Macromolecular photoinitiators comprising polysiloxane groups, process for their preparation and use

Abstract

The present application relates to a kind of macromolecular photoinitiator comprising polysiloxane group and its preparation method and application.The macromolecular photoinitiator is prepared by the reaction of polysiloxane containing carboxylic acid substituent group with curcumin, the macromolecular photoinitiator can be copolymerized with water-soluble monomer, and the migration rate of photoinitiator can be greatly reduced after coating curing;The silicone structure contained in the molecular structure of the photoinitiator has the effect of photobleaching, and can realize deep curing to coating.The preparation method of the present application is simple, and the content of photoinitiating group in the prepared macromolecular photoinitiator is controllable;And macromolecular photoinitiator dissolves fast in aqueous phase, and the initiation activity is high, overcomes the defects such as low initiation efficiency and easy migration of small molecule photoinitiator.Under the irradiation of visible light, the macromolecular photoinitiator comprising polysiloxane group of the present application can effectively initiate the polymerization of water-soluble monomers such as acrylamide, acrylic acid, acrylic acid salt and the like.

Description

Technical Field

[0001] The present invention relates to a photoinitiator, and in particular to a macromolecular photoinitiator containing a polysiloxane group, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, photopolymerization has been widely used in coatings, adhesives, inks, 3D printing, microstructures, and other fields. In particular, materials and processes such as optical adhesives and photoresists in the electronics field all involve photopolymerization reactions. Photocuring is generally considered a "green chemistry" and mainly uses light as a source of power to excite photons to an excited state and undergo accompanying photochemical reactions, such as photolysis or hydrogen abstraction reactions, to form suitable initiating active substances, such as free radicals and cations, which in turn trigger chain reactions to form the desired thin films or profiles. Therefore, the selection of suitable light-absorbing substances, such as photoinitiators or photoinitiator systems, becomes crucial.

[0003] Currently, the vast majority of commercial photoinitiators are oil-soluble and insoluble or have very low solubility in water. These photoinitiators require the use of emulsifiers and a small amount of monomer to disperse into aqueous polymerization systems. Furthermore, they face significant compatibility issues with aqueous systems, impacting photoinitiation efficiency and product performance. To overcome these drawbacks, water-based photoinitiators have emerged. Conventional photoinitiators are not water-soluble, but by introducing hydrophilic groups into their structures, their water solubility can be greatly improved. These hydrophilic groups can include -COOH (carboxyl) and -SO3H (sulfonyl). However, traditional small-molecule photoinitiators undergo photocleavage during photopolymerization, generating free small-molecule organic compounds that can remain, migrate, and be volatile, hindering their application. Consequently, researchers have recently begun developing polymerizable or macromolecular photoinitiators. Macromolecularization of photoinitiators can mitigate or even eliminate the shortcomings of small-molecule photoinitiators. Compared to small-molecule photoinitiators, macromolecular photoinitiators offer the following advantages: high photoactivity, no odor, no migration, and good compatibility with polymers, which give them promising application prospects. Therefore, the development of macromolecular photoinitiators is an effective way to address the volatility and migration drawbacks of small-molecule photoinitiators.

[0004] Prior art CN114656592A provides a water-soluble macromolecular photoinitiator with excellent water solubility, excellent photoinitiation properties, no migration, good compatibility with polymers, and the ability to effectively initiate the polymerization of water-soluble monomers to prepare branched polymers. This patent utilizes the reaction of anhydride monomers with small-molecule photoinitiators containing terminal hydroxyl or amine groups to prepare a polymerizable photoinitiator containing unsaturated double bonds. This polymerizable photoinitiator is then copolymerized with other water-soluble monomers to produce a water-soluble macromolecular photoinitiator containing pendant photoinitiating groups. However, this photoinitiator can only initiate the polymerization of water-soluble monomers such as acrylamides, acrylic acids, and acrylates under ultraviolet light, which partially limits its application scenarios. Compared to ultraviolet light sources, LED light sources in the UVA and visible light bands offer unique advantages such as energy conservation and environmental protection, which have significantly promoted the photocuring industry. Therefore, matching the absorption spectra of traditional photoinitiators with the emission spectra of new LED light sources to develop more effective photoinitiators is a proactive research initiative in response to national environmental protection efforts. Summary of the Invention

