Porous polymer microsphere and preparation method thereof

Abstract

The invention belongs to the field of high polymer materials, and discloses a porous polymer microsphere and a preparation method thereof, and the preparation method comprises the following steps: (1) mixing a polymer seed microsphere with an alcohol solvent, water and a pore-foaming agent, controlling the volume ratio of the alcohol solvent to the water to be greater than 6.5: 5.5, and enabling the mixed solution to form an emulsion under the condition of high-speed stirring; the surfaces of the polymer seed microspheres have hydrophilic groups, (2) stirring the mixed emulsion at a low speed to react for more than 10 minutes to obtain a suspension; and (3) carrying out rotary evaporation on the suspension, and after the solvent is fully volatilized, washing and drying to obtain the porous polymer microspheres. According to the preparation method, only one-step reaction is needed, special additives such as a surface active agent and an etching agent are not needed, an additional pore forming process or complex precision equipment is not needed, and the high-porosity polystyrene microspheres with mutually connected open pore structures and uniform size distribution can be prepared within 2 hours under the room temperature condition. The microspheres have large specific surface area and pore volume.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials and relates to a porous polymer microsphere and a preparation method thereof. Background Art

[0002] Due to its unique interconnected open pore structure, porous polymer microspheres have characteristics such as high specific surface area, ultra-low mass density, and excellent permeability. Compared with traditional microsphere materials, this material shows significant advantages in physical and chemical properties and has currently been widely used in high-tech fields such as chromatographic separation, catalytic carriers, separation engineering, microreactor construction, biomedical engineering, and microelectronic devices, demonstrating important application value.

[0003] The pore structure and pore size of conventional porous polymer microspheres are similar from the surface to the inside. The uniform pore structure usually gives them a single property when used as fillers, such as molecular exclusion property or specific binding property. In recent years, highly interconnected open porous polymer microspheres have shown dual properties of molecular exclusion and specific binding when used as multi-mode filler carriers due to their special structure, and have advantages such as simplicity and high efficiency in the purification of multi-scale samples such as catalytic carriers and viruses, biological macromolecules, etc.

[0004] However, currently, the preparation processes of porous polymer microspheres generally have problems such as complex steps, long time consumption, and high cost. Usually, surfactants need to be added for emulsification, and multiple steps of treatment are involved. For example, the Chinese patent application with the publication number CN105524223 A discloses a four-step method for preparing porous PS-DVB microspheres by seed activation, two-step swelling, and porogen extraction, with a total time consumption of more than 55 hours, and the specific surface area of the obtained microspheres is 21.4 m² / g. The Chinese patent application with the publication number CN116747318 A uses polyvinyl alcohol as an emulsifier to prepare drug co-delivery degradable microspheres by the double emulsion-solvent evaporation method, but this method will form a continuous film on the surface of the microspheres, and additional alkali etching treatment is required to remove the film and regulate the pore structure, which may damage the overall structure of the microspheres. Summary of the Invention

[0005] Aiming at the defects existing in the prior art, the main object of the present invention is to provide a simple, rapid, and efficient preparation method for porous polymer microspheres. By dispersing polystyrene seed microspheres in an oil-in-water emulsion system, highly porous polystyrene microspheres with open through pores can be prepared at room temperature.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A preparation method for a porous polymer microsphere, comprising the following steps: (1) After mixing the polymer seed microspheres with an alcohol solvent, water, and a porogen, control the volume ratio of the alcohol solvent to water to be greater than 6.5:5.5, and form an emulsion from the mixed solution under high-speed stirring conditions; the surface of the polymer seed microspheres has hydrophilic groups, and the volume ratio of the alcohol solvent to water is 1 to 1.5:1; the speed of the high-speed stirring is ≥600 rpm; (2) Stir the mixed emulsion at a low speed for more than 10 min to obtain a suspension; the speed of the low-speed stirring is ≤500 rpm; (3) Rotate evaporate the suspension (at room temperature), after the solvent has fully volatilized, wash and dry to obtain the porous polymer microspheres.

[0007] Both the interior and the outer surface of the porous polymer microspheres have a pore structure, the pore structure on the outer surface is an open pore structure, and the internal pore structure is also an open and interconnected pore structure.

