Low-migration photoinitiator based on click chemistry and its synthesis and application

Abstract

This invention relates to a low-migration photoinitiator constructed based on click chemistry, its synthesis and application, with the following general structural formula: wherein R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, trifluoromethyl, cyano, C1–C 20 Alkyl, aryl, or substituted aryl; the structural formula of R is as follows: wherein R5, R6, R7, and R8 are independently selected from C1–C6. 10 Alkyl or hydroxyl-substituted alkyl groups; n is an integer from 1 to 20; M is a hydrogen ion, alkali metal ion, or organoammonium salt cation; X is a halogen. The low-migration photoinitiator of this invention exhibits a lower tendency to yellow after curing, and its structural optimization can effectively improve the appearance of materials; moreover, the migration amount is reduced by approximately 78.6% to 84.6% compared to commercial photoinitiators. It maintains excellent photoresponse capability, rapid curing ability, and good appearance performance, while also achieving a significant reduction in migration behavior and improved stability, balancing photoinitiation efficiency, low migration performance, and application reliability. It is suitable for applications such as transparent coatings, optical adhesives, and high-quality photocurable systems.

Description

Technical Field

[0001] This invention belongs to the field of polymer compound technology, specifically relating to a low-migration photoinitiator constructed based on click chemistry and its synthesis and application. Background Technology

[0002] Currently, phosphorus oxide photoinitiators are widely used in UV curing systems due to their strong absorption capacity and high photoinitiation efficiency in the long-wave ultraviolet region. Among them, TPO-L, as a typical liquid photoinitiator, has good solubility and formulation compatibility, and plays an important role in industrial applications. However, these photoinitiators are usually small molecule structures, making it difficult for them to participate in polymerization reactions or form stable bonds with the matrix during curing. They remain in a free or weakly interacting form after curing, making them prone to migration during use.

[0003] The migration behavior of photoinitiators is one of the key factors affecting the safety and long-term stability of UV-curable materials. Especially in fields such as UV-curable adhesives, optical materials, biomedical materials, and food contact materials, the migration of photoinitiators or their degradation products can not only affect material properties but also pose potential safety risks. Therefore, achieving effective fixation of photoinitiators in the curing system while ensuring photoinitiation efficiency has become an important research direction.

[0004] In recent years, click chemistry reactions (such as the cycloaddition reaction of azides and alkynes) have been widely used in the construction of functional molecules and polymer materials due to their advantages such as mild reaction conditions, high selectivity, and controllable structure. This type of method provides an efficient route for the modular assembly of multifunctional structural units. Diazahexacyclic propene structures can generate highly reactive intermediates under light irradiation and can undergo insertion reactions with C–H bonds in organic molecules, thereby achieving non-selective covalent fixation of the molecule. Compared with traditional fixation methods that rely on reactions of specific functional groups, this mechanism has better applicability to inert organic matrices.

[0005] However, in existing technologies, click chemistry is mainly used for structure building, while diazacyclopropene structures are mostly used for photolabeling or crosslinking reagents. There is a lack of systematic research integrating photoinitiation function, molecular immobilization mechanism, and low-migration design into a single molecule. Therefore, developing a low-migration photoinitiator that maintains similar photoinitiation performance to TPO-L, achieves multifunctional structural unit assembly through click chemistry, and combines diazacyclopropene structures with ionic structures to realize the synergistic effect of photoinitiation and molecular immobilization, has significant research and application value. Summary of the Invention

[0006] The purpose of this invention is to provide a low-migration photoinitiator based on click chemistry, its synthesis and application, to solve the migration problem of existing phosphorus oxide photoinitiators (such as TPO-L) in UV curing systems, as well as the problems of limited applicability or impact on photoinitiation performance of existing low-migration modification strategies.

[0007] A low-migration photoinitiator constructed based on click chemistry has the following general structural formula:

[0008] The photoinitiator molecule comprises at least one central backbone structure, which connects multiple functional units via linking groups, including: (1) Phosphorus oxide photoinitiating unit, i.e., the following segment in the general structural formula:

[0009] (2) The aryldiazacyclic propylene structural unit, i.e., the following segment in the general structural formula:

[0010] Among them, R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, trifluoromethyl, cyano, and C1–C. 20 Alkyl, aryl, or substituted aryl; preferably, the aryl group is a polyfluorosubstituted aryl group; (3) 1,2,3-triazole connecting structural units, i.e., the following segments in the general structural formula: ; (4) Ionic structural unit, R in the general formula, has the following structural formula:

[0011] in: R5, R6, R7, and R8 are independently selected from C1–C 10 Alkyl or hydroxy-substituted alkyl; 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.

[0012] The structure contains both cationic and anionic groups.

[0013] The overall structure of the low-migration photoinitiator constructed based on click chemistry can be represented as follows: A central framework serves as the core, with photoinitiating units containing phosphorus oxide structures and functional units containing aryldiazacyclic propylene structures connected to one or more sides. Simultaneously, 1,2,3-triazole structures formed through click chemistry facilitate the connection between these functional units, and ionic structural units are introduced into the molecular side chains or connecting chains. The photoinitiating units and the aryldiazacyclic propylene structural units are distributed symmetrically or approximately symmetrically within the molecular structure.

[0014] Specifically, representative compounds are: .

[0015] The low-migration photoinitiator based on click chemistry of the present invention has the following structural features and advantages: (1) Multifunctional integrated molecular structure design This invention constructs a multifunctional integrated molecular structure with a phosphorus oxide-based photoinitiator as its core. The introduction of a phosphorus oxide photoinitiator unit ensures good free radical initiation ability under ultraviolet light irradiation. The introduction of an aryldiazacyclic propylene structural unit enables C–H insertion reactions under light irradiation, thereby enhancing the molecule's fixation ability in the curing network. The introduction of an ionic structural unit increases molecular polarity and volume, significantly reducing migration behavior. The functional modules are connected through a 1,2,3-triazole structural unit, achieving a structurally stable and reaction-controllable molecule. The synergistic existence of these structural units within the same molecule is a key feature distinguishing it from existing single-functional photoinitiators.

