WO2023272792A1

WO2023272792A1 - Method for preparing fluorine-containing alternating polymer

Info

Publication number: WO2023272792A1
Application number: PCT/CN2021/106648
Authority: WO
Inventors: 程振平; 王玉薛; 张丽芬; 涂凯; 成健楠; 朱秀林
Original assignee: 苏州大学
Priority date: 2021-06-28
Filing date: 2021-07-16
Publication date: 2023-01-05
Also published as: CN113444229A

Abstract

A method for preparing a fluorine-containing alternating polymer, comprising the following steps: S1, dissolving α,ω-diiodo perfluoroalkane, α,ω-non-conjugated diene, and an accelerator into an organic solvent, the accelerator being an amine accelerator and/or a haloid accelerator; S2, after deoxidizing and sealing, placing the system under an illumination condition for reaction to obtain a polymerization system; and S3, performing precipitation treatment on the polymerization system to obtain the fluorine-containing alternating polymer. The polymerization strategy is performed without a metal catalyst, and the whole polymerization system only contains two bifunctional monomers, the cheap amine accelerator/haloid, and the organic solvent, so that the method is green and environment-friendly, and the components are simple.

Description

A kind of preparation method of fluorine-containing alternating polymer

technical field

The invention belongs to the technical field of polymer preparation, in particular to a preparation method of a fluorine-containing alternating polymer, which is a preparation method of a main chain type "semi-fluoro" alternating copolymer promoted by a halogen bond complex.

Background technique

In recent years, fluoropolymer materials have been extensively and intensively studied in the fields of surfactants, antifouling coatings, semiconductors, and liquid crystal materials. According to the position of the fluorine-containing chain segment, it can be divided into main chain type and side chain type fluoropolymer. Among them, the main chain type fluoropolymer has discovered many high-end application properties, and at the same time overcomes the traditional fluorine-containing homogeneity. Problems with polymers due to high crystallinity and poor solubility. However, the traditional methods for synthesizing main-chain fluoropolymers are too cumbersome and the conditions are too harsh, so it is necessary to develop a simple preparation method. Recently, Sletten and Jaye have done a lot of work on the preparation of this class of fluoropolymers by iodidene polymerization (ACS Cent. , providing various possibilities for post-polymerization modification and driving the development of modern fluoropolymer materials. In addition, Chen et al. reported the controlled synthesis of various main-chain fluorinated alternating copolymers at room temperature and atmospheric pressure via organic photocatalytic reversible deactivation alternating copolymerization (J.Am.Chem.Soc., 2020, 142, 7108-7115) It breaks through the limitation of traditional high temperature and high pressure polymerization conditions, which is a milestone work.

At the beginning of 2016, researchers proposed a new polymerization strategy, that is, the preparation of fluorine-containing alternating copolymers by radical transfer-addition-termination (START) under visible light conditions (Macromol Rapid Comm, 2017, 38, 1600587 ), and optimized the catalyst and solvent system in follow-up work. However, whether it is a noble metal catalyst or an organic photocatalyst, there are inevitably problems such as metal residue, high price, and complicated chemical synthesis, which restrict the wide application of this strategy. Therefore, it is of great significance to develop a method for preparing backbone fluorinated alternating polymers without any photocatalyst.

With an in-depth understanding of photochemistry, the researchers discovered that halogen bond (XB) complexes, even in the absence of any photocatalyst, can produce intramolecular single electron transfer (SET) after absorbing visible light, under mild conditions Generates free radical intermediates. Thus, such mild halogen-bonded electron donor-acceptor (EDA) complexes have been extensively studied in synthetic chemistry. Czekelius et al. reported the addition of various alkenes through the formation of EDA complexes between phosphine and alkyl iodides using a catalytic amount (10 mol%) of phosphine under blue light irradiation (Org. Lett. , 2019, 21, 7823-7827). In addition, amines have also been investigated as additives to activate carbon-iodide bonds. Kappe and co-workers proposed an efficient continuous-flow strategy for iodofluoroalkylation with cheap and readily available triethylamine (Et ₃ N) under blue light (405 nm) irradiation (Org. Lett., 2019, 21, 5341-5345), its industrialization prospect is broad. The above work provides the possibility to design an optimized polymerization method to obtain the main chain type fluorine-containing alternating copolymers.

