Self-hydrogen-supplying type Ⅱ macromolecular photoinitiator, preparation method and application thereof

Abstract

This invention discloses a self-hydrogen-donating type II macromolecular photoinitiator, its preparation method, and its application. This macromolecular photoinitiator possesses advantages such as self-hydrogen donation, polymerizability, and low migration. The self-hydrogen-donating type II macromolecular photoinitiator of this invention has a symmetrical molecular structure as shown in Formula I: I. Each molecule in its symmetrical molecular structure contains two benzophenone chromophores, two electron-donating amide bonds, and two acrylamide double bonds.

Description

Technical Field

[0001] This invention relates to a photoinitiator, its preparation method, and its application; more specifically, it relates to a self-hydrogen-donating type II macromolecular photoinitiator, its preparation method, and its application. Background Technology

[0002] Ultraviolet (UV) curing technology, with its significant advantages such as high efficiency, energy saving, and environmental friendliness, has been widely used in various fields such as coatings, inks, adhesives, and 3D printing. Photoinitiators are an indispensable core component of UV curing systems, and their performance fundamentally determines the rate of the curing reaction, monomer conversion rate, and various physicochemical properties of the final cured material.

[0003] Among numerous photoinitiators, benzophenone and its derivatives are the most widely used type II photoinitiators. Their mechanism of action involves absorbing ultraviolet light energy and then synergistically interacting with an external hydrogen donor (such as small-molecule amine compounds) to generate reactive free radicals capable of initiating polymerization through hydrogen abstraction. However, this traditional system has a fundamental drawback: both the small-molecule benzophenone photoinitiator itself and its essential amine co-initiators inherently possess small molecular weights, are prone to migration, and are highly volatile. This makes them extremely susceptible to migrating from the cured polymer network, causing not only stickiness and residual odors on the product surface but also long-term pollution and toxicity risks in fields with extremely high safety requirements, such as food packaging, medical devices, and children's products. Furthermore, these small molecules have limited compatibility with the polymer resin matrix, potentially initiating phase separation and affecting the material's optical transparency and mechanical homogeneity.

[0004] To address the migration problem of small-molecule photoinitiators, the industry has generally adopted a "macromolecularization" strategy, which involves chemically bonding photosensitive groups such as benzophenone to the polymer backbone. While this method effectively confines the photoinitiator unit and reduces its own migration, it does not fundamentally solve the problems caused by its paired, equally migratory amine co-initiators. These small-molecule amines are often the main sources of odor, yellowing, and biotoxicity. Therefore, developing a novel macromolecular photoinitiator that integrates highly efficient photoinitiation functionality with an intrinsic, fixed "hydrogen-donating / electron-donating" capability, thereby improving efficiency and completely eliminating dependence on externally added small-molecule amines, is crucial and essential for solving the aforementioned industry pain points. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a self-hydrogen-supplying type II macromolecular photoinitiator, which has the advantages of being self-hydrogen-supplying, polymerizable, and having low migration.

[0006] This invention also provides a method for preparing the self-hydrogen-donating type II macromolecular photoinitiator, as well as its application in photocurable compositions and in UV-curable coatings, inks, adhesives, 3D printing photosensitive resins, electronic component packaging materials, or substrate surface treatment coatings; its synthesis route is simple and efficient, the product structure is clear, and the performance is excellent, which is expected to provide a new generation of core raw material solutions for high-end, safe, and environmentally friendly photocurable materials.

[0007] The technical concept and principle of this invention are as follows: This invention constructs a novel macromolecular structure that integrates a "photosensitive chromophore," an "intramolecular hydrogen donor," and a "polymerizable anchoring group." This molecule not only significantly reduces its own migration through "macromolecularization," but also utilizes an intramolecular self-donating hydrogen mechanism, employing electron-donating groups (such as nitrogen atoms in amide bonds) within its own structure to replace exogenous small-molecule amines, achieving intramolecular electron / hydrogen transfer under light irradiation and directly generating active species. This design completely eliminates the introduction of small-molecule amines into the formulation, fundamentally solving the safety and odor problems caused by the migration, volatilization, and residue of small-molecule co-initiators. Simultaneously, the polymerizable double bonds designed at both ends of this macromolecular structure enable it to be permanently anchored in the formed three-dimensional polymer network through covalent bonds during photopolymerization, achieving both physical and chemical locking, further ensuring the "zero migration" characteristic.

