Method for accelerating RAFT stepwise polymerization based on photochemical flow reactor

Abstract

The invention discloses a method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor, which comprises the following steps: mixing a bifunctional xanthate type RAFT reagent, a bifunctional vinyl acetate type polymeric monomer and a solvent, pumping the mixture into a reaction tube of a first photochemical flow reactor, and carrying out polymerization reaction under the irradiation of an LED lamp to obtain a polymer solution; the polymer solution and the pumped vinyl acetate type chain extension monomer converge and flow into a reaction tube of a second optical flow reactor, and a chain extension reaction is performed under the irradiation of an LED lamp to obtain the brush polymer. The photo-initiated RAFT stepwise polymer has active characteristics, can be functionalized after chain extension to prepare a multifunctional polymer material, and is suitable for different application scenes; the obtained polymer can be degraded under an alkaline condition to generate small molecules, and accords with the green and environment-friendly chemical concept; the stepwise polymerization method is high in reaction rate and can be applied to industrial production and synthesis of the degradable alternating sequence functionalized polymer.

Description

Technical Field

[0001] The present invention relates to the technical field of RAFT step-by-step polymerization, and in particular to a method for accelerating RAFT step-by-step polymerization based on a photochemical flow reactor. Background Art

[0002] Flow chemistry technology is widely used in polymer synthesis. Compared with traditional batch reactors (such as reaction flasks and kettles), flow chemistry reactors offer a larger specific surface area, higher mass and heat transfer efficiencies, and are more suitable for modular operation, effectively improving the efficiency of chemical reactions. They have been widely used in organic synthesis, analytical chemistry, biomedicine, and other fields. Leveraging the advantages of flow chemistry reactors, such as their high specific surface area and high mass and heat transfer efficiencies, RAFT (Reversible Addition-Fragmentation Chain Transfer) polymerization, particularly light-mediated RAFT polymerization, exhibits faster polymerization rates and superior results compared to traditional batch polymerization methods.

[0003] RAFT stepwise polymerization is an important branch derived from RAFT polymerization. With the help of the single-unit monomer insertion reaction of the thiocarbonate group, a polymer with an alternating structure can be obtained in one pot. In addition, degradable and post-modified thiocarbonate groups can be designed and added to the polymer main chain and side chain, which is of great significance for the synthesis of degradable polymer materials with precise alternating structures.

[0004] However, RAFT step-by-step polymerization requires a high degree of reaction, requiring a long reaction time to obtain the target polymer with sufficient molecular weight. While attempts to apply RAFT polymerization to flow polymerization have been numerous in recent years, there have been no reports of applying flow polymerization technology to accelerate RAFT step-by-step polymerization. This technology is of great significance for the rapid synthesis of multifunctional alternating sequence degradable polymers. Summary of the Invention

[0005] The present invention addresses the deficiencies in the prior art and provides a method for accelerating RAFT step-by-step polymerization based on a photochemical flow reactor. A difunctional xanthate-type RAFT agent and a difunctional vinyl acetate-type polymerization monomer are subjected to RAFT step-by-step polymerization in a photochemical flow reactor, thereby solving the problem in the prior art that this type of reaction requires a long reaction time to obtain a target polymer with a sufficient molecular weight. A vinyl acetate-type chain extension monomer is introduced and free radical chain extension is carried out with the obtained target polymer in a photochemical flow reactor to synthesize a brush-like degradable polymer. The RAFT step-by-step polymerization reaction method can be applied to the industrial production of synthesizing degradable alternating sequence functionalized polymers.

[0006] In order to solve the above technical problems, the first aspect of the present invention provides a method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor, comprising the following steps:

[0007] S1, mixing a difunctional xanthate-type RAFT agent and a difunctional vinyl acetate-type polymerization monomer with a solvent to obtain a mixed solution, pumping the mixed solution into a reaction tube of a first photochemical flow reactor, and performing a photoinitiated free radical polymerization reaction under irradiation of an LED lamp to obtain a polymer solution;

[0008] S2. After flowing out of the reaction tube of the first photochemical flow reactor, the polymer solution merges with the pumped-in vinyl acetate type chain extension monomer and flows into the reaction tube of the second optical flow reactor, and undergoes a light-initiated free radical chain extension reaction under the irradiation of an LED lamp to obtain a brush-like polymer.

