JPH11315115A - (meth)acrylic acid-based polymer and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a (meth)acrylic acid-based polymer excellent in dispersing capability and chelating capability and further, in addition, in anti-gelling property and to provide a method for producing the same efficiently by introducing sulfonic acid group quantitatively to terminals thereof and also polymerizing a monomer under an acidic condition. SOLUTION: This method for producing a (meth)acrylic acid-based polymer comprises performing a polymerization reaction under a condition of pH<5 and <40 mol.% degree of neutralization, by combinedly using each >=1 kind of a persulfate salt and a bisulfite salt as initiators and >=60 mol.% hydrophilic monomers containing (meth)acrylic acid so that the concentration of solid portion becomes >=40% at the completion of the polymerization reaction. The obtained polymer has a weight-averaged molecular weight within a range of 3,000-15,000, sulfonic acid groups at its terminals and <2.0 anti-gelling capability defined by the formula: Q = the degree of gelation × 10<5> /weight-averaged molecular weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a (meth) acrylic acid-based polymer suitably used as an aqueous dispersant, scale inhibitor, detergent builder, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, among water-soluble polymers such as polyacrylic acid and polymaleic acid, those having a low molecular weight are suitable for dispersants such as inorganic pigments and metal ions, scale inhibitors, and detergent builders. Used. As a method for obtaining such a low molecular weight water-soluble polymer, for example, JP-A-64-38403 and JP-A-5-38403
A method disclosed in -86125 and the like is known.

In the method disclosed in the above publication,
When one or two or more water-soluble vinyl monomers (ethylenic monomers) are radically polymerized using a water-soluble azo radical polymerization initiator, sulfite ions are used in an amount of 0.1 to 30 mol% with respect to the monomers. Make it exist. The monomer used at this time is not particularly limited as long as it is a water-soluble vinyl monomer. By using this method, a low-molecular-weight water-soluble polymer having a molecular weight of up to tens of thousands can be obtained with good reproducibility.

Further, in the method disclosed in the above-mentioned publication, 95 mol% or more of acrylic acid or acrylate is polymerized in an aqueous solution while maintaining acrylic acid or acrylate in a pH range of 6 to 9 (under neutralization conditions). A water-soluble polymer having an acrylate is obtained. At this time, the average molecular weight of the polymer is 300 to 10,000, and the degree of dispersion is 1.3.
２2.3. Since the water-soluble polymer obtained by this method has a low molecular weight and a narrow dispersity (narrow molecular weight distribution), it has a high dispersing ability and is suitably used for various dispersants, detergent builders, and the like.

Further, Japanese Patent Publication No. 60-24806 discloses a method for producing an acrylate-based low molecular weight polymer. In the method disclosed in this publication, (A) an alkali metal acrylate, (B) acrylamide or 2-hydroxyethyl (meth) acrylate, (C) a hydrophilic copolymerizable with the components (A) and (B). A monomer is mixed with air (1) per mole of component (A) at a predetermined component ratio.
The aqueous solution polymerization is performed so that the polymerization temperature is 0 liter or more and the polymerization temperature is 80 ° C. or less.

The water-soluble acrylate-based polymer obtained by this method has a molecular weight in the range of 500 to 100,000, a narrow molecular weight distribution, no impurities, and little coloring. In addition, 0.5 to 1.5 sulfonic acid groups are introduced per molecule into the linear terminal or side chain of the water-soluble polymer. Therefore, the water-soluble polymer has excellent dispersing ability and chelating ability, and can be suitably used as a dispersant for inorganic pigments, a detergent builder, a detergent, and a scale inhibitor.

[0007] As a technique for producing a low molecular weight polymer which is not a water-soluble polymer as described above, USP
The method disclosed in Japanese Patent No. 3,646,099 can be exemplified. The low molecular weight polymer disclosed in this publication is used for conductive coatings and is obtained by polymerizing (meth) acrylonitrile and a hydrophobic monomer.
mol% or more is mandatory. With this method, 25,000
It is possible to produce polymers having the following molecular weights.

[0008]

However, even when each of the above-mentioned methods is used, it is necessary to efficiently produce a low molecular weight water-soluble polymer having excellent dispersing ability and chelating ability and also excellent gel resistance. Have a problem that they are still insufficient.

Specifically, it is difficult to quantitatively introduce a sulfonic acid group into the terminal or side chain of the polymer by the techniques disclosed in the above or the above publications. Therefore, the dispersing ability and chelating ability of the obtained water-soluble polymer cannot be said to be sufficiently excellent, and are not optimal for use as a dispersing agent, detergent builder, detergent, or scale inhibitor. .

On the other hand, according to the technique disclosed in the above publication, it is possible to introduce a sulfonic acid group to the obtained water-soluble polymer to some extent. However, since the monomer used in this technique is an acrylate (alkali metal salt), the polymerization reaction system is almost completely neutralized.

In such a neutralized polymerization using an acrylate, if the solid content of the reaction system is increased, the viscosity of the aqueous solution of the reaction system increases remarkably as the polymerization proceeds. The molecular weight of the resulting polymer tends to increase significantly. Therefore, the technique disclosed in the above publication has a problem that the production efficiency is reduced because a low-molecular-weight polymer cannot be produced under high-concentration conditions when polymerizing monomers.

Further, the technology disclosed in the above publication is capable of producing a low molecular weight polymer satisfactorily, but is a technology for producing a polymer using 40 mol% or more of a hydrophobic monomer. As a result, the resulting low molecular weight polymer is not water soluble. That is, the technology disclosed in the above publication is a technology for producing a low-molecular-weight polymer for a conductive paint, and a water-soluble polymer is used even if a monomer is simply replaced with a water-soluble polymer. It cannot be manufactured well.

In order for the low-molecular-weight water-soluble polymer to be suitably used as a dispersant, a scale inhibitor, a detergent builder, etc., in addition to the dispersing ability and chelating ability of the water-soluble polymer, gelation is also required. It is preferable that the gel resistance, which is a property not to be produced, is excellent. However, according to the techniques disclosed in the above publications, a water-soluble polymer having excellent gel resistance cannot be obtained, and a water-soluble polymer having sufficient performance as a dispersant, a scale inhibitor, a detergent builder, and the like cannot be obtained. Unable to get united.

The present invention has been made in view of the above problems, and an object of the present invention is to quantitatively introduce a sulfonic acid group into a terminal and to contain a (meth) acrylic acid under acidic conditions. Low-molecular-weight (meth) acrylic acid-based polymer excellent in gel resistance in addition to dispersing ability and chelating ability by polymerizing a monomer composition, and a production method for efficiently producing this polymer And to provide.

