechanism, and may include additives as needed.

[0029] The preparation of the above-mentioned UV-curable composition includes adding a low-migration photoinitiator based on a molecular fixation mechanism to a UV-curable resin system, mixing it evenly under stirring conditions, and obtaining a UV-curable composition.

[0030] The low-migration photoinitiator based on the molecular fixation mechanism of this invention is suitable for photocuring systems containing inert organic matrices. Under light irradiation, the diazacyclopropylene structural unit can generate an active intermediate, which further undergoes a C–H insertion reaction with the matrix molecules, thereby achieving molecular-level fixation of the photoinitiator during curing and effectively reducing migration behavior while maintaining good photoinitiation performance.

[0031] More specifically, the photoinitiator of the present invention is applied in the following fields: (1) UV-curable coating materials, including but not limited to functional coatings, protective coatings and optical coatings; (2) UV-curable ink systems, including printing inks and inkjet printing materials; (3) UV-curable adhesives, including structural adhesives, optical adhesives and encapsulating adhesives, are particularly suitable for adhesive systems that are sensitive to migration behavior; (4) Optoelectronic device packaging materials, including flexible electronic devices, display devices and related packaging systems; (5) Biomedical materials and food contact materials, including photocurable systems with high requirements for safety and low migration performance.

[0032] Compared with existing technologies, this invention, through molecular structure design, synergistically introduces α-hydroxyketone photoinitiating structural units, diazacyclic propylene structural units, and ionic structural units into the same photoinitiator molecule, thereby achieving synergistic regulation of photoinitiation, molecular immobilization, and low migration at the single-molecule level. While maintaining good photoinitiation performance, it effectively suppresses the migration behavior of the photoinitiator, achieving a unity of photoinitiation and low migration functions. Its main advantages are as follows: (1) Compared with traditional α-hydroxy ketone photoinitiators, the photoinitiator of the present invention exhibits considerable photoinitiation activity in typical UV curing systems, while its migration in the cured system is significantly reduced.

[0033] (2) Compared with low migration strategies that rely on increasing molecular weight or introducing polymerizable groups, the present invention introduces structural units that can react with inert organic matrix through molecular structure design, thereby achieving molecular-level fixation of photoinitiators, which has better versatility and stability.

[0034] (3) The low-migration photoinitiator based on the molecular fixation mechanism of the present invention can improve the crosslinking degree of the cured system during UV curing, thereby helping to improve the overall stability of the cured material. The present invention achieves synergistic optimization among photoinitiation performance, low migration performance and structural stability, and is suitable for UV curing systems that are sensitive to migration behavior, especially for UV-cured adhesives and optoelectronic device packaging.

[0035] (4) The low-migration photoinitiator of this invention, based on the molecular fixation mechanism, exhibits higher gel content, lower swelling rate, and superior thermal stability. During the curing process, it can form a more stable and denser network structure, improving the overall stability and structure retention of the cured material. Furthermore, the migration amount of the low-migration photoinitiator of this invention is reduced by approximately 82.6% to 87.0% compared to commercial photoinitiators, which can significantly improve the retention capacity of the photoinitiator in the curing system and achieve synergistic optimization of photoinitiation performance and low-migration performance. Attached Figure Description