[0008] Preferably, the alcohol solvent is a short-chain alcohol with C1-C6; the porogen is a mixed solvent composed of toluene and the following organic solvents, and the organic solvent is one or more of dichloromethane, chloroform, chloroform, acetone, 1,2-dichloroethane, chlorododecane, n-heptane, and n-octane.

[0009] Preferably, the volume ratio of the alcohol solvent to water is 7.6±0.4:5.5.

[0010] Preferably, the alcohol solvent is one or more of ethanol, isopropanol, methanol, cyclohexanol, n-butanol, isopropanol, and tert-butanol.

[0011] The polymerization reaction method used for preparing the polymer seed microspheres is any one or a combination of at least two of emulsion polymerization, microemulsion polymerization, soap-free emulsion polymerization, dispersion polymerization, suspension polymerization, or seed polymerization. The preferred polymerization reaction method is dispersion polymerization.

[0012] Preferably, for the preparation of the polymer seed microspheres: dissolve an initiator and polyvinylpyrrolidone (PVP) in a mixed solvent of water and ethanol, add a monomer with an unsaturated bond, stir evenly, and then stir and react at 70±10°C for 6±2 h; after the reaction is completed, cool, centrifuge, and wash to obtain the polymer seed microspheres; the initiator is ammonium persulfate and / or azobisisobutyronitrile. The monomer with an unsaturated bond is one or more of styrene monomer, chloromethylstyrene, methyl methacrylate, methyl acrylate, or glycidyl methacrylate, butyl acrylate, and glycidyl acrylate.

[0013] Preferably, the polymer seed microspheres are selected from one or more of polystyrene seed microspheres, polymethyl methacrylate seed microspheres, and glycidyl methacrylate seed microspheres; the surface of the polymer seed microspheres has sulfonic acid groups.

[0014] Preferably, the speed of the high-speed stirring is 1000 - 3000 rpm, and the stirring time is 3 - 30 s; the speed of the low-speed stirring is 50 - 500 rpm, and the reaction time is 5 - 60 min.

[0015] Preferably, the speed of the high-speed stirring is 2500 ± 500 rpm, and the stirring time is 10 ± 5 s; the speed of the low-speed stirring is 300 ± 100 rpm, and the reaction time is 20 - 30 min.

[0016] Preferably, the particle size of the polymer seed microspheres is 0.5 - 20 μm. The particle size of the polymer seed microspheres can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 5 μm, 10 μm, 20 μm, etc.

[0017] Preferably, the mass-volume ratio of the polymer seed microspheres to water is 0.25 - 5 g / L, and can be 0.5 g / L, 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L.

[0018] Preferably, the volume ratio of the pore-forming agent to water is 5% - 25%, more preferably 10% - 15%.

[0019] Preferably, the pore-forming agent is a mixed solvent with a toluene volume content of 30% - 70%, and the volume content can be 40%, 50%, 60%.

[0020] Rotary evaporation is carried out using a numerically controlled rotary mixer, and its rotation speed is 5 r / min - 100 r / min; the rotary evaporation time is 1 - 36 h.

[0021] The mechanism of microsphere morphological transformation in the present invention is as follows: When porogens (toluene and dichloromethane) are added to the water-ethanol mixed solution and vigorously stirred, toluene-dichloromethane droplets and the water-ethanol mixture form an emulsion (reaction medium), and phase separation does not occur after standing. This is because alcohols such as ethanol can act as surfactants in the ternary solvent of water and toluene-dichloromethane, reducing the interfacial energy of the emulsion, so that the toluene-dichloromethane droplets can stably exist in the continuous phase. Among them, the synergistic effect of the dosage of ethanol and the stirring speed is crucial for the formation of the emulsion. When polystyrene seed microspheres are dispersed in the above emulsion, the polystyrene seed microspheres absorb the toluene-dichloromethane droplets in the continuous phase and swell, and the polymer chains become flexible and start to move. At the same time, due to the presence of sulfonic acid groups on the surface of the polystyrene seed microspheres (ammonium persulfate is used as the polymerization initiator of the seed microspheres), the surface of the microspheres is hydrophilic, and the water-ethanol mixture can be absorbed by the polystyrene seed microspheres. This osmotic pressure effect from the outside to the inside causes aqueous solution droplets to form inside the polystyrene seed microspheres. After natural air drying, pores are formed at the positions of these droplets, thus forming porous interpenetrating network microspheres.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention only requires one-step reaction, which can be completed within 2 h at room temperature. It does not need to use special additives such as surfactants and etching agents, nor does it need additional pore-forming processes or complex precision equipment. In addition, by adjusting the absorption time of the reaction solvent, the pore size of the microspheres can be flexibly adjusted, with simple operation and strong controllability. Compared with traditional complex processes such as multi-step swelling and alkali etching, the present invention greatly simplifies the preparation process, reduces costs, and at the same time avoids potential damage to the microsphere structure caused by subsequent treatment, which is beneficial to the large-scale preparation of high-performance porous polymer microspheres.