[0016] (2) Modular construction strategy based on click chemistry This invention employs an azide-alkyne click chemistry reaction to link a phosphorus oxide photoinitiator unit containing a terminal alkyne structure with a functional intermediate containing an azide structure, forming a stable 1,2,3-triazole structure. The reaction conditions are mild and applicable to various functional group systems; the structure construction exhibits high selectivity and controllability; and modular combinations of different functional units can be achieved, demonstrating good structural scalability. (3) Introduction method of low migration structural unit This invention effectively suppresses the migration behavior of photoinitiators by introducing ionic structural units into the molecular side chains or linking chains. This structural design is significantly different from the traditional approach of simply increasing the molecular weight or introducing polar groups, achieving low migration while maintaining photoinitiation performance.

[0017] (4) Post-modification strategy for constructing functional structures This invention achieves the introduction of subsequent ionic structural units by converting the methoxy group in the intermediate to generate a hydroxyl reaction site and further introducing a chloroacetyl active site. A convertible site is reserved in the photoinitiator unit; the functional structure is introduced through post-modification; and the flexibility and controllability of molecular structure construction are improved.

[0018] The method for preparing the low-migration photoinitiator based on click chemistry of the present invention includes the following steps:

[0019] 1. Preparation of methoxy-substituted TPO-L intermediates containing terminal alkyne groups.

[0020] (1) Under nitrogen protection, 4-methoxy-2,6-dimethylbenzoyl chloride (compound 1) was added to a dry reaction flask and cooled to 0 °C. Then, diethyl phenylphosphonite (diethoxyphenylphosphine, compound 2) was slowly added dropwise under stirring. After the addition was complete, the reaction system was brought to room temperature and the reaction was stirred to obtain a methoxy-substituted TPO-L intermediate containing an acylphosphonate photoinitiator structure (compound 3). The obtained intermediate can be used directly in the next step of the reaction without further purification.

[0021] (2) The above-mentioned methoxy-substituted TPO-L intermediate (compound 3) containing an acyl phosphonate photoinitiator structure was dissolved in an organic solvent, and sodium iodide or its hydrate was added. The reaction was carried out under heating conditions to convert the phosphonate structure into the corresponding phosphonate intermediate. After the reaction was completed, the precipitated solid was filtered, washed and dried to obtain the phosphonate intermediate (compound 4).

[0022] (3) The above phosphonate intermediate (compound 4) was dissolved in water, and the system was adjusted to acidic conditions with dilute acid to convert it into the corresponding phosphonic acid intermediate. After the reaction was completed, the precipitated solid was separated, washed and dried to obtain the phosphonic acid intermediate (compound 5).

[0023] (4) The above phosphonic acid intermediate (compound 5) was dissolved in an organic solvent, thionyl chloride was added, and an amount of N,N-dimethylformamide was added as a catalyst. The reaction was carried out under heating conditions to obtain phosphonyl chloride intermediate (compound 6). After the reaction was completed, the solvent and excess thionyl chloride were removed. The obtained intermediate could be used directly in the next step of the reaction without further purification.

[0024] (5) The above-mentioned phosphonyl chloride intermediate (compound 6) and propargyl alcohol were added to an organic solvent, and an organic base was added under low temperature conditions. The reaction was carried out under stirring conditions to induce esterification between propargyl alcohol and phosphonyl chloride, thereby introducing a terminal alkyne group into the molecule. After the reaction was completed, water was added to terminate the reaction, and the mixture was extracted with an organic solvent. After drying the organic phase and removing the solvent, the crude product was purified by column chromatography to obtain a methoxy-substituted TPO-L intermediate containing a terminal alkyne group (compound 7).

[0025] 2. Preparation of intermediates containing azide and diazacyclic propylene structures.

[0026] (1) 2,2-bis(bromomethyl)propane-1,3-diol (compound 8) was dissolved in a polar solvent, sodium azide was added, and the reaction was stirred under heating conditions to allow the bromomethyl group to undergo a nucleophilic substitution reaction to convert to azidemethyl. After the reaction was completed, the mixture was cooled to room temperature, water was added, and the mixture was extracted with an organic solvent. After washing, drying, and removing the solvent from the organic phase, the intermediate 2,2-bis(azidomethyl)propane-1,3-diol (compound 9) was obtained.

[0027] (2) The above-mentioned 2,2-bis(azidomethyl)propane-1,3-diol intermediate (compound 9) was dissolved in an organic solvent. An organic base was added under low temperature conditions, and p-toluenesulfonyl chloride was slowly added dropwise under stirring to induce esterification of the hydroxyl groups, generating the corresponding p-toluenesulfonate. After the reaction was completed, water was added to terminate the reaction, and the mixture was extracted with an organic solvent. After washing, drying, and removing the solvent from the organic phase, the 2,2-bis(azidomethyl)propane-1,3-diol bis-p-toluenesulfonate intermediate (compound 10) was obtained.

[0028] (3) The above-mentioned bis-toluenesulfonate intermediate was dissolved in an organic solvent with 4-(3-(trifluoromethyl)-3H-diazacyclopropene-3-yl)phenol and reacted under alkaline conditions to allow the phenolic hydroxyl group in the phenol to undergo a substitution reaction with the p-toluenesulfonate group, thereby introducing the diazacyclopropene structural unit into the molecular skeleton. After the reaction was completed, the reaction system was poured into water and extracted with an organic solvent. After washing, drying and removing the solvent from the organic phase, the crude product was purified by column chromatography to obtain an intermediate (compound 11) containing an azide group and a diazacyclopropene structure.

[0029] 3. Construction of low-migration photoinitiators based on click chemistry.

