Two-photon polymerization initiator as well as preparation method and application thereof

Abstract

The invention provides a two-photon polymerization initiator as well as a preparation method and application thereof. The two-photon polymerization initiator has a structure as shown in a formula 1. The two-photon polymerization initiator provided by the invention can initiate two-photon polymerization of a photocuring material, has the function of a fluorescent probe, and has significantly enhanced fluorescence emission intensity after the photocuring material is cured, so that a strong fluorescence contrast is formed in a polymerized region and an unpolymerized region; in-situ and on-line monitoring of shapes such as boundary dimensions and internal defects of polymerization products can be realized, processing parameters can be adjusted in time, and the yield and the processing efficiency of micro-nano devices are improved.

Description

Technical Field

[0001] The present invention relates to the field of two-photon polymerization, and in particular to a two-photon polymerization initiator, a preparation method thereof, and an application thereof. Background Art

[0002] Two-photon polymerization (TPP) is a technique based on the fundamental principles of two-photon absorption and photopolymerization. It uses ultrashort laser pulses to expose a photosensitizer or photoinitiator with two-photon absorption properties to initiate the photopolymerization of resins or monomers. Because TPP reactions are typically confined to the focal point of a tightly focused laser beam, laser direct writing allows for the controlled fabrication of micro- and nanoscale structures. This technology holds broad application prospects in micro- and nanodevice fabrication, high-density optical storage, and biomedicine.

[0003] However, in the related art, during the process of preparing micro-nano devices through two-photon polymerization, it is difficult to monitor the external dimensions and internal defects of the micro-nano devices in situ and online, resulting in the inability to adjust the processing parameters in a timely manner, resulting in low yield and preparation efficiency of the micro-nano devices. Summary of the Invention

[0004] The present invention provides a two-photon polymerization initiator, a preparation method thereof, and an application thereof. The two-photon polymerization initiator can initiate two-photon polymerization of a photocurable material and simultaneously functions as a fluorescent probe. During the two-photon polymerization process, the initiator can realize in-situ and online monitoring of the external dimensions and internal defects of the polymerization product, thereby facilitating timely adjustment of processing parameters, improving the yield and preparation efficiency of micro-nano devices, and effectively overcoming the defects of the existing technology.

[0005] In one aspect of the present invention, a two-photon polymerization initiator is provided, which has a structure as shown in Formula 1 below:

[0006]

[0007] Wherein, D1 and D2 are each independently selected from the following groups:

[0008]

[0009] A is selected from the following groups A1 to A9:

[0010]

[0011] R1 is selected from R2, R4, and R5 are each independently selected from

[0012] R3 is selected from

[0013] x represents a halogen;

[0014] Alk represents a substituted or unsubstituted alkyl group.

[0015] According to one embodiment of the present invention, D1 is the same as or different from D2; and / or x is selected from F, Cl, Br or I; and / or Alk is selected from C1-C20 alkyl or aromatic ring-containing alkyl.

[0016] Another aspect of the present invention provides a method for preparing the above-mentioned two-photon polymerization initiator, comprising the following steps: reacting compound A0 and compound D0 to obtain the two-photon polymerization initiator;

[0017] The compound A0 is selected from the following compound A 01 ~A 09 One or more of:

[0018]

[0019] The compound D0 is selected from one or more of the following compounds:

[0020]

[0021] Z represents a group that connects the aromatic rings in A0 and D0 together to form the compound represented by Formula 1 through the reaction of A0 and D0.

[0022] According to one embodiment of the present invention, z is selected from A0 is selected from A 01 、A 02 、A 03 、A 04 or A 05 .

[0023] Another aspect of the present invention provides a use of the above-mentioned two-photon polymerization initiator in free radical polymerization or cationic polymerization.

[0024] Another aspect of the present invention provides a photocurable material comprising a photoinitiator and a polymerizable component, wherein the photoinitiator comprises the above-mentioned two-photon polymerization initiator.

[0025] According to one embodiment of the present invention, the mass ratio of the two-photon polymerization initiator to the polymerizable component is 0.01% to 10%.

[0026] According to one embodiment of the present invention, the polymerizable component includes one or more of acrylates, thiol-olefins, styrenes, epoxies, vinyl ethers, lactones, acetals and cyclic ethers.

[0027] According to one embodiment of the present invention, the polymerizable component is a raw material capable of undergoing free radical polymerization, and the photoinitiator is the two-photon polymerization initiator according to claim 1 or 2.

[0028] According to one embodiment of the present invention, the polymerizable component includes raw materials for cationic polymerization, the photoinitiator further includes a cationic co-initiator, and the cationic co-initiator includes one or more of onium salts, metal organics and organosilanes.

[0029] According to one embodiment of the present invention, the mass ratio of the cationic co-initiator to the polymerizable component is 0.01% to 10%.

[0030] Another aspect of the present invention provides a method for curing the above-mentioned photocurable material, comprising the following steps: (1) scanning a preset area of the photocurable material using a first femtosecond laser to cure the preset area to form a cured product; and (2) scanning the cured product under a second femtosecond laser to obtain fluorescence information of the cured product, and determining the morphology of the cured product based on the fluorescence information.

[0031] According to one embodiment of the present invention, the power of the second femtosecond laser is less than the power of the first femtosecond laser; and / or the power of the second femtosecond laser is less than the polymerization threshold of the photocurable material.

[0032] According to one embodiment of the present invention, the first femtosecond laser and the second femtosecond laser are applied by the same laser light source.

[0033] According to one embodiment of the present invention, the method further includes: (3) regulating the curing conditions of step (1) according to the morphology of the cured product, and repeating steps (1) and (2) using the regulated curing conditions; (4) performing steps (1) to (3) once, or repeating steps (1) to (3) multiple times, to determine suitable curing conditions for the photocurable material; and (5) curing the photocurable material under the suitable curing conditions to obtain a microstructured product.

[0034] Another aspect of the present invention provides a microstructure product, which is prepared according to the above curing method.

[0035] The two-photon polymerization initiator provided by the present invention has a structure shown in Formula 1. It is a two-photon polymerization initiator that also functions as a fluorescent probe. It can efficiently initiate two-photon polymerization of photocurable materials and emit fluorescence before and after polymerization. The fluorescence emission intensity of the polymerized area is significantly enhanced, forming a high contrast with the unpolymerized area. Therefore, based on the fluorescence information of the photoinitiator, in-situ and online monitoring of the curing degree of the photocurable material during the two-photon polymerization process, the external dimensions and internal defects of the microstructure (polymerization product), and other morphologies can be achieved, thereby facilitating timely adjustment of processing parameters and improving the production yield and production efficiency of micro-nano devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The scanning electron microscope (SEM) images of the scribed lines processed by the photocurable material in Example 2 at different laser powers are shown;

[0037] Figure 2 Graph showing the fluorescence emission spectra of the two-photon polymerization initiator T1 in Example 3 in monomers with different viscosities (the ordinate is fluorescence intensity, and the abscissa is wavelength);

[0038] Figure 3 The two-photon excitation fluorescence spectra of the photocurable material in Example 4 at different curing times;

[0039] Figure 4 Graphs showing the fluorescence emission spectra of the photocurable material in Example 5 before and after polymerization;

[0040] Figure 5 Graphs showing the fluorescence emission spectra of the photocurable material in Comparative Example 1 before and after polymerization;

[0041] Figure 6 Graphs showing the fluorescence emission spectra of the photocurable material in Comparative Example 2 before and after polymerization. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0043] In the processing of micro-nano devices (two-photon polymerization micromachining), in-situ, online monitoring of the polymerization degree of photocurable materials, the dimensions of the micro-nano structures, and internal defects in the micro-nano structures is crucial for timely adjustment of processing parameters to ensure the yield rate of the processed micro-nano devices (microstructures). However, in related technologies, it is difficult to monitor the dimensions and internal defects of micro-nano devices in-situ, online, resulting in the inability to adjust processing parameters in a timely manner, resulting in low yield rate and low production efficiency (processing efficiency) of micro-nano devices.

