A method for controlled radical polymerization initiated by lithium chloride-regulated solvated electrons

Abstract

The application discloses a kind of lithium chloride regulated solvation electron induced controllable free radical polymerization method, this method uses higher polymerization temperature while adding lithium chloride to carry out regulation, can prepare molecular weight precision controllable, narrow molecular weight distribution polymer, and structure accurate block, star and various topological structure polymers of etc., realize polymer in LED organic polymer fluorescent material, drug design, nanometer material and functional polymer material more extensive use in the field.The lithium chloride regulated solvation electron induced controllable free radical polymerization method of the application, it includes the following steps: in the solvation electron initiation olefin monomer polymerization system of alkali metal lithium / hexamethylphosphorus triamide, lithium chloride is added, and controllable free radical polymerization is carried out, to obtain narrow molecular weight distribution polymer;Wherein, the concentration of lithium chloride in polymerization solution during polymerization is 0.3-0.6mol / L, and the polymerization temperature is 50-60 DEG C.

Description

Technical Field

[0001] This invention relates to a controlled free radical polymerization method, and more specifically to a controlled free radical polymerization method initiated by lithium chloride-controlled solvated electrons. Background Technology

[0002] In recent years, the research and application of controlled radical polymerization have received widespread attention. Controlled radical polymerization products exhibit controllable molecular weight and narrow molecular weight distribution, enabling the preparation of polymers with various topologies such as block and star structures, thus facilitating polymer structure design and product performance improvement. Current controlled radical polymerization methods are mostly based on the "reversible dynamic equilibrium of active / dormant species" mechanism. Common control schemes include nitroxide-stabilized radical polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), and iodine transfer radical polymerization (ITRP). However, due to the limitations of this "reversible dynamic equilibrium of active / dormant species" control mechanism, the concentration of chain-growing radicals is relatively low, resulting in a lower rate of controlled radical polymerization compared to conventional radical polymerization, which is detrimental to industrial applications.

[0003] Dissolving alkali metals in polar solvents such as hexamethylphosphoric triamine can generate solvated electrons. These solvated electrons have a strong electron transfer capability and are commonly used as reducing agents in organic chemistry. When these solvated electrons come into contact with alkene monomers, they can transfer electrons to the monomers, activating and initiating the polymerization of the alkene monomers. In the prior art, a solvated electron solution of sodium alkali metal and lithium alkali metal hexamethylphosphoric triamine can be used to initiate controlled radical polymerization of olefin monomers near room temperature. The polymerization kinetics ln([M]0 / [M]) increases linearly with polymerization time, and the molecular weight of the polymer product also increases linearly with conversion rate (Huang et al., A controlled radical polymerization method initiated by solvated electrons, CN202211256950.1; Xun Li, Zhaoyan Pan, Yichen Xia, Jiayu Rui, Meng Zhu, He Ren, and Jian Huang, Controlled Radical Polymerization Initiated by Solvated Electrons, Macromolecular Rapid Communications, 2023, 44(22), 202300416). The active species in the polymerization is a negatively charged free radical. Due to the coulombic repulsion between negatively charged free radicals, the free radical is not easily bimolecularly terminated and can maintain "activity" indefinitely. Therefore, the polymerization exhibits the properties of controlled radical polymerization. The regulatory mechanism of this polymerization differs from the aforementioned "reversible dynamic equilibrium of active / dormant species," representing a novel type of controlled radical polymerization. However, due to the low reactivity of this "negatively charged radical," the growth rate constant k... p Approximately 10 -3 L·mol·s -1 Therefore, the rate of solvated electron-initiated polymerization is not high. Compared to sodium alkali metal, lithium alkali metal is more soluble in hexamethylphosphoric triamine, achieving a free radical concentration ten times higher than that of the sodium alkali metal initiation system. Thus, the polymerization rate of the lithium alkali metal initiation system is significantly faster than that of the sodium alkali metal initiation system, but it is still insufficient compared to the rate of ordinary free radical polymerization. Although the rate of controlled free radical polymerization initiated by the lithium alkali metal system is improved, the molecular weight distribution of its polymer products is wider (>1.5), which is detrimental to the structural control of the polymer products and the industrial application of the polymerization method.

