JPH11292907A - Production of monodisperse microparticle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject microparticle having a uniform particle diameter and slight smell by adding a given amount of a specific chain transfer agent when a styrene-based monomer and a polymerization initiator are dispersed in water to carry out a polymerization. SOLUTION: The monodisperse microparticles are obtained by dispersing a styrene-based monomer (e.g. styrene, α-methylstyrene) and a polymerization initiator (e.g. potassium persulfate) in water followed by heating to polymerize the styrene-based monomer, wherein α-methylstyrene dimer as a chain transfer agent is added at 0.1-10 wt.%, pref., 0.3-3 wt.%, based on the styrene-based monomer, to the system. The weight ratio of the styrene-based monomer to water as a medium is preferably (5:95) to (20:80). The polymerization is performed normally at 60-90 deg.C for 12-36 h. As the polymerization method, a soap-free emulsion polymerization method without using any emulsifier is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Seed particles (monodispersed fine particles) for producing polymer fine particles used as a light diffusing agent for columns, fillers for columns, or carriers for diagnostics, etc. for rear projection screens for viewing films, spacers for liquid crystal displays, various lighting equipment, etc. And a method for producing the same. In addition, the monodispersed fine particles referred to in the present invention are fine particles having a uniform particle diameter.

[0002]

2. Description of the Related Art It is used as a light-diffusing agent for columns, a filler for columns, a carrier for diagnostics, etc., such as a rear projection screen for viewing a display, a film, a spacer for liquid crystal display, various lighting fixtures, and the like. The polymer fine particles to be obtained are required to have a uniform particle diameter of 1 to 10 μm.

Conventionally, as a method for obtaining polymer fine particles having such particle size characteristics, a method of classifying particles obtained by suspension polymerization so as to obtain required particle size characteristics is mainly used to homogenize particles. Was often done. However, such a method has a problem that the yield of the obtained particles is reduced. Further, as a method for producing fine particles having a narrow particle size distribution, for example, 0.1 to 0.1 obtained by soap-free emulsion polymerization
Also known is a seed polymerization method in which fine particles having a submicron size of about 0.5 μm are dispersed as seed particles in an aqueous or organic medium, and after the monomers are absorbed by the seed particles, polymerization is performed. ing. However, in this method, the amount of the monomer that can be absorbed by the seed particles at one time is small.
In order to obtain polymer particles having a micron size of about 0 μm, it is necessary to repeat the seed polymerization process a plurality of times, and there is a problem that the manufacturing process becomes complicated.

In addition, a swelling polymerization method has been proposed in which the swelling ability of the seed particles with respect to the monomer is increased by previously absorbing the hydrophobic organic compound into the seed particles, and then the monomer is absorbed and polymerized. (Japanese Patent Laid-Open No. 54-126288)
issue). However, this method has a problem that the swelling aid remains in the obtained polymer fine particles. Further, by seed emulsion polymerization using seed particles having a high swelling ability having a molecular weight of 10,000 or less produced by adding a mercaptan-based chain transfer agent at the time of emulsion polymerization, polymer fine particles of about 1 to 10 μm in one polymerization. Has also been proposed (JP-A-54-97582). However, in this method, although polymer particles having a low molecular weight can be obtained, the particle size distribution tends to be widened. In addition, the mercaptan-based chain transfer agent used in this method generally has a strong odor and is not only poor in workability, but also requires an environmental measure because the resulting polymer fine particles also have an odor. .

In order to efficiently obtain polymer fine particles having a particle size of 1 to 10 μm and a narrow particle size distribution by seed polymerization, monodisperse seed particles having a molecular weight of 100,000 or less are required. An object of the present invention is to provide a method for producing seed particles (monodisperse fine particles) satisfying such conditions.

[0006]

The method of the present invention is a method in which a styrene monomer and a polymerization initiator are dispersed in water and heated to polymerize the styrene monomer. It is characterized in that 0.1 to 10% by weight of an α-methylstyrene dimer as an agent is added to a styrene monomer and polymerization is performed.

The present invention provides particles having a uniform particle diameter, a low molecular weight, and a low odor by adding a specific amount of a specific chain transfer agent during polymerization.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. Examples of the styrene monomer used in the present invention include styrene and styrene derivatives such as α-methylstyrene, p-methylstyrene, p-chlorostyrene, and chloromethylstyrene. When these styrene monomers are used, a preferable result is obtained because the chain transfer constant of α-methylstyrene dimer to the monomer is high.

The polymerization initiator used in the present invention may be any one used in ordinary emulsion polymerization and soap-free polymerization, and is not particularly limited. Examples thereof include persulfates such as potassium persulfate and azo-based initiators. A water-soluble polymerization initiator such as an initiator can be used. The amount of the α-methylstyrene dimer used as the chain transfer agent used in the present invention is 0.1 to 10% by weight, more preferably 0.3 to 3% by weight, based on the styrene monomer. . When the amount of the chain transfer agent is less than 0.1% by weight, it is difficult to obtain low molecular weight monodisperse fine particles. When the amount of the chain transfer agent exceeds 10% by weight, the molecular weight of the obtained monodisperse fine particles decreases. However, there is a problem that the particle diameter is not uniform and a long time is required to complete the reaction.