[0008] The technical solution of the present invention is as follows: The self-hydrogen-donating type II macromolecular photoinitiator of the present invention has a symmetrical molecular structure as shown in Formula I:

[0009] I Each molecule of this symmetrical molecular structure contains two benzophenone chromophores, two electron-donating amide bonds, and two acrylamide double bonds. The core skeleton of the self-hydrogen-donating type II macromolecular photoinitiator of this invention is methylenebisacrylamide. The hydrogen atoms of its secondary amine group (-NH-) react with an oxalate monoacrylamide chloride intermediate from a 4-hydroxybenzophenone derivative to form two amide bonds (-NH-CO-), thereby connecting two identical benzophenone moieties to both ends of the core skeleton, ultimately forming an "H"-shaped or "dumbbell"-shaped symmetrical macromolecular structure. This macromolecule is a single compound with a completely symmetrical structure, each molecule containing two benzophenone chromophores, two electron-donating amide bonds (-N-CO-), and two acrylamide double bonds (-NH-CO-CH=CH2). The maximum absorption peak λ of the self-hydrogen-donating type II macromolecular photoinitiator of this invention... max =295nm, maximum molar extinction coefficient: ε = 3.78 × 10 4 L·mol -1 ·cm -1 .

[0010] The preparation method of the self-hydrogen-donating type II macromolecular photoinitiator of the present invention includes the following steps: (1) Under inert gas protection and low temperature conditions, 4-hydroxybenzophenone is reacted with oxalyl chloride in an organic solvent to generate an intermediate with acyl chloride at the end; (2) In the presence of an inert atmosphere and an organic base, the intermediate obtained in step (1) is subjected to an amidation condensation reaction with methylenebisacrylamide in an organic solvent; (3) Separate and purify the reaction product of step (2) to obtain a self-hydrogen-donating type II macromolecular photoinitiator.

[0011] The preparation method of the self-hydrogen-donating type II macromolecular photoinitiator of the present invention further includes the following technical solution: the molar ratio of 4-hydroxybenzophenone to oxaloyl chloride in step (1) is 1:1 to 1.2; the low-temperature condition is a reaction temperature of 0°C to 10°C; the organic solvent is one or a combination of acetonitrile, tetrahydrofuran, dichloromethane, and N,N-dimethylformamide. A further technical solution is that the reaction in step (1) is carried out in the presence of an organic base, which is one or a combination of triethylamine, pyridine, and N,N-diisopropylethylamine. The molar ratio of the organic base to 4-hydroxybenzophenone is 1.1 to 1.2:1. Adding an organic base (such as triethylamine) during the reaction can neutralize the hydrogen chloride byproduct. Furthermore, low temperature (0-10°C) and slow dropwise addition are key to controlling reaction selectivity and preventing excessive reaction or hydrolysis of the oxaloyl chloride bifunctional group.

[0012] The preparation method of the self-hydrogen-supplying type II macromolecular photoinitiator of the present invention can be further described as follows: in step (2), the reaction temperature of the amidation condensation reaction is 0°C to 10°C, and the reaction time is 2 to 6 hours; the molar ratio of the intermediate to methylenebisacrylamide is 2:1; and the organic solvent is one or a combination of acetonitrile, tetrahydrofuran, N,N-dimethylformamide, and dimethyl sulfoxide. A further further technical solution is that the reaction in step (2) is carried out in the presence of an organic base, wherein the organic base is one or a combination of triethylamine, pyridine, and N,N-diisopropylethylamine; and the molar ratio of the amount of organic base to the intermediate with terminal acyl chloride generated in step (1) is 1.1 to 1.2:1. The highly reactive acyl chlorides at both ends of the intermediate undergo an amidation condensation reaction with the two secondary amine groups (-NH-) of the methylenebisacrylamide molecule, removing two molecules of hydrogen chloride to form two stable amide bonds, thereby covalently linking two benzophenone units to a central bridging unit to obtain the target macromolecule.