[0004] Lithium chloride is a strong Lewis acid, and its lithium ions (Li) +Lithium chloride (LCC) has a small ionic radius and high charge density, making it prone to recombination and coordination with electron-rich groups such as anions and ether oxygen bonds. In anionic initiation, LCC can combine with Lewis basic alkyl lithium initiators to form complexes, altering the initiator's properties and affecting the structural properties of the polymer, such as molecular weight distribution. It has been reported that when lithium chloride is added to a solution of the anionic initiator methyl α-lithium isobutyrate (MIBLi), the two can rapidly combine through Lewis acid-base interactions to form LiCl-MIBLi complexes in a 1:1 to 3:1 ratio. These complexes are in dynamic equilibrium, and certain LiCl-MIBLi complexes can effectively suppress side reactions in the anionic polymerization of methyl methacrylate, achieving its living polymerization and yielding polymers with molecular weight distribution values ​​close to 1 (JSWang, R. Warin, R). and Ph. Teyssié, Anionic Polymerization of Acrylic Monomers. 11. NMRI Investigation of the Mixed Complexation of Methylα-Lithioisobutyrate and Lithium Chloride, Macromolecules, 1993, 26, 6776-6781). For the solvated electron-initiated polymerization system of alkali metal lithium / hexamethylphosphoric triamine, the propagating species are negatively charged free radicals with electron-rich properties. Introducing lithium chloride into this polymerization system is expected to allow the negatively charged free radicals to recombine with lithium chloride through Lewis acid-base interactions, thereby regulating the structure of the free radical propagating ion pair and further suppressing bimolecular termination of the free radicals, resulting in polymer products with a narrower molecular weight distribution.

[0005] In existing technologies, considering the temperature tolerance of the negatively charged free radical propagating species and electron transfer reactions in solvated electron-initiated polymerization, polymerization is carried out near room temperature. At this relatively low polymerization temperature, the polymerization exhibits the properties of controlled radical polymerization. Based on the advantage of the relatively fast growth rate of alkali metal lithium / hexamethylphosphoric triamine solvated electron-initiated controlled radical polymerization, increasing the polymerization temperature can further improve the polymerization rate while maintaining its controlled radical polymerization properties. Furthermore, by adjusting the ion-pair structure of the polymeric free radical active species using Lewis acidic lithium chloride, the molecular weight distribution of the polymer product can be further reduced. This leads to the development of a solvated electron-initiated controlled radical polymerization method suitable for industrial applications, producing polymers with precisely controllable molecular weights and narrow molecular weight distributions, thus addressing the problems and shortcomings of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to address the problems and shortcomings of existing technologies, such as high molecular weight distribution (>1.5) and insufficient polymerization rate, by providing a controlled free radical polymerization method initiated by lithium chloride-regulated solvated electrons. This controlled free radical polymerization method uses the solvated electrons of alkali metal lithium / hexamethylphosphoric triamine as the initiation system, with negatively charged free radicals possessing ion-pair structures as the growing active species. Adding lithium chloride to the polymerization system allows for the electrostatic adsorption of excess Li around the negatively charged free radicals through the complex interaction between the negatively charged free radicals and the Lewis acidic lithium chloride. + Cations, forming Li + Ion clusters. Li + Electrostatic repulsion and steric hindrance between ion clusters inhibited the bimolecular termination of free radicals, reducing the molecular weight distribution (D) of the polymer from greater than 1.5 in existing technologies to 1.18–1.29. Increasing the polymerization temperature from near room temperature used in existing technologies to 50–60°C increased the polymerization rate by approximately two times, reaching the level of ordinary free radical polymerization. This invention employs a higher polymerization temperature (50–60°C) with the addition of lithium chloride for regulation; solvated electron-initiated polymerization maintains the properties of controllable free radical polymerization, providing a controllable free radical polymerization method more suitable for industrial applications. This polymerization method can prepare polymers with precisely controllable molecular weights and narrow molecular weight distributions, as well as polymers with accurate block, star, and other topological structures, enabling wider applications of polymers in LED organic polymer fluorescent materials, drug design, nanomaterials, and functional polymer materials.

[0007] This invention is achieved through the following technical solution:

[0008] The present invention discloses a lithium chloride-controlled solvated electron-initiated controlled free radical polymerization method, which includes the following steps: adding lithium chloride to a solvated electron-initiated polymerization system of alkali metal lithium / hexamethylphosphoric triamine to carry out controlled free radical polymerization to obtain a polymer with a narrow molecular weight distribution; wherein, the concentration of lithium chloride in the polymerization solution is 0.3-0.6 mol / L and the polymerization temperature is 50-60℃.

[0009] The controlled free radical polymerization method initiated by lithium chloride-controlled solvated electrons as described above in this invention further includes the following steps: first, preparing a solvated electron solution of alkali metal lithium / hexamethylphosphoric triamine; then, adding an alkene monomer to complete chain initiation; and finally, adding lithium chloride to the polymerization system to carry out controlled free radical polymerization.