[0044] According to the inventors' long-term research, photoinitiators are an important component of the polymerization system. Although their usage is relatively small (generally not exceeding 5% of the photocurable material system), they determine the rate and degree of photopolymerization and are also an important factor affecting the performance of the polymerized products. Therefore, using photoinitiators as a fluorescent probe to characterize the progress of photopolymerization reactions and the morphology of micro-nano structures, such as external dimensions and internal defects, so as to timely regulate processing parameters and improve the yield and processing efficiency of micro-nano devices, is a feasible direction.

[0045] However, existing two-photon polymerization initiators generally have problems such as low fluorescence quantum yield and severe photobleaching effect during the photopolymerization process, making it difficult to use them as fluorescent probes to achieve in-situ and online monitoring of the two-photon polymerization process of photocurable materials.

[0046] Specifically, during the two-photon polymerization process, a liquid photocurable material is typically first dripped onto a substrate (such as a glass slide or a mold containing a glass substrate). A femtosecond laser is then used to scan a predetermined area to cause polymerization or cross-linking (curing) in the predetermined area, thereby producing a microstructure (i.e., a solid-state polymerized product, or cured product) of a predetermined shape and size. The size of the microstructure is much smaller than the size (droplet size) of the liquid photocurable material dripped onto the substrate. Therefore, after the two-photon polymerization process is completed, the substrate comprises two types of materials: a solid-state polymerized product (polymerized area) and a liquid photocurable material (unpolymerized area). The morphology of the unpolymerized area is substantially identical to that of the photocurable material prior to polymerization, and its fluorescence information is also substantially identical to that of the photocurable material prior to polymerization.

[0047] However, existing two-photon polymerization initiators generally have the following problems: (1) The fluorescence emission intensity of the two-photon polymerization initiator remains basically unchanged after the polymerization of the photocurable material and before the polymerization, resulting in no difference in the fluorescence intensity between the polymerization area and the uncollected area. Therefore, the two-photon polymerization initiator cannot be used as a fluorescent probe to monitor the progress of the two-photon polymerization reaction and the shape, size and internal defects of the microstructure in situ and online; (2) The fluorescence intensity of the two-photon polymerization initiator decreases after the photocurable material is polymerized (this phenomenon currently exists in most two-photon polymerization initiators, such as the common diphenylethylene photoinitiators, coumarin ketone photoinitiators and TPO (2,4,6-trimethylolpropane)). Initiators such as benzoyl-diphenylphosphine oxide not only have low fluorescence quantum yields but also suffer from a severe photobleaching effect during the photopolymerization process. During the two-photon polymerization of photocurable materials, the fluorescence intensity of these photoinitiators weakens as the polymerization reaction proceeds, and the fluorescence intensity after polymerization is significantly lower than that before polymerization. This makes the fluorescence intensity of the unpolymerized area stronger than that of the polymerized area, which significantly interferes with the fluorescence information of the polymerized area. It is difficult to distinguish the external dimensions and internal defects of the microstructure formed in the polymerized area, and thus it is difficult to monitor the polymerization degree, external dimensions, internal defects, and other morphologies of the polymerization product based on the fluorescence information of the photoinitiator.

[0048] In addition, according to further research by the inventors, for existing two-photon polymerization initiators such as diphenylethylene photoinitiators and coumarin ketone photoinitiators, in order to increase the fluorescence intensity of the polymerization area for easy observation, a higher-power femtosecond laser is required to increase the light intensity of the femtosecond laser. However, this not only consumes a lot of energy, but also easily causes the detection energy to be higher than the polymerization threshold of the photocurable material (the photocurable material will polymerize under laser power conditions higher than this threshold), causing the area scanned by the laser (including the unpolymerized area) to further cure, thereby affecting parameters such as the shape and size of the polymerization product, making it difficult to monitor the actual product morphology.

[0049] In addition, according to further research by the inventors, if a two-photon polymerization initiator is not used as a fluorescent indicator (fluorescent probe), but fluorescent dyes such as rhodamine B, rhodamine 6G, fluorescein and coumarin 152 are doped into the photocurable material for two-photon polymerization processing, in this case, in order to avoid interference of the unpolymerized area with the fluorescent information of the polymerized area, the photocurable material is usually required to be developed to remove the unpolymerized area (i.e., the unpolymerized material is washed away with an organic solvent), and then the polymerized area is characterized by layer-by-layer scanning using a fluorescence confocal microscope, and the morphology of the polymerized area (polymerization product) is monitored. Therefore, adding fluorescent dyes to photocurable materials cannot achieve in-situ, online monitoring of the external dimensions and internal defects of microstructures. At the same time, the addition of fluorescent dyes will affect the two-photon polymerization process. For example, the two-photon absorption cross-section of rhodamine B at 780nm (a commercial laser commonly used in the field of two-photon polymerization) is 95GM, which is much larger than the two-photon polymerization cross-section of most commercial two-photon polymerization initiators (such as TPO at 780nm. The two-photon absorption cross-section is less than 1GM). This makes the fluorescent dye greatly participate in the absorption of light, thereby affecting the efficiency of two-photon polymerization. Some fluorescent dyes can even quench free radicals and hinder the progress of two-photon polymerization.

[0050] In view of this, an embodiment of the present invention provides a two-photon polymerization initiator having a structure shown in Formula 1 below:

[0051]

[0052] Wherein, D1 and D2 are each independently selected from the following groups:

[0053]

[0054] A is selected from the following groups A1 to A9:

[0055]

[0056] R1 is selected from

[0057] R2, R4, and R5 are each independently selected from

[0058] R3 is selected from

[0059] x represents a halogen, and Alk represents a substituted or unsubstituted alkyl group.

[0060] In formula 1, relative to D1 and D2, A is a structure with a certain electron-withdrawing ability, such as a carbonyl group, a cyclic hydrocarbon ketone, a fluorenone, anthraquinone, etc. Correspondingly, relative to A, D1 and D2 are electron-rich aromatic rings or heteroatom-containing aromatic ring structures. According to the inventors' research, the compound having the structure shown in Formula 1 can efficiently initiate the two-photon polymerization reaction of the photocurable material, and at the same time has excellent fluorescence properties and viscosity-sensitive properties. It can emit fluorescence before and after the polymerization of the photocurable material, and as the curing reaction (polymerization reaction) proceeds, the viscosity of the photocurable material gradually increases, and the fluorescence emission intensity of the two-photon polymerization initiator increases accordingly. As a result, the fluorescence intensity of the photocurable material after polymerization is significantly enhanced compared to the photocurable material before polymerization, so that the fluorescence emission intensity of the polymerized area forms a high contrast with the unpolymerized area. Therefore, without the need for development treatment, the two-photon polymerization process and microstructure morphology can be monitored in situ and online through the changes in the two-photon excitation fluorescence properties of the two-photon polymerization initiator. Specifically, the curing degree (polymerization degree) of the photocurable material, the external dimensions and internal defects of the microstructure, and other morphologies can be monitored to facilitate timely adjustment of processing parameters and improve the preparation yield and processing efficiency of microstructure products.

