A Schiff base photoinitiator and its preparation method and application

Abstract

The present invention provides a Schiff base photoinitiator, a preparation method, and applications. The Schiff base photoinitiator comprises a compound having the structural formula shown below in Formula (I), wherein R is H or OH. The Schiff base photoinitiator provided herein is a visible light initiator, has good compatibility with acrylate monomers, can initiate free radical polymerization (preferably in combination with an iodonium salt), exhibits high initiation activity (preferably for initiating HDDA polymerization), and has a wide range of applications.

Description

Technical Field

[0001] The present invention relates to the field of photoinitiators, and more particularly to a Schiff base photoinitiator, a preparation method and an application thereof. Background Art

[0002] Photopolymerization technology can be widely used in the fields of photocurable inks, coatings, adhesives, microelectronic devices, etc. due to its high efficiency, economy, and adaptability to light. Photoinitiators are an important component of the photocuring system, which plays a decisive role in the photocuring speed and affects the performance of photocurable materials. Photoinitiators can be divided into free radical polymerization photoinitiators and cationic polymerization photoinitiators according to the photolysis mechanism, and can be divided into ultraviolet light (about 250-380nm) photoinitiators and visible light (about 380-800nm) photoinitiators (also called long-wavelength photoinitiators) according to the wavelength of light. Due to the disadvantages of ultraviolet light, such as the need for ultraviolet light emitting equipment, the development of long-wavelength photoinitiators is a research focus in the industry.

[0003] In the existing technology, the synthesis of existing long-wavelength visible light initiators is relatively complex and their compatibility with photocuring systems is poor, which seriously affects the effectiveness of the photoinitiator in initiating polymerization reactions. To address this problem, many research teams have published a variety of photoinitiators, but the photoinitiating activity needs to be further improved. Summary of the Invention

[0004] The first object of the present invention is to provide a Schiff base photoinitiator, which is a visible light initiator and has high initiation activity in the free radical-initiated polymerization reaction of acrylate or methacrylate monomers (especially the polymerization of HDDA). At the same time, the synthesis method of the Schiff base photoinitiator provided by the present invention is simple and easy to purify.

[0005] The Schiff base photoinitiator provided by the present invention includes a compound having the structural formula shown in the following formula (I):

[0006]

[0007] Wherein, R is H or OH.

[0008] The Schiff base photoinitiator provided by the present invention is a single-component visible light initiator with a polymerization reaction wavelength range of 385nm to 470nm. It does not require the addition of a solvent to dissolve the photoinitiator, and can effectively initiate monomer polymerization without the need for an auxiliary agent. Compared with existing photoinitiators (including photoinitiators previously disclosed by the research team of this application), it has a wider range of uses and higher initiation activity. The Schiff base photoinitiator provided by the present invention is an LED photoinitiator. The Schiff base photoinitiator provided by the present invention is more suitable for initiating free radical polymerization of acrylate or methacrylate monomers.

[0009] In a preferred embodiment of the present invention, the Schiff base photoinitiator provided by the present invention is a compound having the structural formula shown in formula (I).

[0010] In a specific embodiment of the present invention, when R is H in the structural formula shown in formula (I), the Schiff base photoinitiator having this structural formula is named TXN1.

[0011] In a preferred embodiment of the present invention, the Schiff base photoinitiator is a compound having the structural formula shown in the following formula (I):

[0012]

[0013] Wherein, R is OH, named TXN. Compared with other Schiff base photoinitiators, the Schiff base photoinitiator with this structural formula has a faster initiation rate and higher double bond conversion rate when initiating HDDA polymerization.

[0014] Another object of the present invention is to provide the use of the above-mentioned Schiff base photoinitiator in initiating free radical polymerization of acrylate or methacrylate monomers.

[0015] Among them, acrylate or methacrylate monomers include but are not limited to methyl methacrylate, butyl methacrylate, methyl acrylate, n-butyl acrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, β-hydroxyethyl methacrylate or β-hydroxyethyl acrylate, preferably 1,6-hexanediol diacrylate.