[0023] (2) In the preparation of the porous polymer microspheres of the present invention, by dispersing polystyrene seed polymer microspheres in an oil-in-water emulsion system, high-porosity polystyrene microspheres with interconnected open pore structures and uniform size distributions are prepared. The specific surface area of the prepared microspheres can reach 28.35 m 2 / g, and the pore volume can reach 9.86 cm 3 / g. Description of the Drawings

[0024] Figure 1 It is the electron scanning electron micrograph of the polystyrene seed microspheres of the present invention.

[0025] Figure 2 It is the electron scanning electron micrograph of the glycidyl methacrylate seed microspheres of the present invention.

[0026] Figure 3 It is the electron scanning electron micrograph of the porous polymer microspheres prepared in Example 1.

[0027] Figure 4 Scanning electron micrograph of the internal interconnected pore structure of the porous polymeric microspheres prepared in Example 1.

[0028] Figure 5 Scanning electron micrograph of the porous polymeric microspheres prepared in Example 2.

[0029] Figure 6 Scanning electron micrograph of the porous polymeric microspheres prepared in Example 3.

[0030] Figure 7 Scanning electron micrograph of the porous polymeric microspheres prepared in Example 4.

[0031] Figure 8 Scanning electron micrograph of the porous polymeric microspheres prepared in Example 5.

[0032] Figure 9 Scanning electron micrograph of the porous polymeric microspheres prepared in Example 6.

[0033] Figure 10 Scanning electron micrograph of the porous polymeric microspheres prepared in Comparative Example 1.

[0034] Figure 11 Scanning electron micrograph of the porous polymeric microspheres prepared in Comparative Example 2.

[0035] Figure 12 Scanning electron micrograph of the porous polymeric microspheres prepared in Comparative Example 3.

[0036] Figure 13 Scanning electron micrograph of the porous polymeric microspheres prepared in Comparative Example 4.

[0037] Figure 14 Scanning electron micrograph of the porous polymeric microspheres prepared in Comparative Example 5.

[0038] Figure 15 Photographs of the suspension of the reaction medium for different examples after stirring for 10 s (emulsified or not). Detailed Description of the Invention

[0039] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto. For process parameters not specifically noted, conventional techniques can be referred to.

[0040] The method for preparing polystyrene seed polymer microspheres comprises the following steps: (1) At room temperature, 0.5 g of ammonium persulfate (APS, initiator) and 0.05 g of polyvinylpyrrolidone (PVP, steric stabilizer) were dissolved into a reactor containing a mixture of water (15 mL) - ethanol (75 mL).

[0041] (2) 11 mL of styrene monomer was added to the reactor.

[0042] (3) The reaction mixture was stirred at room temperature for 10 min under magnetic stirring and then continuously stirred at 70 °C for 6 h.

[0043] (4) The reactor was placed in an ice bath to stop the reaction. Then, the polystyrene seed polymer microspheres were collected by centrifugation at 6000 rpm and washed three times with water for standby. The particle size of the prepared microspheres was about 1 μm, see Figure 1 .

[0044] Preparation method of glycidyl methacrylate seed polymer microspheres (initiator is azobisisobutyronitrile), including the following steps: (1) At room temperature, 3 g of polyvinylpyrrolidone (PVP) was added to a mixture containing ethanol (100 mL) - water (9 mL), and stirred at room temperature for 10 min.

