Polymer, method for producing polymer and polymer flocculant

Abstract

Provided is a polymer flocculant which is capable of controlling the structure of a polymer that is a copolymerization product of a monomer (a) having a structure derived from formula (I) in each molecule and a water-soluble unsaturated monomer (b) having a polymerizable unsaturated bond in each molecule, and which has a branched or cross-linking structure, and is excellent in water-solubility and water dispersibility, ##STR00001## In formula (I), R.sub.1 and R.sub.2 are respectively a linear or branched functional group configured of atoms selected from the group consisting of carbon not having a carbon-carbon unsaturated bond, oxygen, nitrogen, and hydrogen; W is a non-metal element of the group 15; X and Y are each a linear or branched functional group configured of atoms selected from the group consisting of carbon, oxygen, nitrogen, and hydrogen, and each have at least one carbon-carbon unsaturated bond, provided that X and Y have different structures; and Z is a chlorine ion, a bromine ion, or an iodine ion.

Claims

1. A copolymer, comprising, in polymerized form: a cross-linkable monomer (a) of formula (II), ##STR00013## R.sub.10 and R.sub.11 independently being a linear or branched alkyl group comprising 1 to 6 carbon atoms, R.sub.7 being H or a methyl group, R.sub.8 being O or NH, R.sub.9 being C.sub.nH.sub.2n with n being in a range of 1 to 6, R.sub.12 being H, a methyl group, or an alkyl ester group having a linear, branched, or cyclic structure comprising 1 to 6 carbon atoms, and Z is a chlorine ion, a bromine ion, or an iodine ion; and a water-soluble unsaturated monomer (b) having a polymerizable unsaturated bond in the molecule, wherein, in the copolymer, units from the monomer (a) are in a range of from 0.001 to 1.0% by mass with respect to 100% by mass of units from the monomer (b), and wherein, when a viscosity of the copolymer is measured by a rotatory viscometer, at a temperature of 25° C. and a rotation rate of 60 rpm, as an aqueous solution of 0.5 mass %, the viscosity is greater than or equal to 5 mPa.Math.s and less than or equal to 10000 mPa.Math.s.

2. A polymer flocculant, comprising: the copolymer of claim 1.

3. A paper strengthening agent, comprising: the copolymer of claim 1.

4. A method for producing a polymer flocculant including the copolymer of claim 1, the method comprising: dissolving the cross-linkable monomer (a) and the water-soluble unsaturated monomer (b) in water; and polymerizing the cross-linkable monomer (a) and the water-soluble unsaturated monomer (b) dissolved in water in a homogeneous system.

5. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00014## wherein Z is chloride and/or bromide.

6. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00015## wherein Z is chloride and/or bromide.

7. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00016## wherein Z is chloride and/or bromide.

8. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00017## wherein Z is chloride and/or bromide.

9. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00018## wherein Z is chloride and/or bromide.

10. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00019## wherein Z is chloride and/or bromide.

11. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00020## wherein Z is chloride and/or bromide.

12. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00021## wherein Z is chloride and/or bromide.

13. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00022## wherein Z is chloride and/or bromide.

14. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00023## wherein Z is chloride and/or bromide.

15. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00024## wherein Z is chloride and/or bromide.

16. The copolymer of claim 1, wherein the cross-linkable monomer (a) of formula (II) comprises ##STR00025## wherein Z is chloride and/or bromide.

17. A copolymer, comprising, in polymerized form: a cross-linkable monomer (a) of a formula ##STR00026## wherein Z is chloride and/or bromide; and a water-soluble unsaturated monomer (b) having a polymerizable unsaturated bond in the molecule, wherein, in the copolymer, units from the monomer (a) are in a range of from 0.001 to 1.0% by mass with respect to 100% by mass of units from the monomer (b).

18. A polymer flocculant, comprising: the copolymer of claim 17.

19. A paper strengthening agent, comprising: the copolymer of claim 17.

Description

EXAMPLES

(1) Hereinafter, the invention will be described in detail by examples, but the invention is not limited thereto. Furthermore, in the examples, “%” indicates mass %, unless otherwise noted.

(2) First, the invention will be described in detail by the examples, as a flocculant application.