Contents of the invention

The present invention aims to solve the technical problems existing in the above polymerization methods, and provides a preparation method of fluorine-containing alternating polymers. The polymerization strategy is green and environmentally friendly, and the components are simple, which is helpful to promote its application in the fields of electronic devices and biomedicine Applications.

A kind of fluorine-containing alternating polymer prepared by the present invention has the following structural formula:

Wherein, n=2-30.

According to the technical solution of the present invention, the preparation method of the fluorine-containing alternating polymer comprises the following steps,

S1: Dissolve two non-conjugated difunctional monomers (α, ω-diiodoperfluoroalkane and α, ω-non-conjugated diene) and accelerator in an organic solvent and stir to form a homogeneous phase. The accelerator is an amine accelerator and/or a halogen salt accelerator;

S2: After deoxygenation and sealing, place it under light conditions for polymerization to obtain a polymerization system;

S3: Precipitate the polymerization system to remove unreacted α,ω-diiodoperfluoroalkane, α,ω-non-conjugated diene and accelerator in the polymerization system to obtain the fluorine-containing alternating polymer .

Its components are green and simple, except for two types of monomers (α,ω-diiodoperfluoroalkane and α,ω-non-conjugated diene), there are only accelerators and a single solvent. The use of halide salts as accelerators keeps the functional groups at the end of the polymer chain intact.

Further, in the step S3, the polymerization system is diluted before the precipitation treatment, and the solvent used for dilution may be tetrahydrofuran, so as to facilitate the complete removal of unreacted monomers and accelerators.

Specifically, the following steps may be included:

S1: Mix two non-conjugated bifunctional monomers (α, ω-diiodoperfluoroalkane and α, ω-non-conjugated dienes with different structures) and amine additives in a certain molar ratio, and Dissolved in an organic solvent with a certain volume ratio and stirred to form a homogeneous phase, the stirring speed is 1000-2000rpm, preferably 1300rpm;

S2: Ensure an oxygen-free atmosphere through deoxygenation operation, place it under LED light after deoxygenation and sealing;

S3: After the polymerization, break the tube and add a solvent to dilute the polymerization system, then pour it into the precipitant to precipitate to remove unreacted monomers and accelerators, after standing for a period of time, suction filter, and put the filter cake in a vacuum Drying in an oven can obtain the fluorine-containing alternating copolymer.

Wherein, the precipitating agent can adopt methanol or petroleum ether.

Further, water is also added in the step S1, and the addition of water is used to stabilize free radical intermediates and reduce side reactions.

Further, the volume ratio of water to organic solvent is 0.2-1:2.

Further, in the step S1,

When the accelerator is an amine accelerator, the molar ratio of α, ω-diiodoperfluoroalkane, α, ω-non-conjugated diene and the accelerator is 1-1.2: 1.2-1: 0.1-3, preferably 1:1:0.2;

When the accelerator is a halogen salt accelerator, the molar ratio of α, ω-diiodoperfluoroalkane, α, ω-non-conjugated diene and the accelerator is 1-1.4: 1.4-1: 0.5-15, preferably 1:1:9.

Further, the α,ω-diiodoperfluoroalkane is selected from one or more of 1,4-diiodoperfluorobutane and 1,6-diiodoperfluorohexane, preferably 1,6-Diiodoperfluorohexane.

Further, the α, ω-non-conjugated dienes are selected from 1,7-octadiene, 1,9-decadiene, diallyl 1,4-cyclohexanedicarboxylate, adipic acid One or more of diallyl ester, tridecethoxy-1,48-diene and compound A, wherein the structural formula of compound A is as follows:

Further, the amine accelerator is selected from one of N,N,N',N'-tetramethylethylenediamine (TMEDA), triethylamine, ethylenediamine, ethylamine, diethylamine and pyridine One or more, preferably TMEDA; The halogen salt promoter is selected from one or more of sodium iodide, tetrabutylammonium iodide, sodium chloride, tetrabutylammonium bromide and diphenylphosphine chloride Various, preferably sodium iodide.

Further, in the step S1,

When the accelerator is an amine accelerator, the organic solvent is selected from one of chloroform, dimethyl sulfoxide, dimethylethylenediamine, acetone, 1,4-dioxane and dimethyl carbonate. One or more, preferably chloroform;

When the accelerator is a halogen salt accelerator, the organic solvent is selected from one or more of dimethylacetamide, acetone, tetrahydrofuran, dimethyl carbonate and acetonitrile, preferably acetone.