[0016] In a specific embodiment of the present invention, the illumination intensity of the polymerization reaction is preferably 50 to 200 mW / cm 2 The polymerization time is preferably 5s to 5min. The wavelength range of the LED is preferably 385nm-470nm (the applicant of the present invention has found that the Schiff base photoinitiator provided by the present invention has high initiation activity under illumination of 385nm, 405nm, 435nm, 450nm, and 470nm). In a preferred embodiment of the present invention, the amount of the photoinitiator used in the polymerization reaction is (1-5)*10 of the acrylate or methacrylate monomer. -5 mol / g.

[0017] In another preferred embodiment of the present invention, the free radical polymerization is initiated by a combination of the Schiff base photoinitiator and an iodonium salt, which can further enhance the initiation activity. Using the Schiff base visible light photoinitiator and iodonium salt in this preferred embodiment to initiate the polymerization of 1,6-hexanediol diacrylate can significantly improve the conversion rate of the polymerization reaction (e.g., a faster initiation rate and / or a higher double bond conversion rate).

[0018] The iodonium salt may be diphenyliodonium hexafluorophosphate, bis(tert-butylphenyl)iodonium hexafluorophosphate, or bis(p-tolyl)iodonium hexafluorophosphate, preferably bis(tert-butylphenyl)iodonium hexafluorophosphate. When used in combination, the molar ratio of the Schiff base photoinitiator to the iodonium salt is preferably 1:0.5 to 1:2, more preferably 1:1.

[0019] Another object of the present invention is to provide a method for preparing the above-mentioned Schiff base photoinitiator, which comprises the following steps:

[0020] 2-aminothioxanthone and a raw material aldehyde are refluxed for 48 hours to 72 hours under the action of a solvent and acetic acid; the raw material aldehyde is 4-dimethylaminobenzaldehyde or 2-hydroxy-4-dimethylaminobenzaldehyde.

[0021] The inventors of the present invention have found that the Schiff base initiator containing a photosensitizer provided by the present invention can be successfully prepared by reacting 2-aminothioxanthone with a specific aldehyde. The initiator has a long absorption wavelength and a simple synthesis method.

[0022] In a preferred embodiment of the present invention, the molar ratio of 2-aminothioxanthone to the raw material aldehyde is 1:1 to 1:1.2. The solvent can be one of methanol, ethanol, isopropanol, and ether, preferably methanol or ethanol. The amount of solvent added is the amount of solvent commonly used in the art. In a specific embodiment of the present invention, the amount of solvent is 10mL / 0.1gm (2-aminothioxanthone), that is, the amount of solvent used for 0.1g of 2-aminothioxanthone is 10mL. Acetic acid plays a catalytic role in the preparation method, and the amount of acetic acid is preferably one thousandth of the solvent volume. In a specific embodiment of the present invention, after the reaction is completed, it is cooled, filtered, and the filter cake is washed with a reaction solvent. A pure product can be obtained after drying. The filtrate can be reused. The yield of the preparation method provided above is high, which is conducive to industrial production.

[0023] The Schiff base photoinitiator provided by the present invention exhibits high initiation activity (e.g., a faster initiation rate and / or higher double bond conversion rate) under 385-470 nm LED illumination, is compatible with a wide range of light sources, and has a wider range of applications. Compared with the previously disclosed thioxanthone chalcone initiator, it exhibits higher initiation activity under long-wavelength LED illumination and has a wider range of applications. The preparation method provided by the present invention is simple, synthetic, and easy to purify. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The hydrogen nuclear magnetic resonance spectrum of the product obtained in Example 1 is shown in FIG.

[0025] Figure 2 The UV-visible absorption spectrum of the product obtained in Example 1 is shown in FIG.

[0026] Figure 3The hydrogen nuclear magnetic resonance spectrum of the product obtained in Example 2 is shown in FIG.

[0027] Figure 4 This is a photopolymerization kinetics curve of the products provided in Example 1 and Example 2 when initiating polymerization of 1,6-hexanediol diacrylate (HDDA) under LED@385nm light.

[0028] Figure 5 This is a photopolymerization kinetics curve of the products provided in Example 1 and Example 2 when initiating polymerization of 1,6-hexanediol diacrylate (HDDA) under LED@405nm light.

[0029] Figure 6 This is a photopolymerization kinetics curve of the products provided in Example 1 and Example 2 when initiating polymerization of 1,6-hexanediol diacrylate (HDDA) under LED@435nm light.

