Method for preparing small-sized polymer Janus particles using hybrid shell particles as a template

Abstract

The present invention discloses a method for preparing small-sized polymer Janus particles using hybrid shell particles as a template. In the present invention, patch particles are obtained by covalently crosslinking crosslinkable blocks in the hybrid shell; after dissociating the patch particles and recovering the block copolymer, small-sized Janus particles with a well-defined partitioned structure are obtained, that is, precise control over the morphology of Janus nanoparticles is achieved; the morphology of the obtained small-sized Janus particles is as follows: a covalently crosslinked nanogel serves as the head, and several linear molecular chains are grafted to one side of the head as the tail; several different linear molecular chains are grafted to both sides of the covalently crosslinked core respectively; the Janus functional particles have good amphiphilicity, pH responsiveness, temperature responsiveness and structural stability, and are not affected by acids and bases, temperature and solvation of various solvents. The block copolymer used for the hybrid shell template is easy to recover, solving the problem that traditional Janus templates cannot be recycled and reused, and saving the preparation cost.

Description

Technical Field

[0001] The present invention belongs to the field of nanomaterial technology, and particularly relates to a method for preparing small-sized polymer Janus nanoparticles. Background Art

[0002] Polymer Janus particles are an important research field in materials science and have important application values in the fields of biomedicine, heterogeneous catalysis, emulsion stabilization, solubilization of blend systems, etc. Although existing studies have developed a series of methods for preparing polymer Janus particles, such as various block copolymer assembly methods, asymmetric modification methods, polymer coprecipitation phase separation methods, etc., and have constructed polymer Janus particles with a series of morphologies such as rod-shaped, disc-shaped, snowman-shaped, tadpole-shaped, etc., these methods are still difficult to simultaneously meet the three major challenges of precisely constructing a well-defined partition structure, precisely regulating the morphology, and efficiently preparing polymer Janus particles. In particular, when the size of Janus particles is reduced to a relatively small nanoscale size (e.g., 10 nm), it is more difficult to precisely construct a well-defined partition structure on the particle surface. The preparation process of Janus particles with a well-defined partition structure usually includes multiple sub-steps. After each sub-step, a further purification process is mostly required. Such a complex preparation process is difficult to achieve efficient and large-scale preparation. In addition, the precise morphology control of Janus particles in existing work is only limited to fine-tuning of their structural parameters. It is difficult to prepare various different morphologies of Janus particles using a single Janus particle preparation method, and there is no relevant report. Therefore, it is an urgent problem to be solved in this field to achieve the efficient preparation of polymer Janus particles with a well-defined partition structure through a simple preparation process and simultaneously construct Janus particles with different morphologies. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing small-sized polymer Janus nanoparticles with a simple process and precise morphology control of Janus nanoparticles.

[0004] Based on the understanding of the chain conformational transition in the mixed-shell particles, the present invention proposes a method for preparing small-sized polymer Janus particles using the mixed-shell particles as a template; this method obtains patchy particles by covalently crosslinking the crosslinkable blocks in the mixed shell; after dissociating the patchy particles and recovering the block copolymer, small-sized Janus particles with a well-defined partition structure are obtained, that is, precise morphology control of Janus nanoparticles is achieved; the morphology of the obtained small-sized Janus particles is: (I) a covalently crosslinked nanogel as the head, and several linear molecular chains are grafted to one side of the head as the tail; (II) several different linear molecular chains are grafted to both sides of the covalently crosslinked core. The obtained Janus particles have a stable structure and do not dissociate or undergo morphology transformation in various solvents.

