A porous polymer microsphere and its preparation method

Abstract

The present invention belongs to the field of polymer materials and discloses a porous polymer microsphere and a preparation method thereof, comprising the following steps: (1) mixing polymer seed microspheres with an alcohol solvent, water, and a porogen, controlling the volume ratio of the alcohol solvent to water to be greater than 6.5:5.5, and allowing the mixed solution to form an emulsion under high-speed stirring conditions; the surface of the polymer seed microspheres has hydrophilic groups; (2) stirring the mixed emulsion at a low speed for more than 10 minutes to obtain a suspension; (3) subjecting the suspension to rotary evaporation, washing, and drying after the solvent has fully evaporated to obtain porous polymer microspheres. The present invention only requires a one-step reaction, does not require the use of special additives such as surfactants and etchants, and does not require additional porogens or complex precision equipment. Highly porous polystyrene microspheres with interconnected open pore structures and uniform size distribution can be prepared within 2 hours at room temperature. The microspheres have a large specific surface area and pore volume.

Description

Technical Field

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

[0002] Porous polymer microspheres, due to their unique interconnected open pore structure, possess high specific surface area, ultra-low mass density, and excellent permeability. Compared to traditional microsphere materials, these materials exhibit significant advantages in physical and chemical properties and are currently widely used in high-tech fields such as chromatographic separation, catalytic supports, separation engineering, microreactor construction, biomedical engineering, and microelectronics, demonstrating their significant application value.

[0003] Conventional porous polymer microspheres have a similar pore structure and pore size from the surface to the interior. This uniform pore structure typically allows them to exhibit a single property when used as a filler, such as molecular exclusion or specific binding. In recent years, highly interconnected and open porous polymer microspheres, due to their unique structure, have demonstrated the dual properties of molecular exclusion and specific binding when used as multimodal filler carriers. This offers advantages such as simplicity and high efficiency in catalytic carriers and in the purification of multiscale samples such as viruses and biomacromolecules.

[0004] However, the current preparation process of porous polymer microspheres generally has the problems of complex steps, long time consumption and high cost. It usually requires the addition of surfactants for emulsification and involves multi-step processing. For example, the Chinese patent application with publication number CN105524223 A discloses a four-step method for preparing porous PS-DVB microspheres using seed ball activation, two-step swelling and porogen extraction. The total time consumed is more than 55 hours, and the specific surface area of ​​the obtained microspheres is 21.4 m² / g. The Chinese patent application with publication number CN116747318 A uses polyvinyl alcohol as an emulsifier to prepare drug co-delivery degradable microspheres by the emulsion-solution volatilization method. However, this method will form a continuous film on the surface of the microspheres, and additional alkaline etching treatment is required to remove the film and regulate the pore structure. This process may damage the overall structure of the microspheres. Summary of the Invention

[0005] In response to the defects of the existing technology, the main purpose of the present invention is to provide a simple, rapid and efficient method for preparing 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] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing porous polymer microspheres comprises the following steps:

[0008] (1) After mixing polymer seed microspheres with an alcohol solvent, water, and a porogen, the volume ratio of the alcohol solvent to water is controlled to be greater than 6.5:5.5, so that the mixture forms an emulsion under high-speed stirring conditions; the surface of the polymer seed microspheres has hydrophilic groups, 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;

[0009] (2) stirring the mixed emulsion at a low speed for more than 10 minutes to obtain a suspension; the low-speed stirring speed is ≤500 rpm;

[0010] (3) The suspension is subjected to rotary evaporation (at room temperature), and after the solvent is fully volatilized, the suspension is washed and dried to obtain the porous polymer microspheres.

[0011] The porous polymer microspheres have pore structures both inside and outside. The outer pore structure is an open pore structure, and the inner pore structure is also an open and interconnected pore structure.

[0012] Preferably, the alcohol solvent is a short-chain alcohol of C1-C6; the porogen is a mixed solvent consisting of toluene and the following organic solvents, wherein the organic solvent is one or more of dichloromethane, chloroform, chloroform, acetone, 1,2-dichloroethane, chlorododecane, n-heptane, and n-octane.

[0013] Preferably, the volume ratio of the alcohol solvent to water is 7.6±0.4:5.5.

[0014] Preferably, the alcohol solvent is one or more of ethanol, isopropanol, methanol, cyclohexanol, n-butanol, isopropanol, and tert-butanol.

