JPH09302004A - Synthesis for fine monodisperse particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain fine monodisperse particles having a low molecular weight and a narrow particle diameter distribution and being desirable as seeds suited for seed polymerization by adding a specified amount of a specified chain transfer agent to the reaction system in dispersing a polymerizable unsaturated monomer and a polymerization initiator in water and heat-polymerizing the monomer. SOLUTION: In a process for synthesizing fine monodisperse particles by dispersing a polymerizable unsaturated monomer (which may be any monofunctional monomer, desirably a styrene derivative, that is not highly soluble in water) and a polymerization initiator in water and heating the dispersion to polymerize the monomer, a 10C or lower alkyl mercaptan type chain transfer agent (a 6-10C linear alkyl mercaptan is lowly odorous and is therefore desirable) in an amount 0.5-15 times as high as the weight of the polymerization initiator is added to the reaction system. According to the above process, polymer particles having a low molecular weight and having a narrow particle diameter distribution, i.e., being monodisperse can be obtained, and the obtained fine polymer particles have high swelling power and can be used as seeds suitable for seed polymerization.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for synthesizing monodisperse fine particles which can be used as a spacer for liquid crystal display, a filler for columns, a carrier for diagnostic agents, and the like.

[0002]

Polymer particles used as spacers for liquid crystal displays, fillers for columns, carriers for diagnostic agents, etc.
The particle size is required to be uniform. Conventionally, as a method for obtaining such particles, there have been many cases where particles obtained mainly by suspension polymerization are classified to homogenize the particles.
However, in such a method, the yield of the obtained particles was low, and the uniformity of the particles was not sufficiently satisfactory.

As another method for producing monodisperse fine particles,
A seed polymerization method is known in which monodispersed fine particles such as a styrene polymer are allowed to absorb a vinyl monomer and then polymerized to increase the particle diameter. Particle size is 1 to 1 by this method
In order to obtain particles of about 0 μm, it is necessary to repeat the step of allowing the fine polymer particles to absorb the monomer and polymerizing it, a plurality of times. This seed polymerization method has a problem in that the uniformity of particles formed is low and the polymerization rate is low.

In addition to this method, Japanese Patent Publication No. 57-2
A two-step swelling seed polymerization method represented by 4369 is known. According to this method, a polymer having a uniform particle diameter can be obtained, but after a hydrophobic organic compound called a swelling aid is absorbed in the seed particles in advance to enhance the swelling ability of the seed particles, a vinyl-based polymer is used. It is necessary to swell the monomer and perform polymerization. In such a method, two steps for absorbing the swelling aid and the monomer are required, and thus there is a problem that the work becomes complicated. There is also a problem that a swelling aid that does not participate in the polymerization elutes from the particles after the polymerization.

Further, it is known that seed particles having a low degree of polymerization show a high swelling ability without using a swelling auxiliary agent. If such seed particles having a low degree of polymerization are used, it is possible to use one step. It is possible to obtain particles of 1 to 10 μm.
JP-A-54-97582 discloses a method in which a chain transfer agent is added during emulsion polymerization to prepare seed particles having a molecular weight of 10,000 or less, and seed polymerization is performed using the seed particles. However, if you simply add a chain transfer agent,
Although the molecular weight decreases, the particle size distribution tends to widen. Therefore, under the present circumstances, monodisperse particles having a low molecular weight have not been obtained. Further, the mercaptan-based chain transfer agents such as butanethiol and propanethiol used in the method of the above publication generally have a strong odor and have poor workability, which is also a problem.

[0006]

As described above, in seed polymerization, monodisperse seed particles having a low molecular weight of 100,000 or less are required in order to obtain particles having a particle size of 1 to 10 μm.

An object of the present invention is to provide a method for synthesizing polymer particles having a low molecular weight and being monodispersed, that is, having a narrow particle size distribution, which can be used as seed particles in such seed polymerization. .

[0008]

The method for synthesizing monodisperse fine particles of the present invention comprises dispersing a polymerizable unsaturated monomer and a polymerization initiator in water, and heating this to polymerize the monomer. It is a method for synthesizing monodisperse fine particles and has 10 carbon atoms.
It is characterized in that the following alkyl mercaptan-based chain transfer agent is added in an amount of 0.5 to 15 times by weight with respect to the polymerization initiator to polymerize the monomer.