[0015]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned conventional problems, the present inventors have found that they contain at least 50 mol% of (meth) acrylic acid and have a sulfonic acid group at a terminal, It has been found that a (meth) acrylic acid-based polymer having a gel resistance of less than 2.0 becomes a low molecular weight water-soluble polymer having excellent gel resistance in addition to dispersing ability and chelating ability.

Further, the present inventors have proposed that 60 mol of a hydrophilic monomer containing at least 50 mol% of (meth) acrylic acid.
1% or more, under acidic conditions with a pH of less than 5 and a degree of neutralization of less than 40 mol%, by polymerizing the above monomer in combination with one or more of a persulfate and a bisulfite as an initiator. In addition to dispersing ability and chelating ability,
In particular, they have found that a low molecular weight water-soluble polymer excellent in gel resistance can be efficiently produced.

Furthermore, the present inventors have proposed that a hydrophilic monomer containing at least 50 mol% of (meth) acrylic acid
0mol% or more, less than pH5 and degree of neutralization 40mol
When the above monomers are polymerized under acidic conditions of less than 10%, the solids concentration at the end of monomer dropping is set to 40% or more, and the weight average molecular weight is set to 3,000 to 15,000. By doing so, it was found that a low molecular weight water-soluble polymer excellent in gel resistance in addition to dispersing ability and chelating ability could be efficiently produced, and the present invention was completed.

That is, in order to solve the above-mentioned problems, the (meth) acrylic acid-based polymer according to the first aspect of the present invention comprises 50 to 100 mol% of (meth) acrylic acid and 0 to 50 mol% of A polymer obtained by polymerizing a water-soluble monoethylenically unsaturated monomer copolymerizable with (meth) acrylic acid in an aqueous solution, having a sulfonic acid group at a terminal and having the following formula: Q = gelation The gel resistance Q value defined by degree × 10 ⁵ / weight average molecular weight is less than 2.0.

According to the structure of the first aspect, since the (meth) acrylic acid-based polymer has a sulfonic acid group at the polymer terminal, it can be a low-molecular-weight polymer. Despite having a relatively high molecular weight as compared with the polymer having the above-mentioned gel resistance, the polymer can exhibit better gel resistance than the above-mentioned conventional polymer. for that reason,
The (meth) acrylic acid-based polymer can be suitably used for applications such as a dispersant, a scale inhibitor, and a detergent builder.

In order to solve the above-mentioned problems, the (meth) acrylic acid-based polymer according to the second aspect of the present invention has a polymerization average molecular weight of 3,000 to 1 in addition to the constitution according to the first aspect.
It is characterized by being within the range of 5,000.

According to the configuration of the second aspect, when the weight average molecular weight is within this range, the (meth) acrylic acid-based polymer has various properties such as dispersing ability, chelating ability and gel resistance. It can be used most effectively.
Therefore, it can be more suitably used for applications such as dispersants, scale inhibitors, and detergent builders.

In order to solve the above-mentioned problems, the (meth) acrylic acid-based polymer according to the third aspect of the present invention further comprises, in addition to the constitution according to the first or second aspect, a Is characterized in that the solid concentration in the aqueous solution is 40% or more.

According to the structure of the third aspect, since the solid content concentration is high in the polymerization reaction system, a low molecular weight polymer can be obtained efficiently. Therefore, the production efficiency of the (meth) acrylic acid-based polymer can be greatly increased.

According to a fourth aspect of the present invention, there is provided a method for producing a (meth) acrylic acid-based polymer, comprising the steps of: A pH of less than 5 and a degree of neutralization of 40 m when the monomer is subjected to a polymerization reaction
% or less, and further characterized in that one or more of persulfate and bisulfite are used in combination as an initiator system.

According to a fifth aspect of the present invention, there is provided a method for producing a (meth) acrylic acid-based polymer, comprising the steps of: At a pH of less than 5 and a degree of neutralization of 4 when the monomer is subjected to a polymerization reaction.
It is characterized in that it is less than 0 mol%, the solid content concentration at the end of the polymerization reaction is 40% or more, and the weight average molecular weight of the obtained polymer is in the range of 3,000 to 15,000.

According to the method of claim 4 or 5, the polymerization reaction is carried out under acidic conditions having a pH of less than 5 and a degree of neutralization of less than 40 mol%, thereby suppressing an increase in the viscosity of the aqueous solution of the polymerization reaction system. A low molecular weight polymer can be produced favorably. In addition, since the polymerization reaction can proceed under the condition of a higher concentration than in the past, the production efficiency can be greatly increased.

Further, as in the method according to claim 4, persulfate and bisulfite are each used as an initiator system.
The sulfonic acid group can be quantitatively introduced into the obtained (meth) acrylic acid-based polymer by using a combination of two or more kinds. Moreover, the ability to quantitatively introduce sulfonic acid groups indicates that persulfate and bisulfite as initiator systems function very well as initiators. Therefore, there is no need to add an excessive initiator to the polymerization reaction system, and it is possible to suppress an increase in the production cost of the polymer and improve the production efficiency.

If the solid content concentration at the end of the polymerization reaction is high as in the method according to the fifth aspect, the polymerization can be carried out at a high concentration and in one step. Therefore, the concentration step, which may be necessary in the conventional production method, can be omitted. Therefore, the productivity of the (meth) acrylic acid-based polymer is greatly improved, and an increase in the production cost can be suppressed.

Furthermore, if the weight-average molecular weight of the obtained (meth) acrylic acid polymer is within the above range, it is possible to suppress an increase in the amount of the initiator added to the polymerization reaction system. It is more advantageous. In addition to this,
The (meth) acrylic acid polymer can exhibit various performances such as dispersing ability, chelating ability, and gel resistance most effectively.

According to a sixth aspect of the present invention, there is provided a process for producing a (meth) acrylic acid-based polymer, in order to solve the above-mentioned problems, in addition to the above-mentioned fourth aspect, further comprises a persulfate and a bisulfite When using one or more salts in combination, the bisulfite is used in a weight ratio within the range of 0.5 to 5 when the persulfate is set to 1 by weight, and the polymerization reaction system is used. It is characterized in that the total amount of persulfate and bisulfite added is in the range of 2 to 20 g equivalent per 1 mol of monomer.

According to the above-mentioned method, not only the persulfate but also the bisulfite within the above-mentioned range is added to the predetermined amount of the initiator system, so that the obtained polymer is required. As described above, the increase in the molecular weight is suppressed. Therefore, a low molecular weight polymer can be efficiently produced by adding bisulfite to the polymerization reaction system.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
This will be described in detail below. The monomer composition used for obtaining the (meth) acrylic acid-based polymer according to the present invention includes:
It comprises a first monomer (hereinafter, referred to as monomer (I)) and a second monomer (hereinafter, referred to as monomer (II)).

