A raft reagent for catalyst-free photopolymerization of methacrylate and its preparation method and application

Abstract

This invention discloses a RAFT reagent for catalyst-free photocontrolled polymerization of methyl methacrylate, its preparation method, and its application, belonging to the field of photocontrolled polymerization technology. The structure of the RAFT reagent is: ; R is selected from any of the following: The RAFT reagent of this invention, under visible light (green light, 520 nm) initiation, can achieve efficient and high-precision living polymerization of methyl methacrylate (MMA) without additional initiators or catalysts: the polymerization rate is twice that of the traditional RAFT reagent (CPDB), the induction period is shorter, the resulting polymer has an extremely narrow molecular weight distribution, and metal catalyst residue is completely avoided. This provides a key guarantee for the preparation of high-purity, structurally uniform polymers (such as high-performance photoresist resins), breaking through the technical bottlenecks of traditional high-temperature thermal polymerization or metal-catalyzed photocontrolled systems.

Description

Technical Field

[0001] This invention belongs to the field of photopolymerization technology, specifically relating to a RAFT reagent for catalyst-free photopolymerization of methacrylates, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Methacrylate monomers and their polymers are key substrates in fields such as optical resins, photoresists, and biomedical materials due to their excellent optical and mechanical properties and structural designability. Especially in high-precision photoresists, the requirements for polymer molecular weight and structural uniformity (dispersion density, PDI) are extremely stringent.

[0004] However, traditional polymerization techniques for preparing such materials have significant limitations:

[0005] 1. Thermally initiated polymerization: requires high temperature (60-110℃), high energy consumption, difficult to control the rate precisely, and easily leads to a wide molecular weight distribution (PDI>1.5) and chain end deactivation.

[0006] 2. Existing light-controlled polymerization:

[0007] Inactive systems: Although mild conditions (such as visible light initiation) can be achieved, the molecular weight and PDI (PDI>1.2) are usually not precisely controlled.

[0008] Metal catalysis dependence: Existing precision photoresist systems (such as certain photoresist-controlled RAFT or photoresist-controlled ATRP) often rely on metal catalysts (with a dosage >1 mol%). This not only increases cost and process complexity, but more importantly, metal residues can severely interfere with the photochemical reaction of photoresists, leading to uneven development, reduced resolution, and even affecting the performance of high-end photoresist light sources (such as EUV), greatly restricting their application in precision electronics and biomedical fields.

[0009] Therefore, developing a new technology that enables efficient and precise active (controllable) polymerization of methacrylates without high temperatures or metal catalysts and under mild conditions (such as visible light) is crucial for improving the performance and quality of key materials, especially high-performance photoresists. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a RAFT reagent for the catalyst-free photocontrolled polymerization of methyl methacrylate, its preparation method, and its application. The RAFT reagent provided by the present invention exhibits a faster polymerization rate for methyl methacrylate, a shorter induction period, and better controllability.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] In a first aspect, the present invention provides a RAFT reagent for catalyst-free photopolymerization of methacrylates, the structure of which is as follows: ;

[0013] Wherein, R is selected from any of the following:

[0014] .

[0015] This invention provides a novel RAFT reagent that, under visible light (green light, 520 nm) initiation, enables highly efficient and precise living polymerization of methyl methacrylate (MMA) without the need for additional initiators or catalysts. The polymerization rate is twice that of the traditional RAFT reagent (CPDB), with a shorter induction period, an extremely narrow molecular weight distribution in the resulting polymer, and complete avoidance of metal catalyst residue. This provides a crucial guarantee for the preparation of high-purity, structurally uniform polymers (such as high-performance photoresist resins), overcoming the technical bottlenecks of traditional high-temperature thermal polymerization or metal-catalyzed photocontrolled systems.

[0016] A second aspect of the present invention provides a method for preparing the above-mentioned RAFT reagent for catalyst-free photopolymerization of methacrylates, comprising:

[0017] 4-Bromoanisole reacts with magnesium to give the first intermediate;

[0018] The first intermediate reacts with carbon disulfide to give the second intermediate;

[0019] The second intermediate reacts with an oxidizing agent to yield a third intermediate;

[0020] The third intermediate reacts with the compound to yield the RAFT reagent;

[0021] The structure of the first intermediate is as follows: The structure of the second intermediate is The third intermediate structure is ;

[0022] The compound is selected from any one of azobisisobutyronitrile, azobisisovalerate, and ethyl α-bromophenylacetate.

