JP2007001998A - Method for preparing hydrophilic polymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a hydrophilic polymer which is used as a thickener or a water-absorbing material, has a large molecular weight and hardly comprises residual medium. <P>SOLUTION: The hydrophilic polymer is prepared by introducing a hydrophilic monomer and carbon dioxide in a pressure-resistant container, raising the temperature and the pressure in the pressure-resistance container to those equal to or above the critical points of carbon dioxide while stirring the introduced compounds and, after the temperature and the pressure inside the pressure-resistant container are stabilized at prescribed polymerization temperature and pressure, adding a polymerization initiator to induce polymerization. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for producing a hydrophilic polymer used as a thickener or a water-absorbing material, and belongs to a chemical production technique, particularly a polymer production technique.

  Hydrophilic polymers are used as water-soluble thickeners widely used in cosmetics such as shampoos, pharmaceuticals such as poultices, and paints and adhesives, for example. It is also widely used as a raw material for water-absorbing materials used in diapers and the like that absorbs a large amount of water to form a gel.

  These hydrophilic polymers are desired to be supplied in powder form because of their easy handling, and various methods for producing powdery hydrophilic polymers have been proposed. Among them, a method of pulverizing a bulk polymer obtained by bulk polymerization, a method of drying and powdering a gel polymer obtained by solution or suspension polymerization, and the like are well known. Furthermore, a method of obtaining a powdery hydrophilic polymer by precipitation polymerization, which is characterized in that a powder having a uniform particle size can be obtained, is also known.

  The precipitation polymerization is an excellent method because it does not require a step such as pulverization in addition to obtaining a powder having a uniform particle size. However, in this precipitation polymerization, a polymerization medium, that is, a monomer is dissolved, but a polymer in which the polymer is polymerized does not dissolve, and a medium is required. Usually, benzene, xylene, methylene chloride, etc. An organic solvent is used as the medium.

  Since the organic solvent used in these polymerization reactions cannot be ignored in terms of environmental impact, its use is limited and harmful to living organisms. In particular, cosmetics and pharmaceuticals that come into contact with the skin have a problem of containing an organic solvent. Therefore, it is desired that an organic solvent does not remain in a hydrophilic polymer used as a raw material for cosmetics and pharmaceuticals, and the hydrophilic polymer is subjected to a treatment such as heat drying or vacuum drying. Have been supplied.

  However, the method for producing a hydrophilic polymer using an organic solvent is widely used because it has an excellent surface as described above. However, it is absorbed into the hydrophilic polymer produced using these organic solvents. Organic solvents are present and it is difficult to separate them from the hydrophilic polymer, and the equipment and processes required for their removal, and the cost required for them, are excessive. There is a need for processes and methods that do not require expense.

In order to solve these problems, for example, Japanese Patent Publication No. 45-25305 (Patent Document 1) proposes a method using liquid carbon dioxide, which is a gas at normal pressure, as a polymerization medium. Furthermore, in Japanese Patent Application Laid-Open No. Sho 62-23413 (Patent Document 2) and Japanese Patent Application Laid-Open No. 1-163203 (Patent Document 3), a method of performing a polymerization reaction after making carbon dioxide in a supercritical state is proposed. Has been.
Japanese Patent Publication No. 45-25305 (Claims) JP-A-62-23413 (Claims) JP-A-1-163203 (Claims)

  Since carbon dioxide is a gas at normal temperature and pressure, it is used as a polymerization medium in a pressure-resistant container under a heated or pressurized state in a liquid or supercritical state, and is a hydrophilic polymer by precipitation polymerization. When the pressure in the system is returned to normal pressure after the is prepared, carbon dioxide is vaporized and easily separated from the polymer. Further, since the vaporized carbon dioxide can be recovered and reused, it is excellent as a polymerization medium for precipitation polymerization from the viewpoint of environment and harmfulness.