[0036] Figure 1 This is the general structural formula of the low-migration photoinitiator based on the molecular immobilization mechanism of the present invention; Figure 2 These are the structural formulas of T-1, T-2, T-3, and T-4 of the low-migration photoinitiator based on the molecular immobilization mechanism of the present invention; Figure 3 This is a schematic diagram illustrating the synthesis of the low-migration photoinitiator based on the molecular immobilization mechanism of the present invention. Figure 4 This is a schematic diagram of the synthesis of the low-migration photoinitiator T-1 based on the molecular immobilization mechanism of the present invention; Figure 5 This is a schematic diagram illustrating the synthesis of the low-migration photoinitiator T-2 based on the molecular immobilization mechanism of the present invention; Figure 6 This is a schematic diagram illustrating the synthesis of the low-migration photoinitiator T-3 based on the molecular immobilization mechanism of the present invention; Figure 7 This is a schematic diagram illustrating the synthesis of T-4, a low-migration photoinitiator based on a molecular immobilization mechanism, according to the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0038] Example 1 Synthesis of low-migration photoinitiator T-1 based on molecular immobilization mechanism, such as Figure 4 As shown, it includes the following steps: (1) Under ice bath conditions, 2959(1-1) (22.43 g, 0.100 mol) was added to a dry reaction flask, and 300 mL of anhydrous dichloromethane was added to dissolve it. The mixture was then cooled to 0 °C under nitrogen protection. Triethylamine (15.18 g, 0.150 mol, 20.9 mL) and DMAP (0.61 g, 5.0 mmol) were added, followed by the slow addition of a solution prepared from p-toluenesulfonyl chloride (22.88 g, 0.120 mol) and 100 mL of anhydrous dichloromethane, with the addition time controlled at 1 h. After the addition was complete, the reaction was continued at 0 °C for 1 h, and then raised to room temperature for 12 h. After the reaction was completed, 200 mL of deionized water was added to quench the reaction, and the mixture was extracted three times with dichloromethane (3 × 100 mL). The organic phases were combined and washed successively with 1 mol / L hydrochloric acid solution (2 × 100 mL), saturated sodium bicarbonate solution (2 × 100 mL), and saturated sodium chloride solution (100 mL). After drying with anhydrous sodium sulfate, the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography with petroleum ether / ethyl acetate as the eluent (4:1 to 2:1) to give 2959 p-toluenesulfonate intermediate (1-2). 1 H NMR(500 MHz, CDCl3) δ 7.90 – 7.80 (m, 2H), 7.72 – 7.61 (m, 2H), 7.42 – 7.31 (m,2H), 6.96 – 6.86 (m, 2H), 4.28 (td, J = 14.4, 1.4 Hz, 2H), 4.02 (td, J = 14.4,1.4 Hz, 2H), 2.40 (s, 3H), 1.67 (s, 1H), 1.34 (s, 6H). 13 C NMR (125 MHz, CDCl3)δ 202.19, 161.59, 141.19, 136.75, 133.09, 130.49, 129.68, 128.38, 115.38,76.98, 66.88, 65.40, 25.80, 21.15. (2) 2,2-bis(bromomethyl)propane-1,3-diol (1-4) (2.62 g, 10.0 mmol) and 4-[3-(trifluoromethyl)-3H-diazacyclopropene-3-yl]phenol (1-3) (4.45 g, 22.0 mmol) were added to a dry reaction flask, and 80 mL of anhydrous N,N-dimethylformamide was added. Under nitrogen protection and in the dark, anhydrous potassium carbonate (4.15 g, 30.0 mmol) and potassium iodide (0.33 g, 2.0 mmol) were added. After stirring at room temperature for 30 min, the mixture was heated to 55 °C and reacted for 12 h. After the reaction was completed, the reaction solution was cooled to room temperature, poured into 300 mL of deionized water, and extracted three times with ethyl acetate (3 × 100 mL). The organic phases were combined and washed three times (3 × 100 mL) with deionized water and once (100 mL) with saturated sodium chloride solution. After drying with anhydrous sodium sulfate, the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography with petroleum ether / ethyl acetate as the eluent (5:1 to 2:1) to obtain intermediates (1-5) with a central skeleton containing a diazacyclic propylene structure. 1 H NMR (500 MHz, CDCl3) δ 7.30 –7.20 (m, 4H), 6.90 – 6.80 (m, 4H), 3.99 (s, 4H), 3.71 (s, 4H), 1.36 (s, 2H). 