Further, in the step S2, the light wavelength is 373-403nm, preferably 403nm, and the reaction temperature is 20-30°C, preferably 25°C.

Further, in the step S2,

When the accelerator is an amine accelerator, the reaction time is 3min-28h;

When the accelerator is a halogen salt accelerator, the reaction time is 3h-56h.

The polymerization strategy of the present invention is carried out without metal catalysts. The entire polymerization system only contains two kinds of bifunctional monomers, cheap amine accelerators/halogen salts and organic solvents, which are deoxygenated and sealed in containers. It can be reacted for a certain period of time under the induction of visible light at room temperature. Through certain characterization means ( ¹ H NMR, ¹⁹ F NMR), it can be proved that the polymer conforms to a strict alternating arrangement structure, and the system is verified to be a stepwise polymerization system through kinetic research and analysis.

Technical solution of the present invention has the following advantages compared with existing polymerization technology:

1) Traditional noble metal photocatalysts are not only expensive, but also have high production costs, and it is inevitable that some of them will remain in the polymerization system after the reaction, which will affect the performance of the material to a certain extent, and limit its application in the field of fluorine-containing materials. widely used. However, the organic photocatalysts developed in recent years also have some shortcomings, such as difficult synthesis, time-consuming and laborious, etc. However, the present invention has simple components, cheap and easy-to-obtain raw materials, and convenient post-treatment. Compared with traditional metal photocatalysts or organic photocatalysts, the proposed polymerization strategy can effectively avoid its expensive, difficult to synthesize, and difficult to remove. Problems can effectively solve the above existing technical problems, more in line with the concept of green chemistry, and have high practical application value.

2) The traditional method for preparing main-chain fluoropolymers has harsh reaction conditions, not only requires high temperature and high pressure, but also cannot guarantee its safety. However, the proposal of the present invention can realize rapid polymerization under the irradiation of visible light at room temperature, which can not only greatly reduce the production cost, but also avoid complicated reaction conditions, which has important guiding significance for the design and preparation of intelligent fluorine-containing materials.

3) The polymerization system promoted by amines or halogen salts proposed by the present invention can quickly obtain the main chain type fluorine-containing alternating copolymer under the irradiation of visible light at room temperature, and the polymerization with different molecular weight and terminal functional groups can be obtained by adjusting the type and amount of additives. things. Compared with the existing metal-catalyzed or organocatalyzed radical transfer-addition-termination polymerization method, which can greatly improve the polymerization efficiency, this environmentally friendly and efficient polymerization method does not need to consider the residue of raw materials in the system, which is more conducive to the construction of functions non-toxic fluorine-containing materials.

Description of drawings

Fig. 1 is the schematic diagram of ln([M] ₀ /[M]) changing with time in the polymerization system promoted by TMEDA;

Figure 2 shows the polymer molecular weight (M _n,GPC ) and molecular weight distribution in the polymerization system promoted by TMEDA

Schematic diagram of the change with the conversion rate;

Fig. 3 is the nuclear magnetic proton spectrogram of polymer (AB) _n in the polymerization system promoted by TMEDA;

Fig. 4 is the NMR fluorine spectrogram of polymer (AB) _n in the polymerization system promoted by TMEDA;

Fig. 5 is the GPC efflux curve of polymer before and after water is added in the polymerization system promoted by TMEDA;

Fig. 6 is the GPC efflux curve of different sodium iodide consumption catalyzed polymerizations in the polymerization system promoted by NaI;

Fig. 7 is a schematic diagram of ln([M] ₀ /[M]) changing with time in the polymerization system promoted by NaI;

Figure 8 shows the polymer molecular weight (M _{n, GPC} ) and molecular weight distribution in the NaI-promoted polymerization system

Schematic diagram of the change with the conversion rate;

Fig. 9 is the H NMR spectrogram of polymer (AB) _n in the polymerization system promoted by NaI;

Fig. 10 is the NMR fluorine spectrum of the polymer (AB) _n in the NaI-promoted polymerization system.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the examples given are not intended to limit the present invention.

Selected chemical reagents in the embodiment: 1,4-diiodoperfluorobutane (98%, Tissie); 1,6-diiodoperfluorohexane (98%, Tissie); Adipic acid Diallyl ester (98%, TSI); Diallyl 1,4-cyclohexanedicarboxylate (mixture of cis and trans, 98%, TCI); 1,7-octyl Dienes (>97%, Alfa Aesar); 1,9-Decadiene (>97%, Ticia).

