JPH11140213A - Production of porous substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a porous substance, capable of easily obtaining the homogeneous polymer porous substance. SOLUTION: This method for producing a porous substance has characteristics comprising controlling an aqueous monomer solution containing monomers comprising a water-soluble vinylic monomer and a cross-linking agent, one or more kinds of compounds selected from the group consisting of carbonic salts and bicarbonic salts, a surfactant and a polymerization initiator to a pH of <=6.5, and subsequently bringing the aqueous monomer solution into contact with sound waves having a frequency of >=10 kHz, until the gelation of the aqueous monomer solution containing the generated carbon dioxide in a supersaturated state is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a homogeneous porous polymer.

[0002]

2. Description of the Related Art As a method for producing a polymer porous material, a foaming agent such as sodium bicarbonate is mixed with a solution obtained by adding a primary gelling agent such as sodium alginate to an aqueous solution of a water-soluble polymer such as polyvinyl alcohol. The resulting aqueous solution is dropped into a saturated aqueous solution of boric acid containing hydrochloric acid and calcium chloride, and at the same time as the primary gelling agent is gelled with calcium chloride, the foaming agent is decomposed and foamed with hydrochloric acid to form the foamable primary gel. Then, a method of insolubilizing polyvinyl alcohol with boric acid (JP-A-63-137680), adding a photocurable material, a photopolymerization initiator, a primary gelling agent such as sodium alginate, and a surfactant to water. The resulting aqueous solution is mixed and stirred to form a number of fine bubbles, which is then dropped into an aqueous solution of calcium chloride to form a primary gel, which is then irradiated with ultraviolet light and cured. A method (JP 63-137679) to obtain a foam by.

[0003]

[Problems to be solved by the invention]
In the method described in JP-A-137680, it is difficult to uniformly disperse the foaming agent, and even if it is possible to uniformly disperse the foaming agent, the foaming and gelling of the dropped particles is caused by the foaming agent in the particles and the gelling. Since it is caused by the contact between the agent and the acid and calcium chloride in the liquid, foaming and gelation occur first on the surface of the droplet particles, and then foaming gelation occurs internally as the components in the liquid penetrate into the droplet particles. Since the foaming environment differs between the particle surface and the inside, it is difficult to obtain a uniform foam. Further, the aqueous polymer solution has a high viscosity, and it is difficult to industrially mass-produce by dropping from a nozzle even though it is easy to drop from the tip of a syringe at the laboratory level.

In the method described in JP-A-63-137679, even if a surfactant is added and stirred, only a foam having a considerably wide pore size distribution can be obtained, and it is difficult to obtain a uniform foam. or,
If the amount of the surfactant is small, the bubbles are easily lost on the way, and it is necessary to use the surfactant at a relatively high concentration. However, it is still difficult to obtain sufficiently fine bubbles, and the porous material depends on the size of the bubbles. However, there is a problem that it is difficult to control the hole diameter.
Also, when the porous body is poured into a large amount of water, if the amount of the surfactant is large, a large amount of the surfactant is eluted, so that the amount of the surfactant is small, and the uniform, stable, and easy control of the pore size is possible. There has been a strong demand for a method for producing a porous body.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a polymer porous body which has less of the above-mentioned problems, has a uniform pore size, and is easy to control the pore size. That is, the gist of the present invention comprises a monomer comprising a water-soluble vinyl monomer and a crosslinking agent, one or more selected from the group consisting of carbonates and bicarbonates, a surfactant and a polymerization initiator. After the pH of the aqueous monomer solution is reduced to 6.5 or less, the generated carbon dioxide gas is dissolved in a supersaturated state until the gelation of the aqueous monomer solution is completed.
A method for producing a porous body, comprising contacting an aqueous solution of a monomer with a sound wave having a frequency of 10 kHz or more.

[0006] The water-soluble vinyl monomer used in the present invention may be a nonionic vinyl monomer, an anionic vinyl monomer or a cationic vinyl monomer. In the following, (meth) acrylamide and (meth) acrylate mean both acrylamide and methacrylamide, and both acrylate and methacrylate. As nonionic vinyl monomers,
N-alkyl-substituted (meth) acrylamide such as (meth) acrylamide, isopropylacrylamide, t-butyl (meth) acrylamide, dimethyl (meth) acrylamide, and N-hydroxyalkyl-substituted (meth) acrylamide such as N-methylol (meth) acrylamide Hydroxyalkyl (meth) acrylates such as hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, vinylpyrrolidone,
Examples thereof include N-vinylacetamide.

The anionic vinyl monomers include:
Examples thereof include vinyl monomers having a side chain having a sulfone group such as α, β-unsaturated carboxylic acid such as (meth) acrylic acid and maleic acid, and 2-acrylamido-2-methylpropanesulfonic acid.

Examples of the cationic vinyl monomer include dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate, and quaternary ammonium salts thereof, and dimethylaminoethyl (meth) acrylate. Examples thereof include dialkylaminoalkyl (meth) acrylamides such as acrylamide, diethylaminoethyl (meth) acrylamide and dimethylaminopropyl (meth) acrylamide, and quaternary ammonium salts thereof, vinylpyridine and vinylimidazole.

Examples of the crosslinking agent used in the present invention include methylene bisacrylamide, divinylbenzene, polyethylene glycol di (meth) acrylate, and polypropylene glycol di (meth) acrylate.