[0061] Therefore, the two-photon polymerization initiator having the structure shown in Formula 1 is a two-photon polymerization initiator that also functions as a fluorescent probe. While efficiently initiating two-photon polymerization of photocurable materials, it also has excellent fluorescence properties and can be used as a fluorescent probe for in-situ and online monitoring of the progress of two-photon polymerization reactions, thereby guiding the adjustment of processing parameters and improving the preparation yield and processing efficiency of microstructured products.

[0062] In addition, since the fluorescence intensity of the polymerization area is significantly enhanced, when monitoring the fluorescence information, a laser power far lower than the polymerization threshold of the photocurable material can be used to scan the polymerization product after polymerization. This not only saves energy consumption, but also effectively avoids inducing polymerization of the photocurable material in the unpolymerized area, thereby avoiding the influence of the detection process on the shape and size of the microstructure of the polymerization product. It is conducive to more accurate monitoring of the morphology of the two-photon polymerization processing product (polymerization product), and then adjusting the two-photon polymerization processing parameters according to the monitoring results, thereby improving the preparation yield and processing efficiency of the microstructure products, as well as the performance of the obtained microstructure products.

[0063] Furthermore, the present invention eliminates the need to add fluorescent dyes to the photocurable material, thereby reducing their impact on two-photon polymerization efficiency. Furthermore, there's no need to detect the polymer's fluorescence after development. Compared to adding fluorescent dyes to the photocurable material, the present invention allows for in-situ, online monitoring of the polymer's morphology, while offering advantages such as high two-photon polymerization efficiency and a simple process.

[0064] In addition, the two-photon polymerization initiator according to the embodiment of the present invention has a wide range of applications, and can be applied not only to free radical polymerization but also to cationic polymerization.

[0065] Further research has shown that when A in Formula 1 is selected from A1, A2, A3, A4 or A5, Formula 1 has a double bond structure. At this time, the two-photon polymerization initiator with the structure shown in Formula 1 can absorb photon energy to initiate two-photon polymerization of the photocurable material. At the same time, the two-photon polymerization initiator with the structure shown in Formula 1 can also undergo cis-trans isomerization, specifically, it can be changed from EE configuration to EZ configuration and ZZ configuration. The fluorescence emission intensity of the molecules with EZ configuration and ZZ configuration is significantly higher than that of the molecules with EE configuration, and the molecules with EZ configuration and ZZ configuration also have higher structural stability and other properties. As a result, the fluorescence of the two-photon photopolymerization initiator is significantly enhanced after the photocurable material is polymerized, and it can be used as a fluorescent probe for in-situ and online monitoring of the progress of two-photon polymerization reactions.

[0066] In the embodiment of the present invention, D1 and D2 may be the same or different, R2 and R4 may be the same or different, R2 and R5 may be the same or different, and R4 and R5 may be the same.

[0067] In the embodiment of the present invention, the wavy line Indicates the connection site between groups. Taking A and D1 as an example, A and D1 are directly connected at the point where the wavy line is broken.

[0068] For example, A is A3, D1 and D2 are The structure of the compound represented by Formula 1 is as follows:

[0069]

[0070] Specifically, x may be selected from F, Cl, Br or I.

[0071] Specifically, Alk may be selected from a C1-C20 alkyl group (alkyl chain) or an aromatic ring-containing alkyl group (aromatic ring-containing alkyl chain).

[0072] Specifically, R1 can be selected from H, F, Cl, Br, I, C1-C20 alkyl, C1-C20 aromatic ring-containing alkyl,

[0073] Specifically, R2, R4, and R5 can be independently selected from H, a C1-C20 alkyl group, or an aromatic ring-containing alkyl group.

[0074] Specifically, R3 is selected from a C1-C20 alkyl group or an aromatic ring-containing alkyl group.

[0075] Specifically, the carbon number of the aromatic ring-containing alkyl group may be less than or equal to 20, for example, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20.

[0076] In the embodiment of the present invention, the number of carbon atoms in the C1-C20 alkyl group may be 1 (methyl), 2 (ethyl), 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20, and may specifically be a straight-chain alkyl group or an isomeric alkyl group with a branch.

[0077] Typically, the fluorescence emission wavelength range of the two-photon polymerization initiator is 400nm-1100nm. In specific implementations, when detecting fluorescence information of a material containing the two-photon polymerization initiator (such as the polymerized product described below), the fluorescence detection range can be set to 400nm-1100nm. Within this detection range, fluorescence information can be detected. Based on the monitored fluorescence information, the polymerization degree, external dimensions, and internal defects of the photocurable material can be determined, and processing parameters can be adjusted to improve the yield rate and processing efficiency of the microstructure preparation.

[0078] The embodiment of the present invention further provides a method for preparing the above-mentioned two-photon polymerization initiator, comprising the following steps: reacting compound A0 and compound D0 to obtain a two-photon polymerization initiator;

[0079] Compound A0 is selected from the following compound A 01 ~A 09 One of:

[0080]

[0081] Compound D0 is selected from one or more of the following compounds:

[0082]

[0083] Z represents a group that can connect the aromatic rings in A0 and D0 together to form the compound represented by Formula 1 through the reaction of A0 and D0.

[0084] In some embodiments, z can be selected from A0 is selected from A 01 、A 02 、A 03 、A 04 or A 05 In the prepared compound of formula 1, A is selected from A1 to A5.

[0085] Specifically, D0 can be selected from the following compounds D 01 ~D 04 One or more of:

[0086]

[0087] Illustratively, A0 is 4-alkylcyclohexanone (eg, 4-ethylcyclohexanone), and D0 is 5-x-2-furfural (eg, 5-bromo-2-furfural).

[0088] Generally, the reaction of compound A0 and compound D0 is carried out in a solvent. The solvent used includes an organic solvent, which may specifically include but is not limited to one or more of alcohol solvents, ketone solvents, furan solvents, nitrile solvents, amide solvents, etc.

[0089] In some preferred embodiments, the solvent may include ethanol, methanol, acetone, tetrahydrofuran, acetonitrile, N,N-dimethylformamide or N,N-dimethylacetamide.

[0090] During specific implementation, anhydrous ethanol can be used as the solvent.

[0091] In addition, the reaction of Compound A0 and Compound D0 can be carried out under alkaline conditions, and the base may include, but is not limited to, one or more of sodium hydroxide, potassium hydroxide, pyridine, triethylamine, piperidine, or tetrahydropyrrole. The base can act as a catalyst to improve the reaction efficiency.

[0092] Furthermore, the reaction temperature of Compound A0 and Compound D0 can be 0 to 200°C, for example, 0°C, 10°C, 20°C, 30°C, 50°C, 70°C, 90°C, 100°C, 130°C, 150°C, 180°C, 200°C, or any combination thereof. In practice, the reaction can be carried out at room temperature.

