JP2007002146A - Water-soluble polymer particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high molecular weight water-soluble polymer particle having a high content of a monomer having a sulfonic acid group or a salt thereof in a constituent monomer component, and a method for producing the same.
SOLUTION: Reverse phase suspension weight using an aqueous solution of a monomer having a sulfonic acid group-containing monomer or a salt thereof in a total monomer amount of 60 to 100 mol%, a hydrophobic dispersion medium, and an azo radical polymerization initiator. A water-soluble polymer particle having an average molecular weight of 4 million or more and an average particle diameter of 20 to 2000 μm obtained by a legal method, and a method for producing the same.
[Selection figure] None

Description

  The present invention relates to a high-molecular weight water-soluble polymer particle containing a monomer having a sulfonic acid group or a salt thereof as a main constituent and a method for producing the same.

  A monomer having a sulfonic acid group such as sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (hereinafter referred to as AMPS) or a polymer or copolymer of the salt is used as a dispersant, a flocculant, and the like. These effects are particularly noticeable in high molecular weight polymers.

  As a method for producing a water-soluble polymer comprising a monomer having a sulfonic acid group or a salt thereof as a main constituent, Patent Document 1 discloses a method for producing a polymer or copolymer of AMPS sodium salt using an aqueous solution polymerization method. It is disclosed. Patent Document 2 discloses a method for producing AMPS having a molecular weight of 50 to 20 million or a salt thereof using a gel polymerization method.

Further, Patent Document 3 discloses a method for producing a polymer flocculant by a reverse phase suspension polymerization method. According to this method, since the heat of polymerization can be easily removed by a hydrophobic dispersion medium, a constant temperature is obtained. There is a description that a polymer having a high molecular weight and a relatively sharp molecular weight distribution can be obtained.
JP-A-8-217826 JP 2004-323617 A JP 2004-181449 A

  In the methods described in Patent Document 1 and Patent Document 2, since the polymer obtained is a lump, it is necessary to perform pulverization in order to obtain a particulate polymer. As a result, the shape of the obtained particles is not smooth, There was an inconvenience in handling the powder.

  On the other hand, in the method of Patent Document 3, particles having a smooth shape can be obtained. However, since a chain transfer agent for radical polymerization is used, the growth of polymer molecular chains is interrupted and it is difficult to increase the molecular weight. Met. Furthermore, it has been difficult to produce a stable polymer in a copolymer having a high content of a monomer having a sulfonic acid group or a salt thereof.

  An object of the present invention is to provide a high-molecular weight water-soluble polymer particle having a high content of a monomer having a sulfonic acid group or a salt thereof in a constituent monomer component, and a method for producing the same.

  The present invention relates to a reverse phase suspension weight using an aqueous solution of a monomer having a sulfonic acid group-containing monomer or a salt thereof in a total monomer amount of 60 to 100 mol%, a hydrophobic dispersion medium, and an azo radical polymerization initiator. Provided are water-soluble polymer particles having an average molecular weight of 4 million or more and an average particle diameter of 20 to 2000 μm obtained by a legal method, and a method for producing the same.

  According to the present invention, high-molecular-weight water-soluble polymer particles having a high content of a monomer having a sulfonic acid group or a salt thereof in the constituent monomer component can be obtained. Moreover, since the aqueous solution of the polymer of the present invention has a high viscosity and exhibits spinnability, the slipperiness of clothing can be improved when blended in a laundry detergent or the like.

[Monomer aqueous solution]
Examples of the monomer having a sulfonic acid group or a salt thereof used in the present invention include an aromatic unsaturated sulfonic acid such as styrene sulfonic acid or a salt thereof; an aliphatic unsaturated sulfonic acid such as vinyl sulfonic acid or a salt thereof; (Meth) acryloyloxyethanesulfonic acid, sulfonic acid group-containing (meth) acrylate such as 2- (meth) acryloyloxypropanesulfonic acid, or a salt thereof; 2- (meth) acrylamido-2-alkyl (carbon number of alkyl group 1 to 4) Sulfonic acid group-containing (meth) acrylamide or a salt thereof such as propanesulfonic acid; alkyl (meth) allylsulfosuccinic acid ester or a salt thereof, and the like. Sulfonic acid, vinyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid (A PS) or their salts are preferred, AMPS or its salts are particularly preferred.

