Process for the preparation of water-soluble cationic polymer

Abstract: Process for the preparation of a dispersion of fine particles of a copolymer comprising an acrylic monomer containing a dialkylbenzylammonium group dispersed in an aqueous solution of a salt. Two cationic polymers are used in the polymerization of the above monomer in the aqueous solution of a salt. One of the cationic polymers is a (co)polymer comprising an acrylic monomer containing a trialkylammonium group which is soluble both in the aqueous solution of a salt and in water, while the other thereof is a copolymer comprising an acrylic monomer containing a dialkylbenzylammonium group which is soluble in water, but insoluble in the aqueous solution of a salt. The above aqueous solution of a salt is an aqueous solution of a polyvalent anion salt such as sulfate or phosphate. A dispersion of a water-soluble cationic polymer can be prepared by dissolving the above monomer in the aqueous solution and carrying out the polymerization in the presence of the above two polymers.

Description: The present invention relates to a process for the preparation of a, dispersion of a water-soluble cationic polar which is useful as a flocculant or dehydrating agent for waste water disposal or as a papermakers chemical. Known processes for the preparation of a water-soluble cationic polymer which is useful as a flocculant for waste water disposal or as a papermakers chemical include standing polymerization in an aqueous solution, water-in-oil emulsion polymerization (see, for example, Japanese Patent Laid-Open No. 102388/1979), suspension polymerization in a hydrophobic solvent (see, for example, Japanese Patent Laid-Open No. 69196/1979). Further, there has been disclosed a process for preparing a water-soluble, nonionic or anionic polymer by precipitation polymerization in an aqueous solution of ammonium sulfate (see, for example, Japanese Patent Laid-Open No. 70489/1975). Also there have been disclosed a process for carrying out the polymerization in an aqueous solution of a salt in the presence of a polyhydric alcohol (see, for example Japanese Patent Laid-Open No. 20502/1987) and a process for carrying out the polymerization in an aqueous solution of a salt in the presence of a polyelectrolyte as a dispersant (see, for example, Japanese Patent Laid-Open Nos.123610/1986, 20511/1987 and EP-A-183 466). The standing polymerization in an aqueous solution, however, must be carried out with a monomer concentration of at least 10% by weight in order to obtain a high-molecular weight polymer. Therefor, the product is given in a state of water-containing gel, so that it is difficult to dissolve the product as such. Accordingly, the product must be put on the market in a state of a low-concentration solution obtained by further diluting a product or must be dried and powdered. With respect to the low-concentration solution, the transportion cost is disadvantageously enhanced, while with respect to the powdering of the product, must heat energy is necessitated for drying the product and the product disadvantageously causes three-dimensional crosslinking by heating to insolubilize a part thereof. Meanwhile, the water-in-oil emulsion polymerization has a problem that a flammable and valuable organic solvent is consumed wastefully. Further, the suspension polymerization in a hydrophobic solvent has a problem that the production equipment costs a great deal, because a flammable material such as cyclohexane or toluene is used. The precipitation polymerization in an aqueous solution of ammonium sulfate has a problem that the formed polymers adhere to each other to form big lumps, resulting in difficult handling, though it is a preferable method with a low cost of equipment. Furthermore, it is difficult to prepare a polymer in a state of fine particle by using a conventional dispersant. The present invention relates to a process for dispersing a water-soluble cationic polymer in an aqueous solution of a polyvalent anion salt in a state of fine particle. In other words, it aims at providing a process for the preparation of a dispersion of a water-soluble cationic polymer which is