[0030] (1) The aforementioned methoxy-substituted TPO-L intermediate containing a terminal alkyne group (compound 7) and the intermediate containing an azide group and a diazonium ring propene structure (compound 11) were dissolved in an organic solvent, and a cycloaddition reaction of azide and alkyne was carried out in the presence of a catalyst to generate an intermediate containing a 1,2,3-triazole structure. After the reaction was completed, the reaction system was poured into water and extracted with an organic solvent. After washing, drying and removing the solvent from the organic phase, the intermediate (compound 12) was obtained.

[0031] (2) The above intermediate (compound 12) was dissolved in a suitable solvent, and the methoxy group was transformed under conversion conditions to obtain an intermediate containing a hydroxyl group. After the reaction was completed, the corresponding hydroxylated intermediate (compound 13) was obtained through post-treatment.

[0032] (3) Dissolve the above-mentioned hydroxyl-containing intermediate (compound 13) in an organic solvent, add chloroacetyl chloride under low temperature conditions, react under alkaline conditions to cause acylation of the hydroxyl group, introduce chlorine-containing active functional groups, and obtain chlorine-containing intermediate (compound 14).

[0033] (4) The above-mentioned chlorine-containing intermediate (compound 14) and the compound containing tertiary amine group and anionic group are added to the reaction system and reacted under appropriate conditions to introduce ionic structural units into the molecule to obtain the target low-migration photoinitiator (compound 15).

[0034] Preferably, in step 1, the methoxy-substituted TPO-L intermediate containing a terminal alkyne group retains the phosphorus oxide photoinitiating structure while introducing a terminal alkyne reaction site, which can further react with the intermediate containing an azide structure through click chemistry to form a 1,2,3-triazole linkage structure for the construction of the target low-migration photoinitiator.

[0035] Step 2: The intermediate containing both azide and diazacyclopropene structures contains both azide groups and diazacyclopropene structural units. It can be further reacted with a methoxy-substituted TPO-L intermediate containing a terminal alkyne structure through click chemistry to form a 1,2,3-triazole linkage structure, which is used to construct the target low-migration photoinitiator.

[0036] Furthermore, the compounds containing tertiary amine groups and anionic groups include sodium 3-(benzyl(methyl)amino)propane-1-sulfonate, sodium 3-(dimethylamino)propane-1-sulfonate, sodium 4-(dimethylamino)butyrate, and sodium 4-(benzyl(methyl)amino)butyrate.

[0037] A UV-curable composition comprising the aforementioned low-migration photoinitiator constructed based on click chemistry. Preferably, the UV-curable composition comprises a polymerizable monomer or oligomer, a reactive diluent, and the aforementioned low-migration photoinitiator, and may include additives as needed.

[0038] The preparation of the above-mentioned UV-curable composition includes adding a low-migration photoinitiator based on click chemistry to a UV-curable resin system and mixing it uniformly under stirring conditions to obtain a UV-curable composition.

[0039] When the low-migration photoinitiator based on click chemistry is used in a UV curing system, it can reduce the migration behavior of the photoinitiator in the curing system while maintaining photoinitiation performance comparable to TPO-L.

[0040] The low-migration photoinitiator based on click chemistry of the present invention has good photoinitiation ability in monomer or oligomer systems containing unsaturated double bonds and can achieve rapid curing under ultraviolet light irradiation.

[0041] Furthermore, the low-migration photoinitiator based on click chemistry can form a highly cross-linked curing network during the curing process, thereby improving the structural stability of the cured material.

[0042] Preferably, the low-migration photoinitiator based on click chemistry exhibits lower migration levels in the cured system compared to traditional phosphorus oxide photoinitiators; it is suitable for UV curing systems sensitive to migration behavior. It can be used in UV-curable adhesives, optical adhesives, and optoelectronic device encapsulation materials, particularly in low-migration UV-curable materials. It is especially suitable for applications in transparent coatings, optical adhesives, and high-quality UV-curable systems.

[0043] Compared with the prior art, the key innovation of this invention lies in the organic integration of photoinitiation functional units, photocrosslinking functional units and low-migration structural units into the same molecule through molecular structure synergistic design, thereby achieving synergistic optimization of photoinitiation performance and low-migration performance. The present invention has the following beneficial effects: (1) Expanding structural functionality while maintaining excellent photoinitiation performance The photoinitiator of this invention has a phosphorus oxide structure as its core, retaining UV absorption capacity and photoinitiation efficiency comparable to traditional TPO-L type photoinitiators. It can achieve rapid curing under 365 nm UV irradiation conditions, meeting the application requirements of conventional UV curing systems.

[0044] (2) Significantly reduces migration behavior and improves material safety By introducing ionic structural units into the molecular structure, the polarity and molecular size of the photoinitiator in the curing system are significantly improved, thereby effectively suppressing its migration behavior in the cured film. Compared with traditional phosphorus oxide photoinitiators, the photoinitiator of this invention exhibits significantly lower migration in the cured system, making it suitable for applications requiring low migration.

[0045] (3) Improve the degree of crosslinking and the stability of the cured network This invention introduces diazacyclopropylene structural units, which can further participate in the reaction under light irradiation, thereby enhancing the bonding between the photoinitiator and the matrix material, improving the crosslinking degree and structural stability of the curing system, and giving the resulting cured film superior mechanical properties and solvent resistance.

[0046] (4) Modular structure design, with strong versatility of synthesis route This invention utilizes azide-alkyne click chemistry to construct molecular structures. The reaction conditions are mild and highly selective, making it suitable for introducing various functional units. Furthermore, by changing the substituents of the ionic structural units, different photoinitiators can be easily constructed, exhibiting good structural tunability and scalability.

[0047] (5) Click chemistry enables the synergistic integration of photoinitiating functional units and low-mobility functional units. This invention presents a low-migration photoinitiator based on click chemistry, exhibiting a lower tendency to yellow after curing. Structural optimization effectively improves the material's appearance, facilitating its application in transparent coatings, optical adhesives, and high-quality photocuring systems. Furthermore, the migration amount is reduced by approximately 78.6%–84.6% compared to commercial photoinitiators. While maintaining excellent photoresponse, rapid curing capability, and good appearance, it achieves the goals of significantly reducing migration behavior and improving system stability, thus balancing photoinitiation efficiency, low migration performance, and application stability.