  However, a hydrophilic polymer prepared simply using carbon dioxide as a polymerization medium is considered to have less chain transfer than one using an organic solvent as a polymerization medium, whereas the increase in molecular weight is not as expected. This polymer cannot be obtained. Further, the molecular weight distribution indicated by the degree of dispersion (Mw / Mn) was broad, and the powder shape was not good.

The inventors have increased the molecular weight of a hydrophilic polymer prepared using carbon dioxide as a polymerization medium, sharpened the molecular weight distribution, and further improved the powder shape of the resulting hydrophilic polymer. Was examined.

  In order to solve the above problems, the inventors have prepared a step of preparing a hydrophilic polymer by precipitation polymerization of a hydrophilic monomer using carbon dioxide as a polymerization medium in a pressure-resistant container with a viewing window. Observed from the viewing window, the problem is caused by the behavior of carbon dioxide and hydrophilic monomer when preparing the hydrophilic polymer, more specifically, carbon dioxide and hydrophilic monomer. The present invention was completed by finding out that it was caused by the solubility of.

That is, the invention of claim 1 of the present invention is
When polymerizing hydrophilic monomers in supercritical carbon dioxide,
A method for producing a hydrophilic polymer, comprising dissolving a hydrophilic monomer in supercritical carbon dioxide and then polymerizing by adding a polymerization initiator.

The invention according to claim 2 of the present invention is
Fill the pressure vessel with hydrophilic monomer and carbon dioxide,
While stirring the charged compound, the pressure vessel is heated to a temperature equal to or higher than the critical point of the carbon dioxide, and pressurized,
After the pressure vessel is stabilized at a predetermined polymerization temperature and polymerization pressure,
A method for producing a hydrophilic polymer, comprising polymerizing by adding a polymerization initiator.

The invention according to claim 3 of the present invention is
Fill the pressure vessel with hydrophilic monomer and carbon dioxide,
After heating and pressurizing the inside of the pressure vessel up to a temperature and pressure above the critical point of the carbon dioxide over 30 to 90 minutes,
A method for producing a hydrophilic polymer, comprising polymerizing by adding a polymerization initiator.

The invention according to claim 4 of the present invention is
Fill the pressure vessel with hydrophilic monomer and carbon dioxide,
After raising the temperature inside the pressure vessel up to the temperature and pressure above the critical point of carbon dioxide, pressurize,
A method for producing a hydrophilic polymer, wherein polymerization is performed by adding a polymerization initiator all at once or in portions.

The invention according to claim 5 of the present invention is
In the manufacturing method of the hydrophilic polymer in any one of Claims 1-4,
The polymerization initiator concentration is
It is 0.03% by weight or more based on the hydrophilic monomer.

The invention according to claim 6 of the present invention provides
In the manufacturing method of the hydrophilic polymer in any one of Claims 1-4,
The monomer concentration in the pressure vessel is
It is 0.01-0.09 g / ml.

Furthermore, the invention according to claim 7 of the present invention is
In the manufacturing method of the hydrophilic polymer in any one of Claims 1-4,
Removing oxygen in the pressure vessel,
This is performed by exhausting carbon dioxide.

  The method for producing a hydrophilic polymer according to the present invention employs a means in which a hydrophilic monomer is dissolved in supercritical carbon dioxide and then polymerized by adding a polymerization initiator. The disadvantage of the hydrophilic polymer obtained by precipitation polymerization of the hydrophilic monomer as the polymerization medium, that is, the molecular weight distribution width (dispersity) is not broad as expected. It solves the problem that the powder state is not in place.

  Further, in the present invention, in order to achieve the above object, the dissolution of the hydrophilic monomer in the supercritical carbon dioxide is further uniformly dissolved without unevenness of concentration, rather than difficult visual judgment. Since the determination can be made by the dissolution time and the stability of pressure and temperature, the management of the polymerization process is extremely easy.

Of course, it naturally has advantages such as the advantage of using carbon dioxide as a polymerization medium, non-flammability of carbon dioxide, high safety due to non-toxicity, and simplification of the drying process for desolvation.