easily flowable and easily soluble in spite of its high molecular weight. The present invention provides a process for the preparation of a dispersion of a water-soluble cationic polymer which process comprises polymerizing a water-soluble monomer mixture containing at least 5 mole % of a cationic monomer represented by the following general formula (I) in an aqueous solution of a polyvalent anion salt, characterized in that the polymerization is carried out in the presence of both a water-soluble cationic polymer (A) which is insoluble in said aqueous solution of a polyvalent anion salt and a water-soluble cationic polymer (B) which is soluble in said aqueous solution of a polyvalent anion salt, each polymer being used in an amount of 1 to 10% by weight based on the amount of the water-soluble monomer mixture; in that both water-soluble cationic polymers are coexistent at the beginning of polymerisation; in that said water-soluble cationic polymer contains at least 5 mole % of cationic monomer units represented by the following general formula (I); and in that said water-soluble cationic polymer (B) contains at least 20 mole % of cationic monomer units represented by the following general formula (II): wherein R₁ and R₄ are each H or CH₃; R₂, R₃, R₅ and R₆ are each an alkyl group having 1 to 2 carbon atoms; R₇ is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms; A₁ and A₂ are each an oxygen atom or NH; B₁ and B₂ are each an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group and X₁ ⊖ and X₂ ⊖ are each a counter anion. According to another aspect of the present invention there is provided a process for the preparation of a dispersion of a water-soluble cationic polymer which comprises polymerizing a water-soluble monomer mixture containing a cationic monomer represented by the general formula (I) in an aqueous solution of a polyvalent anion salt, characterized in that the formed water-soluble cationic polymer is precipitated in a state of fine particles and that the precipitation of the polymer is controlled so as to give fine particles of the polymer. In a preferred embodiment of the present process, the water-soluble cationic polymer is precipitated in an aqueous solution of a polyvalent anion salt, whereby the viscosity of the resultant dispersion is lowered and the separation of the polymer in the aqueous solution is inhibited. The process for the preparation of a dispersion of a water-soluble cationic polymer according to the present invention is characterized in that the three components described below are coexistent at the beginning of the polymerization, though other components may, if necessary, be used additionally: a water-soluble monomer mixture containing at least 5 mole % of a cationic monomer represented by the general formula (I): wherein R₁ is H or CH₃; R₂ and R₃ are each an alkyl group having 1 to 2 carbon atoms; A₁ is an oxygen atom or NH; B₁ is an alkylene group having 2 to 4 carbon atoms or a hydroxypropyl group and X₁ ⊖ is a counter anion, an aqueous solution of a polyvalent anion salt in which the above water-soluble monomer mixture is soluble and the polymer of the monomer mixture is insoluble, and a dispersant comprising a water-soluble cationic polymer insoluble in an aqueous solution of a polyvalent anion salt and a water-soluble cationic polymer soluble in an aqueous solution of a polyvalent anion salt as essential components. The polyvalent anion salt to be incorporated in the aqueous solution according to the present invention is suitably a sulfate or phosphate and particular examples thereof include ammonium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, ammonium hydrogenphosphate, sodium hydrogenphosphate and potassium hydrogenphosphate. In the present invention, these salts may be each used as an aqueous solution thereof having a concentration of 15% or above. The above cationic monomer represented by the general formula (I) includes quaternary ammonium salts obtained by the reaction of benzyl chloride with dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminohydroxypropyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide or dimethylaminopropylacrylamide. The