Novel photoinitiator as well as preparation method and application thereof

Abstract

The invention discloses a novel photoinitiator as well as a preparation method and application thereof, a thiophenol group substituted by methyl, ethyl or isopropyl is introduced into a molecular structure of the photoinitiator, so that the absorption wavelength of the photoinitiator is adaptive to a UV-LED light source of 365-405nm, and the problem that the existing photoinitiator is insufficient in matching with the UV-LED light source is solved. The preparation method comprises the following steps: carrying out acylating chlorination on 2, 4, 6-trimethylbenzoyl phenylphosphonic acid through thionyl chloride, condensing the 2, 4, 6-trimethylbenzoyl phenylphosphonic acid and substituted p-thiophenol in an organic solvent, and purifying to obtain a target product, and the preparation process is simple and convenient to operate and suitable for industrial production. The obtained photoinitiator shows good compatibility and efficient curing efficiency in a UV-LED photocuring system, can be widely applied to the fields of printing ink, photocureable coatings, UV adhesives and the like, and has important significance in promoting popularization of a UV-LED curing technology.

Description

Technical Field

[0001] This invention belongs to the field of organic chemistry technology, and more specifically, it relates to a novel photoinitiator, its preparation method, and its application. Background Technology

[0002] Photopolymerization technology, with its low volatile organic compound release, high efficiency, energy saving, and environmental friendliness, has been widely used in the fields of rapid-curing coatings, printing inks, and adhesives. The core of this technology lies in the photoinitiator system, which generates active free radicals under ultraviolet radiation, initiating polymerization reactions. Traditional photoinitiators are mainly divided into two categories: cleavage-type and hydrogen-abstraction-type. Cleavage-type initiators, such as benzoin derivatives and acetophenones, generate free radicals through photolytic bond cleavage, but their absorption spectra do not adequately match the radiation bands of emerging ultraviolet light-emitting diodes (LEDs). Hydrogen-abstraction-type initiators, such as benzophenone and thioxanthones, require tertiary amine co-initiators, and the cured products are prone to yellowing and odor residue.

[0003] Ultraviolet (UV) light-emitting diodes (LEDs), as a new generation of UV light sources, have significant advantages such as long lifespan, low energy consumption, and no mercury pollution, and are gradually replacing traditional mercury lamps in the field of photocuring. However, the characteristic radiation band of this light source is concentrated in the 365-405nm range, and the absorption efficiency of existing commercial photoinitiators in this band is generally insufficient. Although acylphosphine oxide initiators have high reactivity, their maximum absorption wavelength is still insufficient to fully cover the long-wave radiation requirements of UV LEDs, resulting in limited curing efficiency. Furthermore, traditional initiators have insufficient solubility in resin systems, which easily leads to compatibility issues, further restricting their application in high-end photocurable materials.

[0004] Furthermore, existing photoinitiator preparation processes suffer from complex operations and poor industrial adaptability, making it difficult to meet the demands of large-scale production. Therefore, developing a novel photoinitiator that can efficiently match UV-LED wavelengths, especially 405nm, while possessing good compatibility and high curing efficiency, and with a simple preparation process, has become a key technological bottleneck in promoting the green and efficient development of photocuring technology. This invention successfully solves the aforementioned technical problems through molecular structure design and preparation process optimization, providing a high-performance photoinitiator solution for UV-LED curing systems. Summary of the Invention

[0005] The purpose of this invention is to provide a novel photoinitiator, its preparation method, and its application. The preparation process is simple to operate and suitable for industrial production. The obtained photoinitiator exhibits good compatibility and high curing efficiency in UV-LED curing systems and can be widely used in printing inks, UV-curable coatings, UV adhesives, and other fields. It is of great significance for promoting the popularization of UV-LED curing technology.

[0006] The technical objective of this invention is achieved through the following technical solution:

[0007] The technical objective of the first aspect of this invention is to provide a novel photoinitiator, the chemical structural formula of which is shown in (1):

[0008] (1)

[0009] R1 is methyl, ethyl, or isopropyl.