[0013] The self-hydrogen-supplying type II macromolecular photoinitiator described above can be used in photocurable compositions and in UV-curable coatings, inks, adhesives, 3D printing photosensitive resins, electronic component packaging materials, or substrate surface treatment coatings. A further technical solution is that the amount of the self-hydrogen-supplying type II macromolecular photoinitiator in the photocurable composition is 0.1% to 3% of the total mass of the composition.

[0014] The present invention has the following beneficial effects: 1) Enhancement by “Diechromophore”: Two benzophenone units are integrated within a single molecule. At the same molar concentration, its absorption capacity for ultraviolet light (especially ~345 nm and ~295 nm) is significantly stronger than that of a single chromophore molecule, which improves the photon capture efficiency and the molar extinction coefficient of the initiator, laying the foundation for high initiation efficiency.

[0015] 2) Intramolecular hydrogen donation effect: The nitrogen atom provided by the amide bond (-NH-CO-) in the molecule has a lone pair of electrons, which can act as an intramolecular hydrogen / electron donor. After photoexcitation, it undergoes intramolecular charge / energy transfer with the neighboring benzophenone carbonyl group, promoting the generation of reactive free radicals. This reduces or even eliminates the dependence on external small molecule amine co-initiators to a certain extent, simplifies the formulation, and reduces yellowing and off-odor problems caused by external amines.

[0016] 3) "Polymerizable Anchoring" Achieves Ultra-Low Migration: The acrylamide double bonds at both ends of the molecule are a key functional design feature. During UV curing, these double bonds can copolymerize with unsaturated monomers such as acrylates in the system, permanently and firmly anchoring the entire photoinitiator molecule within the generated three-dimensional cross-linked polymer network through covalent bonding. This fundamentally solves the migration and volatilization problems of small molecule initiators, endowing the final product with extremely high safety and meeting the most stringent regulatory requirements for food contact and medical applications.

[0017] 4) Optimized compatibility with macromolecular structure: The initiator has a moderate molecular weight (about 600-800 g / mol) and contains aromatic rings, ester bonds, and amide bonds similar to common photocurable resins (such as polyurethane acrylate and epoxy acrylate). Therefore, it has excellent compatibility with the resin matrix, which helps to form a uniform and transparent formulation system and avoids problems such as phase separation and haze caused by poor compatibility.

[0018] 5) Controllable synthesis and well-defined structure: Through a two-step reaction and precise 2:1 stoichiometric ratio control, well-defined compounds with completely symmetrical structures and a single molecular weight can be obtained in high yields, rather than polymers with a wide molecular weight distribution. This ensures batch stability and reproducibility of product performance, which is beneficial for industrial production and quality control. Attached Figure Description

[0019] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the self-hydrogen-supplying type II macromolecular photoinitiator of Example 1 of the present invention.

[0020] Figure 2 This refers to the ultraviolet-visible light absorption of the self-hydrogen-supplying type II macromolecular photoinitiator molecule in Example 1 of the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the embodiments. Example

[0022] In a 250 mL dry three-necked flask equipped with a magnetic stirrer, thermometer, constant-pressure dropping funnel, and nitrogen inlet tube, the air was purged with nitrogen. Oxaloyl chloride (7.09 g, 55 mmol) and 50 mL of anhydrous acetonitrile were added, and the mixture was cooled to 0–5 °C in an ice-water bath. In another container, 4-hydroxybenzophenone (9.91 g, 50 mmol) and triethylamine (6.07 g, 60 mmol) were dissolved in 100 mL of anhydrous acetonitrile, and this solution was transferred to a constant-pressure dropping funnel. Under vigorous stirring and while maintaining an internal temperature below 5 °C, the solution was slowly added dropwise to the oxalyl chloride solution over 2 hours. After the addition was complete, the reaction was continued for 2 hours below 5 °C to obtain reaction solution A containing the intermediate acyl chloride.