  Examples of the salt include metals, ammonium, alkyl or alkenyl ammonium having 1 to 22 carbon atoms, alkyl or alkenyl substituted pyridinium having 1 to 22 carbon atoms, alkanol ammonium having 1 to 22 carbon atoms, basic amino acid, and the like. Alkali metal salts such as sodium and potassium are preferred.

  The monomer component used in the present invention is a monomer having a sulfonic acid group or a salt thereof alone, or a mixture thereof with a monomer copolymerizable therewith, but the ratio of the monomer having a sulfonic acid group or a salt thereof in all monomers. Is from 60 to 100 mol%, preferably from 66 to 100 mol%, more preferably from 85 to 100 mol%, particularly preferably from 95 to 100 mol%.

  Examples of monomers copolymerizable with a monomer having a sulfonic acid group or a salt thereof include carboxyl groups such as (meth) acrylic acid, styrenecarboxylic acid, maleic anhydride, maleic acid, maleic acid monoester, maleic acid monoamide, and itaconic acid. Or a salt thereof; (meth) acryloyloxyalkyl (alkyl group having 1 to 4 carbon atoms), a monomer having a phosphate group such as phosphoric acid or vinylphosphonic acid or a salt thereof; (meth) acrylamide, N-methyl ( (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-ethyl (meth) acrylamide, Nt-butyl (meth) acrylamide, (meth) acryloylmorpholine, 2- (N, N-dimethylamino) ethyl ( (Meth) acrylamide, 3- (N, N-dimethylamino) propyl ( Unsubstituted or substituted (meth) acrylamides such as (meth) acrylamide, 2-hydroxyethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide; methyl (meth) acrylate, (meta ) Ethyl acrylate, 2-hydroxyethyl (meth) acrylate, 2- (N, N-dimethylamino) ethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylic acid Examples include (meth) acrylic acid esters such as esters.

  Moreover, in this invention, you may use a crosslinkable monomer together in the range which does not impair water solubility. Examples of the crosslinkable monomer include monomers having two or more polymerizable unsaturated groups such as vinyl group, (meth) acryloyl group, and allyl group in the molecule. For example, ethylene glycol di (meth) acrylate, polyethylene glycol di ( (Meth) acrylates of polyhydric alcohols such as (meth) acrylate and propylene glycol di (meth) acrylate; divinyl compounds such as divinylbenzene, divinyl ether and divinylethyleneurea; diallyl phthalate, diallyl malate, pentaerythritol tetraallyl ether And the like, and the like.

  The proportion of the crosslinkable monomer is preferably 0.05 mol% or less, more preferably 0.001 mol% or less, based on all monomer components.

  The monomer concentration in the aqueous monomer solution used in the present invention is preferably 50% by weight or more, more preferably 55% by weight or more, from the viewpoint of obtaining a high molecular weight polymer having a high degree of polymerization based on the weight of the aqueous solution. % By weight or more is particularly preferable, and 60% by weight or more is most preferable. Further, from the viewpoint of increasing the monomer diffusion rate in the droplets to obtain a high molecular weight polymer having a high degree of polymerization, it is preferably 90% by weight or less, more preferably 85% by weight or less, and particularly preferably 70% by weight or less.

[Hydrophobic dispersion medium]
As the hydrophobic dispersion medium used in the present invention, an aliphatic hydrocarbon or an alicyclic hydrocarbon is preferable from the viewpoint of obtaining a high molecular weight polymer having a higher degree of polymerization and ease of handling during production. Examples of the aliphatic hydrocarbon include n-hexane, n-heptane, n-decane and the like. Examples of the alicyclic hydrocarbon include cyclohexane and methylcyclohexane. These hydrophobic dispersion media may be used as one kind or a mixture of two or more kinds.

  The amount of the hydrophobic dispersion medium used is preferably 0.5 times or more, more preferably 0.7 times or more from the viewpoint of obtaining particles in which monomer droplets are not fused and aggregated based on the total monomer aqueous solution weight. 0.9 times or more is most preferable. Further, from the viewpoint of cost efficiency of the hydrophobic dispersion medium, it is preferably 6 times or less, more preferably 4 times or less, and most preferably 2 times or less.

