A method for controlled radical polymerization initiated by co-solvent regulated solvated electrons

Abstract

The application discloses a kind of solventization electron initiation controlled radical polymerization method of cosolvent regulation, this polymerization method uses higher polymerization temperature and adds cosolvent tetrahydrofuran simultaneously to regulate, solventization electron initiation polymerization still can keep the nature of controlled radical polymerization, can prepare molecular weight precision controllable, narrow molecular weight distribution polymer, and accurate structure block, star and various topological structure polymers such as polymer.The solventization electron initiation controlled radical polymerization method of cosolvent regulation of the application, it includes the following steps: in the solventization electron initiation polymerization system of alkali metal lithium / hexamethylphosphoramide to olefin monomer, adding cosolvent, carrying out controlled radical polymerization, improve polymerization rate and obtain narrow molecular weight distribution polymer;Wherein, the cosolvent is tetrahydrofuran, the dosage of hexamethylphosphoramide is 20mL, the dosage of tetrahydrofuran is 3-6mL, 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 solvation electrons controlled by a co-solvent. Background Technology

[0002] Traditional free radical polymerization utilizes widely available monomers and mild reaction conditions, employing various methods such as bulk, solution, suspension, or emulsion polymerization. Its development in polymerization mechanisms and industrial applications has matured. Free radical polymerization products account for over 60% of total polymer production, making it one of the most important polymerization methods currently. Polymers such as polyacrylates, polystyrene, ABS resin, polyacrylonitrile, polyvinyl chloride, and styrene-butadiene rubber are all products of free radical polymerization, covering a wide range of applications including plastics, rubber, fibers, coatings, and adhesives. The free radical polymerization mechanism is characterized by slow initiation, rapid propagation, and rapid termination. Limited by this mechanism, the molecular weight of traditional free radical polymers is difficult to control, resulting in a wide molecular weight distribution and difficulty in obtaining polymers with various topologies such as block and star structures, posing challenges to polymer structure design and product performance improvement. Developing controlled free radical polymerization can effectively solve these problems.

[0003] Solvated electrons refer to the excess electrons confined by solvent molecules. Dissolving alkali metals in polar solvents such as hexamethylphosphoric triamine and tetrahydrofuran is a simple method for preparing solvated electrons. Solvated electrons have a redox potential of -2.88V and possess strong electron transfer capabilities, allowing them to undergo electron transfer reactions with unsaturated compounds such as alkenes. In existing technologies, Huang Jian et al. used a solvated electron solution of alkali metal sodium / hexamethylphosphoric triamine to initiate the polymerization of olefin monomers (Huang Jian 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 polymerization exhibits controlled radical polymerization properties, the molecular weight of the product is controllable, and the active species is a negatively charged free radical. Due to the repulsion of like charges, the negatively charged free radical is not easily terminated and can maintain "activity," thus endowing the polymerization with controlled radical polymerization properties. The regulatory mechanism of this polymerization differs from the "reversible dynamic equilibrium of active / dormant species" mechanism currently used in controlled radical polymerization, including nitrile oxide stable radical polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), and iodine transfer radical polymerization (ITRP), making it a novel type of controlled radical polymerization. However, these "negatively charged radicals" have low reactivity and slow growth rates, resulting in polymerization rates lower than traditional radical polymerization, which is detrimental to the industrial application of solvated electron-initiated controlled radical polymerization. Compared to sodium, lithium is more soluble in hexamethylphosphoric triamine. Controlled radical polymerization initiated by solvated electrons in lithium / hexamethylphosphoric triamine can achieve ten times the concentration of active species compared to the sodium system, thus significantly increasing the polymerization rate (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). Although the rate of controlled radical polymerization initiated by lithium is improved, it is still insufficient compared to the rate of ordinary radical polymerization.Furthermore, the molecular weight distribution of lithium-initiated controlled radical polymerization products is often greater than 1.5. These factors are detrimental to the structural control of the polymerization products and the industrial application of the polymerization method.