[0010] A further technical solution of the controlled radical polymerization method initiated by lithium chloride-regulated solvation electrons described above in this invention includes the following steps:

[0011] S1. Dry hexamethylphosphoric triamine thoroughly, then distill it under reduced pressure for later use;

[0012] S2. Under an argon atmosphere, alkali metal lithium slices are added to hexamethylphosphoric triamine solvent treated in step S1 to prepare a blue solvated electron solution, and then the undissolved solid alkali metal lithium slices are removed.

[0013] S3. Add the alkene monomer to the solvated electron solution of step S2 to bring the solvated electron solution into contact with the alkene monomer and complete the chain initiation. The reaction process requires argon protection.

[0014] S4. Add the hexamethylphosphoric triamine solution of lithium chloride to the initiation polymerization solution of step S3 to carry out subsequent controlled free radical polymerization.

[0015] A further technical solution of the above-described lithium chloride-controlled solvated electron-initiated controlled free radical polymerization method of the present invention is that the solvated electron solution, based on 20 mL of hexamethylphosphoric triamine, contains 0.03–0.1 g of alkali metal lithium. A further technical solution is that during the preparation of the solvated electron solution, the contact time between the alkali metal lithium sheet and hexamethylphosphoric triamine is 20–30 minutes, and the preparation temperature is 7.5–12°C. Within the above-described conditions for preparing the solvated electron solution, the concentration of solvated electrons is moderate, and significant spin-pairing or ion-pairing has not yet occurred, thus initiating polymerization that exhibits the properties of controlled free radical polymerization. If the amount of alkali metal lithium is too large or the contact time between the lithium sheet and hexamethylphosphoric triamine is too long, a high concentration of solvated electrons will be generated, making it easier for electrons to undergo ion-pairing or electron-pairing, and the polymerization will no longer exhibit the properties of controlled free radical polymerization. If the amount of alkali metal lithium used is too small or the contact time between the lithium sheet and hexamethylphosphoric triamine is too short, the concentration of solvated electrons generated will be too low, making it difficult for the solvated electrons to initiate monomer polymerization. The preparation temperature of solvated electrons must be controlled to be higher than the melting point of hexamethylphosphoric triamine (7.2℃) but not too high, otherwise the solvated electron solution will lose stability, leading to initiation failure. After preparing the blue solvated electron solution, the undissolved solid alkali metal lithium sheet must be removed from the solvated electron solution; otherwise, when the solvated electron solution comes into contact with alkene monomers subsequently, the residual solid lithium metal may initiate anionic polymerization of the alkene monomers.

[0016] The controlled free radical polymerization method initiated by lithium chloride-regulated solvated electrons described above in this invention can be further further described in that the olefin monomer is methyl methacrylate, methyl acrylate, acrylic acid, styrene, or acrylonitrile.

[0017] A further technical solution of the above-described lithium chloride-controlled solvated electron-initiated controlled radical polymerization method of the present invention can be further described as follows: in step S3, the contact time between the solvated electron solution and the olefin monomer is 3-5 minutes. After 3-5 minutes, a lithium chloride hexamethylphosphoric triamine solution is added to the polymerization solution in step S3, so that the concentration of lithium chloride in the polymerization solution reaches 0.3-0.6 mol / L. After the solvated electron solution contacts the olefin monomer for 3-5 minutes, chain initiation can be completed and negatively charged free radical propagators can be formed. Only then can the added lithium chloride interact with the propagators, achieving the purpose of controlling the solvated electron-initiated controlled radical polymerization and obtaining a polymer with a narrow molecular weight distribution. The reasonable range of lithium chloride concentration in the polymerization solution is 0.3-0.6 mol / L. Within this concentration range, excess Li + Cations are electrostatically adsorbed around negatively charged free radicals, forming Li. + The ion clusters inhibit the bimolecular termination of free radicals, thereby reducing the molecular weight distribution. At excessively low lithium chloride concentrations, the effect is not significant or it loses its regulatory function.