As the monomer (I), (meth) acrylic acid is used, and as the monomer (II), a water-soluble monoethylenically unsaturated monomer is used. The mixing ratio of the monomer (I) and the monomer (II) in the monomer composition is preferably 50 to 100 mol% of the monomer (I) and 0 to 100 mol% of the monomer (II). 50 mol%, more preferably 70 to 100 mol% of monomer (I) and 0 to 30 of monomer (II).
mol%.

As the (meth) acrylic acid used as the monomer (I), specifically, acrylic acid, methacrylic acid, a mixture thereof and the like can be suitably used.

As the water-soluble monoethylenically unsaturated monomer used as the monomer (II), specifically, the monomer (I), that is, (meth) acrylic acid can be sodium or potassium. A salt partially neutralized by an alkali metal or a salt completely neutralized; a salt obtained by partially neutralizing the monomer (I) with ammonia or an organic amine such as monoethanolamine or triethanolamine, or a completely neutralized salt Monoethylenically unsaturated aliphatic monocarboxylic acids such as crotonic acid and α-hydroxyacrylic acid;
A salt obtained by partially or completely neutralizing the above monoethylenically unsaturated monocarboxylic acid with an alkali metal; an ammonia or an organic amine such as monoethanolamine or triethanolamine Salts partially or completely neutralized with salts; monoethylenically unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; the above monoethylenically unsaturated dicarboxylic acids are partially neutralized with an alkali metal Or completely neutralized salt; a salt obtained by partially or completely neutralizing the above monoethylenically unsaturated dicarboxylic acid with ammonia or an organic amine such as monoethanolamine or triethanolamine; vinyl sulfone Acid, allylsulfonic acid, 3-allyloxy-2-
A monoethylenically unsaturated monomer having a sulfonic acid group such as hydroxypropane sulfonic acid; a salt obtained by partially or completely neutralizing the above monoethylenically unsaturated monomer with an alkali metal; Salts obtained by partially or fully neutralizing unsaturated monomers with ammonia or organic amines such as monoethanolamine and triethanolamine; 3-methyl-2-butene-
1-ol (prenol), 3-methyl-3-butene-
Examples thereof include, but are not particularly limited to, unsaturated hydrocarbons containing a hydroxyl group such as 1-ol (isoprenol).

As the monomer (II), one kind or two or more kinds can be appropriately selected from the above-mentioned compounds as needed. In addition, among the above compounds, one or more compounds selected from unsaturated aliphatic dicarboxylic acids, unsaturated hydrocarbons containing a sulfonic acid group, and partially or completely neutralized salts thereof are used. Is more preferable.

As the other monomer, a hydrophobic compound may be used. However, when such a hydrophobic monomer is used as another monomer, the gel resistance of the obtained (meth) acrylic acid polymer may be significantly deteriorated. preferable.

If the above-mentioned hydrophobic monomer is added to other monomers, it must be at least less than 40 mol% of all monomers in the polymerization reaction system. In other words, the ratio of the hydrophilic monomers including the monomers (I) and (II) needs to be 60 mol% or more of all the monomers in the polymerization reaction system. . When the ratio of the hydrophobic monomer exceeds 40 mol% of all monomers,
Since the gel resistance of the obtained (meth) acrylic acid polymer is definitely deteriorated, the (meth) acrylic acid polymer having excellent gel resistance according to the present invention cannot be obtained.

In the present invention, the solvent used in the polymerization reaction system when polymerizing the monomers (I) and (II) is preferably an aqueous solvent, particularly preferably water. is there. In order to improve the solubility of the monomers (I) and (II) in the solvent, an organic solvent may be appropriately added within a range that does not adversely affect the polymerization of each monomer.

Specific examples of the above organic solvent include lower alcohols such as methanol and ethanol; amides such as dimethylformaldehyde; ethers such as diethyl ether and dioxane;
More than one kind can be appropriately selected and used.

In the present invention, the initiator system used for polymerizing the monomers (I) and (II) may be one or more persulfates and one or two persulfates. The above bisulfites are used in combination. The addition ratio of the above-mentioned persulfate and bisulfite is preferably in the range of 0.5 to 5 and more preferably in the range of 1 to 4 with respect to 1 persulfate in weight ratio. Is more preferable.

If the bisulfite is less than 0.5 per persulfate 1, the effect of the bisulfite is not sufficient. For this reason, a sulfonic acid group cannot be quantitatively introduced into the terminal, and the weight average molecular weight of the obtained (meth) acrylic acid polymer tends to increase.

On the other hand, 5 per bisulfite per 1 persulfate
Is exceeded, the bisulfite is wasted in the polymerization reaction system in a state where the effect of the bisulfite cannot be obtained as much as the addition ratio. Moreover, the bisulfite is decomposed in the polymerization reaction system, and generates sulfurous acid gas.

The above-mentioned persulfate and bisulfite are added preferably in an amount of 2 to 20 g, more preferably 6 to 15 g, per mole of the monomer.
g is more preferable. When a persulfate and a bisulfite are added within this range, a sulfonic acid group can be quantitatively introduced into the terminal of the (meth) acrylic acid-based polymer obtained.

If the addition amount of the above persulfate and bisulfite is too small, it becomes impossible to quantitatively introduce a sulfonic acid group into the terminal of the (meth) acrylic acid-based polymer to be obtained. The weight average molecular weight tends to increase. On the other hand, if the addition amount is too large, the effect of persulfate and bisulfite will not be obtained as much as the addition amount, and conversely,
This will have adverse effects such as a decrease in the purity of the (meth) acrylic acid-based polymer obtained.

Specific examples of the above-mentioned persulfate include sodium persulfate, potassium persulfate and ammonium persulfate. On the other hand, examples of the bisulfite include sodium bisulfite, potassium bisulfite, and ammonium bisulfite.

As described above, a monomer composition containing at least 50 mol% of the monomer (I) and at least 0 to 50 mol% of the monomer (II) is prepared under the acidic conditions described below. By performing polymerization using persulfate and bisulfite as an initiator system, a sulfonic acid group is quantitatively introduced into the polymer terminal of the (meth) acrylic acid-based polymer according to the present invention. Therefore, the (meth) acrylic acid-based polymer according to the present invention does not aggregate with a metal salt such as calcium and has good gel resistance. The evaluation of the gel resistance will be described later.

