Preparation method of hard monomer polymer nanoscale microspheres

Abstract

The invention discloses 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: 1, mixing an emulsifier with water, adding ammonia water to adjust the pH value to 7-9, and heating and stirring to dissolve the emulsifier to obtain an emulsifier solution; step 2, adding an initiator and a hard monomer into the emulsifier solution, stirring and heating to 71-76 DEG C, reacting for 3-5 hours, raising the temperature to 81-86 DEG C, and preserving heat for 1-2 hours to obtain an emulsion; the hard monomer is used for preparing an acrylate emulsion; and step 3, dropwise adding the emulsion on a carrier, drying, and scraping to obtain the hard monomer polymer nanoscale microspheres. The polymer microspheres are obtained by directly drying the emulsion, the technological process is simple, only water is used as a dispersing agent, the influence on the environment is smaller, and the price is low. A spherical structure naturally formed by a molecular chain in an emulsion is utilized, so that the size of the microspheres has good uniformity.

Description

Technical Field

[0001] The invention belongs to the technical field of emulsion polymerization, and in particular relates to a method for preparing a hard monomer polymer with nanometer-level microsphere morphology. Background Art

[0002] Polymethyl methacrylate (PMMA) is a high glass transition temperature (T g ) of a polymer, whose T g The temperature is about 105℃, and the molecular chain has strong rigidity. The microspheres have the characteristics of large specific surface area, strong adsorption, strong cohesion and strong surface reaction ability, and are widely used in many fields. For example, in the medical field, it can be used as a drug carrier; in the field of ceramic manufacturing, it can be used as a pore-forming agent to improve the performance of ceramics; in the field of light diffusion film, PMMA microspheres are an important component of liquid crystal display light diffusion film, which can refract light and play a role in light diffusion.

[0003] The existing PMMA microsphere preparation process is mainly a dispersion polymerization method, which is essentially a precipitation polymerization method. The specific process is: ethanol or methanol and water mixed solvent is added to a four-necked bottle as a reaction medium, and a stabilizer polyvinyl pyrrolidone (PVP) is added. After the PVP is completely dissolved, the initiator dibenzoyl peroxide (BPO) and the monomer methyl methacrylate are added, and the polymerization reaction is carried out after pre-dispersion for a period of time under nitrogen protection. The supernatant is removed after centrifugation, and the precipitate is dried to obtain the product. The PVP used in this preparation method is difficult to be degraded by microorganisms due to its stable structure, which will cause damage to water bodies and soil. The particle size of the microspheres prepared by this process is mostly micrometer-level, which is limited in some fields such as optical materials. In addition, the polymerization time of this process usually takes up to 24 hours, the process time is long, and the energy consumption is high.

[0004] Emulsion polymerization is a polymerization method in which a surfactant is used as an emulsifier to dissolve into micelles in water, and then the monomer enters the micelles for polymerization reaction. The hydrophilic end of the emulsifier in this method faces the water phase, and the lipophilic end faces the internal polymer molecular chain, so the emulsion product naturally has a spherical structure. However, most of the existing emulsifiers are small molecules. During the dehydration and drying process, the microspheres in the emulsion continue to evaporate as the water evaporates, the particles begin to contact and squeeze each other, the emulsifiers adhere to each other, and then the spherical structure breaks and disappears. Therefore, there are few reports on the preparation of PMMA microspheres by emulsion polymerization, and they all need to remove the emulsifier, abandon its original microsphere morphology, and perform centrifugation and other processing to prepare PMMA microspheres. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the present invention provides a method for preparing hard monomer polymer nano-scale microspheres for preparing acrylic ester emulsion.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for preparing hard monomer polymer nano-scale microspheres comprises the following steps:

[0008] Step 1: 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, and after the emulsifier is completely dissolved, place and cool to room temperature to obtain an emulsifier solution, wherein: the amount of the emulsifier added is 6.0% to 8.5% of the mass of water;

[0009] Step 2: pour the emulsifier solution prepared in step 1 into a three-necked flask, add initiator and hard monomer, stir and heat to 71-76° C., react for 3-5 hours, raise the temperature to 81-86° C. and keep warm for 1-2 hours, and obtain an emulsion, wherein: the added 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 used as effective components together, and the mass of the effective components accounts for 30%-40% of the total mass of the emulsion.