[Radical polymerization initiator]
The radical polymerization initiator used in the present invention is an azo radical polymerization initiator from the viewpoint of obtaining a high molecular weight polymer having a higher degree of polymerization, and it is difficult to produce a water-insoluble component. A polymerization initiator is preferred. Examples of the water-soluble azo radical polymerization initiator include azobisamidinopropane (salt), azobiscyanovaleric acid (salt), and the like.

  In the present invention, the amount of radical polymerization initiator used is preferably 0.005% by weight or more, more preferably 0.03% by weight or more, based on the total amount of monomers, from the viewpoint of obtaining a high molecular weight polymer having a high degree of polymerization. . Moreover, 1.0 weight% or less is preferable and 0.5 weight% or less is still more preferable.

[Reverse phase suspension polymerization]
The reverse phase suspension polymerization method of the present invention is carried out using the monomer aqueous solution, the hydrophobic dispersion medium and the azo radical polymerization initiator as described above, but it is preferable to use a dispersant.

  The dispersant is not particularly limited. For example, nonionic ions such as sorbitan fatty acid ester, glycerin fatty acid ester, sucrose fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene aryl ether, polyoxyethylene sorbitan fatty acid ether, etc. Surfactants, cellulose esters, cellulose ethers, carboxyl group-containing polymers such as α-olefin and maleic anhydride copolymers or derivatives thereof, or polyether-modified silicones, carboxyl-modified silicones, amino-modified silicones, etc. A modified silicone is mentioned.

  Of these, nonionic surfactants of HLB 2-14 are preferred, sorbitan fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene aryl ethers of HLB 2-14 are more preferred, Two or more kinds may be used in combination.

  From the viewpoint of dispersion stability, the amount of the dispersant used is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and particularly preferably 0.5% by weight or more based on the total amount of the monomer aqueous solution. Further, it is preferably 10% by weight or less, more preferably 5% by weight or less, and particularly preferably 2% by weight or less.

  In the reverse phase suspension polymerization method of the present invention, the order of addition of the monomer aqueous solution, the hydrophobic dispersion medium, the azo radical polymerization initiator, the dispersant and the like is not particularly limited, but the following method is preferable.

  That is, a dispersant is dispersed or dissolved in a hydrophobic dispersion medium, held at a predetermined temperature to be polymerized, and deoxygenated through nitrogen gas. An azo radical polymerization initiator is added to the monomer aqueous solution and mixed uniformly. An aqueous monomer solution containing an azo radical polymerization initiator is added to the stirring hydrophobic dispersion medium. At this time, the monomer aqueous solution may be charged all at once or gradually while dropping. The dropping time is preferably 0.5 to 10 hours, more preferably 1 to 5 hours.

  In the present invention, it is preferable not to use a chain transfer agent from the viewpoint of obtaining a high molecular weight polymer having a higher degree of polymerization, but it may be added as long as it does not affect the degree of polymerization. When added, the amount is preferably 0.01% by weight or less, more preferably 0.001% by weight or less, and particularly preferably 0% by weight based on the total weight of the monomers.

  The temperature of the reverse phase suspension polymerization of the present invention is preferably 10 ° C. or higher, more preferably 30 ° C. or higher, particularly preferably 50 ° C. or higher, preferably 80 ° C. from the viewpoint of obtaining a high molecular weight polymer having a higher degree of polymerization. ° C or lower, more preferably 70 ° C or lower, particularly preferably 65 ° C or lower.

  For the polymerization temperature, it is more preferable to use the boiling point of the hydrophobic dispersion medium or the azeotropic point of the hydrophobic dispersion medium and water than ease of temperature control and stability. The boiling point or azeotropic point can be set by appropriately selecting the type of solvent. The reaction pressure may be normal pressure, but by reducing the pressure, the reaction temperature can be set more freely even in the same dispersion medium.

  The polymer after the reverse phase suspension polymerization of the present invention is water-containing polymer particles. The water-containing polymer particles are distilled off to a predetermined amount of water content by azeotropy of the dispersion medium and water under reflux. Thereafter, the dispersion medium is dried. Examples of the method for drying the polymer particles include hot air drying, infrared drying, indirect heating drying (vacuum drying, stirring type dryer, drum dryer) and the like, and a stirring type dryer is preferable.

  By employing the polymerization method of the present invention, particles having a true spherical shape are obtained, the fluidity is good, and the handling properties of the obtained particles are good. In addition, the spherical particles may contain agglomerated aggregates.