[0010] The second aspect of the present invention aims to provide a method for preparing a novel photoinitiator, comprising the following steps:

[0011] S1. 2,4,6-Trimethylbenzoylphenylphosphonic acid was dispersed in organic solvent I, and thionyl chloride was added dropwise at room temperature (20-30°C). The reaction was carried out at 20-30°C for 1-3 hours and at 40-45°C for 1-3 hours. The solvent was evaporated and dried to obtain the oily product 2,4,6-trimethylbenzoylphenylphosphonic chloride.

[0012] The reaction formula is as follows:

[0013]

[0014] S2. Dissolve the 2,4,6-trimethylbenzoylphenylphosphonochloride and p-thiophenol with the R1 group in organic solvent II. Add triethylamine dropwise at 20-25°C and react at 20-25°C for 1-2 hours. Perform thin-layer chromatography analysis. The reaction is then complete. The product is washed sequentially with water, 4-6% dilute hydrochloric acid, and saturated sodium bicarbonate solution. After washing again with water, the organic phase is separated and concentrated. Then, an alcohol solvent is added to dissolve the product at 60-70°C. The temperature is lowered to 10-20°C, and the product is filtered to obtain a wet product. The solvent is then evaporated to obtain a novel photoinitiator. The reaction formula is as follows:

[0015] .

[0016] Preferably, the molar ratio of 2,4,6-trimethylbenzoylphenylphosphonic acid and thionyl chloride in step S1 is 1:(1.5-1.52).

[0017] Preferably, in step S1, the mass ratio of organic solvent I to 2,4,6-trimethylbenzoylphenylphosphonic acid is (2.5-7.5):1, the reaction temperature is first maintained at 20-30℃ for 1-3 hours, and then the temperature is increased to 40-45℃ for 1-3 hours.

[0018] Preferably, in step S2, the molar ratio of 2,4,6-trimethylbenzoylphenylphosphonochloride, p-thiophenol with different substituents, and triethylamine is 1:(0.9-1):(0.9-1.1), the reaction temperature is 20-25℃, the reaction time is 1-2h, and thin-layer chromatography is used to monitor until the spot of the raw material disappears.

[0019] Preferably, in step S2, the mass ratio of 2,4,6-trimethylbenzoylphenylphosphonochloride, organic solvent II, water, and alcohol solvent is 1:(5-10):(2-5):(4-8), and the alcohol solvent is ethanol.

[0020] Preferably, the organic solvent I in step S1 is at least one of toluene, chloroform, and tetrahydrofuran; and the organic solvent II in step S2 is at least one of toluene, acetonitrile, and ethyl acetate.

[0021] The technical objective of the third aspect of this invention is to provide the above-mentioned novel photoinitiator that can be used in UV-LED light source curing systems with wavelengths in the range of 365-405nm, wherein the application fields include at least one of printing inks, photocurable coatings or UV adhesives.

[0022] In summary, the present invention has the following beneficial effects:

[0023] 1. This invention significantly broadens the ultraviolet absorption spectrum of photoinitiators by introducing methyl, ethyl, or isopropyl-substituted benzenethiophenol groups into the acylphosphine oxide core, enabling efficient spectral matching with UV-LED light sources with wavelengths of 365-405nm. This solves the technical bottleneck of insufficient absorption efficiency of existing photoinitiators in the long-wave ultraviolet region, and is especially suitable for new UV-LED light source systems such as 405nm, providing core material support for the green upgrading of photocuring technology.

[0024] 2. In this invention, the photoinitiator can efficiently generate active free radicals under ultraviolet light-emitting diode radiation, achieving rapid polymerization without relying on tertiary amine co-initiators, effectively avoiding yellowing and odor residue problems caused by auxiliary agent migration; at the same time, the introduction of alkyl substituents significantly improves its compatibility and dispersion stability in the resin system, ensuring high transparency and uniformity of the cured film.