[0005] The method for preparing small-sized polymer Janus particles using hybrid shell particles as a template proposed by the present invention comprises the following specific steps:

[0006] (1) Dissolve two block copolymers in a good solvent, and dropwise add a poor solvent for the nucleating block to obtain hybrid shell particles;

[0007] (2) In the hybrid shell particle dispersion, covalently crosslink the crosslinkable segments in the hybrid shell (such as: photo-crosslinking or adding a crosslinking agent) to obtain a spherical patch particle dispersion;

[0008] (3) Add a good solvent to dissociate the patch particles and perform stepwise sedimentation separation to obtain small-sized Janus particle powder and block copolymer powder for preparing the hybrid shell template respectively;

[0009] (4) Disperse the Janus particles in a good solvent to obtain a Janus particle dispersion;

[0010] (5) In the covalent crosslinked structure of the Janus particles, enrich through the coordination of metal ions with functional groups in the crosslinked structure; by adding a reducing agent, in-situ reduce the metal ions in the metal ion enrichment region to obtain Janus hybrid particles with metal particles located in a determined region of the small-sized Janus particles.

[0011] Furthermore:

[0012] In step (1) of the present invention, the concentration of the block copolymer is 0.01 - 10 g / L. The preferred concentration is 1 - 10 g / L.

[0013] In step (1) of the present invention, the two diblock copolymers can be two diblock copolymers, or a combination of a diblock copolymer and a triblock copolymer; the combination of two diblock copolymers is polystyrene- b -polymethyl methacrylate / polystyrene -b- poly(4-vinylpyridine), polystyrene- b -polyethylene oxide / polystyrene -b- poly(4-vinylpyridine), polystyrene- b -polyethylene oxide / polystyrene -b- poly(methacrylic( N,N -dimethylaminoethyl ester)- co -coumarin methacrylate), poly(2-hydroxyethyl methacrylate)- b -polyethylene oxide / poly(2-hydroxyethyl methacrylate) -b- poly(4-vinylpyridine), poly(2-hydroxyethyl methacrylate)- b -polyethylene oxide / poly(2-hydroxyethyl methacrylate) -b- poly(methacrylic(N,N -dimethylaminoethyl) etc. A combination of a diblock copolymer and a triblock copolymer is polystyrene- b -polymethyl methacrylate / polystyrene -b- poly(4-vinylpyridine)- b -polyethylene oxide etc.

[0014] In step (1) of the present invention, the length ratio of the mixed shell particle nucleating block to the crosslinkable shell-forming block is 2-8. The length ratio of the non-crosslinkable shell-forming block to the crosslinkable shell-forming block is 1.5-4.

[0015] In step (2) of the present invention, the crosslinkable shell-forming segment of the mixed shell particles can be crosslinked by photochemical covalent crosslinking, and can also be crosslinked covalently by adding a crosslinking agent. The covalent crosslinking reaction rate and the crosslinking degree of the Janus particles are controlled by controlling the light intensity or the amount of the crosslinking agent and the crosslinking time. The difference in the crosslinking degree can be used to adjust the density of the crosslinking network; a large crosslinking degree results in a tight network structure, and a small crosslinking degree results in a loose network structure. According to the specific use of the Janus particles and the crosslinking system, photo-crosslinking or crosslinking with different crosslinking agents is selected. Photo-crosslinking is carried out with 365 nm ultraviolet light, and the light intensity is 5-25 W / cm 2 , and the time is 5-30 min. The amount of the crosslinking agent is generally 0.05-20 times the content of the repeating units of the crosslinkable block. For example: poly(methacrylic acid( N,N -dimethylaminoethyl)- co -coumarin methacrylate) is selected for photo-crosslinking with 365 nm ultraviolet light as the crosslinkable block system; 1,4-dibromobutane is selected for crosslinking with poly(4-vinylpyridine) as the crosslinkable block system; poly(methacrylic acid( N,N -dimethylaminoethyl) is selected for crosslinking with 1,2-bis(2-iodoethoxy)ethane as the crosslinkable block system.

[0016] In step (3) of the present invention, after dissociation of the patch particles and stepwise sedimentation separation, small-sized Janus particle powders and block copolymer powders for preparing the mixed shell template are respectively obtained. The conversion rate of the Janus particles is close to 100%. It can achieve highly uniform controllable preparation of Janus particles in the range of 5-30 nm. The block copolymer powder for preparing the mixed shell template can also achieve a recovery rate close to 100% and has high purity, and can be recycled for preparing Janus particles.

[0017] In step (4) of the present invention, since the above-mentioned Janus particles all contain covalent crosslinking network regions that are beneficial to improving their structural stability, they are not affected by acids, alkalis, temperature, and solvation of various solvents.