  Hereinafter, the method for producing a hydrophilic polymer of the present invention will be described in detail with reference to an example of a production apparatus shown in the accompanying drawings. The hydrophilic polymer defined by the present invention can be produced. If so, the manufacturing apparatus is not particularly limited.

  In the method for producing a hydrophilic polymer of the present invention, the hydrophilic monomer constituting the hydrophilic polymer may be an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid or fumaric acid. And unsaturated amides such as partial esters thereof, acrylamide and methacrylamide, etc., and unsaturated carboxylic acids, particularly acrylic acid, are preferably used.

  In the present invention, other vinyl compounds can be used in combination with the hydrophilic monomer. Examples of other vinyl compounds include styrene, alkyl vinyl ether, vinylidene chloride, acrylic acid esters, methacrylic acid esters, vinyl acetate, vinyl pyrrolidone, acrylonitrile, methacrylonitrile, and the like.

  Furthermore, in order to make the obtained hydrophilic polymer take a crosslinked structure, a crosslinking monomer can be used in combination. Specific crosslinkable monomers include tetraallyloxyethane, allylpentaerythritol, allyl saccharose, allyl acrylate, allyl methacrylate, trimethylolpropane diallyl ether, diallyl phthalate, ethylene glycol diacrylate, polyethylene glycol diacrylate, Examples include ethylene glycol dimethacrylate and polyethylene glycol dimethacrylate.

Examples of the polymerization initiator used for polymerizing the hydrophilic monomer include compounds selected from peroxides, azo initiators, and the like, or mixtures thereof.
The amount used is 0.03% by mass or more, preferably 0.04% by mass or more, and more preferably 0.05 to 2.0% by mass with respect to the monomer. It is possible to use the amount exceeding 2.0% by mass, but in that case, it is necessary to examine the removal of the heat of polymerization reaction, and control the polymerization temperature and reduce the molecular weight. Measures are required.

  Specific examples of the polymerization initiator include benzoyl peroxide, lauroyl peroxide, t-butyl hydroperoxide, t-butyl peroxy-2-ethylhexanoate, hydroperoxide, di (2-ethylhexyl) perperoxide. Mention may be made of peroxides such as oxydicarbonate.

  Examples of the azo initiator include 2,2′-azobisisobutyronitrile, 4,4′-azobis-4-cyanovaleric acid, 2,2′-azobis (2,4-dimethylvaleronitrile), 1,1′-azobis (1-acetoxy-1-phenylethane), dimethyl-2,2′-azobis (2-methylpropionate), 2,2′-azobis (2-amidinopropane) dihydrochloride, etc. Can be mentioned.

In the present invention, the hydrophilic monomer is polymerized in a pressure vessel using supercritical carbon dioxide as a polymerization medium.
That is, the polymerization is carried out at a temperature and pressure not lower than a critical temperature (31 ° C.) and a critical pressure (73 atm), at which carbon dioxide as a polymerization medium becomes a supercritical state. Preferably, the hydrophilic monomer is also at a temperature and pressure at which it becomes a supercritical state, for example, when the hydrophilic monomer is acrylic acid, it becomes a supercritical state at a temperature of 65 ° C. or higher. Is preferred.
The amount of the hydrophilic monomer used at that time is determined by the capacity of the pressure vessel. Usually, it is 0.01-0.09g per 1ml capacity | capacitance of a pressure vessel. Further, the amount of carbon dioxide is uniquely determined by the temperature and pressure because the amount of the hydrophilic monomer is very small.

  The method of using the polymerization initiator is an important feature in the present invention. Specifically, as in the prior art, before starting polymerization, the monomer and medium are not charged into the pressure vessel together with the monomer and medium, but after the monomers and carbon dioxide are charged into the pressure vessel, Is heated and pressurized to a temperature and pressure at which carbon dioxide reaches a supercritical state, and after the monomer has dissolved in supercritical carbon dioxide, preferably a uniform dissolved state without concentration unevenness, the polymerization initiator is The polymerization is started by press-fitting into a pressure vessel.