[0025] 3. This invention employs a two-step reaction pathway of acyl chloride-condensation. By optimizing reaction conditions and post-processing procedures, it achieves simplified preparation of high-purity products. Specifically, the acyl chloride step is completed within a mild temperature range, effectively suppressing side reactions; the condensation reaction is monitored in real-time using thin-layer chromatography to ensure complete reaction; and fractional washing combined with solvent crystallization purification technology avoids complex column chromatography operations, significantly improving the feasibility of industrial production. This photoinitiator exhibits excellent initiation efficiency and formulation adaptability in UV-LED curing systems and can be widely applied in green manufacturing processes in fields such as printing inks, UV-curable coatings, and adhesives, providing core material support for the large-scale promotion of UV-LED curing technology. Attached Figure Description

[0026] Figure 1 This is the H-NMR nuclear magnetic spectrum of the final product obtained in Example 1 of the present invention;

[0027] Figure 2 This is the UV spectrum of the final product obtained in Example 1 of the present invention. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used, unless otherwise specified, were all purchased from conventional biochemical reagent stores. All quantitative experiments in the following examples were performed in triplicate, and the data are the average of the three replicates or the average ± standard deviation.

[0030] Example 1

[0031] A novel photoinitiator preparation method includes the following preparation steps:

[0032] S1. 200g of toluene was used to disperse 57.6g of 2,4,6-trimethylbenzoylphenylphosphonic acid. 35.7g of thionyl chloride was added dropwise at room temperature (28℃). The reaction was carried out at 30℃ for 2 hours and then at 42℃ for 2 hours. After the reaction was completed, the toluene was evaporated to dryness. The substrate was dried twice with 100g of toluene to obtain 2,4,6-trimethylbenzoylphenylphosphonic chloride.

[0033] S2. Dissolve 30.6 g of 2,4,6-trimethylbenzoylphenylphosphonochloride and 14.4 g of p-isopropylbenzylthiophenol in 200 g of toluene. Add 10 g of triethylamine dropwise at 25 °C and react at 25 °C for 1.5 h. Perform thin-layer chromatography to determine the reaction end. Wash the mixture sequentially with 50 g of water, 50 ml of 5% dilute hydrochloric acid, saturated sodium bicarbonate solution, and 50 g of water twice to obtain an organic layer. Dry the toluene by rotary evaporation, add 150 g of anhydrous ethanol at 65 °C to dissolve the oily substance, cool to 10 °C, filter to obtain a wet product, and evaporate the solvent by rotary evaporation to obtain the solid product, the photoinitiator.

[0034] Example 2

[0035] A novel photoinitiator preparation method includes the following preparation steps:

[0036] S1. Disperse 57.2 g of 2,4,6-trimethylbenzoylphenylphosphonic acid with 180 g of toluene, add 35.5 g of thionyl chloride dropwise at room temperature (25 °C), react at 30 °C for 1.6 h, then react at 43 °C for 2.6 h, and the reaction is complete. Evaporate the toluene to dryness, and dry the substrate twice with 90 g of toluene to obtain 2,4,6-trimethylbenzoylphenylphosphonic chloride;

[0037] S2. Dissolve 30.1 g of 2,4,6-trimethylbenzoylphenylphosphonochloride and 13.6 g of p-isopropylbenzylthiophenol in 180 g of toluene. Add 9.2 g of triethylamine dropwise at 23°C and react at 25°C for 1.3 h. Perform thin-layer chromatography to determine the reaction end. Wash the mixture sequentially with 45 g of water, 45 g of 5% dilute hydrochloric acid, saturated sodium bicarbonate solution, and 45 g of water twice to obtain an organic layer. Dry the toluene by rotary evaporation, add 140 g of anhydrous ethanol at 70°C to dissolve the oily substance, cool to 10°C, filter to obtain a wet product, and evaporate the solvent by rotary evaporation to obtain the solid product, the photoinitiator.

