A photoinitiator and its preparation method and application

Abstract

The invention belongs to the technical field of photoinitiators, and is specifically related to a kind of photoinitiator and its preparation method and application, by introducing POSS into thioxanthone system, its organic-inorganic hybrid structure can form a synergistic effect with thioxanthone molecule, widen the light absorption range, enable the complex to efficiently respond to ultraviolet light or even visible light, the nanoscale structure network formed by POSS can significantly reduce the mobility of photoinitiator, further improve the durability and safety of material. Through the intermolecular action with thioxanthone molecule, POSS can also promote the absorption of light energy and the efficient generation of free radicals, thereby significantly improving polymerization efficiency. This composite photoinitiator not only provides new ideas for photoinitiator design, but also shows broad application prospects in the fields of light-cured coatings, photosensitive materials and 3D printing.

Description

Technical Field

[0001] The invention belongs to the technical field of photoinitiators, and specifically relates to a photoinitiator and a preparation method and application thereof. Background Art

[0002] Photopolymerization technology (also known as light-curing technology) is a process that uses ultraviolet light or visible light to trigger the rapid conversion of liquid substances with chemical reactivity into solid substances. It has the advantages of being environmentally friendly, solvent-free, highly efficient, widely adaptable, low cost, and low energy consumption. Photoinitiators are key components of photopolymerization technology. They can generate free radicals or cations by absorbing light energy of a specific wavelength, thereby initiating the polymerization reaction of monomers. They have been widely used in the fields of light-curing coatings, inks, 3D printing materials, and biomedical materials.

[0003] Currently, common commercial photoinitiators mainly include acetophenones, oxidative initiators, and thioxanthones. Although these materials can meet some industrial needs, in practical applications, their initiation efficiency is limited by insufficient light absorption capacity at specific wavelengths and low free radical generation efficiency. At the same time, many commercial photoinitiators are prone to migration after curing, which not only affects the performance of the material, but also may cause potential toxicity problems. In addition, the narrow spectral response range also makes these initiators unable to efficiently adapt to the demand for diversified light sources in modern photopolymerization technology. In summary, commercial photoinitiators have significant limitations in initiation efficiency, mobility and spectral response range, which limits their further promotion and application.

[0004] Thioxanthone (TX) is a classic photoinitiator that has attracted much attention for its good light absorption ability and high initiation activity. Its unique molecular structure gives it strong absorption ability in the ultraviolet region, making it particularly suitable for free radical polymerization reactions. However, traditional thioxanthone initiators have some problems, including that the light absorption range is mainly concentrated in the ultraviolet light and the response ability to visible light is weak; the potential for molecular structure functionalization is limited, and it is difficult to meet the needs of composite and multifunctionalization. Summary of the invention

[0005] The purpose of the present invention is to provide a photoinitiator and its preparation method and application, which overcomes many limitations of traditional photoinitiators in terms of efficiency, mobility and spectral response by combining the inorganic skeleton of cage-type polysilsesquioxane (POSS) with the organic photosensitivity of thioxanthone. This composite photoinitiator not only provides new ideas for photoinitiator design, but also shows broad application prospects in the fields of photocurable coatings, photosensitive materials and 3D printing.

[0006] The overall inventive concept adopted by the present invention is:

[0007] As a new type of organic-inorganic hybrid nanoparticle, cage-type polysilsesquioxane (POSS) has high optical transparency and functionalized molecular structure. By introducing POSS into the thioxanthone system, it can not only enhance the spectral response range of the photoinitiator, but also effectively improve the polymerization efficiency through its unique molecular action. The composite of POSS and thioxanthone has achieved a significant improvement in performance. Its organic-inorganic hybrid structure can form a synergistic effect with the thioxanthone molecule, broaden the light absorption range, and enable the composite to efficiently respond to ultraviolet light and even visible light. The nanoscale structural network formed by POSS can significantly reduce the mobility of the photoinitiator and further improve the durability and safety of the material. Through the intermolecular action with the thioxanthone molecule, POSS can also promote the absorption of light energy and the efficient generation of free radicals, thereby significantly improving the polymerization efficiency.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] In a first aspect, the present invention provides a photoinitiator having a structure shown in Formula I:

[0010]

[0011] Formula I;

[0012] Where R is H or R 1 , R 1 for And R 1 The number is 3.

[0013] During the research, the inventors found that the effect of the number of thioxanthone photoinitiator molecules grafted on the silsesquioxane molecules (POSS) on the conversion rate and mobility in the free radical polymerization reaction of unsaturated amides mainly comes from the change in the density of the photoinitiator and its regulatory effect on the local chemical environment of the system.

