A raft agent, its preparation method and application

Abstract

The application discloses a RAFT reagent and a preparation method and application thereof, and belongs to the technical field of RAFT reagent synthesis. The general formula of the RAFT reagent is: R1-R5 are all selected from any one of hydrogen atoms, methyl groups, methoxy groups and halogen atoms; and R6 is selected from any one of C3-C6 alkyl ester groups. The RAFT reagent has a unique molecular structure, exhibits excellent fast light response characteristics, excellent initiation efficiency and a relatively high triplet quantum yield. In the kinetic process, the RAFT reagent not only exhibits an extremely fast polymerization rate, but also has excellent chain transfer capacity, and can be used to prepare acrylic ester and acrylamide polymers with a relatively narrow molecular weight distribution. These characteristics enable the resin to be rapidly cured, and the RAFT reagent can be applied to the field of light-cured 3D printing.

Description

Technical Field

[0001] This invention belongs to the field of RAFT reagent synthesis technology, specifically relating to a RAFT reagent, 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] Photo-controlled reversible addition-fragmentation chain transfer polymerization (Photo-RAFT), as an important branch of photo-controlled reversible deactivation radical polymerization (Photo-RDRP), ingeniously combines the excellent controllability of traditional reversible addition-fragmentation chain transfer polymerization (RAFT) with the precision of light control. By utilizing the light-controlled activity of RAFT reagents (usually as photoinitiators or photosensitizers), it achieves the on-demand generation and quenching of free radical concentrations, theoretically providing an ideal platform for the preparation of polymer materials with precisely controllable structures. Despite its enormous potential, the practical large-scale application and industrialization of Photo-RAFT technology still face several key bottlenecks, mainly stemming from the design of its core component—high-performance photoresponsive RAFT reagents.

[0004] Ideal photo-RAFT reagents need to possess both strong chain transfer capabilities (to maintain the precision of RAFT mechanism control) and excellent photosensitivity (to ensure rapid and efficient photo-triggered radical generation and polymerization kinetic control). However, most existing conventional RAFT reagents for photocontrolled systems are insufficient in terms of photoresponsiveness. They typically suffer from slow photoreaction rates, low quantum yields, and low initiation efficiency, leading to prolonged polymerization induction periods and slow overall curing rates, which greatly limits their performance in scenarios requiring high-speed photocuring (e.g., high-speed printing, large-scale photocoating curing, and high-efficiency additive manufacturing). Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a RAFT reagent, its preparation method, and its applications. Several novel RAFT reagents provided by this invention exhibit excellent initiation efficiency and high triplet quantum yield. In the kinetic process, they not only demonstrate extremely fast polymerization rates but also possess excellent chain transfer capabilities, enabling the preparation of acrylate and acrylamide polymers with narrow molecular weight distributions. Ð <1.1). These characteristics enable rapid curing of resins, allowing them to be applied in the field of photopolymer 3D printing.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A first aspect of the present invention provides a RAFT reagent with the general formula:

[0008] ;

[0009] R1-R5 are selected from any one of hydrogen atom, methyl, methoxy and halogen atom; R6 is selected from any one of C3-C6 alkyl ester groups.

[0010] The structure of the RAFT reagent (structural formula ZC(=S)-SR) mainly consists of a dithioester, an active group (Z group), and a leaving group (R group). The RAFT reagent provided by this invention has a Z group (i.e., The RAFT reagent provided by this invention is an indazole derivative, with the R group (R6) being a C3-C6 alkyl ester group. It possesses a unique molecular structure and exhibits excellent rapid photoresponse characteristics, excellent initiation efficiency, and high triplet quantum yield. In photocontrolled RAFT polymerization, it can significantly shorten the induction period and greatly increase the photopolymerization rate, achieving efficient and rapid photocuring. Kinetically, it not only exhibits an extremely fast polymerization rate but also excellent chain transfer ability, enabling the preparation of acrylate and acrylamide polymers with narrow molecular weight distributions. Ð <1.1). These characteristics enable rapid curing of resins, allowing them to be applied in the field of photopolymer 3D printing.

[0011] In some embodiments of the present invention, R6 is selected from any one of C3-C5 alkyl ester groups.