[0015] The polymer seed microspheres are prepared by polymerization reaction mode of 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 mode is dispersion polymerization.

[0016] Preferably, the polymer seed microspheres are prepared by dissolving an initiator and polyvinylpyrrolidone (PVP) in a mixed solvent of water and ethanol, adding a monomer with an unsaturated bond, stirring evenly, and reacting at 70±10°C for 6±2 hours. After the reaction, the mixture is cooled, centrifuged, and washed 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, glycidyl methacrylate, butyl acrylate, and glycidyl acrylate.

[0017] Preferably, the polymer seed microspheres are selected from one or more of polystyrene seed microspheres, polymethyl methacrylate seed microspheres and polyglycidyl methacrylate seed microspheres; and the surfaces of the polymer seed microspheres have sulfonic acid groups.

[0018] Preferably, the high-speed stirring speed is 1000-3000 rpm, and the stirring time is 3-30 s; the low-speed stirring speed is 50-500 rpm, and the reaction time is 5-60 min.

[0019] Preferably, the high-speed stirring speed is 2500±500 rpm, and the stirring time is 10±5 s; the low-speed stirring speed is 300±100 rpm, and the reaction time is 20-30 min.

[0020] 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.

[0021] 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, or 5 g / L.

[0022] Preferably, the volume ratio of the porogen to water is 5%-25%, more preferably 10%-15%.

[0023] Preferably, the porogen is a mixed solvent with a toluene volume content of 30%-70%, and the volume content can be 40%, 50%, or 60%.

[0024] The rotary evaporation adopts a digital controlled rotary mixer with a rotation speed of 5 r / min~100 r / min; the rotary volatilization time is 1~36 h.

[0025] The morphological transformation mechanism of the microspheres of the present invention is as follows: When porogens (toluene and dichloromethane) are added to a water-ethanol mixture and vigorously stirred, the toluene-dichloromethane droplets and the water-ethanol mixture form an emulsion (reaction medium). After quiescence, phase separation does not occur. This is because alcohols such as ethanol act as surfactants in the water and toluene-dichloromethane ternary solvent, reducing the interfacial energy of the emulsion and allowing the toluene-dichloromethane droplets to exist stably in the continuous phase. The synergistic effect of the ethanol dosage and stirring speed is crucial for emulsion formation. When polystyrene seed microspheres are dispersed in this emulsion, they absorb the toluene-dichloromethane droplets in the continuous phase and swell, causing the polymer chains to become flexible and begin to migrate. At the same time, since the surface of the polystyrene seed microspheres has sulfonic acid groups (ammonium persulfate is used as a polymerization initiator for the seed microspheres), the surface of the microspheres is hydrophilic, and the mixture of water and ethanol can be absorbed by the polystyrene seed microspheres. This osmotic pressure 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, thereby forming porous interpenetrating network microspheres.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention requires only one step of reaction and can be completed within 2 hours at room temperature. It does not require the use of special additives such as surfactants and etchants, nor does it require additional pore-forming processes or complex precision equipment. In addition, the pore size of the microspheres can be flexibly controlled by regulating the absorption time of the reaction solvent. The operation is simple and controllable. Compared with traditional complex processes such as multi-step swelling and alkaline etching, the present invention greatly simplifies the preparation process and reduces costs. At the same time, it avoids the potential damage to the microsphere structure caused by subsequent treatment, which is conducive to the large-scale preparation of high-performance porous polymer microspheres.

[0028] (2) The porous polymer microspheres of the present invention are prepared by dispersing polystyrene seed polymer microspheres in an oil-in-water emulsion system to prepare highly porous polystyrene microspheres with interconnected open pore structures and uniform size distribution. 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a scanning electron microscope image of the polystyrene seed microspheres of the present invention.

[0030] Figure 2 This is a scanning electron micrograph of the glycidyl methacrylate seed microspheres of the present invention.

[0031] Figure 3 This is a scanning electron micrograph of the porous polymer microspheres prepared in Example 1.

[0032] Figure 4 This is a scanning electron micrograph of the interpenetrating pore structure inside the porous polymer microspheres prepared in Example 1.

[0033] Figure 5 This is a scanning electron micrograph of the porous polymer microspheres prepared in Example 2.

[0034] Figure 6 This is a scanning electron micrograph of the porous polymer microspheres prepared in Example 3.

[0035] Figure 7 This is a scanning electron micrograph of the porous polymer microspheres prepared in Example 4.