[0093] Furthermore, the reaction between the compound A0 and the compound D0 can be carried out under stirring.

[0094] In a specific implementation, compound A0, compound D0, a base, and a solvent can be mixed and then stirred for reaction (for example, at room temperature). During the reaction, the progress of the reaction can be monitored by thin layer chromatography (TLC). After the raw materials are substantially reacted (the reaction time can generally be 1 to 5 hours, for example, 4 hours), the reaction solution is mixed with water. Specifically, the reaction solution can be added to water to precipitate the product (two-photon polymerization initiator). The precipitated product is then collected by filtration or the like, washed with water, and then dried. Specifically, the precipitated product can be placed in a vacuum oven for vacuum drying at a drying temperature of 50 to 90° C., for example, 80° C., to obtain the two-photon polymerization initiator. The water used can include deionized water.

[0095] The embodiment of the present invention further provides an application of the above-mentioned two-photon polymerization initiator in free radical polymerization or cationic polymerization.

[0096] Specifically, the two-photon polymerization initiator of the embodiment of the present invention can be applied to free radical polymerization processes, such as free radical polymerization of polymerizable components such as acrylates, thiol-olefins, and styrenes, and can also be applied to cationic polymerization processes, such as cationic polymerization of polymerizable components such as epoxides, vinyl ethers, lactones, acetals, and cyclic ethers. That is, the two-photon polymerization initiator of the embodiment of the present invention can be used as a photoinitiator for polymerizable components capable of free radical polymerization reactions, and can also be used as a photoinitiator for polymerizable components capable of cationic polymerization. While efficiently initiating the two-photon polymerization reaction of these polymerizable components, it can also realize in-situ and online monitoring of the polymerization degree of the polymerization product, the external dimensions and internal defects of the microstructure, and other morphologies, so as to timely adjust the processing parameters and improve the preparation yield and processing efficiency of microstructure products (micro-nano devices).

[0097] Generally speaking, when the above-mentioned two-photon polymerization initiator is used as a free radical polymerization initiator, it can efficiently initiate free radical polymerization of polymerizable components such as acrylates, thiol-olefins, and styrenes without adding a co-initiator; when the above-mentioned two-photon polymerization initiator is used as a cationic polymerization initiator, it can be assisted by a cationic co-initiator, that is, the above-mentioned two-photon polymerization initiator and cationic co-initiator are compounded and used together to initiate cationic polymerization of polymerizable components such as epoxides, vinyl ethers, lactones, acetals, and cyclic ethers.

[0098] Specifically, the polymerizable component can be a conventional polymerizable material in the art, such as a resin and a monomer.

[0099] An embodiment of the present invention provides a photocurable material, comprising a photoinitiator and a polymerizable component, wherein the photoinitiator comprises the above-mentioned two-photon polymerization initiator. As mentioned above, by introducing the above-mentioned two-photon polymerization initiator into the photocurable material, the two-photon polymerization reaction of the photocurable material can be efficiently initiated, and at the same time, in-situ and online monitoring of the polymerization degree of the polymerization product, the external dimensions and internal defects of the microstructure, and other morphologies can be achieved, so as to facilitate timely regulation of processing parameters and improve the preparation yield and processing efficiency of microstructure products (micro-nano devices).

[0100] Generally, the mass ratio of the two-photon polymerization initiator to the polymerizable component can be 0.01% to 10%, for example, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of them, and generally preferably 0.1% to 5%. This is conducive to initiating the two-photon polymerization reaction of the photocurable material, and is convenient for in situ and online monitoring of the polymerization degree of the polymerization product, the external dimensions of the microstructure, and the internal defects based on the fluorescent emission function of the two-photon polymerization initiator.

[0101] In some embodiments, the above-mentioned polymerizable components may include one or more of acrylates, thiol-olefins, styrenes, epoxies, vinyl ethers, lactones, acetals and cyclic ethers. By introducing the above-mentioned two-photon polymerization initiator, the two-photon polymerization reaction of these polymerizable components can be efficiently initiated, thereby improving the efficiency of the polymerization reaction and realizing in-situ and online monitoring of the polymerization degree, external dimensions and internal defects of the polymerized products.

[0102] Specifically, the above-mentioned polymerizable components may include monomers and / or oligomers. For example, the monomers may include one or more of acrylate monomers, vinyl ether monomers, epoxy monomers, thiol-olefin monomers, styrene monomers, etc., and the oligomers may include one or more of epoxy oligomers, acrylic oligomers, styrene resins, cyclic ether resins, etc. Epoxy oligomers include, for example, epoxy resins and / or epoxy acrylates, and acrylic oligomers include, for example, one or more of polyether acrylates, polyester acrylates, polyurethane acrylates, etc.

[0103] For example, the acrylic monomer may include one or more of isobornyl acrylate, trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate, ethoxylated bisphenol A dimethacrylate, and the like.

[0104] Illustratively, the epoxy resin may include 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate (TTA21P).

[0105] In some embodiments, the polymerizable component is a raw material capable of free radical polymerization. In this case, the photoinitiator may be a two-photon polymerization initiator, which can efficiently initiate the free radical polymerization reaction of the photocurable material without adding other co-initiators.

[0106] Generally, the raw materials capable of free radical polymerization may include one or more of acrylates, thiol-olefins, and styrene resins, and specifically may include monomers and / or oligomers of these raw materials.

[0107] In other embodiments, the polymerizable component includes raw materials for cationic polymerization, and the photoinitiator may further include a cationic co-initiator, that is, the photoinitiator includes both a two-photon polymerization initiator and a cationic co-initiator, which can efficiently initiate the two-photon polymerization reaction of the photosensitive material and realize in-situ and online monitoring of the polymerization degree, microstructure dimensions, internal defects and other morphologies of the polymerization product.

[0108] Generally, the raw materials for cationic polymerization may include one or more of epoxies (such as epoxy resins and / or epoxy acrylates, etc.), vinyl ethers, lactones, acetals and cyclic ethers, and specifically may include monomers and / or oligomers of these raw materials.

[0109] Specifically, the cationic co-initiator includes one or more of onium salts, metal organics and organosilanes. For example, the onium salts may include triarylsulfonium salts and / or triaryliodonium salts.

[0110] Specifically, the mass ratio of the cationic co-initiator to the polymerizable component can be 0.01% to 10%, for example, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any two thereof, generally preferably 0.1% to 5%.

[0111] In addition, the above-mentioned photocurable material may further include auxiliary agents, which may specifically include one or more of color pastes, leveling agents, plasticizers, chain transfer agents, etc., wherein the auxiliary agents such as color pastes, leveling agents, plasticizers and chain transfer agents used can all be conventional materials in the field and are not particularly limited.

[0112] Specifically, the mass fraction of the auxiliary agent in the photocurable material can be 0-20%, for example, 0, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20% or any two thereof.

[0113] In some specific embodiments, the composition of the photocurable material is as follows: in parts by weight, the oligomer is 0-80 parts, the monomer is 0-95 parts, the photoinitiator is 0.01-10 parts, and the auxiliary agent is 0-20 parts.