[0005] The present invention provides a macromolecular photoinitiator containing polysiloxane groups, a preparation method thereof, and the use of the photoinitiator in photocurable compositions, particularly visible light-curable coatings. The photoinitiator exhibits migration stability, photobleaching activity, and water solubility, effectively mitigating oxygen inhibition during polymerization initiation.

[0006] In one aspect, the present invention provides a macromolecular photoinitiator comprising a polysiloxane group, the general structural formula of which is shown in Formula 1:

[0007]

[0008] wherein n and m each independently represent an integer between 2 and 20; x and y each independently represent an integer between 1 and 5; and R1 and R2 each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

[0009] During the experiment, the inventors found that if the alkylene chains at both ends of the polysiloxane are too long, the yield of the oxidative carboxylation reaction will be reduced to a certain extent; and the excessively long alkylene chain connected to the curcumin molecule will also reduce the viscosity between the macromolecular photoinitiator and other components in the photocurable composition, thereby affecting the mechanical properties of the coating after the photocurable composition is cured. Therefore, in the present invention, the number of carbon atoms of the alkylene chain ends of the selected polysiloxane molecules is 1-5, and the number of carbon atoms of the alkyl group substituted on the silicon atom in the selected polysiloxane molecules is 1-3.

[0010] Another aspect of the present invention further provides a method for preparing the macromolecular photoinitiator containing a polysiloxane group, comprising the following steps:

[0011] S1: heating an alkylhydroxyl-terminated methylvinyl polysiloxane having a structure shown in Formula 2 with a potassium permanganate solution, and then adding dilute sulfuric acid for acidification to carry out an oxidation reaction;

[0012]

[0013] S2: After the oxidation is complete, the organic layer of the mixed solution is separated and washed once with an equal volume of sodium hydroxide solution and water to obtain a carboxylated polysiloxane represented by formula 3;

[0014]

[0015] S3: Curcumin dissolved in concentrated sulfuric acid is added dropwise to the carboxylated polysiloxane obtained in S2, and heated under stirring to allow the reaction to proceed fully. After no carboxylic acid structure is left in the reaction system, the reaction is dried and filtered, the solvent is dried, and column chromatography is performed to separate the reaction product to obtain a macromolecular photoinitiator containing a polysiloxane group.

[0016] As an embodiment of the present invention, the co-heating temperature of the oxidation reaction in step S2 is 45-95°C; and the heating temperature in step S3 is 35-95°C.

[0017] As an embodiment of the present invention, the concentration of the potassium permanganate solution used in the oxidation reaction is 0.1-0.3 mol / L; the molar ratio of the alkylhydroxy-terminated methylvinyl polysiloxane to potassium permanganate is 1:8-50.5; and the molar ratio of the carboxylated polysiloxane to curcumin is 1:5-26.

[0018] In the present invention, a polysiloxane containing a carboxylic acid substituent is reacted with curcumin under certain conditions through an esterification reaction to prepare a macromolecular photoinitiator containing a polysiloxane group with a silicone structure on the side chain. In the macromolecular photoinitiator containing a polysiloxane group of the present invention, the Si-Si bond contained in the polysiloxane group can be photolyzed to generate free radicals to initiate photopolymerization during free radical polymerization. On the other hand, the Si-H bond can provide hydrogen atoms to act as a hydrogen-donating auxiliary agent. More importantly, the macromolecular photoinitiator containing a polysiloxane group of the present invention contains a silane group with very high reactivity to oxygen molecules. The silane group and oxygen molecules can form a silicon peroxide radical (·SiOO), and the silicon peroxide radical can rearrange to provide a new silane radical that can react with an acrylate monomer or an oxygen molecule. Therefore, the macromolecular photoinitiator containing a polysiloxane group of the present invention has a good anti-oxidation inhibition effect and can effectively improve the efficiency of photocuring. In addition, the silicone (-Si-C=O) structure contained in the macromolecular photoinitiator containing polysiloxane groups provided by the present invention has an excellent photobleaching effect during the photoinitiated polymerization process, and can effectively deep-cure the photocurable composition containing the macromolecular photoinitiator containing polysiloxane groups.

