A method for preparing monodisperse small-particle-size polysiloxane microspheres

Abstract

The invention discloses a method for preparing a monodisperse small-particle polysiloxane microsphere. The method for preparing the polysiloxane microsphere comprises the following steps: (1) adding a zwitterionic surfactant to water, mechanically stirring and mixing, heating to 45-65 DEG C in a water bath, adding a siloxane monomer, and stirring to obtain a silanol solution after the reaction; (2) adding an inorganic alkali solution to the silanol solution, stirring until the mixed solution is milky white and stopping stirring immediately; after the milky white liquid is placed in a 40-70 DEG C water bath and kept warm for 1-5h, it is allowed to stand for 1-5h at room temperature; (3) drying process: the solid-liquid mixture obtained in step (2) is centrifuged, the lower layer solid is removed, washed to neutrality with anhydrous ethanol, and the solid sample obtained is dried and then cooled to room temperature to obtain monodisperse small-particle polysiloxane microsphere. The present invention has the characteristics of being easy to operate, environmentally friendly, low in cost and having a smaller particle size of polysiloxane microsphere.

Description

Technical Field

[0001] The present invention relates to the field of preparation of organosilicon microsphere resins, and in particular to a method for preparing monodisperse small-particle-size polysiloxane microspheres. Background Art

[0002] Due to their high hardness and melting point, polysiloxane microspheres are widely used in industrial production for applications such as light diffusers and chemical fillers. With the development of industries like liquid crystal displays, the research and development of polysiloxane microspheres has attracted increasing attention. Common methods for preparing polysiloxane microspheres include the one-step sol-gel method, the sol-gel method, emulsion polymerization, and the addition method. The one-step sol-gel method and the sol-gel method have gained increasing attention due to their controllable reaction conditions and lower costs. In the one-step sol-gel method, the hydrolysis and polycondensation reactions of siloxane monomers are directly carried out under alkaline catalyst conditions, with hydrolysis and polycondensation occurring simultaneously at the interface between the two phases. In the sol-gel method, the monomers and water undergo hydrolysis under certain conditions to form a homogeneous system, followed by further polycondensation under base catalysis, forming polymer microspheres with a specific cross-linked structure. The one-step sol-gel method is complex to operate, difficult to maintain the hydrolysis and polycondensation reaction interface, and has low production efficiency. In contrast, the sol-gel method, in which the hydrolysis and polycondensation reactions are carried out separately, is simpler to operate and more efficient. Therefore, the sol-gel method is more widely used.

[0003] Patent CN1311266A provides a 1 Si(OR 2 )3 and Si(OR 2 )4 is hydrolyzed under acidic conditions and then an alkaline catalyst solution is added to prepare polysiloxane microspheres. This method can produce polysiloxane microspheres with an average particle size of 0.1 μm to 5 μm. Experimental results show that the average particle size of the polysiloxane microspheres decreases with increasing amounts of tetramethoxysilane. The acidic reagent used in this patent is prone to corrosion of equipment, placing high demands on the equipment.

[0004] Patent CN1205345A provides a method for preparing polysiloxane microspheres by mixing water, anionic surfactants, polymer stabilizers, and hydroxide base, then adding silane monomers and stirring. This method can produce polysiloxane microspheres with an average particle size of 0.5μm-10μm, but has disadvantages such as environmental pollution, increased costs, and complex operation. Patent CN106317409A provides a method for controlling the particle size of polysiloxane microspheres by adjusting the conductivity of deionized water and the molar ratio of deionized water to alkoxysilane. This method can produce polysiloxane microspheres with an average particle size of 1μm-10μm. Patent CN104744700A provides a method for controlling the particle size of polysiloxane microspheres by adjusting the pH value of the reaction system during the polymerization process. This method can produce polysiloxane microspheres with an average particle size of 1.5μm-5μm. These methods have certain disadvantages, and there is little research on polysiloxane microspheres with an average particle size below 1μm. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing polysiloxane microspheres which is simple to operate, environmentally friendly, low in cost and has a small particle size in view of the shortcomings of the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A method for preparing monodisperse small-particle polysiloxane microspheres comprises the following steps:

[0008] (1) Hydrolysis process: Add zwitterionic surfactant to water, stir mechanically to mix evenly, heat to 45°C-65°C in a water bath, add siloxane monomer, stir and react to obtain silanol solution for standby use;

[0009] (2) Polycondensation process: adding an inorganic base solution to the silanol solution obtained in step (1), stirring until the mixed solution turns milky white and then stopping stirring immediately; placing the milky white liquid in a 40-70°C water bath for 1-5 hours, and then allowing it to stand at room temperature for 1-5 hours;

[0010] (3) Drying process: The solid-liquid mixture obtained in step (2) is centrifuged, the lower solid layer is removed, and washed with anhydrous ethanol until neutral. The obtained solid sample is placed in a vacuum drying oven at 100-120°C and dried for 6 hours, and then cooled to room temperature to obtain monodisperse small-particle polysiloxane microspheres.

[0011] The particle size of the monodisperse small-particle polysiloxane microspheres obtained by the invention can be controlled within the range of 0.6 μm to 1.3 μm.

[0012] Preferably, the zwitterionic surfactant in step (1) is a betaine-type zwitterionic surfactant. More preferably, the betaine-type zwitterionic surfactant is selected from at least one of dodecyl hydroxypropyl phosphate betaine, dodecyl dimethyl betaine, tetradecyl sulfobetaine, tetradecyl dimethyl betaine, and cocamidopropyl betaine, and is further preferably dodecyl dimethyl betaine, tetradecyl sulfobetaine, tetradecyl dimethyl betaine, or cocamidopropyl betaine.

[0013] Preferably, the mass ratio of the zwitterionic surfactant to water in step (1) is in the range of 1:18-1:9000, more preferably 1:60-1:1000.

[0014] Preferably, the siloxane monomer in step (1) is methyltrimethoxysilane.

[0015] Preferably, in step (1), the mass ratio of the siloxane monomer to water is in the range of 1:3-1:45, preferably in the range of 1:3-1:15.

[0016] Preferably, the mechanical stirring frequency in step (1) is in the range of 170 rpm-400 rpm, and the stirring time is in the range of 10-50 min.

[0017] Preferably, in step (2), the inorganic base in the inorganic base solution is an alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide, etc., and the solvent is water; the mass concentration of the inorganic base solution is in the range of 0.2%-7%.

[0018] More preferably, the mass ratio of the inorganic base solution in step (2) to the water required for preparing the silanol solution is in the range of 1:2.5-1:70.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The present invention effectively controls the particle size of the polysiloxane microspheres to be between 0.6 μm and 1.3 μm by regulating the type and addition amount of the zwitterionic surfactant.

[0021] (2) Simple operation and low equipment requirements;

[0022] (3) No acid catalyst is used, which has little corrosion to equipment;

[0023] (4) No additional polymer stabilizer is required, which is environmentally friendly;

[0024] (5) The subsequent processing is simple, and the obtained product has a small particle size span, uniform particles and good dispersion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 (a) is a particle size distribution curve and (b) is a scanning electron microscope image of the polysiloxane microspheres obtained in Example 1;

[0026] Figure 2 (a) is a particle size distribution curve and (b) is a scanning electron microscope image of the polysiloxane microspheres obtained in Example 2;

[0027] Figure 3 (a) is a particle size distribution curve and (b) is a scanning electron microscope image of the polysiloxane microspheres obtained in Example 3;

[0028] Figure 4 (a) is a particle size distribution curve diagram and (b) is a scanning electron microscope image of the polysiloxane microspheres obtained in Example 4.

[0029] Figure 5 (a) and a scanning electron microscope image (b) of the particle size distribution curve of the polysiloxane microspheres obtained in Example 5.

[0030] Figure 6 (a) and a scanning electron microscope image (b) of the polysiloxane microspheres obtained in Comparative Example 1.

[0031] Figure 7 (a) and scanning electron microscope image (b) of the polysiloxane microspheres obtained in Comparative Example 2. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific embodiments. However, the embodiments of the present invention are not limited thereto and may be subject to many variations. Any details not specifically described below may be understood by those skilled in the art according to conventional expressions or implemented according to existing technologies.