[Water-soluble polymer particles]
The polymer particles according to the present invention are water-soluble polymer particles. In the present invention, “water-soluble” means that the amount of water-insoluble matter measured by the following method is 0.5% or less.

<Measurement method of water-insoluble content>
In a 500 mL beaker, 1 g of polymer is dissolved in 499 g of water with stirring for 5 hours. The obtained aqueous polymer solution is filtered using a mesh having a mesh size of 100 μm and weighed in advance with 500 mL of water. The residue is dried with a mesh at 120 ° C. in a vacuum dryer for 6 hours, and the water-insoluble content is determined by the following formula (I).

Water insoluble content (%) =
[Amount of polymer residue after drying (g)] / [Amount of polymer when dissolved (g)] × 100 (I)
The average molecular weight of the polymer particles of the present invention is 4 million or more, preferably 4.5 million or more, more preferably 5 million or more, and particularly preferably 6 million or more from the viewpoint of having good spinnability. Further, from the viewpoint of water solubility, it is preferably 20 million or less, more preferably 14 million or less, and particularly preferably 10 million or less.

  In the present specification, the average molecular weight of the polymer particles was measured by gel permeation chromatography (GPC) under the following conditions, and the peak top molecular weight in terms of polyethylene glycol was defined as the average molecular weight.

<GPC measurement conditions>
Column: GMPWXL + GMPWXL (manufactured by Tosoh Corporation)
Developing solvent: 0.2 M phosphate buffer / CH ₃ CN = 9/1 (weight ratio)
Polymer concentration: 0.05 mg / mL
Flow rate: 0.5 mL / min
Temperature: 40 ° C.

  The average particle diameter of the polymer particles of the present invention is 20 μm or more, preferably 50 μm or more, more preferably 125 μm or more, from the viewpoint of the handleability of the product. Moreover, it is 2000 micrometers or less, Preferably it is 710 micrometers or less, More preferably, it is 300 micrometers or less.

  The average particle size of the polymer particles was determined using a sieve specified in JIS Z 8801. Using a 10-stage sieve and saucer with openings of 2000 μm, 1400 μm, 1000 μm, 710 μm, 500 μm, 355 μm, 250 μm, 180 μm, 125 μm and 106 μm, attach to a low-tap machine (manufactured by HEIKO SEISAKUSHO) and apply a 100 g sample for 10 minutes. After sieving by vibration (tapping: 156 times / min, rolling: 290 times / min), the weight of particles remaining on the pan and each sieve is measured. The opening of the sieve having a cumulative weight ratio of 50% or more from the fine powder side is set to a μm, the opening of the sieve that is one step larger than a μm is set to b μm, and the integration of the weight ratio from the tray to the sieve of a μm is c%, In addition, when the weight ratio on the a μm sieve is d%, the average particle diameter is obtained by the following formula (II).

Average particle size = 10 ^A (II)
[Where A = [50− (c−d / (log b−log a) × log b)] / [d / (log b−log a)]. ].

  From the viewpoint of blending the water-soluble polymer particles of the present invention with a detergent for clothing and improving the slipperiness of the clothing, it is preferable that the aqueous solution exhibits spinnability. The spinnability of the aqueous solution can be confirmed, for example, by the following method.

<Method for confirming spinnability>
When a 1.0% by weight aqueous solution of the obtained polymer was gently dropped from a height of 100 mm using a Pasteur pipette (glass, for example, ASAHITECHNO GLASS, IK-PAS-5P) having an inner diameter of 1 mm at 25 ° C. A solution in which a state in which a thread of 20 mm or more is spun from the tip of the Pasteur pipette is visually observed is referred to as an aqueous solution exhibiting spinnability.

  Further, the viscosity of a 1.0% by weight aqueous solution of the polymer can be used as an index of the degree of polymerization of the water-soluble polymer particles of the present invention. The viscosity is measured by the following method.

<Measurement method of viscosity>
Using a 200 mL beaker, 2 g of the polymer is stirred and dissolved with 198 g of water over 12 hours so as not to become mamaco. The prepared aqueous solution is adjusted to 25 ° C. ± 0.5 ° C. in a constant temperature water bath, and then measured using a B-type viscometer under the conditions of 25 ° C. and a rotational speed of 12 rpm.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these Examples.