[0036] Figure 8 This is a scanning electron micrograph of the porous polymer microspheres prepared in Example 5.

[0037] Figure 9 This is a scanning electron micrograph of the porous polymer microspheres prepared in Example 6.

[0038] Figure 10 This is a scanning electron micrograph of the porous polymer microspheres prepared in Comparative Example 1.

[0039] Figure 11 This is a scanning electron micrograph of the porous polymer microspheres prepared in Comparative Example 2.

[0040] Figure 12 This is a scanning electron micrograph of the porous polymer microspheres prepared in Comparative Example 3.

[0041] Figure 13 This is a scanning electron micrograph of the porous polymer microspheres prepared in Comparative Example 4.

[0042] Figure 14 This is a scanning electron micrograph of the porous polymer microspheres prepared in Comparative Example 5.

[0043] Figure 15 These are photos of the suspensions of reaction media from different examples after stirring for 10 s (emulsified or not). DETAILED DESCRIPTION

[0044] The present invention will be described in further detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.

[0045] The preparation method of polystyrene seed polymer microspheres comprises the following steps:

[0046] (1) Dissolve 0.5 g of ammonium persulfate (APS, initiator) and 0.05 g of polyvinylpyrrolidone (PVP, steric stabilizer) in a reactor containing a water (15 mL)-ethanol (75 mL) mixture at room temperature.

[0047] (2) Add 11 mL of styrene monomer to the reactor.

[0048] (3) The reaction mixture was stirred at room temperature for 10 min under magnetic stirring and then at 70 °C for 6 h.

[0049] (4) Place the reactor in an ice bath to stop the reaction. Then centrifuge at 6000 rpm to collect the polystyrene seed polymer microspheres, wash them three times with water, and set aside. The particle size of the prepared microspheres is about 1 μm, see Figure 1 .

[0050] The preparation method of poly(glycidyl methacrylate) seed polymer microspheres (the initiator is azobisisobutyronitrile) comprises the following steps:

[0051] (1) Add 3 g of polyvinylpyrrolidone (PVP) to a mixture of ethanol (100 mL) and water (9 mL) at room temperature and stir at room temperature for 10 min.

[0052] (2) After nitrogen purge 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.

[0053] (3) Heat to 70°C and continue stirring for 3 h.

[0054] (4) After the reaction is stopped, the poly(glycidyl methacrylate) seed polymer microspheres are collected by centrifugation at 6000 rpm and washed three times with water for later use. The particle size of the prepared microspheres is about 1 μm. Figure 2 .

[0055] The preparation method of poly(glycidyl methacrylate) seed polymer microspheres (initiator is ammonium persulfate) comprises the following steps:

[0056] (1) Add 3 g of polyvinylpyrrolidone (PVP) to a mixture of ethanol (100 mL) and water (9 mL) at room temperature and stir at room temperature for 10 min.

[0057] (2) Nitrogen was purged for 10 min to remove oxygen, and 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.

[0058] (3) Heat to 70°C and continue stirring for 3 h.

[0059] (4) After the reaction is stopped, the poly(glycidyl methacrylate) seed polymer microspheres are collected by centrifugation at 6000 rpm and washed three times with water for later use. The particle size of the prepared microspheres is approximately 1 μm.

[0060] Example 1

[0061] The preparation method of porous polymer microspheres comprises the following steps:

[0062] (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them into a mixed solvent of water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0063] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture. Then, vigorously stir the suspension using a vortex stirrer (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0064] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 30 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at a speed of 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous polystyrene polymer microsphere dispersion. The reaction solution was centrifuged (8000 rpm, 5 min), washed (washed twice with anhydrous ethanol) and dried (45°C, 8 h).

[0065] Example 2

[0066] The preparation method of porous polymer microspheres comprises the following steps:

[0067] (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them into a mixed solvent of water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0068] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture. Then, vigorously stir the suspension using a vortex stirrer (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0069] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 20 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at a speed of 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous polystyrene polymer microsphere dispersion. The reaction solution was then centrifuged, washed, and dried.

[0070] Example 3

[0071] The preparation method of porous polymer microspheres comprises the following steps:

[0072] (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in different proportions of water (5.5 mL) and ethanol (7.6 mL).

[0073] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture. Then, vigorously stir the suspension using a vortex stirrer (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0074] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 10 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at a speed of 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous polystyrene polymer microsphere dispersion. The reaction solution was then centrifuged, washed, and dried.

