Multi-hollow polymer microsphere and preparation method thereof

Abstract

The invention provides a multi-hollow polymer microsphere and a preparation method thereof, and belongs to the technical field of colloidal microspheres, the multi-hollow polymer microsphere comprises polystyrene and polyglycidyl methacrylate, and the interior of the multi-hollow polymer microsphere is also provided with a plurality of hollow areas which can be identified by a transmission electron microscope. The preparation method comprises the following steps: step 1, preparing polystyrene (PS) microspheres through a dispersion polymerization method; and step 2, preparing the multi-hollow polystyrene-polyglycidyl methacrylate (PS-PGMA) composite microspheres by a seed emulsion polymerization method comprising a swelling step. According to the method, large-scale preparation can be realized, and the PS seed microspheres are endowed with hydrophilicity without adopting a specific polymerization formula, sulfonation, copolymerization by using hydrophilic monomers and the like, so that the method is very simple and convenient.

Description

Technical Field

[0001] The present invention belongs to the technical field of colloidal microspheres, and particularly relates to a multi-hollow polymer microsphere and a preparation method thereof. Background Art

[0002] The multi-hollow polymer microsphere is a special kind of hollow colloidal microsphere. Different from the porous polymer microsphere with numerous tiny pores inside, the multi-hollow polymer microsphere has multiple cavities with larger sizes but significantly fewer numbers inside. The multi-hollow polymer microsphere has advantages such as a large specific surface area, a large internal space, and a low density, and has been widely studied. Its preparation methods can be mainly divided into two categories: post-treatment of the already formed polymer microspheres and polymerization methods (Langmuir 2025, 41, 8019 - 8030).

[0003] The post-treatment of the already formed polymer microspheres includes methods such as alkali treatment, heat treatment, and solvent treatment.

[0004] The premise of this method is that the polymer particles themselves contain or embed hydrophilic groups. For example, Okubo et al. prepared multi-hollow PS microspheres by gradually treating copolymer particles containing carboxylic acid groups with alkali / acid (Colloid Polym. Sci. 1991, 269, 1257–1262). The principle lies in that during the alkali treatment, the carboxylic acid groups in the copolymer particles are neutralized by the alkali and ionized, and then under the action of the osmotic pressure caused by the ionized carboxylic acid groups, water enters the interior of the particles to form numerous aggregation regions; in the subsequent acid treatment process, in order to minimize the interfacial surface area between the ionized polymer and water, the water aggregation regions experience coalescence to form a multi-hollow structure. Another example is that Okubo et al. heated an aqueous dispersion of micron-sized PS microspheres internally embedded with sulfate groups above Tg for a certain period of time to obtain multi-hollow polystyrene (PS) microspheres (Langmuir 2017, 33, 3468 - 3475). This is because during the heating process, the PS microspheres containing water themselves further absorb water under the action of the osmotic pressure caused by the sulfate groups they embed, and the water-containing regions experience growth and coalescence, and under appropriate conditions, multi-hollow microspheres can be formed.