[0018] A further technical solution of the lithium chloride-controlled solvated electron-initiated controlled radical polymerization method of the present invention can be that the subsequent controlled radical polymerization described in step S4 is carried out at a polymerization temperature of 50-60°C. This polymerization temperature is higher than the polymerization temperature near room temperature used in the prior art. At this higher polymerization temperature, solvated electron-initiated polymerization can still maintain the properties of controlled radical polymerization, and the polymerization rate is increased to the level of ordinary radical polymerization rate, making solvated electron-initiated controlled polymerization more suitable for industrial applications.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] The present invention discloses a lithium chloride-controlled solvated electron-initiated controlled radical polymerization method. This method utilizes the solvated electrons of alkali metal lithium / hexamethylphosphoric triamine to initiate polymerization. The propagating species are negatively charged free radicals with ion-pair structures. Due to the repulsion of like charges, the free radicals are not easily terminated, thus endowing the solvated electron-initiated polymerization with controlled polymerization properties. Based on this, the present invention uses Lewis acidic lithium chloride to regulate and optimize the polymerization initiated by alkali metal lithium / hexamethylphosphoric triamine. + Due to its small ionic radius and high charge density, it readily recombines with Lewis basic negatively charged free radicals, electrostatically adsorbing excess Li around the negatively charged free radicals. + Cations, forming Li + Ion clusters cause the growing free radical to change from being negatively charged to appearing positively charged. Li +The electrostatic repulsion and steric hindrance effects of the ion clusters enhanced the inhibition of free radical bimolecular termination, reducing the molecular weight distribution (D) of the polymer from over 1.5 in the prior art to 1.18–1.29 in the polymer of this invention. The transformation of the aforementioned growing free radicals from being negatively charged to appearing positively charged after the addition of lithium chloride can be confirmed by changes in the solution electric field effect. In a high-voltage DC electric field environment, without lithium chloride, the polymer is biased towards the anode side, indicating that the growing species are negatively charged; after the addition of lithium chloride, the polymer is biased towards the cathode side, indicating that the negatively charged free radicals electrostatically adsorbed excess Li. + Cations, forming Li + Ion clusters, which make the growing species appear positively charged.

[0021] In existing technologies, considering the temperature tolerance of electron transfer reactions in the growth of negatively charged free radicals and chain growth, alkali metal lithium / hexamethylphosphoric triamine-initiated polymerization uses polymerization temperatures near room temperature. At this relatively low polymerization temperature, the polymerization exhibits the properties of controlled radical polymerization. Since the activation energy of the chain growth reaction in solvated electron-initiated polymerization is positive (approximately 20 kJ / mol), the higher the polymerization temperature, the greater the polymerization rate should be. This invention increases the polymerization temperature to 50–60 °C and finds that solvated electron-initiated polymerization can increase the polymerization rate by about 2 times compared to existing technologies while maintaining the properties of controlled radical polymerization, reaching the level of ordinary free radical polymerization rates. Furthermore, the conductivity of the solvated electron-initiated polymerization solution increases with increasing temperature, meaning that higher polymerization temperatures can promote the dissociation of active ion pairs. For dissociated, loose ion pairs, the charge repulsion between negatively charged free radicals is enhanced, and the bimolecular termination of free radicals is suppressed, which is beneficial for reducing the molecular weight distribution. Therefore, increasing the polymerization temperature can accelerate polymerization while reducing the molecular weight distribution of the polymer product.

[0022] This invention utilizes lithium chloride to regulate polymerization at a relatively high temperature (50-60°C). Solvated electron-initiated polymerization maintains the properties of controlled free radical polymerization and yields polymers with narrow molecular weight distributions. The polymerization rate reaches the level of ordinary free radical polymerization, providing a more suitable controlled free radical polymerization method for industrial applications. Specifically: (1) This invention uses lithium chloride to regulate polymerization, strengthening the inhibition of bimolecular termination of free radical propagators and reducing the molecular weight distribution of the polymer product; (2) This invention uses a higher polymerization temperature, which can further reduce the molecular weight distribution of the polymer product while increasing the polymerization rate; (3) Through the dual regulation of lithium chloride addition and increased polymerization temperature, the molecular weight distribution of solvated electron-initiated polymerization is reduced from over 1.5 in the prior art to 1.18-1.29, and the polymerization rate is about twice that of the prior art, reaching the level of ordinary free radical polymerization, providing a more suitable controlled free radical polymerization method for industrial applications; (4) Through… With the addition of lithium chloride and the increase of polymerization temperature, the solvated electron-initiated polymerization can still maintain the properties of controllable free radical polymerization. The polymerization kinetics ln([M]0 / [M]) increases linearly with polymerization time, and the molecular weight and conversion rate also show a linear relationship. (5) The lithium chloride-controlled solvated electron-initiated controllable free radical polymerization method of the present invention has relatively simple and mild reaction conditions and is easy to implement. (6) The applied polymerization can prepare polymers with precise controllable molecular weight and narrow molecular weight distribution, as well as polymers with accurate block, star and other topological structures, so as to realize the wider application of polymers in LED organic polymer fluorescent materials, drug design, nanomaterials and functional polymer materials. Detailed Implementation

[0023] The basic steps of the controlled radical polymerization method initiated by lithium chloride-regulated solvated electrons in the examples are as follows:

[0024] S1. Dry hexamethylphosphoric triamine thoroughly, then distill it under reduced pressure for later use;

[0025] S2. Under an argon atmosphere, alkali metal lithium slices are added to hexamethylphosphoric triamine solvent treated in step S1 to prepare a blue solvated electron solution, and then the undissolved solid alkali metal lithium slices are removed.