[0012] In the RAFT reagent provided by this invention, R6 is a key substituent directly attached to the thiocarbonyl sulfide (-SC=S) group, and its structure has a decisive influence on the photoactivity and stability of the RAFT reagent. When R6 is selected from any of the C3-C5 alkyl ester groups, the photoactivity and stability of the RAFT reagent are even better.

[0013] In some embodiments of the present invention, R6 is Compared to cyclopentadienyl (CP) groups, ester groups have a shorter induction period.

[0014] In some embodiments of the present invention, the RAFT reagent is selected from:

[0015] , ,

[0016] , , or .

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned RAFT reagent, comprising:

[0018] At low temperature and in an organic solvent, 1-H-indazole or its derivatives react with an inorganic base and carbon disulfide to give an intermediate.

[0019] At room temperature, the intermediate reacts with X-R6. After the reaction is complete, the organic phase is filtered and collected. The organic phase is then distilled under reduced pressure and purified to obtain the RAFT reagent.

[0020] The structure of the intermediate is as follows: R1-R5 are all selected from any one of hydrogen atom, methyl, methoxy and halogen atom;

[0021] Where X is a halogen atom, and R6 is selected from any of the C3-C5 alkyl ester groups.

[0022] Currently, the development of novel high-performance photoresponsive RAFT reagents faces a core contradiction: on the one hand, high-end photomanufacturing fields (such as demanding photopolymerization 3D printing) have an urgent need for them, expecting them to achieve rapid and precise polymerization control; on the other hand, the synthesis routes of these reagents are usually complex, lengthy, costly, and difficult to scale up, resulting in poor product purity and batch stability, which seriously restricts their transformation from laboratory to practical industrial applications. Specifically, the multi-step organic synthesis methods for potential high-performance RAFT reagents have limited yields, and the separation and purification efficiency is low and the number of by-products increases during scale-up, making it difficult to economically obtain high-purity products; while trace impurities can significantly interfere with the photocontrolled polymerization process, leading to performance degradation. This poses a huge challenge to the large-scale production of stable, high-purity novel RAFT reagents.

[0023] To address the aforementioned issues, the RAFT reagent proposed in this invention not only exhibits excellent performance but also allows for large-scale preparation via a one-pot method. The synthesis process is simple and has achieved gram- to kilogram-scale synthesis. Furthermore, the yields are consistently above 80%, and pure products with a purity exceeding 90% can be prepared on a large scale through simple purification. Byproducts during the reaction can be removed by distillation, and high-performance liquid chromatography (HPLC) has confirmed that the byproducts consist of only two main reactants; no other byproducts were found.

[0024] To address the main problems currently existing in photo-RAFT, this invention proposes a one-pot method for synthesizing highly efficient RAFT reagents. This method not only enables kilogram-level mass production, but also produces RAFT reagents that exhibit excellent polymerization rates and superior controllability during polymerization kinetics, far exceeding the performance of commercially available RAFT reagents.

[0025] In some embodiments of the present invention, the low temperature is -10 to 10°C, preferably 0 to 5°C.

[0026] Understandably, in the preparation method of this invention, the key step of the reaction is the removal of the proton from the N1 of the indazole ring by 1-H-indazole or its derivatives under the action of an inorganic base, generating an indazole anion. This anion has strong nucleophilicity and subsequently attacks carbon disulfide, generating the crucial sulfur-containing intermediate (indazole-1-thiocarboxylate). The core objective of this reaction is to generate a single, position-specific intermediate. Carbon disulfide is more chemically reactive at higher temperatures and is more prone to hydrolysis, disproportionation, and other side reactions (generating COS, CS, etc.), leading to raw material consumption and impurity generation. The stability of the indazole ring and its derivatives (especially when R1-R5 contain certain specific substituents) may decrease at high temperatures, and heating with a strong base makes them more susceptible to ring-opening, rearrangement, or other unpredictable side reactions. The core significance of using low-temperature conditions (typically -10°C to 10°C) is: (1) to suppress to the greatest extent possible the self-decomposition of carbon disulfide, the thermal degradation of indazole derivatives, side reactions initiated by strong bases, and non-targeted over-reactions; (2) to ensure that the reaction occurs highly selectively at the N1 position of indazole, yielding a single, correct, and high-purity key intermediate (indazole-1-thiocarboxylate); and (3) to lay the foundation for the high-yield and high-purity synthesis of the target RAFT reagent in the next step, thereby ensuring that the final product (RAFT reagent) has excellent rapid photoresponse characteristics, high purity, and good storage stability. Low temperature is an essential and crucial operating condition for achieving the goal of "making the reaction more precise at a specific position (N1 position), improving the purity and yield of the intermediate, and laying a good foundation for subsequent reactions." Good control of this step is the key starting point for the success of the entire synthesis process.