[0010] Step 3: Add the emulsion dropwise onto a PE plastic sheet, dry it at a temperature of 60 to 90° C. for 1 to 3 hours, and after drying, scrape the dried polymer off the plastic sheet to obtain hard monomer polymer nano-scale microspheres.

[0011] Preferably, the emulsifier is a copolymer of styrene and maleic anhydride SMA, T g About 127℃.

[0012] Furthermore, the initiator includes potassium persulfate, ammonium persulfate, azobisisobutyronitrile or dibenzoyl peroxide.

[0013] The hard monomer polymer particles prepared by the invention have a nanometer scale and are obtained by direct drying of the emulsion. The polymer microspheres maintain a structure wrapped by an emulsifier shell.

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

[0015] The present invention uses an emulsifier with a molecular weight of 1000-3000 and a tg of about 127°C, which has a higher molecular weight and tg than commonly used emulsifiers. The emulsifier used in the present invention has a higher rigid structure, which can resist the squeeze force between molecules to a certain extent during the drying and dehydration process, thereby maintaining its spherical structure. In addition to preparing PMMA microspheres, the process proposed in the present invention can also prepare other high-T nano-sized microspheres with the same process. g Polymers such as polystyrene (PS) and polyacrylonitrile.

[0016] The present invention obtains polymer microspheres by directly drying the emulsion, has a simple process flow, uses only water as a dispersant, has less impact on the environment, and is low in price. The spherical structure naturally formed by the molecular chain in the emulsion is utilized, so the size of the microspheres has good uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a microscopic morphology of the PMMA emulsion after drying using a macromolecular emulsifier in Example 1;

[0018] Figure 2 is a microscopic morphology of the PS emulsion using a macromolecular emulsifier after drying in Example 2;

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

[0020] Figure 4 This is a microscopic morphology of the macromolecular emulsifier polybutyl acrylate after drying in Comparative Example 1;

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

[0022] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0023] Embodiment 1:

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

[0025] Step 1: T g An emulsifier styrene-maleic anhydride copolymer (SMA) with a molecular weight of about 1000 and a temperature of about 127° C. is mixed with water (the mass of the emulsifier is 8.0% of the mass of water), and heated and stirred after adding ammonia water. The pH value is adjusted to about 8, and after it is completely dissolved, it is allowed to stand and cooled to room temperature to obtain an emulsifier solution.

[0026] Step 2: Pour the emulsifier solution prepared in step 1 into a three-necked flask, add methyl methacrylate hard monomer until the mass of the effective components (emulsifier and hard monomer) accounts for 30% of the total mass of the emulsion, and add 1% of potassium persulfate by mass of the monomer, start stirring, heat to 71°C after stirring evenly, react for 4 hours, raise the temperature to 86°C and keep warm for 2 hours to prepare PMMA emulsion.

[0027] Step 3: Add PMMA emulsion dropwise onto the PE plastic sheet and dry it at 60°C for 2 hours. After drying, scrape the dried polymer off the plastic sheet.

[0028] Embodiment 2:

[0029] The difference between this embodiment and embodiment 1 is that the monomer used in step 2 is styrene, and the other parameters are the same as those in embodiment 1.

[0030] Embodiment 3:

[0031] The difference between this embodiment and embodiment 1 is that in step 2, methyl methacrylate is added until the mass of the effective component accounts for 40% of the total mass of the emulsion, and the other parameters are the same as those in embodiment 1.

[0032] Comparative Example 1:

[0033] The difference between this embodiment and embodiment 1 is that: T is used in step 2 g The low butyl acrylate is used as the monomer, and the other parameters are the same as those in Example 1.

[0034] Comparative Example 2:

[0035] The difference between this embodiment and embodiment 1 is that a small molecule surfactant is used in step 1: sodium dodecyl sulfate is used as an emulsifier, and the other parameters are the same as those in embodiment 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 relatively good stability, and the appearance of the emulsions does not change significantly after being stored at 60° C. for 3 days. The solid content of the emulsions was tested, and the solid content of the emulsions was close to the theoretical solid content, indicating that all the added monomers were polymerized, and the monomers did not volatilize or polymerize violently, proving that the emulsion preparation process of the present invention can prepare stable emulsions.