[0005] The polymerization methods mainly include seeded emulsion polymerization, one-step emulsion polymerization, and double emulsion template polymerization. Among them, seeded emulsion polymerization is an environmentally friendly method that is easy to prepare in large quantities. In the existing literature, the prerequisite for its preparation is similar to heat treatment, that is, the seed microspheres themselves contain or embed hydrophilic groups. For example, Okubo et al. used micron-sized PS microspheres containing sulfate groups and nonionic surfactants inside as seeds, and prepared multi-hollow PS microspheres through seeded emulsion polymerization of styrene (Langmuir 2007, 23, 8703–8708). Similar to the above heat treatment method, during the seeded polymerization process, the water-containing PS microspheres themselves absorb more water under the action of the osmotic pressure caused by the sulfate groups they embed. The water-containing regions experience growth and merger, and multi-hollow microspheres can be formed under appropriate conditions. Ge Xuewu et al. used sulfonated cross-linked PS microspheres as seeds and prepared multi-hollow PS microspheres through seeded emulsion polymerization of styrene (Langmuir 2013, 29, 14787–14794). The sulfonated cross-linked PS microspheres are first swollen by styrene and water. Under the action of the osmotic pressure caused by the hydrophilic sulfonic acid groups, a multi-hollow structure is first formed inside the seed microspheres, and then through radiation emulsion polymerization, multi-hollow polymer microspheres with various surface morphologies are obtained. Yu Demei et al. used poly(styrene-co-4-styrenesulfonate) as seeds and obtained multi-hollow microspheres through seeded emulsion copolymerization of styrene, divinylbenzene, and glycidyl methacrylate (Journal of Colloid and Interface Science 2016, 473, 44–51). The formation of multi-hollow PS microspheres includes stages such as water absorption, merger of water-containing regions, and fixation of the multi-hollow structure. In the above examples, in order to make the seed microspheres contain or embed hydrophilic groups inside, methods such as using specific polymerization formulations (requiring the simultaneous use of a large amount of nonionic surfactants, which will damage the performance of the microspheres), sulfonating the seed microspheres (requiring the use of concentrated sulfuric acid, which is relatively dangerous), and using hydrophilic comonomers (the steps are relatively complex) to prepare the seed microspheres are adopted, and their steps have certain limitations. In addition, one-step emulsion polymerization also highly depends on specific polymerization formulations, and double emulsion template polymerization has disadvantages such as difficult particle size control and difficult large-scale preparation.

[0006] Therefore, how to simply prepare multi-hollow polymer microspheres in large quantities is an urgent problem to be solved in this field. Summary of the Invention

[0007] The object of the present invention is to provide a multi-hollow polymer microsphere, which is characterized in that it includes two polymer components, namely polystyrene (PS) and poly(glycidyl methacrylate) (PGMA), and the interior of the multi-hollow polymer microsphere has multiple hollow regions that can be identified by transmission electron microscopy.

[0008] A preparation method of multi-hollow polymer microspheres for preparing multi-hollow polymer microspheres, comprising the following steps:

[0009] S1: Using PS as a monomer, polyvinylpyrrolidone (PVP) as a stabilizer, methanol as a solvent, after mixing and stirring for a certain time t0, heating to a specified temperature T0, then adding a methanol solution of azobisisobutyronitrile (AIBN) as an initiator, stirring at the specified temperature T0 for a certain time t1, and finally obtaining PS microspheres after washing and drying.

[0010] S2: Using the PS microspheres as seeds, glycidyl methacrylate (GMA) as a monomer, sodium dodecyl sulfate (SDS) as a stabilizer, dibutyl phthalate (DBP) as a swelling agent, and water as a solvent, after mixing and swelling at a specified temperature T1 for a certain time t2, then stirring for a specified time t3, then heating to a specified temperature T3, and adding a GMA solution or an ethanol solution of AIBN to initiate a polymerization reaction, and finally stirring at the specified temperature T3 for a specified polymerization time t4, and washing to obtain multi-hollow PS-PGMA composite polymer microspheres.

[0011] Further, the whole preparation process is carried out under the conditions of nitrogen passing and condensation reflux, the heating is carried out by oil bath heating, the washing is carried out by centrifugal washing, and the drying is carried out by vacuum drying.

[0012] Further, in S1, the certain time t0 is 30 min, the certain time t1 is 24 h, and the specified temperature T0 is 60 °C.

[0013] Further, in S2, during the mixing and swelling, the mass ratio of the PS microspheres, SDS, water, DBP, and GMA is 0.5:0.125:50:0.5:0.5 - 4.5.

[0014] Further, in S2, AIBN is first added to the GMA solution or ethanol solution and then fed together.