[0023] In some embodiments of the present invention, the molar ratio of 4-bromoanisole, magnesium, carbon disulfide and oxidant is (0.2-0.4):(1.0-1.2):(1.1-1.3):(1.1-1.3).

[0024] In some embodiments of the present invention, the reaction of the 4-bromoanisole with magnesium includes the following steps:

[0025] Magnesium was added to an anhydrous organic solvent, a catalyst was added, and 4-bromoanisole was added in an ice-water bath under a nitrogen atmosphere. The mixture was heated to initiate the reaction, and then the heating was stopped to obtain the first intermediate.

[0026] Preferably, the organic solvent includes tetrahydrofuran.

[0027] Preferably, the catalyst comprises any one or more of elemental iodine and 1,2-dibromoethane.

[0028] In some embodiments of the present invention, the reaction of the first intermediate with carbon disulfide includes the following steps:

[0029] Carbon disulfide was added to the first intermediate and stirred to obtain the second intermediate.

[0030] In some embodiments of the present invention, the reaction of the second intermediate with the oxidant includes the following steps:

[0031] An oxidant was added to the organic solution of the second intermediate, the mixture was stirred, rotary evaporated to remove the organic solvent, filtered, washed with deionized water, and dried under vacuum to obtain the third intermediate.

[0032] In some embodiments of the present invention, the reaction of the second intermediate with the oxidant includes the following steps:

[0033] The second intermediate was dissolved in potassium carbonate solution, filtered, and the solution was collected and extracted with diethyl ether to obtain the fourth intermediate; the structure of the fourth intermediate is as follows: ;

[0034] An oxidant was added to the organic solution of the fourth intermediate, the mixture was stirred, rotary evaporated to remove the organic solvent, filtered, washed with deionized water, and dried under vacuum to obtain the third intermediate.

[0035] Preferably, the oxidant is iodine or potassium ferricyanide.

[0036] Preferably, the organic solvent includes tetrahydrofuran.

[0037] Preferably, the vacuum drying temperature is 30-50℃ and the vacuum drying time is 1-5 h.

[0038] In some embodiments of the present invention, when the compound is azobisisobutyronitrile or azobisisovalerate, the reaction of the third intermediate with azobisisobutyronitrile or azobisisovalerate includes the following steps:

[0039] An organic solvent is added to the third intermediate and azobisisobutyronitrile or azobisisovalerate, and the mixture is refluxed under a nitrogen atmosphere at 75-80°C. After the reaction is complete, the organic solvent is removed, and the product is separated and purified to obtain the RAFT reagent.

[0040] Preferably, the molar ratio of the third intermediate to azobisisobutyronitrile or azobisisovalerate is (0.8-1.2):(1.8-2.2).

[0041] Preferably, the condensation and reflux are carried out at 78°C for 15-20 hours.

[0042] Preferably, column chromatography is used for separation and purification, with petroleum ether and ethyl acetate as eluents in a volume ratio of (5.5-6.5):1, preferably 6:1.

[0043] In some embodiments of the present invention, when the compound is ethyl α-bromophenylacetate, the reaction of the third intermediate with ethyl α-bromophenylacetate includes the following steps:

[0044] The third intermediate was dissolved in an organic solvent, and ethyl α-bromophenylacetate was added. The mixture was stirred, and after the reaction was completed, the organic solvent was removed. The product was separated and purified to obtain the RAFT reagent.

[0045] Preferably, the molar ratio of the third intermediate to ethyl α-bromophenylacetate is (0.8-1.2):(1.0-1.4).

[0046] Preferably, the stirring time is 13-18 h.

[0047] Preferably, column chromatography is used for separation and purification, with petroleum ether and ethyl acetate as eluents in a volume ratio of (4.5-6.5):1.

[0048] A third aspect of the present invention provides the application of the above-described RAFT reagent or the RAFT reagent prepared by the above-described preparation method in the catalyst-free photopolymerization of methacrylate monomers.