[0027] In some embodiments of the present invention, the inorganic base includes any one of potassium hydroxide, sodium hydroxide, calcium hydroxide, and aluminum hydroxide.

[0028] In the first step of the reaction, a strong inorganic base (such as KOH or NaOH) can efficiently and completely deprotonate the N1-H of indazole, generating a high concentration of indazole anions, thereby significantly accelerating the reaction with carbon disulfide and increasing the formation rate and yield of the target intermediate. Weaker bases (potassium carbonate or potassium phosphate) require a longer reaction time, have a slower reaction rate, and are difficult to completely deprotonate. To improve the formation rate and yield of the target intermediate, the inorganic base is preferably potassium hydroxide or sodium hydroxide.

[0029] In some embodiments of the present invention, the molar ratio of the inorganic base, 1-H-indazole or its derivative, carbon disulfide, and X-R6 is (1-1.5):(0.9-1.1):(1.9-2.1):(2-2.5). This molar ratio design is the result of a careful trade-off and experimental optimization of comprehensive chemical equilibrium / kinetics (promoting difficult reactions), raw material properties (compensating for CS2 volatilization), side reaction suppression (reducing byproducts such as disulfide), cost control, ease of purification, and batch-to-batch stability requirements. It perfectly supports the core advantage of this synthetic method—achieving efficient, stable, and scalable production of high-purity, high-performance RAFT reagents through a "one-pot" method. This dosage ratio ensures high purity and yield of key intermediates, suppresses multiple side reactions, achieves high product yield and purity, and guarantees robustness for large-scale production.

[0030] Preferably, the molar ratio of the inorganic base, 1-H-indazole or its derivative, carbon disulfide, and X-R6 is (1.1-1.3):(0.9-1.1):(1.9-2.1):(2.1-2.3). This ratio can further improve the product yield and purity, ensuring large-scale production.

[0031] Preferably, the molar ratio of the inorganic base, 1-H-indazole or its derivative, carbon disulfide, and X-R6 is 1.2:1:2:2.2. This specific ratio can further improve the product yield and purity, ensuring large-scale production.

[0032] In some embodiments of the present invention, the structure of the 1-H-indazole derivative is as follows:

[0033] ;

[0034] R1-R5 are all selected from any one of hydrogen atom, methyl, methoxy and halogen atom, and R1-R5 are not all hydrogen atom at the same time.

[0035] To avoid confusion regarding the 1-H-indazole derivative, this invention further defines its structure. The structure reveals that the 1-H-indazole derivative retains the skeletal structure of 1-H-indazole and is a substituted product of 1-H-indazole. Compared to 1-H-indazole, it also possesses a highly selective reaction site (N1), a tunable electronic structure, a stable conjugated skeleton, and a flexible modification window. This makes the RAFT reagent possess advantages such as strong synthetic feasibility (one-pot method), high structural stability, fast photoresponse speed, and customizable performance.

[0036] In some embodiments of the present invention, the preparation method includes:

[0037] Under low temperature conditions, an inorganic base is dispersed in an organic solvent and stirred continuously; then 1-H-indazole or its derivative is added and stirred continuously; then carbon disulfide is added dropwise. After the addition is complete, the mixture is brought back to room temperature and stirred continuously to obtain an intermediate.

[0038] At room temperature, X-R6 was added dropwise to the reaction system while stirring continuously. The organic phase was then filtered and collected. The organic phase was then distilled under reduced pressure and purified to obtain the RAFT reagent.