[0015] Further, in S2, by adjusting the mass of glycidyl methacrylate in the swelling stage and the polymerization stage, multi-hollow polymer microspheres of various sizes and morphologies are prepared;

[0016] The mass of glycidyl methacrylate in the swelling stage and the polymerization stage is not zero at the same time.

[0017] Further, in S2, the specified temperature T1 is 40 °C, the certain time t2 is 24 h, the specified time t3 is 30 min, the specified temperature T2 is 80 °C, and the specified time t4 is 8 h.

[0018] Further, the average diameter of the prepared polymer microspheres is 1.42 - 1.90 μm.

[0019] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0020] 1. In the present invention, PS seed microspheres are prepared by dispersion polymerization, and multi-hollow PS-PGMA composite microspheres are prepared by seed emulsion polymerization, and both are easy to be prepared in large quantities.

[0021] 2. The present invention does not need to endow PS seed microspheres with hydrophilicity by adopting specific polymerization formulations, sulfonation, copolymerization with hydrophilic monomers, etc. Therefore, it is very simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 and Figure 2 are the scanning electron microscope photograph and transmission electron microscope photograph of the PS microspheres prepared in Step 1 of Example 1, respectively;

[0023] Figure 3 , Figure 4 and Figure 5 are the scanning electron microscope photograph, transmission electron microscope photograph of the PS-PGMA composite microspheres prepared in Step 2 of Example 1, and the transmission electron microscope photograph of the ultra-thin section sample, respectively;

[0024] Figure 6 is the infrared spectrum of the PS microspheres and PS-PGMA composite microspheres prepared in Example 1.

[0025] Figure 7 is the transmission electron microscope photograph of the multi-hollow PS-PGMA composite microspheres prepared in Example 2.

[0026] Figure 8 is the transmission electron microscope photograph of the multi-hollow PS-PGMA composite microspheres prepared in Example 3.

[0027] Figure 9 is the transmission electron microscope photograph of the multi-hollow PS-PGMA composite microspheres prepared in Example 4.

[0028] Figure 10 is the transmission electron microscope photograph of the multi-hollow PS-PGMA composite microspheres prepared in Example 5.

[0029] Figure 11 is the transmission electron microscope photograph of the multi-hollow PS-PGMA composite microspheres prepared in Example 6.

[0030] Figure 12 is the transmission electron microscope photograph of the multi-hollow PS-PGMA composite microspheres prepared in Example 7.

[0031] Figure 13 is the transmission electron microscope photograph of the multi-hollow PS-PGMA composite microspheres prepared in Example 8.

[0032] Figure 14 TEM image of the multi-hollow PS-PGMA composite microspheres prepared in Example 9.

[0033] Figure 15 TEM image of the multi-hollow PS-PGMA composite microspheres prepared in Example 10. Detailed implementation mode

[0034] The following will describe in more detail a multi-hollow polymer microsphere and its preparation method according to the present invention with reference to the accompanying drawings, in which the preferred embodiments of the present invention are shown. It should be understood that those skilled in the art can modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as a broad guidance for those skilled in the art and not as a limitation to the present invention.

[0035] Example 1:

[0036] The preparation method of the multi-hollow polymer microspheres involved in this example includes the following two steps:

[0037] Step 1: Prepare PS seed microspheres by dispersion polymerization.

[0038] Take 1.0 g of PVPK10 as a stabilizer and 26 ml of methanol as a solvent, and put them into a 250 mL three-necked round-bottom flask equipped with a condenser, a nitrogen-passing device and a mechanical stirring device. After stirring for 30 min, heat it in an oil bath to 60 °C, and then inject a solution of 0.05 g of AIBN initiator in 4.0 g of methanol to initiate polymerization. Then continue to stir and polymerize at 60 °C for 24 h. During the above reaction, the condenser and the nitrogen-passing device are in the open state throughout the whole process. After the reaction stops, the obtained product is centrifuged and washed five times (centrifugation speed: 6000 rpm, 30 minutes each time). After the first two centrifugations, ethanol is used to replace the supernatant. After the next two centrifugations, water is used to replace the supernatant. After the 5th centrifugation, the obtained product is freeze-dried to obtain PS microspheres. It is found by scanning electron microscopy that the surface of the prepared PS microspheres is smooth. It is found by transmission electron microscopy that the prepared microspheres are solid, with an average diameter of 1.4 μm. The chemical components of the prepared microspheres are characterized by infrared spectroscopy.

