A method for initiating a photo-controlled living polymerization reaction based on quantum dots
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DALIAN INSTITUTE OF CHEMICAL PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2024-11-28
- Publication Date
- 2026-05-29
Smart Images
Figure CN122103406A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for photocontrolled active polymerization based on quantum dots. Background Technology
[0002] Controlled living radical polymerization (LCPR) is a polymerization method that maintains the growth of active chains in a polymer system through a reversible equilibrium between active and dormant species. Compared to ionic and coordination polymerization, LCPR offers milder reaction conditions, lower environmental requirements, and a wider range of applicable monomers, making it a current hot topic in polymer polymerization. Among these, light-controlled reactive radical polymerization (LCPR) utilizes light as a stimulus to control the start or termination of the polymerization reaction. It offers advantages such as energy efficiency, environmental friendliness, ease of operation, and sensitive response, making it a powerful tool for the precise synthesis of complex functional polymers such as block, hyperbranched, and star-shaped polymers. Currently, LCPR often relies on traditional living radical polymerization systems, such as atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (LCTP), and stable radical polymerization, by adding light-driven redox reagents or designing photosensitive atom transfer reagent molecules. This results in complex system structures, difficult optimization, molecular instability, and poor light control effects, necessitating further improvements.
[0003] In this invention, ZnSe / ZnS quantum dots are simple to prepare, free of heavy metals, have a large absorption cross-section, stable chemical properties, and abundant surface states. They can catalyze the polymerization of acrylate monomers to form a simple, light-controlled, active radical polymerization system, thus preparing novel luminescent composite materials. The novel polymerization mechanism is as follows: When a short-wavelength excitation light (365 nm) irradiates the mixture of quantum dots and polymeric monomers, the quantum dots are excited and transfer energy to the acrylate monomers. The unsaturated double bonds of the monomers are excited and open, completing the chain initiation reaction. During chain growth, the quantum dots utilize their abundant surface states and dangling bonds to adsorb polymer chain radicals, forming dormant species. Under light irradiation, the quantum dots are excited and undergo a redox reaction with the dormant species polymer chains, causing the dormant species polymer chains to be removed from the quantum dot surface, generating ground-state quantum dots and polymer chain radicals, i.e., forming active species, which continue chain growth. This reversible dynamic equilibrium between dormant and active species maintains an almost constant concentration of active species in the system, achieving living polymerization. When illumination stops, the system lacks excited-state quantum dots, and the chain initiation process stops; the reversible dynamic equilibrium between dormant and active species tends to generate dormant species, and the chain growth reaction is suspended; when illumination is restored, polymerization occurs again until it is completed, thus achieving illumination control of the reaction.
[0004] Based on this, the present invention synthesizes a series of colloidal quantum dots, and for the first time realizes the photocontrolled active polymerization of acrylate monomers by a single-component catalyst under short-wavelength excitation light of 365nm. Furthermore, the invention utilizes the characteristics of photocontrolled and active polymerization to synthesize block copolymers, thus preparing a novel quantum dot polymer composite material. Summary of the Invention
[0005] The purpose of this invention is to provide a method for photocontrolled living polymerization of monomers based on quantum dot catalysis. For the first time, 365nm wavelength light-excited quantum dot catalysis is used to achieve photocontrolled living polymerization of acrylate compounds, yielding products and block polymers with specific conversion rates.
[0006] The quantum dots were synthesized via a hot-injection method. A mixture of zinc oleate and 1-octadecene was injected with diphenylphosphine selenide at 300°C for two hours to generate the quantum dot core. Zinc oleate and trioctylphosphine sulfide were then injected to generate the quantum dot ZnS shell. The reaction product mixture was separated and purified after cooling to room temperature.
[0007] The ZnSe / ZnS quantum dots have uniform size, obvious exciton peaks, and narrow fluorescence half-width.
[0008] The quantum dot-initiated polymerization system is a bulk polymerization of ZnSe / ZnS quantum dots mixed with acrylate monomers by irradiation with short-wavelength excitation light (365nm), or a solution polymerization of mixed monomers and non-polar solvents such as toluene.