[0019] As a food additive, curcumin has antioxidant and anti-inflammatory properties. In the field of photoinitiators, it has emerged as a new type of dye photosensitizer. Its light absorption wavelength range is 340-535nm, which can trigger the photopolymerization of substances such as epoxides and vinyl ethers. In the present invention, the inventors prepared the polysiloxane-containing macromolecular photoinitiator by esterification polymerization of curcumin and polysiloxane containing carboxylic acid substituents. On the one hand, the strong polarity of the side chain groups of the polysiloxane-containing macromolecular photoinitiator prepared by the participation of curcumin in the reaction makes it water-soluble and can be used in water-based photocurable compositions. On the other hand, the double bond in the molecular structure of curcumin greatly reduces the degree of outward migration of the prepared polysiloxane-containing macromolecular photoinitiator when copolymerized with a resin. In addition, the absorption spectrum of the prepared polysiloxane-containing macromolecular photoinitiator by the inventors of the present invention is red-shifted to a certain extent compared with the absorption spectrum of curcumin. The polysiloxane-containing macromolecular photoinitiator can absorb visible blue light sources, improve light penetration, and synergistically enhance the deep curing problem of the coating after the photocurable composition containing the polysiloxane-containing macromolecular photoinitiator is cured.

[0020] At the same time, from a safety perspective, the raw materials used in the present invention - polysiloxane and curcumin - are both non-toxic and harmless organic substances. Therefore, during factory-scale production or use, the macromolecular photoinitiator containing polysiloxane groups described in the present invention will not have serious surface migration problems and toxic pollution problems.

[0021] Another aspect of the present invention provides a photocurable composition, which contains the macromolecular photoinitiator containing a polysiloxane group; wherein the content of the macromolecular photoinitiator containing a polysiloxane group accounts for 0.5%-2% of the total mass of the photocurable composition.

[0022] In another aspect, the present invention provides the use of the macromolecular photoinitiator containing polysiloxane groups in the field of photocuring.

[0023] Beneficial effects

[0024] The macromolecular photoinitiator containing polysiloxane groups prepared by the present invention has good compatibility with water-based photocurable resins, low relative mobility, and has better photoinitiation efficiency than its corresponding small molecule photoinitiator, and can be well applied to water-based photocurable systems. In addition, the multifunctional macromolecular photoinitiator of the present invention has a high molar content of photoinitiator groups in the molecule, which can reduce the amount of macromolecular photoinitiator required for water-based photocurable resins; at the same time, because the molecular chain is branched, it has a lower viscosity than the same type of straight-chain macromolecules; it is easy to produce and reduces the amount of solvent used; the silicone structure and polysiloxane structure contained in the macromolecular photoinitiator provided by the present invention give the photoinitiator good photobleaching performance and anti-oxidation and inhibition ability, thereby improving the efficiency of deep curing of coatings. Compared with photocurable compositions made from traditional small molecule photoinitiators, the photocurable composition containing the macromolecular photoinitiator containing polysiloxane groups of the present invention has better appearance, hardness and relative mobility of the coating after curing than the photocurable composition formulated with traditional photoinitiators. DETAILED DESCRIPTION

[0025] Example 1

[0026] S1: 0.05 mol of an alkylhydroxyl-terminated methylvinyl polysiloxane having the structure of Formula 1-1 and 4 L of a 0.1 mol / L potassium permanganate solution were heated to 50° C., and then diluted sulfuric acid was added for acidification to carry out an oxidation reaction;