[0039] Step 2: Prepare multi-hollow PS-PGMA composite microspheres by seed emulsion polymerization.

[0040] 1) Take 0.5 g of PS microspheres as seeds, 0.125 g of SDS as a stabilizer, and 50 ml of water as a solvent, and put them into a 100 mL three-necked round-bottom flask equipped with a condenser, a nitrogen-passing device and a mechanical stirring device.

[0041] 2) Next, 0.5 g of DBP swelling agent and 1.5 g of GMA monomer were added. After mixing and swelling at 40 °C for 24 h, stirring was carried out for another 30 min. Subsequently, the oil bath was heated to 80 °C, and a solution of 0.030 g of AIBN in 1.5 g of GMA was injected to initiate polymerization. Finally, polymerization was continued with stirring at 80 °C for 8 h. During the whole process of the above reaction, the condenser and the nitrogen gas passing device were in the open state. After the reaction stopped, the obtained product was centrifuged and washed 3 times (centrifugation speed 6000 rpm, 5 minutes each time). After the first centrifugation, the upper clear liquid was replaced with ethanol, and after the last two centrifugations, the upper clear liquid was replaced with water. Finally, the obtained product was dispersed in water. Observation with a scanning electron microscope found that the surface of the prepared microspheres became rough. Observation with a transmission electron microscope found that the prepared microspheres were multi-hollow, with an average diameter of 1.65 μm. The chemical components of the prepared microspheres were characterized by infrared spectroscopy, and it was found that the prepared multi-hollow microspheres contained both PS components and PGMA components, so they were multi-hollow PS-PGMA composite microspheres.

[0042] 3) Figure 1 and Figure 2 are the scanning electron microscope photograph and transmission electron microscope photograph of the PS microspheres prepared in Step 1 of Example 1; Figure 3 、 Figure 4 and Figure 5 are respectively the scanning electron microscope photograph, transmission electron microscope photograph of the multi-hollow PS-PGMA composite microspheres prepared in Step 2 of Example 1, and the transmission electron microscope photograph of the ultra-thin section sample; Figure 6 is the infrared spectrum of the PGMA microspheres prepared in Step 1 of Example 1 and the multi-hollow PS-PGMA composite microspheres prepared in Step 2.

[0043] Example 2:

[0044] In Step 1 and Step 2, 1) remains unchanged. In 2), 0.5 g of DBP swelling agent and 1.5 g of GMA monomer were added. After mixing and swelling at 40 °C for 24 h, stirring was carried out for another 30 min. Subsequently, the oil bath was heated to 80 °C, and a solution of 0.015 g of AIBN in 1.0 g of ethanol was injected to initiate polymerization, and the others remained unchanged.

[0045] As Figure 7 shown, the microspheres prepared in Step 2 of this example are multi-hollow microspheres, and the average diameter of the microspheres is 1.49 μm.

[0046] Example 3:

[0047] In Steps 1 and 2, 1) remains unchanged. In 2), 0.5 g of DBP swelling agent and 1.5 g of GMA monomer are added, and after mixing and swelling at 40 °C for 24 h, stirring is carried out for 30 min. Subsequently, the oil bath is heated to 80 °C, and a solution of 0.045 g of AIBN in 3.0 g of GMA is injected to initiate polymerization, while the others remain unchanged.

[0048] As Figure 8 shown, the microspheres prepared in Step 2 of this example are multi-hollow microspheres, and the average diameter of the microspheres is 1.81 μm.