[0014] When the number of grafted thioxanthone photoinitiators is less than 3, such as 1 grafted, the free radical generation rate in the system is relatively low, and the free radical concentration in the system is also relatively dispersed, so the migration of free radicals in the matrix is ​​less spatially restricted. In this case, the mobility is higher; and due to the slow generation of free radicals, the crosslinking density of the entire system may be low, which may affect the final mechanical strength of the material. This lower initiation efficiency will limit the overall conversion rate of the polymerization reaction.

[0015] When the number of grafted thioxanthone photoinitiators is 3, the photoinitiator of this structure not only acts as a photoinitiator in the polymerization, but also as a crosslinker to form a crosslinked network of polymer chains. The photoinitiator molecules significantly increase the local free radical generation rate, thereby accelerating the reaction rate and improving the conversion rate in the initial stage of the polymerization reaction.

[0016] However, when the initiator density is too high, such as when the number of grafted thioxanthone photoinitiators is greater than or equal to 4 (or when the thioxanthone photoinitiator is not modified with POSS), the thioxanthone photoinitiator molecules may experience staggered transitions during electron transitions due to large steric hindrance or π-π stacking, which seriously affects the initiation efficiency. This may lead to the self-shielding effect of light absorption, which will reduce the light utilization efficiency of the photoinitiator.

[0017] In contrast, the silsesquioxane molecule grafted with three photoinitiator molecules significantly increases the local free radical concentration during the reaction, resulting in an accelerated initial polymerization rate. This high free radical concentration helps to quickly increase the conversion rate, but at the same time it limits the diffusion of free radicals in the system, reduces mobility, and forms a denser structure, with higher conversion rate and crosslinking density.

[0018] In a second aspect, the present invention provides a method for preparing the photoinitiator according to the first aspect, comprising the following steps:

[0019] (1) Dissolve thiosalicylic acid in sulfuric acid, add phenoxyacetic acid, and carry out condensation reaction to obtain TX-COOH;

[0020] (2) Mixing TX-COOH and thionyl chloride to carry out chlorination reaction to obtain TX-Cl;

[0021] (3) dissolving octaaminopropyl polysilsesquioxane in a solvent, adding TX-Cl, and performing an acylation reaction to obtain the product;

[0022] Among them, the structures of TX-COOH and TX-Cl are shown below:

[0023] , .

[0024] In some other embodiments, in step (1), the mass ratio of thiosalicylic acid to phenoxyacetic acid is (1-2.5): (3-7.0);

[0025] The concentration of the thiosalicylic acid is 0.01-0.05 g·mL -1 ;

[0026] The condensation reaction conditions are sealed and protected from light, and reacted at room temperature for 70-75 hours.

[0027] In some other embodiments, in step (1), after the condensation reaction is completed, the product is further purified. The purification process comprises: adding the product to water and filtering to obtain a precipitate, dissolving the precipitate in dioxane at 35-45° C., taking the supernatant and adding water to precipitate, filtering and drying to obtain TX-COOH.

[0028] In some other embodiments, in step (2), the mixing ratio of TX-COOH to thionyl chloride is (0.1-0.3) g: (0.5-2.0) mL;

[0029] The chlorination reaction is carried out under light-proof, inert atmosphere, and at room temperature for 10-12 h.

[0030] In some other embodiments, in step (3), the mass ratio of octaaminopropyl polysilsesquioxane to TX-Cl is (300-550): (240-500);

[0031] The concentration of the octaaminopropyl polysilsesquioxane is 100-190 g·L -1 ;

[0032] The solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide and 1,4-dioxane; the solvent can fully dissolve the reactants and does not react with the reactants and products.

[0033] In some other embodiments, in step (3), the acylation reaction is carried out under an inert atmosphere at 45-55° C. for 10-12 h.

[0034] In some other embodiments, in step (3), after the acylation reaction is completed, the product is further purified, and the purification treatment is as follows: adding saturated brine and extracting with ethyl acetate, then extracting the organic phase with 10-15 wt% hydrochloric acid, and then adding anhydrous magnesium sulfate to the extracted organic phase, filtering and drying.

[0035] In a third aspect, the present invention provides the use of the photoinitiator described in the first aspect in free radical polymerization of unsaturated amides, photocurable coatings, photosensitive materials and 3D printing.

[0036] In some other embodiments, the unsaturated amide is acrylamide.

[0037] Beneficial effects of the present invention:

[0038] (1) During the preparation of the POSS-3TX complex, no additional activator is required and the process can be carried out at room temperature or under mild conditions.

