A method for synthesizing a styrene-based photoresist resin

Abstract

This invention discloses a method for synthesizing styrene-based photoresist resin, comprising the following steps: adding styrene and p-tert-butoxystyrene to a DES solvent, ultrasonically dispersing the mixture, and then rapidly adding an initiator under an air atmosphere to obtain a styrene-p-tert-butoxystyrene copolymer, i.e., a styrene-based photoresist resin, via anionic polymerization. The preparation method of this invention is simple and the process is easy to control. Using DES as the polymerization solvent allows the reaction to proceed efficiently under ambient air atmosphere. Furthermore, the hydrogen bond network in DES can form a specific interaction with the oxygen atom in the p-tert-butoxy group, resulting in a significant stabilizing effect on this acid-sensitive protecting group and effectively suppressing the removal of the protecting group and the resulting side reactions during anionic polymerization.

Description

Technical Field

[0001] This invention belongs to the field of photoresist resin technology, and relates to a method for synthesizing styrene-based photoresist resin. Background Technology

[0002] Photoresist is an organic mixture of resins, solvents, and other additives, carefully formulated to precisely transfer minute, nanoscale patterns from a photomask onto a target substrate through a series of sophisticated processes including coating, exposure, baking, and development. The photoresist industry chain is extensive, covering upstream basic chemical raw materials and fine chemicals, midstream photoresist preparation, and downstream PCB manufacturing, display panel production, the semiconductor industry, and various electronic terminal products. As the cornerstone of microfabrication technology in the microelectronics field, photoresist occupies a pivotal position in the field of electronic materials.

[0003] In KrF photoresist, the key component of the film-forming resin is styrene-p-tert-butoxystyrene copolymer (ST-PTBS copolymer). This copolymer, due to the large number of benzene rings in its structure, possesses excellent resistance to dry etching and high transparency at 248 nm wavelength, making it an ideal film-forming resin material for preparing 248 nm photoresist.

[0004] However, in the synthesis of ST-PTBS copolymers, traditional methods often use carbonates, ethers, esters, or siloxy groups as protecting groups for the hydroxyl groups. These methods require complex chemical treatments after polymerization, such as acid catalysis, base catalysis, or hydrogenolysis, reacting at high temperatures (e.g., 60-80°C) for several hours to remove the protecting groups and expose the hydroxyl groups. These methods are not only energy-intensive but also place extremely high demands on the production equipment's resistance to acid and alkali corrosion, significantly increasing production costs and environmental impact. Furthermore, traditional anionic polymerization is extremely sensitive to reaction conditions, typically requiring a strictly anhydrous, oxygen-free, inert atmosphere and low-temperature environment, and relying on organometallic compounds as initiators, making the process complex and costly. More importantly, when monomers containing p-tert-butoxy protecting groups are introduced into the polymerization system, the highly reactive anionic chain ends in traditional organic solvent environments easily induce the desorption of protecting groups or trigger chain transfer side reactions, leading to a wider polymer molecular weight distribution, decreased yield, and difficulty in achieving precise control over the copolymer structure.

[0005] Based on this, developing a simple, environmentally friendly, and cost-controllable method for synthesizing ST-PTBS copolymers has significant practical application value and promotion potential. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention aims to provide a method for synthesizing styrene-based photoresist resin, comprising the following steps: adding styrene and p-tert-butoxystyrene to a DES solvent, ultrasonically dispersing the mixture, and then rapidly adding an initiator under an air atmosphere to obtain a styrene-p-tert-butoxystyrene copolymer, i.e., a styrene-based photoresist resin, through anionic polymerization. The preparation method of this invention is simple and the process is easy to control. Using DES as the polymerization solvent allows the reaction to proceed efficiently under ambient air atmosphere. Furthermore, the hydrogen bond network in DES can form a specific interaction with the oxygen atom in the p-tert-butoxy group, resulting in a significant stabilizing effect on this acid-sensitive protecting group and effectively suppressing the removal of the protecting group and the resulting side reactions during anionic polymerization.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for synthesizing a styrene-based photoresist resin, comprising the following steps in sequence: S1. Mix choline chloride and hydrogen bond donor evenly, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven to dry, and seal and store after drying to obtain DES solvent. S2. Add monomer 1 and monomer 2 to DES solvent, disperse ultrasonically at room temperature, and quickly add initiator in air atmosphere to prepare styrene-p-tert-butoxystyrene copolymer, i.e. styrene photoresist resin, by anionic polymerization. The above reaction route is as follows: , Where m ranges from 20 to 200; and n ranges from 60 to 300.