[0048] (6) It is suitable for a variety of UV curing systems and has a wide range of application prospects. The photoinitiator of this invention is applicable to UV-curable adhesives, optical materials and optoelectronic device packaging, and is especially suitable for application systems with high requirements for low migration and high stability, and has good application prospects. Attached Figure Description

[0049] Figure 1 The general structural formula of the low-migration photoinitiator based on click chemistry 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 constructed based on click chemistry according to the present invention; Figure 3 This is a schematic diagram illustrating the synthesis of the low-migration photoinitiator based on click chemistry of the present invention; Figure 4 This is a schematic diagram of the synthesis of the low-migration photoinitiator T-1 based on click chemistry of the present invention; Figure 5 This is a schematic diagram of the synthesis of the low-migration photoinitiator T-2 based on click chemistry of the present invention; Figure 6This is a schematic diagram of the synthesis of the low-migration photoinitiator T-3 based on click chemistry according to the present invention; Figure 7 This is a schematic diagram of the synthesis of the low-migration photoinitiator T-4 based on click chemistry of the present invention. Detailed Implementation

[0050] 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.

[0051] Example 1 Synthesis of low-migration photoinitiator T-1 based on click chemistry, such as Figure 4 As shown, it includes the following steps: Under nitrogen protection, 4-methoxy-2,6-dimethylbenzoyl chloride (1-1, 10.0 mmol, 1.99 g) was added to a dry three-necked flask and dissolved in anhydrous dichloromethane (50 mL). The mixture was then cooled to 0 °C. Diethyl phenylphosphonite (1-2, 10.0 mmol, 1.98 g) was slowly added dropwise over approximately 30 min with stirring. After the addition was complete, the ice bath was removed, the reaction mixture was allowed to rise to room temperature, and the reaction was continued with stirring for 4 h. After the reaction was complete, the solvent was removed under reduced pressure to obtain a yellow oily intermediate (1-3). 1 H NMR (500 MHz, CDCl3) δ 7.41 – 7.24 (m, 5H), 6.85 (s, 2H), 3.87(q, J = 11.8 Hz, 2H), 3.78 (s, 3H), 2.22 (s, 6H), 1.18 (t, J = 11.8 Hz, 3H). The above intermediates (1-3, 10.0 mmol) were dissolved in acetonitrile (50 mL), and sodium iodide (20.0 mmol, 3.00 g) was added. The mixture was stirred at 80 °C for 12 h. After the reaction was completed, the mixture was cooled and filtered to obtain phosphonate intermediates (1-4). These intermediates were dissolved in water, and the pH was adjusted to approximately 1 with dilute hydrochloric acid to precipitate phosphonic acid intermediates (1-5). The precipitates were then filtered, washed, and dried. 1 H NMR (500 MHz, CDCl3) δ 7.87 – 7.77 (m, 2H), 7.62 – 7.42 (m, 3H), 6.94 (s, 2H), 3.79 (s, 3H), 2.22 (s, 6H). The obtained intermediates (1-5, 10.0 mmol) were dissolved in anhydrous dichloromethane (50 mL), and thionyl chloride (20.0 mmol, 2.38 g) and a catalytic amount of N,N-dimethylformamide (0.5 mL) were added. The reaction was carried out under reflux for 3 h. After the reaction was completed, the solvent and excess thionyl chloride were removed under reduced pressure to obtain phosphonyl chloride intermediates (1-6). These were used directly without further processing.

[0052] The above phosphonyl chloride intermediates (1-6, 10.0 mmol) were dissolved in anhydrous dichloromethane (50 mL), cooled to 0 °C, and propargyl alcohol (15.0 mmol, 0.84 g) and triethylamine (15.0 mmol, 1.52 g) were added. The mixture was stirred at room temperature for 6 h. After the reaction was complete, the mixture was washed with water, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure. The mixture was then purified by column chromatography to obtain methoxy-substituted TPO-L intermediates (1-7) containing terminal alkyne groups. 1 H NMR (500 MHz, CDCl3) δ 7.42 – 7.25(m, 5H), 6.86 (s, 2H), 4.41 (d, J = 6.0 Hz, 2H), 3.79 (s, 3H), 3.32 (t, J = 6.0Hz, 1H), 2.22 (s, 6H). 2,2-bis(bromomethyl)propane-1,3-diol (1-8, 10.0 mmol, 2.62 g) was dissolved in DMF (50 mL), and sodium azide (30.0 mmol, 1.95 g) was added. The mixture was stirred at 80 °C for 12 h. After the reaction was complete, the mixture was cooled, diluted with water, extracted with ethyl acetate, and the organic phase was dried and the solvent was removed to give 2,2-bis(azidomethyl)propane-1,3-diol intermediate (1-9).

[0053] The above intermediates (1-9, 10.0 mmol) were dissolved in anhydrous dichloromethane (50 mL), cooled to 0 °C, and triethylamine (20.0 mmol, 2.02 g) was added. Then, p-toluenesulfonyl chloride (20.0 mmol, 3.81 g) was slowly added dropwise, and the reaction was carried out at room temperature for 6 h. After the reaction was complete, the mixture was washed with water and the organic phase was dried to obtain the bis-toluenesulfonate intermediates (1-10).