[0039] (2) The introduction of POSS not only maintains the ultraviolet light absorption ability of TX-COOH, but also expands and optimizes its spectral response range. The maximum absorption wavelength is around 400 nm, which has a wider wavelength usage range, providing the possibility for improving the performance of composite materials in photoinitiation and photosensitization applications.

[0040] (3) POSS-3TX can release free radicals more evenly and quickly, thereby initiating acrylamide polymerization more efficiently without the need to add a co-initiator. The conversion rate reaches 75% in 200 s. When detected by high-sensitivity fluorescence spectroscopy, the mobility is even lower, with a maximum mobility of only 4.1%. It can significantly improve the initiation efficiency of the initiator and optimize the polymerization kinetics, providing a new direction for the design of efficient photoinitiator systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0042] Figure 1 It is the MALDI-TOF / TOF image of POSS-3TX in the embodiment of the present invention;

[0043] Figure 2 POSS-8NH in the embodiment of the present invention 2 , IR spectra of TX-COOH and POSS-3TX;

[0044] Figure 3 It is the ultraviolet spectrum of TX, TX-COOH and POSS-3TX in the embodiment of the present invention;

[0045] Figure 4 The intensity and double bond conversion rate of acrylamide polymerization initiated by TX-COOH and POSS-3TX in the embodiment of the present invention, wherein A is the intensity of acrylamide polymerization initiated by TX-COOH, B is the intensity of acrylamide polymerization initiated by POSS-3TX, and C is the double bond conversion rate of acrylamide polymerization initiated by TX-COOH and POSS-3TX;

[0046] Figure 5 is the mobility of TX-COOH and POSS-3TX in acrylamide hydrogel in the embodiment of the present invention;

[0047] Figure 6 The mechanical properties of the hydrogel are obtained by initiating monomer polymerization using three photoinitiators, TX-COOH, POSS-TX and POSS-3TX, in the embodiments of the present invention. DETAILED DESCRIPTION

[0048] Those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. Specific conditions are not specified in the examples, and the methods are carried out according to conventional conditions or conditions recommended by the manufacturer. The raw materials used without indicating the manufacturer are all conventional products available commercially.

[0049] 1. Preparation of Photoinitiator

[0050] Experimental reagents

[0051] Thiosalicylic acid (AR) and phenoxyacetic acid (AR) were purchased from MacLean Reagent Co., Ltd.; thionyl chloride (AR) and dimethylformamide (anhydrous grade) were purchased from Aladdin Reagent Co., Ltd.; hydrochloric acid (AR) and sulfuric acid (AR) were purchased from Yantai Yuandong Reagent Co., Ltd.; 1,4-dioxane (AR) was purchased from Fuyu Reagent Co., Ltd.; anhydrous magnesium sulfate (AR) was purchased from Damao Reagent Co., Ltd.; octaaminopropyl polysilsesquioxane was purchased from Hybrid Plastic Co., Ltd.

[0052] The following is a description of the specific implementation methods:

[0053] The synthetic route adopted by the present invention is as follows:

[0054]

[0055] Example 1

[0056] (1) Condensation reaction of thiosalicylic acid and phenoxyacetic acid (TX-COOH)

[0057] Add 60 ml of sulfuric acid to a round-bottom flask, add 1.5 g of thiosalicylic acid to fully dissolve it. Add 4.1 g of phenoxyacetic acid in batches; seal the reaction system and protect it from light. Stir and react at 25°C for 72 hours. After the reaction is completed, add the product dropwise into water and filter to obtain a precipitate. Then, dissolve the precipitate in a 40°C dioxane solution, take the supernatant and add water to precipitate, filter and dry to obtain a yellow solid powder, namely TX-COOH, with a yield of 90%.

[0058] (2) Chlorination reaction of TX-COOH

[0059] 0.2 g of intermediate TX-COOH and 1 mL of thionyl chloride (SOCl 2 ) was reacted in a round-bottom flask without any solvent in the dark. The entire reaction was carried out under nitrogen atmosphere at 25 °C and stirred for 12 hours. The reactor was sealed to prevent SOCl 2 After the reaction is completed, the excess solvent and unreacted SOCl are removed by rotary evaporation. 2 , a yellow solid, thioxanthone chloride (TX-Cl), was obtained with a yield of 100%.