[0008] As a limitation of the present invention, in step S1, the hydrogen bond donor is one of glycerol, ethylene glycol or urea.

[0009] As another limitation of the present invention, in step S1, the molar ratio of choline chloride to hydrogen bond donor is (1:2) to (2:1).

[0010] As a third limitation of the present invention, in step S1, the drying temperature is 80~90 ℃ and the time is 1.5~2 h.

[0011] As a fourth limitation of the present invention, in step S2, monomer 1 is styrene and monomer 2 is p-tert-butoxystyrene; the molar ratio of styrene to p-tert-butoxystyrene is (10~50):(90~50).

[0012] As a fifth limitation of the present invention, in step S2, the initiator is sec-butyllithium.

[0013] As a sixth limitation of the present invention, in step S2, the molar ratio of the total amount of monomer 1 and monomer 2 to the initiator is 1:(0.025~0.125).

[0014] As a seventh limitation of the present invention, in step S2, the reaction temperature during the anionic polymerization is 20~35 ℃ and the reaction time is 60~90 min.

[0015] As a final limitation of the present invention, the prepared styrene-p-tert-butoxystyrene copolymer has a weight-average molecular weight of 3290~11573 and a PD of 1.303~1.673.

[0016] This invention controls the weight-average molecular weight (MAM) of the styrene-p-tert-butoxystyrene copolymer between 3290 and 11573, and the polydispersity index (PD) between 1.303 and 1.673. This is because: if the MAM is too low, the glass transition temperature (Tg) of the resin decreases, leading to a decrease in the resin's film-forming properties and etching resistance, as well as a decrease in development contrast; if the MAM is too high, the resin has poor solubility, resulting in easy residue and tailing during development, and a significant decrease in photosensitivity. The polydispersity index needs to be controlled within a narrow range, as photoresists are extremely sensitive to the uniformity of molecular weight. Low molecular weight components dissolve quickly, while high molecular weight components dissolve slowly, causing uneven microscopic dissolution rates at the nanoscale, directly leading to increased LER and narrower exposure dose tolerance; large batch-to-batch performance fluctuations cannot meet the requirements of semiconductor mass production.

[0017] The DES in this invention provides a highly stable active center environment for anionic polymerization, which can effectively stabilize active anionic centers, suppress side reactions, and provide a self-passivation effect. Anionic polymerization in DES solvent can achieve rapid initiation, no chain transfer / chain termination, and predictable molecular weight. Compared with traditional anionic polymerization, this system does not require ultra-low temperature (-78°C), has a higher tolerance for trace impurities, and is easy to optimize in post-processing.

[0018] This invention utilizes the copolymerization reaction of p-tert-butoxystyrene and styrene without introducing protecting groups to alter the polymerization ratio. The tert-butoxy group in p-tert-butoxystyrene is stable, not only not interfering with the polymerization process but also maintaining its chemical stability in subsequent processing or applications. By precisely controlling the reaction conditions during polymerization, such as temperature, pressure, catalyst type and dosage, styrene-p-tert-butoxystyrene copolymers meeting specific ratio requirements can be prepared.