[0004] Because metal cations are electron-deficient and belong to Lewis acids, they readily react with Lewis basic solvents that provide electrons. For polymerizations where the active species involves a metal cation, or where the active species has an ion-pair structure and the counterion is a metal cation (such as anionic polymerization), adding the Lewis basic solvent tetrahydrofuran (THF) to the polymerization system allows the tetrahydrofuran to interact with the metal cation, thereby altering the structure and activity of the active species and consequently affecting polymerization properties such as polymerization rate, molecular weight, and molecular weight distribution. For example, in organometallic complexes [Co... Ⅱ In controlled radical polymerization, tetrahydrofuran has a significant impact on polymerization kinetics, product molecular weight, and molecular weight distribution (Li Weiwei, Shi Yan, Yang Wantai, Fu Zhifeng, Co). Ⅱ (salen*) in the presence of chloroprene free radical polymerization, Journal of Chemical Engineering of Chinese Universities, 2016, 37(11), 2085-2091); In anionic polymerization initiated by alkyl lithium (DMAPLi), the addition of tetrahydrofuran changes the initiation activity and molecular weight distribution of the polymerization product (Stergios Pispas, Marinos Pitsikalis and Nikos Hadjichristidis, et al., Anionic polymerization of isoprene, butadiene and styrene with 3-dimethylaminopropyllithium, Polymer, 1995, 36(15), 3005-3011). For polymerizations in which the active species has an ion pair structure, such as anionic or cationic polymerization, the polarity of the solvent also affects the tightness or looseness of the ion pair, thereby affecting the polymerization rate and the structure of the polymerization product. As mentioned above, the active species for solvated electron-initiated polymerization is a negatively charged free radical, and the negatively charged free radical and the counterion (Li + Or Na + The structure of the ion pairs is considered. Introducing tetrahydrofuran into the solvated electron-initiated polymerization system is expected to regulate the structure of the ion pairs forming the negatively charged free radical growth seed ion pairs through the Lewis acid-base interaction between tetrahydrofuran and the counterion, further suppressing the bimolecular termination of the free radical and yielding 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 during 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 by adding the co-solvent tetrahydrofuran, 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 controllable free radical polymerization method initiated by solvated electrons regulated by a co-solvent. This polymerization method uses the solvated electrons of alkali metal lithium / hexamethylphosphoric triamine as the initiation system, and the growing active species are negatively charged free radicals with ion-pair structures. Adding tetrahydrofuran as a co-solvent to the polymerization system allows the polar solvent tetrahydrofuran to enter the solvated shell formed by the polar hexamethylphosphoric triamine, making the ion-pair structure of the active species more loose, increasing the conductivity of the polymerization solution, and thus increasing the polymerization rate. The molecular weight distribution (D value) is reduced from above 1.5 in existing technologies to 1.16–1.28. Increasing the polymerization temperature from near room temperature used in existing technologies to 50–60°C further improves the polymerization rate, reaching the level of ordinary free radical polymerization. This invention employs a relatively high polymerization temperature (50–60°C) while simultaneously adding the co-solvent tetrahydrofuran for regulation. This solvated electron-initiated polymerization maintains the properties of controlled radical polymerization, providing a controlled 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 and star topologies, enabling wider applications of these polymers in fields such as 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 co-solvent-controlled solvated electron-initiated controlled free radical polymerization method, comprising the following steps: adding a co-solvent to a solvated electron-initiated polymerization system of alkali metal lithium / hexamethylphosphoric triamine to carry out controlled free radical polymerization, thereby increasing the polymerization rate and obtaining a polymer with a narrow molecular weight distribution; wherein the co-solvent is tetrahydrofuran, and based on 20 mL of hexamethylphosphoric triamine, the amount of tetrahydrofuran is 3-6 mL, and the polymerization temperature is 50-60°C.

[0009] The above-mentioned co-solvent-controlled solvated electron-initiated controlled free radical polymerization method of the present 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 then adding the co-solvent tetrahydrofuran to the polymerization system to carry out controlled free radical polymerization.

[0010] A further technical solution of the co-solvent-controlled solvation electron-initiated controlled free radical polymerization method of the present invention includes the following steps:

[0011] S1. Remove the water from hexamethylphosphoric triamine, purify it by vacuum distillation, and then pass argon gas to remove oxygen.

[0012] S2. Take alkali metal lithium, slice it in n-hexane for later use, and then put the lithium slice into hexamethylphosphoric triamine from step S1 to obtain a blue solvated electron solution.