[0009] The acrylate monomers mentioned include, but are not limited to, one or more of methyl methacrylate, benzyl methacrylate, lauryl methacrylate, n-butyl methacrylate, methyl acrylate, or their derivatives.
[0010] The molecular weight of the polymer product is above 100,000 Daltons.
[0011] To verify whether the synthesized quantum dots can transfer energy to excite monomers for polymerization, and whether the polymerization reaction type is photocontrolled living radical polymerization, the verification scheme adopted in this invention is as follows:
[0012] The basic optical properties and energy transfer of the mixed methyl methacrylate system were preliminarily characterized by steady-state absorption spectroscopy and fluorescence spectroscopy.
[0013] The size and morphology of quantum dots were characterized using transmission electron microscopy.
[0014] Energy transfer in the quantum dot-methyl methacrylate system was characterized by femtosecond transient absorption spectroscopy.
[0015] The generation of methyl methacrylate carbon radical species during the polymerization process was detected by electron paramagnetic resonance (EPR) testing.
[0016] The molecular weight and structure of the polymer products were characterized by gel permeation chromatography and proton nuclear magnetic resonance spectroscopy.
[0017] In this invention, a photocontrolled living polymerization reaction of acrylate monomers is achieved by exciting quantum dots to transfer energy to them. During the polymerization process, the desired conversion rate of the product can be easily obtained by controlling the illumination duration. The molecular weight of the polymerized product is above 100,000 Daltons, and block copolymers can be obtained by utilizing the characteristics of living polymerization. Since the damage to quantum dots caused by traditional small-molecule free radical initiators is avoided, the fluorescence intensity of the quantum dots does not decrease after polymerization, enabling the preparation of novel quantum dot luminescent composite materials.
[0018] The quantum dots of this invention possess unique energy transfer capabilities, abundant surface states, and luminescent properties, fulfilling multiple functions as initiators, chain transfer agents, and luminescent substances in this living polymerization system. This simplifies traditional living radical polymerization systems and yields high molecular weight polymers exceeding 100,000 Daltons. Based on a novel quantum dot polymerization mechanism, this polymerization method eliminates traditional free radical initiators, fundamentally preventing quantum dots from being quenched by them, thus maintaining the fluorescence intensity of the quantum dots and constructing novel quantum dot-polymer composite luminescent materials. Attached Figure Description
[0019] Figure 1 Transmission electron microscopy images and particle size statistics of ZnSe / ZnS quantum dots with three different first exciton absorption peak absorption wavelengths.
[0020] Figure 2 Steady-state absorption and emission diagrams of ZnSe / ZnS quantum dots. a. Steady-state absorption of ZnSe / ZnS quantum dots of different sizes; b. Quantum dots transfer energy to methyl methacrylate (MMA) to initiate a polymerization reaction, causing the fluorescence of the quantum dots to be quenched; after the polymerization reaction ends, the fluorescence of the quantum dots recovers; c. The addition of different types of organic amines to the polymerization reaction system, compared with the ZnSe group, all inhibited the polymerization conversion rate, namely BRN n-butylamine, TEA triethylamine, and DIPA diisopropylamine.
[0021] Figure 3 The mechanism of energy transfer-mediated free radical polymerization was investigated. a) The femtosecond transient absorption spectrum kinetics decayed faster with the addition of reactant (QDs-MMA) compared to the toluene solution control group (QDs-toluene); b) Electron paramagnetic resonance (EPR) showed the presence of carbon radical signals after the addition of MMA; c) CdSe with different bandgap widths was synthesized for the polymerization reaction; d) ZnSe and CdSe quantum dots with different bandgap widths were used in the polymerization system, and the polymerization conversion exhibited an energy-dependent effect.