[0018] In step (5) of the present invention, a large number of functional groups capable of coordinating with metal ions are rich in the covalent crosslinking network of Janus particles, and it is extremely easy to achieve the enrichment of metal ions; in-situ reduction of the particles can prepare small-sized Janus hybrid particles containing metal particles only in the crosslinking network region.

[0019] In step (5) of the present invention, during the metal ion enrichment process, the molar ratio of metal ions to the functional groups capable of coordinating with metal ions is 0.1 - 10; the enrichment time is 10 - 60 min. The metal ions are selected from Ag + , Au 3+ , Pt 4+ , Pd 2+ , etc. The coordinating functional groups are selected from pyridine groups, carboxyl groups, etc.

[0020] In step (5) of the present invention, during the metal ion reduction process, the reducing agent is sodium borohydride (NaBH4), and its molar ratio to the enriched metal ions is 1 - 10; the reduction time is 30 s - 5 min.

[0021] In step (5) of the present invention, the metal ion enrichment and in-situ reduction method can efficiently prepare small-sized Janus hybrid particles, and its preparation efficiency is close to 100%.

[0022] In the present invention, the good solvents are selected from tetrahydrofuran, N,N N,N-dimethylformamide, methanol, and ethanol; the poor solvents are selected from: methanol, ethanol, and water.

[0023] The present invention can be generally applicable to the efficient preparation of various small-sized Janus particles with different components and different structural parameters, and a series of Janus functional particles such as amphiphilic, pH-responsive, and temperature-responsive particles are obtained. The obtained Janus particles all have a clear partition structure and are structurally stable, and are not affected by acids and bases, temperature, and various solvent solvation. Through the modification of the mixed shell template, two completely different Janus morphologies are obtained, namely (I) with a covalently crosslinked nanogel as the head, and several linear molecular chains are grafted to one side of the head as the tail, and (II) several different linear molecular chains are grafted to both sides of the covalently crosslinked core. By enriching metal ions in the covalent crosslinking network region of Janus particles and in-situ reduction, Janus hybrid particles containing metal ions only in a certain region of Janus particles can also be efficiently prepared. The block copolymer used for the mixed shell template is easy to recycle, solving the problem that traditional Janus templates cannot be recycled and reused, and saving the preparation cost. The present invention proposes a new idea for the efficient preparation of small-sized Janus particles, which is applicable to various Janus particles and Janus particle hybrid systems. Various Janus particles with different compositions and structures can be prepared according to actual application requirements (such as emulsion stabilization, drug loading, chemical reaction loading, solubilization in blend systems, etc.). Description of the Drawings

[0024] Figure 1 Distribution curves of the hydrodynamic radii of the PS- b -PMMA / PS- b -P4VP block copolymer, patch particles, and the fluid after dissociation of the patch particles ( R h ).

[0025] Figure 2 Transmission electron micrographs of the patch particles and Janus particles obtained at a concentration of 1 g / L in Example 1.

[0026] Figure 3 Transmission electron micrographs of the patch particles and silver Janus particles obtained at a concentration of 1 g / L in Example 2.

[0027] Figure 4 Distribution curves of the hydrodynamic radii of the PS- b -PMMA / PS- b -P2VP- b -PEO block copolymer, hybrid shell particles, patch particles, the fluid after dissociation of the patch particles, and the recovered PS- b -PMMA ( R h ).

[0028] Figure 5 Transmission electron micrographs of the patch particles and Janus particles obtained at a concentration of 1 g / L in Example 6. The right figure shows the atomic force micrograph of the Janus particles.

[0029] Figure 6 Schematic diagrams of the structures of two different forms of Janus particles and the corresponding transmission electron micrographs in Example 1 (left figure) and Example 6 (right figure), respectively. Detailed Description of the Invention

[0030] The present invention will be further described below in conjunction with the embodiments, but the present invention is not limited to the following embodiments.