[0026] S3. Add the alkene monomer to the solvated electron solution of step S2 to bring the solvated electron solution into contact with the alkene monomer and complete the chain initiation. The reaction process requires argon protection.

[0027] S4. Add the hexamethylphosphoric triamine solution of lithium chloride to the initiation polymerization solution of step S3 to carry out subsequent controlled free radical polymerization.

[0028] Example 1

[0029] 20 mL of distilled and purified hexamethylphosphoric triamine was kept at a constant temperature of 10 °C under argon atmosphere, and then 0.03 g of lithium flakes was added and kept at this temperature for 30 minutes to prepare a blue solvated electron solution. After removing the undissolved solid alkali metal lithium, 10 mL of methyl methacrylate was added and mixed thoroughly. Polymerization was initiated at 50 °C for 3 minutes. Subsequently, 10 mL of hexamethylphosphoric triamine solution containing lithium chloride was added to the polymerization solution to achieve a lithium chloride concentration of 0.45 mol / L, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with a molecular weight distribution of 1.22–1.28, as shown in Table 1. The polymerization rate reached 5.3 × 10⁻⁶. -5 mol·L -1 ·s -1 The rate is comparable to that of ordinary free radical polymerization.

[0030] Table 1. Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate.

[0031] 4 0.387 32.1 36050 1.28 8 0.651 47.8 58140 1.24 12 1.190 69.6 82000 1.22 16 1.548 78.7 96320 1.25 24 2.305 90.0 110300 1.22

[0032] Example 2

[0033] 20 mL of distilled and purified hexamethylphosphoric triamine was kept at a constant temperature of 10 °C under argon atmosphere, and then 0.03 g of lithium flakes was added and kept at this temperature for 30 minutes to prepare a blue solvated electron solution. After removing the undissolved solid alkali metal lithium, 10 mL of methyl methacrylate was added and mixed thoroughly. Polymerization was initiated at 60 °C for 3 minutes. Subsequently, 10 mL of hexamethylphosphoric triamine solution containing lithium chloride was added to the polymerization solution to achieve a lithium chloride concentration of 0.45 mol / L, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with a molecular weight distribution of 1.18–1.24, as shown in Table 2. The polymerization rate reached 6.2 × 10⁻⁶. -5 mol·L -1 ·s -1 The rate is comparable to that of ordinary free radical polymerization.

[0034] Table 2 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0035] 4 0.479 38.1 39480 1.24 8 0.915 59.9 67500 1.22 12 1.552 78.8 85230 1.24 16 1.864 84.5 93130 1.18 24 2.922 94.6 106750 1.18

[0036] Example 3

[0037] 20 mL of distilled and purified hexamethylphosphoric triamine was heated at 7.5 °C under argon atmosphere, and then 0.06 g of lithium flakes was added and kept at this temperature for 25 minutes to prepare a blue solvated electron solution. After removing the undissolved solid alkali metal lithium, 10 mL of methyl acrylate was added and mixed thoroughly. Polymerization was initiated at 55 °C for 3 minutes. Subsequently, 10 mL of hexamethylphosphoric triamine solution containing lithium chloride was added to the polymerization solution to achieve a lithium chloride concentration of 0.3 mol / L, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with a molecular weight distribution of 1.20–1.27, as shown in Table 3. The polymerization rate reached 7.9 × 10⁻⁶. -5 mol·L -1 ·s -1 The rate is comparable to that of ordinary free radical polymerization.

[0038] Table 3 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl acrylate

[0039] 4 0.657 48.2 42160 1.27 8 1.425 75.9 69390 1.23 12 1.922 85.4 78210 1.24 16 2.712 93.4 85180 1.20

[0040] Example 4

[0041] 20 mL of distilled and purified hexamethylphosphoric triamine was kept at a constant temperature of 12 °C under argon atmosphere, and then 0.03 g of lithium sheet was added and kept at this temperature for 20 minutes to prepare a blue solvated electron solution. After removing the undissolved solid alkali metal lithium, 10 mL of acrylonitrile was added and mixed thoroughly, and polymerization was initiated at 50 °C for 5 minutes. Subsequently, 10 mL of hexamethylphosphoric triamine solution containing lithium chloride was added to the polymerization solution to achieve a lithium chloride concentration of 0.6 mol / L, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with a molecular weight distribution of 1.24–1.29, as shown in Table 4. The polymerization rate reached 2.9 × 10⁻⁶. -4 mol·L -1 ·s -1 The rate is comparable to that of ordinary free radical polymerization.