[0027]

[0028] S2: After the oxidation is complete, the organic layer of the mixture is separated and washed once with equal volumes of sodium hydroxide solution and water to obtain the carboxylated polysiloxane-1 represented by formula 1-2 with a yield of 80.5%;

[0029]

[0030] S3: 0.22 mol of curcumin dissolved in concentrated sulfuric acid is added dropwise to the carboxylated polysiloxane-1 obtained in S2, and the mixture is heated to 60°C under stirring to allow it to react fully. After no carboxylic acid structure is left in the reaction system, the mixture is dried and filtered, the solvent is dried, and column chromatography is performed to obtain a macromolecular photoinitiator-1 containing a polysiloxane group as shown in Formula 1-3.

[0031]

[0032] Example 2

[0033] S1: 0.1 mol of an alkylhydroxyl-terminated methylethylvinyl polysiloxane having the structure shown in Formula 2-1 and 0.2 mol / L potassium permanganate solution were heated to 65°C, and then diluted sulfuric acid was added to acidify and perform an oxidation reaction;

[0034]

[0035] S2: After the oxidation is complete, the organic layer of the mixture is separated and washed once with equal volumes of sodium hydroxide solution and water to obtain carboxylated polysiloxane-2 represented by formula 2-2 with a yield of 75.1%;

[0036]

[0037] S3: 0.53 mol of curcumin dissolved in concentrated sulfuric acid is added dropwise to the carboxylated polysiloxane-2 obtained in S2, and the mixture is heated to 40°C with stirring to allow it to react fully. After no carboxylic acid structure is left in the reaction system, the mixture is dried and filtered, the solvent is dried, and column chromatography is performed to obtain a macromolecular photoinitiator-2 containing a polysiloxane group as shown in Formula 2-3.

[0038]

[0039] Example 3

[0040] S1: Heat 0.15 mol of an alkylhydroxyl-terminated methylvinyl polysiloxane having the structure of Formula 3-1 with 5 L of a 0.3 mol / L potassium permanganate solution to 75°C, then add dilute sulfuric acid for acidification to carry out an oxidation reaction;

[0041]

[0042] S2: After the oxidation is complete, the organic layer of the mixture is separated and washed once with equal volumes of sodium hydroxide solution and water to obtain carboxylated polysiloxane-3 represented by formula 3-2 with a yield of 74.5%;

[0043]

[0044] S3: 1.65 mol of curcumin dissolved in concentrated sulfuric acid was added dropwise to the carboxylated polysiloxane-3 obtained in S2, and the mixture was heated to 50°C with stirring to allow it to react fully. After no carboxylic acid structure was left in the reaction system, the mixture was dried and filtered, the solvent was dried, and column chromatography was performed to obtain a macromolecular photoinitiator-3 containing a polysiloxane group as shown in Formula 3-3.

[0045]

[0046] Example 4

[0047] S1: Heat 0.2 mol of an alkylhydroxyl-terminated methylvinyl polysiloxane having the structure of Formula 4-1 with 30 L of a 0.15 mol / L potassium permanganate solution to 85°C, then add dilute sulfuric acid for acidification to carry out an oxidation reaction;

[0048]

[0049] S2: After the oxidation is complete, the organic layer of the mixture is separated and washed once with equal volumes of sodium hydroxide solution and water to obtain carboxylated polysiloxane-4 represented by formula 4-2 with a yield of 76.2%;

[0050]

[0051] S3: 3.0 mol of curcumin dissolved in concentrated sulfuric acid is added dropwise to the carboxylated polysiloxane-4 obtained in S2, and heated to 70°C with stirring to allow it to react fully; after no carboxylic acid structure is left in the reaction system, the mixture is dried and filtered, the solvent is dried, and column chromatography is performed to obtain a macromolecular photoinitiator-4 containing a polysiloxane group as shown in Formula 4-3.