[0031] Example 1. Two diblock copolymers are polystyrene- b -polymethyl methacrylate (PS- b -PMMA) and polystyrene -b- -poly(4-vinylpyridine) (PS- b -P4VP). PS- b- In PMMA, the degree of polymerization of PS is 310 - 550, and the degree of polymerization of PMMA is 130 - 220. PS- b - In P4VP, the degree of polymerization of PS is 302 - 520, and the degree of polymerization of P4VP is 50 - 110. The preparation concentration is 0.01 - 10 g / L. Its good solvent is tetrahydrofuran (THF); the poor solvent is methanol (MeOH); the crosslinking agent is 1,4 - dibromobutane.

[0032] Dissolve PS- b -P4VP and PS- b -PMMA in THF, and slowly add MeOH drop by drop to obtain mixed shell particles. Add the crosslinking agent 1,4 - dibromobutane. The molar ratio of the crosslinking agent to the pyridine unit in P4VP is 2 times. React at room temperature for 24 hours to obtain patch particles. Add THF to dissociate the patch particles, and perform fractional sedimentation separation to obtain Janus particle powder and PS- b -PMMA powder (which can be recycled). The Janus particles are of uniform size, with a diameter of 17 nm. Their morphology is that the covalently crosslinked P4VP nanogel is the head, and several PS linear molecular chains are grafted to one side of the head as the tail. The Janus particle powder can be uniformly dispersed in its good solvent (such as THF) to obtain a Janus particle dispersion. The recycled PS- b -PMMA powder can be recycled for the preparation of mixed shell particles. In the Janus particles, the covalently crosslinked P4VP head has pH responsiveness. PS- b -PMMA / PS- b -P4VP block copolymer, patch particles, and the hydrodynamic radius ( R h ) distribution curve are shown in Figure 1 the figure shown.

[0033] Example 2. Two diblock copolymers are polystyrene- b -polyethylene oxide (PS- b -PEO) and polystyrene - b- poly(4 - vinylpyridine) (PS- b -P4VP). In PS- b -PEO, the degree of polymerization of PS is 510, and the degree of polymerization of PEO is 280. In PS- b -P4VP, the degree of polymerization of PS is 520, and the degree of polymerization of P4VP is 110. The preparation conditions are the same as those in Example 1 to obtain Janus particles with a diameter of 15 nm. In the Janus particles, the covalently crosslinked P4VP head has pH responsiveness.

[0034] Furthermore, by coordinating pyridine groups in the covalently crosslinked P4VP network with metal ions, adsorbing metal ions in the covalently crosslinked network and reducing them, metal particles are in-situ grown to obtain Janus hybrid particles containing metal particles only in the crosslinked P4VP region. The metal salts selected are silver nitrate (AgNO3), chloroauric acid (HAuCl4), and chloroplatinic acid (H2PtCl6), and their molar ratio to the pyridine functional group is 0.1 - 10. The reducing agent is sodium borohydride (NaBH4), and its molar ratio to the metal ions is 1 - 10. The enrichment time is 10 - 60 min, and the reduction time is 30 s - 5 min.

[0035] Example 3. The two diblock copolymers are polystyrene- b -polyethylene oxide (PS- b -PEO) and polystyrene - b- poly(methacrylic( N,N -dimethylaminoethyl ester)-co-poly(methacrylic acid coumarin)) (PS- b -(PDMAEMA- co -CMA)). In PS- b -PEO, the degree of polymerization of PS is 510, and the degree of polymerization of PEO is 280. In PHEMA- b -(PDMAEMA- co -CMA), the degree of polymerization of PS is 510, the degree of polymerization of PDMAEMA is 94, and the molar ratio of the repeating unit numbers of PDMAEMA to CMA is 3 - 20. The preparation conditions are similar to those in Example 1. Its good solvent is THF; the poor solvent is MeOH; crosslinking is carried out by ultraviolet light at 365 nm, the light intensity is 5 - 25 W / cm 2 , and the time is 5 - 30 min. In the Janus particles, the covalently crosslinked PDMAEMA- co -CMA head has pH responsiveness and temperature responsiveness.