[0013] S3. Under an argon atmosphere, the solvated electron solution from step S2 is brought into contact with the olefin monomer to initiate the polymerization of the olefin monomer.

[0014] S4. Add tetrahydrofuran to the polymerization solution from step S3 to carry out subsequent controlled free radical polymerization.

[0015] The above-described co-solvent-controlled solvated electron-initiated controlled free radical polymerization method of the present invention can be further described as follows: the solvated electron solution, based on 20 mL of hexamethylphosphoric triamine and 0.03–0.1 g of alkali metal lithium, is further described as follows: during the preparation of the solvated electron solution, the contact time between the lithium sheet and hexamethylphosphoric triamine is 20–30 minutes, and the preparation temperature is 7.5–10 °C. Within the 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. The polymerization kinetics ln([M]0 / [M]) of the solvated electrons increases linearly with polymerization time, and the polymer molecular weight and conversion rate also show a linear relationship, exhibiting the properties of controlled free radical polymerization. Excessive use of alkali metal lithium or prolonged contact time between lithium and hexamethylphosphoric triamine (HMP) results in a high concentration of solvated electrons. These electrons readily undergo ion-pairing or electron-pairing, causing the polymerization kinetics ln([M]0 / [M]) to not increase linearly with polymerization time. Consequently, the molecular weight of the product becomes uncontrollable, and the polymerization no longer exhibits the properties of controlled free radical polymerization. Conversely, insufficient use of alkali metal lithium or insufficient contact time between lithium and HMP results in a low concentration of solvated electrons, making it difficult for these electrons to initiate monomer polymerization. The preparation temperature for solvated electrons must be controlled to be higher than the melting point of HMP (7.2℃) but not too high; otherwise, the solvated electron solution will lose stability, leading to initiation failure.

[0016] The above-described co-solvent-controlled solvated electron-initiated controlled free radical polymerization method of the present invention can be further described in that the olefin monomer is methyl methacrylate, methyl acrylate, acrylonitrile, styrene, or acrylic acid.

[0017] A further technical solution of the co-solvent-controlled solvated electron-initiated controlled free radical polymerization method of the present invention can be that, before the solvated electron solution in step S3 comes into contact with the alkene monomer, the undissolved solid alkali metal lithium is removed so that it is removed from the polymerization initiation system; otherwise, the solid lithium metal may initiate the anionic polymerization of the monomer.

[0018] A further technical solution of the co-solvent-controlled solvated electron-initiated controlled radical polymerization method of the present invention can be that the contact time between the solvated electron solution and the olefin monomer in step S3 is 4-6 minutes. After 4-6 minutes, tetrahydrofuran is added to the polymerization solution in step S3, with 3-6 mL of tetrahydrofuran used for 20 mL of hexamethylphosphoric triamine. After the solvated electron solution contacts the olefin monomer for 4-6 minutes, chain initiation can be completed and negatively charged free radical propagating species can be formed. Only then can the added tetrahydrofuran interact with the ion pairs of the propagating species, thereby achieving the purpose of controlling the solvated electron-initiated controlled radical polymerization, accelerating polymerization and obtaining a polymer with a narrow molecular weight distribution. Assuming a hexamethylphosphoric acid triamine (HMP) concentration of 20 mL in the polymerization solution, the optimal concentration of tetrahydrofuran (THF) is 3–6 mL. Within this range, the moderately polar THF can penetrate the solvation shell of the highly polar HMP, loosening the ion-pair structure of the active species and increasing the conductivity of the polymerization solution. This results in a higher polymerization rate and a lower molecular weight distribution. Too low a concentration of THF will not achieve this effect, while too high a concentration, due to its lower polarity compared to HMP, will significantly alter the polymerization medium, leading to an increased molecular weight distribution and potentially causing the polymerization to lose its controllable polymerization properties.