[0022] Figure 4 The polymerization process exhibits the following characteristics: a) The conversion rate of methyl methacrylate monomer in ZnSe / ZnS quantum dot polymerization increases proportionally with time, conforming to first-order reaction kinetics, and the reaction rate constant is positively correlated with the quantum dot concentration; b) Photocontrolled polymerization. The conversion rate of the polymerization system is controlled by adjusting the presence or absence of 365nm excitation light.
[0023] Figure 5 Synthesis of block copolymers. a) Schematic diagram and molecular weight data of polymethyl methacrylate (PMMA) blocks of polybenzyl methacrylate (PBEMA) or polybutyl methacrylate (PBUMA); b, c) Gel permeation chromatography before and after block polymerization; d, e) 1H NMR spectra of the products before and after block copolymerization, indicating the formation of the expected block copolymers.
[0024] Figure 6 Substrate expansion. Examples of acrylate monomers that ZnSe / ZnS can polymerize. α conversion, M n Number average molecular weight Molecular weight distribution.
[0025] Figure 7 Quantum dot-polymethyl methacrylate (PMMA) composite luminescent material. a) After polymerization, the quantum dots are linked into the polymer network, resulting in a significant change in solubility. ZnSe / ZnS quantum dots, which originally could only disperse in non-polar solvents, can dissolve in the polar solvent N,N-dimethylformamide (DMF) after forming the quantum dot-PMMA composite luminescent material; b) Scanning electron microscopy shows that the quantum dot-PMMA composite luminescent material has a uniform texture, with the quantum dots encapsulated within the polymer; c) After forming the quantum dot-PMMA composite luminescent material, the ZnSe / ZnS exhibits excellent acid and alkali resistance, as well as superior resistance to photoaging. Detailed Implementation
[0026] The present invention will be further described through embodiments and accompanying drawings.
[0027] Example
[0028] The present embodiment describes the research and preparation of a ZnSe / ZnS quantum dot-polymethyl methacrylate luminescent composite based on a novel ZnSe / ZnS quantum dot polymerization mechanism. The specific method includes the following steps:
[0029] A hot-injection synthesis method for ZnSe / ZnS quantum dots with a first exciton absorption peak at 400-433 nm: 1.26 g of zinc stearate was mixed with 10 mL of 1-octadecene, under nitrogen protection, and heated to 200 °C. 1 mL of a 1 M diphenylphosphine solution of selenium was added, and the mixture was heated to 300 °C and maintained for 2 hours to form quantum dots with a first exciton absorption peak at 400 nm. Then, 0.395 mg of selenium powder was added, and the mixture was maintained for 1 hour to form quantum dots with a first exciton absorption peak at 420 nm. Finally, 0.79 mg of selenium powder was added, and the mixture was maintained for 1 hour to form quantum dots with a first exciton absorption peak at 433 nm. Add 1.7 mL of zinc oleate (0.7 M, oleic acid solution) and 0.6 mL of trioctylphosphine solution (2 M), and maintain heating for 10 minutes to form a ZnS shell. Repeat this shell synthesis process (adding 1.7 mL of zinc oleate and 0.6 mL of trioctylphosphine solution (2 M) to form a ZnS shell) three times, for a total of four shell growth processes. After the liquid is completely injected, stop heating and allow the solution to cool naturally to room temperature. Then, add 30 mL of acetone to precipitate and collect the precipitate, disperse it with 5 mL of n-hexane, precipitate again with 30 mL of acetone, collect the precipitate, disperse it with 5 mL of n-hexane, precipitate again with 30 mL of acetone, collect the precipitate, disperse it again with 5 mL of n-hexane, precipitate again with 30 mL of acetone, collect the precipitate, and finally disperse it with 5 mL of toluene.
