JPH0586125A - Water-soluble polymer and method for producing the same - Google Patents

Abstract

(57) [Summary] [Object] To provide a water-soluble polymer which is preferable as a dispersant, a detergent builder, and the like. [Structure] A structural unit represented by the following general formula (1) as a main component, having a number average molecular weight of 300 to 10,000,
A water-soluble polymer having a dispersity (where the dispersity is a quotient of weight-average molecular weight divided by number-average molecular weight) of 1.3 to 2.3, and the following general formula (2 ) Acrylic acid-based monomer having a compound represented by the formula (4) as a main component is polymerized by an aqueous solution polymerization method while maintaining the pH of the polymerization system in the range of 6 to 9, and the production of the water-soluble polymer described above. Law. (However, in the formula, X represents a hydrogen atom, an alkali metal atom or NH _4. ) (However, in the formula, X represents a hydrogen atom, an alkali metal atom, or NH _4. ) [Effect] The water-soluble polymer according to the present invention has a low molecular weight and a narrow dispersity, and therefore, the dispersibility and biodegradability are low. Both are excellent and can be preferably used as various dispersants, detergent builders and the like.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION The present invention relates to a water-soluble polymer and a method for producing the same. The water-soluble polymer of the present invention can be advantageously used for various dispersants, detergent builders and the like.

[0002]

2. Description of the Related Art Heretofore, polymers such as polyacrylic acid salts and polymaleic acid salts have been known as water-soluble polymers. These water-soluble polymers are used as dispersants for inorganic pigments, metal ions, etc., but are extremely poor in biodegradability due to their high molecular weight, and as a detergent builder because they have pollution problems such as rivers and inshore water. Was not used.

On the other hand, in order to improve the biodegradability of the water-soluble polymer, a method of lowering the molecular weight of the polymer can be considered. As a method for obtaining these low molecular weight compounds, generally,
Methods such as lowering the monomer concentration, increasing the initiator concentration, using a chain transfer agent, raising the reaction temperature, etc. can be taken, but for polyacrylic acid salt, for example, if the above method is fully utilized, the biodegradability will be slightly improved. However, on the contrary, there was a problem that the dispersion performance was remarkably deteriorated and it was not suitable for practical use.

[0004]

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems and provide a water-soluble polymer which maintains dispersion performance and is excellent in biodegradability.

[0005]

Means for Solving the Problems [Summary of the Invention] <Summary> The inventors of the present invention have conducted diligent research for the purpose of solving the above-mentioned problems, and as a result, specified the pH of the system in the aqueous solution polymerization of acrylic acid-based monomers. By polymerizing while maintaining the range, a water-soluble polymer having a controlled molecular weight can be obtained, and it was found that this water-soluble polymer has not only dispersion performance but also high biodegradability, It has arrived.

That is, the water-soluble polymer according to the present invention has a structural unit represented by the following general formula (1) as a main component, a number average molecular weight of 300 to 10,000, and a dispersity (where the dispersity is a weight). The average molecular weight divided by the number average molecular weight is 1.3 to 2.3. (However, in the formula, X represents a hydrogen atom, an alkali metal atom or NH _4. )

In the method for producing a water-soluble polymer according to the present invention, an acrylic acid-based monomer containing a compound represented by the following general formula (2) as a main component is added to the polymerization system in a pH range of 6-9. Polymerize by an aqueous solution polymerization method while maintaining,
Is a method characterized by. (However, in the formula, X represents a hydrogen atom, an alkali metal atom or NH _4. )

<Effect> The water-soluble polymer according to the present invention is
Since it has a low molecular weight and a narrow dispersity, it has excellent dispersibility and biodegradability. Therefore, the water-soluble polymer according to the present invention is preferable as various dispersants, detergent builders and the like.

[Detailed Description of the Invention] <Water-Soluble Polymer> The water-soluble polymer according to the present invention contains a structural unit represented by the following general formula (1) as a main component. (However, in the formula, X represents a hydrogen atom, an alkali metal atom or NH _4. )

The term "mainly composed of" means that the structural unit represented by the general formula (1) is contained in an amount of 95 mol% or more of the whole. The rest is usually composed of a copolymerizable monomer described below and the like. The water-soluble polymer according to the present invention has a number average molecular weight of 300 to 100.
00, preferably 500 to 8000, and having a dispersity of 1.3 to 2.3, preferably 1.3 to 2.0. Here, the dispersity is represented by the following formula (3). If the number average molecular weight is less than 300, the dispersion performance is insufficient, and if it exceeds 10,000, sufficient biodegradability cannot be obtained. Similarly, if the dispersity exceeds 2.3, sufficient biodegradation cannot be obtained. The number average molecular weight and the weight average molecular weight of the water-soluble polymer according to the present invention are measured by gel permeation chromatography.