[0038] Example 3

[0039] A novel photoinitiator preparation method includes the following preparation steps:

[0040] S1. 57.6 g of 2,4,6-trimethylbenzoylphenylphosphonic acid was dispersed in 300 g of chloroform, and 36.1 g of thionyl chloride was added dropwise at room temperature (25°C). The reaction was carried out at 25°C for 1.9 h and at 42°C for 1.8 h. After the reaction was completed, the chloroform was evaporated to dryness, and the substrate was dried twice with 120 g of chloroform to obtain 2,4,6-trimethylbenzoylphenylphosphonic chloride.

[0041] S2. Dissolve 30.6g of 2,4,6-trimethylbenzoylphenylphosphonochloride and 13.5g of p-ethylthiophenol in 250g of acetonitrile. Add 10.8g of triethylamine dropwise at 25℃ and react at 25℃ for 1.5h. Perform thin-layer chromatography to determine the reaction end. Wash the mixture sequentially with 60g of water, 60g of 5% dilute hydrochloric acid, saturated sodium bicarbonate solution, and 60g of water twice to obtain an organic layer. Dry the organic layer with acetonitrile, add 160g of anhydrous ethanol at 60℃ to dissolve the oily substance, cool to 10℃, filter to obtain a wet product, and dry the solvent to obtain the solid product, the photoinitiator.

[0042] Example 4

[0043] A novel photoinitiator preparation method includes the following preparation steps:

[0044] S1. 250g of tetrahydrofuran was used to disperse 57.6g of 2,4,6-trimethylbenzoylphenylphosphonic acid. 36.0g of thionyl chloride was added dropwise at room temperature (20°C). The reaction was carried out at 20°C for 3 hours and then at 45°C for 1.2 hours. After the reaction was completed, the tetrahydrofuran was evaporated to dryness. The substrate was dried twice with 110g of tetrahydrofuran to obtain 2,4,6-trimethylbenzoylphenylphosphonic chloride.

[0045] S2. Dissolve 30.6 g of 2,4,6-trimethylbenzoylphenylphosphonochloride and 11.6 g of p-methylthiophenol in 220 g of ethyl acetate. Add 9.48 g of triethylamine dropwise at 20-25 °C and react at 21 °C for 2 h. Perform thin-layer chromatography analysis to determine the reaction end. Wash the mixture sequentially with 55 g of water, 55 g of 5% dilute hydrochloric acid, saturated sodium bicarbonate aqueous solution, and 55 g of water twice to obtain an organic layer. Dry the organic layer with ethyl acetate, add 140 g of anhydrous ethanol at 68 °C to dissolve the oily substance, cool to 10 °C, filter to obtain a wet product, and dry the solvent to obtain the solid product, the photoinitiator.

[0046] Example 5

[0047] A novel photoinitiator preparation method includes the following preparation steps:

[0048] S1. 220g of 2,4,6-trimethylbenzoylphenylphosphonic acid was dispersed in chloroform and 34.72g of thionyl chloride was added dropwise at room temperature (28℃). The reaction was carried out at 30℃ for 2 hours and then at 43℃ for 2.5 hours. After the reaction was completed, the chloroform was evaporated to dryness, and the substrate was dried twice with 110g of chloroform to obtain 2,4,6-trimethylbenzoylphenylphosphonic chloride.

[0049] S2. Dissolve 28g of 2,4,6-trimethylbenzoylphenylphosphonochloride and 12.32g of p-ethylthiophenol in 230g of acetonitrile. Add 9.8g of triethylamine dropwise at 25℃ and react at 25℃ for 1.2h. Perform thin-layer chromatography analysis to determine the reaction end. Wash the mixture sequentially with 50g of water, 50g of 5% dilute hydrochloric acid, saturated sodium bicarbonate aqueous solution, and 50g of water twice to obtain an organic layer. Dry the organic layer with acetonitrile, add 150g of anhydrous ethanol at 70℃ to dissolve the oily substance, cool to 10℃, filter to obtain a wet product, and dry the solvent to obtain the solid product, the photoinitiator.