Heretofore, polymers having gel resistance have particularly low molecular weights among low molecular weight polymers. That is, in order to obtain good gel resistance, it was necessary to further reduce the molecular weight of the low molecular weight polymer. However, polymers with too low a molecular weight are
It could not be suitably used for applications such as dispersants, scale inhibitors and detergent builders.

On the other hand, in the (meth) acrylic acid-based polymer according to the present invention, a sulfonic acid group can be quantitatively introduced into the terminal of the polymer in the production process. Therefore, although the (meth) acrylic acid-based polymer is a low molecular weight polymer, it has a relatively large molecular weight compared to a conventional gel-resistant polymer,
Good gel resistance can be exhibited. Therefore, it can be suitably used for applications such as dispersants, scale inhibitors, and detergent builders.

The fact that sulfonic acid groups can be quantitatively introduced indicates that persulfates and bisulfites as initiator systems function very well as initiators. Therefore, there is no need to add an excessive initiator to the polymerization reaction system, suppressing an increase in the production cost of the polymer,
Manufacturing efficiency can be improved.

Furthermore, by adding bisulfite to the initiator system, it is possible to prevent the obtained polymer from having an unnecessarily high molecular weight. Therefore, a low molecular weight polymer can be efficiently produced by adding bisulfite to the polymerization reaction system.

The combination of the above-mentioned persulfate and bisulfite is preferable as the initiator system used in the method for producing the (meth) acrylic acid polymer and the (meth) acrylic acid polymer according to the present invention. The combination is not particularly limited, and may be any initiator system which can introduce a sulfonic acid group and can polymerize a low molecular weight polymer in one step.

In the polymerization of the monomer (I) and the monomer (II), the reaction temperature is 90 ° C. or higher, more preferably a temperature near the boiling point of the solvent in an aqueous solvent. The pressure is not particularly limited, and may be any of normal pressure (atmospheric pressure), reduced pressure, and increased pressure.

The polymerization reaction of the monomers (I) and (II) is carried out under acidic conditions.
And the degree of neutralization is less than 40 mol%. When the monomer used for polymerization is only the monomer (I), the degree of neutralization is preferably less than 20 mol%, more preferably 10 mol% or less. On the other hand, the monomer (I)
When performing polymerization using the monomer (II) in addition to the above, it is possible to initially charge a part or all of the monomer (II). The degree is preferably less than 30 mol%, particularly preferably 5 mol%.
It is in the range of not less than 30 mol%.

Conventionally, pH 5 or more or neutralization degree 40 m
When the polymerization reaction is carried out under the condition of ol% or more, the viscosity of the aqueous solution of the polymerization reaction system increases remarkably as the polymerization proceeds. Therefore, there has been a problem that the molecular weight of the obtained polymer is increased more than necessary and a low molecular weight polymer cannot be obtained. However, the pH is less than 5 and the degree of neutralization is 4
By performing the polymerization under a condition of less than 0 mol%, the viscosity of the aqueous solution of the polymerization reaction system does not increase, and a low molecular weight polymer can be produced favorably. In addition, since the polymerization reaction can proceed under the condition of a higher concentration than in the past, the production efficiency can be greatly increased.

In particular, in the method for producing a polymer according to the present invention, the polymerization can be carried out at a high concentration and in one step by carrying out the polymerization reaction under the above acidic conditions. Therefore, the concentration step, which may be necessary in the conventional production method, can be omitted. Therefore, the productivity of the (meth) acrylic acid-based polymer is greatly improved, and an increase in the production cost can be suppressed.

As described above, when the monomer (I) and the monomer (II) are copolymerized, the most preferable neutralization degree is considered in consideration of the reactivity of each monomer. Range is 5m
ol% or more and less than 30 mol%. Under the condition where the degree of neutralization is within this range, it is possible to copolymerize the monomer (I) and the monomer (II) most preferably.

In the method for producing a polymer according to the present invention, the polymerization is carried out under acidic conditions.
The degree of neutralization of the acrylic acid polymer, after the polymerization is completed,
For example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, hydroxides of alkaline earth metals such as calcium hydroxide and magnesium hydroxide, and organic amines such as ammonia, monoethanolamine, diethanolamine and triethanolamine It can be set by appropriately adding an alkali component represented by a class. In addition, only one kind of the alkali component may be used, or a mixture of two or more kinds may be used.

It is possible to set the degree of neutralization by subjecting the (meth) acrylate polymer obtained by the conventional complete neutralization method or partial neutralization method to desalting treatment. In this case, the production process is complicated by the addition of the desalting process, and the production cost is also increased, which is not practical.

In the polymerization, the above-mentioned monomer (I), monomer (II), and persulfate and bisulfite as an initiator system are each added to an aqueous solvent in a predetermined dropping time. It is dripped continuously over. This dropping time is 30
Minutes to 240 minutes, more preferably 45 minutes to 180 minutes. The monomer (II) can be partially or entirely initially charged.

If the dropping time is less than 30 minutes, the effect of the persulfate and bisulfite added as the initiator system will not be efficient. Therefore, it becomes impossible to quantitatively introduce sulfonic acid into the terminal of the obtained (meth) acrylic acid-based polymer, and the weight-average molecular weight of the polymer tends to increase. On the other hand, if the dropping time exceeds 240 minutes, the productivity of the (meth) acrylic acid-based polymer is significantly deteriorated, which is not preferable.

When the above components are dropped, the dropping speed is not particularly limited. For example, the dropping rate may be constant from the start to the end of the dropping, or the dropping rate may be changed over time as needed. However, the above components are dropped so that the concentration of the solid components in the polymerization reaction system, that is, the concentration of the polymerization solid content of the monomer is 40% or more after the completion of the dropping. That is, the solid content concentration at the time when the polymerization reaction is completed may be 40% or more.

As described above, when the solid content concentration is increased in the polymerization reaction system, in the conventional method, the viscosity of the reaction solution increases remarkably with the progress of the polymerization reaction, and the molecular weight of the obtained polymer also increases significantly. Had a problem. However, in the present invention, since the polymerization reaction is performed on the acidic side (pH less than 5 and the degree of neutralization is less than 40 mol%), it is possible to suppress an increase in the viscosity of the reaction solution as the polymerization reaction proceeds. Therefore, a polymer having a low molecular weight can be obtained even when the polymerization reaction is performed under a high concentration condition, so that the production efficiency of the polymer can be greatly increased.

The weight average molecular weight of the (meth) acrylic acid polymer obtained is 3,000 to 15,000, preferably
3,000 to 10,000. When the weight average molecular weight is within this range, the (meth) acrylic acid-based polymer has a dispersing ability,
Various performances such as chelating ability and gel resistance can be exhibited most effectively.