[0019] Furthermore, the anionic polymerization of this invention is carried out in a eutectic solvent (DES). DES, as a novel green solvent, possesses characteristics such as low volatility, high solubility, and good thermal and chemical stability. Anionic copolymerization of styrene and p-tert-butoxystyrene in DES allows the polymerization reaction to proceed efficiently under ambient air conditions, freeing it from dependence on anhydrous, oxygen-free, and low-temperature environments. On the other hand, the hydrogen-bonded network in DES can form specific interactions (hydrogen-bonded interactions) with the oxygen atoms in the p-tert-butoxy group, resulting in a significant stabilizing effect on this acid-sensitive protecting group and effectively suppressing the shedding of the protecting group and the resulting side reactions during anionic polymerization. This synergistic effect significantly reduces the polydispersity index (PD) of the copolymer and greatly increases the retention rate of the protecting group, thereby simplifying operating conditions while achieving precise control over the polymer's microstructure.

[0020] The above-mentioned technical solution of the present invention is a whole in which each step is closely related and mutually influential, and together they determine the morphological characteristics and performance of the product.

[0021] The above technical solution has the following advantages or beneficial effects: 1. This invention uses a copolymerization reaction of tert-butoxystyrene and styrene, without the need to introduce protecting groups to change the polymerization rate. The tert-butoxy structure in tert-butoxystyrene is stable, which not only does not interfere with the polymerization process, but also maintains its chemical stability in subsequent processing or applications. 2. Traditional anionic polymerization requires high monomer selectivity, especially when the monomer contains acid-sensitive protecting groups (such as p-tert-butoxy groups). The highly active chain ends are prone to protectant removal or chain transfer side reactions, resulting in a wider molecular weight distribution and a decrease in protectant retention. At the same time, it requires strict anhydrous, oxygen-free, and low-temperature conditions, which results in high operating costs. The present invention uses DES for anionic polymerization without the need for harsh anhydrous, oxygen-free, and low-temperature conditions. It can be effectively controlled under a room temperature air atmosphere to obtain polymers with uniform molecular weight. More importantly, the hydrogen bond network in DES can form a specific interaction with tert-butoxy groups, producing an unexpected stabilizing effect on acid-sensitive protecting groups, effectively inhibiting protectant removal and side reactions, thereby significantly improving the polydispersity index uniformity and protectant retention of the copolymer. 3. The synthesis method of this invention is simple and controllable, avoiding complex protection and deprotection steps, reducing reaction steps and material consumption, thereby reducing process costs; at the same time, since it avoids the use of acid or base catalysis and heating conditions, this method is less corrosive to equipment and is safer and more environmentally friendly.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0023] Figure 1 The 1H NMR spectrum of styrene-p-tert-butoxystyrene prepared in Example 1; Figure 2 The graph shows the results of measuring the weight-average molecular weight of styrene-p-tert-butoxystyrene prepared in Example 1 using gel permeation chromatography. Detailed Implementation

[0024] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified. Example 1

[0026] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and glycerol at a molar ratio of 1:2, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 80 °C for 2 h. After drying, seal and store to obtain DES solvent. S2. In a flask equipped with a thermometer, add 1 mL of DES, 1.0415 g of styrene (0.01 mol), and 1.7625 g of p-tert-butoxystyrene (0.01 mol). Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, rapidly add 1.9230 mL of 1.3 mol / L sec-butyllithium (0.0025 mol) to the flask and react at 20 ℃ for 90 min. If no significant changes in temperature or color are observed, the reaction is complete and quenched with methanol. Transfer the quenched reaction solution to a separatory funnel, add 50 mL of saturated saline solution, and extract three times with dichloromethane. Wash the extracted organic phase three times with water. Add anhydrous sodium sulfate to the obtained solution and concentrate by rotary evaporation. Add the solution dropwise to methanol to precipitate the precipitate. Place the precipitate in a drying oven and dry at 50 ℃ for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0027] The polymer was characterized, and its proton nuclear magnetic resonance spectrum is as follows: Figure 1As shown. The weight-average molecular weight of the prepared polymer, determined by gel permeation chromatography, was 3290, and the polydispersity index was 1.408 (as shown). Figure 2 (As shown). The molar ratio of styrene to p-tert-butoxystyrene in the product is 50:50, which meets the ratio requirements for KrF photoresist resin. Example 2