[0033] Example 1

[0034] To a four-necked flask equipped with a stirring paddle, thermometer, and reflux condenser, add 450g of water and 0.7g of dodecylhydroxypropyl betaine phosphate. Heat the mixture to 40°C in a water bath. Add 90g of methyltrimethoxysilane and stir at 200rpm for 10 minutes. Then, add 100mL of 1% sodium hydroxide solution and continue stirring until the solution turns milky white. The resulting milky white liquid is incubated at 55°C for 4 hours, allowed to stand at room temperature for 3 hours, and then centrifuged. Remove the precipitate, wash it with anhydrous ethanol until neutral, and dry it in a vacuum drying oven at 120°C for 6 hours. The resulting polysiloxane microspheres have an average particle size of 1.258μm and a span of 1.04. The reason for the average particle size exceeding 1μm may be related to the spatial position of the dodecylhydroxypropyl phosphate group in the dodecylhydroxypropyl betaine phosphate.

[0035] Example 2

[0036] To a four-necked flask equipped with a stirring paddle, thermometer, and reflux condenser, add 450g of water and 2.5g of dodecyldimethylbetaine, place in a water bath and heat to 50°C. Add 90g of methyltrimethoxysilane and stir at 170rpm for 10 minutes. Then add 120mL of 0.4% sodium hydroxide aqueous solution and continue stirring until the solution turns milky white. The resulting milky white liquid is incubated at 55°C for 5 hours, then allowed to stand in 25°C water for 4 hours before centrifugation. Remove the lower precipitate, wash with anhydrous ethanol until neutral, and dry in a vacuum drying oven at 120°C for 6 hours. The resulting polysiloxane microspheres have an average particle size of 0.683μm and a span of 0.998.

[0037] Example 3

[0038] Add 450g of water and 5g of tetradecylsulfobetaine to a four-necked flask equipped with a stirring paddle, thermometer, and reflux condenser, place in a water bath and heat to 55°C. Add 50g of methyltrimethoxysilane and stir at 250rpm for 10min. Then add 150mL of 3% sodium hydroxide aqueous solution and continue stirring until the solution turns milky white. Stop stirring. The resulting milky white liquid is kept at 55°C for 4h, allowed to stand at room temperature for 5h, and then centrifuged. Remove the lower precipitate, wash with anhydrous ethanol until neutral, and dry in a vacuum drying oven at 100°C for 6h. The average particle size of the obtained polysiloxane microspheres is 0.711μm and the span is 0.911.

[0039] Example 4

[0040] Add 450g of water and 7g of tetradecamethyl betaine to a four-necked flask equipped with a stirring paddle, thermometer, and reflux condenser, then heat to 40°C in a water bath. Add 100g of methyltrimethoxysilane and stir at 400rpm for 10 minutes. Then add 120mL of 5% sodium hydroxide aqueous solution and continue stirring until the solution turns milky white. The resulting milky white liquid is incubated at 60°C for 5 hours, allowed to stand at room temperature for 3 hours, and then centrifuged. Remove the lower precipitate, wash with anhydrous ethanol until neutral, and dry in a vacuum drying oven at 120°C for 6 hours. The resulting polysiloxane microspheres have an average particle size of 0.743μm and a span of 1.283.

[0041] Example 5

[0042] In a four-necked flask equipped with a stirring paddle, a thermometer, and a reflux condenser, add 450g of water and 0.5g of cocamidopropyl betaine, place it in a water bath and heat it to 55°C. Add 50g of methyltrimethoxysilane, stir at 300rpm for 30min, then add 8mL of 0.5% sodium hydroxide aqueous solution and continue stirring until the solution turns milky white. Stop stirring. The resulting milky white liquid is kept at 55°C for 5h, left to stand at room temperature for 3h, and then centrifuged. Remove the lower precipitate, wash it with anhydrous ethanol until neutral, and dry it in a vacuum drying oven at 120°C for 6h. The average particle size of the obtained polysiloxane microspheres is 0.634μm and the span is 1.082.