Accelerator: TMEDA (99%, Anaiji Chemical), sodium iodide (99%, Tsi Ai).

Example 1:

Polymerization step facilitated by TMEDA under visible light irradiation in chloroform solvent system

A mixture of 1,6-diiodoperfluorohexane (0.25 mmol), 1,7-octadiene (0.25 mmol) and TMEDA (0.05 mmol) was dissolved in 2 mL of chloroform and added to a clean stirring in the ampoule of the child. Oxygen was then removed by three freeze-pump-thaw cycles, and the ampoules were immediately flame-sealed. Subsequently, the ampoule was placed on a stirrer surrounded by a purple LED light source (λ _max =403nm, 29.7mW cm ^-2 ), and the polymerization temperature was controlled to 25°C by 14°C circulating water cooling and electric fan. After the specified reaction time, the tube was broken and the product was dissolved in a small amount of tetrahydrofuran, and poured into 200 mL ice methanol to precipitate for a certain period of time. Then, the obtained solid product was filtered and dried in a vacuum oven at 30 °C to constant weight, and the yield was calculated by gravimetric analysis.

Example 2:

In the chloroform solvent system, investigate the effect of different amines and their dosage on the polymerization

Through experimental exploration, it can be found that various types of amines can effectively promote polymerization under the irradiation of 403nm visible light, but the polymerization of the system without amines fails. According to the analysis in Table 1, it is known that TMEDA, triethylamine, ethylamine, ethylenediamine, etc. can all obtain good polymerization results, while the effect of pyridine-promoted polymerization is poor. Here, TMEDA is mainly used as a representative of amine accelerators to further study the influence of amines on polymerization behavior. Not only that, by further adjusting the amount of amine accelerator to explore its influence on the polymerization effect, as shown in Table 2, it is found that only a small amount of amine (0.2 equiv.) needs to be added to the system to achieve the ideal polymerization effect, Not only conforms to the concept of green chemistry, but also meets the requirements of polymerization. However, when too much amine is added to the system, the polymerization effect gradually becomes poor. Therefore, the amount of TMEDA accelerator added in the following studies is 0.2 equip. to ensure that the polymerization can be carried out quickly and efficiently.

Table 1. Effect of different amine accelerators on polymerization

Polymerization conditions: [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[Accelerator] ₀ =1:1:0.4, the solvent volume is 2mL, and the solution polymerization is carried out under the irradiation of purple light at room temperature. ^aUntested .

Table 2. Effect of the amount of TMEDA accelerator on polymerization

Polymerization conditions: [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[Accelerator] ₀ =1:1:0.4, the solvent volume is 2mL, and the solution polymerization is carried out under the irradiation of purple light at room temperature.

Example 3:

Using TMEDA as an amine accelerator to investigate the effect of different organic solvents on polymerization

Due to the poor solubility of fluoropolymers in conventional organic solvents, different solvents will greatly affect the polymerization effect, so it is necessary to find a suitable solvent system. Due to the simple components of the system, except for two bifunctional monomers, there is only one amine accelerator. By exploring the influence of various organic solvents on polymerization, it is found that most organic solvents are suitable for this polymerization system, such as chloroform , acetone, dimethyl carbonate, dimethyl sulfoxide, 1,4-dioxane and other organic solvents, but the polymerization rate and results are different, see Table 3 for details.

Table 3. Effect of different solvent systems on polymerization

Polymerization conditions: [C6F12I2]0:[C8H14]0:[TMEDA]0=1:1:0.2, the solvent volume is 2mL, the polymerization time is 21h, and the solution polymerization is carried out under the irradiation of purple light at room temperature.

According to the results shown in Table 3, it can be known that the polymerization system can obtain an ideal polymerization effect in a single solvent, thereby avoiding the cumbersomeness and waste caused by mixed solvents. Of course, mixed solvents can also achieve polymerization, such as Chloroform mixed with acetone, etc. Among them, dimethyl carbonate, as a green solvent, can slow down the occurrence of chain transfer to a great extent. However, when dimethyl carbonate is used as a solvent in this polymerization system, only a part of the molecular chains can continue to react in the late stage of polymerization, resulting in a bimodal distribution in the elution curve of GPC (gel permeation chromatography) and a wide molecular weight distribution. . Chloroform has good solubility to most compounds. When using chloroform solvent system, the polymerization effect is more prominent, the molecular weight is higher and the molecular weight distribution is relatively narrow. Therefore, in the following investigations, chloroform was mainly used as the polymerization solvent system.