Generally, in the case of a low-molecular-weight water-soluble polymer used as a dispersant or a scale inhibitor, if the molecular weight is 1,000 or more, the smaller the molecular weight of the water-soluble polymer (ie, the closer the molecular weight becomes to 1,000, ) Dispersibility and gel resistance show high performance. On the other hand, the chelating ability shows higher performance as the molecular weight of the water-soluble polymer increases. Therefore, it has been difficult for conventional water-soluble polymers to satisfactorily improve all three properties of dispersing ability, chelating ability, and gel resistance.

On the other hand, since the (meth) acrylic acid-based polymer has a sulfonic acid group introduced at its terminal, the dispersibility and the gel resistance are good even if the molecular weight is relatively large. Become. In particular, the gel resistance shows relatively very good performance in consideration of the molecular weight. Therefore, the (meta) according to the present invention
Acrylic acid-based polymers exhibit the same chelating ability as conventional (meth) acrylic acid-based polymers having the same molecular weight, as well as high dispersibility and extremely excellent gel resistance. I have.

Further, in producing a conventional low molecular weight water-soluble polymer exhibiting gel resistance, it is necessary to increase the amount of an initiator added to the polymerization reaction system as compared with the case of producing a high molecular weight polymer. is there. However, since the (meth) acrylic acid-based polymer according to the present invention has a relatively large molecular weight, an increase in the amount of the initiator added to the polymerization reaction system can be suppressed. Therefore, the method for producing a (meth) acrylic acid-based polymer according to the present invention is very advantageous in terms of cost as compared with the conventional method for producing a water-soluble polymer exhibiting gel resistance.

In the present embodiment, the gel resistance was calculated and evaluated as a gel resistance Q value. The gel resistance Q value is calculated from the gelation degree and the weight average molecular weight of the polymer using the following formula.

Q = gelling degree × 10 ⁵ / weight average molecular weight The (meth) acrylic acid polymer according to the present invention has a gel resistance Q value of 2.0 or less. When the gel resistance Q value is within this range, it indicates that the gel has very good gel resistance.

As the degree of gelation in the above formula, a conventionally known method for measuring the degree of gelation of a polymer can be suitably used. For example, a test solution is prepared by adding a low-concentration aqueous solution (for example, 1% by weight) of the (meth) acrylic acid-based polymer according to the present invention and an aqueous calcium chloride solution to a buffer solution and mixing the resultant solution. Is placed at a predetermined temperature and for a predetermined time (for example, 90 ° C., 1 hour), and then the degree of gelation can be measured by measuring the absorbance of the test solution in an ultraviolet (UV) wavelength region.

As described above, the (meth) acrylic acid-based polymer according to the present invention has a sulfonic acid group at a terminal and has high gel resistance. Therefore, the above-mentioned polymer can improve the dispersing ability and the chelating ability by the terminal sulfonic acid group, and has higher gel resistance. As a result, the polymer can be suitably used as a dispersant for inorganic pigments, a scale inhibitor, a detergent builder, and the like.

Further, the method for producing a (meth) acrylic acid-based polymer according to the present invention is characterized in that one or more of persulfate and bisulfite are used in combination as an initiator system, and (meth) acrylic acid is used. This is a method in which a hydrophilic monomer is polymerized under acidic conditions (pH less than 5 and neutralization degree less than 40 mol%).

At this time, it is particularly preferred that the polymerization solid content concentration at the end of the polymerization reaction is 40% or more and the weight average molecular weight of the obtained polymer is in the range of 3,000 to 15,000.

Thus, a (meth) acrylic acid-based polymer having excellent gel resistance in addition to dispersing ability and chelating ability can be efficiently produced. Therefore, a polymer that can be suitably used as a dispersant, a scale inhibitor, a detergent builder, or the like of an inorganic pigment can be produced with high quality and at low cost. Further, costs can be reduced, for example, an increase in the amount of initiator added to the polymerization reaction system can be suppressed.

[0075]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto. Note that “%” in Examples and Comparative Examples indicates “% by weight”. Further, the weight average molecular weight, gel resistance, and terminal sulfonic acid group of the (meth) acrylic acid-based polymer according to the present invention were measured or quantified by the following methods.

The weight average molecular weight (hereinafter abbreviated as Mw) of the (meth) acrylic acid polymer was measured by GPC (gel permeation chromatography). The column of GPC at this time is manufactured by Showa Denko: GF-
7MHQ was used. As the mobile phase, ion-exchanged water (hereinafter referred to as pure water) was added to 34.5 g of disodium hydrogen phosphate dodecahydrate and 46.2 g of sodium dihydrogen phosphate dihydrate, and the total amount was 5, An aqueous solution that had been weighed to 000 g and further filtered through a 0.45 μm membrane filter was used. The reagents used here are all of a special grade. In addition, the reagents used in the following measurement of the degree of gelation and in each of the examples are all of a special grade. Waters: Model 481 (Detection wavelength UV: 214)
nm). The pump used was L-7110 (trade name, manufactured by Hitachi, Ltd.). The flow rate of the mobile phase is 0.5 ml /
Minutes and the temperature was 35 ° C. The calibration curve was created using a standard sample of sodium polyacrylate manufactured by Souwa Kagaku.

In the measurement of the gelation degree, first, a borate buffer solution, a calcium chloride aqueous solution, and a 1% polymer solution were prepared. The borate buffer solution contains 7.42 g of boric acid,
1.75 g of sodium chloride and sodium borate 1
Pure water is added to 7.63 g of 0-hydrate to make a total amount of 1,000 g.
It is what it was. A calcium chloride aqueous solution is prepared by adding pure water to 0.735 g of calcium chloride dihydrate to make a total amount of 2,35.
It was 500 g. The 1% aqueous polymer solution was prepared by diluting the polymer of the present invention with pure water to 1%.

Next, the above solutions were charged in a predetermined order and in a predetermined amount into a 500 ml tall beaker. When the predetermined order and the predetermined amount are shown, 250 ml of pure water is charged as the first, and the borate buffer solution 1 as the second.
0 ml, and as a third, 5% of a 1% aqueous polymer solution
and finally 250 ml of an aqueous calcium chloride solution.

By mixing the solutions charged in this order, the polymer according to the present invention was gelled to prepare a test solution. The tall beaker charged with the test solution was covered, and the tall beaker was allowed to stand for 1 hour in a constant temperature bath adjusted to 90 ° C in advance. One hour later, the test solution was immediately placed in a 5-cm quartz cell, and the absorbance a at a UV wavelength of 380 nm was measured.