[0049] A fourth aspect of the present invention provides a method for catalyst-free photocontrolled polymerization of methacrylate monomers, comprising:

[0050] The methacrylate monomers are mixed with the RAFT reagent described above or the RAFT reagent prepared by the above method, and a solvent is added. Polymerization is carried out under anaerobic conditions and green light irradiation.

[0051] In some embodiments of the present invention, the methacrylate monomers include methyl methacrylate.

[0052] In some embodiments of the present invention, the volume ratio of the methacrylate monomer to the RAFT reagent is 150-250:1.

[0053] In some embodiments of the present invention, the wavelength of the green light is 520 nm.

[0054] The beneficial effects of this invention are as follows:

[0055] To address the issues of slow polymerization and poor controllability of methacrylate monomers, this invention provides a novel RAFT reagent that enables highly efficient and precise living polymerization of methyl methacrylate (MMA) without the need for additional initiators or catalysts. The polymerization rate of MMA is more than twice that of traditional RAFT reagents (CPDB), with a shorter induction period and superior controllability. This significantly improves production efficiency, reduces energy consumption, and facilitates rapid start-up and precise control of the polymerization process. The superior controllability ensures a highly uniform and reproducible chain structure in the polymer, meeting the stringent requirements for material structure precision in high-end applications such as photoresists.

[0056] Simultaneously, the energy source for polymerization is visible light (green light, 520 nm), eliminating the need for high-temperature heating and enabling efficient polymerization initiation at or near room temperature. This not only avoids the high energy consumption and risks of thermal degradation / crosslinking associated with traditional thermal initiation but also makes the operation safer (no high-temperature, high-pressure equipment required), more environmentally friendly (low energy consumption, no volatile high-temperature media), and more secure and environmentally friendly. Furthermore, the polymerization process requires no additional chemical initiators or metal catalysts. This simplifies the polymerization system and post-processing (eliminating the need for complex residue removal steps), and its core advantage lies in completely eliminating the residual problem of high metal ion content (>1 mol%) in traditional metal catalyst systems (such as O-ATRP, PET-RAFT). The resulting polymer has extremely high purity, making it particularly suitable for critical applications that are highly sensitive to metal ions, such as:

[0057] High-end photoresist: avoids interference from metal residues in photochemical reactions, ensures uniform development, pattern resolution and lithography precision (especially crucial for EUV lithography), and fundamentally solves the risk of wavelength shift in lithography light source caused by catalyst residues.

[0058] Biomedical materials: Eliminating the risk of biotoxicity.

[0059] Precision optical components: to avoid impurities that cause a decline in optical performance. Attached Figure Description

[0060] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0061] Figure 1 The RAFT reagent MeSCPDB obtained in Example 1 of this invention 1 H-NMR.

[0062] Figure 2 The UV-Vis absorption spectra of the RAFT reagent MeSCPDB obtained in Example 1 and the RAFT reagent MeSEBPA obtained in Example 4 of this invention are shown.

[0063] Figure 3 The RAFT reagent MeSCBDB obtained in Example 3 of this invention 1 H NMR.

[0064] Figure 4 The RAFT reagent MeSEBPA obtained in Example 4 of this invention 1 H NMR.

[0065] Figure 5 The above is a polymerization kinetic diagram of the RAFT reagent MeSCPDB obtained in Example 1 of the present invention, wherein A is the first-order kinetic curve, B is the evolution of molecular weight and dispersion with conversion rate, and C is the molecular weight distribution curve.

[0066] Figure 6 The graphs show the polymerization kinetics of the traditional RAFT reagent CPDB. In the graphs, A is the first-order kinetic curve, B is the evolution of molecular weight and dispersion with conversion, and C is the molecular weight distribution curve.