The initiator used in the present invention includes peroxide initiators such as benzoyl peroxide and persulfate;
Azo-based initiators such as azobisisobutyronitrile, azobisvaleronitrile, 2,2'-azobis- (2-amidinopropane) dihydrochloride, peroxides such as persulfates and reduction of sodium bisulfite and the like Any initiator can be used as long as it is used in ordinary vinyl polymerization, such as a redox catalyst such as a combination of agents, but it is preferable to use a redox catalyst. When a redox catalyst is used, it is preferable to prepare the peroxide and the reducing agent as separate aqueous solutions and mix them immediately before polymerization. The aqueous monomer solution and various aqueous solutions to be used in the polymerization used in the present invention are used after being deoxygenated with an inert gas such as nitrogen gas, if necessary.

The one or more kinds (hereinafter, referred to as (bi) carbonate) selected from the group consisting of carbonate and bicarbonate used in the present invention include sodium bicarbonate, ammonium bicarbonate, sodium carbonate and the like. it can.

[0012] The monomer concentration of the aqueous monomer solution of the present invention is preferably at least 5 wt%, more preferably at least 10 wt%. The initiator concentration may be any concentration at which sufficient gelation can be achieved. (Bi) carbonate concentration is 0.1 ~
It is preferably 2 wt%, more preferably 0.5 to 1 wt%.

If the pH of the aqueous monomer solution containing (bi) carbonate in an amount of about 1% by weight of the aqueous solution is reduced only to about 6 to 6.5, the generated carbon dioxide gas remains dissolved in a supersaturated state and does not foam immediately. . Therefore, this aqueous solution is brought into contact with a sound wave having a frequency of 10 kHz or more before gelling by polymerization. Contact with a sound wave is preferably within 10 minutes, more preferably within 5 minutes, even more preferably within 3 minutes from the start of polymerization.

The surfactants used in the present invention include aliphatic soaps, carboxylate salts such as alkyl ether carboxylate salts, sulfonates such as alkylbenzene sulfonic acid, higher alcohol sulfates, alkyl ether phosphates and the like. And nonionic surfactants such as alkyl and alkyl allyl polyoxyethylene ethers, polyoxyethylene ethers of sorbitan esters, polyethylene glycol aliphatic esters, and polyoxyethylene alkylamines.
In the case of the present invention, the amount of the surfactant used is 0.01 to
0.5% by weight, less than half of the case where the same surfactant is added, stirred, mixed and foamed,
Therefore, the adverse effect on the environment can be reduced accordingly.

In the pH adjustment for generating carbon dioxide, if the pH is lowered too much, polymerization may be hindered.
Is preferably 5 to 7, and more preferably 6 to 6.5. Sulfuric acid, hydrochloric acid, phosphoric acid,
Various acids such as acetic acid and sodium dihydrogen phosphate can be used. Also, a pH buffer can be added as needed.

The time of contact with the sound wave is not particularly limited as long as the monomer aqueous solution is gelled by polymerization, but may be within 10 minutes, preferably within 5 minutes, more preferably within 3 minutes. The intensity of the sound wave may be such that the entire aqueous monomer solution foams. The pore size can be controlled by adjusting the amount of the surfactant, the frequency of the sound wave, and the output. By combining the above conditions, it is possible to generate bubbles with a more uniform pore size, and by immediately polymerizing the monomer solution containing the bubbles, a porous body having uniform bubbles can be obtained, as compared to a case where it is not brought into contact with a sound wave. can get.

[0017]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 798.4 g of a 50% aqueous acrylamide solution and 0.2 g of methylenebisacrylamide were dissolved in 800 g of ion-exchanged water, adjusted to pH 4.5 with an acid, and added with ion-exchanged water. The total amount is 1776 g. (This is A
On the other hand, 20 g of sodium hydrogen carbonate was dissolved in 176 g of ion-exchanged water. (This is referred to as solution B) After nitrogen gas was blown into both solution A and solution B to replace nitrogen, 20 g of surfactant polyoxyethylene sorbitan monooleate and 1% aqueous solution of potassium persulfate 4 were added to solution A.
ml was added. On the other hand, solution B contains sodium bisulfite 1
4 ml of a 1% aqueous solution were added. Solution A and solution B were mixed using a static mixer so as to have a ratio of 9: 1. The aqueous solution was charged and contacted with a 47 kHz sound wave for 60 seconds to foam the monomer aqueous solution, and then the foamed aqueous solution was placed in a polymerization container at room temperature and allowed to stand. The gelation of the aqueous foaming solution in the polymerization vessel was completed after about 2 minutes while generating heat, and the polymerization was completed after about 20 minutes. The pH of the solution immediately after mixing the solution A and the solution B is 6.5, and 0.1 to
Many bubbles having a pore size of about 0.5 mm were included.

Comparative Example The same procedure as in Example 1 was carried out until the preparation of the liquid A and the liquid B and the mixing of the liquid A and the liquid B at a ratio of 9: 1 using a static mixer. The aqueous monomer solution thus obtained was
The reactor was filled in a polymerization container at room temperature without contacting with a sound wave of 0 kHz or more. After about 3 minutes, the aqueous monomer solution gels with almost no air bubbles, and when the polymerization proceeds and the temperature of the gel rises, carbon dioxide gas is generated from the gel.
A gel in which large holes of about 10 to 10 mm were sparsely obtained was obtained.

[0020]

According to the method of the present invention, the pore size is uniform,
It is possible to produce a polymer porous body whose pore size can be easily controlled.

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Claims (1)

[Claims] 1. An aqueous monomer solution containing a monomer comprising a water-soluble vinyl monomer and a crosslinking agent, at least one selected from the group consisting of carbonates and bicarbonates, a surfactant and a polymerization initiator. After the pH of the aqueous solution is adjusted to 6.5 or less, the monomer aqueous solution is contacted with a sound wave having a frequency of 10 kHz or more before the gelation of the aqueous monomer solution in which the generated carbon dioxide gas is dissolved in a supersaturated state is completed. A method for producing a porous body.