A viscosity-responsive luminescent probe and its application in polymerization process analysis

Abstract

A viscosity-responsive luminescent probe and its use for polymerization process analysis belong to the field of probe technology. The structural formula is as follows: It can be used to measure the viscosity of liquid samples and observe the process of polymer polymerization. This hemicyanine-tetraphenylethylene fluorescent probe L-TPE has dual luminescence properties, that is, it can emit red fluorescence and blue fluorescence of different intensities under different viscosity environments. Using this probe, we can monitor the changes in viscosity and conversion rate in the polymerization reaction in real time, and we can also visualize the polymerization process through the composite light of red fluorescence and blue fluorescence. The present invention provides a novel method for non-destructive real-time monitoring of polymerization reactions.

Description

Technical Field

[0001] The present invention belongs to the technical field of viscosity fluorescence detection, and specifically relates to a luminescent probe that combines two viscosity-responsive groups with different fluorescence emission wavelengths. The luminescent probe has different fluorescence intensities and colors in different viscosity ranges, providing guidance for the development of non-destructive real-time monitoring methods for polymerization reactions. Background Art

[0002] During polymerization, the diffusion of monomer, polymer, and initiator molecules plays a key role, influencing not only the polymerization kinetics but also the properties of the resulting polymer material. Local viscosity significantly influences free radical formation, chain transfer, and chain termination, processes that reach diffusion limits after the reaction reaches a certain conversion rate. For example, changes in viscosity are particularly pronounced in bulk polymerization. A self-acceleration phenomenon, also known as the gelation effect or Tromsdorff effect, is often observed during bulk polymerization. Therefore, monitoring viscosity is crucial for understanding polymerization kinetics and controlling polymer product quality.

[0003] Traditional bulk viscosity detection methods (such as falling ball viscometer, capillary viscometer or expansion method) can only detect macroscopic viscosity, but lack detection at the molecular level. In addition, the fluorescent molecules currently used to monitor polymerization reactions usually need to be bonded to the polymer and can only be monitored by a single method (such as fluorescence intensity or fluorescence color change). Therefore, it is of great value to develop a class of stable and reliable dual-luminescence probes that utilize their high sensitivity, high contrast, fast response and non-invasive characteristics, avoid affecting the inherent properties of the polymer through physical doping, and use dual changes (fluorescence intensity and fluorescence color changes) to achieve rapid and sensitive visual analysis of the polymerization process.

[0004] The probe developed by the present invention can realize the visual analysis of the polymerization process through the dual changes of fluorescence intensity and fluorescence color. The probe L-TPE has two viscosity-responsive groups with different emission wavelengths. During the polymerization process, the red light emission intensity of the L part of the L-TPE molecule (the electron-donating group 4-diethylamino and the strong electron-withdrawing group 1,4-dimethylpyridinium iodide are connected by a conjugated π bond) and the blue light emission intensity of the tetraphenylethylene part (TPE) will increase to varying degrees with the increase of viscosity. By measuring the fluorescence intensity of the L-TPE molecule, the viscosity change during the polymerization process can be monitored. At the same time, by observing the fluorescence color of the L-TPE molecule with the naked eye and calculating the position in the International Illumination Commission (CIE) coordinate system, a visual analysis of the polymerization process can be realized. Summary of the Invention

[0005] The present invention aims to design a dual-fluorophore viscosity probe, L-TPE, to monitor viscosity changes during polymerization by utilizing changes in the red light emission intensity of the L in the L-TPE probe. The polymerization process can be visualized by combining the changes in the blue light emission intensity of the TPE in the L-TPE probe with the red light emission of the L.

[0006] The structural formula of the fluorescent probe L-TPE of the present invention is shown in formula (I):

[0007]

[0008] The preparation method of the viscosity-responsive fluorescent probe of the present invention comprises the following steps: (1) modifying the TPE portion by dehydroxyarylation coupling to obtain an intermediate III; (2) subjecting the product of step (1) to a Knoevenagel condensation reaction of the intermediate III with 1,4-dimethylpyridine iodide in the presence of piperidine as a catalyst to obtain a viscosity-responsive fluorescent probe L-TPE with dual emission.

