Photoinitiator based on intramolecular halogen bonds and adhesive composition and application thereof

Abstract

The invention provides the photoinitiator based on the intramolecular halogen bond, and the photolysis can be delayed by adjusting the central skeleton of the photoinitiator based on the intramolecular halogen bond and the type of atoms or atomic groups forming the intramolecular halogen bond action. The invention further discloses an adhesive composition containing the photoinitiator based on the intramolecular halogen bonds and a preparation method of the adhesive composition. The adhesive composition prepared by adopting the photoinitiator based on the intramolecular halogen bonds has a window period for delaying curing, and can be used for bonding low-ultraviolet-light-transmission base materials.

Description

Technical Field

[0001] This invention belongs to the field of photocuring technology, and particularly relates to a photoinitiator based on intramolecular halogen bonds, its adhesive composition, and its application. Background Technology

[0002] UV adhesives are a type of adhesive that cures upon exposure to ultraviolet light. The photoinitiator in their composition is the key species initiating polymerization. In recent decades, due to its numerous advantages such as safety, environmental friendliness, excellent curing speed, and strong adhesion, UV adhesives have been widely used in high-end electronics. However, UV adhesives currently face a serious problem. When the two substrates to be bonded are opaque (or contain UV absorbers), ultraviolet light cannot penetrate the substrates to act on the photoinitiator and activate the active species, resulting in the adhesive failing to cure.

[0003] If a UV adhesive does not cure immediately upon exposure to light, but instead begins to react after a certain period of time, then delayed curing of the adhesive can be achieved, thus enabling bonding of such substrates. Patents and literature have reported methods for achieving delayed curing through specific formulation designs and matrix resin structural designs. For example, CN118307767A achieves a certain delay time through structural design of epoxy resin. Zhu et al., utilizing the relatively slow curing speed of multifunctional glycidyl ethers, have also developed adhesives suitable for low-temperature delayed curing. RSC Adv 2017, 7 (4046-4053). Harikrishna delayed gelation time by adding organic amine compounds to cationic curing compositions. These organic amine compounds consume the generated hydrogen ions in the early stages of the reaction (Journal of Photochemistry and Photobiology A: Chemistry 2015, 303, 17). Predictably, these strategies are only effective for specific formulation ranges; if the formulation contains highly reactive resins, the system will still cure rapidly. Therefore, such solutions are unlikely to be universally applicable and are difficult to handle complex and varied real-world applications.

[0004] Therefore, there is an urgent need in the field for a delayed curing platform that can be applied to a variety of practical application scenarios (such as highly reactive resins) and that allows for manual adjustment of the delay window according to actual process requirements. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a photoinitiator based on intramolecular halogen bonds, its adhesive composition, and its application.

[0006] In a first aspect, the present invention provides a photoinitiator based on intramolecular halogen bonds, with the following structural formula: , Each of R1 is independently selected from , or ; X is selected from CH2, O, S, Se, NH or NH with substituents; Each Y is independently selected from O, S, Se, NH or NH substituted with a substituent; Z - It is a monovalent anion; R2, R3, and R4 are independently chemically suitable substituents for attachment to the structure described above.

[0007] Preferably, the monovalent anion is selected from BF4. - PF6 - SbF6 - B(Ar)4 - ,Br - I - Cl - CN - TsO - TfO - or MsO - ; and / or R2, R3, and R4 are independently selected from hydrogen, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, carbonyl, carboxyl, aromatic cycloalkyl, ester, amide, hydroxyl, carboxylate, and polymer chain groups.

[0008] In a second aspect, the present invention provides a method for preparing the intramolecular halogen bond-based photoinitiator described in the first aspect, comprising: S1: Reaction of 2-phenylboronic acid pinacol ester-6-methyl-aniline or its derivative with 2,5-dihalo-five-membered aromatic heterocycle under alkaline conditions yields intermediate 1, in which the 2- and 5-positions of the five-membered aromatic heterocycle are substituted with 2-amino-3-methylphenyl or a 2-amino-3-methylphenyl derivative, wherein the five-membered aromatic heterocycle is selected from thiophene, furan, selenophenol, pyrrole or a pyrrole derivative; S2: The intermediate 1 is subjected to diazotization and then reacted with an inorganic iodide salt to obtain intermediate 2 in which the 2-amino group of intermediate 1 is iodine-substituted. S3: The intermediate 2 is reacted with a brominating agent to obtain intermediate 3 in which the hydrogen on the 3-methyl group in the intermediate 2 is brominated; S4: Intermediate 3 is reacted with trifluoromethanesulfonic acid under oxidizing conditions to undergo intramolecular electrophilic cyclic closure to obtain intermediate 4; S5: Combine the intermediate 4 with R1-(CH2) n The -YH reaction yields the bromine in intermediate 4 via R1-(CH2) reaction. n -Y-substituted intermediate 5; R1 is selected from , or Y is selected from O, S, Se, NH or NH with substituents, and n is an integer greater than or equal to 1; S6: Combine the intermediate 5 with Z - The metal salt undergoes an ion exchange reaction to obtain the photoinitiator based on intramolecular halogen bonds, wherein Z - Selected from BF4 - PF6 - SbF6 - B(Ar)4 - ,Br - I - Cl - CN - TsO - TfO - or MsO - .

[0009] In a third aspect, the present invention provides an adhesive composition comprising, by parts by weight: 0.01 - 1 part of the intramolecular halogen bond-based photoinitiator as described in the first aspect or the intramolecular halogen bond-based photoinitiator prepared by the method described in the second aspect; 1-10 parts epoxy resin; 0.01 - 1 part silane coupling agent.

[0010] In a fourth aspect, the present invention provides the use of the adhesive composition described in the third aspect for bonding substrates.