[0045] (2) Purge with nitrogen for 10 min to remove oxygen. 9.3 mL of glycidyl methacrylate and 0.2 g of azobisisobutyronitrile were added to the reactor and stirred at room temperature for 10 min.

[0046] (3) Heat up to 70 °C and continue stirring for 3 h.

[0047] (4) After the reaction stopped, the glycidyl methacrylate seed polymer microspheres were collected by centrifugation at 6000 rpm and washed three times with water for standby. The particle size of the prepared microspheres was about 1 μm, see Figure 2 .

[0048] Preparation method of glycidyl methacrylate seed polymer microspheres (initiator is ammonium persulfate), including the following steps: (1) At room temperature, 3 g of polyvinylpyrrolidone (PVP) was added to a mixture containing ethanol (100 mL) - water (9 mL), and stirred at room temperature for 10 min.

[0049] (2) Purge with nitrogen for 10 min to remove oxygen. 9.3 mL of glycidyl methacrylate and 0.25 g of ammonium persulfate (APS) were added to the reactor and stirred at room temperature for 10 min.

[0050] (3) Heat up to 70 °C and continue stirring for 3 h.

[0051] After the reaction stopped, the poly(glycidyl methacrylate) seed polymer microspheres were collected by centrifugation at 6000 rpm and washed three times with water for later use. The prepared microspheres had a particle size of about 1 μm.

[0052] Example 1 A method for preparing porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in a mixed solvent of water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0053] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixed solvent. Subsequently, use a vortex stirrer to vigorously stir the suspension (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0054] (3) Transfer the above mixed emulsifier to a magnetic stirrer and magnetically stir the emulsion at a speed of 300 r / min for 30 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous polystyrene polymer microspheres, and the reaction solution is centrifuged (8000 rpm, 5 min), washed (washed twice with absolute ethanol), and dried (45 °C, 8 h).

[0055] Example 2 A method for preparing porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in a mixed solvent of water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0056] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixed solvent. Subsequently, use a vortex stirrer to vigorously stir the suspension (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0057] (3) Transfer the above mixed emulsifier to a magnetic stirrer and magnetically stir the emulsion at a speed of 300 r / min for 20 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous polystyrene polymer microspheres, and the reaction solution is centrifuged, washed, and dried.

[0058] Example 3 Preparation method of porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0059] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixed solvent. Subsequently, use a vortex stirrer to vigorously stir the suspension (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0060] (3) Transfer the above mixed emulsifier to a magnetic stirrer and magnetically stir the emulsion at a speed of 300 r / min for 10 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous polystyrene polymer microspheres, and the reaction solution is centrifuged, washed, and dried.

[0061] Example 4 Preparation method of porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0062] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixed solvent. Subsequently, use a vortex stirrer to vigorously stir the suspension (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0063] (3) Transfer the above mixed emulsifier to a magnetic stirrer and magnetically stir the emulsion at a speed of 300 r / min for 5 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous polystyrene polymer microspheres, and the reaction solution is centrifuged, washed, and dried.

[0064] Example 5 Preparation method of glycidyl methacrylate porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared glycidyl methacrylate seed polymer microspheres (initiator is ammonium persulfate) and disperse them in a mixed solvent of water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0065] (2) Add a mixture of toluene (0.25 mL) and dichloromethane (0.2 mL) to the above reaction mixed solvent. Subsequently, use a vortex stirrer to vigorously stir the suspension (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0066] (3) Transfer the above mixed emulsifier to a magnetic stirrer and magnetically stir the emulsion at a speed of 300 r / min for 20 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous poly(glycidyl methacrylate) polymer microspheres, and the reaction solution is centrifuged, washed, and dried.

[0067] Example 6 The difference between this example and Example 5 is that the poly(glycidyl methacrylate) seed polymer microspheres are prepared using azobisisobutyronitrile as the initiator.

[0068] Comparative Example 1 A method for preparing porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in a mixed solvent of water (5.5 mL) and ethanol (3 mL) in different proportions.

[0069] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixed solvent. Use a vortex stirrer to vigorously stir the suspension (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0070] (3) Similarly, transfer the above mixed emulsifier to a magnetic stirrer and magnetically stir the emulsion at a speed of 300 r / min for 20 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous polystyrene polymer microspheres, and the reaction solution is centrifuged, washed, and dried.