[0009] Further, the specific operation of step (1) is as follows: 4-(diethylamino) salicylaldehyde, potassium carbonate, copper oxide and solvent are added to the reaction vessel in sequence, wherein the molar ratio of 4-(diethylamino) salicylaldehyde to potassium carbonate is 1:2-3, and the molar ratio of 4-(diethylamino) salicylaldehyde to copper oxide is 1:1-2; after stirring and activating at room temperature for 0.5-1h, compound II is added, wherein the molar ratio of 4-(diethylamino) salicylaldehyde to compound II is 2-3:1, and the temperature is raised to 50-60°C and refluxed for 4-10h under stirring; after the reaction is completed, the temperature is lowered to room temperature, potassium carbonate and copper oxide are removed by filtration, the filtrate is subjected to reduced pressure distillation to remove the solvent, and the obtained crude product is purified by silica gel column chromatography to obtain intermediate III.

[0010] The structural formula of the 4-(diethylamino) salicylaldehyde is: The structural formula of the compound II is: The structural formula of the intermediate III is:

[0011] The solvent in the above step (1) is tetrahydrofuran or acetone.

[0012] The silica gel column chromatography method uses n-hexane and ethyl acetate in a volume ratio of 4-5:1 as eluent.

[0013] The specific operation of step (2) is as follows: adding intermediate III, 1,4-lutidine iodide, piperidine catalyst and solvent to a reaction vessel in sequence, wherein the molar ratio of intermediate III to 1,4-lutidine iodide is 1:1-2; stirring and activating at room temperature for 0.5-1h, adding 1,4-lutidine iodide, wherein the molar ratio of 1,4-lutidine iodide to intermediate III is 2-3:1, heating to 60-70°C under stirring and reflux reaction for 17-25h; after the reaction is completed, removing the solvent by reduced pressure distillation, and purifying the obtained crude product by silica gel column chromatography to obtain the target product L-TPE.

[0014] The structural formula of the iodinated 1,4-dimethylpyridine is

[0015] The solvent described in step (2) is tetrahydrofuran or ethanol.

[0016] The silica gel column chromatography method described in step (2) uses dichloromethane and methanol in a volume ratio of 10-20:1 as eluent.

[0017] The L-TPE probe obtained by the present invention is used for non-destructive real-time monitoring of the progress of the polymerization reaction process. Different methods can be used for detection. The first is to use the fluorescence emission intensity method to detect the fluorescence emission intensity of the reaction process in real time (generally, the fluorescence emission intensity increases with the viscosity of the process), and then obtain the corresponding process progress; the second is the change of emission color, which is a method visualized by the naked eye. As the viscosity increases during the process, the fluorescence color changes from red to blue and gradually intensifies. The specific method is to add the L-TPE probe or a solution of the L-TPE probe to the polymerization reaction, and the addition amount is 0.08%-0.8% by volume of L-TPE in the reaction system, and then detect the fluorescence intensity or fluorescence color change as the reaction progresses. The fluorescence excitation light can be different depending on the reaction system.

[0018] Further used to detect the polymerization of methyl methacrylate: the fluorescent probe L-TPE prepared above is mixed with a methyl methacrylate prepolymer, and stirred evenly to obtain a polymer mixture doped with the fluorescent probe.

[0019] Alternatively, methyl methacrylate and azobisisobutyronitrile (AIBN) are sequentially added to a reaction vessel, wherein the mass ratio of methyl methacrylate to AIBN is 100-130:1; the mixture is condensed and refluxed at 70-80° C. with stirring for approximately 30 minutes to prepare a methyl methacrylate prepolymer having a certain viscosity, and then cooled to room temperature; a 10 mmol / L L-TPE solution (the volume percentage of L-TPE is 0.08%-0.8% of the prepolymer) is added, and the mixture is stirred uniformly with a glass rod to obtain a polymer mixture doped with a fluorescent probe.