Example 4:

Polymerization of different α,ω-diiodoperfluoroalkanes and α,ω-non-conjugated dienes in chloroform solvent system with TMEDA as amine accelerator

After a polymerization method is proposed, it is necessary to further broaden the scope of application of its monomers. Various functional monomers can be designed by introducing functional functional groups into α,ω-non-conjugated dienes through chemical bonds or physical interactions. As with the non-conjugated monomers involved in Example 1, even the low-activity 1,4-diiodoperfluorobutane can be effectively synthesized with α,ω-non-conjugated dienes of different structures under visible light at room temperature. polymerization. According to the polymerization results in Table 4, it can be known that the polymerization system not only has simple components and mild conditions, but also has high tolerance to polar and ionic groups, and is outstanding in the preparation of main chain semifluorinated polymers. Advantage.

Schematic diagram of the chemical structure of α,ω-diiodoperfluoroalkane (A) and α,ω-non-conjugated diene (B)

Table 4. Examination of monomer applicability

Polymerization conditions: [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[TMEDA] ₀ ＝1:1:0.2, the solvent volume is 2mL, and the solution polymerization is carried out under the irradiation of purple light at room temperature.

Example 5:

In the chloroform solvent system, TMEDA was used as an amine accelerator to investigate the effect of different wavelengths of LED light on polymerization

After screening the polymerization conditions, according to the polymerization steps described in Example 1, the influence of different wavelengths of LED light (373nm-740nm) on the polymerization effect was investigated to broaden the applicability of the polymerization system. The results are shown in Table 5.

Table 5. Effect of different wavelengths of LED light on polymerization

Polymerization conditions: [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[TMEDA] ₀ =1:1:0.2, the solvent volume was 2mL, and solution polymerization was carried out under LED light irradiation at room temperature. ^aUntested .

From the above polymerization results, it can be seen that under the irradiation of light sources with different wavelengths, the polymerization system also exhibits different polymerization effects. When the polymerization cannot be promoted under the irradiation of longer-wavelength LEDs (such as green LEDs and near-infrared LEDs), the polymerization effect is better under the irradiation of shorter-wavelength LEDs (such as purple LEDs and blue LEDs). However, no polymer was formed in the blank experiment without LED light irradiation, indicating that the halogen-bonded complex needs to absorb visible light to generate intramolecular single electron transfer (SET) and then generate free radical intermediates. Therefore, in this system, the violet LED is selected as the polymerization light source.

Embodiment 6:

In the chloroform solvent system, TMEDA was used as the amine accelerator to investigate the influence of different monomer feed ratios on the polymerization

Since the polymerization system is realized by the continuous addition of -CI- of α, ω-diiodoperfluoroalkane and -C=C- of α, ω-non-conjugated diene, the two non-conjugated mono The feed ratio of the polymer will have a certain influence on the molecular weight and yield of the polymer. According to the polymerization results in Table 6, it can be known that the polymerization cannot occur when the molar ratio of 1,6-diiodoperfluorohexane to 1,7-octadiene is 1:0 or 0:1, which means that the two Both monomers are indispensable in this polymerization system. Not only that, when the feed ratio of one of the monomers is enlarged, that is, when the molar ratio of 1,6-diiodoperfluorohexane to 1,7-octadiene is 1:1.2 or 1.2:1, the polymerization The molecular weights of the compounds are relatively low, indicating that an excess of a certain monomer will affect the polymerization effect. Therefore, the feed ratio of the monomer is very important to the polymerization. In this system, the feed ratio of the raw materials is fixed as [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[TMEDA] ₀ =1: 1:0.2.

Table 6. Effect of different monomer feed ratios on polymerization

Polymerization conditions: [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[TMEDA] ₀ =1:1:0.2, the solvent volume is 2mL, and the solution polymerization is carried out under LED light irradiation at room temperature for 21 hours. ^aUntested .