(3) Furthermore, in examples and comparative examples, measured values of a 0.5% viscosity, a 0.5% salt viscosity, and a 0.5% insoluble content of a polymer flocculant, were obtained by performing measurement with respect to a powder-like polymer flocculant, according to the following method.

(4) (Measurement of 0.5% Viscosity)

(5) 2.5 g of a sample was dissolved in water, and thus, 500 g of a polymer aqueous solution of 0.5% was prepared. Regarding the polymer aqueous solution, the viscosity of the polymer aqueous solution after 5 minutes was measured in a condition of a temperature of 25° C. and a rotation rate of 60 rpm, by using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.).

(6) (Measurement of 0.5% Salt Viscosity)

(7) 2.5 g of a sample was dissolved in a sodium chloride aqueous solution of 4%, and thus, 500 g of a polymer aqueous solution of 0.5% was prepared. Regarding the polymer aqueous solution, the salt viscosity of the polymer aqueous solution after 5 minutes was measured in a condition of a temperature of 25° C. and a rotation rate of 60 rpm, by using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.).

(8) (Measurement of 0.5% Insoluble Content)

(9) The total amount (500 g) of the polymer aqueous solution of 0.5%, obtained in advance was filtered through a 80-mesh sieve having a diameter of 20 cm, the moisture was wiped off, and the insoluble content remaining on the sieve was collected, and thus, the mass of the insoluble content was measured by using an electronic balance (manufactured by SHINKO DENSHI CO., LTD.).

Synthesis Example 1

(10) 10.0 g of allyl bromide and 40.0 g of tetrahydrofuran (THF) were put into a beaker of 100 mL, and thus, a THF solution of allyl bromide was obtained. The obtained THF solution of allyl bromide was transfused into a dropping funnel of 100 mL. Next, 10.85 g of dimethyl aminopropyl acrylamide (DMPAA) and 40.0 g of tetrahydrofuran (THF) were put into an eggplant flask of 200 mL, and thus, a THF solution of DMPAA was obtained.

(11) Further, the THF solution of allyl bromide was dropped into the THF solution of DMPAA for 20 minutes while stirring the THF solution of DMPAA with a magnetic stirrer, and was stirred for 2 hours after the dropping was ended, and thus, a precipitate was obtained. After the stirring was ended, standing still was performed for 12 hours, and the supernatant was removed, and then, decantation was performed in 200 mL of THF.

(12) After that, the obtained precipitate was dried under reduced pressure, and thus, a white to pale yellow cross-linkable monomer (a) was obtained.

Synthesis Example 2

(13) The same operation as that of Synthesis Example 1 was performed except that 10.85 g of dimethyl aminopropyl acrylamide was changed to 9.95 g of dimethyl aminoethyl acrylate (DMEA), and thus, a cross-linkable monomer (a) was obtained.

(14) [Test 1: Production of Polymer Flocculant]

(15) A polymer flocculant of each of the examples and each of the comparative examples was produced according to the following method. In addition, the abbreviations of a water-soluble unsaturated monomer and a copolymerizable monomer component in Table 1 and the following description, are as follows.

(16) AAm: Acrylamide (manufactured by Wako Pure Chemical Industries, Ltd.)

(17) DME: Methyl Chloride Salt of N′-N′-Dimethyl Aminoethyl Acrylate (manufactured by Osaka Organic Chemical Industry Ltd.)

(18) MBAAM: Methylene Bisacrylamide (manufactured by Tokyo Chemical Industry Co., Ltd.)

Example 1-1

(19) 250 g of AAm and 0.025 g of a cross-linkable monomer (III-1) were put into a brown bottle of 1000 mL, and distilled water was added such that the total monomer concentration was set to 50%, and the total mass was set to 500 g, and thus, a monomer reaction liquid (AAm/Cross-Linkable Monomer (III-1)=99.99/0.01(%)) was prepared.

(20) Further, DAROCUR-1173 (hereinafter, simply referred to as “D-1173”) (manufactured by Ciba Specialty Chemicals) as a photoinitiator, and a hypophosphorous acid (hereinafter, simply referred to as “HPA”) (manufactured by KANTO CHEMICAL CO., INC.) as a chain transfer agent, were put into the monomer reaction liquid such that the amounts were respectively set to 100 ppm and 50 ppm with respect to the total mass of the monomer reaction liquid, and a solution temperature was adjusted to 25° C. while blowing nitrogen gas for 15 minutes. After that, the monomer reaction liquid was transferred to a stainless steel reaction vessel, was irradiated with a chemical lamp having irradiation intensity of 0.2 W/m.sup.2 for 20 minutes, and thus, polymerization was performed. Accordingly, a hydrogel-like polymer was obtained.