[0052]

[0053] Example 5

[0054] S1: 0.3 mol of an alkylhydroxyl-terminated methylvinyl polysiloxane having the structure of Formula 5-1 and 40 L of a 0.3 mol / L potassium permanganate solution were heated to 80°C, and then diluted sulfuric acid was added to acidify and perform an oxidation reaction;

[0055]

[0056] S2: After the oxidation is complete, the organic layer of the mixture is separated and washed once with equal volumes of sodium hydroxide solution and water to obtain carboxylated polysiloxane-5 represented by formula 5-2 with a yield of 72.4%;

[0057]

[0058] S3: Add 2.2 mol of curcumin dissolved in concentrated sulfuric acid to the carboxylated polysiloxane-5 obtained in S2, and heat to 90°C under stirring to allow it to react fully; after no carboxylic acid structure is left in the reaction system, dry and filter, spin-dry the solvent, and separate by column chromatography to obtain a macromolecular photoinitiator-5 containing a polysiloxane group as shown in Formula 5-3.

[0059]

[0060] Comparative Example 1

[0061] S1: Heat 0.05 mol of an alkylhydroxyl-terminated methylvinyl polysiloxane having the structure of Formula 6-1 with 4 L of a 0.1 mol / L potassium permanganate solution to 50°C, then add dilute sulfuric acid for acidification to carry out an oxidation reaction;

[0062]

[0063] S2: After the oxidation is complete, the organic layer of the mixture is separated and washed once with equal volumes of sodium hydroxide solution and water to obtain carboxylated polysiloxane-6 represented by formula 6-2 with a yield of 71.5%;

[0064]

[0065] S3: 0.20 mol of curcumin dissolved in concentrated sulfuric acid is added dropwise to the carboxylated polysiloxane-6 obtained in S2, and the mixture is heated to 60°C with stirring to allow it to react fully. After no carboxylic acid structure is left in the reaction system, the mixture is dried and filtered, the solvent is dried, and column chromatography is performed to obtain a macromolecular photoinitiator-6 containing a polysiloxane group as shown in Formula 6-3.

[0066]

[0067] The macromolecular photoinitiators containing polysiloxane groups obtained in Examples 1-5 of the present invention and Comparative Example 1 and the traditional small molecule photoinitiator were respectively formulated with other common components into photocurable compositions, which were named Formula 1, Formula 2, Formula 3, Formula 4, Formula 5, Formula 6 and Formula 7, respectively. The 7 groups of photocurable compositions were sprayed and light-cured, and the performance of the formed coatings was tested to compare their performance in terms of complete curing time, paint film appearance, hardness and relative mobility. See Tables 1 and 2 for details.

[0068] Table 1: Formulas of Examples 1-5, Comparative Example 1 and Application Examples of Traditional Photoinitiators

[0069]

[0070]

[0071] In Table 1, photoinitiator 184 is BASF's 184 photoinitiator; the 40% solid water-based UV resin is the UV903 water-based UV radiation-curable resin emulsion produced by Shenzhen Copley Polymer Materials Co., Ltd.; HDDA is 1,6-hexanediol diacrylate, a difunctional acrylate monomer; TEGO Glide410 is a leveling agent produced by Digo Chemical; and TRITON X-405 is a wetting agent produced by Dow Chemical.

[0072] After uniformly mixing and dispersing the components in Table 1, apply the photocurable composition by air spray at a temperature of 15-35°C and a relative humidity of 45-70%. Use a gravity-fed spray gun with a diameter of 15-18mm. The viscosity of the clearcoat, as measured by an NK-2# spray gun, is 30-40 seconds at 15-35°C. The film thickness is 15-25μm. Preheating and leveling time is 10-15 minutes at 55-65°C. UV curing conditions are: a distance of 25-35cm between the UV lamp and the paint film, a UV radiation dose of 800-1000mJ / cm², and allow to dry at room temperature.

