WATER-SWELLABLE POLYMER PARTICLES

Abstract

The present invention is related to water-swellable polymer particles which contain a hydrophilic base polymer (B) and a hydrophobic polymer (P). It is also related to a process for producing the water-swellable polymer particles, an article containing the water-swellable polymer particles and the use of the water-swellable polymer particles.

Claims

1. Water-swellable polymer particles, comprising i) up to 99.9 wt.-% of a hydrophilic base polymer (B) which is optionally crosslinked, and ii) up to 10.0 wt.-% of a hydrophobic polymer (P), which is a copolymer of up to 95.0 mol-% of at least one (meth)acrylic acid ester and/or (meth)acrylic amide of formula (I) ##STR00014## wherein R.sup.1 is hydrogen or a methyl group, V is OR.sup.2 or NR.sup.3R.sup.4, R.sup.2 and R.sup.3 independently from each other are hydrogen or linear or branched C.sub.1 to C.sub.30 alkyl, and R.sup.4 is hydrogen or linear or branched C.sub.1 to C.sub.30 alkyl, and up to 35.0 mol-% of at least one ethlyenically unsaturated amine-containing monomer, based on an overall weight of the water-swellable polymer particles.

2. The water-swellable polymer particles according to claim 1, wherein the hydrophilic base polymer (B) comprises carboxyl groups, sulfonic acid groups and/or salts thereof and mixtures thereof.

3. The water-swellable polymer particles according to claim 1, which have a particle size d.sub.50 equal to or below 250 m.

4. The water-swellable polymer particles according to claim 1, wherein the hydrophilic base polymer (B) is a copolymer of i) at least one acid-containing monomer being an ethylenically unsaturated carboxylic acid-containing monomer and/or a sulfonic acid-containing monomer of formula (IIa) and/or formula (IIb) ##STR00015## wherein Y is O or NH, R.sup.5 is hydrogen or a methyl group, R.sup.6, R.sup.7 and R.sup.8 are independently from each other hydrogen, OH, C.sub.1-C.sub.6-alkyl or C.sub.6-C.sub.14-aryl, n is 0 or 1, M is hydrogen, a metal cation or an ammonium cation and a represents 1 or 1/valency of the metal cation, and Z is (CH.sub.2)m with m in the range of 0 to 10. ##STR00016## ii) optionally at least one amide-containing monomer being a (meth)acrylamide-containing monomer of formula (III) ##STR00017## wherein R.sup.9 is hydrogen or methyl and R.sup.10 and R.sup.11 are independently from each other hydrogen, linear or branched C.sub.1-C.sub.20-alkyl, C.sub.5-C.sub.8-cycloalkyl or C.sub.6-C.sub.14-aryl, or N-Vinylformamide, and iii) optionally a cross-linker.

5. The water-swellable polymer particles according to claim 1, wherein the hydrophilic base polymer (B) comprises a) 10.0 to 70.0 mol-% of the at least one acid-containing monomer, b) 0.0 to 90.0 mol-% of the at least one (meth)acrylamido-containing monomer of formula (III), and c) 0.0 to 30.0 mol-% of the cross-linker.

6. The water-swellable polymer particles according to claim 4, wherein the at least one acid-containing monomer is selected from the group consisting of acrylic acid, methacrylic acid, ethacrylic acid, -chloroacrylic acid, -cyanoacrylic acid, -methylacrylic acid (crotonic acid), -phenylacrylic acid, -acryloxypropionic acid, sorbic acid, -chloro sorbic acid, 2-methylisocrotonic acid, cinnamic acid, p-chlorocinnamic acid, itaconic acid, citraconic acid, mesacronic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, maleic anhydride, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), styrenesulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, 2-methylacrylamido-2-methylpropane sulfonic acid, 2-acrylamidobutane sulfonic acid, 3-acrylamido-3 -methyl-butane sulfonic acid, 2-acrylamide-2,4,4-trimethylpentane sulfonic acid, 2-sulfoethyl acrylate, 2-sulfoethyl methacrylate, 3-sulfopropyl acrylate, 3 -sulfopropyl methacrylate, 2-hydroxy-3-methacryloxypropyl sulfonic acid, a salt thereof, and a mixture thereof.