[0030] Figure 7 This is a photopolymerization kinetics curve of the products provided in Example 1 and Example 2 and the comparative initiator TX-DMAP when initiating the polymerization of 1,6-hexanediol diacrylate (HDDA) under LED@450nm light.

[0031] Figure 8 This is a photopolymerization kinetics curve of the products provided in Example 1 and Example 2 and the comparative initiator TX-DMAP when initiating the polymerization of 1,6-hexanediol diacrylate (HDDA) under LED@470nm light.

[0032] Figure 9 This is a photopolymerization kinetics curve of the products / Iod provided in Example 1 and Example 2 when initiating polymerization of 1,6-hexanediol diacrylate (HDDA) under LED@385nm light.

[0033] Figure 10 This is a photopolymerization kinetics curve of the products / Iod provided in Example 1 and Example 2 when initiating polymerization of 1,6-hexanediol diacrylate (HDDA) under LED@405nm light.

[0034] Figure 11 This is a photopolymerization kinetics curve of the products / Iod provided in Example 1 and Example 2 when initiating polymerization of 1,6-hexanediol diacrylate (HDDA) under LED @ 435nm light.

[0035] Figure 12 This is a photopolymerization kinetics curve of the products / Iod provided in Example 1 and Example 2 and the comparative initiator TX-DMAP / Iod when initiating the polymerization of 1,6-hexanediol diacrylate (HDDA) under LED@450nm light.

[0036] Figure 13 This is a photopolymerization kinetics curve of the products / Iod provided in Example 1 and Example 2 and the comparative initiator TX-DMAP / Iod when initiating the polymerization of 1,6-hexanediol diacrylate (HDDA) under LED@470nm light. DETAILED DESCRIPTION

[0037] The following embodiments of the present invention are further described in detail with reference to the examples. The following examples are provided to illustrate the present invention, but are not intended to limit the scope of the present invention. In the embodiments of the present invention, yield = actual product mass / theoretical mass * 100%. The formula for calculating the double bond conversion is:

[0038] Where A0 is the peak area of ​​carbon-carbon double bond when illumination time is 0; A t is the peak area of ​​carbon-carbon double bond when the illumination time is t.

[0039] Example 1

[0040] This embodiment provides a Schiff base photoinitiator, and the preparation method includes the following steps:

[0041] In a 100 mL round-bottom flask, 0.227 g of 2-aminothioxanthone, 0.164 g of 4-dimethylaminobenzaldehyde, 22.7 mL of ethanol, and 22.7 μL of acetic acid were weighed and heated to reflux for 48 h. After the reaction was completed, the mixture was cooled, filtered, washed with ethanol, and dried to obtain 0.30 g of a yellow solid with a yield of 83.8%.

[0042] The H NMR spectrum of the product obtained in this example is shown in Figure 1 As shown: 1 H NMR (400M, CDCl3) δppm: 3.12 (s, 6H), 6.76-6.82 (d, 2H, J = 8.8Hz), 7.49-7.56 (m, 1H), 7 .59-7.71(m,4H),7.86(s,2H),8.45(s,1H),8.51(s,1H),8.66-8.70(d,1H,J=8.0Hz).

[0043] The ultraviolet spectrum of the tetrahydrofuran solution of the product obtained in this example is shown in FIG. Figure 2 As shown, the above results can confirm that the obtained product is a compound of structural formula (I), R is H, and is named TXN1.

[0044] Example 2

[0045] This embodiment provides a Schiff base photoinitiator, and the preparation method includes the following steps:

[0046] In a 100 mL round-bottom flask, 0.227 g of 2-aminothioxanthone, 0.18 g of 2-hydroxy-4-dimethylaminobenzaldehyde, 22.7 mL of methanol, and 22.7 μL of acetic acid were weighed and heated to reflux for 72 h. After the reaction was completed, the mixture was cooled, filtered, washed with methanol, and dried to obtain 0.33 g of a yellow solid with a yield of 88.2%.