[0039] 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 photocontrolled RAFT polymerization.

[0040] In some embodiments of the present invention, the application involves mixing the monomer, solvent, and RAFT reagent, initiating polymerization upon illumination, and immediately stopping polymerization upon cessation of illumination to obtain a polymer.

[0041] The beneficial effects of this invention are as follows:

[0042] The RAFT reagent provided by this invention has a Z group that is an indazole derivative and an R group that is a C3-C6 alkyl ester group. The RAFT reagent provided by this invention has a unique molecular structure and exhibits excellent rapid photoresponse characteristics, excellent initiation efficiency, and high triplet quantum yield. In photocontrolled RAFT polymerization, it can significantly shorten the induction period and greatly increase the photopolymerization rate, achieving efficient and rapid photocuring. In the kinetic process, it not only exhibits an extremely fast polymerization rate but also excellent chain transfer ability, enabling the preparation of acrylate and acrylamide polymers with narrow molecular weight distributions. Ð <1.1). These characteristics enable rapid curing of resins, allowing them to be applied in the field of photopolymer 3D printing.

[0043] This invention also provides a method for preparing RAFT reagents. The "one-pot" synthesis of highly efficient RAFT reagents not only enables kilogram-level mass production, but also yields RAFT reagents that exhibit exceptional polymerization rates and excellent controllability during polymerization kinetics, far surpassing currently available RAFT reagents. Specifically, this invention achieves direct and efficient conversion of raw materials within a single reactor through an optimized reaction process, eliminating the need for cumbersome intermediate separation and purification, and obtaining the target product in one step. Its core advantages are: First, the "one-pot" design significantly simplifies the complex process of traditional multi-step synthesis, significantly improving synthesis efficiency; second, the synthesis process is stable and highly reproducible, easily achieving large-scale production from gram to kilogram levels, effectively overcoming the bottleneck of the difficulty in industrializing novel photoresponsive RAFT reagents; third, by precisely controlling reaction parameters, the purity of the obtained RAFT reagent consistently reaches over 90% (preferably 95%-99%), perfectly meeting the stringent requirements for high reagent purity in photocontrolled RAFT polymerization, ensuring a highly controllable polymerization process.

[0044] This invention solves the key challenges of simple, controllable, and large-scale preparation of high-performance photoresponsive RAFT reagents, providing core material support for advanced manufacturing fields with stringent speed and precision requirements, such as photopolymer 3D printing, precision photoresist, and microelectronic packaging, and has broad application prospects. Attached Figure Description

[0045] 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.

[0046] Figure 1 The RAFT1 obtained in Embodiment 1 of the present invention 1 H NMR spectrum;

[0047] Figure 2 The RAFT2 obtained in Embodiment 2 of the present invention 1 H NMR spectrum;

[0048] Figure 3 The RAFT3 obtained in Embodiment 3 of the present invention 1 H NMR spectrum;

[0049] Figure 4 The RAFT4 obtained in Embodiment 4 of the present invention 1 H NMR spectrum;

[0050] Figure 5 The RAFT5 obtained in Embodiment 5 of the present invention 1 H NMR spectrum;

[0051] Figure 6The RAFT6 obtained in Embodiment 6 of the present invention 1 H NMR spectrum;

[0052] Figure 7 The polymerization kinetics of RAFT1 obtained in Example 1 of this invention are shown, wherein the model monomer is DMA, A is the apparent polymerization rate detection, B is the curve of molecular weight and dispersion as a function of conversion rate, and C is the molecular weight distribution curve.

[0053] Figure 8 The polymerization kinetics of RAFT2 obtained in Example 2 of this invention are shown, wherein the model monomer is DMA, A is the apparent polymerization rate detection, B is the curve of molecular weight and dispersion as a function of conversion rate, and C is the molecular weight distribution curve.

[0054] Figure 9 The polymerization kinetics of RAFT3 obtained in Example 3 of this invention are shown, wherein the model monomer is DMA, A is the apparent polymerization rate detection, B is the curve of molecular weight and dispersion as a function of conversion rate, and C is the molecular weight distribution curve.