<Method for Producing Water-Soluble Polymer> Such a water-soluble polymer according to the present invention is an aqueous solution of an acrylic acid-based monomer for forming the structural unit (1) while keeping the pH of the polymerization system in the range of 6 to 9. It can be produced by polymerizing by a polymerization method.

<Acrylic Acid Monomer> The acrylic acid monomer used in the production method of the present invention contains a compound represented by the following general formula (2) as a main component. (However, in the formula, X represents a hydrogen atom, an alkali metal atom or NH _4. )

The compound represented by the general formula (2) is specifically acrylic acid and its alkali metal salt or ammonium salt. Examples of the alkali metal atom include sodium and potassium.

The term "mainly composed of" means that the structural unit represented by the above formula (1) is 95 mol% without excessively impairing the dispersion performance and biodegradability of the resulting water-soluble polymer.
It means that other copolymerizable monomer may be used as long as it does not fall below.

Other copolymerizable monomers include, for example, (1) methacrylic acid, itaconic acid, maleic acid, fumaric acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2- Acryloyl propane sulfonic acid and its salts, (2)
Alkyl or alkoxyalkyl esters of dicarboxylic acids such as itaconic acid, maleic acid and fumaric acid,
(3) (meth) acrylamide, (4) vinyl sulfonic acid and salts thereof, (5) methyl acrylate, ethyl acrylate, etc., (6) hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, ( 7) Polyethylene glycol mono (meth) acrylate, N-
Examples thereof include monomers having a copolymerizable double bond in the molecule such as methylol (meth) acrylamide and glycidyl (meth) acrylate.

The salt of the acid compound is an alkali metal salt,
The term "(meth) acryl" and "(meth) acrylate" collectively refer to ammonium salts and the like, and "acryl" and "methacryl" as well as "acrylate" and "methacrylate" are collectively referred to.

<Control of pH> What is important in the production method of the present invention is to carry out the aqueous solution polymerization of the above specific acrylic acid type monomer while keeping the pH of the polymerization system within the range of 6 to 9. ..

In aqueous solution polymerization of acrylic acid type monomers, there is a close correlation between pH and the molecular weight of the obtained polymer, and the molecular weight of the polymer produced is high at both low and high pH. Water-soluble polymer cannot be obtained. INDUSTRIAL APPLICABILITY By maintaining the pH during the polymerization in a specific range, the present invention provides a water-soluble polymer having a low number average molecular weight of 300 to 10,000 and a controlled dispersity of 1.3 to 2.3. It has the greatest feature where it can be used. Therefore, when the pH of the system deviates from the range of the present invention, there arises a problem that the molecular weight remarkably increases and the dispersity also increases.

The pH of the polymerization system does not have to be kept at the same value in all stages from the start to the end of the polymerization, and it is possible for the pH to fluctuate somewhat within the above-mentioned predetermined range.

The pH of the polymerization system can be adjusted before the initiation of the polymerization or at any stage from the initiation of the polymerization to the termination of the polymerization, such as the above-mentioned acid monomer, particularly the acrylic acid monomer to be polymerized, and / or the alkali such as the alkali. It can be carried out by supplying a solution of a metal hydroxide, such as sodium hydroxide or potassium hydroxide, to the polymerization system at one time or continuously, if necessary by varying the supply amount. The most preferred embodiment of the present invention is to continuously supply an acrylic acid monomer whose pH is adjusted in advance with sodium hydroxide or the like to the polymerization system, and to add an aqueous solution of acrylic acid or sodium hydroxide as necessary to adjust the pH. It is a method of carrying out polymerization while controlling.

<Representative Production Example> In the present invention, aqueous solution polymerization of an acrylic acid type monomer is carried out while maintaining the pH of the system within a range of 6-9.

As an aqueous solution polymerization method of such a form,
Batch type, semi-batch type or continuous polymerization method can be mentioned,
A semi-batch or continuous polymerization method in which the acrylic acid-based monomer is polymerized while being supplied is more preferable.