Embodiment 7:

In the chloroform solvent system, TMEDA was used as an amine accelerator to study the kinetic behavior of polymerization

The kinetic behavior of the polymerization was investigated, and the monomer conversion rate was calculated by weight of the polymers obtained at different times of reaction, and the molecular weight and molecular weight distribution of the fluorine-containing alternating copolymer were characterized on a TOSOH HLC-8320 GPC. From the analysis in Figure 1 and Figure 2, it can be seen that the monomer conversion rate increases rapidly in the initial stage of polymerization, and the molecular weight of the polymer continues to increase, which conforms to the kinetic characteristics of gradual polymerization.

Embodiment 8:

NMR Analysis of Polymer (AB) _n

Since the polymer is realized by the continuous addition of -CI- of α,ω-diiodoperfluoroalkane (A) and -C=C- of α,ω-non-conjugated diene (B), the The polymers are arranged in strict alternation. The structure of the polymer can be more intuitively analyzed by ¹ H and ¹⁹ F NMR spectroscopy. Since -CHI-(h) and CF ₂ CH ₂ CHI-(i) are produced by the effective addition of two non-conjugated monomers once, it can be seen from the ¹ H NMR analysis in Figure 3 that the chemical shift integral ratio of h and i The ratio is 1:2, indicating that the newly formed -CHI- is extremely stable, and the polymers are strictly arranged in a linear alternating order. When the integral of -CH=CH ₂ (c) was set to 1.00, the integral of -CHI-(h) was 10.81. According to the following formula 1, it can be calculated that the degree of polymerization of the fluorine-containing alternating polymer is 6, and the molecular weight is 4000 g/mol. Similarly, according to Equation 2, the degree of polymerization can also be calculated as 6 based on the corresponding integral ratios in the ¹⁹ F NMR spectrum of FIG. 4 .

Formula 1: Calculation of degree of polymerization from ¹ H NMR:

Equation 2: Calculation of degree of polymerization from ¹⁹ F NMR:

Embodiment 9:

Polymerization in water/organic solvent system with TMEDA as accelerator

Due to the existence of chain transfer side reactions in this system, a small amount of water was added to the polymerization system to stabilize free radical intermediates, thereby inhibiting the occurrence of chain transfer. The experimental results show that the polymerization efficiency does not change significantly in the mixed solvent system of chloroform/water. However, the mixed solvent system of acetone/water or 1,4-dioxane/water can effectively reduce the occurrence of side reactions and significantly increase the yield of polymers. It can be seen from Figure 5 and Figure 7 that the GPC efflux curve shifted significantly before and after adding water, indicating that the molecular weight of the polymer can be significantly increased by adjusting the amount of solvent and water.

Table 7. Effect of Water/Organic Solvent System on Polymerization

Polymerization conditions: [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[TMEDA] ₀ =1:1:0.2, solution polymerization was carried out under LED light irradiation at room temperature for 21 hours.

Example 10:

Polymerization steps promoted by sodium iodide under visible light irradiation in an acetone solvent system

A mixture of 1,6-diiodoperfluorohexane (0.25 mmol), 1,7-octadiene (0.25 mmol) and sodium iodide (2.25 mmol) was dissolved in 2 mL of acetone and added to a clean in an ampoule with a stir bar. Oxygen was then removed by three freeze-pump-thaw cycles, and the ampoules were immediately flame-sealed. Subsequently, the ampoule was placed on a stirrer surrounded by a purple LED light source (λ _max =403nm, 29.7mW cm ^-2 ), and the polymerization temperature was controlled to 25°C by 14°C circulating water cooling and electric fan. After the specified reaction time, the tube was broken and the product was dissolved in a small amount of tetrahydrofuran, and poured into 200 mL ice methanol to precipitate for a certain period of time. Then, the obtained solid product was filtered and dried in a vacuum oven at 30 °C to constant weight, and the yield was calculated by gravimetric analysis.

Example 11:

Polymerization system promoted by different halogen salts in acetone solvent system

When the addition of sodium iodide can effectively promote the polymerization, it is replaced by other halogen salts (such as iodide salt, chloride salt, bromide salt). According to the polymerization results in Table 8, it can be known that various halogen salts can promote polymerization, among which iodide salt has a better catalytic effect, but tetrabutylammonium triiodide cannot promote polymerization. Therefore, in the following investigations, sodium iodide, which has a simple structure and low price, is used as an accelerator.

Table 8. Effect of different halogen salt accelerators on polymerization

Polymerization conditions: [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[Accelerator] ₀ =1:1:1, the volume of the solvent is 2mL, and the solution polymerization is carried out under LED light irradiation at room temperature for 21 hours. ^aUntested .