[0019] A further technical solution of the co-solvent-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 further improved, reaching the level of ordinary radical polymerization rate, making solvated electron-initiated controlled polymerization more suitable for industrial applications.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The present invention discloses a co-solvent-controlled solvated electron-initiated controlled radical polymerization method. The polymerization is initiated by the solvated electrons of alkali metal lithium / hexamethylphosphoric triamine, producing negatively charged free radicals with ion-pair structures. Due to the repulsion of like charges, the free radicals are not easily terminated; therefore, solvated electron-initiated polymerization exhibits the property of controlled polymerization. Based on this, the present invention uses tetrahydrofuran as a co-solvent to regulate and optimize the polymerization initiated by alkali metal lithium / hexamethylphosphoric triamine. Tetrahydrofuran and hexamethylphosphoric triamine are both polar solvents; as a co-solvent, it can enter the Li... + The solvated shell of hexamethylphosphoric triamine forms a loose, mixed solvated shell. Solvated Li +The increased volume and decreased charge density of the counterion loosen the ion-pair structure of the active species, thus increasing the polymerization rate. For this looser ion-pair structure, the neutralizing effect of the counterion weakens, while the charge repulsion between negatively charged free radicals increases, enhancing the inhibition of bimolecular termination and reducing the molecular weight distribution of the polymer. This change in the ion-pair structure caused by the addition of tetrahydrofuran can be confirmed by changes in the conductivity of the polymerization solution. Compared to the highly polar hexamethylphosphoric triamine (ε = 30.6), tetrahydrofuran (ε = 7.5) has moderate polarity; however, the conductivity of the polymerization solution increases rather than decreases with the addition of tetrahydrofuran, indicating that the conductivity is not affected by simply changing the solution medium. The ether oxygen bond in tetrahydrofuran is electron-donating, classifying it as a Lewis base, and readily reacts with electron-deficient Li₂. + Cation reaction, entering Li + The solvation shell of hexamethylphosphoric triamine forms a loose, mixed solvation shell, which loosens the relatively compact ion pairs and thus increases the conductivity of the solution. With increasing tetrahydrofuran content, the polymerization rate, molecular weight distribution, and solution conductivity all showed simultaneous peaks at 5 ml of tetrahydrofuran (the highest, lowest, and highest values, respectively), verifying this close relationship between polymerization rate, molecular weight distribution, and solution conductivity.

[0022] 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. The activation energy of the chain growth reaction in solvated electron-initiated polymerization is positive (approximately 20 kJ / mol), therefore, the higher the polymerization temperature, the greater the polymerization rate should be. To further improve the polymerization rate, this invention increases the polymerization temperature to 50–60 °C. At this higher polymerization temperature, it was found that alkali metal lithium / hexamethylphosphoric triamine-initiated polymerization still maintains the properties of controlled radical polymerization, and the polymerization rate is further improved. In addition, the conductivity of the solvated electron-initiated polymerization solution is positively correlated with temperature, meaning that a higher polymerization temperature can promote the dissociation of active ion pairs, leading to an increase in solution conductivity. 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 to reducing the molecular weight distribution. Therefore, increasing the polymerization temperature can accelerate polymerization while reducing the molecular weight distribution of the polymer product.

[0023] This invention employs a higher polymerization temperature (50-60°C) and adds a co-solvent tetrahydrofuran for regulation. Solvated electron-initiated polymerization maintains the properties of controllable free radical polymerization, resulting in a polymer with a narrow molecular weight distribution. The polymerization rate is approximately twice that of existing technologies, reaching the level of ordinary free radical polymerization, providing a controllable free radical polymerization method more suitable for industrial applications. Specifically: (1) This invention uses tetrahydrofuran to regulate polymerization, which can increase the polymerization rate while reducing the molecular weight distribution; (2) This invention uses a higher polymerization temperature, which can also accelerate polymerization and reduce the molecular weight distribution; (3) Through the dual regulation of tetrahydrofuran and higher polymerization temperature in this invention, the molecular weight distribution of solvated electron-initiated polymerization is reduced from over 1.5 in existing technologies to 1.16-1.28, and the polymerization rate is approximately twice that of existing technologies, reaching the level of ordinary free radical polymerization, providing a controllable free radical polymerization method more suitable for industrial applications; (4) Through the tetrahydrofuran and higher polymerization temperature in this invention... With dual regulation of degree, 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 are also linearly related; (5) The co-solvent-regulated 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

[0024] The basic steps of the controlled radical polymerization method initiated by solvated electrons under co-solvent regulation in the examples are as follows:

[0025] S1. Remove the water from hexamethylphosphoric triamine, purify it by vacuum distillation, and then pass argon gas to remove oxygen.