13 C NMR (125 MHz, CDCl3) δ 165.74, 133.66, 133.65, 132.47, 130.32, 128.18,126.03, 121.17, 121.12, 121.08, 121.03, 114.60, 71.24, 64.14, 45.07. (3) Add intermediate 1-5 (5.04 g, 10.0 mmol) to a dry reaction flask, add 100 mL of anhydrous N,N-dimethylformamide to dissolve it, and cool to 0 °C under nitrogen protection and in the dark. Add sodium hydride (60% mineral oil dispersion, 0.96 g, 24.0 mmol) in portions, controlling the temperature not to exceed 5 °C, and stir at 0 °C for 30 min after the addition is complete. Then slowly add a solution prepared from 2959 p-toluenesulfonate intermediate (1-2) (8.33 g, 22.0 mmol) and 50 mL of anhydrous N,N-dimethylformamide over a period of 30 min. After the addition is complete, continue the reaction at 0 °C for 1 h, and then raise the temperature to room temperature for 16 h. After the reaction is complete, quench the reaction solution by slowly adding it dropwise to 300 mL of ice water, and extract with ethyl acetate three times (3 × 150 mL). The organic phases were combined and washed three times (3 × 150 mL) with deionized water, then once with saturated sodium chloride solution (150 mL). After drying with anhydrous sodium sulfate, the solvent was removed under reduced pressure. The crude product was recrystallized from ethyl acetate / petroleum ether to give intermediates 1-6. 1 H NMR (500 MHz, DMSO-d6) δ 7.97 – 7.90 (m, 4H), 7.30 – 7.23 (m, 4H), 7.02 – 6.95 (m, 4H), 6.89 – 6.82 (m, 4H), 4.34 – 4.28 (m, 4H), 3.81 – 3.72(m, 12H), 1.53(s, 2H), 1.35(s, 12H). 13 C NMR (125 MHz, DMSO-d6) δ 202.19,165.74, 161.59, 133.66, 133.65, 133.09, 132.47, 130.49, 130.32, 128.18,126.03, 121.17, 121.12, 121.08, 121.03, 115.38, 114.60, 76.98, 73.54, 72.19,69.88, 67.73, 42.10, 25.80. (4) Intermediate 1-6 (9.17 g, 10.0 mmol) was added to a dry reaction flask, and 150 mL of anhydrous dichloromethane was added to dissolve it. The mixture was then cooled to 0 °C under nitrogen protection and in the dark. Triethylamine (3.04 g, 30.0 mmol, 4.2 mL) and DMAP (0.24 g, 2.0 mmol) were added, followed by the slow addition of a solution prepared from chloroacetyl chloride (2.49 g, 22.0 mmol) and 30 mL of anhydrous dichloromethane over 30 min, with the system temperature controlled not to exceed 5 °C. After the addition was complete, the reaction was continued at 0 °C for 1 h, and then raised to room temperature for 12 h. After the reaction was completed, 150 mL of deionized water was added to quench the reaction, and the mixture was extracted three times with dichloromethane (3 × 100 mL). The combined organic phases were washed successively with 1 mol / L hydrochloric acid solution (2 × 100 mL), saturated sodium bicarbonate solution (2 × 100 mL), and saturated sodium chloride solution (100 mL). After drying with anhydrous sodium sulfate, the solvent was removed under reduced pressure. The crude product was recrystallized from ethyl acetate / petroleum ether to obtain intermediates (1-7) containing chloroacetyl active sites. 1 H NMR (500MHz, DMSO-d6 ) δ 7.97 – 7.90 (m, 4H), 7.30 – 7.23 (m, 4H), 7.02 – 6.95 (m,4H), 6.89 – 6.82 (m, 4H), 4.41 (s, 4H), 4.32 (m, 4H), 4.01 (s, 4H), 3.82 –3.72 (m, 8H), 1.54 (s, 12H). 13 C NMR (125 MHz, DMSO-d6 ) δ 202.19, 166.43,165.74, 162.07, 133.66, 133.65, 133.60, 132.47, 130.32, 128.18, 126.03,121.17, 121.12, 121.08, 121.03, 115.57, 114.60, 81.70, 73.54, 72.19, 69.88,67.73, 42.10, 40.46, 25.23. (5) Intermediate 1-7 (10.70 g, 10.0 mmol) and sodium 3-[benzyl(methyl)amino]propane-1-sulfonate (5.84 g, 22.0 mmol) were added to a dry reaction flask, and 150 mL of anhydrous acetonitrile was added. Under nitrogen protection and in the dark, the mixture was stirred at room temperature for 30 min, and then heated to 60 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, and the acetonitrile was removed under reduced pressure. The residue was washed three times (3 × 100 mL) with anhydrous ethyl acetate and twice (2 × 100 mL) with anhydrous acetone to remove unreacted small molecule starting materials. The crude product was recrystallized to obtain the target low-migration photoinitiator T-1. 