[0030] ZnSe / ZnS quantum dot polymerization of methyl methacrylate procedure: Prepare a ZnSe / ZnS quantum dot toluene solution with an absorbance of 1 OD in a 1 cm path length cuvette. Add 800 μL of this solution to the reactor and vacuum dry the liquid (to remove solvent). In a nitrogen-purged glove box, add 2 mL of methyl methacrylate (the molar ratio of quantum dots to methyl methacrylate is 1 / 10). 5 Dissolve ZnSe / ZnS quantum dots in 1 mL of toluene and seal to isolate them from oxygen. Irradiate the mixture with 365 nm light for 8 hours, then add 8 mL of methanol to quench the reaction. A white precipitate will settle out. Centrifuge the mixture and repeat the sedimentation-centrifugation process three times. Collect the precipitate and dry it. The white powder is a high molecular weight ZnSe / ZnS quantum dot-polymethyl methacrylate composite material, with the polymethyl methacrylate having a molecular weight distribution of 50,000 to 200,000.
[0031] Synthesis method of CdSe quantum dots with first exciton absorption peaks at 500-620 nm: 1 mL of cadmium oleate (a solution of 0.5 M cadmium oxide, 0.5 mL oleic acid, and 0.5 mL 1-octadecene) and 10 mL of 1-octadecene were placed in separate three-necked flasks. The mixture was degassed under vacuum at 100 °C for 10 minutes, then purged with nitrogen and heated to 260 °C. 2.5 mL of a 0.1 M selenium powder suspension in 1-octadecene was added to the reaction mixture, and the reaction was carried out at 250 °C for 8 minutes. Then, a 0.1 M selenium powder suspension in 1-octadecene was added dropwise to the reaction mixture (dropping rate 200 μL / min), and equal portions were taken to monitor the absorption of CdSe quantum dots. Using a quartz cuvette with a 1 cm optical path, the absorbance of the reaction solution was measured on a UV-Vis spectrophotometer at 1 OD. When the first exciton absorption peaks of the CdSe quantum dots reached 500, 520, 560 nm, 590 nm and 620 nm, respectively, the reaction was stopped and cooled to room temperature. 30 mL of ethanol was added for precipitation, the precipitate was collected, and 5 mL of toluene was used for dispersion and preservation.
[0032] Using the above chemical preparation methods, we obtained ZnSe / ZnS quantum dots, CdSe quantum dots, and ZnSe / ZnS quantum dot-polymethyl methacrylate composite materials. The same method can be used to polymerize other acrylate monomers (…). Figure 6 This indicates that the method has a certain degree of universality. To explain the universal mechanism of quantum dot photoexcitation energy transfer catalysis of acrylate compounds and to investigate whether this type of polymerization reaction is a living polymerization, we need to use detection methods to verify it. The verification will mainly be carried out from the following two aspects:
[0033] (1) Experiments on the polymerization of ZnSe / ZnS quantum dots induced by energy transfer:
[0034] The absorption peak positions of the first exciton synthesized with more than 2 μmol were 400, 420, and 433 nm. Figure 1 ZnSe / ZnS quantum dots were mixed with 2 mL of methyl methacrylate, and the fluorescence intensity of the quantum dots was measured using a fluorescence spectrometer. Fluorescence quenching was observed, and the fluorescence intensity recovered after irradiation with 365 nm light. Figure 2 (b) This indicates that an energy transfer or charge transfer process exists between quantum dots and molecules, which terminates with the completion of the polymerization reaction. To further investigate the process of ZnSe / ZnS quantum dot-initiated polymerization, 0.5 mmol of triethylamine, a commonly used quantum dot hole scavenger, was added to the reaction solution at the beginning of the above polymerization process under light irradiation. The polymerization conversion rate after adding triethylamine was lower than that without adding triethylamine. Figure 2 c) This indicates that the polymerization of ZnSe / ZnS quantum dots is an energy transfer process, rather than a charge transfer process that relies on the transfer of electrons and holes.