[0011] The intramolecular halogen-based photoinitiator provided by this invention has a delayed photolysis effect. Adhesive compositions containing the intramolecular halogen-based photoinitiator of this invention exhibit significant delayed curing properties and can be used to bond substrates with low ultraviolet (UV) transmittance. Furthermore, by adjusting the type of electron-rich atoms (or groups) and the type of aromatic heterocycles containing X groups in the backbone, the intramolecular halogen-based photoinitiator can achieve different delay times. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other implementation schemes can be obtained based on these drawings without creative effort.

[0013] Figure 1 The 1H NMR spectrum of compound 3 in the synthetic route of XB-1 in Example 1 is shown.

[0014] Figure 2 The 1H NMR spectrum of compound 7 in the synthetic route of XB-1 in Example 1 is shown.

[0015] Figure 3 The proton NMR spectrum of XB-1 in Example 1 is shown.

[0016] Figure 4 The proton NMR spectrum of XB-2 in Example 1 is shown.

[0017] Figure 5 The proton NMR spectrum of XB-3 in Example 1 is shown.

[0018] Figure 6 The proton NMR spectrum of XB-4 in Example 1 is shown.

[0019] Figure 7 The proton NMR spectrum of XB-5 in Example 1 is shown.

[0020] Figure 8 The proton NMR spectrum of XB-6 in Example 1 is shown.

[0021] Figure 9 The proton NMR spectrum of XB-7 in Example 1 is shown. Detailed Implementation

[0022] The present invention will be described in detail below. It should be understood that the following description is merely illustrative and is not intended to limit the scope of the invention; the scope of protection of the invention is defined by the appended claims. Furthermore, those skilled in the art will understand that modifications can be made to the technical solutions of the present invention without departing from its spirit and intent. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter pertains. Before a detailed description of the invention, the following definitions are provided to better understand it.

[0024] In the context of this invention, many embodiments use the expressions "comprising," "including," or "basically / mainly composed of." The expressions "comprising," "including," or "basically / mainly composed of" should be understood as open-ended expressions, indicating that they include not only the elements, components, parts, and method steps specifically listed after the expression, but also other elements, components, parts, and method steps. Additionally, in this document, the expressions "comprising," "including," or "basically / mainly composed of" may also be understood as closed-ended expressions in certain circumstances, indicating that they only include the elements, components, parts, and method steps specifically listed after the expression, and do not include any other elements, components, parts, or method steps. In this case, the expression is equivalent to the expression "composed of."

[0025] It should be noted that, unless explicitly stated in the context, all numerical values ​​or ranges mentioned in this article are defined by the term "about". In this article, for a given numerical value, the term "about" means ±5% of that value, such as ±4%, ±3%, ±2%, or ±1%. For a range of numerical values, the term "about" means ±5% of the upper or lower limit of that range, such as ±4%, ±3%, ±2%, or ±1%.

[0026] In this paper, ordinal numbers such as "first," "second," and "third" are sometimes used to modify or limit elements, components, parts, method steps, solutions, solvents, temperatures, systems, etc. It should be noted that in this paper, these expressions are only used to distinguish the elements, components, parts, method steps, solutions, solvents, temperatures, systems, etc. that they modify or limit, and are not intended to limit their order or importance.

[0027] In view of the problems existing in the prior art, such as the inability of UV adhesives to cure effectively when the substrate to be bonded is opaque or when UV absorbers are added, and the incompatibility of existing delayed-curing adhesives with highly reactive resins, the present invention aims to provide a photoinitiator based on intramolecular halogen bonds, its adhesive composition, and its application to solve at least one of the above-mentioned problems.

[0028] In a first aspect, the present invention provides a photoinitiator based on intramolecular halogen bonds, with the following structural formula: , Each of R1 is independently selected from , or ; X is selected from CH2, O, S, Se, NH or NH with substituents; Each Y is independently selected from O, S, Se, NH or NH substituted with a substituent; Z - It is a monovalent anion; R2, R3, and R4 are independently chemically suitable substituents for attachment to the structure described above.

[0029] In some embodiments, R2, R3, and R4 are independently selected from any substituent group chemically suitable for attachment to the stated structure. In a preferred embodiment, R2, R3, and R4 are independently selected from hydrogen, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, carbonyl, carboxyl, aromatic cycloalkyl, ester, amide, hydroxyl, carboxyl group, polymer chain group, etc.

[0030] In some embodiments, the monovalent anion is selected from any counterion that can maintain the electroneutrality of the intramolecular halogen-based photoinitiator. In a preferred embodiment, the monovalent anion includes, but is not limited to, BF4. - PF6 - SbF6 - B(Ar)4 - ,Br - I - Cl - CN - TsO - TfO - or MsO - .

[0031] It is worth noting that the Y group in the structural formula of the photoinitiator based on intramolecular halogen bonds is an atom that forms a halogen bond with iodine ions. Furthermore, the R1 group in the structural formula of the photoinitiator based on intramolecular halogen bonds is an atomic group that forms a halogen bond with iodine ions, and all R1 groups in this invention contain O. Specifically, iodine ions simultaneously interact with the O in both the Y group and the R1 group to form halogen bonds.

[0032] In one specific embodiment, when Y is O, the color change time of the indicator after illumination by the intramolecular halogen bond-based photoinitiator is 10 min. Further, the delay window of the adhesive composition prepared from the intramolecular halogen bond-based photoinitiator is 11 min. In another specific embodiment, when Y is S, the color change time of the indicator after illumination by the intramolecular halogen bond-based photoinitiator is 13 min. Further, the delay window of the adhesive composition prepared from the intramolecular halogen bond-based photoinitiator is 16 min. Therefore, as the electron cloud density of the atoms forming halogen bonds with iodine ions (e.g., replacing Y with S instead of O) increases, the halogen bond interaction is enhanced, thereby significantly extending the delay window. Based on this, the delay window of the intramolecular halogen bond-based photoinitiator can be artificially controlled by adjusting the type of atoms or atomic groups forming halogen bonds with iodine ions.