7. The water-swellable polymer particles according to claim 4, wherein the hydrophilic base polymer (B) comprises the at least one amide-containing monomer, which is selected from the group consisting of (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-ethylacrylamide, N,N-diethylacrylamide, N-cyclohexylacrylamide, N-benzylacrylamide, N-tert-butylacrylamide, N-Vinylformamide, and a mixture thereof.

8. The water-swellable polymer particles according to claim 4, wherein the hydrophilic base polymer (B) comprises the cross-linker, which is selected from the group consisting of N,N-methylenebisacrylamide, N,N-methylenebismethacrylamide, hexamethylenebismaleimde, ethylene glycol divinyl ether, triethylene glycol divinyl ether, cylcohexanediol divinyl ether, triallyl amine and/or tetra allyl ammonium salts, tetraallyloxyethane, pentaerythrittriallylether, divinyl benzene, triallyl isocyanurate, ethylene diamine, diethylene triamine, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,3-butyleneglycol diacrylate, 1,3-butyleneglycol dimethacrylate, diethyleneglycol diacrylate, diethyleneglycol dimethacrylate, ethyleneglycol dimethacrylate, ethoxylated bisphenol-A-diacrylate, ethoxylated bisphenol-A-dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, neopentylglycol dimethacrylate, polyethyleneglycol diacrylate, polyethyleneglycol dimethacrylate, triethyleneglycol diacrylate, tetraethyleneglycol dimethacrylate, dipentaerythritpentaacrylate, pentaerythrittetraacrylate, pentaerythrittriacrylate, trimethylolpropane tri acrylate, trimethylolpropane trimethacrylate, cyclopentadiene diacrylate, tris(2-hydroxyethyl) isocyanurate tri acrylate, tris(2-hydroxy) isocyanurate trimethylacrylate, divinyl esters of polycarboxylic acids, diallyl esters of polycarboxylic acids, triallyl terephthalate, diallyl maleate, diallyl fumarate, trivinyl trimellitate, divinyl adipate, diallyl succinate, glycidylacrylate, allylglycidether, ethyleneglycol diglycidether, diethyleneglycol diglycidether, polyethyleneglycol diglycidether, polypropyleneglycol diglycidether, polyethyleneglycolmonoallylether acrylate, polyethyleneglycolmonoallylether methacrylate, and a mixture thereof.

9. The water-swellable polymer particles according to claim 1, wherein the hydrophobic polymer (P) is a copolymer of at least two (meth)acrylic acid esters being a first (meth)acrylic acid ester or (meth)acrylic amide of formula (Ia) and a second (meth)acrylic acid ester or (meth)acrylic amide of formula (Ib) ##STR00018## wherein R.sup.12 is hydrogen or a methyl group, W is OR.sup.13 or NR.sup.13R.sup.14, R.sup.13 is a linear or branched C.sub.2 to C.sub.9 alkyl chain, R.sup.14 is hydrogen or a linear or branched C.sub.2 to C.sub.9 alkyl chain, T is OR.sup.16 or NR.sup.16R.sup.17, R.sup.16 is a linear or branched C.sub.10 to C.sub.30 alkyl chain, R.sup.17 is hydrogen or a linear or branched C.sub.10 to C.sub.30 alkyl chain, and at least one ethlyenically unsaturated amine-containing monomer.

10. The water-swellable polymer particles according to claim 9, wherein the first (meth)acrylic acid ester or (meth)acrylic amide of formula (Ia) is selected from the group consisting of ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, tertbutyl (meth)acrylate, n-pentyl (meth)acrylate, 2-methylbutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-methylpentyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate and a mixture thereof, and the second (meth)acrylic acid ester or (meth)acrylic amide of formula (Ib) is selected from the group consisting of stearyl (meth)acrylate, ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, tridecyl (meth)acrylate, 2-propylheptyl (meth)acrylate and a mixture thereof.

11. The water-swellable polymer particles according to claim 1, wherein the at least one ethlyenically unsaturated amine-containing monomer is a (meth)acrylic acid ester or (meth)acrylic amide of formula (IV) ##STR00019## wherein R.sup.18 is hydrogen or a methyl group, X is O or NH, R.sup.19 and R.sup.20 are independently from each other hydrogen or linear or branched C.sub.1 to C.sub.10 alkyl, and p is in the range of 1 to 10.