[0009] The present invention conducts photo-initiated RAFT polymerization of a difunctional xanthate-type RAFT agent and a difunctional vinyl acetate-type polymerization monomer in a photochemical flow reactor to obtain a target polymer with a sufficient molecular weight. Then, a vinyl acetate-type chain extension monomer is introduced to carry out free radical chain extension in the photochemical flow reactor to synthesize a brush-like degradable polymer. The reaction rate is fast and can be applied to the industrial production of synthesizing degradable alternating sequence functionalized polymers.

[0010] Furthermore, the bifunctional xanthate RAFT agent is:

[0011]

[0012] Furthermore, the difunctional vinyl acetate type polymerization monomer is: The vinyl acetate type chain extending monomer is:

[0013] Furthermore, the molar ratio of the bifunctional xanthate RAFT agent to the bifunctional vinyl acetate polymer monomer is 1:(0.9-1.1).

[0014] Furthermore, the concentration of the bifunctional xanthate RAFT agent in the mixed solution is 0.5-1.5 mol / L.

[0015] Furthermore, in S1 and S2, the wavelength of the LED light is 365-520 nm, and the intensity is 0.2-2.0 mW cm - 2 nm -1 .

[0016] Furthermore, in S1, the flow rate of the mixed solution pumped into the first optical flow reactor is 1-50 μL min -1In S2, the pumping rate of the vinyl acetate type chain extension monomer is 1-50 μL min -1 .

[0017] Furthermore, the first photochemical flow reactor and the second photochemical flow reactor both include an outer cylinder and an inner cylinder passing through the outer cylinder, the reaction tubes are wound around the inner cylinder at equal intervals, and the LED lights are wound around the outer cylinder at equal intervals.

[0018] Furthermore, the first photochemical flow reactor and the second photochemical flow reactor are both temperature-controlled by respective heat dissipation devices.

[0019] The second aspect of the present invention provides a brush polymer prepared by the method described in the first aspect, wherein the brush polymer can be degraded by aminolysis under alkaline conditions.

[0020] Beneficial effects of the present invention:

[0021] The photoinitiated RAFT step-by-step polymer of the present invention has active characteristics and can be functionalized after chain extension to prepare multifunctional polymer materials, which are suitable for different application scenarios; the obtained polymer can be degraded under alkaline conditions to generate small molecules, which conforms to the concept of green and environmentally friendly chemistry; the step-by-step polymerization method has a fast reaction rate and can be applied to industrial production to synthesize degradable alternating sequence functionalized polymers. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 This is a schematic diagram of the accelerated RAFT step-by-step polymerization state based on the photochemical flow reactor of the present invention;

[0024] Figure 2 is the H NMR spectrum of DiEXEP1 obtained in Example 1 of the present invention;

[0025] Figure 3 is the H NMR spectrum of DiEXEP2 obtained in Example 2 of the present invention;

[0026] Figure 4 This is a comparison of the polymerization rates of Example 1 and Comparative Example 1 of the present invention;

[0027] Figure 5 This is a comparison of the polymerization rates of Example 2 of the present invention and Comparative Example 2;

[0028] Figure 6is the H NMR spectrum of the polymer obtained in Example 3 of the present invention;

[0029] Figure 7 is the size exclusion chromatogram of the polymers obtained in Examples 2 and 3 of the present invention;

[0030] Figure 8 It is the size exclusion chromatogram of the polymer obtained in Example 3 of the present invention and the degraded composition of Example 4. DETAILED DESCRIPTION

[0031] The following will provide a clear and complete description of the technical solutions of the present invention in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] This embodiment relates to a method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor, comprising the following steps:

[0033] S1, mixing a difunctional xanthate type RAFT agent and a difunctional vinyl acetate type polymerization monomer with a solvent to obtain a mixed solution, and pumping the mixed solution into the reaction tube of the first photochemical flow reactor, referring to Figure 1 , a light-initiated free radical polymerization reaction is carried out under the irradiation of an LED light to obtain a polymer solution;

[0034] S2. After flowing out of the reaction tube of the first photochemical flow reactor, the polymer solution merges with the pumped-in vinyl acetate type chain extension monomer and flows into the reaction tube of the second optical flow reactor, and undergoes a light-initiated free radical chain extension reaction under the irradiation of an LED lamp to obtain a brush-like polymer.