[0028] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and glycerol at a molar ratio of 1:1, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 90 °C for 1.5 h. After drying, seal and store to obtain DES solvent. S2. Add 1 mL of DES, 1.0415 g of styrene (0.01 mol), and 1.7625 g of p-tert-butoxystyrene (0.01 mol) to a flask equipped with a thermometer. Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, quickly add 1.5385 mL of 1.3 mol / L sec-butyllithium (0.002 mol) to the flask and react at 25 ℃ for 80 min. If there is no significant change in temperature or color, the reaction is complete and quenched with methanol. Transfer the quenched reaction solution to a separatory funnel, add 50 mL of saturated saline solution, and extract three times with dichloromethane. Wash the extracted organic phase three times with water. Add anhydrous sodium sulfate to the obtained solution and concentrate by rotary evaporation. Add the solution dropwise to methanol to precipitate the precipitate. Place the solution in a drying oven and dry at 50 ℃ for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0029] The weight-average molecular weight of the prepared polymer was determined to be 4215 and the polydispersity index was 1.303 by gel permeation chromatography. The molar ratio of styrene to p-tert-butoxystyrene in the product was 50:50, which meets the ratio requirements for KrF photoresist resin. Example 3

[0030] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and glycerol at a molar ratio of 2:1, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 85 °C for 1.8 h. After drying, seal and store to obtain DES solvent. S2. Add 1 mL of DES, 1.0415 g of styrene (0.01 mol), and 1.7625 g of p-tert-butoxystyrene (0.01 mol) to a flask equipped with a thermometer. Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, quickly add 1.1538 mL of 1.3 mol / L sec-butyllithium (0.0015 mol) to the flask and react at 35 ℃ for 60 min. If there is no significant change in temperature or color, the reaction is complete and quenched with methanol. Transfer the quenched reaction solution to a separatory funnel, add 50 mL of saturated saline solution, extract three times with dichloromethane, and then wash the extracted organic phase three times with water. Add anhydrous sodium sulfate to the obtained solution and concentrate it by rotary evaporation. Add the solution dropwise to methanol to precipitate the precipitate, place it in a drying oven, and dry at 50 ℃ for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0031] The weight-average molecular weight of the prepared polymer was determined to be 6712 and the polydispersity index was 1.514 by gel permeation chromatography. The molar ratio of styrene to p-tert-butoxystyrene in the product was 50:50, which meets the ratio requirements for KrF photoresist resin. Example 4

[0032] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and glycerol at a molar ratio of 1:2 until homogeneous, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 90 °C for 1.5 h. After drying, seal and store to obtain DES solvent. S2. Add 1 mL of DES, 1.0415 g of styrene (0.01 mol), and 1.7625 g of p-tert-butoxystyrene (0.01 mol) to a flask equipped with a thermometer. Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, quickly add 0.7692 mL of 1.3 mol / L sec-butyllithium (0.001 mol) to the flask and react at 20 ℃ for 90 min. If there is no significant change in temperature or color, the reaction is complete and quenched with methanol. Transfer the quenched reaction solution to a separatory funnel, add 50 mL of saturated saline solution, extract three times with dichloromethane, and then wash the extracted organic phase three times with water. Add anhydrous sodium sulfate to the obtained solution and concentrate it by rotary evaporation. Add the solution dropwise to methanol to precipitate the precipitate, place it in a drying oven, and dry at 50 ℃ for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0033] The weight-average molecular weight of the prepared polymer was determined to be 9124 and the polydispersity index was 1.573 by gel permeation chromatography. The molar ratio of styrene to p-tert-butoxystyrene in the product was 50:50, which meets the ratio requirements for KrF photoresist resin. Example 5