[0075] Example 4

[0076] The preparation method of porous polymer microspheres comprises the following steps:

[0077] (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them in different proportions of water (5.5 mL) and ethanol (7.6 mL).

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

[0079] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 5 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous polystyrene polymer microsphere dispersion. The reaction solution was then centrifuged, washed, and dried.

[0080] Example 5

[0081] The preparation method of poly(glycidyl methacrylate) porous polymer microspheres comprises the following steps:

[0082] (1) Weigh 20 mg of the prepared poly(glycidyl methacrylate) seed polymer microspheres (initiator: ammonium persulfate) and disperse them in a mixed solvent of water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0083] (2) Add a mixture of toluene (0.25 mL) and dichloromethane (0.2 mL) to the above reaction mixture. Then, vigorously stir the suspension using a vortex stirrer (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0084] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 20 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at a speed of 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous poly(glycidyl methacrylate) polymer microsphere dispersion. The reaction solution was then centrifuged, washed, and dried.

[0085] Example 6

[0086] The difference between this embodiment and embodiment 5 is that the poly(glycidyl methacrylate) seed polymer microspheres are prepared using azobisisobutyronitrile as the initiator.

[0087] Comparative Example 1

[0088] The preparation method of porous polymer microspheres comprises the following steps:

[0089] (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them into a mixed solvent of water (5.5 mL) and ethanol (3 mL) in different proportions.

[0090] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture. Stir the suspension vigorously using a vortex mixer (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0091] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 20 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous polystyrene polymer microsphere dispersion. The reaction solution was then centrifuged, washed, and dried.

[0092] Comparative Example 2

[0093] The preparation method of porous polymer microspheres comprises the following steps:

[0094] (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them into a mixed solvent of water (5.5 mL) and ethanol (5 mL) in different proportions.

[0095] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture. Then, vigorously stir the suspension using a vortex stirrer (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0096] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 20 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at a speed of 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous polystyrene polymer microsphere dispersion. The reaction solution was then centrifuged, washed, and dried.

[0097] Comparative Example 3

[0098] The preparation method of porous polymer microspheres comprises the following steps:

[0099] (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them into a mixed solvent of water (5.5 mL) and ethanol (6.5 mL) in different proportions.

[0100] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture. Then, vigorously stir the suspension using a vortex stirrer (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0101] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 20 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at a speed of 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous polystyrene polymer microsphere dispersion. The reaction solution was then centrifuged, washed, and dried.

[0102] Comparative Example 4

[0103] The preparation method of porous polymer microspheres comprises the following steps:

[0104] (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them into a mixed solvent of water (5.5 mL) and ethanol (8.5 mL) in different proportions.

[0105] (2) Add a mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) to the above reaction mixture. Then, vigorously stir the suspension using a vortex stirrer (stirring speed 2500 rpm) for 10 s to mix the solvents and thoroughly emulsify them.

[0106] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 20 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at a speed of 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous polystyrene polymer microsphere dispersion. The reaction solution was then centrifuged, washed, and dried.

[0107] Comparative Example 5

[0108] The preparation method of porous polymer microspheres comprises the following steps:

[0109] (1) Weigh 20 mg of the prepared polystyrene seed polymer microspheres and disperse them into a mixed solvent of water (5.5 mL) and ethanol (7.6 mL) in different proportions.

[0110] (2) A mixture of toluene (0.35 mL) and dichloromethane (0.2 mL) was added to the above reaction mixture. The suspension was then stirred (stirring speed 200 rpm) for 10 s. A vortex stirrer was not used for vigorous stirring of the suspension.

[0111] (3) The mixed emulsifier was transferred to a magnetic stirrer and the emulsion was magnetically stirred at 300 r / min for 30 min. After the reaction, the mixed emulsion was transferred to a CNC rotary mixer at a speed of 25 r / min and the solvent was rotary evaporated for 1.5 h. All processes were carried out at room temperature to obtain a porous polystyrene polymer microsphere dispersion. The reaction solution was then centrifuged, washed, and dried.