When preparing the water-soluble polymer according to the present invention, it is usual to use a radical polymerization initiator. Examples of the radical polymerization initiator include water-soluble radical polymerization initiators such as persulfates such as ammonium persulfate and potassium persulfate, 2,2′-azobis (2-amidinopropane) dihydrochloride, 4,4′- Azo-based initiators such as azobis (4-cyanovaleric acid) are included. When the polymerization initiator is a peroxide such as hydrogen peroxide, it can be used as a redox initiator in combination with a reducing compound such as sulfite, ascorbic acid and amine.

The polymerization of the present invention may optionally be carried out in the presence of a chain transfer agent. Examples of the chain transfer agent include water-soluble compounds such as ammonium formate, hydroxylammonium sulfate, formaldehyde, thioglycolic acid, mercaptoethanol, thioglycerol, isopropanol, and sodium hypophosphite.

As an example of such a polymerization method, a predetermined pH is used.
An aqueous solution of sodium acrylate adjusted to an arbitrary pH within the range is maintained at a predetermined temperature, an aqueous solution of a polymerization initiator is added dropwise to the aqueous solution of sodium acrylate, and an aqueous solution of sodium acrylate is added dropwise to the aqueous solution of acrylic acid or water. By supplying an aqueous solution of sodium oxide dropwise, the pH of the system is adjusted to 6 to
It is possible to exemplify a mode in which polymerization is carried out while maintaining the range of 9.

[0026]

EXAMPLES The following examples and comparative examples serve to explain the present invention more specifically. The performance of the water-soluble polymer was measured according to the following method.

<Molecular weight> The molecular weight was measured by gel permeation chromatography (GPC). A water-based column is used, and the polymer standard substance is an American Polymer Standard.
Sodium polyacrylate of ds company was used. The dispersity was calculated from the following formula (3).

<Biodegradation rate> Biochemical oxygen consumption (BO
D) is 20 according to JIS standard K0102-1986.
The biodegradation rate was calculated from the amount of dissolved oxygen consumed when stirring at 14 ° C. for 14 days, according to the following formula (4).
The activated sludge used was the same as that used under the Chemical Substances Control Law. Where BOD = biochemical oxygen consumption of sample TOD = theoretical oxygen demand of sample

<Dispersion ability> 50 ml stoppered test tube (inner diameter 2.3)
cm, height 17 cm) manganese dioxide (Wako Pure Chemical Industries KK
1g and 500ppm polymer aqueous solution
Take 0 ml and shake up and down 100 times, then at 25 ℃
And allowed to stand in a constant temperature bath for 4 hours. Then, 15 ml of the suspension was gently collected, and the amount of manganese dioxide in the suspension was measured by the potassium permanganate method. Dispersion capacity is suspension 1
Amount of manganese dioxide suspended in 00 ml (mg / 100 ml)
Expressed as

<Ca ion chelating ability> In a 50 ml beaker, 10 mg of the polymer and 50 ml of an aqueous solution containing 0.001 M of calcium chloride and 0.08 M of potassium chloride were taken and mixed in a thermostat at 25 ° C. Valence Ca
The ion concentration was measured by an ion meter. The Ca ion chelating ability was expressed as the amount of Ca ions chelated by 100 g of the polymer (g / 100 g).

<Example 1> 100 g of water was placed in a 500 ml capacity flat-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 100 ° C. while blowing nitrogen gas. Then, in a conical beaker with a capacity of 500 ml, add to a mixed solution of 100 g of acrylic acid and 50 g of water under ice cooling,
An aqueous monomer solution prepared by adding 200 g of a 25% aqueous solution of sodium hydroxide was mixed with a quantitative pump to 3
It was supplied dropwise over time. At the same time, 2, as a polymerization initiator
2'-azobis (2-amidinopropane) dihydrochloride 2g
And 4 g of mercaptoethanol as a chain transfer agent and water 5
The mixed solution with 0 g was added dropwise by another metering pump in 3 and a half hours. P of the reaction solution polymerized in this way
H was kept in the range of 6.2-6.4. After completion of the latter supply, the same temperature was maintained for an additional 1 hour to complete the polymerization.

Example 2 The same procedure as in Example 1 was carried out except that the aqueous monomer solution was prepared from 100 g of acrylic acid, 39 g of water, and 211 g of a 25% aqueous solution of sodium hydroxide. PH of the reaction solution polymerized in this way
Was kept in the range of 7.3 to 7.5 during the polymerization.

Example 3 The procedure of Example 1 was repeated, except that the aqueous monomer solution was prepared from 100 g of acrylic acid, 28 g of water, and 222 g of a 25% aqueous solution of sodium hydroxide. PH of the reaction solution polymerized in this way
Was kept in the range of 7.9 to 8.1 during the polymerization.