[0042] Table 4 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polyacrylonitrile

[0043] 1 0.574 43.7 61250 1.29 2 1.246 71.2 98160 1.27 3 1.682 81.4 112380 1.25 4 2.304 90.0 127120 1.26 5 2.815 94.0 134340 1.24

[0044] Example 5

[0045] 20 mL of distilled and purified hexamethylphosphoric triamine was kept at a constant temperature of 10 °C under argon atmosphere, and then 0.1 g of lithium flakes was added and kept at this temperature for 30 minutes to prepare a blue solvated electron solution. After removing the undissolved solid alkali metal lithium, 10 mL of styrene was added and mixed thoroughly. Polymerization was initiated at 60 °C for 4 minutes. Subsequently, 10 mL of hexamethylphosphoric triamine solution containing lithium chloride was added to the polymerization solution to achieve a lithium chloride concentration of 0.5 mol / L, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with a molecular weight distribution of 1.18–1.25, as shown in Table 5. The polymerization rate reached 6.3 × 10⁻⁶. -5 mol·L -1 ·s -1 The rate is comparable to that of ordinary free radical polymerization.

[0046] Table 5 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polystyrene

[0047] 4 0.487 38.6 21630 1.24 8 0.994 63.0 38820 1.25 12 1.412 75.6 45940 1.21 16 1.988 86.3 53440 1.19 24 2.892 94.5 57160 1.18

[0048] Example 6

[0049] 20 mL of distilled and purified hexamethylphosphoric triamine was heated at 7.5 °C under argon atmosphere, and then 0.1 g of lithium flakes was added and kept at this temperature for 30 minutes to prepare a blue solvated electron solution. After removing undissolved solid alkali metal lithium, 10 mL of acrylic acid was added and mixed thoroughly. Polymerization was initiated at 60 °C for 4 minutes. Subsequently, 10 mL of hexamethylphosphoric triamine solution containing lithium chloride was added to the polymerization solution to achieve a lithium chloride concentration of 0.6 mol / L, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with a molecular weight distribution of 1.20–1.27, as shown in Table 6. The polymerization rate reached 5.0 × 10⁻⁶. -5 mol·L -1 ·s -1 The rate is comparable to that of ordinary free radical polymerization.

[0050] Table 6 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polyacrylic acid

[0051] 4 0.364 30.5 19020 1.27 8 0.712 50.9 35520 1.27 12 1.182 69.3 44510 1.21 16 1.526 78.3 52910 1.22 24 2.124 88.0 59850 1.20

[0052] Comparative Example 1

[0053] 20 mL of distilled and purified hexamethylphosphoric triamine was kept at a constant temperature of 10 °C under argon atmosphere, and then 0.03 g of lithium flakes was added and kept at this temperature for 30 minutes to prepare a blue solvated electron solution. After removing the undissolved solid alkali metal lithium, 10 mL of methyl methacrylate was added and mixed thoroughly, and polymerization was initiated at 50 °C for 3 minutes. Subsequently, 10 mL of lithium chloride-free hexamethylphosphoric triamine was added to the polymerization solution, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with the molecular weight distribution broadening to 1.35–1.51. The results are shown in Table 7. The polymerization rate reached 5.1 × 10⁻⁶. -5 mol·L -1 ·s -1 The rate is comparable to that of ordinary free radical polymerization.

[0054] Table 7 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0055] 4 0.371 31.0 34540 1.43 8 0.692 49.9 58150 1.51 12 1.210 70.2 81260 1.42 16 1.565 79.1 97320 1.46 24 2.276 89.7 108330 1.35

[0056] Comparative Example 2

[0057] 20 mL of distilled and purified hexamethylphosphoric triamine was kept at a constant temperature of 10 °C under argon atmosphere, and then 0.03 g of lithium flakes was added and kept at this temperature for 30 minutes to prepare a blue solvated electron solution. After removing the undissolved solid alkali metal lithium, 10 mL of methyl methacrylate was added and mixed thoroughly. Polymerization was initiated at 50 °C for 3 minutes. Subsequently, 10 mL of hexamethylphosphoric triamine solution containing lithium chloride was added to the polymerization solution to achieve a lithium chloride concentration of 0.15 mol / L, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with the molecular weight distribution broadening to 1.32–1.38. The results are shown in Table 8. The polymerization rate reached 5.1 × 10⁻⁶. -5 mol·L -1 ·s -1 The rate is comparable to that of ordinary free radical polymerization.