12. The water-swellable polymer particles according to claim 1, wherein the at least one ethlyenically unsaturated amine-containing monomer is selected from the group consisting of N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylamide, and a mixture thereof.

13. A process for preparing the water-swellable polymer particles according to claim 1, the process comprising i) providing a suspension comprising the hydrophilic base polymer (B) and a hydrophobic solvent, ii) adding the hydrophobic polymer (P) to the suspension, thereby obtaining the water-swellable polymer particles, and iii) separating the water-swellable polymer particles from the hydrophobic solvent.

14. The process according to claim 13, further comprising exposing the water-swellable polymer particles obtained in the separating iii) to mechanical force and/or a composition having a pH value of at least 12.

15. (canceled)

16. An article, comprising the water-swellable polymer particles according to claim 1.

Description

EXAMPLES

Methods

[0153] Gel permeation chromatography (GPC) was performed on a Waters alliance separation module 2695 with three GPC columns (SDV, 10.sup.6, 10.sup.3 and 10.sup.2 , 5 m, 300 x 8mm from Polymer Standard Service (PSS), Germany). Tetrahydrofuran (THF) containing 0.1% of trifluoroacetic acid was used as eluent. The elution was done with a flow rate of 0.8 mL/min and a column temperature of 35 C. A Waters refractive index (RI) 2410 detector was used. The calibration was carried with PEO/PEG standards (PSS).

[0154] The absorption and centrifuge retention capacity of the polymer samples was determined on a sample from 50-250 mg in a teabag. This teabag was placed in the container of distilled water or in a container containing calcium formate solution (1 wt %). The teabags were placed in the different media for 30 minutes and afterwards these were hung to dry and after these stopped dropping their weight was measured (absorption value). The samples were then put in a centrifuge (Thomas) and centrifuged at 1400 rpm for 3 minutes afterwards their weight was measured again (retention value).

[0155] The particle size of the powder was determined using a Mastersizer 2000 from Malvern, which measures the particle size by measuring the reflection of a laser beam onto the particles. To this end, the samples were dried and the machine was flushed with pressurized air to remove impurities. Afterwards, the sample was added into the machine and the particle size was determined.

Preparation of the Oil-Soluble Polymer (Example P1)

[0156] An oil bath was pre-heated to 75 C. before the reaction. Simultaneously, in a 500 mL round-bottom flask 0.3 g azobisisobutyronitrile was placed, to this 209.4 g of butyl acetate, 52.3 g of stearyl methacrylate (SMA), 29.0 g of a 98 wt % from an ethylhexyl acrylate (EHA) solution and 9.3 g of 2-dimethylaminoethyl methacrylate (DMAEMA) were added. After which the reactor was closed and the monomer solution was flushed with nitrogen for 20 minutes. After the flushing, the reactor was heated to 75 C. in order to start the free radical polymerization. When the reaction was complete the mixture was cooled down and the polymer was analyzed. The obtained copolymer had a solid content from approx. 30%. The average molecular weight from the polymers was determined to be 86 kg/mol with a PDI from 2.9.

[0157] The examples P2-P5 have been prepared via a similar method as described for P1 with the monomer compositions as presented in Table 1 and the molecular weights of these materials have been presented in Table 2.

TABLE-US-00001 TABLE 1 Monomer compositions from the oil-soluble polymers EHA SMA DMAEMA Example (mol %) (mol %) (mol %) P1 42 42 16 P2 40 40 20 P3 35 35 30 P4 50 25 25 P5 44 44 12

TABLE-US-00002 TABLE 2 Molecular weight data obtained from the polymers P1-5. Example M.sub.n (kg/mol) M.sub.w (kg/mol) PDI P1 86 249 2.9 P2 157 291 1.9 P3 nd nd nd P4 84 237 2.8 P5 199 305 1.5

Preparation of the Base Polymer (Example B1)