[0043] Comparative Example 1: Preparation of polysiloxane microspheres using nonionic surfactants

[0044] To a four-necked flask equipped with a stirring paddle, thermometer, and reflux condenser, add 450g of water and 0.5g of alkylphenol polyoxyethylene ether and heat to 55°C in a water bath. Add 50g of methyltrimethoxysilane and stir at 300rpm for 30 minutes. Then, add 8mL of 5% sodium hydroxide solution and continue stirring until the solution turns milky white. The resulting milky white liquid is incubated at 55°C for 5 hours, allowed to stand at room temperature for 3 hours, and then centrifuged. Remove the precipitate, wash with anhydrous ethanol until neutral, and dry in a vacuum drying oven at 120°C for 6 hours. The resulting polysiloxane microspheres have an average particle size of 2.823μm and a span of 1.433.

[0045] Comparative Example 2: Preparation of polysiloxane microspheres using phenyltrimethoxysilane

[0046] Add 450g of water and 2.5g of dodecyl dimethyl betaine to a four-necked flask equipped with a stirring paddle, a thermometer, and a reflux condenser, place it in a water bath and heat it to 50°C. Add 50g of phenyltrimethoxysilane, stir at 170rpm for 10min, then add 120mL of 0.4% sodium hydroxide aqueous solution, continue stirring until the solution turns milky white and stop stirring. The resulting milky white liquid is kept at 55°C for 5h, kept still in 25°C water for 4h, and then centrifuged. Remove the lower precipitate and wash it with anhydrous ethanol until neutral, then place it in a vacuum drying oven at 120°C and dry it for 6h. The obtained polysiloxane microspheres are severely agglomerated, and the accurate average particle size and span cannot be measured.

Claims

1. A method for preparing monodisperse small-particle polysiloxane microspheres, characterized in that: The preparation method comprises the following steps: (1) Hydrolysis process: add a zwitterionic surfactant to water, stir mechanically to mix evenly, heat to 45°C-65°C in a water bath, add a siloxane monomer, stir and react to obtain a silanol solution for standby use; the zwitterionic surfactant is a betaine-type zwitterionic surfactant; the siloxane monomer is methyltrimethoxysilane; (2) Polycondensation process: Add an inorganic base solution to the silanol solution obtained in step (1), stir until the mixed solution turns milky white, and then stop stirring immediately; place the milky white liquid in a water bath at 40-70°C for 1-5 hours, and then let it stand at room temperature for 1-5 hours; (3) Drying process: The solid-liquid mixture obtained in step (2) is centrifuged, the lower solid layer is removed, and washed with anhydrous ethanol until neutral. The obtained solid sample is placed in a vacuum drying oven at 100-120 ° C for 6 hours and then cooled to room temperature to obtain monodisperse small-particle polysiloxane microspheres. The particle size of the monodisperse small-particle polysiloxane microspheres is in the range of 0.6 μm-1.3 μm.

2. The preparation method according to claim 1, wherein: The betaine-type zwitterionic surfactant is selected from at least one of lauryl hydroxypropyl phosphate betaine, lauryl dimethyl betaine, tetradecyl sulfobetaine, tetradecyl dimethyl betaine, and cocamidopropyl betaine.

3. The preparation method according to claim 2, wherein: The betaine-type zwitterionic surfactant is selected from lauryl dimethyl betaine, tetradecyl sulfobetaine, tetradecanedimethyl betaine or cocamidopropyl betaine.

4. The preparation method according to claim 1, wherein: The mass ratio of the zwitterionic surfactant to water in step (1) is in the range of 1:18-1:9000.

5. The preparation method according to claim 4, wherein: The mass ratio of the zwitterionic surfactant to water in step (1) is in the range of 1:60-1:1000.

6. The preparation method according to claim 1, wherein: In step (1), the mass ratio of the siloxane monomer to water is in the range of 1:3-1:

45.

7. The preparation method according to claim 1, wherein: In step (2), the inorganic base solution comprises an alkali metal hydroxide and a solvent comprising water; the mass concentration of the inorganic base solution is in the range of 0.2% to 7%.

8. The preparation method according to claim 7, wherein: The mass ratio of the inorganic base solution in step (2) to the water required for preparing the silanol solution is in the range of 1:2.5-1:70.

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