[0060] (3) Preparation of POSS-3TX complex

[0061] 456 mg of polysiloxane octaamino-functionalized nanoparticles (POSS-8NH 2) was dissolved in 3 mL of anhydrous DMF to form a uniform solution. Under a nitrogen atmosphere at 50°C, the prepared TX-Cl powder (437 mg) was added dropwise and the reaction was stirred for 12 hours. After the reaction was completed, saturated brine was added and extracted with ethyl acetate. The organic phase was then extracted with 10 wt% hydrochloric acid to remove excess POSS. The extracted organic phase was dehydrated with anhydrous magnesium sulfate, filtered and dried to obtain a yellow solid composite photoinitiator, namely POSS-3TX, with a yield of 90%.

[0062] Example 2

[0063] (1) Condensation reaction of thiosalicylic acid and phenoxyacetic acid (TX-COOH)

[0064] Add 60 ml of sulfuric acid to a round-bottom flask, add 1.0 g of thiosalicylic acid to fully dissolve it. Add 3.0 g of phenoxyacetic acid in batches; seal the reaction system and protect it from light. Stir and react at 25°C for 72 hours. After the reaction is completed, add the product dropwise into water and filter to obtain a precipitate. Then, dissolve the precipitate in a 40°C dioxane solution, take the supernatant and add water to precipitate, filter and dry to obtain a yellow solid powder, namely TX-COOH, with a yield of 85%.

[0065] (2) Chlorination reaction of TX-COOH

[0066] 0.1 g of intermediate TX-COOH and 0.5 mL of thionyl chloride (SOCl 2 ) was reacted in a round-bottom flask without any solvent in the dark. The entire reaction was carried out under nitrogen atmosphere at 25 °C and stirred for 12 hours. The reactor was sealed to prevent SOCl 2 After the reaction is completed, the excess solvent and unreacted SOCl are removed by rotary evaporation. 2 , a yellow solid, thioxanthone chloride (TX-Cl), was obtained with a yield of 95%.

[0067] (3) Preparation of POSS-3TX complex

[0068] 300 mg of polysiloxane octaamino functionalized nanoparticles (POSS-8NH 2 ) was dissolved in 3 mL of anhydrous DMF to form a uniform solution. Under a nitrogen atmosphere at 50°C, 240 mg of the prepared TX-Cl powder was added dropwise and the reaction was stirred for 12 hours. After the reaction was completed, saturated brine was added and extracted with ethyl acetate. The organic phase was then extracted with 10 wt% hydrochloric acid to remove excess POSS. The extracted organic phase was dehydrated with anhydrous magnesium sulfate, filtered and dried to obtain a yellow solid composite photoinitiator, namely POSS-3TX, with a yield of 80%.

[0069] Example 3

[0070] (1) Condensation reaction of thiosalicylic acid and phenoxyacetic acid (TX-COOH)

[0071] Add 60 ml of sulfuric acid to a round-bottom flask, add 2.0 g of thiosalicylic acid to fully dissolve it. Add 5.0 g of phenoxyacetic acid in batches; seal the reaction system and protect it from light. Stir and react at 25°C for 72 hours. After the reaction is completed, add the product dropwise into water and filter to obtain a precipitate. Then, dissolve the precipitate in a 40°C dioxane solution, take the supernatant and add water to precipitate, filter and dry to obtain a yellow solid powder, namely TX-COOH, with a yield of 90%.

[0072] (2) Chlorination reaction of TX-COOH

[0073] 0.2 g of intermediate TX-COOH and 2.0 mL of thionyl chloride (SOCl 2 ) was reacted in a round-bottom flask without any solvent in the dark. The entire reaction was carried out under nitrogen atmosphere at 25 °C and stirred for 12 hours. The reactor was sealed to prevent SOCl 2 After the reaction is completed, the excess solvent and unreacted SOCl are removed by rotary evaporation. 2 , a yellow solid, thioxanthone chloride (TX-Cl), was obtained with a yield of 95%.

[0074] (3) Preparation of POSS-3TX complex

[0075] 500 mg of polysiloxane octaamino functionalized nanoparticles (POSS-8NH 2 ) was dissolved in 3 mL of anhydrous DMF to form a uniform solution. Under a nitrogen atmosphere at 50°C, 480 mg of the prepared TX-Cl powder was added dropwise and the reaction was stirred for 12 hours. After the reaction was completed, saturated brine was added and extracted with ethyl acetate. The organic phase was then extracted with 10 wt% hydrochloric acid to remove excess POSS. The extracted organic phase was dehydrated with anhydrous magnesium sulfate, filtered and dried to obtain a yellow solid composite photoinitiator, namely POSS-3TX, with a yield of 80%.