[0055] Figure 10 The polymerization kinetics of RAFT4 obtained in Example 4 of this invention are shown, wherein the model monomer is MA, A is the apparent polymerization rate detection, B is the curve of molecular weight and dispersion as a function of conversion rate, and C is the molecular weight distribution curve.

[0056] Figure 11 The polymerization kinetics of RAFT5 obtained in Example 5 of this invention are shown, wherein the model monomer is MA, A is the apparent polymerization rate detection, B is the curve of molecular weight and dispersion as a function of conversion rate, and C is the molecular weight distribution curve.

[0057] Figure 12 The polymerization kinetics of RAFT5 obtained in Example 5 of this invention are shown, wherein the model monomer is DMA, A is the apparent polymerization rate detection, B is the curve of molecular weight and dispersion as a function of conversion rate, and C is the molecular weight distribution curve.

[0058] Figure 13 The polymerization kinetics of RAFT6 obtained in Example 6 of this invention are shown, wherein the model monomer is MA, A is the apparent polymerization rate detection, B is the curve of molecular weight and dispersion as a function of conversion rate, and C is the molecular weight distribution curve. Detailed Implementation

[0059] 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.

[0060] Example 1

[0061] A RAFT reagent has the following structure:

[0062] .

[0063] Its preparation method includes the following steps:

[0064] RAFT synthesis route:

[0065]

[0066] Potassium hydroxide (24 mmol, 1.2 eq) was dispersed in 200 mL of tetrahydrofuran at 0–10 °C and stirred continuously for 0.5 h. Then 1-H-indazole (20 mmol, 1.0 eq) was added and stirred for another 1 h. Then carbon disulfide (40 mmol, 2.0 eq) was added dropwise. After the addition was complete, the mixture was brought to room temperature and stirred continuously for 5 h.

[0067] Methyl 2-bromopropionate (24 mmol, 2.2 eq) was slowly added dropwise to the reaction system at room temperature, and the mixture was stirred continuously for 10 h. The mixture was then filtered, and the organic phase was collected. The organic phase was distilled under reduced pressure, and the product was placed in a distillation column to recover the reactants and remove other impurities. High-purity RAFT reagent was obtained after distillation. To distinguish it from the RAFT reagents obtained in other examples, the RAFT reagent obtained in Example 1 was named RAFT1.

[0068] The yield was 87%. The purity of RAFT1 was determined to be 96.3% by HPLC.

[0069] Example 2

[0070] A RAFT reagent has the following structure:

[0071] .

[0072] Its preparation method includes the following steps:

[0073] RAFT synthesis route:

[0074]

[0075] Potassium hydroxide (24 mmol, 1.2 eq) was dispersed in 200 mL of tetrahydrofuran at 0–10 °C and stirred for 1 h. Then 3-methyl-1-H-indazole (20 mmol, 1.0 eq) was added and stirred for another 2 h. Then carbon disulfide (40 mmol, 2.0 eq) was added dropwise. After the addition was complete, the mixture was brought to room temperature and stirred for 10 h.

[0076] Methyl 2-bromopropionate (24 mmol, 2.2 eq) was slowly added dropwise to the reaction system at room temperature, and the mixture was stirred continuously for 15 h. The mixture was then filtered, and the organic phase was collected. The organic phase was then distilled under reduced pressure, and the product was placed in a distillation column to recover the reactants and remove other impurities. After distillation, a high-purity RAFT reagent was obtained, named RAFT2.

[0077] The yield was 89%. The purity of RAFT2 was determined to be 98.4% by HPLC.

[0078] Example 3

[0079] A RAFT reagent has the following structure:

[0080] .

[0081] Its preparation method includes the following steps:

[0082] RAFT synthesis route:

[0083]

[0084] Potassium hydroxide (24 mmol, 1.2 eq) was dispersed in 200 mL of tetrahydrofuran at 0–10 °C and stirred for 2 h. Then 6-methoxy-3-methyl-1-H-indazole (20 mmol, 1.0 eq) was added and stirred for 4 h. Then carbon disulfide (40 mmol, 2.0 eq) was added dropwise. After the addition was complete, the mixture was brought to room temperature and stirred for 24 h.