[0058] Table 8 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0059] 4 0.377 32.1 35180 1.38 8 0.671 48.9 59140 1.34 12 1.205 70.0 81650 1.37 16 1.506 77.8 97320 1.32 24 2.234 89.3 115350 1.33

[0060] Comparative Example 3

[0061] 20 mL of distilled and purified hexamethylphosphoric triamine was kept at a constant temperature of 10 °C under argon atmosphere, and then 0.03 g of lithium flakes was added and kept at this temperature for 30 minutes to prepare a blue solvated electron solution. After removing the undissolved solid alkali metal lithium, 10 mL of methyl methacrylate was added and mixed thoroughly. Polymerization was initiated at 30 °C for 3 minutes. Subsequently, 10 mL of lithium chloride-free hexamethylphosphoric triamine was added to the polymerization solution, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with the molecular weight distribution broadening to 1.62–1.73. The results are shown in Table 9. The polymerization rate was 2.4 × 10⁻⁶. -5 mol·L -1 ·s -1 The polymerization rates were 45% and 39% of those in Examples 1 and 2, respectively.

[0062] Table 9 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0063] 4 0.158 14.6 16020 1.69 8 0.250 22.1 27720 1.73 12 0.421 34.4 38460 1.65 16 0.524 40.8 48310 1.68 24 0.842 56.9 64030 1.62

[0064] Comparative Example 4

[0065] 20 mL of distilled and purified hexamethylphosphoric triamine was kept at a constant temperature of 10 °C under argon atmosphere, and then 0.03 g of lithium flakes was added and kept at this temperature for 30 minutes to prepare a blue solvated electron solution. After removing the undissolved solid alkali metal lithium, 10 mL of methyl methacrylate was added and mixed thoroughly. Polymerization was initiated at 35 °C for 3 minutes. Subsequently, 10 mL of hexamethylphosphoric triamine solution containing lithium chloride was added to the polymerization solution to achieve a lithium chloride concentration of 0.45 mol / L, and polymerization continued. The polymerization kinetics ln([M]0 / [M]) increased linearly with polymerization time, and the molecular weight of the polymerized product also increased linearly with conversion rate, with the molecular weight distribution broadening to 1.36–1.48. The results are shown in Table 10. The polymerization rate was 2.8 × 10⁻⁶. -5 mol·L -1 ·s -1 The polymerization rates were 53% and 45% of those in Examples 1 and 2, respectively.

[0066] Table 10 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0067] 4 0.185 16.9 18390 1.48 8 0.338 28.7 29540 1.42 12 0.462 37.0 42860 1.45 16 0.687 49.7 53220 1.36 24 0.923 60.3 67150 1.41

[0068] The results above show that, according to the controlled free radical polymerization method initiated by lithium chloride-regulated solvated electrons of the present invention, when lithium chloride (0.3-0.6 mol / L) is added and a relatively high polymerization temperature (50-60°C) is used, the polymerization kinetics ln([M]0 / [M]) of Examples 1-6 increases linearly with polymerization time, and the molecular weight also shows a linear relationship with conversion rate, demonstrating the properties of controlled polymerization. The polymerization rates of Examples 1-6 are comparable to those of ordinary free radical polymerization, and polymers with narrow molecular weight distribution (D = 1.18-1.29) can be obtained.

[0069] Comparative Examples 1 and 2, with little or no lithium chloride (<0.3 mol / L), showed a significantly broadened molecular weight distribution (D = 1.32–1.51). Compared to Example 1, which used the same polymerization temperature (50°C), the polymerization rates of Comparative Examples 1 and 2 did not change significantly, indicating that lithium chloride has a relatively small effect on the polymerization rate. This invention utilizes the addition of Lewis acidic lithium chloride to regulate solvated electron-initiated polymerization. Due to the Lewis acid-base interaction, Li32O3 forms around the negatively charged growing free radicals. + Ion clusters, the growing free radicals change from being negatively charged to appearing positively charged. Li + The electrostatic repulsion and steric hindrance effects of the ion clusters suppressed the bimolecular termination of free radicals, reducing the molecular weight distribution (D) of the polymer from over 1.5 in the prior art to 1.18–1.29 in the polymer of this invention. The aforementioned transformation of the growing free radicals from being negatively charged to appearing positively charged can be confirmed by changes in the solution electric field effect. In a high-voltage DC electric field environment, without lithium chloride, the polymer is biased towards the anode side, indicating that the growing species are negatively charged; after adding lithium chloride, the polymer is biased towards the cathode side, indicating that the negatively charged free radicals electrostatically adsorbed excess Li. + Cations, forming Li + The ionic clusters give the growing species an apparent positive charge. Comparative Examples 1 and 2, due to the absence or minimal addition of lithium chloride (<0.3 mol / L), lost this regulatory effect or had a negligible regulatory effect, leading to an increase in molecular weight distribution values.