[0158] In a 2 L double walled glass reactor, equipped with an overhead stirrer, thermometer, a nitrogen inlet and a distillation bridge connected to a reflux column, a round-bottom flask filled with the hydrophobic solvent and a vacuum pump, 600.1 g of Exxsol D40 (ExxonMobil Chemical) was placed and heated to a temperature of 30 C. To this hydrophobic phase, 4.0 g of a solution (28.7%) containing a polymeric stabilizer which contain acrylic acid was added. Additionally, 2.5 g of sorbitol monooleate (Span80, Sigma-Aldrich) was dissolved in the hydrophobic phase. This solution was subsequently stripped with nitrogen for 90 minutes. At the same time, in a 1 L beaker glass 158 g of a 50 wt % acrylamide (BASF) solution was placed and to this 0.6 g of a 50 wt % pentetic acid (Triton C, BASF) solution, 176.4 g of a 50 wt % sodium 2-acrylamido-2methylpropane sulfonate solution and 2.5 g of a 2 wt % methylbisacrylamide solution. The pH of this solution was adjusted to a pH of 6.0 using 1.2 g of sulfuric acid (5 wt % solution) after which 7.4 g of water was added. To this aqueous monomer solution 3.6 g of a 1 wt % sodium sulfite and 3.6 g of a 4 wt % 2.2-Azobis(2-methylpropionamidine)dihydrochloride solution were added.

[0159] The nitrogen probe was removed from the hydrophobic phase and 1.2 g of a 0.1 wt % phenothiazine solution was added. The stirrer rate was adjusted and the aqueous monomer phase was added to the hydrophobic phase. The two-phase system was stirred for 2 minutes at the predetermined stirring rate before 3.6 g of a 0.5 wt % tert-butyl hydroperoxide was added to initiate the reaction. After the maximum temperature in the reactor was reached, the temperature in the reactor was increased to 75 C. using a thermostat. After which, the reaction mixture was put under vacuum to distill of the water from the aqueous monomer phase. This yields a suspension of cross-linked polymer particles in the hydrophobic phase. The particle size of these polymer particle was determined using light scattering and the d.sub.50 was determined to be 90 m. To this suspension of polymer particles in oil 0.5 wt % of a 30 wt % P1 solution was added. The particles were subsequently separated from the hydrophobic phase and dried in an oven at 50 C.

[0160] The examples B2-B15, as well as the reference example M1, have been prepared using the same method as described for B1. The compositions of the various examples have been described in Table 3.

TABLE-US-00003 TABLE 3 Composition from the agglomerated polymer particles in oil. Example Oil-soluble polymer Amount (wt %) M1 0 B1 P1 0.5 B2 P1 1 B3 P1 2 B4 P2 0.5 B5 P2 1 B6 P2 2 B7 P3 0.5 B8 P3 1 B9 P3 2 B10 P4 0.5 B11 P4 1 B12 P4 2 B13 P5 0.5 B14 P5 1 B15 P5 2

[0161] To study the influence of the oil soluble polymer on the agglomeration of the primary particles pictures of the system was taken after drying. These pictures show that the agglomeration of the beads in oil using the described polymers was successful (FIGS. 1a and 1b).

Example M1 (Comparative)

[0162] Inverse suspension polymerization polymers without the addition of any extra additives. The obtained product was mainly a fine powder. Small amount of agglomerates was formed due to drying effects.

Example B1

[0163] Polymer P1 (30 wt % in solvent) was added at 0.5 wt % on the total weight of the suspension. Some large lumps (size>1 cm) were formed and the amount of primary particles was significantly reduced because these were agglomerated. Clearly the larger particles were not formed due to drying effects in the oven.

Example B2

[0164] Polymer P1 (30 wt % in solvent) was added at 1 wt % on the total weight of the suspension. Larger agglomerates were formed compared to example M1 and no primary particles were observed anymore. The average agglomerate size increased, but this could not be quantified since the KGA was not able to measure accurately above a size of 3 m. The amount of smaller structures decreased compared to example B1.

Example B3

[0165] Polymer P1 (30 wt % in solvent) was added at 2 wt % on the total weight of the suspension. Only larger (>0.5 cm) agglomerates were formed and no primary particles were observed after the addition of this polymer. The amount of large structures increased when compared with sample B1 and B2. Clearly the addition of more from this oil soluble polymer leads to more agglomeration.

Example B4

[0166] Polymer P2 (30 wt % in solvent) was added at 0.5 wt % based on the total weight of the suspension. After the addition of this polymer the amount of primary particle was significantly reduced and larger agglomerates (>0.5 cm) were formed. The average agglomerate size seemed to be larger compared to the example B1. Therefore, this polymer seems to be more desirable compared to example B1.

Example B5

[0167] Polymer P2 (30 wt % in solvent) was added at 1 wt % based on the total weight of the suspension. The amount of primary particles was significantly reduced and larger agglomerates were obtained. The size of these agglomerates did not vary too much from example B4.