[0035] from Figure 3 Figure a shows the ultrafast transient absorption spectra of ZnSe / ZnS quantum dots with toluene and methyl methacrylate as solvents, respectively, under 400nm blue light excitation and a 1mm optical path. The absorption difference spectrum change of the quantum dots at 426nm was detected. The energy transfer process of the quantum dots occurred within 100ps, generating methyl methacrylate carbon radical intermediates. This radical can be captured by 5,5-dimethyl-1-pyrrolidone-N-oxide (DMPO). The test sample consisted of 0.05mL ZnSe / ZnS toluene solution (2M) mixed with 0.05mL MMA and 5μL DMPO, and detected by room temperature electron paramagnetic resonance (EPR). Figure 3 b) indicates that the polymerization process follows a free radical polymerization mechanism. To further verify the universality of this energy transfer process across different quantum dots, we synthesized a series of CdSe quantum dots. Using a quartz cuvette with a 1 cm optical path, we measured the absorbance of a CdSe solution with an absorbance of 1 OD on a UV-Vis spectrophotometer. The results are as follows. Figure 3 As shown in c. With the addition of ZnSe quantum dots, these quantum dots cover an absorption wavelength of 400–617 nm, equivalent to a bandgap width of 2.0–3.1 eV. As a result, their polymerization conversion rate is negatively correlated with the bandgap. Figure 3 d) This proves that the bandgap size of quantum dots directly affects the conversion rate, and that energy transfer occurs between quantum dots and polymer monomer molecules.
[0036] (2) Experiment on quantum dot-acrylate polymerization as a living radical polymerization:
[0037] Samples were taken at 20, 40, 60, 90, and 120 minutes of polymerization. The product was precipitated with methanol, dried, and weighed for monitoring. The results showed that the reaction rate constant of ZnSe / ZnS quantum dot polymerization of methyl methacrylate molecules was positively correlated with the concentration of quantum dots, indicating that ZnSe / ZnS quantum dots played a chain initiation role in the polymerization reaction. The conversion rate was positively proportional to the light exposure time, conforming to first-order kinetics, indicating that the concentration of active chain-growing species remained constant during the polymerization process, consistent with the characteristics of living radical polymerization. Figure 4 a). To verify the light control capability of the polymerization system, the product was weighed when the light was stopped, and the conversion rate of the polymerization system was calculated. The monomer conversion rate did not increase with time; when the light was turned on again, the monomer conversion rate increased again. Figure 4 b) This indicates that ZnSe / ZnS quantum dots have the ability to control the polymerization process by light, and further shows that ZnSe / ZnS quantum dots and polymer chains tend to form dormant species when there is no light, and the activity of free radicals at the chain ends can be restored when the quantum dots are excited by light.
[0038] Based on the characteristic that the polymer chain ends remain active during living radical polymerization, this system can synthesize block copolymers. We successfully synthesized polymethyl methacrylate block copolymers of polybenzyl methacrylate or polybutyl methacrylate. The shifted peak elution time in gel permeation chromatography and the characteristic peaks appearing in the 1H NMR spectrum of the products both provide structural information about the block copolymers. Figure 5 ).
[0039] (3) Preparation of ZnSe / ZnS quantum dot-PMMA composite material:
[0040] Thanks to the unique polymerization mechanism described above, the solubility of the ZnSe / ZnS quantum dot-polymer differs significantly from that of the unpolymerized ZnSe / ZnS quantum dots. The polymerized product exhibits more polymer-like solubility. Dissolving 5 mL of the white powdered product in 2 mL of the polar solvent DMF yielded the following results: Figure 7 As shown in a, it is convenient for processing and utilization. Figure 7 b showcased a ZnSe / ZnS quantum dot-polymer composite luminescent material product. Furthermore, this material effectively improves the acid and alkali resistance and photo-aging resistance of ZnSe / ZnS quantum dots as luminescent materials. Figure 7 c) It has broad application prospects.
[0041] In summary, this invention elucidates a method for photocontrolled living polymerization of acrylate monomers catalyzed by ZnSe / ZnS quantum dots. It achieves, for the first time, the living radical polymerization of acrylate monomers catalyzed by single-component ZnSe / ZnS quantum dots, and verifies the chain initiation mechanism of energy transfer between quantum dots and molecules. This polymerization system has a simple composition, which can greatly simplify the process optimization process and save time, manpower, and material costs; the photocontrolled effect is significant, and combined with the characteristics of living polymerization, it can synthesize high-value-added products with controllable structure, tunable composition, and diverse functions; it does not damage quantum dots and can be used to construct novel and efficient quantum dot-polymer composite materials, which can be applied in fields such as quantum dot luminescence and catalysis.