On the other hand, of the four components charged as the test solution, 250 ml of an aqueous calcium chloride solution was added to pure water 2
A blank solution was used instead of 50 ml. This blank solution was subjected to the same operation as the test solution, and the absorbance (blank value) b of the blank solution was measured at a UV wavelength of 380 nm. Then, the gelation degree was calculated from the absorbance a and the blank value b according to the following equation.

Gelling degree = ab This gelation degree was used to calculate the gel resistance Q value based on the following equation.

Q = gelling degree × 10 ⁵ / Mw The quantification of the terminal sulfonic acid group was performed by first measuring the (meth) acrylic acid-based polymer of the present invention obtained in an aqueous solution state with 1H
It was measured by -NMR (D ₂ O solvent). As a result, a peak of methylene hydrogen derived from a sulfonic acid group (2.
A peak of methine hydrogen derived from a sulfonic acid group (around 3.0 ppm) was detected.

Therefore, the integral ratio of these peaks to the sum of the peaks of methylene hydrogen and methine hydrogen (about 1 to 2.2 ppm) in the main chain of sodium polyacrylate was calculated and obtained in each Example. The terminal sulfonic acid groups of the (meth) acrylic acid-based polymer were quantified. In the following Examples, the charged mol ratio of sodium bisulfite (SBS) and acrylic acid (AA) was SBS / AA = 1 /
Thirteen. Next, specific examples of the present invention will be described.

Example 1 A 5-liter SUS separable flask equipped with a reflux condenser and a stirrer was charged with 300 g of pure water (initial charge), and the temperature was raised to the boiling point with stirring. Then, while stirring, 8
0% acrylic acid aqueous solution (hereinafter abbreviated as 80% AA) 72
0 g (ie, 8 mol%), 106.7 g of a 15% aqueous sodium persulfate solution (hereinafter abbreviated as 15% NaPS)
(2 g / mol in terms of monomer input), 35%
182.9 g of an aqueous solution of sodium bisulfite (hereinafter abbreviated as 35% SBS) (8 g /
mol) and 126.5 g of pure water were dropped from separate dropping nozzles over 120 minutes.

After the completion of the dropwise addition, the reaction solution was kept at a boiling point reflux state (aging) for further 30 minutes to complete the polymerization. After completion of the polymerization, the reaction solution was allowed to cool, and a 48% aqueous sodium hydroxide solution (hereinafter abbreviated as 48% NaOH) 60
Under stirring, 0 g (that is, 7.2 mol) of the reaction solution was gradually added dropwise to neutralize the solution. In this manner, the solid content concentration of 40
%, An aqueous solution of sodium polyacrylate (1) (hereinafter referred to as polymer (1)) having a final degree of neutralization of 90%.
The weight average molecular weight Mw, the gel resistance Q value, and the amount (actually measured) of the terminal sulfonic acid group of the obtained polymer (1) were quantified. Table 1 shows the results.

[Example 2] In Example 1, 80% A
The amount of A dropped was 810 g (that is, 9 mol%), and 1
The amount of 5% NaPS dropped was 240.0 g (4 g / mol in terms of the amount charged to monomer), and the amount of 35% SBS was 205.7 g (8 g / mol in converted to the amount charged to monomer).
mol), and the polymerization reaction was carried out in the same manner except that the amount of pure water dropped was 104.8 g. Then, 48% NaO
By neutralizing 675 g (ie, 8.1 mol) of H, sodium polyacrylate (2) having a solid concentration of 40% and a final degree of neutralization of 90% (hereinafter referred to as polymer (2)
) Was obtained.

The weight average molecular weight M of the obtained polymer (2)
w, the gel resistance Q value, and the amount of the terminal sulfonic acid group (actually measured value) were measured or quantified in the same manner as in Example 1. Table 1 shows the results.

Example 3 In Example 2, 15% N
The amount of aPS dropped was 360.0 g (6 g / mol in terms of the amount charged to monomer), and the amount of pure water dropped was 29.8 g.
A polymerization reaction was carried out in the same manner as above except that Thereafter, the solid content concentration was reduced by neutralization with the same amount of 48% NaOH (675 g, ie, 8.1 mol) as in Example 2.
An aqueous solution of sodium polyacrylate (3) (hereinafter referred to as polymer (3)) having 0% and a final degree of neutralization of 90% was obtained.

The weight average molecular weight M of the obtained polymer (3)
w, the gel resistance Q value, and the amount of the terminal sulfonic acid group (actually measured value) were measured or quantified in the same manner as in Example 1. Table 1 shows the results.

Example 4 In Example 2, the amount of pure water initially charged was set to 200 g, and the amount of 15% NaPS was dropped to 48 g.
0.0 g (8 g / mol in terms of monomer input)
The polymerization reaction was carried out in the same manner except that the amount of pure water dropped was 54.8 g. Thereafter, 48% of the same amount as in Example 2
Neutralization with NaOH (675 g, or 8.1 mol) gives a solids concentration of 40% and a final neutralization degree of 90%.
Of sodium polyacrylate (4) (hereinafter referred to as polymer (4)).

The weight average molecular weight M of the obtained polymer (4)
w, the gel resistance Q value, and the amount of the terminal sulfonic acid group (actually measured value) were measured or quantified in the same manner as in Example 1. Table 1 shows the results.

Example 5 In Example 1, the amount of pure water initially charged was 150 g, and the dropping amount of 80% AA was 900 g.
(That is, 10 mol%), and the amount of 15% NaPS added was 266.7 g (4 g /
mol), and the amount of 35% SBS dropped was 228.6 g.
(8 g / mol in terms of the amount charged to monomer) and the polymerization reaction was carried out in the same manner except that the amount of pure water dropped was 11.4 g. Thereafter, by neutralizing with 750 g (ie, 9 mol) of 48% NaOH, sodium polyacrylate (5) having a solid content of 45% and a final degree of neutralization of 90% (hereinafter referred to as polymer (5)) Was obtained.

The weight average molecular weight M of the obtained polymer (5)
w, the gel resistance Q value, and the amount of the terminal sulfonic acid group (actually measured value) were measured or quantified in the same manner as in Example 1. Table 1 shows the results.

Example 6 In Example 1, the amount of pure water initially charged was 450 g, and 100% methacrylic acid (hereinafter, referred to as 100% MA) was used instead of 80% AA. 602 g (ie 7 mol
%), And the amount of 15% NaPS dropped was 186.7 g (4 g / mol in terms of the amount charged to monomer).
The amount of SBS dropped was 160.0 g (8 g / mol in terms of the amount charged to monomer), and the amount of pure water dropped was 137.8.
The polymerization reaction was performed in the same manner except that the amount was changed to g. afterwards,
Neutralization using 525 g (that is, 6.3 mol) of 48% NaOH results in sodium polymethacrylate (6) having a solid content of 40% and a final degree of neutralization of 90% (hereinafter referred to as polymer (6)). Was obtained.