[0026] S2. Take alkali metal lithium, slice it in n-hexane for later use, and then put the lithium slice into hexamethylphosphoric triamine from step S1 to obtain a blue solvated electron solution.

[0027] S3. Under an argon atmosphere, the solvated electron solution from step S2 is brought into contact with the olefin monomer to initiate the polymerization of the olefin monomer.

[0028] S4. Add tetrahydrofuran to the polymerization solution from step S3 to carry out subsequent controlled free radical polymerization.

[0029] Example 1

[0030] 20 mL of purified hexamethylphosphoric triamine was placed in an argon atmosphere at 10 °C, and 0.03 g of lithium was added. The mixture was kept at this temperature for 30 minutes to obtain a blue solvated electron solution. Undissolved lithium metal was removed, and 10 mL of methyl methacrylate was added to the solvated electron solution. The mixture was stirred until homogeneous, and polymerization was initiated at 50 °C for 4 minutes. Then, 5 mL of tetrahydrofuran was added for further polymerization. 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 1.22–1.25. The results are shown in Table 1. The polymerization rate was 6.9 × 10⁻⁶. -5 mol·L -1 ·s -1 It reached the level of ordinary free radical polymerization rate.

[0031] Table 1. Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate.

[0032] 4 0.464 37.1 56560 1.24 8 0.942 61.0 94260 1.25 12 1.365 74.5 108610 1.24 16 1.777 83.1 125820 1.22 24 2.642 92.9 133710 1.22

[0033] Example 2

[0034] 20 mL of purified hexamethylphosphoric triamine was placed in an argon atmosphere at 10 °C, and 0.03 g of lithium was added. The mixture was kept at this temperature for 30 minutes to obtain a blue solvated electron solution. Undissolved metallic lithium was removed, and 10 mL of methyl methacrylate was added to the solvated electron solution. The mixture was stirred until homogeneous, and polymerization was initiated at 60 °C for 4 minutes. Subsequently, 5 mL of tetrahydrofuran was added for further polymerization. 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 1.16–1.24 (see Table 2). The polymerization rate was 8.2 × 10⁻⁶. -5 mol·L -1 ·s -1 It reached the level of ordinary free radical polymerization rate.

[0035] Table 2 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0036] 4 0.579 44.0 62940 1.24 8 1.262 71.7 99870 1.23 12 1.636 80.5 111520 1.24 16 2.453 91.4 125950 1.19 24 3.372 96.6 132980 1.16

[0037] Example 3

[0038] 20 mL of purified hexamethylphosphoric triamine was placed in an argon atmosphere at 9 °C, and 0.05 g of lithium was added. The mixture was kept at this temperature for 30 minutes to obtain a blue solvated electron solution. Undissolved metallic lithium was removed, and 10 mL of methyl acrylate was added to the solvated electron solution. The mixture was stirred until homogeneous, and polymerization was initiated at 55 °C for 6 minutes. Then, 3 mL of tetrahydrofuran was added for further polymerization. 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 1.18–1.26 (see Table 3). The polymerization rate was 1.0 × 10⁻⁶. -4 mol·L -1 ·s -1 It reached the level of ordinary free radical polymerization rate.

[0039] Table 3 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl acrylate

[0040] 4 0.733 52.0 66520 1.26 8 1.523 78.2 98010 1.25 12 2.102 87.8 110560 1.24 16 2.985 94.9 120540 1.18

[0041] Example 4

[0042] 20 mL of purified hexamethylphosphoric triamine was heated to 7.5 °C under an argon atmosphere, and 0.03 g of lithium was added. The mixture was kept at this temperature for 20 minutes to obtain a blue solvated electron solution. Undissolved metallic lithium was removed, and 10 mL of acrylonitrile was added to the solvated electron solution. The mixture was stirred thoroughly and polymerization was initiated at 50 °C for 5 minutes. Then, 6 mL of tetrahydrofuran was added for further polymerization. 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 1.21–1.28 (see Table 4). The polymerization rate was 4.1 × 10⁻⁶. -4 mol·L -1 ·s -1 It reached the level of ordinary free radical polymerization rate.