[0033] In one specific embodiment, when the X group in the structural formula of the intramolecular halogen-based photoinitiator is a substituent-substituted NH group, the resulting intramolecular halogen-based photoinitiator exhibits a color change time of 6 minutes after light irradiation. Furthermore, the adhesive composition prepared from the intramolecular halogen-based photoinitiator has a delay window of 7 minutes.

[0034] In another specific embodiment, when the X group is O, the resulting intramolecular halogen-based photoinitiator exhibits a color change time of 8 minutes after light irradiation. Furthermore, the adhesive composition prepared from the intramolecular halogen-based photoinitiator has a delay window of 8 minutes.

[0035] In yet another specific embodiment, when the X group in the structural formula of the intramolecular halogen-based photoinitiator is S, the resulting intramolecular halogen-based photoinitiator exhibits a color change time of 10 min after light irradiation. Furthermore, the adhesive composition prepared from the intramolecular halogen-based photoinitiator has a delay window of 11 min.

[0036] In yet another specific embodiment, when the X group in the structural formula of the intramolecular halogen-based photoinitiator is Se, the resulting intramolecular halogen-based photoinitiator exhibits a color change time of 12 minutes after illumination. Furthermore, the adhesive composition prepared from the intramolecular halogen-based photoinitiator has a delay window of 12 minutes.

[0037] In summary, as the electrophilic substitution reaction capability of the heterocycle containing the X group gradually decreases (pyrrole > furan > thiophene > selenophene), the delay window tends to gradually increase. Therefore, the delay window of the photoinitiator based on intramolecular halogen bonds can be artificially controlled by adjusting the type of the central skeleton of the photoinitiator.

[0038] It is worth noting that a halogen bond (XB) refers to a non-covalent interaction that occurs when an electron-deficient halogen atom approaches another relatively electron-rich atom or molecule. It is widely used in halogen-bonded organic frameworks (XOFs) and halogen-bonded catalysis. The formation mechanism of halogen bonds is mainly based on electrostatic interactions. When a halogen atom approaches an electron-rich atom (such as O or S), the positively charged region of the halogen attracts the lone pair electrons of the electron-rich atom, thus forming a stable halogen bond. For example, iodine atoms, due to their larger atomic radius and polarization ability, typically exhibit stronger forces in halogen bonds. This invention prepares a series of photoinitiators with intramolecular halogen bonds. These photoinitiators have an iodonium salt parent structure, where the central iodine atom forms multiple halogen bonds with electron-rich atoms (i.e., the Y substituent and the O in the R1 group of the intramolecular halogen bond-based photoinitiator). Upon irradiation, the iodonium salt parent structure is bound and does not immediately photodegrade, but rather slowly. Finally, as protic acids gradually accumulate, they rapidly promote the polymerization of epoxy resins. The delayed curing mechanism of XB initiator is as follows: .

[0039] In a second aspect, the present invention provides a method for preparing the intramolecular halogen bond-based photoinitiator described in the first aspect, comprising: S1: Reaction of 2-phenylboronic acid pinacol ester-6-methyl-aniline or its derivative with 2,5-dihalo-five-membered aromatic heterocycle under alkaline conditions yields intermediate 1, in which the 2- and 5-positions of the five-membered aromatic heterocycle are substituted with 2-amino-3-methylphenyl or a 2-amino-3-methylphenyl derivative, wherein the five-membered aromatic heterocycle is selected from thiophene, furan, selenophenol, pyrrole or a pyrrole derivative; S2: The intermediate 1 is subjected to diazotization and then reacted with an inorganic iodide salt to obtain intermediate 2 in which the 2-amino group of intermediate 1 is iodine-substituted. S3: The intermediate 2 is reacted with a brominating agent to obtain intermediate 3 in which the hydrogen on the 3-methyl group in the intermediate 2 is brominated; S4: Intermediate 3 is reacted with trifluoromethanesulfonic acid under oxidizing conditions to undergo intramolecular electrophilic cyclic closure to obtain intermediate 4; S5: Combine the intermediate 4 with R1-(CH2) n The -YH reaction yields the bromine in intermediate 4 via R1-(CH2) reaction. n -Y-substituted intermediate 5; R1 is selected from , or Y is selected from O, S, Se, NH or NH substituted by a substituent, and n is an integer greater than or equal to 1, preferably 1 or 2; S6: Combine the intermediate 5 with Z- The metal salt undergoes an ion exchange reaction to obtain the photoinitiator based on intramolecular halogen bonds, wherein Z - Selected from BF4 - PF6 - SbF6 - B(Ar)4 - ,Br - I - Cl - CN - TsO - TfO - or MsO - .

[0040] In some preferred embodiments, the 2-phenylboronic acid pinacol ester-6-methyl-aniline or a derivative thereof is prepared by a Suzuki-Miyaura reaction of 2-bromo-6-methylaniline or a derivative thereof, wherein the Suzuki-Miyaura reaction is carried out under an inert atmosphere.

[0041] In some embodiments, the synthetic route for the intramolecular halogen-based photoinitiator is as follows: .

[0042] It is worth noting that in the synthesis process of the photoinitiator based on intramolecular halogen bonds, steps S1, S2, S3, S4, S5, or S6 can use any common solvent, including but not limited to methanol, ethanol, acetone, chloroform, water, diethyl ether, toluene, benzene, 1,4-dioxane, N,N-dimethylacetamide, tetrahydrofuran, acetonitrile, dichloromethane, ethyl acetate, petroleum ether, n-hexane, isopropanol, tert-butanol, etc. The reaction atmosphere for step S1 or S4 is selected from any inert gas, such as helium, nitrogen, or argon. The reaction temperature for steps S1, S2, S3, S4, S5, or S6 is selected from any value in the range of -20 to 120°C, such as -20°C, -10°C, 0, 100, 200, 300, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, preferably 0 to 100°C. The stirring speed in steps S1, S2, S3, S4, S5, or S6 can be selected from any value between 10 and 2000 rpm, such as 10 rpm, 20 rpm, 30 rpm, 40 rpm, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, or 2000 rpm, preferably 50 to 1000 rpm.