[0035] As a preferred embodiment, the bifunctional xanthate RAFT agent is DiEXEP1 and / or DiEXEP2, and the structural formulas of DiEXEP1 and DiEXEP2 are respectively:

[0036]

[0037] As a preferred embodiment, the difunctional vinyl acetate type polymer monomer DiVAc is: The vinyl acetate type chain extending monomer VAc is:

[0038] As a preferred embodiment, the molar ratio of the difunctional xanthate RAFT agent to the difunctional vinyl acetate polymer monomer is 1:(0.9-1.1); and the concentration of the difunctional xanthate RAFT agent in the mixed solution is 0.5-1.5 mol / L.

[0039] As a preferred embodiment, in S1 and S2, the wavelength of the LED light is 365-520 nm, and the intensity is 0.2-2.0 mW cm -2 nm -1 In S1, the mixed solution is pumped into the first optical flow reactor at a flow rate of 1-50 μL min -1 In S2, the pumping rate of the vinyl acetate type chain extending monomer is 1-50 μL min -1 .

[0040] As a preferred embodiment, the first photochemical flow reactor and the second photochemical flow reactor both include an outer cylinder and an inner cylinder passing through the outer cylinder, the reaction tubes are wound on the inner cylinder at equal intervals, and the LED lights are wound on the outer cylinder at equal intervals; the first photochemical flow reactor and the second photochemical flow reactor are both temperature-controlled by their own heat dissipation devices, where the heat dissipation devices are fans.

[0041] Another embodiment provides a brush polymer prepared by the method described in the above embodiment, wherein the brush polymer can be degraded by aminolysis under alkaline conditions.

[0042] Example 1

[0043] This embodiment relates to a method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor, comprising the following steps:

[0044] (1) Synthesis of DiEXEP1: 4 g (100 mmol) of NaOH was dissolved in 200 mL of anhydrous ethanol in a 500 mL round-bottom flask, followed by dropwise addition of 9.14 g (120 mmol) of carbon disulfide. After stirring at room temperature for 1 hour, 14.94 g (45 mmol) of 2-bromopropionic acid 2-[(2-bromopropionyl)oxy]ethyl ester (DiEPBr) was added, and the reaction solution was stirred for 5 hours. After the reaction, the solvent was removed by rotary evaporation, 100 mL of saturated brine was added for washing, and the mixture was extracted twice with 80 mL of ethyl acetate. The organic phase was dried over anhydrous sodium sulfate and concentrated by rotary evaporation to obtain a crude product. The crude product was separated by column chromatography to obtain 10.51 g of a yellow oily liquid, the hydrogen nuclear magnetic spectrum of which is shown in FIG. Figure 2 shown.

[0045] (2) Flow RAFT stepwise polymerization of DiEXEP1 and DiVAc: In a glass ampoule, a mixture was prepared with dioxane as solvent, a molar ratio of [DiEXEP1]:[DiVAc] = 1:1, and a DiEXEP1 concentration of 1 mol / L. A trace amount of tetrachloroethane (TCE) was added as an internal standard. The mixture was deoxygenated through a double-row tube. A commercially available medical syringe (10 mL) was used to draw the solution from the ampoule. The syringe needle was then placed in a syringe pump and the injection program (3 μL min) was set. -1 injection rate), injected into the reaction tube of the first photochemical flow reactor (tube outer diameter 1.6 mm, inner diameter 0.8 mm), using a purple LED light strip (405 nm, 0.6 mW cm -2 nm -1 ) irradiation, a fan is turned on to control the temperature. After a predetermined time interval, the light source is turned off and the remaining solution in the pipeline is expelled. The reaction extent is calculated by integrating the proton nuclear magnetic resonance (1H NMR) spectrum, and the polymer molecular weight and molecular weight distribution are characterized by size exclusion chromatography (SEC).

[0046] Example 2

[0047] This embodiment relates to a method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor, comprising the following steps:

[0048] (1) Synthesis of DiEXEP2: 3.88 g (20 mmol) of tetraethylene glycol was dissolved in 100 mL of tetrahydrofuran in a 500 mL round-bottom flask, followed by the addition of 2.805 g (50 mmol) of potassium hydroxide. After stirring at room temperature for 30 minutes, 4.57 g (60 mmol) of carbon disulfide was added. The reaction solution was stirred for 1 hour, and then 7.24 g (40 mmol) of ethyl 2-bromopropionate was slowly added dropwise. The reaction was stirred at room temperature overnight. After the reaction was completed, the solvent was removed by rotary evaporation, 100 mL of ethyl acetate was added to dissolve the solution, and then washed three times with 100 mL of saturated brine. The organic phase was dried over anhydrous sodium sulfate and concentrated by rotary evaporation to obtain a crude product. The crude product was separated by column chromatography to obtain 9.15 g of a yellow oily liquid, the hydrogen nuclear magnetic spectrum of which is shown in FIG. Figure 3 shown.