Example B6

[0168] Polymer P2 (30 wt % in solvent) was added at 2 wt % based on the total weight of the suspension. The amount of primary particles was significantly reduced and larger agglomerates were obtained. The average size of these agglomerates was very similar to those exhibited in example B5. Apparently for this polymer no concentration dependent behavior could be observed.

Example B7

[0169] Polymer P3 (30 wt % in solvent) was added at 0.5 wt % based on the total weight of the suspension. Clearly larger aggregates were formed from the primary particles. The primary particles were not observed anymore after the addition of the polymer. Even at low content of the polymer the amount of primary particles has been significantly reduced, more compared to the previous examples.

Example B8

[0170] Polymer P3 (30 wt % in solvent) was added at 1 wt % based on the total weight of the suspension. Clearly larger aggregates were formed from the primary particles. The primary particles were not observed anymore after the addition of the polymer. No significant differences between this examples and example B7 could be observed.

Example B9

[0171] Polymer P3 (30 wt % in solvent) was added at 2 wt % based on the total weight of the suspension. Clearly larger aggregates were formed from the primary particles. The primary particles were not observed anymore after the addition of the polymer. The smaller agglomerates were formed since the amount of polymer particles in the oil was too low.

Example B10

[0172] Polymer P4 (30 wt % in solvent) was added at 0.5 wt % based on the total weight of the suspension. The formation of some larger agglomerates was observed, but still significant amounts of primary particles were observed. These results are less desirable compared to examples B1 to B9.

Example B11

[0173] Polymer P4 (30 wt % in solvent) was added at 1 wt % based on the total weight of the suspension. The formation of some larger agglomerates was observed, but still significant amounts of primary particles were observed. These results are less desirable compared to examples B1 to B6 and no significant improvement compared to B10 was observed.

[0174] Example B12

[0175] Polymer P4 (30 wt % in solvent) was added at 2 wt % based on the total weight of the suspension. Larger agglomerates were observed and the amount of primary particles seemed to have been reduced compared to examples B10 and B11, but the still not as good as examples B1-B6. Hence, this polymer is less effective in agglomeration of the polymer particles

Example B13

[0176] Polymer P5 (30 wt % in solvent) was added at 0.5 wt % based on the total weight of the suspension. After the addition of the polymer the formation of a large number of larger (>0.5 cm) agglomerates was observed and the amount of primary particles was significantly reduced.

Example B14

[0177] Polymer P5 (30 wt % in solvent) was added at 1 wt % based on the total weight of the suspension. After the addition of this polymer larger agglomerates (>1 cm) were obtained, and the addition of more polymer clearly lead to an increase of the agglomerate size compared to example B13.

Example B15

[0178] Polymer P5 (30 wt % in solvent) was added at 2 wt % based on the total weight of the suspension. After the addition of this polymer larger agglomerates (>1 cm) were obtained, and the addition of more polymer clearly lead to an increase of the agglomerate size compared to example B13. However, the amount of smaller agglomerates was larger when compared to example B14 what could be due to over dosing of the oil soluble polymer.

[0179] All the prepared samples shown in examples B1-B15 could be reduced again to their primary particles just by the application of shear forces, for example by pressing and rubbing the beads between the fingers or using a mortar and pestle. KGA could be used to show that this was feasible.

[0180] FIG. 1a shows the primary particle distribution and

FIG. 1b the sample which was treated with then a hydrophobic polymer and afterwards sheared to break up the agglomerates. Not all the agglomerates were broken during the shearing, but most of them were reduced to primary particles.

[0181] The absorption of the superabsorbers should not be negatively influenced by the agglomeration process and this would be shown using the CAC test. The results from these experiments have been presented in Table 4. Clearly, the adsorption and retention of the superabsorbers, both in water and in 1% calcium formate solution was retained.

TABLE-US-00004 TABLE 4 Adsorption and retention capacity of the different examples dest. H.sub.2O Calcium (g/g) formate (g/g) Absorp- Re- Absorp- Re- Example tion tention tion tention M1 242.74 157.44 20.92 13.78 B7 230.01 148.25 21.21 12.77 B8 217.66 147.01 21.56 13.27 B9 214.70 149.42 19.22 11.02