[0054] The above intermediates (1-10, 10.0 mmol) were dissolved in 60 mL of DMF with 4-(3-(trifluoromethyl)-3H-diazacyclopropene-3-yl)phenol (20.0 mmol, 4.04 g), and potassium carbonate (20.0 mmol, 2.76 g) was added. The mixture was stirred at 60 °C for 12 h. After the reaction was complete, the solution was poured into water, extracted with ethyl acetate, and the organic phase was dried and purified to give intermediates (1-11) containing azide and diazacyclopropene structures. Intermediates containing azide and diazonium propylene structures (1-11, 10.0 mmol) and methoxy-substituted TPO-L intermediates containing terminal alkyne groups (1-7, 20.0 mmol, 6.85 g) were dissolved in a DMF / water mixture (4:1, 50 mL, v / v). Copper sulfate pentahydrate (1.0 mmol, 0.25 g) and sodium ascorbate (2.0 mmol, 0.40 g) were added, and the mixture was stirred at room temperature for 12 h to carry out an azide-alkyne click reaction. After the reaction was completed, the reaction system was poured into water, extracted with ethyl acetate, and the organic phase was dried and the solvent was removed to obtain intermediates containing 1,2,3-triazole structures (1-12). 1 H NMR (500 MHz, CDCl3) δ 7.85 (s, 2H), 7.48 – 7.23 (m,14H), 6.89 – 6.82 (m, 8H), 5.25 (s, 2H), 4.80 (s, 2H), 4.71 (s, 4H), 4.11 (s,4H), 3.79 (s, 6H), 2.22 (s, 12H). Intermediates (1-12) (10.0 mmol) were added to a dry reaction flask, and 150 mL of anhydrous dichloromethane was added to dissolve them. The mixture was then cooled under nitrogen protection and in the dark. 20 °C. Slowly add a 1.0 mol·L⁻¹ solution of boron tribromide in dichloromethane. - ¹, 30 mL, 30.0 mmol), with the system temperature controlled not higher than 10 ℃. After the addition is complete, at The mixture was stirred at 20–0 °C for 2 h, then allowed to rise to room temperature for 12 h. After the reaction was complete, the system was cooled to 0 °C, and quenched by slowly adding 30 mL of anhydrous methanol, followed by the addition of 150 mL of ice water. The organic phase was separated, and the aqueous phase was extracted three times (3 × 100 mL) with dichloromethane. The organic phases were combined and washed successively with deionized water (2 × 100 mL) and saturated sodium chloride solution (100 mL), dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography with dichloromethane / methanol as the eluent in a ratio of 100:1 to 50:1, yielding a hydroxyl-containing intermediate (1-13).1 H NMR (500 MHz, CDCl3) δ 7.54 (s, 2H), 7.45 – 7.22 (m, 14H), 6.89– 6.82 (m, 4H), 6.71 (s, 4H), 5.29 (s, 2H), 4.78 (d, J = 15.8 Hz, 6H), 4.42(s, 2H), 4.22 (s, 4H), 2.22 (s, 12H). The hydroxyl-containing intermediate (1-13) (10.0 mmol) was added to a dry reaction flask, dissolved in 150 mL of anhydrous dichloromethane, and cooled to 0 °C under nitrogen protection and in the dark. Triethylamine (25.0 mmol, 2.53 g, 3.5 mL) and DMAP (1.0 mmol, 0.12 g) were added, followed by the slow dropwise addition of a solution prepared from chloroacetyl chloride (20.0 mmol, 2.26 g) and 30 mL of anhydrous dichloromethane over 30 min, with the reaction temperature controlled not to exceed 5 °C. After the addition was complete, the reaction was continued at 0 °C for 1 h, followed by a 4 h reaction at room temperature. After the reaction was complete, 150 mL of deionized water was slowly added at 0 °C to quench the reaction, and the mixture was extracted three times (3 × 100 mL) with dichloromethane. The organic phases were combined and extracted sequentially with 1 mol·L⁻¹... - The product was washed with hydrochloric acid solution (2 × 100 mL), saturated sodium bicarbonate solution (2 × 100 mL), and saturated sodium chloride solution (100 mL), dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography with dichloromethane / methanol as the eluent (100:1 to 50:1) to give a chlorine-containing intermediate (1-14). 1 H NMR (500 MHz, CDCl3) δ 7.94 (s, 2H), 7.38 – 7.22 (m,14H), 7.05 (s, 4H), 6.86 (d, J = 7.5 Hz, 4H), 4.88 (s, 2H), 4.83 (s, 4H), 4.59(s, 4H), 4.35 (s, 2H), 4.06 (s, 4H), 2.22 (s, 12H). The above-mentioned chlorine-containing intermediate (1-14) and sodium 3-(dimethylamino)propane-1-sulfonate (20.0 mmol, 3.78 g) were dissolved in acetonitrile (50 mL), and the mixture was stirred at 60 °C for 12 h. After the reaction was completed, the solvent was removed, and the crude product was purified by recrystallization to obtain the target low-migration photoinitiator (T-1). 1H NMR (500 MHz, DMSO-d6) δ 7.91 (s, 2H), 7.38 – 7.22 (m, 14H), 7.05 (s, 4H), 6.86 (d, J = 7.5 Hz, 4H), 5.10 (s, 2H), 4.77 (d, J = 14.8 Hz, 6H), 4.43 (s, 4H), 4.15 (s, 4H), 3.40 (t, J = 10.9 Hz,4H), 3.30 (s, 12H), 2.85 (t, J = 12.5 Hz, 4H), 2.40 – 2.26 (m, 4H), 2.22 (s, 12H). Example 2 Synthesis of low-migration photoinitiator T-2 based on click chemistry, such as Figure 5 As shown, it includes the following steps: The chlorine-containing intermediate (1-14) obtained in Example 1 was used as the starting material.

[0055] The intermediate (1-14, 10.0 mmol) was dissolved in acetonitrile (50 mL), and sodium 3-(benzyl(methyl)amino)propane-1-sulfonate (20.0 mmol, 5.31 g) was added. The mixture was stirred at 60 °C for 12 h to allow the chlorinated functional groups in the intermediate to undergo a substitution reaction, thereby introducing the corresponding ionic structural unit into the molecule. After the reaction was complete, the solvent was removed, and the crude product was purified by recrystallization to obtain the target low-migration photoinitiator T-2. 1 H NMR (500 MHz, DMSO-d6) δ 7.66 (s, 2H), 7.39 – 7.04 (m, 25H), 7.02 (s, 4H), 6.88 – 6.78 (m, 4H), 5.14 (s, 2H), 4.79 (s, 4H), 4.68 (s, 2H), 4.63 (s, 4H), 4.26 (s, 4H), 4.20(s, 4H), 3.43 (s, 1H), 3.39 (s, 2H), 3.34 (d, J = 8.9 Hz, 7H), 2.78 (d, J = 2.7Hz, 1H), 2.73 (d, J = 2.1 Hz, 2H), 2.69 (d, J= 2.2 Hz, 1H), 2.35 – 2.15 (m,16H). Example 3 Synthesis of low-migration photoinitiator T-3 based on click chemistry, such as Figure 6 As shown, it includes the following steps: The chlorine-containing intermediate (1-14) obtained in Example 1 was used as the starting material.