[0020] The solvent of the L-TPE solution in the preparation of the polymer mixture doped with the fluorescent probe is dimethyl sulfoxide or methanol.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention connects the excellent electron-donating group 4-diethylamino with the strong electron-withdrawing group 1,4-dimethylpyridinium iodide through a conjugated π bond to construct a red fluorescent hemicyanine skeleton (L) with a D-π-A structure. This structure can avoid the problem that viscosity-responsive fluorescent probes with shorter emission wavelengths are affected by background fluorescence in complex environments. The structure has excellent photostability and is easy to process. It can be used as a high-performance fluorescent material and has important potential application value in the detection of cell viscosity, aerosol viscosity, and liquid food viscosity.

[0023] (2) The present invention obtains a dual-emission viscosity-responsive probe L-TPE by covalently linking the blue light-emitting portion TPE and the red light-emitting portion L, and mixes the probe with a methyl methacrylate prepolymer to form a polymer mixture doped with a fluorescent probe. The probe has the dual property of being able to monitor the polymerization reaction process in real time through the dual changes in fluorescence emission intensity and emission color, overcoming the problem that the viscosity-responsive probe detects viscosity changes in a single manner. The preparation method of the fluorescent probe L-TPE in the present invention is simple and easy, has high sensitivity, does not require chemical bonding with the polymer chain, and has great practical application value in monitoring the bulk polymerization of methyl methacrylate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of L-TPE prepared in Example 1.

[0025] Figure 2 This is the mass spectrum of L-TPE prepared in Example 1.

[0026] Figure 3 Figure 2 is the fluorescence spectrum of TPE-OH under different conditions.

[0027] Figure 4 Figure 2 is the fluorescence spectrum of L-TPE under different conditions.

[0028] Figure 5 Fluorescence spectra of TPE-OH and L-TPE in 90% glycerol state.

[0029] Figure 6 The change of fluorescence intensity of the probe L-TPE under the conditions of initiator and 60℃.

[0030] Figure 7 This is the exponential relationship between the conversion rate of the polymer mixture system and the fluorescence intensity.

[0031] Figure 8 These are fluorescence photos of the polymer mixture system under 365nm light irradiation at different times.

[0032] Figure 9 It is the correspondence between the conversion rate of the polymer mixture system and the CIE coordinate. DETAILED DESCRIPTION

[0033] In order to further understand the present invention, the present invention will be further described below with reference to the accompanying drawings and specific examples, but the embodiments of the present invention are not limited thereto.

[0034] Example 1:

[0035] The preparation of L-TPE includes the following steps:

[0036] (1) Weigh 0.3865g of 4-(diethylamino) salicylaldehyde (2.00mmol) and 0.5528g of potassium carbonate (4.00mmol), add them to a two-necked flask with 10mL of acetone as solvent, and stir at room temperature for 0.5h. Then weigh 0.4254g of compound II (1.00mmol) and 0.0800g of copper oxide (1mmol) and add them to the flask, set the reaction temperature to 50℃, and heat to reflux for 5h. After the reaction is completed, the solution is naturally cooled to room temperature. Purify the product. First filter the mixture to remove solid potassium carbonate and copper oxide, and then remove the acetone solvent by vacuum distillation to obtain a concentrated crude product. Then use ethyl acetate / n-hexane (v / v=1 / 4) as eluent and further purify by column chromatography. The purified product obtained is intermediate III, which is a light yellow solid (0.2811g) with a yield of 65%. Use 1 Intermediate III was characterized by H NMR, and the specific data results are as follows:

[0037] 1 H NMR(600MHz,CDCl3,δ):10.23(s,1H),7.76(d,1H),7.20(d,2H),7.15–7.01(m,18 H),6.33(d,1H),6.10(s,1H),5.11(s,2H),4.25(t,1H),3.40(q,4H),1.19(s,6H).