[0114] An embodiment of the present invention further provides a method for curing the above-mentioned photocurable material (or a method for polymerizing the photocurable material or a method for preparing a microstructured product), comprising the following steps:

[0115] (1) scanning a predetermined area of the photocurable material with a first femtosecond laser to cure the predetermined area (i.e., two-photon polymerization) to form a cured product (polymerized product);

[0116] (2) Scanning the cured product under the second femtosecond laser to obtain fluorescence information of the cured product, and determining the morphology of the cured product based on the fluorescence information.

[0117] Specifically, the morphology of the cured product includes one or more of the shape, size, and internal defects of the cured product.

[0118] Generally, before curing, the photocurable material is in liquid state. In specific implementation, the photoinitiator and polymerizable components can be mixed in a brown glass container in a dark room with yellow light, and stirred evenly to obtain the photocurable material (liquid state).

[0119] Subsequently, in step (1), a liquid photocurable material can be dripped onto the substrate to form a droplet on the substrate, and then a first femtosecond laser is used to scan a predetermined area of the droplet layer by layer to cure the predetermined area. During the curing process, the polymerizable components in the photocurable material undergo two-photon polymerization under the action of a photoinitiator to form a three-dimensional (3D) micro-nanostructured cured product. The predetermined area of the droplet on the substrate can be subjected to two-photon polymerization processing (i.e., the photocurable material in the predetermined area is cured under the first femtosecond laser to obtain a cured product) by a femtosecond laser processing system. In the embodiment of the present invention, a conventional femtosecond laser processing system in the art can be used to perform two-photon polymerization processing (i.e., perform step (1)), and there is no particular limitation on this.

[0120] In step (1), after the curing is completed, the material on the substrate includes a polymerized area (in solid state) and an unpolymerized area (in liquid state). The polymerized area (i.e., the cured product) is the laser scanning area of the first femtosecond laser (i.e., the above-mentioned preset area); the unpolymerized area is other areas of the droplet, which is basically consistent with the morphology of the photocurable material before curing.

[0121] In the embodiment of the present invention, the substrate (substrate) can be a conventional substrate in the art such as a glass slide, and there is no particular limitation on this.

[0122] Specifically, in step (2), a second femtosecond laser can be used to perform multi-layer scanning on the cured product, and fluorescence information such as images and fluorescence spectra of different regions can be collected and integrated to determine the shape, size, and internal defects (such as missing structures of the cured product) of the cured product, thereby monitoring the polymerization process and adjusting the processing parameters according to the monitored information.

[0123] In the embodiment of the present invention, conventional methods in the art may be used to collect fluorescence information of the cured product. For example, a confocal microscope may be used to collect fluorescence information such as a two-photon excitation fluorescence spectrum of the photocured product.

[0124] In an embodiment of the present invention, a two-photon polymerization initiator having a structure shown in Formula 1 is used, and its fluorescence intensity is significantly enhanced after the polymerization of the photocurable material, so that the fluorescence intensity of the photocurable material after polymerization is significantly enhanced compared to before polymerization, thereby significantly enhancing the fluorescence emission intensity of the polymerized area (cured product), forming a high contrast with the unpolymerized area, thereby realizing in-situ and online monitoring of the external dimensions (shape, size) and internal defects of the polymerized product.

[0125] Generally speaking, the integral area of the fluorescence spectrum of the polymerized region (i.e., the integral area of the fluorescence spectrum after polymerization) S2 is at least 10% greater than the integral area of the fluorescence spectrum of the unpolymerized region (i.e., the integral area of the fluorescence spectrum before polymerization) S1. The polymerized region exhibits significantly enhanced fluorescence intensity than the unpolymerized region, and the two form a high contrast.

[0126] In specific implementation, when measuring the fluorescence spectrum integral area S2 of the polymerized area and the fluorescence spectrum integral area S1 of the unpolymerized area, the polymerized area and the unpolymerized area of the same area are selected (that is, the area of the selected polymerized area and the area of the selected unpolymerized area are the same), and then a femtosecond laser (second femtosecond laser) with the same laser power is used to scan the selected polymerized area and the selected unpolymerized area to obtain fluorescence spectrum graphs of the polymerized area and the unpolymerized area of the same area, and the fluorescence spectrum integral area S2 of the polymerized area is obtained based on the fluorescence spectrum graph of the polymerized area, and the fluorescence spectrum integral area S1 of the unpolymerized area is obtained based on the fluorescence spectrum graph of the unpolymerized area.

[0127] Generally, the power of the second femtosecond laser is less than that of the first femtosecond laser, which can further save energy while realizing in-situ and online monitoring of the morphology of the polymerization product.

[0128] Specifically, the power of the first femtosecond laser is usually greater than the polymerization threshold (curing threshold) of the photocurable material, so as to facilitate the rapid polymerization process of the photocurable material.

[0129] Specifically, the power of the second femtosecond laser is typically less than the polymerization threshold of the photocurable material. According to the inventors' research, the fluorescence intensity of the polymerized area is significantly stronger than that of the unpolymerized area, creating a high contrast ratio. Therefore, when scanning the polymerized product with a second femtosecond laser whose power is lower than the polymerization threshold of the photocurable material, fluorescence information of the polymerized product can be obtained, enabling online monitoring of information such as the product's dimensions and internal defects. Furthermore, using a lower-energy second femtosecond laser for monitoring can further save energy and prevent polymerization in the unpolymerized area due to excessive second femtosecond laser power, thereby preventing changes in the morphology of the polymerized product and improving monitoring accuracy.

[0130] The embodiments of the present invention can obtain the polymerization threshold of the photocurable material through conventional methods in the field. For example, femtosecond lasers of different powers can be used to scan the photocurable material and observe whether it can be cured, so as to obtain the polymerization threshold of the photocurable material. That is, when the power of the femtosecond laser reaches or exceeds the threshold, the photocurable material is cured. When the power of the femtosecond laser is less than the threshold, the photocurable material basically does not cure.

[0131] In some embodiments, the wavelength of the first femtosecond laser is 500-1100 nm, the power of the first femtosecond laser is 0.01-500 mW, and the scanning speed of the first femtosecond laser is 5-100000 μm / s, for example, 10 μm / s, but not limited thereto.

[0132] In some embodiments, the wavelength of the second femtosecond laser is 500-1100 nm, the power of the second femtosecond laser is 0.01-500 mW, and the scanning speed of the second femtosecond laser is 5-100000 μm / s, for example, 10 μm / s, but not limited thereto.

[0133] In addition, during the scanning of the polymerization product under the second femtosecond laser, the fluorescence detection range was 400-1100 nm.

[0134] Specifically, the first femtosecond laser and the second femtosecond laser can be provided by the same laser light source, that is, the polymerization process of step (1) and the monitoring process of step (2) can share a set of light sources, which can avoid the need for additional excitation light sources, thereby simplifying the process system.

[0135] In the embodiment of the present invention, a conventional femtosecond laser (laser light source) in the art may be used to provide the first femtosecond laser and the second femtosecond laser.

[0136] In a specific implementation, in step (1), a first femtosecond laser is applied by a laser light source to scan a preset polymerization area of the photocurable material to cure it to form a cured product. After the curing in step (1) is completed, the power of the laser light source is adjusted (i.e., the first femtosecond laser in step (1) is adjusted to the second femtosecond laser in step (2)), and the cured product is scanned layer by layer to obtain fluorescence information of the cured product, thereby characterizing the progress of the photopolymerization reaction (curing reaction) and the morphology of the cured product (micro-nano device), such as the external dimensions and internal defects.