1 H NMR (500 MHz, DMSO-d6 ) δ 7.99 – 7.89 (m, 4H), 7.34 – 7.00 (m, 16H), 7.00 – 6.94 (m, 2H), 6.91 –6.82 (m, 4H), 4.76 (d, J = 10.4 Hz, 8H), 4.31 (t, J = 14.4 Hz, 4H), 4.07 (s,4H), 3.82 – 3.72 (m, 8H), 3.44 – 3.36 (m, 10H), 2.81 (t, J = 12.4 Hz, 4H), 2.36 – 2.25 (m, 4H), 1.54 (s, 12H). Example 2 Synthesis of low-migration photoinitiator T-2 based on molecular immobilization mechanism, such as Figure 5 As shown, it includes the following steps: Intermediate 1-7 (10.70 g, 10.0 mmol) containing a chloroacetyl active site and sodium 3-(dimethylamino)propane-1-sulfonate (4.16 g, 22.0 mmol) were added to a dry reaction flask, followed by 150 mL of anhydrous acetonitrile. The mixture was stirred at room temperature for 30 min under nitrogen protection and in the dark, and then heated to 60 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, and the acetonitrile was removed under reduced pressure. The residue was washed three times (3 × 100 mL) with anhydrous ethyl acetate and twice (2 × 100 mL) with anhydrous acetone to remove unreacted small molecule starting materials. The crude product was recrystallized to obtain the target low-migration photoinitiator T-2. 1H NMR (500MHz, DMSO-d6 ) δ 7.99 – 7.89 (m, 4H), 7.31 – 7.21 (m, 4H), 7.04 – 6.94 (m,4H), 6.91 – 6.81 (m, 4H), 4.41 (s, 4H), 4.31 (t, J = 6.9 Hz, 4H), 3.88 (s,4H), 3.77 (dd, J = 11.9, 5.0 Hz, 8H), 3.40 (m, 4H), 3.30 (s, 12H), 3.01 (m,4H), 2.31 (ddt, J = 15.8, 11.8, 6.1 Hz, 4H), 1.54 (s, 12H). Example 3 Synthesis of low-migration photoinitiator T-3 based on molecular immobilization mechanism, such as Figure 6 As shown, it includes the following steps: Intermediate 1-7 (10.70 g, 10.0 mmol) containing a chloroacetyl active site and sodium 4-[benzyl(methyl)amino]butyrate (4.99 g, 22.0 mmol) were added to a dry reaction flask, followed by 150 mL of anhydrous acetonitrile. The mixture was stirred at room temperature for 30 min under nitrogen protection and in the dark, and then heated to 60 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, and the acetonitrile was removed under reduced pressure. The residue was washed three times (3 × 100 mL) with anhydrous ethyl acetate and twice (2 × 100 mL) with anhydrous acetone to remove unreacted small molecule starting materials. The crude product was recrystallized to obtain the target low-migration photoinitiator T-3. 1 H NMR (500MHz, DMSO-d6) δ 7.94 (d, J = 7.3 Hz, 4H), 7.30 – 7.18 (m, 14H), 6.99 (d, J =7.5 Hz, 4H), 6.86 (d, J = 7.5 Hz, 4H), 4.89 (s, 4H), 4.77 (s, 4H), 4.34 – 4.28 (m, 4H), 3.91 (s, 4H), 3.81 – 3.74 (m, 8H), 3.44 – 3.37 (m, 4H), 3.09 (s,6H), 2.34 (t, J = 5.4 Hz, 4H), 1.98 – 1.79 (m, 4H), 1.54 (s, 12H). Example 4 Synthesis of T-4, a low-migration photoinitiator based on a molecular immobilization mechanism, such as Figure 7 As shown, it includes the following steps: Intermediate 1-7 (10.70 g, 10.0 mmol) containing a chloroacetyl active site and sodium 4-(dimethylamino)butyrate (3.37 g, 22.0 mmol) were added to a dry reaction flask, followed by 150 mL of anhydrous acetonitrile. The mixture was stirred at room temperature for 30 min under nitrogen protection and in the dark, and then heated to 60 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, and the acetonitrile was removed under reduced pressure. The residue was washed three times (3 × 100 mL) with anhydrous ethyl acetate and twice (2 × 100 mL) with anhydrous acetone to remove unreacted small molecule starting materials. The crude product was recrystallized to obtain the target low-migration photoinitiator T-4. 1 H NMR (500 MHz, DMSO-d6) δ 7.94 (d, J = 7.3 Hz, 4H), 7.26 (d, J = 7.5 Hz, 4H), 6.99 (d, J = 7.5 Hz, 4H), 6.86 (d, J = 7.5 Hz, 4H), 4.34 – 4.27 (m, 8H), 3.98 (s, 4H), 3.77 (dd, J =12.2, 5.1 Hz, 8H), 3.40 (m, 4H), 3.29 (s, 12H), 2.34 (t, J = 8.1 Hz, 4H), 2.18– 2.11 (m, 4H), 1.54 (s, 12H). Example 5 Performance characterization of UV-curable compositions To evaluate the performance of the low-migration photoinitiator described in this invention, photoinitiators T-1 to T-4 prepared in Examples 1 to 4 were used as the research object, and the commercial photoinitiator Irgacure 2959 was used as a comparison. Comparative tests were conducted under the same conditions.