[0034] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and glycerol at a molar ratio of 1:1 until homogeneous, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 80 °C for 2 h. After drying, seal and store to obtain DES solvent. S2. Add 1 mL of DES, 1.0415 g of styrene (0.01 mol), and 1.7625 g of p-tert-butoxystyrene (0.01 mol) to a flask equipped with a thermometer. Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, quickly add 0.3846 mL of 1.3 mol / L sec-butyllithium (0.0005 mol) to the flask and react at 20 ℃ for 90 min. If there is no obvious change in temperature or color, the reaction is complete. Quench with methanol. The quenched reaction solution was transferred to a separatory funnel, 50 mL of saturated saline was added, and the solution was extracted three times with dichloromethane. The extracted organic phase was then washed three times with water. Anhydrous sodium sulfate was added to the obtained solution, and the solution was concentrated by rotary evaporation. The solution was then added dropwise to methanol to precipitate the precipitate. The precipitate was placed in a drying oven and dried at 50 °C for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0035] The weight-average molecular weight of the prepared polymer was determined to be 11573 and the polydispersity index was 1.512 by gel permeation chromatography. The molar ratio of styrene to p-tert-butoxystyrene in the product was 50:50, which meets the ratio requirements for KrF photoresist resin. Example 6

[0036] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and ethylene glycol at a molar ratio of 2:1, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 90 °C for 1.5 h. After drying, seal and store to obtain DES solvent. S2. Add 1 mL of DES, 0.2083 g of styrene (0.002 mol), and 3.1725 g of p-tert-butoxystyrene (0.018 mol) to a flask equipped with a thermometer. Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, quickly add 0.3846 mL of 1.3 mol / L sec-butyllithium (0.0005 mol) to the flask and react at 20 ℃ for 90 min. If there is no significant change in temperature or color, the reaction is complete and quenched with methanol. Transfer the quenched reaction solution to a separatory funnel, add 50 mL of saturated saline solution, extract three times with dichloromethane, and then wash the extracted organic phase three times with water. Add anhydrous sodium sulfate to the obtained solution and concentrate it by rotary evaporation. Add the solution dropwise to methanol to precipitate the precipitate, place it in a drying oven, and dry at 50 ℃ for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0037] The weight-average molecular weight of the prepared polymer was determined to be 5123 and the polydispersity index was 1.578 by gel permeation chromatography. The molar ratio of styrene to p-tert-butoxystyrene in the product was 10:90, which meets the ratio requirements for KrF photoresist resin. Example 7

[0038] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and ethylene glycol at a molar ratio of 1:2, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 80 °C for 2 h. After drying, seal and store to obtain DES solvent. S2. In a flask equipped with a thermometer, add 1 mL of DES, 0.4166 g of styrene (0.004 mol), and 2.8200 g of p-tert-butoxystyrene (0.016 mmol). Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, rapidly add 0.3846 mL of 1.3 mol / L sec-butyllithium (0.0005 mol) to the flask and react at 20 ℃ for 90 min. If no significant changes in temperature or color are observed, the reaction is complete and quenched with methanol. Transfer the quenched reaction solution to a separatory funnel, add 50 mL of saturated saline solution, and extract three times with dichloromethane. Wash the extracted organic phase three times with water. Add anhydrous sodium sulfate to the obtained solution and concentrate by rotary evaporation. Add the solution dropwise to methanol to precipitate the precipitate. Place the precipitate in a drying oven and dry at 50 ℃ for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0039] The weight-average molecular weight of the prepared polymer was determined to be 6213 and the polydispersity index was 1.673 by gel permeation chromatography. The molar ratio of styrene to p-tert-butoxystyrene in the product was 20:80, which meets the ratio requirements for KrF photoresist resin. Example 8