[0049] (2) Flow RAFT stepwise polymerization of DiEXEP2 and DiVAc: In a glass ampoule, a mixture was prepared with dioxane as solvent, a molar ratio of [DiEXEP2]:[DiVAc] = 1:1, and a DiEXEP2 concentration of 1 mol / L. A trace amount of tetrachloroethane (TCE) was added as an internal standard. The mixture was deoxygenated through a double-row tube. A commercially available medical syringe (10 mL) was used to draw the solution from the ampoule. The syringe needle was then placed in a syringe pump and the injection program (3 μL min) was set. -1injection rate), injected into the reaction tube of the first photochemical flow reactor (tube outer diameter 1.6 mm, inner diameter 0.8 mm), using a purple LED light strip (405 nm, 0.6 mW cm -2 nm -1 ) irradiation, a fan is turned on to control the temperature. After a predetermined time interval, the light source is turned off and the remaining solution in the pipeline is expelled. The reaction extent is calculated by integrating the proton nuclear magnetic resonance (1H NMR) spectrum, and the polymer molecular weight and molecular weight distribution are characterized by size exclusion chromatography (SEC).

[0050] Comparative Example 1

[0051] This comparative example involves the intermittent RAFT stepwise polymerization of DiEXEP1 and DiVAc. The difference from Example 1 is that step (2) is:

[0052] In a dry glass tube equipped with a three-way stopcock, dioxane was used as the solvent, the molar ratio of [DiEXEP1]:[DiVAc] = 1:1, the concentration of DiEXEP1 was 1 mol / L, a trace amount of tetrachloroethane (TCE) was added as an internal standard, and the mixture was deoxygenated through a double-row tube to seal the glass tube. The glass tube was then placed under 25°C ultraviolet light (405 nm, 0.6 mW cm - 2 nm -1 ) was irradiated under argon atmosphere, and a small amount of the reaction solution was extracted with a long needle for analysis at predetermined time intervals. The degree of reaction was calculated by integrating the hydrogen nuclear magnetic resonance spectrum (1H NMR), and the molecular weight and molecular weight distribution of the polymer were characterized by size exclusion chromatography (SEC). The reaction rate results of Example 1 and Comparative Example 1 are shown in FIG. Figure 4 As shown, it can be seen that the polymerization rate under the flow conditions of Example 1 is increased by 40%, wherein the rate increase ratio is calculated by comparing the time required for the reaction to reach the plateau phase under batch conditions (t1) with the time required under the flow conditions (t2): 100%×(1-t2 / t1).

[0053] Comparative Example 2

[0054] This comparative example involves the intermittent RAFT stepwise polymerization of DiEXEP2 and DiVAc. The difference from Example 2 is that step (2) is:

[0055] In a dry glass tube equipped with a three-way stopcock, dioxane was used as the solvent, the molar ratio of [DiEXEP2]:[DiVAc] = 1:1, the concentration of DiEXEP2 was 1 mol / L, a trace amount of tetrachloroethane (TCE) was added as an internal standard, and the mixture was deoxygenated through a double-row tube to seal the glass tube. The glass tube was then placed under 25°C ultraviolet light (405 nm, 0.6 mW cm -2 nm -1 ) was irradiated under argon atmosphere, and a small amount of the reaction solution was extracted with a long needle for analysis at predetermined time intervals. The reaction extent was calculated by integrating the hydrogen nuclear magnetic resonance spectrum (1H NMR), and the molecular weight and molecular weight distribution of the polymer were characterized by size exclusion chromatography (SEC). The reaction rate results of Example 2 and Comparative Example 2 are shown in FIG. Figure 5 As shown, it can be seen that the polymerization rate under the flow condition of Example 2 is increased by 70%.