[0039] (1) Preparation of UV curing composition Prepare the UV-curing composition according to the following parts by weight: The mixture contains 50 parts of polyurethane acrylate oligomer, 20 parts of bisphenol A epoxy acrylate, 20 parts of 1,6-hexanediol diacrylate (HDDA), 7 parts of trimethylolpropane triacrylate (TMPTA), 3 parts of photoinitiator, 0.3 parts of leveling agent, and 0.2 parts of defoamer.

[0040] Polyurethane acrylate oligomer, bisphenol A epoxy acrylate, HDDA, and TMPTA were sequentially added to a light-protected container and stirred at room temperature for 20 min to ensure homogeneous mixing of the resin system. Then, the corresponding photoinitiators (T-1 to T-4 and Irgacure 2959, respectively) were added, and stirring continued for 30 min in the dark to ensure complete dissolution or uniform dispersion of the photoinitiators. Finally, leveling agent and defoamer were added, and stirring continued for 10 min, followed by ultrasonic degassing for 10 min to obtain the UV-curable composition.

[0041] (2) Preparation of cured film The above UV-curable composition was uniformly coated onto a clean glass slide using a film scraper, with the wet film thickness controlled to be approximately 50 μm. After coating, the film was allowed to stand for 1 min to eliminate surface bubbles, and then cured by irradiation with a 365 nm ultraviolet light source at an intensity of 100 mW·cm. -2 The irradiation time was 30 s to obtain a cured film sample. The obtained sample was placed at room temperature in the dark for 24 h before being used for subsequent tests.

[0042] (3) Ultraviolet absorption performance test The photoinitiator to be tested was dissolved in acetonitrile to prepare a solution with a concentration of 1.0 × 10⁻⁶. -3 mol·L -1 The test solution was prepared. The tests were performed using a UV-Vis spectrophotometer, with acetonitrile as a blank reference. The scanning range was 200–600 nm, and the maximum absorption wavelength of each sample was recorded.