The weight average molecular weight M of the obtained polymer (6)
w, the gel resistance Q value, and the amount of the terminal sulfonic acid group (actually measured value) were measured or quantified in the same manner as in Example 1. Table 1 shows the results.

Next, a comparative example for the above embodiment will be described. Comparative Example 1 is for explaining the effect of the addition of bisulfite in the present invention, Comparative Example 2 is for explaining the effect of polymerizing under acidic conditions, and Comparative Example 3 is for explaining the terminal polymerization. The purpose of this example is to explain the effect of introducing a sulfonic acid group, and Comparative Example 4 is to explain the adverse effect of introducing a hydrophobic monomer.

Comparative Example 1 In Example 1, the amount of pure water initially charged was 300 g, and the amount of 80% AA was 810 g.
(That is, 9 mol%), and the dropping amount of 15% NaPS is 240 g (4 g / mo in terms of the amount charged to the monomer).
1) and the polymerization reaction was carried out in the same manner except that the amount of pure water dropped was 130.5 g. Thereafter, by neutralizing with 675 g (ie, 8.1 mol) of 48% NaOH, comparative sodium polyacrylate (1) having a solid content concentration of 40% and a final neutralization degree of 90% (hereinafter referred to as comparative polymer (1) )) Was obtained. The weight average molecular weight Mw and the gel resistance Q value of the obtained comparative polymer (1) were measured in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 2 In Example 1, 80% A
A, 15% NaPS, 35% SBS, and 48% N added in the course of neutralization after Example 1 with pure water.
aOH was added dropwise in the same amount as in Example 1, and the polymerization reaction was carried out in the same manner as in Example 1 except for this dropping. In addition, 4
The amount of 8% NaOH added was the same as in Example 1. Thus, the comparative sodium polyacrylate (2%) having a solid content concentration of 40% and a final neutralization degree of 90% is obtained by neutralization type (salt type) polymerization, not by polymerization under acidic conditions as in Example 1. (Hereinafter referred to as comparative polymer (2)). The weight average molecular weight Mw and the gel resistance Q value of the obtained comparative polymer (2) were measured in the same manner as in Example 1. Table 1 shows the results.

[Comparative Example 3] Unlike the above Examples 1 to 6 and Comparative Examples 1 and 2, a conventionally known polymerization method, that is, 2 g / m 2 of NaPS at a solid concentration of 20% was used.
and the polymerization was carried out in a neutralized form as in Comparative Example 2.
Thereby, comparative sodium polyacrylate (3)
Thus, an aqueous solution of Comparative Polymer (3) was obtained. This comparative polymer (3) has no sulfonic acid group introduced into the terminal. Further, the weight average molecular weight Mw and the gel resistance Q value of the comparative polymer (3) were measured in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 4 In Example 1, 200 g of pure water and isopropyl alcohol 23 were used as initial charges.
3.7 g were charged. Thereafter, in addition to 80% AA, phenoxy polyethylene glycol acrylate (molecular weight Mw = 236) was used as a hydrophobic monomer,
The weight was 4.4 g. In addition, the drop amount of 15% NaPS was changed to 22%.
4.6 g (4 g / mol in terms of the total number of moles of the monomers to be charged), and the dropping amount of 35% SBS was 192.5 g (converted to the amount relative to the total number of moles of the monomers to be charged). Then 8 g / mol) and 66.9 g of pure water. A polymerization reaction was carried out in the same manner as in Example 1 except for the above conditions. That is, about 5 mol% of hydrophobic monomer
It was copolymerized. Thereafter, by neutralizing with 600 g (ie, 7.2 mol) of 48% NaOH, a comparative sodium polyacrylate-phenoxy polyethylene glycol acrylate copolymer (4) having a solid content of 40% and a final degree of neutralization of 90% was used. A solution of Comparative Polymer (4) was obtained.

If pure water is used as the polymerization solvent, phenoxy polyethylene glycol acrylate, which is a hydrophobic monomer, will not be homogeneous when it is added dropwise.
3.7g is charged.

From the obtained solution of the comparative polymer (4), isopropyl alcohol was distilled off using an evaporator, and the resulting solution was again prepared as an aqueous solution having a solid content of 40% to obtain an aqueous solution of the comparative polymer (4). This comparative polymer (4)
Example 1 shows the weight average molecular weight Mw and gel resistance Q value of
The measurement was performed in the same manner as described above. Table 1 shows the results.

The reaction conditions in each of the above Examples are summarized in Table 2.

[0104]

[Table 1]

[0105]

[Table 2]

As is clear from the results in Table 1, the polymers (1) to (6) according to the present invention all have a weight average molecular weight M
w was 9,000 or less, and it was found that a low-molecular-weight polymer could be favorably obtained by single-stage polymerization even under high concentration conditions. Further, the gel resistance Q value of each polymer was all 2.0 or less, and it was found that the polymer had very good gel resistance.

On the other hand, the comparative polymer (1) obtained in the polymerization reaction system without addition of bisulfite had an Mw of 45,000,
It did not become a low molecular weight polymer. The gel resistance Q of this comparative polymer (1) was 3.11, and the gel resistance was very poor due to the effect of increasing the molecular weight.
The Mw of the comparative polymer (2), which did not undergo polymerization under acidic conditions, was 63,000, indicating that the polymer (1) had a very high molecular weight as compared with the polymer (1) and the comparative polymer (1). Had become. Also, the gel resistance Q value is 4.24,
The gel resistance was also very poor.

As described above, in order to obtain a (meth) acrylic acid polymer having low molecular weight and excellent gel resistance, it is important to use bisulfite for the initiator system and to polymerize under acidic conditions. It turns out that it is.

Next, Mw of the comparative polymer (3) obtained under the condition that a sulfonic acid group was not introduced into the terminal was 5,000, which is comparable to that of the polymers (1) to (6). Although it is a low molecular weight polymer, the gel resistance Q value is 3.92.
It became. This indicates that the gel resistance is very poor even if the molecular weight is low, unless a sulfonic acid group is introduced into the terminal of the polymer.

Further, the Mw of the comparative polymer (4) to which the hydrophobic monomer was added was 9,000, which was also a low molecular weight polymer, but the gel resistance Q value was 2.54. . This indicates that when a hydrophobic monomer is introduced, a monomer having a high concentration and a low molecular weight is obtained, but the gel resistance is reduced.