Claims
1. A method for photocontrolled active polymerization based on quantum dots, characterized in that: Quantum dots mixed with acrylate monomers or monomer solutions undergo a polymerization reaction under short-wavelength excitation light to obtain polymer products.
2. The method according to claim 1, characterized in that: The preparation method of quantum dots is as follows: 1) A. Mix 1.26-6.3g of zinc stearate with 10-20mL of 1-octadecene, purge with nitrogen, heat to 190-300℃, add different volumes of selenium diphenylphosphine solution (1-2M) or selenium according to the target size, heat to 280-400℃ (preferably 300-350℃, more preferably 300-330℃), maintain for 1-5 hours (preferably 2-3 hours); ZnS shell formation: Add 1.7-3 mL of zinc oleate and 0.6-2 mL of sulfur-containing trioctylphosphine solution (1.5-2.5 M), maintain for 10-30 minutes to form ZnS shell; repeat the ZnS shell formation process 0-5 times (preferably 2-3 times); Alternatively, mix 1.26-6.3g of cadmium oleate with 10-20mL of 1-octadecene, purge with nitrogen, heat to 190-300℃, add different volumes of selenium diphenylphosphine solution (1-2M) or selenium according to the target size, heat to 280-400℃ (preferably 300-350℃, more preferably 300-330℃), and maintain for 1-5 hours (preferably 2-3 hours); 2) When the system is cooled to room temperature, acetone is allowed to settle and the precipitate is collected. Then, hexane is used for dispersion and acetone is allowed to settle 0-5 times (preferably 2-3 times). The precipitate is the quantum dot product.
3. The method according to claim 1, characterized in that: The preparation process of the polymerization reaction is as follows: Under nitrogen (oxygen-free) protection, quantum dots and acrylate monomers are mixed in a molar ratio of 1 / 1 to 1 / 10. 7 (Preferred 1 / 10) 3 ~1 / 10 5 After the polymerization reaction is excited by light at 350-405nm (preferably 365-400nm) for 2-24 hours, methanol is added until a white precipitate forms. The precipitate is then centrifuged and dried to obtain the product.
4. The method according to claim 1 or 3, characterized in that: Light control of polymerization reaction: When the system is irradiated with excitation light, the monomer conversion rate increases with time; when there is no excitation light, the monomer conversion rate does not change with time, remains constant, and continues to increase when light is applied again.
5. The method according to claim 1, 3, or 4, characterized in that: Living polymerization reaction: 1) The monomer conversion rate of the polymerization reaction changes proportionally with the light exposure time; after the light exposure stops, the polymerization conversion rate stops increasing, that is, the product with the expected conversion rate can be obtained by setting the light exposure time; usually the time can be more than 2 hours, preferably 10-20 hours; high molecular weight polymer products with a molecular weight greater than 100,000 Daltons can be obtained. 2) Polymer chain ends maintain polymerization activity: Since the polymerization kinetics conform to the characteristics of living polymerization, the polymer chain ends always maintain polymerization activity. That is, when other types of acrylate monomers are added to the polymerization system of the first acrylate monomer that has reached the expected conversion rate, the polymer chain can continue to grow by adding a second acrylate monomer that is different from the first one, forming a block copolymer.
6. The method according to claim 1, 3, 4 or 5, characterized in that: Acrylate monomers include, but are not limited to, one or more of methyl methacrylate, benzyl methacrylate, lauryl methacrylate, n-butyl methacrylate, methyl acrylate, or their derivatives.
7. The method according to claim 1, 3, 4 or 5, characterized in that: The excitation light is monochromatic light with a wavelength of 200-600nm. The wavelength is selected based on the absorption range of the quantum dots, with 365-400nm being preferred.
8. The method according to claim 1, characterized in that: The solvent of the solution is one or more of toluene, chloroform, dichloromethane, and n-hexane.