[0040] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and ethylene glycol at a molar ratio of 1:1, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 90 °C for 1.5 h. After drying, seal and store to obtain DES solvent. S2. Add 1 mL of DES, 0.6249 g of styrene (0.006 mol), and 2.4675 g of p-tert-butoxystyrene (0.014 mol) to a flask equipped with a thermometer. Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, quickly add 0.3846 mL of 1.3 mol / L sec-butyllithium (0.0005 mol) to the flask and react at 20 ℃ for 90 min. If there is no obvious change in temperature or color, the reaction is complete. Quench with methanol. The quenched reaction solution was transferred to a separatory funnel, 50 mL of saturated saline was added, and the solution was extracted three times with dichloromethane. The extracted organic phase was then washed three times with water. Anhydrous sodium sulfate was added to the obtained solution, and the solution was concentrated by rotary evaporation. The solution was then added dropwise to methanol to precipitate the precipitate. The precipitate was placed in a drying oven and dried at 50 °C for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0041] The weight-average molecular weight of the prepared polymer was determined to be 7324 and the polydispersity index was 1.524 by gel permeation chromatography. The molar ratio of styrene to p-tert-butoxystyrene in the product was 30:70, which meets the ratio requirements for KrF photoresist resin. Example 9

[0042] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and urea at a molar ratio of 2:1, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 80 °C for 2 h. After drying, seal and store to obtain DES solvent. S2. Add 1 mL of DES, 0.8332 g of styrene (0.008 mol), and 2.1150 g of p-tert-butoxystyrene (0.012 mol) to a flask equipped with a thermometer. Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, quickly add 0.3846 mL of 1.3 mol / L sec-butyllithium (0.0005 mol) to the flask and react at 20 ℃ for 90 min. If there is no obvious change in temperature or color, the reaction is complete. Quench with methanol. The quenched reaction solution was transferred to a separatory funnel, 50 mL of saturated saline was added, and the solution was extracted three times with dichloromethane. The extracted organic phase was then washed three times with water. Anhydrous sodium sulfate was added to the obtained solution, and the solution was concentrated by rotary evaporation. The solution was then added dropwise to methanol to precipitate the precipitate. The precipitate was placed in a drying oven and dried at 50 °C for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0043] The weight-average molecular weight of the prepared polymer was determined to be 7126 and the polydispersity index was 1.424 by gel permeation chromatography. The molar ratio of styrene to p-tert-butoxystyrene in the product was 40:60, which meets the ratio requirements for KrF photoresist resin. Example 10

[0044] This embodiment prepares a styrene-p-tert-butoxystyrene copolymer, and the preparation process and steps are as follows: S1. Mix choline chloride and urea at a molar ratio of 1:2, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven and dry at 90 °C for 1.5 h. After drying, seal and store to obtain DES solvent. S2. Add 1 mL of DES, 1.0415 g of styrene (0.01 mol), and 1.7625 g of p-tert-butoxystyrene (0.01 mol) to a flask equipped with a thermometer. Sonicate at 40 Hz for 30 min at room temperature and in air atmosphere until dispersion is complete. Then, quickly add 0.3846 mL of 1.3 mol / L sec-butyllithium (0.0005 mol) to the flask and react at 20 ℃ for 90 min. If there is no obvious change in temperature or color, the reaction is complete. Quench with methanol. The quenched reaction solution was transferred to a separatory funnel, 50 mL of saturated saline was added, and the solution was extracted three times with dichloromethane. The extracted organic phase was then washed three times with water. Anhydrous sodium sulfate was added to the obtained solution, and the solution was concentrated by rotary evaporation. The solution was then added dropwise to methanol to precipitate the precipitate. The precipitate was placed in a drying oven and dried at 50 °C for 24 h to obtain the styrene-p-tert-butoxystyrene copolymer.

[0045] The weight-average molecular weight of the prepared polymer was determined to be 8246 and the polydispersity index was 1.412 by gel permeation chromatography. The molar ratio of styrene to p-tert-butoxystyrene in the product was 50:50, which meets the ratio requirements for KrF photoresist resin.