[0085] Methyl 2-bromopropionate (24 mmol, 2.2 eq) was slowly added dropwise to the reaction system at room temperature, and the mixture was stirred continuously for 24 h. The mixture was then filtered, and the organic phase was collected. The organic phase was then distilled under reduced pressure, and the product was placed in a distillation column to recover the reactants and remove other impurities. After distillation, a high-purity RAFT reagent was obtained, named RAFT3.

[0086] The yield was 81%. The purity of RAFT3 was determined to be 91.1% by HPLC.

[0087] Example 4

[0088] A RAFT reagent has the following structure:

[0089] .

[0090] Its preparation method includes the following steps:

[0091] RAFT synthesis route:

[0092]

[0093] Potassium hydroxide (24 mmol, 1.2 eq) was dispersed in 200 mL of tetrahydrofuran at 0–10 °C and stirred for 1 h. Then 4-methoxy-1-H-indazole (20 mmol, 1.0 eq) was added and stirred for another 2 h. Then carbon disulfide (40 mmol, 2.0 eq) was added dropwise. After the addition was complete, the mixture was brought to room temperature and stirred for 10 h.

[0094] Methyl 2-bromopropionate (24 mmol, 2.2 eq) was slowly added dropwise to the reaction system at room temperature, and the mixture was stirred continuously for 5 h. The mixture was then filtered, and the organic phase was collected. The organic phase was then distilled under reduced pressure, and the product was placed in a distillation column to recover the reactants and remove other impurities. After distillation, a high-purity RAFT reagent was obtained, named RAFT4.

[0095] The yield was 85%. The purity of RAFT4 was determined to be 91.4% by HPLC.

[0096] Example 5

[0097] A RAFT reagent has the following structure:

[0098] .

[0099] Its preparation method includes the following steps:

[0100] RAFT synthesis route:

[0101]

[0102] Potassium hydroxide (24 mmol, 1.2 eq) was dispersed in 200 mL of tetrahydrofuran at 0–10 °C and stirred for 1 h. Then 5-methoxy-1-H-indazole (20 mmol, 1.0 eq) was added and stirred for another 5 h. Then carbon disulfide (40 mmol, 2.0 eq) was added dropwise. After the addition was complete, the mixture was brought to room temperature and stirred for another 10 h.

[0103] Methyl 2-bromopropionate (24 mmol, 2.2 eq) was slowly added dropwise to the reaction system at room temperature, and the mixture was stirred continuously for 8 h. The mixture was then filtered, and the organic phase was collected. The organic phase was then distilled under reduced pressure, and the product was placed in a distillation column to recover the reactants and remove other impurities. After distillation, a high-purity RAFT reagent was obtained and named RAFT5.

[0104] The yield was 83%. The purity of RAFT5 was determined to be 90.5% by HPLC.

[0105] Example 6

[0106] A RAFT reagent has the following structure:

[0107] .

[0108] Its preparation method includes the following steps:

[0109] RAFT synthesis route:

[0110]

[0111] Potassium hydroxide (24 mmol, 1.2 eq) was dispersed in 200 mL of tetrahydrofuran at 0–10°C and stirred for 1 h. Then 6-methoxy-1-H-indazole (20 mmol, 1.0 eq) was added and stirred for another 4 h. Then carbon disulfide (40 mmol, 2.0 eq) was added dropwise. After the addition was complete, the mixture was brought to room temperature and stirred for another 12 h.

[0112] Methyl 2-bromopropionate (24 mmol, 2.2 eq) was slowly added dropwise to the reaction system at room temperature, and the mixture was stirred continuously for 12 h. The mixture was then filtered, and the organic phase was collected. The organic phase was then distilled under reduced pressure, and the product was placed in a distillation column to recover the reactants and remove other impurities. After distillation, a high-purity RAFT reagent was obtained, named RAFT6.

[0113] The yield was 88%. The purity of RAFT6 was determined to be 94.2% by HPLC.

[0114] Example 7

[0115] A RAFT reagent has the following structure:

[0116] .