[0067] Figure 7 The above is a polymerization kinetic diagram of the RAFT reagent MeSEBPA obtained in Example 4 of the present invention, wherein A is the first-order kinetic curve, B is the evolution of molecular weight and dispersion with conversion rate, and C is the molecular weight distribution curve. Detailed Implementation

[0068] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0069] Example 1

[0070] A method for preparing a RAFT reagent includes the following steps:

[0071]

[0072] (1) Magnesium shavings (1.1 mmol) were added to a pre-dried 100 mL flask, along with 40 mL of anhydrous tetrahydrofuran, and then two iodine particles were added as a catalyst. Under a nitrogen atmosphere, in an ice-water bath, 4-bromoanisole (1.0 mmol) was added, and the mixture was heated to initiate the reaction. Heating was then stopped, and the mixture was stirred overnight. The solution gradually changed from light brown to colorless, and finally to black. Then, anhydrous carbon disulfide (1.2 mmol) was added, and the mixture was stirred for 2 h. The solution turned dark red.

[0073]

[0074] (2) Iodine (1.2 mmol) was added to the solution from step one and stirred continuously for 10 h. Then, the solution was rotary evaporated to remove THF, and an appropriate amount of sodium thiosulfate aqueous solution was added to reduce the excess iodine. The solution was then filtered and washed three times with deionized water. The solution was then dried under vacuum at 45 °C for 4 h to obtain the intermediate product with a yield of 70%.

[0075]

[0076] (3) The intermediate product obtained in step 2 (1 mmol) and azobisisobutyronitrile (AIBN, 2 mmol) were placed in a three-necked flask, and an appropriate amount of ethyl acetate was added. The mixture was refluxed at 78 °C for 18 h, with nitrogen gas continuously introduced. After heating was stopped, the solution was rotary evaporated to remove the solvent, and then purified by column chromatography using petroleum ether and ethyl acetate in a volume ratio of 6:1. The RAFT reagent MeSCPDB was obtained in 78% yield.

[0077] The RAFT reagent MeSCPDB obtained in Example 1 1 H-NMR such as Figure 1 As shown, the UV-Vis absorption spectrum is as follows: Figure 2 As shown.

[0078] Example 2

[0079] A method for preparing a RAFT reagent includes the following steps:

[0080]

[0081] (1) Magnesium shavings (1.1 mmol) were added to a pre-dried 100 mL flask, followed by 40 mL of anhydrous tetrahydrofuran, and then 1,2-dibromoethane (0.02 mmol) was added as a catalyst. Under a nitrogen atmosphere, in an ice-water bath, 4-bromoanisole (1.0 mmol) was added, and the mixture was heated to initiate the reaction. Heating was then stopped, and the mixture was stirred continuously for 3 h. Then, anhydrous carbon disulfide (1.2 mmol) was added, and the mixture was stirred continuously for 3 h. The solution changed from colorless to deep red.

[0082] The solvent was then removed by rotary evaporation to obtain a dark red viscous liquid, which was dissolved in 0.1 M K2CO3 solution, filtered, and the solution was collected and extracted with diethyl ether to obtain the intermediate in 87% yield.

[0083]

[0084] (2) The intermediate obtained in the first step (1 mmol) was dissolved in deionized water, and iodine (1.2 mmol) was added. The mixture was stirred continuously for 10 h, and the solution was observed to change from dark red to pink and a precipitate was formed. An appropriate amount of sodium thiosulfate aqueous solution was added to reduce the excess iodine. The solution was then extracted with dichloromethane and washed three times with deionized water to obtain an organic phase. The dichloromethane was then removed by rotary evaporation and dried with anhydrous sodium sulfate. The solution was then vacuum dried at 35 °C for 2 h to obtain the intermediate product with a yield of 85%.

[0085]

[0086] (3) The intermediate product obtained in step 2 (1 mmol) and azobisisobutyronitrile (AIBN, 2 mmol) were placed in a three-necked flask, and an appropriate amount of ethyl acetate was added. The mixture was refluxed at 78 °C for 18 h, with nitrogen gas continuously introduced. After heating was stopped, the solution was rotary evaporated to remove the solvent, and then purified by column chromatography using petroleum ether and ethyl acetate in a volume ratio of 6:1. The RAFT reagent MeSCPDB was obtained in 72% yield.