[0137] Generally, the polymerization process of the above-mentioned photocurable material further includes: (3) regulating the curing conditions (polymerization conditions) of step (1) according to the morphology of the cured product, and repeating steps (1) and (2) using the regulated curing conditions; (4) performing steps (1) to (3) once, or repeating steps (1) to (3) multiple times, to determine the appropriate curing conditions for the photocurable material; (5) polymerizing the photocurable material under the appropriate curing conditions to obtain a microstructure product (micro-nano device).

[0138] In specific implementation, each time step (1) is performed, certain curing conditions can be preset, that is, the photocurable material is polymerized under the preset curing conditions to obtain a cured product; then, step (2) is used to monitor the external dimensions and internal defects of the cured product. If these morphologies do not meet the preset requirements, the above-mentioned curing conditions are adjusted to compensate for them according to these morphologies of the cured product, that is, step (1) is performed under the adjusted curing conditions. After step (1) is completed, step (2) is performed again, and so on, until the appropriate curing conditions of the photocurable material are determined, and then the microstructure product is produced under the appropriate curing conditions (that is, step (5) is performed. For example, the conditions such as the laser power and the scanning rate in step (1) can be adjusted to the appropriate curing conditions. The cured product obtained under the appropriate curing conditions is the microstructure product.

[0139] An embodiment of the present invention provides a microstructured product, which is manufactured by the above-mentioned method for curing the photocurable material (ie, manufactured by the above-mentioned photocurable material through a two-photon polymerization method).

[0140] Generally, the microstructure product is a 3D micro-nano structure with a size at the micro-nano level, which can be a conventional micro-nano device in this field.

[0141] The present invention is further described below by way of specific examples. In the following examples, unless otherwise specified, the laser light source used is a femtosecond laser of a confocal microscope (Nikon A1R-si) with a wavelength of 780 nm, a pulse width of 140 fs, and a repetition frequency of 80 MHz.

[0142] [Example 1] Preparation of two-photon polymerization initiator T1

[0143]

[0144] To a 100-mL round-bottom flask were added 1.00 g (7.92 mmol) of 4-ethylcyclohexanone, 2.78 g (15.89 mmol) of 5-bromo-2-furfural, 0.20 g (5.00 mmol) of NaOH, and 15 mL of anhydrous ethanol. The mixture was stirred at room temperature and the reaction progress was monitored by thin-layer chromatography (TLC). After approximately 4 h of reaction, the reaction solution was poured into approximately 500 mL of deionized water to precipitate the product. The precipitated product was collected by filtration and rinsed with deionized water. The washed precipitate was dried in a vacuum oven at 80°C to obtain 3.21 g of the title compound (yield 92.1%).

[0145] The target product was subjected to H NMR spectroscopy ( 1 H-NMR) and high-resolution mass spectrometry (HR-MS) analysis showed that it was the structure shown in T1. The specific analysis results are as follows:

[0146] (1) 1 H-NMR (400MHz, CDCl3): δ (ppm): 1.05 (m, 3H), 1.54 (m, 2H), 1.83 (m, 1H), 2.49–2.53 (m, 2H), 3.22–3.26(m,2H),6.47–6.48(d,J=3.48Hz,2H),6.63–6.64(d,J=3.48Hz,2H),7.46(s,2H). 13 C-NMR (100MHz, CDCl3): δ (ppm): 11.66, 28.66, 33.51, 34.23, 76.74, 114.23, 118.19, 122.53, 125.12, 132.65, 154.63, 188.62;

[0147] (2) HR-MS (EI): m / z [M] + Calcd.For (theoretical value)C 18 H 16 Br2O3 439.9446, Found (actual measured value) 439.9433.

[0148] [Example 2] Determination of polymerization threshold of photocurable materials

[0149] By weight, 2 parts of two-photon polymerization initiator T1 and 100 parts of TMPTA were mixed uniformly to obtain a photocurable material;

[0150] The two-photon polymerization processing platform tested the threshold of photocurable materials. The parameters of the first femtosecond laser were: wavelength 780nm, pulse width 80fs, repetition rate 82MHz; objective lens parameters were: magnification 100, numerical aperture 1.45; and laser scanning speed 10μm / s. During the test, the laser power was controlled to decrease (from 29.4mW to 4.3mW) to scan a predetermined area of the photocurable material (a scribed line approximately 20μm in length) under different laser power conditions. Figure 1 The scanning electron microscope images of the lines with a length of about 20 μm processed at various laser powers are shown in Figure 2. Figure 1 It can be seen that as the laser power decreases, the width of the processed scribed line gradually narrows. When the laser power is lower than 4.3mW, the photocurable material cannot process the scribed line (that is, the photocurable material basically does not cure (polymerize)). The laser power at this time (4.3mW) is the polymerization threshold of the photocurable material.

[0151] [Example 3] Testing the two-photon excitation spectrum (fluorescence spectrum) of the two-photon polymerization initiator T1 in monomers with different viscosities

[0152] The following Experimental Examples 1 to 4 were respectively carried out to test the two-photon excitation spectra of the two-photon polymerization initiator T1 in monomers with different viscosities.

[0153] 1. Experimental Example 1

[0154] 1 part by mass of two-photon polymerization initiator T1 was dissolved in 100 parts by mass of isobornyl acrylate (A, viscosity 9 cps), and the mixture was mixed to obtain a photocurable material.

[0155] The photocurable material was spread on a glass slide to form a droplet, and the two-photon excitation fluorescence spectrum (fluorescence emission spectrum) of the photocurable material was collected using a confocal microscope. The results are as follows: Figure 2 As shown; wherein, during the process of collecting the two-photon excitation fluorescence spectrum of the photocurable material, the power of the femtosecond laser is about 1 mW.

[0156] 2. Experimental Example 2: The difference from Experimental Example 1 is that trimethylolpropane triacrylate (B, viscosity 60 cps) is used instead of isobornyl acrylate (A, viscosity 9 cps). The other conditions are the same as those of Experimental Example 1. The two-photon excitation fluorescence spectrum of the photocurable material measured in Experimental Example 2 is as follows: Figure 2 shown.

[0157] 3. Experimental Example 3: The difference from Experimental Example 1 is that pentaerythritol tetraacrylate (C, viscosity 150 cps) is used instead of isobornyl acrylate (A, viscosity 9 cps). The other conditions are the same as those of Experimental Example 1. The two-photon excitation fluorescence spectrum of the photocurable material measured in Experimental Example 3 is as follows: Figure 2 shown.

[0158] 4. Experimental Example 4: The difference from Experimental Example 1 is that ethoxylated bisphenol A dimethacrylate (D, viscosity 440 cps) is used instead of isobornyl acrylate (A, viscosity 9 cps). The other conditions are the same as those of Experimental Example 1. The two-photon excitation fluorescence spectrum of the photocurable material measured in Experimental Example 4 is as follows: Figure 2 shown.

[0159] from Figure 2 It can be seen that with the increase of monomer viscosity, the two-photon excited fluorescence emission intensity of the photocurable material gradually increases, indicating that the two-photon polymerization initiator T1 has good viscosity-sensitive properties.