monomer to be copolymerized with the cationic monomer represented by the general formula (I) includes (meth)acrylamide and cationic monomers represented by the general formula (II). wherein R₄ is H or CH₃; R₅ and R₆ are each an alkyl group having 1 to 2 carbon atoms; R₇ is H or an alkyl group having 1 to 2 carbon atoms; A₂ is an oxygen atom or NH; B₂ is an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group and X₂ ⊖ is a counter anion. Among the cationic monomers represented by the general formula (II), salts and methylated quaternary salts of dimethylaminohydroxypropyl (meth)acrylate or dialkylaminoethyl (meth)acrylate are particularly preferred. The cationic monomer represented by the general formula (II) is so highly hydrophilic that the excess use thereof hinders the precipitation of the generated polymer. Accordingly, the mol fraction of the cationic monomer represented by the general formula (II) must not exceed that of the monomer represented by the general formula (I). The polymerization concentration thereof is suitably selected in a range of 5 to 30% by weight. Of the two polymers to be added before the beginning of the polymerization for the purpose of obtaining a fine dispersion, the water-soluble cationic polymer insoluble in an aqueous solution of a polyvalent anion salt is preferably a product prepared by the process for the preparation of a water-soluble cationic polymer according to the present invention, which is because the dispersion prepared according to the present invention is easily handlable owing to its low viscosity (as compared with a case of adding the polymer as a viscous solution). The monomer composition of the polymer to be added need not always be equal to that of the objective polymer. Meanwhile, the water-soluble cationic polymer soluble in an aqueous solution of a polyvalent anion salt which is the other polymer is a cationic polymer comprising at least 20 mole % of a cationic monomer represented by the general formula (II) and the balance of (meth)acrylamide. These two polymers are each added in an amount of 1 to 10% by weight based on the total amount of the monomers used. The coexistence of a polyhydric alcohol such as glycerin or polyethylene glycol often further improves the state of precipitation. The polymerization according to the present invention is carried out by the use of a conventional water-soluble free-radical initiator. It is particularly preferable to use a water-soluble azo compound such as 2,2′-azobis(2-amidinopropane) hydrochloride or 2,2′-azobis(N,N-dimethyleneisobutyramidine) hydrochloride. The additional dissolution of various salts in the polymer dispersion after the completion of the polymerization is effective in lowering the viscosity of the polymer dispersion and in making the specific gravity of the aqueous solution equal to that of the polymer particle. It is preferable from the standpoint of workability that the viscosity of the dispersion be 1000 cP or below, while it is effective in inhibiting the separation of the polymer that the polymer particle and the aqueous solution have specific gravities equal to each other. The process for the preparation of a dispersion of a water-soluble cationic polymer according to the present invention is characterized in that the polymerization is carried out in an aqueous solution of a polyvalent anion salt to precipitate the generated water-soluble cationic polymer and that the precipitation is controlled so as to give the fine particle of the polymer. In this connection, the precipitation of a polymer with an aqueous solution of a polyvalent anion salt is a known phenomenon which is easily illustrated based on the Hofmeister's series. In the process for the preparation of a dispersion of a water-soluble cationic polymer according to the present invention, the benzyl group-containing cationic monomer unit represented by the general formula (I) is particularly easily salted out and an amide group is next easily salted out. The mechanism how the two polymers added as dispersants exhibit the effects is presumably that a suitable polymerization field is provided and the association is hindered by an electrical repulsive