(21) The hydrogel-like polymer was taken out from the vessel, and was crushed by using a small meat chopper. The crushed hydrogel-like polymer was dried at temperature of 70° C. for 16 hours, and then, was pulverized, and thus, a powder-like polymer (A-1) was obtained.

Example 1-2

(22) The same operation as that of Example 1-1 was performed except that the amount of HPA was changed to 100 ppm.

Example 1-3

(23) The same operation as that of Example 1-1 was performed except that the amount of HPA was changed to 200 ppm.

Example 1-4

(24) The same operation as that of Example 1-3 was performed except that the amount of HPA was changed to 500 ppm, and the amount of the cross-linkable monomer (III-1) to be put was changed to 0.050 g (AAm/Cross-Linkable Monomer (III-1)=99.985/0.02(%)).

Example 1-5

(25) The same operation as that of Example 1-3 was performed except that the cross-linkable monomer (III-1) was changed to a cross-linkable monomer (III-5).

Example 1-6

(26) 55 g of AAm, 387.5 g of a DME aqueous solution of 80 wt %, and 0.01 g of the cross-linkable monomer (III-1) were put into a brown bottle of 1000 mL, distilled water was added such that the total monomer concentration was set to 73%, and the total mass was set to 500 g, and thus, a monomer reaction liquid (AAm/DME/Cross-Linkable Monomer (III-1)=15.067/84.930/0.003(%)) was prepared.

(27) Further, D-1173 as a photoinitiator, and a hypophosphorous acid as a chain transfer agent, were put into the monomer reaction liquid such that the amounts were respectively set to 20 ppm and 20 ppm with respect to the total mass of the monomer reaction liquid, and a solution temperature was adjusted to 25° C. while blowing nitrogen gas for 15 minutes.

(28) After that, the monomer reaction liquid was transferred to a stainless steel reaction vessel, was irradiated with a chemical lamp having irradiation intensity of 0.2 W/m.sup.2 for 20 minutes, and thus, polymerization was performed. Accordingly, a hydrogel-like polymer was obtained.

(29) The hydrogel-like polymer was taken out from the vessel, and was crushed by using a small meat chopper. The crushed hydrogel-like polymer was dried at a temperature of 70° C. for 16 hours, and then, was pulverized, and thus, a powder-like polymer (A-2) was obtained.

Example 1-7

(30) 55 g of AAm, 387.5 g of a DME aqueous solution of 80 wt %, and 0.045 g of the cross-linkable monomer (III-1) were put into a brown bottle of 1000 mL, and distilled water was added such that the total monomer concentration was set to 73%, and the total mass was set to 500 g, and thus, a monomer reaction liquid (AAm/DME/Cross-Linkable Monomer (III-1)=15.066/84.921/0.013(%)) was prepared.

(31) Further, D-1173 as a photoinitiator, and HPA as a chain transfer agent were put into the monomer reaction liquid such that the amounts were respectively set to 130 ppm and 50 ppm with respect to the total mass of the monomer reaction liquid, and a solution temperature was adjusted to 25° C. while blowing nitrogen gas for 15 minutes.

Comparative Example 1-1

(32) A polymer (B-1) was obtained by performing the same operation as that of Example 1-1, except that the cross-linkable monomer (III-1) was not used.

Comparative Example 1-2

(33) The same operation as that of Example 1-1 was performed except that the cross-linkable monomer (III-1) was changed to MBAAM (AAm/MBAAM=99.99/0.01).

Comparative Example 1-3

(34) The same operation as that of Comparative Example 1-2 was performed except that the amount of HPA was changed to 100 ppm.

Comparative Example 1-4

(35) The same operation as that of Comparative Example 1-2 was performed except that the amount of HPA was changed to 200 ppm.