[0049] Example 4:

[0050] In Steps 1 and 2, 1) remains unchanged. In 2), 0.5 g of DBP swelling agent is added, and after mixing and swelling at 40 °C for 24 h, stirring is carried out for 30 min. Subsequently, the oil bath is heated to 80 °C, and a solution of 0.015 g of AIBN in 1.5 g of GMA is injected to initiate polymerization, while the others remain unchanged.

[0051] As Figure 9 shown, the microspheres prepared in Step 2 of this example are multi-hollow microspheres, and the average diameter of the microspheres is 1.57 μm.

[0052] Example 5:

[0053] In Steps 1 and 2, 1) remains unchanged. In 2), 0.5 g of DBP swelling agent and 0.5 g of GMA monomer are added, and after mixing and swelling at 40 °C for 24 h, stirring is carried out for 30 min. Subsequently, the oil bath is heated to 80 °C, and a solution of 0.005 g of AIBN in 1.0 g of ethanol is injected to initiate polymerization, while the others remain unchanged.

[0054] As Figure 10 shown, the microspheres prepared in Step 2 of this example are multi-hollow microspheres, and the average diameter of the microspheres is 1.42 μm.

[0055] Example 6:

[0056] In Steps 1 and 2, 1) remains unchanged. In 2), 0.5 g of DBP swelling agent and 0.5 g of GMA monomer are added, and after mixing and swelling at 40 °C for 24 h, stirring is carried out for 30 min. Subsequently, the oil bath is heated to 80 °C, and a solution of 0.025 g of AIBN in 2.0 g of GMA is injected to initiate polymerization, while the others remain unchanged.

[0057] As Figure 11 shown, the microspheres prepared in Step 2 of this example are multi-hollow microspheres, and the average diameter of the microspheres is 1.64 μm.

[0058] Example 7:

[0059] In Steps 1 and 2, 1) remains unchanged. In 2), 0.5 g of DBP swelling agent and 1.0 g of GMA monomer are added. After mixing and swelling at 40 °C for 24 h, stir for another 30 min. Then, heat in an oil bath to 80 °C and inject a solution of 0.015 g of AIBN in 0.5 g of GMA to initiate polymerization, with other conditions remaining unchanged.

[0060] As Figure 12 shown, the microspheres prepared in Step 2 of this example are multi-hollow microspheres, and the average diameter of the microspheres is 1.49 μm.

[0061] Example 8:

[0062] In Steps 1 and 2, 1) remains unchanged. In 2), 0.5 g of DBP swelling agent and 1.0 g of GMA monomer are added. After mixing and swelling at 40 °C for 24 h, stir for another 30 min. Then, heat in an oil bath to 80 °C and inject a solution of 0.030 g of AIBN in 2.0 g of GMA to initiate polymerization, with other conditions remaining unchanged.

[0063] As Figure 13 shown, the microspheres prepared in Step 2 of this example are multi-hollow microspheres, and the average diameter of the microspheres is 1.70 μm.

[0064] Example 9:

[0065] In Steps 1 and 2, 1) remains unchanged. In 2), 0.5 g of DBP swelling agent and 2.0 g of GMA monomer are added. After mixing and swelling at 40 °C for 24 h, stir for another 30 min. Then, heat in an oil bath to 80 °C and inject a solution of 0.025 g of AIBN in 0.5 g of GMA to initiate polymerization, with other conditions remaining unchanged.

[0066] As Figure 14 shown, the microspheres prepared in Step 2 of this example are multi-hollow microspheres, and the average diameter of the microspheres is 1.73 μm.

[0067] Example 10:

[0068] In Steps 1 and 2, 1) remains unchanged. In 2), 0.5 g of DBP swelling agent and 2.0 g of GMA monomer are added. After mixing and swelling at 40 °C for 24 h, stir for another 30 min. Then, heat in an oil bath to 80 °C and inject a solution of 0.040 g of AIBN in 2.0 g of GMA to initiate polymerization, with other conditions remaining unchanged.