[0047] The H NMR spectrum of the product obtained in this example is shown in Figure 3 As shown: 1 H NMR (CDCl3, 500 MHz) δ ppm: 3.07 (s, 6H, N(Me)2), 6.22-6.25 (d, 1H, J = 6.0 Hz), 6.30-6.34 (dd, 1H, J = 2.0 Hz, J = 7.0 Hz), 7.23-7.26 (d, 1H, J = 2.0 Hz, J = 7.5 Hz), 7.48-7.52 (m, 1H), 7.56-7.66 (m, 4H), 8.47-8.50 (d, 1H, J = 6.0 Hz), 8.63-8.67 (m, 2H), 13.51 (s, 1H, OH). The theoretical values ​​were consistent with the experimental values, confirming that the obtained product was the compound of structural formula (I), R was OH, and was named TXN.

[0048] Example 3

[0049] This embodiment provides a Schiff base photoinitiator, and the preparation method includes the following steps:

[0050] In a 100 mL round-bottom flask, 0.227 g of 2-aminothioxanthone, 0.18 g of 2-hydroxy-4-dimethylaminobenzaldehyde, and 22.7 mL of ethanol were weighed. 22.7 μL of acetic acid was added and the mixture was heated to reflux for 48 h. After the reaction was completed, the mixture was cooled, filtered, washed with methanol, and dried to obtain 0.31 g of a yellow solid with a yield of 82.9%.

[0051] The H NMR spectrum of the product obtained in this example and the H NMR spectrum of the product obtained in Example 2 Figure 1 The product is a compound of structural formula (I), R is OH, and is named TXN.

[0052] Experimental example

[0053] Initiation of HDDA polymerization

[0054] 1) 3×10 -5mol of the product provided in Example 1 (i.e., the Schiff base photoinitiator TXN1 obtained in Example 1) or the product provided in Example 2 (i.e., the Schiff base photoinitiator TXN obtained in Example 2) or the TX-DMAP photoinitiator provided in the comparative example, 3.0000 g of 1,6-hexanediol diacrylate (HDDA) were weighed in a 10 mL centrifuge tube, ultrasonically mixed, and set aside.

[0055] The photocuring kinetics of Schiff base photoinitiators TXN and TXN1 were detected by real-time infrared method, where the light source was LED @ 385nm and the light intensity was 88mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 4 shown.

[0056] The photocuring kinetics of the Schiff base photoinitiator TXN obtained by combining Schiff base photoinitiator TXN and TXN1 were detected by real-time infrared method, where the light source was LED@405nm and the light intensity was 121mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 5 shown.

[0057] The photocuring kinetics of the Schiff base photoinitiator TXN obtained by combining Schiff base photoinitiator TXN and TXN1 were detected by real-time infrared method, where the light source was LED @ 435nm and the light intensity was 130mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 6 shown.

[0058] The photocuring kinetics of Schiff base photoinitiators TXN and TXN1 were detected by real-time infrared method, where the light source was LED @ 450nm and the light intensity was 162mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 7 As shown. Figure 7 It can be seen that when the single-component system initiates HDDA polymerization, the double bond conversion rate of the TXN system is 76.1% at 5 min, the double bond conversion rate of the TXN1 system is 66.6%, and the double bond conversion rate of the TX-DMAP system is 44.3%; compared with the TX-DMAP system, the Schiff base photoinitiator TXN and TXN1 systems have faster initiation rates and higher double bond conversion rates.

[0059] The photocuring kinetics of Schiff base photoinitiators TXN and TXN1 and the comparative photoinitiator system were tested by real-time infrared method. The light source was LED @ 470nm, and the light intensity was 158mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 8 As shown. Figure 8 It can be seen that when the single-component system initiates HDDA polymerization, the double bond conversion rate of the TXN system is 68.2% after 5 min; the double bond conversion rate of the TXN1 system is 33.8%, and the double bond conversion rate of the TX-DMAP system is 1.1%; compared with the TX-DMAP system, the Schiff base photoinitiators TXN and TXN1 have faster initiation rates and higher double bond conversion rates.

[0060] 2) 0.0112 g of the Schiff base photoinitiator of Example 1 or the Schiff base photoinitiator of Example 2, 0.0161 g of bis-tert-butylphenyl iodonium hexafluorophosphate (Iod), and 3.0000 g of 1,6-hexanediol diacrylate (HDDA) were weighed into a 10 mL centrifuge tube, ultrasonically mixed, and set aside.