When a chain transfer agent in the above range is used in the present invention, monodispersed fine particles having a molecular weight of 100,000 or less, a low odor and a uniform particle diameter can be obtained. In the present invention, the ratio of the styrene monomer to water as the medium is not particularly limited, but from the viewpoint of polymerization stability and productivity, the weight ratio (monomer / water) is 5/95 to 20. The range of / 80 is preferred.

The polymerization in the present invention can be carried out according to a usual method. That is, a predetermined amount of water, a styrene-based monomer, α-methylstyrene dimer as a chain transfer agent, and a polymerization initiator are put into a reaction vessel, and a nitrogen gas is blown for a certain time to replace the atmosphere with nitrogen, and then heated. By doing so, the polymerization reaction proceeds. The temperature of the polymerization reaction varies depending on the type and concentration of the monomer and the polymerization initiator used, but is usually from 60 ° C to 90 ° C. The polymerization time varies depending on the conditions of the polymerization reaction, but is usually 12 to 36.
Time.

In the present invention, it is preferable to employ a so-called soap-free emulsion polymerization without using an emulsifier,
According to this method, particles having a uniform particle diameter are easily obtained. The monodispersed fine particles obtained according to the present invention can be used as seed particles for seed polymerization in the form of a water dispersion after the reaction as it is, or after washing and purification with water or alcohol, or in a dry powder state.

[0013]

EXAMPLES Hereinafter, the method of the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Table 1 shows the results of the weight average molecular weight, the particle size, the monodispersity, and the odor of the polymer particles obtained in Examples and Comparative Examples. [Example 1] 100 parts by weight of styrene as a monomer, 900 parts by weight of ion-exchanged water as a medium, and 0.5 part by weight of α-methylstyrene dimer as a chain transfer agent were placed in a reaction vessel and stirred. Nitrogen was blown in for 1 hour to sufficiently replace the atmosphere with nitrogen, and then heated to 70 ° C. Thereafter, 1.2 parts by weight of potassium persulfate was dissolved in a small amount of ion-exchanged water and added to the reaction system. Then 70 ° C
After stirring was continued for 24 hours while keeping the temperature, the reaction system was cooled to room temperature to stop the reaction. At the end of the reaction, the polymerization conversion was 9
It was 8%, and the polymer particles after the reaction had almost no odor. After the obtained polymer particles were washed with water and methyl alcohol, they were subjected to solid-liquid separation and dried in an oven at 60 ° C. This is dissolved in tetrahydrofuran and GP
When the molecular weight was measured by C, the weight average molecular weight was Mw = 75,000. In addition, a laser diffraction type particle size distribution analyzer SALD-2 manufactured by Shimadzu Corporation.
When the number distribution of the polymer particles was measured using 000, the median diameter was 0.590 μm, and the mode diameter was 0.562.
At μm, the ratio of the median diameter to the mode diameter was 1.05, and the monodispersity was high.

The median diameter is the particle diameter at which the cumulative number distribution is 50%, and the mode diameter is the most frequent particle diameter in the number distribution. Example 2 The amount of α-methylstyrene dimer used was 1
A polymerization reaction was performed under the same conditions as in Example 1 except that the amount was changed to parts by weight. Example 3 The amount of α-methylstyrene dimer used was 2
A polymerization reaction was performed under the same conditions as in Example 1 except that the amount was changed to parts by weight. Example 4 A polymerization reaction was carried out under the same conditions as in Example 1 except that the amount of the α-methylstyrene dimer was changed to 0.2 part by weight. Comparative Example 1 A polymerization reaction was performed under the same conditions as in Example 1 except that normal octyl mercaptan was used instead of α-methylstyrene dimer as a chain transfer agent. Comparative Example 2 A polymerization reaction was carried out under the same conditions as in Example 4, except that normal pentyl mercaptan was used instead of α-methylstyrene dimer as a chain transfer agent. Comparative Example 3 A polymerization reaction was carried out under the same conditions as in Example 1 except that normal dodecyl mercaptan was used instead of α-methylstyrene dimer as a chain transfer agent.

[0015]

[Table 1]

As is evident from the results shown in Table 1, the present invention is excellent in reducing odor and molecular weight by using α-methylstyrene dimer as a chain transfer agent. When a commonly used mercaptan-based chain transfer agent is used, the odor is strong (Comparative Examples 1 and 2) or the effect of lowering the molecular weight is inferior (Comparative Example 3).

[0017]

According to the method of the present invention, monodisperse fine particles having a low molecular weight and a uniform particle diameter can be obtained, and the odor of the monodisperse fine particles is reduced since a mercaptan-based chain transfer agent having a strong odor is not used. Excellent workability. When the monodispersed fine particles of the present invention are used as seed particles in, for example, seed polymerization, polymer fine particles having a desired particle diameter and a narrow particle diameter distribution can be obtained by one seed polymerization.

Claims (1)

[Claims] 1. A method for producing monodispersed fine particles by dispersing a styrene-based monomer and a polymerization initiator in water and heating the resulting styrene-based monomer to polymerize, wherein α-methylstyrene dimer is used as a chain transfer agent. Wherein 0.1 to 10% by weight is added to the styrene monomer.