[0036] Example 4. The two diblock copolymers are poly(2-hydroxyethyl methacrylate)- b -polyethylene oxide (PHEMA- b -PEO) and poly(2-hydroxyethyl methacrylate) -b- poly(4-vinylpyridine) (PHEMA- b -P4VP). In PHEMA- b -PEO, the degree of polymerization of PHEMA is 450, and the degree of polymerization of PEO is 280. In PHEMA- b-The degree of polymerization of PHEMA in P4VP is 450, and the degree of polymerization of P4VP is 122. The preparation conditions are similar to those in Example 1. The good solvent is MeOH; the poor solvent is acidic water; and the cross-linking agent is 1,4-dibromobutane. In Janus particles, the covalently cross-linked P4VP head is pH responsive.

[0037] Example 5. Two diblock copolymers are poly(hydroxyethyl methacrylate)- b -Polyethylene oxide (PHEMA- b -PEO) and poly(hydroxyethyl methacrylate) -b- Polymethacrylic acid ( N,N -dimethylaminoethyl ester) (PHEMA- b -PDMAEMA). PHEMA- b -The degree of polymerization of PHEMA in PEO is 450, and the degree of polymerization of PEO is 280. b -PDMAEMA has a DP of 450 for PHEMA and 130 for PDMAEMA. The preparation conditions are similar to those in Example 1. The good solvent is MeOH; the poor solvent is water; and the cross-linking agent is 1,2-bis(2-iodoethoxy)ethane. In Janus particles, the covalently cross-linked PDMAEMA head has pH responsiveness and temperature responsiveness.

[0038] Example 6. The two block copolymers are a combination of a diblock copolymer and a triblock copolymer. The diblock copolymer is polystyrene- b -Polymethyl methacrylate (PS- b -PMMA). The triblock copolymer is polystyrene -b- Poly(4-vinylpyridine)- b -Polyethylene oxide (PS- b -P4VP- b -PEO). PS- b -The degree of polymerization of PS in PMMA is 528, and the degree of polymerization of PMMA is 220. b -P2VP- b -PEO has a degree of polymerization of PS of 770, a degree of polymerization of P2VP of 113, and a degree of polymerization of PEO of 91. The preparation conditions are the same as those in Example 1. The good solvent is THF, the poor solvent is MeOH, and the cross-linking agent is 1,4-dibromobutane. The obtained Janus particles are uniform in size and have a diameter of 20 nm. The Janus particles are amphiphilic, and their morphology is that several PS and PEO linear molecular chains are covalently grafted on both sides of the covalently cross-linked P4VP core. This is quite different from the morphology of the Janus particles obtained in Examples 1-5. See Figure 5 .