[0043] In a third aspect, the present invention provides an adhesive composition comprising, by parts by weight: 0.01 - 1 part of the intramolecular halogen bond-based photoinitiator as described in the first aspect or the intramolecular halogen bond-based photoinitiator prepared by the method described in the second aspect; 1-10 parts epoxy resin; 0.01 - 1 part silane coupling agent.

[0044] It is worth noting that "by mass parts" in this invention means that the number of parts of each component in the adhesive composition is calculated based on mass.

[0045] In some embodiments, the mass fraction of the photoinitiator based on intramolecular halogen bonds is 0.01-1 part, such as 0.01 part, 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part, 1 part, preferably 0.1-0.5 parts.

[0046] In some embodiments, the epoxy resin can be any type of epoxy resin. In a preferred embodiment, the epoxy resin is selected from one or more of the group consisting of bisphenol A type glycidyl ether epoxy resin, bisphenol F type glycidyl ether epoxy resin, a mixture of bisphenol A and bisphenol F type glycidyl ether epoxy resins, rubber toughening type glycidyl ether epoxy resin, aliphatic epoxy resin and / or alicyclic epoxy resin. In a more preferred embodiment, the epoxy resin is in parts by weight of 1-10 parts, such as 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, or 10 parts, preferably 2-10 parts.

[0047] It is worth noting that the adhesive composition may contain one or more (e.g., two, three, etc.) epoxy resins. In one specific embodiment, the adhesive composition contains a combination of bisphenol F epoxy resin (NPEF-170) and 2021p epoxy resin. In another specific embodiment, the adhesive composition contains only 2021p epoxy resin. In yet another specific embodiment, the adhesive composition contains a combination of bisphenol A epoxy resin (NPEF-128) and bisphenol F epoxy resin (NPEF-170). Delayed curing is achieved when the adhesive composition contains one or more (e.g., two) epoxy resins.

[0048] In some embodiments, the silane coupling agent can be any silane coupling agent. In a preferred embodiment, the silane coupling agent is selected from one or more of the group consisting of 3-glycidoxypropyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, (3-epoxypropylpropoxy)trimethoxysilane, (3-epoxypropylpropoxy)triethoxysilane, and / or 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. In a more preferred embodiment, the silane coupling agent is present in parts by mass of 0.01 to 1, such as 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, preferably 0.01 to 0.5.

[0049] It is worth noting that the adhesive composition may contain one or more (e.g., two, three, etc.) silane coupling agents.

[0050] The photoinitiator based on intramolecular halogen bonds described in this invention has a conjugated parent molecule with intramolecular DA (electron donor-electron withdrawer) interactions, resulting in a large conjugated system and a shift in absorption wavelength towards longer wavelengths. This allows the photoinitiator based on intramolecular halogen bonds to absorb at 365 nm, thus eliminating the need for additional photosensitizers.

[0051] In a fourth aspect, the present invention provides the use of the adhesive composition described in the third aspect for bonding substrates, comprising: (1) The adhesive composition is irradiated with ultraviolet light and initiated, and the adhesive composition enters a delayed curing window; (2) During the window period, the adhesive composition is bonded to the substrate.

[0052] The adhesive composition of this invention is applicable to a variety of substrates (such as glass, crystalline materials, plastics, etc.). Because the adhesive composition of this invention has a delayed curing window, for substrates with low ultraviolet (UV) transmittance, the adhesive composition can be pre-applied to the substrate surface. After excitation with UV light, the adhesive composition can remain in a flowing state within a certain window, during which time it can bond to the low UV transmittance substrate. Therefore, the adhesive composition of this invention can also achieve good bonding effects on low UV transmittance substrates. The low UV transmittance substrates of this invention include opaque substrates, substrates containing UV absorbers, multilayer composite substrates, etc.

[0053] It should be noted that there are no particular limitations on the adhesive application thickness. Any adhesive thickness can be selected depending on the bonding requirements. Different UV irradiation times can be determined for different adhesive thicknesses. In a preferred embodiment, the adhesive composition of the present invention is used with an application thickness of 0.2-1 mm, a wavelength of 200-500 nm, and a curing energy of 200-100000 mJ / cm². 2 After irradiation with ultraviolet (UV) light, the adhesive composition undergoes delayed curing with a delayed curing window of 3 to 30 minutes, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30 minutes. The specific delayed curing window can be flexibly selected according to actual process requirements. The UV light source can be any light source capable of producing the aforementioned wavelengths and curing energy, such as mercury lamps, LED light sources, or xenon lamps.

[0054] The adhesive composition of the present invention has at least one of the following beneficial effects: The photoinitiator based on intramolecular halogen bonds described in this invention has an iodonium salt parent structure, where the central iodine atom can form multiple halogen bonds with electron-rich atoms (or groups) within the molecule. This allows the iodonium salt parent structure to be bound and not immediately photodegraded upon exposure to light, but rather photodegraded slowly.

[0055] The adhesive composition prepared using the intramolecular halogen bond-based photoinitiator described in this invention can be used to bond substrates with low ultraviolet light transmittance. During use, the adhesive composition is pre-applied to the substrate surface. After excitation with ultraviolet light, the adhesive composition does not immediately cure but remains in a fluid state within a certain window, providing sufficient time for bonding opaque substrates. Furthermore, by adjusting the structural type of electron-rich atoms or central skeleton aromatic heterocycles within the intramolecular halogen bond-based photoinitiator, the delay window can be artificially controlled. This allows for different operating windows to be provided according to specific process requirements, greatly improving the convenience and user-friendliness of construction.