  The dissolved state of the monomer and supercritical carbon dioxide is determined by visual observation using a pressure-resistant vessel with a viewing window. That is, it is certain to visually determine that both of them become transparent from the cloudy state, but the monomer and the supercritical carbon dioxide can be in a uniform dissolved state even under the following conditions. It has been confirmed and applied instead of visual observation.

  That is, a hydrophilic monomer and carbon dioxide are put into a pressure vessel, and while stirring, the temperature is raised to a temperature above the critical point of carbon dioxide, and the pressure is increased. When stable at the polymerization pressure, or when a hydrophilic monomer and carbon dioxide are charged into a pressure vessel, and the temperature is raised to a temperature and pressure above the critical point of carbon dioxide over 30 to 90 minutes and pressurized. Can be when the monomer and supercritical carbon dioxide reach a homogeneous dissolved state.

  The entire amount of the polymerization initiator may be injected all at once, but if it is divided, a polymer having a higher molecular weight can be obtained. If necessary, it is desirable to discharge and exhaust part of the carbon dioxide loaded in the pressure vessel to remove air (oxygen) in the pressure vessel.

An example of the manufacturing apparatus used for this invention is demonstrated based on the layout shown by FIG. The pressure resistant container 1 for polymerization reaction used in the present invention is placed in a constant temperature water tank 2. In the pressure vessel 1, a stirrer 3 that is rotated by the magnetic force of the magnet inside the mounting table of the pressure vessel 1 and a viewing window (not shown) are provided.
Carbon dioxide is charged into the pressure vessel 1 from the cylinder 4 using the high-pressure pump 5, and the polymerization initiator is pressed into the pressure vessel 1 from the initiator column 6 using carbon dioxide.
In the figure, 7 is a buffer container, 8 is a filter, 9 is a pressure gauge, and 10 is a thermometer.

A 125 ml stainless steel pressure vessel for polymerization was charged with 6.5 g of acrylic acid and carbon dioxide was injected. After part of the carbon dioxide was evacuated and degassed, the temperature was increased and the pressure was increased until the temperature in the polymerization pressure vessel reached a temperature of 65 ° C. and a pressure of 20 MPa.
At about 40 minutes after carbon dioxide injection, the fact that acrylic acid and carbon dioxide were uniformly dissolved was visually observed through a viewing window provided in the pressure-resistant container for polymerization, and the temperature and pressure were kept constant with a meter. In addition, it was confirmed that it is stable.
7.5 mg of 2,2′-azobis (2,4-dimethylvaleronitrile) (V-65 manufactured by Wako Pure Chemical Industries, Ltd.) dissolved in 1.0 g of acrylic acid was injected. The pressure was adjusted to 25 MPa, and the reaction was carried out for 6 hours while stirring.
After the temperature in the polymerization pressure vessel was cooled to room temperature, carbon dioxide was discharged.
A spherical fine white polymer powder having a uniform particle size of 100 to 250 nm is obtained, and the molecular weight (Mw) of this powder measured by GPC (standard material: polyethylene oxide) is 700,000 and the molecular weight distribution is The dispersity (Mw / Mn) was 2.07.

In the above examples, the monomer concentration was 6 wt / vol% (0.06 g per 1 ml of the pressure vessel capacity for polymerization), but the hydrophilicity obtained by polymerization only by changing the concentration. The measurement results of the molecular weight (Mw) and dispersity (Mw / Mn) of the polymer are shown in FIG.
As is apparent from FIG. 2, the molecular weight increased with increasing monomer concentration at a monomer concentration of 2-8%, but decreased at 10% monomer concentration.
This is presumably because when the monomer concentration is high, heat removal from the polymerization heat becomes insufficient, the temperature in the polymerization pressure-resistant vessel rises, and an excessive amount of radicals are generated. The degree of dispersion is almost constant regardless of the monomer concentration.

