A method for preparing a hard monomer polymer nanoscale microsphere

Abstract

The application relates to a preparation method of hard monomer polymer nanoscale microspheres, and belongs to the technical field of emulsion polymerization. The specific scheme comprises the following steps: step one, mixing an emulsifier with water, adding ammonia water to adjust the pH value to 7-9, heating and stirring to dissolve the emulsifier to obtain an emulsifier solution; step two, adding an initiator and a hard monomer into the emulsifier solution, stirring and heating to 71-76 DEG C, increasing the temperature to 81-86 DEG C after reaction for 3-5 h, and keeping the temperature for 1-2 h to obtain an emulsion; the hard monomer is a hard monomer for preparing an acrylate emulsion; step three, dropping the emulsion on a carrier, drying, and scraping to obtain hard monomer polymer nanoscale microspheres. The polymer microspheres are obtained by directly drying the emulsion, the process flow is simple, only water is used as a dispersant, the influence on the environment is smaller, and the price is low. The spherical structure of the molecular chain is naturally formed in the emulsion, so that the microsphere size has good uniformity.

Description

Technical Field

[0001] This invention belongs to the field of emulsion polymerization technology, specifically relating to a method for preparing a hard monomer polymer with a nanoscale microsphere morphology. Background Technology

[0002] Polymethyl methacrylate (PMMA) is a material with a high glass transition temperature (T0). g The polymer of ) whose T g With a temperature of approximately 105℃, the molecular chains possess strong rigidity. Its microspheres exhibit characteristics such as large specific surface area, strong adsorption, significant aggregation, and strong surface reactivity, making them widely used in various fields. For example, in the medical field, they can serve as drug carriers; in the ceramics manufacturing field, they can act as pore-forming agents to improve ceramic performance; and in the field of light diffusion films, PMMA microspheres are an important component of the light diffusion film in liquid crystal displays, enabling light to be refracted and thus diffused.

[0003] Existing PMMA microsphere preparation processes primarily utilize dispersion polymerization, which is essentially a type of precipitation polymerization. The specific process involves adding a mixture of ethanol or methanol and water as the reaction medium to a four-necked flask, along with the stabilizer polyvinylpyrrolidone (PVP). After the PVP is completely dissolved, the initiator benzoyl peroxide (BPO) and the monomer methyl methacrylate are added. After pre-dispersion under nitrogen protection for a period, the mixture is heated to the reaction temperature for polymerization. The resulting product is centrifuged, the supernatant is removed, and the precipitate is dried to obtain the final product. This method suffers from several drawbacks. The PVP used in this process has a stable structure that makes it difficult for microorganisms to degrade, potentially leading to water and soil degradation. The resulting microspheres are mostly in the micrometer range, limiting their application in certain fields, such as optical materials. Furthermore, the polymerization time is typically up to 24 hours, resulting in a long process time and high energy consumption.

[0004] Emulsion polymerization is a polymerization method in which surfactants, acting as emulsifiers, dissolve in water to form micelles, and then monomers enter the micelles for polymerization. In this method, the hydrophilic end of the emulsifier faces the aqueous phase, and the lipophilic end faces the internal polymer molecular chains, thus the emulsion product naturally has a spherical structure. However, most existing emulsifiers are small molecules. During the dehydration and drying process, as water evaporates, the microspheres in the emulsion begin to contact and compress against each other, causing the emulsifiers to stick together, and subsequently the spherical structure breaks down and disappears. Therefore, there are few reports on the preparation of PMMA microspheres via emulsion polymerization, and those that do require the removal of emulsifiers, the abandonment of the original microsphere morphology, and processing such as centrifugation to prepare PMMA microspheres. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a method for preparing hard monomer polymer nanospheres for acrylate emulsion preparation.

[0006] The technical scheme adopted by the present application is as follows:

[0007] A preparation method of hard monomer polymer nanoscale microspheres comprises the following steps:

[0008] Step one: mix an emulsifier with a molecular weight of 1000-3000 with water in a certain proportion, add ammonia water to make the pH value of the solution between 7 and 9, then heat and stir, place and cool to room temperature after the emulsifier is completely dissolved to obtain an emulsifier solution, wherein: the addition amount of the emulsifier is 6.0%-8.5% of the mass of water;

[0009] Step two: pour the emulsifier solution prepared in step one into a three-necked flask, add an initiator and a hard monomer, stir and heat to 71-76 DEG C, the temperature is raised to 81-86 DEG C after reaction for 3-5 hours, and the temperature is kept for 1-2 hours, and the emulsion is discharged, wherein: the addition amount of the initiator is 0.5%-2.0% of the mass of the hard monomer; the hard monomer is one of styrene, methyl methacrylate and acrylonitrile; the emulsifier and the hard monomer are collectively used as effective components, and the mass of the effective components accounts for 30%-40% of the total mass of the emulsion.