<Example 4> In the same manner as in Example 1 except that an aqueous monomer solution was prepared from 100 g of acrylic acid, 28 g of water and 222 g of a 25% aqueous solution of sodium hydroxide, and 6 g of thioglycerol was used as a chain transfer agent. went. The pH of the reaction solution polymerized in this manner was kept in the range of 7.8 to 8.0 during the polymerization.

Example 5 100 g of water was placed in a 500 ml capacity flat-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 100 ° C. while blowing nitrogen gas. In a conical beaker with a volume of 500 ml, add 100 g of acrylic acid and 28 g of water to the mixture under ice cooling.
An aqueous monomer solution prepared by adding 222 g of a 25% aqueous solution of sodium hydroxide was mixed with a quantitative pump to 3
It was supplied dropwise over time. At the same time, a mixed solution of 1.27 g of ammonium persulfate as a polymerization initiator and 50 g of water was dropwise added to the mixture for 3 and a half hours to start polymerization. The pH of the reaction solution polymerized in this manner was kept in the range of 7.4 to 7.6. After the supply of the latter,
Polymerization was completed by maintaining the same temperature for another 30 minutes.

Example 6 100 g of water was placed in a 500 ml flat bottom flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 100 ° C. while blowing nitrogen gas. In a conical beaker with a volume of 500 ml, add 100 g of acrylic acid and 28 g of water to the mixture under ice cooling.
A monomer aqueous solution prepared by adding 222 g of a 25% aqueous solution of sodium hydroxide and dissolving 5 g of sodium hypophosphite monohydrate as a chain transfer agent was added dropwise by a metering pump in 3 hours. At the same time, a mixed solution of 1.27 g of ammonium persulfate as a polymerization initiator and 50 g of water was added dropwise by another metering pump in 3 and a half hours. The pH of the reaction liquid thus polymerized is 7.
It was kept in the range of 4-7.6. After the completion of the latter supply, the same temperature was maintained for an additional one and a half hours to complete the polymerization.

Example 7 100 g of water was placed in a 500 ml capacity flat-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introduction tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 100 ° C. while blowing nitrogen gas. In a conical beaker with a volume of 500 ml, add 100 g of acrylic acid and 28 g of water to the mixture under ice cooling.
A monomer aqueous solution prepared by adding 220 g of a 25% aqueous solution of sodium hydroxide, dissolving 10 g of ammonium formate as a chain transfer agent, and further adding 10 g of a 25% aqueous solution of sodium hydroxide was added dropwise by a metering pump in 3 hours. Supplied. At the same time, a mixed solution of 12.7 g of ammonium persulfate as a polymerization initiator and 50 g of water was added,
It was supplied dropwise by another metering pump in 3 and a half hours. The pH of the reaction solution polymerized in this way is 8.2 to 8.4.
Kept in the range of. After the completion of the latter supply, the same temperature was maintained for an additional 1 hour to complete the polymerization.

Example 8 100 g of water was placed in a 500 ml flat bottom flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 100 ° C. while blowing nitrogen gas. In a conical beaker with a volume of 500 ml, add 100 g of acrylic acid and 28 g of water to the mixture under ice cooling.
An aqueous monomer solution prepared by adding 199 g of a 25% aqueous solution of sodium hydroxide was mixed with a metering pump to obtain 3
It was supplied dropwise over time. At the same time, a mixed solution of 1.27 g of ammonium persulfate as a polymerization initiator and 50 g of water was added dropwise by another metering pump in 3 and a half hours. When the pH of the reaction solution was 7.3 or less, the pH of the reaction solution was kept in the range of 7.3 to 7.5 by automatically supplying a 25% aqueous solution of sodium hydroxide dropwise. After the supply of the aqueous solution of the polymerization initiator was completed, the same temperature was maintained for another 30 minutes to complete the polymerization.