[0069] As Figure 15 shown, the microspheres prepared in Step 2 of this example are multi-hollow microspheres, and the average diameter of the microspheres is 1.90 μm.

[0070] The above embodiments show that in the presence of the swelling agent DBP, by separately changing the mass of GMA in the swelling stage and the polymerization stage within a large range (both are not zero at the same time), multi-hollow microspheres can be prepared.

[0071] The above are only the preferred embodiments of the present invention and do not impose any limitation on the present invention. Any person skilled in the art, without departing from the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solutions and technical contents disclosed in the present invention, which are all within the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A multi-hollow polymer microsphere, characterized in that, It includes two polymer components, namely polystyrene and glycidyl methacrylate, and the interior of the multi-hollow polymer microspheres has multiple hollow regions that can be identified by transmission electron microscopy.

2. A method for preparing multi-hollow polymer microspheres, for preparing the multi-hollow polymer microspheres as described in claim 1, characterized in that, It includes the following steps: S1: Using polystyrene as the monomer, polyvinylpyrrolidone as the stabilizer, methanol as the solvent, after mixing and stirring for a certain time t0, heating to a specified temperature T0, then adding a methanol solution of azobisisobutyronitrile as the initiator, stirring at the specified temperature T0 for a certain time t1, and finally obtaining polystyrene microspheres after washing and drying. S2: Using the polystyrene microspheres as seeds, glycidyl methacrylate as the monomer, sodium dodecyl sulfate as the stabilizer, dibutyl phthalate as the swelling agent, water as the solvent, mixing and swelling at a specified temperature T1 for a certain time t2, then stirring for a specified time t3, then heating to a specified temperature T3, and adding a glycidyl methacrylate solution or ethanol solution of azobisisobutyronitrile to initiate the polymerization reaction, and finally stirring at the specified temperature T3 for a specified polymerization time t4, and washing to obtain multi-hollow polystyrene-glycidyl methacrylate composite polymer microspheres.

3. The preparation method of the multi-hollow polymer microspheres according to claim 2, characterized in that, The whole preparation process is carried out under the conditions of nitrogen passing and condensation reflux. The heating is carried out by oil bath heating, the washing is carried out by centrifugal washing, and the drying is carried out by vacuum drying.

4. The preparation method of the multi-hollow polymer microspheres according to claim 3, wherein In the above S1, the certain time t0 is 30 min, the certain time t1 is 24 h, and the specified temperature T0 is 60 °C.

5. The preparation method of the multi-hollow polymer microspheres according to claim 4, characterized in that, In the above S2, during the mixing and swelling, the mass ratio of the polystyrene microspheres, sodium dodecyl sulfate, water, dibutyl phthalate, and glycidyl methacrylate is 0.5:0.125:50:0.5:0.5 - 4.

5.

6. The preparation method of the multi-hollow polymer microspheres according to claim 5, wherein In the above S2, after adding azobisisobutyronitrile to the glycidyl methacrylate solution or ethanol solution first, then feeding them together.

7. The preparation method of the multi-hollow polymer microspheres according to claim 6, characterized in that, In the above S2, by adjusting the mass of glycidyl methacrylate in the swelling stage and the polymerization stage, multi-hollow polymer microspheres of various sizes and morphologies are prepared; The masses of glycidyl methacrylate in the swelling stage and the polymerization stage are not zero at the same time.

8. The preparation method of the multi-hollow polymer microspheres according to claim 7, characterized in that, In the above S2, the specified temperature T1 is 40 °C, the certain time t2 is 24 h, the specified time t3 is 30 min, the specified temperature T2 is 80 °C, and the specified time t4 is 8 h.

9. The preparation method of the multi-hollow polymer microspheres according to claim 8, wherein, In the above S2, the average diameter of the prepared polymer microspheres is 1.42 - 1.90 μm.

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