[0056] Furthermore, the photoinitiator based on intramolecular halogen bonds contains active groups that can participate in curing, thus suppressing the possibility of small molecule compound migration and preventing adhesive layer failure.

[0057] Synthesis example Synthesis of photoinitiators based on intramolecular halogen bonds (XB-1, XB-2, XB-3, XB-4, XB-5, XB-6, XB-7) as well as nonXB-1 and nonXB-2.

[0058] Synthesis of XB-1 The synthetic route for XB-1 is as follows: .

[0059] The specific synthesis steps are as follows: Step 1: 5 mmol of 2-bromo-6-methylaniline, 10 mmol of potassium acetate (KOAc), 10 mmol of pinacol diborate, and 0.25 mmol of dichloro(1,1'-bis(diphenylphosphino)ferrocene)palladium (Pd(dppf)Cl2) were placed in a Shrek tube and purged three times with nitrogen. Then, 10 mL of 1,4-dioxane was added to the Shrek tube, and the mixture was heated and stirred overnight at 100°C. After the reaction was complete, the reaction solution was washed with water, then extracted with dichloromethane, and the organic solvent was removed by rotary evaporation. The crude product of compound 2 was used directly in the next step of the reaction.

[0060] Step 2: The crude product of compound 2, 20 mmol of potassium carbonate (K₂CO₃), and 0.5 mmol of tetrakis(triphenylphosphine)palladium (Pd(PPh₃)₄) were sequentially added to a flask, and the mixture was purged with nitrogen three times. Then, 10 mmol of 2,5-dibromothiophene and 20 mL of toluene were added to the flask. Finally, the mixture was heated and stirred overnight at 100 °C. After the reaction was complete, the reaction solution was washed with water, then extracted with dichloromethane, and the organic solvent was removed by rotary evaporation. The crude product of compound 3 was recrystallized to obtain compound 3. The 1H NMR spectrum of compound 3 is detailed below. Figure 1 . 1 H NMR (CDCl3, 400 MHz): δ 7.52 (dd, J =7.3, 1.1 Hz, 2H), 7.19 (d, J = 14.9 Hz, 2H), 7.04 (dt, J = 7.7, 0.8 Hz, 2H), 6.75 (s, 2H), 4.67 (s, 2H).

[0061] Step 3: Dissolve 5 mmol of compound 3 in 10 mL of dichloromethane, then slowly add 10 mmol of sodium nitrite and 50 mmol of hydrochloric acid at 0 °C. After the addition is complete, continue stirring for half an hour. Then, add 10 mmol of potassium iodide to the reaction solution in three portions. After the reaction is complete, wash the reaction solution with water, then extract with dichloromethane, and remove the organic solvent by rotary evaporation. The crude product of compound 4 obtained is used directly in the next step of the reaction.

[0062] Step 4: The crude product of compound 4, 10.5 mmol of NBS (N-bromosuccinimide), and 20 mmol of azobisisobutyronitrile were added to a flask, and 100 mL of dichloromethane was added to dissolve them. The reaction mixture was then heated to 60°C and stirred overnight. After the reaction was complete, the reaction mixture was washed with water, then extracted with dichloromethane, and the organic solvent was removed by rotary evaporation. The crude product of compound 5 was used directly in the next step of the reaction.

[0063] Step 5: 2 mmol of compound 5 and 4 mmol of m-chloroperoxybenzoic acid (m-CPBA) were placed in a Shrek tube and purged with nitrogen three times. Then, 20 mL of dichloromethane and 8 mmol of trifluoromethanesulfonic acid were added. After the reaction was complete, sodium bicarbonate was added to remove the acidic species, followed by extraction with dichloromethane. The organic solvent was removed by rotary evaporation, and the resulting solid was washed with n-hexane to give compound 6.

[0064] Step 6: Dissolve 2 mmol of glycidyl ether in 5 mL of tetrahydrofuran, then add 2 mmol of compound 6. After the addition is complete, reflux in an oil bath at 80 °C. After the reaction is complete, quench the reaction solution with water, extract with dichloromethane, and remove the organic solvent by rotary evaporation. Recrystallize the crude product of compound 7 to obtain compound 7. The 1H NMR spectrum of compound 7 is detailed in [link to NMR spectrum]. Figure 2 . 1 H NMR (CDCl3, 400 MHz): δ 7.59 (dd, J = 7.3,1.1 Hz, 2 H),7.52(s, 2H),7.39 (d, J = 7.5 Hz,2H), 4.75-4.64 (m, 4H), 3.73-3.65 (m, 4H),3.48 (dd, J = 11.2, 3.2 Hz, 2H), 3.42 (dd, J = 7.7, 3.1 Hz, 2H), 3.35 (d, J =3.1 Hz, 2H).

[0065] Step 7: Dissolve 1 mmol of compound 7 in 5 mL of acetonitrile, then add 1.1 mmol of potassium hexafluoroantimonate, resulting in the precipitation of a large amount of precipitate. Filter the reaction solution and wash with n-hexane to obtain the intramolecular halogen-bonded photoinitiator XB-1. The 1H NMR spectrum of XB-1 is detailed in [link to NMR spectrum]. Figure 3 . 1 H NMR (CDCl3, 400 MHz): δ 7.90 (dd, J = 7.1, 1.4 Hz, 2H), 7.53-7.43 (m, 4H), 4.75-4.64 (m, 4H), 3.73-3.65 (m, 4H), 3.48 (dd, J =11.3, 3.1 Hz, 2H), 3.42 (dd, J = 7.7, 3.1 Hz, 2H), 3.35 (d, J = 3.2 Hz, 2H).