[0160] [Example 4] Application of two-photon polymerization initiator T1 in free radical polymerization

[0161] 2 parts by mass of a two-photon polymerization initiator T1 and 100 parts by mass of TMPTA were mixed to obtain a photocurable material.

[0162] (1) Spreading a light-curable material on a glass slide to form a droplet, providing a first femtosecond laser through a femtosecond laser, so that the light-curable material undergoes two-photon polymerization (i.e., curing) under the action of the first femtosecond laser, to obtain a polymerized product (after the polymerization is completed, the material on the glass slide includes a polymerized area (i.e., a solid polymerized product) and an unpolymerized area (in a liquid state); wherein the objective lens parameters are: 20 times, numerical aperture 0.75); the laser processing power (i.e., the power of the first femtosecond laser) is approximately 30 mW;

[0163] Wherein, referring to the process of step (1), different curing times (see Figure 3 0.5min, 1.0min, 2.0min, Figure 3 0 min in the figure represents the fluorescence emission spectrum of the unpolymerized photocurable material (unpolymerized area);

[0164] (2) The laser power of the femtosecond laser of the confocal microscope was adjusted to 3 mW, and the two-photon excitation fluorescence spectra of the photocurable material at different curing times were collected. When collecting the fluorescence emission spectra of the polymerized area and the unpolymerized area, the polymerized area and the unpolymerized area of the same area were selected. The measured fluorescence emission spectra of the polymerized area were as follows: Figure 3 shown.

[0165] from Figure 3It can be seen that two-photon excitation fluorescence can be monitored in the photocurable material before polymerization (0 min) and after polymerization (0.5 min, 1.0 min, 2.0 min), that is, the two-photon polymerization initiator T1 can emit fluorescence before and after the polymerization of the photocurable material. Moreover, with the increase of illumination time (photocuring time), the curing degree of the photocurable material improves, the viscosity of the system gradually increases, and the fluorescence emission intensity of the two-photon polymerization initiator T1 also gradually increases, indicating that the two-photon polymerization initiator T1 has good viscosity-sensitive properties.

[0166] Among them, the fluorescence emission intensity of the two-photon polymerization initiator T1 reached its maximum after 2 minutes of illumination, and its fluorescence emission intensity basically stopped increasing as the illumination time continued to increase, indicating that the photocurable material was basically cured. The fluorescence emission intensity of the photocurable material after complete curing was enhanced by about 2.4 times compared with that before polymerization (the integrated area of the fluorescence spectrum S2 after complete curing was approximately 413412 (i.e., S2 = 413412), and the integrated area of the fluorescence spectrum S1 before polymerization was approximately 174333 (i.e., S1 = 174333), and the fluorescence enhancement factor = S2 / S1). This resulted in a strong contrast between the polymerized and unpolymerized areas. Therefore, the changes in the two-photon excitation fluorescence characteristics of the two-photon polymerization initiator can be used to realize in situ and online monitoring of the two-photon polymerization process and microstructure morphology. Specifically, the curing degree (polymerization degree) of the photocurable material, the external dimensions and internal defects of the microstructure, and other morphologies can be monitored to facilitate timely adjustment of processing parameters and improve the preparation yield and processing efficiency of microstructure products.

[0167] [Example 5] Application of two-photon polymerization initiator T1 in cationic polymerization

[0168] 2 parts by mass of photoinitiator T1, 2 parts by mass of triarylsulfonium salt, and 100 parts by mass of epoxy resin TTA21P were mixed to obtain a photocurable material;

[0169] A photocurable material is spread flat on a glass slide to form a droplet. A femtosecond laser is used to provide a first femtosecond laser, causing the photocurable material in a predetermined area to undergo two-photon polymerization under the first femtosecond laser to obtain a polymerized product (after the polymerization is completed, the material on the glass slide includes a polymerized area (i.e., a solid polymerized product) and an unpolymerized area (in a liquid state)). The objective lens parameters are: 20x, numerical aperture 0.75; and the laser processing power (i.e., the power of the first femtosecond laser) is approximately 20 mW.

[0170] After the polymerization is completed, the femtosecond laser power of the femtosecond laser is adjusted to 3 mW, the material on the slide is scanned, and the fluorescence emission spectra of the polymerized area (polymerized product) and the unpolymerized area are collected using a confocal microscope in the spectral mode. When collecting the fluorescence emission spectra of the polymerized area and the unpolymerized area, the polymerized area and the unpolymerized area of the same area are selected, and the measured fluorescence emission spectrum of the polymerized area ( Figure 4 The fluorescence emission spectrum corresponding to the “after polymerization” in the figure) and the fluorescence emission spectrum of the unpolymerized area ( Figure 4 The fluorescence emission spectrum corresponding to “before polymerization” in Figure 4 shown.

[0171] from Figure 4 It can be seen that two-photon excited fluorescence can be monitored in the photocurable material before and after polymerization, that is, the two-photon polymerization initiator T1 can emit fluorescence before and after the polymerization of the photocurable material, and its fluorescence intensity is significantly enhanced after the polymerization of the photosensitive material, as shown in Figure 2. Figure 4 As shown, the integral area S2 of the fluorescence spectrum after polymerization is approximately 134104 (i.e., S2=134104), and the integral area S1 of the fluorescence spectrum before polymerization is approximately 18668 (i.e., S1=18668). It can be seen that the fluorescence intensity of the two-photon polymerization initiator T1 after the photosensitive material is polymerized is approximately 7.2 times the fluorescence intensity before the photosensitive material is polymerized.

[0172] [Comparative Example 1] Application of diphenylethylene photoinitiator T2 in two-photon polymerization

[0173]

[0174] The difference between Comparative Example 1 and Example 5 is that 0.02 parts of photoinitiator T2 are used to replace 2 parts of two-photon polymerization initiator T1 in Example 5, and the other conditions are the same as those in Example 5.

[0175] In this comparative example 1, the fluorescence emission spectrum of the polymerized region ( Figure 5 The fluorescence emission spectrum corresponding to the “after polymerization” in the figure) and the fluorescence emission spectrum of the unpolymerized area ( Figure 5 The fluorescence emission spectrum corresponding to “before polymerization” in Figure 5 As shown, from Figure 5 It can be seen that although two-photon excitation fluorescence can be monitored in the photocurable material before and after polymerization, the fluorescence intensity of the photocurable material (also the fluorescence intensity of the diphenylethylene photoinitiator T2) gradually decays as the polymerization reaction proceeds. Compared with the fluorescence intensity of the diphenylethylene photoinitiator T2 before the polymerization of the photocurable material, the fluorescence intensity of the diphenylethylene photoinitiator T2 after the polymerization of the photocurable material is significantly reduced. Figure 5As shown, the integral area S2 of the fluorescence spectrum after polymerization is about 15800 (i.e., S2=15800), and the integral area S1 of the fluorescence spectrum before polymerization is about 41586 (i.e., S1=41586). It can be seen that the fluorescence intensity of the distyrene photoinitiator T2 after the polymerization of the photocurable material is about 38% of its fluorescence intensity before the polymerization of the photocurable material, and its fluorescence intensity after the polymerization of the photocurable material is reduced by about 62%.