Comparative Example 1-5

(36) A polymer (B-2) was obtained by performing the same operation as that of Example 1-6, except that the cross-linkable monomer (III-1) was not used, the water-soluble unsaturated monomer was changed to only AAm and a DME aqueous solution of 80 wt %, and the amount of HPA was changed to 26 ppm.

(37) In each of the (co)polymers obtained in Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-5, a 0.5% viscosity, a 0.5% salt viscosity, and a 0.5% insoluble content were measured. The results are shown in Table 1.

(38) TABLE-US-00001 TABLE 1 Water-Soluble Concentration of Cross- Amount of Concentration 0.5% 0.5% Salt 0.5% Insoluble Unsaturated Cross-Linkable Linkable Monomer HPA of D-1173 Viscosity Viscosity Content Monomer Monomer (ppm) (ppm) (ppm) (mPa .Math. s) (mPa .Math. s) (g) Example 1-1 AAm Cross-Linkable 100 50 100 10.0 24.1 0.2 (Polymer A-1) Monomer (III-1) Example 1-2 AAm Cross-Linkable 100 100 100 9.1 14.9 0.3 Monomer (III-1) Example 1-3 AAm Cross-Linkable 100 200 100 9.5 10.9 0 Monomer (III-1) Example 1-4 AAm Cross-Linkable 500 200 100 8.8 10.4 0.6 Monomer (III-1) Example 1-5 AAm Cross-Linkable 100 200 100 8.3 9.8 0.1 Monomer (III-5) Example 1-6 AAm/DME Cross-Linkable 30 20 20 3060 53 20 (Polymer A-2) Monomer (III-1) Example 1-7 AAm/DME Cross-Linkable 130 50 130 2820 39 20 Monomer (III-1) Comparative AAm — — 50 14.4 24 0 Example 1-1 (Polymer B-1) Comparative AAm MBAAM 100 50 31.3 — 117.5 Example 1-2 Comparative AAm MBAAM 100 100 59.4 — 135.6 Example 1-3 Comparative AAm MBAAM 100 200 15.9 — 128.9 Example 1-4 Comparative AAm/DME — — 26 20 2570 40 0 Example 1-5 (Polymer B-2) ※ AAm: Acrylamide ※ DMPAA-Allyl: Synthesized Cross-Linking Agent ※ MBAAM: Commercially Available Cross-Linking Agent

(39) [Test 2: Sludge Treatment]

(40) A kaolinite aqueous solution of 3% was prepared as a model sample of sludge, and 300 mL of digestive sludge was sampled into a beaker of 500 mL. Next, the polymer of the type shown in Table 2, was formed into a polymer aqueous solution of 0.3% by distilled water, and the polymer aqueous solution was added to the digestive sludge by the added amount shown in Table 2. Next, a flock was generated by stirring the digestive sludge for 30 seconds with a metal spatula, and the flock was filtered by a sieve with a mesh of 2 mm square, and thus, it was determined that a grain diameter of a flock which passed through the mesh, was less than 2 mm, and a grain diameter of a flock which did not pass through the mesh, was greater than or equal to 2 mm. In addition, a settling time of the flock was determined. The grain diameter and the settling time of the flock are shown in Table 2.

(41) TABLE-US-00002 TABLE 2 Added Flock Settling Amount Grain Diameter Time Polymer (ppm) (mm) (second) Example 2-1 A-1 160 Greater than or 14 equal to 2 mm Comparative B-1 160 Less than 2 mm 21 Example 2-1 Model Sludge: Kaolinite Aqueous Solution of 3% Added Amount of Flocculant: 160 ppm

(42) Further, digestive sludge of a certain sewage treatment plant was prepared as a sample of the sludge, and 300 mL of the digestive sludge was sampled into a beaker of 500 mL. Next, the polymer of the type shown in Table 3, was formed into a polymer aqueous solution of 0.5% by distilled water, and the polymer aqueous solution was added to the digestive sludge by the added amount shown in Table 3. Next, a flock was generated by stirring the digestive sludge for 30 seconds with a metal spatula, and the flock was filtered by a sieve with a mesh of 15 mm square, and thus, it was determined that a grain diameter of a flock which passed through the mesh, was less than 15 mm, and a grain diameter of a flock which did not pass through the mesh, was greater than or equal to 15 m.

(43) In addition, a flock strength was determined as follows. The grain diameter and the strength of the flock are shown in Table 3.