[0117] Its preparation method includes the following steps:

[0118] RAFT synthesis route:

[0119]

[0120] Under conditions of 0–10 °C, potassium hydroxide (24 mol, 1.2 eq) was dispersed in 20 L of tetrahydrofuran and stirred continuously for 0.5 h; then 1-H-indazole (20 mol, 1.0 eq) was added and stirred for another 1 h; then carbon disulfide (40 mol, 2.0 eq) was added dropwise. After the addition was complete, the mixture was brought back to room temperature and stirred continuously for 5 h.

[0121] Methyl 2-bromopropionate (24 mol, 2.2 eq) was slowly added dropwise to the reaction system at room temperature, and the mixture was stirred continuously for 10 h. The mixture was then filtered, and the organic phase was collected. The organic phase was distilled under reduced pressure, and the product was placed in a distillation column to recover the reactants and remove other impurities. High-purity RAFT reagent, named RAFT1, was obtained after distillation.

[0122] The yield was 85%. The purity of RAFT1 was determined to be 94% by HPLC.

[0123] Example 8

[0124] A RAFT reagent has the following structure:

[0125] .

[0126] Its preparation method includes the following steps:

[0127] RAFT synthesis route:

[0128]

[0129] Potassium hydroxide (24 mol, 1.2 eq) was dispersed in 20 L of tetrahydrofuran at 0–10 °C and stirred for 2 h. Then 6-methoxy-3-methyl-1-H-indazole (20 mol, 1.0 eq) was added and stirred for 4 h. Then carbon disulfide (40 mol, 2.0 eq) was added dropwise. After the addition was complete, the mixture was brought to room temperature and stirred for 24 h.

[0130] Methyl 2-bromopropionate (24 mol, 2.2 eq) was slowly added dropwise to the reaction system at room temperature, and the mixture was stirred continuously for 24 h. The mixture was then filtered, and the organic phase was collected. The organic phase was distilled under reduced pressure, and the product was placed in a distillation column to recover the reactants and remove other impurities. High-purity RAFT reagent, named RAFT2, was obtained after distillation.

[0131] The yield was 87%. The purity of RAFT2 was determined to be 96% by HPLC.

[0132] Experimental Example 1: Kinetics of RAFT reagent under visible light:

[0133] Kinetic experiments were conducted under visible light at 425 nm to determine the apparent polymerization rates of the different RAFT reagents prepared in Examples 1-6. k p app The model unit is... N,N Dimethylacrylamide (DMA) and methyl acrylate (MA). The monomer and RAFT reagent were prepared into a solution at a molar ratio of 200:1, and an equal volume of DMSO solution was added. The solution was then subjected to light irradiation under anaerobic conditions, and the fluorescence was detected by FTIR at 6200-6000 cm⁻¹. -1 The changes in the absorption peak of the CH bond at C=C were analyzed quantitatively to determine the conversion rate of the monomer.

[0134] The test results are shown in Table 1 and Figures 7-13 As shown.

[0135] Table 1 Polymerization kinetics of different RAFT reagents

[0136]

[0137] Note: The physical meanings of the parameters in Table 1 are as follows:

[0138] (1) k p app (min -1 ): Apparent polymerization rate. k p app The higher the value, the faster the polymerization speed.

[0139] (2) α(%): Monomer conversion rate. The monomer conversion rate varies with the illumination time; the longer the illumination time, the higher the conversion rate.

[0140] (3) M n,Theo (g / mol): Theoretical molecular weight. M n,GPC (g / mol): Measured molecular weight. The closer the theoretical molecular weight is to the measured molecular weight, the better the controllability of the RAFT reagent and the higher the initiation efficiency.

[0141] (4) Ð : Polymer dispersibility. Ð The closer the value is to 1, the narrower the molecular weight distribution of the polymer and the better the controllability.

[0142] (6) Time (min): Illumination time. This data directly reflects production efficiency. The shorter the time, the more suitable it is for mass production.