In the above examples, the concentration of the polymerization initiator was 0.1%, but only the concentration was changed, and the molecular weight (Mw) and dispersity (Mw / Mw) of the hydrophilic polymer obtained by polymerization. The measurement results of Mn) are shown in FIG. 3, and the yield is shown in FIG.
As is clear from FIG. 3, a polymer having a high molecular weight and a low degree of dispersion was obtained as the concentration of the polymerization initiator was lowered. When the concentration of the polymerization initiator was 0.04 wt%, the polymer with the highest molecular weight and low dispersion having a molecular weight of about 1.1 million and a dispersity of 1.7 was obtained. As is clear from FIG. When the concentration was less than 0.03 wt%, polymerization did not occur, and a high yield of about 60% was obtained at 0.04 wt% and about 90% at 0.05 wt% or more.

  Further, in the above examples, in order to examine the influence of the divided addition of the polymerization initiator, the polymerization initiator was divided into two or three equal parts and added and polymerized. As can be seen in FIG. 5, the molecular weight is greatly increased by dividing the polymerization initiator, and the polyacrylic acid having a high molecular weight of about 800,000, which is 1.7 times that of the case where the partial charging is not performed. was gotten. The degree of dispersion is almost constant, and the influence of additional addition of the polymerization initiator on the degree of dispersion is hardly observed.

In addition, the influence of a monomer concentration and a polymerization initiator density | concentration was not recognized about the particle size and shape of the polyacrylic acid obtained by said experiment.

According to the present invention, a hydrophilic polymer using a medium having a large molecular weight, a small residual medium, and a low toxicity can be obtained. It can be widely used in the cosmetics industry using coalesce, the care-related industry, and the paint and adhesives industry.

It is an arrangement | sequence diagram of the manufacturing apparatus used for this invention. It is a figure which shows the monomer concentration dependence of the molecular weight and dispersion degree of the polymer by this invention. It is a figure which shows the initiator concentration dependence of the molecular weight and dispersion degree of the polymer by this invention. It is a figure which shows the initiator density | concentration dependence of the polymer yield by this invention. It is a figure which shows the influence of the polymerization initiator division addition on the molecular weight and dispersion degree of the polymer by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pressure-resistant container 2 Constant temperature water tank 3 Stirrer 4 Carbon dioxide cylinder 5 High pressure pump 6 Initiator column 7 Buffer container 8 Filter 9 Pressure gauge 10 Thermometer

Claims (7)

When polymerizing hydrophilic monomers in supercritical carbon dioxide,
A method for producing a hydrophilic polymer, comprising dissolving a hydrophilic monomer in supercritical carbon dioxide and then adding a polymerization initiator for polymerization. Fill the pressure vessel with hydrophilic monomer and carbon dioxide,
While stirring the charged compound, the pressure vessel is heated to a temperature equal to or higher than the critical point of carbon dioxide, and the pressure is increased.
After the pressure vessel is stabilized at a predetermined polymerization temperature and polymerization pressure,
A method for producing a hydrophilic polymer, comprising polymerizing by adding a polymerization initiator. Fill the pressure vessel with hydrophilic monomer and carbon dioxide,
After heating and pressurizing the inside of the pressure vessel up to a temperature and pressure above the critical point of the carbon dioxide over 30 to 90 minutes,
A method for producing a hydrophilic polymer, comprising polymerizing by adding a polymerization initiator. Fill the pressure vessel with hydrophilic monomer and carbon dioxide,
After raising the temperature inside the pressure vessel up to the temperature and pressure above the critical point of carbon dioxide, pressurize,
A method for producing a hydrophilic polymer, wherein polymerization is carried out by adding polymerization initiators all at once or in portions. The polymerization initiator concentration is
It is 0.03 weight% or more with respect to the said hydrophilic monomer, The manufacturing method of the hydrophilic polymer in any one of Claims 1-4 characterized by the above-mentioned. The monomer concentration in the pressure vessel is
It is 0.01-0.09g / ml, The manufacturing method of the hydrophilic polymer in any one of Claims 1-4 characterized by the above-mentioned. Removing oxygen in the pressure vessel,
The method for producing a hydrophilic polymer according to any one of claims 1 to 4, wherein the method is carried out by exhausting carbon dioxide.