[0050] Comparative Example 1

[0051] A novel method for preparing a photoinitiator differs from Example 1 in that in step S2, p-isopropylthiophenol is replaced with an equal amount of unsubstituted thiophenol, while other conditions remain the same as in Example 1.

[0052] Comparative Example 2

[0053] A novel method for preparing a photoinitiator differs from Example 1 in that in step S2, p-isopropylthiophenol is replaced with an equal amount of p-isopropylphenol, while other conditions remain the same as in Example 1.

[0054] Comparative Example 3

[0055] A novel method for preparing a photoinitiator differs from Example 1 in that in step S2, p-isopropylthiophenol is replaced with an equal amount of p-tert-butylthiophenol, while other conditions remain the same as in Example 1.

[0056] Comparative Example 4

[0057] A novel method for preparing a photoinitiator differs from Example 1 in that in step S2, p-isopropylthiophenol is replaced with an equal amount of p-chlorothiophenol, while other conditions remain the same as in Example 1.

[0058] The performance of the novel photoinitiators prepared in Examples 1-5 and Comparative Examples 1-4 was tested, and the test results are shown in Table 1.

[0059] Take 1 part by weight of the photoinitiator sample prepared in Examples 1-5 and Comparative Examples 1-4 and mix it with 99 parts by weight of 1,6-hexanediol diacrylate. Stir until dissolved to obtain the sample before curing.

[0060] Take the sample before curing, coat it evenly on the test plate, and then irradiate it with a 365-405nm ultraviolet light radiation device with an ultraviolet light source power of 2kw to obtain the fully cured sample.

[0061] Table 1

[0062] Test Project Peak absorption wavelength (nm) Absorbance at 405nm (AU) Curing time (s) Solubility of alcohol g / 100mL Yellowing index (ΔE) Migration rate (%) Example 1 390 0.83 8 58 1.5 2.3 Example 2 390 0.80 9 55 1.6 2.8 Example 3 390 0.81 8 60 1.5 3.2 Example 4 390 0.82 8 57 1.6 3.4 Example 5 390 0.81 9 53 1.6 3.8 Comparative Example 1 380 0.58 15 32 3.2 12.2 Comparative Example 2 380 0.23 ＞55 30 4.8 30.1 Comparative Example 3 390 0.75 12 45 2.8 8.9 Comparative Example 4 380 0.50 20 38 3.5 15.6

[0063] As shown in the table, the photoinitiators in Examples 1-5 exhibit excellent performance across various indicators: the peak absorption wavelength is stable at 390 nm, the absorbance at 405 nm reaches 0.80-0.83 AU, the curing time is only 8-9 s, the ethanol solubility is 53-60 g / 100 mL, the yellowing index ΔE ≤ 1.6, and the migration rate is as low as 2.3%-3.8%. This is due to the synergistic effect of the para-alkylbenzene thiophenol substituents in their molecular structure. The electron-donating effect of the alkyl group expands the conjugated system, enabling efficient matching of the absorption spectrum with the UV-LED light source, while also enhancing compatibility with the resin. The presence of the thiophenol group ensures efficient generation of free radicals, shortening the curing time, while the steric hindrance effect of the alkyl chain reduces intermolecular interactions, lowering the risk of yellowing and reducing mass migration.