(44) (Flock Strength)

(45) A. In a case where the flock is crushed with hands, an elastic force to rebound is felt.

(46) B: In a case where the flock is crushed with hands, the flock does not rebound, and the elastic force is not felt.

(47) TABLE-US-00003 TABLE 3 Added Flock Amount Grain Diameter Flock Polymer (ppm) (mm) Strength Example 2-2 A-2 160 Greater than or A equal to 15 mm Comparative B-2 160 Less than 15 mm B Example 2-2 Sludge: N Sewage Treatment Plant Added Amount of Flocculant: 160 ppm

(48) From Table 1, it was known that a polymer with less insoluble content of 0.5% was able to be obtained by using the cross-linkable monomer (a). On the other hand, it was known that a polymer having a high 0.5% insoluble content was obtained in a case of using MBAAM.

(49) Further, as it is obvious from Table 2, in a case where the model sludge was subjected to a flocculation treatment by using the polymer obtained in Example 1-1 (Example 2-1), a grain diameter of a flock to be obtained was large, a settling time was fast, and drainage was excellent.

(50) In addition, as it is obvious from Table 3, in a case where the actual sludge was subjected to the flocculation treatment by using the polymer obtained in Example 1-6 (Example 2-2), a grain diameter of a flock to be obtained was large, and a strength was also high. Accordingly, it was confirmed that the polymer obtained in Example 1-1 and Example 1-6, was excellent in the flocculation performance.

(51) On the other hand, in the case of using the polymer obtained in Comparative Example 1-1 (Comparative Example 2-1), a grain diameter of a flock was small, a settling rate was slow, and drainage was poor, compared to the examples. Further, in the case of using the polymer obtained in Comparative Example 1-5 (Comparative Example 2-2), a grain diameter of a flock was small, and a strength was also low, compared to the examples. Accordingly, the polymer obtained in Comparative Example 1-1, was not excellent in the flocculation performance, compared to the examples.

(52) Next, the invention will be described in detail by the example, as a paper strengthening agent application.

(53) Furthermore, in the examples and the comparative examples, measured values of a 15% viscosity and a molecular weight, were obtained by performing measurement with respect to a powder-like paper strengthening agent, according to the following method.

(54) (Measurement of 15% Viscosity)

(55) 15 g of a sample was dissolved in water, and thus, 100 g of a polymer aqueous solution of 15% was prepared. Regarding the polymer aqueous solution, the viscosity of the polymer aqueous solution after 5 minutes was measured in a condition of a temperature of 25° C. and a rotation rate of 3 rpm, by using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.).

(56) (Measurement of Weight Average Molecular Weight)

(57) 0.05 g of a sample was dissolved in water, and thus, 20 g of a polymer aqueous solution of 0.5% was prepared. Next, the polymer aqueous solution was dissolved in an aqueous solution in which sodium chloride and an acetic acid were respectively 0.5 mol/1, and thus, a polymer aqueous solution of 0.1% was prepared.

(58) A weight average molecular weight Mw was measured by using the polymer aqueous solution, with GPC (manufactured by SHIMADZU CORPORATION). Furthermore, the measurement was performed at a flow rate of 0.5 ml/min, by using pullulan as a standard substance.

(59) [Test 3: Production of Polymer Paper Strengthening Agent]

(60) A polymer paper strengthening agent of each of the examples and each of the comparative examples was produced according to the following method. In addition, the abbreviations of a water-soluble unsaturated monomer and a copolymerizable monomer component in Table 4 and the following description, are as follows.

(61) AAm: Acrylamide (manufactured by Wako Pure Chemical Industries, Ltd.)

(62) DM: N′-N′-Dimethyl Aminoethyl Methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.)

(63) IA: Itaconic Acid (manufactured by Wako Pure Chemical Industries, Ltd.)

Example 3-1

(64) 176.6 g of AAm, 16.6 g of DM, 6.8 g of IA, and 0.5 g of the cross-linkable monomer (III-1) were put into a brown bottle of 1000 mL, and distilled water was added such that the total monomer concentration was set to 40%, and the total mass was set to 500 g, and thus, a monomer reaction liquid (AAm/DM/IA/Cross-Linkable Monomer (III-1)=88.08/8.28/3.39/0.25(%)) was prepared.