Example 9 A 500 ml flat-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introduction tube, a pH meter and a dropping nozzle was placed, and 10 g of acrylic acid, 70 g of water and 25 g of sodium hydroxide were added. % Aqueous solution (20 g) was added, and this was kept in an oil bath at 100 ° C. while blowing nitrogen gas. Add 100 g of acrylic acid in a conical beaker with a capacity of 500 ml.
A monomer aqueous solution prepared by adding 199 g of a 25% aqueous solution of sodium hydroxide was added dropwise to a mixture of 28 g of water and 28 g of water under ice cooling with a metering pump in 3 hours. At the same time, a mixed solution of 1.27 g of ammonium persulfate as a polymerization initiator and 50 g of water was added dropwise by another metering pump in 3 and a half hours. When the pH of the reaction solution is 7.3 or less, the pH of the reaction solution is adjusted to 7.3 by automatically supplying a 25% aqueous solution of sodium hydroxide dropwise.
It was kept in the range of ~ 7.5. After the supply of the aqueous solution of the polymerization initiator was completed, the same temperature was maintained for another 30 minutes to complete the polymerization.

<Example 10> 100 g of water was placed in a 500 ml flat-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 95 ° C. while blowing nitrogen gas. A monomer aqueous solution prepared by adding 160 g of a 25% aqueous solution of sodium hydroxide to a mixed solution of 72 g of acrylic acid and 118 g of water in a conical beaker having a capacity of 500 ml under ice cooling was added in 3 hours by a metering pump. It was supplied dropwise. At the same time, a mixed solution of 1.14 g of ammonium persulfate as a polymerization initiator and 50 g of water was dropwise fed for 3 hours and a half by another quantitative pump. The pH of the reaction solution polymerized in this way was kept in the range of 7.5 to 7.8. After the completion of the latter supply, the same temperature was maintained for another 30 minutes to complete the polymerization.

<Embodiment 11> 100 g of water was placed in a 500 ml capacity flat-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 100 ° C. while blowing nitrogen gas. To this, a monomer aqueous solution prepared by adding 96 g of a 25% aqueous solution of sodium hydroxide to a mixed solution of 43.2 g of acrylic acid and 211 g of water in a conical beaker with a capacity of 500 ml under ice cooling was mixed with a metering pump. It was supplied dropwise over time. At the same time, a mixed solution of 0.65 g of potassium persulfate as a polymerization initiator and 50 g of water was added dropwise by another metering pump in 3 and a half hours. The pH of the reaction solution polymerized in this way was kept in the range of 7.8 to 8.0. After completion of the latter supply, the same temperature was maintained for an additional 1 hour to complete the polymerization.

<Embodiment 12> 100 g of water was placed in a 500 ml flat bottom flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 100 ° C. while blowing nitrogen gas. A monomer aqueous solution prepared by adding 48 g of a 25% aqueous solution of sodium hydroxide to a mixed solution of 21.6 g of acrylic acid and 280 g of water in a conical beaker having a capacity of 500 ml under ice cooling was mixed with a quantitative pump. It was supplied dropwise over time. At the same time, a mixed solution of 0.5 g of ammonium persulfate as a polymerization initiator and 50 g of water was added dropwise by another metering pump in 3 and a half hours. The pH of the reaction solution polymerized in this way was kept in the range of 7.7 to 7.9. After completion of the latter supply, the same temperature was maintained for an additional 1 hour to complete the polymerization.

Example 13 100 g of water was placed in a 500 ml capacity flat-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 100 ° C. while blowing nitrogen gas. A monomer aqueous solution prepared by adding 25.4 g of a 25% aqueous solution of sodium hydroxide to a mixed solution of 10.8 g of acrylic acid and 315 g of water in a conical beaker having a capacity of 500 ml under ice cooling was quantitatively pumped. Was added dropwise in 3 hours. At the same time, a mixed solution of 0.25 g of ammonium persulfate as a polymerization initiator and 50 g of water was added dropwise by another metering pump in 3 and a half hours. The pH of the reaction solution polymerized in this way is 8.5 to
It was kept in the range of 8.7. After completion of the latter supply, the same temperature was maintained for an additional 1 hour to complete the polymerization.

Example 14 The same procedure as in Example 13 was conducted except that the aqueous monomer solution was prepared from 10.8 g of acrylic acid, 315 g of water and 24 g of a 25% aqueous solution of sodium hydroxide. The pH of the reaction solution polymerized in this manner was kept in the range of 7.9 to 8.2 during the polymerization.

Example 15 The same procedure as in Example 13 was repeated except that an aqueous monomer solution was prepared from 10.8 g of acrylic acid, 315 g of water and 24 g of a 25% aqueous solution of sodium hydroxide, and 1.27 g of ammonium persulfate was used. I went. The pH of the reaction solution polymerized in this way was kept in the range of 7.2 to 7.4 during the polymerization.