[0176] [Comparative Example 2] Application of coumarin ketone photoinitiator T3 in two-photon polymerization

[0177]

[0178] The difference between Comparative Example 2 and Example 5 is that 0.1 parts of coumarin ketone photoinitiator T3 are used to replace 2 parts of two-photon polymerization initiator T1 in Example 5, and the other conditions are the same as those in Example 5.

[0179] In this comparative example 2, the fluorescence emission spectrum of the polymerized region ( Figure 6 The fluorescence emission spectrum corresponding to the “after polymerization” in the figure) and the fluorescence emission spectrum of the unpolymerized area ( Figure 6 The fluorescence emission spectrum corresponding to “before polymerization” in Figure 6 As shown, from Figure 6 It can be seen that although two-photon excitation fluorescence can be monitored in the photocurable material before and after polymerization, the fluorescence intensity of the photocurable material (also the fluorescence intensity of the coumarin ketone photoinitiator T3) gradually decays as the polymerization reaction proceeds. Compared with the fluorescence intensity of the coumarin ketone photoinitiator T3 before the polymerization of the photocurable material, the fluorescence intensity of the coumarin ketone photoinitiator T3 after the polymerization of the photocurable material is significantly reduced. Figure 6 As shown, the integral area S2 of the fluorescence spectrum after polymerization is approximately 195053 (i.e., S1=195053), and the integral area S1 of the fluorescence spectrum before polymerization is approximately 261536 (i.e., S1=261536). It can be seen that the fluorescence intensity of the coumarin ketone photoinitiator T3 after the polymerization of the photocurable material is approximately 75% of its fluorescence intensity before the polymerization of the photocurable material, and its fluorescence intensity after the polymerization of the photocurable material is reduced by about 25%.

[0180] In summary, compared with conventional two-photon polymerization initiators such as diphenylethylene photoinitiators and coumarin ketone photoinitiators, the two-photon polymerization initiator of the embodiment of the present invention has good fluorescence properties and viscosity-sensitive properties. It can emit fluorescence before and after the polymerization of the photocurable material, and as the curing reaction (polymerization reaction) proceeds, the viscosity of the photocurable material gradually increases, and the fluorescence emission intensity of the two-photon polymerization initiator increases accordingly. Therefore, the fluorescence intensity of the photocurable material after polymerization is significantly enhanced compared with the photocurable material before polymerization, so that the fluorescence emission intensity of the polymerized area is significantly enhanced, forming a higher contrast with the unpolymerized area. Therefore, without the need for development treatment, the two-photon polymerization process and microstructure morphology can be monitored in situ and online through the two-photon excitation fluorescence of the two-photon polymerization initiator. Specifically, the curing degree (polymerization degree) of the photosensitive material, the external dimensions and internal defects of the microstructure, etc. can be monitored to facilitate timely adjustment of processing parameters and improve the preparation yield of microstructure products.

[0181] In addition, compared with conventional two-photon polymerization initiators such as diphenylethylene photoinitiators and coumarin ketone photoinitiators, the fluorescence intensity of the two-photon polymerization initiator of the embodiment of the present invention is significantly enhanced after the polymerization of the photocurable material, which is beneficial for monitoring the polymerization degree, external dimensions, internal defects and other morphologies of the polymerization product based on the fluorescence information of the photoinitiator, and realizing in-situ and online monitoring of the two-photon polymerization process and microstructure morphology.

[0182] In addition, the two-photon polymerization initiator according to the embodiment of the present invention has a wide range of applications, and can be applied not only to free radical polymerization but also to cationic polymerization.

Claims

1. A two-photon polymerization initiator, characterized in that It has the structure shown in Formula 1 below: Wherein, D1 and D2 are each independently selected from the following groups: A is selected from the following groups A1 to A9: R1 is selected from R2, R4, and R5 are each independently selected from R3 is selected from x represents a halogen; Alk represents a substituted or unsubstituted alkyl group.

2. The two-photon polymerization initiator according to claim 1, characterized in that The D1 is the same as or different from the D2; and / or, x is selected from F, Cl, Br or I; And / or, Alk is selected from C1-C20 alkyl groups or aromatic ring-containing alkyl groups.

3. A method for preparing the two-photon polymerization initiator according to claim 1 or 2, characterized in that: The following steps are involved: A method for preparing the two-photon polymerization initiator by reacting compound A0 and compound D0; The compound A0 is selected from the following compound A 01 ~A 09 One or more of: The compound D0 is selected from one or more of the following compounds: Z represents a group that connects the aromatic rings in A0 and D0 together to form the compound represented by Formula 1 through the reaction of A0 and D0.

4. The method for preparing a two-photon polymerization initiator according to claim 3, wherein: z is selected from A0 is selected from A 01 、A 02 、A 03 、A 04 or A 05 .

5. Use of the two-photon polymerization initiator according to claim 1 or 2 in free radical polymerization or cationic polymerization.

6. A light-curing material, characterized in that: The invention comprises a photoinitiator and a polymerizable component, wherein the photoinitiator comprises the two-photon polymerization initiator according to claim 1 or 2.

7. The light-curable material according to claim 6, characterized in that: The mass ratio of the two-photon polymerization initiator to the polymerizable component is 0.01% to 10%.

8. The light-curable material according to claim 6 or 7, characterized in that: The polymerizable components include one or more of acrylates, thiol-olefins, styrenes, epoxies, vinyl ethers, lactones, acetals, and cyclic ethers.

9. The light-curable material according to claim 6 or 7, characterized in that: The polymerizable component is a raw material that can undergo free radical polymerization, and the photoinitiator is the two-photon polymerization initiator according to claim 1 or 2.

10. The light-curable material according to claim 6 or 7, characterized in that: The polymerizable component includes raw materials for cationic polymerization, and the photoinitiator also includes a cationic co-initiator. The cationic co-initiator includes one or more of onium salts, metal organics and organic silanes.

11. The light-curable material according to claim 10, characterized in that: The mass ratio of the cationic auxiliary initiator to the polymerizable component is 0.01% to 10%.

12. A method for curing a light-curable material according to any one of claims 6 to 11, characterized in that: The following steps are involved: (1) scanning a predetermined area of the photocurable material with a first femtosecond laser to cure the predetermined area to form a cured product; (2) Scanning the cured product under a second femtosecond laser to obtain fluorescence information of the cured product, and determining the morphology of the cured product based on the fluorescence information.

13. The curing method according to claim 12, characterized in that: The power of the second femtosecond laser is less than the power of the first femtosecond laser; And / or, the power of the second femtosecond laser is less than the polymerization threshold of the photocurable material.

14. The curing method according to claim 12, characterized in that: The first femtosecond laser and the second femtosecond laser are applied from the same laser light source.

15. The curing method according to any one of claims 12 to 14, characterized in that: Also includes: (3) adjusting the curing conditions of step (1) according to the morphology of the cured product, and repeating steps (1) and (2) using the adjusted curing conditions; (4) performing steps (1) to (3) once, or repeating steps (1) to (3) multiple times, to determine suitable curing conditions for the photocurable material; (5) Curing the photocurable material under the appropriate curing conditions to obtain a microstructured product.

16. A microstructured product, characterized in that: It is prepared according to the curing method according to any one of claims 12 to 15.

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