(65) Further, D-1173 as a photoinitiator, and a hypophosphorous acid as a chain transfer agent, were put into the monomer reaction liquid such that the amounts were respectively set to 20 ppm and 1000 ppm with respect to the total mass of the monomer reaction liquid, and a solution temperature was adjusted to 25° C. while blowing nitrogen gas for 15 minutes.

(66) After that, the monomer reaction liquid was transferred to a stainless steel reaction vessel, and was irradiated with a chemical lamp having irradiation intensity of 0.2 W/m.sup.2 for 20 minutes, and thus, polymerization was performed. Accordingly, a hydrogel-like polymer was obtained.

(67) The hydrogel-like polymer was taken out from the vessel, and was crushed by using a small meat chopper. The crushed hydrogel-like polymer was dried at a temperature of 70° C. for 16 hours, and then, was pulverized, and thus, a powder-like polymer (C-1) was obtained.

Comparative Example 3-1

(68) A polymer (C-2) was obtained by performing the same operation as that of Example 3-1, except that the cross-linkable monomer (III-1) was changed to only AAm, DM, and IA.

(69) In each of the (co)polymers obtained in Example 3-1 and Comparative Example 3-1, a 15% viscosity and a weight average molecular weight were measured. The results are shown in Table 4.

(70) TABLE-US-00004 TABLE 4 Weight Concentration of Average Water-Soluble Cross-Linkable Amount of Concentration 15% Molecular Unsaturated Cross-Linkable Monomer HPA of D-1173 Viscosity Weight Monomer Monomer (ppm) (ppm) (ppm) (mPa .Math. s) (Mw) Example 3-1 AAm/DME/IA Cross-Linkable 2500 1000 20 33,780 1425000 (Polymer C-1) Monomer (III-1) Comparative AAm/DME/IA — 2500 1000 20 52,600 1251000 Example 3-1 (Polymer C-2)

(71) [Test 3: Measurement of Paper Strength]

(72) 1000 ppm of a 0.5% aqueous solution of a polymer C-1 with respect to the total amount, was added while stirring a waste corrugated fiberboard of CSF480 in 868.4 g of slurry of 0.8%, and the stirring was continuously performed for 20 seconds. After that, papermaking was performed by using the obtained pulp slurry, in a square sheet machine. A wet sheet subjected to the papermaking, was dried at 110° C. for 3 minutes in a drum dryer, and thus, handmade paper having a basis weight of 125 g/m.sup.2, was obtained. The obtained dry paper was subjected to humidity conditioning for 24 hours in a constant temperature and humidity room of 20° C. and RH65%, and then, a specific burst strength (JIS-P8112) was measured. The same operation was performed with respect to a polymer C-2. The results are shown in Table 5.

(73) TABLE-US-00005 TABLE 5 Specific Burst Strength Polymer (kPa .Math. m.sup.2/g) Example 4-1 C-1 2.84 Comparative Example 4-2 C-2 2.64

(74) From Table 4, it was known that a polymer having a low 15% viscosity was obtained by using the cross-linkable monomer (III-1), despite the same value of the weight average molecular weight. Further, as it is obvious from Table 5, in a case where the polymer C-1 obtained in Example 3-1 was added at the time of performing the papermaking, and a paper strength was measured (Example 4-1), it was known that a specific burst strength became higher. Accordingly, it was confirmed that the polymer obtained in Example 3-1, was excellent in the paper strength improving performance.

(75) On the other hand, in the case of using the polymer C-2 obtained in Comparative Example 3-1 (Comparative Example 4-2), a specific burst strength became lower, compared to the examples. Accordingly, the polymer obtained in Comparative Example 3-1, was not excellent in the paper strength improving performance, compared to the examples.

INDUSTRIAL APPLICABILITY

(76) Hereinbefore, as described above in detail, according to the invention, it is possible to prepare a polymer flocculant which is capable of generating a coarse flock, is capable of controlling the structure of the polymer with a general aqueous solution polymerization method, and is excellent in water-solubility and water dispersibility, with a branched or cross-linking structure, by using two or more types of different cross-linkable monomers. In addition, it is possible to prepare a paper strengthening agent which is excellent in a specific burst strength.