The polymerization method in the synthetic method of the present invention is a so-called soap-free polymerization method which does not use an emulsifier, and it is known that the particle size distribution of the produced particles is extremely narrow. In the present invention, polymer fine particles having a narrow molecular size distribution and a low molecular weight are produced by adding a certain amount of a specific chain transfer agent during such polymerization.

The polymerizable unsaturated monomer used in the present invention is not particularly limited as long as it is a monofunctional monomer and does not significantly dissolve in water. For example, styrene, α
-Styrene derivatives such as methylstyrene, p-methylstyrene, p-chlorostyrene and chloromethylstyrene; vinyl esters such as vinyl acetate and vinyl propionate;
Unsaturated nitriles such as acrylonitrile; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, stearyl (meth) acrylate, ethylene glycol (meth) Acrylate, trifluoroethyl (meth)
Examples thereof include (meth) acrylic acid ester derivatives such as acrylate, pentafluoropropyl (meth) acrylate, cyclohexyl (meth) acrylate, and methoxypolyethylene glycol (meth) acrylate. Among these monomers, the styrene derivative is preferable. These monomers may be used alone or in plural kinds.

The polymerization initiator used in the present invention is
What is used by usual emulsion polymerization and soap free polymerization can be used, For example, potassium persulfate or an azo initiator can be used although it is not particularly limited.

The alkyl mercaptan chain transfer agent used in the present invention has 10 or less carbon atoms. If the number of carbon atoms exceeds 10, the effect of chain transfer decreases, and it is necessary to add a large amount of chain transfer agent in order to reduce the molecular weight to a desired value. When a large amount of chain transfer agent is used, the particle size distribution tends to widen, which is not desirable. Even if the carbon number is small, the effect of reducing the molecular weight can be sufficiently obtained, so that the lower limit of the carbon number is not particularly limited as long as the carbon number is 10 or less. However, mercaptans having a small number of carbon atoms, that is, having a short chain length, generally have an odor and are not preferable in terms of work. Therefore,
More preferably, a linear alkyl mercaptan having 6 to 10 carbon atoms, which has a low odor, is used.

In the present invention, the amount of the alkyl mercaptan chain transfer agent used is 0.5 by weight with respect to the polymerization initiator.
˜15 times, more preferably 1 to 13 times. If the amount of the chain transfer agent used is too small, the effect of lowering the molecular weight is not sufficient, and if the amount of the chain transfer agent used is too large, the molecular weight decreases but the particle size distribution becomes large, which is not preferable. By using the chain transfer agent within the range specified in the present invention, it is possible to obtain a monodisperse polymer particle having a low molecular weight of 100,000 or less.

In the present invention, the ratio of the polymerizable unsaturated monomer and water as a medium is not particularly limited, but considering the yield and particle size distribution, the weight ratio (monomer:
Water) is preferably 5:95 to 20:80. When the content of the monomer is less than 5% by weight, the yield with respect to charging is remarkably small, which is not preferable from the viewpoint of productivity. When the content of the monomer exceeds 20% by weight, it is difficult to obtain a well-controlled particle size distribution.

In the present invention, the polymerization can be carried out according to a usual method. That is, it can be carried out by placing a predetermined amount of water, a polymerizable monomer, a chain transfer agent, and an initiator in a container, blowing nitrogen gas for a certain period of time to replace the atmosphere, and then raising the temperature. At this time, the polymerization initiator is preferably added in a state of being dissolved in water. The polymerization temperature is
It can be appropriately selected in consideration of the types and concentrations of the monomers and polymerization initiators used, but it is usually in the range of 60 to 90 ° C. The polymerization time also varies depending on the polymerization conditions and the like,
Usually, the polymerization reaction is completed in about 12 to 36 hours.

The polymer fine particles after the polymerization can be separated from the medium by centrifugation or the like. The separated polymer fine particles can be purified by repeatedly washing with alcohol or water. After washing, it can be isolated as a powder by spray drying, reduced pressure drying, or the like.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the synthesis method of the present invention will be described with reference to specific examples. The synthetic method of the present invention is not limited to these examples.

Example 1 Styrene as a polymerizable monomer (hereinafter abbreviated as "St")
10 parts by weight, 90 parts by weight of ion-exchanged water as a medium, n-decyl mercaptan as a chain transfer agent (having 1 carbon atom)
0; hereinafter abbreviated as "n-DM") 1 part by weight was put into a flask container and mixed. A cooling pipe, a stirring blade, and a nitrogen introduction pipe were attached to this container, and nitrogen was flown in for 1 hour to replace the polymerization atmosphere with nitrogen. Subsequently, the stirring blade was rotated at 100 rpm, the temperature was raised to 70 ° C., and nitrogen replacement was further performed for 1 hour. Then, 0.1 part by weight of potassium persulfate (hereinafter abbreviated as "KPS") was dissolved in a small amount of water and poured into the system using a syringe.