[0043] Table 1. Results of UV absorption performance test

[0044] As shown in Table 1, the low-migration photoinitiators T-1 to T-4 of this invention, based on the molecular fixation mechanism, maintain UV absorption capacity similar to that of the commercial photoinitiator Irgacure 2959. At the same time, the absorption peak shifts slightly towards longer wavelengths, indicating that the structural modification does not significantly weaken the photoresponse performance and is beneficial to improving the UV light utilization efficiency and subsequent curing reaction process.

[0045] (4) Photo-initiation performance test (Photo-DSC) The exothermic behavior of photopolymerization was tested using optical differential scanning calorimetry (ODC). Dipropylene glycol diacrylate (DPGDA) was used as the model monomer, and the photoinitiator to be tested was added at 3 wt% of the DPGDA mass. The mixture was stirred until homogeneous in the dark. Approximately 8 mg of the sample was placed in an aluminum crucible and tested under nitrogen protection. The test temperature was 50 °C, and the UV light intensity was 40 mW·cm². -2 Record the polymerization exothermic curve after light exposure and calculate the time t required to reach the maximum exothermic rate.max And double bond conversion rate (DBC).

[0046] Table 2. Photoinitiation performance test results

[0047] As shown in Table 2, the time required to reach the maximum exothermic rate from T-1 to T-4 was 2.7–2.9 s, and the double bond conversion rate was 75%–77%, both close to that of the commercial photoinitiator Irgacure 2959. The results indicate that after introducing diazacyclic propylene structural units and ionic structural units, the resulting photoinitiator still maintains a relatively fast photopolymerization response and good free radical initiation ability.

[0048] (5) Curing kinetics test (real-time FT-IR) The double bond transformation process of acrylate in the UV-cured system was tested using real-time Fourier transform infrared spectroscopy. The UV-curable composition was coated onto the surface of a KBr or glass substrate, with a film thickness controlled to approximately 20 μm. Irradiation with 365 nm ultraviolet light at an intensity of 100 mW·cm⁻¹ was employed. -2 Infrared spectra were continuously collected during the test, monitoring at approximately 1635 cm⁻¹. -1 The change of the C=C characteristic absorption peak with illumination time was studied, and the double bond conversion rate was calculated based on the change in absorption peak area. The maximum polymerization rate Rp,max and the time (s) required to reach 90% final conversion rate were calculated based on the conversion-time curve.

[0049] Table 3 Curing kinetics test results

[0050] As shown in Table 3, the maximum polymerization rate of the low-migration photoinitiator based on the molecular fixation mechanism of this invention is close to that of the commercial photoinitiator Irgacure2959, and the time required to reach the target conversion rate varies little, indicating that it can maintain rapid curing ability while achieving low migration performance.

[0051] (6) Curing performance test The UV-curable composition was coated onto the surface of a glass slide, with a wet film thickness of approximately 50 μm. It was then irradiated under a 365 nm UV light source with a light intensity of 100 mW·cm². - ². The surface drying method was used to evaluate the curing speed. After different irradiation times, the surface of the film was lightly touched with a clean cotton swab, and the time when no cotton fibers adhered to the film surface and no obvious drag marks were produced was taken as the surface drying time.

[0052] Table 4 Curing performance test results

[0053] As shown in Table 4, the curing speed of the low-migration photoinitiator based on the molecular fixation mechanism of this invention is comparable to that of the commercial photoinitiator Irgacure 2959, indicating that the introduction of the functional structure did not significantly affect the film quality and process applicability.

[0054] (7) Gel content test The cured film was cut into samples of the same size, and the initial mass W1 was measured. The samples were then immersed in ethyl acetate for 24 h to remove unreacted monomers, oligomers, and soluble components. After immersion, the samples were removed, the surface solvent was gently blotted off with filter paper, and the samples were dried to constant weight in a vacuum drying oven at 60 °C. The dried mass W2 was measured. The gel content was calculated using the following formula: Gel content (%) = W2 / W1 × 100%.