[0112] Table 1 Formulations and characterization results of porous polymer microspheres in different examples

[0113]

[0114] The result shows that the addition of ethanol plays an important role in keeping the emulsion droplets stable and subsequent volatilization rate. Meanwhile, the extension of the reaction time plays a positive role in increasing the pore size. First. When the ethanol amount is insufficient, although the strong stirring initial stage will form a milky white turbid emulsion, phase separation will occur rapidly subsequently, now in a thermodynamically unstable state, the toluene-dichloromethane droplets initially dispersed in the continuous phase will assemble over time, ultimately causing oil-water two-phase separation, and porous polymer microspheres cannot be prepared, such as comparative examples 1-3, experimental result shows, because the toluene-dichloromethane droplets assemble over time, a large amount of microspheres are infiltrated into the microspheres, making it impossible for microspheres to maintain spherical morphology, and collapse occurs. When the ethanol amount is excessive, the existence of excess ethanol makes the solution system be in a thermodynamically stable state, and the system presents a single-phase transparent homogeneous solution, and can no longer maintain emulsion stability, and the toluene-dichloromethane mixed solution does not assemble, and porous polymer microspheres cannot be prepared equally, such as comparative example 4 results show that microspheres maintain spherical morphology and porous does not occur on the surface. When the amount of ethanol added is the preferred amount, the milky white emulsion formed after vigorous 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 increases, the microsphere particles absorb more reaction medium, causing them to form droplets inside, which penetrate into the core 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 microspheres and an average pore size, and the specific surface area and pore volume gradually increase. However, in Example 4, due to the short reaction time, the reaction medium mainly acts on the surface of the microspheres and less penetrates into the interior of the microspheres. The experimental results show that the microspheres maintain a spherical morphology, and the micropore depth formed on the surface of the microspheres is shallow, resulting in a small number of microsphere holes. 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 medium absorbed by the microspheres is limited, resulting in a small number of microsphere holes. The results of Comparative Example 5 show that when the amount of ethanol added is the preferred amount but the emulsion is not vigorously stirred, phase separation occurs after standing, the reaction medium cannot penetrate into the interior of the microspheres, and porous microspheres cannot be prepared.

[0115] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing porous polymer microspheres, characterized in that: The following steps are involved: (1) After mixing polymer seed microspheres with ethanol, water and a porogen, the volume ratio of ethanol to water is controlled to be greater than 6.5:5.5 and less than 8.5:5.5, so that the mixture forms an emulsion under high-speed stirring conditions; the surface of the polymer seed microspheres has hydrophilic groups; the high-speed stirring speed is ≥600 rpm; (2) stirring the emulsion at a low speed for more than 10 minutes to obtain a suspension; the low-speed stirring speed is ≤500 rpm; (3) The suspension is subjected to rotary evaporation to fully evaporate the solvent, and then washed and dried to obtain porous polymer microspheres; The polymer seed microspheres are selected from one or more of polystyrene seed microspheres, polymethyl methacrylate seed microspheres and polyglycidyl methacrylate seed microspheres; The porogen is a mixed solvent of toluene and dichloromethane.

2. The preparation method according to claim 1, characterized in that The volume ratio of the ethanol to water is 7.6±0.4:5.

5.

3. The preparation method according to claim 2, characterized in that The polymer seed microspheres are prepared by dissolving an initiator and polyvinyl pyrrolidone in a mixed solvent of water and ethanol, adding a monomer with an unsaturated bond, stirring evenly, and reacting at 70±10° C. for 6±2 hours. After the reaction is completed, the mixture is cooled, centrifuged, and washed to obtain the polymer seed microspheres. The initiator is ammonium persulfate and / or azobisisobutyronitrile.

4. The preparation method according to any one of claims 1 to 3, characterized in that The polymer seed microspheres have sulfonic acid groups on their surfaces.

5. The preparation method according to claim 4, characterized in that The high-speed stirring speed is 1000-3000 rpm, and the stirring time is 3-30 s; the low-speed stirring speed is 50-500 rpm, and the reaction time is 5-60 min.

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

7. The preparation method according to any one of claims 1 to 3, characterized in that The mass volume ratio of the polymer seed microspheres to water in step (1) is 0.25-5 g / L; the particle size of the polymer seed microspheres is 0.5-20 μm.

8. The preparation method according to claim 7, characterized in that The volume ratio of the porogen to water is 5%-25%; the porogen is a mixed solvent with a toluene volume content of 30%-70%.

9. The porous polymer microspheres prepared by the method according to any one of claims 1 to 8, characterized in that: The porous polymer microspheres have pore structures both inside and outside, wherein the outer pore structure is an open pore structure and the inner pore structure is an open and interconnected pore structure.

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