[0056] The intermediate (1-14, 10.0 mmol) was dissolved in acetonitrile (50 mL), and sodium 4-(dimethylamino)butyrate (20.0 mmol, 3.06 g) was added. The mixture was stirred at 60 °C for 12 h to allow the chlorinated functional groups in the intermediate to undergo a substitution reaction, thereby introducing the corresponding ionic structural units into the molecule. After the reaction was complete, the solvent was removed, and the crude product was recrystallized to obtain the target low-migration photoinitiator T-3. 1 H NMR (500 MHz, DMSO-d6) δ 7.60 (s, 2H),7.49 – 7.20 (m, 14H), 7.05 (s, 4H), 6.91 – 6.82 (m, 4H), 5.14 (s, 2H), 4.92(s, 2H), 4.67 (s, 4H), 4.42 (s, 4H), 4.31 (s, 4H), 3.45 (s, 1H), 3.40 (s,2H), 3.35 (d, J = 8.0 Hz, 13H), 2.42 – 2.27 (m, 4H), 2.20 (d, J = 17.8 Hz, 12H), 2.11 (dd, J = 22.2, 2.5 Hz, 3H), 2.05 (s, 1H). Example 4 Synthesis of low-migration photoinitiator T-4 based on click chemistry, such as Figure 7 As shown, it includes the following steps: The chlorine-containing intermediate (1-14) obtained in Example 1 was used as the starting material.

[0057] The intermediate (1-14, 10.0 mmol) was dissolved in acetonitrile (50 mL), and sodium 4-(benzyl(methyl)amino)butyrate (20.0 mmol, 4.59 g) was added. The mixture was stirred at 60 °C for 12 h to allow the chlorinated functional groups in the intermediate to undergo a substitution reaction, thereby introducing the corresponding ionic structural unit into the molecule. After the reaction was complete, the solvent was removed, and the crude product was recrystallized to obtain the target low-migration photoinitiator T-4. 1 H NMR (500 MHz, DMSO-d6) δ 7.80 (s,2H), 7.41 – 7.06 (m, 25H), 7.04 (s, 4H), 6.90 – 6.79 (m, 4H), 5.08 (s, 2H), 4.94 (s, 2H), 4.79 (s, 4H), 4.68 (s, 4H), 4.60 (s, 4H), 4.12 (s, 4H), 3.44(s, 1H), 3.42 – 3.33 (m, 9H), 2.41 – 2.32 (m, 3H), 2.29 (d, J = 2.9 Hz, 1H), 2.22 (s, 12H), 2.12 – 1.93 (m, 4H). Example 5 Performance characterization of UV-curable compositions To evaluate the overall performance of the low-migration photoinitiators based on click chemistry of the present invention, the low-migration photoinitiators T-1 to T-4 prepared in Examples 1 to 4 were used as the experimental group, and the commercial photoinitiator ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L) was used as the comparative example. Under the same conditions, their photoresponse ability, photoinitiation performance, curing behavior, yellowing resistance, migration performance and storage stability were systematically evaluated.

[0058] First, prepare the UV curing system according to the following parts by weight: 50 parts polyurethane acrylate oligomer (PUA), 20 parts bisphenol A epoxy acrylate (EA), 20 parts 1,6-hexanediol diacrylate (HDDA), 7 parts trimethylolpropane triacrylate (TMPTA), 3 parts photoinitiator, 0.3 parts leveling agent, and 0.2 parts defoamer. Add each component sequentially to a brown reaction bottle and mechanically stir for 20 minutes at room temperature to ensure thorough mixing. Then add the corresponding photoinitiator and continue stirring in the dark for 30 minutes until a uniform, transparent liquid is formed. Add the leveling agent and defoamer, continue stirring for 10 minutes, and then sonicate for 10 minutes to remove air bubbles, obtaining the UV curing composition to be tested.

[0059] The obtained UV-curable composition was uniformly coated onto a clean glass substrate using an automated coating machine, with the wet film thickness controlled using a 50 μm wire rod. After coating, the substrate was allowed to stand for 1 min to eliminate flow marks and surface bubbles, and then cured by irradiation with a 365 nm LED UV light source at an intensity controlled at 100 mW·cm². - ², irradiation time 30 s. After curing, place the sample in a dark environment at room temperature for 24 h for later use.

[0060] (1) Light absorption performance test Weigh approximately 5 mg of each photoinitiator and prepare a solution with a concentration of 1.0 × 10⁻⁶ using acetonitrile. -4 mol·L - The solution was ultrasonically dispersed for 5 min and then filtered for later use. Tests were performed using a UV-Vis spectrophotometer, with acetonitrile as a blank reference. The scan range was 250–500 nm, and the scan rate was 300 nm·min. - ¹, record the maximum absorption wavelength and absorption intensity.

[0061] Table 1. Results of light absorption performance test

[0062] As shown in Table 1, the low-migration photoinitiator constructed based on click chemistry in this invention maintains an absorption wavelength similar to that of the commercial photoinitiator TPO-L, while the absorption intensity is slightly improved. This indicates that the click chemistry construction process does not significantly affect the photoinitiation center structure and still maintains a high photoresponse capability, which is beneficial to the utilization of light energy in the subsequent photocuring process.