[0039] The above content is a relatively typical example of the present invention, but the present invention should not be limited to the content disclosed in these examples. Therefore, any equivalent or modified implementation completed without departing from the spirit disclosed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing small-sized polymer Janus particles using hybrid shell particles as a template, characterized in that, Patch particles are obtained by covalently crosslinking the crosslinkable blocks in the mixed shell; after dissociating the patch particles and recovering the block copolymer, small-sized Janus particles with a well-defined partition structure are obtained, that is, precise control over the morphology of Janus nanoparticles is achieved; the morphology of the obtained small-sized Janus particles is as follows: (I) a covalently crosslinked nanogel as the head, with several linear molecular chain tails grafted on one side of the head; (II) several different linear molecular chains are grafted on both sides of the covalently crosslinked core; the specific steps are as follows: (1) Dissolve two block copolymers in a good solvent, and dropwise add a poor solvent for the nucleating block to obtain mixed shell particles. Then, covalently crosslink the crosslinkable segments in the mixed shell in the mixed shell particle dispersion to obtain a spherical patch particle dispersion. Add a good solvent to dissociate the patch particles and perform stepwise sedimentation separation; Wherein: The two diblock copolymers are polystyrene- b -polymethyl methacrylate PS- b -PMMA and polystyrene -b- -poly(4-vinylpyridine) PS- b -P4VP; PS- b -PMMA has a degree of polymerization of PS ranging from 310 to 550 and a degree of polymerization of PMMA ranging from 130 to 220; PS- b -P4VP has a degree of polymerization of PS ranging from 302 to 520 and a degree of polymerization of P4VP ranging from 50 to 110; Dissolve PS- b -P4VP and PS- b -PMMA in the good solvent tetrahydrofuran (THF), and slowly dropwise add the poor solvent methanol (MeOH) to obtain hybrid shell particles; add the crosslinking agent 1,4-dibromobutane, and the molar ratio of the crosslinking agent to the pyridine unit in P4VP is 2:1; react at room temperature for 24 hours to obtain patchy particles; add THF to dissociate the patchy particles, and separate them by fractional sedimentation to obtain Janus particle powder and PS- b -PMMA powder; the Janus particles are uniform in size, and their morphology is that the covalently crosslinked P4VP nanogel is used as the head, and several PS linear molecular chains are grafted on one side of the head as the tail; Or: Two diblock copolymers are polystyrene- b -poly(ethylene oxide) PS- b -PEO and polystyrene- -b- poly(4-vinylpyridine) PS- b -P4VP; PS- b -PEO has a degree of polymerization of 510 for PS and 280 for PEO; PS- b -P4VP has a degree of polymerization of 520 for PS and 110 for P4VP; Dissolve PS- b -P4VP and PS- b -PEO in the good solvent tetrahydrofuran (THF), and slowly add dropwise the poor solvent methanol (MeOH) to obtain mixed shell particles; add the cross-linking agent 1,4-dibromobutane, and the molar ratio of the cross-linking agent to the pyridine unit in P4VP is 2:1; react at room temperature for 24 hours to obtain patchy particles; add THF to dissociate the patchy particles, and perform fractional sedimentation separation to obtain Janus particle powder and PS- b -PEO powder respectively; the Janus particles are uniform in size, and their morphology is that the covalently cross-linked P4VP nanogel is used as the head, and several PS linear molecular chains are grafted on one side of the head as the tail; Or alternatively: Two diblock copolymers are polystyrene- b -polyethylene oxide PS- b -PEO and polystyrene -b- poly(methacrylic( N,N -dimethylaminoethyl ester)-co-poly(methacrylic acid coumarin)) PS- b -(PDMAEMA- co -CMA); PS- b -PEO has a degree of polymerization of 510 for PS and 280 for PEO; PHEMA- b -(PDMAEMA- co -CMA) has a degree of polymerization of 510 for PS, 94 for PDMAEMA, and a molar ratio of repeating units of 3 - 20 between PDMAEMA and CMA; Dissolve PS- b -PEO and PS- b -(PDMAEMA- co -CMA) in THF, and slowly dropwise add MeOH to obtain hybrid shell particles; crosslinking is carried out using ultraviolet light at 365 nm with a light intensity of 5 - 25 W / cm 2 , and the time is 5 - 30 min; react at room temperature for 24 hours to obtain patch particles; add THF to dissociate the patch particles, and separate them by fractional sedimentation to obtain Janus particle powder and PS- b -(PDMAEMA- co -CMA) powder; the Janus particles have uniform sizes, and their morphology is that the covalently crosslinked PEO nanogel serves as the head, and several PS linear molecular chains are grafted to one side of the head as the tail; (2) In the covalent crosslinked structure of Janus particles, enrichment is carried out through the coordination of metal ions with functional groups in the crosslinked structure; by adding a reducing agent, the metal ions in the metal ion enrichment region are in-situ reduced to obtain Janus hybrid particles with metal particles located in the determined region of small-sized Janus particles; During the metal ion enrichment process, the molar ratio of metal ions to the functional groups capable of coordinating with metal ions is 0.1 - 10; the enrichment time is 10 - 60 min; during the metal ion reduction process, sodium borohydride is used as the reducing agent, the molar ratio of the reducing agent to the enriched metal ions is 1 - 10, and the reduction time is 30 s - 5 min.

2. The method according to claim 1, wherein The concentration of the block copolymer described in step (1) is 0.01 - 10 g / L.

3. The method according to claim 1, characterized in that In step (2), the metal ion is Ag + , Au 3+ , Pt 4+ or Pd 2+ ; the coordinated functional group is selected from a pyridine group and a carboxyl group.

Images