[0070] Since the activation energy for solvated electron-initiated polymerization chain growth is positive (approximately 20 kJ / mol), the higher the polymerization temperature, the greater the polymerization rate. Examples 1 and 2 used relatively high polymerization temperatures (50–60 °C), resulting in higher polymerization rates. In contrast, Comparative Examples 3 and 4 used relatively low polymerization temperatures (30–35 °C), with polymerization rates only 39–53% of those of Examples 1 and 2 (polymerization temperature 50–60 °C), or approximately twice that of Comparative Examples 3 and 4. Compared to Example 1, which added the same amount of lithium chloride (0.45 mol / L), Comparative Example 4 showed a significantly broader molecular weight distribution (D = 1.36–1.48). Comparative Example 3, without lithium chloride, had a higher molecular weight distribution of 1.62–1.73. The results of Comparative Examples 3 and 4 indicate that polymerization temperature not only affects the polymerization rate but also has a significant impact on the molecular weight distribution. The conductivity of the solvated electron-initiated polymerization solution increases with increasing temperature, meaning that higher polymerization temperatures can promote the dissociation of active species ion pairs. For dissociated and loose ion pairs, the charge repulsion between negatively charged free radicals is enhanced, and the bimolecular termination of free radicals is suppressed, which is conducive to reducing the molecular weight distribution.

[0071] The above results indicate that both lithium chloride and polymerization temperature have a significant impact on molecular weight distribution, and increasing the polymerization temperature can accelerate polymerization. However, simply adding lithium chloride (Comparative Example 4, 35℃, 0.45 mol / L lithium chloride, D = 1.36–1.48) or increasing the polymerization temperature (Comparative Example 1, 50℃, 0 mol / L lithium chloride, D = 1.35–1.51) cannot reduce the molecular weight distribution to the ideal level. This invention, under the dual control of lithium chloride and a higher polymerization temperature, obtained a polymer product with a narrow molecular weight distribution (D = 1.18–1.29); while maintaining controllable polymerization properties, the polymerization rate was increased by approximately two times, reaching the level of ordinary free radical polymerization. The applied polymerization solves the problems of high molecular weight distribution and slow polymerization rate in existing technologies, providing a more suitable controllable free radical polymerization method for industrial applications, capable of preparing polymers with precisely controllable molecular weight and narrow molecular weight distribution.

Claims

1. A method for controlled free radical polymerization initiated by lithium chloride-regulated solvated electrons, characterized in that, Includes the following steps: First, a solvated electron solution of alkali metal lithium / hexamethylphosphoric triamine is prepared. Then, an olefin monomer is added to complete chain initiation. Next, lithium chloride is added to the polymerization system to carry out controlled free radical polymerization to obtain a polymer with a narrow molecular weight distribution. The concentration of lithium chloride in the polymerization solution is 0.3~0.6 mol / L, and the polymerization temperature is 50~60℃. The polymer with a narrow molecular weight distribution has a molecular weight distribution D value of 1.18~1.

29. The olefin monomer is methyl methacrylate, methyl acrylate, acrylic acid, styrene, or acrylonitrile.

2. The controlled free radical polymerization method initiated by lithium chloride-controlled solvation electrons according to claim 1, characterized in that, Includes the following steps: S1. Dry hexamethylphosphoric triamine thoroughly, then distill it under reduced pressure for later use; S2. Under an argon atmosphere, alkali metal lithium slices are added to hexamethylphosphoric triamine solvent treated in step S1 to prepare a blue solvated electron solution, and then the undissolved solid alkali metal lithium slices are removed. S3. Add the alkene monomer to the solvated electron solution of step S2 to bring the solvated electron solution into contact with the alkene monomer and complete the chain initiation. The reaction process requires argon protection. S4. Add the hexamethylphosphoric triamine solution of lithium chloride to the initiation polymerization solution of step S3 to carry out subsequent controlled free radical polymerization.

3. The controlled radical polymerization method initiated by lithium chloride-controlled solvation electrons according to claim 1 or 2, characterized in that, The solvated electron solution, based on the amount of hexamethylphosphoric triamine being 20 mL, contains 0.03~0.1 g of alkali metal lithium.

4. The controlled free radical polymerization method initiated by lithium chloride-controlled solvated electrons according to claim 3, characterized in that, In the preparation of the solvated electron solution, the contact time between the alkali metal lithium sheet and hexamethylphosphoric triamine is 20-30 minutes, and the preparation temperature is 7.5-12℃.

5. The controlled radical polymerization method initiated by lithium chloride-controlled solvation electrons according to claim 2, characterized in that, The contact time between the solvated electron solution and the olefin monomer in step S3 is 3-5 minutes. After 3-5 minutes, the hexamethylphosphoric triamine solution of lithium chloride is added to the polymerization solution in step S3 to make the concentration of lithium chloride in the polymerization solution reach 0.3-0.6 mol / L.

6. The controlled radical polymerization method initiated by lithium chloride-controlled solvation electrons according to claim 2, characterized in that, The subsequent controlled free radical polymerization described in step S4 has a polymerization temperature of 50~60℃.