[0063] (2) Photoinitiation performance test HDDA was used as the model monomer, and a photoinitiator was added to the model system at 3 wt% of the system mass. The mixture was stirred for 30 min under light-protected conditions to ensure thorough dispersion. Approximately 8 mg of sample was placed in an aluminum crucible and analyzed using Photo-DSC. The test temperature was set at 50 °C, and the nitrogen flow rate was controlled at 50 mL / min. - ¹, UV intensity is 40 mW·cm - ². Record the heat release curve and calculate the time to reach the maximum heat release rate (tmax) and the cumulative heat release.

[0064] Table 2. Photoinitiation performance test results

[0065] As shown in Table 2, the low-migration photoinitiator based on click chemistry of the present invention maintains the ability to generate rapid free radicals, while the cumulative heat release is slightly higher than that of the commercial photoinitiator TPO-L, indicating that the click chemistry construction structure does not significantly reduce the photoinitiation efficiency.

[0066] (3) Curing conversion rate test The above UV-curable composition was uniformly coated onto the surface of an infrared test piece, with a film thickness controlled to approximately 20 μm. Continuous irradiation with 365 nm ultraviolet light was used, and infrared spectra were acquired every 1 second, monitoring at 1635 cm⁻¹. - The double bond absorption peak at position ¹ changes, and the double bond conversion rate is calculated based on the change in peak area.

[0067] Table 3. Double bond conversion rate test results

[0068] As shown in Table 3, the low-migration photoinitiator based on click chemistry of the present invention maintains a high curing conversion ability, which is slightly higher than that of the commercial photoinitiator TPO-L. This indicates that the click chemistry linkage structure does not significantly affect the curing efficiency of the low-migration photoinitiator of the present invention.

[0069] (4) Yellowing resistance test The cured samples were then irradiated with 365 nm ultraviolet light for 60 seconds. The b* values ​​of the samples before and after irradiation were measured using a colorimeter according to the CIE L*a*b* color space. Five different locations were selected for each sample for testing, and the average value was taken. The change in yellow index was calculated. The smaller the change, the smaller the color change of the sample during ultraviolet irradiation and the better its yellowing resistance.

[0070] Table 4 Results of yellowing resistance test

[0071] As shown in Table 4, the Δb* of T-1 to T-4 is 2.8 to 3.4, which is lower than the 5.6 of the commercial photoinitiator TPO-L. This indicates that the cured film prepared using the low-migration photoinitiator of the present invention has a small change in yellow component during continued ultraviolet irradiation and has good yellowing resistance, which is beneficial for its application in photocuring systems with high appearance requirements, such as transparent coatings and optical adhesives.

[0072] (5) Migration performance test A 4.0 cm × 4.0 cm sample of cured film was cut and accurately weighed, with three replicates per group. Each sample was placed in a stoppered glass bottle, and 20.0 mL of 50% (v / v) ethanol aqueous solution was added as a simulation solution. The samples were then soaked at 50 °C in the dark for 48 h. After soaking, the samples were cooled to room temperature, and the supernatant was filtered through a 0.22 μm organic filter membrane for high-performance liquid chromatography (HPLC) analysis.

[0073] A C18 reversed-phase column (250 mm × 4.6 mm, 5 μm) was used at a column temperature of 30 ℃. The mobile phase was acetonitrile / water = 70:30 (v / v), with isocratic elution at a flow rate of 1.0 mL / min. - ¹ The injection volume was 20 μL, and the detection wavelength was 365 nm. A series of standard solutions were prepared using TPO-L and standards T-1 to T-4, respectively, to establish standard curves relating the peak area to the concentration of each analyte. The correlation coefficient R² of the standard curves was not less than 0.999. The concentration of the photoinitiator in the immersion solution was calculated based on the standard curves corresponding to the samples, and the average of three parallel tests was used as the migration rate, expressed in mg·L⁻¹. - ¹.

[0074] Table 5 Migration performance test results

[0075] As shown in Table 5, the migration amount of the low-migration photoinitiator based on click chemistry of the present invention is reduced by about 78.6% to 84.6% compared with the commercial photoinitiator TPO-L, indicating that the click chemistry construction strategy can effectively improve the retention ability of the photoinitiator in the curing system.

[0076] (6) Storage stability test The UV-curable composition was placed in a sealed brown bottle and kept at a constant temperature of 60 °C for 7 days. The viscosity change of the system before and after storage was tested, and the viscosity change rate was calculated.

[0077] Table 6 Storage stability test results

[0078] As shown in Table 6, the low-migration photoinitiator based on click chemistry of the present invention exhibits small viscosity changes during storage, which is much lower than the viscosity change rate of the commercial photoinitiator TPO-L. The low-migration photoinitiator of the present invention demonstrates good storage stability.

[0079] Based on the test results of light absorption performance, photoinitiation performance, curing conversion behavior, yellowing resistance, migration performance and storage stability, it can be seen that the present invention achieves a modular structural design of low-migration photoinitiators through a click chemistry construction strategy, and further improves the overall performance of the system while maintaining excellent photoinitiation ability.

[0080] The UV absorption performance test results show that the low-migration photoinitiator of this invention maintains an absorption wavelength and light absorption capacity similar to the commercial photoinitiator TPO-L, indicating that the introduction of the functional structural unit does not significantly weaken the photoresponse performance and can still effectively respond to conventional 365 nm UV light sources, providing a good foundation for the utilization of light energy in the subsequent rapid curing process.

[0081] The results of photoinitiation performance and curing conversion rate tests further show that the system of the present invention maintains a fast free radical generation capacity and a high double bond conversion level, indicating that the click chemical linkage structure does not significantly affect the activity of the photoinitiation center. While ensuring the low migration design, it can still maintain excellent curing efficiency and high reaction completion.

[0082] The yellowing resistance test results show that the low-migration photoinitiator constructed based on click chemistry in this invention has a low yellowing tendency after curing, indicating that structural optimization can effectively improve the appearance performance of the material, which is beneficial to its application in transparent coatings, optical adhesives and high-quality photocuring systems.