[0066] Synthesis of XB-2 The synthetic route for XB-2 is as follows: .

[0067] The synthesis method of XB-2 follows the same steps as XB-1. The difference is that glycidyl ether in step 6 is replaced with ethyleneoxymethanol. The 1H NMR spectrum of the prepared intramolecular halogen bond-based photoinitiator XB-2 is detailed in [link to NMR spectrum]. Figure 4 . 1HNMR (CDCl3, 400 MHz): δ 7.90 (dd, J = 7.3, 1.1 Hz, 2H), 7.55 (t, J = 7.4 Hz,2H), 7.47-7.41 (m, 2H), 6.70 (ddt, J = 15.1, 9.8, 0.9 Hz, 2H), 4.78 (dd, J =3.9, 0.9 Hz, 8H), 4.21 (dd, J = 15.1, 2.7 Hz, 2H), 4.14 (dd, J = 9.8, 2.7 Hz, 2H).

[0068] XB-3 Synthesis The synthetic route for XB-3 is as follows: .

[0069] The synthesis method of XB-3 follows the same steps as XB-1. The difference lies in replacing the glycidyl ether in step 6 with 2-epoxypropanemethanethiol. The 1H NMR spectrum of the prepared intramolecular halogen-bonded photoinitiator XB-3 is detailed below. Figure 5 . 1 H NMR (CDCl3, 400 MHz): δ 7.88 (dd, J = 7.3, 1.1 Hz, 2H), 7.58 (t, J =7.2 Hz, 2H), 7.39-7.33 (m, 2H), 3.75-3.65 (m, 6H), 3.46 (dd, J = 7.7, 2.4 Hz, 2H), 3.26 (tt, J = 3.4, 2.3 Hz, 2H), 3.03 (dd, J = 13.3, 3.4 Hz, 2H), 2.81 (dd, J = 13.4, 3.3 Hz, 2H).

[0070] XB-4 Synthesis The synthesis route for XB-4 is as follows: .

[0071] The synthesis method of XB-4 follows the same steps as XB-1. The difference lies in replacing 2,5-dibromothiophene in step 2 with 2,5-dibromofuran. The 1H NMR spectrum of the prepared intramolecular halogen-bonded photoinitiator XB-4 is detailed below. Figure 6 . 1H NMR (CDCl3, 400 MHz): δ 8.20 (dd, J = 9.0, 1.3 Hz, 2H), 7.57 (dd, J =8.9, 7.6 Hz, 2H), 7.50 (dq, J = 7.5, 1.1 Hz, 2H), 4.74-4.63 (m, 4H), 3.73-3.65 (m, 4H), 3.48 (dd, J = 11.3, 3.1 Hz, 2H), 3.42 (dd, J = 7.7, 3.1 Hz, 2H), 3.35 (p, J = 3.2 Hz, 2H).

[0072] XB-5 Synthesis The synthesis route for XB-5 is as follows: .

[0073] The synthesis method of XB-5 follows the same steps as XB-1. The difference lies in replacing 2,5-dibromothiophene in step 2 with 2,5-dibromofuran, and replacing glycidyl ether in step 6 with 2-epoxypropanemethanethiol. The 1H NMR spectrum of the prepared intramolecular halogen-bonded photoinitiator XB-5 is detailed in [link to NMR spectrum]. Figure 7 . 1 H NMR (CDCl3, 400 MHz): δ 8.19(dd, J = 8.9, 1.1 Hz, 2H), 7.53 (dd, J = 9.0, 7.0 Hz, 2H), 7.43-7.38 (m, 2H), 3.75-3.64 (m, 6H), 3.46 (dd, J = 7.7, 2.4 Hz, 2H), 3.26 (tt, J = 3.4, 2.3 Hz, 2H), 3.03 (dd, J = 13.3, 3.4 Hz, 2H), 2.81 (dd, J = 13.4, 3.3 Hz, 2H).

[0074] XB-6 Synthesis The synthesis route for XB-6 is as follows: .

[0075] The synthesis method of XB-6 follows the same steps as XB-1. The difference lies in replacing 2,5-dibromothiophene in step 2 with N-methyl-2,5-dibromopyrrole. The 1H NMR spectrum of the prepared intramolecular halogen bond-based photoinitiator XB-6 is detailed below. Figure 8 . 1H NMR (CDCl3, 400 MHz): δ 7.87 (dd, J = 6.9, 1.1 Hz, 2H), 7.58-7.52(m, 2H), 7.46-7.41 (m, 2H), 4.75-4.64 (m, 4H), 3.85 (s, 2H), 3.73-3.65 (m,4H), 3.48 (dd, J = 11.3, 3.1 Hz, 2H), 3.42 (dd, J = 7.7, 3.1 Hz, 2H), 3.35 (p, J = 3.2 Hz, 2H).

[0076] XB-7 synthesis The synthesis route for XB-7 is as follows: .

[0077] The synthesis method of XB-7 follows the same steps as XB-1. The difference lies in replacing 2,5-dibromothiophene in step 2 with 2,5-dibromoselenophene. The 1H NMR spectrum of the prepared intramolecular halogen bond-based photoinitiator XB-7 is detailed in [link to details]. Figure 9 . 1 H NMR (CDCl3, 400 MHz): δ 7.67 (t, J = 7.6 Hz, 2H), 7.39-7.33 (m, 2H), 7.20 (dd, J = 7.6, 1.1 Hz, 2H), 4.82-4.71 (m, 4H), 3.73-3.65 (m, 4H), 3.48 (dd, J = 11.3, 3.1 Hz, 2H), 3.42 (dd, J = 7.7, 3.1 Hz, 2H), 3.35 (p, J = 3.2 Hz, 2H).

[0078] Synthesis of nonXB-1 The synthetic route for nonXB-1 is as follows: .