[0087] Example 3

[0088] A method for preparing a RAFT reagent includes the following steps:

[0089]

[0090] (1) Magnesium shavings (1.1 mmol) were added to a pre-dried 100 mL flask, along with 40 mL of anhydrous tetrahydrofuran, and then two iodine particles were added as a catalyst. Under a nitrogen atmosphere, in an ice-water bath, 1.0 mmol of 4-bromoanisole was added, and the mixture was heated to initiate the reaction. Heating was then stopped, and the mixture was stirred overnight. The solution gradually changed from light brown to colorless, and finally to black. Then, 1.2 mol of anhydrous carbon disulfide was added, and the mixture was stirred for 2 h. The solution turned dark red.

[0091]

[0092] (2) Iodine (1.2 mmol) was added to the solution from step one and stirred continuously for 10 h. Then, the solution was rotary evaporated to remove THF, and an appropriate amount of sodium thiosulfate aqueous solution was added to reduce the excess iodine. The solution was then filtered and washed three times with deionized water. The solution was then dried under vacuum at 45 °C for 4 h to obtain the intermediate product with a yield of 70%.

[0093]

[0094] (3) The intermediate product (1 mmol) obtained in the second step and azobisisovalerate (2 mol) were placed in a three-necked flask, and an appropriate amount of ethyl acetate was added. The mixture was refluxed at 78 °C for 20 h, with nitrogen gas continuously introduced. After heating was stopped, the solution was rotary evaporated to remove the solvent, and then purified by column chromatography. The eluent was petroleum ether and ethyl acetate in a volume ratio of 8:1. The RAFT reagent MeSCBDB was obtained in 81% yield.

[0095] The RAFT reagent MeSCBDB obtained in Example 3 of this embodiment... 1 H-NMR such as Figure 3 As shown.

[0096] Example 4

[0097] A method for preparing a RAFT reagent includes the following steps:

[0098]

[0099] (1) Magnesium shavings (1.1 mmol) were added to a pre-dried 100 mL flask, followed by 40 mL of anhydrous tetrahydrofuran, and then 1,2-dibromoethane (0.02 mmol) was added as a catalyst. Under a nitrogen atmosphere, in an ice-water bath, 4-bromoanisole (1.0 mmol) was added, and the mixture was heated to initiate the reaction. Heating was then stopped, and the mixture was stirred continuously for 3 h. Then, anhydrous carbon disulfide (1.2 mmol) was added, and the mixture was stirred continuously for 3 h. The solution changed from colorless to deep red.

[0100] The solvent was then removed by rotary evaporation to obtain a dark red viscous liquid, which was dissolved in 0.1 M K2CO3 solution, filtered, and the solution was collected and extracted with diethyl ether to obtain the intermediate in 87% yield.

[0101]

[0102] (2) The intermediate obtained in the first step (1 mmol) was dissolved in tetrahydrofuran, and ethyl α-bromophenylacetate (EBPA, 1.2 mmol) was added. The mixture was stirred continuously for 15 h, and the solution was observed to change from dark red to pink. Then, the tetrahydrofuran was removed by rotary evaporation, and the solution was purified by column chromatography with petroleum ether and ethyl acetate in a volume ratio of 5:1. The RAFT reagent MeSEBPA was obtained in 83% yield.

[0103] The RAFT reagent MeSEBPA obtained in Example 4 of this embodiment 1 H-NMR such as Figure 4 As shown, the UV-Vis absorption spectrum is as follows: Figure 2 As shown.

[0104] Example 5

[0105] Dynamics of the MeSCPDB obtained in Example 1 under visible light.

[0106] The kinetic experiment used methyl methacrylate (MMA) as the model monomer for polymerization. The ratio of RAFT reagent to monomer was [MMA]:[MeSCPDB] = 200:1. An equal volume of DMSO was added as a solvent. Polymerization was carried out under anaerobic conditions and irradiation with green light (520 nm). The monomer content was quantitatively analyzed by detecting the peak area of ​​the stretching vibration of the carbon-hydrogen bond (C=CH) on the carbon-carbon double bond (C=C) in the system using Fourier transform infrared spectroscopy, obtaining the conversion rate and ln[M]0 / [M] under different irradiation times. t A line graph showing the change of the value over time was generated. Simultaneously, samples were taken at different conversion rates and gel permeation chromatography was performed to observe the molecular weight distribution and dispersibility of the polymer at different conversion rates.