[0038]

[0039] (2) Weigh 0.1953g of intermediate compound III (0.37mmol) and 0.0870g of 1,4-dimethylpyridine iodide (0.37mmol) and transfer them to a 50mL two-necked flask. Then add 5 drops of piperidine as a catalyst and 10mL of ethanol as a reaction solvent to the flask. Add magnetic stirring and stir the reaction system at 70°C for 18h. After the reaction is completed, the solution is cooled to room temperature and evaporated under reduced pressure to remove the ethanol solvent to obtain a crude product. It is further purified by column chromatography using dichloromethane / methanol (v / v=13:1) as an eluent. The resulting red solid product is recorded as L-TPE with a yield of about 40%. 1 HNMR, 13 L-TPE was characterized by C NMR and MS, and the specific data results are as follows:

[0040] 1 H NMR (600MHz, CDCl3, δ): 8.70 (s, 2H), 7.95 (s, 1H), 7.65 (d, 2H), 7.51 (s, 1H), 7.20 (d, 2H), 7.13 (s, 3H), 7.12 (s, 15H),6.97(d,1H),6.34(d,1H),6.07(s,1H),5.16(s,2H),4.43(s,3H),3.38(s,4H),1.27(d,1H),1.16(s,6H).

[0041] 13 C NMR (151MHz, CDCl3, δ):160.04,154.89,151.64,143.57,141.35,140.31,138.44,134.80,131.70,1 31.26,127.73,126.52,126.25,121.93,116.05,111.85,105.34,95.50,70.24,47.44,44.91,12.74.

[0042] MS:m / z:627.3387([M-Br] + ,C 45 H 43 N2O + , theoretical calculated value 627.3375).

[0043]

[0044] Example 2

[0045] Study on the viscosity response properties of L-TPE.

[0046] The fluorescence emission spectra of 4-(1,2,2-triphenylethylene)phenol (TPE-OH) and L-TPE under different environments (glycerol-tetrahydrofuran mixed solution and liquid nitrogen with different volume fractions) were measured using a fluorescence spectrometer under the same test parameters and solution concentration conditions. Figure 3 As shown in the figure, the fluorescence signal of the TPE-OH probe in pure tetrahydrofuran solution is almost unobservable; in the 90% glycerol state, there is a weak blue light emission (around 470nm); in the liquid nitrogen frozen solution, the fluorescence intensity of TPE-OH is further enhanced, with fluorescence changes visible to the naked eye. The experimental results show that the fluorescence changes of the TPE group in the glycerol viscosity range (low viscosity range) are difficult to capture with the naked eye, but under liquid nitrogen freezing conditions (i.e. high viscosity range), fluorescence monitoring under high viscosity changes can be achieved. Figure 4 As shown in the figure, L-TPE has a weak red light emission (near 589nm) in the state of pure tetrahydrofuran solution; in the solution with 90% glycerol content, the naked eye can see that its red light emission fluorescence intensity has increased significantly (corresponding to the lower viscosity range). The results show that the L-TPE probe has good viscosity response properties within the viscosity range of glycerol. Comparing the fluorescence emission of TPE-OH at a wavelength of 470nm and the fluorescence emission of L-TPE probe at 589nm under the same conditions, as shown in the figure, Figure 5 As shown in the figure, their emission intensities differ significantly; the fluorescence intensity of TPE-OH in the 90% glycerol state is only 1 / 11 of that of the L-TPE probe under the same conditions (the corresponding emission wavelength and red fluorescence intensity are different). When frozen in liquid nitrogen, the blue light emission intensity of TPE-OH is similar to the red light emission intensity of L-TPE in the 90% glycerol state.

[0047] This indicates that the red and blue fluorescence emission of the L-TPE molecule with dual viscosity-responsive fluorescent groups can be observed in more viscous media, while the red emission of the probe is dominant in lower viscosity media.