[0038] The emulsions in Examples 1-3 became lumps after drying and could not form a film structure. This is because the T g The minimum film-forming temperature of the emulsion is higher than room temperature, and the emulsion is in a block shape after drying. The microscopic morphology of the polymers in Example 1 and Example 2 is as follows: Figure 1 and Figure 2As shown in the figure, a clear spherical structure can be seen, and the microspheres are uniform in size and neatly arranged, indicating that the rigidity of the macromolecular emulsifier SMA used in the present invention can prevent the microsphere structure from being broken due to mutual squeezing of the microspheres during the emulsion drying process. Figure 1 and Figure 2 The diameters of 30 microspheres were randomly selected and compared with the average particle size in the emulsion. The results are as follows: Figure 3 As shown, the average particle size of PMMA and PS microspheres in the emulsion is about 120nm, and the average particle size after drying is about 95nm. 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 is completely evaporated, the swelling effect disappears and the size of the microspheres also decreases.

[0039] In Comparative Example 1, low T g The monomer is used to prepare the emulsion, which is in the state of a film at the macroscopic level after drying, and its microscopic morphology is as follows Figure 4 As shown in the figure, the microsphere morphology disappears and the microscopic structure is also a membrane. This is because the low T g The monomer chain segments have good flexibility, and the chain segments move more easily under the same conditions. During the drying process, the molecular chains move more violently. The force generated by the movement causes the spherical structure of the emulsifier wrapping the molecular chains to be destroyed, and the molecular chains entangle with each other, eventually forming a membrane structure.

[0040] In Comparative Example 2, a small molecule emulsifier was used to prepare an emulsion, which was also in a block shape after drying. The microscopic morphology is as follows Figure 5 As shown in the figure, it can be seen that the polymer molecular chains are in a state of mutual adhesion. This is because the small molecule emulsifier plays a certain plasticizing role in the drying process. The emulsifiers stick to each other, resulting in the destruction of the spherical structure and the exposure of the molecular chains. However, the PMMA molecules T g High, molecular chain movement is difficult, unable to move to low T g The molecular chains of the emulsion are entangled with each other to form a membrane structure.

[0041] Comparative Examples 1 and 2 illustrate that the emulsion of the present invention retains its spherical structure after drying because the macromolecular emulsifier SMA and high T g As a result of the joint 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 to each other; the chain segments of the hard monomer molecular chain are not easy to move, and the force on the SMA shell during movement is small.

[0042] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing hard monomer polymer nano-scale microspheres, characterized in that: The following steps are involved: Step 1: Mix the emulsifier with water, add ammonia water to adjust the pH to 7-9, heat and stir to dissolve the emulsifier to obtain an emulsifier solution; Step 2, adding an initiator and a hard monomer to the emulsifier solution, stirring and heating to 71-76° C., reacting for 3-5 hours, raising the temperature to 81-86° C. and keeping the temperature for 1-2 hours to obtain an emulsion; the hard monomer is a hard monomer for preparing an acrylic emulsion; Step 3: Add the emulsion dropwise onto the carrier, and scrape it off after drying to obtain hard monomer polymer nano-scale microspheres.

2. The preparation method according to claim 1, characterized in that: In step 1, the amount of emulsifier added is 6.0% to 8.5% of the mass of water.

3. The preparation method according to claim 1, characterized in that: In step 1, the molecular weight of the emulsifier is 1000-3000.

4. The preparation method according to claim 1 or 3, characterized in that: In step 1, the emulsifier is a copolymer of styrene and maleic anhydride.

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

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

7. The preparation method according to claim 1, characterized in that: The emulsifier and the hard monomer serve as effective components together, and the mass of the effective components accounts for 30% to 40% of the total mass of the emulsion.

8. The preparation method according to claim 1, characterized in that: In step 2, the initiator includes potassium persulfate, ammonium persulfate, azobisisobutyronitrile or dibenzoyl peroxide.

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

10. The preparation method according to claim 1, characterized in that: The drying temperature is 60-90°C and the time is 1-3h.

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