[0107] The kinetic experimental results of MeSCPDB are as follows: Figure 5 As shown, it exhibits excellent controllability during the polymerization process. In five samplings during polymerization, the polymer dispersity was consistently less than 1.2, indicating that MeSCPDB provides excellent controllability over methacrylate monomers, regardless of whether the conversion rate is low or high. Furthermore, at different conversion rates, the number-average molecular weight of the polymer (NMR) remains consistent. M n,GPC ) and theoretical value ( Mn,Theo The results are very close, which also indicates that MeSCPDB has excellent control over methacrylate monomers during polymerization, and that MeSCPDB has very high initiation efficiency. I (≈ 100%), there is basically no bimolecular termination reaction, and no "dead chain" is produced, that is, a polymer chain without RAFT end groups.

[0108] Compared to the traditional RAFT reagent CPDB used for methacrylates, MeSCPDB has an induction period of 84 min, significantly shorter than the induction period of CPDB (237 min) under the same conditions. MeSCPDB exhibits an apparent polymerization rate of 0.0025 min during polymerization. -1 This is compared to CPDB (0.0013 min). -1 The polymerization rate was nearly doubled. This resulted in the polymerization taking half the time of CPDB to reach 70% conversion, significantly improving the polymerization efficiency of methacrylate polymers.

[0109] Furthermore, the light source exhibits excellent control over MeSCPDB during the polymerization process; polymerization immediately stops when illumination is stopped and resumes when illumination is resumed. Moreover, no dark polymerization occurred in MeSCPDB during a 60-minute dark treatment. Even when the dark treatment time was extended to 10 hours, virtually no dark polymerization was observed. Therefore, the light source demonstrates excellent control over MeSCPDB.

[0110] Comparative Example 1

[0111] Dynamics of CPDB under visible light.

[0112] The experimental conditions for CPDB are the same as those for MeSCPDB, and the polymerization kinetics diagram is shown below. Figure 6 As shown.

[0113] CPDB, a typical RAFT reagent used for the polymerization of methacrylate monomers, is usually employed in thermally initiated RAFT polymerization because its polymerization rate is too low (0.0012 min) when used for methacrylate monomer polymerization under visible light. -1 The relatively long induction period (237 min) of CPDB greatly limits its application in photocontrolled polymerization. Furthermore, since thermal initiation inevitably involves a bimolecular termination reaction, polymers prepared in this way are prone to producing polymer chains without RAFT end groups, affecting polymer dispersibility.

[0114] Example 6

[0115] Dynamics of MeSEBPA obtained in Example 4 under visible light.

[0116] The experimental conditions were the same as those for MeSCPDB in Example 5, except for the RAFT reagent.

[0117] The kinetic experimental results of MeSEBPA are as follows: Figure 7 As shown, although MeSEBPA exhibits lower controllability compared to MeSCPDB, its PDI remains below 1.4, falling within the range of controllable polymerization. Meanwhile, its polymerization rate ( k p app = 0.0028 min -1 Similar to MeSCPDB, but without a long induction period (essentially zero), MeSEBPA significantly improves polymerization efficiency and drastically reduces polymerization time. Furthermore, polymerization stops immediately upon cessation of illumination and resumes upon re-illumination, demonstrating excellent control over the light source.

[0118] Example 7

[0119] Dynamics of the MeSCBDB obtained in Example 3 under visible light.

[0120] The experimental conditions were the same as those for MeSCPDB in Example 5, except for the RAFT reagent.

[0121] The kinetic results of MeSCBDB are similar to those of MeSCPDB, with essentially the same polymerization rate and controllability, demonstrating good control over methyl methacrylate during polymerization. Polymerization immediately stopped upon cessation of light exposure and resumed upon re-introduction of light, indicating that MeSCBDB also exhibits excellent controllability over the light source.