After continuing the reaction at 70 ° C. for 24 hours, the temperature was lowered to room temperature to stop the reaction. The polymerization conversion rate at the end was 80%. The produced polymerization liquid was centrifuged to perform solid-liquid separation between the medium and the obtained polymer fine particles. Next, ethanol, a mixed medium of ethanol and water, and water were washed twice in this order and centrifuged to remove excess polymerization initiator, monomer, and chain transfer agent, and to wash polymer particles. .

[Measurement of Particle Diameter] The washed polymer particles were dispersed in an appropriate medium and deposited and fixed on a collodion membrane supported by a metal mesh. This is a transmission electron microscope (TE
M). The particle diameter of 50 to 100 arbitrary particles in the photograph taken by this observation was measured to determine the number average particle diameter (Dn) and the weight average particle diameter (Dw). In addition, Dw / Dn was calculated as an index of uniformity of particle diameter. In Example 1, the number average particle size Dn was 571 nm and the particle size distribution was Dw / Dn = 1.0013.

[Measurement of Molecular Weight] The obtained polymer particles are isolated, dried, and then dissolved in tetrahydrofuran to give G
The molecular weight was measured by PC. In the first embodiment,
The weight average molecular weight Mw was 48,000.

Example 2 As a chain transfer agent, 1 part by weight of n-DM was used instead of 8 parts by carbon number.
Polymer particles were synthesized in the same manner as in Example 1 except that 0.5 part by weight of n-octyl mercaptan (hereinafter abbreviated as "n-OM") was used, and the particle size and the molecular weight were measured. The results are shown in Table 1.

Example 3 As a chain transfer agent, 1 part by weight of n-DM was used in place of 5 carbon atoms.
Polymer particles were synthesized in the same manner as in Example 1 except that 0.2 part by weight of n-pentyl mercaptan (hereinafter abbreviated as "n-PM") was used, and the particle diameter and molecular weight were measured. The results are shown in Table 1.

Examples 4 and 5 Polymer fine particles were synthesized in the same manner as in Examples 1 and 2 except that the amounts of the chain transfer agent were changed as shown in Table 1, and the particle diameter and the molecular weight were measured. The results are shown in Table 1.

Comparative Example 1 Polymer fine particles were synthesized in the same manner as in Example 1 except that the chain transfer agent was not added, and the particle size and molecular weight were measured. The results are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that n-dodecyl mercaptan having 12 carbon atoms (hereinafter abbreviated as "n-DDM") was used as the chain transfer agent instead of n-DM. The coalesced particles were synthesized, and the particle size and the molecular weight were measured. The results are shown in Table 1.

Comparative Examples 3 and 4 Polymer fine particles were synthesized in the same manner as in Examples 1 and 2 except that the amounts of the chain transfer agent were changed as shown in Table 1, and the particle diameter and the molecular weight were measured. The results are shown in Table 1.

[0028]

[Table 1]

As is clear from the results shown in Table 1, the fine polymer particles obtained by polymerizing the alkyl mercaptan having the carbon number specified in the present invention in the amount specified in the present invention have a narrow particle size distribution and 100,000 or less. It can be seen that the molecular weight is low.

[0030]

According to the present invention, polymer particles having a low molecular weight and a narrow particle size distribution, that is, monodisperse polymer particles can be obtained. The polymer fine particles thus obtained have a low molecular weight and thus have a high swelling power, and can be used as seed particles (seed particles) suitable for the above-mentioned seed polymerization.

Claims (3)

[Claims] 1. A method of synthesizing monodisperse fine particles by dispersing a polymerizable unsaturated monomer and a polymerization initiator in water, and heating this to polymerize the monomer, wherein the number of carbon atoms is 10 or less. 5. The method for synthesizing monodisperse fine particles, which comprises adding the alkyl mercaptan chain transfer agent of 1 to 0.5 to 15 times by weight of the polymerization initiator to polymerize the monomer. 2. The method for synthesizing monodisperse fine particles according to claim 1, wherein the chain transfer agent is a linear alkyl mercaptan having 6 to 10 carbon atoms. 3. The ratio of the monomer to water is 5: 95-2.
The method for synthesizing monodisperse fine particles according to claim 1 or 2, wherein the method is 0:80.