[0043] Table 4 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polyacrylonitrile

[0044] 1 0.835 56.6 94880 1.26 2 1.602 79.9 137510 1.28 3 2.515 91.9 155650 1.25 4 3.318 96.4 165350 1.21

[0045] Example 5

[0046] 20 mL of purified hexamethylphosphoric triamine was placed in an argon atmosphere at 8 °C, and 0.1 g of lithium was added. The mixture was kept at this temperature for 25 minutes to obtain a blue solvated electron solution. Undissolved metallic lithium was removed, and 10 mL of styrene was added to the solvated electron solution. The mixture was stirred thoroughly and polymerization was initiated at 60 °C for 5 minutes. Then, 4 mL of tetrahydrofuran was added for further polymerization. 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 1.17–1.26 (see Table 5). The polymerization rate was 8.2 × 10⁻⁶. -5 mol·L -1 ·s -1 It reached the level of ordinary free radical polymerization rate.

[0047] Table 5 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polystyrene

[0048] 4 0.556 42.7 33520 1.23 8 1.124 67.5 50860 1.26 12 1.626 80.3 60590 1.19 16 2.205 89.0 66530 1.21 24 3.413 96.7 71840 1.17

[0049] Example 6

[0050] 20 mL of purified hexamethylphosphoric triamine was heated to 7.5 °C under an argon atmosphere, and 0.09 g of lithium was added. The mixture was kept at this temperature for 28 minutes to obtain a blue solvated electron solution. Undissolved metallic lithium was removed, and 10 mL of acrylic acid was added to the solvated electron solution. The mixture was stirred until homogeneous and polymerization was initiated at 60 °C for 6 minutes. Then, 5 mL of tetrahydrofuran was added for further polymerization. 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 1.21–1.28. The results are shown in Table 6. The polymerization rate was 6.6 × 10⁻⁶. -5 mol·L -1 ·s -1 It reached the level of ordinary free radical polymerization rate.

[0051] Table 6 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polyacrylic acid

[0052]

[0053]

[0054] Comparative Example 1

[0055] 20 mL of purified hexamethylphosphoric triamine was placed in an argon atmosphere at 10 °C, and 0.03 g of lithium was added. The mixture was kept at this temperature for 30 minutes to obtain a blue solvated electron solution. Undissolved metallic lithium was removed, and 10 mL of methyl methacrylate was added to the solvated electron solution. The mixture was stirred thoroughly and then subjected to further polymerization at 50 °C. 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 1.36–1.42. The results are shown in Table 7. The polymerization rate was 5.9 × 10⁻⁶. -5 mol·L -1 ·s -1 .

[0056] Table 7 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0057] 4 0.319 27.3 43220 1.39 8 0.617 46.0 77450 1.41 12 0.985 62.7 98530 1.42 16 1.254 71.5 119540 1.36 24 1.918 85.3 136540 1.37

[0058] Comparative Example 2

[0059] 20 mL of purified hexamethylphosphoric triamine was placed in an argon atmosphere at 10 °C, and 0.03 g of lithium was added. The mixture was kept at this temperature for 30 minutes to obtain a blue solvated electron solution. Undissolved metallic lithium was removed, and 10 mL of methyl methacrylate was added to the solvated electron solution. The mixture was stirred until homogeneous, and polymerization was initiated at 50 °C for 4 minutes. Subsequently, 10 mL of tetrahydrofuran was added for further polymerization. The polymerization kinetics, ln([M]0 / [M]), deviated from a linear relationship with polymerization time and molecular weight with conversion rate, with the molecular weight distribution broadening to 1.38–1.48. The results are shown in Table 8. The polymerization rate was 5.5 × 10⁻⁶. -5 mol·L -1 ·s -1 .

[0060] Table 8 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0061]

[0062]

[0063] Comparative Example 3

[0064] 20 mL of purified hexamethylphosphoric triamine was placed in an argon atmosphere at 10 °C, and 0.03 g of lithium was added. The mixture was kept at this temperature for 30 minutes to obtain a blue solvated electron solution. Undissolved metallic lithium was removed, and 10 mL of methyl methacrylate was added to the solvated electron solution. The mixture was stirred thoroughly, and subsequent polymerization was carried out at 35 °C. 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 1.51–1.67. The results are shown in Table 9. The polymerization rate was 4.2 × 10⁻⁶. -5 mol·L -1 ·s -1 This is 51% of the polymerization rate in Example 2.