[0046] Comparative Example 1 This comparative example uses the synthesis method described in the literature "Synthesis of well-defined poly(p-alkoxystyrene) by anionic polymerization in the presence of di-n-butylmagnesium" to prepare poly(4-tert-butoxystyrene) as a photoresist resin. The specific method and operation steps are as follows: This synthetic method was conducted under strictly anhydrous and oxygen-free conditions. The monomer 4-tert-butoxystyrene was purified by vacuum distillation after drying with calcium hydride. The polymerization solvent tetrahydrofuran was purified by dehydration using a sodium / benzophenone system and by double vacuum distillation using a sodium / naphthalene system. Pretreated 4-tert-butoxystyrene monomer (21 g, 119 mmol) was added to a 500 mL Schlenk flask, and dissolved oxygen was removed by three cycles of freezing, degassing, and thawing. Then, 70 mL of purified tetrahydrofuran was added, followed by two more freezing and degassing cycles. The flask was placed under argon protection and cooled at -40 °C in an ethanol bath for 30 min. Then, a heptane solution of n-butylmagnesium (n-Bu2Mg) (83.5 mL, 83.5 mmol) was added and stirred for 30 min. Finally, a cyclohexane solution of sec-butyllithium (s-BuLi) (1.97 mL, 2.76 mmol) was added to initiate polymerization, and the system was reacted at -40 °C for 24 h. The polymerization reaction was terminated by quenching with methanol. The resulting magnesium salt precipitate was removed by filtration, and the filtrate was concentrated and then poured into excess methanol to precipitate. The crude product was purified twice by dissolving in tetrahydrofuran and precipitating with methanol, and then dried under vacuum at 40 °C for 24 h to obtain a white solid poly(4-tert-butoxystyrene) with a separation yield of 97% and a molecular weight distribution index (PDI) of 1.06.

[0047] While the synthesis method of this comparative example can obtain narrow-dispersion poly(4-tert-butoxystyrene), it relies on ultra-low temperatures, large amounts of organometallic additives, non-green solvents, and stringent anhydrous and oxygen-free operations, resulting in a complex process, high cost, and difficulty in scale-up. This invention utilizes anionic polymerization in DES, achieving equivalent or even better narrow-dispersion control under mild conditions, without additives, and with green solvents. Furthermore, the process is simpler, lower in cost, and more environmentally friendly, significantly superior to the comparative example.

[0048] Comparative Example 2 This comparative example uses the synthesis method described in the literature "Development of Sub-5 nm Patterning by Directed Self-Assembly using Multiblock Copolymers." to prepare styrene-4-hydroxystyrene copolymer as a photoresist resin. The specific method and operation steps are as follows: Styrene and 4-tert-butoxystyrene monomers were purified by drying with sodium benzoate. The polymerization solvent, tetrahydrofuran, was purified by vacuum distillation in the presence of 1,1-diphenylhexyllithium. Using sec-butyllithium (s-BuLi) as an initiator, living anionic polymerization was carried out at -78 °C under high vacuum or argon protection via a multi-step sequential feeding method: first, styrene polymerization was initiated to form living polystyrene segments, followed by the addition of 4-tert-butoxystyrene to continue polymerization and form a block copolymer precursor. After polymerization, the reaction was terminated with methanol, and the styrene-b-4-tert-butoxystyrene copolymer was precipitated in excess methanol and freeze-dried. Then, the styrene-b-4-tert-butoxystyrene copolymer was hydrolyzed in 1,4-dioxane with hydrochloric acid to convert the poly-4-tert-butoxystyrene blocks into poly(4-hydroxystyrene), yielding the target styrene-4-hydroxystyrene diblock copolymer. The degree of hydrolysis was determined by... 1 H NMR confirmed that the molecular weight (Mw) of the obtained diblock copolymer was greater than 95%, and the molecular weight distribution (Mw / Mn) was 27 kg / mol.

[0049] While this comparative example achieves a block copolymer with an extremely narrow dispersion, it relies on ultra-low temperature (-78°C), strictly anhydrous and oxygen-free operation, flammable and explosive THF solvents, carcinogenic deprotecting solvents (1,4-dioxane), and expensive high-vacuum amplification equipment. The process is complex, costly, and environmentally unfriendly. This invention utilizes anionic polymerization in DES, achieving narrow dispersion control that meets photoresist requirements near room temperature, without special equipment, and using environmentally friendly solvents. Its overall advantages are significantly superior to this comparative example.