[0048] Therefore, the viscosity-responsive fluorescent molecule L-TPE with dual-color emission can be used as a fluorescent probe to monitor the bulk polymerization process of methyl methacrylate with large viscosity changes (see Example 4).

[0049] Example 3

[0050] The study on the stability of the probe L-TPE shows that the initiator and temperature have no effect on the probe and it is stable.

[0051] Dissolve 24.0 mg of AIBN in 20 mL of methanol solvent to prepare a 7.3 mmol / L AIBN solution (the concentration is the same as during polymerization). Weigh 15.1 mg of L-TPE probe and dissolve it in 2 mL of methanol solvent to obtain a L-TPE probe stock solution with a concentration of 10.0 mmol / L. Dilute it with methanol and AIBN solution to a concentration of 10 μmol / L. Excite at a wavelength of 504 nm and use the fluorescence intensity of the methanol solution of the untreated L-TPE probe as a reference (I0 is the fluorescence intensity of the fluorescent probe in pure methanol) to obtain the relative fluorescence intensity of L-TPE under different conditions. Figure 6 As shown in the results, heating at 60 °C for 3 h and heating at 60 °C for 3 h in the presence of AIBN did not affect the fluorescence properties of the probe, indicating that the probe exhibited excellent anti-interference ability to polymerization temperature and initiator.

[0052] Example 4

[0053] The fluorescence intensity response of the probe L-TPE was applied to the methyl methacrylate bulk polymerization system.

[0054] Add 30 μL of 10 mmol / L L-TPE solution to 30 mL of prepolymer and stir with a glass rod to obtain a polymer mixture doped with fluorescent probe. Then continue heating at 60°C. Take out at different intervals and measure the fluorescence emission intensity. Figure 7 As shown, at an excitation wavelength of 504 nm, the fluorescence intensity clearly increases with the conversion rate as the reaction proceeds, demonstrating that the L-TPE probe can be used to monitor polymerization reactions. Notably, the data show that the conversion rate of the generated methyl methacrylate is exponentially proportional to the fluorescence intensity, which is important for obtaining polymerization information without disrupting the reaction system.

[0055] Example 5

[0056] The fluorescence color response of the probe L-TPE was applied to the methyl methacrylate bulk polymerization system.

[0057] Then, the fluorescence color changes of the polymer mixture at different reaction times were photographed under the excitation light of a 365nm handheld UV lamp. Figure 8 As shown in the figure, with the further increase of conversion rate, the orange fluorescence turns into cyan. And by changing the excitation wavelength to 377nm, the blue fluorescence of TPE and the red fluorescence of L system are excited at the same time, and each emission spectrum of the polymer at different conversion rates is converted to its corresponding position on the CIE chromaticity diagram, and the detailed relationship between conversion rate and fluorescence color is determined. Figure 8As shown in the figure, it can be found that as the conversion rate of methyl methacrylate increases, the fluorescence color changes. When the conversion rate is 21%, the fluorescence color is recorded as orange, and the CIE coordinates are (0.48, 0.43). When the conversion rate reaches about 89%, the fluorescence color is displayed as cyan (0.28, 0.34). The fluorescence colors corresponding to the different conversion rates are shown in the figure. Figure 9 As shown, it was demonstrated that the L-TPE probe can visualize the polymerization process through changes in fluorescence color.