[0064] The comparative examples were significantly inferior to the examples. In Comparative Example 1, due to the lack of substitution of thiophenol, the conjugated system had insufficient electron density, resulting in a blue shift of the absorption wavelength to 380 nm and a decrease in absorbance at 405 nm to 0.58 AU. This led to a prolonged curing time of 15 s, a sharp drop in solubility to 32 g / 100 mL, and an increase in mobility to 12.2%. In Comparative Example 2, thiophenol was replaced with phenol. The strong electronegativity of the oxygen atom disrupted the conjugated plane, resulting in an absorbance of only 0.23 AU, a curing time exceeding 55 s, a yellowing index as high as 4.8, and a mobility of 30.1%, demonstrating the indispensability of the thiophenol group for free radical initiation. Although Comparative Example 3 used tert-butyl substitution, the large steric hindrance affected the molecular conjugation efficiency, resulting in a 7.3% decrease in absorbance compared to the examples and a prolonged curing time to 12 s. In Comparative Example 4, the electron-withdrawing effect of the chlorine atom caused a blue shift of the absorption wavelength, resulting in an absorbance of only 0.50 AU, a curing time of 20 s, and an increase in mobility to 15.6%. The above differences confirm that the alkyl substituent at the para position of thiophene is a key factor in improving the spectral matching of photoinitiators, curing efficiency, and material stability through the synergistic optimization of electronic effects and steric hindrance. Deviating from this structural design will lead to a comprehensive decline in performance.

[0065] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A novel photoinitiator, characterized in that, The chemical structural formula of the initiator is shown in (1): （1） R1 is methyl, ethyl, or isopropyl.

2. The method for preparing a novel photoinitiator according to claim 1, characterized in that, Includes the following steps: S1. 2,4,6-Trimethylbenzoylphenylphosphonic acid was dispersed in organic solvent I, and thionyl chloride was added dropwise to carry out the reaction. The solvent was evaporated and dried to obtain the oily product 2,4,6-trimethylbenzoylphenylphosphonic chloride. The reaction formula is as follows: ； S2. The 2,4,6-trimethylbenzoylphenylphosphonochloride and p-thiophenol with the R1 group are dissolved in organic solvent II. Triethylamine is added dropwise to carry out the reaction. After the reaction is carried out, the product is washed with water, acid, and alkali, followed by another water washing. The organic phase is separated and concentrated. Then, it is purified by crystallization in an alcohol solvent and dried to obtain a novel photoinitiator. The reaction formula is as follows: 。 3. The method for preparing a novel photoinitiator according to claim 2, characterized in that, In step S1, the molar ratio of 2,4,6-trimethylbenzoylphenylphosphonic acid to thionyl chloride is 1:(1.5-1.52).

4. The method for preparing a novel photoinitiator according to claim 2, characterized in that, In step S1, the mass ratio of organic solvent I to 2,4,6-trimethylbenzoylphenylphosphonic acid is (2.5-7.5):

1. The reaction temperature is first maintained at 20-30℃ for 1-3 hours, and then the temperature is increased to 40-45℃ for 1-3 hours.

5. The method for preparing a novel photoinitiator according to claim 2, characterized in that, In step S2, the molar ratio of 2,4,6-trimethylbenzoylphenylphosphonochloride, p-thiophenol with different substituents, and triethylamine is 1:(0.9-1):(0.9-1.1). The reaction temperature is 20-25℃, the reaction time is 1-2h, and the reaction is monitored by thin-layer chromatography until the spot of the raw material disappears.

6. The method for preparing a novel photoinitiator according to claim 2, characterized in that, In step S2, the mass ratio of 2,4,6-trimethylbenzoylphenylphosphonochloride, organic solvent II, water, and alcohol solvent is 1:(5-10):(2-5):(4-8), and the alcohol solvent is ethanol.

7. The method for preparing a novel photoinitiator according to claim 2, characterized in that, The organic solvent I mentioned in step S1 is at least one of toluene, chloroform, and tetrahydrofuran; the organic solvent II mentioned in step S2 is at least one of toluene, acetonitrile, and ethyl acetate.

8. The application of the novel photoinitiator according to claim 1 in a UV-LED curing system, characterized in that: The photoinitiator is used in UV-LED light source curing systems with a wavelength range of 365-405nm, and the application fields include at least one of printing inks, UV-curable coatings, or UV adhesives.

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