[0065] Table 9 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0066] 4 0.214 19.2 31060 1.62 8 0.413 33.8 53290 1.51 12 0.654 48.0 74840 1.67 16 0.842 56.9 88590 1.58 24 1.302 72.8 113880 1.53

[0067] Comparative Example 4

[0068] 20 mL of purified hexamethylphosphoric triamine was placed in an argon atmosphere at 10 °C, and 0.03 g of lithium was added. The mixture was kept at this temperature for 30 minutes to obtain a blue solvated electron solution. Undissolved metallic lithium was removed, and 10 mL of methyl methacrylate was added to the solvated electron solution. The mixture was stirred until homogeneous, and polymerization was initiated at 35 °C for 4 minutes. Then, 5 mL of tetrahydrofuran was added for further polymerization. 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 1.35–1.45. The results are shown in Table 10. The polymerization rate was 4.8 × 10⁻⁶. -5 mol·L -1 ·s -1 This is 58% of the polymerization rate in Example 2.

[0069] Table 10 Relationship between ln([M]0 / [M]), molecular weight, molecular weight distribution and polymerization time of polymethyl methacrylate

[0070] 4 0.301 26.0 37510 1.44 8 0.618 46.1 68620 1.45 12 0.885 58.7 89780 1.37 16 1.198 69.8 101450 1.39 24 1.792 83.3 122850 1.35

[0071] The results above show that, according to the co-solvent-controlled solvated electron-initiated controlled free radical polymerization method of the present invention, when adding the co-solvent tetrahydrofuran (3-6 mL) and using a relatively high polymerization temperature (50-60 °C), 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 = 1.16-1.28) can be obtained.

[0072] In Comparative Examples 1 and 2, the amount of tetrahydrofuran was zero or excessive (>6 mL). Compared with Example 1, the polymerization rate decreased and the molecular weight distribution significantly broadened (D = 1.36–1.48), indicating that an appropriate amount of tetrahydrofuran (3–6 mL) can accelerate polymerization while reducing the molecular weight distribution. As a moderately polar solvent, tetrahydrofuran (ε = 7.5) can enter the Li... + The solvation shell of hexamethylphosphoric triamine (ε = 30.6) forms a loose mixed solvation shell, which loosens the ion pair structure of the active species, thus increasing the polymerization rate and reducing the molecular weight distribution. This change in the ion pair structure of the active species caused by tetrahydrofuran can be confirmed by the change in the conductivity of the polymerization solution. With the addition of tetrahydrofuran (3–6 mL), the conductivity of the polymerization solution increases accordingly, indicating that the electron-donating tetrahydrofuran reacts with the electron-deficient Li... + Cation reaction, entering Li + The solvation shell of hexamethylphosphoric triamine forms a loose mixed solvation shell, which loosens the relatively compact growth seed ion pairs and increases the conductivity of the solution. In Comparative Example 1, the amount of tetrahydrofuran was zero, so it did not have the effect of changing the ion pair structure mentioned above; in Comparative Example 2, the amount of tetrahydrofuran was too large, which significantly reduced the polarity of the polymerization medium, resulting in the ion pairs becoming more compact. Therefore, compared with Example 1, the polymerization rate of Comparative Examples 1 and 2 decreased, and the molecular weight distribution broadened. In addition, the polymerization kinetics ln([M]0 / [M]) of Comparative Example 2 deviated from linearity with polymerization time and the change of molecular weight with conversion rate, indicating that slight chain termination or chain transfer occurred during polymerization. In the chain growth reaction of solvation electron-initiated polymerization, there is an electron migration process. The stabilizing effect of tetrahydrofuran on electrons is weaker than that of hexamethylphosphoric triamine. Excessive tetrahydrofuran affects the controllable polymerization properties. The ion pair structure of Comparative Example 2 is relatively compact, and the charge neutralization effect of the counterions is enhanced, which leads to a decrease in the charge repulsion between negatively charged free radicals and an increase in the probability of free radical termination. This may also be one of the reasons affecting the properties of controlled polymerization.