force, though it is not apparent. Particularly, a water-soluble cationic polymer insoluble in an aqueous solution of a polyvalent anion salt exhibits such complicated behavior as the dissolution thereof in the aqueous solution in the presence of the monomers. By way of illustration only, examples of the process for the preparation of a dispersion of a water-soluble cationic polymer according to the present invention will now be described. The present invention is not limited to the following Examples, but includes all embodiments as far as they are not deviated from the scope of the technical idea constituted of the matters described in the claim. Example 1 2.5g of an acryloyloxyethyldimethylbenzylammonium chloride-acrylamide copolymer having a degree of cationization of 10 mole %, 2.5g of polyacryloyloxyethyltrimethylammonium chloride, 335g of ion-exchanged water, 112.5g of ammonium sulfate, 35.1g of acrylamide and 14.9g of acryloyloxyethyldimethylbenzylammonium chloride were placed in a 1ℓ five-necked separable flask fitted with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube. The resulting system was purged with nitrogen. 1mℓ of a 1% aqueous solution of 2,2′-azobis(2-amidinopropane) hydrochloride was added to the flask to carry out the polymerization at a bulk temperature of 50°C for 10 hours. The particle size of the polymer in the obtained dispersion was 10µm or below and the viscosity of the dispersion was 500 cP. Comparative Example 1 335g of ion-exchanged water, 112.5g of ammonium sulfate, 35.1g of acrylamide and 14.9g of acryloyloxyethyldimethylbenzylammonium chloride were placed in the same five-necked separable flask as that used in Example 1. The resulting system was purged with nitrogen. 1mℓ of a 1% aqueous solution of 2,2′-azobis(2-amidinopropane) hydrochloride was added to the flask to carry out the polymerization at a bulk temperature of 50°C for 10 hours. The particle size of the obtained polymer was 2 to 3mm and the polymer immediately settled out. Example 2 17.5kg of ion-exchanged water, 5kg of ammonium sulfate, 3.2kg of acrylamide, 1.33kg of acryloyloxyethyldimethylbenzylammonium chloride, 1.1kg of a 20% aqueous solution of polyacryloyloxyethyltrimethylammonium chloride and 1.5kg of the polymer dispersion prepared in Example 1 were placed in a 35ℓ jacketed reaction vessel made of stainless steel and fitted with an agitating blade of a ribbon type. The resulting system was purged with nitrogen. 1g of 2,2′-azobis(2-amidinopropane) hydrochloride was added to the vessel to carry out the polymerization at a bulk temperature of 50°C for 10 hours. The particle size of the polymer in the obtained dispersion was 10µm or below and the viscosity of the dispersion was 2500 cP. 1.3kg of ammonium sulfate was further added to the dispersion. The viscosity of the resulting dispersion was 230 cP, though the particle size was unchanged. Comparative Example 2 17.5kg of ion-exchanged water, 5kg of ammonium sulfate, 3.2kg of acrylamide, 1.33kg of acryloyloxyethyldimethylbenzylammonium chloride and 1.1kg of a 20% aqueous solution of polyacryloyloxyethyltrimethylammonium chloride were placed in the same reaction vessel as that used in Example 2. The resulting system was purged with nitrogen. 1g of 2,2′-azobis(2-amidinopropane) hydrochloride was added to the reaction vessel to carry out the polymerization at a bulk temperature of 50°C for 10 hours. The particle size of the polymer in the obtained dispersion was 100µm. Example 3 15.7kg of ion-exchanged water, 4.6kg of ammonium sulfate, 2.1kg of acrylamide, 3.1kg of acryloyloxyethyldimethylbenzylammonium chloride, 0.9kg of acryloyloxyethyltrimethylammonium chloride, 0.1kg of glycerin, 1.5kg of a 20% aqueous solution of polyacryloyloxyethyltrimethylammonium chloride and 1.5kg of the polymer dispersion prepared in Example 1 were placed in the same reaction vessel as that used in Example 2. The resulting system was purged with nitrogen. 