[0071] Comparative Example 2 A method for preparing porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in a mixed solvent of water (5.5 mL) and ethanol (5 mL) in different proportions.

[0072] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture solvent. Subsequently, use a vortex stirrer to vigorously stir the suspension (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0073] (3) Transfer the above mixed emulsifier to a magnetic stirrer and magnetically stir the emulsion at a speed of 300 r / min for 20 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous polystyrene polymer microspheres, and the reaction solution is centrifuged, washed, and dried.

[0074] Comparative Example 3 A method for preparing porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in a mixed solvent of water (5.5 mL) and ethanol (6.5 mL) in different proportions.

[0075] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture solvent. Subsequently, use a vortex stirrer to vigorously stir the suspension (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0076] (3) Transfer the above mixed emulsifier to a magnetic stirrer and magnetically stir the emulsion at a speed of 300 r / min for 20 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous polystyrene polymer microspheres, and the reaction solution is centrifuged, washed, and dried.

[0077] Comparative Example 4 A method for preparing porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in a mixed solvent of water (5.5 mL) and ethanol (8.5 mL) in different proportions.

[0078] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture solvent. Subsequently, use a vortex stirrer to vigorously stir the suspension (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0079] (3) Transfer the above-mentioned mixed emulsifier to a magnetic stirrer, and magnetically stir the emulsion at a speed of 300 r / min for 20 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min, and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous polystyrene polymer microspheres, and the reaction solution is centrifuged, washed, and dried.

[0080] Comparative Example 5 A method for preparing porous polymer microspheres, comprising the following steps: (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in a mixed solvent of water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0081] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixed solvent. Subsequently, stir the suspension (stirring speed 200 rpm) for 10 s, and do not use a vortex stirrer to vigorously stir the suspension.

[0082] (3) Transfer the above-mentioned mixed emulsifier to a magnetic stirrer, and magnetically stir the emulsion at a speed of 300 r / min for 30 min. After the reaction is completed, transfer the mixed emulsion to a digital control rotary mixer with a rotation speed of 25 r / min, and rotary evaporate the solvent for 1.5 h. All processes are carried out under room temperature environmental conditions to obtain a dispersion of porous polystyrene polymer microspheres, and the reaction solution is centrifuged, washed, and dried.

[0083] Table 1 Formulations and Characterization Results of Porous Polymer Microspheres in Different Examples

[0084] The results show that the addition amount of ethanol plays an important role in maintaining the stability of emulsion droplets and the subsequent evaporation rate. At the same time, the extension of reaction time plays a positive role in increasing the pore size. First, when the amount of ethanol is insufficient, although a milky turbid emulsion will be formed at the initial stage of strong stirring, phase separation will occur rapidly thereafter. At this time, it is in a thermodynamically unstable state, and the toluene-dichloromethane droplets initially dispersed in the continuous phase will aggregate over time, eventually leading to the separation of the oil and water phases, and porous polymer microspheres cannot be prepared. For example, in Comparative Examples 1-3, the experimental results show that due to the aggregation of toluene-dichloromethane droplets over time, a relatively large amount penetrates into the interior of the microspheres, causing the microspheres to be unable to maintain a spherical morphology and collapse. When the amount of ethanol is too large, the presence of excessive ethanol makes the solution system in a thermodynamically stable state, and the system presents a single-phase transparent homogeneous solution, which can no longer maintain the stability of the emulsion, and the toluene-dichloromethane mixture does not aggregate, and porous polymer microspheres cannot be prepared either. For example, the results of Comparative Example 4 show that the microspheres maintain a spherical morphology and no pores appear on the surface. When the addition amount of ethanol is the preferred amount, the milky white emulsion formed after strong stirring can remain stable for a long time without phase separation, and is easily absorbed by the microsphere particles to form porous polymer microspheres. At the same time, as the reaction time is extended, the microsphere particles absorb more reaction media, forming droplets inside them, which penetrate into the core part of the microspheres, resulting in an increase in pore size and the generation of internal pores. For example, in Examples 1-3, the experimental results show that as time goes by, the obtained porous microspheres maintain a spherical morphology of the microspheres, and the average pore size, specific surface area and pore volume gradually increase. In Example 4, due to the short reaction time, the reaction media mainly act on the surface of the microspheres and less penetrate into the interior of the microspheres. The experimental results show that the microspheres maintain a spherical morphology, and the depth of the micropores formed on the surface of the microspheres is relatively shallow, resulting in a small number of pores in the microspheres. In Examples 5 and 6, due to the use of poly(glycidyl methacrylate) seed polymer microspheres, there are atypical hydrophilic epoxy groups on their surfaces. During the reaction process, the amount of reaction media absorbed by the microspheres is limited, resulting in a small number of pores in the microspheres. The results of Comparative Example 5 show that when the addition amount of ethanol is the preferred amount, but the emulsion formed without strong stirring will undergo phase separation after standing, and the reaction media cannot penetrate into the interior of the microspheres, and porous microspheres cannot be prepared either.