Example 12:

In the polymerization system promoted by sodium iodide, the influence of different solvent systems on the polymerization

Due to the limited types of organic solvents that can satisfy both sodium iodide and fluorine-containing alternating copolymers with good solubility, only a few solvents are listed in Table 9. According to the polymerization results, it can be seen that when tetrahydrofuran (THF) and dimethylacetamide (DMA) are selected as the polymerization solvent system, the polymerization proceeds, but the polymerization yield and polymer molecular weight are difficult to meet the polymerization requirements. Not only that, we explored the effect of mixed solvents on the polymerization, such as MeCN/DMC, but the polymerization effect was not good. In contrast, when acetone is used as the polymerization solvent system, the polymerization effect is more prominent, therefore, in the following investigation, the polymerization is carried out in acetone.

Table 9. Influence of Organic Solvents on Polymerization

Polymerization conditions: [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[NaI] ₀ =1:1:1, the solvent volume was 2mL, and solution polymerization was carried out under LED light irradiation at room temperature for 21 hours.

Example 13:

Influence of the amount of sodium iodide on polymerization in acetone solvent system

According to the fact that the amount of amine in Example 2 has a certain influence on the polymerization result, continue to explore the effect of its amount on the polymerization in the polymerization system promoted by sodium iodide. According to Figure 6, it can be known that when the amount of NaI is continuously increased, the high molecular weight part of the polymer gradually increases, and the molecular weight distribution also broadens accordingly. When adding 9.0 equivalents of sodium iodide, the polymerization reached the optimum state. Continuing to increase the amount of sodium iodide will make the polymerization effect worse, which is not conducive to the realization of ideal polymerization.

Example 14:

In the acetone solvent system, the effect of different LED lights on the polymerization system promoted by sodium iodide was investigated

After screening the polymerization conditions, according to the polymerization steps described in Example 10, the influence of different wavelengths of LED light (373nm-460nm) on the polymerization effect was investigated to broaden the applicability of the polymerization system. The results are shown in Table 10.

Table 10. Effect of different wavelengths of LED light on polymerization

Polymerization conditions: [C ₆ F ₁₂ I ₂ ] ₀ :[C ₈ H ₁₄ ] ₀ :[NaI] ₀ =1:1:9, the solvent volume was 2mL, and the solution polymerization was carried out under LED light irradiation at room temperature. ^aUntested .

From the above polymerization results, it can be seen that under the irradiation of light sources with different wavelengths, the polymerization system also exhibits different polymerization effects. When the polymerization cannot be promoted under the irradiation of blue LED light, only under the irradiation of shorter wavelength LED light (373-403nm), the polymerization can proceed. The failure of polymerization in the blank experiment under dark conditions further indicates that the halogen-bonded complexes need to absorb visible light to generate intramolecular single electron transfer (SET) and then generate free radical intermediates. Light source screening experiments show that shorter wavelength LED light is a suitable light source in the NaI-promoted polymerization system.

Example 15:

Study on the Kinetic Behavior of Polymerization Promoted by Sodium Iodide and the Structure Analysis of Polymer in Acetone Solvent System

In order to further study the polymerization behavior of the system and the structural characteristics of the polymer, the polymerization kinetics of 1,6-diiodoperfluorohexane and 1,7-octadiene were studied. It can be seen from Figures 7 and 8 that as the polymerization time increases, the molecular weight of the polymer increases slowly, which still conforms to the characteristics of gradual polymerization. Moreover, the polymer has a wide molecular weight distribution, and the GPC elution curve shows a bimodal distribution. Mainly due to the low concentration of functional groups in the late polymerization system, only a part of the polymer chain can continue to grow. The microstructure of the polymer can be analyzed by ¹ H NMR (Figure 9) and ¹⁹ F NMR (Figure 10). When the feeding ratio of the two monomers is 1:1, the two ends of the polymer chain are respectively -CF ₂ I and -C=C-, the newly formed -CHI- is extremely stable, and the polymers are strictly arranged in a linear alternating order.