[0076] Example 4

[0077] (1) Condensation reaction of thiosalicylic acid and phenoxyacetic acid (TX-COOH)

[0078] Add 60 ml of sulfuric acid to a round-bottom flask, add 2.5 g of thiosalicylic acid to fully dissolve it. Add 7.0 g of phenoxyacetic acid in batches; seal the reaction system and protect it from light. Stir and react at 25°C for 72 hours. After the reaction is completed, add the product dropwise into water and filter to obtain a precipitate. Then, dissolve the precipitate in a 40°C dioxane solution, take the supernatant and add water to precipitate, filter and dry to obtain a yellow solid powder, namely TX-COOH, with a yield of 80%.

[0079] (2) Chlorination reaction of TX-COOH

[0080] 0.3 g of intermediate TX-COOH and 2.0 mL of thionyl chloride (SOCl 2 ) was reacted in a round-bottom flask without any solvent in the dark. The entire reaction was carried out under nitrogen atmosphere at 25 °C and stirred for 12 hours. The reactor was sealed to prevent SOCl 2 After the reaction is completed, the excess solvent and unreacted SOCl are removed by rotary evaporation. 2 , a yellow solid, thioxanthone chloride (TX-Cl), was obtained with a yield of 90%.

[0081] (3) Preparation of POSS-3TX complex

[0082] 550 mg of polysiloxane octaamino functionalized nanoparticles (POSS-8NH 2 ) was dissolved in 3 mL of anhydrous DMF to form a uniform solution. Under a nitrogen atmosphere at 50°C, 500 mg of the prepared TX-Cl powder was added dropwise and the reaction was stirred for 12 hours. After the reaction was completed, saturated brine was added and extracted with ethyl acetate. The organic phase was then extracted with 10 wt% hydrochloric acid to remove excess POSS. The extracted organic phase was dehydrated with anhydrous magnesium sulfate, filtered and dried to obtain a yellow solid composite photoinitiator, namely POSS-3TX, with a yield of 80%.

[0083] 2. Performance Characterization

[0084] (1) MALDI-TOF / TOF test on POSS-3TX

[0085] POSS-3TX was tested by MALDI-TOF / TOF using the following matrix: α -cyano-4-hydroxycinnamic acid. MALDI-TOF / TOF of POSS-3TX Figure 1 As shown in Figure 2, the theoretical value of POSS-3TX is M = 1684.3413, which was determined by matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF), and the actual measured value is [M+H] + =1685.6949, which is consistent with the theoretical value. 1598.5056 is [POSS-3TX-5NH 2 +H] + ; 1447.6060 is [POSS-2TX-5NH 2 +H] + ; 1277.1545 is [POSS-1TX-5NH 2 +3C+4O+H] +; 1178.3857 is [POSS-1TX-5NH 2 +3C+H] + ; 1165.5266 is [POSS-1TX-5NH 2 +2C+H] + ; 1141.7236 is [POSS-1TX-5NH 2 +H] + ; 931.6005 is [POSS+10C+H] + This is consistent with the calculated results, further proving that POSS-3TX was successfully prepared.

[0086] According to the MALDI-TOF / TOF test results of POSS-3TX, the present invention determines that the photoinitiator has a structure shown in Formula I, in combination with the fact that the position of TX accessing POSS is not fixed, and the steric hindrance of POSS and the lowest energy mode after π-π stacking between the benzene rings in TX are comprehensively considered:

[0087]

[0088] Formula I;

[0089] Where R is H or R 1 , R 1 for And R 1 The number is 3.

[0090] (2) POSS-8NH 2 , TX-COOH and POSS-3TX infrared spectra

[0091] POSS-8NH 2 The infrared spectra of TX-COOH and POSS-3TX are as follows Figure 2 As shown, POSS-8NH 2The infrared spectrum of the POSS-3TX complex shows that its characteristic peaks are concentrated in the vibration region of Si–O–Si and N–H. Strong absorption peaks appear in the range of 1050–1150 cm⁻¹, which are attributed to the symmetric and asymmetric stretching vibrations of the Si–O–Si bonds in the POSS skeleton, indicating that its organic-inorganic hybrid structure is complete. The peaks in the range of 3300–3500 cm⁻¹ are characteristic signals of amino (N–H) stretching vibrations, and the moderate intensity absorption peaks of 1550–1650 cm⁻¹ further verify the N–H bending vibration, indicating that the POSS surface is successfully modified with high-density amino groups, providing abundant active sites for subsequent reactions with TX-Cl. In the POSS-3TX complex, the characteristic peaks of Si–O–Si remain unchanged, indicating that the skeleton structure of POSS is not destroyed in the reaction. At the same time, the TX-COOH peak (1685 cm⁻¹) is slightly shifted to 1690 cm⁻¹ in the complex, and the peak intensity is weakened, indicating that the TX-COOH molecules react chemically with the amino groups on the POSS surface. In addition, the C–Cl characteristic peak (700–800 cm⁻¹) completely disappeared in the composite, further confirming that the chlorine in TX-Cl had been bound to POSS-8NH 2 The reaction was complete. The characteristic peak of the aromatic ring C=C (1500–1600 cm⁻¹) did not change significantly, indicating that the aromatic structure of TX-COOH remained intact during the recombination process.