[0055] Table 5. Results of gel content test

[0056] As shown in Table 5, the low-migration photoinitiator gel content based on the molecular fixation mechanism of this invention is significantly increased, indicating the formation of a more stable and dense cross-linked network structure, which is beneficial to enhancing the stability of the system.

[0057] (8) Swelling performance test After the cured film sample is dried to constant weight, its mass W is measured. d The sample was then soaked in ethyl acetate for 24 hours. After soaking, the sample was removed, and residual solvent on the surface was quickly absorbed with filter paper. The mass W after swelling was immediately measured. s The swelling ratio is calculated using the following formula: Swelling rate (%) = (W s -W d ) / W d ×100%.

[0058] Table 6 Results of swelling performance test

[0059] As shown in Table 6, compared with the commercial photoinitiator Irgacure2959, the swelling rate of the low-migration photoinitiator based on the molecular immobilization mechanism of this invention is significantly reduced, indicating that a more stable cross-linking network is formed, which helps to reduce the migration behavior of small molecules.

[0060] (9) Thermal stability test Thermogravimetric analysis (TGA) was used to evaluate the thermal stability of the cured film. Approximately 5–10 mg of the cured film was cut into small pieces and placed in a test crucible for testing under a nitrogen atmosphere. The test temperature range was 25–700 °C, with a heating rate of 10 °C / min. -1 Record the temperature T corresponding to a 5% mass loss of the sample. d5%.

[0061] Table 7 Thermal stability test results

[0062] As shown in Table 7, compared with the commercial photoinitiator Irgacure2959, the cured film prepared using the low-migration photoinitiator of this invention has a higher 5% thermogravimetric temperature, indicating that the overall thermal stability of the obtained cured network is improved, and demonstrating that the structural design helps to improve the thermal stability of the system.

[0063] (10) Migration performance test The cured film was cut into samples of the same size and mass and placed in an ethanol simulation solution for immersion at 50 °C for 48 h. After immersion, the supernatant was collected, and external standard curves were established using the corresponding standards for each photoinitiator to be tested. The content of unreacted parent photoinitiator in the extract was calculated. The detection wavelength was 273 nm, and the mobile phase was an acetonitrile / water system. The migration amount was calculated based on the standard curve and expressed as a percentage relative to the initial amount of photoinitiator added.

[0064] Table 8 Migration performance test results

[0065] As shown in Table 8, compared with the commercial photoinitiator Irgacure2959, the migration amount of the low-migration photoinitiator based on the molecular fixation mechanism of the present invention is reduced by about 82.6% to 87.0%, indicating that the retention ability of the photoinitiator in the curing system can be effectively improved by regulating the molecular structure, and a significant low-migration effect can be achieved while maintaining good curing performance.

[0066] In summary, the low-migration photoinitiator system based on molecular immobilization mechanism constructed in this invention effectively suppresses migration behavior while maintaining excellent photoinitiation performance. Multi-dimensional testing results, including UV absorption performance, Photo-DSC, real-time FT-IR, curing performance, gel content, swelling performance, thermal stability, and migration performance, show that the system of this invention maintains UV response capability, free radical initiation efficiency, and rapid curing capability comparable to the commercial photoinitiator Irgacure 2959, without significantly reducing photocuring performance due to the introduction of the functional structure.

[0067] Meanwhile, the low-migration photoinitiator based on the molecular fixation mechanism of this invention exhibits higher gel content, lower swelling rate and better thermal stability, indicating that it can form a more stable and denser network structure during the curing process, thereby improving the overall stability and structure retention of the cured material.

[0068] Furthermore, migration performance test results show that the migration amount of the system of the present invention is reduced by about 82.6% to 87.0% compared with commercial photoinitiators, indicating that the retention ability of photoinitiators in the curing system can be significantly improved by regulating the molecular structure, thereby achieving synergistic optimization of photoinitiation performance and low migration performance.