[0079] The nonXB-1 was synthesized according to the method reported in the literature (Angew Chem. Int. Ed. 2015, 54, 8736-8739.10.1002 / anie.201503134).

[0080] Synthesis of nonXB-2 The synthetic route for nonXB-2 is as follows: .

[0081] The nonXB-2 was synthesized according to the method reported in the literature (Angew Chem. Int. Ed. 2015, 54, 8736-8739.10.1002 / anie.201503134).

[0082] Example Adhesive compositions are prepared using XB-1, XB-2, XB-3, XB-4, XB-5, XB-6, or XB-7.

[0083] Example 1 Example 1 uses the compound XB-1 prepared in this invention as a photoinitiator to prepare an adhesive composition.

[0084] The preparation method is as follows: 0.2 parts of XB-1, 5 parts of bisphenol F epoxy resin (NPEF-170), 5 parts of 2021p epoxy resin, and 0.1 parts of silane coupling agent (A-187) are thoroughly mixed in a high-speed mixer to obtain an adhesive composition.

[0085] Example 2 Example 2 uses XB-2 to prepare an adhesive composition. The preparation method is the same as in Example 1, except that 0.2 parts of XB-2 were used as the photoinitiator.

[0086] Example 3 Example 3 uses XB-3 to prepare an adhesive composition. The preparation method is the same as in Example 1, except that 0.21 parts of XB-3 were used as the photoinitiator.

[0087] Example 4 Example 4 describes the preparation of an adhesive composition using XB-4. The preparation method is the same as in Example 1, except that 0.2 parts of XB-4 were used as the photoinitiator.

[0088] Example 5 Example 5 describes the preparation of an adhesive composition using XB-5. The preparation method is the same as in Example 1, except that 0.2 parts of XB-5 were used as the photoinitiator.

[0089] Example 6 Example 6 describes the preparation of an adhesive composition using XB-6. The preparation method is the same as in Example 1, except that 0.2 parts of XB-6 were used as the photoinitiator.

[0090] Example 7 Example 7 describes the preparation of an adhesive composition using XB-7. The preparation method is the same as in Example 1, except that 0.22 parts of XB-7 were used as the photoinitiator.

[0091] Example 8 Example 8 uses XB-1 to prepare an adhesive composition. The preparation method is the same as in Example 1, except that 10 parts of 2021p epoxy resin are used, bisphenol F epoxy resin is not used, and 0.4 parts of XB-1 are used.

[0092] Example 9 Example 9 uses XB-1 to prepare an adhesive composition. The preparation method is the same as in Example 1, except that the epoxy resin used is 5 parts of bisphenol A epoxy resin (NPEF-128) and 5 parts of bisphenol F epoxy resin (NPEF-170), and 0.1 parts of XB-1 is used.

[0093] Comparative examples were prepared using nonXB-1 or nonXB-2 to prepare adhesive compositions.

[0094] Comparative Example 1 Comparative Example 1 used nonXB-1 to prepare an adhesive composition. The preparation method was the same as in Example 1, except that 0.14 parts of nonXB-1 were used.

[0095] Comparative Example 2 Comparative Example 2 used nonXB-2 to prepare an adhesive composition. The preparation method was the same as in Example 1, except that 0.14 parts of nonXB-2 were used.

[0096] Test case Test Example 1: Evaluation of the acid-producing performance of photoinitiators.

[0097] The acid-producing performance of the synthesized photoinitiator was evaluated as follows: Using Rhodamine B as a pH indicator, the pH of the photoinitiator prepared in the synthesis example was recorded under light irradiation (365 nm, 3000 mJ / cm). 2 After completion, the color change time of the indicator was measured. The test results are shown in Table 1 (test concentration was 10). -5 M).

[0098] Table 1. Color change time of indicator after photoinitiator exposure.

[0099] As shown in Table 1, the color change time of the indicators prepared by the intramolecular halogen bond-based photoinitiators XB-1, XB-2, XB-3, XB-4, XB-5, XB-6, or XB-7 after light irradiation is all above 6 minutes. Compared with the photoinitiators nonXB-1 or nonXB-2 that do not form intramolecular halogen bonds, the photoinitiators based on intramolecular halogen bonds exhibit a significant delayed photolysis effect.

[0100] Test Example 2: Performance evaluation of adhesive compositions.

[0101] The adhesive compositions prepared in Examples 1-9 and Comparative Examples 1-2 were evaluated in the following aspects: 1. Delay window: A 0.5 mm thick adhesive layer was prepared using a coating machine and placed under 365 nm ultraviolet light (light intensity: 600 mW / cm²). 2 Irradiate for 10 seconds. Gently pick at the adhesive layer with a toothpick every 1 minute. The time when the adhesive layer begins to string is defined as the delayed curing window (unit: min).

[0102] 2. Time required for shear strength to reach 0.1 MPa: Samples were prepared using the chip shearing method, with glass substrates bonded together, the bonding area being 3 mm × 3 mm. The cured adhesive was tested every 2 minutes using a Dage chip pusher, and the time required for the strength value to first equal or exceed 0.1 MPa (in minutes) and the actual shear strength value measured at that time (in MPa) were recorded.

[0103] 3. Final shear strength: Record the shear strength (unit: MPa) after 24 h.

[0104] The performance test results of the adhesive compositions prepared in Examples 1-9 and Comparative Examples 1-2 are detailed in Table 2.