[0073] Performance test hardness: According to GB / T 13448-2006, use a Zhonghua brand pencil with a hardness range of 6B to 6H to measure the pencil hardness of the cured coating;

[0074] Complete curing time: After the coating has cured for a certain period of time, when no trace is left after scratching the coating with your fingers, the coating is completely cured.

[0075] Relative mobility: The specimens were crushed, and 0.1 g of each was extracted with 15 mL of acetonitrile at room temperature for 3 days. Finally, the same amount of the extract was used for UV absorption testing. The relative mobility of Formulas 1, 2, 3, 4, 5, and 6 relative to Formula 7 can be obtained using Equations (1) and (2).

[0076] C = A / (∈ ​​× b) Formula (1)

[0077]

[0078] Where C is the concentration of photoinitiator in the extract (mol·L -1 ); A is absorbance; ε is molar extinction coefficient (L·mol -1 cm -1 ); b is the thickness of the sample cell (cm); C 光引发剂-n The concentration of the macromolecular photoinitiator-n provided in the embodiment in the extract (n=1-6); C 光引发剂184 is the concentration of photoinitiator 184 in the extract; R is the relative mobility of the macromolecular initiator.

[0079] Table 2 Performance test results of coatings in various application examples

[0080]

[0081]

[0082] It can be seen from the above table that, compared with the traditional photoinitiator 184, the macromolecular photoinitiator containing polysiloxane groups prepared by the present invention has an equal or even less dosage, and the coating formed by the prepared coating not only has excellent surface hardness, but also has high gloss. In addition, due to the photobleaching property of the macromolecular photoinitiator containing polysiloxane groups, the coating formed by the photoinitiator has good transparency; the deep curing rate of the coating added with the macromolecular photoinitiator containing polysiloxane groups provided by the present invention is also greatly improved; moreover, compared with the photoinitiator 184, the macromolecular photoinitiator containing polysiloxane groups provided by the present invention has an extremely low relative mobility, and its application in the field of food packaging will not cause pollution to food.

[0083] The present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A photocurable composition, characterized in that The photocurable composition contains a macromolecular photoinitiator containing a polysiloxane group and an aqueous photocurable resin, wherein the macromolecular photoinitiator containing a polysiloxane group accounts for 0.5% to 2% of the total mass of the photocurable composition; The polysiloxane-based macromolecular photoinitiator has a structure shown in Formula 1: wherein n and m each independently represent an integer between 2 and 20; x and y each independently represent an integer between 1 and 5; and R1 and R2 each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

2. The photocurable composition according to claim 1, wherein The preparation method of the macromolecular photoinitiator containing polysiloxane groups comprises the following steps: S1: heating an alkylhydroxyl-terminated methylvinyl polysiloxane having a structure shown in Formula 2 with a potassium permanganate solution, and then adding dilute sulfuric acid for acidification to carry out an oxidation reaction; S2: After the oxidation is complete, the organic layer of the mixed solution is separated and washed with sodium hydroxide solution and water to obtain a carboxylated polysiloxane represented by general formula 3; S3: Curcumin dissolved in concentrated sulfuric acid is added dropwise to the carboxylated polysiloxane obtained in S2, and heated under stirring to allow the reaction to proceed fully. After no carboxylic acid structure is left in the reaction system, the reaction is dried and filtered, the solvent is dried, and column chromatography is performed to separate the reaction product to obtain a macromolecular photoinitiator containing a polysiloxane group. The molar ratio of the alkylhydroxyl-terminated methylvinyl polysiloxane to potassium permanganate is 1:8-50.5; The molar ratio of the carboxylated polysiloxane to curcumin is 1:5-26.

3. The photocurable composition according to claim 2, characterized in that The concentration of the potassium permanganate solution in the oxidation reaction is 0.1-0.3 mol / L.

4. The photocurable composition according to claim 2, characterized in that The co-heating temperature of the oxidation reaction in step S1 is 45-95°C.

5. The photocurable composition according to claim 2, wherein The esterification heating temperature in step S3 is 35-95°C.

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