Example 1
Sugar ester (S-770, Mitsubishi Chemical Foods Co., Ltd.) 6.00 g was dissolved in n-hexane 950 g and refluxed at about 62 ° C. in a nitrogen atmosphere. Then, AMPg sodium salt 665 g, 2,2′-azobis (2-Methylpropionamidine) dihydrochloride (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) 0.80 g (0.1 wt% monomer) dissolved in 590 g of ion-exchanged water over 1 hour The mixture was dropped and dispersed, and further stirred for 30 minutes. Only the aqueous phase was separated from the azeotropic reflux liquid and allowed to cool when the water content was reduced to 30% by weight. The obtained solid granular material was dried under reduced pressure to obtain 664 g of colorless granular AMPS sodium salt homopolymer (yield: 99.99%). 8%). The particle shape of the obtained polymer observed with a scanning electron microscope was almost spherical. The obtained particles were free flowing and had high fluidity.

Example 2
Sugar ester (S-770, Mitsubishi Chemical Foods) 6.00 g was dissolved in cyclohexane 800 g and refluxed at about 62 ° C. in a nitrogen atmosphere. AMPS 600 g, sodium hydroxide 160 g, acrylic acid 10 g, 2, 2'-azobis (2-methylpropionamidine) dihydrochloride (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) 2.40 g (0.3 wt% to monomer) dissolved in ion-exchanged water 510 g Was added dropwise over 1 hour to disperse and stirred for another 30 minutes. After azeotropic dehydration / drying as in Example 1, 672 g (99.4%) of colorless granular polymer (AMPS sodium salt / sodium acrylate = 95: 5 (molar ratio) copolymer) was obtained. The particle shape of the obtained polymer observed with a scanning electron microscope was almost spherical. The obtained particles were free flowing and had high fluidity.

Example 3
Sugar ester (S-770, Mitsubishi Chemical Foods Co., Ltd.) 6.00 g was dissolved in n-hexane 800 g and refluxed at about 62 ° C. under a nitrogen atmosphere. AMPS 600 g, sodium hydroxide 160 g, acrylic acid 10 g, 0.80 g (0.1% by weight to monomer) of 2,2′-azobis (2-methylpropionamidine) dihydrochloride (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 510 g of ion-exchanged water. The resulting mixture was added dropwise over 1 hour to disperse and stirred for another 30 minutes. After azeotropic dehydration / drying in the same manner as in Example 1, 674 g (99.7%) of colorless granular polymer (a copolymer of AMPS sodium salt / sodium acrylate = 95: 5 (molar ratio)) was obtained. The particle shape of the obtained polymer observed with a scanning electron microscope was almost spherical. The obtained particles were free flowing and had high fluidity.

Example 4
When 2.00 g of sugar ester (S-770, Mitsubishi Chemical Foods) was dissolved in 950 g of n-hexane and refluxed at about 62 ° C. in a nitrogen atmosphere, 440 g of AMPS sodium salt, polyethylene glycol dimethacrylate (NK) Ester 23G, Shin-Nakamura Chemical Co., Ltd. 0.011 g (0.0005 mol% to monomer), 2,2′-azobis (2-methylpropionamidyne) dihydrochloride (V-50, Wako Pure Chemical Industries, Ltd.) Co., Ltd.) 0.50 g (0.1% by weight to monomer) dissolved in 390 g of ion-exchanged water was dropped and dispersed over 1 hour, and the mixture was further stirred for 30 minutes. After azeotropic dehydration / drying as in Example 1, 438 g (yield 99.5%) of colorless granular polymer (AMPS sodium salt crosslinked polymer) was obtained. The particle shape of the obtained polymer observed with a scanning electron microscope was almost spherical. The obtained particles were free flowing and had high fluidity.

Example 5
Sugar ester (S-770, Mitsubishi Chemical Foods Co., Ltd.) 6.00 g was dissolved in 800 g of cyclohexane, and the pressure was reduced to 60 kPa under a nitrogen atmosphere and refluxed at about 55 ° C., and then 600 g of AMPS, 160 g of sodium hydroxide, 10 g of acrylic acid, 2,2′-azobis (2-methylpropionamidyne) dihydrochloride (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) 0.80 g (0.1% by weight to monomer) ion-exchanged water What was melt | dissolved in 560g was dripped and disperse | distributed over 1 hour, and also it stirred for 30 minutes. After azeotropic dehydration / drying in the same manner as in Example 1, 674 g (99.7%) of colorless granular polymer (a copolymer of AMPS sodium salt / sodium acrylate = 95: 5 (molar ratio)) was obtained. The particle shape of the obtained polymer observed with a scanning electron microscope was almost spherical. The obtained particles were free flowing and had high fluidity.