[0092] The overall infrared spectrum results show that POSS-8NH 2 With excellent activity and structural integrity, the reaction with TX-Cl successfully achieved the synthesis of POSS-3TX complex, and verified the effectiveness of the reaction and the structural characteristics of the target product.

[0093] (3) UV spectra of TX, TX-COOH and POSS-3TX

[0094] The UV spectra of TX, TX-COOH and POSS-3TX are as follows: Figure 3 As shown in Figure 2, the UV spectrum of commercial thioxanthone (TX) shows that it has obvious absorption characteristics in the UV region, which are mainly caused by the π→π* transition of the aromatic ring and the n→π* transition of the carbonyl group. A strong absorption peak appears in the range of 250–270 nm, which is attributed to the π→π* transition of the aromatic ring; a moderate absorption peak is observed in the range of 350–380 nm, representing the n→π* transition of the carbonyl group. These absorption characteristics indicate that TX has good photosensitivity and is suitable for application in the field of photoinitiators. Compared with TX, TX-COOH has some changes in absorption characteristics, especially the n→π* transition absorption peak in the range of 350–390 nm shows a slight blue shift, indicating that the introduction of chlorine atoms changes the electronic distribution of the molecule.

[0095] The overall spectrum shows that the photosensitivity of TX-COOH is maintained after chlorination, accompanied by the optimization of the molecular structure. For the POSS-3TX complex, its UV spectrum retains the characteristic absorption peaks of TX-COOH and changes significantly due to the introduction of the POSS skeleton. The π→π* transition peak intensity in the range of 250–270 nm is enhanced, indicating that POSS has a synergistic effect on the electronic environment of the TX-COOH aromatic ring; while the n→π* transition peak in the range of 400 nm is slightly red-shifted, reflecting that the chemical combination of POSS and TX-COOH changes the electronic environment of the carbonyl group. These spectral characteristics show that the introduction of POSS not only maintains the UV light absorption ability of TX-COOH, but also expands and optimizes its spectral response range, providing the possibility of improving the performance of the composite material in photoinitiation and photosensitive applications.

[0096] (4) Double bond conversion rate of acrylamide polymerization initiated by TX-COOH and POSS-3TX

[0097] The strength and double bond conversion rate of acrylamide polymerization initiated by TX-COOH and POSS-3TX are shown in Figure 4 As shown, A is the intensity of acrylamide polymerization initiated by TX-COOH, B is the intensity of acrylamide polymerization initiated by POSS-3TX, and C is the double bond conversion rate of acrylamide polymerization initiated by TX-COOH and POSS-3TX. POSS-3TX and TX-COOH were used as photoinitiators to initiate the free radical polymerization of acrylamide, and the double bond conversion rate was monitored every 20 seconds by infrared spectroscopy to analyze its polymerization kinetic behavior.

[0098] from Figure 4 It can be seen that when POSS-3TX is used as an initiator, the double bond conversion rate is significantly faster than that of TX-COOH, and the initiation efficiency is higher (e.g. Figure 4 In the initial stage of the reaction (0–60 s), POSS-3TX exhibited a fast polymerization rate, and its double bond conversion rate quickly reached about 50% within 60 s (as shown in Figure 4 ), while TX-COOH only reaches about 30% (as shown in B Figure 4). This indicates that POSS-3TX has a higher initial free radical generation efficiency. This may be because POSS-3TX improves the light absorption ability by introducing POSS groups and improves the molecular stability of the initiator, thereby improving the initiation efficiency. As the reaction proceeds, the polymerization rate of POSS-3TX gradually decreases, reaching a double bond conversion rate of about 60% at 200 seconds, close to the polymerization equilibrium. In contrast, although the polymerization rate of TX-COOH increases in the later period, the overall efficiency is still lower than that of POSS-3TX, which only reaches a double bond conversion rate of about 50% at 200 seconds. This shows that POSS-3TX can release free radicals more evenly and quickly, thereby initiating acrylamide polymerization more efficiently.