[0122] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A RAFT reagent for catalyst-free photopolymerization of methacrylates, characterized in that, Its structure is as follows: ; Wherein, R is selected from any of the following: 。 2. A method for preparing the RAFT reagent for catalyst-free photocontrolled polymerization of methacrylates as described in claim 1, characterized in that, include: 4-Bromoanisole reacts with magnesium to give the first intermediate; The first intermediate reacts with carbon disulfide to give the second intermediate; The second intermediate reacts with an oxidizing agent to yield a third intermediate; The third intermediate reacts with the compound to yield the RAFT reagent; The structure of the first intermediate is as follows: The structure of the second intermediate is The third intermediate structure is ; The compound is selected from any one of azobisisobutyronitrile, azobisisovalerate, and ethyl α-bromophenylacetate.

3. The preparation method according to claim 2, characterized in that, The molar ratio of 4-bromoanisole, magnesium, carbon disulfide and oxidant is (0.2-0.4):(1.0-1.2):(1.1-1.3):(1.1-1.3).

4. The preparation method according to claim 2, characterized in that, The reaction of the 4-bromoanisole with magnesium includes the following steps: Magnesium was added to an organic solvent, a catalyst was added, and 4-bromoanisole was added in an ice-water bath under a nitrogen atmosphere. The mixture was heated to initiate the reaction, and then the heating was stopped to obtain the first intermediate. The organic solvent includes tetrahydrofuran; The catalyst comprises any one or more of elemental iodine and 1,2-dibromoethane.

5. The preparation method according to claim 2, characterized in that, The reaction of the first intermediate with carbon disulfide includes the following steps: Carbon disulfide was added to the first intermediate and stirred to obtain the second intermediate.

6. The preparation method according to claim 2, characterized in that, The reaction of the second intermediate with the oxidant includes the following steps: An oxidant was added to the organic solution of the second intermediate, the mixture was stirred, rotary evaporated to remove the organic solvent, filtered, washed with deionized water, and dried under vacuum to obtain the third intermediate. Alternatively, the reaction of the second intermediate with the oxidant includes the following steps: The second intermediate was dissolved in potassium carbonate solution, filtered, and the solution was collected and extracted with diethyl ether to obtain the fourth intermediate; the structure of the fourth intermediate is as follows: ; An oxidant was added to the organic solution of the fourth intermediate, the mixture was stirred, rotary evaporated to remove the organic solvent, filtered, washed with deionized water, and dried under vacuum to obtain the third intermediate. The oxidant is iodine or potassium ferrocyanate; The organic solvent includes tetrahydrofuran; The vacuum drying temperature is 30-50℃, and the vacuum drying time is 1-5 h.

7. The preparation method according to claim 2, characterized in that, When the compound is azobisisobutyronitrile or azobisisovalerate, the reaction of the third intermediate with azobisisobutyronitrile or azobisisovalerate includes the following steps: An organic solvent is added to the third intermediate and azobisisobutyronitrile or azobisisovalerate, and the mixture is refluxed under a nitrogen atmosphere at 75-80°C. After the reaction is complete, the organic solvent is removed, and the product is separated and purified to obtain the RAFT reagent. The molar ratio of the third intermediate to azobisisobutyronitrile or azobisisovalerate is (0.8-1.2):(1.8-2.2). Alternatively, when the compound is ethyl α-bromophenylacetate, the reaction of the third intermediate with ethyl α-bromophenylacetate includes the following steps: The third intermediate was dissolved in an organic solvent, and ethyl α-bromophenylacetate was added. The mixture was stirred, and after the reaction was completed, the organic solvent was removed. The product was separated and purified to obtain the RAFT reagent. The molar ratio of the third intermediate to ethyl α-bromophenylacetate was (0.8-1.2):(1.0-1.4). The stirring time was 13-18 h.

8. The application of the RAFT reagent according to claim 1 or the RAFT reagent prepared by the preparation method according to claims 2-7 in the catalyst-free photopolymerization of methacrylate monomers.

9. A method for catalyst-free photocontrolled polymerization of methacrylate monomers, characterized in that, include: The methacrylate monomers and the RAFT reagent of claim 1 or the RAFT reagent prepared by the preparation method of claims 2-7 are mixed, a solvent is added, and polymerization is carried out under anaerobic conditions and green light irradiation.

10. The method as described in claim 9, characterized in that, The methacrylate monomers include methyl methacrylate; The volume ratio of the methacrylate monomer to the RAFT reagent is 150-250:1; The wavelength of the green light is 520 nm.

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