[0056] Example 3

[0057] This embodiment relates to a method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor, comprising the following steps:

[0058] Deoxygenation of vinyl acetate monomer (VAc) was performed in a glass ampoule, and the deoxygenated monomer was drawn up using a medical syringe. A three-way PEEK connector, tubing, and a syringe pump were connected to the outlet of the reaction tube of the original first photochemical flow reactor in Example 2. After the flow polymerization of DiEXEP2 and DiVAc reached a plateau after 12 hours, the syringe pump was used to inject 10 μL / min of the solution. -1 The Vac injection line was connected to the polymer solution at a three-way PEEK head and then entered the reaction tube of the second optical flow reactor (tube outer diameter 1.6 mm, inner diameter 0.8 mm). A purple LED light strip (405 nm, 0.6 mW cm -2 nm -1 ) for 12 hours. Turn off the light source, push the remaining solution in the pipe out and expose it to air, and add a tetrahydrofuran mixture (10% v / v) to dilute and terminate the product. The diluted solution is slowly added dropwise to petroleum ether for precipitation. After the solution is clarified, the supernatant is discarded to obtain a polymer, which is then dried under vacuum at 40°C to constant weight. The polymer structure is characterized by hydrogen nuclear magnetic resonance spectroscopy (1H NMR), as shown in Figure 5. Figure 6 The polymer molecular weight and molecular weight distribution were determined by size exclusion chromatography (SEC), as shown in Figure 7 As shown, it can be seen that the chain extension was successfully carried out.

[0059] Example 4

[0060] This example relates to the degradation of the brush polymer obtained in Example 3, and specifically includes the following steps:

[0061] (1) The brush polymer obtained in Example 3 was dissolved in tetrahydrofuran in an ampoule and deoxygenated. At the same time, n-propylamine was deoxygenated in another ampoule. The molar number of RAFT agent groups contained in the polymer was estimated. Then, an equimolar amount of n-propylamine was injected into the ampoule containing the polymer solution. The ampoule was sealed and stirred for 15 minutes. After that, the seal was opened and the ampoule was exposed to air. A small amount of triethyl phosphite was added. The solvent and unreacted n-propylamine were removed using a double-row tube. The molecular weight and molecular weight distribution were determined by SEC. Figure 8 As shown, it can be seen that the aminolysis of the polymerization product was successfully carried out to generate small molecular compounds with a narrow molecular weight distribution.

[0062] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor, characterized in that: The steps include: S1, mixing a difunctional xanthate-type RAFT agent and a difunctional vinyl acetate-type polymerization monomer with a solvent to obtain a mixed solution, pumping the mixed solution into a reaction tube of a first photochemical flow reactor, and performing a photoinitiated free radical polymerization reaction under irradiation of an LED lamp to obtain a polymer solution; S2. After flowing out of the reaction tube of the first photochemical flow reactor, the polymer solution merges with the pumped-in vinyl acetate type chain extension monomer and flows into the reaction tube of the second optical flow reactor, and undergoes a light-initiated free radical chain extension reaction under the irradiation of an LED lamp to obtain a brush-like polymer.

2. The method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor according to claim 1, characterized in that: The bifunctional xanthate RAFT agent is:

3. The method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor according to claim 1, characterized in that: The difunctional vinyl acetate type polymerization monomer is: The vinyl acetate type chain extending monomer is:

4. The method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor according to claim 1, wherein: The molar ratio of the bifunctional xanthate type RAFT agent to the bifunctional vinyl acetate type polymerization monomer is 1:(0.9-1.1).

5. The method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor according to claim 1, characterized in that: The concentration of the bifunctional xanthate RAFT agent in the mixed solution is 0.5-1.5 mol / L.

6. The method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor according to claim 1, characterized in that: In S1 and S2, the LED light has a wavelength of 365-520 nm and an intensity of 0.2-2.0 mW cm -2 nm -1 .

7. The method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor according to claim 1, characterized in that: In S1, the mixed solution is pumped into the first optical flow reactor at a flow rate of 1-50 μL min -1 In S2, the pumping rate of the vinyl acetate type chain extension monomer is 1-50 μL min -1 .

8. The method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor according to claim 1, characterized in that: The first photochemical flow reactor and the second photochemical flow reactor both include an outer cylinder and an inner cylinder passing through the outer cylinder. The reaction tubes are wound around the inner cylinder at equal intervals, and the LED lights are wound around the outer cylinder at equal intervals.

9. The method for accelerating RAFT stepwise polymerization based on a photochemical flow reactor according to claim 1, wherein: The first photochemical flow reactor and the second photochemical flow reactor are both temperature-controlled by respective heat dissipation devices.

10. A brush polymer prepared by the method according to any one of claims 1 to 9, characterized in that: The brush polymer can be degraded by aminolysis under alkaline conditions.

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