[0099] From the perspective of kinetic properties, POSS-3TX exhibits a faster initial reaction rate and a higher final double bond conversion rate, reflecting its excellent performance in acrylamide polymerization. In contrast, the initiation efficiency of TX-COOH is limited, which may be related to its lower molecular stability and free radical release rate. The experimental results show that by combining TX-COOH with POSS, the initiation efficiency of the initiator can be significantly improved and the polymerization kinetic behavior can be optimized, providing a new direction for the design of efficient photoinitiator systems.

[0100] (5) Mobility experiment and analysis

[0101] The TX-COOH and POSS-3TX released from the polyacrylamide hydrogel immersed in water were detected by fluorescence spectroscopy to evaluate their mobility in the gel. Specifically, the hydrogel containing TX-COOH or POSS-3TX was immersed in deionized water, and the aqueous solution was collected at different time points and the fluorescence absorption intensity was detected to reflect the concentration of the material released into the water. The results are shown in FIG. Figure 5 shown.

[0102] from Figure 5 It can be seen that the mobility of TX-COOH is significantly higher than that of POSS-3TX. Within 12 h after the start of immersion, the fluorescence absorption intensity of the aqueous solution in which the hydrogel containing TX-COOH was immersed continued to increase with time, indicating that the TX-COOH molecules were quickly released from the hydrogel, indicating that its migration rate was high. Specifically, before migration, the concentration of TX-COOH was 715 mg / L; at 12 h, the migration concentration of TX-COOH reached a significant level of about 47.19 mg / L, and the mobility was 6.6%. This may be due to the small size of TX-COOH molecules, strong interaction with water, and weak binding with the polyacrylamide hydrogel network.

[0103] In contrast, the migration rate of POSS-3TX is significantly reduced. In the experiment, the amount of POSS-3TX released into water under the same immersion conditions was significantly lower than that of TX-COOH. The concentration of POSS-3TX before migration was 1400 mg / L, and the absorption intensity only rose to about 57.4 mg / L within 12 h, with a migration rate of 4.1%. This is because POSS-3TX has a larger molecular structure, and the intermolecular force is enhanced by the combination of POSS and TX-COOH, making it more stable in the hydrogel network and not easily released into the aqueous solution. In addition, the high hydrophobicity of POSS-3TX further reduces its solubility and migration rate in the aqueous phase.

[0104] The results show that TX-COOH has a high migration rate in polyacrylamide hydrogels, which may lead to a rapid decrease in effective content during long-term applications, limiting its reliability in long-term use. However, POSS-3TX, due to its lower mobility, exhibits excellent stability and long-term effectiveness, and is suitable for application scenarios with high requirements for migration control. This result shows that by compounding TX-COOH with POSS, the migration performance of the material can be significantly improved, and at the same time provides a theoretical basis for the optimal design of functional materials.

[0105] (6) Mechanical experimental performance and analysis

[0106] Comparison of mechanical properties of hydrogels obtained by polymerization of monomers initiated by three photoinitiators: TX-COOH, POSS-TX and POSS-3TX

[0107] For comparison, we also synthesized isopropyl-functionalized POSS-TX (prepared according to the preparation method in 2.3. of In-Situ Photoinduced Formation of Self-Assembled AgNPs Using POSS-TX as Nano-Photoinitiator in PEGMEA / PEGDA Polymer Matrix and Creating Self-Wrinkled Pattern, JPC 11193).

[0108] The hydrogel preparation process is as follows: First, 5.00 g of acrylamide was weighed and dissolved in 5.00 ml of ethanol in each sample bottle. After fully dissolved, polyethylene glycol diacrylate (Mn = 200) (0.8 × 10 -5 mol, 1.6 mg), and after ultrasonic dissolution for 10 min, TX-COOH (0.8×10 -5 mol, 8.00 mg), POSS-TX (0.8×10-5 mol, 28 mg), POSS-3TX (2.5×10 -5 mol, 14 mg) were added to the hydrogel prepolymer solution, mixed with a vortexer, and the solution was kept away from light. Before light curing, nitrogen was continuously passed through the solution for 30 min to isolate oxygen. After the UV lamp was turned on and stabilized for 5 min, 2 mL of the prepolymer solution was added to the mold and irradiated for curing to obtain the corresponding hydrogel sample.