[0085] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing a porous polymer microsphere, characterized in that It includes the following steps: (1) After mixing polymer seed microspheres with an alcohol solvent, water, and a pore-forming agent, control the volume ratio of the alcohol solvent to water to be greater than 6.5:5.5, and form an emulsion from the mixed solution under high-speed stirring conditions; the surface of the polymer seed microspheres has hydrophilic groups; the speed of the high-speed stirring is ≥600 rpm; (2) Stir the emulsion at a low speed for more than 10 min to obtain a suspension; the speed of the low-speed stirring is ≤500 rpm; (3) Rotate evaporate the suspension, after the solvent is fully volatilized, wash and dry to obtain porous polymer microspheres.

2. The preparation method according to claim 1, characterized in that, The alcohol solvent is a short-chain alcohol of C1-C6; the pore-forming agent is a mixed solvent composed of toluene and the following organic solvents, and the organic solvent is one or more of dichloromethane, chloroform, trichloromethane, acetone, 1,2-dichloroethane, chlorododecane, n-heptane, and n-octane.

3. The preparation method according to claim 2, characterized in that, The volume ratio of the alcohol solvent to water is 7.6±0.4:5.5; the alcohol solvent is one or more of ethanol, isopropanol, methanol, cyclohexanol, n-butanol, isopropanol, and tert-butanol.

4. The preparation method according to claim 3, characterized in that, Preparation of the polymer seed microspheres: Dissolve an initiator and polyvinylpyrrolidone in a mixed solvent of water and ethanol, add a monomer with an unsaturated bond, stir evenly, and then stir and react at 70±10°C for 6±2 h; after the reaction, cool, centrifuge, and wash to obtain polymer seed microspheres; the initiator is ammonium persulfate and / or azobisisobutyronitrile.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The polymer seed microspheres are selected from one or more of polystyrene seed microspheres, polymethyl methacrylate seed microspheres, and poly(glycidyl methacrylate) seed microspheres; the surface of the polymer seed microspheres has sulfonic acid groups.

6. The preparation method according to claim 5, characterized in that, The speed of the high-speed stirring is 1000 - 3000 rpm, and the stirring time is 3 - 30 s; the speed of the low-speed stirring is 50 - 500 rpm, and the reaction time is 5 - 60 min.

7. The preparation method according to claim 6, characterized in that, The speed of the high-speed stirring is 2500±500 rpm, and the stirring time is 10±5 s; the speed of the low-speed stirring is 300±100 rpm, and the reaction time is 20 - 30 min.

8. The preparation method according to any one of claims 1 to 4, characterized in that, In step (1), the mass-volume ratio of the polymer seed microspheres to water is 0.25 - 5 g / L; the particle size of the polymer seed microspheres is 0.5 - 20 μm.

9. The preparation method according to claim 8, wherein The volume ratio of the pore-forming agent to water is 5% - 25%; the pore-forming agent is a mixed solvent with a toluene volume content of 30% - 70%.

10. The porous polymer microspheres prepared by the method according to any one of claims 1 to 9, characterized in that, The interior and outer surface of the porous polymer microspheres both have a pore structure, the outer surface pore structure is an open pore structure, and the interior pore structure is an open and interconnected pore structure.

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