Claims

1. A visual viscosity-responsive luminescent probe with dual fluorophores, characterized in that: The structural formula of the luminescent probe L-TPE is shown in formula (I):

2. The method for preparing a visualized viscosity-responsive luminescent probe with dual fluorophores according to claim 1, characterized in that: The following steps are involved: (1) Modification of tetraphenylethylene by dehydroxyarylation coupling to obtain intermediate III; (2) The product of step (1) is subjected to a Knoevenagel condensation reaction between intermediate III and 1,4-dimethylpyridine iodide in the presence of piperidine as a catalyst to obtain a viscosity-responsive luminescent probe L-TPE with dual emission; the structural formula of intermediate III is:

3. The method according to claim 2, characterized in that The specific operation of step (1) is as follows: 4-(diethylamino) salicylaldehyde, potassium carbonate, copper oxide and solvent are added to a reaction vessel in sequence, wherein the molar ratio of 4-(diethylamino) salicylaldehyde to potassium carbonate is 1:2-3, and the molar ratio of 4-(diethylamino) salicylaldehyde to copper oxide is 1:1-2; after stirring and activating at room temperature for 0.5-1h, compound II is added, wherein the molar ratio of 4-(diethylamino) salicylaldehyde to compound II is 2-3:1, and the temperature is raised to 50-60°C and refluxed for 4-10h under stirring; after the reaction is completed, the temperature is lowered to room temperature, potassium carbonate is removed by suction filtration, the filtrate is subjected to reduced pressure distillation to remove the solvent, and the obtained crude product is purified by silica gel column chromatography to obtain intermediate III; The structural formula of 4-(diethylamino)salicylaldehyde is: The structural formula of compound II is: The solvent is tetrahydrofuran or acetone.

4. The method according to claim 3, characterized in that Silica gel column chromatography uses n-hexane and ethyl acetate in a volume ratio of 4-5:1 as eluent.

5. The method according to claim 2, characterized in that The specific operation of step (2) is as follows: adding intermediate III, 1,4-lutidine iodide, piperidine catalyst and solvent to a reaction vessel in sequence, wherein the molar ratio of intermediate III to 1,4-lutidine iodide is 1:1-2; stirring and activating at room temperature for 0.5-1h, adding 1,4-lutidine iodide, wherein the molar ratio of 1,4-lutidine iodide to intermediate III is 2-3:1, heating to 60-70°C under stirring and reflux reaction for 17-25h; after the reaction is completed, removing the solvent by reduced pressure distillation, and purifying the obtained crude product by silica gel column chromatography to obtain the target product L-TPE; The structural formula of 1,4-dimethylpyridine iodide is 6. The method according to claim 5, characterized in that In step (2), the solvent is tetrahydrofuran or ethanol.

7. The method according to claim 5, characterized in that In step (2), the silica gel column chromatography method uses dichloromethane and methanol in a volume ratio of 10-20:1 as eluent.

8. Use of the probe according to claim 1 for non-destructive real-time monitoring of the progress of a polymerization reaction; using a change in emission color, which is a method for visualizing with the naked eye, as the viscosity increases during the process, the fluorescence color changes from red to blue and gradually intensifies.

9. The method according to claim 8, characterized in that The specific method is to add the L-TPE probe or the solution of the L-TPE probe to the polymerization reaction, and the added amount is 0.08%-0.8% by mass or volume percentage of L-TPE in the reaction system. Then, as the reaction proceeds, the fluorescence color changes, and the fluorescence excitation light can be different depending on the reaction system.

10. The method according to claim 8, characterized in that For detecting the polymerization of methyl methacrylate: the luminescent probe L-TPE prepared above is mixed with a methyl methacrylate prepolymer and stirred evenly to obtain a polymer mixture doped with the luminescent probe; Alternatively, methyl methacrylate and AIBN are sequentially added to a reaction vessel, wherein the mass ratio of methyl methacrylate to AIBN is 100-130:1; the mixture is condensed and refluxed at 70-80° C., stirred for 30 minutes, to prepare a methyl methacrylate prepolymer having a certain viscosity, and then cooled to room temperature; a 10 mmol / L L-TPE solution is added, wherein the volume percentage of L-TPE is 0.08%-0.8% of the prepolymer, and the mixture is stirred evenly with a glass rod to obtain a polymer mixture doped with a luminescent probe; The solvent of the L-TPE solution in the preparation of the polymer mixture doped with the luminescent probe is dimethyl sulfoxide or methanol.

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