[0073] For solvated electron-initiated polymerization, the activation energy for chain growth is approximately 20 kJ / mol. According to the Arrhenius equation, the higher the polymerization temperature, the greater the polymerization rate. Comparative Examples 3 and 4 used a lower polymerization temperature (35°C), and their polymerization rates were only 51% and 58% of those of Example 2, which was polymerized at a higher temperature (60°C). In other words, the polymerization rate of Example 2 was about twice that of Comparative Examples 3 and 4, indicating that a higher polymerization temperature is beneficial to increasing the rate of solvated electron-initiated polymerization. The polymerization rate of Comparative Example 4 was slightly higher than that of Comparative Example 3, due to the accelerating effect of tetrahydrofuran (5 mL) in Comparative Example 4. The conductivity of the solvated electron-initiated polymerization solution increased with increasing temperature, indicating that increasing the temperature can promote the dissociation of the active species ions on the structure. In the 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 beneficial to reducing the molecular weight distribution. Comparative Examples 3 and 4, due to their lower polymerization temperatures, exhibited relatively compact ion-pair structures of the active species, resulting in significantly higher molecular weight distributions (D = 1.35–1.67) compared to Examples 1 and 2, which were polymerized at higher temperatures (D = 1.16–1.25). Comparative Example 3, in particular, achieved a high molecular weight distribution of 1.51–1.67 due to its lower polymerization temperature and the absence of tetrahydrofuran. The results of Comparative Examples 3 and 4 demonstrate that polymerization temperature not only affects the polymerization rate but also has a considerable influence on the molecular weight distribution of the polymerized product.

[0074] The above results indicate that the co-solvent tetrahydrofuran and polymerization temperature have a significant impact on both molecular weight distribution and polymerization rate. However, simply adding tetrahydrofuran (Comparative Example 4) or increasing the polymerization temperature (Comparative Example 1) cannot reduce the molecular weight distribution or increase the polymerization rate to the ideal level. This invention, under the dual control of tetrahydrofuran and a higher polymerization temperature, can effectively reduce the molecular weight distribution (D = 1.16–1.28) of the polymerized product and increase the polymerization rate while maintaining controllable polymerization properties. The polymerization rate is approximately twice that of existing technologies and is comparable to the rate of ordinary free radical polymerization. The applied polymerization method 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 solvated electrons under co-solvent regulation, characterized in that, Includes the following steps: S1. Remove the water from hexamethylphosphoric triamine, purify it by vacuum distillation, and then pass argon gas to remove oxygen. S2. Take alkali metal lithium, slice it in n-hexane for later use, and then put the lithium slice into hexamethylphosphoric triamine from step S1 to obtain a blue solvated electron solution. S3. Under an argon atmosphere, the solvated electron solution from step S2 is brought into contact with the olefin monomer to initiate the polymerization of the olefin monomer. S4. Add the co-solvent to the polymerization solution of step S3 to carry out subsequent controlled free radical polymerization; The co-solvent is tetrahydrofuran, with 3-6 mL of tetrahydrofuran used as 20 mL of hexamethylphosphoric triamine, and the free radical polymerization temperature is 50-60°C; the solvated electron solution has 0.03-0.1 g of alkali metal lithium used as 20 mL of hexamethylphosphoric triamine; the olefin monomer is methyl methacrylate, methyl acrylate, acrylonitrile, styrene, or acrylic acid.

2. The method for controlled free radical polymerization initiated by solvation electrons under co-solvent regulation according to claim 1, characterized in that, In step S2, the contact time between the lithium sheet and hexamethylphosphoric triamine is 20-30 minutes, and the preparation temperature is 7.5-10℃.

3. The method for controlled free radical polymerization initiated by solvation electrons under co-solvent regulation according to claim 1, characterized in that, Before the solvated electron solution described in step S3 comes into contact with the alkene monomer, the undissolved solid alkali metal lithium is removed, thus removing it from the polymerization initiation system.

4. The method for controlled free radical polymerization initiated by solvation electrons under co-solvent regulation according to claim 1, characterized in that, In step S3, the contact time between the solvated electron solution and the olefin monomer is 4-6 minutes, and after 4-6 minutes, tetrahydrofuran is added to the polymerization solution in step S3.

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