<Example 16> In Example 13, the oil bath temperature was set to 110 ° C and the aqueous monomer solution was changed to acrylic acid 1
The same procedure was carried out except that 0.8 g, 315 g of water and 24 g of a 25% aqueous solution of sodium hydroxide were used. The pH of the reaction solution thus polymerized was 7.4 during the polymerization.
It was kept in the range of ˜7.6.

Example 17 The same procedure as in Example 13 was carried out except that the monomer aqueous solution was prepared from 10.8 g of acrylic acid, 316 g of water and 22.8 g of a 25% aqueous solution of sodium hydroxide. The pH of the reaction solution polymerized in this way was kept in the range of 6.6 to 6.8 during the polymerization.

Example 18 The procedure of Example 13 was repeated except that the monomer aqueous solution was prepared from 10.8 g of acrylic acid, 320 g of water, and 19.2 g of a 25% aqueous solution of sodium hydroxide. The pH of the reaction liquid thus polymerized was kept in the range of 6.1 to 6.4 during the polymerization.

Comparative Example 1 The procedure of Example 1 was repeated, except that the monomer aqueous solution was prepared from 100 g of acrylic acid, 28 g of water, and 227 g of a 25% aqueous solution of sodium hydroxide. The pH of the reaction liquid thus polymerized was in the range of 9.7 to 9.9 during the polymerization.

Comparative Example 2 The procedure of Example 1 was repeated except that the aqueous monomer solution was prepared from 100 g of acrylic acid, 95 g of water, and 155 g of a 25% aqueous solution of sodium hydroxide. PH of the reaction solution polymerized in this way
Was in the range of 5.8 to 6.1 during the polymerization.

<Comparative Example 3> A capacity of 500 equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing pipe and a pH meter.
In a flat bottom flask of ml, acrylic acid 21.6g and water 420
g and an aqueous monomer solution prepared from 48 g of a 25% aqueous solution of sodium hydroxide were added, and this was kept in an oil bath at 100 ° C. while blowing nitrogen gas. To this, a mixed solution of 0.5 g of ammonium persulfate as a polymerization initiator and 10 g of water was added all at once, and polymerization was carried out at the same temperature for 6 hours.
The pH of the reaction solution gradually decreased from 9.1 to 8.0 during the polymerization.

Comparative Example 4 The procedure of Example 9 was repeated except that the aqueous monomer solution was prepared from 100 g of acrylic acid, 95 g of water, and 155 g of a 25% aqueous solution of sodium hydroxide. The pH of the reaction liquid thus polymerized was in the range of 5.8 to 6.0 during the polymerization.

Comparative Example 5 100 g of water was placed in a 500 ml capacity flat-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube, a pH meter and a dropping nozzle.
This was kept in an oil bath at 100 ° C. while blowing nitrogen gas. An aqueous monomer solution prepared from 21.6 g of acrylic acid and 328 g of water was dropwise added to this by a metering pump in 3 hours. At the same time, a mixed solution of 0.65 g of ammonium persulfate as a polymerization initiator and 50 g of water was added dropwise by another metering pump in 3 and a half hours. The pH of the reaction liquid thus polymerized was in the range of 3.0 to 4.5. After the latter feed was completed, the temperature was maintained for another hour to complete the polymerization, followed by addition of sodium hydroxide 25
% Aqueous solution of 45.6 g was added for post-neutralization. Table 1 shows the analysis results of the water-soluble polymers obtained in the above Examples and Comparative Examples.

[0054]

[Table 1]

[0055]

EFFECTS OF THE INVENTION The water-soluble polymer according to the present invention has a low molecular weight and a narrow dispersity, and therefore has excellent dispersibility and biodegradability, and can be preferably used as various dispersants, detergent builders and the like. This is the same as described above in the section “Means for solving the problems”.

Claims (2)

[Claims] 1. A structural unit represented by the following general formula (1) as a main component, having a number average molecular weight of 300 to 10,000 and a polydispersity (where the polydispersity is the weight average molecular weight divided by the number average molecular weight). The water-soluble polymer is characterized in that the quotient is 1.3 to 2.3. (However, in the formula, X represents a hydrogen atom, an alkali metal atom or NH _4. ) 2. An acrylic acid-based monomer containing a compound represented by the following general formula (2) as a main component and having a polymerization system pH of 6:
The method for producing a water-soluble polymer according to claim 1, wherein the polymerization is carried out by an aqueous solution polymerization method while maintaining the range of -9. (However, in the formula, X represents a hydrogen atom, an alkali metal atom or NH _4. )