[0050] Comparative Example 3 This comparative study prepared a styrene-p-tert-butoxystyrene copolymer. The preparation process was similar to that in Example 1, except that in step S2, 1.0415 g of styrene and 1.7625 g of p-tert-butoxystyrene were replaced with 1.8747 g of styrene and 0.3525 g of p-tert-butoxystyrene.

[0051] In this comparative example, the styrene to p-tert-butoxystyrene feed ratio was drastically adjusted from 1:1 to 9:1, resulting in a severe excess of styrene. This led to the preferential consumption of p-tert-butoxystyrene during polymerization, causing a continuous increase in the proportion of styrene in the remaining monomers. Ultimately, this resulted in the formation of almost pure polystyrene homopolymer. Simultaneously, the reduced total monomer mass led to an increased relative concentration of the initiator and a lower molecular weight. The final product was a mixture of copolymer and polystyrene homopolymer with a very wide compositional distribution. This loss of copolymer homogeneity resulted in a significant decrease in mechanical properties and thermal stability, leading to poor polymer quality.

[0052] Comparative Example 4 This comparative study prepared a styrene-p-tert-butoxystyrene copolymer. The preparation process was similar to that in Example 1, except that in step S2, 1.9230 mL of 1.3 mol / L sec-butyllithium was replaced with 2.6923 mL.

[0053] In this comparative preparation, the amount of sec-butyllithium initiator was increased from 1.9230 mL to 2.6923 mL. In anionic polymerization systems, the number-average molecular weight of the polymer is inversely proportional to the initiator concentration; therefore, excessive initiator will lead to a significant decrease in polymer molecular weight. Copolymers with excessively low molecular weight have poor mechanical properties (such as low strength and brittleness), failing to meet application requirements, which is the main reason for poor polymer quality.

[0054] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. 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 claims of the present invention.

Claims

1. A method for synthesizing a styrene-based photoresist resin, characterized by, Follow these steps in sequence: S1. Mix choline chloride and hydrogen bond donor evenly, place in a sealed flask, stir at 80 °C for 2 h, then place in a drying oven to dry, and seal and store after drying to obtain DES solvent. S2. Add monomer 1 and monomer 2 to DES solvent, disperse ultrasonically at room temperature, and quickly add initiator in air atmosphere to prepare styrene-p-tert-butoxystyrene copolymer, i.e. styrene-based photoresist resin, by anionic polymerization.

2. The method for synthesizing a styrene-based photoresist resin according to claim 1, characterized in that, In step S1, the hydrogen bond donor is one of glycerol, ethylene glycol, or urea.

3. The method for synthesizing a styrene-based photoresist resin according to claim 1, characterized in that, In step S1, the molar ratio of choline chloride to hydrogen bond donor is (1:2) to (2:1).

4. The method for synthesizing a styrene-based photoresist resin according to claim 1, characterized in that, In step S1, the drying temperature is 80~90 ℃ and the time is 1.5~2 h.

5. The method for synthesizing a styrene-based photoresist resin according to claim 1, characterized in that, In step S2, monomer 1 is styrene and monomer 2 is p-tert-butoxystyrene; the molar ratio of styrene to p-tert-butoxystyrene is (10~50):(90~50).

6. The method for synthesizing a styrene-based photoresist resin according to claim 1, characterized in that, In step S2, the initiator is sec-butyllithium.

7. The method for synthesizing a styrene-based photoresist resin according to claim 1, characterized in that, In step S2, the molar ratio of the total amount of monomers 1 and 2 to the initiator is 1:(0.025~0.125).

8. The method for synthesizing a styrene-based photoresist resin according to claim 1, characterized in that, In step S2, the reaction temperature during anionic polymerization is 20~35 ℃ and the reaction time is 60~90 min.

9. A method for synthesizing a styrene-based photoresist resin according to any one of claims 1 to 8, characterized in that, The prepared styrene-p-tert-butoxystyrene copolymer had a weight-average molecular weight of 3290~11573 and a PD of 1.303~1.673.

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