[0023] In another flask, methylenebisacrylamide (3.58 g, 25 mmol) and triethylamine (6.07 g, 60 mmol) were dissolved in 80 mL of anhydrous N,N-dimethylformamide (DMF) to obtain solution B. Under ice-water bath cooling and stirring, solution B was slowly added dropwise to reaction solution A through a dropping funnel over 1 hour. After the addition was complete, the reaction was continued with stirring for 4 hours at a temperature below 5°C.

[0024] After the reaction was complete, the reaction solution was cooled to room temperature and then slowly poured into 800 mL of ice water with stirring. Immediately, a large amount of pale yellow solid precipitated out. The solid was filtered, and the obtained solid was washed successively with a large amount of cold water, 5% sodium bicarbonate solution, and water until neutral, and finally washed with a small amount of cold ethanol. The wet solid was dried under vacuum at 50 °C for 12 hours to obtain a yellow crude product.

[0025] The crude product was dissolved in hot ethyl acetate, decolorized with activated carbon, and hot-filtered. The filtrate was concentrated to 1 / 3 of its original volume, and an equal volume of petroleum ether was added. The mixture was then allowed to stand overnight at 4°C for crystallization. After filtration, the resulting white crystals were washed with cold diethyl ether and dried under vacuum to obtain 24.5 g of the target product as a white powder, with a yield of approximately 65%. The product was characterized by 1H NMR and mass spectrometry. Figure 1 , Figure 2 It was confirmed to be the target macromolecular structure, namely a self-hydrogen-donating type II macromolecular photoinitiator.

[0026] Example 2 The molar ratio of 4-hydroxybenzophenone to oxaloyl chloride was adjusted to 1:1.2, and the amount of methylenebisacrylamide was adjusted accordingly. Other conditions were the same as in Example 1. After the reaction was completed, H-NMR monitoring showed that the starting material methylenebisacrylamide had basically disappeared, and the yield after purification was 68%.

[0027] Example 3 Application Example (UV Curing Varnish) Preparation of the photocurable composition: The self-hydrogen-donating type II macromolecular photoinitiator prepared in Example 1 of this invention (3 wt% of the total mass of the formulation), tripropylene glycol diacrylate (TPGDA, 60 wt%), 1,6-hexanediol diacrylate (HDDA, 30 wt%), polyurethane acrylate oligomer (CN9001, Sartoma, 7 wt%), and 0.1 wt% leveling agent (BYK-333) were mixed evenly to obtain a clear and transparent photocurable coating. The above coating was evenly coated onto a clean polyester (PET) film using a wire bar coater, with a wet film thickness of 20 μm. The coating was placed under a UV LED point light source with a dominant output wavelength of 365 nm (light intensity of 80 mW / cm²) for 3 seconds, and the coating quickly dried to form a cured film with high hardness, smooth surface, and good adhesion.

[0028] Example 4: Migration Test The cured film prepared in Example 3 was cut to the specified size and immersed in a 50% (v / v) ethanol aqueous solution (food simulant) and placed in a constant temperature oven at 40°C for 10 days. The immersion solution was removed, concentrated, and analyzed using high performance liquid chromatography-mass spectrometry (HPLC-MS). The results showed that no characteristic peaks from the macromolecular photoinitiator of this invention or its obvious degradation products were detected in the immersion solution. In contrast, under the same test conditions, the immersion solution of a cured film with the same formulation using an equimolar amount of a conventional small molecule benzophenone (BP) and methyl diethanolamine (MDEA) compound initiator showed obvious migration of BP and MDEA.