[0069] Therefore, the low-migration photoinitiator of the present invention can balance high photoinitiation efficiency, good curing performance, excellent structural stability and significantly low migration characteristics, making it suitable for UV curing systems that are sensitive to migration behavior, and especially suitable for applications such as UV curable coatings, functional inks, adhesives, optoelectronic device packaging and high-safety functional materials.

Claims

1. A low-migration photoinitiator based on a molecular immobilization mechanism, characterized in that, The general structural formula is as follows: Among them, R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, cyano, C1–C20 alkyl, aryl, or substituted aryl; The structural formula for R is: R5, R6, R7, and R8 are independently selected from C1-C10 alkyl, hydroxy-substituted alkyl, aryl, substituted aryl, benzyl, or substituted benzyl; n is an integer from 1 to 20; M is a hydrogen ion, an alkali metal ion, or an organic ammonium salt cation; and X is a halogen.

2. The low-migration photoinitiator based on a molecular immobilization mechanism according to claim 1, characterized in that, Including the following compounds: 。 3. The method for synthesizing a low-migration photoinitiator based on a molecular immobilization mechanism according to claim 1, characterized in that, Includes the following steps: (1) Synthesis of p-toluenesulfonate intermediate; (2) Synthesize a central framework intermediate containing a diazacyclic propylene structure; (3) The intermediate containing the central skeleton of diazacyclopropene structure obtained in step (2) and the p-toluenesulfonate intermediate obtained in step (1) are added to the reaction system and a nucleophilic substitution reaction is carried out under alkaline conditions to obtain an intermediate containing both diazacyclopropene structural unit and α-hydroxy ketone structural unit. (4) Dissolve the intermediate obtained in step (3) which contains both diazacyclic propylene structural units and α-hydroxy ketone structural units in an organic solvent, and add chloroacetyl chloride under low temperature conditions to undergo an acylation reaction to obtain an intermediate compound containing a chloroacetyl active site. (5) The intermediate containing the chloroacetyl active site obtained in step (4) is reacted with a compound containing a tertiary amine group and an anionic group. The tertiary amine group and the chloroacetyl group undergo a quaternization reaction through a nucleophilic substitution reaction to obtain a low-migration photoinitiator.

4. The synthesis method according to claim 3, characterized in that, The synthesis method of p-toluenesulfonate intermediate in step (1) is as follows: 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone is added to a reaction flask, and then an anhydrous organic solvent is added to dissolve it. The mixture is then cooled to 0 °C under nitrogen protection. Subsequently, an organic base is added, and p-toluenesulfonyl chloride is added under stirring to undergo a sulfonation reaction.

5. The synthesis method according to claim 3, characterized in that, The synthesis method of the central skeleton intermediate containing the diazacyclopropene structure in step (2) is as follows: 2,2-bis(bromomethyl)propane-1,3-diol and 4-[3-(trifluoromethyl)-3H-diazacyclopropene-3-yl]phenol are added to the reaction system and a nucleophilic substitution reaction is carried out under alkaline conditions.

6. The synthesis method according to claim 3, characterized in that, The compounds containing tertiary amine groups and anionic groups in step (5) include sodium 3-[benzyl(methyl)amino]propane-1-sulfonate, sodium 3-(dimethylamino)propane-1-sulfonate, sodium 4-[benzyl(methyl)amino]butyrate, and sodium 4-(dimethylamino)butyrate.

7. A UV-curable composition, characterized in that, It includes the low-migration photoinitiator based on the molecular fixation mechanism described in claim 1.

8. The application of the low-migration photoinitiator based on the molecular immobilization mechanism according to claim 1, characterized in that, For use in photocuring systems containing inert organic matrices.

9. The application according to claim 8, characterized in that, The photocuring system includes UV-curable coatings, UV-curable inks, UV-curable adhesives, optoelectronic device encapsulation materials, biomedical material systems, and food contact materials.

Images