Comparative Example 1
A solution obtained by dissolving 1.00 g of sugar ester (S-770, Mitsubishi Chemical Foods) in 185 g of n-hexane, 20.0 g of AMPS, 2.70 g of sodium hydroxide, 0.055 g of ammonium persulfate (0.25 weight) % Of monomer) dissolved in 20 g of ion-exchanged water was dispersed, heated to 62 ° C. under a nitrogen atmosphere, and stirred for 3 hours. Only the aqueous phase was separated from the azeotropic reflux liquid and allowed to cool when the water content was reduced to 30% by weight. The obtained solid granular material was dried under reduced pressure to obtain 22.0 g of a colorless granular polymer (AMPS sodium salt homopolymer). (Yield 99.1%) was obtained. The particle shape of the obtained polymer observed with a scanning electron microscope was almost spherical. The obtained particles were free flowing and had high fluidity.

Comparative Example 2
Sugar ester (S-770, Mitsubishi Chemical Foods Co., Ltd.) 0.77 g was dissolved in n-hexane 234 g and refluxed at about 62 ° C. under a nitrogen atmosphere. AMPS sodium salt 165 g, acrylic acid 2.4 g, 2.90 g of 2,2′-azobis (2-methylpropionamidyne) dihydrochloride (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) (2.2 wt% monomer) was dissolved in 170 g of ion-exchanged water. The mixture was added dropwise over 1 hour to disperse and stirred for another 30 minutes. After azeotropic dehydration / drying as in Example 1, 168 g (yield 97.7%) of colorless granular polymer was obtained. The particle shape of the obtained polymer observed with a scanning electron microscope was almost spherical. The obtained particles were free flowing and had high fluidity.

Comparative Example 3
Sugar ester (S-770, Mitsubishi Chemical Foods Co., Ltd.) 0.77 g was dissolved in n-hexane 234 g and refluxed at about 62 ° C. under a nitrogen atmosphere. AMPS sodium salt 165 g, acrylic acid 2.4 g, Mercaptoethanol (Sigma Aldrich Japan Co., Ltd.) 0.34 g (0.6 mol% to monomer), 2,2′-azobis (2-methylpropionamidine) dihydrochloride (V-50, Wako Pure Chemical Industries, Ltd.) Co., Ltd.) 0.20 g (0.1% by weight to monomer) dissolved in 170 g of ion-exchanged water was dropped and dispersed over 1 hour, and the mixture was further stirred for 30 minutes. After azeotropic dehydration / drying as in Example 1, 164 g (yield 96.3%) of colorless granular polymer was obtained. The particle shape of the obtained polymer observed with a scanning electron microscope was almost spherical. The obtained particles were free flowing and had high fluidity.

  Table 1 shows the polymerization conditions of Examples 1 to 5 and Comparative Examples 1 to 3 and the physical properties of the obtained polymer particles.

Claims (4)

  It is obtained by a reverse phase suspension polymerization method using an aqueous solution of a monomer having a sulfonic acid group in all monomers or a salt thereof having a ratio of 60 to 100 mol%, a hydrophobic dispersion medium, and an azo radical polymerization initiator. Water-soluble polymer particles having an average molecular weight of 4 million or more and an average particle diameter of 20 to 2000 μm.   The water-soluble polymer particle according to claim 1, wherein the monomer concentration in the monomer aqueous solution is 50 to 90% by weight.   In the presence of an azo radical polymerization initiator, reverse phase suspension polymerization using an aqueous solution of a monomer having a sulfonic acid group or a salt thereof in an amount of 60 to 100 mol% and a hydrophobic dispersion medium in the presence of an azo radical polymerization initiator. A process for producing water-soluble polymer particles having an average molecular weight of 4 million or more and an average particle diameter of 20 to 2000 μm. The production method according to claim 3, wherein the polymerization is carried out without using a chain transfer agent.