[0029] Comparative Example 1 A commercially available polymeric benzophenone photoinitiator (trade name, such as certain acrylic resins containing BP side groups) was used to replace the product of this invention at the same mass fraction (3 wt%) to formulate a UV-curable varnish as in Example 4. After curing, the varnish film was found to have slightly poor transparency and a slight haze, and the curing speed was slower than that of the formulation of this invention (requiring more than 5 seconds to achieve surface dryness). Although the migration test results were better than those of small molecule BP, trace amounts of UV-absorbing substances could still be detected after the migration test solution was concentrated, presumably low molecular weight polymer components.

[0030] The above experimental results demonstrate that the self-hydrogen-donating type II macromolecular photoinitiator provided by this invention not only has a reliable synthesis method, but also exhibits excellent comprehensive performance in photocuring applications: high initiation efficiency, excellent compatibility with resins, and near-zero migration characteristics achieved through polymerizable double bonds, giving it significant advantages and application potential in the high-end photocuring field.

Claims

1. A self-hydrogen-donating type II macromolecular photoinitiator, characterized in that, The initiator has a symmetrical molecular structure as shown in Formula I: I Each molecule in its symmetrical molecular structure contains two benzophenone chromophores, two electron-donating amide bonds, and two acrylamide double bonds.

2. A method for preparing a self-hydrogen-donating type II macromolecular photoinitiator as described in claim 1, characterized in that, Includes the following steps: (1) Under inert gas protection and low temperature conditions, 4-hydroxybenzophenone is reacted with oxalyl chloride in an organic solvent to generate an intermediate with acyl chloride at the end; (2) In the presence of an inert atmosphere and an organic base, the intermediate obtained in step (1) is subjected to an amidation condensation reaction with methylenebisacrylamide in an organic solvent; (3) Separate and purify the reaction product of step (2) to obtain a self-hydrogen-donating type II macromolecular photoinitiator.

3. The method for preparing the self-hydrogen-donating type II macromolecular photoinitiator according to claim 2, characterized in that, The molar ratio of 4-hydroxybenzophenone to oxaloyl chloride in step (1) is 1:1 to 1.2; the low-temperature condition is a reaction temperature of 0°C to 10°C; the organic solvent is one or a combination of acetonitrile, tetrahydrofuran, dichloromethane, and N,N-dimethylformamide.

4. The method for preparing the self-hydrogen-donating type II macromolecular photoinitiator according to claim 2, characterized in that, In step (2), the reaction temperature of the amidation condensation reaction is 0°C to 10°C, and the reaction time is 2 to 6 hours; the molar ratio of the intermediate to methylenebisacrylamide is 2:1; the organic solvent is one or a combination of acetonitrile, tetrahydrofuran, N,N-dimethylformamide, and dimethyl sulfoxide.

5. The method for preparing the self-hydrogen-donating type II macromolecular photoinitiator according to claim 2, characterized in that, The reaction described in step (1) is carried out in the presence of an organic base, which is one or a combination of triethylamine, pyridine, N,N-diisopropylethylamine, and the molar ratio of the organic base to 4-hydroxybenzophenone is 1.1~1.2:

1.

6. The method for preparing the self-hydrogen-donating type II macromolecular photoinitiator according to claim 2, characterized in that, The reaction described in step (2) is carried out in the presence of an organic base, which is one or a combination of triethylamine, pyridine, and N,N-diisopropylethylamine; the molar ratio of the amount of organic base to the intermediate with the terminal acyl chloride generated in step (1) is 1.1~1.2:

1.

7. The application of a self-hydrogen-supplying type II macromolecular photoinitiator as described in claim 1 in photocurable compositions and in UV-curable coatings, inks, adhesives, 3D printing photosensitive resins, electronic component packaging materials, or substrate surface treatment coatings.

8. The application according to claim 7, characterized in that, The amount of the self-hydrogen-supplying type II macromolecular photoinitiator used in the photocurable composition is 0.1% to 3% of the total mass of the composition.

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