[0061] TX-DMAP was used as a comparative photoinitiator. The sample was prepared as follows: 0.0107 g TX-DMAP, 0.0161 g Iod, and 3.0000 g 1,6-hexanediol diacrylate (HDDA) were weighed in a 10 mL centrifuge tube, ultrasonically mixed, and set aside.

[0062] The photocuring kinetics of the above samples were tested by real-time infrared method, where the light source was LED @ 385nm and the light intensity was 88mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 9 shown.

[0063] The photocuring kinetics of the above samples were tested by real-time infrared method, where the light source was LED@405nm and the light intensity was 121mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 10 shown.

[0064] The photocuring kinetics of the above samples were tested by real-time infrared method, where the light source was LED @ 435nm and the light intensity was 130mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 11 shown.

[0065] The above samples and the comparative photoinitiator system were respectively tested for their photocuring kinetics using real-time infrared method, where the light source was LED@450nm and the light intensity was 162mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 12 As shown. Figure 12 It can be seen that when the photoinitiator / Iod system initiates HDDA polymerization, the double bond conversion rate of the TXN system is 80.5% after 3 minutes; the double bond conversion rate of the TXN1 system is 80.8%, and the double bond conversion rate of the TX-DMAP system is 61.4%; compared with the TX-DMAP system, the Schiff base photoinitiator TXN has a faster initiation rate and a higher double bond conversion rate.

[0066] The above samples and the comparative photoinitiator system were tested for their photocuring kinetics using real-time infrared method, where the light source was LED @ 470nm and the light intensity was 158mW / cm 2 The initial illumination time is 8s, and the conversion rate-time curve of the HDDA monomer carbon-carbon double bond functional group is as follows: Figure 13 As shown. Figure 13 It can be seen that when the photoinitiator / Iod system initiates HDDA polymerization, the double bond conversion rate of the TXN system is 82.2% after 5 min; the double bond conversion rate of the TXN1 system is 81.9%; and the double bond conversion rate of the TX-DMAP system is 64.5%; compared with the TX-DMAP system, the Schiff base photoinitiators TXN and TXN1 have faster initiation rates and higher double bond conversion rates.

[0067] Finally, the method of the present invention is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A Schiff base photoinitiator, characterized in that The Schiff base photoinitiator includes a compound having the structural formula shown in the following formula (I): （I） ； （I） Wherein, R is H or OH.

2. The Schiff base photoinitiator according to claim 1, characterized in that The R is OH.

3. The Schiff base photoinitiator according to claim 1, characterized in that The Schiff base photoinitiator is an LED photoinitiator.

4. The Schiff base photoinitiator according to claim 1, characterized in that The Schiff base photoinitiator initiates free radical polymerization of acrylate or methacrylate monomers. 5 . Use of the Schiff base photoinitiator according to claim 1 in initiating a free radical polymerization reaction of acrylate or methacrylate monomers.

6. The use according to claim 5, characterized in that The illumination intensity of the free radical polymerization reaction is 50 to 200 mW / cm 2 , the polymerization time is 5s~5min.

7. The use according to claim 6, characterized in that The wavelength range of the free radical polymerization reaction is 385-470 nm.

8. The use according to any one of claims 5 to 7, characterized in that The acrylate or methacrylate monomer is 1,6-hexanediol diacrylate, methyl methacrylate, butyl methacrylate, methyl acrylate, n-butyl acrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, β-hydroxyethyl methacrylate or β-hydroxyethyl acrylate.

9. The use according to claim 8, characterized in that The acrylic acid ester or methacrylic acid ester monomer is 1,6-hexanediol diacrylate.

10. The use according to any one of claims 5 to 7, characterized in that The free radical polymerization is initiated by combining the Schiff base photoinitiator with an iodonium salt.

11. The method for preparing the Schiff base photoinitiator according to any one of claims 1 to 4, characterized in that: The steps include: 2-aminothioxanthone and a raw material aldehyde are refluxed for 48 hours to 72 hours under the action of a solvent and acetic acid; the raw material aldehyde is 4-dimethylaminobenzaldehyde or 2-hydroxy-4-dimethylaminobenzaldehyde.

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