[0109] The mechanical properties of the hydrogels were tested by a universal tensile testing machine to obtain the stress-strain curves of the hydrogel samples and compare the measured elongation at break, e.g. Figure 6 As shown in the figure, the mechanical properties of the hydrogels (G-POSS-TX, G-POSS-3TX) initiated by the nano-photoinitiator polymerization modified by POSS are enhanced compared with the hydrogels (G-TX-COOH) initiated by the polymerization of TX-COOH. This is because the molecular structure of POSS is a nano-scale rigid particle structure. This structure can be integrated into the polymer network of the hydrogel. When the hydrogel is subjected to external force, the POSS molecules can absorb and disperse energy by deformation, thereby reducing stress concentration and preventing the generation and expansion of cracks. The mechanical properties of G-POSS-3TX are better than those of G-POSS-TX. The stress of G-POSS-3TX is about 1.4 times that of G-POSS-TX (stress 0.78 MPa), reaching a maximum of 1.1 MPa, and the average elongation at break is 1177%, which is 1.8 times that of G-POSS-TX (elongation at break 650%). This is because POSS-3TX not only acts as a photoinitiator to initiate polymerization, but is also rich in amino groups, which can form hydrogen bonds with acrylamide polymer chains and act as a cross-linking agent to cross-link polymer chains into a network. This cross-linked network structure can limit the movement of polymer chains, and POSS-3TX, as a cross-linking point, can disperse the stress between polymer chains during stretching, so that the hydrogel can withstand greater external forces without breaking, thereby enhancing the tensile strength of the hydrogel.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A photoinitiator, characterized in that The structure shown in Formula I is prepared by the following steps: (1) Dissolve thiosalicylic acid in sulfuric acid, add phenoxyacetic acid, and carry out condensation reaction to obtain TX-COOH; (2) Mixing TX-COOH and thionyl chloride to carry out chlorination reaction to obtain TX-Cl; (3) octaaminopropyl polysilsesquioxane and TX-Cl are mixed in a mass ratio of 456:437, 300:240, 500:480 or 550:500, and an acylation reaction is carried out at 45-55° C. under an inert atmosphere for 10-12 h; Among them, the structures of TX-COOH and TX-Cl are shown below: 、 ； Formula I; Wherein, R is H or R1; R1 is And the number of R1 is 3.

2. A method for preparing the photoinitiator according to claim 1, characterized in that: The following steps are involved: (1) Dissolve thiosalicylic acid in sulfuric acid, add phenoxyacetic acid, and carry out condensation reaction to obtain TX-COOH; (2) Mixing TX-COOH and thionyl chloride to carry out chlorination reaction to obtain TX-Cl; (3) dissolving octaaminopropyl polysilsesquioxane in a solvent, adding TX-Cl, and performing an acylation reaction to obtain the product; Among them, the structures of TX-COOH and TX-Cl are shown below: 、 。 3. The method for preparing a photoinitiator according to claim 2, characterized in that: In step (1), The mass ratio of thiosalicylic acid to phenoxyacetic acid is (1-2.5): (3-7.0); The concentration of the thiosalicylic acid is 0.01-0.05 g·mL -1 ; The condensation reaction conditions are sealed and protected from light, and reacted at room temperature for 70-75 hours.

4. The method for preparing a photoinitiator according to claim 3, characterized in that: In step (1), After the condensation reaction is completed, the product is purified. The purification process is as follows: the product is added to water and filtered to obtain a precipitate, the precipitate is dissolved in dioxane at 35-45° C., the upper clear liquid is added with water to precipitate, and TX-COOH is obtained by filtering and drying.

5. The method for preparing a photoinitiator according to claim 2, characterized in that: In step (2), the mixing ratio of TX-COOH to thionyl chloride is (0.1-0.3) g: (0.5-2.0) mL; The chlorination reaction is carried out under light-proof, inert atmosphere, and at room temperature for 10-12 h.

6. The method for preparing a photoinitiator according to claim 2, characterized in that: In step (3), The concentration of the octaaminopropyl polysilsesquioxane is 100-190 g·L -1 ; The solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide and 1,4-dioxane.

7. The method for preparing a photoinitiator according to claim 3, characterized in that: In step (3), after the acylation reaction is completed, the product is purified. The purification process is as follows: adding saturated brine and extracting with ethyl acetate, then extracting the organic phase with 10-15 wt% hydrochloric acid, adding anhydrous magnesium sulfate to the extracted organic phase, filtering and drying.

8. Use of the photoinitiator according to claim 1 in free radical polymerization of unsaturated amides, photocurable coatings, photosensitive materials and 3D printing.

9. The use according to claim 8, characterized in that: The unsaturated amide is acrylamide.

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