[0010] Step three: drop the emulsion onto a PE plastic sheet, dry at a temperature of 60-90 DEG C for 1-3 hours, and scrape the dried polymer from the plastic sheet to obtain hard monomer polymer nanoscale microspheres.

[0011] Preferably, the emulsifier is a copolymer SMA of styrene-maleic anhydride, T g about 127 DEG C.

[0012] Further, the initiator comprises potassium persulfate, ammonium persulfate, azobisisobutyronitrile or dibenzoyl peroxide.

[0013] The hard monomer polymer particles prepared by the present application are nanoscale, obtained by directly drying the emulsion, and the polymer microspheres maintain the structure of being wrapped by the emulsifier shell.

[0014] Compared with the prior art, the present application has the following beneficial effects:

[0015] The emulsifier used in the present application has a molecular weight of 1000-3000 and a tg of about 127 DEG C, which is higher than that of the commonly used emulsifier. The emulsifier used in the present application has a higher rigid structure, which can resist the extrusion force between molecules to a certain extent during the drying and water loss process, so that the spherical structure is maintained. The process proposed in the present application can not only prepare PMMA microspheres, but also can prepare other high T g polymers such as polystyrene (PS) and polyacrylonitrile.

[0016] This invention obtains polymer microspheres by directly drying an emulsion. The process is simple, uses only water as a dispersant, has less environmental impact, and is inexpensive. Utilizing the naturally formed spherical structure of molecular chains within the emulsion, the microspheres exhibit excellent size uniformity. Attached Figure Description

[0017] Figure 1 These are microscopic images of the PMMA emulsion using macromolecular emulsifiers in Example 1 after drying.

[0018] Figure 2 These are microscopic images of the PS emulsion using macromolecular emulsifiers in Example 2 after drying.

[0019] Figure 3 This is a comparison graph of the average particle size of the microspheres prepared in Examples 1 and 2 and their average particle size in the emulsion;

[0020] Figure 4 This is a microscopic morphology image of polybutyl acrylate, a macromolecular emulsifier used in Comparative Example 1, after drying.

[0021] Figure 5 This is a microscopic morphology image of the PMMA emulsion using a small molecule emulsifier in Comparative Example 2 after drying. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Example 1:

[0024] This embodiment provides a method for preparing polymethyl methacrylate polymer nanospheres with high glass transition temperature, the method comprising the following steps:

[0025] Step 1: Place T g At approximately 127°C, a styrene-maleic anhydride copolymer (SMA) with a molecular weight of approximately 1000 was mixed with water (the mass of the emulsifier was 8.0% of the mass of water). Ammonia was added, and the mixture was heated and stirred to adjust the pH to approximately 8. After the emulsifier was completely dissolved, it was left to stand and cooled to room temperature to obtain an emulsifier solution.

[0026] Step two: pour the emulsifier solution prepared in step one into a three-necked flask, add methyl methacrylate hard monomer to make the mass of effective components (emulsifier and hard monomer) account for 30% of the total mass of the emulsion, and add 1% of the mass of the monomer of potassium persulfate, start stirring, heat to 71℃ after stirring evenly, and then react for 4 hours, then increase the temperature to 86℃ and keep for 2 hours to prepare the PMMA emulsion.

[0027] Step three: drop the PMMA emulsion onto the PE plastic sheet, dry at a temperature of 60℃ for 2 hours, and then scrape the dried polymer from the plastic sheet after drying.

[0028] Example 2:

[0029] The difference between this example and example 1 is that the monomer used in step two is styrene, and the other parameters are the same as those in example 1.

[0030] Example 3:

[0031] The difference between this example and example 1 is that methyl methacrylate is added in step two to make the mass of effective components account for 40% of the total mass of the emulsion, and the other parameters are the same as those in example 1.

[0032] Comparative example 1:

[0033] The difference between this example and example 1 is that T g low butyl acrylate is used as the monomer in step two, and the other parameters are the same as those in example 1.

[0034] Comparative example 2:

[0035] The difference between this example and example 1 is that a small molecule surfactant, sodium dodecyl sulfate, is used as the emulsifier in step one, and the other parameters are the same as those in example 1.