As described above, the method for producing a (meth) acrylic acid-based polymer according to the present invention is characterized in that at least one of persulfate and bisulfite is used as an initiator under acidic conditions of pH less than 5. 60 mol% of a hydrophilic monomer containing 50 mol% or more of (meth) acrylic acid
As described above, the (meth) acrylic acid-based polymer according to the present invention obtained by performing the polymerization reaction so that the solid content concentration at the end of the polymerization reaction is 40% or more is obtained. Having a weight average molecular weight in the range of 3,000 to 15,000 and having a sulfonic acid group at a terminal,
The gel resistance Q value is less than 2.0.

Therefore, the (meth) acrylic acid-based polymer according to the present invention has a low molecular weight and, due to the terminal sulfonic acid group, has excellent dispersing ability and chelating ability, as well as very excellent gel resistance. Can be shown. As a result, the polymer can be suitably used as a dispersant for inorganic pigments, a scale inhibitor, a detergent builder, and the like.

[0113]

As described above, the (meth) acrylic acid-based polymer according to claim 1 of the present invention has a content of 50 to 100 mol%.
(Meth) acrylic acid, and 0-50 mol%
A polymer obtained by polymerizing a water-soluble monoethylenically unsaturated monomer copolymerizable with (meth) acrylic acid in an aqueous solution, having a sulfonic acid group at a terminal and having the following formula: Q = gelation The gel resistance Q value defined by degree × 10 ⁵ / weight average molecular weight is less than 2.0.

Further, the (meth) acrylic acid-based polymer according to the second aspect of the present invention has a polymerization average molecular weight in the range of 3,000 to 15,000 in addition to the constitution according to the first aspect. There is a certain configuration.

Further, (meth) according to claim 3 of the present invention.
As described above, the acrylic acid-based polymer has a configuration in which the solid content concentration in the aqueous solution at the time when the polymerization reaction is completed is 40% or more, in addition to the configuration described in claim 1 or 2. .

Therefore, in each of the above-mentioned constitutions, although the polymer has a low molecular weight, it has a high chelating ability and a high dispersibility despite its relatively large molecular weight as compared with the conventional gel-resistant polymer. In addition to the performance, it can exhibit better gel resistance than the above-mentioned conventional polymers. In addition, the production efficiency is extremely good. Therefore, the (meth) acrylic acid-based polymer can be suitably used for applications such as a dispersing agent, a scale inhibitor, and a detergent builder, and is extremely cost-effective than a conventional polymer. This has the effect that it can be performed.

The method for producing a (meth) acrylic acid-based polymer according to the fourth aspect of the present invention is characterized in that the hydrophilic monomer containing 50 mol% or more of (meth) acrylic acid contains 60 m
ol% or more, the pH at the time of polymerizing the monomer is less than 5 and the degree of neutralization is less than 40 mol%, and further, as an initiator system, at least one kind of persulfate and bisulfite is used in combination. It is a method used.

The method for producing a (meth) acrylic acid-based polymer according to the fifth aspect of the present invention is characterized in that, as described above, 60% by mol of a hydrophilic monomer containing 50% by mol or more of (meth) acrylic acid. In addition to the above, when the monomer is subjected to a polymerization reaction, the pH is less than 5, the degree of neutralization is less than 40 mol%, and the solid content concentration at the end of the polymerization reaction is
% Or more, and the weight average molecular weight of the obtained polymer is in the range of 3,000 to 15,000.

Therefore, the above method has an effect that a polymer having a low molecular weight can be efficiently produced under a higher concentration condition than before.

Further, in the case of the method according to claim 4,
Because the initiator system can work very well,
There is no need to add an excessive initiator to the polymerization reaction system, so that an increase in the production cost of the polymer can be suppressed and the production efficiency can be improved.

In the case of the method according to the fifth aspect, the obtained (meth) acrylic acid-based polymer can exhibit the most effective properties such as dispersing ability, chelating ability and gel resistance in the most effective manner. Moreover, such a polymer can be polymerized in one step at a high concentration without increasing the amount of the initiator. For this reason, productivity can be significantly improved by omitting the concentration step, and an increase in manufacturing cost can be effectively suppressed.

The method for producing a (meth) acrylic acid-based polymer according to claim 6 of the present invention is as described above.
In addition to the constitution described above, when using one or more kinds of persulfate and bisulfite in combination, if the weight ratio of persulfate is 1, the bisulfite is added in a weight ratio of 0.5.
And the total amount of persulfate and bisulfite added to the polymerization reaction system is in the range of 2 to 20 g equivalent per 1 mol of monomer.

Therefore, in the above method, the polymer obtained is prevented from having a higher molecular weight than necessary. Therefore, by adding bisulfite to the polymerization reaction system, there is an effect that a low molecular weight polymer can be efficiently produced.

Claims (6)

[Claims] 1. A method of polymerizing 50 to 100 mol% of (meth) acrylic acid and 0 to 50 mol% of a water-soluble monoethylenically unsaturated monomer copolymerizable with (meth) acrylic acid in an aqueous solution. Having a sulfonic acid group at a terminal and having a gel resistance Q value defined by the following formula, Q = gelling degree × 10 ⁵ / weight average molecular weight, of less than 2.0. (Meth) acrylic acid polymer. 2. The (meth) acrylic acid polymer according to claim 1, wherein the polymerization average molecular weight is in the range of 3,000 to 15,000. 3. The (meth) acrylic acid-based polymer according to claim 1, wherein the solid content concentration in the aqueous solution at the time when the polymerization reaction is completed is 40% or more. 4. Use is made of not less than 60 mol% of a hydrophilic monomer containing not less than 50 mol% of (meth) acrylic acid,
The polymerization reaction of the monomer has a pH of less than 5 and a degree of neutralization of less than 40 mol%, and further, as an initiator system, a combination of at least one of a persulfate and a bisulfite. A method for producing a (meth) acrylic acid polymer. 5. A method using a hydrophilic monomer containing at least 50 mol% of (meth) acrylic acid in an amount of at least 60 mol%,
The pH at the time of the polymerization reaction of the monomer is less than 5, the degree of neutralization is less than 40 mol%, the solid content concentration at the end of the polymerization reaction is 40% or more, and the weight average of the obtained polymer is A method for producing a (meth) acrylic acid-based polymer, wherein the molecular weight is in the range of 3,000 to 15,000. 6. A combination of one or more persulfates and bisulfites, wherein the weight ratio of the bisulfite is 0.5 to 5 when the weight ratio of the persulfate is 1. 5. The method according to claim 4, wherein the total amount of the persulfate and bisulfite added to the polymerization reaction system is in the range of 2 to 20 g equivalent per 1 mol of the monomer. A method for producing a (meth) acrylic acid-based polymer.