[0083] Migration performance test results show that the migration amount of the low-migration photoinitiator of this invention is reduced by about 78.6% to 84.6% compared with commercial photoinitiators. This indicates that the structural regulation effect formed by click chemistry can significantly improve the retention ability of photoinitiators in the curing system, thereby effectively reducing migration behavior, reducing potential migration risks and improving the long-term stability of materials.

[0084] Storage stability test results further show that the low-migration photoinitiator constructed based on click chemistry in this invention still maintains a small viscosity change under accelerated storage conditions, indicating that it has good formulation compatibility and storage stability, and can meet the requirements of actual processing and long-term use.

[0085] In summary, this invention achieves the synergistic integration of photoinitiation and low-migration functional units through click chemistry. While maintaining excellent photoresponse, rapid curing capability, and good appearance performance, it achieves the goal of significantly reducing migration behavior and improving system stability. It can balance photoinitiation efficiency, low migration performance, and application reliability, and is suitable for application fields with high requirements for migration behavior and long-term stability, such as UV-curable coatings, functional inks, optical adhesives, electronic packaging, and high-performance functional materials.

Claims

1. A low-migration photoinitiator constructed based on click chemistry, characterized in that, The general structural formula is as follows: R1, R2, R3, and R4 are independently selected from hydrogen, fluorine, trifluoromethyl, cyano, and C1–C. 20 Alkyl, aryl, or substituted aryl; The structural formula for R is as follows: R5, R6, R7, and R8 are independently selected from C1–C 10 Alkyl or hydroxyl-substituted alkyl; n is an integer from 1 to 20; M is a hydrogen ion, alkali metal ion, or organic ammonium salt cation; X is a halogen.

2. The low-migration photoinitiator based on click chemistry according to claim 1, characterized in that, Including the following compounds: 。 3. The method for synthesizing low-migration photoinitiators based on click chemistry according to claim 1, characterized in that, Includes the following steps: (1) Preparation of methoxy-substituted TPO-L intermediates containing terminal alkyne groups; (2) Preparation of intermediates containing azide groups and diazonium heterocyclic propylene structures; (3) The methoxy-substituted TPO-L intermediate containing terminal alkyne group obtained in step (1) and the intermediate containing azide group and diazonium ring propylene structure obtained in step (2) are subjected to a cycloaddition reaction of azide and alkyne in the presence of a catalyst to generate an intermediate containing 1,2,3-triazole structure. (4) The intermediate containing the 1,2,3-triazole structure obtained in step (3) is subjected to methoxy transformation under transformation conditions to obtain the hydroxylated intermediate; (5) Add chloroacetyl chloride to the hydroxyl-containing intermediate obtained in step (4) under low temperature conditions and react under alkaline conditions to induce acylation of the hydroxyl group and introduce a chlorine-containing active functional group to obtain a chlorine-containing intermediate. (6) The chlorine-containing intermediate obtained in step (5) and the compound containing tertiary amine groups and anionic groups are added to the reaction system to carry out the reaction, so as to introduce ionic structural units into the molecule and obtain a low-migration photoinitiator based on click chemistry.

4. The synthesis method according to claim 3, characterized in that, Step (1) to prepare TPO-L intermediates containing terminal alkyne methoxy substituted groups includes the following steps: (S1) Under nitrogen protection, 4-methoxy-2,6-dimethylbenzoyl chloride was added to a dry reaction flask and cooled to 0°C; then, diethyl phenylphosphonite was slowly added dropwise under stirring; the mixture was then brought to room temperature and the reaction was continued with stirring to obtain a methoxy-substituted TPO-L intermediate containing an acylphosphonate photoinitiator structure. (S2) Add sodium iodide or its hydrate and react under heating conditions to convert the phosphonate structure into the corresponding phosphonate intermediate; (S3) Dissolve the phosphonate intermediate obtained in step (S2) in water and adjust the system to acidic conditions with dilute acid to obtain the phosphonic acid intermediate; (S4) The phosphonic acid intermediate obtained in step (S3) is added to thionyl chloride and N,N-dimethylformamide is added in a catalytic amount, and the reaction is carried out under heating conditions to obtain phosphonyl chloride intermediate; (S5) The phosphonyl chloride intermediate obtained in step (S4) and propargyl alcohol are added to an organic solvent, an organic base is added under low temperature conditions, and an esterification reaction is carried out under stirring conditions to obtain a methoxy-substituted TPO-L intermediate containing a terminal alkyne group.

5. The synthesis method according to claim 3, characterized in that, Step (2) Preparation of intermediates containing azide and diazonium heterocyclic propylene structures includes the following steps: (S11) Dissolve 2,2-bis(bromomethyl)propane-1,3-diol in a polar solvent, add sodium azide, and stir the reaction under heating conditions to undergo a nucleophilic substitution reaction to convert it to azidomethyl, giving the 2,2-bis(azidomethyl)propane-1,3-diol intermediate; (S12) Dissolve the 2,2-bis(azidomethyl)propane-1,3-diol intermediate in an organic solvent, add an organic base under low temperature conditions, and slowly add p-toluenesulfonyl chloride under stirring conditions to generate the 2,2-bis(azidomethyl)propane-1,3-diol bis-p-toluenesulfonate intermediate. (S13) The intermediate 2,2-bis(azidomethyl)propane-1,3-diol bis-toluenesulfonate was dissolved in an organic solvent and 4-(3-(trifluoromethyl)-3H-diazacyclopropene-3-yl)phenol was subjected to a substitution reaction under alkaline conditions to obtain an intermediate containing an azide group and a diazacyclopropene structure.

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

7. A UV-curable composition, characterized in that, It includes the low-migration photoinitiator based on click chemistry as described in claim 1.

8. The application of the low-migration photoinitiator according to claim 1, characterized in that, Used in the field of photocurable materials.

9. The application according to claim 8, characterized in that, The photocurable materials include UV-curable adhesives, optical adhesives, and optoelectronic device encapsulation materials.

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