1g of 2,2′-azobis(2-amidinopropane) hydrochloride was added to the reaction vessel to carry out the polymerization at a bulk temperature of 50°C for 10 hours. The particle size of the polymer in the obtained dispersion was 10µm or below and the viscosity of the dispersion was 3200 cP. 2.1kg of ammonium sulfate was further added to the dispersion. The viscosity of the resulting dispersion was 280 cP, though the particle size was unchanged. Comparative Example 3 15.7kg of ion-exchanged water, 4.6kg of ammonium sulfate, 2.1kg of acrylamide, 0.9kg of acryloyloxyethyltrimethylammonium chloride, 0.1kg of glycerin and 1.5kg of a 20% aqueous solution of polyacryloyloxyethyltrimethylammonium chloride were placed in the same reaction vessel as that used in Example 2. The resulting system was purged with nitrogen. 1g of 2,2′-azobis(2-amidinopropane) hydrochloride was added to the reaction vessel at a bulk temperature of 50°C for 10 hours. The particle size of the polymer in the obtained dispersion was about 100µm. Example 4 17.0kg of ion-exchanged water, 4.2kg of ammonium sulfate, 0.4kg of acrylamide, 3.9kg of acryloyloxyethyldimethylbenzylammonium chloride, 1.7kg of acryloyloxyethyltrimethylammonium chloride and 2.5kg of a 20% aqueous solution of polyacryloyloxyethyltrimethylammonium chloride were placed in the same reaction vessel as that used in Example 2, followed by the addition of 2.5kg of a fine dispersion of an acrylamide-acryloyloxyethyldimethylbenzylammonium chloride copolymer having a degree of cationization of 80 mole % (containing 200% by weight of the copolymer and 20% by weight of ammonium sulfate). The resulting system was purged with nitrogen. 1g of 2,2′-azobis(N,N′-dimethyleneisobutyramidine) hydrochloride was added to the reaction vessel to carry out the polymerization at a bulk temperature of 45°C for 10 hours. After the completion of the polymerization, 0.5kg of ammonium chloride was added to the reaction vessel. The particle size of the polymer in the obtained dispersion was about 10µm or below and the viscosity of the dispersion was 400 cP. Comparative Example 4 17.0kg of ion-exchanged water, 4.2kg of ammonium sulfate, 0.4kg of acrylamide, 3.9kg of acryloyloxyethyldimethylbenzylammonium chloride, 1.7kg of acryloyloxyethyltrimethylammonium chloride and 2.5kg of a 20% aqueous solution of polyacryloyloxyethyltrimethylammonium chloride were placed in the same reaction vessel as that used in Example 2. The resulting system was purged with nitrogen. 1g of 2,2′-azobis(N,N′-dimethyleneisobutyramidine) hydrochloride was added to the reaction vessel to carry out the polymerization at a bulk temperature of 45°C for 10 hours. After the completion of the polymerization, 0.5kg of ammonium chloride was added to the vessel, followed by mixing. The particle size of the polymer in the obtained dispersion was about 100µm. Example 5 18.3kg of ion-exchanged water, 1.5kg of anhydrous sodium sulfate, 3.5kg of anhydrous aluminum sulfate, 3.1kg of acrylamide, 1.4kg of acrylamidopropyldimethylbenzylammonium chloride, 1kg of a 20% aqueous solution of polyacrylaminopropyltrimethylammonium chloride and 0.2kg of an acrylamidopropyldimethylbenzylammonium chlorideacrylamide copolymer having a degree of cationization of 10 mole % were placed in the same reaction vessel as that used in Example 2. The resulting system was purged with nitrogen. 1g of 2,2′-azobis (2-amidinopropane) hydrochloride was added to the vessel to carry out the polymerization at a bulk temperature of 50°C for 10 hours. The particle size of the polymer in the obtained dispersion was 10µm or below and the viscosity of the dispersion was 3000 cP. 1kg of sodium chloride was added to the dispersion. The viscosity of the resulting dispersion was 780 cP, though the particle size was unchanged. Comparative Example 5 18.3kg of ion-exchanged water, 1.5kg of anhydrous sodium sulfate, 3.5kg of anhydrous aluminum sulfate, 3.1kg of acrylamide, 1.4kg of acrylamidopropyldimethylbenzylammonium chloride and 1kg of a 20% aqueous solution of polyacrylamidopropyltrimethylammonium chloride were placed in the same reaction vessel as that used in Example 2. The resulting system was purged with nitrogen. 1g of 2,2′-azobis(2-amidinopropane) hydrochloride was added to the reaction vessel to carry out the polymerization at a bulk temperature of 50°C for 10 hours. The particle size of the polymer in the obtained dispersion was 100µm.