[0143] Table 1 shows that different RAFT reagent structures significantly affect photopolymerization kinetics, with specific structures (such as RAFT2 and RAFT6-MA) exhibiting excellent performance, confirming the advantage of this invention that "structural design can improve photoresponse speed and production efficiency." RAFT2 responds extremely quickly to DMA monomers. k p app It is 3.7 times faster than RAFT1, demonstrating the significant improvement in photopolymerization rate resulting from structural innovation. RAFT5 exhibits superior efficiency for MA monomers. k p app =0.495 is the highest value in Table 1, indicating that a specific RAFT-monomer combination can further break the rate limit. RAFT exhibits different polymerization rates for different monomers. This is due to the intrinsic polymerization rate of the monomers themselves. The intrinsic polymerization rate (MA) of methyl acrylate is higher than that of... N,N -Dimethylacrylamide (DMA) has a polymerization rate one to two orders of magnitude higher. Therefore, it exhibits a different polymerization rate during polymerization, but its polymerization rate far exceeds that of traditional RAFT reagents (CDTPA). k p app = 0.008 min -1 Furthermore, no obvious induction period was observed during the polymerization process.

[0144] These RAFT reagents all exhibit excellent controllability, with good polymer dispersibility for both acrylate and acrylamide monomers. Ð All are less than 1.2. Among them, RAFT3, 4, and 6 maintain... Ð While achieving a concentration ≤ 1.07 (narrow distribution), RAFT3 also achieves α > 70% (highly efficient conversion), demonstrating its "fast and controllable" characteristics. RAFT3 achieves a DMA conversion rate of 70.5%. Ð = 1.04, further proving that the new structure does not sacrifice controllability. RAFT4 and RAFT6 M n,GPC Deviation from theoretical value <2%, Ð With a value as low as 1.05, it is evident that the polymer chain length distribution is highly uniform, meeting the requirements of high-precision photolithography and 3D printing.

[0145] As shown in Table 1, RAFT2 and RAFT5 reduce the reaction time to 3.5 min and 2.5 min respectively, improving efficiency by 3-4 times, indicating that the present invention can easily achieve mass production.

[0146] Light sources offer excellent control over polymerization reactions. For example... Figures 7-13In Figure A, no obvious aggregation was observed after the light was turned off (OFF), indicating that the light source has good control over it. Aggregation begins when the light is on and stops immediately after the light is turned off.

[0147] 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, characterized in that, The RAFT reagent is selected from: 、 、 , , or .

2. A method for preparing the RAFT reagent according to claim 1, characterized in that, include: At low temperature and in an organic solvent, 1-H-indazole or its derivatives react with an inorganic base and carbon disulfide to give an intermediate. The low temperature is -10 to -10℃; At room temperature, the intermediate reacts with X-R6. After the reaction is complete, the organic phase is filtered and collected. The organic phase is then distilled under reduced pressure and purified to obtain the RAFT reagent. The structure of the 1-H-indazole derivative is as follows: Wherein, R1-R5 are as described in the corresponding compounds of claim 1; Where X is a halogen atom, and R6 is... .

3. The preparation method according to claim 2, characterized in that, The inorganic base includes any one of potassium hydroxide, sodium hydroxide, calcium hydroxide, aluminum hydroxide, potassium carbonate, and potassium phosphate.

4. The preparation method according to claim 2, characterized in that, The molar ratio of the inorganic base, 1-H-indazole or its derivative, carbon disulfide and X-R6 is (1-1.5):(0.9-1.1):(1.9-2.1):(2-2.5).

5. The preparation method according to claim 2, characterized in that, The preparation method includes: Under low temperature conditions, an inorganic base is dispersed in an organic solvent and stirred continuously; then 1-H-indazole or its derivative is added and stirred continuously; then carbon disulfide is added dropwise. After the addition is complete, the mixture is brought back to room temperature and stirred continuously to obtain an intermediate; the low temperature is -10 to 10°C. At room temperature, X-R6 was added dropwise to the reaction system while stirring continuously. The organic phase was then filtered and collected. The organic phase was then distilled under reduced pressure and purified to obtain the RAFT reagent.

6. The application of the RAFT reagent according to claim 1 or the RAFT reagent prepared by the preparation method according to any one of claims 2-5 in photocontrolled RAFT polymerization; The application involves mixing the monomer, solvent, and RAFT reagent, initiating polymerization upon irradiation, and immediately stopping polymerization upon ignition to obtain the polymer.

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