[0036] The test results of the polymer microspheres obtained in examples 1-3 and comparative examples 1-2 are as follows:

[0037] The emulsions in examples 1-3 have good stability, and there is no obvious change in the appearance of the emulsion after being stored at a temperature of 60℃ for 3 days. The solid content of the emulsion is close to the theoretical solid content, indicating that all the added monomers have undergone polymerization reaction, and the monomers have not volatilized or polymerized violently, proving that the emulsion preparation process in the present application can prepare stable emulsion.

[0038] The emulsion in examples 1-3 becomes blocky after drying, and cannot form a film structure. This is because the T g of the emulsifier and the monomer are both relatively high, resulting in a minimum film-forming temperature of the emulsion higher than room temperature, and the emulsion becomes blocky after drying. The polymer micro-morphology of examples 1 and 2 is as follows: Figure 1 and Figure 2As shown in the figure, a distinct spherical structure can be observed, with the microspheres being uniform in size and neatly arranged. This indicates that the rigidity of the macromolecular emulsifier SMA used in this invention during the emulsion drying process can prevent the microsphere structure from breaking due to mutual compression. Figure 1 and Figure 2 Thirty microspheres were randomly selected from each sample to measure their diameter, and the results were compared with the average particle size in the emulsion. Figure 3 As shown, the average particle size of PMMA and PS microspheres in the emulsion is about 120 nm, and the average particle size after drying is about 95 nm. The size of the spherical structure after drying is significantly reduced. This is because the latex particles absorb water and swell in water, thus occupying more volume. After the water evaporates completely, the swelling effect disappears, and the size of the microspheres also decreases.

[0039] Using low T in Comparative Example 1 g The monomer-prepared emulsion, after drying, has a macroscopic film-like state and a microscopic morphology as shown in the figure. Figure 4 As shown, the microsphere morphology disappears, and the microstructure is also a membrane. This is because of low T g Monomer segments have good flexibility, and under the same conditions, the segments move more easily. During the drying process, the molecular chain movement is more intense. The force generated by the movement causes the spherical structure of the emulsifier that encapsulates the molecular chain to break down, and the molecular chains become entangled with each other, eventually forming a film structure.

[0040] Comparative Example 2 used a small molecule emulsifier to prepare an emulsion, which, after drying, also formed a blocky substance with the following microstructure: Figure 5 As shown, the polymer molecular chains are in a state of mutual adhesion. This is because the small molecule emulsifier plays a certain plasticizing role during the drying process. The adhesion of the emulsifiers leads to the destruction of the spherical structure, exposing the molecular chains. However, the PMMA molecules... g At high temperatures, molecular chain movement is difficult, making it impossible to move to lower temperatures. g The molecular chains of an emulsion are intertwined to form a membrane structure.

[0041] Comparative Examples 1 and 2 illustrate that the emulsion in this invention retains its spherical structure after drying due to the macromolecular emulsifier SMA and high T g As a result of the combined action of the polymers, the shell formed by the macromolecular emulsifier has a certain strength, which can maintain the spherical structure during the process of the emulsion losing water and will not stick together; the segments of the hard monomer molecular chain are not easy to move, and the force on the SMA shell during the movement is small.

[0042] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing hard monomer polymer nanospheres, characterized in that, Includes the following steps: Step 1: Mix the emulsifier with water, add ammonia to adjust the pH to 7-9, heat and stir to dissolve the emulsifier to obtain an emulsifier solution; the amount of emulsifier added is 6.0%~8.5% of the water mass, the emulsifier is a copolymer of styrene and maleic anhydride, and the molecular weight of the emulsifier is 1000-3000; Step 2: Add the initiator and hard monomer to the emulsifier solution, stir and heat to 71-76 °C, react for 3-5 hours, then raise the temperature to 81-86 °C and hold for 1-2 hours to obtain the emulsion; the hard monomer is a hard monomer for preparing acrylate emulsions; the emulsifier and hard monomer together are the effective components, and the mass of the effective components accounts for 30%-40% of the total mass of the emulsion; Step 3: The emulsion is dropped onto the carrier, dried, and then scraped off to obtain hard monomer polymer nanospheres.

2. The preparation method according to claim 1, characterized in that: In step two, the hard monomer includes styrene, methyl methacrylate, or acrylonitrile.

3. The preparation method according to claim 1, characterized in that: The amount of initiator added is 0.5% to 2.0% of the mass of the hard monomer.

4. The preparation method according to claim 1, characterized in that: In step two, the initiator includes potassium persulfate, ammonium persulfate, azobisisobutyronitrile, or benzoyl peroxide.

5. The preparation method according to claim 1, characterized in that: The carrier is a PE plastic sheet.

6. The preparation method according to claim 1, characterized in that: The drying temperature is 60~90 ℃, and the time is 1-3 hours.

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