Claims: A process for the preparation of a dispersion of a water-soluble cationic polymer which process comprises polymerizing a water-soluble monomer mixture containing at least 5 mole % of a cationic monomer represented by the following general formula (I) in an aqueous solution of a polyvalent anion salt, characterized in that the polymerisation is carried out in the presence of both a water-soluble cationic polymer (A) which is insoluble in said aqueous solution of a polyvalent anion salt and a water-soluble cationic polymer (B) which is soluble in said aqueous solution of a polyvalent anion salt, each polymer being used in an amount of 1 to 10% by weight based on the amount of the water-soluble monomer mixture; in that both water-soluble cationic polymers are coexistent at the beginning of polymerisation; in that said water-soluble cationic polymer (A) contains at least 5 mole % of cationic monomer units represented by the following general formula (I); and in that said water-soluble cationic polymer (B) contains at least 20 mole % of cationic monomer units represented by the following general formula (II): wherein R₁ and R₄ are each H or CH₃; R₂, R₃, R₅ and R₆ are each an alkyl group having 1 to 2 carbon atoms; R₇ is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms; A₁ and A₂ are each an oxygen atom or NH; B₁ and B₂ are each an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group and X₁ and X₂ are each a counter anion. A process according to claim 1, wherein the cationic monomer represented by the general formula (II) is selected from salts and methylated quaternary ammonium salts of dimethylaminohydroxypropyl(meth)acrylate, dialkylaminoethyl (meth)acrylate and mixtures thereof. A process according to claim 1, wherein the cationic monomer represented by the general formula (II) is (meth)acryloyloxyethyltrimethylammonium chloride. A process according to any one of claims 1 to 3, wherein the water-soluble monomer to be copolymerized with the cationic monomer represented by the general formula (I) is selected from (meth)acrylamide, cationic monomers represented by the general formula (II) and mixtures thereof, with the proviso that the mol fraction of the cationic monomer represented by the general formula (II) is lower than that of the cationic monomer represented by the general formula (I). A process according to any one of the preceding claims, wherein said water-soluble cationic polymer insoluble in an aqueous solution of a polyvalent anion salt comprises at least 5 mole % of cationic monomer units represented by the general formula (I) and the balance of one-member selected from (meth)acrylamide, cationic monomers represented by the general formula (II) and mixtures thereof. A process according to any one of the preceding claims, wherein the monomer units constituting said water-soluble cationic polymer soluble in an aqueous solution of a polyvalent anion salt are all represented by the general formula (II). A process according to any one of the preceding claims, wherein said cationic monomer represented by the general formula (I) is selected from benzylated quaternary ammonium salts of dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminohydroxypropyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, dimethylaminopropylacrylamide and mixtures thereof. A process according to any one of claims 1 to 6, wherein said cationic monomer represented by the general formula (I) is (meth)acryloyloxyethyldimethylbenzylammonium chloride. A process according to any one of the preceding claims, wherein the water-soluble cationic polymer insoluble in an aqueous solution of a polyvalent anion salt is added to the monomer solution as fine particles dispersed in an aqueous solution of a polyvalent anion salt. A process according to any one of the preceding claims, wherein the polyvalent anion salt concentration of the aqueous solution is 15% by weight or more. A process according to any one of the preceding claims, wherein said polyvalent anion salt is a sulfate, a phosphate or a mixture thereof. A process according to claim 11, wherein said polyvalent anion salt is ammonium sulfate. A process according to any one of the preceding claims, wherein a salt is additionally dissolved in the dispersion after the completion of the polymerization. A process according to any one of the preceding claims, wherein the specific gravity of the polymer in the dispersion is equal to that of the aqueous solution. A process according to any one of the preceding claims, wherein the viscosity of the polymer dispersion is 1000 cP or below. A process according to any one of the preceding claims, wherein the water-soluble monomer concentration based on the total amount of the aqueous solution is 5 to 30% by weight. A process according to any one of the preceding claims, wherein a water-soluble azo free-radical initiator is used as a polymerization initiator. A process according to claim 17, wherein the polymerization initiator is selected from 2,2'-azobis(2-amidinopropane) hydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutyramidine) hydrochloride and mixtures thereof. A process according to any one of the preceding claims, wherein the particle size of the polymer is 10 µm or below.

Inventors: KAWANO MUTSUMI, TAKEDA HISAO, KAWANO, MUTSUMI, TAKEDA, HISAO
Applicants: KYORITSU YUKI CO LTD, KYORITSU YUKI CO. LTD.
Application year: 1989
Main classification: C08F220
IPC codes: C08F20, D21H17, C08F2, C08F220