[0105] Table 2. Performance test results of the adhesive compositions prepared in Examples 1-9 and Comparative Examples 1-2

[0106] Table 2 shows that, compared with Comparative Examples 1 and 2, Examples 1-9 all exhibit a significant delay window, demonstrating that the adhesive containing the photoinitiator based on intramolecular halogen bonds of this invention has a significant delayed curing performance. Examples 1-3 show that as the electron cloud density of the atoms forming halogen bonds with iodine ions increases (e.g., replacing oxygen atoms with sulfur atoms), the delay window is significantly prolonged. Examples 1, 4, 6, and 7 show that the delay time changes successively with the changes in heterocycles on the molecular central skeleton. The pattern of change is consistent with the ability of these heterocycles to undergo electrophilic substitution reactions. It is well known that the electrophilic substitution order on pyrrole, thiophene, furan, and selenophene rings is: pyrrole > furan > thiophene > selenophene. The pyrrole ring is the most electron-rich, which makes the positive charge center of the iodine salt directly connected to it less electron-deficient, resulting in the weakest halogen bond; while selenophene is the least electron-rich, thus forming the strongest halogen bond. From the above two points, it can be seen that the delay window can be controlled by adjusting the electron-rich atoms (groups) and the types of aromatic heterocycles in the skeleton. The examples used highly reactive alicyclic epoxy resins, which, even with photoinitiators, were still able to achieve delayed curing. In contrast, the photoinitiators used in Comparative Examples 1 and 2 lacked intramolecular halogen bonds and exhibited no delaying effect, demonstrating the crucial role of halogen bonds in determining the delaying ability of photoinitiators.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any modifications, substitutions, improvements, etc., made within the spirit and principles of the present invention shall be protected by the present invention.

Claims

1. A photoinitiator based on intramolecular halogen bonds, with the following structural formula: ， in, R1 is selected independently from , or ; X is selected from CH2, O, S, Se, NH or NH with substituents; Each Y is independently selected from O, S, Se, NH or NH substituted with a substituent; Z - It is a monovalent anion; R2, R3, and R4 are independently chemically suitable substituents for attachment to the structure described above.

2. The photoinitiator based on intramolecular halogen bonds as described in claim 1, wherein, The monovalent anion is selected from BF4. - PF6 - SbF6 - B(Ar)4 - ,Br - I - Cl - CN - TsO - TfO - or MsO - ; and / or R2, R3, and R4 are independently selected from hydrogen, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, carbonyl, carboxyl, aromatic cycloalkyl, ester, amide, hydroxyl, carboxylate, and polymer chain groups.

3. A method for preparing the photoinitiator based on intramolecular halogen bonds as described in claim 1 or 2, comprising: S1: Reaction of 2-phenylboronic acid pinacol ester-6-methyl-aniline or its derivative with 2,5-dihalo-five-membered aromatic heterocycle under alkaline conditions yields intermediate 1, in which the 2- and 5-positions of the five-membered aromatic heterocycle are substituted with 2-amino-3-methylphenyl or a 2-amino-3-methylphenyl derivative, wherein the five-membered aromatic heterocycle is selected from thiophene, furan, selenophenol, pyrrole or a pyrrole derivative; S2: The intermediate 1 is subjected to diazotization and then reacted with an inorganic iodide salt to obtain intermediate 2 in which the 2-amino group of intermediate 1 is iodine-substituted. S3: The intermediate 2 is reacted with a brominating agent to obtain intermediate 3 in which the hydrogen on the 3-methyl group in the intermediate 2 is brominated; S4: Intermediate 3 is reacted with trifluoromethanesulfonic acid under oxidizing conditions to undergo intramolecular electrophilic cyclic closure to obtain intermediate 4; S5: Combine the intermediate 4 with R1-(CH2) n The -YH reaction yields the bromine in intermediate 4 via R1-(CH2) reaction. n -Y-substituted intermediate 5; R1 is selected from , or Y is selected from O, S, Se, NH or NH with substituents, and n is an integer greater than or equal to 1; S6: Combine the intermediate 5 with Z - The metal salt undergoes an ion exchange reaction to obtain the photoinitiator based on intramolecular halogen bonds, wherein Z - Selected from BF4 - PF6 - SbF6 - B(Ar)4 - ,Br - I - Cl - CN - TsO - TfO - or MsO - .

4. The method of claim 3, wherein 2-phenylboronic acid pinacol ester-6-methyl-aniline or a derivative thereof is prepared by 2-bromo-6-methylaniline or a derivative thereof via a Suzuki-Miyaura reaction, wherein the Suzuki-Miyaura reaction is carried out under an inert atmosphere.

5. An adhesive composition, comprising, by weight parts: 0.01 - 1 part of the intramolecular halogen bond-based photoinitiator according to claim 1 or 2, or the intramolecular halogen bond-based photoinitiator prepared by the method according to claim 3 or 4; 1-10 parts epoxy resin; 0.01 - 1 part silane coupling agent.

6. The adhesive composition of claim 5, wherein: The epoxy resin is selected from one or more of the following groups: bisphenol A type glycidyl ether epoxy resin, bisphenol F type glycidyl ether epoxy resin, a mixture of bisphenol A type and bisphenol F type glycidyl ether epoxy resins, rubber toughening type glycidyl ether epoxy resin, aliphatic epoxy resin and / or alicyclic epoxy resin; and / or The silane coupling agent is selected from one or more of the group consisting of 3-glycidoxypropyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, (3-epoxypropylpropoxy)trimethoxysilane, (3-epoxypropylpropoxy)triethoxysilane and / or 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

7. An application of the adhesive composition of claim 5 or 6 for bonding substrates.

8. The application of claim 7, wherein the substrate is a low ultraviolet light transmittance substrate.

9. The application as described in claim 7 or 8, comprising: (1) The adhesive composition is irradiated with ultraviolet light and initiated, and the adhesive composition enters a delayed curing window; (2) During the window period, the adhesive composition is bonded to the substrate.

10. The application of claim 9, wherein the adhesive composition has an application thickness of 0.2-1 mm, the ultraviolet light wavelength is 200-500 nm, and the curing energy is 200-100000 mJ / cm². 2 .

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