The invention discloses a main chain type "semifluoro" alternating copolymer prepared by forming a halogen bond (XB) complex between α, ω-diiodoperfluoroalkanes and amine/halogen salts under visible light irradiation aggregation strategy. Specifically, the polymerization method includes the following steps: 1) mixing two non-conjugated monomers and an accelerator according to a certain molar ratio, and dissolving them in an organic solvent with a certain volume ratio. 2) The polymerization temperature is controlled at 25°C by circulating water cooling and an electric fan, and irradiated with LED light of a certain wavelength for 3min-56h. 3) After the reaction, break the tube and dilute the product with tetrahydrofuran, pour it into ice methanol for precipitation for a period of time, suction filter and dry to obtain the fluorine-containing alternating copolymer. 4) It is worth noting that amines and halogen salts have a certain influence on the polymerization effect, and can obtain fluorine-containing polymers with different functional groups at the end of the polymer chain, thus providing more possibilities for post-modification and structural design of the polymer . Therefore, this polymerization strategy has simple components, low cost, and easy post-processing, which provides a new idea for designing smart fluoropolymer materials in a green and environmentally friendly way.

Apparently, the above-mentioned embodiments are only examples for clear description, and are not intended to limit the implementation. For those of ordinary skill in the art, on the basis of the above description, other changes or changes in various forms can also be made. It is not necessary and impossible to exhaustively list all the implementation manners here. However, the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims

A method for preparing fluorine-containing alternating polymers, comprising the following steps,

S1: Dissolving α, ω-diiodoperfluoroalkane, α, ω-non-conjugated diene and accelerator in an organic solvent, the accelerator is an amine accelerator and/or a halogen salt accelerator;

S2: After deoxidation and sealing, place it under light conditions to react to obtain a polymerization system;

S3: Precipitate the polymerization system to obtain the fluorine-containing alternating polymer, whose structural formula is as follows:

Wherein, n is any integer in 2-30.
The preparation method of fluorine-containing alternating polymer according to claim 1, characterized in that water is also added in the step S1.
The preparation method of fluorine-containing alternating polymer according to claim 2, characterized in that the volume ratio of water to organic solvent is 0.2-1:2.
The preparation method of fluorine-containing alternating polymer as claimed in claim 1, characterized in that, in the step S1,

When the accelerator is an amine accelerator, the molar ratio of α, ω-diiodoperfluoroalkane, α, ω-non-conjugated diene and the accelerator is 1-1.2: 1.2-1: 0.1-3;

When the accelerator is a halogen salt accelerator, the molar ratio of α,ω-diiodoperfluoroalkane, α,ω-non-conjugated diene and the accelerator is 1-1.4:1.4-1:0.5-15.
The preparation method of fluorine-containing alternating polymers as claimed in claim 1 or 4, wherein the α, ω-diiodoperfluoroalkane is selected from 1,4-diiodoperfluorobutane, 1, One or more of 6-diiodoperfluorohexane.
The preparation method of fluorine-containing alternating polymers as claimed in claim 1 or 4, wherein the α, ω-non-conjugated diene is selected from 1,7-octadiene, 1,9-decadiene , diallyl adipate, diallyl 1,4-cyclohexanedicarboxylate, tridecethoxy-1,48-diene and one or more of compound A, wherein compound A The structural formula is as follows:
The preparation method of fluorine-containing alternating polymer as claimed in claim 1 or 4, is characterized in that, the amine accelerator is selected from N, N, N', N'-tetramethylethylenediamine, triethylamine , ethylenediamine, ethylamine, diethylamine and pyridine; the halogen salt promoter is selected from sodium iodide, tetrabutylammonium iodide, sodium chloride, tetrabutylammonium bromide and one or more of diphenylphosphine chloride.
The preparation method of fluorine-containing alternating polymer as claimed in claim 1, characterized in that, in the step S1,

When the accelerator is an amine accelerator, the organic solvent is selected from one of chloroform, dimethyl sulfoxide, dimethylethylenediamine, acetone, 1,4-dioxane and dimethyl carbonate. one or more kinds;

When the accelerator is a halogen salt accelerator, the organic solvent is selected from one or more of dimethylacetamide, acetone, tetrahydrofuran, dimethyl carbonate and acetonitrile.
The preparation method of fluorine-containing alternating polymer according to claim 1, characterized in that, in the step S2, the wavelength of light is 373-403nm.
The preparation method of fluorine-containing alternating polymer as claimed in claim 1 or 9, characterized in that, in the step S2,

When the accelerator is an amine accelerator, the reaction time is 3min-28h;

When the accelerator is a halogen salt accelerator, the reaction time is 3h-56h.